I. Studies of the mechanisms of solvolysis of multisubstituted sulfamoyl and benzoyl chlorides. II. Applications of a new N-heterocyclic carbene to the development of metal complexes and to cyanosilylation reactions .

摘要

Nucleophilic substitution reactions with the reaction center being the carbonyl carbon of benzoyl chloride derivatives and with the reaction center being the sulfur of sulfamoyl chloride derivatives were studied under solvolytic conditions and the simple and extended Grunwald-Winstein equations were applied. The sensitivities of the rates of solvolysis towards changes in solvent nucleophilicity and solvent ionizing power are closely related to the amounts of bond forming and bond breaking at the transition state of the rate-determining step.;In the solvolyses of N,N-dimethylsulfamoyl chloride, it was found that the bond formation is an important factor in the rate-determining step. The 2,6-dichlorobenzoyl chloride and 2,4,6-trichlorobenzoyl chloride were found to follow a dissociative SN2 mechanism due to the steric hindrance from two ortho-chlorine substituents. For 2,4-dichlorobenzoyl chloride, two different mechanisms were found. These are the additionelimination mechanism in nucleophilic solvents and the dissociative SN2 mechanism in electrophilic solvents. The 3,5- and 3,4-dichlorobenzoyl chlorides were both found to follow an addition-elimination mechanism. Due to the decrease of steric hindrance on replacing the two chlorine atoms by the fluorine atoms at ortho-positions, 2,6-difluorobenzoyl chloride follows an addition-elimination mechanism in nucleophilic solvents and the dissociative SN2 mechanism only in the more electrophilic solvents. The 3,4,5-trimethoxybenzoyl chloride was found to follow the dissociative SN2 mechanism due to the strong electron-supplying resonance effect of the para-substituent being dominant over the weaker electron-withdrawing inductive effect of the three methoxy groups.;Based on the successful correlations of the specific rates of solvolysis of di- and tri-substituted benzoyl chloride derivatives, it is concluded that the application of the Grunwald-Winstein equations, especially the extended form, can give valuable mechanistic information concerning a solvolysis reaction at an acylcarbon.;N-Heterocyclic carbenes (NHCs) have been found to be extremely efficient ligands for the synthesis of metal complexes which are used in important organic reactions, such as olefin metathesis and the Heck reaction. We have exploited a very useful commercially available source for a carbene ligand, a triazole inner salt, given the common name nitron. We have succeeded in synthesizing ruthenium and palladium complexes incorporating this ligand and we have found that these complexes are highly active in ring-closing metathesis and Heck reactions.;Cyanosilylation is the most important method for preparing cyanohydrins, which are very useful building blocks in organic synthesis. The reactions of carbonyl compounds with trimethylsilyl cyanide (TMSCN) need a catalyst to activate the TMSCN. We have found the inexpensive and commercially available organocatalyst, lithium hexamethyldisilazide (LiHMDS) functions efficiently in this capacity and allows one to carry out the cyanosilylation of suitable aldehydes and ketones under mild conditions.