ALKENE DISSOCIATION FROM A D(0) YTTROCENE-ALKYL-ALKENE COMPLEX GENERATES A PYRAMIDAL ALKYL YTTRIUM COMPLEX THAT INVERTS SLOWLY

The d(0) yttrium(III)-alhyl-alkene chelate CpY-2[eta(1):eta(2)-CH2CH2 CH(CH3)CH=CH2] (5) was prepared by reaction of 3-methyl-1,4-pentadiene with (Cp(2)-YH)(2). VariabLe-temperature C-13 NMR spectroscopy of 5 showed that the environments of the two diastereotopic Cp ligands wer e averaged by a fluxional process which requires both reversible alken e dissociation and inversion at the yttrium center; the energy barrier fur alkene dissociation pins yttrium inversion is 9.6 +/- 0.3 kcal mo l(-1).