Ga. Naganagowda et al., 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, MAGN RES CH, 38(4), 2000, pp. 223-228
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.