Insertion of CO2 into the Ru−C Bonds of cis- and trans-Ru(dmpe

Organometallics 2009, 28, 2385–2390

2385

Insertion of CO2 into the Ru-C Bonds of cis- and trans-Ru(dmpe)2Me2 (dmpe ) Me2PCH2CH2PMe2) Olivia R. Allen,† Scott J. Dalgarno,‡ Leslie D. Field,*,† Paul Jensen,§ and Anthony C. Willis⊥ School of Chemistry, The UniVersity of New South Wales, NSW 2033, Australia, School of EPS-Chemistry, Heriot-Watt UniVersity, Riccarton, Edinburgh, EH14 4AS, U.K., School of Chemistry, UniVersity of Sydney, NSW 2006, Australia, and Research School of Chemistry, Australian National UniVersity, Canberra, ACT 0200, Australia ReceiVed December 15, 2008

The reaction of cis-Ru(dmpe)2Me2 (1) and trans-Ru(dmpe)2Me2 (2) [dmpe ) 1, 2-bis(dimethylphosphino)ethane] with carbon dioxide was investigated. Addition of 3-4 atm of CO2 at 300 K to transRu(dmpe)2Me2 (2) results in the formation of the expected methyl acetate complex trans-Ru(dmpe)2(OCOMe)Me (3) and bis-acetate complex trans-Ru(dmpe)2(OCOMe)2 (5). Addition of 3-4 atm of CO2 at 300 K to cis-Ru(dmpe)2Me2 (1) leads to the formation of the expected methyl acetate complex cisRu(dmpe)2(OCOMe)Me (4) and to the bis-acetate complex cis-Ru(dmpe)2(OCOMe)2 (6) when the reaction mixture is heated at 333 K. A carbonate byproduct, Ru(dmpe)2CO3 (7), is also formed in both reactions. As part of this study, a new ruthenium methyl hydride complex has been synthesized, Ru(dmpe)2CH3H (8), and its isomerization properties and reactions with CO2 are reported. At 300 K, addition of CO2 to 8 forms the methyl formate product Ru(dmpe)2(O2CH)CH3 (9). The reaction with CO2 is reversible, and on heating, the methyl formate 9 decarboxylates and CO2 insertion into the metal carbon bond eventually forms the hydrido acetate complex Ru(dmpe)2(O2CCH3)H (12) as the thermodynamic product. This means that the insertion of CO2 into the Ru-H bond is kinetically favored, but the thermodynamic product results from insertion into the Ru-C bond. All complexes have been characterized by multinuclear NMR spectroscopy, with IR spectroscopy and elemental analyses where complexes were thermally stable. Complexes 5, 7, 8, and 12 have also been characterized by X-ray crystallography. Introduction At the moment there is significant interest in the use of CO2 as a chemical feedstock. This growing attention is due to environmental,1 legal,2 and social issues.3 The development of practical methods of carbon dioxide fixation is essential in the management of this greenhouse gas and has been the subject of much discussion and research in recent times.4 The activation and functionalization of carbon dioxide via a transition metal center is well established and is of interest because of the possibility of utilizing CO2 as an inexpensive 1-carbon fragment in synthesis,5-13 and a range of different products including * To whom correspondence should be addressed. Fax: +61 2 9385 2700. Tel: +61 2 9385 8008. E-mail: [email protected]. † The University of New South Wales. ‡ Heriot-Watt University. § University of Sydney. ⊥ Australian National University. (1) Climate Change 2001: The Scientific Basis; Cambridge University Press, 2001. (2) In Kyoto Protocol to the United Nations Framework ConVention on Climate Change, Kyoto, 1997. (3) Clark, B.; York, R. Theory Soc. 2005, 34, 391–428. (4) Arakawa, H.; Aresta, M.; Armor, J. N.; Barteau, M. A.; Beckman, E. J.; Bell, A. T.; Bercaw, J. E.; Creutz, C.; Dinjus, E.; Dixon, D. A.; Domen, K.; DuBois, D. L.; Eckert, J.; Fujita, E.; Gibson, D. H.; Goddard, W. A.; Goodman, D. W.; Keller, J.; Kubas, G. J.; Kung, H. H.; Lyons, J. E.; Manzer, L. E.; Marks, T. J.; Morokuma, K.; Nicholas, K. M.; Periana, R.; Que, L.; Rostrup-Nielson, J.; Sachtler, W. M. H.; Schmidt, L. D.; Sen, A.; Somorjai, G. A.; Stair, P. C.; Stults, B. R.; Tumas, W. Chem. ReV. 2001, 101, 953– 996. (5) Aresta, M. ActiVation Small Mol. 2006, 1–41. (6) Aresta, M.; Dibenedetto, A. Dalton Trans 2007, 28, 2975–2992.

