Mono(pentamethylcyclopentadienyl) Complexes of Cerium(III). Synthesis, Molecular Structure, Thermal Stability, and Reactivity of (C5Me5)CeX2 (X = 2,6-Di-tert-butylphenoxo, CH(SiMe3)2, and N(SiMe2)2) Complexes

Reaction of Ce(OAr)3 (1) with LiR (R = C5Me5, 1,3-diphenyl-2-methylindene) affords novel RCe(OAr)2 (R = C5Me5, 2; R = 1,3-diphenyl-2-methylindene, 3) compounds. Metathesis of the remaining aryloxide ligands in 2 with bulky main-group alkyl and amide compounds (LiCH(SiMe3)2 and NaN(SiMe3)2) provide neutral C5Me5CeR2 complexes (R = CH(SiMe3)2, 5; R = N(SiMe3)2, 6). Compound 5 is a polymerization catalyst for ethylene but not for propylene. Compounds 2 and 6 disproportionate in solution with formation of equilibrium mixtures containing C5Me5CeX2, (C5Me5)2CeX, and CeX3 complexes. Structural studies on 2, 5, and 6 show monomeric, formally five-coordinate compounds in the solid state. Compound 2 crystallizes in the monoclinic space group P21 with a = 9.575 (1) Å, b = 17.026 (2) Å, c = 11.530 (1) Å, β = 112.02 (1)°, and Z = 2. Compound 5 crystallizes in the hexagonal space group P63 with a = 18.477 (2) Å, c = 15.991 (3) Å, and Z = 6. Compound 6 crystallizes in the monoclinic space group P21/c with a = 19.252 (6) Å, b = 13.430 (4) Å, c = 12.503 (3) Å, β = 90.28 (2)° , and Z = 4. All compounds display interesting secondary interactions of the metal with C-H and/or Si-C bonds in the solid state.