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

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-C 6H4P(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 [MCl 2(COD)] with the organotin reagent 2-Me3SnC 6H4P(X)Ph2 in a 1:2 mol ratio. The reaction of [PdCl2(COD)] with 2-Me3SnC6H 4P(X)Ph2 in a 1:1 mol ratio, and the reaction of 3 with palladium(ii) acetate, give dinuclear, anion-bridged complexes [Pd 2(μ-Cl)2{κ2-2-C6H 4P(X)Ph2}2] [X = S (5), Se (6)] and [Pd 2(μ-OAc)2{κ2-2-C6H 4P(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-C6H 4PPh2)(PR3)] [R = Ph (14), 4-tolyl (16)]. The structure of complex 16 establishes that the bridging 2-C6H 4PPh2 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-OC6H4CHNC 6H4-4-R, X = S, R = OMe (17), NO2 (18); X = Se, R = OMe (19), NO2 (20)]