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, <b>1a</b> or η⁵-penta­methylcyclopentadienyl, <b>1b</b>) with different carbodiimide substrates RNCNR′ <b>2-R-R</b>′ (R = <i>t</i>-Bu; R′ = Et; R = R′ = <i>i</i>-Pr; <i>t</i>-Bu; SiMe₃; 2,4,6-Me-C₆H₂ and 2,6-<i>i</i>-Pr-C₆H₃) was investigated to explore the frontiers of ring strained, unusual four-membered heterometallacycles <b>5-R</b>. 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 <b>5-R</b>, 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