Phosphorus-Stabilized Titanium Carbene Complexes: Synthesis, Reactivity and DFT Studies.

The synthesis of two novel titanium carbene complexes from the bis(thiophosphinoyl)methanediide geminal dianion 1 (SCS^2-) is described. Dianion 1 reacts cleanly with 0.5 equivalents of [TiCl₄(thf)₂] to afford the bis-carbene complex [(SCS)₂Ti] (2) in 86% yield. The mono-carbene complex [(SCS)TiCl2(thf)] (3) can also be obtained by using an excess of [TiCl₄(thf)₂]. The structures of 2 and 3 are confirmed by Xray crystallography. A strong nucleophilic reactivity towards various electrophiles (ketones and aldehydes) is observed. The reaction of 3 with N,N'-dicyclohexylcarbodiimide (DCC) and phenyl isocyanate leads to the formation of two novel diphosphinoketenimines 8a and 8b. The bis-titanium guanidinate complex 9 is trapped as the by-product of the reaction with DCC. The X-ray crystal structures of 8a and 9 are presented. The mechanism of the reaction between complex 3 and DCC is rationalized by DFT studies. [ABSTRACT FROM AUTHOR]