MATRIX-ISOLATION AND TRANSIENT ABSORPTION STUDIES OF (BIS(BIS(PENTAFLUOROETHYL)PHOSPHINO)ETHANE)TETRACARBONYLCHROMIUM - INTERMOLECULAR ALKANE COMPLEXES AND INTRAMOLECULAR F-COORDINATION

Photolysis of (eta-2-dfepe)Cr(CO)4 [dfepe = (C2F5)2PCH2CH2P(C2F5)2] has been conducted in rigid matrices at 12 K (Ar, CH4, N2, CO) and 30 K (Xe) and in alkane and perfluoroalkane solutions. In Ar, CH4, and Xe matrices a combination of IR and UV-vis spectroscopic data demonstrate photodissociation of the cis carbonyl ligand to generate fac-(dfepe)Cr(CO)3L, where L is either the matrix host or an intramolecularly coordinated F atom donated by one of the pendant CF3CF2- groups of the dfepe ligand. Only traces of the mer isomer were observed. In nitrogen matrices there is evidence for formation of both fac- and mer-(dfepe)Cr(CO)3N2. Carbonyl stretching frequencies of the matrix-isolated photoproducts were measured and bonding force constants and ligand effect constants were calculated. In solution both the Cr-CO and Cr-P bonds are photolabile. Results of nanosecond and microsecond transient absorption spectroscopic experiments in hexane and cyclohexane solvents indicate formation of alkane complexes of the type (eta-2-dfepe)Cr(CO)3(alkane) and (eta-1-dfepe)Cr(CO)4(alkane), as well as formation of intramolecularly F-coordinated species Cr(CO)4(eta-1-dfepe) and Cr(CO)3 (eta-2-dfepe). By use of transient absorption techniques, rates of reaction of these species in alkane solvents with and without added trapping ligands (CO, water, triethylsilane) have been measured. The F-coordinated species react with CO approximately 50 times faster than the alkane complexes. In experiments using (eta-1-dfepe)Cr(CO)5, similar results have been obtained which support the interpretation of the behavior of (eta-2-dfepe)Cr(CO)4. Products from (CO)-C-13 trapping of the transients generated in hexane show that all four possible isomers, fac- and mer-(eta-2-dfepe)Cr(CO)3*CO and cis- and trans-(eta-1-dfepe)Cr(CO)4*CO, are formed in significant quantities. Experiments carried out at a different (CO)-C-13 pressures show that (CO)-C-13 trapping of cis-(eta-1-dfepe)Cr(CO)4(L) is competitive with ring closure back to (eta-2-dfepe)Cr(CO)4.