Investigations of Four-Coordinate and Five-Coordinate Nickel(I) Macrocyclic Ligand Complexes

Citation

Ingle, David Michael (1980) Investigations of Four-Coordinate and Five-Coordinate Nickel(I) Macrocyclic Ligand Complexes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/17rv-gv36. https://resolver.caltech.edu/CaltechTHESIS:07182025-170908470

Abstract

The affinity for the binding of carbon monoxide as a fifth ligand to several formally-nickel(I) complexes of tetraazamacrocyclic ligands has been studied; CO binding constants measured in DMF range from zero to 10⁵. Reduced nickel complexes, which may occur either as four-coordinate nickel(I) species or, for those ligands having conjugated α-diimine moieties, as four-coordinate nickel(II)-stabilized ligand radicals, have been found to bind carbon monoxide as a fifth ligand, forming paramagnetic, presumably five-coordinate nickel(I) carbonyl complexes. Intramolecular electron transfer appears to occur upon the binding of CO to several of the four-coordinate nickel(II)stabilized ligand radicals to give five-coordinate nickel(I) carbonyl complexes. Intramolecular electron transfer within a four-coordinate framework appears to occur for one complex, [1, 1,-difluoro-4, 5, 12, 13- tetramethyl-1-bora-3, 6, 11, 14-tetraaz a-2, 15-dioxacyclopentadeca-3, 5, 11,- 13, -tetraenato] nickel(I), for which the nickel(I) form appears to lie 0. 75 ± 0.15 kcal/mole higher in energy than the nickel(II) ligand radical form.

These nickel complexes have been characterized by elemental analysis, bulk magnetic susceptibility, carbon monoxide binding constants, electron paramagnetic resonance spectroscopy, electronic absorption spectroscopy, infrared spectroscopy, and electrochemical analysis. These nickel complexes appear to be quite analogous to their copper counterparts. On the basis of chemical and physical similarities to the nickel complexes, particularly with respect to their infrared spectra, four-coordinate copper complexes may be formally described as either copper(I) or copper(III)-stabilized ligand dianion species, depending on the ligand system, although both copper species have very similar chemical properties.

A discussion of EHMO calculations on the system is included. In the four-coordinate Ni(II) ligand radical the HOMO is a ligand π* orbital having some metal character; in the five-coordinate Ni(I) carbonyl complexes, the HOMO is the d_x²-y² orbital.

An approach to the synthesis of cofacial dimethylglyoxime dimer complexes using 1, 4-bis(difluoroboro)butane is included in Appendix n.

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