Synthesis, Structures, and Optical Properties of Ruthenium(II) Complexes of the Tris(1-pyrazolyl)methane Ligand

Four new complex salts [Ru^(II)Cl(Tpm)(L^A)_2][PF_6]_n [Tpm = tris(1-pyrazolyl)methane; n = 1, L^A = pyridine (py) 1 or ethyl isonicotinate (EIN) 2; n = 3, L^A = N-methyl-4,4′-bipyridinium (MeQ^+) 3 or N-phenyl-4,4′-bipyridinium (PhQ^+) 4] have been prepared and characterized. Electronic absorption spectra show intense d → π^* metal-to-ligand charge-transfer (MLCT) absorption bands, while cyclic voltammetry reveals a reversible Ru^(III/II) wave, accompanied by quasireversible or irreversible L^A-based reductions for all except 1. Single crystal X-ray structures have been obtained for 1•Me_2CO, 2, and 3•Me_2CO. For 2–4, molecular first hyperpolarizabilities β have been measured in acetonitrile solutions via the hyper-Rayleigh scattering (HRS) technique at 800 nm. Stark (electroabsorption) spectroscopic studies on the MLCT bands in frozen butyronitrile allow the indirect estimation of static first hyperpolarizabilities β_0. The various physical data obtained for 3 and 4 are compared with those reported previously for related cis-{Ru^(II)(NH_3)_4}^(2+) species [Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845]. TD-DFT calculations on the complexes in 1–4 confirm that their lowest energy absorption bands are primarily Ru^(II) → L^A MLCT in character, while Ru^(II) → Tpm MLCT transitions are predicted at higher energies. DFT agrees with the Stark, but not the HRS measurements, in showing that β_0 increases with the electron-accepting strength of L^A. The 2D nature of the chromophores is evidenced by dominant β_(xxy) tensor components

Rhodium(I) complexes of the conformationally rigid IBioxMe4Ligand : isolation of a stable low-coordinate T-shaped complex

The isolation, characterization and reactivity of a T-shaped rhodium(I) complex containing Glorius’ bioxazoline derived N-heterocyclic carbene ligand IBioxMe4 is described: [Rh(IBioxMe4)3][BArF4] (1). 1 represents a rare example of a solution-stable “naked” 14-electron complex and is characterized in the solid state by highly distorted ligand geometries and Rh···C distances >3.1 Å for the IBioxMe4 alkyl substituents. Consistent with the bulky nature of the NHC ligand, no reaction was observed with excess IBioxMe4, PCy3, or norbornadiene. Reaction of 1 with CO, however, led to coordinatively saturated [Rh(IBioxMe4)3(CO)][BArF4] (2)

Osmium(II)–bis(dihydrogen) complexes containing caryl,CNHC–chelate ligands: Preparation, bonding situation, and acidity

The hexahydride complex OsH6(PiPr3)2 (1) reacts with the BF4-salts of 1-phenyl-3-methyl-1-H-benzimidazolium, 1-phenyl-3-methyl-1-H-5,6-dimethyl-benzimidazolium, and 1-phenyl-3-methyl-1-H-imidazolium to give the respective trihydride-osmium(IV) derivatives OsH3(κ2-Caryl,CNHC)(PiPr3)2 (2–4). The protonation of these compounds with HBF4·OEt2 produces the reduction of the metal center and the formation of the bis(dihydrogen)-osmium(II) complexes [Os(κ2-Caryl,CNHC)(η2-H2)2(PiPr3)2]BF4 (5–7). DFT calculations using AIM and NBO methods reveal that the Os–NHC bond of the Os-chelate link tolerates a significant π-backdonation from a doubly occupied dπ(Os) atomic orbital to the pz atomic orbital of the carbene carbon atom. The π-accepting capacity of the NHC unit of the Caryl,CNHC-chelate ligand, which is higher than those of the coordinated aryl group and phosphine ligands, enhances the electrophilicity of the metal center activating one of the coordinated hydrogen molecules of 5–7 toward the heterolysis. As a result, these compounds are strong Brønsted acids with pKawater values between 2.5 and 2.8. In acetonitrile the hydrogen molecules of 5 and 6 are displaced by the solvent, the resulting bis(solvento) compounds [Os(κ2-Caryl,CNHC)(CH3CN)2(PiPr3)2]BF4 (8, 9) react with acetylacetonate (acac) and cis-1,2-bis(diphenylsphosphino)ethylene (bdppe) to give Os(κ2-Caryl,CNHC)(acac)(bdppe) (10, 11) as a mixture of the two possible isomers, namely with P trans to the aryl group or to the NHC moiety.Financial support from the Spanish MINECO (Projects CTQ2011-23459 and CTQ2013-44303-P), the Red de Excelencia Consolider (CTQ2014-51912-REDC), the DGA (E35), the European Social Fund (FSE) and FEDER, and Universal Display Corporation is acknowledged. T.B. thanks the Spanish MINECO for funding through the Juan de la Cierva programme.Peer reviewe