114802-65-2Relevant academic research and scientific papers
Structural features in electron-deficient (η-pentamethylcyclopentadienyl)titanium-diene complexes and their catalysis in the selective oligomerization of conjugated dienes
Yamamoto, Hitoshi,Yasuda, Hajime,Tatsumi, Kazuyuki,Lee, Keonil,Nakamura, Akira,Chen, Jie,Kai, Yasushi,Kasai, Nobutami
, p. 105 - 119 (2008/10/08)
A series of titanium-diene complexes of the type TiX(C5Me5)(s-cis-diene) (X = Cl, Br, I) was synthesized by the stoichiometric reaction of TiX3(C5Me5) with (2-butene-1,4-diyl)magnesium derivatives or by the reaction of TiX3(C5Me5) with RMgX (R = i-Pr, t-Bu, Et; X = Cl, Br, I) in the presence of a conjugated diene. All complexes were isolated as highly air-sensitive blue crystals in 30-60% yields. The complexes of unsubstituted and C(1) and/or C(4) alkyl-substitutecl dienes (butadiene, 1,3-pentadiene, 1,4-diphenylbutadiene) exhibit unique prone (endo) conformation while the complexes of C(2) and/or C(3) alkyl-substituted dienes (isoprene, 2,3-dimethylbutadiene, 2,3-diphenylbutadiene) prefer the supine (exo) conformation as revealed by the 1H and 13C NMR spectroscopic together with the X-ray diffraction analyses. The indirect 13C-13C coupling constants prove the pronounced η4-diene metal bonding nature for the prone titanium-diene complexes and substantial participation of bent metallacyclo-3-pentene structure for the supine complexes. TiCl(C5Me5)(s-cis-C4H6) of prone geometry crystallizes in space group P21/c with a = 6.999 (1) A?, b = 14.625 (3) A?, c = 13.842 (2) A?, β = 95.61 (2)°, and Z = 4. TiCl(C5Me5)(s-cis-1,4-diphenylbutadiene) belongs to orthorhombic space group Pnma with a = 8.260 (1) A?, b = 16.395 (3) A?, c = 16.308 (3) A?, and Z = 4. TiCl(C5Me5)(s-cis-2,3-diphenylbutadiene) of supine geometry crystallizes in space group C2/c with a = 22.049 (3) A?, b = 8.107 (2) A?, c = 26.869 (4) A?, β = 110.11 (1)°, and Z = 8. The extended Hu?ckel molecular orbital calculations reveal that the prone and supine structures of TiCl-(C5Me5)(C4H6) are energetically very close to each other. The nature of Ti-C4H6 bonding is discussed on the basis of population analysis. A low-valent species Ti(C5Me5)(isoprene) (g = 1.999 in EPR) generated by the reduction of TiCl(C5Me5)(isoprene) or on treatment of TiCl2(C5Me5) with (enediyl)magnesium catalyzes a highly selective (>99%) tail-to-head linear dimerization of isoprene and 2,3-dimethylbutadiene.
