Formation of Unsaturated Vicinal Zr+/P Frustrated Lewis Pairs by the Unique 1,1-Carbozirconation Reactions

Treatment of the metallocene cation complexes [Cp*2MCH3]+[B­(C6F5)4]− (M = Zr or Hf) with trimethylsilyl­(diarylphosphino)­acetylenes Ar2P–CC-SiMe3 (Ar = Ph or p-tolyl) resulted in the formation of internal phosphane stabilized cations [Cp*2M-C­(CH3)C­(SiMe3)­PAr2]+ 4 through the unique 1,1-carbometalation reaction under mild conditions. In contrast, when the low Lewis basicity phosphane containing alkyne (C6F5)2P–CC–SiMe3 was used, normal 1,2-carbometalation occurred to produce complexes 5, which show agostic coordination of a Me–Si group to the metal center. Complex 4a reacts with n-butyl isocyanide to give the coordination product 6, which has the Zr–P bond retained. Treatment of 4a with N2O gave the five-membered metallaheterocycle 7 by oxidation of the phosphane. The vicinal M+/P complexes 4 also show some typical FLP reactivity. They add to cinnamaldehyde or paraformaldehyde, for example, to produce carbonyl addition products 8 and 9, respectively. Complex 4a adds to the NO functionality of nitrosobenzene with formation of 10. The vicinal M+/P systems 4 behave as reactive frustrated Lewis pairs toward hetercumulenes, undergoing 1,2-addition to the CO bond of CO2 and the SO bond of SO2 to form the respective adducts 11 and 12. The Zr+/P FLP 4a reacts with PhNSO to give the addition product 13, in which the phosphane Lewis base has added to the nitrogen atom and the Zr+ Lewis acid to both atoms of the SO unit. The reaction of complex 4a with the metal complex [Ir­(COD)­Cl]2 affords a heterobimetallic Zr/Ir product 14. The vicinal M+/P complexes 4 can be also used as efficient catalysts for the regioselective dimerization of phenyl acetylene.