Stannylene-Based Lewis PairsSarah Freitag, Kilian M. Krebs, Jens Henning, Janina Hirdler, Hartmut Schubert, and Lars Wesemann*

Institute of Inorganic Chemistry, University of Tubingen, Auf der Morgenstelle 18, 72076 Tubingen, Germany

*S Supporting Information

ABSTRACT: Intramolecular stannylene-based Lewis pairs with phos-phine Lewis bases were synthesized at the ortho position in benzene orthe peri position in acenaphthene. The spectroscopic data of the Lewispairs are discussed, and the reactivity toward unsaturated hydrocarbonsand organic azides is presented.

■ INTRODUCTIONResearch concerning frustrated Lewis pairs (FLPs) is currentlyof major interest because of their reactivity toward smallmolecules such as dihydrogen, olefins, aryl azides, carbondioxide, and alkynes.1−3 Furthermore, FLPs were investigatedto act as catalysts in hydrogen transfer reactions or in the metal-free reduction of syngas.1,4 This research was started withphosphines as Lewis bases and boranes as Lewis acids.1

Carbenes as well as amines and imines were also introduced toact as the Lewis bases in FLPs.5,6 In the case of the Lewis acidicpart of the FLPs recently the use of alanes and transition metalswas published.2,7 Generally FLPs were studied as inter-molecular Lewis pairs of two molecules or intramolecularcombinations of a Lewis acidic and a Lewis basic fragment inone molecule. Recently we have presented a synthesis forphosphastannirane A (Chart 1), a three-membered cyclic

molecule, showing reactivity in addition reactions with alkynes(B) and reversible addition of 1-pentene (C).8 This stannylene-based Lewis pair A was synthesized straightforwardly byreaction of the lithiated benzyldiphenlyphosphine withisopropyl-substituted m-terphenyltin chloride.In order to study the intramolecular Sn−P interaction more

generally, we started to synthesize Lewis pairs with suitablebackbones. ortho-Substituted benzene and ortho-substitutednaphthalene or acenaphthene are prominent molecules for theinvestigation of such intramolecular interactions.9−17 In thispublication we present the formation of two Sn−P Lewis pairson the basis of ortho substitution at benzene and 5,6-

substitution at acenaphthene together with a discussion oftheir molecular structures, spectroscopic data, and reactivitytoward alkynes and azides.

■ RESULTS AND DISCUSSIONSynthesis. The benzene-based Sn−P Lewis pair was

synthesized straightforwardly following a Br−Li exchange at(2 -b romopheny l )d ipheny lphosph ine to g ive (2 -(diphenylphosphino)phenyl)lithium (1), which was reactedwith isopropyl-substituted m-terphenyltin chloride 2 (Scheme1). The diarylstannylene 3 was recrystallized from a mixture of

benzene and hexamethyldisiloxane to give crystals suitable forX-ray diffraction. Other solvent mixtures did not give crystals ofhigh quality.Following a reaction sequence corresponding to the synthesis

of 3, the Lewis pair 5 was synthesized starting with 5-bromo-6-(diisopropylphosphino)acenaphthene (4) in moderate yield(Scheme 2). Lewis pairs 3 and 5 are both sensitive towardmoisture and air and were characterized by heteronuclear NMRspectroscopy, crystal structure analysis, and elemental analysis.

Crystallographic Analysis. Single-crystal X-ray diffractiondata were obtained for both stannylenes 3 and 5. The crystalsare orange (3) or brown (5) and are soluble in all common

Special Issue: Applications of Electrophilic Main Group Organo-metallic Molecules

Received: July 26, 2013

Chart 1. Recent Examples of Sn−P Lewis Pairs and Productsof the Reactions with Phenylacetylene (B) and Pentene (C)a

aR = C6H3-2,6-Trip2, Trip = C6H2-2,4,6-iPr3.

Scheme 1. Synthetic Procedure for the Benzene-Based LewisPair 3a

aTrip = C6H2-2,4,6-iPr3.

Article

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solvents. Crystal structure and refinement data are given in theSupporting Information. In Figures 1 and 2 the molecular

structures of 3 and 5 are respectively depicted together withselected interatomic distances and angles. The phosphinoaryl-and phosphinoalkyl-substituted stannylenes 3 and 5 both formP−Sn donor−acceptor bonds in the solid state: 2.7489(4) Å

(3) and 2.6362(6) Å (5). These bond lengths can be comparedwith the P−Sn bond length of 2.663(1) Å in the three-membered cycle A. They lie in the range of published P−Snbond lengths and belong to the group of longer distances.18−26

