Photoinduced C-N bond cleavage in 2-azido-1,3-diphenyl-propan-1-one derivatives: photorelease of hydrazoic acid.
Photolysis of 3-azido-1,3-diphenyl-propan-1-one (1a) in toluene yields 1,3-diphenyl-propen-1-one (2), whereas irradiation of 3-azido-2,2-dimethyl-1,3-diphenyl-propan-1-one (1b) results in the formation of mainly 2,2-dimethyl-1,3-diphenyl-propan-1-one. Laser flash photolysis (308 nm) of 1a,b in acetonitrile reveals a transient absorption (lambda max = approximately 310 nm) due to the formation of radicals 4a and 4b, respectively, which have lifetimes of approximately 14 micros at ambient temperature. TD-DFT calculations (B3LYP/6-31+G(d)) reveal that the first and second excited states of the triplet ketone (T1K (n,pi*) and T2K (pi,pi*)) in azide 1a are almost degenerate, at approximately 74 and 76 kcal/mol above the ground state (S0), respectively. Similarly, azide 1b has T1K and T2K 75 and 82 kcal/mol above S0, respectively. The calculated transition state for cleaving the C-N bond is located 71 and 74 kcal/mol above S0 in azides 1a and 1b, respectively. The calculated bond dissociation energies for breaking the C-N bond are 55 and 58 kcal/mol for azides 1a and 1b, respectively, making C-N bond breakage accessible from T1K in azides 1 at ambient temperature. In comparison, the irradiation of azides 1 in argon matrices at 14 K lead to the formation of the corresponding triplet alkyl nitrenes (1-n), via intramolecular energy transfer from T2K. The characterization of 1-n was supported by isotope labeling, IR spectroscopy, and molecular modeling.
Klima
Rodney F
RF
Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221-0172, USA.
Jadhav
Abhijit V
AV
Singh
Pradeep N D
PN
Chang
Mingxin
M
Vanos
Christine
C
Sankaranarayanan
Jagadis
J
Vu
Mai
M
Ibrahim
Nazarin
N
Ross
Elaine
E
McCloskey
Shaun
S
Murthy
Rajesh S
RS
Krause
Jeanette A
JA
Ault
Bruce S
BS
Gudmundsdóttir
Anna D
AD
D001386:Azides / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D010777:Photochemistry; D011407:Propane / Q000031:analogs & derivatives* / Q000737:chemistry
D001386:Azides; C007972:hydrazoic acid; D002244:Carbon; D009584:Nitrogen; D011407:Propane