4776
Organometallics 2002, 21, 4776-4784
Effect (or Lack Thereof) of Ancillary Groups on the Preparation and Spectroscopic Properties of Ruthenium Silyl Complexes Containing the Cp(PR3)2Ru Moiety Samuel T. N. Freeman, Lori L. Lofton, and Frederick R. Lemke* Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701-2979 Received May 28, 2002
The preparation and characterization of Cp(PR3)2RuSiX3 [PR3 ) PPhMe2, SiX3 ) SiCl3 (1), SiHCl2 (2), SiH2Cl (3), SiHMeCl (4), SiH3 (7), SiMeH2 (8), SiMe3 (9); PR3 ) PPh2Me, SiX3 ) SiCl3 (10), SiHCl2 (5), SiH2Cl (6), SiMeCl2 (11)] are described. Ruthenium silyl complexes 1-6 are prepared by the reaction of the ruthenium hydrides, Cp(PR3)2RuH, with the corresponding chlorosilane, ClSiX3; the ruthenium dihydrides [Cp(PR3)2RuH2]Cl were obtained as coproducts. Increasing the steric demand of the phosphine decreased the reactivity of the corresponding ruthenium hydride toward chlorosilanes. Silyl complexes 1-4 undergo chloride/hydride exchange with LiAlH4 to give the corresponding ruthenium hydrosilyl complexes Cp(PPhMe2)2RuSiHX2 [SiHX2 ) SiH3 (7), SiMeH2 (8)]. Methylation of 1 with AlMe3 produces Cp(PPhMe2)2RuSiMe3 (9). Complexes 10 and 11 were prepared by the reaction of Cp(PPh2Me)2RuMe with neat hydrosilanes HSiX3 (SiX3 ) SiCl3, SiMeCl2) at 100 °C. The effects of the silicon substituents on the spectroscopic properties of 1-11 and the related Cp(PMe3)2RuSiX3 complexes were examined as a function of Tolman’s electronic parameter (χi) for the substituents on silicon. The NMR resonance PR3 δ(31P) and the NMR coupling constants, 1JSiH and 2JSiP, exhibit a linear relationship with ∑χi(SiX3). On the other hand, the silyl groups differentiated into three classes, dichlorosilyl, monochlorosilyl, and “non-chlorosilyl”, when the NMR resonances SiX3 δ(29Si), SiH δ(1H), and SiMe δ(13C) were examined as a function of ∑χi(SiX3). This “chloro effect” was attributed to Ru-Si silylene character from d(Ru)-σ*(Si-Cl) π-back-bonding interactions. Surprisingly, changing the phosphine attached to ruthenium had no effect on the spectroscopic properties of the silyl group. Introduction The bonding of silicon to a transition metal center is an area of considerable interest and attention.1-4 Metal silicon complexes play key roles in important catalytic processes such as hydrosilylation5-8 and dehydrogenative silylation.9-11 Ancillary groups on silicon exhibit a substantial influence on the product distribution in these processes. RuCl2(PPh3)3 efficiently catalyzed the * To whom correspondence should be addressed. E-mail: flemke1@ ohiou.edu. (1) Corey, J. Y.; Braddock-Wilking, J. Chem. Rev. 1999, 99, 175292. (2) Sharma, H. K.; Pannell, K. H. Chem. Rev. 1995, 95, 1351-1374. (3) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons: New York, 1991; pp 245-307. (4) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons: New York, 1991; pp 309-364. (5) Marciniec, B., Ed. Comprehensive Handbook on Hydrosilylation; Pergamon Press: New York, 1992. (6) Ojima, I.; Li, Z.; Zhu, J. In The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; John Wiley & Sons: New York, 1998; Vol. 2, pp 1687-1792. (7) Harrod, J. F. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; Wiley: Chichester, 1994; Vol. 3, pp 1486-1496. (8) Speier, J. L. Adv. Organomet. Chem. 1979, 17, 407-447. (9) Ezbiansky, K.; Djurovich, P. I.; LaForest, M.; Sinning, D. J.; Zayes, R.; Berry, D. H. Organometallics 1998, 17, 1455-1457. (10) Christ, M. L.; Sabo-Etienne, S.; Chaudret, B. Organometallics 1995, 14, 1082-1084. (11) Delpech, F.; Mansas, J.; Leuser, H.; Sabo-Etienne, S.; Chaudret, B. Organometallics 2000, 19, 5750-5757.
