Formation and crystallographic elucidation of stable [4 + 2]-coordinate nickel(ii) N,S-heterocyclic carbene (NSHC) complexes

Abstract

A series of square-planar N,S-heterocyclic carbene (NSHC) complexes trans-[NiX(2)(N-RBzTh)(2)] (BzTh = benzothiazolin-2-ylidene) (R/X = Bz/Br; Me/I; Et/I; Pr(i)/I; Bu(i)/I) have been synthesized and characterized by X-ray single-crystal diffraction analysis. These are the first crystallographically established NSHC complexes of nickel in the literature. The N,S-heterocyclic carbene (NSHC) rings invariably twist away from co-planarity with the metal coordination plane such that the N-substituent moves on top and below the metal to facilitate electrostatic gamma-hydride interaction, thus giving an essentially [4 + 2] coordination at the Ni(ii) center. These compounds are active toward reductive Ullmann-type coupling reactions in Bu(4)NBr showing higher activities towards bromoanisole or bromotoluene than bromobenzene. The complex trans-[NiI(2)(N-Pr(i)BzTh)(2)] with the shortest NiH anagostic separation and a near-ideal orthogonal orientation between the carbene and metal planes gives the highest yields.

Solvent-free synthesis of benzothiazole-based quaternary ammonium salts: precursors to ionic liquids

“…Optimization of each reaction, primarily the reaction temperature, afforded good yields of these salts comparable or better to those previously reported. 24,25,37 The yields were found to increase with increasing chain length of the alkylating agent. Three crystal structures of long chain alkylbenzothiazolium iodides were analyzed (12-14a).…”

“…(Syntheses of iodide salts 2a-9a, and 14a, and trifluoromethanesulfonate salts 2c and 9c have been previously reported, but the data available is limited to spectroscopic results without physical characterization. [23][24][25] The ions pack in a bilayer-type structure with the alkyl chains interdigitated and the cation head groups and iodide ions forming a polar region. This type of packing has been observed previously in long alkyl chain imidazolium ionic liquids, 26 as well as other similar molecules with polar head groups and long non-polar alkyl chains.…”

“…[23][24][25] The ions pack in a bilayer-type structure with the alkyl chains interdigitated and the cation head groups and iodide ions forming a polar region. This type of packing has been observed previously in long alkyl chain imidazolium ionic liquids, 26 as well as other similar molecules with polar head groups and long non-polar alkyl chains. 27 There is no pi-stacking between cationic head groups.…”

CH⋯Pd interactions: One dimensional heteropolynuclear complexes

“…These hydrogen bonds are played an important role in packing and stabilizing the structures formed, and sometimes they are played an important role as a possible exchange path for magnetic interactions [10]. The CAHÁ Á ÁM interactions are relevant with d 8 systems and considered to be of importance for understanding the catalytic reactions [11]. These CAHÁ Á ÁM interactions are best described as the three-center four electrons (3c-4e).…”

1D cyanide complexes with 2-pyridinemethanol: Synthesis, crystal structures and spectroscopic properties

“…CeH/M interactions have been characterized either as agostic or anagostic, depending upon geometrical parameters [10e12]. While agostic CeH/M interactions can controlled the tacticity of polymers [13], anagostic CeH/M interactions are generally observed in several catalytic processes [14]. The investigation on cyanide bridged polymeric metal complexes containing Cu(II) ion using square planar tetracyanopalladate(II) [15e17] and tetracyanoplatinate(II) [18e20], which are generally formed by d 8 metal ions, as building blocks are quite limited in the literature.…”