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, (eta(5)-C5H5)(eta(5)-C4H4N)Fe, undergoes a eta(5) --> eta(1) haptotropic shift of the pyrrolyl ligand upon long-wavelength photolysis (lambda(exc) > 495 nm) both in alkane solvent-sat room temperature and in frozen matrixes at 12 K. Room-temperature photolysis (lambda(exc) > 495 nm) in GO-saturated cyclohexane solution generated (eta(5)-C5H5)(eta(1)-N-C4H4N)Fe(CO)(2). Irradiation with lambda(exc) = 532 nm also produced an allyl monocarbonyl species, exo-(eta(5)-C5H5)(eta(3)-C-C4H4N)- Fe(CO), identified by IR spectroscopy. In CO-doped matrixes at 12 K both (eta(5)-C5H5)(eta(3)-N-C4H4N)Fe(CO) and (eta(5)-C5H5)(eta(1)-N-C4H4N)Fe(CO)(2) are formed following broad-band irradiation (lambda(exc) > 495 nm) of (eta(5)-C5H5)(eta(1)-C4H4N)Fe, in a ratio dependent on the concentration of CO in the matrix. Initial irradiation with lambda(exc) = 538 nn followed by broad-band photolysis (lambda(exc) > 495 nn) in CO-doped matrixes formed additional monocarbonyl species, exo-(eta(5)-C5H5)-(eta(3)-C-C4H4N)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 (eta(5)-C5H5)(eta(1)-N-C4H4N)-Fe(CO)(2) in either CO-saturated cyclohexane or toluene produced (eta(5)-C5H5)(eta(1)-N-C4H4N)Fe-(CO), which reacted with CO with rate constants measured at 298 K of (3.0 +/- 0.3) x 10(8) and (3.3 +/- 0.3) x10(8) M-1 s(-1), respectively, regenerating (eta(5)-C5H5)(eta(1)-N-C4H4N)Fe(CO)(2).