Reactions of CO2 and CS2 with [RuH(η2-CH2PMe2)(PMe3)3

Article pubs.acs.org/Organometallics

Reactions of CO2 and CS2 with [RuH(η2‑CH2PMe2)(PMe3)3] Leslie D. Field,*,† Peter M. Jurd,† Alison M. Magill,† and Mohan M. Bhadbhade‡ †

School of Chemistry and ‡Mark Wainwright Analytical Centre, University of New South Wales, Sydney, Australia, 2052 S Supporting Information *

ABSTRACT: Carbon disulfide reacted with the cyclometalated ruthenium complex [RuH(η2-CH2PMe2)(PMe3)3] (1) at low temperature to yield the dithioformate complex [Ru(η1-SC(S)H)(η2-CH2PMe2)(PMe3)3] (4), where the CS2 inserts into the metal hydride bond. On warming, complex 4 rearranges to give the known complex [Ru(S2CHPMe2CH2-κ3S,S,C)(PMe3)3] (3), where the CS2 is inserted in a metal phosphorus bond. Further reaction of this complex with excess CS2 over a period of days resulted in insertion of a second CS2 unit into one Ru−S bond to yield [Ru(SC(S)SCH(-S)PMe2CH2-κ3S,S,C)(PMe3)3] (5). Complex 5 was characterized crystallographically and by multinuclear NMR spectroscopy. In contrast, reaction of [RuH(η2CH2PMe2)(PMe3)3] (1) with CO2 resulted in insertion of CO2 into the Ru−C bond to give [RuH(OC(O)CH2PMe2κ2O,P)(PMe3)3] (2). Low-temperature NMR spectroscopic studies did not show any evidence for prior formation of a formate complex.

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INTRODUCTION There is a growing body of scientific evidence to suggest the detrimental environmental impact associated with anthropogenic greenhouse emissions. Of primary concern is the atmospheric concentration of carbon dioxide arising from the consumption of fossil fuels in both transport and energy generation.1 As a consequence, sustainable and dynamic methods of abatement have become of increasing interest within political and scientific communities. One method exhibiting significant potential to reduce the amount of CO2 liberated into the atmosphere is to use CO2 as a feedstock in the synthesis of fine chemical products from simple organic substrates. A key challenge presented in this approach is the development of catalysts capable of activating the chemically inert carbon dioxide molecule to enable its subsequent reactivity. In recent years there has been significant research into the development of such catalytic systems based on transition metal complexes with an emphasis on synthetic targets such as formic acid,2 acetic acid,3 methanol,4 and acrylic acid.5 A key step in catalytic cycles that result in the functionalization of CO2 is often insertion of CO2 into a metal−carbon or metal−hydride bond.6 We and others have previously studied the stoichiometric reactivity of CO2 with complexes containing M−H or M−C (particularly M−CH3) bonds, in which CO2 directly inserts into the metal−hydride or metal−carbon bond to form metal formates and metal acetates, respectively.7 For example, Whittlesey et al. have reported the insertion of CO2 into the metal−hydride bonds of Ru(dmpe)2H2 (dmpe = 1,2-bis(dimethylphosphino)ethane), resulting in the formation of both formate and bis(formate) products.8 © 2013 American Chemical Society

There have been fewer studies addressing the relative reactivity of M−H and M−C bonds with respect to CO2 insertion. We have previously investigated the reaction between CO2 and cis- and trans-RuMeH(dmpe)2 and found that reversible insertion of CO2 into the M−H bonds initially results in formation of metal formate complexes.7d The thermodynamic reaction product is, however, that arising from insertion into the metal−carbon bond, viz., transRu(OC(O)CH3)H(dmpe)2 (Scheme 1). Scheme 1

Karsch has studied the reactivity of the isomeric ironcentered complexes Fe(PMe3)4 and FeH(η2-CH2PMe2)(PMe3), which exist in a temperature- and solvent-dependent equilibrium, with carbon dioxide.9 The products generated upon reaction with CO2 depended on the isomeric form assumed by the complex, with the CO2 adduct [Fe(PMe3)4(η2CO2)] complex generated from Fe(PMe3)4 when the reaction was undertaken in pentane. In more polar solvents, insertion of Received: November 22, 2012 Published: January 11, 2013 636

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Organometallics

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CO2 into the iron−carbon bond of FeH(η2-CH2PMe2)(PMe3)3 occurred to yield [FeH(OC(O)CH2PMe2-κ2O,P)(PMe3)3]. In a related study,10 the cyclometalated complex I, prepared by reduction of [Fe(PP3)Cl2] (PP3 = P(CH2CH2CH2PMe2)3), was reported to react with two equivalents of CO2 at room temperature to form II, in which CO2 has inserted into both the Fe−H and Fe−C bonds (Scheme 2).

(2), which arises from insertion of the CO2 into the Ru−C bond of 1 (Scheme 4). Scheme 4

