Photochemistry of (η5-C5H5)(η5-C4H4N)Fe and (η5-C5H5)(η1-N-C4H4N)Fe(CO)2 in Low-Temperature Matrixes and Room-Temperature Solution. Evidence for a Photoinduced Haptotropic Shift of the π-Coordinated Pyrrolyl Ligand

Abstract

Azaferrocene, (η5-C5H5)(η5-C4H4N)Fe, undergoes a η5 → η1 haptotropic shift of the pyrrolyl ligand upon long-wavelength photolysis (λexc > 495 nm) both in alkane solvents at room temperature and in frozen matrixes at 12 K. Room-temperature photolysis (λexc > 495 nm) in CO-saturated cyclohexane solution generated (η5-C5H5)(η1-N-C4H4N)Fe(CO)2. Irradiation with λexc = 532 nm also produced an allyl monocarbonyl species, exo-(η5-C5H5)(η3-C-C4H4N)Fe(CO), identified by IR spectroscopy. In CO-doped matrixes at 12 K both (η5-C5H5)(η1-N-C4H4N)Fe(CO) and (η5-C5H5)(η1-N-C4H4N)Fe(CO)2 are formed following broad-band irradiation (λexc > 495 nm) of (η5-C5H5)(η5-C4H4N)Fe, in a ratio dependent on the concentration of CO in the matrix. Initial irradiation with λexc = 538 nm followed by broad-band photolysis (λexc > 495 nm) in CO-doped matrixes formed additional monocarbonyl species, exo-(η5-C5H5)(η3-C-C4H4N)Fe(CO), and a species absorbing at 1962 cm-1, which is either the appropriate endo-isomer or aza-allyl species. Laser ...