An extensive study of interaction energies in ion pairs of pyrrolidinium and imidazolium ionic liquids is presented. The Cnmpyr and Cnmim cations with varying alkyl chains from Methyl, Ethyl, n-Propyl to n-Butyl were combined with a wide range of routinely used IL anions such as chloride, bromide, mesylate (CH3SO3 or Mes), tosylate (CH3PhSO3 or Tos), bis(trifluoromethanesulfonyl)amide (NTf2), dicyanamide (N(CN)2 or dca), tetrafluoroborate (BF4) and hexafluorophosphate (PF6). A number of energetically favourable conformations were studied for each cation-anion combination. The interaction energy and its dispersion component of the single ion pairs were calculated using a sophisticated state-of-the-art approach: a second-order of Symmetry Adapted Perturbation Theory (SAPT). A comparison of energetics depending on the cation-anion type, as well as the mode of interaction was performed. Dispersion forces were confirmed to be of importance for the overall stabilisation of ionic liquids contributing from 28 kJ mol(-1) in pyrrolidinium ion pairs to 59 kJ mol(-1) in imidazolium ion pairs. The previously proposed ratio of total interaction energy to dispersion components and melting points was assessed for this set of ionic liquids and was found to correlate with their melting points for the anionic series, producing separate trends for the Cnmim and Cmpyr series of cations. Chlorides, bromides and tetrafluoroborates formed close-to-ideal correlations when both types of cations, Cnmim and Cnmpyr, were combined in the same trend. Correlation of the dispersion component of the interaction energy with transport properties such as conductivity and viscosity was also considered. For imidazolium-based ionic liquids strong linear correlations were obtained, whereas pyrrolidinium ionic liquids appeared to be insensitive to this correlation.

A series of bisNHC chelate ligands with alkyl bridges of different chain lengths and their palladium complexes have been prepared. The influence of the different bridges on the solid-state structure and reactivity of the complexes has been studied. The catalytic activity of the palladium complexes was successfully tested in the Mizoroki−Heck reaction and the catalytic CH activation of methane. The ethylene-bridged palladium complex showed the highest catalytic activity in the CH activation of methane and the Mizoroki−Heck coupling of bromoarenes, while for unreactive chloroarenes bisNHC complexes with longer bridges give better results.

A series of novel pyrimidine functionalized palladium(II)(NHC) complexes with aryl and alkyl substituents [1-(2-Pyrimidyl)-3-(aryl or alkyl)imidazoline-2-ylidene palladium(II) chlorides] was synthesized by transmetalation via the corresponding silver complexes. All compounds have been fully characterized by 1H and 13C NMR spectroscopy, elemental analysis, and in two cases by X-ray single crystal structures. Different solid state structures were observed for aryl and alkyl substituted ligands: for the sterically less demanding methyl substituent, a complex is formed, where two ligands are coordinated to one metal center [Pd(L)2Cl]+, while in the mesityl case a [Pd(L)Cl2] structure was observed. They show good catalytic activity in the CH activation of methane as well as in the Mizoroki-Heck reaction, where especially the methyl substituted complex shows a remarkably high activity combined with a very high selectivity.

Although examples of nickel(ii), palladium(ii) and platinum(ii) N-heterocyclic tetracarbene complexes are known in the literature, particularly platinum(ii) tetracarbene complexes are rare. We developed a new synthetic route via biscarbene acetate complexes, which make homoleptic as well as heteroleptic platinum(ii) tetracarbene complexes accessible. The reported photoluminescence data show that these complexes have good quantum yields and photostability and are a promising class of emitters for PhOLEDs. Characterization of the compounds includes a solid-state structure of the homoleptic complex bis(1,1'-diisopropyl-3,3'-methylenediimidazoline-2,2'-diylidene)platinum(ii) dibromide.

No abstract