Tri(?-cyclopentadienyl)uranium(IV) silyl and siloxide compounds. Crystal structure of [U(?5-C5H5)3(OSiPh 3)]. Insertion of lsocyanide into a uranium-silicon bond

The complex [U(?5-C5H5)3(SiPh3)](1) has been synthesized from [U(?5-C5H5)3Cl] and Li(SiPh3) and fully characterized. The direct U-Si bond in (1) is quite reactive towards proton acidicmolecules, moreover it reacts with 2,6-dimethylphenyl isocyanide to give the insertion product [U(?5-C5H5)3{C(NC6H3Me2-2,6)SiPh3}](3), the 1H n.m.r. and i.r. data for which show that the isocyanide ligand is ?2-co-ordinated to the uranium atom. The synthesis of [U(?5-C5H5)3(OSiPh3)](2) by reaction of [U(?5-C5H5)3(NEt2)] with SiPh3(OH) and its X-ray structural determination are also reported. Compound (2) crystallizes from diethyl ether in the monoclinic space group P21/n with a= 15.368(5), b= 17.333(5), c= 10.778(5)Å and ?= 106.27(3)° for Z= 4. The main features are the almost linear U-O-Si bond angle of 172.6(6)° and the short U-O distance of 2.135(8)Å.