From Pyrazolate-Based Binuclear Copper(I) Complexes to Octanuclear σ-Mesityl-Bridged μ4-Oxo-Cuprocuprates: Controlled Dioxygen Splitting by Organocopper Scaffolds

The synthesis of a series of new pyrazole-based binucleating compartmental ligands, 3,5-bis(R2R3N)-(4-R1)-pyrazoles L1H−L6H (L1H, R1 = H, R2 = Me, R3 = 2-py(CH2); L2H, R1 = Ph, R2 = Me, R3 = 2-py(CH2); L3H, R1 = H, R2 = Cy, R3 = 2-py(CH2); L4H, R1 = Ph, R2 = Cy, R3 = 2-py(CH2); L5H, R1 = Ph, R2, R3 = 2-py(CH2), L6H, R1 = Ph, R2 = Me, R3 = 8-quin), together with the X-ray crystal structure of L3H is reported. After deprotonation and subsequent reaction with 2 equiv of [CuI(CH3CN)4](BF4) and PMe3, L3H forms the stable binuclear CuI complex [L3{Cu(PMe3)}2](BF4) (1). The analogous reaction with L6H and 2 equiv of tert-butyl isonitrile affords [L6{Cu(CNtBu)}2](BF4) (2). 1 and 2 represent the first examples of binuclear CuI−pyrazolate complexes of the type [LCuI2]X that have been characterized by their X-ray crystal structures. With respect to the planes spanned by the pyrazolate backbone, 1 shows a cis orientation of the PMe3 ligands, whereas 2 exhibits a trans arrangement of the tBuNC ligands. L1H−L6H are shown to react with 4 equiv of mesitylcopper and stoichiometric amounts of dioxygen, leading to the formation of the unusually stable organocopper frameworks 3−8. These complexes follow a general structural principle that is best described by the heteroleptic O-centered cuprate anion [(MesCuI)4(μ4-O)]2− linked via four trans-oriented σ-mesityl bridges to two flanking binuclear CuI-pyrazolates [(L1−L6)CuI2]+. Thus, 1 and 2 can also be viewed as capping binuclear CuI-complex units that are concealed by two ancillary PMe3 and tBuNC ligands, respectively. The exemplary reaction of 4 with an excess of dimethyl acetylenedicarboxylate (DMDAC) supports the observed cuprate features of 3−8, since after hydrolysis the corresponding (syn-)addition product MesC(CO2Me)C(CO2Me)H (9) and the free ligand L2H are found as major products.