Synthesis, DFT Studies, and Reactions of Scandium and Yttrium Dialkyl Cations Containing Neutral fac-N3 and fac-S3 Donor Ligands

• Published in: Organometallics 2008-07, Vol.27 (14), p.3458-3473
• Main Authors: Tredget, Cara S, Clot, Eric, Mountford, Philip
• Format: Article
• Language: English
• Subjects: Chemical Physics; Physics
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om800279d

Reaction of Sc(CH2SiMe3)3(THF)2 with 1,4,7-trithiacyclononane gave Sc([9]aneS3)(CH2SiMe3)3, the first organometallic group 3 complex of [9]aneS3 ([9]aneS3 = 1,4,7-trithiacyclononane). The corresponding reaction for yttrium gave equilibrium mixtures of Y([9]aneS3)(CH2SiMe3)3 and starting materials. Density functional theory (DFT) was used to compare the energies of formation and metal−ligand interaction energies for M([9]aneS3)R3 with those for the previously reported fac-N3 donor complexes M(fac-N3)R3 (R = Me or CH2SiMe3; fac-N3 = 1,4,7-trimethyltriazacyclononane (Me3[9]aneN3) or HC(Me2pz)3). Reaction of M(CH2SiMe3)3(THF)2 with [NHMe2Ph][BArF 4] (ArF = C6F5) in the presence of a face-capping ligand L (L = HC(Me2pz)3, Me3[9]aneN3, or [9]aneS3) gave the cationic complexes [M(L)(CH2SiMe3)2(THF)]+, which has been structurally characterized for M = Sc and L = [9]aneS3. The corresponding base-free cations [M(L)(CH2SiMe3)2]+ were studied by 29Si NMR spectroscopy and/or DFT and found to possess β-Si−C agostic alkyl groups in most instances. The isolated cations [Sc(fac-N3)(CH2SiMe3)2(THF)]+ underwent THF substitution reactions with OPPh3 or pyridine, Sc−alkyl migratory insertion with carbodiimides, and C−H bond metathesis with PhCCH. The olefin polymerization capabilities of a series of complexes M(L)R3 have been determined. The scandium complexes were found to be very productive for ethylene polymerization for L = HC(Me2pz)3, Me3[9]aneN3, or [9]aneS3 and R = CH2SiMe3 when activated with 1 equiv of [CPh3][BArF 4]. When activated with 2 equiv of [CPh3][BArF 4], the compounds were also very active for the polymerization of 1-hexene.