Polymer-supported phosphines

There have been numerous attempts to link phosphines or their corresponding homogeneous catalysts to solid supports. Heterogenization can be achieved via covalent bonding or ionic interactions. Moreover, conventional small metal phosphine catalyst can be encapsulated in chaimels or cavities of a heterogeneous 

MeeTREN =Ttis(2-(dimethylamino) Ro-(Sio3-sfaf-SDPP2e)-Br ethyl)amine ggQQ g 1 

In contrast, SDPP homopolymerization proceeded in a fast and uncontrolled manner. The polymer was tested in the rhodium-catalyzed hydroformylation of 1-octene where a higher //i-ratio but a lower activity was found in comparison to the reaction with the monomeric ligand PPh3. 

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In 1993 Bergbreiter prepared two soluble polymer-supported phosphines that exhibited an inverse temperature-dependent solubility in water [52]. Although PEG-supported phosphine undergoes a phase-separation from water at 95-100 °C, the PEO-poly(propylene oxide)-PEO supported catalyst was superior as it is soluble at low temperatures and phase-separates at a more practical 40-50 °C. Treatment of a diphenylphosphinoethyl-terminated PEO-PPO-PEO triblock copolymer... 

Bis(phosphino)amines (208)-(211) were readily prepared by condensation of Ph2PCl and the appropriate secondary amine in diethyl ether, tetrahydrofuran, dichloromethane, or benzene, with triethylamine as base.454-457 Polymer-supported phosphine-phosphino(amines) (212) have also been reported.458 Hersh and co-workers have described a novel series of bis(p-toluenesulfonylamino) phosphines (213) and (214) from bis(dichlorophosphino) starting materials and A,vV -(ditoluenesul-fonyl)-l, 2-diaminoethane.459... 

CH30C6H4Br, f-BuONa, Pd(OAc)2, polymer supported phosphine ligand, toluene, SOT, 15-20h, 84% yield. ... 

Soluble polymer-supported phosphines may be a valuable tool for Pd-catalyzed library synthesis in solution [145],... 

Scheme 10.12 Examples of catalysis by non-chiral polymer-supported phosphines.

The peptide-based phosphine ligand 105 was identified from a polymer-supported phosphine library of 75 members [154]. Enantioposition-selective desymmetrization of the meso-cyclopentenediol derivative 100 was promoted by a palladium complex of 105 to afford the cyclic carbamate 101 with 76% ee. This result demonstrated that the combinatorial approach is effective in the lead-generation stage of stereoselective catalyst development [155, 156]. The resin-supported palladium complex of Ac-D-Phg-Pro-D-Val-Pps-D-Leu-NH resin 106, which has also been developed through the combinatorial approach. 

Supported catalysts involving palladium on carbon and dendrimer-encapsulated palladium and a polymer-supported phosphine palladium catalyst have facilitated C-C coupling reactions in SCCO2. Polymer-tethered substrates or amine bases have also been successfully used for the Mizoroki-Heck and Suzuki-Miyaura reactions in SCCO2. For example, REM resin underwent a Mizoroki-Heck reaction with iodobenzene to yield, after cleavage, ( )-methyl cinnamate 48 (74%) (Scheme 88). It is assumed that SCCO2 acts as a good solvent that swells the polymers and exposes reactive sites. 

In addition, we have found that the stereochemistry of the Michael acceptor also plays an important role in the efficiency of phosphine-mediated intramolecular MBH reactions. In all examined cases with PPhs or polymer-supported phosphine as the catalyst, cyclization substrates enones 275 possessing (Z)-alkenes afforded the desired product 276 in a higher yield than ( )-275 under identical conditions (Scheme 1.99). The reason for this difference in reactivity is most likely steric in nature, as substrates where the p-substituent is ds to the electron-withdrawing substituent are more accessible to reaction with the nucleophilic catalyst than their trans counterparts. 

Scheme 9 Benzodiazepine-quinazoline alkaloids library by polymer supported phosphine-mediated aza-Wittig reaction [170]...

Grieder and Thomas prepared a diverse library of natural product-like benzodiazepine-quinazolinone alkaloids similar to the family of circumdatins (Figure 11.72). Starting from benzodiazepinedione derivatives, the synthesis relied on a modified Eguchi protocol using a polymer-supported phosphine-mediated intramolecular aza-Wittig reaction in a key step of the reaction sequence. Following this route two sublibraries of tricyclic derivatives similar to the circumdatins D and E were prepared. 

Living atom-transfer radical copolymerization (ATPR) of4-styryldiphenylpho-sphine (SDPP) with styrene was applied by Poli s group as a new method for the construction of polymer-supported phosphine ligands (Scheme 2.44) [142]. Copolymers with a statistical distribution of the monomers were obtained by means of CuBr/MegTREN as catalyst. Ethyl bromoisobutyrate was used as initiator. A small amount of CuBr2 was added to prevent a slower deactivation... 

Reduction of amides to nitriles by polymer-supported phosphine oxide has been described (Relies and Schluenz, 1974 Harrison et al., 1977). 

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