title: A new insight into the chemistry of iridium(III) complexes bearing phenyl phenylphosphonite cyclometalate and chelating pyridyl triazolate: the excited-state proton transfer tautomerism via an inter-ligand PO-H···N hydrogen bond.
abstract: Treatment of [IrCl3(tht)3], where tht = tetrahydrothiophene, with two equiv. of phenyl diphenylphosphinite (pdpitH) gave [Ir(pdpitH)(pdpit)(tht)Cl2] (1), which on further reaction with 3-t-butyl-5-(2-pyridyl)-1,2,4-triazole (bptzH) and NaOAc using a one-pot reaction afforded [Ir(pdpit)2(bptz)] (2). In sharp contrast, the reaction of [IrCl3(tht)3], pdpitH, and bptzH in the presence of a stronger base, Na2CO3, afforded a phenyl phenylphosphonite (pppo)-containing Ir(III) complex [Ir(pdpit)(pppo)(bptz)] (3) that reveals a strong PO-H-N inter-ligand hydrogen bond (H-bond), as evidenced by the single crystal X-ray structural analysis. For confirmation, addition of diazomethane to a diethylether solution of 3 led to the isolation of two methylated Ir(III) isomeric complexes, i.e. [Ir(pdpit)(pppoMe)(bptz)] (4) and [Ir(pdpit)(pppo)(bptzMe)] (5), possessing either a PO-Me or N-Me bonding fragment, respectively. The absorption spectrum of 3 in CH2Cl2 resembles that of 4, implying the dominant PO-H character in solution. Despite the prevailing PO-H character both in the solid crystal and in solution, its corresponding emission resembles that of 5, leading us to propose a mechanism incorporating the excited-state inter-ligand proton transfer (ESILPT) from PO-H to N-H isomeric form via the pre-existing PO···H···N hydrogen bond. The thermodynamics of proton transfer tautomerism are discussed on the basis of absorption/emission spectroscopy in combination with computational approaches; additional support is given by the relationship between emission pattern versus the position of protons and methyl substituents. The results demonstrate for the first time a paradigm of excited-state proton transfer for the transition metal complexes in the triplet manifold.
authors.affiliation: Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan. ychi@mx.nthu.edu.tw.
authors.forename: Cheng-Huei
authors.initials: CH
authors.lastname: Lin
authors.forename: Jia-Ling
authors.initials: JL
authors.lastname: Liao
authors.forename: Yu-Sin
authors.initials: YS
authors.lastname: Wu
authors.forename: Kuan-Yu
authors.initials: KY
authors.lastname: Liao
authors.forename: Yun
authors.initials: Y
authors.lastname: Chi
authors.forename: Chi-Lin
authors.initials: CL
authors.lastname: Chen
authors.forename: Gene-Hsiang
authors.initials: GH
authors.lastname: Lee
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
mesh_terms: D002614:Chelating Agents / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D006860:Hydrogen Bonding; D007495:Iridium / Q000737:chemistry*; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D010720:Phosphines / Q000737:chemistry*; D013237:Stereoisomerism; D014230:Triazoles / Q000737:chemistry*
chemical_list: D002614:Chelating Agents; D056831:Coordination Complexes; D010720:Phosphines; D014230:Triazoles; D007495:Iridium; C044646:phosphine; D009584:Nitrogen