New osmium cluster compounds containing the heterocyclic ligand 2,3-bis-(diphenylphosphino)quinoxaline (dppq): Ligand isomerization and crystal structures of dppq, the isomeric clusters Os3(CO)10(dppq), and HOs3(CO)9[ -2,3-PhP(h1-C6H4)(Ph2P)quinoxaline]
- University of North Texas
- ORNL
Treatment of the labile cluster 1,2-Os{sub 3}(CO){sub 10}(MeCN){sub 2} (1) with the diphosphine ligand 2,3-bis(diphenylphosphino)quinoxaline (dppq) at room temperature affords 1,2-Os{sub 3}(CO){sub 10}(dppq) (2b) as the kinetic product of ligand substitution in 84% yield. 2b isomerizes to the thermodynamically more stable dppq-chelated cluster 1,1-Os{sub 3}(CO){sub 10}(dppq) (2c) as the sole observable product under CO at temperatures below 358 K. The kinetics for the conversion of 2b {yields} 2c have been investigated by NMR spectroscopy in CDCl{sub 3} over the temperature range 323-353 K, and the reaction was found to exhibit a rate law that is first order in 2b. The calculated activation parameters [{Delta}H{sup {ne}} = 25.4(4) kcal/mol; {Delta}S{sup {ne}} = -3(1) eu] support an intramolecular isomerization scenario, one that involves the migration of phosphine and CO groups about the cluster polyhedron. The disposition of the dppq ligand in the isomeric Os{sub 3}(CO){sub 10}(dppq) clusters has been established by X-ray crystallography and {sup 31}P NMR spectroscopy. Photolysis of 2c at 366 nm leads to CO loss and ortho metalation of one of the aryl groups on the Ph{sub 2}P moiety to furnish the hydride cluster HOs{sub 3}(CO){sub 9}[{mu}-PhP({eta}{sup 1}-C{sub 6}H{sub 4})(Ph{sub 2}P)quinoxaline] (3). The isomerization behavior exhibited by 2b follows that of related diphosphine-substituted Os{sub 3} clusters prepared by us.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1025873
- Journal Information:
- Journal of Organometallic Chemistry, Vol. 696, Issue 7; ISSN 0022-328X
- Country of Publication:
- United States
- Language:
- English
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