TY - JOUR
T1 - Rationalizing the different products in the reaction of N2 with three-coordinate MoL3 complexes
AU - Christian, Gemma
AU - Stranger, Robert
AU - Yates, Brian F.
AU - Cummins, Christopher C.
PY - 2007
Y1 - 2007
N2 - The reaction of N2 with three-coordinate MoL3 complexes is known to give rise to different products, N-MoL3, L 3Mo-N-MoL3 or Mo2L6, depending on the nature of the ligand L. The energetics of the different reaction pathways are compared for L = NH2, NMe2, N(iPr)Ar and N(tBu)Ar (Ar = 3,5-C6H3Me2) using density functional methods in order to rationalize the experimental results. Overall, the exothermicity of each reaction pathway decreases as the ligand size increases, largely due to the increased steric crowding in the products compared to reactants. In the absence of steric strain, the formation of the metal-metal bonded dimer, Mo2L6, is the most exothermic pathway but this reaction shows the greatest sensitivity to ligand size varying from significantly exothermic, -403 kJ mol-1 for L = NMe2, to endothermic, +78 kJ mol-1 for L = N(tBu)Ar. For all four ligands, formation of N-MoL3 via cleavage of the N2 bridged dimer intermediate, L3Mo-N-N-MoL3, is strongly exothermic. However, in the presence of excess reactant MoL3, formation of the single atom-bridged complex L3Mo-N-MoL3 from N-MoL3 + MoL3 is both thermodynamically and kinetically favoured for L = NMe2 and N(iPr)Ar, in agreement with experiment. In the case of L = N(tBu)Ar, the greater steric bulk of the tBu group results in a much less exothermic reaction and a calculated barrier of 66 kJ mol-1 to formation of the L3Mo-N-MoL3 dimer. Consequently, for this ligand, the energetically and kinetically favoured product, consistent with the experimental data, is the nitride complex L3Mo-N.
AB - The reaction of N2 with three-coordinate MoL3 complexes is known to give rise to different products, N-MoL3, L 3Mo-N-MoL3 or Mo2L6, depending on the nature of the ligand L. The energetics of the different reaction pathways are compared for L = NH2, NMe2, N(iPr)Ar and N(tBu)Ar (Ar = 3,5-C6H3Me2) using density functional methods in order to rationalize the experimental results. Overall, the exothermicity of each reaction pathway decreases as the ligand size increases, largely due to the increased steric crowding in the products compared to reactants. In the absence of steric strain, the formation of the metal-metal bonded dimer, Mo2L6, is the most exothermic pathway but this reaction shows the greatest sensitivity to ligand size varying from significantly exothermic, -403 kJ mol-1 for L = NMe2, to endothermic, +78 kJ mol-1 for L = N(tBu)Ar. For all four ligands, formation of N-MoL3 via cleavage of the N2 bridged dimer intermediate, L3Mo-N-N-MoL3, is strongly exothermic. However, in the presence of excess reactant MoL3, formation of the single atom-bridged complex L3Mo-N-MoL3 from N-MoL3 + MoL3 is both thermodynamically and kinetically favoured for L = NMe2 and N(iPr)Ar, in agreement with experiment. In the case of L = N(tBu)Ar, the greater steric bulk of the tBu group results in a much less exothermic reaction and a calculated barrier of 66 kJ mol-1 to formation of the L3Mo-N-MoL3 dimer. Consequently, for this ligand, the energetically and kinetically favoured product, consistent with the experimental data, is the nitride complex L3Mo-N.
UR - http://www.scopus.com/inward/record.url?scp=34248161056&partnerID=8YFLogxK
U2 - 10.1039/b701050h
DO - 10.1039/b701050h
M3 - Article
SN - 1477-9226
SP - 1939
EP - 1947
JO - Dalton Transactions
JF - Dalton Transactions
IS - 19
ER -