Loss Of Dinitrogen Research Articles

Studies of the kinetics of the reactions of nitriles with dinitrogen complexes of molybdenum(0) and tungsten (0). Factors affecting the rate of dissociative loss of dinitrogen

The kinetics of the substitution of nitriles for dinitrogen in trans-[M(N 2) 2-(dppe) 2] (M = Mo, W; dppe = 1,2-bis(diphenylphosphino)ethane) and cis-[M(N 2) 2(PMe 2Ph) 4] (M = Mo, W) complexes have been studied in toluene solution at various temperatures. In the case of trans-[Mo(N 2) 2(dppe) 2], one dinitrogen is replaced by a nitrile in toluene and the kinetic data support an S n1 dissociative mechanism ( k(PhCN) 3.6 X 10 -4 s -1 at 303 K; E a 28 kcal/mol; Δ H ≠ 27 kcal/mol; Δ S ≠ 15 cal/mol-deg). The analogous reaction with trans-[W(N 2) 2(dppe) 2] was found to proceed only photochemically, with loss of one dinitrogen. The thermal activation energy for N 2 dissociation from trans-[W(N 2) 2(dppe) 2] in toluene is estimated to be 38 kcal/mol. In the cis-[M)N 2) 2(PMe 2Ph) 4] (M = Mo, W) reactions in toluene, both dinitrogen ligands are replaced by nitriles in two consecutive dissociative steps ( k(Mo)/ k(W) ≈ 10 2 for each step).

The reaction of para-tolydiazonium tetrafluoroborate with bis (dinitrogen)-bis(1,2-bis(diphenylphosphino)ethane)molybdenum

Reactions of para-tolyldiazonium tetrafluoroborate with trans-Mo(N 2) 2 (dppe) 2 (where dppe = 1,2-bis(diphenylphosphino ethane) result in the oxidation of the molybdenum complex with complete loss of dinitrogen. A similar reaction occurs with MoBr(N 2)(dppe) 2.

Insertion reactions of diazocyclopentadienes with halo—transition metal complexes

The reactivity of diazocyclopentadiene and diazotetraphenylcyclopentadiene, known precursors of interesting carbenes, towards some rhodium, iridium and manganese complexes has been investigated. It was found that reactions of halo-bridged-dirhodium species and manganese pentacarbonyl halides with diazocyclopentadienes at room temperature yielded halo-substituted cyclopentadienyl complexes. This reaction can be considered an insertion of the diazo species into the metal halogen bond accompanied by loss of dinitrogen. The intermediacy of free carbenes is considered unlikely.