Abstract
Alkylidyne-capped molybdenum (IV) clusters have shown applications in metal-organic reactions as heterogeneous catalysts. A series of alkylidyne-capped clusters have been synthesized and characterized using spectroscopic techniques. The inductive ability of the alkyl group on the bridging carboxylates was varied to analyze the effect on rates of terminal ligand substitution. The rate data for the first substitution step was collected using variable-temperature 1H NMR. Trends in reactivity for the first substitution step are supported using Hammett constants. A new trinuclear molybdenum cluster with bridging dichloroacetates has been crystallized and fully characterized. As a byproduct of this cluster under basic conditions, a new polyoxomolybdate cluster (Mo10) was discovered. Lastly, a chloroacetate bridged trinuclear molybdenum (IV) cluster was synthesized to support the trend in reactivity that showed the rate of terminal methanol substitution increases with decreasing electron-withdrawing alkyl group character. The magnitudes of the activation parameters reported herein for four Mo3+ clusters all indicate a D or Id reaction mechanism for terminal ligand substitution.