STRUCTURAL STUDIES ON CYCLOPENTADIENYL COMPOUNDS OF TRIVALENT CERIUM - TETRAMERIC (MEC5H4)3CE AND MONOMERIC (ME3SIC5H4)3CE AND [(ME3SI)2C5H3]3CE AND THEIR COORDINATION CHEMISTRY

The coordinated tetrahydrofuran in (MeC5H4)3Ce(THF) can be removed by Me3Al in a Lewis acid-base reaction or by the “toluene-reflux method” to give base-free (MeC5H4)3Ce which is a monomer in the gas phase though a tetramer in the solid state: monoclinic, P21/a, with a = 12.497 (5) Å, b = 26.002 (8) Å, c = 9.664 (3) Å, β = 97.33 (3)°; R = 0.041 for 2117 data, F2 > 2σ(F2). The structure is made up of a cyclic tetramer in which two MeC5H4 rings are η5-bonded to each cerium atom and one MeC5H4 ring is bridging two cerium atoms such that the MeC5H4 ring is η5-bonded to one cerium and η1-bonded to the other. With larger cyclopentadienyl groups, the binary metallocenes (η5-Me3SiC5H4)3Ce, (η5-Me3CC5H4)3Ce, and [η5-(Me3Si)2C5H3]3Ce are monomeric in the gas phase and the solid state. The structure of the latter is based upon a trigonal-planar geometry; the crystals are monoclinic, I2/c, with a = 22.752 (5) Å, b = 11.386 (3) Å, c = 17.431 (4) Å, β = 105.70 (3)°, R = 0.046 for 2519 data, and F2 > 3σ(F2). All of the binary metallocenes form 1:1 complexes with isocyanides and organocyanides, and the crystal structure of two of them have been determined; (MeC5H4)3Ce(CNCMe3) is monoclinic, P21/c, with a = 14.259 (3) Å, b = 9.382 (2) Å, c = 17.652 (3) Å, β = 106.16 (3)°, R = 0.050 for 1501 data, and F2 > 3σ(F2), and [(Me3Si)2C5H3]3Ce(CNCMe3) is also monoclinic, P21/c, with a = 11.462 (3) Å, b = 17.146 (4) Å, c = 26.826 (6) Å, β = 112.93 (3)°, R = 0.047 for 2437 data, and F2 > 3σ(F2). © 1990, American Chemical Society. All rights reserved.