A New Concept for Chelate Ligands with Planar Chirality

Half-sandwich arene ruthenium complexes: synthetic strategies and relevance in catalysis

Half-sandwich arene ruthenium complexes exhibit versatile chemistry, serve as excellent precursors and find potential applications in many organic transformations. This review mainly focuses on the chemistry of piano-stool ruthenium complexes with special emphasis on the achiral or chiral-at-ruthenium center. Also, it deals with the synthesis, nomenclature and stereochemistry of arene ruthenium complexes along with mechanistic insights into the epimerization reactions and their applications in catalytic organic transformations with some selected examples.

4,6-Bis(supermesitylphosphanylidenemethyl)dibenzofuran. Synthesis, X-ray structure and reactivity towards group 11 metals

New kinetically stabilized mono- and bis-phosphaalkene ligands (2 and 3, respectively) were synthesized via the phospha-Wittig approach. Ligand 3 was characterized by X-ray diffraction. The coordinating behaviour of the bidentate ligand was investigated towards group 11 metal centers in order to test its capacity to bind two coordination sites located in a trans-fashion. The [Au(3)][BF4], [Ag(3)(H2O)][BF4] and [Cu(3)(CH3CN)][BF4] complexes 4 , 5 and 6, respectively, were characterized by X-ray diffraction. The peculiar geometries of 4 and 6 were rationalized by means of DFT calculations.

Di- and tetranuclear palladium complexes incorporating phospha- and diphosphaferrocenes as ligands

Monophosphaferrocenes and 4 react with [Pd(COD)Cl2] (COD = cyclooctadiene) to afford cis- [Pd(1 or 4)2Cl2] complexes that slowly decompose in solution to give dimeric complexes 3 and 6 of general formula [[Pd(1 or 4)Cl]2]. In these dimers, which incorporate a Pd-Pd bond, phosphaferrocenes act as four electron donors through the phosphorus-atom lone pair (mu2-bonded) and through one orbital of appropriate symmetry at iron. These dimers can also be more conventionally prepared from the reaction of cis- [Pd(1 or 4) Cl2] complexes with [Pd(dba)2] (dba = dibenzylidene acetone). The reaction of octaethyldiphosphaferrocene (7) with [Pd(COD)Cl2] yields a dinuclear complex [Pd2(7)2Cl4] (8) in which the two ligands 7 are coordinated in a trans fashion through the phosphorus-atom lone pairs. Decomposition of 8 in solution yields a dimeric dicationic complex of general formula [[Pd2(7)2Cl]2]2+[FeCl4]2- (9a) incorporating four palladium atoms. In each ligand. one phospholyl ring behaves as a two-electron donor through the phosphorus-atom lone pair whereas the second binds two palladium centers in a mu2-fashion. A plausible mechanism that explains the formation of dimers 3, 6, and 9a involves the preliminary oxidation of the mono- or diphosphaferrocene ligand. Parallel experiments aimed at confirming this hypothesis have shown that complex 9a can be synthesized from the reaction of FeCl2 with complex 8. Also presented is another synthetic approach to the synthesis of the tetranuclear complex 9b (counterion is GaCl4-) from the reaction of the palladium(0) complex [Pd(7)2] (10) with [Pd(COD)Cl2] the presence of GaCl3 as chloride abstractor.

Preparation and characterization of ruthenium(II) monophosphaferrocene complexes. Reactivity, dynamic solution behavior, and X-ray structure of [RuH(2)(eta(2)-H(2))(PCy(3))2(2-phenyl-3,4-dimethylphosphaferrocene)]

The bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1) reacts with 2-phenyl-3,4-dimethylphosphaferrocene (L(1)) to give RuH(2)(H(2))(PCy(3))(2)(L(1)) (2). This dihydride-dihydrogen complex has been characterized by X-ray crystallography and variable-temperature (1)H and (31)P NMR spectroscopy. The exchange between the dihydrogen ligand and the two hydrides is characterized by a DeltaG() of 46.2 kJ/mol at 263 K. H/D exchange is readily observed when heating a C(7)D(8) solution of 2 (J(H-D) = 30 Hz). The H(2) ligand in 2 can be displaced by ethylene or carbon monoxide leading to the corresponding ethylene or carbonyl complexes. The reaction of 1 with 2 equiv of 3,4-dimethylphosphaferrocene (L(2)) yields the dihydride complex RuH(2)(PCy(3))(2)(L(2))(2) (5).