Phosphine complexes cobalt

Other examples are [Rh2(CO)2(CsMes)2(/i-Te)] (186), reported by Herrmann (177) from the reaction between [Rh2(C5Me5)2(/i-CO)2] and elemental tellurium, which is assumed to contain a bent, two-coordinate tellurium analogous to that found in 164. Also known is the phosphine cobalt complex [Co2(PMe3)6(/i-Te)2] (187), prepared by Klein (178) from the reaction between the Zintl anion [SnTe4]4 and [CoCl(PMe3)3]. The tellurium... 

A special kind of oxidative addition occurs between phosphine cobalt hydride complexes and boron halides ... 

Yong et al. developed a cobalt-catalyzed [2+2+2] cyclotrimerization of terminal alkynes in good yields in aqueous media (80/20 mixture of water and ethanol) at room temperature. A cyclopentadienyl cobalt complex bearing a pendant phosphine ligand was used as a catalyst (Eq. 4.59). The cyclotrimerization of internal alkynes resulted in lower yields and required an elevated temperature, most likely due to steric interactions. For example, cyclotrimerization of 2,5-dimethyl-3-hexyne gave hexaisopropylbenzene in 51% yield and the reaction of diphenylethyne resulted in a 47% yield of hexaphenylbenzene.112... 

With [P(C6H5)3] > 0.06 M the CO evolution is first-order with respect to the cobalt complex and zero-order in phosphine, indicating that as in the case of the acyl carbonyls, the observed rate coefficient is. ... 

Modified cobalt complexes of the type frans-Co2(CO)6(phosphine)2 are promising candidates for certain transition metal-catalyzed reactions, in particular for the hydroformylation of long-chained olefins [117]. A series of complexes Co2(CO)6[P(alkyl) (aryl)m]2 (n 0,1,2,3 m S - n) was synthesized and used for solubility measurements. Since the basicity of phosphines affects the catalytic activity, use of fluorous substituents might induce unexpected changes in the activity. Therefore, also derivatives with an additional ethyl spacer between the fluorous group and the phosphine moiety were examined (Sect. 3.1). 

It should be recognized that the stability of cobalt complexes under carbon monoxide can be enhanced by the addition of ligands, as is the case for phosphine-modified cobalt hydroformylation catalysts (57, 58). The stability will also probably depend on properties of the solvent employed. Nevertheless, the plot shown in Fig. 4 appears to be quite useful for assessing long-term cobalt stability under H2/CO in the absence of strongly coordinating solvents or ligands. 

Both the rhodium and the cobalt complexes catalyze olefin isomerization as well as olefin hydroformylation. In the case of the rhodium(I) catalysts, the amount of isomerization decreases as the ligands are altered in the order CO > NR3 > S > PR3. When homogeneous and supported amine-rhodium complexes were compared, it was found that they both gave similar amounts of isomerization, whereas with the tertiary phosphine complexes the supported catalysts gave rather less olefin isomerization than their homogeneous counterparts (44, 45). 

C1bHi5As, Arsine, triphenyl-iron complex, 26 61 C H 5OjP, Triphenyl phosphite ruthenium complex, 26 178 CuHijP, Phosphine, triphenyl-cobalt complex, 26 190—197 cobalt-gold-ruthenium, 26 327 gold complex, 26 90, 325, 326 gold-manganese complex, 26 229 iridium complexes, 26 117-120, 122-125, 201, 202... 

C18H18, Benzene, l,3-butadiene-l,4-diyl-bis-cobalt complex, 26 195 C,8H33P, Phosphine, tricyclohexyl iron complex, 26 61 nickel complexes, 26 205, 206 C H 7OP, Benzenemethanol, 2-(diphenyl-phosphino)-... 

PChH , Phosphine, dimethylphenyl-iron complex, 26 61 PC, Hn, Phosphine, diphenyl-manganese complex, 26 158, 226-230 ruthenium complex, 26 264 PC 3H27, Phosphine, tributyl-iron complex, 26 61 PC,H , Phosphine, methyldiphenyl-iron complex, 26 61 PC, H Phosphine, triphenyl-cobalt complex, 26 190-197 cobalt-gold-ruthenium, 26 327... 