Scheme 2 The 31P{1H} NMR spectrum of 2 showed four resonances: an apparent doublet of triplets at δ 21.0 ppm (2JPP = 21.0 and 33.2 Hz), two doublets of doublets of doublets resonances at δ 1.7 ppm (2JPP = 260.8, 33.2, 23.7 Hz) and δ 0.2 ppm (2JPP = 260.8, 33.2, 23.7 Hz), and an apparent doublet of triplets at δ −10.3 ppm ( 2J PP = 21.0 and 24.0 Hz). The signals corresponding to the two mutually trans phosphine ligands, at δ 1.7 and 0.2 ppm, show a strong second-order coupling effect as a consequence of the large 260.8 Hz coupling constant (Figure 1). A combination of two-dimensional and selective heteronuclear decoupling experiments was used to identify the 31 P signal at δ 1.7 ppm as belonging to the phosphorus of the metallocyclic ring. The signal at δ −10.3 corresponds to the phosphorus trans to the hydride ligand, while the phosphorus trans to the oxygen donor resonates at δ 21.0 ppm. If 13CO2 is used, the signals at δ 1.7 and 0.2 show additional couplings to the isotopically labeled carbon nucleus (2JPC = 12.9 Hz and 3JPC = 5.4 Hz, respectively). The 1H NMR spectrum of [RuH(OC(O)CH2PMe22 κ O,P)(PMe3)3] (2) showed a high-field signal that appeared as a doublet of quartet resonance at δ −8.29 ppm (2JPH = 96.6 and 27.1 Hz), corresponding to the hydride ligand. Two multiplet resonances were observed at δ 2.54 and 2.32 ppm for the geminal methylene protons in the metallocyclic ring, with a mutual 2JHH splitting of 15.5 Hz. Both signals also displayed coupling to 13C (if 13CO2 was used) and 31P nuclei. Resonances for the metallocyclic ring carbons were observed at δ 41.4 and 175.3 ppm in the 13C{1H} NMR spectrum. Crystals of [RuH(O13C(O)CH2PMe2-κ2O,P)(PMe3)3] (2) suitable for X-ray crystallography were grown by slow evaporation of a toluene-d8 solution of the complex. The complex displays a distorted octahedral geometry (Figure 2, Table 1), with the main distortion arising from a reduction in the P(1)−Ru(1)−P(4) bond angle from the expected 180° to 154.92(5)° to accommodate the steric requirements of the PMe3 ligands. The metallocycle ring is puckered, with the methylene group directed below the coordination plane of the metal, on the same face as the hydride ligand. The ruthenium− phosphine bond distances are unexceptional. The ruthenium− oxygen bond distance, 2.201(3) Å, is slightly longer than typically observed for ruthenium acetate bonds, but is entirely consistent with the only other structurally characterized ruthenium phosphinoacetate complex, [Ru(p-cymene)Cl(OC(O)CH2PPh2-κ2-O,P)]·SnMe3Cl (2.100(2) Å).14 The reaction of [RuH(η2-CH2PMe2)(PMe3)3] (1) with CO2 to yield [RuH(OC(O)CH2PMe2-κ2O,P)(PMe3)3] (2) is the same as the solution-phase reaction reported by Karsch for [FeH(η2-CH2PMe2)(PMe3)3], which afforded the analogous [FeH(OC(O)CH2PMe2-κ2O,P)(PMe3)3].9 We have, however, not seen any evidence to suggest that a second molecule of CO2 inserts into the Ru−H bond in solution at ambient temperature.

The analogous ruthenium complex, [RuH(η2-CH2PMe2)(PMe3)3], has been prepared previously.11 While the reaction of this compound with CO2 has not been investigated, the reaction with CS2 resulted in the formation of the metallocyclic product [Ru(S2C(H)PMe2CH2-κ3S,S,C)(PMe3)3],11a ostensibly arising from insertion of CS2 into the Ru−H bond followed by rearrangement to give the observed product. We now wish to report the results of our investigation of the reactivity of [RuH(η2-CH2PMe2)(PMe3)3] with CO2 and also a reinvestigation of the reaction with CS2.

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RESULTS The synthesis of the cyclometalated ruthenium complex [RuH(η2-CH2PMe2)(PMe3)3] (1) by reduction of [Ru(PMe3)4Cl2] with sodium amalgam has been previously reported.11 The reaction was, however, sluggish, and the starting material was consumed only after prolonged stirring at 70 °C for a week. Alternatively, the complex has been observed as the product of thermolysis of cis-[RuH(CH2Ph)(PMe3)4]12 or cis-[RuH(CHC(OSiMe3)tBu)(PMe3)4].13 We have found a more straightforward and rapid route to prepare 1 by reduction of [Ru(PMe3)4Cl2] with potassium graphite intercalate (C8K) in THF-d8 (Scheme 3). The reaction was complete after sonication of the reaction mixture at room temperature for 20 min. Scheme 3

The C8K was removed by filtration through Celite, and the THF-d8 solution of 1 was used immediately without further purification. The 1H and 31P{1H} NMR spectra of 1 were identical to those reported previously.11 The 13C{1H} NMR spectrum showed a phosphorus-coupled resonance at δ −22.6 ppm, corresponding to the metal-bound carbon atom, together with the expected resonances for the remaining carbon atoms. Reaction of [RuH(η2-CH2PMe2)(PMe3)3] (1) with CO2. Addition of ca. 1.5 atm of CO2 resulted in an immediate reaction to yield [RuH(OC(O)CH2PMe2-κ2O,P)(PMe3)3] 637

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Organometallics

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Figure 1. Experimental (bottom) and simulated (top) THF-d8).

31

P{1H} NMR spectrum of [RuH(OC(O)CH2PMe2-κ2O,P)(PMe3)3] (2) (242 MHz,

observed below 250 K. Above this temperature, only signals corresponding to complex 2 were observed. If there is insertion of CO2 into the reactive Ru−H bond of 1, it may be reversible and too rapid to be detected by NMR spectroscopy. The observed insertion into the Ru−C bond clearly leads to a stable product, probably as a result of relieving ring strain in the small cyclometalated ring system. Reaction of [RuH(η2-CH2PMe2)(PMe3)3] (1) with CS2. At room temperature, the reaction of [RuH(η2-CH2PMe2)(PMe3)3] (1) with CS2 is rapid and leads to quantitative formation of [Ru(S2C(H)PMe2CH2-κ3S,S,C)(PMe3)3] (3) as described by Werner.11a In this case, there is notional insertion of CS2 into one of the metal−phosphorus bonds. The NMR spectra of this complex were identical to those previously reported, and we were able to identify the previously unreported resonance corresponding to the metal-bound methylene group in the 1H NMR spectrum, which occurs as a phosphorus-coupled multiplet at δ 0.78 ppm. In the 13C{1H} NMR spectrum, the methylene carbon resonates at δ −4.6 ppm, while the CH group of the metallocyclic ring gives rise to a signal at δ 50.8 ppm. The condensation of CS2, phosphines, and metal hydrides has been reported in a number of instances.15 In refluxing methanol, [Ru(PMe2Ph)4(S2CH)]PF6 rearranged to yield [Ru(PMe2Ph)3(S2C(H)PMe2Ph-κ2S,S)]PF6.15a Dissolution of cis-[M(CO) 3 (dppm)H] (M = Re, Mn; dppm = bis(diphenylphosphino)methane) in CS2 resulted in formation of [M(CO)3(S2C(H)PPh2CH2PPh2-κ3S,S,P].15b The reaction of potassium dithioformate with [Fe(H2O)6](BF4)2 and 1,2bis(diphenylphosphino)ethane (dppe) in ethanol similarly resulted in the formation of [Fe(dppe)(S 2 C(H)PPh2CH2CH2PPh2-κ3S,S,P)].15c Such reactions are generally proposed to proceed either via nucleophilic attack of a phosphine at the carbon atom of a coordinated dithioformate ligand or by hydride migration from the metal center onto the carbon atom of a S2CPR3 ligand, formed by insertion of CS2 into a M−P bond.15c,d

