Organo Ruthenium–Nickel Dithiolates with Redox-Responsive Nickel Sites

• Published in: Organometallics 2013-11, Vol.32 (21), p.6324-6329
• Main Authors: Chambers, Geoffrey M, Angamuthu, Raja, Gray, Danielle L, Rauchfuss, Thomas B
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om4006824

Described is a new family of RuNi dithiolates featuring geometrically flexible Ni centers, which enable both acid–base and redox chemistry, behavior that is characteristic of the hydrogenases. Treatment of Ni(pdt)(dxpe) with (cymene)2Ru2Cl4 affords the salt [(cymene)Ru(Cl)(pdt)Ni(diphos)]Cl (pdt2– = 1,3-propanedithiolate, diphos = dppe = 1,2-bis(diphenylphosphino)ethane ([1Cl]Cl) and diphos = dcpe = 1,2-bis(dicyclohexylphosphino)ethane ([2Cl]Cl)). Cyclic voltammetry revealed that in CH2Cl2 solution [1Cl]Cl reduces irreversibly near −1.6 V vs Fc0/+ followed by the appearance of a reversible 1e– couple assigned to the [1]0/+ couple. Reduction of [1Cl]Cl and [2Cl]Cl with cobaltocene produced the neutral derivatives (cymene)Ru(pdt)Ni(diphos) ([1]0, [2]0). Crystallographic characterization of these compounds revealed short Ru–Ni distance of 2.5539(5) ([1]0) and 2.600(3) Å ([2]0). The 2e– reduction of these chlorides converts the Ni site from square planar to tetrahedral, highlighting the flexibility of the Ni center in these complexes. Variable-temperature NMR studies show that [1]0 and [2]0 are dynamic by virtue of ring flipping in the RuNi(pdt) core. Complexes [1]0 and [2]0 are basic: their conjugate acids, [H1]+ and [H2]+, exhibit pK a PhCN values of 18.94 and 21.65, respectively. Crystallographic characterization of [H1]+ as its aryl borate salt revealed an unsymmetrical Ru–H···Ni interaction and confirmed that the Ni center converted from tetrahedral to square planar, again demonstrating the flexibility of this site.