Substituted metal carbonyls. 26.1 One-step synthesis, structures, NMR, and dynamic laser-light scattering of Re2(μ-OMe)2[μ-Ph2P(CH2) nPPh2](CO)6 (n = 1-4)

Abstract

Oxidative decarbonylation of Re2(CO)10 by Me3NO in a mixture of THF and MeOH followed by addition of alkyl-chained diphosphine Ph2P(CH2)nPPh2 (PP) (n = 1-4) gives Re2(μ-OMe)2-(μ-PP)(CO)6 in 34, 29, 28, and 10% yields, respectively. This methanolytic oxidation across the Re-Re bond provides a general and one-step route for the synthesis of these dirhenium hexacarbonyl complexes with diphosphine and methoxo bridges. The molecular structure of Re2(μ-OMe)2(μ-Ph2PCH2PPh 2)(CO)6 was determined by single-crystal X-ray diffraction analysis. It contains two fac-[Re(CO)3] moieties bridged by dppm and two methoxo ligands. The {Re2O2} core is significantly more planar than that in the Fe(C5H4PPh2)2 analogue. That such a dinuclear core is maintained in spite of the different steric demands of the different bridging diphosphines illustrates the great geometric tolerance of the bridging methoxo groups. The fluxionality of the dppm, dppe, and dppp complexes has been studied and compared by molecular modeling and solution 1H NMR spectroscopy. Dynamic laser-light scattering (DLS) shows that the dppe complex aggregates in CH2Cl2 to form small clusters with an average radius of ∼370 nm. The use of a combination of DLS and NMR in organometallic chemistry is unprecedented.