Synthesis, Structure, and Reactivity of Trigonal Bipyramidal Ruthenium(IV) Trialkyl Complexes

The alkylation of [Ru(NPPh3)(PPh3)(2)Cl-3] with Me3SiCH2MgCl afforded the Ru-IV trialkyl complex [Ru(CH2SiMe3)(3)(PPh3)Cl] (1), which exhibits a trigonal bipyramidal geometry with the three alkyl groups occupying the equatorial plane. DFT calculations reveal that 1 possesses a (d(xz),d(yz))(4) singlet ground state, consistent with the observed diamagnetism of the complex. The electronic spectrum of 1 displayed two absorptions at 455 and 505 nm, which, on the basis of TDDFT calculations, are attributed to metal-centered d-d transitions with a significant contribution from the alkyl ligands. Chloride abstraction of 1 with Ag(OTf) (OTf- = triflate) provided the triflate complex [Ru(CH2SiMe3)(3)(PPh3)(OTf)] (2) that proved to be a useful starting material for Ru-IV trialkyl complexes. Substitution of 2 with NaX afforded [Ru(CH2SiMe3)(3)(PPh3)(X)] (X = N-3(-) (3) or SCN- (4)). Treatment of 2 with excess sodium 2,3,5,6-tetrafluorophenoxide (NaORf) in tetrahydrofuran resulted in desilylation of two alkyl groups, and formation of the dimethyl complex [Ru(CH2SiMe3)Me-2(PPh3)(ORf)] (5). 2 underwent reductive elimination of the C-C bond with 1,10-phenanthroline (phen) in CH2Cl2 to give cis-[Ru(phen)(2)(PPh3)Cl](OTf) (6). The crystal structures of 1, 2, 4, and 5 have been determined