ORGANOMETALLIC INTERMEDIATES IN THE GROUP-4 METALLOCENE-CATALYZED DEHYDROCOUPLING OF ORGANOSILANES .2. VARIATIONS IN THE INTERMEDIATES OF DIMETHYLTITANOCENE REACTIONS WITH SEVERAL SILANES

As previously described, organosilanes react with dimethyltitanocene (DMT) to give three reduced titanium intermediates, Cp2Ti(mu-SiRR'H)(mu-H)TiCp2, 1, [CP2Ti(mu-SiRR'H)]2, 2, and [Cp2Ti(H)]2(mu-H), 3. When R = Me and R' = n-Bu, the DMT is quantitatively converted to 1, which is persistent at room temperature. When R' = H, DMT is initially converted quantitatively to 1, which then rapidly declines to give an equilibrium mixture of 1, 2, and 3, with 2 as the dominant species. When R = Ph and R' = Ph or Me, 1 is again produced quantitatively, but it rapidly declines to produce an unidentified paramagnetic product, rather than 2 or 3. It is believed that 2 is unstable with respect to dissociation in these cases due to the steric bulk of the substituents.