Premium
Synthesis of [Ir 3 Rh(CO) 12 ] and Fluxional Behaviour of Some of Its Substituted Derivatives
Author(s) -
Bondietti Giacomo,
Laurenczy Gábor,
Ros Renzo,
Roulet Raymond
Publication year - 1994
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19940770718
Subject(s) - chemistry , norbornadiene , denticity , diphenylphosphine , intramolecular force , stereochemistry , medicinal chemistry , crystallography , bicyclic molecule , ligand (biochemistry) , crystal structure , phosphine , catalysis , organic chemistry , biochemistry , receptor
Abstract 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 [Ir 3 Rh(CO) 12 ] ( 1 ). Substitution of CO by monodentate ligands gave [Ir 3 Rh(CO) 8 (μ 2 ‐CO) 3 L] (L = Br – , 2 ; I – , 3 ; bicyclo[2.2.1]hept‐2‐ene, 4 ; PPh 3 , 5 ). Clusters 2 – 5 have C s 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 PPh 3 from the Rh‐ to a basal Ir‐atom. Substitution of CO by polydentate ligands gave [Ir 3 Rh(CO) 7– x (μ 2 ‐CO) 3 (η 4 ‐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 ), [Ir 3 Rh(CO) 7 (μ 2 ‐CO) 3 (η 2 ‐diars)] (diars = 1,2‐phenylenebis‐(dimethylarsine); 8 ), [Ir 3 Rh(CO) 7 (μ 2 ‐CO) 3 (η 4 ‐L)] (L = methylenebis(diphenylphosphine), bonded to 2 basal Ir‐atom ( 9a ) or one Ir‐ and one Rh‐atom ( 9b )), [Ir 3 Rh(CO) 6 (μ 2 ‐CO) 3 (η 4 ‐nbd)PPh 3 ] ( 12 ), and [Ir 3 Rh(CO) 6 (μ 2 ‐CO) 3 (μ 3 ‐L)] (L = 1,3,5‐trithiane, 10 ; L = CH(PPh 2 ) 3 , 11 ). Complexes 6 – 8 , 9a , 10 , and 11 have C s symmetry, the others C 1 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 Ir 4 and Ir 2 Rh 2 compounds showed that substitution of Ir by Rh in the basal face of an Ir 4 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.