Takuji Okamoto

Regio- and stereochemistry in the sequential insertion of carbonyl compounds into zirconium-diene complexes

Abstract Group 4 metal-diene complexes of the type Zr(η-C 5 H 5 ) 2 (s- cis -diene) and Zr(η-C 5 H 5 ) 2 -(s- trans -diene) (diene = butadiene, isoprene, pentadiene and their derivatives) were found to undergo regioselective 1 1 addition with a variety of aldehydes, ketones, esters and acid amides at the sterically more crowded terminal carbon of the ligated diene to give the ( Z )-oxazirconacyclo-4-heptenes. Further addition of carbonyl compounds to the resulting oxametallacycle leads to 1 2 adducts of ( E )-1,3-dioxazircona-6-nonene structure when the precursor oxazirconacycloheptene has a less bulky hydrogen group at the C(5) position. Highly selective, three-component, sequential addition was first realized by treatment of a ketone or an aldehyde with Zr(C 5 H 5 ) 2 (diene)/ester, Zr(C 5 H 5 ) 2 (diene/alkene and Zr(C 5 -H 5 ) 2 (diene)/alkyne adducts.

Novel route to niobocene-allyl compounds by hydrometalation of conjugated dienes with NbH(C5H5)2(olefin)

Abstract Niobium hydrido-olefin complexes, NbH(C5H5)2(olefin), are found to react readily with conjugated dienes such as butadiene, isoprene, and pentadiene, to give Nb(C5H5)2(η3-allyl) derivatives of syn or syn,syn geometry, in >80% yields with high regioselectivity. All the complexes were isolated as crystals and their structures were determined by NMR and EIMS spectroscopy. The reaction pathway leading to syn- or syn,syn-η3-allylniobium compounds is discussed on the basis of the regiochemistry of the products and the results of a deuterium labeling experiment. These complexes react readily with aldehydes to give homoallyl alcohols upon hydrolysis of the products. The corresponding tantalum derivatives were found to be inert to all dienes tested.