Reaction of [Ru(COD)Cl-2](x) (COD = 1,5-cyclooctadiene) with NaLOEt afforded L-OEt(COD)RuCl (1). The average Ru-O, average Ru-C and Ru-Cl distances in 1 are 2.129, 2.164, and 2.398(3) Angstrom, respectively. Treatment of 1 with AgBF4 in acetone/H2O afforded [L-OEt(COD)Ru(OH2)]BF4 (2), which reacts with L to give the respective adducts [L-OEt(COD)RuL]BF4 (L = t-BuNH2 (3), p-MeC6H4NH2 (4), NH3 (5), N2H4 (6), pyridine (7), 4,4'-bipyridine (8), MeCN (9), Et2S (10), and Me2SO (11)). The structures of 3 and 4 have been characterized by X-ray crystallography. The average Ru-O, Ru-C, and Ru-N distances in 3 are 2.115, 2.162, and 2.197(6) Angstrom, respectively. The corresponding bond distances for 4 are 2.113, 2.160 and 2.174(5) Angstrom. Reaction of 8 with 2 afforded the 4.4'-bipyridine-bridged binuclear complex [{L-OEt(COD)Ru}(2)(mu-4,4'-bipy)](PF6)(2) (12). Deprotonation of complexes 2 and 4 gave the hydroxide L-OEt(COD)RuOH (13) and the amide L-OEt(COD)Ru(NUC6H4Me-p) (14). respectively. The structure of [L-OEt(CO)(PPh3)Ru(OH2)]BF4 (15) has been characterized by X-ray crystallography. The average Ru-O(L-OEt), Ru-C, Ru-P, and Ru-O(aquo) distances in 15 are 2.118, 1.83(1), 2.285(3), and 2.091(7) Angstrom, respectively. Interaction of 15 with p-MeC6H4NH2, PPh3, and NaN3 gave [L-OEt(CO)-(PPh3)Ru(p-MeC6H4NH2)]BF4 (16), [L-OEt(PPh3)(2)Ru(CO)]PF6 (17), and L-OEt(CO)(PPh3)RuN3 (18). respectively. Deprotonation of 15 and 16 afforded the hydroxide L-OEt(CO)(PPh3)Ru(OH) (19) and amide LOEt(CO)-(PPh3)Ru(NHC6H4Me-p) (20), respectively. Treatment of Ru(CO)Cl(H)(PPh3), with NaLOEt afforded the hydride L-OEt(CO)(PPh3)RuH (21), which reacts with tosyl azide to give the Ru(II) tosylamide L-OEt(CO)(PPh3)Ru-(NHSO2C6H4Me-p) (22). Reaction of [L-OEt(PPh3)(2)Ru(MeOH)](+) with t-BuNC, CNpy (4-cyanopyridine), Me2SO, (26)), isolated as their PF6 salts. The cyclic voltammograms for the Ru-L-OEt complexes show reversible oxidation couples assignable to Ru(III/II) couples. The availability of electrons in the LOEtRu complexes for back-bonding can be accessed by their nu(C=O) and Ru(III/II) potentials.