Solution Behavior and Structural Properties of Cu(I) Complexes Featuring m-Terphenyl Isocyanides

Abstract

The synthesis of the m-terphenyl isocyanide ligand CNAr (Mes2) (Mes = 2,4,6-Me 3C 6H 2) is described. Isocyanide CNAr (Mes2) readily functions as a sterically encumbering supporting unit for several Cu(I) halide and pseudo halide fragments, fostering in some cases rare structural motifs. Combination of equimolar quantities of CNAr (Mes2) and CuX (X = Cl, Br and I) in tetrahydrofuran (THF) solution results in the formation of the bridging halide complexes (mu-X) 2[Cu(THF)(CNAr (Mes2))] 2. Addition of CNAr (Mes2) to cuprous chloride in a 2:1 molar ratio generates the complex ClCu(CNAr (Mes2)) 2 in a straightforward manner. Single-crystal X-ray diffraction has revealed ClCu(CNAr (Mes2)) 2 to exist as a three-coordinate monomer in the solid state. As determined by solution (1)H NMR and FTIR spectroscopic studies, monomer ClCu(CNAr (Mes2)) 2 resists tight binding of a third CNAr (Mes2) unit, resulting in rapid isocyanide exchange. Contrastingly, addition of 3 equiv of CNAr (Mes2) to cuprous iodide readily affords the tris-isocyanide species, ICu(CNAr (Mes2)) 3, as determined by X-ray diffraction. Similar coordination behavior is observed in the tris-isocyanide salt [(THF)Cu(CNAr (Mes2)) 3]OTf (OTf = O 3SCF 3), which is generated upon treatment of (C 6H 6)[Cu(OTf)] 2 with 6 equiv of CNAr (Mes2) in THF. The disparate coordination behavior of the [CuCl] fragment relative to both [CuI] and [CuOTf] is rationalized in terms of structure and Lewis acidity of the Cu-containing fragments. The putative triflate species [Cu(CNAr (Mes2)) 3]OTf itself serves as a good Lewis acid and is found to weakly bind C 6H 6 in an eta (1)- C manner in the solid-state. Density Functional Theory is used to describe the bonding and energetics of the eta (1)- C Cu-C 6H 6 interaction.

Tris-isocyanide copper(I) complexes: Synthetic, structural, and theoretical study

“…Reported (isocyanide)Cu I complexes are prepared by the treatment of CuX (X = Cl, Br, I) or [Cu(NCMe) 4 ]X (X = BF 4 , PF 6 ) with the appropriate amount of isocyanides [26][27][28][29]36,37]. Single known complex of the type [CuBr(CNR) n ], viz.…”

“…The 1 H and 13 C{ 1 H} NMR spectra of 1-4 featuring one set of signals, which correspond to resonances of protons or 13 C, respectively, of substituent R in the CNR ligands. Analytical and spectroscopic data give evidences that CuBr forms tris-isocyanide complexes with selected CNR's similarly to {CuI} analogs [36,37].…”

“…the tris-isocyanide complexes [CuX(CNR) 3 ] (X = I, R = 4-MeC 6 H 4 [36], 2,5-(Mes) 2 C 6 H 3 [37]; X = Br, R = t-Bu [33]) and the bis-isocyanide complexes [CuCl(CNR) 2 ] (R = 2,5-(Mes) 2 C 6 H 3 [37], t-Bu [29]) were obtained and structures of two chloride and two iodide derivatives were verified by X-ray crystallography. In the cases of [CuI(CNC 6 H 3 (Mes)-2,5) 3 ] and [CuCl(CNC 6 H 3 (Mes)-2,5) 2 ], different coordination behavior is rationalized in terms of Lewis acidity of the Cu-containing fragments, which is greater for the {CuI} fragment relative to the {CuCl} fragment [37] and this explains the higher Lewis acid catalytic activity of {Cu}I salts than their {CuCl} analogues. Within respect to the Lewis acidity and catalytic behavior of copper species featuring the {CuX} functionality, this range should be completed by addition of the {CuBr} moiety.…”

Protecting-Group-Free Access to a Three-Coordinate Nickel(0) Tris-isocyanide

“…Using the m-terphenyl isocyanide CNAr Mes2 (Mes = 2,4, 6-Me 3 C 6 H 2 ), 23 we previously reported the synthesis of the three-coordinate Ni complex Ni(CNAr Mes2 ) 3 , 24 which shares several structural and electronic features with the binary carbonyl Ni(CO) 3 . Nevertheless, a thallium(I) triflate (TlOTf) coordination-site protection strategy was necessary for the synthesis of Ni(CNAr Mes2 ) 3 because of facile formation of the tetra-isocyanide complex, Ni(CNAr Mes2 ) 4 , upon combination of CNAr Mes2 and the Ni(0) source, Ni(COD) 2 (COD = 1,5-cyclooctadiene).…”

Thallium(I) as a Coordination Site Protection Agent: Preparation of an Isolable Zero‐Valent Nickel Tris‐Isocyanide

“…For neutral d 10 [Ni(CO) 3 ], analogues possessing strongly s-donating phosphines, such as [Ni-(PR 3 ) 3 ], have been widely investigated, [4] whereas recent attention has been given to three-coordinate species featuring NHC ligands. [8] Herein we present the use of CNAr Mes 2 in the isolation of the tris-isocyanide complex [Ni(CNAr Mes 2 ) 3 ]. However, isolation or experimental verification of this species have not been achieved.…”