hydrosilylation of phenylacetylene with HSiMeCl2, but no hydrosilylation products were observed when the hydrosilane was changed to HSiEt3.12 We have been studying the effects of silicon and ruthenium ancillary groups on the formation and properties of ruthenium silicon complexes. Ruthenium alkyl complexes Cp(PR3)2RuR′ (R ) Ph, Me; R′ ) Me, CH2SiMe3) react with various hydrosilanes (HSiX3) to form ruthenium silyl (Cp(PR3)2RuSiX3) and ruthenium hydridobis(silyl) (Cp(PR3)RuH(SiX3)2) complexes.13,14 The formation of ruthenium silyl complexes was favored by electron-deficient hydrosilanes; PMe3 coordinated to ruthenium center also favored the formation of ruthenium silyl complexes. Silicon ancillary groups effected the relative reactivity of hydrosilanes toward Cp(PMe3)2RuCH2SiMe3, following the order HSiCl3 > HSiMeCl2 > HSiMe2Cl . HSiEt3. Ruthenium silyl complexes Cp(PMe3)2RuSiX3 were also prepared from the reaction of the ruthenium hydride complex Cp(PMe3)2RuH with a variety of chlorosilanes.15,16 Electron-deficient chlorosi(12) Yardy, N. M.; Lemke, F. R. Main Group Chem. 2000, 3, 143147. (13) Lemke, F. R.; Simons, R. S.; Youngs, W. J. Organometallics 1996, 15, 216-221. (14) Lemke, F. R.; Chaitheerapapkul, C. Polyhedron 1996, 15, 25592565. (15) Lemke, F. R. J. Am. Chem. Soc. 1994, 116, 11183-11184.
10.1021/om0204235 CCC: $22.00 © 2002 American Chemical Society Publication on Web 09/24/2002
Ruthenium Silyl Complexes
lanes (SiCl4, HSiCl3) were 6 orders of magnitude more reactive toward the ruthenium hydride than more electron-rich chlorosilanes (Me2SiCl2). Furthermore, significant silicon ancillary group effects were observed in the spectroscopic properties of these ruthenium silyl complexes. Herein, we report our continued studies on ancillary group effects in ruthenium silyl complexes Cp(PMe3)2RuSiX3. The effect of different phosphines (PMe2Ph, PMePh2, PPh3) on the reaction of ruthenium hydrides with chlorosilanes and the properties of ruthenium silyl complexes is described. Surprisingly, the various phosphines exhibit no effect on the spectroscopic properties of the corresponding silyl complexes Cp(PR3)2RuSiX3. Results Synthesis of Ruthenium Silyl Complexes. The ruthenium silyl complexes used in this study were prepared by several different methods. One method employed the direct reaction of Cp(PR3)2RuH (PR3 ) PPh2Me, PPhMe2, PPh3) with the corresponding chlorosilane X3SiCl to produce a nearly equimolar mixture of Cp(PR3)2RuSiX3 and [Cp(PR3)2RuH2]Cl (eq 1). The
preparation of a series of ruthenium silyl complexes containing the Cp(PMe3)2Ru moiety had been reported using a similar method.15,16 Cp(PPhMe2)2RuSiX3 [SiX3 ) SiCl3 (1), SiHCl2 (2), SiH2Cl (3), SiHMeCl (4)] were obtained from the addition of SiCl4, SiHCl3, SiH2Cl2, and SiHMeCl2 to a yellow solution of Cp(PPhMe2)2RuH in CH2Cl2; [Cp(PPhMe2)2RuH2]Cl was obtained as a byproduct. No reaction was observed between Cp(PPhMe2)2RuH and SiMeCl3, SiMe2Cl2, or SiPhCl3. Under similar conditions, Cp(PPh2Me)2RuH was observed to react only with SiHCl3 and SiH2Cl2 to produce Cp(PPh2Me)2RuSiX3 [SiX3 ) SiHCl2 (5), SiH2Cl (6)] and [Cp(PPh2Me)2RuH2]Cl. No reaction was observed between Cp(PPh3)2RuH and any of the other chlorosilanes listed above. In the reaction of Cp(PR3)2RuH (PR3 ) PPhMe2, PPh2Me) with chlorosilanes, the ruthenium dihydrides [Cp(PR3)2RuH2]Cl were sometimes obtained in yields of >100% based on the stoichiometry described in eq 1. These unusual yields of [Cp(PR3)2RuH2]Cl were due to HCl, from the hydrolysis of the chlorosilanes with trace amounts of water, which readily protonated the ruthenium hydrides Cp(PR3)2RuH. Excessive ruthenium dihydride formation was also reported in the reaction of Cp(PMe3)2RuH with chlorosilanes; this problem was overcome by the addition of NEt3 to the reaction mixture.16 The addition of NEt3 to the reaction mixture (16) Lemke, F. R.; Galat, K. J.; Youngs, W. J. Organometallics 1999, 18, 1419-1429.
