Reactions of monodentate tertiary phosphines with the dirhenium(II) alkyne complexes [Re 2Cl 3(μ-dppm) 2(CO)-( η2-RCCH)]X (X = PF 6 or O 3SCF 3) to form ylides

Abstract

The η 2-alkyne adducts [Re 2 CL 3( μ- dppm) 2( CO)( η 2- RCCH)] XR = H, Pr n, Bu n or Ph; X = PF 6 or O OSCF 3 have been reacted with monodentate tertiary phosphines PR 3 (R 3 = Me 3, Et3, Me 2PH or Me 2Ph of Me PHa 2 to afford in hight yield (> 600% a new class of resonance stabilized ylides of composition [Re 2Cl 3(μ-dppm) 2(CO)(C(R)CH(PR 3)]X. These diamagnetic complexes have been characterized by IR, 1H NMR and 31P{ 1H} NMR spectroscopies and cyclic voltammetry, and the structure of a representative example determined by single crystal X-ray crystallography. Crystal data for [Re 2Cl 3(μ-dppm) 2(CO)(C(Pr n)CH(PMe 2Ph))]SO 3 CF 3·0.83C 7H 8 at 173 K: monoclinic space group Pn (No. 7), a = 16.404(4), b = 11.907(2), c = 19.866(2) Å, β = 110.58(1)°, V = 3632(2) A ̊ 3 , Z = 2. The structure was refined in full-matrix least-squares to R=0.052 ( R w=0.068) for 4156 data with I > 3 σ( I). This structure determination shows that the basic geometry present in the parent complexes [Re 2Cl 3(μ-dppn) 2(CO)(η 2- RCCH)]X is retained, the principal difference being the conversion of the η 2-alkyne ligand RCCH to the η 1-bound ylide C(R)CH(PR 3). The ReRe bond length of 2.311(1) Å signifies the retention of an Re≡Re bond.