N—N Double Bond Cleavage And The Ortho Metalation of Azoarenes Using Ru₃(nph)(co)₁₀

The reaction of Ru₃(NAr)(CO)₁₀with azoarenes under CO results in the cleavage of the N-N double bond to yield Ru₃(NAr)₂(CO)₉and ArNCO. In the absence of CO the insertion into one of the C-H bonds ortho to the azo functional group also occurs. The product distribution is sensitive to the para substituent on the azobenzene, with electron-withdrawing groups favoring N═N bond cleavage, while ortho metalation is favored with electron-donating groups. A single-crystal X-ray crystallographic study of one of the clusters containing an ortho-metalated azoarene, HRu3(NPh)(CH₃OC₆H₃NNC₆H₄OCH₃)(CO)₈[PI space group, α= 9.237 (4) A, b = 10.917 (6) A, c = 17.199 (6) A, a = 100.47 (3)°, β= 99.80 (3)°, y = 90.59 (4)°, Z = 2], revealed a closed trinuclear cluster containing a triply bridging NPh, a semibridging carbonyl, an ortho-metalated azoarene, and a bridging hydride trans to the carbon of the ortho-metalated ring. Spectroscopic methods indicate the cluster interconverts in solution at room temperature among three isomers. Reaction of HRu₃(NPh)(CH₃0C₆H₃NNC₆H₄0CH₃)(C0)₈with carbon monoxide leads to N-N double bond cleavage, while the reaction with excess azoarene yields a new cluster containing two or-tho-metalated azoarenes. The analogous reaction of Ru₃(NPh)(CO)₁₀with N-phenylbenzaldimine was also examined and found to give only the product resulting from ortho metalation of the phenyl ring.