complexes, with trimetallic titanium hydride clusters effecting the hydrodeoxygenative cyclotetramerization of CO to yield cyclobuten-3,4-diyl-1,2-diolate motifs. Common to these systems are the formation of strong, bridging M-O-M groups in the reaction products that likely provide a thermodynamic driving force for the deoxygenation step (Figure ). While, to the best of our knowledge there are no examples of coupling and deoxygenation of CO with main group metals, the semi-metals silicon and boron have both been used to such end.