A Boron‐Fluorinated Tris(pyrazolyl)borate Ligand (^FTp*) and Its Mono‐ and Dinuclear Copper Complexes [Cu(^FTp*)₂] and [Cu₂(^FTp*)₂]: Synthesis, Structures, and DFT Calculations

Abstract

Reaction of [Si(3,5-Me2 pz)4 ] (1) with [Cu(MeCN)4 ][BF4 ] (2) gave the mono- and dinuclear copper complexes [Cu2 ((F) Tp*)2 ] (3) and [Cu((F) Tp*)2 ] (4). Both complexes contain the so-far unprecedented boron-fluorinated (F) Tp* ligand ([FB(3,5-Me2 pz)3 ](-) with pz=pyrazolyl) originating from 1, acting as a pyrazolyl transfer reagent, and the [BF4 ](-) counter anion of 2, serving as the source of the {BF} entity. The solid-state structures as well as the NMR and EPR spectroscopic characteristics of the complexes were elaborated. Pulsed gradient spin echo (PGSE) experiments revealed that 3 retains (almost entirely) its dimeric structure in benzene, whereas dimer cleavage and formation of acetonitrile adducts, presumably [Cu((F) Tp*)(MeCN)], is observed in acetonitrile. The short Cu⋅⋅⋅Cu distance of 269.16 pm in the solid-state is predicted by DFT calculations to be dictated by dispersion interactions between all atoms in the complex (the Cu-Cu dispersion contribution itself is only very small). As revealed by cyclic voltammetry studies, 3 shows an irreversible (almost quasi-reversible at higher scan rates) oxidation process centred at E(pa) =-0.23 V (E(0) 1/2 =-0.27 V) (vs. Fc/Fc(+) ). Oxidation reactions on a preparative scale with one equivalent of the ferrocenium salt [Fc][BF4 ] (very slow reaction) or air (fast reaction) furnished blue crystals of the mononuclear copper(II) complex [Cu((F) Tp*)2 ] (4). As expected for a Jahn-Teller-active system, the coordination sphere around copper(II) is strongly distorted towards a stretched octahedron, in accordance with EPR spectroscopic findings.

Asymmetric Carboxycyanation of Aldehydes by Cooperative AlF/Onium Salt Catalysts: from Cyanoformate to KCN as Cyanide Source

“…Also, heteroaromatic substrates were tolerated (entries 16,17) and even highere nantioselectivities could be attained than with the first-generation protocol. With enals like trans-cinnamaldehyde or -crotonaldehyde as imilar efficiency was found for both protocols (entries [18][19][20][21].F or crotonaldehyde we demonstrated that ah ighc atalytic efficiency is maintained with reduced catalyst loadings. For instance, with a reduced catalystl oading of 0.1 mol %ayield of 81 %a nd 94 % ee wasobtained (entry 21).…”

“…PGSE (Pulsed Gradient Spin Echo) NMR experiments performed on both {Al 2 F 3 } and {Al‐F}OTf indicate that {Al 2 F 3 } retains (almost entirely) a dimeric structure in CHCl 3 , whereas {Al‐F}OTf is monomeric (the Supporting Information contains the details and results of the NMR experiments).…”

Divergent Solution and Solid-State Structures of Mono- and Dinuclear Nickel(II) Pyridone Complexes

“…Cleavage of BF 4 – to form fluoride ions in the presence of transition metals has been reported, − although it is a rare observation and only occurs only in systems with strong N - heterocyclic ligands such as pyridines, pyrazoles, and imidazoles. The decomposition is thought to be the result of F coordination of BF 4 – to a coordinately unsaturated metal center (ML n ) followed by B–F bond cleavage to yield a [ML n –1 F] − complex and a L·BF 3 adduct .…”

Ein Aluminium‐Fluorid‐Komplex mit gekoppelter Ammonium‐Einheit als außergewöhnlich aktiver kooperativer Katalysator in der asymmetrischen Carboxycyanierung von Aldehyden

“…Eine Rçntgenstruktur-analyse (Abbildung 1, rechts) sowie PGSE-NMR-Experimente ("pulsed gradient spin echo"; siehe die Hintergrundinformationen) bestätigen eine monomere Struktur der {Al-F}X-Komplexe. [17] {Al-F}OTf lieferte 3a in quantitativer Ausbeute und mit gutem ee (Nr. 11).…”