NCN-Pincer Cobalt Complexes Containing Bis(oxazolinyl)phenyl Ligands

Hosokawa, Satomi; Ito, Junichi; Nishiyama, Hisao

doi:10.1021/om400450n

Cited by 11 publications

(8 citation statements)

References 43 publications

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“…Cobalt-promoted C−H bond activation dates back to the 1950s, when Murahashi reported Co 2 (CO) 8catalyzed cyclocarbonylation of N-benzylideneaniline (eq 5) 25 and azobenzene. 26 In terms of stoichiometric reactions, Co 2 (CO) 8 has been shown to react with a brominated bis(oxazolinyl)phenyl ligand to form a cobaltacycle (eq 6), 27 presumably through a dinuclear oxidative addition process. Inspired by these studies, we decided to test the feasibility of using Co 2 (CO) 8 to activate POCOP pincer C−H bonds.…”

Section: Synthesis and Structures Of Cobalt Pocop Pincermentioning

confidence: 99%

Cobalt POCOP Pincer Complexes via Ligand C–H Bond Activation with Co₂(CO)₈: Catalytic Activity for Hydrosilylation of Aldehydes in an Open vs a Closed System

Krause

Guan

2018

Organometallics

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A series of cobalt POCOP pincer complexes with the formulas {2,6-(iPr2PO)2-4-R′-C6H2}Co(CO)2 (R′ = H (1a), NMe2 (1b), OMe (1c), CO2Me (1d)), {2,6-(Ph2PO)2C6H3}Co(CO)2 (1e), and {2,6-(tBu2PO)2C6H3}Co(CO) (2f) have been synthesized through C–H bond activation of the corresponding pincer ligands with Co2(CO)8. These complexes have been demonstrated to catalyze the hydrosilylation of PhCHO with (EtO)3SiH, which exhibits an induction period and the decreasing reactivity order 1b > 1c > 1a > 1d > 1e. The catalytic protocol can be applied to various aldehydes with turnover numbers of up to 300. The CO ligands in the dicarbonyl complexes have been shown to exchange with 13CO at room temperature and partially dissociate from cobalt at high temperatures. Substitution of CO by tert-butyl isocyanide has been accomplished with 1a at 50–80 °C, resulting in the formation of {2,6-(iPr2PO)2C6H3}Co(CNtBu)(CO) (3a) and {2,6-(iPr2PO)2C6H3}Co(CNtBu)2 (4a). The catalytic reactions are more efficient when they are carried out in an open system or if the catalysts are preactivated by the aldehydes. The structures of 1a–e, 3a, and 4a have been studied by X-ray crystallography.

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Section: Synthesis and Structures Of Cobalt Pocop Pincermentioning

confidence: 99%

Cobalt POCOP Pincer Complexes via Ligand C–H Bond Activation with Co₂(CO)₈: Catalytic Activity for Hydrosilylation of Aldehydes in an Open vs a Closed System

Krause

Guan

2018

Organometallics

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“…Surprisingly, as cobalt is concerned only a few PCP pincer complexes featuring a direct cobalt–carbon single bond have been reported in the literature. An overview of cobalt PCP pincer systems ( A – E ), mostly based on the Co(I)/Co(III) oxidation states, is depicted in Scheme . − It has to be noted that several related cobalt complexes containing anionic pincer-type PNP, PSiP, NCN, and NNN frameworks are described. − …”

Section: Introductionmentioning

confidence: 99%

Synthesis and Reactivity of Four- and Five-Coordinate Low-Spin Cobalt(II) PCP Pincer Complexes and Some Nickel(II) Analogues

Murugesan¹,

Stöger²,

Carvalho³

et al. 2014

Organometallics

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Anhydrous CoCl2 or [NiCl2(DME)] reacts with the ligand PCPMe-iPr (1) in the presence of nBuLi to afford the 15e and 16e square planar complexes [Co(PCPMe-iPr)Cl] (2) and [Ni(PCPMe-iPr)Cl] (3), respectively. Complex 2 is a paramagnetic d7 low-spin complex, which is a useful precursor for a series of Co(I), Co(II), and Co(III) PCP complexes. Complex 2 reacts readily with CO and pyridine to afford the five-coordinate square-pyramidal 17e complexes [Co(PCPMe-iPr)(CO)Cl] (4) and [Co(PCPMe-iPr)(py)Cl] (5), respectively, while in the presence of Ag+ and CO the cationic complex [Co(PCPMe-iPr)(CO)2]+ (6) is afforded. The effective magnetic moments μeff of all Co(II) complexes were derived from the temperature dependence of the inverse molar magnetic susceptibility by SQUID measurements and are in the range 1.9 to 2.4 μB. This is consistent with a d7 low-spin configuration with some degree of spin–orbit coupling. Oxidation of 2 with CuCl2 affords the paramagnetic Co(III) PCP complex [Co(PCPMe-iPr)Cl2] (7), while the synthesis of the diamagnetic Co(I) complex [Co(PCPMe-iPr)(CO)2] (8) was achieved by stirring 2 in toluene with KC8 in the presence of CO. Finally, the cationic 16e Ni(II) PCP complex [Ni(PCPMe-iPr)(CO)]+ (10) was obtained by reacting complex 3 with 1 equiv of AgSbF6 in the presence of CO. The reactivity of CO addition to Co(I), Co(II), and Ni(II) PCP square planar complexes of the type [M(PCPMe-iPr)(CO)]n (n = +1, 0) was investigated by DFT calculations, showing that formation of the Co species, 6 and 8, is thermodynamically favorable, while Ni(II) maintains the 16e configuration since CO addition is unfavorable in this case. X-ray structures of most complexes are provided and discussed. A structural feature of interest is that the apical CO ligand in 4 deviates significantly from linearity, with a Co–C–O angle of 170.0(1)°. The DFT-calculated value is 172°, clearly showing that this is not a packing but an electronic effect.

