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Journal of Organometallic Chemistry 696 (2011) 4079e4089

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Journal of Organometallic Chemistry

journal homepage: www.elsevier .com/locate/ jorganchem

Synthesis and characterization of a trianionic pincer supported Mo-alkylideneanion and alkyne insertion into a Mo(IV)-Cpincer bond to formmetallocyclopropene(h2-vinyl) complexes

Muhammad T. Jan, Soumya Sarkar, Subramaniam Kuppuswamy, Ion Ghiviriga, Khalil A. Abboud,Adam S. Veige*

University of Florida, Department of Chemistry, Center for Catalysis, P.O. Box 117200, Gainesville, FL 32611, USA

a r t i c l e i n f o

Article history:Received 6 May 2011Received in revised form5 June 2011Accepted 7 June 2011

Dedicated to Professor Kenneth G. Caultonon the occasion of his 70th birthday.

Keywords:Trianionic pincerMetallocyclopropeneAlkylidyneAlkylideneVinylInsertion

* Corresponding author. Tel.: þ1 352 392 9844; faxE-mail address: veige@chem.ufl.edu/ (A.S. Veige).

0022-328X/$ e see front matter Published by Elseviedoi:10.1016/j.jorganchem.2011.06.006

a b s t r a c t

This report describes two approaches to form complexes featuring MoeC multiple bonds and a trianionicpincer ligand. Treating the trianionic pincer ligand precursor [tBuOCO]H3 (1) with MeLi provides thecorresponding dilithio salt [tBuOCHO]Li2(THF)3 (6) in situ, which further reacts with Mo(NAr)(CHCMe2Ph)(OTf)2(DME) to provide the terphenyl diphenolate complex [tBuOCHO]Mo(NAr)CHCMe2Ph(5). Complex 5 is characterized by 1H, 13C{1H} NMR spectroscopy, combustion analysis, and single crystalX-ray diffraction. The solid state structure of 5 reveals a distorted trigonal pyramidal geometry for theMo(VI) ion. Treating 5 with one equiv. of phosphorane in toluene converts the diphenolate ligand intoa trianionic pincer ligand by deprotonation of the pincer Cipso-H proton to give the alkylidene salt{[tBuOCHO]Mo(NAr)(CHCMe2Ph)}{Ph3PCH3} (7). Treating [tBuOCO]MoNMe2(NHMe2)2 (2), containinga d2 Mo(IV) ion, with terminal alkynes (HeChCR, R ¼ Ph, 3,5-F2C6H3, 3,5-(CF3)2C6H3 and SiMe3)produces in excellent yield the corresponding metallocyclopropylidene complexes 10-R (R ] H, F, CF3)and 11 (R ¼ SiMe3). X-ray diffraction studies on single crystals of 10-H and 11 reveal three importantfeatures: 1) a highly distorted hexacoordinate Mo(VI) center, 2) a metallocyclopropene(h2-vinyl) frag-ment, and 3) a highly distorted CH group in the metallocyclopropene unit. A single point calculation andan NBO analysis performed on 10-H0 confirms the multiple bond between Mo1 and C28. The highestoccupied KohneSham molecular orbital (HOMO) represents a p-combination between dyz of Mo1 andthe py orbital of C28, and the corresponding p*-combination of those orbitals constitutes the lowestunoccupied molecular orbital (LUMO).

Published by Elsevier B.V.

1. Introduction

Alkyne metathesis (AM) [1e10] and nitrile-alkyne crossmetathesis (NACM) [11e15] continue to receive interest with recentdiscoveries by Johnson [12e16], Moore [17], and Fürstner [18,19]stimulating the synthesis and study of new alkylidyne complexes.Discovering new complexes that metathesize alkynes rapidly atambient temperature is a key goal. Another goal is to find new andefficient methods for the synthesis of MhCR bonds. Fürstner et al.[18,19] utilize Br3WhCPh(dme) [20,21] as an accessible reagent toform siloxy-based alkylidyne complexes [22]. For example,(Ph3SiO)3MohCPh(OEt2) reacts with many substrates bearingdiverse functional groups, and the activity is impressive [23]. In the

: þ1 352 392 3255.

r B.V.

presence of 5 Å molecular sieves, (Ph3SiO)3MohCPh(OEt2)completes the metathesis of 1-phenyl-1-propyne within 5 min.Moore [17], employing the Lewis acid B(C6F5)3, activateMo-nitridestoward metathesis with alkynes. This discovery implies that M-nitrides, already known to exchange N-atoms with nitriles [23,24],may be a general entry point to alkyne metathesis catalysts [15,16].Recently, we proposed that a trianionic pincer ligand may providethe appropriate ligand arrangement for a reactive AM or NACMcatalyst [25]. Trianionic pincer ligands [26e28] bind in the merid-ional plane of a metal ion [26,29,30], and thus eliminate anythermal barrier to obtaining the T-shaped pendant ligandarrangement proposed for metallocyclobutadiene transition states[12,31]. The difficulty thus far is metalating a trianionic pincerligand while retaining the MhCR fragment. Starting with a pre-installed MhCR bond in (ArO)2R3WhCR0 and treating with thetrianionic pincer ligand precursor 3,300-di-tert-butyl-1,10:30,100-ter-phenyl]-2,200-diol [tBuOCO]H3 (1) [26], lead to the formation of the

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e40894080

corresponding trianionic pincer-alkylidene complex [tBuOCO]W]

CHR(OAr) (where, ArO ¼ 2,6,-iPrC6H3) [25]. In this manuscript weexplore the possibility of first metalating the trianionic pincerligand followed by MhCR installation. Deprotonating an existingalkylidene and reductive coupling of terminal alkynes are the twosynthetic routes employed in this study. Neither approach wassuccessful, and alkylidyne complexes of trianionic pincer ligandsremain elusive, however, two noteworthy findings emerge fromthis study: 1) the discovery of a convenient method to converta terphenyl diphenolate ligand into a trianionic pincer ligand, and2) insertion into the trianionic pincer M-Cipso bond of [tBuOCO]MoNMe2(NHMe2)2 (2) [26] by alkynes leads to the formation ofnew metallocyclopropene complexes.

2. Results and discussion

2.1. Synthesis and characterization of [tBuOCHO]Mo(NAr)(CHCMe2Ph) (5)

One approach to the synthesis of a trianionic pincer supportedalkylidyne complex is to first synthesize the corresponding alkyli-dene and then deprotonate. Schrock et al. [32] demonstrate thistechnique by employing triphenylphosphorane Ph3P]CH2 asa mild base to deprotonate the alkylidene complex Mo(NAr)(CHCRMe2)[OCMe(CF3)2]2 [R ¼ Me (3-Me), Ph (3-Ph);Ar ¼ 2,6-iPr2C6H3] to form the corresponding anionic alkylidynespecies (4-R; R ¼ Me, Ph) (Eq. (1)).

