Date of Award
Doctor of Philosophy
Ziling (Ben) Xue
Craig E. Barnes, Charles D. Feigerle, X. Peter Zhang, John R. Collier
This dissertation focuses on the unique chemistry of d0 alkylidyne and bis (alkylidene) complexes with β-silicon atoms. The goals of this dissertation research were to prepare and characterize these new d0 transition metal complexes, to study their reactivities including thermodynamics and kinetics of the inter-conversion between the alkylidyne and bis(alkylidene) complexes, and to explore the mechanism of the reactions of O2 or water with d0 alkylidyne complexes.
A summary of the research in this dissertation is provided in Chapter 1.Chapter 2 reports the study of an unusual exchange between new alkyl alkylidyne and bis(alkylidene) complexes promoted by phosphine coordination.
A novel d0 tungsten alkylidyne complex (Me3SiCH2)3W(≡CSiMe3)(PMe3) (3a) was prepared from (Me3SiCH2)3W≡CSiMe3 (4a) and PMe3, and found to undergo a rare exchange with its bis(alkylidene) tautomer (Me3SiCH2)2W(=CHSiMe3)2(PMe3) (3b). The thermodynamics of this equilibrium were investigated by variable-temperature31P NMR to give the thermodynamic parameters ΔHo and ΔSo of the exchange. Kinetic studies show that the α-hydrogen exchange between 3a and 3b follows first-order reversible kinetics.
Activation parameters ΔH≠ and ΔS≠ for the forward (3a → 3b) and reverse reactions (3b → 3a) are reported. Reaction of 4a with PMe2Ph to give alkylalkylidyne 5a and bis(alkylidene) 5b tautomeric mixture has also been studied, and the exchange here is compared with that involving 3a and 3b. Preparation and characterization of two new alkyl alkylidene alkylidyne complexes, and kinetic studies of their formation are presented in Chapter 3. The 3a º 3b equilibrium mixture under heating in the presence of excess PMe3 was found to undergo α-hydrogen abstraction and convert to (Me3SiCH2)(Me3SiCH=)W(≡CSiMe3)(PMe3)2 (8a-b). This reaction follows second-order kinetics – first order with respect to 3 and PMe3. In the presence of excess PMe3, pseudo first-order kinetics was observed to give the activation parameters ΔH≠ and ΔS≠ for the reaction. Preparation of(Me3SiCH2)(Me3SiCH=)W(≡CSiMe3)(PMe2Ph)2 (9a-b) is also reported and compared with the formation of 8a-b. Chapter 4 describes the synthesis of (Me3SiCH2)3(Me3SiC≡)W←O=PMe3(11) and its reaction with O2 to yield an unusual oxo-siloxy complex O=W(OSiMe3)(CH2SiMe3)3 (12). Unexpected –SiMe3 migration from an alkylidyne to an oxo ligand occurs in the reaction. In the absence of O=PMe3, the reaction of (Me3SiCH2)3W≡CSiMe3 (4a) and O2 did not yield 12. 12 was isolated as (Me3SiCH2)3(Me3SiC≡)W←O=W(OSiMe3)(CH2SiMe3)3 (13), an adduct with (Me3SiCH2)3W≡CSiMe3 (4a). Studies with 18O-labelled 18O2 have been conducted to determine whether the oxygen atoms in 12 come from 18O2. Highresolution mass spectrometry (HRMS) was used to analyze the products.
Chapter 5 reports the study of the reaction of (Me3SiCH2)3W≡CSiMe3 (4a) with H2O and the unexpected formation of CH4 and 12 in this reaction. The reaction of 4a with D2O showed α-hydrogen scrambling during the reaction and formation of methane isotopomers, which were studied by HRMS. Reactions of (Me3SiCH2)3(Me3SiC≡)W←O=PMe3 (11) with H2O were also studied, and found to yield the oxo complex 12 as well.
Morton, Laurel Anne, "Tungsten Alkyl Alkylidyne and Bis(Alkylidene) Complexes. Their Unusual Inter-Conversion and Reactions with Phosphines, Dioxygen and Water. " PhD diss., University of Tennessee, 2005.