Metal-ligand multiple bonds in nickel complexes supported by chelating bisphosphine ligands.

摘要

Multiply bound functionalities to transition metals occupy a central role in organo-metallic chemistry. These species have transformed synthetic methods and with them areas ranging from organic chemistry to materials. Multiple bonds between light elements and first row transition metals were deemed impossible until recently when the Hillhouse and other groups showed these predictions to be incorrect. The present thesis describes our efforts in synthesizing Ni=C, Ni=Si, Ni=N, Ni=O and Ni=S moieties.;Chapter 1offers a general introduction to the starting materials used throughout, with many examples being improvements of existing procedures or entirely new. The methods used for investigating the compounds presented are also discussed, with an emphasis on computational methods since they are less established than spectroscopic and structural methods.;Chapter 2 focuses on the chemistry of silyl/silylene complexes, which are important in the context of silicon-containing materials. To this end, a silyl species, in which one of the substituents of silicon is hydrogen, supported by a nickel dtbpe (dtbpe = 1,2-bis-(ditert-butylphosphino)ethane) fragment was investigated. It was observed that instead of removing it, the hydrogen migrates from silicon to nickel, forming a three-center bond, which was investigated by DFT calculations.;Chapter 3 provides information about the isolation and characterization of a stable nickel(III) imide complex. By using a sterically protected amide group, the paramagnetic arylamido complex (dtbpe)Ni-NH(dmp) was synthesized. This amide precursor led to the isolation of a stable nickel imido species, (dtbpe)Ni=N(dmp). Oxidation of the imido compound led to Rdtbpe)Ni=N(dmp) +], a rare example of a Ni(III) complex.;Chapter 4 describes our efforts to synthesize a nickel(III) carbyne species. A nickel carbene, (dtbpe)Ni=CH(dmp), was obtained from the photolysis of the corresponding (dtbpe)Ni{eta2-N2CH(dmp)} and structurally characterized. Oxidation of the Ni(II) carbene, (dtbpe)Ni=CH(dmp), takes place with rearrangement of the Ni coordination environment, involving phosphine migration to the carbene carbon in the expected Ni(III) intermediate species, [(dtbpe)Ni=CH(dmp)+]. These results were explained with the aid of DFT calculations, which indicate that in the case of the imido complex (dtbpe)Ni=N(dmp) the HOMO is an antibonding orbital, while in the case of the carbene (dtbpe)Ni=CH(dmp) it is a bonding one, making the electron removal process difficult.;In Chapter 5 a different chelate ligand, dippnapht, was introduced that replaces the ethylene back-bone of the dtbpe ligand with 1,8-naphthylene. The purpose of this adjustment was to create a more rigid chelate ring which would prevent the phosphine/ylide rearrangement observed during the oxidation of the (dtbpe)Ni=CH(dmp) carbene. This ligand, dippnapht offered a different steric environment for the nickel center and different reactivity was observed as a consequence. The Ni(I) monochloride (dippnapht)NiCl is a monomeric trigonal planar species while the bridging disulfide was isolated as the eta2-persulfido complex (dippnapht)Ni{eta 2-S2}.