Ph3P=CH2MoN

R

R = Me, 3-MeR = Ph, 3-Ph

OCF3CF3

OCF3CF3 Mo

OCF3CF3

OCF3

CF3N

R

R = Me, 4-MeR = Ph, 4-Ph

CH3PPh3

(1)

Fig. 1. Molecular structure of 6-Et2O presented with ellipsoids drawn at the 50%probability level and some hydrogen atoms removed for clarity. Selected bonddistances [Å]: Li1eO1 ¼ 1.908(4), Li1eO2 ¼ 1.907(4), Li1eO3 ¼ 1.910(8),Li2eO2 ¼ 1.972(4), Li2eO1 ¼ 1.979(4), Li2eO5 ¼ 1.965(4), Li2eO4 ¼ 2.063(4),Li1eC21 ¼ 2.385(4), C21eH21 ¼ 0.92(2). Bond angles [�]: Li1eO2eLi2 ¼ 79.26(15),Li1eO1eLi2 ¼ 79.06(15), O4eLi2eO5 ¼ 100.48(17), O2eLi1eO1 ¼ 102.73(16),O2eLi2eO1 ¼ 97.94(17).

Initially, we explored the feasibility of this approach byattempting to synthesize the corresponding terphenyl diphenolatecomplex [tBuOCHO]Mo(NAr)CHCMe2Ph (5) (Scheme 1). Treating[tBuOCO]H3 (1) with 2.04 equiv. of nBuLi in THF solution andremoval of all volatiles provides the necessary dilithio salt [tBuO-CHO]Li2(THF)3 (6) as a white crystalline solid in 96% yield (Scheme1). The 1H NMR spectrum (C6D6) of 6 exhibits a singlet at 1.70 ppm

OH

OHH

1

O

OLiLiO

O2.04 n-BuLi

THFO

6

Scheme 1. Synthesis of [tBuOCHO]Li2(THF)3 (6

attributable to equivalent tBu groups, and a characteristic Cipso-H ofthe central aryl ring resonates as a broad singlet at 8.54 ppm.Multiplets at 3.33 and 1.18 ppm (free THF protons appear at 3.57and 1.47 ppm), account for the 12 protons of three THF moleculesassociated with each dilithio unit. The 13C{1H} NMR spectrumcomplements the 1H NMR spectrum (see Supplementaryinformation). Recrystallization of 6 in Et2O at �35 �C results intwo Et2O molecules displacing two THF molecules and the thirdTHF is partially displaced (50%) to form [tBuOCHO]Li2(TH-F)0.5(Et2O)2.5 (6-Et2O). Single crystals amendable to an X-raydiffraction experiment grow during recrystallization in Et2O. Thecrystals react rapidly and turn red when exposed to air. Fig. 1depicts the molecular structure of 6-Et2O [33] and confirms that2.5 Et2O ligands coordinate to the Liþ ions.

O

O

5

MoN

Ph(CF3SO3)2

MoN

Ph

OO

- DME- 2 CF3SO3Li

THF

) and [tBuOCHO]Mo(NAr)CHCMe2Ph (5).

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e4089 4081

It is not necessary to isolate the dilithio salt 6. Generation of 6 insitu followed by addition of a metal-containing reagent providesa convenient method to synthesize metal complexes supported bythe pincer ligand. For example, treating in situ generated 6 (THF)with one equiv. of Mo(NAr)(CHCMe2Ph)(OTf)2(DME) at �35 �C andthen slowly warming to 25 �C, yields analytically pure crystalline[tBuOCHO]Mo(NAr)(CHCMe2Ph) (5) in 72% yield. 1H, 13C{1H} NMRspectroscopy, single crystal X-ray diffraction, and combustionanalysis confirm the identity and purity of 5. Crystals suitable fora single crystal X-ray experiment grow from a concentrated solu-tion of 5 in Et2O at�35 �C. Complex 5 crystallizes in the monoclinicspace group P21/c, Fig. 2 depicts its solid state structure [33], andTable 1 lists crystallographic data refinement parameters. The

Fig. 2. Molecular structure of 5 presented in two different perspectives with ellipsoids drawdistances [Å]: Mo1eO1 ¼ 1.9417(12), Mo1eO2 ¼ 1.9534(11), Mo1eN1 ¼ 1.7195(14), Mo1eCO1eMo1eC27 ¼ 98.29(6), O2eMo1eN1 ¼ 114.56(6), O2eMo1eC27 ¼ 101.40(6), N1eMo1e

Table 1X-ray crystallographic structure parameters and refinement data.

6-OEt2 5

Empirical formula C38H57Li2O5 C48H57MoNO2

Formula weight 607.72 775.89Cryst syst Orthorhombic MonoclinicSpace Group aba2 P21/CDimens (mm) 0.22 � 0.11 � 0.09 0.22 � 0.18 � 0.09a (Å) 17.8917(14) 9.4899(10)b (Å) 20.2972(16) 20.144(2)c (Å) 20.5319(16) 20.004(2)a (deg) 90 90b (deg) 90 101.717(2)g (deg) 90 90V (Å3) 7456.2(1) 4118.8(7)Z 8 4Abs coeff (mm�1) 0.069 0.357F (000) 2648 1640Dcalcd (g/cm3) 1.083 1.251g (Mo Ka) (Å) 0.71073 0.71073Temperature (K) 173(2) 100(2)q range (deg) 1.81e27.50 1.38e27.50Completeness to qmax 99.7% 99.8%No. of reflns collcd 26357 44139No. of ind reflns [Rint] 8501 [0.0362] 9445 [0.0452]Data/restraints/param 8501/1/507 9445/0/440Final R1 indices [I > 2s(I)] R1 ¼ 0.0503,

wR2 ¼ 0.1275 [6579]R1 ¼ 0.0288,wR2 ¼ 0.0699 [7430]

R indices (all data) R1 ¼ 0.0669,wR2 ¼ 0.1363

R1 ¼ 0.0424,wR2 ¼ 0.0733

Diff peak/hole e �3 0.636/�0.316 0.717/�0.533Goodness of fit on F2 1.001 1.033

complex is Cs-symmetric with a Mo(VI) ion in a distorted trigonalpyramidal geometry. The dimethylphenylalkylidene occupies theapical position, whereas the OCO ligand, bound in its diphenolateform, and the 2,6-diisopropylarylimido occupy the trigonal plane.Close to 120� each, the trigonal plane comprises anglesof O1eMo1eO2 ¼ 117.07(5), O1eMo1eN1 ¼ 118.90(6),O2eMo1eN1 ¼ 114.56(6)�. The imido ligand is nearly linearcreating an angle of Mo1eN1eC37 ¼ 175.34(13)�, whereas the sp2

alkylidene bends toward the OCO ligand with an angle ofMo1eC27eC28 ¼ 145.94(14)�. Typical for diphenolate Mo-alkylidenes bearing an arylimido ligand, the Mo1eC27 bondlength is 1.8873(17) Å [34e37] and the Mo]N bond distance is1.7195(14) Å.

n at the 50% probability level and hydrogen atoms removed for clarity. Selected bond27 ¼ 1.8873(17). Bond angles [�]: O1eMo1eO2 ¼ 117.07(5), O1eMo1eN1 ¼ 118.90(6),C27 ¼ 101.41(7), Mo1eN1eC37 ¼ 175.34(13), Mo1eC27eC28 ¼ 145.94(14).

