Cationic and Neutral Rhodium( I ) Oxazolinylcarbene Complexes

Reaction of [Rh(μ‐O t Bu)(diene)] 2 [diene = 1,5‐cyclooctadiene (COD) or bicyclo[2.2.1]hepta‐2,5‐diene (NBD)] with the oxazolinylcarbene ligand precursor 2‐(4,4‐dimethyl)oxazolinylimidazolium bromide (“Me 2 carboxH + Br − ”, 2 ) yielded the five‐coordinate complexes [RhBr(Me 2 carbox)(diene)] [diene = COD ( 3 ), NBD ( 4 )]. Single‐crystal X‐ray structure analyses established a distorted trigonal bipyramidal configuration for 3 , whereas the molecular structure of 4 is distorted square pyramidal. The dynamic properties of these five‐coordinate complexes have been investigated by variable temperature 1 H NMR spectroscopy, indicating polytopal rearrangements of the five‐coordinate complexes. The two compounds were converted into the square‐planar cationic complexes [Rh(Me 2 carbox)(diene)] + ( 5 and 6 , respectively), which have been isolated and fully characterised. The rhodium complex [RhBr(Me 2 carbox)(CO)] ( 7 ) was obtained in high yield in a one‐step reaction of the ligand precursor 2 and [Rh(acac)(CO) 2 ] (acac = acetylacetonate). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)