163 Journal of Organomerallic Chemistry, 378 (1989) 163-169 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP JOM 20348 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Reaction of ( q4-butadiene) -zirconocene and -hafnocene with 2-methyL24trosopropane Gerhard Erker * and Mark G. Humphrey Institut ftir Organische Chemie der Universitiir Wiirzburg, Am Hubland, D-8700 Wiirzburg (F.R.G.) (Received April 6th, 1989) Abstract (q4-Butadiene)-zirconocene and -hafnocene each react with two molar equiv- alents of 2-methyl-Znitrosopropane to give nine-membered metallacycles Cp,MON(R)CH,CH=CHCH,N(R)O @a: R = t-Bu; M = Zr; 8b: R = t-Bu, M = Hf), which have a truns-carbon-carbon double bond in the ring. In solution two different dynamic processes can be observed by variable temperature NMR spec- troscopy. Enantiomerization of the chiral ring system (AG&, (390 K) = 19 kcal/ mol) is observed at high temperature, whereas at low temperature an equilibration process involving hindered N-CMe, rotation becomes slow on the NMR time scale (AG,$, (190 K) = 8 kcal/ mol). Introduction (Conjugated diene)-zirconocene and -hafnocene complexes (1-cis, zyxwvutsrqponmlkjihgfedcb l-tram) often undergo carbon-carbon coupling with carbonyl compounds to give metallacyclic products. With aldehydes or ketones, reaction of l/ l stoichiometry is sometimes observed, yielding seven-membered metallacyclic a-ally1 complexes (oxametalla- cycloheptenes 2). In some cases a second molar equivalent of an organic carbonyl compound is consumed, yielding a nine-membered metallacycle (3) [l]. Similarly, the butadiene Group 4 metallocene complexes react cleanly with many metal carbonyls to give metallacyclic heteroatom-stabilized Fischer-type carbene complexes 4 in high yield [2]. These metallacyclic (7r-allyl)metallocenes commonly insert a ketone or aldehyde to give chiral medium-sized metallacycles 5. Complexes 5 exhibit dynamic behavior in solution. The chiral metallacyclic nine-membered ring systems containing a trans-configurated C=C bond show energy barriers to enanti- omerization similar to that of their parent hydrocarbon trans-cyclononene [3]. The N=O functionality in nitrosoalkanes has bonding features similar to those found in organic and inorganic carbonyl groups, and so it was tempting to speculate that (butadiene)-zirconocene and -hafnocene complexes might show similar reac- 0022-328X/89/%03.50 0 1989 Elsevier Sequoia S.A.