Recently there has been considerable interest in the organometallic chemistry of late transition metals in high oxidation states. Second-and third-row metals in particular were stabilized in high oxidation states by using organic ligand environments. Certain catalytic reactions mediated by these late metals were proposed to occur through high oxidation state intermediates, as opposed to the traditionally formulated redox pairs. [1±4] Some of the most thoroughly investigated examples in this class are the high oxidation state neutral iridium(v) and rhodium(v) complexes studied initially by Maitlis et al. such as [(C 5 Me 5 )IrMe 4 ], [5] [(C 5 Me 5 )Ir(H) 2 -(SiR 3 ) 2 ], and [(C 5 Me 5 )Rh(H) 2 (SiR 3 ) 2 ] [6±10] and the Ir V complex cation [(C 5 Me 5 )IrMe 3 L] reported later by Bergman and Aliamo. [11] Higher oxidation states of first-row metals have been discussed as reactive intermediates, but isolated examples are rare. [12] We showed that cationic cobalt(iii) alkyl complexes [(C 5 Me 5 ){P(OMe) 3 }CoR] are olefin hydrosilylation catalysts and must proceed through the Co V intermediate [(C 5 Me 5 ){P(OMe) 3 }Co(R)(H)(SiR 3 )] or the Co III intermediate [(C 5 Me 5 ){P(OMe) 3 }Co(R)(h 2 -HÀSiR 3 )] . [13,14] Here we report the synthesis and X-ray crystallographic characterization of a bis-hydrido bis-silyl cobalt(v) complex.
For cobalt-mediated bond-activation reactions we have used olefin complexes of the type [(C 5 Me 5 )Co(olefin) 2 ] (1) as catalysts, [13, 15±17] which provides a source of [(C 5 Me 5 )Co] through olefin dissociation. [18] Heating a solution of 1 a in C 6 D 6 (olefin C 2 H 4 ) with 5 equiv of Ph 2 SiH 2 (15 min, 70 8C) led to a rapid disappearance of starting material and, along with the appearance of ethylene and Ph 2 (Et)SiH, the formation of two products 2 a and 3 in approximately 1:1 molar ratio, as determined by 1 H NMR spectroscopy [Eq. ( 1)]. [19] Equivalent hydrido ligands and silyl methylene protons support a trans configuration of 2 a, while a single set of 13 C phenyl signals indicates a trans configuration for 3.