140604-91-7Relevant academic research and scientific papers
Matrix isolation and transient absorption studies of (bis(bis(pentafluoroethyl)phosphino)ethane)tetracarbonyl-chromium: Intermolecular alkane complexes and intramolecular F-coordination
Brookhart, Maurice,Chandler, Wayne,Kessler, Robert J.,Liu, Yumin,Pienta, Norbert J.,Santini, Catherine C.,Hall, Chris,Perutz, Robin N.,Timney, John A.
, p. 3802 - 3815 (1992)
Photolysis of (η2-dfepe)Cr(CO)4 [dfepe = (C2F5)2PCH2CH2P(C 2F5)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 (η2-dfepe)Cr(CO)3(alkane) and (η1-dfepe)Cr(CO)4(alkane), as well as formation of intramolecularly F-coordinated species Cr(CO)4(η1-dfepe) and Cr(CO)3(η2-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 (η1-dfepe)Cr(CO)5, similar results have been obtained which support the interpretation of the behavior of (η2-dfepe)Cr(CO)4. Products from 13CO trapping of the transients generated in hexane show that all four possible isomers, fac- and mer-(η2-dfepe)Cr(CO)3*CO and cis- and trans-(η1-dfepe)Cr(CO)4*CO, are formed in significant quantities. Experiments carried out at a different 13CO pressures show that 13CO trapping of cis-(η1-dfepe)Cr(CO)4(L) is competitive with ring closure back to (η2-dfepe)Cr(CO)4.
