ABSTRACT
Twelve novel Re(I) acetonitrile complexes of the type [Re(CO)3(L)(MeCN)][WCA], with L being a chelating bis(NHC) ligand with alkylene-bridged and N-substituted bis(imidazolineylidene) moieties, and WCA (WCA = weakly coordinating anion) representing PF6(-) and [Al(OC(CF3)3)4](-), have been synthesized. 1D and 2D NMR spectroscopy as well as IR spectroscopy, elemental analysis and X-ray crystallography have been applied in characterization. The propylene-bridged complex, displaying mesitylene groups R, is discussed in depth revealing interesting chemical behaviour both in solid state and in solution. DFT calculations were undertaken to better understand the properties of such compounds. In addition, the X-ray molecular structure of the first rhenium CCC pincer complex is reported.
ABSTRACT
Using new 'normal'-substituted 1,2,3-triazolylidene silver compounds as starting materials allowed for preparation of a series of molybdenum, ruthenium, rhodium, and palladium transition metal complexes bound to the new 1,2,3-triazolylidene ligand system. In this work, the first triazolylidene Mo compound is presented as well as the first structural investigation of a silver complex with a monodentate 1,2,3-triazolylidene. Furthermore, the triazolylidene Pd complex and the Mo complex were tested as precatalysts in Suzuki-Miyaura coupling and epoxidation catalysis, respectively.
Subject(s)
Organometallic Compounds/chemistry , Organometallic Compounds/chemical synthesis , Silver/chemistry , Triazoles/chemistry , Catalysis , Crystallography, X-Ray , Ligands , Models, Molecular , Molecular StructureABSTRACT
To date, only few examples of tetrazolylidene carbenes coordinated to transition metal complexes have been described. A direct comparison of "normal" tetrazolylidenes (1,4-substitution pattern) and "abnormal" tetrazolylidenes (also referred to as "mesoionic carbenes"; 1,3-substitution pattern) has not been performed at all. In this work, we describe coordination of both ligand types to a row of transition metals. For example, the first examples of tetrazolylidene Mo, Ag, or Ir complexes have been isolated and fully characterized. The mesoionic tetrazolylidene Ag compound 2d is shown to be a viable carbene transfer reagent. By means of NMR, IR, and Raman spectroscopy, as well as X-ray crystallography and computational results, the pronounced differences between the two ligand substitution patterns are highlighted. It is shown that simply changing the position of a methyl group from N3 to N4 in the heterocycle can cause enormous differences in ligand characteristics.
Subject(s)
Coordination Complexes/chemistry , Tetrazoles/chemistry , Transition Elements/chemistry , Coordination Complexes/chemical synthesis , Ligands , Models, MolecularABSTRACT
This tutorial review summarizes all works and highlights recent advances published in the growing field of group 7 N-heterocyclic carbene (NHC) complexes. It provides a valuable source for all scientists that are interested in conducting research with new compounds bearing these metals. The article provides an overview of all manganese NHC complexes that are known to date. There are a lot of examples where manganese NHC complexes show unpredicted behaviour during synthesis, very different from other transition metal NHC complexes and their higher homologues rhenium and technetium. These differences are depicted and discussed. Furthermore, the chemistry of technetium NHC compounds and their chemical behaviour are discussed. To date published work on technetium NHC chemistry has been restricted to the oxidation state +v. It was found that such compounds are very reactive but show great stability in dry air. Their radioactivity makes such compounds interesting candidates for radiochemical applications. Since most group 7 NHC chemistry was conducted on rhenium NHC complexes, this tutorial review highlights the chemical behaviour of such compounds. Rhenium(i) complexes reveal luminescent properties, making them interesting candidates for applications ranging from biological markers to organic light-emitting diodes (OLEDs). Another interesting feature is the radioactivity of some compounds, which makes them excellent candidates for radiopharmaceutical research; hence their synthesis and reactivity are discussed.
ABSTRACT
We provide an overview on the state-of-the-art in transition-metal complexes formed with water-soluble NHC ligands. Paths to introducing water solubility by ligand design are elucidated and some general properties of water-soluble NHC complexes are highlighted. The enhanced hydrophilicity of water-soluble catalysts offers advantages in applications. While studies based on C-C coupling reactions still dominate the field, recent reports show water-soluble NHC complexes can be applied in metathesis and hydrogenation reactions and turn out to be among the best performing catalysts known. Nevertheless, wide areas of this young field remain to be investigated, offering great potential for future research.
Subject(s)
Coordination Complexes/chemistry , Transition Elements/chemistry , Catalysis , Models, Molecular , Molecular Structure , StereoisomerismABSTRACT
A new ammonia adduct of a N-heterocyclic carbene (NHC) has been isolated, which can be used as a reagent for the synthesis of transition metal carbene complexes. It represents the first example of a 1,2,3-triazolylidene with a 1,2,4-substitution pattern, thus opening a new subclass ('normal' 1,2,3-triazolylidenes) of sterically and electronically tunable NHCs.