Figure 2. ORTEP drawing of the structure of [RuH(O13C( O)CH2PMe2-κ2O,P)(PMe3)3] (2). Thermal ellipsoids are shown at the 50% probability level.

Table 1. Selected Bond Lengths (Å) and Angles (deg) for [RuH(O13C(O)CH2PMe2-κ2O,P)(PMe3)3] (2) Bond Lengths (Å) Ru(1)−P(1) Ru(1)−P(3) Ru(1)−O(1) O(1)−C(1) C(1)−O(2) P(1)−Ru(1)−P(2) P(1)−Ru(1)−P(4) P(2)−Ru(1)−P(3) P(3)−Ru(1)−P(4)

2.296(1) 2.249(1) 2.201(3) 1.267(6) 1.242(6) Bond Angles 103.85(5) 154.92(5) 95.80(5) 96.11(5)

Ru(1)−P(2) Ru(1)−P(4) Ru(1)−H(1) C(1)−C(2) C(2)−P(1) (deg)

P(1)−Ru(1)−P(3) P(1)−Ru(1)−O(1) P(2)−Ru(1)−P(4) P(3)−Ru(1)−O(1)

2.356(1) 2.308(1) 1.779 1.515(7) 1.829(5) 95.62(5) 80.01(9) 96.92(5) 175.60(9)

We have previously observed insertion of CO2 into Ru−H bonds in preference to Ru−C bonds at low temperature.7d The reaction between 13CO2 and 1 was studied using lowtemperature NMR spectroscopy; however no reaction was 638

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Scheme 5

In an attempt to determine the pathway by which [Ru(S2C(H)PMe2CH2-κ3S,S,C)(PMe3)3] (3) is formed, the reaction of complex 1 with CS2 was studied using lowtemperature NMR spectroscopy. At temperatures below 250 K, four new resonances of equal intensity appear in the 31P{1H} NMR spectrum at δ 6.8, −0.7, −7.3, and −43.6 ppm. The resonances at −43.7 and −0.7 ppm show a large trans 2JPP coupling constant of 215.8 Hz; the couplings between the other phosphorus nuclei are less well resolved. In the 1H NMR spectrum, the resonance corresponding to the hydride ligand of complex 1 disappears, and a new resonance at δ 11.4 ppm grows in. The chemical shift of this new resonance is entirely consistent with the formation of a dithioformate complex, [Ru(η1-SC(S)H)(η2-CH2PMe2)(PMe3)3] (4), formed by insertion of CS2 into the Ru−H bond of complex 1 (Scheme 5). Upon warming to temperatures above 250 K, complex 4 rapidly rearranges to yield [Ru(S2C(H)PMe2CH2-κ3S,S,C)(PMe3)3] (3) by migration of the phosphine in the threemembered ring to the thioformate carbon with coordination of the thioformate sulfur to make the thioformate a bidentate ligand. Upon standing at room temperature, solutions of 3 in THFd8 containing an excess of CS2 undergo a second insertion of CS2 into a Ru−S bond, to yield [Ru(SC(S)SCH(−S)PMe2CH2-κ3S,S,C)(PMe3)3] (5) (Scheme 6).

In the 1H NMR spectrum of 5, the metallocyclic methylene protons are diastereotopic and resonate at δ 1.26 and 0.77 ppm. The CH proton appears as a doublet of doublets at δ 3.8 ppm with JPP = 8.2 and 5.9 Hz. Complex 5 displays moderate solubility in THF-d8 and precipitates upon standing to yield crystals suitable for X-ray diffraction (Figure 3, Table 2).

Scheme 6

Figure 3. ORTEP drawing of the structure of [Ru(SC(S)SCH(−S)PMe2CH2-κ3S,S,C)(PMe3)3] (5). Thermal ellipsoids are shown at the 50% probability level.

Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) for [Ru(SC(S)SCH(−S)PMe2CH2-κ3S,S,C)(PMe3)3] (5) Bond Lengths Ru(1)−S(1) Ru(1)−C(1) Ru(1)−P(3) S(1)−C(2) C(2)−S(3) C(3)−S(4) C(1)−P(1)

The 31P{1H} NMR spectrum of complex 5 contains four resonances at δ 55.3 (Pa), 5.4 (P†), −1.2 (Pb), and −6.5 ppm (P†). The two lower field resonances both appear as doublet of doublets, while the two resonances to higher field appear as the expected doublet of doublet of doublet (eight line) multiplets. The low-field resonance (at δ 55.3) is assigned to the metallocyclic phosphorus, while the signal at δ 1.2 ppm corresponds to the phosphorus trans to the metal-bound methylene group. The two remaining signals, which could not be definitively assigned, correspond to the phosphorus nuclei trans to sulfur atoms. The absence of obvious coupling between the phosphorus in the metallocyclic ring and one of the metalbound phosphorus nuclei trans to the sulfur ligands may be indicative of a stereochemical dependence of the 3JPP coupling constants on the geometry of the P−Ru−C−P bonding relationship. While Karplus-type relationships are less well established for vicinal 3JPP couplings, there have been several reports detailing such relationships.16

