Linear and cyclic tetranuclear copper(I) complexes containing anions of N,N'-bis(pyrimidine-2-yl)formamidine

摘要

The reaction of Kpmf (pmf = anion of N,N'-bis(pyrimidyl-2-yl)formamidine, Hpmf) with CuSCN afforded the complexes K[Cu-4(pmF)(3)(SCN)(2)], 1, and Cu-4(pmf)(4), 2. Reaction of 1 with [(n-Bu)(4)N]PF6 in THF gave the complex [(n-Bu)(4)N][Cu-4(pmf)(3)(SCN)(2)], 3. Their structures were characterized by X-ray crystallography. Complexes 1 and 3 are the first linear tetranuclear complexes containing only Cu(I) atoms, while complex 2 is cyclic. The four Cu(I) atoms of complexes 1 and 3 are helically bridged by three tetradentate pmf(-) ligands. The [Cu-4(pmf)(3)(SCN)(2)](-) anions of 1 show weak interactions with adjacent [K(THF)(5)](+) cations through the sulfur atoms, forming infinite chains which are subjected to a series of intermolecular pi-pi interactions. In complex 2, the pmf(-) ligands are coordinated to the copper atoms in bidentate fashion through the two central amine nitrogen atoms, leaving the pyrimidine nitrogen atoms uncoordinated. Unexpected fluxional behaviors were observed for complexes 1 and 3 in solution. By the DNMR analysis, the free energy of activation (DeltaG(c)(not equal)) for the exchange is 12.8 kcal mol(-1) at 278 K (T-c), and the rate constant of exchange (K-c) is 470 s(-1) for 1. The DeltaG(c) (not equal) and K-c are 12.6 kcal mol(-1) at 273 K and 433 s(-1), respectively, for 3.