Investigation of ligand steric effect on the hydrogen gas produced via a nickel-catalyzed dehydrogenation of ammonia-borane utilizing unsymmetrical triazolylidene ligands

Seven new unsymmetrical triazolylidene ligands 4-(4-R-phenyl)-1-R′-1,2,4-triazoly-1-lidene (where R = H, CH₃, CF₃, F; and R′ = CH₃, iPr, Bzl, methylcyclohexane) were employed in a nickel-catalyzed dehydrogenation of ammonia borane to investigate the steric effects associated with the different N(1) substitutions in the triazole ring. The bulkier substituents benzyl and methylcyclohexane afforded the highest weight percent H₂ gas produced. To quantify the steric effect, both percent buried volume (%V_bur) and solid angle G parameter (%) were employed. The G-parameter is a more useful tool when only the crystal structures of the precursor ligands are available.