formic acid and alkyl formates4,13,14 have been synthesized from CO2. An important step in the functionalization of small molecules such as carbon dioxide is their insertion into metal-hydride and metal-carbon bonds.15-19 Examples of CO2 insertion into group 8 metal-hydride and metal-carbon bonds are relatively rare.6,19-26 (7) Omae, I. Catal. Today 2006, 115, 33–52. (8) Louie, J. Curr. Org. Chem. 2005, 9, 605–623. (9) Darensbourg, D. J. Chem. ReV. 2007, 107, 2388–2410. (10) Gibson, D. H. Chem. ReV. 1996, 96, 2063–2095. (11) Leitner, W. Coord. Chem. ReV. 1996, 153, 257–284. (12) Dinjus, E.; Leitner, W. Transition metal catalyzed activation of carbon dioxide. In Carbon Dioxide Chemistry: EnVironmental Issues; Paul, J., Pradier, C.-M., Eds.; Royal Society of Chemistry: Cambridge, 1994; Vol. 153, pp 82-92. (13) Aresta, M.; Dibenedetto, A. Catal. Today 2004, 98, 455–462. (14) Baiker, A. Appl. Organomet. Chem. 2000, 14, 751–762. (15) Aresta, M.; Quaranta, E.; Tommasi, I. New J. Chem. 1994, 18, 133–42. (16) Jessop, P. G.; Rastar, G.; James, B. R. Inorg. Chim. Acta 1996, 250, 351–357. (17) Yin, X.; Moss, J. R. Coord. Chem. ReV. 1999, 181, 27–59. (18) Behr, A. Carbon Dioxide Activation by Metal Complexes. In Carbon Dioxide ActiVation by Metal Complexes; Weller, Ed.; VCH: Weinheim, 1988; pp 31-45. (19) Urakawa, A.; Jutz, F.; Laurenczy, G.; Baiker, A. Chem.-Eur. J. 2007, 13, 3886–3899. (20) Hartwig, J. F.; Bergman, R. G.; Andersen, R. A. Organometallics 1991, 10, 3344–62. (21) Hartwig, J. F.; Bergman, R. G.; Andersen, R. A. Organometallics 1991, 10, 3326–44. (22) Hartwig, J. F.; Bergman, R. G.; Andersen, R. A. J. Am. Chem. Soc. 1991, 113, 6499–508. (23) Whittlesey, M. K.; Perutz, R. N.; Moore, M. H. Organometallics 1996, 15, 5166–5169.

10.1021/om801184k CCC: $40.75  2009 American Chemical Society Publication on Web 03/23/2009

2386 Organometallics, Vol. 28, No. 8, 2009

Allen et al.

Scheme 1

Previously, studies on the reaction of ruthenium hydrides with CO2 have been carried out with the dihydride complex Ru(dmpe)2H2 (dmpe ) Me2PCH2CH2PMe2).19,23 Perutz and coworkers initially completed an NMR study on the insertion of CO2 into the Ru-H bond of Ru(dmpe)2H2, demonstrating that, with excess CO2, the double-insertion product cis-Ru(dmpe)2(O2CH)2 could be formed and also that the second insertion is reversible so that the double-insertion product is in equilibrium with both the cis and trans isomers of the monoinsertion products. Building on this work, Baiker and co-workers have recently published an experimental and DFT study on the hydrogenation of CO2 by Ru(dmpe)H2 at high pressures.19,27 The monoinsertion product Ru(PMe3)4(OCHO)H from the reaction of Ru(PMe3)4H2 and CO2 has also been reported.28 In this paper we report the insertion of CO2 into the metal carbon bonds of cis- and trans-Ru(dmpe)2Me2 (1 and 2), respectively, to form the corresponding acetate and carbonate complexes. In addition, we also report the synthesis, characterization, and reactions of the methyl hydride Ru(dmpe)2MeH (8) with CO2, where both the metal-carbon and metal-hydride bonds can undergo CO2 insertion reactions.

Results and Discussion Reaction of cis-Ru(dmpe)2Me2 (1) and trans-Ru(dmpe)2Me2 (2) with CO2. cis-Ru(dmpe)2Me2 (1) was synthesized by the reaction of Ru2(OCOCH3)4Cl with Mg(Me)2,29 and transRu(dmpe)2Me2 (2) was synthesized from the reaction of transRu(dmpe)2Cl2 with MeLi according to literature procedures.30 The cis and trans isomers can be synthesized in pure form; however the trans isomer can be readily isomerized to the more thermodynamically stable cis isomer, and the isomerization properties have previously been reported.30 Complex 2 has a singlet resonance in the 31P{1H} NMR spectrum at δ 46.7 ppm and a characteristic resonance at δ -1.2 ppm in the 1H NMR spectrum for the metal-bound methyl groups with a pentet structure arising from the coupling to four equivalent phosphorus nuclei. Reaction of trans-Ru(dmpe)2Me2 (2) with 1 atm of CO2 in C6D6 proceeds readily at room temperature to give the trans monoinsertion product transRu(dmpe)2(OCOMe)Me (3) (Scheme 1). The reaction is complete within 24 h. Complex 3 exhibits a singlet resonance in the 31P{1H} spectrum at δ 45.0 ppm and a characteristic pentet (24) Ittel, S. D.; Tolman, C. A.; English, A. D.; Jesson, J. P. J. Am. Chem. Soc. 1978, 100, 7577–85. (25) Field, L., D.; Shaw, W., J.; Turner, P. Chem. Commun. 2002, 1, 46–7. (26) Field, L. D.; Lawrenz, E. T.; Shaw, W. J.; Turner, P. Inorg. Chem. 2000, 39, 5632–5638. (27) Baiker, A.; Urakawa, A.; Iannuzzi, M.; Hutter, J. Chem.-Eur. J. 2007, 13, 6828–6840. (28) Jessop, P. G.; Hsiao, Y.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1996, 118, 344–55. (29) Umezawa-Vizzini, K.; Lee, T. R. J. Organomet. Chem. 1999, 579, 122–125. (30) Field, L. D.; Magill, A. M.; Shearer, T. K.; Dalgarno, S. J.; Turner, P. Organometallics 2007, 26, 4776–4780.

