Synthesis and reactivity of molybdenum organometallic complexes supported by amide ligands

Abstract

Chapter 1. Synthesis and Reactivity of Molybdenum Alkyl Complexes Supported by a Diamidoamine Ligand. The synthesis of a new diamidoamine ligand, CH3N[CH2CH2NH(3-(CF3)C6H4)]2 (H2L) is reported. Molybdenum complexes of the type X[LMoC13] (X = Et3NH, Bu4N) are readily synthesized as purple air and moisture sensitive crystalline solids. They may be alkylated by Grignard reagents to yield the monoalkyl complex LMo(Cl)(CH2CMe3), the alkylidyne complex LMo(CCMe3)(CH2CMe3) via a,a - elimination of dihydrogen, and the stable complex LMo(CH2TMS)2 (TMS = SiMe3). LMo(CH2TMS)2 is readily oxidized by cyclohexene sulfide and hexachloroethane to yield, initially, molybdenum alkylidenes that readily undergo decomposition reactions to the bridging sulfide complex {LMoS}2 and [LMo(CTMS)Cl]2, respectively. However, the alkylidene complex LMo(CHTMS)(q2 - MeCCMe) may be isolated if LMo(CH2TMS)2 is heated in the presence of five equivalents of 2-butyne. It is a rare example of an alkylidene and alkyne in the coordination sphere of a group six metal. The relationship between oxidation and alkyne binding is discussed. Chapter 2. Early Transition Metal Pyrrolyl Complexes: Structure, Spectroscopy, Hapticity, and Fluxional Processes.

(cont.) A review of group 4, 5,and 6 transition metal pyrrolyl complexes is presented. The focus is on the unique bonding and dynamic processes that the pyrrolyl (and related ligands) can undergo. It is concluded that 1 bound pyrrolyl ligands are poor it donors. Chapter 3. Synthesis and Characterization of Molybdenum Imido Alkylidene Bis(amide) Complexes. The synthesis of bis(amide) complexes Mo(NR)(CHR')(X)2 (R = Ar, Ad, 2,6-Br2-4-MeC6H2 X = N(t-Bu)Ar', NC4H4) from the bis(triflate) complexes Mo(NR)(CHR')(OTf)2(DME) (OTf = trifluoromethanesulfonate, DME = 1,2- dimethoxyethane) is reported. These complexes are of interest as potential precursors for the in situ generation of active and enantioselective metathesis catalysts. The tert-butyl anilide complexes are found to be unreactive towards enantiopure diols. The bis(pyrrolyl) complexes exist in rapid equilibrium between a dimeric form [Mo(NR)(CHR')(NC4H4)2]2 and one in which all pyrrolyl resonances are equilibrating rapidly. The nature of the bis(pyrrolyl) complexes was interrogated by variable temperature 1H and 13C NMR for R = Ar and Ad. The dimeric form was confirmed through an x-ray structural study of {Mo(NAr)(syn-CHCMe2Ph)(S -NC4H4)(r 1-NC4H14)} { Mo(NAr)(syn-CHCMe2Ph)(rq -NC4H4)2 }.

(cont.) Chapter 4. Reactivity of Molybdenum Imido Alkylidene Bis(pyrrolyl) Complexes. The Lewis amphoteric nature of the bis(pyrrolyl) complexes reported in chapter 3 is examined by demonstrating that these complexes react with both trimethylphosphine (at the molybdenum center) and B(C6Fs)3 (at a q5 pyrrolyl nitrogen). A structure of a trimethylphosphine adduct is reported. The bis(pyrrolyl) complexes are found to serve as excellent precursors for the in situ generation of olefin metathesis catalysts at room temperature and millimolar concentration. Furthermore, catalysts not accessible via traditional routes may now be accessed from bis(pyrrolyl) precursors. The bis(pyrrolyl) complexes also react with simple olefins such as ethylene and isobutylene to yield what are proposed to be a bimetallic dimer [Mo(NAr)(NC4H4)2]2 and a 2-propylidene complex via olefin metathesis. The impact of in situ synthesis on syn and anti isomer ratios is discussed as is reactivity with protic reagents other than alcohols.