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Citation: Sun, M.; Ge, S.; Zhao, J.;

McDonald, R.; Ma, G. Ruthenium(II)

Phosphine/Picolylamine Dichloride

Complexes Hydrogenation and DFT

Calculations. Catalysts 2022, 12, 377.

https://doi.org/10.3390/

catal12040377

Academic Editor: C. Heath Turner

Received: 3 February 2022

Accepted: 24 March 2022

Published: 28 March 2022

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catalysts

Article

Ruthenium(II) Phosphine/Picolylamine Dichloride ComplexesHydrogenation and DFT CalculationsManluan Sun 1,†, Sai Ge 1,*,†, Jianguo Zhao 1,*, Robert McDonald 2 and Guibin Ma 1,2

1 Institute of Carbon Materials Science, Shanxi Datong University, Datong 037009, China;dtusml@sxdtdx.edu.cn (M.S.); guibin@ualberta.ca (G.M.)

2 Department of Chemistry, University of Albert, Edmonton, AB T6G 2G2, Canada; bob.mcdonald@ualberta.ca* Correspondence: gs_sxdtdx@163.com (S.G.); jgzhaoshi@163.com (J.Z.)† These authors contributed equally to this work.

Abstract: Treating [Ru(PPh3)3Cl2] with the amine 2-picolylamine (Picam) ligand in a 1:1 molarratio, the Ru(II) complex trans-Ru(PPh3)2(Picam)Cl2 (1) is obtained in methylene chloride andcan be isolated as a pure solid compound. The single-crystal structure of 1 was determined byX-ray crystallography. The geometry at the Ru metal center is a distorted octahedral environmentwith a trans arrangement of the two chlorides. A trans effect of the bond lengths was observedwithin the structure. Similarly, treating [Ru(PPh3)3Cl2] with 1:1:1 molar ratios of 2-picolylamine(Picam) and 1,1′-bis(diphenylphosphine)ferrocene (DPPF) ligands yielded the Ru(II) complex trans-Ru(DPPF)(Picam)Cl2 (2). In identical conditions, the homogeneous hydrogen transfer catalyticreactivity of complexes 1 and 2 has been tested in a basic 2-propanol solution and they indicatedifferent catalytic activity. It was discovered that monodentate and bidentate phosphine ligands ofRu(II) complexes, as well as cis- and trans-chloro configuration display different catalytic propertiesfrom our experimental data, in agreement with literature data. Based on DFT calculations, the rela-tive molecular catalytic reactivity of all available experimental data is understood from the relativecalculated molecular energy.

Keywords: hydrogenation; ruthenium complexes; hydrogen transfer mechanism; DFT calculation

1. Introduction

The use of catalysts to accelerate chemical reactions is a very efficient route in chem-ical synthesis and industrial manufacturing [1]. Most transition metals and lanthanidesshow various catalytic activities due to unoccupied d and f orbitals [2,3]. Ruthenium,in the second transition metal group, has been studied extensively due to its excellentcatalytic properties for either photocatalysis or hydrogenation catalysis in various reac-tions [4]. J. Halpern and B. James were the first researchers to explore the hydrogenationcatalytic property of ruthenium metal chlorides RuCl3 in the early 1960s [5,6]. Thereafter,different Ru metal chemicals and complexes were used as either heterogeneous [7,8] orhomogenous catalysts [9,10].

The synthesis routes that transfer hydrogenation through ruthenium(II) catalyzing be-come popular [11,12]. Ruthenium(II) complexes containing mixed nitrogen and phosphinoligands are efficient catalysts and a large number of derivatives with different combina-tions of P and N donor ligands has been synthesized [13,14]. Noyori’s research grouphas developed a highly active catalytic system with both chiral phosphine and amine(P–P and H2N–NH2) ligands, e.g., trans-RuCl2(diphosphine)(1,2-diamine) [15,16]; it wasdetermined that the Ru–H/–NH2 motif plays a key role in generating highly catalytichydrogenation reactivities as well as catalyzing the transfer hydrogenation of ketones in a2-propanol solution [17,18].

