Electronic Excitations in Fischer-Type Cr and W Aminocarbene Complexes: A Combined ab Initio and Experimental Study

The influence of the substitution on the carbene ligand in the series of Fischer-type Cr and W aminocarbene complexes was studied experimentally by UV–vis spectroscopy and theoretically by comparative ab initio SA-CASSCF/MS-CASPT2 and TD-DFT methods. Both calculations interpreted the experimental UV–vis spectra and their variations caused by substitution effects well. TD-DFT analysis of individual transitions using electron density redistributions indicated that the variation of the absorption spectra due to substitution is accompanied by a change in the character of the low-lying excited states participating in the visible bands. Correlated MS-CASPT2 calculations confirmed the TD-DFT assignments of the lowest-lying transitions in the visible region almost quantitatively.