Sterically Demanding Phosphines with 2,6-Dibenzhydryl-4-methylphenyl Core: Synthesis of Ru∥ , Pd∥, and Pt∥ Complexes, and Structural and Catalytic Studies

The synthesis of sterically demanding aminophosphine and phosphinite ligands Ar*NHPPh2 (1) and Ar*OPPh2 (2), based on 2,6-dibenzhydryl-4-methylphenyl core having bulky benzhydryl groups, and their Ru-parallel to , Pc-parallel to and Pt-parallel to complexes is described. The reactions of 1 and 2 with [Ru(eta(6)-p-cymene)Cl-2](2) in 2:1 molar ratios produced mononuclear complexes [RuCl2{(eta(6)-p-cymene)PPh2-EAr*}-k(l)-P] (E = NH (3) and O (4)). Interestingly, complexes 3 and 4, upon refluxing in chlorobenzene, displace the p-cymene ring by one of the phenyl rings of side arms, forming rare eta(6)-arene coordinated tethered complexes [RuCl2{(PPh2-EAr*)-k(l)-P-eta(6)- arene}] (E = NH (5) and O (6)). Treatment of 1 and 2 with [M(COD)Cl-2] [M = Pd, Pt] in 2:1 ratios afforded mononuclear complexes [MCl2 {(PPh2 EAr*)-k(1)-P}(2)] (E = NH, M= Pd (7), Pt (8); E = 0, M= Pd (9), Pt (10)). Similarly, 1:1 reactions of 1 and 2 with [Pd(COD)Cl-2] produced chloro-bridged dinuclear complexes [PdC1(2) {(PPh2EAr*)-k(1)-P}](2) (E = NH (11) and O (12)), whereas [Pt(COD)Cl-2] yielded only the mononuclear complexes 8 and 10. The reactions of 1 and 2 with [Pd(eta(3)-C3H5 )Cl](2 )in 2:1 molar ratios produced the mononuclear complexes [PdCl{(eta(3)-C3H5 )(PPh2 EAr*)-k(1)-P}] (E = NH (13) and O (14)). Many of these complexes have been structurally characterized, which show C-H center dot center dot center dot pi interactions between the methine hydrogen of the benzhydryl and with one of the carbon atoms of the phenyl ring attached to the phosphorus center. The complex [RuCl2 {eta(6)-p-cymene)PPh2-NHAr*}-k(1)-P] (3) shows very short C-H center dot center dot center dot pi interactions of 2.36 A; in addition, C-H...M interactions were observed between the methine hydrogen of one of the benzhydryl groups and palladium centers in 11 and 13. The tethered ruthenium complex 5 is found to be an excellent catalyst for the catalytic oxidation of various styrene derivatives.