Figure 1. ORTEP diagram of trans-Ru(dmpe)2(O2CCH3)2 (5) (50% ellipsoids). Table 1. Selected Bond Distances (Å) and Angles (deg) for trans-Ru(dmpe)2(O2CCH3)2 (5) Ru (1)-P(1) Ru(1)-O(1) O(2)-C(7) P(1)-Ru(1)-P(2) P(2)-Ru(1)-O(1) O(1)-C(7)-C(8)

Bond Distances 2.3206(4) Ru(1)-P(2) 2.1231(11) O(1)-C(7) 1.229(2) C(7)-C(8) Bond Angles 83.597(14) P(1)-Ru(1)-O(1) 84.98(3) O(1)-C(7)-O(2) 113.41(16) O(2)-C(7)-C(8)

2.3292(4) 1.277(2) 1.525(2) 81.54(4) 127.09(15) 119.49(16)

resonance at δ -1.61 ppm (JPH ) 6.0 Hz) in the 1H NMR spectrum for the metal-bound methyl groups with a singlet at δ 1.95 ppm corresponding to the new acetate group. In the 31 P{1H} NMR spectrum a transient intermediate complex is observed, but this has yet to be identified.31 Under more forcing conditions (3-4 atm CO2), a second insertion occurs to produce the trans-bis-acetate product transRu(dmpe)2(OCOMe)2 (5) after several days. The 31P{1H} NMR spectrum of 5 displays a singlet at 46.3 ppm, indicating the trans geometry, and there is a resonance at 1.69 ppm in the 1H NMR spectrum that can be attributed to the methyl of the acetate group. The second CO2 insertion is significantly slower than the first, and this suggests that the reaction mechanism could be dissociative rather than involving a concerted mechanism, as proposed for the CO2 insertion into metal hydrides.19,23,27 The end product 5 has been prepared previously;32 however, little characterizing data were published and during this work pale yellow crystals were obtained suitable for X-ray crystallographic analysis from a solution of toluene and pentane. An ORTEP depiction is shown in Figure 1. The X-ray analysis confirms the trans configuration of the complex and a Ru-O bond length of 2.123 Å (Table 1), which is slightly shorter than that of the similar hydrido formate complex (2.243 Å).23 The asymmetric stretch of the CO2 bond at 1608 cm-1 compares well with other complexes known in the literature.32 Reaction of the cis-dimethyl complex cis-Ru(dmpe)2Me2 (1) with 3-4 atm of CO2 for 6 h leads to the formation of the unsymmetrically substituted complex cis-Ru(dmpe)2(OCOMe)(31) The intermediate is represented by a singlet in the 31P{1H} NMR spectrum at δ 44.5 ppm and also has a quintet in the proton spectrum at high field at δ-1.71 ppm, very close to that of the trans-methyl acetate complex 3. In the 13C{1H} NMR spectrum there is a carbonyl resonance at δ 162.5 ppm (which correlates to the 31P resonance at δ 44.5 ppm). The intermediate builds up over the first 3 h of reaction and diminishes as 3 is formed. (32) Wong, W.-K.; Chiu, K. W.; Statler, J. A.; Wilkinson, G.; Motevalli, M.; Hursthouse, M. B. Polyhedron 1984, 3, 1255–65.

Insertion of CO2 into the Ru-C bonds of Ru(dmpe)2Me2

Organometallics, Vol. 28, No. 8, 2009 2387 Scheme 2

Table 2. Selected Bond Distances (Å) and Angles (deg) for Ru(dmpe)2(CO3) (7) Ru (1)-P(1) Ru(1)-P(3) Ru(1)-O(1) O(1)-C(13) O(3)-C(13)

Bond Distances 2.3378(16) Ru(1)-P(2) 2..475(14) Ru(1)-P(4) 2.147(3) Ru(1)-O(2) 1.275(7) O(2)-C(13) 1.252(6)

Bond P(1)-Ru(1)-P(2) 83.36(6) P(1)-Ru(1)-P(4) 177.42(8) P(2)-Ru(1)-P(4) 97.78(8) O(1)-Ru(1)-O(2) 61.64(13) O(2)-C(13)-O(3) 120.9(5) Ru(1)-O(1)-C(13) 93.2(3)

2.2631(15) 2.3384(16) 2.165(3) 1.348(6)

Angles P(1)-Ru(1)-P(3) 97.96(6) P(2)-Ru(1)-P(3) 94.61(6)(2) P(3)-Ru(1)-P(4) 84.27(7) O(1)-C(13)-C(2) 114.7(4) O(1)-C(13)-O(3) 124.4(5) Ru(1)-O(2)-C(13) 90.4(3)

Me (4) (Scheme 2). The presence of 4 is indicated by the presence of four doublet of doublet of doublet resonances in the 31P{1H} NMR spectrum at 30.7, 38.2, 43.8, and 54.3 ppm with a very large coupling of 341 Hz between the mutually trans phosphorus nuclei. The 1H NMR spectrum displays a methyl resonance at -0.08 ppm indicative of a cis-unsymmetrical complex with one methyl group and a resonance at 2.17 ppm representing the acetate moiety. The second insertion of CO2 is slow, and a further week of heating (60 °C) was required for complete conversion of the starting material 1; after 4 weeks of heating a mixture of bis-acetate products transRu(dmpe)2(OCOMe)2 (5) and cis-Ru(dmpe)2(OCOMe)2 (6) were the exclusive products. The 31P{1H} NMR spectrum displayed a singlet at 46.3 ppm indicative of the trans-bis-acetate product 5 and two virtual triplets at 37.7 and 53.9 ppm indicative of the cis-bis-acetate complex 6. If the mixture is irradiated with UV light, the trans complex isomerizes entirely to the cis isomer within 2 h. In the reactions of both cis-Ru(dmpe)2Me2 (1) and transRu(dmpe)2Me2 (2) with CO2, the carbonate complex Ru(dmpe)2(CO3) (7) is formed as a reaction byproduct. Carbonates have now been observed as common byproducts in reactions of transition metals with CO2, and while they could arise from the reaction of CO2 with adventitious water, they can also arise from the reductive disproportionation of CO2 to CO and CO32-.33 Pale blue crystals of 7 were obtained from the reaction of 2 with CO2 in C6D6 as a stable byproduct. Complex Ru(dmpe)2(CO3) (7) has been reported previously by Anderson and co-workers,20 although no structural data were obtained. The structure of 7 (Figure 2, Table 2) is analogous to that of Fe(dmpe)2(CO3),6 and the bond lengths and angles of the ruthenium carbonate moiety are comparable to those of [Ru(η2-O2CO)(p-cymene)(PCy3)]34 and mer-Ru(κ2-O2CO)(CO)(Cyttp) · CH2Cl2 · 2H2O.35 (33) Allen, O. R.; Dalgarno, S. J.; Field, L. D. Organometallics 2008, 27, 3328–3330. (34) Demerseman, B.; Mbaye, M. D.; Semeril, D.; Toupet, L.; Bruneau, C.; Dixneuf, P. H. Eur. J. Inorg. Chem. 2006, 6, 1174–1181. (35) Blosser, P. W.; Gallucci, J. C.; Wojcicki, A. J. Mol. Catal. A: Chem. 2004, 224, 133–144.

