Higher Homologues of Titanocene-Methylidene

Alkylidenation Several attempts have been made to prepare titanium alkylidene complex 17. The reaction of titanocene dichloride with triethylaluminum does not afford an alkylidene-bridged complex similar to the Tebbe reagent, probably due to the presence of a jS-hydrogen, and produces instead the aluminotitanium hydride 

Olefin metathesis of the Tebbe reagent offers an alternative route for the preparation of titanocene-alkylidenes 17, which can be employed for the alkyUdena- 

Indirect but mechanistically interesting use of the Tebbe reagent for the olefination of carbonyl compounds is the formation of conjugated dienes via titanacydo- 

Entry Carbonyl compound Titanacydobutane 11 Product Yield Ref. 

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The major obstacle to this approach is that there are few reagents capable of generating higher homologues of titanocene-methylidene. Although the procedure is not straightforward, the titanacycle 21 formed by the addition of diisobutylaluminum hydride to the double bond of (l-propenyl)titanocene chloride 22 serves as a titanocene-propylidene 23 equivalent in carbonyl olefmation (Scheme 14.12) [22]. 

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