Ferrocene-based catalysts

Summary of the Major Catalytic Applications of Ferrocene-Based Catalysts.300... 

SUMMARY OF THE MAJOR CATALYTIC APPLICATIONS OF FERROCENE-BASED CATALYSTS... 

A commonly used intermediate in the synthesis of ferrocene-based catalysts is chlorocarbonylferrocene. Formation of this acid chloride from the corresponding acid is capricious and can often result in low yields. To circumvent these difficulties, recently, Rotello and co-workers have investigated the use of the corresponding acid fluoride as a synthetic intermediate (Scheme 69) <1999JOC3745>. 

Planar Chiral Ferrocenes as Lewis- or Br0nsted-Base Catalysts.163... 

Major Applications of Ferrocene Diphosphine-Based Catalysts 1847... 

Ferrocene-based complexes have some potential for the enantioselective reduction of ketones, but compared to other ligand classes this is relatively limited [3]. Rh complexes of bppfa, bophoz and josiphos are among the most selective catalysts for the hydrogenation of a-functionalized ketones (Table 25.9 Fig. 25.18, 30-32). Ru complexes of walphos and ferrotane are quite effective for... 

The palladium based catalyst systems were also effective in the construction of carbon-nitrogen bonds on benzannulated five membered heterocycles. The 4-chloroindole derivative shown in 6.78. was coupled with piperazine in excellent yield, using a ferrocene based ligand.109 The analogous 5-bromo-benzimidazole derivative gave similar results (6.79.),110... 

Fu and co-workers have detailed the use of planar chiral DMAP and PPY analogs as catalysts for the resolution of secondary unsaturated alcohols (Fig. 1) [15]. Both ferrocene and ruthenocene-based catalysts have been examined, with the iron-based catalysts generally proving less reactive but more selective [16]. Catalysts are prepared in racemic form and are subsequently resolved by preparative chiral HPLC. 

Asymmetric hydroboration of prochiral alkenes has been achieved using transition metal catalysts and chiral phosphines as ligands to obtain enantiomerically pure alkyl boronates <1997CC173>. Catalysts such as Rh(COD)2+BF4 , Rh(COD)2+Cl, Rh+BF4 , etc., in combination with chiral phosphines like DIOP 71, BINAP 72, CHIRAPHOS 73, DIPAMP 74, BDPP 75, ferrocene-based diphosphines 76<1999TL4977>, etc., have been employed for the asymmetric hydroboration of prochiral alkenes with moderate to high ee (DIOP = 2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino)butane BINAP = 2,2-bis(diphenyl-phos-phanyl)-l,1-binaphthyl CHIRAPHOS = 2,3-bis(diphenylphosphino)butane DIPAMP = l,2-bis[(2-methoxyphe-nyl)phenylphosphino]ethane BDPP = 2,4-bis(diphenylphosphino)pentane). 

The use of ferrocene-based ligands such as 3 and PPFA (8) result in the formation of catalysts that extended the scope of the arylation reaction to more difficult transformations [37,38,56]. For example, di-n-butylamine could now be effectively coupled with electronically neutral as well as electron-deficient aryl bromides. Reaction of 4-ferf-butylbromobenzene with di-n-butylamine with the ( )-BlNAP/Pd- or DPPF/Pd-based catalysts resulted in significant amounts of terf-butylbenzene formation, however the use of ligands 3 and 8 resulted in formation of the desired product in excellent yield, Eq. (25). 

Hartwig reported that ferrocene-based diphosphine 13 catalyzes the arylation of aniline at room temperature, Eq. (91) [72]. Additionally, the (f-BuljP/Pd-based system effects the room-temperatuxe condensation of anilines and aryl bromides. However, the (f-BuljP/Pd-catalyst is considerably more active [50]. While the reaction with 4-bromotoluene and anihne proceeded in 20 h using 5 mol% 15/Pd(dba)2, the reaction between bromoben-zene and aniline was complete in 1 h using only 1 mol% of the (f-BuljP-derived catalyst. 

The use of ferrocene-based ligands 26 and 27 also effected the Pd-catalyzed formation of diaryl ethers,Eq. (193) [148,149]. The 27/Pd-catalyst is more reactive and mediates the transformation in better yield and at lower temperatures. 

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