Recent results from structural biology demonstrate the catalytic significance of Ni(SR)2L2 centers attached to a second metal that binds CO, in particular the NiFe hydrogenases and acetyl CoA synthase. In experiments aimed at developing bimetallic derivatives exhibiting an affinity for CO, we have studied Ru(II) derivatives of nickel diaminodithiolates and the reactivity of these complexes toward CO and other small molecules. The reaction of [Cp*Ru(NCMe)3]OTf and NiS2N2 (S2N2 = N,N′-bis(2-mercaptoethyl)-N,N′-dimethyl-1,3-diaminoethane) gives [Cp*Ru(NiS2N2)]2(OTf)2 (2(OTf)2), which exists as a monomer-dimer equilibrium in MeCN solution. Crystallographic analysis of 2(OTf)2 reveals a centrosymmetric dication with the Ru being quasi-octahedral and the NiS2N2 coordination sphere being relatively planar, the metal centers being linked via pairs of μ2-SR and μ3-SR units. Complex 22+ oxygenates and sulfidizes with O2 and S8, respectively, to give [Cp*Ru(NiS2N2)(η2- E2)]+ (E = O, S), which were characterized spectroscopically and crystallographically. Solutions of 2 (OTf)2 also react with CO and MeNC to give the corresponding adducts [Cp*Ru(NiS2N2)L]OTf, where L = CO and MeNC. The vCO = 1901 cm-1 for the CO adduct indicates the excellent donating power of the NiS2N2 ligand. The Cp*Ru+ derivative of the bulkier version of the NiS2N2 species, Ni(bme*-daco) (bme*-daco = [1,5-bis(2-mercapto-2-methylpropyl)-1,5-diazacyclooctane]), is the monomeric analogue of 1+, [Cp*Ru(NCMe)(Ni-(bme*-daco))]+, whose structure was confirmed spectroscopically and crystallographically. In this species the thiolato ligands are doubly bridging and the Cp*Ru subunit adopts the usual piano-stool geometry with a terminal MeCN ligand. The MeCN is readily displaced by CO and O2 to give the corresponding adducts. The reaction of CpRu(PPh3)2Cl and NiS2N2 produced the PPh3 adduct [CpRu(NiS2N2)(PPh3)]Cl, wherein the PPh3 ligand is nonlabile. The corresponding reaction of NiS2N2 with sources of (arene)RuCl+ gave the expected adducts [(arene)Ru(Cl)(NiS2N2)]+, isolated as their OTf- salts.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry