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 alkynes were examined. Re(O)R3(PMe3) (R = Me and CH2SiMe3) and cis-Re(O)Me2Cl(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 of the formal insertion of ethyne into the Re-P bonds. Substituted alkynes, 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 of Re(O)(CH2SiMe3)3(CHCH(PMe3)) and [Re(O)Me2(CHCH(PMe2Ph))2]Cl, the insertion products are best described as anologs of resonance stabilized ylides in which the resonance stabilization involves the high oxidation state organometallic fragment Valence bond and MO descriptions of the 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-ray 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: C17H44OPSi3Re, 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, monoclinic, a = 14.026(4) angstrom, b = 10.691(3) angstrom, c = 18.388(5) angstrom, beta = 99.49(2)-degrees, P2(1)/n, Z = 4. Crystal data for Re(O)Me3(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.