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(η(6)-p-cymene)Cl2]2 and [Pd(η(3)-C3H5)Cl]2 in 1 : 1 stoichiometry yielded the corresponding binuclear complexes, [Ru2(η(6)-p-cymene)2Cl4{1,3-{Ph2PC(O)}2(C6H4)}] (5) and [Pd2(η(3)-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 styrene derivatives.

A phosphomide based PNP ligand, 2,6-{Ph2PC(O)}2(C5H3N), showing PP, PNP and PNO coordination modes

“…Synthesis of [Cu(NCCH 3 ){2,6-{Ph 2 PC(O)} 2 (C 5 H 3 N)}](BF 4 ) (12) A solution of 1 (0.05 g, 0.099 mmol) in acetonitrile (10 mL) was added dropwise to a solution of [Cu(NCCH 3 ) 4 ](BF 4 ) (0.0312 g, 0.099 mmol) in CH 3 CN (5 mL). The reaction mixture was stirred for 4 h to give a dark brown solution.…”

“…11 We have recently reported the synthesis of the bisphosphomide ligand [1,3-{Ph 2 PC(O)} 2 (C 6 H 4 )] and studied its coordination behavior in detail. 12 The PCP pincer complexes of these ligands have been synthesized via C-H bond activation as well as by oxidative addition of the prefunctionalized ligand with zero-valent metal precursors. We envisioned that a similar carbonyl-linked PNP ligand system would be even more interesting since the presence of both phosphorus and oxygen donor atoms could enable it to adopt variable coordination modes.…”

A cyclodiphosphazane based pincer ligand, [2,6-{μ-(tBuN)2P(tBuHN)PO}2C6H3I]: NiII, PdII, PtII and CuI complexes and catalytic studies

“…18,25,26 The pincer complexes of phosphorus donor ligands have been studied extensively. [27][28][29][30][31][32][33][34][35] The steric and electronic properties of pincer ligands can be controlled by carefully modifying the substituents on donor groups and aromatic backbones. 34,36 However, modification of stereochemical parameters often requires tedious multistep synthesis.…”

The story of acyl phosphines: Synthesis, reactivity, and catalytic applications

“…The P-C(O) bond length in all complexes is about 1.88 Å (Table 4). [28] Furthermore, PNP-type pincer complexes of group 10 metals were also synthesized. The reaction ligand 20c of metal precursors, namely, [Ni(DME)Cl 2 ] or M (COD) Cl 2 (M = Pd, Pt) in the presence of one equivalent of AgBF 4 or AgClO 4 afforded the pincer-type complexes 123 as depicted in Scheme 34.…”