Laleh Jafarpour

A sterically demanding nucleophilic carbene : 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) : thermochemistry and catalytic application in olefin metathesis

Abstract The sterically demanding nucleophilic carbene ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr, 4) has been synthesized. The reaction of [Cp*RuCl]4 (5; Cp*=η5-C5Me5) with this ligand affords a coordinatively unsaturated Cp*Ru(IPr)Cl (6) complex. Solution calorimetric results in this system provide information concerning the electron donor properties of the carbene ligand. Steric parameters associated with this ligand are determined from the X-ray crystal structure study. The carbene ligand reacts with RuCl2(C(H)Ph)(PCy3)2 (1) to yield a mixed carbene–phosphine ruthenium complex RuCl2(C(H)Ph)(IPr)(PCy3) (9). A single-crystal X-ray diffraction study has been performed on 9. The thermal stability of 9 has been studied at 60°C and its catalytic activity has been evaluated for the ring closing metathesis of diethyldiallylmalonate.

Transition-metal systems bearing a nucleophilic carbene ancillary ligand: from thermochemistry to catalysis

Publisher Summary Specific applications benefit from or require the use of sterically demanding phosphine ligation to stabilize reactive intermediates. Therefore, there is a need for strongly nucleophilic, bulky ligands that are resistant to oxidizing agents and form stable bonds with metals. The enthalpies of reaction can be converted to relative enthalpies of reaction on a mole of product basis by dividing the enthalpies by 4 which represents the number of bonds made in the course of reaction. The enthalpies of reaction for nucleophilic carbenes depend on the stereoelectronic properties of the ligands affecting the availability of the carbene lone pair. Increase in the steric congestion around the carbene carbon atom hinders a closer approach of the ligand, therefore affording smaller metal-lone pair overlap. The nucleophilic carbenes are phosphine-mimics but they are much more. They reside at the upper end of the Tolman electronic and steric parameter scales. Much remains to be explored with these ligands.

Development of olefin metathesis catalyst precursors bearing nucleophilic carbene ligands

Abstract From solution calorimetric measurements involving binding of nucleophilic carbenes to a ruthenium centered organometallic system, steric and electronic properties of the carbenes were assessed. An understanding of these fundamental properties led to the development of novel olefin metathesis catalysts bearing these nucleophilic carbenes as ancillary ligands. The discovery and development of olefin metathesis active ruthenium catalysts bearing a nucleophilic carbene ancillary ligand are described.

Mixed donor ligands based on sp2-hybridized nitrogen donors: asymmetric hydrosilylation catalyzed by rhodium complexes that contain the 2-(2-oxazolin-2-ylmethyl)pyridine system

Abstract The synthesis and coordination chemistry of a mixed pyridine–oxazoline bidentate ligand, 2-(2-oxazolin-2-ylmethyl)pyridine, are described. Crystal structure data along with variable temperature NMR studies establish the structures of achiral and chiral versions of this ligand system. In addition, the catalytic asymmetric hydrosilylation of acetophenone has been examined.