S(1)−Ru(1)−S(4) P(2)−Ru(1)−P(3) P(2)−Ru(1)−S(1)

2.426(2) Ru(1)−S(4) 2.204(7) Ru(1)−P(2) 2.286(2) Ru(1)−P(4) 1.647(8) C(2)−S(2) 1.741(8) S(3)−C(3) 1.786(8) C(3)−P(1) 1.735(7) Bond Angles

2.405(2) 2.272(2) 2.327(2) 1.683(8) 1.809(8) 1.806(8)

93.17(7) 93.79(7) 178.12(8)

170.9(2) 171.68(8) 87.67(7)

C(1)−Ru(1)−P(4) P(3)−Ru(1)−S(4) P(3)−Ru(1)−S(1)

The ruthenium core of complex 5 exhibits a slightly distorted octahedral geometry, with the three PMe3 ligands coordinating in a facial arrangement. The ruthenium−ligand bond distances are unexceptional. With the exception of C(3)−S(3) (1.809(8) Å) and S(1)−C(2) (1.647(8) Å), the sulfur−carbon bond distances fall between the distances typical of C−S single bonds (1.82 Å) and CS double bonds (1.67 Å),17 which suggests a degree of delocalization within the metallocyclic ring. A similar 639

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Signals and couplings that could not be definitively assigned are denoted by a dagger (†) superscript (e.g., P†). Elemental analyses were performed by the Campbell Microanalytical Laboratory at the University of Otago, Dunedin, New Zealand. [RuH(η 2-CH2 PMe2 )(PMe3 ) 3](1). The synthesis of RuH(η2 CH2PMe2)(PMe3)3 (1) has been previously reported;11 however, in this work, the complex was prepared using a novel procedure. In a typical procedure, THF-d8 (ca. 0.5 mL) was vacuum transferred into an NMR tube containing trans-RuCl2(PMe3)4 (41.2 mg, 0.087 mmol) and C8K (50.1 mg, 0.370 mmol, 4.3 equiv). The resulting mixture was sonicated for 20 min, then filtered through Celite and glass wool to give a dark orange solution. NMR spectroscopic analysis showed RuH(η2-CH2PMe2)(PMe3)3 was formed as the major product (ca. 85%), together with a minor amount of cis-RuH2(PMe3)4 (ca. 15%).25 1 H NMR (600 MHz, THF-d8): δ −10.42 (dq, 2JHPb = 83.2 Hz, 2JHPa = 2 JHPc = 2JHPd = 27.0 Hz, 1 H, RuH), −0.86 to −0.80 (m, 1 H, CHaH), −0.45 to −0.39 (m, 1 H, CHHb), 1.20 (d, 2JHPb = 5.3 Hz, 9 H, Pb(CH3)3), 1.31−1.34 (m, 3 H, Pa(CH3)aMe), 1.33 (dd, 2JHPc = 6.6 Hz, 2JHPa = 1.0 Hz, 9 H, Pc(CH3)3), 1.37 (dd, 2JHPd = 7.1 Hz, 2JHPa = 1.9 Hz, 9 H, Pd(CH3)3), 1.46 (dd, 2JHPa = 9.9 Hz, 2JHPd = 2.9 Hz, 3 H, PaMe(CH3)b). 1H{31P} NMR (600 MHz, THF-d8): δ −10.42 (br s, ν1/2 = 10 Hz, 1 H, RuH), −0.83 (dd, 2JHaHb = 6.5 Hz, 3JHaH = 3.4 Hz, 1 H, CHaH), −0.42 (dd, 2JHbHa = 6.5 Hz, 3JHbH = 3.9 Hz, 1 H, CHHb), 1.20 (s, 9 H, Pb(CH3)3), 1.33 (s, 9 H, Pc(CH3)3), 1.30 (s, 3 H, Pa(CH3)aMe), 1.37 (s, 9 H, Pd(CH3)3), 1.46 (s, 3 H, PaMe(CH3)b). 13 C{1H} NMR (151 MHz, THF-d8): δ −22.63 (ddt, 1JCPa = 30.3 Hz, 2 JCP† = 5.3, 9.5 Hz, CH2), 14.37−14.45 (dm, 1JCPa = 6.1 Hz, Pa(CH3)aMe), 22.61−22.81 (dm, 1JCPa = 18.84 Hz, PaMe(CH3)b), 22.98 (dq, 1JCPb = 16.2 Hz, 3JCP† = 3.5 Hz, Pb(CH3)3), 26.50 (ddt, 1JCPd = 21.2 Hz, 3JCP† = 2.3, 4.5 Hz, Pd(CH3)3), 28.93 (dddd, 1JCPc = 19.7 Hz, 3JCP† = 7.6, 3.7, 2.0 Hz, Pc(CH3)3). 31P{1H} NMR (243 MHz, THF-d8): δ −29.69 (ddd, 2JPaPd = 194.1 Hz, 2JPaPc = 37.5 Hz, 2JPaPb = 25.3 Hz, 1 P, Pa), −8.80 (br app q, 2JPbP = 25.7 Hz, 1 P, Pb), 2.68 (ddd, 2 JPcPa = 37.5 Hz, 2JPcPb = 25.3 Hz, 2JPcPd = 5.2 Hz, 1 P, Pc), 6.53 (ddd, 2 JPdPa = 194.1 Hz, 2JPdPb = 27.1 Hz, 2JPdPc = 5.2 Hz, 1 P, Pd). NMR spectroscopic data obtained were consistent with that reported in the literature.11b [Ru(OC(O)CH2PMe2-κ2O,P)(PMe3)3H] (2). NMR Scale. THF-d8 (ca. 0.6 mL) was vacuum transferred into an NMR tube containing trans-RuCl2(PMe3)4 (31.3 mg, 0.0658 mmol) and C8K (47.1 mg, 0.348 mmol, 5.3 equiv) and sonicated for 20 min. The reaction mixture was filtered through Celite and glass wool, and the resulting dark orange solution degassed and frozen before an excess of 13CO2 was added under vacuum. The solution was warmed to room temperature, causing the dark orange-brown solution to turn a light yellow over the course of ca. 5 min. 1H NMR (600 MHz, THF-d8): δ −8.29 (dq, 2JHPb = 97.1 Hz, 2JHPa = 2JHPc = 2JHPd = 27.2 Hz, 1 H, RuH), 1.28 (d, 2JHPc = 7.9 Hz, 9 H, Pc(CH3)3), 1.30 (d, 2JHPb = 5.9 Hz, 9 H, Pb(CH3)3), 1.39 (dd, 2JHPa = 6.1 Hz, 2JHP† = 1.6 Hz, 3 H, Pa(CH3)aMe), 1.41 (d, 2JPdH = 6.9 Hz, 9 H, Pd(CH3)3), 1.60 (d, 2 JPaH = 7.2 Hz, 3 H, PaMe(CH3)b), 2.28 (dddd, 2JHaHb = 15.6 Hz, 4 JHaHc = 1.5 Hz, 2JHaPa = 7.3 Hz, 2JHa13CO2 = 4.9 Hz, 1 H, CHaH), 2.50

