Platinum(II)/platinum(IV) interconversions in bond activation processes.

摘要

This dissertation focuses on synthetic and mechanistic studies of platinum alkyl/aryl hydride complexes relevant to C-H bond activation. Activation parameters for methane loss from Tp′PtMe₂H have been determined: ΔH‡ = 35.4 ± 1.1 kcal/mol and ΔS ‡ = 14.3 ± 0.7 cal/(mol K). Tp′PtMe ₂H undergoes thermolysis in Et₃Si-H to form Tp′ Pt(SiEt₃)(H)₂, and cleavage of the Pt-SiEt ₃ bond with methanol provides a clean route to Tp′PtH ₃.; Chiral cationic platinum(II) complexes of the type [κ2-((Hpz*)BHpz* ₂)Pt(R)(L)][BAr′₄] [R = Me; L = MeCN, tBuNC, py, CO, CH₂=CH₂, PMe₂Ph; R = Ph, L = MeCN] [pz* = 3,5-dimethylpyrazolyl, BAr′ ₄ = tetrakis(3,5-trifluoromethylphenyl)borate] have been prepared via acid-induced reductive elimination of methane from Tp′PtMe ₂H, and elimination of benzene from Tp′PtPh ₂H, and trapping of the intermediate solvent adducts. Deprotonation of the pyrazolium ring leads to the synthesis of neutral platinum(II) complexes of the type Tp′PtR(L) [R = Me, L = MeCN, SMe₂, CO. CH₂=CH₂; R = Ph, L = MeCN].; Tp′PtMe(H)₂ has been prepared from Tp ′PtMe(CO) via reaction with water in a basic acetone/water solvent mixture. Two cationic platinum(II) monohydride complexes [κ2 -((Hpz*)BHpz*₂)Pt(H)(L)][BAr′ ₄] [L = MeCN, CH₂=CH₂] have been isolated following protonation of Tp′PtMe(H)₂ and ligand addition. Protonation without ligand addition generates a deep red hydride-bridged dimer, [κ2-((Hpz*)BHpz*₂)Pt(μ-H)]₂[BAr ′₄]₂. Protonation of Tp′ PtMe(H)₂ and trapping with silanes forms platinum(IV) silyl dihydride complexes [κ2-((Hpz*)BHpz*₂)Pt(H) ₂(SiR₃)][BAr′₄] [R₃ = Et₃, Ph₃, Ph₂H]. Spectroscopic and structural data support a five-coordinate platinum(IV) silyldihydride formulation.; Reductive elimination of methane from Tp′PtMeH ₂ can be induced by reaction with substoichiometric amounts of B(C ₆F₅)₃ in aromatic solvents to yield platinum(IV) aryl dihydride complexes Tp′Pt(Ar)(H)₂ [Ar = Ph, Tol, o-Xyl, m-Xyl, p-Xyl].; The first platinum(IV) formyl complex and platinum(IV) acyl complexes have been synthesized. Nucleophilic addition to the carbonyl ligand in Tp ′PtMe(CO) leads to the formation of platinum(II) formyl or acyl anions, which undergo either protonation or methylation at metal to give platinum(IV) products. The acyl complexes Tp′Pt(C(=O)R)Me₂ [R = Me, Ph] and acyl hydride complexes Tp′Pt(C(=O)H)Me(H) [R = Me, Ph] have been fully characterized.