A new and unexpected coordination mode of a bis-phosphine monoxide (BPMO) ligand in a palladacycle complex

Abstract

A new bis-phosphine monoxide ligand of the formula [P(O)Ph2CH2PPh2C(H)C(O)C6H4-p-NO2] (1) was synthesized and its coordination chemistry explored. The reaction of this ligand with the dinuclear complex [Pd(bzq)(μ-Cl)]2 yields a mononuclear complex of formula [Pd(bzq)(P(O)Ph2C(H)PPh2C(H)C(O)C6H4-p-NO2)] (2) by means of bridge splitting reactions. The synthesized compounds have been characterized by elemental analysis, spectroscopic and crystallographic methods. A novel coordination mode for phosphine monoxide ligand (1) was found in cyclopalladated benzo[h]quinolinate complex, the ligand is coordinating to the palladium metal center through the carbon atom of methine group lying between the two phosphorus atoms and the oxygen atom of carbonyl group, acting as a chelating C,O-donor ligand. The 31P{1H} NMR spectrum of (1) contains two doublets centered at 11.45 and 29.54 ppm, due to the phosphonium and phosphine oxide groups, respectively, while in (2) the corresponding peaks are centered at 27.01 and 42.58 ppm, resulting in a 14 ppm downfield shift on complexation of the ligand to the palladium center. Overall, these types of ligands display interesting reactivity due to their diverse coordination modes and ability to attract considerable attention as an active research field.