1H and 13C NMR spectral studies on dicyclopentadiene complexes of rhodium(I) containing N-heterocycles

Abstract

The bridge cleavage reaction of [Rh(μ-CI)(DCPD)]₂ (DCPD = <em>endo</em>-dicyclopentadiene) with <em>exo-</em>bidentate N-he-terocycles (N - N) yields binuclear complexes of the type [{RhCl(DCPD)₂(μ-N-N)] [where N-N =pyrazine(pyz), 4,4'-bipyridyl(bpy) or <em>trans</em>-1,2-bis(4-pyridyl)ethylene(bpel)]. The ¹H NMR spectral assignments of DCPD and [Rh(μ -Cl)(DCPD)]₂ have been unequivocally confirmed by two-dimensional NMR spectroscopy. The stereochemical aspects of the latter are reflected in selective homonuclear ¹H{¹H} nuclear overhauser enhancement studies. The N-N bridged structure for the complexes [{RhCl(DCPD}]₂ (μ-N-N)] has been proposed based on the recurrence of spectral features of their precursor in addition to those of the uncoordinated N-heterocycles. The synergistic effect in the metal-olefin bonding in these complexes in manifested in the upfield shifts of olefinic proton and carbon resonances as compared with those of free DCPD. The complexes, [{RhCl(DCPD)}₂(μ -N-N)] undergo facile substitution of DCPD with carbon monoxide to afford carbonyl complexes retaining the [Rh(μ -N-N)Rh] unit.