Cationic and Neutral (Ar‐BIAN)Copper(I) Complexes Containing Phosphane and Arsane Ancillary Ligands: Synthesis, Molecular Structure and Catalytic Behaviour in Cycloaddition Reactions of Azides and Alkynes

Abstract

A series of new cationic and neutral (Ar‐BIAN)copper(I) complexes [in which Ar‐BIAN = bis(aryl)acenaphthenequinonediimine] was synthesised and characterised by elemental analysis, 1D and 2D NMR spectroscopy and single‐crystal X‐ray diffraction. The cationic complexes of the general formula [Cu(Ar‐BIAN)L2]BF4 [L2 = (PPh3)2 (1), dppe (2), dppf (3), (AsPh3)2 (4); Ar = 4‐iPrC6H4 (a), 4‐MeOC6H4 (b), 4‐NO2C6H4 (c), 2‐iPrC6H4 (d), Ph2PCH2CH2PPh2 (dppe), (Ph2PC5H4)2Fe (dppf)] were synthesised by reaction of [Cu(EPh3)4]BF4 (E = P or As) and equimolar amounts of Ar‐BIAN ligands, or by reaction of equimolar amounts of [Cu(NCMe)4]BF4, 4‐iPrC6H4‐BIAN (a) and diphosphanes dppe or dppf, in dichloromethane, whereas the neutral complexes of the types [CuX(Ar‐BIAN)(EPh3)] [X = Cl, E = P (5); X = I, E = P (6); X = Cl, E = As (9)] and [{CuX(Ar‐BIAN)}2] [X = Cl (7), I (8); Ar = a, b, c, d, 2,4,6‐Me3C6H2 (e), 2,6‐iPr2C6H3 (f)] were prepared by reaction of CuCl or CuI with equimolar amounts of Ar‐BIAN and EPh3 (E = P, As or Sb) in acetonitrile under reflux conditions. The type of ancillary ligand EPh3 and the aryl substituents on Ar‐BIAN play crucial roles in determining the formation of cationic or neutral copper(I) complexes. No copper(I) complexes containing coordinated SbPh3 were isolated; all the corresponding attempts led to dimeric complexes 7 or 8. Most of the complexes crystallised easily. Their study by X‐ray diffraction revealed distorted‐tetrahedral geometries around the copper(I) centres, which are quite influenced by the various aryl substituents on Ar‐BIAN and the ancillary ligands EPh3. All complexes 1–9 except cationic dppf derivative 3a are active catalysts for cycloaddition reactions of alkynes and azides, and also show good tolerance towards functionalised substituents of alkynes and azides. Among them, the PPh3‐coordinated complexes 1, 5 and 6 afforded the highest catalytic activities [turnover frequency = 26.9–45.7 h–1].

A Series of Cu2I2 Complexes of 10‐(Aryl)phenoxarsines: Synthesis and Structural Diversity

“…Complexes of copper(I) halides with triaryl arsine ligands (AsAr 3 ) are commonly found in three main structural types: mononuclear complexes with distorted tetrahedral metal atom environments of composition [(AsAr 3 ) n L 3‐n CuX] as homoleptic (n=3) or heteroleptic (n=1,2) complexes, and [(AsAr 3 )(L−L)CuX], where L−L – two P, N or S‐mono‐ or one bidentate donor ligands; dinuclear complexes with four/four and four/three coordinated metal atoms of composition [(AsAr 3 )LCu(μ‐X)] 2 and [(AsAr 3 ) 2 Cu(μ‐X) 2 Cu(AsAr 3 )]; tetranuclear complexes (AsPh 3 ) 4 Cu 4 X 4 , with cuban‐like metal‐halogen core. The heteroleptic dinuclear copper(I) complex Cu 2 Cl 2 (AsPh 3 ) 2 (3‐amino‐5,6‐dimethyl‐1,2,4‐triazine) 2 displays strongly fluorescence effect due to the intraligand charge transfer .…”

Redox‐active BIAN‐based Diimine Ligands in Metal‐Catalyzed Small Molecule Syntheses**

“…The authors postulated that the stabilization of soluble copper(I) species and the prevention of coordinative saturation were key factors of high catalyst activities. [90,91] The application of photoactive BIAN-copper complexes to visible light-driven radical additions was reported by Soo and coworkers. A bromo-substituted [( Ar BIAN) 2 Cu] + initiated a radical chain reaction that enabled the synthesis of various Scheme 20.…”

“…[88] A rare example of a copper-catalyzed reaction with BIAN ligands was reported by Aviles and Gomes. [90,91] The azidealkyne cycloaddition proceeded smoothly with only 1 mol % of catalyst (Scheme 22). A wide survey of copper-BIAN catalyst was performed, including monomeric and dimeric, neutral and cationic complexes with various BIAN ligands and co-ligands such as phosphines.…”

Synthesis and the Optical and Electrochemical Properties of Indium(III) Bis(arylimino)acenaphthene Complexes

“…Ar-BIAN ligands were first reported in the 1960s and have been widely investigated as robust ligands for catalytically active transition metal centers since the early 1990s . Although many coordination complexes between transition metal and Ar-BIAN ligands have been described, − their main group and lanthanide counterparts remain poorly explored, with a limited selection of main group Ar-BIAN complexes being synthesized and crystallographically characterized. , …”

“…Ar-BIAN ligands are highly tunable species that are readily synthesized from cheap and commercially available anilines and acenaphthenequinone. , Functionalized Ar-BIAN compounds are acknowledged as oxidatively and thermally stable ligands for transition metal centers. The extensive π-system of the acenaphthene ring combined with the sterically modular aniline provide a broad range of π-acceptor frameworks, offering precise control over the steric, optical, and electronic properties. , Consequently, Ar-BIAN ligands have been employed in the preparation of numerous transition metal molecular compounds, which could be of use in photosensitization applications due to the characterized MLCT (metal-to-ligand charge transfer) transition from the d-orbitals of the transition metal to the π* orbitals of the Ar-BIAN ligand. ,, The low-lying π* orbitals of Ar-BIAN ligands have been successfully exploited as “capacitors” for multielectron reductions in redox noninnocent ligands. − Consequently, there have been reports of transition metal Ar-BIAN complexes being used as catalysts for organic reactions such as cycloaddition of azides and alkynes, , as well as olefin polymerization, work that had been pioneered by Brookhart and co-workers using Ni­(II) and Pd­(II) Ar-BIAN complexes. − More recently, Cu­(II) Ar-BIAN complexes have been investigated as catalysts for the reverse atom transfer radical polymerization (ATRP) of styrene . Moreover, applications of Cu­(I) Ar-BIAN complexes as light harvesters that can absorb to the NIR region have also been reported. ,, …”