Extremely bulky copper(i) complexes of [HB(3,5-{1-naphthyl}2pz)3]− and [HB(3,5-{2-naphthyl}2pz)3]− and their self-assembly on graphene

Abstract

The synthesis and characterization, using NMR (¹H and ¹³C), infrared spectroscopy, and X-ray crystallography, of the ethene and carbon monoxide copper(I) complexes of hydridotris(3,5-diphenylpyrazol-1-yl)borate ([Tp^Ph₂]⁻) and the two new ligands hydridotris(3,5-bis(1-naphthyl)pyrazol-1-yl)borate ([Tp^(1Nt)₂]⁻) and hydridotris(3,5-bis-(2-naphthyl)pyrazol-1-yl)borate ([Tp^(2Nt)₂]⁻) are described. X-ray crystal structures are presented of [Cu(Tp^Ph₂)(C₂H₄)] and [Cu(Tp^(2Nt)₂)(C₂H₄)]. The compound [Cu(Tp^Ph₂)(C₂H₄)] features interactions between the protons of the ethene ligand and the π-electron clouds of the phenyl substituents that make up the binding pocket surrounding the copper(I) center. These dipolar interactions result in strongly upfield shifted signals of the ethene protons in ¹H-NMR. [Cu(Tp^(1Nt)₂)(CO)] and [Cu(Tp^(2Nt)₂)(CO)] were examined using infrared spectroscopy and were found to have CO stretching vibrations at 2076 and 2080 cm⁻¹ respectively. The copper(I) carbonyl complexes form self-assembled monolayers when drop cast onto HOPG and thin multilayers of a few nanometers thickness when dip coated onto graphene. General macroscopic trends such as the different tendencies to crystallize observed in the complexes of the two naphthyl-substituted ligands appear to extend well to the nanoscale where a well-organized monolayer could be observed of [Cu(Tp^(2Nt)₂)(CO)].