In compound 3 we find a much shorter contact between the Patom and the Sn(II) atom, Sn−P = 2.7489(4) Å, in comparisonto the ortho-Sn(IV)-substituted phosphinophenyl molecule D(Chart 2), Sn−P = 3.125(4) Å.9,27,28 Therefore, the angles at

the carbon atoms inside the four-membered ring (Sn−P−C−C) are smaller in 3 than in D (3, P−C2−C1 = 108.81(9)°,C2−C1−Sn = 108.11(9)°; D, P1−C6−C1 = 113.1(13)°, Sn1−C1−C6 = 117.9(12)°). Obviously the Sn(II) atom in 3 exhibitsa much stronger Lewis acidity than the Sn(IV) atom in D.Intramolecular Lewis pairs in ortho-substituted benzenederivatives were also studied in the case of P−B and Sn−Ninteractions (E and F in Chart 2).12,29 Since the presented Sn−P interaction in the acenaphthene Lewis pair 5 is the firstinteraction between these elements in peri position, we can onlycompare this interaction with a variety of other element−element interactions studied also in peri position atacenaphthene or naphthalene.10−12,14 Following the geo-metrical considerations made by Woollins for peri-substitutedacenaphthene derivatives, we found a very small splay angle of0.7°, indicating a Sn−P interaction.30 The displacements fromthe mean acenaphthene plane to the same side of 0.4 Å (Snatom) and 0.01 Å (P atom) and the buckling of theacenaphthene framework (central torsion angles 2 and 1°) liein the range of published substitution derivatives.30 Sn−Ninteractions were found in a bis(naphthyl)tin(II) compound,and weak interactions between bromine and tin(IV) atomswere studied in an acenaphthene derivative.10,31

NMR Spectroscopy. Selected NMR spectroscopic data forA, 3, 5, and D are given in Table 1. The 119Sn NMR resonancesof the Sn(II)−P Lewis pairs A, 3, and 5 (Chart 3) show atendency to resonate at higher field with increasing ring size.The same tendency has been observed for dialkylamino basestabilized stannylenes: the molecule with the four-memberedring shows a 119Sn signal at 442 ppm, and the signal for the

Scheme 2. Formation of the Acenaphthene-Based Lewis Pair5a

aTrip = C6H2-2,4,6-iPr3.

Figure 1. ORTEP plot of the molecular structure of 3. Hydrogenatoms have been omitted; ellipsoids are given at the 50% probabilitylevel. Interatomic distances (Å) and bond angles (deg): Sn−P =2.7489(4), Sn−C1 = 2.235(1), Sn−C3 = 2.233(1), P−C2 = 1.809(1),C1−C2 = 1.403(2); C1−Sn−P = 62.5(1), Sn−P−C2 = 78.9(1), C3−Sn−C1 = 105.8(1), C3−Sn−P = 100.1(1), P−C2−C1 = 108.8(1),C2−C1−Sn = 108.11(9), C4−C1−Sn = 133.1(1), C5−C2−P =128.4(1), P−C2−C1−Sn = 13.4(1).

Figure 2. ORTEP plot of the molecular structure of 5. Hydrogenatoms have been omitted; ellipsoids are given at the 50% probabilitylevel. Interatomic distances (Å) and bond angles (deg): Sn−P =2.6362(6), Sn−C1 = 2.238(2), Sn−C3 = 2.269(2), P−C2 = 1.807(2),P−C4 = 1.838(2), P−C5 = 1.837(2); C1−Sn−C3 = 109.2(1), C1−Sn−P = 77.6(1), C3−Sn−P = 101.7(1), Sn−P−C2 = 100.4(1), Sn−P−C4 = 121.4(1), Sn−P−C5 = 114.6(1), C4−P−C5 = 107.0(1), C2−P−C4 = 108.0(1), C2−P−C5 = 103.8(1), C8−C2−P = 115.8(2),C6−C1−Sn = 122.9(2), C8−C1−Sn = 119.8(2), C7−C2−P =123.7(2), C1−C8−C2 = 125.1(2).

Chart 2. a

aR = [C6H3-2,6-(NMe2)2].

Table 1. Selected NMR Data for Previously ReportedCompounds A and D and New Molecules 3 and 5

compd δ(119Sn) (ppm) 1JSn−P (Hz) δ(31P) (ppm)

Aa 716 83 −38.6364b −50.3b

3 554 754 −41.5808,b 740b −42.1,b −46.0b

5 −139 1756 20.3Da −102 18 (3J) −1.0

aNMR data for A8 and D.9 b31P solid-state NMR experiment: in thecase of 3 in the solid-state NMR spectrum two signals were detected.The observation of two signals in the solid-state NMR spectrum of 3 isprobably due to polymorphism.