7 10-H 11

C67H74MoNO2P C38H46MoN2O2 C39 H60 MoN2 O3Si1052.18 658.71 728.92Monoclinic Monoclinic TriclinicP2(1)/n C2/c P-10.17 � 0.13 � 0.10 0.17 � 0.15 � 0.08 0.19 � 0.09 � 0.0312.8341(6) 44.272(3) 8.80011(4)23.6529(12) 8.7288(5) 14.8131(8)21.8974(11) 17.4256(10) 15.0514(7)90 90 89.631(4)104.500(1) 98.675(4) 81.779(4)90 90 76.811(4)6435.5(5) 6657.0(7) 1890.19(16)4 8 20.268 0.429 0.4162224 2768 7761.086 1.314 1.2810.71073 0.71073 0.71073100(2) 100(2) 100(2)1.29e27.50 1.86e27.50 1.94e27.50100.0% 99.9% 99.4%142042 38395 2904514791 [0.0915] 7653 [0.0432] 8641 [0.1669]14791/0/666 7653/0/406 8641/0/438R1 ¼ 0.0352,wR2 ¼ 0.0627 [9580]

R1 ¼ 0.0286,wR2 ¼ 0.0719 [5703]

R1 ¼ 0.0597,wR2 ¼ 0.0893 [4432]

R1 ¼ 0.0724,wR2 ¼ 0.0678

R1 ¼ 0.0450,wR2 ¼ 0.0764

R1 ¼ 0.1481,wR2 ¼ 0.1112

0.447/�0.549 0.820/�0.585 0.559/�0.7390.865 1.032 0.882

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e40894082

The 1H and 13C{1H} NMR spectral data of 5 are consistent withthe solid state structure. The most salient feature in the 1H NMRspectrum is a singlet at 12.43 ppm attributable to the alkylideneproton. The corresponding alkylidene carbon resonates at283.0 ppm in the 13C{1H} NMR spectrum. Diagnostic isopropyl-methyl protons on the imido appear as two doublets at 1.12 ppmand 0.83 ppm and a methine-proton resonates as a septet at3.16 ppm, consistent with a Cs-symmetric complex. Consistent withdocumented examples [26] in the diphenolate form, the OCOcentral ring Cipso-H appears downfield at 8.65 ppm.

2.2. Synthesis and characterization of {[tBuOCO]Mo(NAr)(CHCMe2Ph)}{Ph3PCH3} (7)

Complex 5 contains the OCO ligand in the diphenolate form. Ifan alkyl group is present within the coordination sphere it canabstract the central Cipso-H proton to convert the ligand into a tri-anionic pincer ligand [38]. An alternative method is to add anappropriate external base to deprotonate the Cipso-H. Two possi-bilities may result from addition of an external base: 1) the basedeprotonates the alkylidene to form an alkylidyne (Scheme 2A), or2) the base deprotonates the aryl Cipso-H of the pincer ligand toform a trianionic pincer complex (Scheme 2B).

Treating 5 with 1 equiv. of phosphorane in toluene solutionprovides an oil after solvent removal, and upon washing andtriturating with pentane provides the trianionic pincer-alkylidenesalt {[tBuOCO]Mo(NAr) (CHCMe2Ph)}{Ph3PCH3} (7) as an orange-yellow solid in 76% yield (Scheme 2B). Single crystals amenableto X-ray diffraction interrogation deposit from a concentratedsolution of 7 in THF at �32 �C. Fig. 3 depicts the solid statestructure of 7 which crystallizes in the monoclinic space groupP2(1)/n and Table 1 lists structural refinement data. The complex isCs-symmetric and the Mo(VI) coordination geometry is in betweentrigonal bipyramidal and square-pyramidal. The geometry is

O

O

Ph3P=CH2

5

MoN

Ph

O

O

Ph3P=CH2

C6D6

5

MoN

Ph

76%

x

Scheme 2. Illustration of the two potential products upon addition of Ph3P¼CH2 to 5. A: PhPCipso-H proton of 5 to convert the diphenolate ligand into a trianionic pincer ligand.

somewhat closer to a sq-pyramid considering the calculatedAddison parameter s for 7 is 0.28 [39]. However, the preference forsq-pyramidal is a consequence of the chelating trianionic pincerligand. The basal plane contains the pincer, including the arlyoxideattachments that are unable to adopt a 180� angle. The anioniccomplex 7 exhibits significantly elongated Moeligand bondscompared to the neutral complex 5, though the alkylidene MoeCbond contracts slightly by 0.019(2)Å to 1.868(2) Å. In 7, the Mo]Nbond (1.7796(15) Å) and MoeO bonds (MoeOavg ¼ 2.0437(14) Å)are 0.0601(2) Å and 0.0961(14) Å longer than 5, respectively,which is a consequence of the additional electron density atthe Mo center. This contrasts a Schrock example [32] that exhibitsM] N bond shortening upon formation of the anion by 0.06(1) Å.However, in that case the Liþ counter-ion coordinates totwo alkoxide ligands and possibly reduces their p-donationcapacity which is compensated by additional p-donation anda short Mo]N bond (1.67(1) Å from the N-atom of the imido).Another difference between 7 and 5 is the angle at the imidonitrogen. In 7 the angle is significantly smaller (4.4(2)�) than in 5creating an angle C27eMo1eN1 ¼ 170.9(2)� which is within thelinear imido range and should not be misconstrued as an sp2 [40]hybridized N-atom [41,42].

Complementing the solid state structure, the 1H NMR and 13C{1H} NMR spectra of 7 exhibit signals attributable to the pincerligand in the trianionic form and the presence of a bound alkylidene.The alkylidene proton resonates at 9.78 ppm and the correspondingalkylidene carbonappears at 270ppm. Perhaps a consequence of theelongated Moeimido bond, the arylimido group rotates freely insolution at 25 �C resulting in a broad multiplet at 1.32 ppm for theisopropyl-methyl protons, and themethine-proton is not detectabledue to broadening. The doublet expected for the phosphonium-methyl protons could not be located; however, the 31P NMR spec-trum reveals a singlet at 21.28 ppm confirming the presence of thecationic counter-ion.

O

O

MoN

Ph

CH3PPh3

CH3PPh3

O

O

7

MoN

Ph

A

B

3¼CH2 does not deprotonate the alkylidene proton of 5. B: PhP3¼CH2 deprotonates the

Fig. 3. Molecular structure of 7 presented in two different perspectives with ellipsoids drawn at the 50% probability level. The counter-ion [Ph3PCH3]þ and hydrogen atoms areremoved for clarity. Selected bond distances [Å]: Mo1eO1 ¼ 2.0443(13), Mo1eO2 ¼ 2.0430(12), Mo1eN1 ¼ 1.7796(15), Mo1eC12 ¼ 2.1749(19) Mo1eC39 ¼ 1.868(2). Bond angles[�]: O1eMo1eO2 ¼ 157.30(5), O1eMo1eN1 ¼ 98.43(6), O1eMo1eC12 ¼ 79.35(6), O1eMo1eC39 ¼ 95.06(7), O2eMo1eN1 ¼ 94.14(6), O2eMo1eC12 ¼ 78.95(6),O2eMo1eC39 ¼ 97.79(7), N1eMo1eC12 ¼ 140.67(7), N1eMo1eC39 ¼ 111.56(8), C12eMo1eC39 ¼ 107.74(8), C27eN1eMo1 ¼ 170.9(2).