delocalization has been reported previously for [Ni(SC(S)SC(PMe3)S-κ3S,C,S)(PMe3)].18 The insertion of CS2 into metal−sulfur bonds has been reported previously.19 In particular, at 70 °C CS2 inserts into one U−S bond of [(Cp*)2U(SR)2] (R = Me, iPr, tBu) to yield the trithiocarbonates [(Cp*)2U(SR)(κ2-S2CSR))].19a Under more forcing conditions, a second CS2 insertion into the remaining thiolate bond occurs to yield a bis(trithiocarbonate). The thiolate-bridged diiron complexes [(Cp*)Fe(μ2-SR)3Fe(Cp*)] (R = Me, Et) react in refluxing CS2 over several hours to give the bridged monoinsertion products [(Cp*)Fe(μSR)2(μ-η1:η1-S2CSR)Fe(Cp*)] in quantitative yield.19b

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CONCLUSION CO2 inserts into the strained metal−carbon bond of RuH(η2CH2PMe2)(PMe3)3] (1) under mild conditions to give a metallocyclic ester. The apparent absence of any observable CO2 insertion into the reactive Ru−H bond of 1 is surprising; however these metal−hydride insertions are often reversible, and it may be that the insertion and subsequent decarboxylation reactions are too fast to observe on an NMR time scale. Instead, CO2 insertion into the metal−carbon bond leads to a thermodynamically more favorable (less strained) product. While CO2 and CS2 are structurally very similar, their reactivities can be remarkably different.20 In contrast to CO2, the CS2 inserts into the Ru−H bond of 1 to generate a dithioformate, [Ru(η1-SC(S)H)(η 2-CH2PMe2)(PMe3)3] (4), which was characterized spectroscopically at low temperature but which undergoes a facile rearrangement to give a stable product, [Ru(S2C(H)PMe2CH2-κ3S,S,C)(PMe3)3] (3), where the thioformate adopts a bidentate bonding mode as part of a tripodal S,S,C ligand. [Ru(S2C(H)PMe2CH2-κ3S,S,C)(PMe3)3] (3) reacts further with CS2 to insert a second CS2 to form [Ru(SC(S)SCH(-S)PMe2CH2-κ3S,S,C)(PMe3)3] (5), where the ruthenium center is coordinated by a tridentate ligand containing alkyl, thiolato, and thioformato coordinating groups.

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EXPERIMENTAL SECTION

Unless stated otherwise, all manipulations described were performed under a dry, high-purity argon atmosphere using standard Schlenk and glovebox procedures at ambient laboratory temperature. Isotopically labeled carbon dioxide (13CO2) was obtained from Aldrich and used as supplied, while carbon disulfide (CS2) was obtained from Ajax and vacuum distilled prior to use. Potassium graphite intercalate, C8K,21 and trans-RuCl2(PMe3)422 were prepared according to literature procedures. Tetrahydrofuran, pentane, and diethyl ether were dried using an Innovative Technology Pure-Solv 400-4-MD solvent purification system. Tetrahydrofuran-d8 and toluene-d8 were dried over, and distilled from, sodium/benzophenone ketyl. All deuterated solvents were vacuum distilled immediately prior to use. 1 H, 13C, and 31P NMR spectra were acquired on a Bruker Avance III 300 NMR spectrometer at 300, 76, and 122 MHz; a Bruker Avance III 400 NMR spectrometer at 400, 100, and 162 MHz; a Bruker Avance III 600 NMR spectrometer at 600, 150, and 242 MHz; or a Bruker Avance III 700 NMR spectrometer at 700, 176, and 284 MHz, respectively. Unless otherwise stated, all NMR analyses were performed at 298 K with 13C and 31P spectra referenced in accordance to IUPAC guidelines using the unified scale.23 Signal assignments were performed using [1H−31P] HMBC and multiplicity edited [1H−13C] HSQC 2D NMR experiments as well as 1D 1H COSY and 1H NOESY NMR techniques. Systems containing complex coupling patterns were deconvoluted with the aid of Spinworks 3 NMR Simulation software.24