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stannylenes exhibiting five-membered rings appears at 169 or178 ppm.12,31,32 The solid-state 31P NMR spectrum of 3 is inagreement with the solution NMR spectrum, indicating that themolecules in solution and in the solid state are similar. A littledeeper insight into the phosphorus−tin interaction can begained from the 119Sn NMR chemical shifts. Wrackmeyerproposed a paramagnetic deshielding contribution for tin NMRchemical shifts of tin(II) compounds.33 This contribution arisesfrom magnetically induced charge circulation including theformally vacant Sn 5p orbital and the Sn−R bonding electronsrather than the lone pair at the tin. Taking a look at the threeLewis pairs A, 3 and 5, we see that the Sn−R bonding is largelythe same. Only for the smallest ring A is the bridgingsubstituent an sp3 carbon, and for the larger rings 3 and 5 sp2

carbons are present. We suggest the far more importantinfluence on the paramagnetic deshielding contribution to bethe different Lewis pair interaction: i.e., the donation of thephosphorus lone pair into the Sn 5p orbital. Thus, a moreefficient donor−acceptor interaction would reduce the para-magnetic deshielding by hindering the charge circulation andlead to an NMR resonance shift to higher frequencies. For thethree Lewis pairs A, 3, and 5 the 119Sn resonance frequency canbe interpreted as an indicator for increasing efficiency of the P−Sn coordination in the row A, 3, and 5. In this series the size ofthe P−Sn heterocycles increases and the phosphorussubstituents vary in the case of the acenaphthene derivativefrom phenyl to isopropyl. Thus, also the higher basicity of theisopropyl-substituted phosphane in compound 5 could beresponsible for the increased efficiency of the P−Sn donation in5. This interpretation is consistent with the results of DFTcalculations (see below). Additionally, a supporting observationmight be that the 1JSn−P coupling constant increases in the sameorder.Quantum Chemical Calculations. DFT calculations were

performed on the full molecules 3 and 5 applying the functionalrevPBE-D3(BJ) and a triple-ζ basis set for all electrons.34−41

The Lewis pair A has been calculated previously using the sameparameters.8 The geometries were optimized, and subsequentlynatural bond orbital (NBO) analyses were calculated with theprogram ADF2012,42−44 including the program NBO5.0.45

Detailed information on the computations is given in theSupporting Information. The geometries and donor−acceptorinteractions were reproduced (Figure 3).Reactivity Studies. Recently we have shown that the three-

membered ring A reacts with alkynes and 1-pentene at roomtemperature to give the five-membered cycles B and C.8 Inorder to compare the reactivity of the three Sn−P Lewis pairsA, 3, and 5 (Chart 3), we have studied reactions of the newmolecules 3 and 5 with alkynes. Furthermore, the reactivitytoward adamantyl azide was investigated. The four-membered-

ring molecule 3 reacts regioselectively with phenylacetylene atroom temperature over a period of 13 days to give the six-membered ring 6 (Scheme 3), whereas in the case of the Lewis

pair 5 no reaction with phenylacetylene was detected even afterstirring for several days at room temperature or for 1 day at 70°C. The reaction product 6 was characterized by elementalanalysis, NMR spectroscopy, and single-crystal structureanalysis. By using 31P NMR spectroscopy, the progress of thereaction can easily be monitored: the starting material shows aresonance at −41.5 ppm, and the alkyne insertion product 6exhibits a signal at −1.4 ppm. Both resonances are flanked bytin satellites, with the Sn−P coupling constants in molecule 6being much smaller (99 Hz; 119Sn−31P and 117Sn−31P couplingare not resolved) in comparison to the coupling constants inmolecule 3 (754 Hz, 119Sn−31P; 720 Hz, 117Sn−31P), whichexhibits a direct Sn−P bond (Table 1). Furthermore, the 119Snresonance shifts from 554 ppm (3) to −209 ppm (6).Phosphastannirane A (119Sn NMR: 716 ppm) shows analogousreactions with phenylacetylene to give molecule B (119Sn NMR:100 ppm). Obviously in both cases the alkyne insertionproducts 6 and B (Chart 1) show a resonance in the 119SnNMR at much higher field in comparison to the respectivestarting materials 3 and A. The 119Sn NMR resonance of alkyneinsertion product 6 can also be compared with the signal fortypical triply coordinated tin in [SnPh3]

− at −98.4 ppm.46 Inthe case of the 31P NMR signals in analogy to the low-field shiftfrom compound A (−38.6 ppm) to B (37.4 ppm) we detect ashift from −41.5 ppm (3) to −1.0 ppm (6). A diagnostic signalin the 1H NMR spectrum for the regioselective alkyne insertionis the resonance for the olefinic proton Sn−CH in 6, whichappears at 10.04 ppm and shows coupling to the phosphorusatom (3JP−H = 53.4 Hz) and tin atom (2JSn−H = 26.7 Hz). The

Chart 3. Three-, Four-, and Five-Membered Rings as Sn−PLewis Pairsa

aR = C6H3-2,6-Trip2, Trip = C6H2-2,4,6-iPr3.

