TY - DATA T1 - Fine-Tuning the Energy Barrier for Metal-Mediated Dinitrogen NN Bond Cleavage PY - 2014/07/16 AU - Andrew J. Keane AU - Brendan L. Yonke AU - Masakazu Hirotsu AU - Peter Y. Zavalij AU - Lawrence R. Sita UR - https://acs.figshare.com/articles/journal_contribution/Fine_Tuning_the_Energy_Barrier_for_Metal_Mediated_Dinitrogen_N_N_Bond_Cleavage/2273989 DO - 10.1021/ja505309j.s001 L4 - https://ndownloader.figshare.com/files/3910012 KW - activation parameters KW - cleavage KW - bond KW - Energy Barrier KW - energy barrier height KW - Cp KW - group 5 bimetallic dinitrogen complexes N2 - Experimental data support a mechanism for NN bond cleavage within a series of group 5 bimetallic dinitrogen complexes of general formula, {Cp*M­[N­(iPr)­C­(R)­N­(iPr)]}2(μ-N2) (Cp* = η5-C5Me5) (M = Nb, Ta), that proceeds in solution through an intramolecular “end-on-bridged” (μ-η1:η1-N2) to “side-on-bridged” (μ-η2:η2-N2) isomerization process to quantitatively provide the corresponding bimetallic bis­(μ-nitrido) complexes, {Cp*M­[N­(iPr)­C­(R)­N­(iPr)]­(μ-N)}2. It is further demonstrated that subtle changes in the steric and electronic features of the distal R-substituent, where R = Me, Ph and NMe2, can serve to modulate the magnitude of the free energy barrier height for NN bond cleavage as assessed by kinetic studies and experimentally derived activation parameters. The origin of the contrasting kinetic stability of the first-row congener, {Cp*V­[N­(iPr)­C­(Me)­N­(iPr)]}2(μ-η1:η1-N2) toward NN bond cleavage is rationalized in terms of a ground-state electronic structure that favors a significantly less-reduced μ-N2 fragment. ER -