Aspects of Homogeneous Carbon Monoxide FixationSelective Conversion of Carbonyl Ligands on (η₅-C₅H₅)Fe(CO)₃⁺ to C₂ Organic Compounds

Abstract

Procurement of transition metal catalysts that convert carbon monoxide and dihydrogen to organic molecules represents an important research objective of modern inorganic chemistry. Im petus for this research derives from the use of coal, a source of CO/H 2 synthesis gas mixtures, as a future source of petrochemi cals (1). Although heterogeneous catalysis in the FischerTropsch synthesis (2,3) of complex hydrocarbon mixtures from synthesis gas has long been established, homogeneous catalysis of these reactions would have the added advantage of a potentially high and manipulative product selectivity.A selective homoge neous catalytic synthesis of C 2 organics -especially C 2 -oxygenates such as ethylene glycol (4), acetaldehyde, and acetic acidwould provide a much desired coal-based source of organic feed stocks (1).One approach favored by us for the rational design of such catalysts first requires an understanding of reaction pathways by which ligated CO undergoes hydrogenation and subsequent syn thesis reactions (ie. chain growth of the C 1 ligand), before eliminating the desired organic molecule. Fully characterized organometallic complexes are used as model systems to collect this mechanistic information.Then more labile (and hopefully catalytic) systems are designed and tested. Limited mechanistic data is now available for stoichiometric conversion of CO ligands to the C2 organic compounds ethane Ç5,6^7), ethylene (6,8), acetaldehyde (9), methylacetate (10), and a coordinated enediol of glycolaldehyde (11). Clearly a need exists for more extensive information on CO fixation and synthesis reaction pathways.We have delineated viable coordinated ligand reactions and their attendant intermediates for the stoichiometric conversion of CO ligands selectively to the C2 organics ethane, ethylene, methyl (or ethyl) acetate, and acetaldehyde.We now outline results from three lines of research:(1) r^-Alkoxymethyl iron complexes CpFe(C0)2CH20R (2) are available by reducing coordinated CO on CpFe(C0)3+ (1) [Cp = n 5 -C5H5]. Compounds 2 then form r^-alkoxyacetyl complexes via migratory-insertion (i .e. CO