Scission of Carbon Monoxide Using TaR 3 , R=(N( t Bu)Ph) or OSi( t Bu) 3 : A DFT Investigation

Abstract

The experimentally known reduction of carbon monoxide using a 3-coordinate [Ta(silox)3] (silox = OSi-(tBu)3) complex initially forms a ketenylidene [(silox)3Ta-CCO], followed by a dicarbide [(silox)3Ta-CC-Ta-(silox)3] structure. The mechanism for this intricate reaction has finally been revealed by using density functional theory, and importantly a likely structure for the previously unknown intermediate [(silox)3Ta-CO]2 has been identified. The analysis of the reaction pathway and the numerous intermediates has also uncovered an interesting pattern that results in CO cleavage, that being scission from a structure of the general form [(silox)3Ta-C nO] in which n is even. When n is odd, cleavage cannot occur. The mechanism has been extended to consider the effect of altering both the metal species and the ligand environment. Specifically, we predict that introducing electron-rich metals to the right of Ta in the periodic table to create mixed-metal dinuclear intermediates shows great promise, as does the ligand environment of the Cummins-style 3-coordinate amide structure. This latter environment has the added complexity of improved electron donation from amide rotation that can significantly increase the reaction exothermicity. Show more