Activation of heteroallenes by coordinatively unsaturated nickel(II) alkyl complexes supported by the hydrotris(3-phenyl-5-methyl)pyrazolyl borate (Tp^Ph,Me) ligand

Activation of sulfur containing heteroallenes by nickel(ii) alkyl complexes supported by the bulky hydrotris(3-phenyl-5-methylpyrazolyl)borate (Tp^Ph,Me) ligand is described. Exposure of Tp^Ph,MeNiCH₂Ph (1a) and Tp^Ph,MeNiCH₂Si(CH₃)₃ (1b) to CS₂ resulted in formation of the insertion products Tp^Ph,MeNi(η²-CS₂)CH₂Ph (2a) and Tp^Ph,MeNi(η²-CS₂)CH₂Si(CH₃)₃ (2b) in moderate yields. Reaction of 1a and MeNCS produced two species in a 1:1 ratio, identified as Tp^Ph,MeNi(η²-MeNC)CH₂Ph (3) and Tp^Ph,MeNi(η²-MeNCS)SCH₂Ph (4). Isolation of the unexpected insertion product (3) prompted an investigation into the activity of 1a-b in the presence of isocyanides (i.e.^tBuNC), which resulted in isolation of Tp^Ph,MeNi(η^2-tBuNC)CH₂Ph (5a) and Tp^Ph,MeNi(η^2-tBuNC)CH₂Si(CH₃)₃ (5b). Similarly, reaction of 1a with OCS led to the isolation of a rare example of a Ni(i) carbonyl species Tp^Ph,MeNiCO (6). Alternatively, complex 6 was also formed by exposure of 1a-b to an atmosphere of CO. Isolation of the intermediate species (Tp^Ph,MeNi(η²-CO)CH₂TMS (7b) and Tp^Ph,MeNi(CO)(C(O)R, (8a-b) with R = Ph, TMS)) shed light on the formation of such species.