Synthesis and characterization of tungsten carbonyl complexes containing N-methyl substituted urea and thiourea ligands

Six new mixed-ligand tungsten carbonyl complexes containing N-methyl substituted urea and thiourea of the type W(CO)(4)[RCH2N-(C=X)NH2] where X = O or S and R = morpholine, piperidine and diphenylamine are reported. These have been prepared by refluxing hexacarbonyl tungsten( 0) with corresponding ligands in THF to produce cis-disubstituted products, [(L-L)W(CO)(4)] where L- L = a chelating bidentate ligand, morpholinomethyl urea (MMU), morpholinomethyl thiourea (MMTU), piperidinomethyl urea (PMU), piperidinomethyl thiourea (PMTU), diphenylaminomethyl urea (DAMU) and diphenylaminomethyl thiourea (DAMTU). The compounds have been characterized by elemental analysis, IR, electronic and C-13 NMR spectra, magnetic moments and conductivity measurements. The IR spectra suggests that in all the complexes, the ligands are bidentate chelating, coordinating the metal through carbonyl oxygen or thiocarbonyl sulphur and the ring nitrogen or tert-nitrogen of diphenylamine. The CO force constants and CO-CO interaction constants for these derivatives have also been calculated using Cotton-Kraihanzel secular equations, which indicate poor pi-bonding ability of the ligands. C-13 NMR and electronic spectra reveal loss of cis-carbonyl ligands to produce cis- disubstituted tetracarbonyl derivatives. Molecular modeling studies have been carried out using Hyperchem release 7.52 which suggest a distorted octahedral geometry for these complexes.