We have previously synthesized a series of Ru(II) complexes and studied their hydrogen-transfer reactivity by the selection of 1,1′-bis(diphenylphosphino)ferrocene (DPPF) as a

Catalysts 2022, 12, 377. https://doi.org/10.3390/catal12040377 https://www.mdpi.com/journal/catalysts

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‘constant’ bidentate P–P ligand and varied the bidentate N–N ligand using different diamineand diimine ligands [18]. We found that bidentate diimines have comparable catalytic abil-ity as do bidentate diamines. Recently we also demonstrated that monodentate or bidentateamine/imine Ru(II) complexes show very different catalytic reactivities [19]. The Ru(II)with a monodentate imine pyridine ligand (Py) demonstrated less activity compared to thatfor the bidentate diimine 2,2′-bipyridine (Bipy) or 1,10-phenanthroline (Phen) [18] and evenworse compared to that for the 2-aminopyridine ligand [19]. Only when both bidentate lig-ands of phosphine and diamine/diimine are present can it provide the stable square planestructure (Scheme 1(1)) during the reaction period and through this stable square planecan conduct the hydride transfer to the substrate. This leads us to believe that the stablesquare plane catalytic transitional structure is the main contributing factor to a fast transferfor carrying forward the hydrogenation reaction. Herein we have designed two Ru(II)complexes with one side fixed using a mixed amine and imine ligand of 2-picolylamine,meanwhile varying the other side with monodentate triphenylphosphine and bidentateDPPF. We will compare catalytic activities of the two complexes of RuCl2(PPh3)2(Picam) (1)and RuCl2(DPPF)(Picam) (2) under the same conditions to determine how these differenttwo types of phosphines, affect the reactivity (monodentate (PPh3) and bidentate (DPPF))and to understand which factors control the catalytic capability of the synthesis complexes.This will in turn contribute to our understanding of the catalytic mechanism. So far ad-vanced theoretical simulations by DFT calculations to assist to understand the molecularinteraction have been addressed previously [20,21]. To fully understand this system incomparison to related literature data [14,22]. Gaussian DFT calculations for two types ofphosphine ligands (monodentate and bidentate) in different geometries were systematicallyconducted, and these calculations helped us to explain the experimental results.

Scheme 1. Square plane (1) as site for hydride transfer to substrate, bifunctional intermediate unit (2).

2. Results and Discussion2.1. Synthesis of Complexes

The reaction of trans-RuCl2(PPh3)3 with a 1:1 molar ratio of 2-picolylamine (Pi-cam) in methylene chloride complexes 1 yielded RuCl2(PPh3)2(Picam) (see Figure 1).From complex 1 via consecutive substitution reactions by addition of one equiv. of 1,1′-bis(diphenylphosphino)ferrocene (DPPF) to a solution of (RuCl2(PPh3)3+2-picolylamine)under aerobic conditions resulted in a rapid color change from blackish-purple to red, andstraightforward work-up of the solutions gave high yields of high-purity yellow productsof complex 2. In addition, trans-RuCl2(PPh3)2(Picam) complex 1 was crystallized fromthe solution.

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Figure 1. The synthesized procedure of trans-Ru(II)Cl2(P)2(N)2 complexes (1) and (2).

