Dinuclear Rh(I,I) and Rh (II,II) complexes containing bridging asymmetrically 2,7-disubstituted naphthyridines

Article abstract of DOI:10.1016/S0020-1693(96)05147-X

The dirhodium(I) complex cis-[Rh₂(mphonp)₂(CO)₄] (1) was prepared by reaction of 5-methyl-7-phenyl-1,8-naphthyridin-2-one (Hmphonp) with [{RhCl(CO)₂}₂] in methanol in the presence of base (NaOMe). The mphonp^- ligands adopt a head-tail orientation relative to one another and bridge the Rh(I) atoms in the O2,N1 coordination mode. Treatment of RhCl₃ · 3H₂O with mphonp^- in methanol affords the dirhodium(II) complex [Rh₂(mphonp)₄] (2) in which cyclometalation leads to a novel chelating N8,C72 mode by two of the naphthyridine ligands. The Rh(II) atoms are bridged by the remaining mphonp^- ligands with the O2,N1 coordination pattern being supplemented by N⁸ as an axial donor atom. This mode requires a pronounced tilting of the bridging ligands towards the Rh-Rh axis leading to very long Rh-O2 distances (av. 2.30(2) A) and wide Rh-N1-C2 angles (av. 133(2)°). The Rh-Rh distances are 2.883(4) and 2.566(3) A in complexes 1 and 2, respectively (X-ray analyses).