Organometallics, Vol. 21, No. 22, 2002 4777
of Cp(PR3)2RuH (PR3 ) PPhMe2, PPh2Me) with chlorosilanes led to a mixture of ruthenium silyl and other unidentified ruthenium-containing species. When other bases were surveyed (pyridine, LiN(SiMe3)2, NHPh2, piperidine, pyrazine, 1,8-bis(dimethylamino)naphthalene, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole, imidazole, pyrazole, 3,5-dimethylpyrazole, 4-(dimethylamino)pyridine), either a mixture of ruthenium complexes was obtained or the base had no effect on the overall reaction. An exception was DBU (1,8-diazabicyclo[5,4,0]undec-7-ene). The reaction of Cp(PPhMe2)2RuH with chlorosilanes in the presence of DBU led to the formation of ruthenium silyl complexes 1, 2, and 4 in high yields (>80%) with the added advantage that all of the ruthenium moiety ends up in the silyl complex (eq 2). Of the bases listed above, none were found to be effective and noninterfering in the reaction of Cp(PPh2Me)2RuH with chlorosilanes.
Other Cp(PPhMe2)2RuSiX3 complexes were prepared by derivatization of complexes 1-4. The ruthenium hydrosilyl complexes Cp(PPhMe2)2RuSiX2H [SiX2H ) SiH3 (7), SiMeH2 (8)] were prepared by the chloride/ hydride exchange between chlorosilyl complexes 1-4 and LiAlH4 in Et2O (eq 3). The trimethylsilyl derivative Cp(PPhMe2)2RuSiMe3 (9) was obtained from the reaction of 1 with AlMe3 in toluene at room temperature (eq 4). The reaction of complex 4 with AlMe3 led to a complicated mixture of methylsilyl ruthenium complexes. By these methods, complexes 7-9 were obtained in good yields (75-85%) as yellow, air-sensitive solids.
Due to difficulties in the isolation of Cp(PPh2Me)2RuSiX3 complexes prepared according to eq 1 (vide infra), additional Cp(PPh2Me)2RuSiX3 complexes were obtained by the reaction of a hydrosilane with a ruthenium alkyl complex.14 Cp(PPh2Me)2RuSiX3 [SiX3 ) SiCl3 (10), SiMeCl2 (11)] were obtained from the reaction of Cp(PPh2Me)2RuMe, prepared by reacting Cp(PPh2Me)2RuCl with MeMgCl in THF, with the corresponding neat hydrosilane HSiX3 at 100 °C (eq 5). The reaction of Cp(PPh2Me)2RuMe with HSiMe2Cl produced a complex mixture of products, with Cp(PPh2Me)2RuH, [Cp(PPh2Me)2RuH2]+, and Cp(PPh2Me)2RuCl being the most prevalent.
4778
Organometallics, Vol. 21, No. 22, 2002
Freeman et al. Scheme 1
Ruthenium Dihydride to Ruthenium Chloride Conversion. The isolation and purification of the Cp(PPh2Me)2RuSiX3 complexes prepared according to eq 1 proved to be difficult due to the facile conversion of [Cp(PPh2Me)2RuH2]Cl to Cp(PPh2Me)2RuCl. Silyl complexes 5 and 6 were always obtained contaminated with the ruthenium chloride Cp(PPh2Me)2RuCl. In a NMR tube, the reaction of Cp(PPh2Me)2RuH with HSiCl3 in CD2Cl2 formed a nearly equimolar mixture of silyl complex 5 and the ruthenium dihydride [Cp(PPh2Me)2RuH2]Cl. However, as this reaction mixture was monitored by 1H NMR, the Cp (5.12 ppm) and RuH (-8.43 ppm) resonances of [Cp(PPh2Me)2RuH2]Cl disappeared with the concomitant appearance of the Cp (4.31 ppm) resonance of Cp(PPh2Me)2RuCl. Also, during this experiment, the solution changed from ruthenium silyl yellow (the ruthenium dihydride is colorless in solution) to ruthenium chloride orange. Similar results were observed for the reaction of Cp(PPh2Me)2RuH with H2SiCl2. As described in the previous section, removal of [Cp(PPh2Me)2RuH2]Cl by the addition of a base to the Cp(PPh2Me)2RuH/chlorosilane reaction mixture was not successful. Stabilization of the [Cp(PPh2Me)2RuH2]+ cation was attempted by metathesis of the chloride with a noncoordinating anion. A variety of sodium salts (NaBF4, NaBPh4, NaBArf4 {Arf ) 3,5-bis(trifluoromethyl)phenyl}) were added to the Cp(PPh2Me)2RuH/chlorosilane reaction mixture in an attempt to remove the chloride as NaCl. However, this approach was not successful. Finally, a low-yield (
