Crystallographic report: Crystal structures of organometallic aqua complexes [Cp*Rh III (bpy)(OH 2 )] 2+ and [Cp*Rh III (6,6′‐Me 2 bpy)(OH 2 )] 2+ used as key catalysts in regioselective reduction of NAD + analogues

Crystal structures of organometallic aqua complexes [Cp*Rh III (bpy)(OH 2 )] 2+ ( 1 , Cp* = η 5 ‐C 5 Me 5 , bpy = 2,2′‐bipyridine) and [Cp*Rh III (6,6′‐Me 2 bpy)(OH 2 )] 2+ ( 2 , 6,6′‐Me 2 bpy = 6,6′‐dimethyl‐2,2′‐bipyridine) used as key catalysts in regioselective reduction of NAD + analogues were determined definitely by X‐ray analysis. The yellow crystals of 1 (PF 6 ) 2 and orange crystals of 2 (CF 3 SO 3 ) 2 used in the X‐ray analysis were obtained from aqueous solutions of 1 (PF 6 ) 2 and 2 (CF 3 SO 3 ) 2 . The Rh–O aqua length of 2.194(4) Å obtained for 1 (PF 6 ) 2 is significantly different from that of 2.157(3) Å obtained for the previously reported disorder model [Cp*Rh III (bpy)(0.7H 2 O/0.3CH 3 OH)](CF 3 SO 3 ) 2 ·0.7H 2 O in which the coordinated water is replaced by a coordinated methanol. The five‐membered ring involving the Rh atom and the 6,6′‐Me 2 bpy chelating unit in 2 (CF 3 SO 3 ) 2 is not flat, whereas the five‐membered chelate ring in 1 (PF 6 ) 2 is nearly flat. Such a non‐planar structure in 2 (CF 3 SO 3 ) 2 is ascribed to the steric repulsion between the 6,6′‐Me 2 bpy ligand and the Cp* ligand. Copyright © 2005 John Wiley & Sons, Ltd.