Figure 3. NBO results for compounds A, 3, and 5 (left to right):picture of the phosphorus lone pair orbital (left; in each case blue andred) and the tin vacant orbital (right; in each case turquoise andorange). A representation of the angle describing the relativeorientation of the two orbitals is included.

Scheme 3. Reaction of the Benzene-Based Lewis Pair withPhenylacetylene and Adamantyl Azidea

aR = C6H3-2,6-Trip2, Trip = C6H2-2,4,6-iPr3.

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respective carbon atom Sn−CHC exhibits a resonance atunexpected high frequency, beyond 200 ppm.8,47,48 In the five-membered cycle B the respective proton shows a signal at 8.66ppm, also with coupling to the phosphorus atom (3JP−H = 59.4Hz) and tin atom (2JSn−H = 61.1 Hz). The molecular structureof the zwitterionic molecule 6 in the solid state (Figure 4) can

be compared with that of a bicyclic distannide reported byVeith et al. and the structure of the insertion product of(trimethylsilyl)acetylene in phosphastannirane A.8,49 In mole-cule 6 a triply coordinated stannide and a tetracoordinatedphosphonium cation are formed. The sum of the angles at thetin atom (285.3°) is smaller than the sum of angles in [Ph3Sn]

−

(290.3°) and slightly larger than the sum of angles at tin in theinsertion products of the phophastannirane.8,46 This effectmight be due to the ring formation: the angle C1−Sn−C4inside the ring is the smallest angle at the tin atom in 6. Thedistance between the carbon atoms C4 and C5, 1.352(2) Å, islonger than a triple bond and lies in the range of reactionproducts of phenylacetylene with frustrated Lewis pairs: P(o-tol)3/B(C6F5)3 (1.346(3) Å); P(o-tol)3/Al(C6F5)3 (1.341(3)Å).50

The reactivity of the Lewis pairs 3 and 5 was also studied inreactions with adamantyl-substituted azide. At room temper-ature the azide reacts with the Lewis pair 3 to form a five-membered cycle, whereas the peri-substituted Lewis pair showsno reaction (Scheme 3). The azide product 7 was characterizedby elemental analysis, NMR spectroscopy, and single-crystalstructure analysis. In principle two reaction pathways arepossible for the reaction of the triarylphosphine-stabilizedstannylene with the adamantyl azide: a Staudinger-typeaddition at phosphorus or the reaction with the stannylene togive a stannaimine.51−54 The Lewis pair 3 reacts with the azidewith evolution of nitrogen and formation of Sn−N and PNbonds to give the five-membered cycle 7. A reaction with afurther equiv was not detected, even after heating for severalhours with an excess of azide reagent. This reaction should becompared with the reaction of a bis(P∧O)-chelated stannylenewith adamantyl azide, which does not result in the evolution of

nitrogen but in an azide group connected at phosphorus andtin.53 In the 119Sn NMR spectrum a shift to high field and adecrease in the 119Sn−31P coupling constant was detected forproduct 7. In Figure 5 the molecular structure determined in

the solid state is depicted. The lengths of the PN (1.613(5),1.608(4) Å) and Sn−N (2.305(4), 2.292(4) Å) bonds lie in thetypical ranges for these type of bonds.53,55,56 The sums of theangles at tin, 290.56 and 292.76°, indicate a pyramidallycoordinated Sn(II) atom.The chemistry of intramolecular stannylene-based Lewis

pairs will be further explored, especially with respect to theinfluence of ring size and effects of substituents at tin andphosphorus on the reactivity.

■ CONCLUSIONSLewis pairs with stannylenes acting as the Lewis acids andphosphines as the Lewis bases were constructed at the orthoposition in benzene and peri position in acenaphthene (Chart3). The Lewis pair exhibiting the four-membered ring is lessreactive with respect to alkyne addition in comparison tophosphastannirane A (Chart 3). The acenaphthene derivative 5shows no reaction with alkynes. Considering the reactivity andNMR spectroscopic data, we conclude that the effectiveness ofthe P−Sn interaction increases in the order A, 3, and 5.

