Molecular structure and properties of the rhodium(II) complexes with chemilabile ether–phosphine ligands P(2-MeOC6H4)3 and P(2,6-(MeO)2C6H3)3

Reactions of dirhodium tetraacetate [Rh2(O2CCH3)4] with tris(2-methoxyphenyl)phosphine (OMP) yield the oxygen-metallated complexes [Rh2(μ-OAc)3{μ-(2-OC6H4)P(2-MeOC6H4)2}(HOAc)] (1·HOAc) and [Rh2(μ-OAc)3{μ-(2-OC6H4)P(2-MeOC6H4)2}(NCMe)] (1·NCMe). In the case of tris(2,6-dimethoxyphenyl)phosphine (DOMP) analogous compound [Rh2(μ-OAc)3{μ-(2-O-(6-MeO)C6H3)P(2,6-(MeO)2C6H3)2}(HOAc)] (2·HOAc) was obtained. In both ligands the CH3+ cation of one of the methoxy substituents is split off and the phosphine replaces one of the acetato bridges to form the bridge with Rh24+ core closing the six-member ring via P and O atoms. The compounds have been characterized using UV–vis, IR, 1H-, 13C{1H}- and 31P{1H}-NMR spectroscopies. The crystal structure of compound 1·NCMe has been determined. The Rh(1)Rh(2) distance is distinctly longer than that in [Rh2(OAc)4(H2O)2] (3·2H2O). Axial sites of dirhodium core are occupied by a molecule of acetonitrile and a methoxy group of one of the nonmetallated phenyl rings. Detailed NMR studies reveal dynamic properties of complex 1 involving exchange between axial methoxy substituents and tilting of the metallated ring. The complexes 1 and 2 react with carbon monoxide giving complexes with a CO ligand coordinated in axial coordination sites.