Complexes of rhodium(I) with 1,8-naphthyridine and related ligands. Crystal structure of [Rh2(µ-napy)2(nbd)2][ClO4]2·H2O

Abstract

Reactions of stoicheiometric amounts of 1,8-naphthyridine (R-napy) type ligands with [{RhCl(diolefin)}₂] or [Rh(diolefin)(OCMe₂)_x][ClO₄] lead to formation of the complexes [RhCl(diolefin)(napy)], [Rh(diolefin)(2,7Me₂-napy)][ClO₄][diolefin = cyclo-octa-1,5-diene (cod), norborna-2,5-diene (nbd), tetrafluorobenzobarrelene (tfbb), trimethyltetrafluorobenzobarrelene (Me₃tfbb)], [Rh₂(µ-R-napy)₂(diolefin)₂][ClO₄]₂·H₂O (R = H or 2-Me; diolefin = nbd or tfbb), or [Rh(cod)(2Me-napy)][ClO₄]. Mononuclear complexes of the type [Rh(diolefin)(R-napy)₂][ClO₄] are obtained in the presence of an excess of the R-napy ligand. Several tetracarbonyl or dicarbonyl derivatives of formulae [Rh(napy)₂(CO)₂][ClO₄], [Rh₂(µ-R-napy)₂(CO)₄][ClO₄]₂, [Rh₂(µ-R-napy)₂(CO)₂(PPh₃)₂][ClO₄]₂, and [(diolefin)Rh(µ-napy)₂Rh(CO)(PPh₃)][ClO₄]₂ have been prepared from [Rh(CO)(PPh₃)(OCMe₂)_x][ClO₄] or by carbonylation reactions. The structure of [Rh₂(napy)₂(nbd)₂][ClO₄]₂·H₂O has been determined by X-ray diffraction methods. Crystals are orthorhombic, space group Pccn with Z= 4 in a unit cell of dimensions a= 17.539(11), b= 10.252(7), and c= 17.211(12)Å. The structure was solved by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.063 for 1 427 independent observed reflections. The cationic complex [Rh₂(napy)₂(nbd)₂]²⁺, having an imposed symmetry C₂, is binuclear with two napy ligands bridging the two metals. The co-ordination around each Rh atom is completed by a nbd molecule interacting through the two olefin bonds. The distance between the bridged Rh atoms is 2. 916(3)Å.