Synthesis and Structural Characterization of New Cu(I) Complexes with the Antithyroid Drug 6-n-Propyl-thiouracil. Study of the Cu(I)-Catalyzed Intermolecular Cycloaddition of Iodonium Ylides toward Benzo[b]furans with Pharmaceutical Implementations

The reaction of copper(I) iodide with 6-n-propylthiouracil (ptu) in the presence or absence of the triphenylphosphine (tpp) or tri(p-tolyl)phosphine (tptp) in a 1:1:2 molar ratio forms the mixed ligand Cu(I) complex with formula [CuI(ptu)(2)](toluene) (1), [CuI(tpp)(2)(ptu)] (2), and [CuI(tptp)(2)(ptu)] (3). The complexes have been characterized by FT-IR, NMR, UV-vis, spectroscopic techniques, and single crystal X-ray crystallography. Two sulfur atoms from two ptu ligands and one iodide form a trigonal geometry around the metal center in 1. Intramolecular interactions through hydrogen bonds lead to a bend ribbon polymeric supramolecular architecture with zigzag conformation. Two phosphorus atoms from two arylphosphines, one sulfur atom, and one iodide anion form a tetrahedron around the copper ion in case of 2 and 3. Intramolecular hydrogen bonding interactions lead to dimerization. Complexes 1-3 and the already known ones with formulas, [(tpSb)(2)Cu(mu(2)-I)(2)Cu(tpSb)(2)] (4) (tbSb = triphenylstibine), [(tpp)Cu(mu(2)-I)(2)Cu(tpp)(2)] (5), [(tpp)Cu(mu(2)-Cl)(2)Cu(tpp)(2)] (6), [CuCl(tpp)(3)center dot(CH3CN)] (7), and [AuCl(tpp)] (8), were used to study their catalytic activity on the intermolecular cycloaddition of iodonium ylides toward benzo[b]furans formation. The results show that both the metal and the ligand type affect the catalytic affinity of the complexes. The highest yield of benzo[b]furan was derived when complexes 2, 3, and 4 were used as catalysts. The mechanism of the Cu(I)-catalyzed and uncatalyzed intramolecular cycloaddition of iodonium ylide has been also thoroughly explored by means of ab initio electronic structure calculation methods, and the results are compared with the experimental ones.