Formyl transition metal compounds

Indirect electrosynthesis of reactive formyl transition metal compounds involves an initial step of reduction of metal carbonyls to radicals followed by transfer of a hydrogen atom from trialkyltin hydrides190. Electroreduction of metal carbonyls yields products of dimerization and loss of CO from the radical anion. Electroreduction in the presence of R3SnH yields the formylmetalcarbonyls ... 

Transition metal complexes have been used in a number of reactions leading to the direct synthesis of pyridine derivatives from acyclic compounds and from other heterocycles. It is pertinent also to describe two methods that have been employed to prepare difficultly accessible 3-alkyl-, 3-formyl-, and 3-acylpyridines. By elaborating on reported194,195 procedures used in aromatic reactions, it is possible to convert 3-bromopyridines to products containing a 3-oxoalkyl function196 (Scheme 129). A minor problem in this simple catalytic process is caused by the formation in some cases of 2-substituted pyridines but this is minimized by using dimethyl-formamide as the solvent.196... 

Abstract Development in the field of transition metal-catalyzed carbonylation of epoxides is reviewed. The reaction is an efficient method to synthesize a wide range of / -hydroxy carbonyl compounds such as small synthetic synthons and polymeric materials. The reaction modes featured in this chapter are ring-expansion carbonylation, alternating copolymerization, formylation, alkoxycarbonylation, and aminocarbonylation. 

The intrinsic low thermodynamic stability of most formyl derivatives of transition metals (with respect to the decarbonylation product) is confirmed by the observation that when these compounds are prepared by an indirect route, they normally undergo decarbonylation. For example, a formyl derivative of iron(O) was synthesized by reacting [Fe(CO)4] " with acetic-formic anhydride [reaction (c)] however the resulting product [reaction (d)], decarbonylated slowly (ti/2 12 days at 25°C) ... 

Hydroformylation or oxosynthesis is a well-known homogeneous, transition metal catalyzed reaction which has known considerable and continuous development since its discovery by Otto Roelen in the laboratories of Ruhrchemie AG in 1938 [1], This reaction, which can be considered as the addition of a formyl group and hydrogen to a double bond, has been successfully applied in the industrial context by using two basic processes the homogeneous process where the rhodium or cobalt catalyst and the substrate are in the same phase (Shell, UCC, BASF, RCH processes) [2] and the aqueous/organic biphasic process where the water-soluble rhodium catalyst and the organic compounds are in two different phases (Ruhr-chemie/Rhone-Poulenc process) [3]. 

The reaction of CO2 with a metal hydride produces formate complexes M-0C(0)H, not formyl derivatives M-C(0)0H, and the insertion into M-C bonds gives the appropriate carboxylate compounds M-0C(0)R. In a similar fashion, the reactions with M-OH and M-OR (R = alkyl, aryl) generate the corresponding bicarbonate M-0C(0)0H and carbonate M-0C(0)0R species, respectively. The reaction of CO2 with a zinc hydroxide moiety is particularly important in biological systems, namely, for the reversible hydration of CO2 to HCOs catalyzed by Zn(ll) in carbonic anyhdrases. Moreover, it has been postulated that the insertion of CO2 into M-O bonds is essential in the co-polymerization of CO2 and epoxides and in the preparation of cyclic carbonates and polycarbo-In a similar vein, the insertion of CO2 into the M-N bond of both main group and transition metal... 

The reactivity of olefins toward electrophilic reagents is modified considerably on coordination to a transition metal. Cycloctatetraene, for example, is usually polymerized by electrophilic reagents. However, tricarbonyl(cyclo-octatetraene)iron undergoes a facile formylation in reasonable yield. The coordinated formyl compound XIX can be used in further synthetic transformations, as shown below, and the tricarbonyliron group readily removed by oxidation with ceric ion [Eq. (55) (Johnson el al., 1969, 1971)J. 

Besides phosphines and phosphites preferentially used as ligands in hydro-formylation, phosphoramidites have also been proposed. Phosphoramidites (sometimes also called phosphoroamidites) are a class of organic phosphorus compounds derived from phosphites in which the P-OR groups have been replaced by P-NR2 groups (Figure 2.31). Three different P-substituents produce a chiral (stereogenic) phosphorus atom. Phosphoramidites play a crucial role in the synthesis of nucleic acids [1] and have also been frequently considered as mono- or bidentate ligands in transition-metal catalysis [2]. 

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