Helgard G. Raubenheimer
Title: Professor Extraordinary
Office: 2002 Inorganic Building
Phone: +27 (0)21 808-3850
Fax: +27 (0)21 808-3849
E-mail
Educational Background:
PhD, University of Stellenbosch, 1970
Postdoctoral studies: TU Munich
Sabbaticals: TUM, ETH (Zurich)
Awards:
Gold Medal (Research) of the South African Chemical Institute, 2002
Rector's Award for Research at Stellenbosch University, 2003
Alexander von Humboldt, DAAD and Oppenheimer Memorial Trust scholarships
Memorial lectureships: Victor Pretorius (University of Pretoria, 2000); P.D. Hahn (Royal Society, UCT, 2004)
Dedication of a Special Edition of Zeitschrift für Naturforschung B on the occasion of 65th birthday; contribution by 26 internationally recognized chemists. Such publications (for example by D Seebach) also appeared in other journals.
Recipient of Havenga Medal, South Africa Academy for Science and Arts, 2008.
Received invitations from editors of Chem Soc Reviews and Chemical Reviews to write reviews on latest results obtained in Stellenbosch, 2008.
Research Emphasis:
Coordination Chemistry, gold compounds, carbene ligands, heterocyclic ligands
The central theme of our work is 'Ligand and Complex Design of Carbene and Related Complexes'. Investigations are mostly directed toward homogeneous catalysis, anti-tumour activity (specifically of gold-containing compounds) and most recently, crystal engineering and solid state dynamics.
Research Description:
Anionic Fischer-type Carbene Complexes: After the first preparation of transition metal metalloxycarbene complexes in the early seventies, we recently returned to this theme with renewed energy. We have now shown that the compounds (CO)5W=C(R)OZr(Cl)Cp2 (R = Me, Ph) act via a non-standard mechanism as active precursors for short as well as longer chain alpha-olefin oligomerisations, polimerisations and co-polymerisations.
In an in-depth first investigation of reactions between related carbene anions, (CO)5M=C(X)Y- (X = Me, Ph and Y = O, S, NMe; X = OR, SR, NR2 and Y = CH2), and the soft metal fragment Ph3PAu+, we have unearthed new compounds, unknown bonding patterns and useful isolobal as well as synthetic synthon relationships that are presently still further extended in mechanistic studies. We have also introduced the 'complex of complexes' concept using the related bidentate ligands (CO)5M=C(azolyl)O- (azolyl = neutral N-donor group). The coordination of the complex ligand to a second metal atom is not only influenced by donor atoms and chelate ring size but also by the first metal and ligands attached thereto creating the opportunity for ligand fine-tuning in an unprecedented manner.
NHC complexes: Extensive investigations are being undertaken in the extremely active N-heterocyclic carbene area of research. Our most recent contributions involve the first N-heterocyclic carbene complexes with remote and abnormal heteroatoms, rNHC’s. The limits of the rNHC concept have now been tested by preparing complexes with the heteroatom only present in a neighbouring ring. An important objective here remains complete elucidation of the nature of the metal-carbene bond and differentiation between the relative importance of ionic (cationic charge on heteroatom) and covalent (carbene) forms.
N-heterocyclic compounds as N- or S-donor ligands: An investigation into the coordination of a group of ligands derived from the vitamin B1 analogue 4-methylthiazole, has revealed that the soft Au(I) metal centre, when provided with a choice between borderline (hard/soft) imine and soft endo- and exocyclic thioether ligands, prefers imine coordination completely contradicting HSAB generalisations in the literature.
In a now completed comprehensive study of gold(I), gold(II) and gold(III) complexes that contain synthetically important pfp and tht ligands, a gold(II) compound that unprecedentedly contains no chelating ligands has been rationally synthesised by unusual radical transfer and gold-gold bond formation.
Combining my knowledge of classical coordination chemistry, the synthetic skills of postdoc Liliana Dobrzanska and the solid state expertise of Len Barbour, have led to some startling discoveries reported in three papers. We illustrate how careful manipulation (engineering) combined with an innovative attitude could lead to functional materials.
Selected Publications:
- One-N, six-membered heterocyclic carbene complexes and the remote heteroatom concept. H.G. Raubenheimer and S. Cronje. Dalton Trans., 2008, 1265-1272.
- Carbene complexes of gold: preparation, medical application and bonding. H.G. Raubenheimer and S.Cronje. Chem. Soc. Rev., 2008, 37, 1998-2011.
- Intermolecular aurophilic interactions facilitate assembly of a complex rotaxane in solution. U.E.I. Horvath, J.McKenzie, S. Cronje, H.G. Raubenheimer and L.J. Barbour. Chem. Comm., 2009, 6598-6600
- Ligating properties of anionic Fischer-type carbene complexes, [(CO)5M=C(X)Y]−. H.G. Raubenheimer, S.Cronje, and C.E. Strasser. Dalton Trans., 2009, 8145-8154.
- Beyond conventional N-heterocyclic carbenes: abnormal, remote, and other classes of NHC ligands with reduced heteroatom stabilization . O. Schuster, L. Yang, H.G. Raubenheimer and M. Albrecht. Chem. Rev., 2009, 109, 3445-3478.
- Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II). E. Stander-Grobler, O. Schuster, G. Heydenrych, E. Tosch, M. Albrecht, G. Frenking and H.G. Raubenheimer. Organometallics, 2010, 29, 5821-5833.
- Gold coordination during homogeneous alkyne and allene cyclisation catalysis: Coordination to substrates, to ancillary ligands and in intermediates. H.G. Raubenheimer and H. Schmidbaur. S.Afr. J. Sci., 2011, 107(3/4), Art. #459, 13 pages.