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.本研究报道了一系列新型基于吡唑（pyrazole）的双核分隔配体（binucleating compartmental ligands）3,5-双(R₂R₃N)-(4-R₁)-吡唑L1H−L6H的合成，以及配体L3H的X射线晶体结构（X-ray crystal structure）。各配体的取代基参数如下：L1H的R1=H、R2=Me、R3=2-py(CH₂)；L2H的R1=Ph、R2=Me、R3=2-py(CH₂)；L3H的R1=H、R2=Cy、R3=2-py(CH₂)；L4H的R1=Ph、R2=Cy、R3=2-py(CH₂)；L5H的R1=Ph、R2、R3=2-py(CH₂)；L6H的R1=Ph、R2=Me、R3=8-quin。将L3H去质子化（deprotonation）后，与2当量的[Cu(I)(CH₃CN)₄](BF₄)及三甲基膦（PMe3）反应，可得到稳定的双核一价铜配合物[L3{Cu(PMe3)}₂](BF₄)（记为1）。L6H与2当量的叔丁基异腈（tert-butyl isonitrile）发生类似反应，则生成[L6{Cu(CNtBu)}₂](BF₄)（记为2）。配合物1和2是首例经X射线晶体结构表征的[LCuI₂]X型双核一价铜-吡唑根（pyrazolate）配合物。相对于吡唑骨架所构成的平面，1中的三甲基膦配体呈顺式取向，而2中的叔丁基异腈配体则为反式排布。研究表明，L1H−L6H可与4当量的均三甲苯基铜（mesitylcopper）及化学计量量的氧气（dioxygen）反应，生成异常稳定的有机铜框架3−8。这类配合物遵循通用结构原则：由杂核氧中心铜酸盐（cuprate）阴离子[(MesCuI)₄(μ₄-O)]²⁻通过四个反式取向的σ-均三甲苯基桥连两个侧翼的双核一价铜-吡唑盐阳离子[(L1−L6)CuI₂]⁺。据此，1和2也可被视为封端型双核一价铜配合单元，分别被两个辅助配体三甲基膦和叔丁基异腈所遮蔽。以配合物4与过量的乙炔二羧酸二甲酯（dimethyl acetylenedicarboxylate，DMDAC）的代表性反应为例，可验证3−8的铜酸盐结构特征：水解后，主要产物为对应的顺式加成产物MesC(CO₂Me)=C(CO₂Me)H（记为9）以及游离配体L2H。