Reactions of Titanocene Bis(trimethylsilyl)acetylene Complexes with Carbodiimides: An Experimental and Theoretical Study of Complexation versus C–N Bond Activation

The reaction of the low valent metallocene­(II) sources Cp′2Ti­(η2-Me3SiC2SiMe3) (Cp′ = η5-cyclopentadienyl, 1a or η5-penta­methylcyclopentadienyl, 1b) with different carbodiimide substrates RNCNR′ 2-R-R′ (R = t-Bu; R′ = Et; R = R′ = i-Pr; t-Bu; SiMe3; 2,4,6-Me-C6H2 and 2,6-i-Pr-C6H3) was investigated to explore the frontiers of ring strained, unusual four-membered heterometallacycles 5-R. The product complexes show dismantlement, isomerization, or C–C coupling of the applied carbodiimide substrates, respectively, to form unusual mono-, di-, and tetranuclear titanium­(III) complexes. A detailed theoretical study revealed that the formation of the unusual complexes can be attributed to the biradicaloid nature of the unusual four-membered heterometallacycles 5-R, which presents an intriguing situation of M–C bonding. The combined experimental and theoretical study highlights the delicate interplay of electronic and steric effects in the stabilization of strained four-membered heterometallacycles, accounting for the isolation of the obtained complexes.