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e4089 4083

2.3. Synthesis and characterization of metallocyclopropenecomplexes (10-H, 10-F, 10-CF3)

A second approach to alkylidyne installation involves treatinga d2 metal ion with a terminal alkyne and base to induce reductivecoupling. Cummins et al. demonstrate this technique by treatingthe useful synthon molybdaziridine hydride complex, Mo(H)(h-Me2CNAr)(N[iPr]Ar)2, with I2 and HeChCeR (R ¼ Ph, Me, nBu,(CH2)3CN, 4-CF3C6H4, CH2NPh2) to form the cationic alkynecomplexes 8-R [43,44]. Treating 8-R with LiN(SiMe3)2 forms thecorresponding dinuclear alkylidyne complexes 9-R (Eq. (2)).Replacing the anilide ligands with aryloxide ligands and subse-quent metathesis with diphenylacetylene provides mononuclearalkylidyne complexes.

(Ar[iPr]N)3Mo

H

R

I LiN(SiMe3)2- HN(SiMe3)2- LiI

(Ar[iPr]N)3MoMo(N[iPr]Ar)3

R

R

Ar = 3,5-Me2C6H3R = Ph, Me, nBu, (CH2)3CN, 4-CF3C6H4, CH2NPh2

8-R 9-R

0.5

(2)

Previously reported, the trianionic pincer amido-amine complex2 [26], in theory, is well-suited for reductive coupling. The Mo(IV)ion in complex 2 is d2, and within the coordination sphere is theinternal base eNMe2, Scheme 3A. However, treating complex 2with one equivalent of the terminal alkynes HeChCeR (R ¼ Ph,3,5-F2C6H3, and 3,5-(CF3)2C6H3) does not result in reductivecoupling. Instead, addition of alkynes to 2 results in the quantitative(NMR) formation of the corresponding metallocyclopropene [45]complexes 10-R (R ¼ H, F, CF3) (Scheme 3B).

Complexes 10-R are isolable in 82%, 80%, and 83% yield, forR¼H, F, and CF3, respectively, as red-orangemicrocrystalline solids.Crystals of 10-H amenable to X-ray diffraction grow froma concentrated solution of 10-H in Et2O solvent at �32 �C. Fig. 4depicts the molecular structure of 10-H [33] and Table 1 listsstructural refinement data. The molybdenum ion is coordinated by

a dimethylamido group (Mo1eN1 ¼ 1.9427(16) Å), a dimethyl-amine (Mo1eN2 ¼ 2.4244(17) Å, the OCO ligand aryloxides, andtwo carbon atoms. The metallocyclopropene results from a formaltwo-electron reduction of the alkyne and insertion into theMeCispo

bond of the central pincer ring. The metallocyclopropene fragmentcontains a short MoeCalkylidene bond (Mo1eC28 ¼ 1.9494(19) Å)which is typical [46e50] of Moecyclopropene complexes, thoughCummins [44] reports a much shorter Mo]C bond of 1.899(8) Å fora Me3Si-substituted Mo(VI) derivative. The MoeCalkyl bond(Mo1eC27¼ 2.1504(19) Å) is shorter than known derivatives whichtypically range between 2.25 and 2.32 Å [46e50]. The shorter bondmay be due to the higher oxidation state of Mo in 10-H (þ6)compared to the reported examples in which Mo is þ4. Consistentwith known Mo-derivatives, as well as W-cyclopropenes [51e54]

(except two (1.342(6) Å) [55] and 1.263(2) Å [56]) is the C27eC28bond length of 1.420(3) Å for the CeC bond in 10-H. Interestingly,the phenyl ring attached to C28 is coplanar with the metal-locyclopropene, suggesting conjugation exists between them. Thecentral aryl ring of the diphenolate ligand is one of the metal-locyclopropene substituents and creates considerable strain on theC27 atom creating angles of Mo1eC27eC12 ¼ 88.30(11),C28eC27eC12 ¼ 124.13(17), and C28eC27eMo1 ¼ 62.28(10)�.Deviations from archetypical [46,47] Mo-derivatives are the smallMo1eC27eC12 (normally 115(2)�) and the large C28eC27eMo1angle (normally 57.7(2)�). Clearly, tethered to the diphenolateligand, C27 is highly distorted and cannot be formally assigned asan sp3-hybridized atom. The H27A atom was located from thedifference Fourier map and refined to yield a C27eH27A bondlength of 0.864(19) Å. The experimental bond length is much

A

B

2

O

O

Mo

R

RNH

N

R = H, 10-H (82%)R = F, 10-F (80%)R = CF3, 10-CF3 (83%)

O

O

Mo NN

HNH

R

R

C6D6

2

O

O

Mo NN

HNH

O

O

Mo

O

O

MoNH

NH

0.5Ph

Ph

Scheme 3. Illustration of the two potential products upon addition of a terminal alkyne to 2. A: Alkyne addition to 2 does not reductively couple. B: Alkyne inserts into the Mo-Cipso

bond to give metallocyclopropene complexes 10-R (R ¼ H, F, CF3).

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e40894084

shorter than even a CspeH bond (1.08 Å), however it is consistentwith analogous Mo-derivatives that range between 0.854(24) and1.023(39) Å [46,47,57].

The 1H and 13C{1H} NMR spectra of 10-H are consistent with thesolid state structure. In particular, the 1H NMR spectrum exhibits

Fig. 4. Molecular structure of 10-Hwith ellipsoids drawn at the 50% probability level andhydrogen atoms removed for clarity. Selected bond distances [Å]: Mo1eO1 ¼ 1.9915(13),Mo1eO2 ¼ 1.9909(13), Mo1eN1 ¼ 1.9427(16), Mo1eN2 ¼ 2.4244(17),Mo1eC27 ¼ 2.1504(19), Mo1eC28 ¼ 1.9494(19), C27eC28 ¼ 1.420(3),C27eH27A ¼ 0.0864(19). Bond angles [�]: O1eMo1eO2 ¼ 145.61(5),O1eMo1eN1 ¼ 102.36(6), O1eMo1eN2 ¼ 73.40(6), O1eMo1eC27 ¼ 105.05(6),O1eMo1eC28 ¼ 89.16(6), O2eMo1eN1 ¼ 100.93(6), O2eMo1eN2 ¼ 79.51(6),O2eMo1eC27 ¼ 81.19(6), O2eMo1eC28 ¼ 113.73(6), N1eMo1eN2 ¼ 95.49(6),N1eMo1eC27 ¼ 125.10(7), N1eMo1eC28 ¼ 94.74(7), N2eMo1eC27 ¼ 137.65(7),N2eMo1eC28 ¼ 161.32(7), C27eMo1eC28 ¼ 40.15(7), Mo1eC27eC12 ¼ 88.30(11),C28eC27eC12 ¼ 124.13(17), Mo1eC27eC28 ¼ 62.28(10), Mo1eC28e C27 ¼ 77.57(11),Mo1eC27eH27A¼ 122.50(13), C12eC27eH27A¼ 114.3(13), C28eC27eH27A¼ 121.6(13).

two singlets at 1.60 ppm and 1.40 ppm for the OCO tBu protons,indicating the complex is C1-symmetric. The amido methyls reso-nate as two singlets at 3.65 and 3.58 ppm, whereas the aminemethyl protons resonate as a singlet at 1.73 ppm integrating to sixprotons. In the IR spectrum of 10-H the NeH stretch appears at3280 cm�1. The metallocyclopropene proton attached to C27resonates at 4.82 ppm. Consistent with the unusual metricparameters for C27, it also resonates downfield at 73.1 ppm in the13C{1H} NMR spectrum of 10-H. A resonance appears downfield at252 ppm, typical for alkylidene carbons, and is attributable to C28of metallocyclopropene. The NMR spectral data of 10-F and 10-CF3are similar to 10-H. To confirm their spectral assignments (seeSupporting information) a suite of 1D and 2D NMR techniques wereperformed on a benzene-d6 solution of 10-F to provide the absoluteassignment of all 1H and 13C{1H} NMR signals. Table 2 lists the NMRassignments for 10-F.

