Syntheses of Pd(II)/Pt(II) complexes with non-chelating 4-pyridylselenolate ligand ranging from mononuclear to macrocyclic structures and their utility as catalysts in Suzuki C-C coupling reaction

Treatment of Na2PdCl4 or [MCl2(PhCN)(2)] with bis(4-pyridyl)diselenide yielded an insoluble product of composition [MCl2(4,4'-(C5H4N)(2)Se-2)](n) (1). The reactions of Na2PdCl4 with one and two eq. of Na(4-SeC5H4N) afforded insoluble products [PdCl(4-SeC5H4N)](n) (2) and [Pd(4-SeC5H4N)(2)](n) (3), respectively. On treatment with PPh3, 2 and 3 gave trans-[PdCl(4-SeC5H4N)(PPh3)(2)] (4a) and trans-[Pd(4-SeC5H4N)(2)(PPh3)(2)] (5a), respectively. The oxidative addition of bis(4-pyridyl) diselenide to Pt(PPh3)(4) exclusively yielded trans-[Pt(4-SeC5H4N)(2)(PPh3)(2)] (5b). The treatment of two eq. of Na(4-SeC5H4N) with cis-[PtX2(PR3)(2)] afforded 5b (X = Cl) and trans-[Pt(4-SeC5H4N)(2)(PEt3)(2)] (5c) (X = Cl or CF3SO3). The reactions of cis-[MCl2((PP)-P-boolean AND)] and [M2Cl2(mu-Cl)(2)(PR3)(2)] with two eq. of Na(4-SeC5H4N) exclusively yielded cis-[M(4-SeC5H4N)(2)((PP)-P-boolean AND)] (M/(PP)-P-boolean AND = Pd/dppe (6a), Pt/dppm (6b) and Pt/dppp (6c)) and [MCl(4-SeC5H4N)(PR3)](n) (7), respectively. The complex trans-[PtCl(4-SeC5H4N)(PEt3)(2)] (4b) was isolated from the redistribution reaction between 5c and cis-[PtCl2(PEt3)(2)]. The complex [PdCl(4-SeC5H4N)(PPh3)](n) (7b) exists in bi-and tri-nuclear forms, whereas [MCl(4-SeC5H4N)(PEt3)](n) (7a, 7c) and [PtCl(4-SeC5H4N)(PMe2Ph)](n) (7d) retain their trinuclear structure in solution. Molecular structures of 4a, 4b, 5a, 5c, 6a, 6c, 7a, 7b and 7c were established by single crystal X-ray diffraction analyses. The complexes trans-[PdCl(4-SeC5H4N)(PPh3)(2)] and [PdCl(4SeC(5)H(4)N)(PPh3)](n) can act as catalysts for Suzuki C-C cross coupling reaction.