ortho-Metallated triphenylphosphine chalcogenide complexes of platinum and palladium: synthesis and catalytic activity

Abstract

Treatment of [PtI₂(COD)] (COD = 1,5-cyclooctadiene) with 2-LiC₆H₄P(S)Ph₂ gives the complex cis-[Pt{κ²-2-C₆H₄P(S)Ph₂}₂] (1) containing a pair of ortho-metallated triphenylphosphine sulfide rings. The selenium counterpart, [Pt{κ²-2-C₆H₄P(Se)Ph₂}₂] (2), which exists as cis- and trans-isomers in solution, and the palladium analogues, cis-[Pd{κ²-2-C₆H₄P(X)Ph₂}₂] [X = S (3), Se (4)], are obtained by transmetallation of [MCl₂(COD)] with the organotin reagent 2-Me₃SnC₆H₄P(X)Ph₂ in a 1 : 2 mol ratio. The reaction of [PdCl₂(COD)] with 2-Me₃SnC₆H₄P(X)Ph₂ in a 1 : 1 mol ratio, and the reaction of 3 with palladium(II) acetate, give dinuclear, anion-bridged complexes [Pd₂(μ-Cl)₂{κ²-2-C₆H₄P(X)Ph₂}₂] [X = S (5), Se (6)] and [Pd₂(μ-OAc)₂{κ²-2-C₆H₄P(S)Ph₂}₂] (8), respectively. Complexes 5 and 8 could not be made directly from triphenylphosphine sulfide by standard ortho-palladation procedures. The bridging framework in complexes 5 and 6 is cleaved by tertiary phosphines to give mononuclear derivatives [PdCl{κ²-2-C₆H₄P(X)Ph₂}(PR₃)] [X = S, R = Ph (11); X = Se, R = Ph (13); X = Se, R = 4-tolyl (15)]. The selenium-containing compounds 13 and 15 decompose slowly in solution giving dinuclear complexes [PdCl(μ₂-Se-κ²-P,Se-2-SeC₆H₄PPh₂)PdCl(μ-2-C₆H₄PPh₂)(PR₃)] [R = Ph (14), 4-tolyl (16)]. The structure of complex 16 establishes that the bridging 2-C₆H₄PPh₂ group is generated by reduction of the phosphine selenide unit, not by ortho-metallation of the coordinated triphenylphosphine. The chloro-bridges of 5 and 6 are also cleaved by acetylacetonate (acac) and deprotonated Schiff bases forming mononuclear species [Pd{κ²-2-C₆H₄P(X)Ph₂}L₂] [L₂ = acac, X = S (9), Se (10); L₂ = 2-OC₆H₄CHNC₆H₄-4-R, X = S, R = OMe (17), NO₂ (18); X = Se, R = OMe (19), NO₂ (20)]. The ability of complexes 5, 6 and the Schiff base-derivatives 17–20 to catalyse Heck–Mizoroki and Suzuki–Miyaura C–C bond-forming reactions has also been investigated.