Reactions of trans-Ru(dmpe)2MeH (8) and trans-Ru(dmpe)2MeH (9) with CO2. The ruthenium methyl hydride complex trans-Ru(dmpe)2MeH (8) was synthesized from the corresponding hydrido chloro complex by reaction with 1 equiv of methyllithium (Scheme 3). The 31P{1H} NMR spectrum displays a singlet at 47.3 ppm indicative of four chemically equivalent phosphorus atoms, and the 1H NMR presents two phosphorus coupled pentets at -12.63 and -1.51 ppm for the hydride and methyl groups, respectively. Crystals suitable for X-ray crystallographic analysis were grown from pentane at 255 K. The structure of 8 (Figure 3, Table 3) is a slightly distorted octahedron with the length of the ruthenium-carbon bond at 2.245 Å being comparable to that of the dimethyl complex at 2.236 Å.30 When a solution of trans-Ru(dmpe)2MeH (8) in THF was exposed to UV light for 10 min, signals indicative of isomerization to the cis isomer (9) are apparent in the NMR spectra. Under irradiation, the trans isomer can be almost completely converted to the cis isomer; however, under prolonged irradiation, 9 is unstable and reacts to form other products.36 When THF solutions of complex trans-Ru(dmpe)2MeH (8) or cis-Ru(dmpe)2MeH (9) were exposed to 3-4 atm of 13CO2, the starting materials reacted immediately (Scheme 4). NMR spectra showed that trans-Ru(dmpe)2MeH (8) gave exclusively trans-Ru(dmpe)2(O2CH)Me (10) and cis-Ru(dmpe)2MeH (9) gave exclusively cis-Ru(dmpe)2(O2CH)Me (11). The trans isomer 10 has a single resonance at 44.3 ppm in the 31P{1H} NMR spectrum, and a distinctive 13C coupled doublet at δ 8.68 ppm in the 1H NMR spectrum characteristic of a formate along with a 31P coupled pentet at δ -1.61 ppm representing a ruthenium-bound methyl group. The cis isomer 11 has four

Figure 2. ORTEP diagram of Ru(dmpe)2(CO3) (7) (50% ellipsoids). Scheme 3

2388 Organometallics, Vol. 28, No. 8, 2009

Allen et al.

Figure 3. ORTEP diagram of trans-Ru(dmpe)2MeH (8) (50% ellipsoids). Table 3. Selected Bond Distances (Å) and Angles (deg) for trans-Ru(dmpe)2MeH (8) Ru(1)-P(1) Ru(1)-P(3) Ru(1)-C(13) P(1)-Ru(1)-P(2) P(1)-Ru(1)-P(4) P(2)-Ru(1)-P(4) H(1)-Ru(1)-C(13)

Bond Distances 2.2839(6) Ru(1)-P(2) 2.2818(6) Ru(1)-P(4) 2.245(2) Ru(1)-H(1) Bond Angles 84.41(2) P(1)-Ru(1)-P(3) 95.48(2) P(2)-Ru(1)-P(3) 175.17(2) P(3)-Ru(1)-P(4) 178.20

2.2778(6) 2.2841(6) 1.66 174.60(2) 95.50(2) 84.15(2)

Scheme 4

doublet of doublet of doublet resonances in the 31P{1H} NMR spectrum with a large coupling between the two mutually trans phosphorus atoms of 338 Hz. When 13C-labeled CO2 is employed in the reaction, there is a 13C-coupled doublet at δ 8.10 ppm in the 1H NMR spectrum indicating the presence of a formate and a multiplet at δ -0.51 ppm for the rutheniumbound methyl group. While the formate complexes 10 and 11 can be observed spectroscopically in solution, the complexes are unstable and readily lose CO2. The reversible insertion/elimination of CO2 into ruthenium-hydride23 and iron-hydride bonds26 has been previously observed. If either 10 or 11 is heated (60 °C) the sole product is the hydrido acetate trans-Ru(dmpe)2(O2CCH3)H (12) (Scheme 4). The formation of trans-Ru(dmpe)2(O2CCH3)H (12) can be rationalized by decarboxylation to form trans-Ru(dmpe)2MeH (36) The major product formed after prolonged irradiation of Ru(dmpe)2CH3H is Ru(dmpe)2H2, and this probably arises via reductive elimination of methane from 9 with subsequent C-H activation of the reaction solvent (THF), followed by beta hydride elimination to give the dihydride product.40-43

Figure 4. ORTEP diagram of trans-Ru(dmpe)2(O2CCH3)H (12) (50% ellipsoids and only one component of each of the disordered atoms is shown). Table 4. Selected Bond Distances (Å) and Angles (deg) for trans-Ru(dmpe)2(O2CMe)H (12) Ru (1)-P(1) Ru(1)-P(3) Ru(1)-O(1) P(1)-Ru(1)-P(2) P(1)-Ru(1)-P(4) P(2)-Ru(1)-P(4) H(1)-Ru(1)-O(1)

Bond Distances 2.312(4) Ru(1)-P(2) 2.265(3) Ru(1)-P(4) 2.217(7) Ru(1)-H(1) Bond Angles 154.17(18) P(1)-Ru(1)-P(3) 92.1(4) P(2)-Ru(1)-P(3) 165.3(5) P(3)-Ru(1)-P(4) 168.40 O(1)-C(13)-O(2)

