Neutral and cationic complexes with P-bonded 2-pyridylphosphines as N-donor ligands toward rhodium. Electrical charge vs steric hindrance on the conformational control

Article abstract of DOI:10.1021/ic0600477

Bimetallic palladium(II)-rhodium(I) and gold(I)-rhodium(I) complexes of the type [(4,4′-Me₂-bipy)(C₆F₅)Pd(μ- PPh_3-n-Py_n)Rh(diene)](BF₄)₂ and [(C₆F₅)Au(μ-PPh_3-nPy_n)Rh(diene)] (BF₄) (n = 2, 3; Py = 2-pyridyl) have been synthesized. The P donor atom of the bridging ligands (μ-PPh_3-nPy_n) is coordinated to the Pd or to the Au center. The resulting complexes react with [Rh(diolefin)(solv)₂]⁺ (solv = acetone) in a way similar to pyrazolylborates, affording square-planar or pentacoordinated rhodium complexes with two or the three N-donor ends chelating the Rh atom. The metallacycles formed upon chelation can adopt one of two conformations in the square-planar Rh(I) complexes, either bringing the other metal close to the Rh center or bringing it to a remote position. The first conformation is preferred for the gold P-coordinated complexes and the second for the palladium complexes. The X-ray structures of [(4,4′-Me₂-bipy)](C₆F ₅)Pd(μ-PPhPy₂)Rh(COD)](BF₄)₂ (COD = 1,5 cyclooctadiene) and [Au(C₆F₅)(μ-PPhPy ₂)Rh-(TFB)](BF₄) (TFB = 5,6,7,8-tetrafuoro-1,4-dihydro-1, 4-etenonaphthalene) are reported.