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

Abstract

Treatment of Na₂PdCl₄ or [MCl₂(PhCN)₂] with bis(4-pyridyl)diselenide yielded an insoluble product of composition [MCl₂(4,4′-(C₅H₄N)₂Se₂)]_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(P^∩P)] and [M₂Cl₂(μ-Cl)₂(PR₃)₂] with two eq. of Na(4-SeC₅H₄N) exclusively yielded cis-[M(4-SeC₅H₄N)₂(P^∩P)] (M/P^∩P = 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(4-SeC₅H₄N)(PPh₃)]_n can act as catalysts for Suzuki C–C cross coupling reaction.