The synthesis, characterization and reactivity of diphosphine-bridged nickel A-frames
Abstract
The reaction of Ni(cod)$\sb2$ with dmpm and LX$\sb2$ (L = CCH$\sb2,$ COCO, CNPh; X = Cl, Br) is a convenient synthesis of a new series of nickel A-frame complexes with bridging CCH$\sb2,$ CO and CNPh ligands. The substitutional lability of the bridging CO in (Ni$\sb2$ (dmpm)$\sb2$(CO)Cl$\sb2$) allowed the replacement of this ligand with other neutral molecules such as dimethylacetylene dicarboxylate, hexafluoro-2-butyne and CS$\sb2.$ These are the first examples of nickel A-frames with bridging acetylene and CS$\sb2$ groups. Thermolysis of (Ni$\sb2$(dmpm)$\sb2$(CO)Cl$\sb2$) yielded a coordinatively unsaturated nickel trimer. Five nickel A-frames where crystallographically characterized. The structures of the compounds displayed symmetric and distorted A-frame geometries. The (Ni$\sb2$(dmpm)$\sb2$(CO)Br$\sb2$) A-frame has the shortest Ni-Ni distance of any structurally characterized A-frame to date. Extended Huckel molecular orbital calculations where used in developing an understanding of the electronic structure and the trends in the lowest energy absorption bands of the UV-vis spectra of a series of A-frames with different diphosphines and different bridging ligands. Variable temperature two-dimensional $\rm\sp{31}P\{\sp1H\}$ EXSY NMR spectroscopy was used to determine the rates of reaction and activation parameters for a terminal ligand redistribution reaction of dppm nickel A-frames.
Degree
Ph.D.
Advisors
Kubiak, Purdue University.
Subject Area
Chemistry
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