■ EXPERIMENTAL SECTIONGeneral Procedures. All manipulations were carried out with

exclusion of air and moisture under an argon atmosphere usingstandard Schlenk techniques and gloveboxes. Solvents were purified bystandard methods. Elemental analyses were performed by the Institutfur Anorganische Chemie Universitat Tubingen using a Vario ELanalyzer and a Vario MICRO EL analyzer. The starting materials [2,6-Trip2(C6H3)SnCl] (Trip = C6H2-2,4,6-iPr3),

57−60 o-Li(OEt2)-phenyl-diphenylphosphine,61 and 5-bromo-6-diisopropylphosphinoacenaph-thene62 were synthesized following a literature procedure. All furtherchemicals used were purchased commercially and were not furtherpurified.

NMR. NMR spectra were recorded with a Bruker DRX-250 NMRspectrometer equipped with a 5 mm ATM probe head and operating

Figure 4. ORTEP plot of the molecular structure of 6. Hydrogenatoms have been omitted; ellipsoids are given at the 50% probabilitylevel. Interatomic distances (Å) and bond angles (deg): Sn−C1 =2.217(2), Sn−C3 = 2.244(2), Sn−C4 = 2.195(2), C1−C2 = 1.407(2),P−C2 = 1.802(2), P−C5 = 1.798(2), C5−C4 = 1.352(2); C1−Sn−C3= 94.52(5), C1−Sn−C4 = 89.50(6), C3−Sn−C4 = 106.3(1), Sn−C1−C2 = 123.3(1), C1−C2−P = 120.6(1), C2−P−C5 = 114.41(7),P−C5−C4 = 119.0(1), C5−C4−Sn = 126.0(1).

Figure 5. ORTEP plot of the molecular structure of 7. Hydrogenatoms have been omitted; ellipsoids are given at the 50% probabilitylevel. Two molecules of compound 7 together with two molecules ofhexane were found in the asymmetric unit. Interatomic distances (Å)and bond angles (deg) (values for the second molecule are given inbrackets): Sn−N = 2.305(4) [2.292(4)], Sn−C1 = 2.245(6)[2.213(5)], Sn−C3 = 2.321(6) [2.324(6)], P−N = 1.613(5)[1.608(4)], C1−C2 = 1.391(7) [1.408(7)], P−C2 = 1.798(5)[1.796(5)]; N−Sn−C3 = 107.2(2) [109.4(2)], C1−Sn−N = 80.3(2)[80.3(2)], C1−Sn−C3 = 103.0(2) [104.5(2)], N−P−C2 = 107.0(2)[106.5(2)], C1−C2−P = 115.9(4) [115.7(4)].

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at 250.13 (1H) and 101.25 MHz (31P), a Bruker AVII+ 400 NMRspectrometer equipped with a 5 mm QNP (quad nucleus probe) headoperating at 400.13 (1H), 100.13 (13C), and 161.97 (31P) MHz, and aBruker AVII+ 500 NMR spectrometer with a 5 mm ATM probe headand operating at 500.13 (1H, Ξ = 100%), 125.76 (13C, Ξ =25,145020%), 202.5 (31P, Ξ = 40.480742%), and 186.5 MHz (119Sn,Ξ = 37.290632%). Chemical shifts are reported in δ values in ppmrelative to external TMS (1H), 85% aqueous H3PO4 (

31P), and SnMe4(119Sn) using the chemical shift of the solvent 2H resonance frequency.The proton and carbon signals were assigned by a detailed analysis of1H, 13C, 1H−1H COSY, 1H−13C HSQC, 1H−13C HMBC, and13C{1H} DEPT-135. Solid-state 31P NMR spectra were recorded withramped amplitude cross-polarization magic-angle spinning (CP/MAS)on a Bruker DSX-200 super widebore NMR spectrometer using a 4mm double-bearing MAS probe head.Crystallography. X-ray data for compounds 3 and 5−7 were

collected with a Bruker Smart APEX II diffractometer with graphite-monochromated Mo Kα radiation. The programs used were Bruker’sAPEX2 v2011.8-0, including SADABS for absorption correction andSAINT for structure solution, as well as the WinGX suite of programsversion 1.70.01 or the program ShelXle, including SHELXS forstructure solution and SHELXL for structure refinement.63−67 Resultsof the crystal structure determination are presented in the SupportingInformation.Synthesis of Compound 3. (C6H3-2,6-Trip2)SnCl (800 mg, 1.26

mmol) was dissolved in a mixture of hexane (30 mL) and benzene (6mL) to give an orange solution and cooled to −40 °C. o-Li(OEt2)-phenyldiphenylphosphane (431 mg, 1.26 mmol) was suspended inhexane (10 mL) and benzene (2 mL) and added dropwise to thecooled solution. The orange solution was stirred for 3 h at roomtemperature and filtered through Celite, and the solvent was removedin vacuo. A light orange solid was obtained (yield 1.03 g, 95%). X-ray-quality crystals were grown from a mixture of benzene andhexamethyldisiloxane. 1H NMR (400.13 MHz, C6D6): δ 1.18 (br s,12H, o-CHMe2), 1.32 (d, 12H, o-CHMe2,