2.2. Crystal Structure of trans-[RuCl2(PPh3)2(Picam)] (1)

Unfortunately, no crystal structure data for complex 1 is available from the literature.By our effort, compound 1 was crystallized from a dissolved powder sample and the crystalstructure was solved in a single crystal by X-ray crystallography diffraction in the solidstate [23,24]. Selected bond lengths and bond angles are listed in the caption of Figure 2. Thegeometry at the Ru metal for complex 1 is an octahedral environment (Figure 2) with a transarrangement of the two chloride ligands. The bond lengths of Ru–N are Ru–N(1)=2.1482(19)and Ru–N(2)=2.155(2) Å for Ru–imine and Ru–amine nitrogen atoms, respectively. Bondlengths of Ru–P(1)=2.3346(6) and Ru–P(2)=2.3190(6) Å as well as Ru–Cl(1)=2.4295(6) andRu–Cl(2)=2.4321(6) Å are also determined. It is obvious that the Ru–N bond length for theimine (Py) N atom is slightly shorter than that for the amine (–NH2) N atom. The trans effectis observed in the structure, such as a relatively shorter bond length for Ru–N(1) (2.1482(19)Å) and a relatively longer Ru–P(1) (2.3346(6) Å) bond. In contrast, a longer Ru–amine Nbond length (2.155(2) Å) with a shorter Ru–P(2) (2.3190(6) Å bond are seen, which are alsothe same trans effect to Ru–Cl(1) and Ru–Cl(2) bond lengths, whereas the Ru–P(1) bondtrans to the imine–N displays a slightly longer distance (0.0156 Å) than Ru–P(2) trans to theamine–N. The angle N(1)–Ru–N(2) for Picam is 76.26(8)◦, whereas the Cl(1)–Ru–Cl(2) andCl(1)–Ru–N(1) angles are 164.89(2)◦ and 80.64◦, respectively, leading to a more distortedoctahedral geometry than those obtained with symmetric diamine ligands (Figure 2) [18].The Ru–N(1)–C(1)–N(2) torsion angle is less than that for N(2)–N(1)–P(2)–P(1), whichindicates that Ru metal with a bidentate mixed amine/imine ligand is more planar.

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Figure 2. Crystal structure of trans-[RuCl2(PPh3)2(Picam)] (1) showing 30% thermal probability andgreen shows the Ru(II) core structure.

Selected Bond Lengths (Å) and Angles (◦): Ru–N(1)=2.1482(19); Ru–N(2)=2.155(2);Ru–Cl(1)=2.4295(6); Ru–Cl(2)=2.4321(6); Ru–P(1)=2.3346(6); Ru–P(2)=2.3190(6). Cl(1–Ru–Cl(2)=164.89(2); Cl(1)–Ru–P(1)=99.29(2); Cl(1)–Ru–N(1)=80.65(6); P(1)–Ru–P(2)=98.75(2);Cl(1)–Ru–P(2)=104.91(2); P(1)–Ru–N(1)=165.19(5).

2.3. Comparison of Reactivities of Catalytic Hydrogen Transfer of a Ketone

Herein, the activity of homogeneous catalytic transfer hydrogenation of ketones (C=Obond) for the synthesized pre-catalysts of Ru(II) complexes 1 and 2 was tested in basicisopropanol at 80 ◦C under an inert nitrogen atmosphere (Figure 3) [25,26]. All of the testedcomplexes performed the homogeneous catalytic hydrogen transfer reactivity effectivelyunder the given conditions (Table 1). Under identical conditions, activities of transferhydrogenation of acetophenone in a basic 2-propanol for complexes 1 and 2 are verydifferent (Table 1). The time dependence of the conversion rate versus the reaction time isshown in Figure 4 for complexes 1 and 2 under the experimental conditions (see Table 1).The conversion data indicate that complex 2 is a more efficient hydrogen-transfer catalyst

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than complex 1 under these conditions. The only structural difference between these twocomplexes is the monodentate phosphine ligand in 1 and bidentate phosphine ligand in 2.

Figure 3. Catalytic hydrogen transfer reaction.

Table 1. Catalyzed transfer hydrogenation reduction of acetophenone.

Precursor Catalysts Reaction Time (h) Conversion (%) TOF (h−1)

RuCl2(PPh3)2 (Picam) (1) 24 62.2 6600

RuCl2(DPPF) (Picam) (2) 24 90.0 10,320

Figure 4. Conversion versus reaction time for complexes 1 and 2 under the condition given in theexperimental section.

