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

Thermolysis of [1‐(3‐butenyl)‐2,3,4,5‐tetramethylcyclopentadienyl]carbonyldiiodocobalt, (η 5 ‐C 5 Me 4 CH 2 CH 2 CHCH 2 )‐Co(CO)I 2 ( 2 ), in boiling octane affords the dimeric diiodide [(η 5 ‐C 5 Me 4 CH 2 CH 2 CHCH 2 )‐COI 2 ] 2 ( 3 ) without any interference of the 3‐butenyl chain with the cobalt center. 2 reacts with various two‐electron ligands L (LP(OMe) 3 , P(OPh) 3 , PPh 3 , PMe 3 , PMe 2 Ph, t BuNC] to give a series of cobalt(III) complexes of the general formulae (η 5 ‐C 5 Me 4 CH 2 CH 2 CHCH 2 )‐Co(L)I 2 ( 4 – 9 ). Sodium amalgam reduction of these “open‐chain” complexes 4 – 9 yields novel cobalt(1) complexes containing an intramolecularly coordinated CC bond (η 5 :η 2 ‐C 5 Me 4 CH 2 CH 2 CHCH 2 )‐Co(L). For LCO ( 12 ), P(OMe) 3 ( 13 ), and P(OPh) 3 ( 14 ) low‐melting crystals are isolated and fully characterized by analytical and spectroscopic methods.