Allenkomplexe des Titanocens und Zirkonocens: Darstellung und Reaktivität

Allene Complexes of Titanocene and Zirconocene: Synthesis and Reactivity Bis(trimethylphosphane)titanocene ( 1 ) and (η 2 ‐Ethene)(trimethylphosphane)titanocene ( 2 ) react with one equivalent of allene ( 3a ), phenylallene ( 3b ), 1,1‐dimethylallene ( 3c ), and 1,1‐diphenylallene ( 3d ) readily by displacement of one trimethylphosphane from 1 and of ethene from 2 to give regiospecifically the corresponding (η 2 ‐allene)(trimethylphosphane)‐titanocene complexes 4a–d in good yields. From (η 2 ‐1‐butene)(trimethylphosphane)zirconocene ( 6 ) and 3d the corresponding (1,2‐η 2 ‐3,3‐diphenylallene)zirconocene complex 7d is obtained in the same manner. The structures of these new allene complexes have been established unambiguously by 1 H‐ and 13 C‐NMR‐spectroscopy. A crystal structure analysis of the titanocene complex 4d confirms the spectroscopic structure determination. All the above mentioned allene‐metallocene complexes consume readily a second equivalent of the allene derivatives to produce, in most cases, regiospecifically the corresponding 1‐metalla‐2,5‐dimethylenecyclopentane derivatives 5a–d (M = Ti) and 8c, d (M = Zr); only the (allene)zirconocene complex 7a gives rise to a 1:1 mixture of the regioisomers 8a and 9 . More conveniently 5a–d and 8c , d are synthesized directly from metallocene dichloride and the corresponding allenes 3 .