METAL TO LIGAND CHARGE-TRANSFER PHOTOCHEMISTRY OF METAL-METAL BONDED COMPLEXES .9. PHOTOCHEMISTRY OF CPFE(CO)2RE(CO)3 4,4'-ME2-BPY,CPFE(CO)2RE(CO)3 PYRIDINE-2-CARBALDEHYDE N-ISOPROPYLIMINE)

In this article we report the photochemistry of the two metal-metal-bonded complexes CpFe(CO2Re(CO3(alpha-diimine) (alpha-diimine = 4,4'-dimethyl-2,2'-bipyridine (bpy'), pyridine-2-carbaldehyde N-isopropylimine (iPr-PyCa)) which are characterized by strongly allowed metal to ligand charge-transfer (MLCT) transitions in the visible region. At 218 K the bpy' complex (1) showed a wavelength dependent photochemistry. Low-energy excitation into the MLCT band produced homolysis products, irradiation with UV light gave rise to release of CO and to the formation of a CO-bridged photoproduct. The iPr-PyCa complex (2) showed a wavelength dependent photochemistry already at r.t. Again, homolysis of the metal-metal bond occurred upon low-energy excitation. UV irradiation of 2 also resulted in release of CO but in this case an iPr-PyCa bridged complex was formed. In this photoproduct, which could also be formed via a radical coupling mechanism upon prolonged irradiation of 2, the iPr-PyCa ligand is most probably sigma-N,sigma-N' coordinated to Re and eta-2-CN to Fe. From the experimental data it was concluded that the homolysis reaction occurred from the repulsive 3-sigma-sigma-* state of the metal-metal bond and release of CO from a 3LF state at higher energy, localized at the CpFe(CO)2 fragment.