Bis(2-diphenylphosphinoxynaphthalen-1-yl)methane: transition metal chemistry, Suzuki cross-coupling reactions and homogeneous hydrogenation of olefins

Abstract

Transition metal complexes of bis(2-diphenylphosphinoxynaphthalen-1-yl)methane (1) are described. Bis(phosphinite) 1 reacts with Group 6 metal carbonyls, [Rh(CO)₂Cl]₂, anhydrous NiCl₂, [Pd(C₃H₅)Cl]₂/AgBF₄ and Pt(COD)I₂ to give the corresponding 10-membered chelate complexes 2, 3 and 5–8. Reaction of 1 with [Rh(COD)Cl]₂ in the presence of AgBF₄ affords a cationic complex, [Rh(COD){Ph₂P(–OC₁₀H₆)(µ-CH₂)(C₁₀H₆O–)PPh₂-κP,κP}]BF₄ (4). Treatment of 1 with AuCl(SMe₂) gives mononuclear chelate complex, [(AuCl){Ph₂P(–OC₁₀H₆)(µ-CH₂)(C₁₀H₆O–)PPh₂-κP,κP}] (9) as well as a binuclear complex, [Au(Cl){µ-Ph₂P(–OC₁₀H₆)(µ-CH₂)(C₁₀H₆O–)PPh₂-κP,κP}AuCl] (10) with ligand 1 exhibiting both chelating and bridged bidentate modes of coordination respectively. The molecular structures of 2, 6, 7, 9 and 10 are determined by X-ray studies. The mixture of Pd(OAc)₂ and 1 effectively catalyzes Suzuki cross-coupling reactions of a range of aryl halides with aryl boronic acid in MeOH at room temperature or at 60 °C, giving generally high yields even under low catalytic loads. The cationic rhodium(I) complex, [Rh(COD){Ph₂P(–OC₁₀H₆)(µ-CH₂)(C₁₀H₆O–)PPh₂-κP,κP}]BF₄ (4) catalyzes the hydrogenation of styrenes to afford the corresponding alkyl benzenes in THF at room temperature or at 70 °C with excellent turnover frequencies.