Selective dynamics of [Rh(1,5-COD)(bidentate)]BF₄ complexes via NMR exchange spectroscopy

NMR exchange measurements on [Rh(1,5-COD)(bidentate)]BF₄ complexes (bidentate = chiral bis-phosphine, a P,N-phosphino-oxazoline, a P,S-phosphito-thioether and a bis-pyrazolylborate) show selective 1,5-COD dynamics which can be superficially attributed to olefin rotation. It is suggested that the mechanism actually involves: (i) M-L¹ bond breaking (L¹ = N or S-donor); (ii) isomerization of the T-shaped species; (iii) rotation around the remaining M-L² bond and (iv) recomplexation. The solid state structures of the two compounds [M(1,5-COD)(10)]BF₄, M = Rh, Ir and 10=(S,R)-2-[4-(isopropyl)oxazol-2-yl]-2′-diphenylphosphino-1,1′- binaphthyl, were determined by X-ray diffraction methods.