A family of organoruthenium nitrites: alkyne insertion, linkage isomerization and ring nitration

The reaction of [Ru(C6H2OH-2-CHNR-3-Me-5)(PPh3)(2)(CO)(NO2)] 1 (R = Et, p-MeC6H4 or p-ClC6H4) with an excess of alkyne HC=CX (X = H, Ph or CH2OH) in CH2Cl2-MeOH medium was accompanied by linkage isomerization of nitrite (O,O'-bonded --> N-bonded) and formation of a six-membered vinyl-phenolato chelate ring to give [Ru(eta (2)-C6H2CXCH-1-O-2-CHNHR-3-Me-5)(PPh3)(2)(CO)(NO2)] 4. The active substrate is the solvate 1 . MeOH, and the 2 + 2 addition of the bulky =CX (X = Ph or CH2OH) group proceeds regiospecifically to the carbon end of the Ru-C bond. Compound 4 has also been obtained metathetically by treating 3 (the chloro analogue of 4) with NaNO2 in neutral media. However in acid media ring nitration of 3 (R = Et, X = Ph) occurs furnishing [Ru(eta (2)-C6HCPhCH-1-O-2-CHNHEt-3-NO2-4-Me-5)(PPh3)(2)(CO)Cl] 7 which can metathetically be converted into the corresponding N-bonded NO2 analogue, 8. The iminium proton is hydrogen bonded to the phenolato oxygen in 4, 7 and 8 and also weakly to a nitro oxygen in 4 and 8 (IR and H-1 NMR data). All the species display a quasireversible cyclic voltammetric Ru-III-Ru-II couple, the E-1/2 of which shifts to higher potential by approximate to 200 mV upon replacing chloride by nitrite (3 --> 4; 7 --> 8) as well as upon aromatic nitration (3 --> 7). The crystal structures of the solvate 4b .C6H6 in which R = p-MeC6H4 and X = H, 4h in which R = p-ClC6H4 and X = CH2OH and 7 have been determined. The sigma -vinyl-phenolato chelate ring is approximately planar. The Ru-N bond in the planar RuNO2 fragment of 4b .C6H6 and 4h is lengthened by approximate to0.1 Angstrom due to the trans influence of the vinyl group. The Ru-C(vinyl) bond in 7 is significantly shortened due to electron withdrawal by the nitro group, thus promoting Ru-ligand back bonding. The distances of the iminium nitrogen from phenolic oxygen and a nitrito oxygen (in 4b .C6H6 and 4h) lie in the ranges 2.55-2.67 and 2.90-2.98 Angstrom respectively.