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 Ph2C[double bond, length as m-dash]C(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([small mu ]-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-Calkyl bond which is commensurate with the observed reactivity.