Studies on the stabilisation of rhodium carbonyl clusters and tethering to inorganic oxide supports
Studies on the stabilisation of rhodium carbonyl clusters and tethering to inorganic oxide supports
Phosphine derivatives of Rh4(CO)12 and Rh6(CO)16 have been studied in solution and the solid state by i.r. and 31P n.m.r. spectroscopies. Similar investigations have been carried out on analogous derivatives anchored to inorganic exides by a pendant phosphino-silane ligand and intact cluster tethering was indicated. The stabilisation of clusters by multidentate legands has been examined and the crystal structure of Rh4(CO)9(CH2SCH2SCH2S) determined. The structure is a formally unsaturated `butterfly' with an unusual unsupported bridging carbonyl ligand spanning the `wing-tips'. Fluxional behaviour was observed by variable temperature 13C n.m.r. and a carbonyl exchange mechanism proposed involving a tetrahedral intermediate. The patented homogeneous catalyst [Rh17S2(CO)32]3- has been heterogenised by anchoring to inorganic oxides via a pendant isocyanide-silane ligand and its catalysis of synthesis gas investigated. The isocyanide derivatives have been characterised in solution by 13C, 103Rh n.m.r. and i.r. spectra and the electrochemistry of the parent carbonyl examined. The role of bridging and capping main-group atoms in transition metal cluster stabilisation has been reviewed and some rhodium phosphido clusters investigated by variable temperature 13C and 31P n.m.r. Assignment of the 31P n.m.r. resonances of Rh4(μ -PPh_2)_4 (CO)_6 and Rh_4(μ -PPh2)4 (CO)5(PPh2Et) was achieved by the aid of 2-D n.m.r. studies. The low temperature exchange mechanism proposed for Rh4(μ-PPh_2)_4(CO)_6 indicated reversible rupture of a phosphido linkage. This is only observed at above ambient temperature in the (PPh_2Et) derivative. Anchoring of a monophosphine-silane adduct and a phosphido-silane analogue to inorganic oxides was attempted and comparison of i.r. spectra suggested the former has been successful.
University of Southampton
1986
Crowte, Robert John
(1986)
Studies on the stabilisation of rhodium carbonyl clusters and tethering to inorganic oxide supports.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Phosphine derivatives of Rh4(CO)12 and Rh6(CO)16 have been studied in solution and the solid state by i.r. and 31P n.m.r. spectroscopies. Similar investigations have been carried out on analogous derivatives anchored to inorganic exides by a pendant phosphino-silane ligand and intact cluster tethering was indicated. The stabilisation of clusters by multidentate legands has been examined and the crystal structure of Rh4(CO)9(CH2SCH2SCH2S) determined. The structure is a formally unsaturated `butterfly' with an unusual unsupported bridging carbonyl ligand spanning the `wing-tips'. Fluxional behaviour was observed by variable temperature 13C n.m.r. and a carbonyl exchange mechanism proposed involving a tetrahedral intermediate. The patented homogeneous catalyst [Rh17S2(CO)32]3- has been heterogenised by anchoring to inorganic oxides via a pendant isocyanide-silane ligand and its catalysis of synthesis gas investigated. The isocyanide derivatives have been characterised in solution by 13C, 103Rh n.m.r. and i.r. spectra and the electrochemistry of the parent carbonyl examined. The role of bridging and capping main-group atoms in transition metal cluster stabilisation has been reviewed and some rhodium phosphido clusters investigated by variable temperature 13C and 31P n.m.r. Assignment of the 31P n.m.r. resonances of Rh4(μ -PPh_2)_4 (CO)_6 and Rh_4(μ -PPh2)4 (CO)5(PPh2Et) was achieved by the aid of 2-D n.m.r. studies. The low temperature exchange mechanism proposed for Rh4(μ-PPh_2)_4(CO)_6 indicated reversible rupture of a phosphido linkage. This is only observed at above ambient temperature in the (PPh_2Et) derivative. Anchoring of a monophosphine-silane adduct and a phosphido-silane analogue to inorganic oxides was attempted and comparison of i.r. spectra suggested the former has been successful.
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Published date: 1986
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Local EPrints ID: 460714
URI: http://eprints.soton.ac.uk/id/eprint/460714
PURE UUID: 60ff6b63-4aa4-427b-834a-ed4585dbdd44
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Date deposited: 04 Jul 2022 18:28
Last modified: 04 Jul 2022 18:28
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Author:
Robert John Crowte
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