Unidentate coordination of 2,2 '-bipyridine and 1,10-phenanthroline in a cyclometallated rhodium(III) complex. Evidence from H-1 and C-13 NMR spectra

The binuclear cyclometallated complex [RhCl(mu-Cl)(bBzlH(2)bz)](2) [bBzlH(2 )bzH = 1,3-bis(benzimidazolyl)benzene] undergoes a dichloro bridge cleavage reaction with 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen) in the presence of perchlorate to yield a mononuclear complex of the type RhCl(OCl O3) (bBzlH(2)bz) (N-N) (N-N = bipy or phen). Surprisingly, the N-heterocycl e, bipy or phen, is neither chelating nor bridging bidentate in the complex . Such a monodentate coordination of bipy or phen was detected using two-di mensional H-1-H-1 correlated and NOE experiments (DQF-COSY and ROESY),H-1-C -13 single- and multiple-bond correlated two-dimensional NMR experiments (P FG-HSQC and PFG-HMBC) and H-1,C-13 spin-lattice relaxation time measurement s. The non-coordination of the pendant nitrogen of the heterocycle bipy or phen is evidenced by the observation of two sets of signals together with t he presence of interligand NOEs only between the coordinated part of the he terocycle and the bisbenzimidazole as seen in the corresponding ROESY spect rum. Further, the H-1 and C-13 spin-lattice relaxation times show lower val ues for the nuclei in the coordinated part of the heterocycle, bipy or phen , than for the uncoordinated parts, supporting the fact that only one of th e two nitrogens of the heterocycle has coordinated to the metal and thus be haves as monodentate ligand. Copyright (C) 2000 John Wiley & Sons, Ltd.