Synthesis and reactivity of the yttrium-alkyl-carbene complex [Y(BIPM)(CH2C6H5)(THF)] (BIPM = {C(PPh2NSiMe3)2})

Abstract

Reaction of [YI₃(THF)_3.5] with three equivalents of [KBz] (Bz = CH₂C₆H₅) affords the tri-benzyl complex [Y(Bz)₃(THF)₃] (2) in excellent yield. Complex 2 reacts with H₂C(PPh₂NSiMe₃)₂ (H₂BIPM) to afford the yttrium-alkyl-carbene complex [Y(BIPM)(Bz)(THF)] (3, BIPM = {C(PPh₂NSiMe₃)₂}). Compound 3 reacts with one equivalent of benzophenone to give the alkoxy 1,2-migratory insertion product [Y(BIPM)(OCPh₂Bz)(THF)] (4) rather than the alkene Wittig-product Ph₂CC(PPh₂NSiMe₃)₂. Reaction of 4 with one or more equivalents of benzophenone does not afford any detectable alkene products, rather it apparently catalyses rearrangement of monomeric 4 to afford dimeric [{Y(μ-BIPM)(OCPh₂Bz)}₂] (5). Investigations reveal that formation of 5 is proportional to the amount of benzophenone added, but the benzophenone is recovered at the end of the reaction. Reaction of 3 with diphenyldiazene affords the 1,2-migratory insertion product [Y(BIPM){N(Ph)N(Ph)(Bz)}(THF)] (6) Compounds 2, 3, 4, 5, and 6 have been variously characterised by X-ray crystallography, multi-nuclear NMR spectroscopy, FTIR spectroscopy, and CHN micro-analyses. Density functional theory calculations on 3 reveal the HOMO to be localised at the Y–C_alkyl bond which is commensurate with the observed reactivity.