[1 + 4]-Cycloadditions of silylenes to 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene

Abstract

2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene 1 undergoes [1 + 4]-cycloaddition with the stable bis(amino)silylenes Si[(NCH₂Bu^t)₂C₆H₄-1,2] 3, Si[(NBu^t)₂C₂H₂] 4 and Si[(NBu^t)₂C₂H₄] 7 to afford the structurally characterised 5, 6 and 11. The intermediate aminosilylsilylene resulting from the dissociation of the disilene [Si{(NBu^t)₂C₂H₄}]₄9 was trapped as its [1 + 4]-cycloadduct with 1, which was also structurally characterised. The reversibility of the cycloaddition was demonstrated for 5 through reaction with [Mo(CO)₄(nbd)] to afford [Mo(CO)₃(η⁶-P₃C₃Bu^t₃)] (13) and a mixture of cis- (14a) and trans-[Mo(CO)₄(3)₂] (14b) of which 14b has been structurally characterised by a single crystal X-ray diffraction study.