2.4. Synthesis andcharacterizationofmetallocyclopropenecomplex11

The reductive coupling of alkynes (Eq. (2)) by Cummins et al.does not work for terminal alkynes substituted with the electron-donating groups eSiMe3 and eC(CH3)3. The alkynes do add to the

2

O

O

MoSiMe3

NH

N

11 (86%)

O

O

Mo NN

HNH

Me3Si

C6D6

(3)

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e4089 4085

molybdenum ion to form the corresponding silyl (8-SiMe3) andtert-butyl (8-tBu) alkyne complexes [43]. Subsequent treatment of8-SiMe3 with Li[BHEt3] provides the trisanilide Mo-cyclopropenecomplex (Ar[iPr]N)3Mo(h-CH2CSiMe3). Converting the anilideligands to adamantylalkoxides and thermolysis ultimately results

Table 2Atomic labeling key representation and the complete assignments of the 1H and 13C{1H} NMR chemical shifts determined from the 1He1H and 1He13C (one-bond andlong-range) couplings observed in the DQCOSY, gHMQC and gHMBC spectra,correspondingly. The chemical shifts of the ligands were assigned based on nOes.The NMR spectra of 10-F were recorded in benzene-d6 at 15 �C on a Varian Inovaspectrometer, operating at 500 MHz for 1H, and at 125 MHz for 13C. The probe wasa 3-channel indirect detection, with z-axis gradients.

C10 C11

C7C8

C9

C13

C14

C15 C16

C18

C3C4

O2

O3

MoC12

C6C1

C5C2

C17

C32

C31

C34C33

C28

C27

C30C29

C19 C20 C21

C22C23

C24

C25

C26

F

F

N1N2C38

C37

C36

C35H

Position Alternate position dC dH

1 e 158.8 e

2 e 138.7 e

3 e 126.2 7.414 e 119.0 7.045 e 128.0 7.626 e 130.2 e

7 e 144.4 e

8 e 129.3 7.399 e 128.1 6.8410 e 131.5 6.7811 e 145.7 e

12 e 126.0 e

13 e 132.1 e

14 e 126.8 6.8715 e 118.5 6.3916 e 123.8 6.8717 e 134.1 e

18 e 174.3 e

19 e 71.0 4.6320 e 247.6 e

21 e 140.4 e

22 26 114.3 6.6923 25 161.8 e

24 e 102.1 6.1127 31 35.2 e

28, 29, 30 e 30.7 1.3532, 33, 34 e 30.7 1.5435 e 63.6 3.5536 e 49.9 3.4637 38 39.7 1.61

Fig. 5. Molecular structure of 11 with ellipsoids drawn at the 50% probability level andhydrogen atoms removed for clarity. Selected bond distances [Å]: Mo1eO1 ¼ 1.997(3),Mo1eO2 ¼ 1.997(3), Mo1eN1 ¼ 1.938(4), Mo1eN2 ¼ 2.424(4), Mo1eC23 ¼ 2.116(5),Mo1eC24 ¼ 1.966(5), C23eC24 ¼ 1.421(6). C23eH1 ¼ 0.91(4). Bond angles [�]:O1eMo1eO2 ¼ 145.93(12), O1eMo1eN1 ¼ 101.85(14), O1eMo1eN2 ¼ 79.16(13),O1eMo1eC24 ¼ 113.99(16), O1eMo1eC23 ¼ 81.85(16), O2eMo1eN1 ¼ 145.93(12),O2eMo1eN2 ¼ 73.61(13), O2eMo1eC23 ¼ 105.28(16), O2eMo1eC24 ¼ 89.78(15),N1eMo1eN2 ¼ 95.27(15), N1eMo1eC23 ¼ 125.27(16), N1eMo1eC24 ¼ 93.39(17),N2eMo1eC23 ¼ 137.99(16), N2eMo1eC24 ¼ 162.43(15), C24eMo1e C23 ¼ 40.53(17),Mo1eC23eC12 ¼ 88.8(3), C24eC23eC12 ¼ 126.9(4), Mo1eC23eC24 ¼ 64.0(3),Mo1eC24e C23 ¼ 75.4(3), Mo1eC23eH1 ¼ 124(3), C24eC23eH1 ¼ 118.0(3),C12eC23eH1 ¼ 115.0(3).

in silyl migration to produce the alkylidyne complex(AdO)3MhCCH2SiMe3 [44]. A similar silyl migration from a metal-locyclopropene was reported by Green [48]. In our system trime-thylsilyacetylene (HeChCSiMe3) reacts with 2 in the same way asthe electron-deficient arylalkynes to form the correspondingsilylmetallocyclopropene 11 in 86% yield as a red-orange solidaccording to Eq. (3). Thermolysis of 11 in a sealed NMR tube (C6D6)at 120 �C for 3 h did not result in silyl migration as no discernablechange in the 1H NMR spectrum was observed.

The NMR spectroscopic data for complex 11 is similar to thosefor complexes 10-R (see Supplementary information). An impor-tant difference includes the downfield signal for the alkylidenecarbon within the metallocyclopropene at 281.1 ppm, presumablya consequence of the more electron-donating eSiMe3 substituent.Also, restricted rotation of the dimethylamine results in two signalsfor the methyl protons at 25 �C; one appears at 1.61 ppm and thesecond overlaps with the tBu protons. Lowering the temperature ofthe NMR probe to �65 �C shifts the resonances such that both arewell resolved at 1.87 and 1.15 ppm.

Complex 11 crystallizes in Et2O at �35 �C as single crystalssuitable for X-ray analysis. The metric parameters and coordinationgeometry are akin to those observed for 10-H. Similar featuresinclude a short Mo1eC24 ¼ 1.966(5) Å (10-H: 1.9494(19) Å),a single bond between Mo1 and C23 ¼ 2.116(5) Å (10-H:2.1504(19) Å), and a single bond between C23 and C24 ¼ 1.421(6) Å(10-H: 1.420(3) Å). The experimentally determined C23eH1 bondlength of C23eH1¼ 0.91(4) Å is statistically similar to that found in10-H (0.864(19) Å (Fig. 5).

3. Computational results

3.1. Density function theory geometry optimization of 10-H0

Spin-restricted density functional theory calculations, includinggeometry optimization, NBO analysis, and single point analysis wereperformed to model 10-H. The computed bond distances for 10-H0

agree with crystallographically determined values: the calculated(experimental) MoeO distances are 2.0291 Å (1.9915(13) Å) and

Fig. 6. Highest occupied molecular orbital (HOMO; left) and lowest unoccupied molecular orbital (LUMO; right) for 10-H0 .

