To evaluate bifunctional ligand reactivity involving NH acidic sites in the secondary coordination sphere, complexes where the proton has been substituted with a methyl group (NMe) are often investigated. An alternative strategy involves 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. Comparison of the CO stretching frequencies of the four Rh complexes suggest that substitutions of NH with NMe, as well as with O, lead to significant electronic differences. These electronic differences result in different reactivities with respect to ligand addition/substitution of the Rh carbonyl complexes. Overall, the data suggest that electronic differences arising due to the NH substitutions can be significant and should be considered when the NH group is substituted in investigations of the participation of the NH proton in a reaction. Ancillary NH groups contained within ligands can participate in reactions through metal-ligand cooperation. Substitution of the NH moiety by NMe or O can be used in the evaluation of its role. This study investigates how such substitutions also affect the electronics and the binding strengths of the ligand. image

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

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 Ir-III-H species at room temperature. For the bromide and iodide analogs, the corresponding Ir-III-H species were also observed but only after heating the solutions. The neutral Ir-I 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 Ir-III-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 Ir-III-H was not observed, attributable to strong hydrogen bonding interactions of the imidazolyl proton with the fluoride anion.

A series of low-valent square-planar Rh complexes [LHRh][X] (X = PF6, Br, Cl, I) bearing two protic imidazolyl phosphines (one kappa 2) and a CO ligand were synthesized and fully characterized. A comparison of the CO stretching frequencies with those of the previously reported [LHIr][X] complexes indicates a much lower electron density at the Rh centers. This lower electron density at Rh results in a lower propensity to undergo ligand to metal proton transfer, and in contrast to observations with Ir, the [LHRh][X] complexes (X = Cl, Br, I) do not equilibrate with their metal-protonated congeners. Furthermore, the weaker bond strengths of Rh complexes compared to Ir lead to an increased degree of fluxionality in the former, along with a difference in reactivity with hydrogen (H2) and iodine (I2).

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

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.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A group of symmetrically-trisubstituted-1,3,5-triazine-based molecules have been studied extensively in order to create Piedfort pairs that are intended to be employed in sequestration of small molecules. Extensive inter and intramolecular interactions observed in the solid-state of the studied triazine molecules lead to the formation of one-dimensional ribbon and two-dimensional sheet motifs. Koneramine formation was applied as a new strategy to increase the bulkiness of the substituents on 1,3,5-triazine ring that prevented the formation of ribbons and sheets yet yielded hydrogen-bonded dimer. The protonated forms of one of the triazine compound showed that the triazine ring nitrogens are more basic than amine nitrogens on the periphery; protonated N-2,N-4,N-6-triphenyl-1,3,5-triazine-2,4,6-triamine resulted in eccentric Piedfort pairs that displayed aesthetic structural patterns possessing variety of inter and intramolecular interactions including stacking between electron deficient triazine ring of one member and electron rich aryl ring of another member.

By employing a simple strategy of reacting SO2 gas with easily attainable hydride donors such as 2-substituted-1,3-dimethy1-2,3-dihydro-1H-benzo[d]imidazole, benzimidazoline and SO2 were converted into benzimidazolium bisulfate at room temperature and atmospheric pressure. Bisulfate originated from SO2 and hydride from benzimidazoline and aerial oxygen. Metastable dimers of bisulfate anions were observed in the solid state and in solution where the anions are not stabilized by encapsulation in cages but through hydrogen bonding from benzimidazolium cations. All three benzimidazolines and resulted benzimidazolium bisulfates have been characterized using H-1 and C-13 NMR spectroscopy, high resolution electrospray ionization mass spectrometry, and single crystal X-ray diffraction techniques.