ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The redox condensation of [Ir(CO)4]-, [Ir(cod)(THF)2]+, and [Rh(cod)(THF)2]+ (cod = cycloocta-1,5-diene) followed by saturation with CO (1 atm) in THF afforded the first synthetic route to pure [Ir3Rh(CO)12] (1). Substitution of CO by monodentate ligands gave [Ir3Rh(CO)8(μ2-CO)3L] (L = Br-,2; I-, 3; bicyclo[2.2.1]hept-2-ene, 4; PPh3, 5). Clusters 2-5 have Cs symmetry with the ligand L bound to the basal Rh-atom in axial position. They are fluxional in solution at the NMR time scale due to two CO scrambling processes: the merry-go-round of basal CO's and changes of basal face. An additional process takes place in 5 above room temperature: the intramolecular migration of PPh3 from the Rh- to a basal Ir-atom. Substitution of CO by polydentate ligands gave [Ir3Rh(CO)7-x(μ2-CO)3(η4-L)x] (L = bicyclo[2.2.1]hepta-2,5-diene (= norbornadiene; nbd), x = 1, 6; L = nbd, x = 2, 13; L = cod, x = 1, 7; L = cod x = 2, 15), [Ir3Rh(CO)7(μ2-CO)3(η2-diars)] (diars = 1,2-phenylenebis-(dimethylarsine); 8), [Ir3Rh(CO)7(μ2-CO)3(η4-L)] (L = methylenebis(diphenylphosphine), bonded to 2 basal Ir-atom (9a) or one Ir- and one Rh-atom (9b)), [Ir3Rh(CO)6(μ2-CO)3(η4-nbd)PPh3] (12), and [Ir3Rh(CO)6(μ2-CO)3(μ3-L)] (L = 1,3,5-trithiane, 10; L = CH(PPh2)3, 11). Complexes 6-8, 9a, 10, and 11 have Cs symmetry, the others C1 symmetry. They are fluxional in solution due to CO scrambling processes involving 1, 3, or 4 metal centres as deduced from 2D-EXSY spectra. Comparison of the activation energies of these processes with those of the isostructural Ir4 and Ir2Rh2 compounds showed that substitution of Ir by Rh in the basal face of an Ir4 compound slows the processes involving 3 or 4 metal centres (merry-go-round and change of basal face), but increases the rate of carbonyl rotation about an Ir-atom.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19940770718
Permalink
