Oxidatively Induced P–O Bond Formation through Reductive Coupling between Phosphido and Acetylacetonate, 8-Hydroxyquinolinate, and Picolinate Groups

Abstract

The dinuclear anionic complexes [NBu4][(RF)2M(II)(μ-PPh2)2M'(II)(N(^)O)] (RF = C6F5. N(^)O = 8-hydroxyquinolinate, hq; M = M' = Pt 1; Pd 2; M = Pt, M' = Pd, 3. N(^)O = o-picolinate, pic; M = Pt, M' = Pt, 4; Pd, 5) are synthesized from the tetranuclear [NBu4]2[{(RF)2Pt(μ-PPh2)2M(μ-Cl)}2] by the elimination of the bridging Cl as AgCl in acetone, and coordination of the corresponding N,O-donor ligand (1, 4, and 5) or connecting the fragments "cis-[(RF)2M(μ-PPh2)2](2-)" and "M'(N(^)O)" (2 and 3). The electrochemical oxidation of the anionic complexes 1-5 occurring under HRMS(+) conditions gave the cations [(RF)2M(μ-PPh2)2M'(N(^)O)](+), presumably endowed with a M(III),M'(III) core. The oxidative addition of I2 to the 8-hydroxyquinolinate complexes 1-3 triggers a reductive coupling between a PPh2 bridging ligand and the N,O-donor chelate ligand with formation of a P-O bond and ends up in complexes of platinum(II) or palladium(II) of formula [(RF)2M(II)(μ-I)(μ-PPh2)M'(II)(P,N-PPh2hq)], M = M' = Pt 7, Pd 8; M = Pt, M' = Pd, 9. Complexes 7-9 show a new Ph2P-OC9H6N (Ph2P-hq) ligand bonded to the metal center in a P,N-chelate mode. Analogously, the addition of I2 to solutions of the o-picolinate complexes 4 and 5 causes the reductive coupling between a PPh2 bridging ligand and the starting N,O-donor chelate ligand with formation of a P-O bond, forming Ph2P-OC6H4NO (Ph2P-pic). In these cases, the isolated derivatives [NBu4][(Ph2P-pic)(RF)Pt(II)(μ-I)(μ-PPh2)M(II)(RF)I] (M = Pt 10, Pd 11) are anionic, as a consequence of the coordination of the resulting new phosphane ligand (Ph2P-pic) as monodentate P-donor, and a terminal iodo group to the M atom. The oxidative addition of I2 to [NBu4][(RF)2Pt(II)(μ-PPh2)2Pt(II)(acac)] (6) (acac = acetylacetonate) also results in a reductive coupling between the diphenylphosphanido and the acetylacetonate ligand with formation of a P-O bond and synthesis of the complex [NBu4][(RF)2Pt(II)(μ-I)(μ-PPh2)Pt(II)(Ph2P-acac)I] (12). The transformations of the starting complexes into the products containing the P-O ligands passes through mixed valence M(II),M'(IV) intermediates which were detected, for M = M' = Pt, by spectroscopic and spectrometric measurements.