Tuning the stereochemistry of pentacoordinate cobalt(III) halide complexes: a rare case of trigonal bipyramidal stereochemistry for cobalt(III)

Jaynes, B. Scott; Ren, Tong; Liu, Shuncheng; Lippard, Stephen J.

doi:10.1021/ja00050a063

Cited by 31 publications

(22 citation statements)

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“…This clearly suggests that the structure of Co(III) complex 1 is a trigonal-bipyramid with high spin state or a square-pyramid with an intermediate one. 55 It is consistent with the crystal structure of 1 with trigonal-bipyramidal geometry as mentioned before. These findings suggest that complex 1 has a four-coordinate squareplanar, 38,39 five-coordinate square-pyramidal, or five-coordinate trigonal-bipyramidal structure in solution.…”

Section: ■ Experimental Sectionsupporting

confidence: 90%

Co(III) Complexes with N₂S₃-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase

et al. 2018

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It has been before reported that, in addition to hydration of nitriles, the Fe-type nitrile hydratase (NHase) also catalyzes the hydrolysis of tert-butylisocyanide ( tBuNC). In order to investigate the unique isocyanide hydrolysis by NHase, we prepared three related Co(III) model complexes, PPh[Co(L)] (1), PPh[Co(L-O)] (2), and PPh[Co(L-O)] (3), where L is bis( N-(2-mercapto-2-methylpropionyl)aminopropyl)sulfide. The suffixes L-O and L-O indicate ligands with a sulfenate and a sulfinate and with two sulfinates, respectively, instead of the two thiolates of L. The X-ray analyses of 1 and 3 reveal trigonal bipyramidal and square pyramidal structures, respectively. Complex 2, however, has five-coordinate trigonal-bipyramidal geometry with η-type S-O coordination by a sulfenyl group. Addition of tBuNC to 1, 2, and 3 induces an absorption spectral change as a result of formation of an octahedral Co(III) complex. This interpretation is also supported by the crystal structures of PPh[Co(L-O)( tBuNC)] (4) and (PPh)[Co(L-O)(CN)] (5). A water molecule interacts with 3 but cannot be activated as reported previously, as demonstrated by the lack of absorption spectral change in the pH range of 5.5-10.2. Interestingly, the coordinated tBuNC is hydrolyzed by 2 and 3 at pH 10.2 to produce tBuNH and CO molecule, but 1 does not react. These findings provide strong evidence that hydrolysis of tBuNC by NHase proceeds not by activation of the coordinated water molecule but by coordination of the substrate. The mechanism of the hydrolysis reaction of tBuNC is explained with support provided by DFT calculations; a positively polarized C atom of tBuNC on the Co(III) center is nucleophilically attacked by a hydroxide anion activated through an interaction of the sulfenyl/sulfinyl oxygen with the nucleophile.

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Section: ■ Experimental Sectionsupporting

confidence: 90%

Co(III) Complexes with N₂S₃-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase

et al. 2018

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“…The low-spin nature of these Co(III) complexes is ostensibly due to the presence of strong-field aryl ligands in the coordination sphere of Co. A comparison can be drawn with the report of Lippard et al on five-coordinate Co(III) complexes of the type (NNNN)CoX, where NNNN is a dianionic, tetradentate tropocoronand ligand. 56 In their case, X = Cl corresponded to a paramagnetic Co(III) center whereas X = alkyl corresponded to a diamagnetic Co(III). Fivecoordinate, low-spin Co(III) compounds with acyl and alkenyl donors were also reported by Klein et al 57 X-ray Structural Studies.…”

