Metal–coumarin complexes: synthesis and characterization of 7-isocyanocoumarin ligands and Mo(CO) 4(7-isocyanocoumarin) 2 complexes. X-ray crystal structure of Mo(CO) 4(7-isocyano-4-trifluoromethylcoumarin) 2

Abstract

The preparation and characterization of four different 7-isocyanocoumarin ligands is described. The four ligands are 3,4-dimethyl-7-isocyanocoumarin (Dmic), 7-isocyano-4-methylcoumarin (Mic), 3-chloro-7-isocyano-4-methylcoumarin (Cmic) and 7-isocyano-4-trifluoromethylcoumarin (Tic). Reaction of the four 7-isocyanocoumarin ligands with Mo(CO) 4(pip) 2 (pip=piperidine) gave the Mo(CO) 4L 2 complexes. IR and UV–vis spectra of the complexes indicate that the 7-isocyanocoumarin ligands are significantly stronger π-acids than simple aromatic isocyanide ligands. An intense visible absorption band, assigned to a metal-to-ligand charge transfer (MLCT) transition, is present in the UV–vis spectra of the four Mo(CO) 4L 2 complexes. Excitation into the MLCT band of the Mic, Cmic, and Dmic complexes gave yellow–orange emission at room temperature in methylene chloride solution. Photolysis of Mo(CO) 4(Mic) 2 with P(Ph) 3 in THF solution produced Mo(CO) 3(PPh 3)(Mic) 2.