2.296(12) 2.291(14) 1.55 176.10(2) 107.0(3) 87.3(4) 111.6(7)

(9), where CO2 can insert into the metal-carbon bond. transRu(dmpe)2MeH (8) is a further example of a complex where CO2 insertion can then occur either at the metal-hydride bond or the metal-carbon bond and where the metal-hydride insertion is more facile (but reversible) and the metal-carbon insertion leads to a thermodynamically more stable product. In previous work,37 we have reported that the kinetic formate product of insertion of CO2 into the Fe-H and Fe-C bonds of Fe(dmpe)2(CH2CN)(H) arises from reversible reaction at the Fe-H bond, but the eventual thermodynamic product in the reaction results from insertion into the Fe-C bond. trans-Ru(dmpe)2(O2CCH3)H (12) was synthesized independently by the reaction of cis-Ru(dmpe)2H2 with 1 equiv of acetic acid. Crystals suitable for X-ray crystallographic analysis were grown from a solution of diethyl ether and pentane at 255 K. The structure (Figure 4, Table 4) shows a very distorted octahedron with a ruthenium oxygen bond length of 2.217 Å, which is comparable to that in trans-Ru(dmpe)2(O2CCH3)2 (5).

Conclusions Ruthenium dimethyl complexes of the type Ru(dmpe)2Me2 react with CO2, producing new stable ruthenium acetate complexes. There are distinct differences between the cis and trans isomers of Ru(dmpe)2Me2 when reacted with CO2. The trans isomer trans-Ru(dmpe)2Me2 (2) reacts much more readily, forming the expected trans methyl acetate product transRu(dmpe)2(OCOMe)Me (3) and then the trans bis-acetate transRu(dmpe)2(OCOMe)2 (5). The reaction with the cis isomer cis-Ru(dmpe)2Me2 (1) proceeds more slowly and produces the expected cis methyl acetate product cis-Ru(dmpe)2(OCOMe)Me (4) and then the double-insertion product cis-Ru(dmpe)2(37) Allen, O. R.; Field Leslie, D.; Magill, A. M.; Dalgarno, S. J. Organometallics 2008, manuscript submitted.

Insertion of CO2 into the Ru-C bonds of Ru(dmpe)2Me2

Organometallics, Vol. 28, No. 8, 2009 2389

Table 5. Crystal Data and Refinement Details for 5, 7, 8, and 12 empirical formula M temp (K) cryst syst space group unit cell dimens a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z F(calc) (g cm-3) µ(Mo KR) (mm-1) N Nind Nobs (I > 2σ(I)) R1(F)a wR2(F2)

5

7

8

12

C16H38O4P4Ru 519.44 200 tetragonal P43212

C16H38D3P4O6Ru 557.44 150(2) monoclinic P21/n

C13H36P4Ru 417.37 100(2) orthorhombic Pna21

C28H72P8O4Ru 922.76 100(2) orthorhombic P21/c

9.0425(1) 9.0425(1) 29.0790(4)

9.709(2) 18.743(3) 14.004(2)

17.6025(14) 9.1856(7) 12.2908(9)

17.1167(8) 8.9490(5) 28.1916(4)

1987.3(3) 4 1.395 1.097 68720 5960 5592 0.0241 0.0531

4318.3(4) 4 1.419 1.024 64331 8287 4372 0.0517 0.1050

101.036(2) 2377.70(5) 4 1.451 0.945 37225 2734 2499 0.0164 0.0398

2501.3(7) 4 1.480 0.909 23924 5734 3850 0.0447 0.0901

a R1 ) ∑||Fo| - |Fc||/∑|Fo| for Fo > 2σ(Fo); wR2 ) (∑w(Fo2 - Fc2)2/∑(wFc2)2)1/2 all reflections w)1/[σ2(Fo2) + (0.04P)2 + 5.0P] where P ) (Fo2 + 2Fc2)/3.

(OCOMe)2 (6). These results indicate that the stereochemistry of the starting material is a key factor in the rate of reaction with CO2 and the nature of products formed and that the stereochemical integrity at the metal center is retained as the insertion occurs. We have also reported the synthesis of the first ruthenium hydrido methyl complex trans-Ru(dmpe)2MeH (8), and competitive insertion of CO2 into the Ru-H and Ru-C bonds shows that CO2 inserts rapidly (but reversibly) into the ruthenium hydride bond before inserting irreversibly into the ruthenium carbon bond to form the hydrido acetate trans-Ru(dmpe)2(O2CCH3)H (12) as the thermodynamic product. This result indicates that the insertion of CO2 into the metal-H bond is kinetically favored, but the thermodynamic product results from insertion into the metal-C bond.

Experimental Section General Information. All manipulations were carried out using standard Schlenk techniques. Air-sensitive NMR samples were prepared in an argon-filled glovebox, with solvent vacuumtransferred into an NMR tube fitted with a concentric Teflon valve. Benzene-d6 was dried over sodium/benzophenone and vacuumdistilled immediately prior to use. Diethyl ether, hexane, pentane, toluene, and benzene were dried over sodium wire before distillation under nitrogen from sodium/benzophenone. All compressed gases were obtained from the British Oxygen Co. (BOC) gases. Carbon dioxide (>99.995%) was used as received. 1H, 31P, and 13C NMR spectra were recorded on a Bruker DRX300 NMR spectrometer at 300.1, 121.5, and 75.5 MHz, respectively, and referenced as follows: 1H: methyl resonance of benzene-d6 residual at δ 7.15, THF-d8 residuals at δ 3.58 and 1.73. 31P: external phosphoric acid in D2O at 0.0 ppm. 13C: benzene-d6 at δ 128.0, THF-d8 at δ 67.57 and 25.37 ppm. UV irradiation of metal complexes was performed using an Oriel 300 W high-pressure mercury vapor lamp with the incident beam directed through a water-filled jacket to filter infrared radiation. cis-Ru(dmpe)2Me2 (1) and trans-Ru(dmpe)2Me2 (2) were prepared following literature methods.29,30 Ru(dmpe)2H2 and Ru(dmpe)2HCl were prepared using a modified literature preparation.38,39 Synthesis of trans-Ru(dmpe)2(O2CCH3)CH3 (3). 13CO2 (3-4 atm) was condensed into a NMR tube frozen in liquid N2 containing (38) Fox, D. J.; Bergman, R. G. J. Am. Chem. Soc. 2003, 125, 11772.

