Metathesis Polymerization Reactions Induced by the Bimetallic Complex (Ph4P)2[W2(μ-Br)3Br6]

The reactivity of the bimetallic complex (Ph4P)2[W2(μ-Br)3Br6] ({W2.5W}7+, a'2e3) towards ring opening metathesis polymerization (ROMP) of norbornene (NBE) and some of its derivatives, as well as the mechanistically related metathesis polymerization of phenylacetylene (PA), is presented. Our results show that addition of a silver salt (AgBF4) is necessary for the activation of the ditungsten complex. Polymerization of PA proceeds smoothly in tetrahydrofuran (THF) producing polyphenylacetylene (PPA) in high yields. On the other hand, the ROMP of NBE and its derivatives is more efficient in CH2Cl2, providing high yields of polymers. 13C Cross Polarization Magic Angle Spinning (CPMAS) spectra of insoluble polynorbornadiene (PNBD) and polydicyclopentadiene (PDCPD) revealed the operation of two mechanisms (metathetic and radical) for cross-linking, with the metathesis pathway prevailing

Homogeneous catalytic hydrogen formation using a ditungsten cluster and low valency metal ions in aqueous acidic solutions

The formally triply-bonded nonachlorodimetallates [W2(μ-Cl)3Cl6]3- (6) and [Re2(μ-Cl)3Cl6]- (8) undergo a two-electron homogeneous reduction by the chromous or vanadous ions to give the quadruply-bonded species [W2Cl8]4- (4) and [Re2Cl8]2- (7). In aq. HCl solutions complex 6 is an effective catalyst for the anaerobic oxidation of CrII and VII to CrIII and VIII with simultaneous dihydrogen formation. © 1989