TY - JOUR
T1 - Kinetic studies of the photoinduced formation of transition metal-dinitrogen complexes using time-resolved infrared and UV-vis spectroscopy
AU - Grills, David C.
AU - Huang, Kuo Wei
AU - Muckerman, James T.
AU - Fujita, Etsuko
N1 - Funding Information:
We thank Prof. M.W. George for the provision of unpublished data. This work was performed at Brookhaven National Laboratory, funded under contract DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Office of Basic Energy Sciences. K.-W.H. acknowledges a Gertrude and Maurice Goldhaber Distinguished Fellowship.
PY - 2006/7
Y1 - 2006/7
N2 - Previous kinetic studies of photoinitiated transition metal-dinitrogen bond forming reactions are reviewed, with an emphasis on room temperature reactivity, and in particular, the techniques of time-resolved infrared (TRIR) spectroscopy and UV-vis flash photolysis. Our recent results on the reactivity of the formally 16-electron, but agostically stabilized, complex, mer,trans-W(CO)3(PCy3)2 (W) (Cy = cyclohexyl) toward N2 in toluene and n-hexane solution are then discussed. Laser flash photolysis of a toluene solution of W-N2 in the presence of excess N2 resulted in the photoejection of N2. The back reaction of W with N2 was followed by monitoring the decay of the transient absorption of W at 600 nm. The second-order rate constant for the reaction of N2 with W in toluene to generate W-N2 was found to be (3.0 ± 0.2) × 105 M-1 s-1. The rate of the reverse reaction was found to be 100 ± 10 s-1, allowing an estimation of the equilibrium constant, KN2 = (3.0 ± 0.5) × 103 M- 1. Time-resolved step-scan FTIR (s2-FTIR) spectroscopy was also used to spectroscopically characterize the W intermediate and monitor its back-reaction with N2 in n-hexane solution. The rate of formation of W-N2 measured by s2-FTIR agreed well with that measured by flash photolysis. Finally, density functional theory (DFT) calculations have been performed on the model complexes, mer,trans-W(CO)3(PH3)2(L) (L = none and N2) in order to understand the observed IR and UV-vis spectra of W and W-N2 and to determine the nature of the frontier molecular orbitals of W and W-N2, allowing their lowest energy excited states to be assigned.
AB - Previous kinetic studies of photoinitiated transition metal-dinitrogen bond forming reactions are reviewed, with an emphasis on room temperature reactivity, and in particular, the techniques of time-resolved infrared (TRIR) spectroscopy and UV-vis flash photolysis. Our recent results on the reactivity of the formally 16-electron, but agostically stabilized, complex, mer,trans-W(CO)3(PCy3)2 (W) (Cy = cyclohexyl) toward N2 in toluene and n-hexane solution are then discussed. Laser flash photolysis of a toluene solution of W-N2 in the presence of excess N2 resulted in the photoejection of N2. The back reaction of W with N2 was followed by monitoring the decay of the transient absorption of W at 600 nm. The second-order rate constant for the reaction of N2 with W in toluene to generate W-N2 was found to be (3.0 ± 0.2) × 105 M-1 s-1. The rate of the reverse reaction was found to be 100 ± 10 s-1, allowing an estimation of the equilibrium constant, KN2 = (3.0 ± 0.5) × 103 M- 1. Time-resolved step-scan FTIR (s2-FTIR) spectroscopy was also used to spectroscopically characterize the W intermediate and monitor its back-reaction with N2 in n-hexane solution. The rate of formation of W-N2 measured by s2-FTIR agreed well with that measured by flash photolysis. Finally, density functional theory (DFT) calculations have been performed on the model complexes, mer,trans-W(CO)3(PH3)2(L) (L = none and N2) in order to understand the observed IR and UV-vis spectra of W and W-N2 and to determine the nature of the frontier molecular orbitals of W and W-N2, allowing their lowest energy excited states to be assigned.
KW - Binding rates
KW - Dinitrogen complex
KW - Flash photolysis
KW - Nitrogen fixation
KW - Time-resolved Infrared
UR - http://www.scopus.com/inward/record.url?scp=33745171773&partnerID=8YFLogxK
U2 - 10.1016/j.ccr.2006.01.002
DO - 10.1016/j.ccr.2006.01.002
M3 - Review article
AN - SCOPUS:33745171773
SN - 0010-8545
VL - 250
SP - 1681
EP - 1695
JO - Coordination Chemistry Reviews
JF - Coordination Chemistry Reviews
IS - 13-14
ER -