Cyclometalated formazan derivatives of ruthenium and osmium: Structure of Ru((o-C6H4)N=NC(Ph)=NNPh)(CO)(PPh3)2

Article abstract of DOI:10.1021/ic50222a017

1,5-Diphenylformazans, PhN=NC(R)=NNHPh (R = H, Me, or Ph), react with the complexes RuH₂(CO)(PPh₃)₃, RuH₂(CO)(AsPh₃)₃, RuHCl(CO)(PPh₃)₃, Os(O₂CCF₃)₂(CO)(PPh₃)₂, and OsH(O₂CCF₃)(CO)(PPh₃)₂ in boiling 2-methoxyethanol or dimethylformamide over a period of 30 min to 4 h to afford cyclometalated formazan derivatives M((o-C₆H₄)N=NC(R)=NNPh)(CO)(EPh₃)₂ (M = Ru, E = P, R = H, Me, or Ph; M = Ru, E = As, R = Ph; M = Os, E = P, R = H, Me, or Ph) as deep green, air-stable, crystalline solids. The initial products formed in these reactions appear to be N¹,N⁵-chelate formazan complexes which subsequently rearrange and undergo cyclometalation. Isomeric intermediates of the form Ru(PhN=NCH=NNPh)H(CO)(PPh₃)₂ have been isolated as pink (cis-PPh₃ ligands) or purple (trans-PPh₃ ligands) complexes from the reaction of RuH₂(CO)(PPh₃)₃ with PhN=NCH=NNHPh and have been shown to convert to the green cyclometalated complex Ru((o-C₆H₄)N=NCH=NNPh)(CO)(PPh₃)₂ on further heating. The structure of the green complex Ru((o-C₆H₄)N=NC(Ph)=NNPh)(CO)(PPh₃)₂ has been established by an X-ray diffraction study. The complex crystallizes in space group C_2h⁵-P2₁/c (a = 18.539 (3) ?, b = 25.381 (6) ?, c = 19.391 (4) ?, β = 97.36 (1)° at 0°C) with two pseudosymmetrically related molecules per asymmetric unit. The structure, described by 399 variable parameters, was refined with use of 8498 reflections having F_o² > 3σ(F_o²) to values for R and R_w of 0.081 and 0.107. The compound contains six-coordinated ruthenium(II) bound to a trans pair of triphenylphosphine ligands (average Ru-P = 2.384 (5) ?), a carbonyl group (average Ru-C = 1.83 (1) ?, C-O = 1.17 (1) ?), and a planar, tridentate, cyclometalated formazan ligand coordinated through nitrogen atoms N¹ (Ru-N = 2.163 (7) ?) and N⁴ (Ru-N = 2.02 (1) ?) and the ortho carbon atom of the phenyl ring on the N⁵ nitrogen atom (Ru-C = 2.091 (9) ?). The bond lengths found for the formazan skeleton are consistent with extensive electron delocalization throughout the chelate rings and the adjoining phenyl groups.