3JH−H = 6.7 Hz), 1.45 (d,12H, p-CHMe2,

3JH−H = 6.9 Hz), 3.02 (sept, 2H, p-CHMe2,3JH−H =

6.9 Hz), 3.39 (sept 4H, o-CHMe2,3JH−H = 6.7 Hz), 6.26 (m, 1H, Ar),

6.97−7.00 (m, 2H, Ar), 7.05−7.09 (m, 6H, Ar), 7.16−7.21 (m, 1H,Ar), 7.30 (s, 4H, C6H2), 7.33−7.37 (m, 1H, p-C6H3), 7.39−7.41 (m,2H, m-C6H3), 7.49−7.53 (m, 4H, Ar). 13C{1H} NMR (62.90 MHz,C6D6): δ 24.0 (o-CHMe2), 24.9 (p-CHMe2), 26.7 (o-CHMe2), 31.7 (o-CHMe2), 35.2 (p-CHMe2), 121.8 (m-C6H2), 127.0, 127.3 (d, JP−C =5.0 Hz), 129.0 (d, JP−C = 5.0 Hz), 130.4 (d, JP−C = 1.9 Hz), 130.7,131.6, 132.6, 133.1 (d, JP−C = 14.6 Hz), 134.2 (d, JP−C = 12.6 Hz),136.4 (d, JP−C = 36.9 Hz), 140.6 (i-C6H2), 143.1 (d, JP−C = 44.5 Hz),147.5 (o-C6H2), 148.4 (p-C6H2), 148.5 (d, JP−C = 1.8 Hz), 169.8 (d,JP−C = 10.0 Hz), 180.8 (d, JP−C = 60.3 Hz). 31P{1H} NMR (101.25MHz, C6D6): δ −41.5 (s, J119Sn−P = 754 Hz, J117Sn−P = 720 Hz); 31P CP/MAS NMR (81.01 MHz): δ −42.1 (s, JSn−P = 808 Hz), −46.0 (s, JSn−P= 740 Hz). 119Sn{1H} NMR (93.25 MHz, C6D6): δ 554 (d, JSn−P =754 Hz). Anal. Calcd for C54H63PSn: C, 75.26; H, 7.37. Found: C,74.92; H, 7.57.Synthesis of Compound 5. 5-Bromo-6-(diisopropylphosphino)-

acenaphthene (150 mg, 0.43 mmol) in Et2O (20 mL) was treated withn-BuLi (1.6 M in hexane; 0.26 mL, 0.43 mmol) at −20 °C. Themixture was stirred at room temperature for 2 h and the resultingorange suspension was added dropwise to a cooled solution (−20 °C)of (C6H3-2,6-Trip2)SnCl (274 mg, 0.43 mmol) in Et2O (20 mL). Themixture was stirred for another 2 h at room temperature, the solventwas removed in vacuo and the residue was treated with hexane (50mL). The resulting precipitate was filtered off and the solvent wasremoved in vacuo. Brown crystals were obtained after crystallizationfrom benzene (2 mL). Yield: 256 mg (69%). 1H NMR (400.13 MHz,C6D6): δ 0.59−0.71 (m, 6H, −CHMe2), 1.00−1.12 (m, 6H,−CHMe2), 1.21−1.26 (m, 6H, Trip-CHMe2), 1.38−1.41 (m, 10H,Trip-CHMe2), 1.53 (d, 14H, Trip-CHMe2,

3JH,H = 7.04 Hz), 1.68 (br,6H, Trip-CHMe2), 2.00 (br, 1H, −CHMe2), 2.38 (br, 1H, −CHMe2),3.06−3.16 (m, 6H, 4 x Trip-CHMe2, 1 × CH2), 3.25 (br, 3H, Trip-CHMe2, 1 × CH2), 3.71 (br, 2H, Trip-CHMe2), 6.44 (d, 1H, 3JH,H =7.03 Hz, Ar), 7.09 (d, 1H, 3JH,H = 7.12 Hz, Ar), 7.20−7.24 (m, 5H,