Experimental condition: in 2-propanol, under N2, 80 ◦C, KOH Cat/Base/Substrate =1/20/1000. TOF calculated at reaction time at 5 min, the conversion percentage did notmuch change between 5 min and 24 h.

We prepared different structural Ru(II) complexes to explore their catalytic hydrogena-tion transfer reactivities. Initially, we selected the bidentate P–P ligand of1,1′-bis(diphenylphosphino)ferrocene (DPPF) and the bidentate N–N ligands of diamine ordiimine, yielding ruthenium six-coordinate complexes with trans-chloride and equatorialcis-P and cis-N yielding a square-planar structure. The catalysis tests demonstrated thattheir catalytic activities are similar, with the diamine slightly more favorable than the di-amine [18]. Very recently we have tuned the nitrogen ligands of monodentate or bidentateamine/imine Ru(II) complexes showing that Ru(II) with a monodentate imine ligand ofpyridine (Py) has less activity compared that for the bidentate diimine 2,2′-bipyridine

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(Bipy) or 1,10-phenanthroline (Phen) [18,19]. Herein we demonstrated that the catalyticreactivities of monodentate phosphine (P) ligands are less efficient than bidentate phos-phine (P–P). Only with bidentate ligands of both phosphine (P–P) and nitrogen (N–N) canit provide the stable square-planar structure during the reaction period, indicating thisequatorial square-planar structure is critical to maintaining the highly catalytic hydrogentransfer reactivity.

In addition, coordinated chlorides were considered being replaced by hydrides in thehydrogen transfer reactivities. In all Ru(II) complex pre-catalysts, the chlorides in trans-configuration showed lower catalytic activities than that for the cis-chlorides configuration.It has been reported in the literature that monodentate phosphine (P) is almost twice ascatalytic in cis-chlorides than in trans-chlorides. Meanwhile, bidentate phosphine (P–P) isalmost 10 times as reactive in cis-chlorides than in trans-chlorides [27]. The cis-hydridesare much more efficient in transferring hydrides from the Ru metal center to the ketonesubstrates. In summary of our tested results and literature data, the relative activities ofRu(II) complexes in different structures and configurations as hydrogen transfer catalystsare shown in Figure 5. The reactivities are closely controlled by the coordination type ofligands and by the chloride configuration.

Figure 5. Relative activity of Ru(II) complexes as hydrogen transfer catalysts.

2.4. DFT Analysis and Mechanism of Hydrogen Transfer

To understand the correlation between structural geometry and catalytic activities,geometry optimizations and energy calculations for eight different structures for bothchlorides (Figure 5) and hydride (chloride position was replaced by hydride in Figure 5)were performed. DFT calculations were performed for eight structures with monodentateand bidentate phosphine ligands, along with both chlorides and hydrides in cis- and trans-geometric configurations. To simplify without changing the geometry the monodentate andbidentate of phosphine were replaced by PH3 and H2P–(CH2)2–PH2, respectively. In total,two groups with eight geometric structures were selected to conduct the DFT optimization.Four Ru(II) complex structures of monodentate (PH3) with two chlorides and two hydridesin trans- and cis- geometry configurations were optimized by DFT calculations. The relativeenergies of the four structures are plotted and shown in Figure 6a. From an energyperspective, trans-chloro Ru monodentate phosphine complex ([RuCl2(H3P)2)(Picam)])is the most stable geometry, with a calculated energy 82.2 kJ/mol lower than the cis-chloro complex ([RuCl2(H3P)2(Picam)]). Meanwhile, the relationship is exactly oppositefor the Ru-hydride structures, with the cis-hydride complex ([RuH2(H3P)2(Picam)]) beingmore stabilized than the trans-hydride complex with a relatively lower energy of 15.0kJ/mol (Figure 6b). For the bidentate phosphine ligand system, trans-chloro Ru complex

