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Cyril & Tutta Vetter Choppin Hall Room 614 |
Research Bi-
and Polymetallic Cooperativity in Homogeneous Catalysis Carbonylation
Catalysis: Asymmetric
Hydroformylation Catalysis Polyphosphine
Synthetic Methodology Molecular Modeling in Homogeneous Catalyst Design |
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We have designed and synthesized a new
class of binucleating polydentate phosphine ligands for preparing novel
bimetallic transition metal complexes. Considerable interest has been shown
in showing that multiple metal centers can exhibit cooperative behavior in
catalytic reactions and show superior activities and selectivities relative
to monometallic complexes. This goal
has been dramatically achieved through the design and synthesis of a new
binucleating tetraphosphine ligand that can bridge and chelate two metal
centers. This ligand, called et,ph-P4, exists in the two
diastereomeric forms shown to the left. [Rh2(norb)2(et,ph-P4)](BF4)2 (norb = norbornadiene, structure shown to right) is a precursor for a remarkable bimetallic hydroformylation catalyst. Hydroformylation is the largest homogeneous industrial catalytic process for converting alkenes, H2 and CO, into aldehyde products. |
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"A Bimetallic Hydroformylation Catalyst:
Homobimetallic Cooperativity Produces High Regioselectivities and Reaction
Rates" |
Our bimetallic catalyst has similar activity, but higher selectivities for linear aldehyde products compared to current commercial Rh/PPh3 catalysts. The activity and selectivity of our bimetallic catalyst is extremely unusual because electron-rich chelating phosphines like et,ph-P4 are well known to generally deactivate rhodium toward hydroformylation and lower the selectivity to linear aldehyde. We have demonstrated (Science, 1993) that this catalyst represents one of the most dramatic examples of bimetallic cooperativity in homogeneous catalysis. |
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Bimetallic Hydroformylation Catalysis: In Situ Characterization of a Dinuclear Rh(II) Hydride Complex and Observation of the Largest Rhodium-Hydride NMR Coupling Constant. Rhonda D. Carter, Donna K. Howell, Wei-Jun Peng, Spencer G. Train, W. Dale Treleaven and George G. Stanley, Angew. Chem. Int. Ed. Engl., 35, 2253-2256 (1996); Angew. Chem., 108, 2402-2405 (1996) |
The exceptional activity of our catalyst arises from the presence of a stable cationic charge on each rhodium center (dicationic overall) and efficient bimetallic cooperativity between the two rhodium centers in the form of several intramolecular hydride transfer steps. We have performed extensive in situ FT-IR
and NMR studies on our catalyst system and have strong to tentative
structural assignments for all complexes observed in the NMR. This work has
been featured on the cover of Angewandte Chemie (1996). We
have proposed that the active bimetallic catalyst has the highly unusual
dicationic dihydride Rh(+2) metal-metal bonded structure shown below.
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We are actively continuing our studies into this exciting new bimetallic catalyst system, with emphasis on asymmetric catalytic reactions and extensions of bimetallic cooperativity into other new types of catalytic reactions. Our research laboratory has state-of-the-art computerized autoclave facilities and a high pressure IR cell (see figure to the left) for in situ catalytic studies. There is considerable industrial interest in this radically new catalyst, and we are working closely with several chemical companies on this project. |
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