a degassed solution of 2 (0.02 g, 0.05 mmol) in C6D6. The NMR tube was allowed to warm to room temperature, and signals attributable to trans-Ru(dmpe)2(O2CCH3)CH3 (3) were visible after 2 h in the 31P{1H} NMR spectrum in approximately 45% yield. 31 P{1H} NMR (C6D6, 121.5 MHz, 300 K): δ 45.01 (s) ppm. 1H NMR (C6D6, 300 MHz, 298 K): δ -1.61 (p, JPH ) 5.9 Hz, 3H, RuCH3), 1.01 (s, 12H, 4 × PCH3), 1.22 (m, 4H, 2 × PCH2), 1.34 (s, 12H, 4 × PCH3), 1.72 (m, 4H, 2 × PCH2), 1.95 (d, JPH ) 5.8 Hz, 3H, RuO2CH3) ppm. Selected 13C{1H} NMR (C6D6, 75 MHz, 300 K): δ 174.7 (s, O2CCH3) ppm. Synthesis of cis-Ru(dmpe)2(OCOCH3)CH3 (4). 13CO2 (3-4 atm) was condensed into a NMR tube frozen in liquid N2 containing a degassed solution of cis-Ru(dmpe)2Me2 (1) (0.02 g, 0.05 mmol) in C6D6. The NMR tube was allowed to warm to room temperature. Signals attributable to cis-Ru(dmpe)2(OCOCH3)CH3 (4) were visible after 6 h in the 31P{1H} NMR spectrum in approximately 2% yield. 31 P{1H} NMR (C6D6, 121.5 MHz, 300 K): δ 30.7 (ddd, JPP ) 30.5 Hz, JPP ) 23 Hz, JPP ) 14 Hz, phosphorus trans to acetate group), 38.3 (ddd, JPP ) 30.5 Hz, JPP ) 341.0 Hz, JPP ) 13.0 Hz, JPC ) 4.0 Hz), 43.8 (ddd, JPP ) 23.0 Hz, JPP ) 341.0 Hz, JPP ) 23.0 Hz, JPC ) 2.2 Hz), 54.3 (ddd, JPP ) 14.0 Hz, JPP ) 13.0 Hz, JPP ) 23.0 Hz, phosphorus trans to acetate group) ppm. 1H NMR (C6D6, 300 MHz, 298 K): δ -0.08 (septet, 3H, RuCH3), 0.66 (d, JPH ) 6.7 Hz, 3H, 1 × PCH3), 0.83 (d, JPH ) 8.2 Hz, 3H, 1 × PCH3), 0.94 (d, JPH ) 5.2 Hz, 3H, 1 × PCH3), 1.05-1.20 (br m, 16H, PCH2), 1.09 (d, JPH ) 7.2 Hz, 3H, 1 × PCH3), 1.38 (d, JPH ) 8.5 Hz, 1 × PCH3), 1.69 (d, JPH ) 6 Hz, 3H, 1 × PCH3), 1.72 (d, JPH ) 6 Hz, 3H, 1 × PCH3), 2.17 (d, JCH ) 6.2 Hz, 3H, C(O)CH3) ppm. Selected 13C{1H} NMR (C6D6, 75 MHz, 300 K): δ 174.6 (s, COOMe) ppm. Synthesis of trans-Ru(dmpe)2(OC(O)CH3)2 (5). NMR Scale: 13 CO2 (3-4 atm) was condensed into a NMR tube frozen in liquid N2 containing a degassed solution of trans-Ru(dmpe)2Me2 (2) (0.02 g, 0.05 mmol) in C6D6. The NMR tube was allowed to warm to (39) Kaplan, A. W.; Ritter, J. C. M.; Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 6828–6829. (40) Bianchini, C.; Peruzzini, M.; Zanobini, F. J. Organomet. Chem. 1987, 326, C79–C82. (41) Gutierrez-Puebla, E.; Monge, A.; Nicasio, M. C.; Perez, P. J.; Poveda, M. L.; Carmona, E. Chem.-Eur. J. 1998, 4, 2225–2236. (42) Slugovc, C.; Mereiter, K.; Trofimenko, S.; Carmona, E. Angew. Chem., Int. Ed. 2000, 39, 2158–2160. (43) Ferrando-Miguel, G.; Coalter, J. N., III; Gerard, H.; Huffman, J. C.; Eisenstein, O.; Caulton, K. G. New J. Chem. 2002, 26, 687–700.