Ar), 7.30−7.35 (m, 2H, Ar), 7.44 (br, 2H, Ar). 13C{1H} NMR (100.13MHz, C6D6): δ 14.8 (br, −CHMe2), 18.0 (br, −CHMe2), 18.9 (br,−CHMe2), 19.3 (br, −CHMe2), 22.4 (s, −CHMe2), 23.5 (s,−CHMe2), 24.1 (br s, Trip-CHMe2), 24.4 (br s, Trip-CHMe2), 25.7(br s, Trip-CHMe2), 27.5 (br s, Trip-CHMe2), 29.9 (s, −CH2), 30.4 (s,−CH2), 30.7 (br s, Trip-CHMe2), 31.2 (s, Trip-CHMe2), 34.5 (s, Trip-CHMe2), 117.4 (d, Ar-CH, JP−C = 5.44 Hz), 121.1 (Ar-CH), 121.6 (brs, Trip-CH), 124.4 (s, −CH−C6H3), 125.8 (d, quat. Ar, JP−C = 25.8Hz), 131.1 (s, −CH−C6H3), 131.2 (d, Ar-CH, JP−C = 3.91 Hz), 139.2(d, quat Ar, JP−C = 11.6 Hz), 139.7 (d, Ar-CH, JP−C = 10.23 Hz), 141.7(s, quat. Ar), 141.9 (d, quat Ar, JP−C = 1.58 Hz), 145.0 (d, quat Ar, JP−C= 26.8 Hz), 145.9 (s, quat. Ar), 147.8 (s, quat Trip-C), 150.9 (d, quatAr, JP−C = 2.12 Hz), 159.4 (d, quat Ar, JP−C = 9.27 Hz), 161.3 (d, quatAr, JP−C = 11.9 Hz). 31P{1H} NMR (161.97 MHz. C6D6): δ 20.3 (s,J119Sn−P = 1742 Hz, J117Sn−P = 1666 Hz). 119Sn{1H} NMR (93.25 MHz,C6D6): δ −139 (d, JSn−P = 1756 Hz). Anal. Calcd for C54H71PSn: C,74.56; H, 8.23. Found: C, 74.66; H, 8.31.

Synthesis of Compound 6. 3 (100 mg, 0.12 mmol) was dissolvedin hexane (6 mL), and phenylacetylene (18 mg, 0.174 mmol, 1.5equiv) in hexane (3 mL) was added dropwise to the stirred solution.The solution was stirred at room temperature for 10 days, changingfrom clear orange to cloudy red. The reaction progress was monitoredby NMR spectroscopy. Further phenylacetylene (93 mg, 0.91 mmol)was added to the solution. The reaction mixture was stirred for anadditional 4 days and dried in vacuo to yield the red product.Crystallizazion from hexane at −40 °C yielded crystals suitable forelemental analysis. Red X-ray-quality crystals were grown by diffusionof pentane into a concentrated benzene solution. 1H NMR (400.13MHz, C6D6): δ 1.23 (d, 6H, o-CHMe2,

