Regioselectivity catalysts

Three generations of dendritic phosphines have been prepared from 3,5-diaminobenzoylglycine and 9-fluorenylmethoxycarbonyl-L-phenylalanine. The dendrimers were then attached to MBHA resin, treated with CH20 and Ph2PH, and converted to their Rh complexes. The polymer-supported complexes are excellent catalysts for the hydroformylation of alkenes, which could be recycled.283 The bidentate diphosphine A,A-bis-(P-(phosphabicyclo[3.3.1] nonan) methyl)aniline was prepared by phosphanomethylation of aniline. It forms a Rh-complex which is a highly regioselective catalyst in the hydroformylation of citronellene.284... 

The electronic and steric properties of the phosphine ligand(s) can have dramatic effects on the rate and selectivity of the rhodium catalysts. As mentioned above, electron-rich alkylated phosphines generally have a negative effect on the rate and regioselectivity, while more electron deficient phosphines such as PPhs and phosphites (see Electron Deficient Compound) generate more active and regioselective catalysts (Table 3). 

In situ regioselective quinoline hydrogenation with transition metal complexes, such as [Rh(COD)Cl2], [Ir(COD)Cl2], [IrfCOE Ch], and [Ru(MeCN)4Cl2] stabilized by Tp and Tp ligands via one-pot reaction has been described. The results have been compared with those obtained with [Ir(Tp)(C2H4)2]. The system [Rh(COD)Cl2]/Tp is the most efficient and regioselective catalyst precursor for this reaction.65... 

In the more limited space of TS-1 (Ti-MFl) essentially complete rcgiosclcctivity to the fivemembered ring ethers was achieved in the 2-step reaction of 4-pcntene-l-ol and 4-hexen-l-ol with hydrogen peroxide [76].These reactions represent fine examples of a zeolite acting as bifunctional regioselective catalyst. Conditions 4-pentene-l-ol, room temperature, TS-1, acetone, 2-butanol or water as the solvent, 30 % aq. H2O2. 4-Hexen-l- ol, acetone 60 °C. 

Moscardi has modeled the insertion of propene into the Zr—H bond and found that secondary propene insertion into the Zr—H bond with formation of the Zr(i-Pr) initiating species is indeed competitive with primary insertion, even on highly regioselective catalysts. This molecular modeling study has also shown that the Zr(i-Pr) initiating species is slower compared to Zr(n-Pr) with respect to the following propene insertion and that isomerization of Zr(i-Pr) to Zr(n-Pr) can follow a relatively low energy pathway by associative displacement with the monomer after /1-H transfer on the Zr(i-Pr) species (Scheme 49). 

For example, a highly active and regioselective catalyst for the hydroformylation of 1-hexene and 1-octene in ILs was obtained from the combination of the dicationic 2,7-di[5-(3-methylimidazolium)pentyl]-9,9-dimethyl-4,5-di(2,8-dimethyl-10-phenoxaphosphino)xanthene hexafluorophosphate and [Rh(GO)2(acac)]. No catalyst leaching or losses in catalytic performance were observed during 1-octene hydroformylation recycle experiments in [C4CiIm]PF6. At low catalyst loadings, the activity and regioselectivity were competitive with a one-phase catalysis in conventional solvents. 

Selective oxidation of only the terminal groups in alkenes is of great interest for both the pharmaceutical and chemical industries. MeAPO-18 [Me is Co(II) or Mn(II)] is such a regioselective catalyst, which enables the molecular oxygen to oxidize only the terminal CH3 groups. The framework Co(II) ions [or Mn(II)], which readily change their oxidation and coordination number during the catalytic performance, are believed to be vital for the catalysis (367). Namely,... 

This difference of affinity between RuH2(CO)(PPh3)3 and Ru3(CO)j2 toward specific functional groups has been exploited in a regioselective, catalyst-specific C(sp )-C(sp ) bond formation through the use of substrates bearing both a ketone and an imine fragment (Scheme 19.58) [79]. 

Regioselective, catalyst-controlled benzylation (Scheme 8.2) is accomplished by treatment of methyl a-L-rhamnopyranoside with borinate ester 1 (5 mol%), benzyl bromide (BnBr, 1.5 equivalents), silver(I) oxide (1.1 equivalents) as a halide abstracting agent and base, in acetonitrile solvent at 40°C. After 48 hours, conventional workup and purification by flash chromatography gave 3 in 89% yield. The 2-OBn regioisomer is the major byproduct of this reaction and was isolated in 11% yield... 

Frew JJR, Damian K, Van Rensburg H, Slawin AMZ, Tooze RP, Clarke ML. Palladium(tf) complexes of new bulky bidentate phosphanes active and highly regioselective catalysts for the hydroxycarbonylation of styrene. Chem. Eur. J. 2009 15 10504-10513. 

Reactions of unsymmetric internal alkynes are more challenging, since two hydroamination products can be formed. The feasibility to control regioselectivity depends on the steric properties of both substrate and catalyst and a universal regioselective catalyst remains to be elaborated. When anilines are employed as reactants, high a t/-Markovnikov selectivity is obtained with titanocene catalysts 47 and 48 (Table 11) [182, 183] while aliphatic amines gave poor results. Again, the bis(indenyl)titanium catalyst 49 showed superior a t/-Markovnikov selectivity... 

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