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Treatment of compounds with general formula RuCl2(PP)(PPh 3) (PP = dppb (3a); binap (3b); dcypb ( 3c)) or [RuCl2(PP)]2 (PP = dppb (4); dcypb (5)) with PhCHN2 generates alkylidene complexes of the type RuCl2(PP)(CHPh) (2a--c), the first such systems to exhibit high ROMP activity without halide or phosphine abstraction. Low polymer polydispersity is found in ring-opening metathesis polymerization (ROMP) of norbornene via these catalysts. Investigations into the role of dissociated PPh3 show that free phosphine acts as a poison, dramatically retarding the rate of polymerization via 3 relative to catalysts derived from 4 or 5. Chelate retention is suggested by the narrow polydispersities and increased cis olefin content of the polymers obtained, and is consistent with the detrimental effects of phosphine scavenger. Reaction of RuCl2(PPh3)3 with bis(dicyclohexyl)-1,4-phosphinobutane (dcypb) under N2 gives access to PPh3-free RuCl(dcypb)(mu-Cl) 3Ru(dcypb)(N2) 5 in which the presence of N 2 and dative chloride bridges stabilize two equivalents of "RuCl 2(dcypb)". Under Ar or vacuum atmosphere, decomposition occurs via Ru-promoted dehydrogenation of the dcypb ligand, while reaction with chlorinated solvents rapidly yields paramagnetic RuCl(dcypb)(mu-Cl)3RuCl(dcypb) 6. However, the N2-stabilized species 5 is easily handled under N2 in non-chlorinated solvents, giving an ideal entry point into Ru-dcypb chemistry. The N2 ligand within 5 is readily displaced under H2 or CO atmosphere, yielding RuCl(dcypb)(mu-Cl)3Ru(dcypb)(H2) 6 or RuCl2(dcypb)(CO)2, the latter as a mixture of ccc (8) and tcc (9) isomers. Interestingly, the CO ligands can be displaced, and the symmetrical dimer RuCl(dcypb)(CO)(mu-Cl)2RuCl(dcypb)(CO) 10 is formed by decarbonylation of 8/9 on prolonged storage under N2. The incorporation of the stable silylene ligand 1,3-di-tert-butyl-1,3,2-diazasilol-2-ylidene (SiLN2) in to the ligand scaffold of a metathesis catalyst was undertaken to probe its utility as a phosphine mimic. Reaction of [(dcypb)ClRu(mu-Cl)3Ru(dcypb)(N2)] (5) with 4 equivalents of the silylene yields coordinatively unsaturated RuCl(eta 3-dcypb)(SiLN2) (12). Complex 12 is a rare example of a trans-spanning diphosphine complex, this geometry resulting from an unprecedented attack of the metal on the tetramethylene ligand backbone. (Abstract shortened by UMI.) |
