Structures of two haptotropic isomers generated by the sliding of 1,3,5-triene ligands on a Pd-Pd-Pd chain

摘要

Two haptotropic isomers of [Pd_3(μ_3-DMVC)_2(CH_3CN)_2][BF_4]_2 (DMVC = 1,2-di-(E)-carbomethoxyvinylcyclopentene) were structurally determined by X-ray crystallographic analyses; a monoclinic crystal contained a symmetric sandwich complex (μ_3-η~2:η~2:η~2-coordination of DMVC ligands) and a triclinic crystal contained an unsymmetric sandwich complex (μ_3-η~2:η~3:η~1-coordination of DMVC ligands), where the latter are connected to each other by C-H… O hydrogen bonds.rnWe recently revealed that pπ-conjugated olefins and polycyclic aromatic hydrocarbons act as versatile sandwich ligands for metal chains or sheets. The ligand-metal connection in such multinuclear sandwich complexes is comprised of an array of contiguous multiple π-coordination bonds, which exhibit unique hapticity changes. For example, sliding of tetraene ligands on the Pd_4 chain takes place when the diphenyltetraene-tetra-palladium sandwich complex accepts two terminal ligands or two electrons (Scheme 1).