Dinuclear Copper Complexes Triply Bridged by a Tetraphosphane, rac‐Ph2PCH2P(Ph)CH2P(Ph)CH2PPh2

Abstract

Reaction of [Cu(MeCN)4]BF4 with rac‐Ph2PCH2P(Ph)CH2P(Ph)CH2PPh2 (rac‐dpmppm) gave [Cu2(µ‐rac‐dpmppm)(MeCN)4](BF4)2 (1), and that of CuCl with rac‐dpmppm in the presence of 2,6‐xylyl isocyanide (XylNC) and NH4PF6 afforded [Cu2(µ‐rac‐dpmppm)(XylNC)4](PF6)2 (2). Complex 1 was converted by treatment with diimino ligands (N^N) to a series of CuI2 complexes, [Cu2(µ‐rac‐dpmppm)(N^N)2]2+ (N^N = phen (3), 4‐Mephen (4), 4,7‐Me2phen (5), 5,6‐Me2phen (6), 2,9‐Me2phen (7), 3,4,7,8‐Me4phen (8), 4,7‐Ph2phen (9), bpy (10), 4,4′‐Me2bpy (11), and 1,8‐naphtyridine (nap) (12)), where phen = 1,10‐phenanthroline and bpy = 2,2′‐bipyridyl. The isolated complexes were characterized by spectroscopic and X‐ray crystallographic analyses to reveal that two CuI ions are triply bridged by a rac‐dpmppm ligand in κ2,κ2 fashion resulting in robust Z‐form dicopper structures, where the Cu···Cu distances vary from 4.2 to 5.6 Å depending on the ancillary ligands through altering conformation of the fused six‐membered chelate rings. The bulky ligands of XylNC and 2,9‐Me2phen deform the conformation to boat (2) and twist boat (7) forms, leading to elongation of Cu···Cu separation (Cu···Cu = 5.3488(5) Å (2), 5.5681(6) Å (7)), and other non‐bulky ligands render them deformed chair forms with Cu···Cu = 4.2051(5) Å (8) to 4.7341(5) Å (10). The solution behaviors of 5 and 11 were examined by variable temperature 1H NMR measurements to show fluxional exchange of the two nitrogen atoms attaching to the tetrahedral Cu centers with ΔG‡ of 14 kcal/mol at room temperature. Photophysical properties of 3–12 were also investigated to show rapid fluorescence at 394–467 nm in CH2Cl2 solutions and phosphorescence at 582–608 nm in the solid states. Reaction of [Cu(MeCN)4]BF4 with rac‐dpmppm and NaBH4 in MeOH/CHCl3 afforded [Cu4(µ4‐H)(µ‐Cl)2(µ‐rac‐dpmppm)2]BF4 (13), in which two rac‐dpmppm ligands exhibited a new coordination mode of κ2,κ1,κ1 M3‐bridge to hold two {Cu2(µ‐Cl)(µ‐rac‐dpmppm)}+ units connected by a central µ4‐hydride.