Preparation, characterization and thermal reactions of 1-oxa-2-ziconacyclopentanes and 1-oxa-2-zirconacyclohexane: crystal structures of [{Zr(C5H5)2(OCH2CH2CHMe)}2] and [Zr(C5Me5)2{OCH2(CH2)2CH2}]

1-Oxa-2-zirconacyclopentanes [{[graphic omitted]H2)}2](R = H, 3a; or Me, 3b) and [{[graphic omitted]HMe)}2]3c(cp =η-C5H5) formed from the intramolecular hydrozirconation of [Zr(cp)2H(Cl)] with potassium allyl or homoallyl alcoholates have been characterized as dimeric five-co-ordinated metallocene structures. Complex 3c crystallizes in space group P21/n(Z= 2) with a= 17.090(4), b= 8.345(3), c= 8.841(3)Å, β= 102.90(2)°, and R= 0.039 for 2030 reflections. Monomeric [[graphic omitted]H2)]9 and [[graphic omitted]H2}]12 have been prepared by the reaction of appropriate Grignard reagents with [Zr(C5Me5)2Cl2]. Complex 12 crystallizes in space group Pnn2 (Z= 4) with a= 15.634(2), b= 15.024(3), c= 9.571(1)Å, and R= 0.074 for 1336 reflections. Remarkable differences in the thermal stability and modes of decomposition have been observed among these complexes depending on the co-ordination numbers of the zirconium atoms and the size of the metallacycles. The mechanisms of the thermal reaction of 3 are discussed on the basis of the product analysis and by use of the deuteriated derivatives.