Thiamine analogues with 3‐methyl and 4‐(2‐hydroxyethyl) substituents on the backbone of thiazole ring, were used to synthesize monodentate Ru(II)‐thiazolylidene complexes in a single step via transmetalation under mild conditions. These novel complexes catalyze the conversion of ketones and aldehydes to alcohols by transfer hydrogenation in a 5:2 HCO2H/NEt3 buffer in water. However, their efficiency was found to be much lower than the thiamine‐derived bidentate Ru(II) complexes, which strongly indicates that the ‘N‐H’ plays a crucial role in the reaction.