Ruthenium Derivatives of NiS2N2Complexes as Analogues of Bioorganometallic Reaction Centers

Recent results from structural biology demonstrate the catalytic significance of Ni(SR) 2 L 2 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 NiS 2 N 2 (S 2 N 2 = N,N ‘-bis(2-mercaptoethyl)- N,N ‘ -dimethyl-1,3-diaminoethane) gives [Cp*Ru(NiS 2 N 2 )] 2 (OTf) 2 ([ 1 ] 2 (OTf) 2 ), which exists as a monomer−dimer equilibrium in MeCN solution. Crystallographic analysis of [ 1 ] 2 (OTf) 2 reveals a centrosymmetric dication with the Ru being quasi-octahedral and the NiS 2 N 2 coordination sphere being relatively planar, the metal centers being linked via pairs of μ 2 -SR and μ 3 -SR units. Complex [ 1 ] 2 2+ oxygenates and sulfidizes with O 2 and S 8, respectively, to give [Cp*Ru(NiS 2 N 2 )(η 2 -E 2 )] + (E = O, S), which were characterized spectroscopically and crystallographically. Solutions of [ 1 ] 2 (OTf) 2 also react with CO and MeNC to give the corresponding adducts [Cp*Ru(NiS 2 N 2 )L]OTf, where L = CO and MeNC. The ν CO = 1901 cm - 1 for the CO adduct indicates the excellent donating power of the NiS 2 N 2 ligand. The Cp*Ru + derivative of the bulkier version of the NiS 2 N 2 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 O 2 to give the corresponding adducts. The reaction of CpRu(PPh 3 ) 2 Cl and NiS 2 N 2 produced the PPh 3 adduct [CpRu(NiS 2 N 2 )(PPh 3 )]Cl, wherein the PPh 3 ligand is nonlabile. The corresponding reaction of NiS 2 N 2 with sources of (arene)RuCl + gave the expected adducts [(arene)Ru(Cl)(NiS 2 N 2 )] +, isolated as their OTf - salts.