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“…Recently, several N,C,N-pincer Co(III) complexes were obtained via oxidative addition of 2bromo-substituted ligand precursors of bis(oxazolinyl)phenyl with Co 2 (CO) 8 . 30 The solid-state structure of complex 1 was confirmed by an X-ray diffraction study of single crystals obtained from npentane solutions (Figure 1). For five-coordinate structures an index τ was introduced from Addison et al, 31 69(3)°, but its Co−P bonds are not substantially shorter relative to those of other complexes bearing a related intact bisphosphine ligand set.…”

Section: ■ Introductionmentioning

confidence: 81%

Cobalt-Promoted Tandem C(sp²)–H Activation and C–C Coupling of Vinyldiphenylphosphine: σ- vs π-Coordination Modes within Cyclometalation

2015

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We have studied the reactivity of a series of terminal alkenyldiphenylphosphines {Ph2P(CH2) n -CHCH2), n = 0, 1, 2, 3} under mild conditions (−70 °C) in reaction with univalent Co(I). Methane and ethane elimination occurs when different olefinic P,C-coordination modes are established. Subsequent C–H activation and C–C coupling take place in the reaction of Co(CH3)(PMe3)4 with vinyldiphenylphosphine (1:2 molar ratio) to form a novel anionic P,C,P-type ligand with asymmetric ring sizes attached to the cobalt center of (PMe3)2Co{κ3-(P,C,P)-(Ph2)CH2CHCH-CH(PPh2)} (1). X-ray study of 1 revealed that the complex has a unique cyclometalated structure of a three-membered ring within the newly assembled bis-phosphine ligand. Cyclometalation via selective vinyl-group C(sp2)–H activation of stoichiometric amounts allyl-diphenylphosphine with Co(CH3)(PMe3)4 afforded for the first time σ-allyl coordination incorporated in a five-membered cobaltacycle of (PMe3)2Co{κ2(P,C)-HCCHCH2PPh2} (2); subsequent C–C coupling is not observed. By contrast, equimolar mixtures of pentenyl-diphenylphosphine and Co(CH3)(PMe3)4 afforded a η3-coordinated π-allyl complex of composition (PMe3)2Co{η3-κ4-(P,C,C,C)-H2CCH-CH(CH2)2PPh2} (3). All unprecedented complexes were characterized by multinuclear NMR spectroscopy and X-ray diffraction, and their mechanisms of formation are discussed.

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NCN-Pincer Cobalt Complexes Containing Bis(oxazolinyl)phenyl Ligands

Cited by 11 publications

References 43 publications

Cobalt POCOP Pincer Complexes via Ligand C–H Bond Activation with Co₂(CO)₈: Catalytic Activity for Hydrosilylation of Aldehydes in an Open vs a Closed System

Cobalt POCOP Pincer Complexes via Ligand C–H Bond Activation with Co₂(CO)₈: Catalytic Activity for Hydrosilylation of Aldehydes in an Open vs a Closed System

Synthesis and Reactivity of Four- and Five-Coordinate Low-Spin Cobalt(II) PCP Pincer Complexes and Some Nickel(II) Analogues

Cobalt-Promoted Tandem C(sp²)–H Activation and C–C Coupling of Vinyldiphenylphosphine: σ- vs π-Coordination Modes within Cyclometalation

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NCN-Pincer Cobalt Complexes Containing Bis(oxazolinyl)phenyl Ligands

Cited by 11 publications

References 43 publications

Cobalt POCOP Pincer Complexes via Ligand C–H Bond Activation with Co2(CO)8: Catalytic Activity for Hydrosilylation of Aldehydes in an Open vs a Closed System

Cobalt POCOP Pincer Complexes via Ligand C–H Bond Activation with Co2(CO)8: Catalytic Activity for Hydrosilylation of Aldehydes in an Open vs a Closed System

Synthesis and Reactivity of Four- and Five-Coordinate Low-Spin Cobalt(II) PCP Pincer Complexes and Some Nickel(II) Analogues

Cobalt-Promoted Tandem C(sp2)–H Activation and C–C Coupling of Vinyldiphenylphosphine: σ- vs π-Coordination Modes within Cyclometalation

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Resources

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Cobalt POCOP Pincer Complexes via Ligand C–H Bond Activation with Co₂(CO)₈: Catalytic Activity for Hydrosilylation of Aldehydes in an Open vs a Closed System

Cobalt POCOP Pincer Complexes via Ligand C–H Bond Activation with Co₂(CO)₈: Catalytic Activity for Hydrosilylation of Aldehydes in an Open vs a Closed System

Cobalt-Promoted Tandem C(sp²)–H Activation and C–C Coupling of Vinyldiphenylphosphine: σ- vs π-Coordination Modes within Cyclometalation