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

Dalton Transactions Pub Date: 2014-06-19 DOI: 10.1039/C4DT01236D

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-OC6H4CH[double bond, length as m-dash]NC6H4-4-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.

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