The complex [Ru(η5-C7H11)2H]BF4 (C7H11 = 2,4-dimethylpenta-2,4-dienyl) is highly reactive towards two- and six-electron ligands. e.g. giving with CO complex [RuCO(η4-C7H12)(η5-C7H11)]BF4. The 2,4-dimethylpenta-1,3-diene ligand (C7H12) of the latter complex is readily displaced giving, e.g. with excess cyclohexa-1,3-diene (C6H8) complex [RuCO(η4-C6H8)(η5-C7H11)]BF4. These reactions provide a convenient entry into monopentadienylruthenium chemistry.