Section: ■ Introductionmentioning

confidence: 63%

Synthesis of (POCOP)Co(Ph)(X) Pincer Complexes and Observation of Aryl–Aryl Reductive Elimination Involving the Pincer Aryl

et al. 2018

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A series of square-planar, low-spin Co(II) and Co(III) complexes supported by the POCOP pincer ligand have been prepared for the purpose of exploring the reactions potentially involved in aryl halide coupling catalysis (POCOP = 2,6-diisopropylphosphinoxyphenyl). The investigations determined that the Co(III)−aryl intermediates of the envisioned catalytic cycle are accessible, but the desired catalysis is derailed by a C−C reductive elimination reaction that involves the POCOP ligand. Metalation of the parent (POCOP)H ligand with CoCl 2 and DMAP led to the formation of (POCOP)CoCl (A-1). Metathesis of A-1 with Me 3 SiX reagents allowed isolation of (POCOP)CoBr (A-2), (POCOP)CoI (A-3), and (POCOP)CoOTf (A-4). Reactions of A-1 with NaO t Bu, MeLi, and PhLi led to (POCOP)CoO t Bu (A-5), (POCOP)CoMe (A-6), and (POCOP)CoPh (A-7). Treatment of A-1 with PhSH surprisingly led to (POCOP)CoSPh (A-8) without the need for added base. A-7 could be oxidized to (POCOP)Co(Ph)(Cl) (B-1) using Nchlorosuccinimide; however, samples of B-1 produced in this fashion were unstable with respect to decomposition to A-1. Oxidation of A-7 to (POCOP)Co(Ph)(OAc) (B-2) was accomplished with PhI(OAc) 2 , and metathesis of B-2 with Me 3 SiX produced clean samples of B-1 and (POCOP)Co(Ph)(I) (B-3) that were thermally stable. Treatment of B-1 or B-3 with NaSPh resulted in the formation of (POCOP)Co(Ph)(SPh) (B-4). Complexes B-1−B-4 are low-spin Co(III) complexes. Thermolysis of B-4, instead of the expected C−S reductive elimination, resulted in the C−C elimination with the POCOP aryl, producing (POCOP)-Ph (D-1). Hydrolysis of D-1 yielded the known 2-phenylresorcinol (D-2). The solid-state structures of A-8, B-3, and B-4 were determined by X-ray crystallography.

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“…Most of these are systems with electron-rich, often anionic ligands, and many are derived from macrocyclic ligand systems, [7][8][9][10][11] largely as a result of extensive modeling studies of vitamin B 12 . [12,13] Para-as well as diamagnetic square-pyramidal [14] and trigonal-bipyramidal [8] systems have been reported, and, in the course of the search for the elusive Co = O functional group, [15] a tetracoordinate amido-Co III complex was also structurally characterized. [11] All these complexes have interesting reactivities that are not observed in classical Co III systems, such as the efficient production of alkyl radicals [16] and CÀH activation.…”

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confidence: 99%

Stable Five‐ and Six‐Coordinate Cobalt(III) Complexes with a Pentadentate Bispidine Ligand

et al. 2008

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Tuning the stereochemistry of pentacoordinate cobalt(III) halide complexes: a rare case of trigonal bipyramidal stereochemistry for cobalt(III)

Cited by 31 publications

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Co(III) Complexes with N₂S₃-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase

Co(III) Complexes with N₂S₃-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase

Synthesis of (POCOP)Co(Ph)(X) Pincer Complexes and Observation of Aryl–Aryl Reductive Elimination Involving the Pincer Aryl

Stable Five‐ and Six‐Coordinate Cobalt(III) Complexes with a Pentadentate Bispidine Ligand

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Tuning the stereochemistry of pentacoordinate cobalt(III) halide complexes: a rare case of trigonal bipyramidal stereochemistry for cobalt(III)

Cited by 31 publications

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Co(III) Complexes with N2S3-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase

Co(III) Complexes with N2S3-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase

Synthesis of (POCOP)Co(Ph)(X) Pincer Complexes and Observation of Aryl–Aryl Reductive Elimination Involving the Pincer Aryl

Stable Five‐ and Six‐Coordinate Cobalt(III) Complexes with a Pentadentate Bispidine Ligand

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Co(III) Complexes with N₂S₃-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase

Co(III) Complexes with N₂S₃-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase