Synthons for coordinatively unsaturated complexes of tungsten, and their use for the synthesis of high oxidation-state silylene complexes

Reduction of CP*WCl4 afforded the metalated complex (eta(6)-C5Me4CH2)(dmpe)W(H)Cl(1) (Cp* = C5Me5, dmpe = 1,2-bis(dimethylphosphino)ethane). Reactions with CO and H-2 suggested that 1 is in equilibrium with the 16-electron species [Cp*(dmpe)WCl], and 1 was also shown to react with silanes R2SiH2 (R-2 = Ph-2 and PhMe) to give the tungsten(IV) silyl complexes Cp*(dmpe)(H)(Cl)W(SiHR2) (6a, R-2 = Ph-2; 6b, R-2 = PhMe). Abstraction of the chloride ligand in 1 with LiB(C6F5)(4) gave a reactive species that features a doubly metalated Cp* ligand, [(eta(7)-C5Me3(CH2)(2))(dmpe)W(H)(2)][B(C6F5)(4)] (4). In its reaction with dinitrogen, 4 behaves as a synthon for the 14-electron fragment [Cp*(dmpe)W](+), to give the dinuclear dinitrogen complex {[Cp*(dmpe)W](2)(mu-N-2)}{B(C6F5)(4)}(2) (5). Hydrosilanes R2SiH2 (R-2 = Ph-2, PhMe, Me-2, Dipp(H); Dipp = 2,6-diisopropylphenyl) were shown to react with 4 in double Si-H bond activation reactions to give the silylene complexes [Cp*(dmpe)H2W=SiR2][B(C6F5)(4)] (8a-d). Compounds 8a,b (R-2 = Ph-2 and PhMe, respectively) were also synthesized by abstraction of the chloride ligands from silyl complexes 6a,b. Dimethylsilylene complex 8c was found to react with chloroalkanes RCl (R = Me, Et) to liberate trialkylchlorosilanes RMe2SiCl. This reaction is discussed in the context of its relevance to the mechanism of the direct synthesis for the industrial production of alkylchlorosilanes.