Phosphine complexes with nickel

Ellis, J.W., Harrison, K.N., Hoye, P.A.T., Orpen, A.G., Pringle, P.G., and Smith, M.B., Water-soluble tris(hydroxymethyl)phosphine complexes with nickel, palladium, and platinum. Crystal structure of Pd P(CH2OH)3 4].cntdot.CH3, Inorg. Chem., 31, 3026, 1992. 

A large number of nickel(O) phosphine complexes with rj2-bonded unsaturated organic molecules have been reported. Here we will review relevant examples of complexes with f 2-bonded molecules which contain a number of Ni—C bonds not exceeding the number of bonds from nickel to non-carbon atoms (usually phosphorus). The early examples (up to 1972) of complexes with alkenes have been extensively reviewed.11... 

Hydrides of Ni(I) and Ni(II) are known (37). A Ni(II) hydride appears to be an intermediate in the catalysis of olefin isomerization by phosphine complexes of nickel (61). Dilworth (62) has pointed out that stable hydride species are not obtained in model complexes with sulfur ligands. However, they may be possible within the confines of a protein chelate. 

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. 

The complexes [Ni(acrylonitrile)2] and [Ni(COD)2] catalyze [3 + 2] cycloadditions of (26) with electron deficient l,2 isubstituted alkenes to afford 2,3- or 3,4-disubstituted methylenecyclopentanes such as (32) and (33). Similar reactions have been reported by use of tertiary phosphine complexes of nickel(0) and palladium(0) (equation 13 and Table 1). The reaction proceeds regioselectively to give (32) or (33) depending on both the alkene stmcture and catalytic system. Reactions catalyzed by phos-phine-palladium(0) complexes afford only products of the type (32), via selective cleavage of the C(2)— C(3)bondof(26). 

Ditertiary phosphines also form planar complexes with nickel(II). Ni((C6H5)2PCH2CH2P(C6H5)2)Br2 (8) and Ni(Et2P-CH2-CH2-PEt2)Br2 (99) have been prepared and are diamagnetic and apparently planar. 

Numerous complexes of nickel(II) and nickel(O) catalyze the addition of the Si-H bond to olefins. Among such catalysts are nickel-phosphine complexes, e.g., Ni(PR3)2X2 (where X=C1, I, NO3 R=alkyl and aryl), Ni(PPh3)4, and Ni-(CO)2(PPh3)2, as well as bidentate complexes of NiCl2-(chelate) and Ni(acac)2L (I phosphine), and Ni(cod)2(Pr3)2 [1-5]. A characteristic feature of nickel-phosphine-catalyzed olefin hydrosilylation is side reactions such as H/Cl, redistribution at silicon and the formation of substantial amounts of internal adducts in addition to terminal ones [69]. Phosphine complexes of nickel(O) and nickel(II) are used as catalysts in the hydrosilylation of olefins with functional groups, e.g., vinyl acetate, acrylonitrile [1-4], alkynes [70], and butadiynes [71]. 

Phosphine complexes of nickel are used as catalysts in the hydrosilylation of olefins with functional groups, such as vinyl acetate, acrylonitrile, and methylacrylate, as well as in the hydrosilylation of acetylene derivatives. 

A proposed mechanism [9] for the hydrosilylation of olefins catalyzed by platinum(II) complexes (chloroplatinic acid is thought to be reduced to a plati-num(II) species in the early stages of the catalytic reaction) is similar to that for the rhodium(I) complex-catalyzed hydrogenation of olefins, which was advanced mostly by Wilkinson and his co-workers [10]. Besides the Speier s catalyst, it has been shown that tertiary phosphine complexes of nickel [11], palladium [12], platinum [13], and rhodium [14] are also effective as catalysts, and homogeneous catalysis by these Group VIII transition metal complexes is our present concern. In addition, as we will see later, hydrosilanes with chlorine, alkyl or aryl substituents on silicon show their characteristic reactivities in the metal complex-catalyzed hydrosilylation. Therefore, it seems appropriate to summarize here briefly recent advances in elucidation of the catalysis by metal complexes, including activation of silicon-hydrogen bonds. 

Treatment of the amino-phosphine complex with H2 generates a hydrido nickel complex with a pendant ammonium substituent. Catalysis, which was established electrochemicaUy, is proposed to involve oxidation of the Ni(ll) hydride to a Ni(III) hydride, a process which enhances the acidity of the hydrido ligand sufficiently to allow its deprotonation by the pendant amine (Fig. 12.12). This proton transfer gives an easily oxidized Ni(I) intermediate. Catalysis of the H2 oxidation by mononuclear nickel complexes foreshadows the preparation of related bimetallic species exhibiting hydrogenase reactivity. 

Studies of the dimerization of propylene in the absence of catalytic systems based on phosphine complexes of nickel(l) have been reported [607]. Formation of active complexes containing alkylaluminum compounds like AlEt, Et2AlCl, and Et3Al2Cl3 with NiClfPPhjlj have been observed for propylene dimerization [609]. NifPPhjlzCl or NiCl(PPh3)3 and the BF3-OEt2 system are also efficient for the conversion of propylene to dimers. Addition of Bronsted acids increases the catalytic activity. 

Bartik, T. Bunn, B.B. Bartik, B. Hanson, B.E. (1994) Synthesis, reactions, and catalytic chemistry of the water-soluble chelating phosphine l,2-bis[bis(m-sodiosulfonatophenyl)-phosphinojethane (dppets) complexes with nickel, palladium, platinum, and rhodium, Inorg. Chem., 33, 164-9. 

The first polyphosphino maeroeyeles designed speeifieally for use as transition metal binders were reported in 1977 in back-to-baek eommunications by Rosen and Kyba and their eoworkers. The maeroeyeles reported in these papers were quite similar in some respeets, but the synthetic approaches were markedly different. DelDonno and Rosen began with bis-phosphinate 18. Treatment of the latter with Vitride reducing agent and phosphinate 19, led to the tris-phosphine,20. Formation of the nickel (II) complex of 20 followed by double alkylation (cyclization) and then removal of Ni by treatment of the complex with cyanide, led to 21 as illustrated in Eq. (6.15). The overall yield for this sequence is about 10%. 

In a Kumada-Corriu reaction, an aryl halide is oxidatively coupled with a homogeneous nickel(ll)-phosphine catalyst [2], This species reacts with a Grignard reagent to give biaryl or alkylaryl compounds. Later, palladium-phosphine complexes were also successfully applied. By this means, stereospecific transformations were achieved. 

Nickel(II) salts are able to catalyze the coupling of Grignard reagents with alkenyl and aryl halides. A soluble 6 -phosphine complex, Ni(dppe)2Cl2, is a particularly effective catalyst.266 The main distinction between this reaction and Pd-catalyzed cross... 

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