Nickel carbonyl, reduction

Most ring syntheses of this type are of modern origin. The cobalt or rhodium carbonyl catalyzed hydrocarboxylation of unsaturated alcohols, amines or amides provides access to tetrahydrofuranones, pyrrolidones or succinimides, although appreciable amounts of the corresponding six-membered heterocycle may also be formed (Scheme 55a) (73JOM(47)28l). Hydrocarboxylation of 4-pentyn-2-ol with nickel carbonyl yields 3-methylenetetrahy-drofuranone (Scheme 55b). Carbonylation of Schiff bases yields 2-arylphthalimidines (Scheme 55c). The hydroformylation of o-nitrostyrene, subsequent reduction of the nitro group and cyclization leads to the formation of skatole (Scheme 55d) (81CC82). 

C-C bonds can be formed by reaction with alkyl iodides or more usefully by reaction with metal carbonyls to give aldehydes and ketones e.g. Ni(CO)4 reacts with LiR to form an unstable acyl nickel carbonyl complex which can be attacked by electrophiles such as H+ or R Br to give aldehydes or ketones by solvent-induced reductive elimination ... 

A variety of catalysts including copper, nickel, cobalt, and the platinum metals group have been used successfully in carbonyl reduction. Palladium, an excellent catalyst for hydrogenation of aromatic carbonyls is relatively ineffective for aliphatic carbonyls this latter group has a low strength of adsorption on palladium relative to other metals (72,91). Nonetheless, palladium can be used very well with aliphatic carbonyls with sufficient patience, as illustrated by the difficult-to-reduce vinylogous amide I to 2 (9). 

When dicobalt octacarbonyl, [Co(CO)4]2, is the catalyst, the species that actually adds to the double bond is tricarbonylhydrocobalt, HCo(CO)3. Carbonylation, RCo(CO)3- -CO—>RCo(CO)4, takes place, followed by a rearrangement and a reduction of the C—Co bond, similar to steps 4 and 5 of the nickel carbonyl mechanism shown in 15-30. The reducing agent in the reduction step is tetra-carbonylhydrocobalt HCo(CO)4, ° or, under some conditions, H2. When HCo(CO)4 was the agent used to hydroformylate styrene, the observation of CIDNP indicated that the mechanism is different, and involves free radicals. Alcohols can be obtained by allowing the reduction to continue after all the carbon monoxide is... 

Nickel-Catalyzed Reductive Coupling of Dienes and Carbonyl Compounds... 

Keywords Allylation Carbonyl compound Dienes Homoallylation Nickel catalysis Reductive coupling... 

Nickel-Catalyzed Reductive Allylation of Carbonyl Compounds with 1,3-Dienes... 

Recently, the heterogenization technique has allowed more-selective reactions to be observed. For example, butadiene gives 95% of 1,3,6-octatriene (example 28 in Table 1) on a catalyst obtained by reduction of NiBr2(supported phenylphosphines)2 with NaBH4 (44). Nickel-carbonyl complexes have also been supported on phosphinated silica (55). 

I, Table X) requires tertiary phosphine-nickel halide or tertiary phosphine-nickel carbonyl complexes at 140-170°C. This implies oxidative addition of aromatic halides to nickel, replacement of the halide with amines, and reductive elimination. 

For a review encompassing the intermolecular nickel-catalyzed reductive coupling of dienes to carbonyl compounds, see Tamaru, Y. /. Organomet. Chem. 1999, 576, 215-231. 

Kimura M, Tamaru Y (2007) Nickel-Catalyzed Reductive Coupling of Dienes and Carbonyl Compounds. 279 173-207 King GC, see Di Giusto DA (2005) 261 131-168 Kirchner B, see Thar J (2007) 268 133-171... 

The active catalyst is presumably formed through reduction of the Ni species, aided by hydrogen or group VIB metals and their carbonyls, to the nickel carbonyl. Nickel carbonyl is converted to the active catalyst by ligand dissociation. The exact nickel species is the result of complex equilibria, equations 11-17. The zero valent complex adds methyl iodide, after CO dissociation. This is believed to be the rate-determining step and has first order kinetics with respect to both iodide and Ni. It was found that temperature greater than 100 C is needed for the oxidative addition (29). 

Selective catalytic hydrogenation with chromium-promoted Raney nickel is reported (e.g. citral and citronellal to citronellol) NaHCr2(CO)io and KHFe(CO)4 reduction of a/3-unsaturated ketones (e.g. citral to citronellal) has been described (cf. Vol. 7, p. 7). The full paper on selective carbonyl reductions on alumina (Vol. 7, p. 7) has been published." Dehydrogenation of monoterpenoid alcohols over liquid-metal catalysts gives aldehydes and ketones in useful yields. ... 

It has been claimed that attempts to prepare iron and nickel carbonyl complexes of 1,2-and 1,4-dihydropyridines resulted in reduction of the metal (67AG(E)988). This problem has been avoided by using dihydropyridines with electron withdrawing groups on the nitrogen... 

Isoelectronic with nickel carbonyl are the anions, Ni(CN)44- and Pd(CN)44-, which are obtained as their potassium salts by reduction of the corresponding cyanides of oxidation state +2 with potassium in liquid ammonia (32, 65, 186). The infrared spectrum of the nickel complex has been reported (67) to show only one band at 1985 cm-1, in the triple-bond... 

The method described is a modification of that of Gatter-mann and Koch.1 The aldehyde has also been prepared by related methods such as the action of hydrogen cyanide and hydrogen chloride on toluene in the presence of aluminum chloride,2 and nickel carbonyl with toluene and aluminum chloride.3 The reduction of />tolunitiile by stannous chloride forms the aldimine which on hydrolysis gives an almost quantitative yield of the aldehyde.4 />-Xylene can be oxidized by various reagents, particularly chromyl chloride,5 to />-tolualdehyde. 

The reductive coupling of phenacyl bromides using nickel carbonyl (68CC33) or an electrolytic procedure (81S625) provides excellent yields of 2,4-diarylfurans. Coupling of a-bromoaldimines with sodium or lithium provides mainly 3,4-disubstituted pyrroles, whereas isopropylmagnesium bromide yields mainly 2,4-disubstituted pyrroles (Scheme 77)... 

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