Preparative and Structural Studies on Ruthenium(II)‐Thiolate Cyanocarbonyls: Comparison to the [Fe(CO) x (CN) y (SR) z ] n− Coordination Modes of Active Sites of Hydrogenases

Ruthenium‐thiolate cyanocarbonyl compounds [Na·2THF][Ru(CO)(CN)(S‐C 5 H 4 N) 2 ] ( 2 ), and [PPN] [Ru(CO)(CN)(S‐C 5 H 4 N) 2 ] ( 3 ) were prepared from reactions of [Na][N(SiMe 3 ) 2 ] and cis ‐[Ru(CO) 2 (S‐C 5 H 4 N) 2 ] ( 1 ) obtained from reaction of Ru 3 (CO) 12 , Me 3 NO 2 H 2 O, and 2‐mercaptopyridine in THF. Complexes 1, 2 and 3 were characterized by IR and single‐crystal X‐ray diffraction. The IR spectrum of complex 2 in the aprotic solvent THF reveals two weak absorption bands for the CN − ligands at 2098 w and 2086 w cm −1 and one strong absorption band 1931 s cm −1 assigned to the carbonyl stretching frequency that support the dimeric architecture with two [Ru(CO)(CN)(S‐C 5 H 4 N) 2 ] − units connected through CN‐Na + ‐NC interactions, as observed in the single‐crystal X‐ray structure. Ethylation of complex 3 by electrophile [Et 3 O][BF 4 ] occurring initially at the more accessible, delicately balanced nucleophilic site to yield the charge‐controlled, collision product 4 (Scheme II), and subsequently isomerizing to neutral [Ru(CO)(CNEt)(S‐C 5 H 4 N) 2 ] ( 5 ) demonstrated the enhanced nucleophilicity toward electrophiles with replacement of carbonyl ligand with cyanide ligand in complex 1 , indicative of the strong σ‐donor role of the cyanide vs CO ligand. In comparison with displaying a reversible redox process of complex [Fe(CO)(CN)(S‐C 4 H 3 N 2 ) 2 ] − , the electrochemistry of complex 3 reveals an irreversible oxidation at 0.29 V (vs Ag/AgNO 3 ).