115227-34-4Relevant academic research and scientific papers
Monocyclopentadienylzirconium and -hafnium alkyls: Synthesis, hydrogen-transfer reactions, and catalytic features in the reactivity with α-olefins. X-ray structure of CpZr(η4-butadiene)(dmpe)Cl [dmpe = 1,2-bis(dimethylphosphino)ethane]
Wielstra, Ytsen,Gambarotta, Sandro,Spek, Anthony L.
, p. 572 - 577 (2008/10/08)
The dissociation of one of the two equatorial dmpe [dmpe = 1,2-bis(dimethylphosphino)ethane] of CpM(dmpe)2X [X = Cl (1), Me (2); M = Zr (a), Hf (b)], allows the preparation of the new class of butadiene derivatives CpM(η4-butadiene)(dmpe)X [X = Cl (4a,b), Me (5a)], via mild-condition ligand-replacement reaction. The structure of 4 was demonstrated by X-ray diffraction analysis. Crystal data are as follows: monoclinic, P21/n, a = 8.230 (1), b = 15.896 (1), c = 16.571 (1), β = 95.43 (1), Z = 4, R = 0.043, Rw = 0.044 for 2634 observed reflections. The symmetrical η4 bonding mode of the butadiene moiety suggests that the low-valent character of zirconium is preserved on these compounds. Complex 4 is the starting material for the preparation of a series of linear alkyl and hydride derivatives CpM(η4-butadiene)(dmpe)X [X = H (6a,b), Et (7), n-Pr (10), n-Bu (11)] via a simple substitution reaction. The same alkyl complexes can be also conveniently synthesized via insertion of an α-olefin into the Zr-H bond of 6. Complex 7 is also formed in a one-step reaction of 2 with 3 equiv of ethylene. The alkyl derivatives 7, 10, and 11 are in equilibrium with the corresponding hydride 6 as demonstrated by the ability of 7 or 10 or 11 to transform into any other of these three compounds, upon reaction with the corresponding α-olefin. The presence of β-hydrogen is the prerequisite for the occurrence of these equilibria. This dynamic feature is responsible for the catalytic performance of 7 observed in the selective dimerization of ethylene to 1-butene. Deuterium-exchange experiments suggested that the catalytic cycle is initiated by H transfer from the β positions of the alkyl chain to the butadiene moiety.
