Attempted deprotonation of 1,2-di(fluorenylidene)cyclobutane, 8, using n-butyl or tert-butyl-lithium led instead to 1,4-addition across the 1,3-butadiene unit to yield the 1-(9H-fluorenyl-2-(9-butyl-9H-fluorenyl)cyclobutene 10 or 11, respectively; analogously, n-butyl-lithium and trans-3,4-bis(trimethylsilyl)-1,2-di(fluorenylidene)cyclobutane, 12, furnished the corresponding 1,4-adduct 13. Bromination of 8 with N-bromosuccinimide led to mono-, di- and tri-bromo derivatives whereby, in the trans-di-bromo systems, the helical character of the trans bromines could either match (in 16) or oppose (in 17) the helicity of the fluorenylidenes. In accordance with DFT calculations, the diastereomer 17 is the favoured product, and a pure sample of 16 in solution underwent equilibration via cleavage of the C(3)–C(4) linkage such that 17 became the major isomer. Attempted addition of bromine to 3,4-di(fluorenylidene)-1,2-diphenylcyclobutene, 24, unexpectedly yielded the diketone 2,3-di(9H-fluoren-9-ylidene)-1,4-diphenylbutane-1,4-dione, 25. The structures of 10, 11, 13, 16, 17 and 25 were determined by X-ray crystallography.

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 (η6-arene)osmium(II) complex demonstrates bifunctional behavior through [4 + 2] cycloaddition with ethylene, cleavage of dihydrogen under mild conditions, and protonation/chloride addition with [Et2OH]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 (η6-arene)ruthenium(II) β-diketiminato complex proved more active for the catalytic dehydrogenation of N,N-dimethylamine borane (Me2NBH3) 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.

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.Keywords: ammonia borane; dehydrocoupling; hydrogen generation; N,N-dimethylamine borane; ruthenium(II) β-diketiminato complexes

Utilizing the aza-Wittig reaction involving the ylid 3,5-(CF3)2C6H3NPPh3 and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, a highly fluorinated and electron-withdrawing β-diketiminate was obtained. Using strong bases, nBuLi, Ag2O, or TlOEt, the corresponding β-diketiminato-Li, -Ag, or -Tl chelated complexes were prepared. Subsequent in situ transmetalation with (Ru(η6-C6H6)Cl2)2 or (Ru(η6-p-cymene)Cl2)2 afforded the half-sandwich chloro-substituted Ru(II) β-diketimino complexes in high yield. The synthesis of the Lewis acidic catalysts featuring a vacant coordination site at the metal center was accomplished using [Na]BArF (BArF = tetrakis[3,5-bis(trifluoromethyl)phenyl]boron). These complexes are active for the Lewis acid catalyzed Diels–Alder reaction between α,β-unsaturated aldehydes, that is, methacrolein, acrolein, and dienes, that is, cyclopentadiene and 2,3-dimethyl-1,3-butadiene, with conversions in the range of 66–98% under mild conditions. Whereas the herein described catalysts generally promote exo selectivity of the [4 + 2] cycloaddition between methacrolein and cyclopentadiene, the reaction involving acrolein shows predominantly the formation of the endo adduct, similar to that observed for the noncatalyzed reaction. Importantly, the coordinatively unsaturated complexes demonstrate moderate Lewis acidity, which allows for the controlled reaction between methacrolein and 2,3-dimethyl-1,3-butadiene to 1,3,4-trimethyl-3-cyclohexene-1-carboxaldehyde without further isomerization to the bicyclic ketone, which is in contrast to strong Lewis acidic catalysts based on transition metals or main-group elements reported in the literature.

A series of ruthenium−benzene complexes with β-diketiminate ligands modified with electron-withdrawing groups were prepared and characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The complexes are stable in air and undergo controlled hydrolysis in water. The complexes were evaluated for anticancer activity in vitro, and two of them proved to be highly cytotoxic, comparable or even superior to cisplatin. This work shows the potential utility of the β-diketiminate ligand in the rational design of new anticancer metal-containing drugs. A related complex with a η6-C6H5CF3 ligand was prepared and found to undergo a nucleophilic addition reaction at the coordinated arene ring to afford a substituted η5-cyclohexadienyl derivative.