New bisphosphomide ligands, 1,3-phenylenebis((diphenylphosphino)methanone) and (2-bromo-1,3-phenylene)bis((diphenylphosphino)methanone): synthesis, coordination behavior, DFT calculations and catalytic studies

Abstract

The bisphosphomide, 1,3-{Ph₂PC(O)} ₂C₆H₄ (1), was prepared by the reaction of isophthaloyl chloride with diphenylphosphine in the presence of triethylamine. The corresponding bromo-derivative, 2-Br-1,3-{Ph₂PC(O)} ₂C₆H₃ (2), was obtained by the reaction of 2-bromoisophthaloyl chloride with diphenylphosphine. The reaction of 1 with elemental sulfur or selenium yielded the bis(chalcogenides), 1,3-{Ph₂P(S)C(O)} ₂C₆H₄ (3) and {1,3-Ph₂P(Se)C(O)} ₂C₆H₄ (4). The reaction between 1 and [Ru(η⁶-p-cymene)Cl₂]₂ and [Pd(η³-C₃H₅)Cl] ₂ in 1:1 stoichiometry yielded the corresponding binuclear complexes, [Ru₂ (η⁶-p-cymene) ₂Cl₄{1,3-{Ph₂PC(O)} ₂ (C₆H₄)}] (5) and [Pd₂ (η³-C₃H₅)₂Cl₂{1,3-{Ph₂PC(O)} ₂ (C₆H₄)}] (6). The reaction of 1 with AgClO₄ followed by the addition of [Pd(COD)Cl₂] at room temperature resulted in the formation of a pincer complex [PdCl{2,6-{Ph₂PC(O)} ₂ (C₆H₃)}] (9), via transmetallation. Pincer complex formation through C–H activation requires drastic conditions and yields are generally moderate. The oxidative addition reaction between 2 and [Ni(COD) ₂] gave a pincer complex [NiBr{2,6-{Ph₂PC(O)} ₂ (C₆H₃)}] (8), whereas the 2:1 reaction of 2 with [Pd₂ (dba)₃] yielded the palladium analogue [PdBr{2,6-{Ph₂PC(O)} ₂(C₆H₃)}] (9) in quantitative yield. The reaction between 1 and CuX in a 1:1 molar ratio produced binuclear complexes, [Cu₂(μ-X) ₂{1,3-{Ph₂PC(O)} ₂ (C₆H₄)}₂] (10, X = Cl; 11, X = Br; 12, X = I), whereas the reaction between 1 and [Cu(NCCH₃)₄]BF₄ led to the isolation of a spirocyclic complex, [Cu(CH₃CN) ₂{1,3-{Ph₂PC(O)} ₂ (C₆H₄)}]BF₄ (13). The silver complexes [Ag₂ (μ-ClO₄)₂{1,3-{Ph₂PC(O)}₂ (C₆H₄)}₂] (14), [Ag₂(μ-OTf) ₂{1,3-{Ph₂PC(O)}₂ (C₆H₄)}₂] (15) and [Ag₂X₂{1,3-{Ph₂PC(O)} ₂ (C₆H₄)}] (16, X = ClO₄; 17, X = OTf) were obtained by treating 1 with AgClO₄ or AgOTf in 1:1 or 1:2 molar ratios. The reactions of 1 with [AuCl(SMe₂)] in 1:1 and 1:2 molar ratios afforded mono- and binuclear complexes, [AuCl{1,3-{Ph₂PC(O)} ₂ (C₆H₄)}₂] (18) and [Au₂Cl₂{1,3-{Ph₂PC(O)} ₂ (C₆H₄)}AuCl] (19), in good yield. The structures of complexes 5, 7–10, 12 and 14a were confirmed by single-crystal X-ray diffraction studies. DFT calculations were performed in order to gain additional insights into the structure and bonding of the pincer complexes. An additional analysis of the orbital interactions in the case of palladium complex 9 is also included. The in situ generated rhodium complex of bisphosphomide 1 showed moderate to good selectivity in the hydroformylation of hex-1-ene and styrenederivatives.