Synthesis, Structural Characterization and Catalytic Evaluation of Anionic Phosphinoferrocene Amidosulfonate Ligands

Abstract

Triethylammonium salts of phosphinoferrocene amidosulfonates with electron-rich dialkyphosphino substituents, R 2 PfcCONHCH 2 SO 3 (HNEt 3 ) (4a-c), where fc = ferrocene-1,1 -diyl, and R = i-Pr (a), cyclohexyl (Cy; b), and t-butyl (c), were synthesized from the corresponding phosphinocarboxylic acids-borane adducts, R 2 PfcCO 2 H·BH 3 (1a-c), via esters R 2 PfcCO 2 C 6 F 5 ·BH 3 (2a-c) and adducts R 2 PfcCONHCH 2 SO 3 (HNEt 3 )·BH 3 (3a-c). Compound 4b was shown to react with [Pd(µ-Cl)(η-C 3 H 5 )] 2 and AgClO 4 to afford the zwitterionic complex [Pd(η 3 -C 3 H 5 ) (Cy 2 PfcCONHCH 2 SO 3 -κ 2 O,P)] (5b), in which the amidosulfonate ligand coordinates as a chelating donor making use of its phosphine moiety and amide oxygen. The structures of 3b·CH 2 Cl 2 , 4b and 5b·CH 2 Cl 2 were determined by single-crystal X-ray diffraction analysis. Compounds 4a-c and their known diphenylphosphino analogue, Ph 2 PfcCONHCH 2 SO 3 (HNEt 3 ) (4d), were studied as supporting ligands in Pd-catalyzed cyanation of aryl bromides with K 4 [Fe(CN) 6 ] and in Suzuki-Miyaura biaryl cross-coupling performed in aqueous reaction media under mild reaction conditions. In the former reaction, the best results were achieved with a catalyst generated from [PdCl 2 (cod)] (cod = η 2 :η 2 -cycloocta-1,5-diene) and 2 equiv. of the least electron-rich ligand 4d in dioxane-water as a solvent. In contrast, the biaryl coupling was advantageously performed with a catalyst resulting from palladium(II) acetate and ligand 4a (1 equiv.) in the same solvent.

Synthesis, Coordination, and Catalytic Use of 1′-(Diphenylphosphino)ferrocene-1-sulfonate Anion

“…The derivatization of the phosphorus substituent is clearly reflected in the 31 P NMR spectra, which show distinct singlets at δ P 42.0, −16.5 and 24.5 for 3 – 5 , respectively. In addition to the downfield shift of the 13 C NMR signal of the ferrocene C -SO 3 carbon (δ C ∼94 for 3 and 4 , δ C ∼99 for 5 ), the presence of the sulfonate moiety was further confirmed by IR spectra showing bands due to the ν as (SO 3 ) and ν s (SO 3 ) vibrations (ν as ∼1150–1250 cm –1 , ν s ∼1040 cm –1 ) …”

“…To avoid the synthetic challenges associated with the use of aggressive sulfonating agents, we initially prepared phosphinoferrocene sulfonates indirectly by the assembly of suitable functional building blocks. The resulting compounds Ia-d and II (Chart ), in which the phosphinoferrocene and sulfonate moieties are connected by an amide linkage, not only were highly hydrophilic but also showed favorable catalytic activity. , In contrast, Erker et al. synthesized a series of 2-phosphinoferrocene-1-sulfonic acids III , , which are indeed closer to the archetypal phosphinosulfonate donors, by utilizing an ortho-lithiation/functionalization approach developed previously for the synthesis of 2-phosphinobenzenesulfonates IV from the corresponding sulfonic acids. , Similar to the studies conducted on IV -type ligands, Pd­(II) and Ni­(II) complexes with these ferrocene ligands were employed as catalysts for various (co)­polymerization reactions. , …”

Synthesis and Catalytic Use of Polar Phosphinoferrocene Amidosulfonates Bearing Bulky Substituents at the Ferrocene Backbone

“…To alleviate these problems, we have recently devised an alternative approach based on amide coupling reactions between phosphinocarboxylic acids and aminosulfonic acids, producing the functional amidophosphine ligands 1 R (Scheme , left; R = Ph, Cy). , These coupling reactions proceed with good to excellent yields, employ stable, safe, and readily accessible starting materials, and typically produce pure crystalline products . Utilizing this approach, we synthesized several phosphinoferrocene amidosulfonates, which proved to be useful ligands for catalytic reactions in aqueous systems . Notably, even a single amidosulfonate tag was sufficient to overcome the hydrophobicity of phosphinoferrocene ligands, which limits their applications in aqueous catalysis …”

Selective Ethylene Dimerization by Palladium(II) Complexes Bearing a Phosphinoferrocene Sulfonate Ligand

“…Continuing our research focused on hydrophilic, ferrocene-based phosphinosulfonate ligands that has led to the preparation of compounds C and D (Scheme ), we have recently reported the synthesis of 1′-(diphenylphosphino)­ferrocene-1-sulfonic acid (H L in Scheme ). This compound is a sterically distinct isomer of B -type ligands and can be conveniently isolated in the form of the stable salt (Et 3 NH) L .…”