Khansaa Hussein

Redistribution at silicon by ruthenium complexes. Bonding mode of the bridging silanes in Ru2H4(μ-η2:η2:η2:η2-SiH4)(PCy3)4and Ru2H2(μ-η2:η2-H2Si(OMe)2)3(PCy3)2

The bis(dihydrogen) complex RuH2(η2-H2)2(PCy3)2 (1) reacts with 2 equiv. of H2SiMePh to produce a mixture of Ru2H4(μ-η2:η2:η2:η2-SiH4)(PCy3)4 (2) and RuH2(η2-H2)(η2-HSiPh3)(PCy3)2 (4) together with HSiMePh2, HSiMe2Ph and traces of HMe2SiSiMe2H as a result of redistribution at silicon. The bridging SiH4 ligand in 2 is coordinated to the two ruthenium via four σ-Si–H bonds in agreement with NMR, X-ray data (on 2, and 2′ the analogous PiPr3 complex) and DFT calculations. Each interaction involves σ-donation to a ruthenium and back-bonding from the other ruthenium. Elimination of SiH4 and formation of RuH2(CO)2(PCy3)2 (5), RuH2(tBuNC)2(PCy3)2 (6) or RuH(η2-H2)Cl(PCy3)2 (7) were observed upon the reaction of 2 with CO, tBuNC, CH2Cl2, respectively. No reaction occurred in the presence of H2, but H/D exchange was observed under D2 atmosphere. Another redistribution reaction at silicon can be obtained by adding 4 equiv. of HSi(OMe)3 to 2 to produce Si(OMe)4 and Ru2H2(μ-η2:η2-H2Si(OMe)2)3(PCy3)2 (3) displaying three bridging (μ-η2:η2 alkoxysilane) ligands. Complex 3 is characterized by multinuclear NMR spectroscopies and by a crystal structure. DFT calculations show that the model complex Ru2H2(μ-η2:η2-H2Si(OR)2)3(PR3)2 (R = H, Me) is a minimum on the potential energy surface, and support the dihydride formulation with three bridging H2Si(OMe)2 ligands coordinated to the two ruthenium through σ-Si–H bonds.

A density functional theory study of dinitrogen bonding in ruthenium complexes

Abstract Dinitrogen ruthenium complexes were theoretically studied by means of DFT technique. Several isomers of RuH 2 (N 2 )(PH 3 ) 2 , RuH 2 (N 2 ) 2 (PH 3 ) 2 and RuH 2 (H 2 )(N 2 )(PH 3 ) 2 were studied. Calculations of relative energies, geometrical parameters, vibrational frequencies and natural orbital bond analysis were performed. It is shown that the most stable isomer for each series is characterized by a trans position of the phosphines with the dinitrogen ligand trans to one hydride. As usually observed, the dinitrogen moiety adopts an end-on bonding mode and is weakly elongated from free N 2 (generally not >1%). As shown by NBO analysis, such a bonding mode involves σ-donation of about 0.2 electron from the lone pair orbital of the ruthenium-bound nitrogen toward ruthenium and back-donation of roughly 0.2 electron from the 4d occupied orbital of ruthenium to the two π g * dinitrogen orbitals.

Polycarbodiimidogermylene: synthesis, characterization, properties and theoretical studies

Abstract Polycarbodiimidogermylene was prepared by transmetallation between dichlorogermylene, dioxane ( I ) and dilithium cyanamide, by transamination between bis(triethylgermyl)carbodiimide and ( I ), or by dehydrochloration between ( I ) and carbodiimide in the presence of triethylamine. The germylene structure was confirmed by its reactivity with 3,5-di- t -butylorthocatechol, which preserves the germylene structure, and with 3,5-di- t -butylorthoquinone, which leads to the expected spirogermane. The carbodiimide form was evident by its infrared spectrum, in agreement with DFT/B3LYP calculations. Geometry optimizations of isomers of the carbodiimide and cyanamide forms for ClGe(NCNGe) n Cl ( n =1–3) confirm that the carbodiimide form is thermodynamically more stable by at least 10 kcal mol −1 . By the reaction of polycarbodiimidogermylene with dimethyldisulfide the number of terminal chlorine atoms in the polymer chains was found to be between 12 and 14 NCN groups per 2 chorines, as was further confirmed by elemental analyses. Polycarbodiimidogermylene is a semiconductor, having a volume conductivity of about 10 −2 S cm −1 . Its UV spectrum shows absorptions between 650 and 2000 nm corresponding to transitions between 0.6 and 1.9 eV, confirming transitions in the forbidden gap.

A DFT study of germane activation in ruthenium complexes. σ-coordination versus oxidative addition

The coordination of GeH4 to the ruthenium complex RuH2(η2-H2)2(PH3)2 can lead to oxidative addition or σ-bond coordination of the germane. The corresponding germyl or σ-isomers have been optimized by DFT using the B3LYP hybrid functional. The most stable isomer corresponds to a germyl bis(dihydrogen) complex RuH(GeH3)(η2-H2)2(PH3)2 (1T-b1) with trans phosphines. It is only 2 kcal mol−1 below the σ-isomer RuH2(η2-H2)(η2-H–GeH3)(PH3)2 (1C-a1). This is in contrast to what has been previously observed in the corresponding silane chemistry, in which σ-coordination was favoured. However, calculated binding energies for GeH4 or SiH4 to the RuH2(H2)(PH3)2 fragment are very similar (−21.3 and −22.2 kcal mol−1, respectively). The nature of the metal–germane interaction is analysed by natural bond orbital (NBO) calculations.

X-Ray structure and theoretical studies of RuH2(η2-H2)(η2-H-SiPh3)(PCy3)2, a complex with two different η2-coordinated σ bonds

Weak interactions between the silicon and the hydrides are responsible for the stabilization of the title complex bearing two different coordinated σ-bonds, (η2-H2) and (η2-H–SiPh3).