Asymmetric Hydrogenation of Indazole-Containing Enamides Relevant to the Synthesis of Zavegepant Using Neutral and Cationic Cobalt Precatalysts.

The cobalt-catalyzed asymmetric hydrogenation of indazole-containing enamides relevant to the synthesis of the calcitonin gene-related peptide (CGRP) receptor antagonist, zavegepant (1), approved for the treatment of migraines, is described. Both neutral bis(phosphine)cobalt(II) and cationic bis(phosphine)cobalt(I) complexes served as efficient precatalysts for the enamide hydrogenation reactions, providing excellent yield and enantioselectivities (up to >99.9%) for a range of related substrates, though key reactivity differences were observed. Hydrogenation of indazole-containing enamide, methyl (Z)-2-acetamido-3-(7-methyl-1H-indazol-5-yl)acrylate, was performed on a 20 g scale.

Alcohol Synthesis by Cobalt-Catalyzed Visible-Light-Driven Reductive Hydroformylation.

A cobalt-catalyzed reductive hydroformylation of terminal and 1,1-disubstituted alkenes is described. One-carbon homologated alcohols were synthesized directly from CO and H2, affording anti-Markovnikov products (34-87% yield) with exclusive regiocontrol (linear/branch >99:1) for minimally functionalized alkenes. Irradiation of the air-stable cobalt hydride, (dcype)Co(CO)2H (dcype = dicyclohexylphosphinoethane) with blue light generated the active catalyst that mediates alkene hydroformylation and subsequent aldehyde hydrogenation. Mechanistic origins of absolute regiocontrol were investigated by in situ monitoring of the tandem catalytic reaction using multinuclear NMR spectroscopy with syngas mixtures.

Reversible dehydrogenation of a primary aryl borane.

The consecutive activation of B-H bonds in mesitylborane (H2BMes; Mes = 2,4,6-(CH3)3C6H2) by a 16-electron rhodium(i) monocarbonyl complex, (iPrNNN)Rh(CO) (1-CO; iPrNNN = 2,5-[iPr2P[double bond, length as m-dash]N(4-iPrC6H4)]2N(C4H2)-) is described. Dehydrogenative extrusion of the {BMes} fragment led to the isolation of (iPrNNN)(CO)RhBMes (1-BMes). Addition of H2 gas to 1-BMes regenerated 1-CO and H2BMes, highlighting the ability of 1-CO to facilitate interconversion of {BMes} with dihydrogen. Reactivity studies revealed that 1-BMes promotes formal group transfer and that {BAr} fragments accessed by dehydrogenation are reactive entities.

Synthesis and Reactivity of Organometallic Intermediates Relevant to Cobalt-Catalyzed Hydroformylation.

Intermediates relevant to cobalt-catalyzed alkene hydroformylation have been isolated and evaluated in fundamental organometallic transformations relevant to aldehyde formation. The 18-electron (R,R)-(iPr DuPhos)Co(CO)2 H has been structurally characterized, and it promotes exclusive hydrogenation of styrene in the presence of 50 bar of H2 /CO gas (1:1) at 100 °C. Deuterium-labeling studies established reversible 2,1-insertion of styrene into the Co-D bond of (R,R)-(iPr DuPhos)Co(CO)2 D. Whereas rapid ß-hydrogen elimination from cobalt alkyls occurred under an N2 atmosphere, alkylation of (R,R)-(iPr DuPhos)Co(CO)2 Cl in the presence of CO enabled the interception of (R,R)-(iPr DuPhos)Co(CO)2 C(O)CH2 CH2 Ph, which upon hydrogenolysis under 4 atm H2 produced the corresponding aldehyde and cobalt hydride, demonstrating the feasibility of elementary steps in hydroformylation. Both the hydride and chloride derivatives, (X=H- , Cl- ), underwent exchange with free 13 CO. Under reduced pressure, (R,R)-(iPr DuPhos)Co(CO)2 Cl underwent CO dissociation to form (R,R)-(iPr DuPhos)Co(CO)Cl.

Di-chlorido-bis-[2-(pyridin-2-yl-κN)-1H-benzimidazole-κN 3]nickel(II) monohydrate.

In the title complex, [NiCl2(C12H9N3)2]·H2O, a divalent nickel atom is coordinated by two 2-(pyridin-2-yl)-1H-benzimidazole ligands in a slightly distorted octa-hedral environment defined by four N donors of two N,N'-chelating ligands, along with two cis-oriented anionic chloride donors. The title complex crystallized with a water mol-ecule disordered over two positions. In the crystal, a combination of O-H⋯Cl, O-H.·O and N-H⋯Cl hydrogen bonds, together with C-H⋯O, C-H⋯Cl and C-H⋯π inter-actions, links the complex mol-ecules and the water mol-ecules to form a supra-molecular three-dimensional framework. The title complex is isostructural with the cobalt(II) dichloride complex reported previously [Das et al. (2011 ▸). Org. Biomol. Chem. 9, 7097-7107].

