Amine borane type substrates show significant potential as safe and effective chemical hydrogen storage materials. β-Diketiminato(η6-arene)-Ru(II) complexes have shown the ability to rapidly perform the heterolytic cleavage of H2 under mild conditions through bifunctional metal-ligand interaction. The presented work explores the applicability of such complexes toward the catalytic dehydrogenation of different substituted amine boranes, in particular, ammonia borane (AB) and N,N-dimethylamine borane (DMAB). Complex [(η6-C6H6)-Ru(2,6-(CH3)2-C6H3NC(CH3))2CH]OTf (1) showed excellent activity in the catalytic release of a single equivalent of H2 within 0.5 h from a concentrated DMAB solution in THF (3.2 M) at near ambient temperatures. Studies involving structural analogues of 1 allowed insight into the operational dehydrocoupling mechanism. It is concluded from this preliminary work that in solution, 1 forms a homogeneous bifunctional active species that does not undergo deactivation, even after prolonged exposure to H2 at elevated pressures.

The strongly chelating anionic β-diketiminate ligand has been employed to formulate complexes involving almost every metal of the periodic table; however, the heavier metals of the d block remain relatively unexplored. This paper describes the synthesis and characterization of the first two osmium β-diketiminato compounds, including a coordinatively unsaturated cationic complex. In parallel to the analogous Ru(II) complexes, the cationic (η 6arene)osmium(II) complex demonstrates bifunctional behavior through [4 + 2] cycloaddition with ethylene, cleavage of dihydrogen under mild conditions, and protonation/chloride addition with [Et 2 OH]Cl. Metal-centered activity in both the Ru(II) and Os(II) β-diketiminates has until now remained elusive, as the cationic Os complex is shown to readily coordinate an aryl isonitrile. The applicability of Os(II) β-diketiminato complexes in catalytic olefin hydrogenation demonstrates significantly greater activity in terms of conversion and TOF for a range of substrates, including styrene, cyclohex-1-ene, and 1-methylcyclohex-1-ene. Moreover, selective hydrogenation of the exocyclic alkenyl group in limonene was observed, whereas the corresponding isostructural Ru(II) complexes are inactive. In contrast, the cationic (η 6arene)ruthenium(II) β-diketiminato complex proved more active for the catalytic dehydrogenation of N,N-dimethylamine borane (Me 2 NBH 3 ) than the equivalent Os(II) species. A detailed DFT study of the Ru(II) and Os(II) β-diketiminato species using charge decomposition analysis (CDA) demonstrates differences in metal−ligand interactions, which in turn considerably influences the extent of bifunctional reactivity.

3,3-(Biphenyl-2,2'-diyl)-1-alpha,alpha,alpha-trifluoro-p-tolyl-allene, 9, sequentially forms head-to-tail, 12, cis-tail-to-tail, 13, and trans tail-to-tail, 14, 1,2-dialkylidene-cyclobutane dimers, each of which has been characterised by X-ray crystallography. Thermolysis at 180 degrees C yields the dispirotetracene, 15, and di-indenotetracene, 16; the latter compound forms an air-stable Diels-Alder adduct, 17, with N-methylmaleimide. In contrast, the dibenzo[a,d]cycloheptenylidene-allenes, (C(14)H(10))C=C=C(Br)Ph, 20a, and (C(14)H(10))C=C=C(H)Ph, 21a, do not dimerise under relatively mild conditions. However, protonation of the bromo-allene, 20a, and subsequent addition of hydride, provide a facile entry to the difficultly accessible bowl-shaped dibenz[cd,h]azulene framework, as in 30, that had not previously been structurally characterised. Among others, the X-ray crystal structures of 12, 13, 14, 17, 20a, 21a and 30 are reported.

In comparison to β-diketiminates, a highly exploited class of N,N-chelating ligands, the corresponding βthioketoiminates, monothio-substituted analogues, have received only minor attention. β-Thioketoiminates are straightforwardly prepared through treatment of an appropriate β-ketoiminate with Lawesson's reagent. Employing standard synthetic techniques for η 6 -arene Ru(II) and Os(II) β-diketiminate complexes, an analogous series of chlorido-metal complexes supported by different sized N-aryl substituted β-thioketoiminate ligands is reported. However, metal ligation of a β-thioketoiminate bearing an electron-withdrawing CF 3 group was not possible. The metal− chlorine bond in these complexes is readily activated by various sodium or silver salts of weakly coordinating anions, affording coordinately unsaturated cationic formally 16-electron species. All η 6 -C 6 H 6 metal β-thioketoiminate complexes were characterized by NMR and in the solid state using single crystal X-ray diffraction techniques. Structural studies reveal that incorporation of a thio-group induces substantial bond angle distortion within the metallocycle. The reactivity of the cationic η 6 -C 6 H 6 Ru(II) β-thioketoiminate complexes toward alkynes and isonitriles is analogous to that of the β-diketiminate species. Specifically, the reaction with 1-hexyne results in a [4 + 2] cycloaddition involving the metal and β-C sites, while reaction with isonitrile completely displaces the η 6 -C 6 H 6 ligand. A comprehensive DFT study employing charge decomposition analysis (CDA) reveals a strong covalent metal−sulfur bond which dominates the metal β-thioketoiminate interaction. The M−S bond (M = Ru or Os) is strengthened by charge transfer from metal to sulfur, in contrast to the β-diketiminate species where back electron donation from the metal to the nitrogen centers is negligible. The first reported β-selenoketoiminate was prepared by reacting a β-ketoiminate with the Woolins' reagent. However, this seleno-analog demonstrated significant instability with respect to hydrolysis, and coordination to an η 6 -arene Ru(II) or Os(II) moiety proved unsuccessful.

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