Metal-mediated 1,2-heteroatom shift reactions of alkynes. Acetylene-vinylidene rearrangements on dinuclear palladium and platinum frameworks

Metal-assisted acetylene-vinylidene transformations via 1,2-H shifts of terminal acetylenes constitute a well established method for the synthesis of vinylidene complexes. The mechanism of those reactions has been extensively studied, both theoretically and experimentally. This is not the case for heteroatom-substituted acetylenes. The few examples known of vinylidene complex formation via 1,2-heteroatomic shifts remain curiosities and a general method for effecting acetylene-vinylidene isomerizations of heteroatom-substituted acetylenes has so far not been developed.; The dipalladium(I) complex ({dollar}rm Pdsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} (dppm = bis(diphenylphosphino)methane) has previously been shown to react with dihalo- and haloalkynes with formation of vinylidene complexes via 1,2-halide shifts. It therefore proved to be a suitable framework for further studies on acetylene-vinylidene rearrangements.; This dissertation focuses on reactions of ({dollar}rm Pdsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} and ({dollar}rm Ptsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} with several sulfur- and oxygen-substituted acetylenes. The heteroatom-substituted acetylenes used in this study included MeSC{dollar}equiv{dollar}CSMe, MeSC{dollar}equiv{dollar}CMe, MeOC{dollar}equiv{dollar}CMe and MeOC{dollar}equiv{dollar}CEt. Reactions of ({dollar}rm Pdsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} with each of the above mentioned alkynes were found to lead to the formation of vinylidene complexes in the presence of catalytic amounts of {dollar}rm HBFsb4{lcub}cdot{rcub}Etsb2O.{dollar} In the absence of {dollar}rm HBFsb4{lcub}cdot{rcub}Etsb2O, lbrack Pdsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} did not react with the unsymmetrical acetylenes MeSC{dollar}equiv{dollar}CMe, MeOC{dollar}equiv{dollar}CMe and MeOC{dollar}equiv{dollar}CEt. With MeSC{dollar}equiv{dollar}CSMe it had previously been shown to react with formation of the acetylene adduct ({dollar}rm Pdsb2Clsb2(mu{dollar}-dppm){dollar}sb2(mu{dollar}-MeSCCSMe)), 1.1 could directly be isomerized into the corresponding vinylidene complex ({dollar}rm Pdsb2Clsb2(mu{dollar}-dppm){dollar}sb2(mu{dollar}-C=C(SMe){dollar}sb2)rbrack{dollar} in the presence of different Lewis acids. ({dollar}rm Ptsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} paralleled the behavior of ({dollar}rm Pdsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} in the acid-catalyzed reactions. Vinylidene complex formation was observed in reactions of ({dollar}rm Ptsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} with MeSC{dollar}equiv{dollar}CSMe, MeSC{dollar}equiv{dollar}CMe and MeOC{dollar}equiv{dollar}CMe in the presence of very small amounts of {dollar}rm HBFsb{lcub}cdot{rcub}Etsb2O.{dollar} In contrast to ({dollar}rm Pdsb2Clsb2(mu{dollar}-dppm){dollar}sb2{dollar}), however, ({dollar}rm Ptsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} also reacted with MeSC{dollar}equiv{dollar}CSMe, MeSC{dollar}equiv{dollar}CMe and MeOC{dollar}equiv{dollar}CMe in the absence of a Lewis acid with formation of vinylidene complexes. The reaction rates were found to be considerably lower in the uncatalyzed reactions. In the reaction of ({dollar}rm Ptsb2Clsb2(mu{dollar}-dppm){dollar}sb2rbrack{dollar} with the symmetrical acetylene MeSC{dollar}equiv{dollar}CSMe, the acetylene adduct ({dollar}rm Ptsb2Clsb2(mu{dollar}-dppm){dollar}sb2(mu{dollar}-MeSCCSMe)) could initially be observed. It was found to transform into the corresponding vinylidene complex and the mononuclear product ({dollar}rm PtClsb2{dollar}(dppm)) over time. A possible mechanism for the newly-established acid-catalyzed acetylene-vinylidene isomerizations has been developed. Conclusive experimental prove of this mechanism has not yet been obtained.; Preliminary experiments with the purpose of finding future applications...