Cyclometalated Formazan Derivatives of Ruthenium and Osmium: Structure of Ru((o-C6H4)N=NC(Ph)=NNPh) (CO)(PPh3)2

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; = 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 N’,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 (ris-PPh3 ligands) or purple (frarw-PPh3 ligands) complexes from the reaction of RuH2(CO)(PPh3)3 with PhN=NCH=NNHPh and have been shown 1-1-1-1 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 C2h5-P21/c (a = 18.539 (3) Å, b = 25.381 (6) Å, c = 19.391 (4) Å, 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 F02 > 3σ (F02) to values for R and Rw 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) Å), a carbonyl group (average Ru-C = 1.83 (1) Å, C-O = 1.17 (1) Å), and a planar, tridentate, cyclometalated formazan ligand coordinated through nitrogen atoms N1 (Ru-N = 2.163 (7) Å) and N4 (Ru-N = 2.02 (1) Å) and the ortho carbon atom of the phenyl ring on the N5 nitrogen atom (Ru-C = 2.091 (9) Å). The bond lengths found for the formazan skeleton are consistent with extensive electron delocalization throughout the chelate rings and the adjoining phenyl groups.