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Synthesis, characterization, and properties of some molybdenum diene complexes and related compounds

University of British Columbia

Reduction of [C’Mo(NO)I₂]₂ (Cp’ = η ⁵-C₅H₅ (Cp) or η ⁵-C₅Me₅ (Cp*)) by sodium amalgam in THF at -20°C in the presence of acyclic, conjugated dienes affords novel Cp'Mo(NO)( η⁴-s-trans-diene) complexes in isolated yields of -10 - 60%. When the diene is 2,3-dimethylbutadiene, CpMo(NO)( η⁴-cw-2,3-dimethylbutadiene) product complexes are also isolable in addition to the trans-diene isomers. However, these cis-diene compounds are the kinetic products and convert in solutions irreversibly to the isomeric trans-diene complexes. A preliminary kinetic study of this isomerization indicates that the isomerization is first order. Reactivity studies of the η⁴-trans-diene complexes show that they react reluctantly with Lewis bases such as carbon monoxide and phosphines to form the η²-diene complexes, CpMo(NO)(L)( η²-diene) (L = CO, PMePh₂, PMe₃). The η⁴-trans-diene complexes react with alkynes and acetone in ligand coupling reactions to form products in which the diene ligands have coupled with the unsaturated organic molecules. Three of these complexes have been structurally characterized using X-ray crystallography, those being CpMo(NO)[ σ,η³-endo-C(Me)₂-CH-CH-C(Me)₂C(Me)C(Ph)], CpMo(NO)[ σ,η³-exo-C(Me)₂-CH-CH-C(Me)₂C(Me)₂O], and Cp*Mo(NO)[σ,η³-endo-CH₂-CH-CH-CH₂C(Me)₂O]. These complexes and some of their analogues have also been characterized extensively using ¹H and ¹³C NMR spectroscopy. The product of the reaction between CpMo(NO)( η⁴-trans-2,5-dimethyI-2,4-hexadiene) and acetone, CpMo(NO)[σ,η³-exo-C(Me)₂-CH-CH-C(Me)₂C(Me)₂O], reacts further with acetone to form the trimer, [CpMo(NO)]₃ (μ₂: η²-: η¹-OMe₂)₃ which has also been characterized by X-ray crystallography. In a preliminary study of the reactivity of the η⁴-trans-diene complexes with electrophiles, it has been found that they react with protonic acids (HX: X = I, O₃SC₆H₄CH₃,O₂CCF₃) to form CpMo(NO)(η³-allyl)X complexes in which the proton has added to the diene ligand and the anion of the acid has coordinated to the metal center. The diiodo dimers [CpM(NO)I₂]₂ (M = Mo, W) react with 10 equivalents of PMe₃ to produce the new electron-rich nitrosyl complexes M(NO)I(PMe₃)₄, the other product being [(C₅H₅)PMe₃]I. It has been shown that the formation of the tetrakis(phosphine) complexes proceeds sequentially via the isolable intermediate species (η ⁵-C₅H₅)M(NO)I₂ (PMe₃) and [(η ⁵-C₅H₅)M(NO)I(PMe₃)₂]I. Treatment ofthe diiodo dimers with 4 equivalents of PMe₃ in the presence of sodium amalgam affords excellent yields of the related complexes (η ⁵-C₅H₅)M(NO)(PMe₃)₂.

Text

2010-10-10

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http://hdl.handle.net/2429/29075

Chemistry

University of British Columbia

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