| Abstract
| - This paper reports the synthesis and characterization of a variety of ruthenium complexescoordinated with phosphine and N-heterocyclic carbene (NHC) ligands. These complexes include severalalkylidene derivatives of the general formula (NHC)(PR3)(Cl)2RuCHR‘, which are highly active olefinmetathesis catalysts. Although these catalysts can be prepared adequately by the reaction of bis(phosphine)ruthenium alkylidene precursors with free NHCs, we have developed an alternative route that employsNHC-alcohol or -chloroform adducts as “protected” forms of the NHC ligands. This route is advantageousbecause NHC adducts are easier to handle than their free carbene counterparts. We also demonstratethat sterically bulky bis(NHC) complexes can be made by reaction of the pyridine-coordinated precursor(NHC)(py)2(Cl)2RuCHPh with free NHCs or NHC adducts. Two crystal structures are presented, one ofthe mixed bis(NHC) derivative (H2IMes)(IMes)(Cl)2RuCHPh, and the other of (PCy3)(Cl)(CO)Ru[η2-(CH2-C6H2Me2)(N2C3H4)(C6H2Me3)], the product of ortho methyl C−H bond activation. Other side reactionsencountered during the synthesis of new ruthenium alkylidene complexes include the formation of hydrido-carbonyl-chloride derivatives in the presence of primary alcohols and the deprotonation of rutheniumvinylcarbene ligands by KOBut. We also evaluate the olefin metathesis activity of NHC-coordinatedcomplexes in representative RCM and ROMP reactions.
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