Highly reduced group VI metal carbonyl complexes and their reactions with electrophiles.

摘要

Derivatives of carbonylmetallates of group 6 metals, such as Fischer type carbene complexes and arene tricarbonyl complexes, are of great interest because of their flourishing applications in organic synthesis. Chapter 1 gives a brief review of such complexes and their reductive activation.; Chapter 2 focuses on the reductive activation of imidazolidine pentacarbonyl complexes [M{lcub}=C(HNCH₂)₂{rcub}(CO)₅] (M = Cr, W). These complexes are close analogs of imidazolidinone and provide an intriguing organometallic model for the role of biotin (Vitamin H) in biosynthetic carboxylations. The carbenoid ligands in these complexes can be reductively activated and react with CO₂ at the beta heteroatom, a reaction that parallels the carboxylation process of biotin.; Chapter 3 examines a range of approaches to the two-electron reduction of [Cr(η6-C₆H₆)(CO)₃]. Reducing reagents such as metal naphthalenides (M = Li, K), potassium electride and alkali metals can be used in this reduction. The resulted dianion [Cr(η 4-C₆H₆)(CO)₃]2− shows dramatic counterion effects on the υ_CO in IR spectra, and protonation reactions are examined to explore the salt effects on the chemical reactivities of the dianionic complex.; Chapter 4 describes the addition of the iminium salt [Me₂N=CMe ₂][BF₄] to the reductively activated η4-benzene ligand in [Cr(η4-C₆H₆)(CO)₃ ]2− and the resulting Cr(0) complex [Cr(η 5-C₆H₆)(CMe₂NMe₂)(CO) ₃]− is then characterized. The unusual up field chemical shift in NMR spectra of the methyl protons and carbons suggests a magnetic shielding effect indicative of a modest ring current despite the open conjugation of the cyclohexadienyl ligand.; Chapter 5 explores the addition of the reductively activated benzene ligand in [Cr(η4-C₆H₆)(CO)₃ ]2− to di-isopropyl squarate ester. Instead of the expected bis-addition, as in the well-established organolithium reagent addition, only one molecule of the dianion reacts with this ester and gives an exo-linked cyclohexadienyl monoanion as product. The counterion of the dianion is important in the reaction with the squarate: with Li +, the dianion adds to the α, β unsaturated ester in a 1,4-addition reaction; with K+ the dianion was oxidized by the ester to give [Cr(η6-C₆H₆)(CO) ₃].; Chapter 6 establishes that facile substitution of K[Cr(η6 -C₆H₇)(CO)₃] with PPh₃ resulted in an unexpected product, trans-[Cr(CO)₄(PPh ₃)₂]. The structure of this complex was determined by single crystal X-ray diffraction. Crystals contain two conformational isomers, differing in the orientations of the PPh₃ ligands.; In Chapter 7, we report that complexes [{lcub}M(CO)₃(η 7-C₇H₇){rcub}(PF₆)] (M = Cr, W) can be reduced by 2 equivalents of potassium naphthalenide, and the resulted anions [M(CO)₃(η5-C₇H₇)] − can react with the cationic [M(CO)₃(η 7-C₇H₇)]+ to give the neutral dimers [{lcub}M(CO)₃{rcub}₂{lcub}μ-(η6-C ₇H₇-η6-C₇H₇){rcub}] with exo-linkage C-C bonds. The structures of both dimers resembled the structures o