oa South African Journal of Chemistry - Trimethylamine oxide induced substitution reaction of MM' (CO)10 (M,M' = Mn, Re): synthesis and characterization of MM'(CO)9L (L = group 15 donor ligands)



Reaction of MM'(CO)10 (M,M' = Mn, Re) with equimolar amounts of Me3NO in CH3CN readily gives MM'(CO)9(CH3CN) in high yield (>80%). Competitive reactions reveal that the rate of reaction increases Re2(CO)10 > MnRe(CO)10 > Mn2(CO)10, with substitution of MnRe(CO)10 occurring at Re (>90%). Reaction of MM'(CO)9(CH3CN) with L gives axial: equatorial isomer mixtures of MM'(CO)9L [L = P(OMe)3, P(OiPr)3, P(O-o-tol)3, PMe2Ph, PMePh2, PPh3, P(CH2Ph)3 and the products have been characterized by i.r. and n.m.r. (31P, 1H) spectroscopy as well as cleavage reactions with Br2. Isomerization of equatorial to axial isomers was studied by n.m.r. spectroscopy and the rate and extent of isomerization was observed to be dependent on both steric and electronic properties of L. Axial and equatorial isomers of MM'(CO)9L were unambiguously identified by 31P n.m.r. spectroscopy since the axial isomer gives an absorption 10-20 p.p.m. downfield of the equatorial isomer. I.r. spectroscopy can not generally be used to establish the axial: equatorial isomer ratios for MM'(CO)9L owing to similarities between the two spectra, especially in polar solvents.


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