Nickel complexes bipyridyl

Combination of nickel bromide (or nickel acetylacetonate) and A. A -dibutylnorephcdrinc catalyzed the enantioselective conjugate addition of dialkylzincs to a./Tunsaturated ketones to afford optically active //-substituted ketones in up to ca. 50% ee53. Use of the nickel(II) bipyridyl-chiral ligand complex in acetonitrile/toluenc as an in situ prepared catalyst system afforded the //-substituted ketones 2, from aryl-substituted enones 1, in up to 90% ee54. 

Into a Schlenk tube was placed Auf 1,5-cyclooctadiene)-nickeI(0) (2.6 mmol), 2,2 -bipyridyl (2.6mmol), 1,5-cyclooctadiene (0.2ml), DMF (4ml), and toluene (8 ml). The reaction mixture was heated to 80°C for 0.5 h under argon. The dibromide comonomers 623 and 634 dissolved in degassed toluene (8 ml molar ratio of dibromides to nickel complex 0.65) were added under argon to the DMF-toluene solution and the polymerization maintained at 80°C for 3 days in the dark. 2-Bromofluorene (molar ratio of dibromides to monobromide 0.1) dissolved in degassed toluene (1ml) was added and the reaction continued for 12 h. The polymers were precipitated by addition of the hot solution dropwise to an equivolume mixture of concentrated HC1, methanol, and acetone. The isolated polymers were then dissolved in toluene or dichlor-omethane and reprecipitated with methanol/acetone (1 1). The copolymers were dried at 80°C in vacuo. The isolated yields of copolymers 240a-c were 79-85%. 

Catalytic Enantioselective Conjugate Addition of Dialkylzincs to Enones. A chiral nickel complex modified with DBNE and an achiral ligand such as 2,2 -bipyridyl in acetonitrile/toluene is an highly enantioselective catalyst for the addition of dialkylzincs to enones. p-Substituted ketones with up to 90% ee are obtained (eq 23). The method is the first highly enantioselective catalytic conjugate addition of an oiganometallic reagent to an enone. 

The arylation reaction of primary and secondary amines has been investigated using nickel or palladium complexes as catalysts, and bromo- or chloroarenes as arylating agents. Among the complexes tested, the more efficient catalyst is the bis (bipyridyl) nickel (II) bromide, bipy2NiBr2, which affords for example high yields in the arylation of allylamine with /n-bromotrifluoromethylbenzene. The reduction of the haloarene, sometimes observed with the nickel complexes, becomes predominant with palladium catalysts whatever the complex used. 

Eisch et al. (24) performed a mechanistic study of the desulfurization of dibenzothiophene by a nickel(0)-bipyridyl complex and reported that a radical anion of the thiophene nucleus was formed and underwent C-S bond cleavage into S and an aromatic radical. In addition, they suggested that the oxidative reaction of the nickel(0)-bipyridyl complex toward dibenzothiophene had the characteristics of stepwise electron transfer rather than nucleophilic attack. However, no correlations occurred between the desulfurization rate and the reaction indexes of Fr(E), Fr(N), and Fr(R), as shown in Table II. The results suggested no evidence for either electron transfer or nucleophilic attack in this study. Moreover, the radical reaction was not... 

Little C—Se bond formation by palladium catalysis has been reported, although these reactions should be feasible considering the ability of palladium complexes to catalyze C—S, C—P, and C—As bond formation. However, nickel complexes have been used for carbon-selenium bond formation. In 1985, Cristau and co-workers used bis(bipyridyl)nickel(ll) bromide to form aryl selenides from aryl halides and sodium benzeneselenoate. ... 

Now that the regular features of affinity for metals have been reviewed, some interesting irregular features can be discussed. Selectivity for particular ions is dependent on such irregularities. The strong tendency of cupric ions to form planar complexes means that copper is uniquely sensitive to a type of steric effect imposed by bulky groups. Thus, in Table 11.2, the stability constants for the cupric complexes of bipyridyl, phenan-throline, and folic acid lie below those of the corresponding nickel complexes, which is contrary to the natural order discussed in Section 11.2. 

