Browsing by Author "Raubenheimer, Helgard G."

Now showing 1 - 7 of 7
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    18-Membered heterometallacyclic gold(I) compounds : structural influences of co-crystallized solvent
    (De Gruyter, 2012-08) Dobrzanska, Liliana; Strasser, Crishtoph E.; Schmidbaur, Hubert; Raubenheimer, Helgard G.
    ABSTRACT: No abstract available.
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    Asikliese karbeenkomplekse maak eerste opslae in goudstormloop
    (LitNet Academic, 2012-12) Raubenheimer, Helgard G.
    OPSOMMING: Die eerste karbeenkomplekse van goud is reeds in 1971 deur Bonati en Minghetti gerapporteer. Verdere ontwikkelings na die 1980’s was stadig. Sedert 2007, toe die belangstelling in goudchemie reeds geweldig toegeneem het – en kort daarna amper dol geraak het – is die oorspronklike tipe asikliese diaminokarbeenkomplekse (ADK-komplekse) van goud weer te voorskyn gehaal, aangepas, beter gekarakteriseer en gebruik in teoretiese studies, luminessensie-ondersoeke, reaksies onder ongewone, hoë-energietoestande, stoïchiometriese omsettings, enkelkristalstudies en katalitiese reaksies waarin die goudatoom as reaktiewe sentrum optree. Die katalitiese ondersoeke konsentreer aanvanklik op chemo- en regioselektiewe transformasies, maar bereik uiteindelik ’n hoogtepunt met uiters suksesvolle enantioselektiewe sikliserings van geselekteerde alkynverbindings, waarin eers dikernige katalisatore en uiteindelik selfs monokernige ADK-goudkomplekse gebruik word. Sekere ADK-ligande beïnvloed die metaal elektronies en terselfdertyd stel dit die katalisator in staat om chirale inligting gedurende die aktiveringsproses optimaal aan die substraat oor te dra. In die lig van al hierdie inligting word nuwe voorstelle vir verdere ondersoek hier gemaak.
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    AuII : skaars of afgeskeep? 'n Kritiese literatuuroorsig
    (LitNet, 2016-06-17) Raubenheimer, Helgard G.
    AFRIKAANSE OPSOMMING: Verbindings van AuII is reeds langer as 60 jaar bekend. ’n Literatuurstudie toon dat slegs ’n beperkte aantal struktuur- en bindingstipes tot dusver in suiwer vorm geïsoleer en gekarakteriseer kon word. Die grootste enkele groep bevat AuII as gekomplekseerde, kovalentgebonde [AuII–AuII]-eenhede en die twee goudatome is óf ligandgebrug (die grootste gros) óf óngebrug (’n handvol). Monokernige AuII-verbindings kom ook voor en word gekenmerk óf deur die teenwoordigheid van die eksotiese ligand Xe, óf weens chelaatvorming met bidentate of heksadentate S- of S- en O-donor-ligande, óf weens vierkantigvlak porfirien-kompleksvorming waarin imien-N en amied-N donorfunksies vervul. Die vorming van AuII gedurende nanogoudsintese, ’n rol daarvoor in homogene katalise, sowel as die stabilisering daarvan op verskillende vaste ondersteuningsplatforms, toon dat meer bruikbare toepassings in die toekoms verwag kan word. In die lig van resultate wat veral sedert 2000 verkry is, word die bestaande literatuur hier georden en bespreek en tekorte in die chemie van AuII uitgewys. Verskeie voorstelle vir verdere ondersoek word gemaak.
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    Computational investigation of Au...H hydrogen bonds involving neutral AuI N-heterocyclic carbene complexes and amphiprotic binary hydrides
    (Springer, 2019-04-26) Groenewald, Ferdinand; Raubenheimer, Helgard G.; Dillen, Jan; Esterhuysen, Catharine; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    In this computational study we investigate the ability of various neutral R-AuI-NHC (NHC = N-heterocyclic carbene) complexes [R = H, CH3, Cl, OH] to form hydrogen bonds with the amphiprotic binary hydrides NH3, H2O and HF. Optimised geometries of the adducts calculated at various levels of theory all exhibit Au···HX hydrogen bonds. In adducts of complexes containing NHC ligands with α -N–H units (NH)carbene···XH interactions also exist, yielding hydrogen-bonded rings with graph-set notation R22(6) that correspond to pseudo chelates with k²C,H coordination. AIM analysis at the MP2/aug-cc-pVTZ-pp level of theory indicates that the (NH)carbene···XH hydrogen bonds are generally stronger than the Au···HX interactions, except for those involving HF. The Au···HX interactions vary with the Lewis basicity of the Au(I) centre as a result of the nature of the R ligand, while the (NH)carbene···XH hydrogen bonds are unaffected by R. Energy Decomposition Analysis at the BP86/TZP level of theory identifies the origin of this difference as the greater component of polarisation involved in Au···HX interactions. Replacing the α(N)Hs with methyl groups prevents formation of a strong (NH)carbene···XH interaction, thus reducing the overall stabilisation of the adducts.
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    Excimer and Exciplex Formation in Gold(I) Complexes Preconditioned by Aurophilic Interactions
    (Wiley, 2020-02) Schmidbaur, Hubert; Raubenheimer, Helgard G.
    Excimers and exciplexes are defined as assemblies of atoms or molecules A/A’ where interatomic/intermolecular bonding appears only in excited states such as [A2]* (for excimers) and [AA’]* (for exciplexes). Their formation has become widely known because of their role in gas-phase laser technologies, but their significance in general chemistry terms has been given little attention. Recent investigations in gold chemistry have opened up a new field of excimer and exciplex chemistry that relies largely on the preorganization of gold(I) compounds (electronic configuration AuI (5d10)) through aurophilic contacts. In the corresponding excimers, a new type of Au···Au bonding arises, with bond energies and lengths approaching those of ground-state Au@Au bonds between metal atoms in the Au0 (5d106s1) and AuII(5d9) configurations. Excimer formation gives rise to a broad range of photophysical effects, for which some of the relaxation dynamics have recently been clarified. Excimers have also been shown to play an important role in photoredox binuclear gold catalysis.
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    Gold acyl complex formation and decarbonylation during indene synthesis from catalytically active vinylidene complexes
    (Wiley, 2015-04) Raubenheimer, Helgard G.
    The development of targeted gold acyl complexes, which are generated from dialkynes via vinylidene intermediates, and can decarbonylate to form indenes by proto-aurolysis is highlighted.
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    Gold coordination during homogeneous alkyne and allene cyclisation catalysis : coordination to substrates, to ancillary ligands and in intermediates
    (AOSIS Publishing, 2011-03-16) Raubenheimer, Helgard G.; Schmidbaur, Hubert
    The ever-increasing role of homogeneous gold catalysis in organic synthesis and the consequent need to be able to rationally control the rate and outcome of such reactions has emphasised the importance of each successive metal–carbon coordination step. Concentrating on alkyne and allene cyclisation and upon reaction mechanisms postulated on the basis of empirical and theoretical results, we have examined the coordination of gold fragments to triple bonds, the modification of gold(I) precatalysts to effect specific reaction pathways or enantioselectivity and the isolation of coordinated intermediates or model compounds thereof. Some of the recent advances that have been made in various laboratories are described in this compact review.