Ruthenium-based olefin metathesis catalysts coordinated with unsymmetrical N-heterocyclic carbene ligands: synthesis, structure, and catalytic activity.

[摘要]：A series of ruthenium-based olefin metathesis catalysts coordinated with unsym. N-heterocyclic carbene (NHC) ligands was prepd. and fully characterized. These complexes are readily accessible in one or two steps from com. available [(PCy3)2Cl2Ru=CHPh]. All of the complexes reported herein promote the ring-closing of diethyldiallyl and diethylallylmethallyl malonate, the ring-opening metathesis polymn. of 1,5-cyclooctadiene, and the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene, in some cases surpassing in efficiency the existing second-generation catalysts. Esp. in the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene, all new catalysts demonstrate similar or higher activity than the second-generation ruthenium catalysts and, most importantly, afford improved E/Z ratios of the desired cross-product at conversion above 60%. The influence of the unsym. NHC ligands on the initiation rate and the activation parameters for the irreversible reaction of these ruthenium complexes with Bu vinyl ether were also studied. Finally, the synthesis of the related chlorodicarbonyl(carbene) rhodium(I) complexes allowed for the study of the electronic properties of the new unsym. NHC ligands that are discussed in detail.

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