Katrin Schmidt

ansa-metallocene derivatives XXXIX biphenyl-bridged metallocene complexes of titanium, zirconium, and vanadium : syntheses, crystal structures and enantioseparation

Chiral, biphenyl-bridged metallocene complexes of general type biph(3,4-R 2 C 5 H 2 ) 2 MCl 2 (biph = 1,1′-biphenyldiyl) were synthesized and characterized. For the dimethyl-substituted titanocenes and zirconocenes (R = CH 3 ; M = Ti, Zr), preparations with increased overall yields and an optical resolution method were developed. The bis(2-tetrahydroindenyl) complexes (R,R = (CH 2 ) 4 ; M = Ti, Zr) were obtained by an alternative synthetic route and characterized with regard to their crystal structures. Syntheses of the phenyl-substituted derivatives (R = C 6 H 5 ; M = Ti, Zr) and of a chiral, methyl-substituted vanadocene complex (R = CH 3 ; M = V) are also reported.

ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes : syntheses, crystal structures and interconversion reactions

Abstract The ring-bridged chromocene carbonyl complex Me 2 Si(C 5 Me 4 ) 2 Cr(CO) 1 is obtained by reaction of Me 2 Si(C 5 Me 4 ) 2 Li 2 with CrCl 2 · THF in the presence of CO. Reaction with CO transforms the monocarbonyl complex 1 to a dicarbonyl complex Me 2 Si(C 5 Me 4 )(C 5 ( endo -3-H)(2-CH 2 )Me 3 )Cr(CO) 2 2 ; in this reaction, a hydrogen atom is shifted from one of the α-CH 3 groups to the adjacent β-position of a C 5 ring ligand. The rate of this reaction is first order in complex and CO concentration, with an activation enthalpy of H ≠ = 51 ± 3 kJ mol −1 and an activation entropy of S ≠ = 136 ± 10 J mol −1 K −1 . In toluene solution at 50°C, complex 2 isomerizes to Me 2 Si(C 5 Me 4 )(C 5 ( exo -3-H)(2-CH 2 )Me 3 )Cr(CO) 2 3 , then to Me 2 Si(C 5 Me 4 )(C 5 ( exo -1-H)(2-CH 2 )Me 3 )Cr(CO) 2 4 and further to Me 2 Si(C 5 Me 4 )(C 5 ( endo -5-H)(2-CH 2 )Me 3 )Cr(CO) 2 5 . The kinetics of these isomerizations, which involve hydrogen migrations and ring rotation reactions, indicate monomolecular reactions. Possible reaction paths and transition states are discussed. The structures of complexes 1–5 were determined by 1 H NMR spectroscopy, those of 1, 2, 4 and 5 also by single-crystal X-ray diffraction. Complex 1 : space group P 2 1 / n , a = 13.257(7)A, b = 10.186(5)A, c = 14.739(7) A, β = 90.89(4)°; V = 1990.1(7)A 3 ; Z = 4. Complex 2 : space group Pbca , a = 8.699(3) A, b = 14.713(6) A, c = 32.801(14)A; V = 4198(3)A 3 ; Z = 8. Complex 4 : space group P 2 1 , a = 9.497(2)A, b = 9.895(3) A, c = 11.371(2)A, β = 103.919(8)°; V = 1037.1(4) A 3 ; Z = 2. Complex 5 : space group P 2 1 / c , a = 16.555(4)A, b = 13.036(3)A, c = 10.044(2)A, β = 107.45(1)°; V = 2067.8(8)A 3 ; Z = 4.