Transcript Discovery of Molecular Oxidation Catalysts Using Metallo-Enzyme Mimicry and Combinatorial Chemistry Stephen B.

Discovery of Molecular Oxidation Catalysts Using
Metallo-Enzyme Mimicry and Combinatorial Chemistry
Stephen B. Colbran & D. Brynn Hibbert, School of Chemistry,
University of New South Wales, Sydney, NSW 2052, Australia
Aims
• To synthesize and screen a library of molecules combining an organometallic N-heterocyclic
carbene (NHC) centre and one or more ‘classical’ metal sites as homogeneous catalysts for
selective oxidations of organic substrates.
Results
• Routes to the precursor polytopic ligands with the NHC and bis(pyridylmethyl)amine (bpa) donor
domains to make multi-metallic complexes were developed.
• Problems of metal selectivity between the ligand domains restricted the library of complexes to
the novel bi- and tri-metallic systems 1 and 2.
• Serial screens for catalysis of styrene oxidation using series 1 and 2 were conducted. Catalytic
activity above that found for the monomeric constituent metal centres was not uncovered.
• Density functional calculations of M(IV)=O (M = Ti–Cu) species were
undertaken and point to peak activity for the latter transition metals ...
NiIV, CuIV (Zn is inactive and does form a M=O species). The reactivity
scales with increasing radical character for the oxo ligand
(i.e. as the metal centre becomes more MIII–O• like)
M1
N
N
N
N
M
N
N
1 . M 1 {(N H C )--(b p a )}M a
M 1 = R hC l(cyclo o ctad ie n e )
M a = C o 2 + , N i 2+ , C u 2 + , Z n 2 +
N
a
N
N
M1
Mb N
N
N
Ma N
N
N
N
M 1 = P d C l: M a ,b = C o 2 + , C u 2 + , Z n 2 +
M a ,b = P d C l: M 1 = R h C l, P d C l, A g C l
2 . M 1 {(p y -N H C 2 )--(b p a ) 2 }M a ,M b