(ddd, 2JHbHa = 15.6 Hz, 4JHbPa = 9.3 Hz, 2JHb13CO2 = 6.7 Hz, 1 H, CHHb). 1H{31P} NMR (600 MHz, THF-d8): δ −8.29 (s, 1 H, RuH), 1.28 (s, 9 H, Pc(CH3)3), 1.30 (s, 9 H, Pb(CH3)3), 1.39 (s, 3 H, Pa(CH3)aMe), 1.41 (s, 9 H, Pd(CH3)3), 1.60 (s, 3 H, PaMe(CH3)b), 2.28 (ddd, 1JHaHb = 15.6 Hz, 2JHa13CO2 = 4.9 Hz, JHaHc = 1.5 Hz, 1 H, CHaH), 2.50 (dd, 2JHbHa = 15.6 Hz, 2JHb13CO2 = 6.7 Hz, 1 H, CHHb). 13 C{1H} NMR (76 MHz, THF-d8): δ 19.24−19.96 (m, Pa(CH3)aMe), 20.27 (dt, 1JCPb = 17.0 Hz, 3JCPd = 3JCPa = 3JCPc = 2.6 Hz, Pb(CH3)3), 21.49 (ddd, 1JCPd = 19.4 Hz, 3JCP† = 7.1 Hz, 3JCPb = 3.7 Hz, Pd(CH3)3), 24.26−24.95 (m, PaMe(CH3)b), 25.88 (ddt, 1JCPc = 27.2 Hz, 3JCPa = 2.7 Hz, 3JCPb = 3JCPd = 3.4 Hz, Pc(CH3)3), 41.08 (ddd, 1JC13CO2 = 50.2 Hz, 1JCPa = 24.9 Hz, 3JCP† = 5.4 Hz, CH2), 175.27 (dd, 2JCPa = 11.5 Hz, 3 JCPd = 6.9 Hz, RuO13C(O)). 31P{1H} NMR (243 MHz, THF-d8): δ −10.27 (app dt, JPbPd = JPbPa = 24.0 Hz, JPbPc = 21.0 Hz, 1 P, Pb), 0.14 640

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RuCl2(PMe3)4 (42.4 mg, 0.0891 mmol) and C8K (50.8 mg, 0.376 mmol, 4.2 equiv) in THF-d8. The frozen sample was warmed to ca. 198 K and placed into the NMR probe cooled to 230 K. The 31P{1H} NMR spectra obtained at this temperature showed the formation of a minor amount of a previously unobserved cis unsymmetrical intermediate, which increased in concentration over time. Upon near complete consumption of the starting material, the sample temperature was reduced to 210 K to stabilize the intermediate product and enable [1H−31P] HMBC, 13C{1H}, and [1H−13C] HSQC NMR analysis to be performed. The NMR spectroscopic data obtained established the intermediate to be the dithioformate complex [Ru(η1SC(S)H)(η2-CH2PMe2)(PMe3)3] (4). The product was rapidly converted to [Ru(S2C(H)PMe2CH2-κ3S,S,C)(PMe3)3] (3) upon warming to 250 K. [Ru(η1-SC(S)H)(η2-CH2PMe2)(PMe3)3] (4): Selected 1H NMR (600 MHz, THF-d8, 210 K): δ −0.38 (app dd, 1JHH = 14.0 Hz, JHP = 8.2 Hz, 2 H, CH2), 11.18−11.41 (m, 1 H, SC(S) H). Selected 1H{31P} NMR (600 MHz, THF-d8, 210 K): δ −0.38 (br d, 1JHH = 14.0 Hz, 2 H, CH2), 11.18−11.41 (br s, 1 H, SC(S)H). Selected 13C{1H} NMR (151 MHz, THF-d8, 210 K): δ −16.63 to −15.57 (m, CH2), 241.30−243.07 (m, SC(S)H). 31P{1H} NMR (243 MHz, THF-d8, 210 K): δ −43.75 to −42.31 (dm, 2JPaPc = 215.8 Hz, 1 P, Pa), −6.27 (app t, 3JPbP = 33.6 Hz, 1 P, Pb), 0.04 (dm, 2JPcPa = 215.8 Hz, 1 P, Pc), 7.40 (m, 1 P, Pd). [Ru(SC(S)SCH(−S)PMe2CH2-κ3S,S,C)(PMe3)3] (5). Excess CS2 (ca. 0.1 mL) was added to a degassed solution of [RuH(η2CH2PMe2)(PMe3)3] (1), generated in situ from trans-RuCl2(PMe3)4 (52 mg, 0.11 mmol) and C8K (77 mg, 0.57 mmol, 5.2 equiv) in THFd8. The resulting mixture was allowed to stand for ca. 36 h, resulting in near quantitative formation of [Ru(SC(S)SCH(−S)PMe2CH2κ3S,S,C)(PMe3)3] (5). 1H NMR (300 MHz, THF-d8): δ 0.77 (m, 1 H, CHHb), 1.26 (m, 1 H, CHaH), 1.35 (d, 2JHPc = 7.22 Hz, 9 H, Pc(CH3)3), 1.38 (d, 2JHPb† = 2JHPd† = 7.22 Hz, 18 H, Pb†(CH3)3, Pd†(CH3)3), 1.63 (d, 2JHPa = 11.9 Hz, 3 H, PaMe(CH3)b), 1.83 (d, 2JHPa = 11.9 Hz, 3 H, Pa(CH3)aMe), 3.80 (dd, 2JHPa = 8.1 Hz, 3JHPc = 6.1 Hz, 1 H, CH). 1H{31P} NMR (300 MHz, THF-d8): δ 0.77 (d, 2JHbHa = 11.9 Hz, 1 H, CHHb), 1.26 (d, 2JHaHb = 11.9 Hz, 1 H, CHaH), 1.35 (s, 9 H, Pc(CH3)3), 1.38 (s, 18 H, Pb†(CH3)3, Pd†(CH3)3), 1.63 (s, 3 H, PaMe(CH3)b), 1.83 (s, 3 H, Pa(CH3)aMe), 3.80 (s, 1 H, CH). 13C{1H} NMR (176 MHz, THF-d8): δ 4.59−5.29 (m, CH2), 14.55 (d, 1JCPa = 33.5 Hz, Pa(CH3)Me), 14.77 (d, 1JCPa = 42.8 Hz, PaMe(CH3)), 19.36 (d, 1JCPc = 24.6 Hz, Pc(CH3)3), 20.14 (d, 1JCPb† = 1JCPd† = 26.1 Hz, 6 C, Pb†(CH3)3, Pd†(CH3)3), 53.46−53.98 (dm, 1JCpa = 70.7 Hz, CH), 225.73−225.82 (m, SC(S)S). 31P{1H} NMR (122 MHz, THF-d8): δ −6.47 (ddd,2JPb†Pd† = 27.2 Hz, 2JPb†Pc = 25.5 Hz, 3JPb†Pa = 9.1 Hz, 1 P, Pb†), −1.22 (ddd, 3JPcPa = 42.1 Hz, 2JPcPd† = 34.4 Hz, 2JPcPb† = 25.5 Hz, 1 P, Pc), 5.86 (dd, 2JPd†Pc = 34.4 Hz, 2JPd†Pb† = 27.2 Hz, 1 P, Pd†), 55.32 (dd, 3JPaPc = 42.1 Hz,3JPaPb† = 9.1 Hz, 1 P, Pa). IR (KBr): 941 cm−1 (ν(CS)). Anal. Calcd for C14H36P4RuS4: C, 30.15; H, 6.51. Found: C, 30.22; H, 6.40. A crystal suitable for X-ray analysis precipitated from the reaction mixture ca. 5 days after CS2 addition. Crystallography. The X-ray diffraction measurement for [RuH(OC(O)CH2PMe2-κ2O,P)(PMe3)3] (2) was carried out at MX1 beamline at the Australian Synchrotron Facility, Melbourne. The crystal, mounted on the goniometer using a cryo loop for diffraction measurements, was coated with paraffin oil and then quickly transferred to the cold stream using a Cryo stream attachment. Data were collected using Si ⟨111⟩ monochromated synchrotron X-ray radiation (λ = 0.71023 Å) at 100(2) K and were corrected for Lorentz and polarization effects using the XDS software.26 The structure was solved by direct methods, and the full-matrix least-squares refinements were carried out using SHELXL.27 A single crystal of [Ru(SC(S)SCH(−S)PMe2CH2-κ3S,S,C)(PMe3)3] (5) was attached, with Exxon Paratone N, to a short length of fiber supported on a thin piece of copper wire inserted in a copper mounting pin. The crystal was quenched in a cold nitrogen gas stream from an Oxford Cryosystems Cryostream. A Bruker kappa APEXII area detector diffractometer employing graphite-monochromated Mo Kα radiation generated from a fine-focus sealed tube was used for the data collection. The structure was solved by direct methods, and the

