Solution Equilibria in Trialkyl-Phosphite Derivatives of [Ir4(CO)12]. Crystal Structure of [Ir4(CO)11{P(OCH2)3CEt}]

✍ Scribed by Katya Besançon; Gábor Laurenczy; Tito Lumini; Raymond Roulet; Giuliana Gervasio

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: German
• Weight: 576 KB
• Volume: 76
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19930760816

✦ Synopsis

Abstract

The monosubstituted [Ir~4~(CO)~11~L] clusters (L = P(OPh)~3~, 1; L = P(OMe)~3~, 2; L = P(OCH~2~)~3~CEt, 3) were obtained in good yields by the reaction of [Ir~4~(CO)~11~I]^−^ with the corresponding phosphite. In the solid state, cluster 3 has a C~s~ geometry with all terminal ligands as shown by an X‐ray analysis. Three isomers are present in solution: one with terminal ligands (A) and two with three edge‐bridging CO's and with L in axial (B) or radial (C) position (see Scheme). The thermodynamic and kinetic parameters of isomerisations B ⇌ A and A ⇌ C were determined by simulation of the variable‐temperature ^31^P‐NMR spectra. The three isomers correspond to three minima on the kinetic pathway of CO scrambling, whose relative energies vary independently within a small range (1–9 kJ mol^−1^ at 298 K). At low temperature, isomer C is always the least stable and is not observed for 1 which bears the most bulky phosphite ligand. The isomerisations are due to two intramolecular merry‐go‐rounds of CO groups about two unequivalent faces of the unbridged species A.