RESUMO
To evaluate bifunctional ligand reactivity involving NH acidic sites in the secondary coordination sphere of metal complexes, complexes where the proton has been substituted with a methyl group (NMe) are often investigated. An alternative strategy would involve substitution of the NH group for an O. This contribution considers and compares the merits of these approaches; the synthesis and characterization of cationic square planar Rh carbonyl complexes bearing diprotic bispyrazole pyridine ligand L1, and the bis-methylated pyrazole pyridine ligand L1Me are described. The syntheses and characterization of the novel monoprotic pyrazole isoxazole pyridine ligand L2 and aprotic bisisoxazole pyridine ligand L3, and their corresponding Rh carbonyl complexes are also described. The different CO stretching frequencies of all four Rh-complexes suggest that substitutions of NH with NMe, as well as O, lead to significant electronic differences, and these differences are further demonstrated to lead to different ligand addition/substitution reactivities of the four isoelectronic Rh-complexes. Overall, the results suggest that the electronic differences arising due to NH substitutions can be significant and must be accounted for prior to invoking the participation of the proton.
RESUMO
Herein we report a hydrogen-bonded three-dimensional network originating from a single source precursor, sym-triisopropylaminotriazine, that is both a donor and an acceptor of hydrogen bonds. The C3h symmetric design allowed the formation of intermolecular hydrogen bonds leading to helices in all three directions. The eccentric Piedfort units present in the framework with a distance of 8.15 Å between the two triazine rings allowed the CHCl3 guest to be parked.
RESUMO
Syntheses of Vaska-type complexes [IrP2X(CO)] (P = phosphine, X = halide) with all four common halides (fluoride, chloride, bromide, and iodide) was attempted using a protic and hemilabile imidazolyl di-tert-butyl phosphine ligand. In the solid-state, all four complexes were found to be ionic with the halides in the outer-sphere, and the fourth coordination site of the square plane occupied by the imidazole arm of the ligand. In solution, however, the chloride complex was found to be in equilibrium with an octahedral IrIII-H species at room temperature. For the bromide and iodide analogs, the corresponding IrIII-H species were also observed but only after heating the solutions. The neutral IrI Vaska's analogs for X = Cl, Br, and I were obtained upon addition of excess halide salt, albeit heating was required for X = Br and I. The IrIII-H species are proposed to originate from tautomerization of minor amounts of the electron rich neutral Vaska analog (halide inner-sphere and phosphines monodentate) that are in equilibrium with the ionic species. Heating is required for the larger anions of bromide and iodide to overcome a kinetic barrier associated with their movement to an inner-sphere position prior to tautormerization. For the fluoride analog, the IrIII-H was not observed, attributable to strong hydrogen bonding interactions of the imidazolyl proton with the fluoride anion.
