Kohlenwasserstoffverbrückte Metallkomplexe, XXI Addition von Tetracarbonylosmat und ‐ruthenat an koordinierte ungesättigte Kohlenwasserstoffe: Dreikernige Komplexe mit zwei σ,α‐Allyl‐, Methylallyl‐, Cyclohexadien‐, Cycloheptadien‐, Cyclohexadienyl‐, Cycloheptatrien‐ und „Thiophen”︁‐Brücken Hydrocarbon‐bridged Metal Complexes, XXI. – Addition of Tetracarbonylosmate and ‐ruthenate to Coordinated Unsaturated Hydrocarbons: Trinuclear Complexes with two σ,α‐Allyl, Methylallyl, Cyclohexadiene, Cycloheptadiene, Cyclohexadienyl, Cycloheptatrien, and “Thiophene” Bridges The addition of organometallic nucleophiles [M(CO)4]2‐ (M = Os, Ru) to [(Cp)(ON)(OC)Mo(allyl)]+, [Cp(OC)2Mo(butadiene)]+, [(OC)3Fe(cycloheptadienyl)]+, [(OC)3Fe(cycloheptadienyl)]+, [(OC)3Mn(benzene)]+, [(OC)3Mn(thiophene)]+, [(OC)3‐Mo(cycloheptatrienyl)]+ leads to the heterotrimetallic η1:η2‐, η1:η3‐, η1:η4‐, η1:η5‐, η1:η6‐hydrocarbon‐bridged complexes 1 ‐ 7. The structures of cis‐(OC)4Os[(μ‐η1:η4‐C7H9)Fe(CO)3]2 (4), cis‐(OC)4Os[(μ‐η1:5‐C6H6‐Mn(CO)3]2 (6), and cis‐(OC)4Os‐[μ‐η1:η6‐C7H7‐Mo(CO)3]2 (7b) have been determined by X‐ray analysis. The fluxional behaviour of 6 in solution has been studied in a temperature range from – 70 to +60°C. The comparison of observed and calculated 1H‐NMR data indicates a 1,2‐shift mechanism (ΔG+ = 49 kJ/mol).