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

2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene 1 undergoes [1 + 4]-cycloaddition with the stable bis(amino)silylenes Si[(NCH2But)(2)C6H4-1,2] 3, Si[(NBut)(2)C2H2] 4 and Si[(NBut)(2)C2H4] 7 to afford the structurally characterised 5, 6 and 11. The intermediate aminosilylsilylene resulting from the dissociation of the disilene [Si{(NBut)(2)C2H4}](4) 9 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)(eta(6)-P3C3Bu3t)] (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.