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([RuCl2(H2P(CH2)2PH2)(Picam)]) is also the most stabilized geometry, 28.1 kJ/mol lowerthan cis-chloro complex ([RuCl2(H2P(CH2)2PH2)(Picam)]), as shown in Figure 6a. Cis-and trans-hydrides of ([RuH2(H2P(CH2)2PH2)(Picam)]) complexes show the same trendwith an energy difference of 4.2 kJ/mol (as shown in Figure 6a). The HOMO and LUMOmolecular orbitals (MO) for the bidentate ligand Ru(II) complexes in different geometricarrangements are shown in Figure 7, and those for the monodentate ligands are shown inFigure 8. The HOMO MO indicates that most electron density occurs around the hydrideand chloride, suggesting these hydrides are very active in contributing electrons to formchemical bonds with other atoms. In principle theory, the high density electron atom caneasily overlap with other atoms to form chemical bonds.

Figure 6. Relatively energy of conformation changes for bidentate (a) and monodentate (b) phosphineligands bonding to ruthenium Picam complexes, as calculated by the DFT Gaussian program.

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Figure 7. HOMO and LUMO molecular orbitals for the bidentate ligand Ru(II) complexes atdifferent geometries.

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Figure 8. HOMO and LUMO molecular orbitals for the monodentate ligand Ru(II) complexes atdifferent geometries.

DFT calculation results show that for both monodentate and bidentate phosphineligands, the cis-chloro to cis-hydride transformation is more energy favorable. This explainswhy the cis-chloro configuration shows highly catalytic reactivity. Comparing the monoden-tate with the bidentate, the latter ligand requires less energy than the monodentate ligand(Figure 6). This suggests that the monodentate phosphine ruthenium complex consumes

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more energy to form a hydride Ru-complex, which is the activated catalyst species. This isalso consistent with the experimental test results for this system from the data presentedhere and in the literature [14,22].

Regarding these types of catalysts, one of the proposed mechanisms for reduction of ke-tones is through hydride bifunctional group H-bonding interactions between a ‘P2RuH–NH’unit and the ketone (Scheme 1(2)), finally the ketones are reduced and form alcohols [27,28].Perhaps this is because the monodentate ligand for either nitrogen N(Py) or phosphine(PPh3) bonding to Ru(II) is not as stable as the bidentate ligands and is easily dissociated insolution. Consequently, due to the loss of the square plane, the foundation for activationof the ‘P2RuH–NH’ unit is no longer available, so the formation of a transition activationstructure between ‘RuH–NH’ and substrate ketone cannot occur [19]. Our DFT calculationresults also indicate that bidentate phosphine and amine/imine bidentate ligands are moreenergy favorable than monodentate phosphine ligands probably because these two typesof bidentate ligands can maintain a stable square equatorial plane. This is the critical condi-tion to ensure greater catalyst efficiency through the proposed bifunctional intermediatemechanism to reduce the ketones. All the DFT and experiment results indicate that thecis-chloro bidentate phosphine ruthenium complex is the best and fastest pre-catalyst.

3. Materials and Methods

The phosphines (PPh3 and DPPF), 2-picolylamine (Picam) and the ketones were usedas received from Aldrich. RuCl3·3H2O was donated by Colonial Metals, Inc.; RuCl2(PPh3)3,was synthesized by the literature methods [29]. All the solvents were dried before use.

Standard Schlenk techniques were adopted to conducted experiments and manipula-tions under an inert atmosphere. The solvents, ruthenium precursors of [RuCl2(PPh3)3],NMR spectra and Chromatography (GC) analyses were prepared and operated exactly aspreviously described [18,19]. Elements were analysed by The Carlo Erba EA 1108 elementalanalyzer. IR, GC and EA were conducted in The Analytical and Instrumentation Laboratory,Chemistry Department, University of Alberta.

