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.

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.

Stepwise formation of iridium(III) complexes with monocyclometalating and dicyclometalating phosphorus chelates.

With the motivation of assembling cyclometalated complexes without nitrogen-containing heterocycle, we report here the design and systematic synthesis of a class of Ir(III) metal complexes functionalized with facially coordinated phosphite (or phosphonite) dicyclometalate tripod, together with a variety of phosphine, chelating diphosphine, or even monocyclometalate phosphite ancillaries. Thus, treatment of [IrCl(3)(tht)(3)] with stoichiometric amount of triphenylphosphite (or diphenyl phenylphosphonite), two equiv of PPh(3), and in presence of NaOAc as cyclometalation promoter, gives formation of respective tripodal dicyclometalating complexes [Ir(tpit)(PPh(3))(2)Cl] (2a), [Ir(dppit)(PPh(3))(2)Cl] (2b), and [Ir(dppit)(PMe(2)Ph)(2)Cl] (2c) in high yields, where tpitH(2) = triphenylphosphite and dppitH(2) = diphenyl phenylphosphonite. The reaction sequence that afforded these complexes is established. Of particular interest is isolation of an intermediate [Ir(tpitH)(PPh(3))(2)Cl(2)] (1a) with monocyclometalated phosphite, together with the formation of [Ir(tpit)(tpitH)(PPh(3))] (3a) with all tripodal, bidentate, and monodentate phosphorus donors coexisting on the coordination sphere, upon treatment of 2a with a second equiv of triphenylphosphite. Spectroscopic studies were performed to explore the photophysical properties. For all titled Ir(III) complexes, virtually no emission can be observed in either solution at room temperature or 77 K CH(2)Cl(2) matrix. Time-dependent DFT calculation indicates that the lowest energy triplet manifold involves substantial amount of metal centered (3)MC dd contribution. Due to its repulsive potential energy surface (PES) that touches the PES of ground state, the (3)MC dd state executes predominant nonradiative deactivation process.