Application Of Rhenium-Complexes In Organic Synthesis

Chemistry of rhenium have been widely developed because of their applications in catalysis, and become one of the important transition metal catalysts in homogeneous catalysis. But most of the studies were focused on oxygen atom transfer reactions, sp2 C-H bonds activation, reduction reactions and carbon-heteroatom bonds activation. In this thesis, high valence, low toxicity and air stable rhenium complexes were used to catalyze sp3 C-H bonds activations, including the benzylic oxidation, oxidative cyanation of tertiary amine, and amination of benzyl. Futhermore, nitrogen atom transfer reaction and strecker reaction were also notice in the treatise.Five parts are included in this thesis:Part 1. Activation of sp3 C-H Bonds Catalyzed by ReOCl3(OPPh3)(SMe2)----Ben-zylic Oxidation ReactionBenzylic oxidation were catalyzed by a small amount of ReOCl3(OPPh3)(SMe2) (5 mol%) with aqueous tert-butyl hydroperoxide (TBHP) as oxidant in pyridine. A wide range of benzylic sp3 C-H substrates were tested, and diphenylmethane type substrates gave the best yields, while the phenyl propane, phenyl butane and phenyl iso-propane resulted in the lowest yields. We proposed that rhenium (V) compounds can mediate by being oxidized to rhenium (VII) compounds, which can activate the oxidation the saturated C-H bond to the corresponding carbonyl compounds. The simplicity, low toxicity and inexpensive reagents renders this system attractive for large-scale applications.Part 2. Synthesis of Rhenium Complexes and Their Using in Catalytic Activation of sp3 C-H Bonds---- Oxidative a-Cyanation of Tertiary AminesThe new rhenium complexes had been synthesized successfully and been used for oxidation cyanation of tertiary amines. It was the first report on the use of rhenium-based catalysts for oxidation cyanation of sp3 C-H bonds at theα-position of tertiary amines using TMSCN as a cyanide donor under mild and acid-free reaction conditions. The reactions can give rise to the corresponding a-cyanated amines in good yields by using TBHP as oxidant at room temperature in the presence of 5 mol% Re-Bu complex catalysts. Substituted N,N-dimethylanilines bearing both electrondonating and electron-withdrawing substituents gave the corresponding cyanated products. The oxidative cyanation of tertiary amines provides an economical method for synthesizing various compounds N-aryl-a-amino acids products or N,N-disubstituted 1,2-diamines products. The mild reaction conditions, a safer and more effective cyanide anion source, good yields, the simplicity of the reaction procedure and environmentally friendly feature make this method attractive for scale-up purposes.Part 3. Activation of sp3 C-H Bonds Catalyzed by ReOI2(OEt)(PPh3)2----Benzylic Amination ReactionWe have discovered an highly efficient rhenium-catalyzed intermolecular C-H amination procedure with the combination of TsNH2 and NBS as the nitrene precursor. By employing ReOI2(OEt)(PPh3)2 as catalyst, the amidations of a range of benzylic substrates can be effected by directly using TsNH2/NBS as amidating reagents, and the products were obtained in 60-94% yields. Even the electron-deficient substrates were reactive in this case. The reactions are insensitive to atmospheric moisture and oxygen, and neither dried solvent nor an inert atmosphere is required. This is really the first known rhenium complex catalyzed benzylic sp3 C-H amination reaction. These highly atom-economical transformations will become a powerful tool in synthetic organic chemistry.Part 4. Nitrogen Atom Transfer (NAT) Reactions Catalyzed by ReOI2(OEt)(P-Ph3)2----Sulfide Amination ReactionReOI2(OEt)(PPh3)2 had been described as catalysts for nitrogen atom transformation. The imination sulfides had been achieved under mild reaction conditions at room temperature using inexpensive rhenium complex as a catalyst and the combination of TsNH2/PhI(OAc)2 as the co-nitrene sources. A series of sulfides have been converted into their corresponding sulfilimines using 5 mol% ReOI2(OEt)(PPh3)2 as catalyst. The discovery of this safe, non-toxic method for rhenium-catalyzed nitrogen atom transfer (NAT) reactions shows that it is still a great challenge for atom transfer chemistry of rhenium. Studies concerning the asymmetric reaction for synthesis of chiral sulfimides are in progress.Part 4. Strecker Reaction Catalyzed by ReO2I(PPh3)2A mild, efficient and environmentally friendly method has been developed for the synthesis of a-aminonitriles via a three-component condensation of aldehyde, amine and TMSCN in the presence of a catalytic amount of rhenium complex. This method is quite general and it works well with a wide variety of aldehydes and amines to afford the corresponding products with good to excellent yields at room temperature. The major advantage of this method is low catalyst loading (0.5 mol%) and a short reaction time needed (10min). Further studies in the asymmetric reaction such as the use of chiral rhenium complexes in the synthesis of chiral a-aminonitriles are in progress.