Rhodium, iridium and gold complexes: Applications in Catalysis 

By Dr Maria Lopez Gomez

Both scorpionate ligands and carbenes have been used for the stabilisation of otherwise unstable metal complexes and have been applied in catalysis.

Three main aspects have been considered when designing scorpionate ligands to study the systematic oxidation chemistry of a metal complex: the coordination mode of the scorpionate ligand, where the donor sets may change from soft to hard; the geometry of the resulting complexes, where uncoordinated rings or hydrogen can be orientated on top of the rhodium metal, and the flexibility of the chelate rings. These factors allow the stabilisation of Rh(II) (as in the redox-induced κ²-κ³ isomerisation in Tp' rhodium complexes where the uncoordinated pyrazolyl is orientated pseudo-parallel to the rhodium coordination plane) or enable B-H activation processes as in rhodaboratranes. This work links the chemistry of the S₃- and N₃-donors. Two series of heteroscorpionate Rh(I) complexes will be discussed, along with the Tm analogues and a series of iridaboratranes. Rhodium complexes with B-H···metal interactions and flexible scorpionate ligands, exhibit good activities as catalysts in transfer hydrogenation from PrⁱOH/KOH. Preliminary results showed higher acetophenone conversions than previously reported for analogue scorpionate Rh(I) complexes.

Moving from a rhodium catalyzed system to gold, over 2 × 10⁵ tonnes of hydrazine (H₂NNH₂) are produced annually and processed worldwide for pharmaceutical, agrochemical, polymer and aeronautic industries. Despite its industrial importance, and the central role of carbon-nitrogen bond formation in organic synthesis, this cheap N-containing building block has rarely been used as substrate in homogeneous organometallic catalysis. Anti-Bredt N-heterocyclic carbenes resemble cyclic alkyl amino carbenes (CAACs) more than NHCs, and are potential ligands for efficient gold-catalyzed intermolecular hydroaminations. A new gold(I) complex, bearing an anti-Bredt NHC, was synthesised by taking advantage of the reversible insertion of the free carbene into the N-H bond of hexamethyldisilazane, and it allowed for the room temperature hydroamination of terminal alkynes at room temperature.

Date: Friday, 27 February 2015

Time: 11:30

Venue: The Avogadro, Chemistry Building

Enquiries: Daniela Bezuidenhout, [email protected], Tel: 0124202626