FULL PAPER DOI:10.1002/ejic.201301473 Resorcinarenyl-Phosphines in Suzuki–Miyaura Cross- Coupling Reactions of Aryl Chlorides Laure Monnereau, [a] Hani El Moll, [a] David Sémeril,* [a] Dominique Matt,* [a] and Loïc Toupet [b] Keywords: Calixarenes / Phosphane ligands / Cross-coupling / Palladium Two phosphines built on a bowl-shaped resorcin[4]arene skeleton, namely 5-diphenylphosphanyl- and 5-diisoprop- ylphosphanyl-4(24),6(10),12(16),18(22)-tetramethylenedioxy- 2,8,14,20-tetrapentylresorcin[4]arene, have been synthesised and tested in the Suzuki–Miyaura cross-coupling reaction of aryl halides. Combining these ligands with [Pd(OAc) 2 ] re- sulted in highly active catalysts that allowed the formation of o,o'-biphenyls starting from aryl chlorides. The remarkable Introduction Palladium-mediated Suzuki–Miyaura cross-coupling be- tween aryl halides and arylboronic acids [1] is a powerful tool in modern synthetic chemistry. [2–4] In the past few years, considerable effort has been directed towards the dis- covery of efficient catalysts of this family that are able to promote the cross-coupling of hindered aryl chlorides. Re- search in this field has resulted in the design and synthesis of a variety of novel, bulky and/or electron-rich ligands, in particular phosphines [5–14] and N-heterocyclic carb- enes. [15–19] Bulkiness and basicity are two key features in these catalysed reactions. Notably, bulky phosphines are ex- pected to favour the formation of monophosphine interme- diates over bis-phosphine complexes, thereby lowering the barrier for the oxidative addition step. Bulky ligands are furthermore known to efficiently promote the reductive eli- mination process. [20,21] As an extension of our studies on monophosphines based on cone-shaped macrocycles, [22–25] we now describe the synthesis of two bulky phosphines, both based on a res- orcinarene cavitand, as well as their use in palladium-cata- lysed Suzuki–Miyaura cross-coupling reactions of aryl chlorides and bromides. Their properties have been com- [a] Laboratoire de Chimie Inorganique Moléculaire et Catalyse, UMR 7177 CNRS, Université de Strasbourg, 1 Rue Blaise Pascal, 67008 Strasbourg Cedex, France E-mail: dsemeril@unistra.fr dmatt@unistra.fr http://inorganics.online.fr [b] Institut de Physique, UMR 6251 CNRS, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201301473. Eur. J. Inorg. Chem. 2014, 1364–1372 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1364 activities observed possibly arise from 1) the capacity of the phosphines to operate transiently as P ,O chelators, thereby increasing the electron density of the metal, and 2) the ability of the ligands to embed metal–organic units, which, when occurring, makes the ligand considerably bulkier so as to dis- favour the coordination of a second phosphine. Both features are known to facilitate the oxidative addition step. pared with those of cavity-free, potential P ,O- and P ,arene- chelating ligands. The applications of cavity-derived phosphines in homo- geneous catalysis have recently been comprehensively re- viewed. [26,27] Results and Discussion Phosphine 2 was prepared in two steps from bromo-cavi- tand 1 according to Scheme 1. Its synthesis began with a halogen/lithium exchange followed by reaction with ClPPh 2 at room temperature. A similar procedure was applied to the synthesis of dialkylphosphine 4, but a higher reaction temperature was needed. Owing to the high sensitivity of 4 towards oxygen, this phosphine was isolated as the corre- sponding BH 3 adduct 3. Phosphine 2 and phosphine–bor- ane 3 were both purified by chromatography (yields: 70 and 43%, respectively). We noted that in the synthesis of 3 sig- nificant amounts of the non-brominated version of 1 formed (i.e., with H in place of Br). Free phosphine 4 was quantitatively obtained by heating compound 3 in dieth- ylamine at 60 °C for 16 h. Both phosphines 2 and 4 appear as a singlet in their 31 P NMR spectra [–15.7 ppm (2) and +7.1 ppm (4)]. The 1 H NMR spectra of 2 and 4 are in keep- ing with C s -symmetrical molecules, each of them showing the presence of two distinct AB patterns for the methylenic OCH 2 O protons. Treatment of phosphines 2 and 4 with H 2 O 2 quantita- tively gave the phosphine oxides 5 and 6, respectively. Crys- tals of 5 suitable for an X-ray diffraction study were ob- tained by slow diffusion of methanol into a dichlorometh- ane solution of the product. In the solid state (Figure 1),