Carbonyl phosphines coordination

The synthesis of acrylic acid or its ester (228) from ethylene has been investigated in AcOH from the standpoint of its practical production 12]. The carbonylation of styrene is a promising commercial process for cinnamate (229) production[207,213,214]. Asymmetric carbonylation of styrene with Pd(acac)2 and benzoquinone in the presence of TsOH using 2,2 -dimethoxy-6, 6 -bis(diphenylphosphino)biphenyl (231) as a chiral ligand gave dimethyl phenylsuccinate 230 in 93% ee, although the yield was not satisfactory, showing that phosphine coordination influences the stereochemical course of the oxidative carbonylation with Pd(II) salt[215]. 

Hydrido carbonyl phosphine complexes of the general formula CoH(CO)w-(PR3)4. are regarded as the catalysts in these reactions. The active species are probably hydrido complexes with lower coordination numbers formed by the loss of carbon monoxide or phosphine from these precursors. 

No detailed investigation of the reaction mechanism (kinetic measurements, etc.) was performed. The actual catalyst is probably the coordinatively unsaturated CoH(CO)2(PR3) species which may be formed by the loss of one ligand from both hydrido carbonyl phosphine complexes present in the reaction mixture ... 

Controlling the Number of Metal Sites to Which a Poly(tertiary phosphine) Coordinates in Tungsten Carbonyls... 

The carbethoxy tertiary phosphine Bu2P(CH2) C02Et (n — 1) forms an octahedral, cationic rhodium(III) complex (31), in which the carbonyl group coordinates to rhodium. Homologous ligands ( = 2, 3) from four-coordinate rhodium(II) complexes in which the ligands are only phosphorus bound.275... 

Among the complexes which may function in this way are pentacyano-cobaltate ion, iron pentacarbonyl, the platinum-tin complex, and iridium and rhodium carbonyl phosphines. It has been suggested that with tristriphenylphosphine Rh(I) chloride, a dihydride is formed and that concerted addition of the two hydrogen atoms to the coordinated olefin occurs (16). There are few examples of the homogeneous reduction of other functional groups besides C=C, C=C, and C=C—C=C penta-cyanocobaltate incidentally is specific in reducing diolefins to monoolefins. 

Mixed phosphite ester-phosphine coordinated acylcobalt carbonyl derivatives have also been prepared. Methyl(triphenylphosphine)cobalt tricarbonyl, which cannot be produced by a simple ligand replacement reaction, can be obtained by another method. Hieber and Lindner (21) found that bis(triphenylphosphine)dicobalt hexacarbonyl reacts with sodium amalgam to form sodium(triphenylphosphine)cobalt tricarbonyl and that this compound reacted with methyl iodide to form methyl-(triphenylphosphine)cobalt tricarbonyl. 

These reaetions are most commonly utilized for preparation of olefin coordination compounds (Table 6.11). Usually, the following ligands are substituted halogens, nitriles, isonitriles, carbonyls, phosphines, etc. 

The a-keto amides are less susceptible to hydrolysis and preparation of a-keto esters and acids are preferable for synthesizing various derivatives thereof. Various aryl iodides and bromides can be converted into a-keto esters on reactions with alcohols and carbon monoxide in the presence of a base such as tertiary amines or potassium acetate with catalytic amounts of tertiary phosphine-coordinated palladium complexes (Eq. 11).[42]-[46] jjjgjj yields of a-keto esters can be achieved only when iodide substrates are used. Double carbonylation of aryl bromides to a-keto esters can be accomplished with difficulty at much slower rates. Alkyl and benzyl iodides give no double carbonylation products. 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

---