(dddd, JPdPa = 260.8 Hz, JPdPc = 33.2 Hz, JPdPb = 23.7 Hz, JPd13CO2 = 5.4 Hz, 1 P, Pd), 1.68 (dddd, JPaPd = 260.8 Hz, JPaPc = 33.2 Hz, JPaPb = 23.7 Hz, JPa13CO2 = 13.1 Hz, 1 P, Pa), 21.04 (app dt, JPcPd = JPcPa = 33.2 Hz, JPcPb = 21.0 Hz, 1 P, Pc). A crystal suitable for X-ray analysis was obtained by concentrating the reaction mixture after 10 min at room temperature, redissolving the oily residue in toluene-d8, filtration, and slow evaporation of the solvent. Preparative Scale. THF (ca. 5 mL) was vacuum transferred into an ampule containing trans-RuCl2(PMe3)4 (0.1951 g, 0.410 mmol) and C8K (0.2178 g, 1.61 mmol). The ampule was sealed and stirred overnight at room temperature, after which time the mixture was filtered, degassed, placed under an atmosphere of CO2, and stirred for 30 min. The yellow solution was concentrated to dryness under reduced pressure, and the sticky residue washed with pentane (ca. 5 mL). The residue was dissolved in Et2O (10 mL) and filtered, and the solvent removed by evaporation. The pale yellow solid was washed with pentane (5 mL) and dried in vacuo. Yield: 0.0761 g (41%). Anal. Calcd for C13H36P4RuO2: C, 34.74; H, 8.07. Found: C, 34.83; H, 8.17. IR (Fluorolube, cm−1): 1582 (ν(CO)). The NMR spectra were identical to those described above; however no coupling was observed to 13C in the 1H or 31P spectra. [Ru(CH2PMe2CHS2-κ3C,S,S)(PMe3)3] (3). This compound has been previously reported;11a however, in this work, the complex was prepared using a modified procedure. An NMR tube fitted with a concentric Teflon valve was charged with trans-RuCl2(PMe3)4 (52 mg, 0.11 mmol) and C8K (77 mg, 0.57 mmol, 5.2 equiv). THF-d8 (ca. 0.5 mL) was added by vacuum transfer, and the resulting mixture was sonicated for 20 min before being filtered through Celite and glass wool. The dark red solution was degassed, and excess CS2 (ca. 0.1 mL) vacuum transferred into the solution. After 10 min, the solvent and unreacted CS2 were removed under reduced pressure and the remaining red-brown residue was redissolved in THF-d8. Ru(CH2PMe2CHS2-κ3C,S,S)(PMe3)3 was formed as the major product (>85%) with minor unidentified impurities. 31P{1H} and 1H NMR spectroscopic data were in good agreement with that previously reported.11a 1H NMR (300 MHz, THF-d8): δ 0.77−0.87 (m, 2 H, CH2), 1.21−1.25 (m, 18 H, 2 × Pb(CH3)3), 1.48 (d, 2JHPc = 7.0 Hz, 9 H, Pc(CH3)3), 1.56 (dd, 2JHPa = 11.9 Hz, 3JHPc = 0.9 Hz, 6 H, Pa(CH3)2), 4.56 (dt, 2JHPa = 15.3 Hz, 3JHPb = 4.1 Hz, 1 H, CH). 1 H{31P} NMR (300 MHz, THF-d8): δ 0.82 (s, 2 H, RuCH2), 1.23 (s, 18 H, 2 × Pb(CH3)3), 1.48 (s, 9 H, Pc(CH3)3), 1.56 (s, 6 H, Pa(CH3)2), 4.56 (s, 1 H, CH). 13C{1H} NMR (75 MHz, THF-d8): δ −4.61 (app tt, 1JCPa = 2JCPc = 69.4 Hz, 2JCPb = 7.4 Hz, CH2), 15.98 (app dd, 1JCPa = 46.5 Hz, 4JCPc = 1.6 Hz, Pa(CH3)2), 20.33 (ddd, 1JCPb = 13.3 Hz, 3JCPc = 11.5 Hz, 4JCPa = 1.6 Hz, 2 × Pb(CH3)3), 20.90 (dq, 1 JCPc = 25.1 Hz, 3JCPb = 4JCPa = 1.3 Hz, Pc(CH3)3), 50.83 (ddt, 1JCPa = 73.8 Hz, 3JCPc = 7.5 Hz, 3JCPb = 2.7 Hz, CH). 31P{1H} NMR (122 MHz, THF-d8): δ −0.58 (td, 2JPcPb = 27.0 Hz, 3JPcPa = 6.7 Hz, 1 P, Pc), 8.64 (dd, 2JPbPc = 27.0 Hz, 3JPbPa = 13.6 Hz, 2 × Pb), 28.00 (dt, 3JPaPc = 6.7 Hz, 3JPaPb = 13.6 Hz, 1 P, Pa). Low-Temperature Reaction of 13 CO 2 with [RuH(η 2 CH2PMe2)(PMe3)3] (1). An excess of 13CO2 was added to a frozen, degassed solution of [RuH(η2-CH2PMe2)(PMe3)3] (1), generated from trans-RuCl2(PMe3)4 (41.8 mg, 0.0878 mmol) and C8K (50.2 mg, 0.371 mmol, 4.2 equiv) in THF-d8 (ca. 0.5 mL). The frozen sample was warmed to ca. 198 K and injected into the NMR probe at 210 K. 31 1 P{ H}, 1H, and 1H{31P} NMR spectroscopic data obtained showed the sample to be exclusively the precursor material 1, as was observed for the same spectra taken at 230 K. At 250 K, a small amount of [RuH(O13C(O)CH2PMe2-κ2O,P)(PMe3)3] (13C-2) was formed, and this product increased in concentration at this temperature over the course of the following 20 min. The probe temperature was increased to 270 K, with the 31P{1H} NMR showing a further increase in the product concentration. Complete conversion of the starting material occurred upon warming the sample to 298 K. Low-Temperature Reaction of CS2 with [RuH(η2-CH2PMe2)(PMe3)3] (1). Excess CS2 (ca. 0.1 mL) was added to a frozen, degassed solution of [RuH(η2-CH2PMe2)(PMe3)3] (1), generated from trans641