Desulfuration.1 This complex as such or in combination with 2,2 -bipyridyl (bpy) or triphenylphosphine (a NiCRAL) can effect desulfuration of heteroarenes. aryl thioethers, dithioketals, sulfoxides, or sulfones in DME or THF at 63° in 1.5-30 hours. NiCRA is sufficient for aryl thioethers, dithioketals, but NiCRALs are more efficient for desulfuration of heteroarenes. Yields can be comparable with those obtained with Raney nickel. 

Tetramethyl- or tetraphenyl- (cyclobutadiene)nickel dihalides undergo reductive ligand substitution with nitrogen donor ligands such as 2,2 -bipyridine or 1,4-diaza-1,3-dienes with the addition of sodium metal237. The 2,2/-bipyridyl ligand is readily displaced and reaction of this complex with a variety of olefins and alkynes leads to cycloaddition reactions with the cyclobutadiene ligand. 

Similarly, the complex 3 was formed from 3,3-dimethylcyclopropene and 2,2 -bipyridyl( 4-cy-cloocta-l,5-diene)nickel, which on treatment with maleic anhydride at 25 °C gave anti-3,3,6,6-tetramethyltricyclo[3.1.0.02,4]hexane (4) in >90% yield. Displacement of the hydrocarbon ligand from 3 with 3,3-dimethylcyclopropene proceeds at > 90"C. Since the complex 3 is regenerated in this step, 3 is the catalyst in the cyclodimerization of the cyclopropene.120... 

The air-sensitive violet complex thus formed was treated with methyl-magnesium bromide and then hydrolyzed to give /rans-Ph(Me3Si)C= CPh(SiMe3) (90, 91). Apparently, this is the first example of transfer of silyl groups from a metal to a coordinated hydrocarbon ligand. It seems that a similar step is involved in the dehydrogenative cis double silylation of acetylenes catalyzed by diethyl(bipyridyl)nickel(II) (156). 

Review articles covering different aspects of the coordinating properties of 1,10-phenanthroline (phen) and 2,2 -bipyridyl (bipy) are available.836-838 Selected examples of nickel(II) complexes with phen and bipy are collected in Table 46. 

Nickel(HI) complexes of formula [Ni(N—N)3](Q04)3 with N—N = 2,2 -bipyridyl and 1,10-phenanthroline and substituted derivatives have been isolated as products of the electrolysis in acetonitrile of the corresponding nickel(II) salts. Electrode potentials for the NPVNi11 couples in MeCN (0.1MNaClO4) were in the range 1.51-1.82 V.3079 The same diimine complexes have also been formed in strong acidic solutions.3080,3081... 

Other aqueous preparative methods include aerial oxidation of an alkaline solution of CoS04 and NaCNO to give the fulminatocobaltate(III) anion [Co(CNO)6]3-, reduction of ruthenate(VI) by excess of fulminate to give [Ru(CNO)6]4, and displacement of 2,2 -bipyridyl or 1,10-phenan-throline from nickel(II) or cobalt(III) complexes to give [Ni(CNO)4]2 or [Co(CNO)6]3. Liquid ammonia may replace water as solvent [Ni(NH3) ]2+ and [Co(NH3)6]3+, for example, react with sodium fulminate in this solvent to form [Ni(CNO)4]2 and [Co(CNO)6]3. In all these reactions fulminate behaves very like cyanide with [AuClJ-, however, reduction to form the gold(I) complex [Au(CNO)2] takes place and no gold(III) complex can be isolated. 

The organometallic complexes are quite various cobaltocene/bis(ethylaceto-acetato) copper (II) [366], CuCl or CuBr/bipyridyl [367, 368], cobaltoxime complex [369], reduced nickel/halide system [370], organoborane [371], ruthenium complex/trialkoxyaluminum system [372]. 

Tucci and Holm [163] have demonstrated an alternative reaction scheme, starting from the complex [NIi(bpy)(CH3)2(SR")2], where bpy is 2,2 -bipyridyl and R" is aromatic. In this case, the thiol displaced one methyl group from the nickel as methane, in a reaction reminiscent of methyl-CoM reductase, and coordinated to the nickel. Further addition of CO liberated CH3COSR" in high yield. This reaction demonstrates the feasibility of a reaction in which both the thiol and acetyl groups coordinate the nickel. 

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