Nickel-phosphine catalysts

Dibutylbenzene has been prepared from cyclohexanone by tedious, multistep procedures.3 4 The present one-step method is based on the selective cross-coupling of a Grignard reagent with an organic halide in the presence of a phosphine-nickel catalyst.3... 

The couplings are usually exothermic, and care must be taken not to add the phosphine-nickel catalyst to a mixture of a Grignard reagent and an organic halide, particularly in a large-scale preparation. For example the addition of a small amount of [Ni(dppp)Cl2] to a mixture of vinyl chloride and 4-chlorophenylmagnesium bromide in ethyl ether at 0° led, after a few minutes induction period, to an uncontrollable, violent reaction. 

In the reaction of tert-butyl Grignard reagent and -bromostyrene, (dppf)NiCl2 was the most effective catalyst in allowing the reaction to proceed cleanly and give only the desired product. Other phosphine-nickel catalysts afforded a varying amount of the iso-butylated product [Eq. (125) 301]. 

Addition to Multiple Bonds. 3,3-Dimethylcyclopropene undergoes cyclodimerization and cyclotrimerization on treatment with phosphine-palladium and phosphine-nickel, catalysts, providing a new route to a-trishomobenzene derivatives. ... 

Ylid nickel catalysts [Ni(0)/R3PCR CR"0/R3PCXY] not only show superior performance in the polymerization of acetylene as compared to phosphine nickel catalysts [Ni(0)/ R3PCR CR"0/R3P],- in highly polar solvents the normalized polymerization activity (mol acetylene/mol Ni h bar) probably exceeds that of all known nickel systems. (Fig. 1) However, catalyst activity alone is not sufficient to make this chemistry useful, unless all of the technologically unattractive properties of classical polyacetylene (URPAC) can be overcome. (Tab. 5)... 

It has been found that certain 2 + 2 cycloadditions that do not occur thermally can be made to take place without photochemical initiation by the use of certain catalysts, usually transition metal compounds. Among the catalysts used are Lewis acids and phosphine-nickel complexes.Certain of the reverse cyclobutane ring openings can also be catalytically induced (18-38). The role of the catalyst is not certain and may be different in each case. One possibility is that the presence of the catalyst causes a forbidden reaction to become allowed, through coordination of the catalyst to the n or s bonds of the substrate. In such a case, the... 

Several nickel catalysts for the carbonylation of methanol have been reported,54"57 and an IR study has been described.58 The carbonylation of MeOH to form MeOAc and HOAc was studied using phosphine-modified Nil2 as the metal catalyst precursor. The reaction was monitored using a high-pressure, high-temperature, in situ Cylindrical Internal Reflectance FTIR reactor (CIR-REACTOR). 

Reaction of 3 with 1 equivalent of a phosphine results in formation of "phosphine-modified catalysts (4). The complex formed from 7r-allyl-nickel chloride, tricyclohexylphosphine, and methylaluminum dichloride (4a) has been isolated and its structure determined crystallographically (see Fig. 1) (57) The phosphine is bonded to the nickel atom, and interaction with the Lewis acid takes place via a chlorine bridge. The bridging chlorine atom is almost symmetrically bound to both the nickel... 

Phosphine-free catalysts of this type are of low thermal stability, and the exchange reaction is performed preferentially in the presence of olefins. /ra i-Pentachlorophenylbis(triphenylphosphine) nickel chloride undergoes a similar reaction (68). 

Among transition metal complexes used as catalysts for reactions of the above-mentioned types b and c, the most versatile are nickel complexes. The characteristic reactions of butadiene catalyzed by nickel complexes are cyclizations. Formations of 1,5-cyclooctadiene (COD) (1) and 1,5,9-cyclododecatriene (CDT) (2) are typical reactions (2-9). In addition, other cyclic compounds (3-6) shown below are formed by nickel catalysts. Considerable selectivity to form one of these cyclic oligomers as a main product by modification of the catalytic species with different phosphine or phosphite as ligands has been observed (3, 4). 

Some nickel catalysts supported on phosphinated silica were shown to be superior to their homogeneous analogs (224). 

