Molecular structure and properties of the rhodium(II) complexes with chemilabile ether–phosphine ligands P(2-MeOC 6H 4) 3 and P(2,6-(MeO) 2C 6H 3) 3

Abstract

Reactions of dirhodium tetraacetate [Rh 2(O 2CCH 3) 4] with tris(2-methoxyphenyl)phosphine (OMP) yield the oxygen-metallated complexes [Rh 2(μ-OAc) 3{μ-(2-OC 6H 4)P(2-MeOC 6H 4) 2}(HOAc)] ( 1·HOAc) and [Rh 2(μ-OAc) 3{μ-(2-OC 6H 4)P(2-MeOC 6H 4) 2}(NCMe)] ( 1·NCMe). In the case of tris(2,6-dimethoxyphenyl)phosphine (DOMP) analogous compound [Rh 2(μ-OAc) 3{μ-(2-O-(6-MeO)C 6H 3)P(2,6-(MeO) 2C 6H 3) 2}(HOAc)] ( 2·HOAc) was obtained. In both ligands the CH 3 + cation of one of the methoxy substituents is split off and the phosphine replaces one of the acetato bridges to form the bridge with Rh 2 4+ 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 [Rh 2(OAc) 4(H 2O) 2] ( 3·2H 2O). 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.