3.1. Synthesis of trans-RuCl2(PPh3)2(Picam) (1)

Synthesis of trans-RuCl2(PPh3)2(Picam) (1): RuCl2(PPh3)3 (0.80 g, 0.84 mmol) was loadedin a round-bottom flask suspended in 10 mL of methylene chloride, then 2-picolylamine (Picam)(90 µL, 0.88 mmol) was added. The mixture was stirred at room temperature for 2 hand concentrated under reduced pressure; addition of pentane afforded a yellow powderprecipitate. After filtration the product was washed twice with diethyl ether (Et2O) anddried under vacuum. Yield: 520 mg (77.0%). Anal. Calcd for C42H38Cl2N2P2Ru: C, 62.69;H, 4.76; N, 3.48. Found: C, 62.81; H, 4.78; N, 3.51. 1H NMR (CDCl3, 20 ◦C): 8.60–6.50 (m,34H; phenyl and C5H4N protons), 4.45 (s; br, 2H; CH2), 3.28 (s; br, 2H; NH2). 13C{1H}NMR (CDCl3, 20 ◦C): 162.7 (s; NCCH2), 157.6 (s; NCH of C5H4N), 136.6–120.1 (m; aromaticcarbons), 50.8 (s; CH2). 31P{1H} NMR (CDCl3, 20 ◦C): 44.0 (d, 2JPP = 32.6 Hz), 40.1 (d,2JPP = 32.6 Hz).

3.2. trans-RuCl2(DPPF)(Picam) (2)

Complex 2 was synthesized using the same procedure and solvents as describedfor the synthesis of 1. Yield: 81 mg (97.0%); characterization details were given in ourprevious publication [19].

3.3. Crystal Structure Determination

Data collection was performed on a Bruker PLATFORM/SMART 1000 CCD diffrac-tometer. The structures were solved using the Patterson search/structure expansion(DIRDIF-99) and were refined using full-matrix least-squares on F2 (SHELXL-2018) [23,24].The selected crystal data and structural refinement details for 1 are listed in Table 2.

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Table 2. Crystal data and structure refinement details for complex 1.

Empirical formula C42H38Cl2N2P2Ru·2CH2Cl2 (1)Formula weight 974.51Crystal system

Crystal DimensionsMonoclinic

0.42 × 0.23 × 0.14 mmSpace group P21/c (No. 14)

Unit cell parametersa (Å) 18.1129 (11)

b (Å) 9.8700(6)c (Å) 24.4824(15)β (◦) 102.8701(8)

Volume (Å3) 4266.9(5)Z 4

Calculated density (g cm−3) 1.517Temperature, K 193.2(1)

µ (MoKα), (mm−1) 0.853θ range for data collection (◦)

Index ranges

Independent reflectionsObserved reflections

Data/restraints/parametersGoodness-of-fit on F2

0.3 to 27.48

−23 ≤ h ≤ 23−12 ≤ k ≤ 12−31 ≤ l ≤ 31

97738046

9773/0/4961.043

Final R indices[F0

2 ≥ 2σ(F0)]wR2 [F0

2 ≥ −3σ(F02)]

R1 = 0.0362wR2 = 0.0924

Large difference peak and hole −1.062 and 0.881 e/Å3

3.4. General Procedure for the Catalytic Transfer Hydrogenation

Hydrogen-transfer experiments were carried out in standard Schlenk glassware [25,26].All reactions were set up in a dry glove-box under N2 using 10−5 M catalyst in 2-propanol(10 mL), the test calculated amount of acetophenone (PhCOCH3) was loaded in a finalmolar ratio of catalyst/KOH/substrate was in 1:20:1000. The temperature was set to 80 ◦Cunder refluxed and quickly magnetic stirring. The yields were calculated after the productswere isolated and measured using gas chromatography (GC) by comparison with data ofknown compounds.

