Organometallic consequences of a redox reaction: Terminal trimethylsilylmethylidene titanium complexes prepared by a one-electron oxidation step

One-electron oxidation of the titanium(III) bis-trimethylsilylmethyl complex (nacnac)Ti(CH2SiMe3)2 (1) (nacnac− = [ArNC(Me)]2CH, Ar = 2,6-iPr2C6H3), readily prepared from (nacnac)TiCl2(THF) and 2 equiv. of LiCH2SiMe3 in Et2O, with AgOTf results in formation of the five-coordinate and terminal titanium alkylidene complex (nacnac)TiCHSiMe3(OTf)(THF) (2)-THF concurrent with extrusion of tetramethylsilane and precipitation of silver metal. Complex 2-THF eliminates THF slowly under dynamic vacuum to generate the four-coordinate alkylidene 2 along with some decomposition products. Alternatively, the four-coordinate and non-solvento alkylidene complex, 2, can be prepared from 1 and AgOTf in pentane. Complex 2 undergoes cross-metathesis transformation to afford [ArNC(Me)CHC(Me)CHSiMe3]TiNAr(OTf) (3) as the major product after 34 h at room temperature. Complexes 1, 2, 2-THF, and 3 have been fully characterized spectroscopically, and single crystal X-ray diffraction analysis for 1 and 2-THF are presented.

Four and five-coordinate trimethylsilylmethylidene complexes can be readily assembled via a one-electron oxidatively induced α-hydrogen abstraction step. Shown is the crystal structure of a rare example of terminal trimethylsilylmethylidene complex of titanium. This complex was prepared by a general one-electron oxidation reaction of the corresponding bis-alkyl Ti(III) precursor.Figure optionsDownload as PowerPoint slide