3JH−H = 6.8 Hz), 1.36 (d, 6H,o-CHMe2,

3JH−H = 6.8 Hz), 1.41 (d, 6H, p-CHMe2,3JH−H = 6.9 Hz),

1.42 (d, 6H, p-CHMe2,3JH−H = 6.8 Hz), 1.43 (d, 6H, o-CHMe2,

3JH−H= 6.8 Hz), 1.53 (d, 6H, o-CHMe2,

3JH−H = 6.8 Hz), 3.07 (sept, 2H, p-CHMe2,

3JH−H = 6.9 Hz), 3.54 (sept, 2H, o-CHMe2,3JH−H = 6.8 Hz),

3.69 (sept, 2H, o-CHMe2,3JH−H = 6.8 Hz), 6.70−6.79 (m, 4H, Ar),

6.84−6.97 (m, 6H, Ar), 7.00−7.04 (m, 2H, Ar), 7.10−7.17 (m, 3H,Ar), 7.18−7.22 (m, 1H, Ar), 7.27 (s, 1H, Ar), 7.33 (s, 4H, m-C6H2),7.37−7.44 (m, 5H, Ar), 8.08−8.11 (m, 1H, SnCCH), 10.04 (d, 1H,SnCH, 3JP−H = 53.4 Hz, 2JSn−H = 26.7 Hz). 13C{1H} NMR (100.13MHz, C6D6): δ 22.6 (o-CHMe2), 24.0 (p-CHMe2), 24.2 (p-CHMe2),24.4 (o-CHMe2), 25.8 (o-CHMe2), 26.0 (o-CHMe2), 30.9 (o-CHMe2),31.2 (o-CHMe2), 34.1 (p-CHMe2), 119.0 (d, JP−C = 87.0 Hz), 119.2(d, JP−C = 85.0 Hz), 120.4 (m-C6H2), 120.6 (m-C6H2), 124.1 (d, JP−C =13.0 Hz), 124.2 (d, JP−C = 92.4 Hz), 124.8 (d, JP−C = 80.6 Hz), 125.3,125.8, 128.3, 128.4 (d, JP−C = 4.3 Hz), 128.5 (d, JP−C = 11.8 Hz), 128.6(d, JP−C = 12.4 Hz), 129.3, 132.0 (d, JP−C = 2.6 Hz), 132.4 (d, JP−C =3.1 Hz), 132.5 (d, JP−C = 17.2 Hz), 134.2 (d, JP−C = 8.9 Hz), 134.5 (d,JP−C = 11.0 Hz), 139.0 (d, SnC(CH)CP, JP−C = 17.3 Hz), 142.8 (d,JP−C = 21.2 Hz), 143.0 (i-C6H2), 146.7 (m-C6H2), 147.0 (m-C6H2),149.0, 164.0 (i-C6H3), 179.4 (d, SnCCP, JP−C = 21.5 Hz), 213.3 (d,SnCH, JP−C = 26.0 Hz). 31P{1H} NMR (101.25 MHz, C6D6): δ −1.4(s, JSn−P = 99 Hz). 119Sn{1H} NMR (93.25 MHz, C6D6): δ −209 (d,JSn−P = 105 Hz). Anal. Calcd for C62H69PSn: C, 77.26; H, 7.22. Found:C, 77.10; H, 6.99.

Synthesis of Compound 7. 3 (100 mg, 0.12 mmol) was dissolvedin hexane (6 mL), and 1-azidoadamantane (21 mg, 0.12 mmol) inbenzene (3 mL) was added dropwise to the orange solution. After 2.5h the solvent was removed in vacuo to yield the light orange productquantitatively on the basis of NMR spectroscopy. Yellow X-ray-qualitycrystals were obtained from a concentrated hexane solution at −40 °C.1H NMR (400.13 MHz, C6D6): δ 1.37 (d, 12H, o-CHMe2,

3JH−H = 6.1Hz), 1.48 (d, 12H, p-CHMe2,

3JH−H = 6.7 Hz), 1.52 (br s, 6H,CH2(CH)2), 1.75 (br s, 6H, NCH2CH), 1.89 (br s, 3H, NCH2CH),3.12 (sept, 2H, p-CHMe2,

3JH−H = 6.9 Hz), 3.60 (br s, 4H, o-CHMe2),6.91−6.96 (m, 3H, Ar), 7.06−7.22 (m, 5H, Ar), 7.27 (s, 1H, Ar),7.32−7.35 (m, 1H, p-C6H3), 7.39−7.40 (m, 6H, m-C6H3, m-C6H2),7.62−7.71 (m, 5H, Ar). 13C{1H} NMR (100.13 MHz, C6D6): δ 23.0(br, o-CHMe2), 24.4 (p-CHMe2), 26.4 (o-CHMe2), 30.6 (CH(CH2)2),31.2 (o-CHMe2), 34.8 (p-CHMe2), 36.1 (CH2(CH)2), 47.3 (d,

3JP−C =8.0 Hz, NC(CH2)3), 56.5 (d, 2JP−C = 4.3 Hz, NC(CH2)3), 120.6 (br,m-C6H2), 124.6 (p-C6H3), 125.9 (d, JP−C = 14.1 Hz), 128.3, 129.3 (d,

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dx.doi.org/10.1021/om400736e | Organometallics XXXX, XXX, XXX−XXXE

JP−C = 3.6 Hz), 130.8 (d, JP−C = 21.8 Hz), 131.1 (m-C6H3), 131.4 (d,JP−C = 1.9 Hz), 132.8 (d, JP−C = 79.6 Hz), 133.8 (d, JP−C = 10.1 Hz),135.6 (d, JP−C = 16.7 Hz), 137.4 (d, JP−C = 128.6 Hz), 141.2 (br, i-C6H2), 147.1 (br, m-C6H2, p-C6H2), 177.3 (d, i-C6H3, JP−C = 2.3 Hz),180.6 (d, SnCCP, JP−C = 23.4 Hz). 31P{1H} NMR (101.25 MHz,C6D6): δ 23.3 (s, JSn−P = 184 Hz). 119Sn{1H} NMR (93.25 MHz,C6D6): δ 275 (d, JSn−P = 187 Hz). Anal. Calcd for C64H78NPSn: C,76.03; H, 7.78; N, 1.39. Found: C, 75.68; H, 7.74; N, 1.60.

■ ASSOCIATED CONTENT*S Supporting InformationTables and CIF files giving details about the quantum chemicalcalculations and crystallographic data for the publishedstructures. This material is available free of charge via theInternet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*E-mail for L.W.: lars.wesemann@uni-tuebingen.de.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis work was supported by the Fonds der ChemischenIndustrie.

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