Homoleptic octahedral CoII complexes as precatalysts for regioselective hydroboration of alkenes with high turnover frequencies.

Homoleptic complexes adopting octahedral coordination modes are usually less active in catalysis due to the saturated coordination around metal centers that prevents substrate activation in a catalytic event. In this work, we demonstrated that a homoleptic octahedral cobalt complex (1) of 4'-pyridyl-2,2';6',2''-terpyridine that experienced monoprotonation at the non-coordinating pyridyl moiety upon crystallization could serve as a highly efficient precatalyst for the hydroboration of styrene derivatives with Markovnikov selectivity. The solid-state structure of this precatalyst along with relevant homoleptic CoII and FeII complexes has been characterized by X-ray crystallography. In the solid state, 1 features one-dimensional hydrogen-bonded chains that are further stacked by interchain π⋯π interactions. The newly synthesized complexes (1-3) along with several known analogues (4-6) were examined as precatalysts for the hydroboration of alkenes. The best-performing system, 1/KOtBu was found to promote Markovnikov hydroboration of substituted styrenes with high turnover frequencies (TOFs) up to ∼47 000 h-1, comparable to the most efficient polymeric catalyst [Co(pytpy)Cl2]n reported to date. Although some limitations in substrate scope as well as functional group tolerance exist, the catalyst shows good promise for several relevant hydrofunctionaliation reactions.

Vanadium-catalysed regioselective hydroboration of epoxides for synthesis of secondary alcohols.

Regioselective epoxide ring-opening through hydroboration catalysed by a vanadium(III) dialkyl complex supported by a redox-active terpyridine ligand is reported. Secondary alcohols were obtained in high yields via effective Markovnikov hydroboration of terminal epoxides, showcasing a new catalytic application of an earth-abundant vanadium(III) complex.

Markovnikov alcohols via epoxide hydroboration by molecular alkali metal catalysts.

Synthesis of branched "Markovnikov" alcohols is crucial to various chemical industries. The catalytic reduction of substituted epoxides under mild conditions is a highly attractive method for preparing such alcohols. Classical methods based on heterogeneous or homogeneous transition metal-catalyzed hydrogenation, hydroboration, or hydrosilylation usually suffer from poor selectivity, reverse regioselectivity, limited functional group compatibility, high cost, and/or low availability of the catalysts. Here we report the discovery of highly regioselective hydroboration of nonsymmetrical epoxides catalyzed by ligated archetypal reductants in organic chemistry ‒ alkali metal triethylborohydrides. The chemoselectivity and turnover efficiencies of the present catalytic approach are excellent. Thus, terminal and internal epoxides with ene, yne, aryl, and halo groups were selectively and quantitatively reduced under a substrate-to-catalyst ratio (S/C) of up to 1000. Mechanistic investigations point to a mechanism reminiscent of frustrated Lewis pair action on substrates in which a nucleophile and Lewis acid act cooperatively on the substrate.

Diplumbane-catalysed solvent- and additive-free hydroboration of ketones and aldehydes.

A new diplumbane, namely [Pb(CH2SiMe3)3]2, was synthesized and structurally characterized. This group 14 element compound was found to catalyse the hydroboration of ketones and aldehydes under mild conditions without the use of additives and solvents, leading to the synthesis of a range of alcohols in high yields after hydrolysis.

1-D manganese(ii)-terpyridine coordination polymers as precatalysts for hydrofunctionalisation of carbonyl compounds.

Reductive catalysis with earth-abundant metals is currently of increasing importance and shows potential in replacing precious metal catalysis. In this work, we revealed catalytic hydroboration and hydrosilylation of ketones and aldehydes achieved by a structurally defined manganese(ii) coordination polymer (CP) as a precatalyst under mild conditions. The manganese-catalysed methodology can be applied to a range of functionalized aldehydes and ketones with turnover numbers (TON) of up to 990. Preliminary results on the regioselective catalytic hydrofunctionalization of styrenes by the Mn-CP catalyst are also presented.

Copper(II)-Catalyzed Selective Hydroboration of Ketones and Aldehydes.