2390 Organometallics, Vol. 28, No. 8, 2009 room temperature. Signals attributable to trans-Ru(dmpe)2(OC(O)CH3)2 (5) were visible after 5 days in the 31P NMR spectrum in approximately 55% yield. Preparative Scale: Dmpe (1.37 g, 9 mmol) was added to a slurry of Ru(PPh3)2(O2CMe)2 (3.4 g, 4.5 mmol) in hexane. The mixture was refluxed for 18 h, after which time a pale yellow precipitate had formed. The solid was isolated by filtration and recrystallized from toluene layered with pentane to give crystals suitable for X-ray crystallographic analysis (1.47 g, 4.57 mmol, 61%). Anal. Calcd for C16H38O4P4Ru: C, 37.00; H, 7.37. Found: C, 37.30; H, 7.56. 31 P{1H} NMR (C6D6, 121.5 MHz, 300 K): δ 46.3 (s) ppm. 1H NMR (C6D6, 300 MHz, 298 K): δ 1.2 (s, 24H, PCH3), 1.69 (d, JCH ) 5.7 Hz, 6H, 2 × C(O)CH3), 1.94 (t, 8H, PCH2) ppm. Selected 13C{1H} NMR (C6D6, 75 MHz, 300 K): δ 176.1 (s, COOMe) ppm. IR (Fluorolube): 1608 (νasym(CO2)), 1321 (νsym(CO2)) cm-1. Synthesis of cis-Ru(dmpe)2(OC(O)CH3)2 (6). NMR Scale: 13CO2 (3-4 atm) was condensed into a NMR tube frozen in liquid N2 containing a degassed solution of cis-Ru(dmpe)2Me2 (1) (0.02 g, 0.05 mmol) in C6D6. The NMR tube was warmed to 333 K. Signals attributable to cis-Ru(dmpe)2(OC(O)CH3)2 (6) were visible after 3 days in the 31P{1H} NMR spectrum in approximately 82% yield. Preparative Scale: A solution of trans-Ru(dmpe)2(OC(O)CH3)2 (5) in toluene was irradiated with a 300 W mercury lamp for 2 h; only peaks attributable to cis-Ru(dmpe)2(OC(O)CH3)2 (6) were visible in the NMR spectra. 31P{1H} NMR (C6D6, 121.5 MHz, 300 K): δ 37.7 (virtual t, JPP ) 24.7 Hz), 53.9 (virtual t, JPP ) 24.7 Hz) ppm. 1H NMR (C6D6, 300 MHz, 298 K): δ 0.68 (d, JPH ) 7.4 Hz, 6H, 2 × PCH3), 0.99 (d, JPH ) 9.2 Hz, 6H, 2 × PCH3), 1.08-1.30 (br m, 8H, PCH2), 1.63 (t, JPH ) 3.1 Hz, 6H, 2 × PCH3), 1.91 (t, JPH ) 3.9 Hz, 6H, 2 × PCH3), 2.15 (d, JCH ) 5.8 Hz, 6H, 2 × C(O)CH3) ppm. Selected 13C{1H} NMR (C6D6, 75 MHz, 300 K): δ 175.4 (s, COOMe) ppm. Synthesis of cis-Ru(dmpe)2(CO3) (7). NMR Scale: CO2 (3-4 atm) was added at 77 K to an NMR tube containing a degassed solution of cis-Ru(dmpe)2Me2 (1) or trans-Ru(dmpe)2Me2 (2) (0.2 g, 0.05 mmol) in C6D6. The NMR tube was allowed to warm to room temperature, and after 3 days pale blue crystals had precipitated that were suitable for X-ray crystallographic analysis. 31 P{1H} NMR (C6D6, 121.5 MHz, 300 K): δ 35.0 (virtual t, splitting ) 20.7 Hz), 49.7 (virtual t, splitting ) 20.7 Hz). Other NMR data are identical to those reported previously.20 Synthesis of trans-Ru(dmpe)2MeH (8). trans-Ru(dmpe)2HCl (0.39 g, 0.82 mmol) was dissolved in toluene (20 mL), and 1 equiv of MeLi (1.5 M in diethyl ether, 0.54 mL) was added dropwise. A precipitate formed immediately, and the color changed from yellow to off-white. The mixture was allowed to stir for 18 h, and the toluene was removed under reduced pressure. The product was extracted into pentane (50 mL), concentrated to 10 mL, and cooled to 255 K to produce crystals of trans-Ru(dmpe)2MeH suitable for X-ray crystallographic analysis (0.21 g, 0.5 mmol, 62%). Anal. Calcd for C13H36P4Ru: C, 37.41; H, 8.69. Found: C, 36.94; H, 8.51. 31 P{1H} NMR (THF-d8, 121.5 MHz, 300 K): δ 47.3 (s) ppm. 1H NMR (THF-d8, 300 MHz, 300 K): δ -12.63 (p, 1H, RuH, JPH ) 21.5 Hz), -1.51 (p, 3H, RuCH3, JPH ) 5.5 Hz), 1.22 (s, 12H, PCH3), 1.37 (s, 12H, PCH3), 1.50 (m, 8H, PCH2) ppm. 13C{1H} NMR (THF-d8, 75 MHz, 300 K): δ -25.4 (s, RuCH3), 14.6 (m, RuPCH3), 26.6 (m, RuPCH3), 32.8 (m, RuPCH2) ppm. Synthesis of cis-Ru(dmpe)2MeH (9). An NMR sample of transRu(dmpe)2MeH (8) in THF-d8 was exposed to 300 W UV light for 20 min in a standard NMR tube. In this time, the trans isomer was quantitatively converted to the cis isomer. 31P{1H} NMR (THF-d8, 121.5 MHz, 300 K): δ 34.2 (ddd, JPP ) 13.0 Hz, JPP ) 23.0 Hz, JPP ) 17.5 Hz), 37.4 (ddd, JPP ) 13.0 Hz, JPP ) 17.0, JPP ) 22.0 Hz), 45.1 (ddd, JPP ) 303.0 Hz, JPP ) 22.0 Hz, JPP ) 17.5 Hz), 48.7 (ddd, JPP ) 303.0 Hz, JPP ) 17.0 Hz, JPP ) 23.0 Hz) ppm. 1H NMR (THF-d8, 300 MHz, 298 K): δ -9.42 (m, 1H RuH), -1.04 (m, 3H, RuCH3), 1.00 (d, 3H, 1 × PCH3, JPH ) 5.6 Hz), 1.18 (d,

