Efficient Aqueous-Phase Heck Reaction Catalyzed by a Robust Hydrophilic Pyridine-Bridged Bisbenzimidazolylidene-Palladium Pincer Complex

Abstract

The first efficient example of NHC-palladium pincer complex catalyzed aqueous Heck reaction with extremely low catalyst loading was realized without obvious hydrolysis of products by using a robust hydrophilic pyridine-bridged bisbenzimidazolylidene-palladium complex as a molecular catalyst, which tolerated various electronic properties of substituted functional groups in arenes.

Key words

aqueous phase - benzimidazole - Heck reaction - N-heterocyclic carbene - palladium

References and Notes

• 1a Heck RF. Acc. Chem. Res.  1979,  12:  146 
• 1b Heck RF. Nolley JP. J. Org. Chem.  1972,  37:  2320 
• 1c Mizoroki T. Mori K. Ozaki A. Bull. Chem. Soc. Jpn.  1971,  44:  581 
• For selected recent reviews of Heck reaction, see:
• 2a Torborg C. Beller M. Adv. Synth. Catal.  2009,  351:  3027 
• 2b Nicolaou KC. Bulger PG. Sarlah D. Angew. Chem. Int. Ed.  2005,  44:  4442 
• 2c Dounay AB. Overman LE. Chem. Rev.  2003,  103:  2945 
• 2d Whitcombe NJ. Hii KK. Gibson SE. Tetrahedron  2001,  57:  7449 
• 2e Beletskaya IP. Cheprakov AV. Chem. Rev.  2000,  100:  3009 
• 3a Metal-Catalyzed Cross-Coupling Reactions   2nd ed.:  de Meijere A. Diederich F. John Wiley and Sons; New York: 2004. 
• 3b Transition Metals for Organic Synthesis Building Blocks and Fine Chemicals   Vol. 1:  Beller M. Bolm C. Wiley-VCH; Weinheim: 1998. 
• 3c Comprehensive Organic Synthesis   Vol. 4:  Trost BM. Fleming I. Pergamon Press; Oxford: 1991. 
• 3d Heck RF. Org. React.  1982,  27:  345 
• 4 Birkholz M.-N. Freixa Z. van Leeuwen PWNM. Chem. Soc. Rev.  2009,  38:  1099 ; and references therein
• 5a Alonso DA. Nájera C. Chem. Soc. Rev.  2010,  39:  2891 
• 5b Pan D. Jiao N. Synlett  2010,  1577 
• 5c Modern Arylation Methods   Ackermann L. Wiley-VCH; Weinheim: 2009. 
• 6a Chanda A. Fokin VV. Chem. Rev.  2009,  109:  725 
• 6b Carril M. SanMartin R. Dominguez E. Chem. Soc. Rev.  2008,  37:  639 
• 6c Comprehensive Organic Reactions in Aqueous Media   2nd ed.:  Li CJ. Chan TH. Wiley; New York: 2007. 
• 6d Li CJ. Chem. Rev.  2005,  105:  3095 
• 6e Aqueous-Phase Organometallic Catalysis: Concepts and Applications   2nd ed.:  Cornils B. Herrmann WA. Wiley-VCH; Weinheim: 2004. 
• 6f Organic Synthesis in Water   Grieco PA. Blackie Academic and Professional; London: 1998. 
• 7a Mauger CC. Mignani GA. Aldrichimica Acta  2006,  39:  17 
• 7b Zapf A. Beller M. Chem. Commun.  2005,  431 
• 7c Jeffery T. Tetrahedron Lett.  1994,  35:  3051 
• For recent reviews, see:
• 8a Hahn FE. Jahnke MC. Angew. Chem. Int. Ed.  2008,  47:  3122 
• 8b Crabtree RH. Coord. Chem. Rev.  2007,  251:  596 
• 8c N-Heterocyclic Carbenes in Transition Metal Catalysis, In Topics in Organometallic Chemistry   Vol. 21:  Glorius F. Springer; Berlin: 2007.  p.1-218  
• 8d Marion N. Díez-González S. Nolan SP. Angew. Chem. Int. Ed.  2007,  46:  2988 
• 8e Kühl O. Chem. Soc. Rev.  2007,  36:  592 
• 8f Hahn FE. Angew. Chem. Int. Ed.  2006,  45:  1348 
• 9 Fleckenstein C. Roy S. Leuthäußer S. Plenio H. Chem. Commun.  2007,  2870 
• 10a Tu T. Bao X. Assenmacher W. Peterlik H. Daniels J. Dötz KH. Chem. Eur. J.  2009,  15:  1853 
• 10b Tu T. Assenmacher W. Peterlik H. Schnakenburg G. Dötz KH. Angew. Chem. Int. Ed.  2008,  47:  7127 
• 10c Tu T. Assenmacher W. Peterlik H. Weisbarth R. Nieger M. Dötz KH. Angew. Chem. Int. Ed.  2007,  46:  6368 
• 11a Tu T. Feng X. Wang Z. Liu X. Dalton Trans.  2010,  10598 
• 11b Tu T. Mao H. Herbert C. Xu M. Dötz KH. Chem. Commun.  2010,  46:  7796 
• 11c Tu T. Malineni J. Bao X. Dötz KH. Adv. Synth. Catal.  2009,  351:  1029 
• 11d Tu T. Malineni J. Dötz KH. Adv. Synth. Catal.  2008,  350:  1791 
• 13a Peris E. Crabtree RH. Coord. Chem. Rev.  2004,  248:  2239 
• 13b Peris E. Loch JA. Mata J. Crabtree RH. Chem. Commun.  2001,  201 

12

General Procedure for the Aqueous Heck Reactions Catalyzed by Palladium Complex 2
Palladium pincer complex 2 (50 ppm) was added to the 5 mL flask containing iodoarene (1 mmol), acrylate (1.5 mmol), Et₃N (2.5 mmol), and TBAI (1 mmol) in H₂O (2 mL) under air. After heating at 100 ˚C for certain time (monitored by TLC), the reaction mixture was allowed to cool to r.t., and the aqueous layer was extracted with EtOAc (5 × 3 mL). The combined organic extracts were dried over anhydrous Na₂SO₄. After evaporation under vacuum, the crude product was purified by flash column chromatography (hexane-EtOAc, 100:1).