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e40894086

2.018 Å (1.9909(13) Å), the MoeN1 (amide) distance is 1.9602 Å(1.9427(16)Å) and that forMo-N2 (amine) is 2.4887Å (2.4244(17)Å).The calculation is also in agreement with the metric parameters ofC27, which is significantly distorted from an idealized tetrahedralgeometry. The calculated (experimental) MoeC27eC12 is 92.33�

(88.30(11)�), MoeC27eC28 is 62.15� (62.28(10)�) and that ofC28eC27eC12 is 125.07� (124.13 (17)�). The metallocyclopropenemoiety represents the most interesting feature of this molecule. Thecalculated (experimental) MoeC28 bond length is 1.9674 Å (1.9494(19) Å) and that of MoeC27 is 2.1742 Å (2.1504(19) Å). The shortdistance between Mo and C23 is consistent with the assignment ofa double bond characteristic of known examples [45e50]. NBO [58]population analysis provides additional support for the bondingbetween Mo1 and C28. The NBO analysis reveals two types ofbonding interactions between Mo1 and C28 supporting the assign-ment of a double bond: a) s-type with occupancy of 1.90767, and b)p-type with occupancy of 1.81470 electrons. Finally, the C27eC28bond of 1.4342 Å matches 10-H (1.420(3) Å).

The highest occupied KohneSham molecular orbital (HOMO)represents a p-combination between dyz of Mo1 and the py orbitalof C28, and the corresponding p*-combination of those orbitalsconstitutes the lowest unoccupied molecular orbital (LUMO) witha HOMOeLUMO gap of 3.18 eV (Fig. 6). This electronic differencewould result in an absorption centered at 390 nm in the UVevisspectrum of 10-R. The complexes 10-R and 11 are all orange-redand their UVeVis spectra exhibit two absorptions at 250 and350 nm (see Supplementary information). Assigned to the 350 nmis the HOMOeLUMO transition, and the more intense higherenergy transition at 250 nm is most likely a pep* LMCT.

4. Conclusions

The synthesis of [tBuOCHO]Mo(NAr)CHCMe2Ph (5) demon-strates a convenient method of converting a terphenyl diphenolateligated complex into the corresponding trianionic pincer ligand.Treating 5with Ph3P]CH2 results in the formation of the trianionicpincer complex {[tBuOCHO]Mo(NAr)(CHCMe2Ph)}{Ph3PCH3} (6).Employing the dilithio salt [tBuOCHO]Li2(THF)3 (6) can be advan-tageous because trilithio salts containing an aryleLi bond are proneto reducing the metal ion during metallation [27]. The two-stepsynthesis of attaching the aryloxides to the metal ion followed bydeprotonation of the CipsoeH bond may be a viable approach fora wider scope of trianionic pincer ligated metal complexes.

The synthesis of the metallocyclopropene complexes 9-R and 10demonstrates the susceptibility of trianionic pincer ligandMeCpincer bonds to insertion. Instead of deprotonating terminalalkynes to induce reductive coupling and alkylidyne formationaccording to Scheme 3A, the MoeCpincer bond of 2 acts as an

internal nucleophile toward the bound alkyne to form a metal-locyclopropene (Scheme 3B). Insertion of an alkyne into a coordi-nated arene to form metallocyclopropenes is known [52e54], andoccurs swiftly once a coordination site opens on the metal ion.Insertion into the MoeCpincer bond of 2 occurs for both electron-deficient and -rich terminal alkynes, thus the metal-locyclopropene appears to be unavoidable and alternative syntheticroutes and ligand designs are required to access trianionic pinceralkylidyne complexes, which are the subject of ongoing studies.

5. Experimental

5.1. General

Unless specified otherwise, all manipulations were performedunder an inert atmosphere using standard Schlenk or gloveboxtechniques. Glassware was oven dried before use. Pentane, toluene,diethyl ether (Et2O), tetrahydrofuran (THF), and 1,2-dimethoxyethane (DME) were dried using a GlassContours dryingcolumn. Benzene-d6 (Cambridge Isotopes) was dried over sodium-benzophenone ketyl and distilled or vacuum transferred andstored over 4-Å molecular sieves. Commercially available Mo(NAr)(CHCMe2Ph)(OTf)2(DME) (where Ar ¼ 2,6-diisopropyl phenyl) wasused without further purification. Complex [tBuOCO]Mo(NMe2)(NHMe2)2 (2) [26] and [tBuOCO]H3 (1) [26]were prepared accordingto published literature procedures. All alkynes were purified bypassing through neutral alumina, an anhydrous magnesium sulfatepacked column anddegassed by three cycles of freezeepumpethawprior to use. NMR spectra were obtained on Varian Mercury BroadBand 300 MHz, Varian Mercury 300 MHz, or on Varian Inova500MHz spectrometers. Chemical shifts are reported in d (ppm). For1H and 13C{1H} NMR spectra the solvent resonance was referencedas an internal reference. 19F and 31P{1H} NMR spectra were refer-enced externally to fluorobenzene and 85% H3PO4, respectively.Elemental analyses were performed at Complete Analysis Labora-tory Inc., Parsippany, New Jersey. FT-IR spectra were recorded ona Thermoscientific instrument using KBr salt plates.

5.2. Synthesis of [tBuOCHO]Li2(THF)3 (6)

A glass vial was charged with [tBuOCO]H3 (1) (133 mg,0.354 mmol) and THF (2 mL) and then cooled to�35 �C. To the coldsolution, nBuLi (0.29 mL, 0.722 mmol; 2.5 M solution in hexanes)was added drop-wise over a period of 5 min. The resulting mixturewas warmed to 23 �C, and was stirred for 30 min at ambienttemperature. All volatiles were removed in vacuo to yield a color-less crystalline solid of 6 (210 mg, 96%). 1H NMR (300 MHz, C6D6),d (ppm): 8.54 (bs, 1H, Ar-H), 7.66 (dd, J ¼ 7.3 Hz, 2H, Ar-H), 7.53 (dd,

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e4089 4087

J¼ 7.6 Hz, 2H, Ar-H), 7.27e7.37 (m, 3H, Ar-H), 3.33 (t, J¼ 6.7 Hz,12H,eOCH2), 1.70 (s, 18H, eC(CH3)3), 1.18 (t, J ¼ 6.7 Hz, 12H, eCH2). 13C{1H} NMR (75.36 Hz, C6D6) d (ppm): 166.6, 141.7, 138.6, 132.1, 130.7,130.1, 127.5, 127.4, 127.3, 114.0, 68.5 (s, eOCH2), 36.0 (s, eC(CH3)3),30.8 (s, eC(CH3)3), 25.7 (s, eOCH2CH2).

