ALKYNE REACTIONS WITH RHENIUM(V) OXO ALKYL PHOSPHINE COMPLEXES-PHOSPHINE DISPLACEMENT VERSUS APPARENT RE-P INSERTION

Reactions of rhenium(V) oxo alkyl phosphine complexes with various alk ynes were examined. Re(O)R3(PMe3) (R = Me and CH2SiMe3) and cis-Re(O)M e2Cl(PMe2R)2 (R = Me and Ph) react with ethyne to give respectively Re (O)R3(CHCH(PMe3)) and [Re(O)Me2(CHCH(PMe2R))2]Cl, which are products o f the formal insertion of ethyne into the Re-P bonds. Substituted alky nes, on the other hand, react with Re(O)Me3(PMe3) to give the adducts Re(O)Me3(RC=CR') (R = R' = Me, Et, or Ph; R = Me or Ph and R' = H). On the basis of spectroscopic studies and the X-ray crystal structures o f Re(O)(CH2SiMe3)3(CHCH(PMe3)) and [Re(O)Me2(CHCH(PMe2Ph))2]Cl, the in sertion products are best described as anologs of resonance stabilized ylides in which the resonance stabilization involves the high oxidati on state organometallic fragment Valence bond and MO descriptions of t he delocalization are presented. The mechanism by which the insertion products are formed is proposed to involve phosphine displacement and subsequent attack on coordinated ethyne by external phosphine. The X-r ay crystal structure of Re(O)Me3(PhC=CPh) was also determined. Crystal data for Re(O)(CH2SiMe3)3(CHCH(PMe3)) at -151(1)-degrees-C: C17H44OPS i3Re, orthorhombic, a = 14.097(6) angstrom, b = 13.242(5) angstrom, c = 13.807(6) angstrom, P2(1)2(1)2(1), Z = 4. Crystal data for [Re(O)Me2 (CHCH(PMe2Ph))2]Cl.CH3CN at -80(1)-degrees-C: C2AH35ClNOP2Re, monoclin ic, a = 14.026(4) angstrom, b = 10.691(3) angstrom, c = 18.388(5) angs trom, beta = 99.49(2)-degrees, P2(1)/n, Z = 4. Crystal data for Re(O)M e3(PhC=CPh) at -83(1)-degrees-C: C17H19ORe, orthorhombic, a = 15.537(5 ) angstrom, b = 18.181(6) angstrom, c = 5.402(2) angstrom, Pnma, Z = 4 .