Synergistic Cu2 Catalysts for Formic Acid Dehydrogenation.

Hexanuclear copper hydride complexes, [Cu6(μ3-H)2( meso-L4)3(RNC)4](PF6)4 (R = tBu (6a), Cy (6b)), were prepared by using a new linear tetraphosphine, meso-Ph2PCH2P(Ph)(CH2)4P(Ph)CH2PPh2 ( meso-L4), and were converted into active catalysts of [Cu2(μ-O2CH)( meso-L4)(RNC)2]+ under the reaction conditions of formic acid dehydrogenation, where unsymmetric dinuclear copper sites supported by the tetradentate phosphine and isocyanide ligands were essential to demonstrate effective catalytic activity.