Erratum: Di-chlorido-bis-[2-(pyridin-2-yl-κN)-1H-benzimidazole-κN 3]nickel(II) monohydrate. Corrigendum.

[This corrects the article DOI: 10.1107/S2414314620000401.].

Consecutive N2 loss from a uranium diphosphazide complex.

A new 'diphosphazidosalen' ligand was synthesized and successfully transferred to uranium using salt metathesis strategies. The resultant 8-coordinate uranium(iv) diphosphazide complex [κ6-1,2-{(N3)PPh2(2-O-C6H4)}2C6H4]UCl2 (1) is unstable to consecutive N2 loss, affording the asymmetric species [κ5-1-{(N3)PPh2(2-O-C6H4)}-2-{N=PPh2(2-O-C6H4)}C6H4)]UCl2 (2), defined by a phosphazide-phosphinimine mixed-ligand framework, and ultimately, the uranium(iv) phosphasalen complex [κ4-1,2-{N=PPh2(2-O-C6H4)}2C6H4]UCl2(THF) (3).

An H-Substituted Rhodium Silylene.

Divergent reactivity of organometallic rhodium(I) complexes, which led to the isolation of neutral rhodium silylenes, is described. Addition of PhRSiH2 (R=H, Ph) to the rhodium cyclooctene complex (iPr NNN)Rh(COE) (1-COE; iPr NNN=2,5-[iPr2 P=N(4-iPrC6 H4 )]2 N(C6 H2 )- , COE=cyclooctene) resulted in the oxidative addition of an Si-H bond, providing rhodium(III) silyl hydride complexes (iPr NNN)Rh(H)SiHRPh (R=H, 2-SiH2 Ph; Ph, 2-SiHPh2 ). When the carbonyl complex (iPr NNN)Rh(CO) (1-CO) was treated with hydrosilanes, base-stabilized rhodium(I) silylenes κ2 -N,N-(iPr NNN)(CO)Rh=SiRPh (R=H, 3-SiHPh; Ph, 3-SiPh2 ) were isolated and characterized using multinuclear NMR spectroscopy and X-ray crystallography. Both silylene species feature short Rh-Si bonds [2.262(1) Å, 3-SiHPh; 2.2702(7) Å, 3-SiPh2 ] that agree well with the DFT-computed structures. The overall reaction led to a change in the iPr NNN ligand bonding mode (κ3 →κ2 ) and loss of H2 from PhSiRH2 , as corroborated by deuterium labelling experiments.

Crystal structure of a dimeric ß-diketiminate magnesium complex.

The solid-state structure of a dimeric ß-diketiminate magnesium(II) complex is discussed. The compound, di-µ-iodido-bis-[(-{4-amino-1,5-bis-[2,6-bis-(propan-2-yl)phen-yl]pent-3-en-2-yl-idene}aza-nido-κ2N,N')magnesium(II)] toluene sesquisolvate, [Mg2(C29H41N2)2I2]·1.5C7H8, crystallizes as two independent mol-ecules, each with 2/m crystallographic site symmetry, located at Wyckoff sites 2c and 2d. These have symmetry-equivalent magnesium atoms bridged by µ-iodide ligands with very similar Mg-I distances. The two Mg atoms are located slightly below (∼0.5 Å) the least-squares plane defined by N-C-C-N atoms in the ligand scaffold, and are approximately tetra-hedrally coordinated. One and one-half toluene solvent mol-ecules are disordered with respect to mirror-site symmetry at Wyckoff sites 4i and 2a, respectively. In the former case, two toluene mol-ecules inter-act in an off-center parallel stacking arrangement; the shortest C to C' (π-π) distance of 3.72 (1) Šwas measured for this inter-action.

Elucidation of the resting state of a rhodium NNN-pincer hydrogenation catalyst that features a remarkably upfield hydride (1)H NMR chemical shift.

Rhodium(I) alkene complexes of an NNN-pincer ligand catalyze the hydrogenation of alkenes, including ethylene. The terminal or resting state of the catalyst, which exhibits an unprecedentedly upfield Rh-hydride (1)H NMR chemical shift, has been isolated and a synthetic cycle for regenerating the catalytically active species has been established.

Ultra-fast electron capture by electrosterically-stabilized gold nanoparticles.

Ultra-fast pre-solvated electron capture has been observed for aqueous solutions of room-temperature ionic liquid (RTIL) surface-stabilized gold nanoparticles (AuNPs; ∼9 nm). The extraordinarily large inverse temperature dependent rate constants (k(e)∼ 5 × 10(14) M(-1) s(-1)) measured for the capture of electrons in solution suggest electron capture by the AuNP surface that is on the timescale of, and therefore in competition with, electron solvation and electron-cation recombination reactions. The observed electron transfer rates challenge the conventional notion that radiation induced biological damage would be enhanced in the presence of AuNPs. On the contrary, AuNPs stabilized by non-covalently bonded ligands demonstrate the potential to quench radiation-induced electrons, indicating potential applications in fields ranging from radiation therapy to heterogeneous catalysis.