Research Themes

Research in the Haynes group focusses on mechanistic aspects of homogeneous transition metal catalysed reactions, particularly industrially important processes such as methanol carbonylation and alkene hydroformylation. Synthetic, spectroscopic, kinetic and computational methods are used to study the structure and reactivity of organometallic complexes and their roles in catalysis.

Mechanisms of rhodium and iridium catalysed methanol carbonylation 

The catalytic carbonylation of methanol to acetic acid is one of the most significant industrial applications of homogeneous transition metal catalysis. In collaboration with BP Chemicals, we have undertaken detailed mechanistic studies on rhodium and iridium catalysed processes, both operated on a large scale commercially. Highlights include the first spectroscopic detection of a highly reactive Rh-methyl intermediate in the rhodium-catalysed process [1] and elucidation of the role of promoters in the iridium-based CativaTM process.[2]

Ligand effects on organometallic reactivity 

We are interested in how the rates of key steps in catalytic cycles can be influenced by the electronic and steric properties of "spectator" ligands, e.g. phosphines, imines and N-heterocyclic carbenes. Strongly donating ligands tend to promote oxidative addition and retard migratory CO insertion, whereas sterically bulky ligands tend to have the opposite effects on these steps.[3] In a study of the mechanism of rhodium/xantphos-catalysed methanol carbonylation it was found that the key intermediates contained xantphos coordinated as a tridentate "pincer" ligand and the nucleophilicity of the metal center is enhanced by a Rh---O interaction.[4] Our experimental studies are complimented by theoretical (DFT) calculations, in collaboration with Prof. Anthony Meijer.

Supported catalysts

Another area of research is the heterogenisation of metal catalysts in on solid supports such as polymers and metal-organic frameworks (MOFs). A collaborative UK Catalysis Hub project looked at how the behaviour of Crabtree's hydrogenation catalyst is modified when encapsulated in a MOF using ionic interactions.[5]  In other recent projects we investigated rhodium carbonylation catalysts supported on MOFs and on dispersible microporous polymer nanoparticles.[6]

References 

1. (a) J. Am. Chem. Soc., 1991, 113, 8567; (b) J. Am. Chem. Soc., 1993, 115, 4093 

2. J. Am. Chem. Soc. , 2004, 126, 2847 

3. (a) J. Am. Chem. Soc., 2002, 124, 13597; (b) Organometallics, 2003, 22, 1047; (c) Organometallics, 2003, 22, 4451 

4. Organometallics, 2011, 30, 6166

5. Angew. Chem. Int. Ed., 2018, 57, 4532.

6. (a) Catal. Sci. Technol., 2022, 12, 664; (b) Chem. Commun., 2022, 58, 11252