Synthesis Using Thioether Stabilizers

The modulation of reaction conditions during nanoparhcle synthesis plays a significant role in controlling particle size and shape. Obare and coworkers investigated the effects of reaction temperature and reaction time on the pyrolysis of [Pd3(OAc)e] to form thioether-stabiUzed Pd nanopartides [48]. Both conditions were found to have a profound influence on nanoparhcle size, as well as size distribution. A 1 h period of pyrolysis of a toluene soluhon containing a 1 5 raho of [Pd3(OAc)6] to n-dodecyl sulfide was carried out at temperatures of 95, 100, 110, 

---

The use in organic synthesis of carbanions stabilized by one or more adjacent thioether groups is now a well-established technique [272-275]. A landmark in this development was the work of Corey and Seebach on 1,3-dithianes [276]. They pointed out the use of the anions of 1,3-dithianes as... 

The free radical addition of a thiol to carbon-carbon double or triple bonds is a well-established reaction. It represents one of the most useful methods of synthesizing sulfides under mild conditions. Since its discovery [5] and its much later formulation as a free-radical chain reaction (Scheme 1) [6], the anti-Markovnikov addition of thiols to unsaturated compounds has been the subject of many reviews [8, 9]. These reactions were originally initiated by thermal decomposition of peroxides or azocompounds, by UV irradiation or by radiolysis [10]. (An example of addition of 1-thiosugar to alkenes initiated by 2,2 -azobisisobutyronitrile (AIBN) [11] is reported in equation (1)). More recently, organoboranes have been used as initiators and two examples (Et3B and 9-bora-bicyclo [3.3.1.] nonane) are reported in equations (2) and (3) [12,13]. Troyansky and co-workers [14a] achieved the synthesis of macrocycles like 12- and 13-membered sulfur-containing lactones by the double addition of thiyl radical to alkynes. An example is depicted in equation (4). The same approach has also been applied to the construction of 9- and 18-membered crown thioethers [14b]. The radical chain addition of thiyl radicals to differently substituted allenes has been considered in detail by Paste and co-workers [15], who found that preferential attack occurs at the central allenic carbon and gives rise to a resonance-stabilized ally radical. The addition of benzenethiol to allenic esters has been reported and the product formation has been similarly inferred (equation (5)) [16]. 

Due to the stability and availability of carboxylic acids, they remain some of the most attractive starting points for the synthesis of complex organic compounds. Using these compounds as substrates, the decarboxylative thiolation of carboxylic acids has been achieved using silver nitrate as a promoter (Scheme 5.15) [16]. Disulfides served as the sulfur source for this chemistry, and moderate to good yields of the thioethers from a host of aUcyl carboxylic acids. 

With the exception of dendrimers, very few procedures yield metalhc nanopartides in high yield that are monodisperse. In 2007, Obare and coworkers reported a straightforward procedure for the synthesis and sizethis approach, thioethers were found to be effective Ugands for the preparation of Pd nanopartides via a one-step procedure. Palladium acetate was used as the precursor and reacted with thioethers in a 1 5 Pd thioether ratio. Here, the thioether played two roles (i) as a reducing agent for the Pd nanopartides and (ii) as a stabilizer for the nanopartides formed. In this way, uniform Pd nanopartides with diameters of 1.7 0.2, 1.910.2, 2.510.1, 3.5 0.1 and 4.110.1 nm were obtained in a one-step procedure at 99% yield, and required no size selection process. Selected images to illustrate the uniformity of the nanopartides obtained by this procedure are shown in Figure 9.2. 

---