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Synlett 2004(8): 1379-1382  
DOI: 10.1055/s-2004-829094
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Soluble Fluorous Palladium Complex that Promotes Heck Reactions and Can Be Recovered and Reused

Dennis P. Curran*, Karin Fischer, Gustavo Moura-Letts
Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
Fax: +1(412)6249861; e-Mail: curran@pitt.edu;
Further Information

Publication History

Received 8 March 2004
Publication Date:
22 June 2004 (online)

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Abstract

A new fluorous SCS pincer palladium complex is synthesized and shown to efficiently promote typical Heck reactions under microwave or thermal heating. The complex is air stable and can be recovered after reactions for reuse by fluorous solid phase extraction. By analogy to related complexes, it may function as a precursor of soluble ligandless palladium metal.

Key words

fluorous chemistry - Heck reaction - palladium pincer complex - solid phase extraction - catalysis

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1H NMR (300 MHz, CDCl3): δ = 4.68 (s, 4 H, CH2), 7.08 (m, 4 H), 7.59 (d, 4 H, 3 J = 8.3 Hz), 7.93 (d, 4 H, 3 J = 8.3 Hz). 19F NMR (282.4 MHz, CDCl3): δ = -79.57 (m, 3 F, 3 J = 8.5 Hz), -109.86 (m, 2 F, CαF2), -120.32 (m, 4 F, CβF2, CδF2), -121.59 (m, 2 F, CεF2), -124.96 (m, 2 F, CγF2). 13C NMR (75 MHz, CDCl3): δ = 50.32 (CH2), 122.79, 125.59, 128.33, 130.23, 130.68, 136.75, 149.04, 161.84. EIMS: m/z = 1100 (M+), 1063 (M - Cl), 958 (M - PdCl), 513 (M - C8F17 - PdCl), 428 (HSPhC6F13). LCMS (APCl, neg. mode): m/z = 1037, 957 (M - HPdCl), 427 (M - SPhC6F13). MS (APCl, pos. mode): m/z = 1063 (M - Cl).

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Complex 3 crystallizes in space group P21/n with three crystallographically independent but chemically similar molecules per asymmetric unit. The metric symmetry is suggestive of orthorhombic, with β equal to 90.02 (2)° but the crystal packing does not show any symmetry higher than monoclinic. Each molecule consists of a Pd atom coordinated to a tridentate 1,3-bis(thiomethyl)benzene SCS ligand with a Pd-Cl bond trans to the Pd-C bond. The environment about Pd is slightly distorted square planar. Distortions are caused by the rigid SCS ligand, which results in non-linear S-Pd-S angles of 171.07 (7)°, 170.11 (7)° and 167.40 (7)° in the three independent molecules of 3. Pd-Cl bonds average 2.391 (2) Å, Pd-S bonds average 2.302 (2) Å, and Pd-C bonds average 1.977 (8) Å. All three molecules have similar, well resolved Pd(SCS)Cl cores, but differ in the orientation of the fluoroalkylaryl groups attached to S. For all molecules, the two fluoroalkylaryl groups are on opposite sides of the Pd(SCS)Cl plane. Differences lie in the twisting of the aryl rings. In two of the three molecules, one of the fluoroalkyl chains is highly disordered and some fluorines and carbons at the ends of these chains cannot be resolved.

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The recovered complex exhibited the same spectra as that starting complex and had a bromine content of <0.15% by elemental analysis.