Coordination of a disubstituted alkene in a chelated d0-metal-alkyl-alkene complex.: Evidence for equilibrium between complexes with coordinated and free alkenes

Addition of (Cp-2*YH)(2)(4) to 2-methyl-1,4-pentadiene produced the yttrium-alkyl-alkene chelate complex Cp-2*YCH2CH2CH2C-(CH3)=CH2 (2) in which a disubstituted alkene is complexed to the metal center. Evidence for coordination of the alkene unit of 2 comes from the H-1 and C-13 NMR chemical shifts of the vinyl units and from observation of nOe effects between Cp* protons and vinyl hydrogens. The disubstituted alkene ligand of 2 is weakly bound, and evidence for an equilibrium with substantial amounts of complex 3 with a free alkene was obtained from variable temperature H-1 NMR spectroscopy. (C) 1998 Elsevier Science S.A.