Phosphine complexes of cobalt

The introduction of alkyl phosphine complexes of cobalt carbonyl as hydroformylation catalysts was reported to have a significant effect on product composition (50, 51). Slaugh and Mullineaux (52) reported that hexanol with a 91% linear distribution was formed by the hydroformylation of 1-pentene at 150°C, 500 psi, H2/CO 2.0, catalyst [Co2(CO)8 + 2(n-C4H9)3P]. Under the same conditions except at a temperature of 190°C, the n-hexanol was 84% of the hexyl alcohol produced. 

Table 99 Preparations Some 1,1-Dithio- and Diseleno-phosphinate Complexes of Cobalt...

As was shown in the preceeding section, tertiary phosphines are capable of promoting the formation of dusters of the electron-rich transition metals. At the same time, they are able to suppress the formation of metal pnictides or chalco-genides that is always observed in the reaction of phosphine complexes of cobalt or nickel chlorides with E(SiMe3)2 (E = PPh, AsPh, S, Se). 

Most hydroformylation investigations reported since 1960 have involved trialkyl or triarylphosphine complexes of cobalt and, more recently, of rhodium. Infrared studies of phosphine complex catalysts under reaction conditions as well as simple metal carbonyl systems have provided substantial information about the postulated mechanisms. Spectra of a cobalt 1-octene system at 250 atm pressure and 150°C (21) contained absorptions characteristic for the acyl intermediate C8H17COCo(CO)4 (2103 and 2002 cm-1) and Co2(CO)8. The amount of acyl species present under these steady-state conditions increased with a change in the CO/ H2 ratio in the order 3/1 > 1/1 > 1/3. This suggests that for this system under these conditions, hydrogenolysis of the acyl cobalt species is a rate-determining step. 

One of the most interesting alternatives to the Shirakawa catalyst has been the systems disclosed by Luttinger 22-23) and later elaborated by Lieser et al. 24). The tris(2-cyanoethyl)phosphine complex of nickel chloride reacts with sodium boro-hydride to produce a catalyst system capable of polymerizing acetylene in solutions in either alcohol or, quite remarkably, water. A more efficient catalyst is obtained by replacing the nickel complex with cobalt nitrate. Interest in Luttinger polyacetylene seems to have waned in the last few years. 

Table 49 Structures Some Phosphine Oxide Complexes of Cobalt(II)...

Cyclopentadienyl complexes of cobalt exist mainly in three oxidation states Co Co, and Co. Co is represented by complexes of the type CpCoL2, where L is CO, alkene, alkyne, or phosphine. Apart from derivatives of cobaltocene, half-sandwich complexes (see Half-sandwich Complexes) (CpCoX)2 or CpCoLX with cobalt in oxidation state II are known. CpCo occurs in various CpCoL Xm compositions (Section 9.2). 

Apart from the compounds already mentioned, vanadium, manganese, and cobalt chlorides, tetra-alkoxy derivatives of titanium, acetylacetonates of V, Cr, Mo, Mn, and Ni, Cp derivatives of Zr and Nb, and triphenyl phosphine complexes of Ti and Fe were found to be active. Later lanthanide complexes were included in the list of dinitrogen-reducing systems, the most effective being compounds of samarium and yttrium. 

The use of Co2(CO)g as a hydrogenation catalyst in the absence of CO generally results in decomposition to metal. Phosphine derivatives of cobalt carbonyl complexes, which are more robust hydrogenation catalysts, will be discussed next. 

Reaction of binuclear complexes of rhodium (O) with hydrogen to regenerate hydridorhodium (I) complexes under hydroformylation conditions has been established.The extension of these arguments to complexes with triphosphines or polymers with a high density of phosphine anchor-site has been made for complexes of cobalt and rhodium. ... 

Complexes of cobalt have also been used as catalysts for the oxidation of tertiary phosphines with molecular oxygen. In methanol solvent the compound Co2(CN)4(PMe2Ph)502 reacts with PMe2Ph, converting it into the oxide.Since the oxygen compound is readily formed again from the product complex Co(CN)2(PMe2Ph)3, a catalytic cycle can be obtained (28, 29) for the phosphine oxidation. 

Interest has again continued in studies of the generation and reactivity of phosphinidene species (RP ), phosphorus analogues of carbenes, and this area has been reviewed. A review has also appeared of the use of terminal phosphinidene complexes in the formation of phosphorus-element bonds. Further studies of phosphanylidene-a -phosphoranes, RP = PR3, (regarded as phosphine-complexed phosphinidenes, i.e., ArP -PRs), have shown that the species Me3P=PAr (Ar = Mes or 2,6-Mes2C6H3) are good vehicles for the delivery of the terminal phosphinidene moiety ArP to zirconium and vanadium sites. Terminal phosphinidene complexes of cobalt, ruthenium, rhodium and osmium, and iridium, have also been... 

Cobalt phosphine complexes of the type CpCo(diphosphine) have been known since 1986 to be molecular electrocatalysts for hydrogen production [80]. Catalysis by this family of compounds occurs through a [CpCo (diphosphine)H] intermediate that is only reduced at relatively large overpotentials. This limitation has led to... 

A range of nine Schiff Base and related complexes of cobalt(II) with up to seven phosphines or phosphites interacting in the axial position have been studied in CH2CI2 solution(6) (Table II). Their EPR spectra were recorded at 77 K and at about 200 K. The frozen solution spectra exhibited three well separated g-features at ca. g = 2.14-2.47, 2.11-2.18 and 2.02. The two g-features at higher field exhibited well resolved cobalt (hfs) and each line was split into two by further coupling to one phosphorus atom. Resolution on... 

HCo(N2)(PPh3)3 has been used to oligomerize propylene [577]. 2-Methyl-l-pentene is the main product. The addition of 3 moles of tri-n-butyl-phosphine/ mol of cobalt complex considerably reduced the oligomerization rate. A mechanism as shown in the following reactions is proposed (5771 ... 

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