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

Azaferrocene, (η 5 -C 5 H 5 )(η 5 -C 4 H 4 N)Fe, undergoes a η 5 → η 1 haptotropic shift of the pyrrolyl ligand upon long-wavelength photolysis (λ exc > 495 nm) both in alkane solvents at room temperature and in frozen matrixes at 12 K. Room-temperature photolysis (λ exc > 495 nm) in CO-saturated cyclohexane solution generated (η 5 -C 5 H 5 )(η 1 - N -C 4 H 4 N)Fe(CO) 2 . Irradiation with λ exc = 532 nm also produced an allyl monocarbonyl species, exo -(η 5 -C 5 H 5 )(η 3 - C -C 4 H 4 N)Fe(CO), identified by IR spectroscopy. In CO-doped matrixes at 12 K both (η 5 -C 5 H 5 )(η 1 - N -C 4 H 4 N)Fe(CO) and (η 5 -C 5 H 5 )(η 1 - N -C 4 H 4 N)Fe(CO) 2 are formed following broad-band irradiation (λ exc > 495 nm) of (η 5 -C 5 H 5 )(η 5 -C 4 H 4 N)Fe, in a ratio dependent on the concentration of CO in the matrix. Initial irradiation with λ exc = 538 nm followed by broad-band photolysis (λ exc > 495 nm) in CO-doped matrixes formed additional monocarbonyl species, exo -(η 5 -C 5 H 5 )(η 3 - C -C 4 H 4 N)Fe(CO), and a species absorbing at 1962 cm - 1, which is either the appropriate endo- isomer or aza-allyl species. Laser flash photolysis experiments of (η 5 -C 5 H 5 )(η 1 - N -C 4 H 4 N)Fe(CO) 2 in either CO-saturated cyclohexane or toluene produced (η 5 -C 5 H 5 )(η 1 - N -C 4 H 4 N)Fe(CO), which reacted with CO with rate constants measured at 298 K of (3.0 ± 0.3) × 10 8 and (3.3 ± 0.3) ×10 8 M - 1 s - 1, respectively, regenerating (η 5 -C 5 H 5 )(η 1 - N -C 4 H 4 N)Fe(CO) 2 .