An object of the present invention is to provide a formic acid dehydrogenation catalyst capable of highly efficient production of hydrogen, deuterium gas, or deuterium free of carbon monoxide by dehydrogenation of formic acid. ), A dinuclear metal complex represented by the formula (1), a tautomer or stereoisomer thereof, or a salt thereof. In the above formula (1), M1 and M2 are transition metals, which may be the same or different, Q1 to Q6 are each independently carbon or nitrogen, and R1 to R6 are each Independently, a hydrogen atom, an alkyl group, a phenyl group, a nitro group, a halogen group, a sulfonic acid group, etc., and L1 and L2 are each independently an aromatic anion ligand or an aromatic ligand. And when it has a substituent, one or a plurality of the substituents may be present, and Y1 and Y2 are each independently an arbitrary ligand or absent, and m is a positive Integer, 0, or a negative integer. [Selection figure] None
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