Hydrido Cobalt Research Articles

Solvent-Free Hydrosilylation of Alkenes Catalyzed by Well-Defined Low-Valent Cobalt Catalysts

A solvent-free cobalt-catalyzed highly selective hydrosilylation of alkenes has been developed. It was found that both Co(PMe3)4 and CoCl(PMe3)3 are highly active catalysts for hydrosilylation of alkenes. The former promoted Markovnikov-type hydrosilylation of the aryl alkenes, while the latter catalyzed anti-Markovnikov-type hydrosilylation of the alkyl alkenes. These two catalytic systems tolerate a variety of functional groups and provide high selectivity and medium to high yield. In the exploration of the reaction mechanism, a dinuclear silyl cobalt(I) complex [(PMe3)2Co(μ–η2-HSiPh2)2Co(PMe3)2] (4) from the Co(PMe3)4 system and a silyl cobalt dihydride [(PMe3)3Co(H)2SiClPh2] (5) from the CoCl(PMe3)3 system were obtained. It is proposed that the silyl cobalt(I) intermediate, [Co(PMe3)3(SiHPh2)], is the real catalyst for the Co(PMe3)4 system, while the hydrido cobalt(I) intermediate, [HCo(PMe3)3], is the real catalyst for the CoCl(PMe3)3 system. Complexes 4 and 5 were characterized by spectroscopic methods and single-crystal X-ray diffraction.

Dehydration of primary amides to nitriles catalyzed by [CNC]-pincer hydrido cobalt(III) complexes

The dehydration reactions from primary amides to nitriles were catalyzed by the [CNC]-pincer hydrido cobalt(III) complexes [(ortho-F4C6CHNC10H6)Co(III)(H)(PMe3)2] (1), [(2,5-F2C6H2CHNC10H6)Co(III)(H)(PMe3)2] (2) and [(2,4,5-F3C6HCHNC10H6)Co(III)(H)(PMe3)2] (3) as catalysts with (EtO)3SiH as an efficient reducing agent. These hydrido cobalt(III) complexes as catalysts are suitable for many substrates and have good functional group tolerance. Among the three cobalt hydrides, complex 2 is the best catalyst. This is the first hydrido cobalt complex-catalyzed dehydration of primary amides to nitriles.

Synthesis and characterization of bissilyl cobalt and iron hydrides bearing disilazane ligands via Si-H bond activation

Abstract The reaction between 2-pyridinetetramethyldisilazane 1 and CoMe(PMe3)4 led to the formation of the novel bissilyl cobalt(III) hydride CoH((C5H4N)-N(SiMe2)2)(PMe3)3 (2) via the cleavage of two Si-H bonds with the elimination of methane. The reaction of phenyltetramethyldisilazane 3 with CoMe(PMe3)4 could directly provide the hydrido cobalt(III) complex CoH((C6H5)-N(SiMe2)2)(PMe3)3 4. Complex 4 is an analogue to complex 2. This result indicates that a pre-coordination of the nitrogen atom in pyridine to the cobalt center before Si-H bond activation can be excluded in the formation mechanism of 2. This exclusion is further supported by the in situ 1H NMR spectra of the reaction mixtures between 2-pyridinetetramethyldisilazane 1 with CoMe(PMe3)4 in C6D6 in different reaction times. A new bissilyl iron hydride FeH((C5H4N)-N(SiMe2)2)(PMe3)3 (5) was obtained through the reaction of Fe(PMe3)4 with 1. Complexes 2, 4 and 5 with two metal-Si bonds are very stable and did not react with MeI, EtBr, acetylacetone, CO or CO2. The molecular structures of complexes 2, 4 and 5 were determined by single crystal X-ray diffraction.

Synthesis and Properties of a Se-Coordinated Hydrido Cobalt(III) Complex Supported by Trimethylphosphine

Synthesis and Properties of a Se-Coordinated Hydrido Cobalt(III) Complex Supported by Trimethylphosphine

Synthesis and Reactivity of Silyl Iron, Cobalt, and Nickel Complexes Bearing a [PSiP]-Pincer Ligand via Si–H Bond Activation

The synthesis and characterization of a series of Ni, Co, and Fe complexes bearing a tridentate bis(phosphino)silyl ligand (κ3-(2-Ph2PC6H4)2SiMeH, [PSiP]-H, 1) are reported. 1 reacted with Ni(PMe3)4 to afford the mononuclear nickel(0) complex [η2(Si–H)-PSiP]Ni(PMe3) (2). The halogeno nickel complexes [PSiP]Ni(X)(PMe3) (X = Cl (3), Br (4), I (5)) were synthesized in the reactions of 2 with Me3SiCl or MeHSiCl2, EtBr, and MeI. Complex 2 underwent ligand substitution of PMe3 by CO to give [η2(Si–H)-PSiP]Ni(CO) (6). Complex 3 reacted with NaOMe to deliver [PSiP]Ni(OMe)(PMe3) (7) through anionic ligand substitution, while the neutral ligand replacement of PMe3 by CO in 3 afforded the rare hexacoordinate 20-electron nickel(II) complex [PSiP]Ni(Cl)(CO)2 (8). Unexpectedly, reaction of 1 with NiMe2(PMe3)3 produced the tetracoordinate nickel(0) complex [Me2PSiP]2Ni (9). The complex [Me2PSiP]Ni(CO)2 (10) was acquired from 9 after the substitution of one [PSiP] ligand by two carbonyl ligands. 1 reacted with Co(PMe3)4 or CoCl(PMe3)3 to afford the hydrido cobalt(II) complex [PSiP]CoH(PMe3) (11) or hydrido cobalt(III) complex [PSiP]Co(H)(Cl)(PMe3) (13). Complex 12, [PSiP]Co(H)(I)(PMe3), could be obtained from the reaction of MeI with 11 or 13. Treatment of 13 with 1 equiv of MeLi or n-BuMgBr in THF resulted in the clean formation of cobalt(I) complex [PSiP]Co(PMe3)2 (14) via reductive elimination. The simple anhydrous inorganic salt NiCl2 or CoCl2 could also react with 1 in the presence of PMe3 to form the corresponding silyl complexes 3 and [PSiP]Co(Cl)(PMe3) (15) via Si–H bond cleavage. 1 reacted with Fe(PMe3)4 to form the hexacoordinate octahedral hydrido iron(II) complex [PSiP]Fe(H)(PMe3)2 (16). The molecular structures of complexes 2–5, 10, 12, 13, 15, and 16 were determined by X-ray single crystal diffraction. 16 has excellent catalytic reactivity for the reduction of aldehydes and ketones.