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full-matrix least-squares refinements were carried out using SHELXL.27

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(16) (a) Couffignal, R.; Kagan, H. B.; Mathey, F.; Samuel, O.; Santini, C. C. R. Acad. Sci. C Chim. 1980, 291, 29−32. (b) Grossmann, G.; Lang, R.; Ohms, G.; Scheller, D. Magn. Reson. Chem. 1990, 28, 500−504. (17) Allen, F. H.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. Typical Interatomic Distances: Organic Compounds. In International Tables for Crystallography; Prince, E., Ed.; 2006; Vol. C: Mathematical, Physical and Chemical Tables, pp 790−811. (18) Mason, M. G.; Swepston, P. N.; Ibers, J. A. Inorg. Chem. 1983, 22, 411−418. (19) (a) Lescop, C.; Arliguie, T.; Lance, M.; Nierlich, M.; Ephritikhine, M. J. Organomet. Chem. 1999, 580, 137−144. (b) Chen, Y. H.; Peng, Y.; Chen, P. P.; Zhao, J. F.; Liu, L. T.; Li, Y.; Chen, S. Y.; Qu, J. P. Dalton Trans. 2010, 39, 3020−3025. (20) (a) Carmona, E.; Campora, J.; Munoz, M. A.; Paneque, M.; Poveda, M. L. Pure Appl. Chem. 1989, 61, 1701−1706. (b) Pandey, K. K. Coord. Chem. Rev. 1995, 140, 37−114. (21) Weitz, I. S.; Rabinovitz, M. J. Chem. Soc., Perkin Trans. 1 1993, 117−120. (22) McNeill, K.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1997, 119, 11244−11254. (23) Harris, R. K.; Becker, E. D.; De Menezes, S. M. C.; Granger, P.; Hoffman, R. E.; Zilm, K. W. Pure Appl. Chem. 2008, 80, 59−84. (24) Marat, K. Spinworks 3.1.8; University of Manitoba, 2011. (25) Jones, R. A.; Wilkinson, G.; Colquohoun, I. J.; McFarlane, W.; Galas, A. M. R.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1980, 2480−2487. (26) Kabsch, W. J. Appl. Crystallogr. 1993, 26, 795−800. (27) Sheldrick, G. M. Acta Crystallogr. A 2008, 64, 112−122.

ASSOCIATED CONTENT

S Supporting Information *

Crystal structure and refinement parameters for compounds 13 C-2 and 5. A cif file giving crystallographic data for [RuH(O13C(O)CH2PMe2-κ2O,P)(PMe3)3] (13C-2) and [Ru(SC(S)SCH(−S)PMe2CH2-κ3S,S,C)(PMe3)3] (5). This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +61 2 9385 2700. Fax: +61 2 9385 8008. E-mail: L. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Australian Research Council and the University of New South Wales for funding and the Australian Synchrotron for beam time.

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REFERENCES

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