Industrial Applications. Several large scale industrial processes are based on some of the reactions listed above, and more are under development. Most notable among those currently in use is the already mentioned Wacker process for acetaldehyde production. Similarly, the production of vinyl acetate from ethylene and acetic acid has been commercialized. Major processes nearing commercialization are hydroformylations catalyzed by phosphine-cobalt or phosphine-rhodium complexes and the carbonylation of methanol to acetic acid catalyzed by (< 3P) 2RhCOCl. 

This complex has four strong, sharp IR bands arising from the bound C02 at 1650, 1280, 1215 and 745 cm-1. A second structurally characterized example of this enhancement of the electrophilic C02 character is provided by the iridium bis(chelating phosphine) complex (P2)2IrC02Me, which shows similar features to the cobalt complex above. There are many other systems for which this mode of coordination is proposed and an extended discussion of these is available.149... 

The hydroformylation of conjugated dienes with unmodified cobalt catalysts is slow, since the insertion reaction of the diene generates an tj3-cobalt complex by hydride addition at a terminal carbon (equation 10).5 The stable -cobalt complex does not undergo facile CO insertion. Low yields of a mixture of n- and iso-valeraldehyde are obtained. The use of phosphine-modified rhodium catalysts gives a complex mixture of Cs monoaldehydes (58%) and C6 dialdehydes (42%). A mixture of mono- and di-aldehydes are also obtained from 1,3- and 1,4-cyclohexadienes with a modified rhodium catalyst (equation ll).29 The 3-cyclohexenecarbaldehyde, an intermediate in the hydrocarbonylation of both 1,3- and 1,4-cyclo-hexadiene, is converted in 73% yield, to the same mixture of dialdehydes (cis.trans = 35 65) as is produced from either diene. 

The iron compound readily sublimes and yields well-formed, black lustrous crystals. The cobalt complex will also readily sublime, but dependent upon the temperature at which the crystals are formed, they can be either black or brown in color. The crystal structures of both the cobalt and iron complexes have been determined.3 The nickel complex sublimes only in small amounts with difficulty. All three complexes are unstable to air and water, and the nickel complex readily undergoes thermal decomposition above 100°C. All three compounds will also readily form complexes with a variety of donor ligands such as tertiary arsines or phosphines. The nickel compound usually forms 2 1 adducts such as [(C6HS )3P]2Ni(NO)I, while the iron and cobalt complexes often undergo disproportionation.5... 

An interesting example of 1,2-diketone reduction using methods other than metal/phosphine catalysts is the use of a cobalt complex, in combination with quinine, for the reduction of benzil218. In this example the product was formed in 78% e.e. (Scheme 43). 

Three commercial homogeneous catalytic processes for the hydroformyla-tion reaction deserve a comparative study. Two of these involve the use of cobalt complexes as catalysts. In the old process a cobalt salt was used. In the modihed current version, a cobalt salt plus a tertiary phosphine are used as the catalyst precursors. The third process uses a rhodium salt with a tertiary phosphine as the catalyst precursor. Ruhrchemie/Rhone-Poulenc, Mitsubishi-Kasei, Union Carbide, and Celanese use the rhodium-based hydroformylation process. The phosphine-modihed cobalt-based system was developed by Shell specih-cally for linear alcohol synthesis (see Section 7.4.1). The old unmodihed cobalt process is of interest mainly for comparison. Some of the process parameters are compared in Table 5.1. 

In the sixties it was recognized that ligand substitution on the cobalt carbonyl might influence the performance of the catalyst. It has been found that aryl phosphines or phosphites have little influence in fact they may not even coordinate to cobalt under such high CO pressures. Tertiary alkyl phosphines, however, have a profound influence [5] the reaction is much slower, the selectivity to linear products increases, the carbonyl complex formed, HCoL(CO)3, is much more stable, and the catalyst acquires activity for hydrogenation. This process has been commercialized by Shell. As a result of the higher stability of the cobalt complex, the Shell process can be operated at lower pressures and higher temperatures (50-100 bar vs 200-300 bar for HCo(CO)4, 170°C vs 140°C). 

Many P(CH3)3 complexes of the first-row transition metals may be conveniently prepared by direct reaction with the appropriate anhydrous chromium (II), (III),3 cobalt(II),4 iron(II)s or hydrated iron(II),s nickel(II)4a>6,7 salt. The compound [(CH3)3P] 2FeCl2 is the starting material for a variety of phosphine iron complexes.4,8,9... 

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