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.

Synthesis of (3-(pyridin-4-yl)propyl)phosphonic acid.Synthesis of (3-(pyridin-4-yl)propyl)phosphonic acid was performed in two steps as shown in scheme S1.Synthesis of diethyl (3-(pyridine-4-yl)propylphosphonate. Lithium diisopropyl amide (LDA) (18.5 ml, 1.2 eq.) was added dropwise to a solution 4-methyl pyridine (Sigma Aldrich) (1.5 ml, 15.25 mmol, 1 eq.) in 30 ml dry THF at -30 o C under an inert atmosphere. After the reaction mixture was stirred at low temperature for 3 h, diethyl 2-bromoethyl phosphonate (2.85 ml, 15.25 mmol, 1 eq.) was added as a solution in 20 ml dry THF. The reaction mixture was allowed to reach room temperature overnight then was portioned between water and chloroform. The organic layer was separated, dried over MgSO4 and concentrated. The crude product was purified by column chromatography (SiO2, dichloromethane: methanol, 24 : 1 (v : v)). The fractions with Rf = 0.15 were separated to give 1.91 g of diethyl (3-(pyridine-4-yl)propylphosphonate (h = 0.48).