Syntheses, Structures, and Reactivities of Early-Transition-Metal Silyl, Amide, and Imide Complexes

This dissertation describes syntheses, characterization, and reactivities of Groups 4 and 5 metal amide silyl complexes free of anionic π-ligands such as cyclopentadienyl (Cp).

A summary of the research in this dissertation is provided in Chapter 1. Chapter 2 reports unusual equilibria involving zirconium amides, silyl anions, and zirconium silyl complexes through amide-silyl ligand exchange reactions. Silyl anion SiBu^{tPh_{2− (}}2) was found to substitute an amide ligand in Zr(NMe2)4 (3) to give (Me2N)3Zr(SiButPh2)2− (1a) and Zr(NMe2)5− (1b) in THF. Silyl anion 2 also selectively attacks the –N(SiMe3)2 ligand in (Me2N)3Zr[N(SiMe3)2] (6) to give 1a and N(SiMe3)2− (7). Both reactions 2 3 + 2 2 º 1a + 1b and 6 + 2 2 º 1a + 7 are reversible, leading to unusual ligand exchange equilibria. The thermodynamics of these equilibria has been investigated to give their ΔH°, ΔS°, and ΔG°298 K.

Silyl amide complexes (Me2N)3Ta[N(SiMe3)2](SiButPh2) (^{_{14) and (Me2N)M[N(SiMe3)2]2(SiButPh2) (M = Zr, 17a; Hf, 17b) were found to undergo γ-H abstraction by the silyl ligands to give metallaheterocyclic complexes (Me2N)3-}}Ta[N(SiMe3)SiMe2CH2] (^{_{15) and {(Me2N)[(Me3Si)2N]M[N(SiMe3)SiMe2CH2]}2}}(M = Zr,^{_{18a; Hf, 18b), respectively. The 14 →15 conversion follows first-order kinetics and its ΔH‡and ΔS‡have been studied. The formation of 18a involves the formation of an intermediate, followed by γ-H abstraction. Kinetic studies of these consecutive reactions, a second-order followed by a first-order γ-H}} abstraction, were conducted by an analytical method and a numerical method. The reactions of ^{_{18a and 18b with O2 were found to give metallahetercyclic}} complexes {(Me2N)[(Me3Si)2N]M[N(SiMe3)SiMe2CH2O]}2 (M = Zr,^{_{cis-19a and trans-19a; Hf, cis-19b and trans-19b) with two –NMe2 ligands in cis- and trans- configurations, respectively. These results are described in Chapter 3.}}

In Chapter 4, the formation of per-amides H2N-M[N(SiMe3)2]3 (M = Zr,^{_{21a; Hf, 21b) from ammonolysis reactions and formation of imides Li}+(THF)n{HN–-M[N(SiMe3)2]3} (M = Zr,} 22a; Hf, 22b) from deprotonation of 21a-b by LiN(SiMe3)2 or Li(THF)3SiButPh2 are reported. One –SiMe3 group in 22a-b undergoes silyl migration to give Li+(THF)2{Me3SiN–-M[NH(SiMe3)][N(SiMe3)2]2} (M = Zr, 23a; Hf, 23b) containing an imide =N(SiMe3) ligand. The first-order kinetics of the 22a → 23a conversion was investigated between 290 and 315 K. THF in the mixed solvent was found to promote the conversion, and the effect of THF on the rate constants was studied.

Preparation, characterization, and X-ray crystal structures of Group 4 amide chloride complexes {Hf[N(SiMe3)2](NMe2)2Cl}2, [(Me3Si)2N]2MCl2-Li(THF)3Cl (M = Zr,_{^{26a; Hf, 26b) and [(Me3Si)2N]2MCl2(THF) (M = Zr, 27a; Hf, 27b) are reported in Chapter 5. Kinetic studies of the decomposition of (Me2N)2Zr[N(SiMe3)2](SiButPh2) (28a), prepared from {Zr[N(SiMe3)2](NMe2)2Cl}2 (24a) and LiSiButPh2, have been carried out.}}