Functionalized cyclopentadienyl ligands, III. Preparation of cobalt half‐sandwich complexes with intramolecular CC bond coordination

Thermolysis of [1‐(3‐butenyl)‐2,3,4,5‐tetramethylcyclopentadienyl]carbonyldiiodocobalt, (η5‐C5Me4CH2CH2CHCH2)‐Co(CO)I2 (2), in boiling octane affords the dimeric diiodide [(η5‐C5Me4CH2CH2CHCH2)‐COI2]2 (3) without any interference of the 3‐butenyl chain with the cobalt center. 2 reacts with various two‐electron ligands L (LP(OMe)3, P(OPh)3, PPh3, PMe3, PMe2Ph, tBuNC] to give a series of cobalt(III) complexes of the general formulae (η5‐C5Me4CH2CH2CHCH2)‐Co(L)I2 (4–9). Sodium amalgam reduction of these “open‐chain” complexes 4–9 yields novel cobalt(1) complexes containing an intramolecularly coordinated CC bond (η5:η2‐C5Me4CH2CH2CHCH2)‐Co(L). For LCO (12), P(OMe)3 (13), and P(OPh)3 (14) low‐melting crystals are isolated and fully characterized by analytical and spectroscopic methods.