Variable-temperature 'H N M R studies of the oxoalkoxides, WO(OR), (R = Me, Et, Pr', or cyc/o-C,H,,), show these compounds to be dynamic in solution. For R = M e or Et, limiting spectra have been obtained which are consistent with alkoxide-bridged binuclear structures, and for R = M e or cyc/o-C,H,,, X-ray diffraction studies confirm that these structures are adopted in the solid state. The alkoxide bridges are asymmetric [R = Me, 2.032(7) and 2.242(12) A (average); R = cyc/o-C,H,,, 2.044(4) and 2.250(4) A] and coplanar with the terminal 0x0 groups, the longer W-OR bonds being trans to the short W=O bonds.Tungsten-1 83 N M R chemical shifts of t h e compounds with R = Me, Et, cyclo-C,H,,, But or C6H,Pri2-2,6 are very sensitive t o the nature of the alkoxo ligand, and range from 6 -62.9 for [{WO(OMe),},] to -493.6 for mononuclear [WO(OC,H,Pri,-2,6),]. Possible solution equilibria are discussed in the light of these N M R results. An attempt to prepare [WO(OC,H,Me-4),] yielded [W(OC,H,Me-4),], and an X-ray crystal structure determination showed this compound to be octahedral with an average W-0 bond length of 1.895(9) A.

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The synthesis of substituted poly(p-phenylenenvinylene) (PPV) was carried out via metathesis polycondensation of 2,5-diheptyl-l ,Cdivinylbenzene (DHepDVB). A stable molybdenumcarbene complex served as catalyst. The preparation of the educt employed (DHepDPV, 3a) is described. The obtained poly(2,5-diheptyl-1,4-phenylenevinylene) (DHepPPV, 5), an intensely yellow product, has an all-trans-configuration and, with a degree of polymerization of = 10 is soluble in conventional organic solvents.

Oligomers of 2,5-dialkyl-1,4-phenylenevinylenes (DR-OPV, R = C4H9, C7H,,, CloHzl and C6Hll (CyH) were prepared via metathesis polycondensation of the respective 2,5-dialkyl-1,4-divinyIbenzenes. The synthesis of the monomers is described. The highly active metal-alkylidene complex MO(NATM"~)(CHCM~~P~)[OCM~(CF~)~I~ (A@ = 2,6-dimethylphenyl) serves as a catalyst. The degree of polymerization can be controlled by variation of the solvent and by the length of the side chains, since the reaction proceeds as a precipitation polycondensation. The DR-OPVs are bilious-green products and, depending on the molecular weight, soluble in various solvents like toluene, THF and CHCI,. The solutions are highly fluorescent and coloured. The DR-OPVs have vinylic end groups. The vinylene double bonds are of all-trans configuration. Due to their rigidrod structure, the DR-OPVs synthesized have a distinct tendency to crystallize in a highly ordered state, forming a sanidic layer structure.

SUMMARY: In this paper we report on the synthesis of all-trans oligomers of 2,5-diheptyloxy-p-phenylenevinylene (2,5-diheptyloxy-PV) via olefin metathesis condensation of 2,5-diheptyloxy-1,4-divinylbenzene" (2,. The preparation of the monomer is also described. The Schrock type molybdenum alkylidene complex Mo(NPhMez)(CHCMe~Ph)(OCMe[CF312)2 was used as metathesis catalyst. The oligomer product obtained was characterized by means of 'H NMR, IR and UVNis spectroscopy and gel permeation chromatography.