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

摘要

The reaction of the low valent metallocene(Ⅱ) sources Cp'_2Ti(η~2-Me_3SiC_2SiMe_3) (Cp' = η~5-cyclopentadienyl, 1a or η~5-penta-methylcyclopentadienyl, 1b) with different carbodiimide substrates RN= C=NR' 2-R-R' (R = t-Bu; R' = Et; R = R' = i-Pr; t-Bu; SiMe_3; 2,4,6-Me-C_6H_2 and 2,6-i-Pr-C_6H_3) 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 tetranudear 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.