Cobalt complexes alkylation

Prior equilibrium. Consider the net reaction between certain metal halide and alkyl cobalt complexes, RCo + MX = Co+ + RM + X". There is a rapid equilibrium ... 

The second structural type found for organometallic cobalt porphyrins contains an organic fragment bridged between the cobalt and one pyrrolic nitrogen. Cobalt complexes of N-alkyl- or N-arylporphyrins arc well established (but will not be specifically addressed here). The bridged complexes are derivatives of these where the N-alkyl group also forms a cr-bond to cobalt. They are also related to the axially... 

Bis(aryl)cobalt(II) compounds have been prepared by reaction of R MgX (where R = C6H6 Cl n = 2-4) with Co(PR3)2Cl2.203 They undergo both thermally and oxidatively induced decomposition, with the corresponding biphenyl a product. The reactions of alkyl-cobalt complexes have been reviewed recently, and include thermolysis, photolysis, oxidation, and reduction reactions.25 Homolysis of the Co—C bond is a feature of reactions. 

Acyl cobalt complexes are reduced to their alkyl counterparts in good yields with Et3SiH/TFA (Eq. 248).183-310-425 Acyl ferrocene derivatives are reduced to the respective methylene compounds with Et3SiH/TFA (Eqs. 249180 and 250).179 Acylcyclopentadienylmanganese tricarbonyl is similarly reduced in good yield.351... 

The benzyl ligand of benzylbis(dimethylglyoximato)pyridine cobalt complex has been selectively converted to 3,5-dibenzyl-l,2,4-oxadiazole by a reaction with alkyl nitrite in the presence of light (426). The reaction proceeds by the in situ formation of an oxime and a nitrile oxide (Scheme 1.44). 

Modified cobalt complexes of the type frans-Co2(CO)6(phosphine)2 are promising candidates for certain transition metal-catalyzed reactions, in particular for the hydroformylation of long-chained olefins [117]. A series of complexes Co2(CO)6[P(alkyl) (aryl)m]2 (n 0,1,2,3 m S - n) was synthesized and used for solubility measurements. Since the basicity of phosphines affects the catalytic activity, use of fluorous substituents might induce unexpected changes in the activity. Therefore, also derivatives with an additional ethyl spacer between the fluorous group and the phosphine moiety were examined (Sect. 3.1). 

For a decade or so [CoH(CN)5] was another acclaimed catalyst for the selective hydrogenation of dienes to monoenes [2] and due to the exclusive solubility of this cobalt complex in water the studies were made either in biphasic systems or in homogeneous aqueous solutions using water soluble substrates, such as salts of sorbic add (2,4-hexadienoic acid). In the late nineteen-sixties olefin-metal and alkyl-metal complexes were observed in hydrogenation and hydration reactions of olefins and acetylenes with simple Rii(III)- and Ru(II)-chloride salts in aqueous hydrochloric acid [3,4]. No significance, however, was attributed to the water-solubility of these catalysts, and a new impetus had to come to trigger research specifically into water soluble organometallic catalysts. 

Cobalt complexes with square planar tetradentate ligands, including salen, cor-rin, and porphyrin types, all catalyse the reduction of alkyl bromides and iodides. Most preparative and mechanistic work with these reactions has used cobalamines, including vitamin-B,. A generalised catalytic cycle is depicted in Scheme 4.10 [219]. At potentials around -0.9 V vs. see, the parent ligated Co(lll) compound un-... 

A picnic-basket porphyrin is reminiscent of the lacunar cyclidenes mentioned earlier, in which an alkyl chain tied the ends of the cyclidene together and formed a pocket for the complexation of dioxygen. Cobalt complexes of the picnic-basket porphyrins 31 bind dioxygen reversibly at room temperature with high oxygen affinities (84). The oxygen affinity increases as the basket size decreases (as determined by the length... 

Because such alkylation proceeds by S l mechanism, even cobalt complexes derived from unreactive (in an SN2 sense) halides can be formed. The cobalt complexes are air-stable compounds, but are affected by direct daylight. The incorporated Co—C bond is weak and, therefore, photolysis of 33 sets free the anomeric radical 11. In the presence of olefins 12 this radical adds to the double bond, followed by subsequent combination to give the insertion product 35 (Scheme 9). 

Co2(CO)8-catalyzed reactions of benzylic acetates with trimethylsilane and CO proceed under mild reaction conditions to give trimethylsilylethers of /3-phenethylalcohol in 43-76% yield. The highest yields are observed for benzyl acetates with electron-donating substituents.111 Secondary alkyl acetates are also good substrates in the reaction system, yielding enol silyl ethers.112 In addition, the cobalt complex is an effective catalyst for siloxymethylation of five-membered cyclic ortho esters, as shown in Eq. (41).113... 

Propargylation (8,148-149 10,129). In the presence of a Lewis acid, cobalt-complexed propargylic ethers alkylate silyl enol ethers with high -selectivity. Example ... 

Sulfur dioxide is capable of reacting with metal alkyl, aryl or u-allyl complexes in an insertion-type reaction to yield S-sulfinate (4), O-sulfinate (5) or 0,< -sulfinate complexes (6).13 It can also insert into the metal-metal bond in the cobalt complex (7) to give the S02-bridged complex (8).38... 

Nishinaga and co-workers isolated a series of stable cobalt(III)-alkyl peroxide complexes such as (170) and (171) in high yields from the reaction of the pentacoordinated Co"-Schiff base complex with the corresponding phenol and 02 in CH2C12. Complex (170 R=Bu ) has been characterized by an X-ray structure. These alkyl peroxide complexes presumably result from the homolytic addition of the superoxo complex Co111—02 to the phenoxide radical obtained by hydrogen abstraction from the phenolic substrate by the CoUI-superoxo complex. The quinone product results from / -hydride elimination from the alkyl peroxide complex (172)561,56,565,566 The quinol (169) produced by equation (245) has been shown to result from the reduction of the CoIU-alkyl peroxide complex (170) by the solvent alcohol which is transformed into the corresponding carbonyl compound (equation 248).561... 

Cobalt(III)-alkyl peroxide complexes with the formula Co(BPI)(OOR)(OCOR ) (205 BPI = l,3-bis(2 -pyridylimino)isoindoline R= Bu , CMe2Ph R = Me, Ph, Bu ) have been prepared from the oxidation of Con(BPI)(OCOR ) complexes by alkyl hydroperoxides. The X-ray crystal structure of complex (205) (R=Bu R = Ph) revealed a distorted octahedral environment, with a monodendate OOBuc group and a bidendate carboxylate.635... 

Acyclic /V-alkylimines, asymmetric hydrogenation, 10, 56 Acyclic ( j3-allyl)cobalt complexes, oxidation reactions, 7, 58 Acyclic allylic esters, alkylation, 11, 76 Acyclic aromatic imines, asymmetric hydrogenation, 10, 56 Acyclic 1-buly l-( )5-pencadienyl) iron cations, preparation and reactivity, 6, 156... 

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