Synthesis and Study of Ruthenium Silylene Complexes of the Type [(η⁵-C₅Me₅)(Me₃P)₂RuSiX₂]⁺(X = Thiolate, Me, and Ph)

Abstract

Various ruthenium silyl complexes of the type Cp*(Me 3 P) 2 RuSiR 3 (Cp* = η 5 -C 5 Me 5; SiR 3 = SiCl 3 ( 1 ), Si(NMe 2 ) 3 ( 2 ), Si(SEt) 3 ( 3 ), Si(S-2-Naph) 3 ( 4 ), ( 5 ), Si(SCy) 2 Cl ( 6 ), and Si(SMes) 2 Cl ( 7, Mes = 2,4,6-trimethylphenyl)) were prepared by the reaction of Cp*(Me 3 P) 2 RuCH 2 SiMe 3 with the appropriate silane HSiR 3 . Compound 3 was converted to the triflate Cp*(Me 3 P) 2 RuSi(SEt) 2 OTf ( 8 ) by the reaction of 3 with Me 3 SiOTf. Similar reactions produced Cp*(Me 3 P) 2 RuSi(NMe 2 ) 2 OTf ( 13 ), Cp*(Me 3 P) 2 RuSi(NMe 2 )(OTf) 2 ( 14 ), Cp*(Me 3 P) 2 RuSi(SMes) 2 OTf ( 18 ), and Cp*(Me 3 P) 2 RuSi(SMes)(Cl)OTf ( 19 ). By NMR spectroscopy, compound 8 in dichloromethane solution appears to possess a labile triflate group. Reactions of the triflates 8 and Cp*(Me 3 P) 2 RuSi(S- p- Tol) 2 OTf ( 10 ) with NaBPh 4 provided the silylene complexes [Cp*(Me 3 P) 2 RuSi(SR) 2 ][BPh 4 ] ( 20, R = Et; 21, R = p- Tol). Similarly, the reaction of 6 with NaBPh 4 gave [Cp*(Me 3 P) 2 RuSi(SCy) 2 ][BPh 4 ] ( 22 ), and the reaction of 4 with B(C 6 F 5 ) 3 produced [Cp*(Me 3 P) 2 RuSi(S-2-Naph) 2 ][MeB(C 6 F 5 ) 3 ] ( 23 ). Silylene complexes 20 − 23 display characteristic 29 Si NMR shifts in the region of δ 250−270. The non-heteroatom-stabilized silylene complexes [Cp*(Me 3 P) 2 RuSiR 2 ][B(C 6 F 5 ) 4 ] ( 24, R = Me; 25, R = Ph), obtained via reactions of (Et 2 O)LiB(C 6 F 5 ) 4 with Cp*(Me 3 P) 2 RuSiR 2 OTf ( 11, R = Me; 12, R = Ph) exhibit 29 Si NMR shifts around δ 300. The crystal structure of 24 revealed a Ru−Si distance of 2.238(2) Å, and the Cp*(centroid)−Ru−Si−Me dihedral angle is 34°. Compound 24 reacts quantitatively with 1 equiv of PMe 3 or PPh 3 in dichloromethane- d 2 to form the base-stabilized silylene complexes [Cp*(Me 3 P) 2 RuSiMe 2 (PR 3 )][B(C 6 F 5 ) 4 ] ( 28, R = Me; 29, R = Ph), identified by 1 H and 31 P NMR spectroscopy. These complexes are thermally labile and decompose with elimination of the dimethylsilylene fragment to give [Cp*(Me 3 P) 2 RuPR 3 ][B(C 6 F 5 ) 4 ] (R = Me, Ph). The ylide CH 2 PPh 3 reacts with 24 to form [Cp*(Me 3 P) 2 RuSiMe 2 CH 2 PPh 3 ][B(C 6 F 5 ) 4 ] ( 32a ), and the characterization of [Cp*(Me 3 P) 2 RuSiMe 2 CH 2 PPh 3 ][OTf] ( 32b ) by X-ray crystallography suggests that the complex is best viewed as a ruthenium silyl derivative with the positive charge localized on the “ylide” phosphorus atom. Reactions of 20 and 24 with hydrogen proceed slowly and result in relatively complex product mixtures that contain various ruthenium hydride species. The reaction involving 20 also produced HSi(SEt) 3, perhaps via redistribution of initially formed H 2 Si(SEt) 2 . For the reaction of 24 with hydrogen, no H 2 SiMe 2 was detected in the product mixture. The reaction of 20 with H 3 SiSiPh 3 gave [Cp*(Me 3 P) 2 Ru(H)(SiH 2 SiPh 3 )][BPh 4 ] ( 35 ) and HSi(SEt) 3, and the corresponding reaction of H 3 SiMes in dichloromethane gave [Cp*(Me 3 P) 2 RuHCl][BPh 4 ] ( 34 ), BPh 3, and H 2 SiMes(SEt), among other products. By NMR spectroscopy, the intermediate [Cp*(Me 3 P) 2 Ru(H)(SiH 2 Mes)][BPh 4 ] ( 36 ) was observed for the latter process. Compound 36, generated independently by reaction of [Cp*(Me 3 P) 2 Ru(NCMe)][BPh 4 ] with H 3 SiMes, was shown to react with HSi(SEt) 3 to give H 2 SiMes(SEt).