Heterobimetallic dioxygen activation: Synthesis and reactivity of mixed Cu-Pd and Cu-Pt bis(m-oxo) complexes

Heterobimetallic CuPd and CuPt bis(mu-oxo) complexes have been prepared by the reaction of (PPh₃)₂MO₂ (M = Pd, Pt) with LCu(I) precursors (L = beta-diketiminate and di- and triamine ligands) and characterized by low-temperature UV-vis, resonance Raman, and ¹H and ³¹P{¹H} NMR spectroscopy in conjunction with DFT calculations. The complexes decompose upon warming to yield OPPh₃, and in one case this was shown to occur by an intramolecular process through crossover experiments using double-labeling (oxo and phosphine). The reactivity of one of the complexes, L^Me2Cu(mu-O)₂Pt(PPh₃)₂ (L^Me2 = beta-diketiminate), with a variety of reagents including CO₂, 2,4-di-tert-butylphenol, 2,4-di-tert-butylphenolate, [NH₄][PF₆], and dihydroanthracene, was compared to that of homometallic Pt₂ and Cu₂ counterparts. Unlike typical [Cu₂(mu-O)₂]²⁺ cores which have electrophilic oxo groups, the oxo groups in the [Cu(mu-O)₂Pt]⁺ core behave as bases and nucleophiles, similar to previously described Pt₂ compounds. In addition, however, the [Cu(mu-O)₂Pt]⁺ core is capable of oxidatively coupling 2,4-di-tert-butylphenol and 2,4-di-tert-butylphenolate. Theoretical evaluation of the electron affinities, basicities, and H-atom transfer kinetics and thermodynamics of the Cu₂ and CuM (M = Pd, Pt) cores showed that the latter are more basic and form stronger O-H bonds.