In Situ High-Pressure NMR Studies of Co2(CO)6[P(p-CF3C6H4)3]2 in Supercritical Carbon Dioxide: Ligand Substitution, Hydrogenation, and Hydroformylation Reactions

The dimeric cobalt complex Co2(CO)6[P(p-CF3C6H4)3]2 (1) reacts reversibly with hydrogen to produce HCo(CO)3[P(p-CF3C6H4)3] (4). The carbonyl and the phosphine ligands of both 1 and 4 are very labile. Compound 1 reacts with CO to give Co2(CO)7[P(p-CF3C6H4)3] (2), and compound 4 reacts with CO and P(p-CF3C6H4)3 (L) to give HCo(CO)4 (5) and HCo(CO)2[P(p-CF3C6H4)3]2 (6), respectively. The 31P NMR studies show that, in the presence of 1, the line width of the 31P resonance of L is temperature dependent, and at constant temperature, its broadening is proportional to the square root of the concentration of 1. This broadening is attributed to its exchange reaction with the mononuclear cobalt radical (CO)3LCo• (3), which is generated by the homolysis of 1. Compound 1 catalyzes the hydroformylation of olefins in supercritical carbon dioxide. In contrast to the unsubstituted Co2(CO)8, the phosphine-modified catalyst system is stable under low CO pressures and the hydroformylation reactions can be carried out at low pressures. In situ monitoring of 31P and 59Co NMR spectra of the solution shows that the phosphine-containing hydrido cobalt complexes 4 and 6 are the only hydrido cobalt complexes present in detectable concentrations in 1-catalyzed hydroformylation reactions; nevertheless, the possibility that the observed activity for 1 comes primarily from the more active HCo(CO)4, present in concentrations below detectable limits, has not been rigorously excluded.

5600031 Process for preforming cobaltous salts using shell-type preformer catalysts

A process for preparing oxo alcohols and aldehydes by the cobalt catalyzed hydroformylation of C2 to C17 linear or branched monoolefins with subsequent hydrogenation of the hydroformylation product, in which oxo process aqueous solutions of cobalt salts are converted to active hydrido cobalt carbonyl species in a preformer reactor under preforming reaction conditions, the improvement characterized by the preformer reactor containing a shell-type, metal on substrate, preformer catalyst.

Activation of molecular hydrogen in cobalt-catalyzed hydroformylation

The mechanism of the activation of molecular hydrogen in cobalt-catalyzed hydroformylation of olefins has been studied by high pressure IR spectroscopy using HCo(CO) 4 ( 1) under 100 bar H 2 (or D 2) in the absence or presence of CO at room temperature. The treatment of 1 with 100 bar H 2 resulted in the formation of CO 2(CO) 8 ( 2) and a small amount of Co 4(CO) 12 ( 3), and the transient formation of HCo 3(CO) 9 ( 4). In the reaction of 1 with one equivalent of 3,3-dimethyl-butene-1 under 100 bar H 2 both hydrogenation and hydroformylation occur, but the former is much faster. In the presence of large amounts of 1 the predominant path for the hydrogenation of the olefin involves the reaction of two equivalents of 1 with the olefin even under 100 bar of H 2. Under a very low partial pressure of CO the stability of 1 is increased and the hydrogenation significantly slowed down. The preferred path of the hydroformylation of the olefin involves the addition of H 2 and CO from gas phase even in the presence of large amount of HCo(CO) 4 ( 1) under 100 bar H 2 and 2.3 bar COat room temperature. The studies reveal that the mechanism of H 2 activation in the presence of HCo(CO) 4 ( 1) is highly dependent on the reaction conditions. Under 100 bar H 2 and at room temperature the activation of molecular hydrogen starts at a coordinatively unsaturated acyl cobalt carbonyl, yielding an aldehyde and an unknown cobalt species. It is believed that this species is a coordinatively unsaturated hydrido cobalt carbonyl like {HCo(Co) 3}, and can activate and catalytically hydroformylate the olefin.

FACILE PHOTOGENERATION OF COORDINATTVELY UNSATURATED ACTIVE SPECIES FROM A HYDRIDOPHOSPHONITECOBALT(I) COMPLEX AND ITS APPLICATION TO DOUBLE-BOND MIGRATION OF OLEFIN

Abstract Pyrex-filtered irradiation of a thermally inert complex [CoH[PPh(OMe)2]4] dissociated PPh(OMe)2 from cobalt without cleavage of a hydrido–cobalt bond, yielding an active species “CoH[PPh(OMe)2]3”. The photogenerated species caused double-bond migration of 3-phenylpropene to (E)- and (Z)-1-phenylpropenes.