3.5. Computational Details

The DFT calculations of geometry and energy were performed with the Gaussian03 program [30]. Becke’s three-parameter hybrid functional with the Lee-Yang-Parr correla-tion functional (B3LYP) was employed for all calculations [31]. The LanL2DZ basis set onRu and the 6-311G basis set on P, C, and H were selected. Once an optimized geometrywas finished, imaginary frequencies were checked at the same level by vibration analysisto verify the genuine minimum on the potential energy surface (PES) and to evaluate thezero-point energy (ZPE) correction.

4. Conclusions

Two different types of phosphine complexes, Ru(II) trans-RuCl2(PPh3)2(Picam) (1) andtrans-RuCl2(DPPF)(Picam) (2) as pre-catalysts were studied for their transfer hydrogenationcatalytic activities under the same experimental conditions. The transfer hydrogenationactivities demonstrated that the bidentate phosphine (DPPF) coordinated to Ru metal hashigher catalytic activity than the monodentate phosphine (PPh3). These results are similarto data previously reported whereby the nitrogen bonding ligands were varied [18,19].Combining the new results with previous data, we conclude that both bidentate phos-phine and nitrogen ligands need to be present to maintain the highly catalytic transfer

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hydrogenation activity. These results indicate that phosphine and nitrogen ligands bondstrongly to Ru(II) and thus guarantee the formation of stabilized planar ‘P2RuN2

′ units insitu, which is critical as an efficient hydrogenation transfer catalyst. DFT calculations forboth monodentate and bidentate phosphine chlorides and hydrides show their differentenergy requirements, however, both cis-chloro and cis-hydrides are more energy favorableto formation with bidentate ligands compared to monodentate ligands. By reviewing allavailable data, we achieved a full understanding of the different geometric complexes andtheir varying catalytic reactivities.

Author Contributions: Conceptualization, S.G. and J.Z.; methodology, M.S., S.G. and G.M.; software,R.M. and G.M..; validation, M.S., S.G. and G.M..; formal analysis, M.S., S.G.; investigation, M.S.,S.G.; resources, S.G. and J.Z.; data curation, M.S., S.G., J.Z., R.M. and G.M..; writing—originaldraft preparation, M.S., S.G., J.Z., R.M. and G.M.; writing—review and editing, S.G., J.Z. and G.M..;supervision, S.G. and J.Z. All authors have read and agreed to the published version of the manuscript.

Funding: This research was funded by National Natural Science Foundation of China (52071192),Shanxi Science and Tech-nology Major Project (20181102003), Shanxi Science and Technology Achieve-ments Transformation Guide Project (201804D131041). Science and Technology Innovation Projectof Universities in Shanxi Province (2019L0773, 2019L0771). Shanxi Province Science Foundation forYouths (20210302124435, 20210302123339). Science and Technology Innovation Project of DatongPincheng District (201904).

Data Availability Statement: Not applicable.

Acknowledgments: This work was performed at the Institute of Carbon Materials Science of ShanxiDatong University in Datong, and supported by Foundation items: National Natural Science Founda-tion of China (52071192), Shanxi 1331 project foundation for graphene industrialization applicationtechnology of collaborative innovation center, Shanxi new carbon functional materials engineeringresearch center, Shanxi Science and Technology Major Project (20181102003), Shanxi Science andTechnology Achievements Transformation Guide Project (201804D131041). Science and TechnologyInnovation Project of Universities in Shanxi Province (2019L0773, 2019L0771). Shanxi Province Sci-ence Foundation for Youths (20210302124435, 20210302123339). The authors would like to thankthe University of Alberta for support to maintain the X-ray Crystallography, and Analytical andInstrumentation laboratories at the Department of Chemistry, which was essential for this work. Theauthors thank Guy Bernard for his helpful comments and also thank G. Yang for helping to conductpartial Gaussian DFT calculations.

Conflicts of Interest: The authors declare no conflict of interest.

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