Three characteristic reactions of organocobalt compounds in organic synthesis

Abstract

Organocobalt compounds in organic synthesis have three characteristic reactions. The first occurs because cobalt has a high affinity to carbon-carbon π -bonds or carbon-nitrogen π -bonds. The second occurs because cobalt has a high affinity to carbonyl groups. The third is due to cobalt easily tending to form square-planar bipyramidal six-coordination structures with four nitrogen atoms or two nitrogen atoms and two oxygen atoms at the square-planar position, and to bond with one or two carbon atoms at the axial position. The first characteristic reactions are the representative reactions of organocobalt compounds with a mutually bridged bond between the two π -bonds of acetylene and the cobalt-cobalt bond of hexacarbonyldicobalt. These are reactions with a Co 2 (CO) 6 INTRODUCTIONOrganometallic intramolecular coordination compounds, especially five-membered ring compounds of organotin compounds, have been studied since 1965, and many reviews 1 -13 and some books 14 -16 have published on the subject. These compounds are mainly synthesized by cyclometalation reactions with transition metal compounds. The first publication on this subject is generally considered to be the reaction of diazobenzene with nick elocene by Kleiman and Dubeck 17 in 1963 as shown in equation (1).*Correspondence to: Iwao Omae, Nihon Pharmaceutical University, 10281, Komuro, Ina-cho, Saitama, An earlier article on the direct synthesis of 2-phenyl-3-indazolinone by carbonylation of azobenzene with a cobalt Materials, Nanoscience and CatalysisThree characteristic reactions of organocobalt compounds 319 carbonyl catalyst, as shown in equation (2), was published in 1956. 18 It was also synthesized in 1967 through a twostep reaction, that is, (i) cyclopalladation of azobenzene via the five-membered ring product, and (ii) carbonylation, as shown in equation (3). 19From these two reactions, the former reaction [equation (2)] is presumed also to proceed via cyclometallation, that is, cyclocobaltation with the cobalt carbonyl catalyst, as shown in equation (4). Actually, many cyclomatalations with cobalt compounds have been reported. 20 -35 For example, a similar cyclometalated organocobalt compound was prepared by the reaction of azobenzene with methyltetra(trimethylphosphine)cobalt, as shown in equation (5). 20 Further, one year previously, in 1955, the same type of heterocyclic compound was prepared by the same type of carbonylation reaction with an organocobalt compound, as shown in equation (6). 36 This publication by Murahashi 36 may be considered to be the first reaction relating cyclometalation reactions.In the chemical industry, organocobalt is an essential constituent in many important catalysts. Specifically, they are key components in the multimillion-pound technology of hydroformylation; that is, the catalytic transformation of olefins into aldehydes using homogeneous catalysts. This article reports on three characteristic reactions of the organocobalt compounds in organic syntheses on the basis of their structures and reactivities...

Alkyne hexacarbonyl dicobalt complexes in medicinal chemistry and drug development

“…Mass spectrometry usually reveals a consecutive loss of CO ( m/z = 28) [24] . In synthetic chemistry, hexacarbonyl dicobalt complexes are important intermediates in the Pauson-Khand reaction and the Nicholas reaction (see Figure 5 ) [25] . In the Pauson-Khand reaction the hexacarbonyl dicobalt moiety functions as a carbon monoxide source, which enables the formation of a cyclopentenone ring by cyclization of an alkene, an alkyne and a carbon monoxide (a [2 + 2 + 1] cycloaddition).…”

Cobalt(II)‐Catalyzed Isocyanide Insertion Reaction with Amines under Ultrasonic Conditions: A Divergent Synthesis of Ureas, Thioureas and Azaheterocycles

“…Then, several structurally varied isocyanides were also investigated. When other aliphatic and aromatic isocyanides (2b-e) were employed, the reactions also proceeded smoothly in moderate yields (52%-93%) ( Table 1, entries [15][16][17][18]. However, the reaction of pyridin-3-amine 3q could not furnish the desired product (Table 1, entry 23).…”

“…[12] In addition, since Kharaschs [13] pioneering works on the homocoupling reactions of Grignard reagents, cobalt catalysts, which are widely available, not expensive, and have low toxicity, have received particular attention. [14][15][16][17] As a continuation of our work on the insertion of isocyanides into active N À H bonds under ultrasound irradiation, [18] herein, we hoped to apply this insertion strategy to construct of ureas, thioureas, 2-aminobenzoxazoles, 2-aminobenzothiazoles, and 2-aminobenzimidazoles [19] by trapping the insertion coupling intermediates of isocyanides with amines.…”

Applications of the Nicholas Reaction in the Synthesis of Natural Products

“…The Nicholas reaction, first reported by Nicholas in the 1970s [1,2], involves the reaction of a propargylic cobalt carbonylstabilised cation with a nucleophile [3][4][5][6][7][8][9]. Scheme 1 outlines the general features of the reaction.…”