The isomer distribution of the nickel catalyst system in general is similar qualitatively to that of the Rh catalyst system described earlier. However, quantitatively it is quite different. In the Rh system the 1,2-adduct, i.e., 3-methyl-1,4-hexadiene is about 1-3% of the total C6 products formed, while in the Ni system it varies from 6 to 17% depending on the phosphine used. There is a distinct trend that the amount of this isomer increases with increasing donor property of the phosphine ligands (see Table X). The quantity of 3-methyl-1,4-pentadiene produced is not affected by butadiene conversion. On the other hand the formation of 2,4-hexadienes which consists of three geometric isomers—trans-trans, trans-cis, and cis-cis—is controlled by butadiene conversion. However, the double-bond isomerization reaction of 1,4-hexadiene to 2,4-hexadiene by the nickel catalyst is significantly slower than that by the Rh catalyst. Thus at the same level of butadiene conversion, the nickel catalyst produces significantly less 2,4-hexadiene (see Fig. 2). 

In the literature there are many reports of the formation of active catalyst for the 1 1 codimerization or synthesis of 1,4-hexadiene employing a large variety of Co or Fe salts, in conjunction with different kinds of ligands and organometallic cocatalysts. There must have been many structures, all of which are active for the codimerization reaction to one degree or another. The scope of the catalyst compositions claimed to be active as the codimerization catalysts is shown in Table XV (69-82). As with the nickel catalyst system discussed earlier, the preferred Co or Fe catalyst system requires the presence of phosphine ligands and an alkylaluminum cocatalyst. The catalytic property can be optimized by structural control of these two components. 

Tillack and co-workers developed a rhodium-catalyzed asymmetric hydrosilylation of butadiyne 258 to afford allenylsilane 260 (Scheme 4.67) [106]. Among more than 30 chiral phosphine ligands investigated, the highest enantioselectivity was observed when the catalyst was prepared from [Rh(COD)Cl]2 (1 mol%) and (S,S)-PPM 259 (2 mol%) to afford the optically active allene 260 with 27% ee. Other metals such as Ir, Pd, Pt or Ni were less effective for example, a nickel catalyst prepared from NiCl2 and (R,R)-DIOP 251 or (S,S)-PPM 259 gave the allene 260 with 7-11% ee. 

While the reductive elimination is a major pathway for the deactivation of catalytically active NHC complexes [127, 128], it can also be utilized for selective transformations. Cavell et al. [135] described an interesting combination of oxidative addition and reductive elimination for the preparation of C2-alkylated imida-zohum salts. The in situ generated nickel catalyst [Ni(PPh3)2] oxidatively added the C2-H bond of an imidazolium salt to form a Ni hydrido complex. This complex reacts under alkene insertion into the Ni-H bond followed by reductive elimination of the 2-alkylimidazolium salt 39 (Fig. 14). Treatment of N-alkenyl functionalized azolium salts with [NiL2] (L = carbene or phosphine) resulted in the formation of five- and six-membered ring-fused azolium (type 40) and thiazolium salts [136, 137]. 

The effect of tin compounds, especially tetra-alkyl and tetra-aryl tin compounds, is similar to that of phosphine, though lower temperature and pressure are required for the catalyst s optimum activity. Tin can promote the activity of the nickel catalyst to a level that matches that of rhodium under mild conditions of system pressure and temperature e.g. 400 psig at 160 C. The tin-nickel complex is less stable than the phosphine containing catalyst. In the absence of carbon monoxide and at high temperature, as in carbonyl-ation effluent processing, the tin catalyst did not demonstrate the high stability of the phosphine complex. As in the case of phosphine, addition of tin in amounts larger than required to maintain catalyst stability has no effect on reaction activity. 

In the case of phosphine, the active catalyst is presumably either bisphosphine dicarbonyl or the phosphine tricarbonyl complex. Kinet-ically the bis-phosphine nickel complex cannot be the predominant species. However, in the presence of very high phosphine concentration it may have an important role in the catalyst cycle. After ligand loss and methyl iodide oxidative addition, both complexes presumably give the same 5 coordinate alkyl species. 

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