Nickel hydrido complex

In the first stage Lewis acids are absent and further hydroeyanation of the monoolefm products 3-PN 40 and 2M3BN 41 does not readily oeeur. The monoeyanation of butadiene is similar to HCN addition to olefins. An individual feature of hydrocyanation of conjugated dienes is the intermediate appearance of TT-allylic complexes 43, which participate in the successive carbon-carbon coupling. Equations (12) and (13) demonstrate the reaction of butadiene with the hydrido-nickel complex 42 leading to formation of nitrile 40 (a) and explain the generation of byproducts, i.e., the branched nitrile 41 via an alternative pathway (b) [68-70]. 

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. 

Several hydrido(phenoxo) complexes of nickel, trans-[NiH(OPh)L2] (6) (a L= P Prs b L = PCys c L = PBnj), have been prepared by the metathesis reaction of NaOPh with trans-[NiHClL2] (Eq. 6.6). The complex 6c was obtained as the phenol-solvated complex whose structure was determined by X-ray analysis [9]. An analogous platinum complex trans-[PtH(OPh)(PEt3)2] (7) was prepared by the reaction of trans-[PtH(N03)(PEt3)2] with NaOPh (Eq. 6.7). The complex 7 is air-stable but thermally sensitive and decomposes at room temperature. The structure was elucidated by X-ray analysis [10]. 

Because of its low acidity, hydrogen cyanide seldom adds to nonactivated multiple bonds. Catalytic processes, however, may be applied to achieve such additions. Metal catalysts, mainly nickel and palladium complexes, and [Co(CO)4]2 are used to catalyze the addition of HCN to alkenes known as hydrocyanation.l67 l74 Most studies usually apply nickel triarylphosphites with a Lewis acid promoter. The mechanism involves the insertion of the alkene into the Ni—H bond of a hydrido nickel cyanide complex to form a cr-alkylnickel complex173-176 (Scheme 6.3). The addition of DCN to deuterium-labeled compound 17 was shown to take place... 

Recently, the nickel-catalyzed isomerization of geraniol and prenol has been investigated in homogeneous and two-phase systems. The best results with respect to activity and selectivity have been obtained in homogeneous systems with a bis(cy-cloocta-l,5-diene)nickel(0)/l,4-bis(diphenylphosphanyl)butane/trifluoroacetic acid combination. Catalyst deactivation occurs in the course of the reaction owing to coordination of the aldehyde group that is formed to the nickel species or as a result of protonolysis of hydrido or (jr-allyl)nickel complexes [2],... 

By the late 1950s, Chatt and Bernard Shaw had succeeded in preparing several alkyl-, aryl- and hydrido-metal complexes of the nickel triad. Because of our mutual interest in the kinetic trans effect of platinum(ii) complexes, Chatt and I decided to examine the rates of ligand substitution of these new organometallics. Shaw prepared the compounds and Harry Gray did the kinetic studies. Years later Chatt gave the following account of why the research was so rapidly accomplished. 

C9H14O, 2-Cyclopentene-l-one, 2,3,4,5-tetramethyl-, 29 195 C,H,j02, 4W-pyran-4-one, 2,3,5,6-tetra-hydrido-2,3,5,6-tetramethyl-, 29 193 QHjiOjP, Isopropyl phosphite, nickel complex, 28 101... 

PO2WC2SH21, Tungsten, dicarbonyl(T) -cyclopentadienyl)hydrido(triphenyl-phosphine)-, 26 98, 28 7 PO3C3H, Trimethyl phosphite, cobalt and rhodium complexes, 28 283, 284 iron complexes, 26 61, 28 171, 29 158 nickel complex, 28 101 P03C,H,5, Triethyl phosphite, iron complexes, 26 61, 28 171, 29 159 nickel complexes, 28 101,104-106 P03C,H2, Isopropyl phosphite, nickel complex, 28 101... 

OjPCgHii, Phosphonous acid, phenyl-, dimethyl ester, nickel complex, 28 101 O2PWC25H21, Tungsten, dicarbonyl( f -cyclopentadienyl)hydrido(triphenylphos-phine)-, 26 98... 

Organometallic Reactions Involving Hydrido-Nickel, -Palladium, and -Platinum Complexes. 

The reaction of [Ni(ethene)3] with a hydride donor such as trialkyl(hydrido)-aluminate results in the formation of the dinuclear anionic complex [ Ni(eth-ene)2[2l 11 [22]. The nickel(O) centers in this complex are in a trigonal planar environment of two ethene molecules and a bridging hydride ion, with the ethene carbons in the plane of coordination. The two planes of coordination within the dinuclear complex are almost perpendicular to each other, and the Ni-H-Ni unit is significantly bent, with an angle of 125° and a Ni-Ni distance of 2.6 A [22],... 

The anion [Fe3Co(CO)12] has recently been reported to be prepared by Chini from the redox reaction of Fe3(CO)12 with Co(CO)infrared spectra indicate a Co4(CO)i2 structure with nickel in the basal plane (234). 

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 borohydride reduction of nickel(II) compounds in protic solvents may result either in the formation of nickel(O) complexes66,71 or in the formation of hydrido complexes of nickel(II). Two easily interconvertible isomers, Ni(triphos)2, have been obtained in the reduction of Ni(N03)2 in the presence of the ligand triphos, but their structures are not known with certainty. 

By reducing hydrated nickel(II) nitrate with NaBHt, in the presence of the tetradentate tripodal ligand np3 (equation 80), the complex [Ni(np3)j (66) has been obtained.263 Complex (66) undergoes oxidative reaction with HC104 or HBF4 to afford the nickel(II) hydrido complex [NiH ps)]-1".264 It also reacts with CO to give the carbonyl derivative263 and with white... 

Some complexes of nickel(0) with phosphines have been found to react with several Bronsted acids in non-aqueous solvents and under an inert atmosphere to give hydrido complexes of nickel(I) and nickel(II) (equations 85-87).264,268,269... 

When nickel(II) salts containing a coordinating anion (halide and pseudohalide) are reacted with NaBH4 in the presence of np3, trigonal bipyramidal nickel(I) complexes of the type [NiXnp3], in which the coordinating anion occupies die axial position, 39,340 are obtained. When nickel(II) salts with poorly coordinating anions are used, non-stoichiometric hydrido complexes of nickel(II) are obtained (equations 108 and 109). 

A few representative examples of simple organometallic compounds of nickel(II) including carbonyl and hydrido compounds are reported here. A more complete listing of such types of compound is given in Comprehensive Organometallic Chemistry (vol. 6, p. 37) and references therein. Selected structural data for organometallic nickel(II) complexes with monodentate phosphines are reported in Table 61. 

The hydrido complexes are diamagnetic, and are square planar or five-coordinate. Their stability, in general, increases with the number of coordinated phosphines. In the complex [Ni(BH4)(H)(PCy3)2] (153) the nickel atom is coordinated in the equatorial positions by two hydrogens of the borohydride and by one hydride anion. 

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