Formation of C3 or higher products proposed to result from reactions of formyl intermediates with CO and H2 (or hydrides) is exceptionally rare. Jones and co-workers have observed the formation of one such species on reaction of CO with a magnesium hydride complex. The steric influence of the -diketiminate ligands were shown to be crucial in determining the Longer Carbon Chains: Reaction of metal-hydride complexes with CO to give higher (>C3) coupled products have been achieved using multimetallic and transition metal hydride complexes. C4 squarate and C6 hexolate ligands have been reported by reductive coupling of CO using titanium-and tantalum-hydride complexes respectively. Though in neither case were formyl or other intermediates identified, the fundamental C-C coupling steps likely proceed via formyl intermediates and subsequent loss of dihydrogen. These successes give precedent for future work in this field and point to multimetallic hydride complexes as attractive candidates for further CO homologation. Dehydration/Deoxygenation: A modest number of metal-hydride complexes have been reported to react with CO to yield deoxygenated ligands, wherein the C : O ratio is greater than one. Ethylidene, enolate, allyloxide, and squarate ligands have been reported from reaction of multimetallic hydrides with CO. In the latter three cases, ethylene, propene, and -butyrolactone were successfully liberated from the metal centre, respectively. In all these instances, cooperative multimetallic complexes were employed (M = Ta, Ln, Y, Ti). Many of the known reactions occur at highly electropositive metals and are likely thermodynamically driven through the formation of strong M-O bonds. However there is extremely limited mechanistic evidence for how these dehydration or deoxygenation events occur.