title: Thermochromic organometallic complexes: experimental and theoretical studies of 16- to 18-electron interconversions of adducts of arene Ru(II) carboranes with aromatic amine ligands.
abstract: A series of 18-electron complexes of general formula [Ru(p-cym)(1,2-dicarba-closo-dodecaborane-1,2-dithiolato)(L)] (p-cym = para-cymene; L = 4-dimethylaminopyridine (2), nicotinamide (3), 3-ethynylpyridine (4), N-methylimidazole (5), 4-cyanopyridine (6), and pyridine (7)) were synthesised by reactions between the 16-electron precursor [Ru(p-cym)(1,2-dicarba-closo-dodecaborane-1,2-dithiolato)] (1) and corresponding heterocyclic bases. X-ray crystal structures of complexes 2 and 5 were determined. In dichloromethane and chloroform solutions at ambient temperature, the 18-electron complexes 2-7 are in equilibrium with the 16-electron precursor 1. Each equilibrium is displaced towards the formation of the blue 16-electron or yellow 18-electron complex by increasing or decreasing the temperature of the solution, respectively, which results in controlled and reversible thermochromism. Binding constants (K) and Gibbs free energies (ΔG°) of the six equilibria have been determined by a combination of experiments (Job plots, UV-visible titrations, NMR studies) and also by computation (time-dependent density functional theory, TD-DFT). A linear free energy relationship for log K versus pK(a) for the pyridine and imidazole ligands was established. The predicted strong interactions of 1 with other aromatic amine ligands, such as amphetamine derivatives, were verified experimentally. This appears to be the first report of reversible 16/18-electron interconversions with associated thermochromic properties for a well-known family of complexes.
authors.affiliation: Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Nicolas P E
authors.initials: NP
authors.lastname: Barry
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Deeth
authors.forename: Guy J
authors.initials: GJ
authors.lastname: Clarkson
authors.forename: Ivan
authors.initials: I
authors.lastname: Prokes
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Sadler
mesh_terms: D000588:Amines / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004583:Electrons; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D012428:Ruthenium / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000588:Amines; D009942:Organometallic Compounds; D012428:Ruthenium