Reactions of co-ordinated ligands. Part 42. The synthesis and reactions of cationic η4-tetraphenylcyclobutadieneruthenium complexes; X-ray crystal structures of [Ru(NCMe)(η4-C4Ph4)(η-C5H5)][BF4] and [Ru{η5-CH(Ph)C(Ph)C(Ph)C(Ph)O}(η-C5H5)]