Guanidinate complexes of niobium and tantalum.

Title: Guanidinate complexes of niobium and tantalum.
Authors: Tin, Ma Khin Than.
Date: 1998
Abstract: This work is concerned with the preparation and examination of guanidinate complexes. One method of synthesis of such ligands, as presented in Chapter 2, is the insertion of carbodiimide into a metal-amido group. The direct reactions of $\rm M(NMe\sb2)\sb5$ with either dicyclohexylcarbodiimide (CyN=C=NCy) or diisopropylcarbodiimide $\rm(\sp{i}PrN{=}C{=}N\sp{i}Pr)$ proceeded smoothly at room temperature under nitrogen to yield $\rm\lbrack RNC(NMe\sb2)NR\rbrack M(NMe\sb2)\sb4$ (M = Ta, Nb; R = Cy, $\rm\sp{i}Pr).$ The spectroscopic characterization of these materials is consistent with a symmetrical chelating bidentate guanidinate anion bonded to a pseudo-octahedral metal center. In chapter 3, we prepared $\rm N,N\sp\prime,N\sp{\prime\prime}$-tricyclohexylguanidine and triisopropylguanidine. With this guanidine ligand, we focus on the elimination of amido ligands from homoleptic Ta(V) and Nb(V) dimethylamido complexes. The complex $\rm TaCl(NMe\sb2)\sb3\{\lbrack CH\sb3)\sb2CHN\rbrack\sb2CN(H)CH(CH\sb3)\sb2\}$ was also isolated and crystallographically characterized. In Chapter 4, the direct reaction of Ta and Nb alkyl complexes $\rm M(Me)\sb{x}Cl\sb{y}$ (M = Ta, x = 3, y = 2; M = Nb, x = 2, y = 3) with $\rm N,N\sp\prime,N\sp{\prime\prime}$-tricyclohexylguanidine and $\rm N,N\sp\prime,N\sp{\prime\prime}$-triisopropylguanidine was investigated. The preliminary results of efforts to get a second alkyl elimination are also reported. (Abstract shortened by UMI.)
CollectionTh├Ęses, 1910 - 2010 // Theses, 1910 - 2010
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