Diverse reaction courses in the controlled carbometalation of heterocumulenes with zirconium-diene complexes and molecular structures of carbon dioxide, isocyanate, and ketene 1:1 and 1:2 inserted compounds

Article abstract of DOI:10.1021/om00107a003

The carbometalation of various heterocumulenes (carbon dioxide, isocyanates, ketenes) was systematically investigated by using a series of zirconium-diene complexes of the type ZrL₂(s-cis-diene) and ZrL₂(s-trans-diene) (L = η⁵-C₅H₅, η⁵-C₅Me₅; diene = butadiene, isoprene) to clarify the essential factor(s) in determining the regio- and stereochemistry of the products. The mode of CO₂ insertion reaction changes drastically depending upon the bulkiness of the auxiliary ligand and the geometry (s-cis, s-trans) of ligated dienes. The 1:1 reactions of the ZrL₂(butadiene) complex with t-C₄H₉NCO, C₆H₅NCO, or C₆H₅(CH₃)CCO yield Zr-O bound complexes having (σ,syn-η³-allyl)metal structures, while the isoprene derivatives always give seven-membered-ring (Z)-oxametallacyclic isomers. The use of a bulky ketene, Ph₂CCO, resulted in an abnormal addition that provides a unique six-membered oxametallacycle. (C₅Me₅)₂Zr[C₄H₆C(=O)O] belongs to the monoclinic space group P2₁/n with a = 8.816 (1) A?, b = 28.916 (3) A?, c = 9.388 (1) A?, β = 108.89 (1)°, and Z = 4. (C₅Me₅)₂Zr[C₄H ₆C(=N-t-Bu)O] crystallizes in space group Pbca with a = 14.458 (2) A?, b = 16.677 (3) A?, c = 22.446 (3) A?, and Z = 8. A 1:2 adduct, (C₅Me₅)₂Zr[OC(=NC₆H ₅)C₄H₆C(=NC₆H₅)O], crystallizes in space group P2₁2₁2₁ with a = 9.082 (2) A?, b = 17.275 (3) A?, c = 22.301 (4) A?, and Z = 4. The six-membered oxametallacycle (C₅Me₅)₂Zr[CH=C(CH₃)CH(CH ₃)C(=C(C₆H₅)₂)O] crystallizes in space group P2₁/c with a = 12.282 (3) A?, b = 16.082 (3) A?, c = 17.981 (4) A?, β = 108.56 (3)°, and Z = 4. Thus, the configuration of the β-carbon (sp², sp³) in the product together with the steric bulk of substituents on C(2) and/or C(3) of the ligated diene is found to be crucial in determining the reaction courses and the regio- and stereochemistry of the products.