5.3. Synthesis of [tBuOCHO]Mo(NAr)(CHCMe2Ph) (5)

A glass vial was charged with [tBuOCO]H3 (1) (133 mg,0.354 mmol) and THF (2 mL) and then cooled to�35 �C. To the coldsolution, nBuLi (0.29 mL, 0.722 mmol; 2.5 M solution in hexanes)was added drop-wise over a period of 5 min. The resulting mixturewas warmed to 23 �C, and was stirred for 30 min at ambienttemperature to form [tBuOCHO]Li2(THF)3 (6) in situ. The reactionsolutionwas again cooled to �35 �C and a similarly cold solution ofMo(NAr) (CHCMe2Ph) (OTf)2(DME) (280mg, 0.354mmol) in 2mL ofTHF was added drop-wise over a period of 10 min. Upon addition,the solution color immediately changes from colorless to red. Thereaction mixture was warmed to 23 �C and the solutionwas stirredcontinuously for 1 h. The reaction solution was filtered througha thin layer of Celite� on a frit to remove any insoluble materials. Allvolatiles were removed in vacuo, and the crude product wasredissolved in toluene and filtered again. All volatiles were removedin vacuo, and the remaining microcrystalline solid was trituratedwith cold pentane (3 � 1 mL) to obtain analytically pure reddish-orange 5 (196 mg, 72%). Single crystals deposit from a concen-trated solution of 5 in Et2O at �35 �C. 1H NMR (300 MHz, C6D6),d (ppm): 12.43 (s, 1H, Mo]CH), 8.65 (t, J ¼ 1.8 Hz, 1H, Cipso-H), 7.39(dd, J¼ 8.6Hz, J¼ 1.2Hz, 2H, Ar-H), 7.30 (dd, J¼ 7.9Hz, J¼ 1.8Hz, 2H,Ar-H), 7.20 (m, 1H, Ar-H) 7.10 (dd, J ¼ 7.6 Hz, J ¼ 1.8 Hz, 2H, Ar-H),7.02e7.07 (m, 1H, Ar-H), 6.94 (t, J ¼ 1.8 Hz, 1H, Ar-H), 6.81e6.91 (m,7H, Ar-H), 3.16 (sept, 2H, J¼ 7.0,eCH(CH3)2), 1.71 (s, 6H,eCH3), 1.43(s, 18H, eC(CH3)3), 1.12 (d, J ¼ 6.7 Hz, 6H, eCH(CH3)2), 0.83 (d,J ¼ 7.0 Hz, 6H, eCH(CH3)2). 13C{1H} NMR (75.36 Hz, C6D6), d (ppm):283.0 (s,Mo]CH),161.6,154.3,149.7,147.2,144.3,140.6,132.9,132.2,128.9, 128.8, 128.6, 127.5, 127.3, 126.6, 126.4, 124.4, 123.4, 121.8, 55.8(s, eC(CH3)2Ph), 35.9 (s, eC(CH3)3), 32.2 (s, eCH3), 30.3 (s,eC(CH3)3), 29.0 (s, eCH(CH3)3), 24.2 (s, eCH(CH3)3), 23.5 (s,eCH(CH3)3). Anal. Calcd. for C48H57MoNO2: C, 74.30; H, 7.40; N,1.81.Found: C, 74.18; H, 7.33; N, 1.76.

5.4. Synthesis of {[tBuOCO]Mo(NAr)(CHCMe2Ph)}{Ph3PCH3} (7)

A glass vial was charged with 5 (193mg, 0.249mml) and 2mL oftoluene. To the vial containing 5, a toluene solution (2mL) of Ph3P]CH2 (72 mg, 0.259 mmol) was added drop-wise at 23 �C and theresulting mixture was stirred for 3 h at 23 �C. After stirring, an oilymaterial settles at the bottom of the vial and the solution wasdecanted. The remaining oily material was washed with toluene(2� 1 mL) and then triturated with pentanes (3� 1 mL) to obtain 5as an analytically pure orange-yellow solid (199 mg, 76%). Singlecrystals grow by cooling a concentrated THF solution of 7 to�35 �C.1H NMR (300 MHz, C6D6), d (ppm): 9.78 (s, 1H, Mo]CH), 7.85 (m,1H, Ar-H), 7.40e7.47 (m, 6H, Ar-H), 6.90e7.01 (m, 17H, Ar-H),6.64e6.79 (m, 8H, Ar-H), 1.93 (bs, 9H, eCPh(CH3)2 and PeCH3), 1.70(s, 18H, eC(CH3)3), 1.32 (bm, 12H,eCH(CH3)2). 13C{1H} NMR(75.36 Hz, C6D6), d (ppm): 270.0 (s, Mo]CH), 181.6 (s, MoeCpincer),166.0, 154.7, 153.6, 142.0, 139.4, 135.2 (d, JCP ¼ 3.1 Hz), 134.2, 133.0(d, JCP ¼ 10.4 Hz), 130.0 (d, JCP ¼ 15.3 Hz), 129.7, 128.9, 127.5, 126.3,126.0,125.6,125.4,124.9,124.5,122.6,119.6 (bs),116.0 (aryl), 52.6 (s,eC(CH3)2Ph), 36.0 (s, eC(CH3)3), 31.8 (s, eCH3 and eCH(CH3)3), 31.1(s, eC(CH3)3), 25.1 (s, eCH(CH3)3). 31P{1H} NMR (121M Hz, C6D6)d (ppm): 21.3. Anal. Calcd. for C67H74MoNO2P: C, 76.48; H, 7.09; N,1.33. Found: C, 76.35; H, 7.18; N, 1.07.

5.5. General synthesis of 10-R (R ¼ H, F, CF3) and 11

The following method was employed for the synthesis of 10-R,R ¼ H, F, CF3 and 11, the details for the synthesis of 10-H arepresented as a representative example. A glass vial was chargedwith [tBuOCO]Mo(NMe2)(NHMe2)2 (2) (200 mg, 0.332 mmol) and2 mL of benzene. PhChCH (36.5 mL, 0.332 mmol) was added tothe stirring solution of 2 at 23 �C and the mixture was stirred for3 h at 23 �C. Insoluble materials were removed by filtrationthrough a thin layer of Celite� and the filtrate was evaporated invacuo to obtain a solid which was triturated with pentanes(3 � 1 mL). Redissolving the complex in pentanes and filteringto remove any remaining insoluble materials followed by solventremoval provides analytically pure red-orange 10-H (180 mg,82%).

5.6. Characterization data for 10-H

10-H: yield 82%. 1H NMR (300 MHz, C6D6), d (ppm): 7.68 (d,J¼ 7.0 Hz,1H, Ar-H), 7.45 (d, J¼ 7.0, 2H, Ar-H), 7.21 (d, J¼ 8.3 Hz, 2H,Ar-H), 6.86e7.10 (m, 7H, Ar-H), 6.72 (t, J¼ 7.3,1H, Ar-H), 6.40 (m,1H,Ar-H), 4.82 (s, 1H, Mo-CH), 3.65 (s, 3H, N-CH3), 3.58 (s, 3H, N-CH3),1.73 (s, 6H, NH-CH3), 1.60 (s, 9H, eC(CH3)3), 1.40 (s, 9H, eC(CH3)3).13C{1H} NMR (75.36 Hz, C6D6), d (ppm): 252.0 (s, Mo]C), 174.6, 163,159.3, 146.2, 144.8, 139.2, 138.9, 134.3, 133.2, 132.7, 132.0, 130.9,129.6, 129.1, 128.2, 127.9, 127.8, 127.5, 127.3, 126.6, 124.2, 119.1, 118.5,73.1 (s, Mo-CH, 64.2 (s, N-CH3), 50.8 (s, N-CH3), 43.7 (s, NH-CH3),35.8 (s, eC(CH3)3), 31.2 (s, eC(CH3)3). Anal. Calcd. forC38H46MoN2O2: C, 69.28; H, 7.04; N, 4.25. Found: C, 69.19; H, 6.98;N, 4.07.

