Anion influences on the structures of pyridyl-iminosulfonate copper(II) complexes and their reactivity in Chan–Lam couplings

Reaction of pyridylcarbaldehyde with taurine or orthanilic acid in the presence of copper salts provided copper complexes (PyC(H)N-CxHy-SO3)CuX with X = chloride, nitrate, acetate, or triflate and CxHy = o-C6H4 or C2H4. All complexes were characterized by single crystal X-ray diffraction and formed either mononuclear water adducts, dimeric complexes, or one-dimensional coordination polymers. Activities in the Chan–Lam coupling of aniline with phenylboronic acid varied by less than a factor of two between catalysts with various anions, supporting previous mechanistic claims that the anion does not participate in the formation of copper–boron intermediates. There is no difference in the performance of a catalyst with an alkyl backbone, indicating that sulfonate dissociation is not part of the catalytic cycle.

Replacing sulfonate by carboxylate: application of pyridyliminocarboxylato copper(II) complexes in rac-lactide polymerization and Chan–Evans–Lam coupling

Copper(II) complexes carrying pyridylmethyleneaminobenzoate or –propanoate ligands, LCuX, were prepared in one-pot reactions from pyridinecarboxaldehyde, aminobenzoic acid or β-alanine, and CuX2 (X = Cl, NO3, OAc, or OTf). All complexes were characterized by single-crystal X-ray diffraction studies and formed either dimers, tetramers, or coordination polymers. Attempted preparation of the respective alkoxide complexes, LCu(OR), was unsuccessful, but use of LCuX/NaOMe mixtures in rac-lactide polymerization indicated under some conditions coordination–insertion polymerization via a copper alkoxide as the mechanism. The complexes performed poorly in rac-lactide polymerization, showing low activities (12 h to completion at 140 °C), low to moderate heterotacticity (Pr = 0.6–0.8), and poor polymer molecular weight control (intramolecular transesterification). They were competent catalysts for Chan–Evans–Lam couplings with phenylboronic acid, without any indication of side reactions such as deboration or aryl homocoupling. The complexes were active in undried methanol, without addition of base, ligand, or molecular sieves. Aniline, n-octylamine, and cyclohexylamine were coupled quantitatively under identical reaction conditions. There is only little influence of the anion on activities (less than a factor of 2) but a strong influence on induction periods. The complexes were not active in CEL coupling with alcohols, phenols, or alkylboronic acids.

Synthesis of pyrido[1,2-a]indole malonates and amines through aryne annulation

Pyrido[1,2-a]indoles are known as medicinally and pharmaceutically important compounds, but there is a lack of efficient methods for their synthesis. We report a convenient and efficient route to these privileged structures starting from easily accessible 2-substituted pyridines and aryne precursors. A small library of compounds has been synthesized utilizing the developed method, affording variously substituted pyrido[1,2-a]indoles in moderate to good yields.

[4-Bromo-N-(pyridin-2-yl-methyl-idene)aniline-κN,N']bis-(1,1,1,5,5,5-hexa-fluoro-pentane-2,4-dionato-κO,O')nickel(II)

The title compound, [Ni(C₅HF₆O₂)₂(C₁₂H₉BrN₂)], the Ni^II atom exhibits a pseudo-octa­hedral coordination geometry. The structure packs through C—H⋯Br inter­actions, forming a hydrogen-bonded ladder. There are also strong hydrogen-bonding inter­actions between two of the O atoms of the β-diketonate ligands and two H atoms on the pyridine ring of the Schiff base ligand.

[(4-Bromo-phen-yl)(2-pyridyl-methyl-idene)amine-κN,N']bis-(1,1,1,5,5,5-hexa-fluoro-pentane-2,4-dionato-κO,O')cobalt(II)

In the title complex, [Co(C₅HF₆O₂)₂(C₁₂H₉BrN₂)], the Co^II atom exhibits a pseudo-octa­hedral coordination geometry, comprising two N-donor atoms from a bidentate chelate (4-bromo­phen­yl)(2-pyridyl­methyl­idene)amine (ppa^Br) ligand [Co—N = 2.098 (2) and 2.209 (2) Å] and four O-donor atoms from two bidentate chelate 1,1,1,5,5,5-hexa­fluoro­pentane-2,4-dionate (hfac) ligands [Co—O range = 2.0452 (19)–2.0796 (19) Å]. The packing of the structure involves weak π–π inter­actions between the pyridyl and benzene rings of neighbouring ppa^Br ligands [centroid–centroid distance = 3.928 (2) Å] and inter­actions between the Br atom on the ppa^Br ligand and the hfac ligand [Br⋯C = 3.531 (2) Å].