Synthesis and Characterization of Trinuclear [Ni2Ru] Complexes with Bridging Thiolate or Selenolate Donors for Electrocatalytic Proton Reduction

Two new trinuclear compounds [{Ni(xbSmS)}2Ru(phen)2](PF6)2 (1) and [{Ni(xbSmSe)}2Ru(phen)2](PF6)2 (2) were synthesized by the reaction of [Ni(xbSmS)] and [Ni(xbSmSe)], respectively, with cis‐[Ru(phen)2(Cl)2] [H2xbSmS = 1,2‐bis(4‐mercapto‐3,3‐dimethyl‐2‐thiabutyl)benzene; H2xbSmSe = 1,2‐bis(2‐thiabutyl‐3,3‐dimethyl‐4‐selenol)benzene; phen = phenanthroline]. The two [Ni2Ru] complexes were characterized by ESI‐MS, NMR spectroscopy, elemental analysis, single‐crystal X‐ray crystallography, and electrochemical techniques. X‐ray structure determinations showed that the trinuclear complex cations in 1 and 2 contain two square‐planar nickel centers bound in cis positions to the octahedral ruthenium ion by a bridging thiolate or selenolate donor atom. Electrocatalytic proton reduction occurs for both complexes in acetonitrile with the addition of varying amounts of acetic acid at a potential of –2.1 V vs. Fc+/Fc with faradaic yields of around 65 %. Two trinuclear [Ni2Ru] compounds are reported, comprising square‐planar nickel centers bound in cis positions to an octahedral ruthenium ion by a bridging thiolate or selenolate donor. Unexpectedly, changing the thiolate donor atom to selenolate does not make a difference, neither in the reduction potentials nor in the electrocatalytic activity of the resulting compounds for proton reduction.