5.7. Characterization data for 10-F

10-F: yield 80%. 1H NMR (300 MHz, C6D6), d (ppm): 7.65 (d,J ¼ 6.7 Hz, 1H, Ar-H), 7.43 (d, J ¼ 5.5 Hz, 2H, Ar-H), 7.06 (overlappeddoublets, J¼ 7.6 Hz, J¼ 7.3 Hz,1H, Ar-H), 6.89 (m, 3H, Ar-H), 6.81 (d,J ¼ 7.3, 1H, Ar-H), 6.72 (dd, J ¼ 8.6 Hz, J ¼ 2.4 Hz, 2H, Ar-H), 6.42 (t,J ¼ 7.0 Hz, 1H, Ar-H), 6.11e6.18 (m, 1H, Ar-H), 4.65 (s, 1H, Mo-CH),3.58 (s, 3H, N-CH3), 3.51 (s, 3H, N-CH3), 1.68 (s, 6H, NH-CH3), 1.56 (s,9H,eC(CH3)3),1.38 (s, 9H,eC(CH3)3). 13C{1H} NMR (75.36 Hz, C6D6),d (ppm): 248.4 (s, Mo]C), 174.8, 164.0 (d, JCF ¼ 12.1 Hz), 160.7 (d,JCF ¼ 13.4 Hz), 159.2 (bs), 146.2, 144.9, 141.0, 140.9, 140.8, 139.3,134.6, 132.5, 132.0, 130.7, 129.8, 127.3, 126.8, 126.6, 124.3, 119.4,118.9, 114.0 (overlapped doublets, JCF ¼ 18.3 Hz, JCF ¼ 17.1 Hz), 102.6(t, JCF ¼ 25.6 Hz) (aryl),71.5 (s, Mo-CH, 63.8 (s, N-CH3), 50.2 (s, N-CH3), 40.2 (s, NH-CH3), 35.8 (s, eC(CH3)3), 31.2 (s, eC(CH3)3). Anal.Calcd. for C38H43MoN2O2: C, 65.79; H, 6.25; N, 4.04. Found: C,65.79; H, 6.17; N, 3.93.

5.8. Characterization data for 10-CF3

10-CF3: yield 83%. 1H NMR (300 MHz, C6D6), d (ppm): 7.62 (bs,3H, Ar-H), 7.42 (m, 2H, Ar-H), 7.33 (bs, 1H, Ar-H), 7.05 (t, J ¼ 7.6 Hz,1H, Ar-H), 6.74e6.90 (m, 4H, Ar-H), 6.24 (t, J¼ 7.3 Hz,1H, Ar-H), 4.63(s, 1H, Mo-CH), 3.60 (s, 3H, N-CH3), 3.50 (s, 3H, N-CH3), 1.64 (s, 6H,NH-CH3), 1.54 (s, 9H,eC(CH3)3), 1.38 (s, 9H,eC(CH3)3). 13C{1H} NMR(75.36 Hz, C6D6), d (ppm): 246.1 (s, Mo]C), 175.4, 159.28, 146.2,144.8, 139.4, 139.3, 134.5, 132.3, 132.0, 131.7, 130.7 (q, JCF ¼ 32.2 Hz,eCF3), 129.8, 129.0, 127.8, 126.9, 126.5, 126.2, 124.3, 122.9, 119.9,119.6, 119.0, 71.5 (s, Mo-CH, 64.2 (s, N-CH3), 50.3 (s, N-CH3), 40.2 (s,NH-CH3), 35.8 (s, eC(CH3)3), 31.1 (s, eC(CH3)3), 30.7 (s, eC(CH3)3).Anal. Calcd. for C40H44F6MoN2O2: C, 60.45; H, 5.58; N, 3.52. Found:C, 60.37; H, 5.39; N, 3.46.

M.T. Jan et al. / Journal of Organometallic Chemistry 696 (2011) 4079e40894088

5.9. Characterization data for 11

11: yield 86%. 1H NMR (500 MHz, toluene-d8), d (ppm): 7.57 (d,J¼ 7.5 Hz, 1H, Ar-H), 7.34 (d, J¼ 7.5 Hz, 1H, Ar-H), 7.29 (t, J¼ 7.6, 2H,Ar-H), 6.94 (t, J¼ 7.6 Hz, 2H, Ar-H), 6.88 (d, J¼ 7.5, 1H, Ar-H), 6.74 (t,J¼ 7.6 Hz,1H, Ar-H), 5.01 (s, 1H, Mo-CH), 3.58 (s, 3H, N-CH3), 3.51 (s,3H, N-CH3), 1.46 (s, 9H,eC(CH3)3), 1.33 (s, 9H,eC(CH3)3), 0.15 (s, 9H,eSi(CH3)3). 13C{1H} NMR (125.70 Hz, toluene-d8), d (ppm): 281.1 (s,Mo]C), 176.0, 143.8, 138.8, 134.4, 133.1, 129.8, 127.4, 127.9, 126.0,124.1, 119.6, 118.9 (aryl), 85.1 (s, Mo-CH), 58.6 (s, N-CH3), 53.6 (s,NH-CH3), 42.1 (s, N-CH3), 35.4 (s, eC(CH3)3), 30.3 (s,eC(CH3)3), 30.1(s, eC(CH3)3), 0.3 (s, eSi(CH3)3). C35H50MoN2O2Si: C, 64.20; H, 7.70;N, 4.28. Found: C, 63.97; H, 7.59; N, 4.17.

5.10. Density function theory geometry optimization of 10-H0

Spin-restricted density functional theory calculations, includinggeometry optimization, NBO analysis, and single point analysiswere performed for 10-H0 using a hybrid functional (the three-parameter exchange functional of Becke (B3) [59] and the corre-lation functional of Lee, Yang, and Parr (LYP) [60] (B3LYP) asimplemented in the Gaussian 03 program suite [61]. The LANL2DZbasis set and effective core potential were used for all atomswithin 10-H0 [62]. The geometry was optimized using atomiccoordinates from the crystal structure as an initial input andcalculations for the vibrational frequencies were performedalongside the geometry optimization to ensure the stability of theground state as denoted by the absence of imaginary frequencies.Molecular orbital pictures were generated from Gabedit at iso-values of 0.06 au [63].

Acknowledgment

ASV thanks UF, NSF CAREER (CHE-0748408), the Camille andHenry Dreyfus Foundation, and The Alfred P. Sloan Foundation forfinancial support of this work. KAA thanks UF and the NSF CHE-0821346 for funding the purchase of X-ray equipment. Computa-tional resources were provided by the University of Florida High-Performance Computing Center.

Appendix. Supplementary material

CCDC 824553, 824554, 824555, 824556, and 824557 containsthe supplementary crystallographic data for 6-OEt2, 5, 10-H, 7, and11, respectively. Copies of the data can be obtained free of chargefrom the Director, CCDC, 12 Union Road, Cambridge CB2 1EX, UK(fax: þ44 1223 336033. email: deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk/).

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.jorganchem.2011.06.006.

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