REACTIONS OF MONODENTATE TERTIARY PHOSPHINES WITH THE DIRHENIUM(II) ALKYNE COMPLEXES [RE2CL3(MU-DPPM)(2)(CO)-(ETA(2)-RCCH)]X (X=PF6 OR O3SCF3) TO FORM YLIDES

The eta(2)-alkyne adducts [Re2Cl3(mu-dppm)(2)(CO) (eta(2)-RCCH)]X (R=H , Pr-n, Bu(n) or Ph; X=PF6 or O3CF3) have been reacted with monodentat e tertiary phosphines PR(3) (R(3)=Me(3), Et(3), Me(2)Ph or MePh(2)) to afford in high yield (> 60%) a new class of resonance stabilized ylid es of composition [Re2Cl3(mu-dppm)(2)(CO)(C(R)CH(PR(3)))]X. These diam agnetic complexes have been characterized by IR, H-1 NMR and P-31(H-1) NMR spectroscopies and cyclic voltammetry, and the structure of a rep resentative example determined by single crystal X-ray crystallography . Crystal data for [Re2Cl3(mu-dppm)(2)(CO)(C(Pr-n)CH(PMe(2)Ph))] SO3CF 3 . 0.83C(7)H(8), at 173 K: monoclinic space group Pn (No. 7), a=16.40 4(4), b=11.907(2), c=19.866(2) Angstrom, beta=110.58(1)degrees V=3632( 2) Angstrom(3), Z=2. The structure was refined in full-matrix least-sq uares to R=0.052 (R(w)=0.068) for 4156 data with I>3 sigma(1). This st ructure determination shows that the basic geometry present in the par ent complexes [Re2Cl3(mu-dppm)(2)(CO)(eta(2)RCCH)]X is retained, the p rincipal difference being the conversion of the eta(2)-alkyne ligand R CCH to the eta(1)-bound ylide C(R)CH(PR(3)). The Re-Re bond length of 2.311(1) Angstrom signifies the retention of an Re=Re bond.