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Variable‐Temperature and ‐Pressure 31 P‐NMR Study of the Intramolecular PPh 3 Migration in the Cluster Compound [Ir 2 Rh 2 (CO) 11 PPh 3 ]
Author(s) -
Laurenczy Gábor,
Bondietti Giacomo,
Merbach André E.,
Moullet Bertrand,
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.19940770216
Subject(s) - chemistry , intramolecular force , phosphine , isomerization , ligand (biochemistry) , proton nmr , stereochemistry , crystallography , cluster (spacecraft) , catalysis , organic chemistry , biochemistry , receptor , computer science , programming language
The reaction of [Ir 2 Rh 2 (CO) 12 ] with 1 mol‐equiv. of PPh 3 yields [Ir 2 Rh 2 (CO) 11 PPh 3 ] ( 1 ) as a mixture of two isomers with the phosphine ligand axially bound either to one basal Rh‐atom in the kinetically preferred isomer 1 R or to one basal Ir‐atom in the thermodynamically preferred isomer 11 . Both isomers are fluxional on the 13 C‐NMR time scale at low temperature due to CO scrambling. Around room temperature, a new type of fluxional process starts to operate which is responsible for the isomerisation 1R⇄11 , i.e. the intramolecular migration of the reputedly inert PPh 3 ligand from one metal centre to another. The activation volumes of conversions 1R → 11 and 11 → 1R are both positive, indicating that the migration of PPh 3 is dissociative in character. This article reports the first application of variable pressure 31 P‐NMR to mechanistic studies.