Jq. Wang et al., Real time infrared spectroscopic probe of the reactions of Fe(CO)(3) and Fe(CO)(4) with N-2 in the gas phase, J PHYS CH A, 105(15), 2001, pp. 3765-3772
Time-resolved infrared absorption spectroscopy has been used to study the g
as-phase reactions of Fe(CO)(3), Fe(CO)(3)N-2, and Fe(CO)(4) with N-2, wher
e Fe(CO)(3) is generated by 308 nm laser photolysis of Fe(CO)(5). The heret
ofore unknown complex Fe(CO)(3)(N-2)(2) forms by addition of N-2 to Fe(CO)(
3)N-2 with a rate constant of (5.4 +/-. 1.8) x 10(-16) cc molecule(-1) s(-1
). This rate constant is much smaller than is typical for the addition of s
mall ligands to coordinately unsaturated metal carbonyls, and data are cons
istent with this reaction being activated. The bond dissociation energy (BD
E) for the loss of a N-2 ligand from Fe(CO)(4)N-2 is 17.6 +/- 1.8 kcal mol(
-1). The activation energy for the loss of N-2 from Fe(CO)(3)(N-2)(2) is 14
.1 +/- 5.2 kcal mol(-1). The kinetics of the system are consistent with a m
odel that involves equilibria between Fe(CO)(3), Fe(CO)(3)N-2, and Fe(CO)(3
)(N-2)(2) as well as reactions of coordinatively unsaturated species with F
e(CO)(5). Using this kinetic model, an upper limit for the BDE for the Fe-N
-2 bond in Fe(CO)(3)N-2 has been estimated and the BDE for the Fe-N-2 bond
in Fe(CO)(3)(N-2)(2) has been determined under the assumption that one of t
he relevant reactions has a minimal activation energy.