Mixed carbon-oxygen coordination

Our results for the three coordination modes considered here indicate that the CO2 molecule prefers to adopt either a mixed carbon-oxygen coordination (III) or a pure coordination ( ) to the metal center, while a pure carbon coordination ( ) appears to be unfavorable. Further, the results suggest a rather weak CO - transition metal bond consistent with the low stability of adsorbed CO and CO2 in molecular complexes. 

Figure 5. Coordination of CO to Ni via mixed carbon and oxygen coordination (a) orbitals forming a covalent bond between Ni and C (panel A) orbitals of a oxygen lone pair forming a dative bond to Ni (panel B) (b) schematic diagram of the many-electron wave function.

It is necessary to underline that mixing a carbonaceous support with a precursor containing carbon, oxygen, nitrogen, and hydrogen with appropriate coordination to the transition metal, two parallel reaction steps coexist during the pyrolysis treatment. The first one is the graphitization of the support until the structure collapses... 

The aldehyde or ketone, when treated with aluminum triisopropoxide in isopropanol as solvent, reacts via a six-membered cyclic transition state 4. The aluminum center of the Lewis-acidic reagent coordinates to the carbonyl oxygen, enhancing the polar character of the carbonyl group, and thus facilitating the hydride transfer from the isopropyl group to the carbonyl carbon center. The intermediate mixed aluminum alkoxide 5 presumably reacts with the solvent isopropanol to yield the product alcohol 3 and regenerated aluminum triisopropoxide 2 the latter thus acts as a catalyst in the overall process ... 

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