EXCITED-STATE RAMAN-SPECTROSCOPY OF W(CO)4(ALPHA-DIIMINE) COMPLEXES

The Raman spectra of W(CO)4(diimine) complexes (diimine = 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, and pyridine-2-carbaldehyde isopropylimine) in the lowest tungsten to diimine charge-transfer excited state are reported. The excited-state peaks are assigned to ligand ring deformation modes and to carbonyl stretching modes. The effect of the electron transfer on 2,2′-bipyridine and 4,4′-dimethyl-2,2′-bipyridine ring mode frequencies is similar to that previously observed on the prototypical ruthenium compounds. The totally symmetric cis-carbonyl stretching mode in the charge-transfer excited state is about 50 cm−1 higher in energy than that of the molecule in the ground electronic state. The increase is interpreted in terms of loss of metal-carbonyl π back-bonding in the charge-transfer excited state. © 1990, American Chemical Society. All rights reserved.