Aqueous organometallic chemistry: Synthesis and characterization of γ, δ unsaturated alkynyl substituted Fischer carbene complexes of group 6 transition metals

A number of γ, δ unsaturated alkynyl substituted carbene complexes [(CO)5M=C(OCH3)CHR(CH2C\equivCH)], 4-7 (4: M = Cr, R = CH2C\equivCH; 5: M = Mo, R = CH2C\equivCH; 6: M = W, R = CH2C\equivCH and 7: M = W, R = CH(CH2)2CH3) have been synthesized from group 6 metal-carbene complexes [(CO)5M=C(OCH3)CH3], 1-3 (1: M = Cr, 2: M = Mo, 3: M = W) under biphasic reaction conditions. The alkoxy group has been readily replaced by amino groups in 6 as rotamers 8a-b and 9a-b (syn and anti isomers), (CO)5WC(NHR')-CH(CH2CCH)2, [8a-b: R' = CH3; 9a-b: R' = CH2Ph]. Further, when a CH2Cl2 solution of 4-6 was stirred at room temperature in the presence of trimethylamine-N-oxide for 30 min, the ester derivative CO(OCH3)CH-(CH2CCH)2 was formed. UV-Vis spectra have been recorded for both alkoxy and amino carbene complexes, 4-8, which showed the gradual hypsochromic shift of metal-to-ligand charge transfer bands from Cr to W. Compounds 4-9 have been isolated as yellow oils in moderate to good yields and they have been characterized by IR, 1H, 13C NMR spectroscopic analysis.