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Type of Document	Dissertation
Author	Jenkins, David Matthew
URN	etd-02102005-144940
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-02102005-144940
Title	Low spin pseudotetrahedral cobalt tris(phosphino)borate complexes
Degree	PhD
Option	Chemistry
Advisory Committee	Advisor Name Title Harry B. Gray Committee Chair David MacMillan Committee Member John E. Bercaw Committee Member Jonas Peters Committee Member
Keywords	imide low spin pseudotetrahedral nitride imido
Date of Defense	2005-01-31
Availability	restricted
Abstract A synthetic protocol is developed for the preparation of a thallium complex featuring the tris(phosphino)borate ligand [PhBP3] ([PhBP3] = [PhB(CH2PPh2)3]-). The transmetallating reagent, [PhBP3]Tl, is characterized by single crystal X-ray diffraction and solution NMR spectroscopy, and is the first example of a stable homoleptic Tl(I) phosphine complex. The synthesis and characterization of [PhBP3]Co-X (X = I, Br or Cl) is discussed. These halide complexes are structurally characterized and magnetic investigations establish that they are low spin when monomeric. The low spin iodide complex is a monomer in solution and in the solid state. The other halides exhibit a monomer/dimer equilibrium that complicates their magnetic behavior. Theoretical calculations help provide a rationale as to why these pseudotetrahedral species are low spin. A classic high spin species supported by [PhBP3] is compared to the low spin complexes. Spin state control involving pseudotetrahedral [PhBP3]Co(II) complexes is explored. Both high and low spin, as well as spin crossover, complexes are synthesized and structurally characterized. The complexes are discussed in terms of the relationship between local geometry and spin state. Changing the axial or tripodal ligand can cause a different spin state to be favored. Since the energy difference between the states is small, ligand changes at remote positions from the metal center have a significant effect on spin crossover phenomena. Theoretical calculations help illuminate why the low spin state is preferred for many of the complexes. The first examples of cobalt imide complexes ([PhBP3]Co?NR (R = aryl or alkyl)) are prepared and they are supported by the [PhBP3] ligand. These diamagnetic species are evaluated by NMR and single crystal X-ray diffraction. Theoretical studies suggest that they have a similar molecular orbital bonding scheme as the previously prepared group 9 imides. A cobalt bridging nitride complex (([PhBP3]Co)2(N)) is synthesized and structurally characterized. This mixed-valence species is evaluated by magnetometry to determine its ground state, which is low spin (S = 1/2). Several cobalt diazoalkane complexes are prepared. These diamagnetic species adopt two different bonding modes depending on the nature of the diazoalkane ligand.
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