Conformational behaviour of dinuclear Rh(I) complexes of the open-chain tetrapyrrolic ligand 2,2′-bidipyrrin (H2BDP)

The reaction of 2,2′-bidipyrrins H2BDP with the RhI complexes [Rh(COD)(μ-OMe)]2 and [Rh(CO)2(μ-Cl)]2 yields the neutral species [{Rh(COD)}2BDP] (7, 8) and [{Rh(CO)2}2BDP] (2, 9), respectively. Treatment of the COD complexes with carbon monoxide results in the exchange of all COD ligands against CO. Ligand exchange studies on the carbonyl complexes 2 and 9 with different phosphane donors reveal the regioselective exchange of one CO per metal ion. In most cases, the reaction is accompanied by a large conformational change of the tetrapyrrole from a syn to an anti conformation. This conformational change was resolved by a combination of NMR spectroscopy and X-ray diffraction studies.