A novel nonanuclear copper(II) complex obtained by a facile one-pot self-assembly was found to catalyze the hydroboration of ketones and aldehydes with the absence of an activator under mild, solvent-free conditions. The catalyst is air- and moisture-stable, displaying high efficiency (1980 h-1 turnover frequency, TOF) and chemoselectivity on aldehydes over ketones and ketones over imines. This represents a rare example of divalent copper catalyst for the hydroboration of carbonyls.

Cobalt(II) Coordination Polymer as a Precatalyst for Selective Hydroboration of Aldehydes, Ketones, and Imines.

Highly effective hydroboration precatalyst is developed based on a cobalt(II)-terpyridine coordination polymer (CP). The hydroboration of ketones, aldehydes, and imines with pinacolborane (HBpin) has been achieved using the recyclable CP catalyst in the presence of an air-stable activator. A wide range of substrates containing polar C═O or C═N bonds have been hydroborated selectively in excellent yields under ambient conditions.

Cobalt-Catalyzed α-Alkylation of Ketones with Primary Alcohols.

An ionic cobalt-PNP complex is developed for the efficient α-alkylation of ketones with primary alcohols for the first time. A broad range of ketone and alcohol substrates were employed, leading to the isolation of alkylated ketones with yields up to 98%. The method was successfully applied to the greener synthesis of quinoline derivatives while using 2-aminobenzyl alcohol as an alkylating reagent.

Highly Selective Hydroboration of Alkenes, Ketones and Aldehydes Catalyzed by a Well-Defined Manganese Complex.

Well-defined manganese complexes based on inexpensive, readily available ligands, 2,2':6',2''-terpyridine and its derivatives have been prepared and employed for the selective hydroboration of alkenes, ketones and aldehydes. Highly Markovnikov regioselective hydroboration of styrenes as well as excellent chemoselective hydroboration of ketones over alkenes were achieved, for the first time, by an earth-abundant manganese catalyst.

An expedient stereoselective and chemoselective synthesis of bicyclic oxazolidinones from quinols and isocyanates.

A mild and efficient synthesis of bicyclic oxazolidinones from quinols and isocyanates, under DBU-mediated conditions at room temperature, is described. The aza-Michael addition to substituted cyclohexadienones is stereoselective and chemoselective.

Erratum: 4-[3-(Chloro-meth-yl)-1,2,4-oxadiazol-5-yl]pyridine. Corrigendum.

The title and the chemical diagram of the paper by Kang, Li, Zeng, Wang & Wang [Acta Cryst. (2007), E63, o4654] are corrected.[This corrects the article DOI: 10.1107/S1600536807055559.].

Ethyl 5-formyl-2,4-dimethyl-1H-pyrrole-3-carboxyl-ate.

The molecule of the title compound, C(10)H(13)NO(3), is approximately planar. A network of N-H⋯O and weak C-H⋯O hydrogen bonds helps to consolidate the crystal structure.

2-Chloro-N-(4-fluoro-phen-yl)acetamide.

In the title compound, C(8)H(7)ClFNO, an intra-molecular C-H⋯O hydrogen bond forms a six-membered ring. In the crystal structure, mol-ecules are linked by inter-molecular N-H⋯O hydrogen bonds, forming infinite chains along the c axis.

2-[3,4-Dibut-oxy-5-(5-phenyl-1,3,4-oxadiazol-2-yl)-2-thien-yl]-5-phenyl-1,3,4-oxadiazole.

In the title compound, C(28)H(28)N(4)O(4)S, the dihedral angles between the central thio-phene ring and its pendant oxadiazole rings are 1.2 (3) and 9.8 (3)°. The dihedral angles between the oxadiazole and phenyl rings are 2.9 (3) and 1.8 (3)°. Some short intra-molecular C-H⋯O contacts occur.

5,5'-Diethyl-2,2'-(triazene-1,3-di-yl)di-1,3,4-thia-diazole.

In the mol-ecule of the title compound, C(8)H(11)N(7)S(2), the conformation about the N=N bond is trans and the thia-diazole rings are oriented at a dihedral angle of 2.92 (3)°. In the crystal structure, inter-molecular N-H⋯S hydrogen bonds link the mol-ecules into chains. There are π-π contacts between the thia-diazole rings [centroid-to-centroid distances = 3.699 (3) and 3.720 (2) Å].