No abstract

The reaction of [Cp*RuCl] 4 (1) with carbene ligands affords unsaturated Cp*Ru(L)Cl [Cp* ) η 5 -C 5 Me 5 ; L ) 1,3-R 2 -imidazol-2-ylidene [R ) cyclohexyl (ICy, 2); 4-methylphenyl (ITol, 3); 4-chlorophenyl (IpCl, 4); adamantyl (IAd, 5)] and 4,5-dichloro-1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMesCl, 6)] complexes 2-6 in high yield. Solution calorimetric investigations of this series provides a measure of the electron donor properties of all ligands, and comparisons are made with IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] and the widely used PCy 3 . Structural information from single X-ray studies for complexes 2, 3, 5, 6, Cp*Ru(IMes)Cl (7), Cp*Ru(PCy 3 )Cl (8), and Cp*Ru(P i Pr 3 )Cl (9) permits a quantitative treatment of steric parameters associated with these ligands.

The synthesis and structural characterization of a series of palladium complexes bearing N-heterocyclic carbenes (NHC) as supporting ligands are described. The reaction of commercially available [Pd(allyl)Cl]2 and isolated or in situ generated NHC leads to monomeric palladium complexes where one NHC is bound to the metal center, as indicated by spectroscopic and single-crystal X-ray diffraction studies. The relative reactivity trend for these complexes as catalysts in aryl amination is discussed in terms of ligand steric properties, which vary as a function of imidazole-nitrogen substituents and perturbation resulting in modulation of ring planarity. The concept of buried volume is used to quantify the steric demand of each NHC in the corresponding complexes.

The exchange reaction of one phosphine ligand in Cl 2 (PCy 3 ) 2 RudCHPh (1; Cy ) cyclohexyl, C 6 H 11 ) with the sterically demanding carbene ligands 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), 1,3-bis(4-methylphenyl)imidazol-2-ylidene (ITol), and 1,3-bis(4-chlorophenyl)imidazol-2-ylidene (IpCl) leads to the isolation of the new complexes (PCy 3 )(IMes)Cl 2 -RudCHPh (2), (PCy 3 )(ITol)Cl 2 RudCHPh (3), and (PCy 3 )(IpCl)Cl 2 RudCHPh (4). Similarly, one IMes ligand can be substituted for one PCyp 3 ligand in Cl 2 (PCyp 3 ) 2 RudCHCHdC(CH 3 ) 2 (5; Cyp ) cyclopentyl, C 5 H 9 ) to produce (PCyp 3 )(IMes)Cl 2 RudCHPh (6) in high yield. X-ray structure analysis of 6 confirmed a near-square-pyramidal coordination sphere around the metal center. Improved catalytic properties and thermal stability are observed for 2 and 6 in comparison to the parent 1 and 5.

ring closure reactions ring closure reactions O 0130 -058(p-cymene)RuLCl 2 (L: 1,3-Bis(2,4,6-trimethylphenyl)imidazol-2ylidene and 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and Related Complexes as Ring Closing Metathesis Catalysts.-Several novel (η 6 -arene)ruthenium complexes (I) and (II) are synthesized and tested for their efficiency as ring closing metathesis catalysts. It is shown, that the bis(mesityl)imidazolylidene-containing complexes (Ia) and (II) efficiently catalyze the RCM reaction of diallylmalonate (III), while the corresponding bis(diisopropylphenyl) complex (Ib) is less effective.