Studies on the Efficient Generation of PhosphorusCarbon Bonds via a Rearrangement of P III Esters Catalysed by Trimethylhalosilanes

Unprecedented CP systems : Me 3 SiX (X=Br, I) catalyses rearrangements of P III esters R′R′′POR into the corresponding phosphoryl systems, providing a simple, mild and efficient route to a variety of structures containing PC bonds. The mechanism has been found to be fundamentally different from that of the Arbuzov–Michaelis reaction and includes three definite steps a, b and c (see scheme). magnified image Halotrimethylsilanes Me 3 SiX (X=Br, I) catalyse rearrangements of tricoordinate phosphorus esters R′R′′POR into the corresponding phosphoryl systems R′R′′P(O)R. This provides a simple and efficient route to a variety of structures containing phosphoruscarbon bonds, under mild conditions and with good yields. The reaction mechanism was investigated in detail by 31 P NMR spectroscopy and independent synthesis of the reaction intermediates. It has been demonstrated that the primary products of this catalytic reaction are halogeno P III structures R′R′′PX and silyl ethers ROSiMe 3 and that they subsequently react to give the corresponding phosphorus silyl esters—Me 3 SiOPR′R′′—and alkyl halides RX. At higher temperatures these intermediates then react to form R′R′′P(O)R compounds. This paper also features the surprising observation that when esters Ph 2 POR and halotrimethylsilanes Me 3 SiX (X=Br, I) are used in 2:1 ratio, phosphonium salts Ph 2 R 2 P + X − and trimethylsilyl diphenylphosphinate—Ph 2 P(O)OSiMe 3 —are formed as the major products. Experimental evidence indicates that the mechanisms of both reactions are fundamentally different from that of the Michaelis–Arbuzov reaction. Me 3 SiCl is not reactive and this paper explains why.