Catalytic S-X Activation

2-norbornene was carried out in the presence of Cp RuCl(cod), the ds-adduct 89 was formed, indicating the inclusion of ds-insertion of alkene into the Ru-S bond and following C-S bond-forming reductive eliminahon (Eq. 7.58). The authors proposed the complex [Cp RuCl( x-SPh)]2 (90), formed by the oxidative addihon of (PhS)2 to Cp RuCl(cod), as one possible candidate for the active catalyst (Eq. 7.59). 

The activation of S-X bonds, where X is different from H or S, has also attracted much attention, because two different functional groups can be introduced by a single procedure. 

The first example was reported in 1989 by Ando et al. and showed the germylthi-olatiori and germylselenatioif, that is, palladium-catalyzed addition of the strained S-Ge bond of thiadigermirane and Se-Ge bond of selenadigermirane to acetylene (C2H2) to provide 91 (Eq. 7.60) [61]. 

A possible intermediate for Pd(PPh3)4-catalyzed thioboration of 1 -alkyne 

Tanaka et al. reported on the related palladium-catalyzed selenophosphorylatiori and thiophosphorylatiorf, i.e., additions of Y-P (Y = Se, S) bonds in 109 to an alkyne provides 110 in up to 95% yield (Eq. 7.63) [63, 64]. The oxidative addition of the se-lenophosphate to M(PEt3)3 (M = Pd, Pt) (Eq. 7.64) afforded 111, and the oxidative addition to Pd(PPh3)4 was mentioned in the paper. While no information about the insertion process was provided, considering the regio- and sterochemistry of Pd-cat-alyzed addition of Y-Y and Y-H bonds to alkynes (Eqs. 7.9, 7.30 and 7.47), the insertion of alkyne into Pd-Y (not Pd-P) is more likely. 

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As we have seen, reviewing catalytic S-X bond activations, some reactions complete their catalytic cycles by C-S bond-forming reductive elimination from C-M-S complexes. Hartwig et al. have reported on the mechanism of the C-S bond-forming reductive elimination from Pd(L)(R)(SR ) 122 (Eq. 7.72) [69]. 

H6(Me3Si)C7B-Me]Ti(H5C5B-Me) Theoretical studies Catalytic activity calculations S, X, H, B, C, IR 144... 

The active species in the catalytic cycles are square-planar Pd complexes of the formula [Pd (X)(S)(L-L)]Y where L-L is a chelating ligand with the same or different donor atoms among P, N, O and S X is the growing polyketone chain or hydride S may be a solvent molecule, a co-monomer, or a keto group from the chain. Finally, Y is a counter-anion of weak nucleophilicity in order to avoid competition with the co-monomer for coordination to palladium (Scheme 7.1). 

When it is possible to fill a reactor with catalyst up to the bulk density, these surface areas per unit volume can be achieved. We now will calculate the rate of production per unit volume of catalyst that can be obtained provided transport limitations do not interfere. We assume a product having a molecular weight of 80. Usually the number of catalytically active atoms at the surface of a solid catalyst is smaller than the total number of surface atoms, which in metal surfaces is of the order of lO m . Here we will assume that 2 X lO atoms m are catalytically active. The turnover number indicates the number of molecules reacting s per active site. The turnover number usually ranges between 10 and 10 s [1]. For this calculation we will take a turnover number of 1 s. Finally we use a working day of 8 h-the fine-chemical industry does not usually work continuously. 

It is assumed that the composite catalytic reaction involves several elementary steps, e.g., adsorption, surface reaction, and desorption, which may individually be treated according to TTST, i.e., each step is assumed to possess its own transition state. For example, for the adsorption of A, the forward step is represented by, A + S [X ] - A S. The free energy changes of activation associated with each step may, of course, be substantially different providing justification of the common assumption of the rate determining step (rds). The rate of the forward elementary step i is proportional to the universal frequency, V = kgT jh [2], a transmission coefficient, K, varying between 0 and 1 [3], and the concentration of the transition-state complex (TSC)... 

In Figure 17.7b we represent an autopoietic unit composed by boundary-forming molecules L and by a catalytic system C. The precursor(s) X are now transformed into L molecules thanks to the catalytic activity of C, which is also reproducing itself by uptak-ing the precursor(s) Y. Notice that all component of the systems (L and C) are produced from within, the systems is self-bounded, and its behaviour is determined by internal laws. Therefore the system in Figure 17.7b is autopoietic. Also in this case, this system interacts with the environment by taking up building blocks (X and Y) and releasing waste products (W and Z). 

Notation 5+ = G" " regarded as a site in the language of heterogeneous catalysis S -Y = active form of the site S X = inactive form of the site T" = transitional phase catalytic site ... 

Fig. 10.7 Catalytic activity in O2 satiffated H2SO4 solution at pH 1 vs. pyrolysis tune for N234 pristine carlxtn black that was first etched in NH3 at 950 °C and then impregnated with 0.2 wt% Fe (as iron acetate) half-shaded star). A second pyrolysis of this material performed at 950 °C in pure NH3 black squares) ot in Ar black circles) resulted in a sharp increase in the catalytic activity (according to Fig. 5 in ref. [31] reproduced with permission of the American Chemical S(x iety)...

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