Synthesis of [(CO)5MS=CFcCH3] and exploration of the nature of M-S vs. M-O bonds in [(CO)5ME=CFcCH3]; (M = Cr, Mo, W and E = O, S) complexes

Abstract

Photolysis of a methanol solution containing substituted alkyne, group VI metal hexacarbonyl and P4S10 at low temperature under an inert atmosphere leads to metal-sulfur coordinated complexes of chromium, molybdenum, and tungsten. The structure of pentacarbonylthioacetylferrocene-S-chromium (1) is confirmed by single crystal x-ray diffraction study and both the complexes (1 and 2) are confirmed using IR and NMR spectral studies. The sulfur-coordinated metal carbonyl complexes are thought to be formed by the initial activation of metal carbonyl with acetylenic ligand which then rearranges into metal coordinated thioacetylferrocene by dithiophosphoryl radical (formed in situ by reaction of P4S10 and methyl alcohol under photolytic condition). The stability of pentacarbonylthioacetylferrocene of group VI metal complexes are further compared with their acetylferrocene derivatives of Group VI metal complexes using DFT studies. Density functional theory was performed on six complexes [(CO)5ME=CFcCH3] (where M = Cr, Mo and W; while E = O and S) to assess their geometry and electronic structure aspects. Natural bonding orbital (NBO) and energy-decomposition analysis (EDA) were carried out to probe the nature and strength of the M-E interactions. NBO and EDA analysis predict M-E bond strength in the following order: Cr-E < Mo-E < W-E. The M-E bond covalency increases as we move down the group from Cr, Mo to W, which rationalizes the observed trends in the M-E bonds. While comparing the nature of the E (O and S) linkage in bonding, we found that -S analogue shows exceptionally robust σ and π interactions compared to the -O analogue. The reasonably strong M-S interactions resulted in the isolation of these -thio analogues.