Allen et al. 3H, 1 × PCH3, JPH ) 5.0 Hz), 1.19 (m, 3H, 1 × PCH3), 1.20 (m, 1 × PCH3), 1.26 (m, 3H, 1 × PCH3), 1.29 (m, 3H, 1 × PCH3), 1.33 (m, 3H, 1 × PCH3), 1.35 (m, 3H, 1 × PCH3), 1.43 (br m, 8H, PCH2) ppm. 13C{1H} NMR (THF-d8, 75 MHz, 298 K): δ -25.4 (RuCH3), 13.3, 14.1, 15.5, 19.2, 20.4, 22.4, 22.6, 22.7 (8 × m PCH3), 31.0 (m, PCH2) ppm. Synthesis of trans-Ru(dmpe)2(Me)(O2CH) (10). CO2 (3-4 atm) was condensed into a NMR tube frozen in liquid N2 containing a degassed solution of trans-Ru(dmpe)2MeH (8) (0.02 g, 0.05 mmol) in THF-d8. The NMR tube was allowed to warm to room temperature, and the 31P{1H} NMR spectrum showed transRu(dmpe)2(Me)(O2CH) (10) to be the exclusive product. In the absence of CO2, complex 10 rapidly loses CO2 to re-form transRu(dmpe)2MeH (8). 31P{1H} NMR (C6D6, 121.5 MHz, 300 K): δ 44.3 (s) ppm. 1H NMR (C6D6, 300 MHz, 300 K): δ -1.61 (p, 3H, RuCH3, JPH ) 6.3 Hz), 0.99 (s, 12H, PCH3), 1.26 (m, 4H, PCH2), 1.35 (s, 12H, PCH3), 1.84 (m, 4H, PCH2), 8.68 (d, 1H, RuO2CH, JCH ) 185.9 Hz) ppm. 13C{1H} NMR (C6D6, 75 MHz, 300 K): δ -27.2 (m, RuCH3), 12.2 (m, RuPCH3), 15.5 (m, RuPCH3), 29.5 (m, RuPCH2), 168.1 (s, RuO2CH) ppm. 31P{1H} NMR (THF-d8, 121.5 MHz, 300 K): δ44.7 (s) ppm. 1H NMR (THF-d8, 300 MHz, 300 K): δ -1.79 (p, 3H, RuCH3, JPH ) 5.7 Hz), 1.22 (s, 12H, PCH3), 1.37 (s, 12H, PCH3), 1.51 (m, 4H, PCH2), 1.96 (m, 4H, PCH2), 7.93 (d, 1H, RuO2CH, JCH ) 186.0 Hz) ppm. 13C{1H} (THF-d8, 75 MHz, 300 K): δ -26.5 (m, RuCH3), 13.0 (m, RuPCH3), 16.0 (m, RuPCH3), 30.5 (m, RuPCH2), 167.6 (s, RuO2CH) ppm. Synthesis of cis-Ru(dmpe)2(Me)(O2CH) (11). 13CO2 (3-4 atm) was condensed into a NMR tube frozen in liquid N2 containing a degassed solution of cis-Ru(dmpe)2MeH (9) (0.02 g, 0.05 mmol) in THF-d8. The NMR tube was allowed to warm to room temperature, and the 31P NMR spectrum showed cis-Ru(dmpe)2(Me)(O2CH) (10) to be the exclusive product. 31P{1H} NMR (THF-d8, 121.5 MHz, 298 K): δ 53.4 (dddd, JPP ) 31.2 Hz, JPP ) 22.9 Hz, JPP ) 13.1 Hz, JPC ) 1.1 Hz), 42.1 (dddd, JPP ) 338.1 Hz, JPP ) 31.2 Hz, JPP ) 12.3 Hz, JPC ) 3.5 Hz), 36.4 (dddd, JPP ) 22.9 Hz, JPP ) 338.1 Hz, JPP ) 22.9 Hz, JPC ) 1.9 Hz), 28.0 (dddd, JPP ) 13.1 Hz, JPP ) 12.3 Hz, JPP ) 22.9 Hz, JPC ) 0.3 Hz) ppm. Selected 1H NMR (THF-d8, 300 MHz, 298 K): δ -0.51 (m, 3H, RuCH3), 8.10 (dd, 1H, RuO2CH JCH ) 195.0 Hz, JPH ) 3.5 Hz) ppm. Selected 13C{1H} (THF-d8, 75 MHz, 300 K): 167.9 (m, RuO2CH) ppm. Synthesis of trans-Ru(dmpe)2(O2CCH3)H (12). CO2 (3-4 atm) was condensed into a NMR tube frozen in liquid N2 containing a degassed solution of Ru(dmpe)2MeH (9) (0.02 g, 0.05 mmol) in C6D6, and after heating for 24 h the NMR spectra showed transRu(dmpe)2(O2CCH3)H (12) to be the major product in approximately 88% yield. Preparative Scale: A solution of acetic acid (1.36 mL, 0.68 mmol, 0.5 M) was added dropwise to a solution of cis-Ru(dmpe)2H2 (0.28 g, 0.68 mmol) in diethyl ether (75 mL) at -80 °C. The mixture was allowed to warm to room temperature and stirred for a further 18 h. The solvent was removed under reduced pressure to leave a pale yellow solid, which was washed in cold pentane to remove any remaining starting material cis-Ru(dmpe)2H2. The solid was recrystallized from diethyl ether and pentane at -20 °C (0.12 g, 0.27 mmol, 40%). 31P{1H} NMR (C6D6, 300 MHz, 298 K): δ 46.1 (s) ppm. 1H NMR (C6D6, 300 MHz, 300 K): δ -22.54 (p, 1H, RuH), 1.14 (s, 12H, PCH3), 1.30 (m, 4H, PCH2), 1.36 (s, 12H, PCH3), 1.88 (m, 4H PCH2), 2.08 (s, RuO2CMe) ppm. 13C{1H} NMR (C6D6, 75 MHz, 300 K): δ 15.4 (m, PCH3), 22.6 (m, PCH3), 24.5 (s, RuO2CCH3), 31.3 (m, PCH2), 175.3 (s, RuO2CCH3) ppm. [ESI; m/z, (%)] 461.00, (35%) M + H. Supporting Information Available: This material is available free of charge via the Internet at http://pubs.acs.org. OM801184K