Novel Titanium-Cobalt Complexes Formed by Reductive Cleavage of a Co-Co Bond in Co₂(CO)₈ by Titanocene tert-Butoxides: Synthesis, Characterization, and Mechanistic Aspects for Metal-Metal Bond Recombination

Reactions of titanium(III) complexes (η⁵-C₅R ₅)₂TiO^tBu (R = H (1), Me (4)) with Co ₂(CO)₈ are found to be efficient methods to synthesize Ti-Co heterobimetallic complexes. A Ti-Co₃ complex, (η ⁵-C₅H₅)₂Ti(O ^tBu)(μ₄-OC)Co(CO)₉ (3), was formed from 1 and Co₂(CO)₈, whereas a Ti-Co bimetallic complex, (η⁵-C₅Me₅)₂Ti(O ^tBu)(μ-OC)Co(CO)₃ (5), was obtained by the reaction of 4 with Co₂(CO)₈. In both cases, the reaction was complete within 5 min. The products were completely characterized by NMR, IR, and X-ray crystallography. Complex 3 contains a quadruply bridging CO group, the oxygen terminus of which is connected to the Ti moiety, whereas the carbon terminus is bound to three Co atoms in the Co₃(CO)₉ moiety. In contrast, complex 5 is dinuclear, and its Ti atom is connected to the Co(CO)₃ group by an isocarbonyl bridge. A η⁵-C ₅H₅ analogue of 5, [η⁵-C₅H ₅)₂Ti(O^tBu)(μ-OC)Co(CO)₃] (6), was formed at the initial stage of the reaction of 1 with Co ₂(CO)₈ in toluene. This dinuclear complex 6 was isolated from a reaction medium of a 5:1 mixture of 1 and Co₂(CO) ₈, being characterized by spectroscopy. As further evidence for the formation of the Ti-Co hetero-bimetallic complex, reaction of 6 with THF gave the Ti-Co complex [(η⁵-C₅H₅) ₂Ti(O^tBu)(n-THF)]⁺[Co(CO)₄] ^- (7), which was completely characterized by spectroscopy, crystallography, and elemental analysis. Thermal decomposition of 6 produced a mixture of 3 and 1, whereas treatment of 6 with Co₂(CO)₈ gave 3; this is good evidence for the intermediacy of 6 in the formation of 3 from 1 with Co₂(CO)₈.