| Mechanistic investigations were conducted to understand the factors that may influence the rates of formation of carbon-carbon (C-C) and carbon-nitrogen (C-N) bonds in group 10 metal-catalyzed cross-coupling reactions. Studies were also conducted to understand the factors that may control enantioselectivities in allylic amination reactions of monosubstituted allylic esters catalyzed by phosphoramidite complexes of iridium. The factors influencing the rates of formation of C-C bonds in cross coupling reactions were investigated by studying the rates of reductive elimination of biaryls from electronically symmetrical ((DPPF)Pt(C6H4-4-R)2) and dissymmetrical bis-aryl platinum complexes ((DPPF)Pt(C6H4-4-R)(C 6H4-4-X); R = NMe2, OMe, CH3, H, Cl, CF3; X = NMe2, OMe, CH3, H, Cl, F, CF 3). The reductive elimination from symmetrical complexes occurred faster from complexes with more electron-donating para-substituent. In contrast, the reductive elimination from unsymmetrical complexes occurred faster from complexes with a larger difference in the electronic properties of the two platinum-bound aryl groups. To evaluate a recent suggestion that amine coordinates to palladium(0) species and that the amine complex undergoes oxidative addition faster than the bent 14-electron palladium (0) species, oxidative additive addition of bromobenzene to Pd(BINAP)2 in the absence and presence of amine was studied. The rates of oxidative addition of bromobenzene to Pd(BINAP)2 were found to be much less than first order in amine. Further, detailed mechanistic investigations on the reactions of haloarenes with amines catalyzed by Pd-BINAP complexes revealed that the apparent order in amine measured under catalytic conditions resulted from catalyst decomposition. The kinetic data supported a pathway in which Pd(BINAP) 2 lies off the catalytic cycle.; Mechanistic investigations on Ir-catalyzed enantioselective allylic amination led to the discovery of an inexpensive and practical phosphoramidite ligand for Ir-catalyzed allylic substitution reactions. This phosphoramidite ligand contains only one stereochemically resolved element whereas the original ligand contained three stereochemically resolved elements. In addition, a practical method based on novel combination of palladium-allyl and iridium-allyl chemistry was developed for the transformation of monosubstituted racemic allylic esters into enantioenriched branched allylic substitution products. |
