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

Abstract

Reaction of [Cu(MeCN) 4 ]BF 4 with rac ‐Ph 2 PCH 2 P(Ph)CH 2 P(Ph)CH 2 PPh 2 ( rac ‐dpmppm) gave [Cu 2 (µ‐ rac ‐dpmppm)(MeCN) 4 ](BF 4 ) 2 ( 1 ), and that of CuCl with rac ‐dpmppm in the presence of 2,6‐xylyl isocyanide (XylNC) and NH 4 PF 6 afforded [Cu 2 (µ‐ rac ‐dpmppm)(XylNC) 4 ](PF 6 ) 2 ( 2 ). Complex 1 was converted by treatment with diimino ligands (N ^ N) to a series of Cu I 2 complexes, [Cu 2 (µ‐ rac ‐dpmppm)(N ^ N) 2 ] 2+ (N ^ N = phen ( 3 ), 4‐Mephen ( 4 ), 4,7‐Me 2 phen ( 5 ), 5,6‐Me 2 phen ( 6 ), 2,9‐Me 2 phen ( 7 ), 3,4,7,8‐Me 4 phen ( 8 ), 4,7‐Ph 2 phen ( 9 ), bpy ( 10 ), 4,4′‐Me 2 bpy ( 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 Cu I ions are triply bridged by a rac ‐dpmppm ligand in κ 2 ,κ 2 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‐Me 2 phen 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 1 H NMR measurements to show fluxional exchange of the two nitrogen atoms attaching to the tetrahedral Cu centers with Δ G ‡ of 14 kcal/mol at room temperature. Photophysical properties of 3 – 12 were also investigated to show rapid fluorescence at 394–467 nm in CH 2 Cl 2 solutions and phosphorescence at 582–608 nm in the solid states. Reaction of [Cu(MeCN) 4 ]BF 4 with rac ‐dpmppm and NaBH 4 in MeOH/CHCl 3 afforded [Cu 4 (µ 4 ‐H)(µ‐Cl) 2 (µ‐ rac ‐dpmppm) 2 ]BF 4 ( 13 ), in which two rac ‐dpmppm ligands exhibited a new coordination mode of κ 2 ,κ 1 ,κ 1 M 3 ‐bridge to hold two {Cu 2 (µ‐Cl)(µ‐ rac ‐dpmppm)} + units connected by a central µ 4 ‐hydride.