2,3,5-Metallotriazoles: Amphoteric Mesoionic Chelates from Nitrosoguanidines.

Soluble nitrosoguanidine- and N-methylnitrosoguanidine-based metallotriazole complexes of ruthenium(II) monocarbonyls have been prepared and characterized. Both nitrosoguanidines prove to be strong chelates with the formally π-accepting nitroso nitrogen binding cis to carbon monoxide and a π-donating amide trans to the CO. The resulting ensemble consists of ruthenium examples of 1-metallo-2,3,5-triazoles. The ruthenium coordination sphere is completed by anions, either H-, Cl-, or Ph-, trans to the nitroso group as well as two mutually trans PPh3 groups. The π-donating amide group is formally sp2 hybridized with a planar nitrogen to give a strongly bound five-membered chelating anion. Together, these results illustrate the remarkable potential for the nitrosoguanidinates as a family of new metal chelates.