Alkynyl Ti–M complexes based on M(CO)4 and MO2 building blocks (M = Mo, W)

The synthesis and properties of heterobimetallic Ti–M complexes of type {[[Ti](μ-η1:η2-Ctriple bond; length of mdashCSiMe3)][M(μ-η1:η2-Ctriple bond; length of mdashCSiMe3)(CO)4]} (M = Mo: 5, [Ti] = (η5-C5H5)2Ti; 6, [Ti] = (η5-C5H4SiMe3)2Ti; M = W: 7, [Ti] = (η5-C5H5)2Ti; 8, [Ti] = (η5-C5H4SiMe3)2Ti) and {[Ti](μ-η1:η2-Ctriple bond; length of mdashCSiMe3)2}MO2 (M = Mo: 13, [Ti] = (η5-C5H5)2Ti; 14, [Ti] = (η5-C5H4SiMe3)2Ti). M = W: 15, [Ti] = (η5-C5H5)2Ti; 16, [Ti] = (η5-C5H4SiMe3)2Ti) are reported. Compounds 5–8 were accessible by treatment of [Ti](Ctriple bond; length of mdashCSiMe3)2 (1, [Ti] = (η5-C5H5)2Ti; 2, [Ti] = (η5-C5H4SiMe3)2Ti) with [M(CO)5(thf)] (3, M = Mo; 4, M = W) or [M(CO)4(nbd)] (9, M = Mo; 10, M = W; nbd = bicyclo[2.2.1]hepta-2,5-diene), while 13–16 could be obtained either by the subsequent reaction of 1 and 2 with [M(CO)3(MeCtriple bond; length of mdashN)3] (11, M = Mo; 12, M = W) and oxygen, or directly by oxidation of 5–8 with air. A mechanism for the formation of 5–8 is postulated based on the in-situ generation of [Ti](Ctriple bond; length of mdashCSiMe3)((η2-Ctriple bond; length of mdashCSiMe3)M(CO)5), {[Ti](μ-η1:η2-Ctriple bond; length of mdashCSiMe3)2}-M(CO)4, and [Ti](μ-η1:η2-Ctriple bond; length of mdashCSiMe3)((μ-Ctriple bond; length of mdashCSiMe3)M(CO)4) as a result of the chelating effect exerted by the bis(alkynyl) titanocene fragment and the steric constraints imposed by the M(CO)4 entity. The molecular structure of 5 in the solid state were determined by single crystal X-ray diffraction analysis. In doubly alkynyl-bridged 5 the alkynides are bridging the metals Ti and Mo as a σ-donor to one metal and as a π-donor to the other with the [Ti](Ctriple bond; length of mdashCSiMe3)2Mo core being planar.