Dinuclear titanium metallocene-type complexes with the bridging (dimethylsilylidene)bis(cyclopentadienyl) ligand. X-ray structures of [{TiCl2(.eta.5-C5Me5)}2{.mu.-.eta.5-.eta.5-(C5H4)2SiMe2}] and of [{TiCl(.eta.5-C5H5)}2(.mu.-O){.mu.-.eta.5-.eta.5-(C5H4)2SiMe2}]