FULL PAPER DOI: 10.1002/ejic.200800024 A Phosphanyl-Substituted Benzo-1,3,2-Dioxaborol as Ambiphilic Bifunctional Lewis Donor–Acceptor Unit Samir Chikkali, [a] Silja Magens, [b] Dietrich Gudat,* [a] Martin Nieger, [c] Ingo Hartenbach, [a] and Thomas Schleid [a] Keywords: Phosphanes / Boranes / Lewis acids / Lewis bases / Donor–acceptor systems Condensation of 3-[(diphenylphosphanyl)methyl]benzene- 1,2-diol (1) with phenyl boronic acid gave a phosphane-func- tionalised benzo-1,3,2-dioxaborol 3. The ability of this spe- cies to act as a Lewis base through the P-centered donor and as a Lewis acid through the B-centered acceptor sites was demonstrated by the reactions with (cod)PdCl 2 and some ni- trogen donors (4-dimethylaminopyridine, diaza-[2.2.2]-bicy- clooctane, pyridine). These reactions yielded either palla- dium–phosphane complexes or amine–borane adducts that were characterised by spectroscopic data and, in some cases, by single-crystal X-ray diffraction studies. Reactions of a Pd complex of the phosphane-functionalised benzo-1,3,2-di- Introduction Tertiary phosphanes that carry additional Lewis acid functionalities are receiving increasing interest as ambi- philic bifunctional ligands. The reaction behaviour of these species has been found to depend significantly on the Lewis acidity of the acceptor moiety: ligands for which the ac- ceptor is a strong Lewis acid form stable metal complexes through PM–ClB or PMB interactions [1] or un- dergo unusual reactions such as the activation of dihydro- gen. [2] In contrast, species featuring Lewis acid sites of moderate acceptor power may serve as templates for direct- ing catalytic reactions by precoordination of substrates with complementary donor functionalities. [3,4] Having recently begun to explore the chemistry of the catechol phosphane 1, [5] we have demonstrated that its reac- tion with boric acid B(OH) 3 proceeds selectively at the diol unit to give the borate-templated anionic diphosphane 2, which may bind as a trans-spanning bidentate ligand to a univalent metal ion such as Ag + . [6] With regard to this be- haviour, it was anticipated that reaction of 1 with phenyl boronic acid PhB(OH) 2 might give rise to an ambiphilic phosphane-functionalised dioxaborol 3, which may then be [a] Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70550 Stuttgart, Germany E-mail: gudat@iac.uni-stuttgart.de [b] Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70550 Stuttgart, Germany [c] Laboratory of Inorganic Chemistry, University of Helsinki, A. I. Virtasen aukio 1, Helsinki, Finland Eur. J. Inorg. Chem. 2008, 2207–2213 © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2207 oxaborol 3 with dabco, or of the dmap adduct of 3 with (cod)- PdCl 2 , gave materials that were characterised by analytical data and solid-state NMR spectroscopic data as triple Lewis acid/base complexes and that contain both PPd and BN dative bonds. Even though these adducts were unstable in solution, the results of these experiments demonstrate the ability of 3 to act as a bifunctional donor/acceptor ligand, which is of potential use as a building block for main chain organometallic polymers or multimetallic complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) able to act as a bifunctional ambiphilic ligand through the P-centred donor and B-centred acceptor sites. We describe here the synthesis of ambiphilic ligands of this type and present a first investigation of their reaction behaviour towards Lewis acids and bases. The results of these studies may open a new avenue towards the construction of me- tallopolymers and multimetallic complexes (Scheme 1). [7] Scheme 1. Results and Discussion Catechol phosphane 1 was synthesised as previously re- ported [5] by hydrophosphanation of dihydroxy benzalde- hyde with diphenylphosphane, followed by reduction of the resulting phosphane oxide with LiAlH 4 . Reaction of 1 with 1 equiv. phenyl boronic acid in CH 2 Cl 2 for 1 h at room tem- perature and subsequent evaporation of volatiles gave a quantitative yield of a white solid which was identified as analytically pure dioxaborol 3 by elemental analysis and spectroscopic (NMR, MS) data. The broad 11 B NMR sig- nal [δ( 11 B) = 31.7 ppm] and the sharp 31 P{ 1 H} NMR signal [δ( 31 P) = –11 ppm] are found in regions that are characteris-