Two series of new enantiopure bidentate bis(diamidophosphite) ligands with diazaphospholidine and diazaphosphepine heterocyclic backbones were prepared. The ligands have a highly modular structure, which is well suited to the synthesis of a small library of compounds. Preparation was accomplished by the successive addition of enantiomerically pure substituted diamines (N,N′-dibenzylcyclohexane-1,2-diamine (1), N,N′-dimethylcyclohexane-1,2-diamine (2), and N,N′-dimethyl-1,1′-binaphthyl-2,2′-diamine (3)) and enantiomerically pure diols (butanediol (a), cyclohexanediol (b), di-O -isopropylidenethreitol (c), and binaphthol (d)) to phosphorus trichloride. The corresponding bis(diamidophosphite) selenides were prepared, and the 1 J PSe values were calculated in order to evaluate the σ-donor ability of the new ligands. The cationic Rh(I) complexes [Rh(COD)(P,P)]BF4 were synthesized with 8 of the 12 new bis(diamidophosphite) ligands. The complexes were used as catalytic precursors for the asymmetric hydrogenation of benchmark substrates, namely methyl α-acetamidoacrylate (4), methyl (Z)-α-acetamidocinnamate (5), and dimethyl itaconate (6). The influence of the nature of both the terminal and bridging fragments of the bis(diamidophosphite) ligands on the asymmetric induction is discussed. Most proved to be effective catalysts for the process, attaining total conversion and excellent enantioselectivity (>99% ee) with the complex containing the (R;R al,R al ;R)- 3c ligand in the hydrogenation of the three substrates. The best performing catalytic precursor [Rh(COD)((R;R al,R al;R)- 3c)]BF4 was tested in the hydrogenation of selected cyclic enamides (7–9) and β-acetamidoacrylate (10).

New imidazolium-tagged chiral diamidophosphite ligands, (S,S)-a and (R)-b, derived from (S,S)-N,N′-dibenzyl-1,2-cyclohexanediamine and (R)-N,N′-dimethyl-1,1′-binaphthyl-2,2′-diamine, respectively, and the corresponding palladium allylic complexes of general formula [PdCl(η3-2-Me-C3H4)(κ1 P-L)]BF4 (1a,b) and [Pd(η3-2-Me-C3H4)(κ1 P-L)2](BF4)3 (2a,b) were synthesized and fully characterized, including the X-ray crystal structure for 1b. These original Pd/L catalytic systems were applied in asymmetric allylic alkylation, amination, and sulfonylation using rac-3-acetoxy-1,3-diphenyl-1-propene as a substrate in neat ionic liquids, [bmim][PF6] and [Pyr][NTf2]. The best results in terms of enantioselectivity were obtained with the catalytic precursor 1b in [Pyr][NTf2]. The catalytic phase containing 1b for the allylic amination could be recycled up to six times without significant loss of asymmetric induction.

Enantiopure bis(diamidophosphite) ligands with a heterocyclic terminal fragment derived from (R)-and (S)-N,N′-dimethyl-1,1′-binaphthyldiamine and bridging fragments derived from (S,S)-2,3-butanediol (a), (4R,5R)-4,5-di(hydroxymethyl)-2,2-dimethyl-1,3-dioxolane (b), and (R)-and (S)-1,1′-bi-2-naphthol (c) were used to prepare the palladium complexes with general formula [Pd(η 3 -2-CH 3 -C 3 H 4 )(P-P)][X] (X = PF 6 , 1a-(S;S al ,S al ;S), 1b-(R;R al ,R al ;R), 1b-(S;R al ,R al ;S), 1c-(R;R al ;R), 1c-(R;S al ;R); X = BPh 4 , 2a-(R;S al ,S al ;R), 2c-(R;R al ;R)), which have been fully characterized. The solid-state structure for complexes 1a-(S;S al ,S al ;S) and 1b-(R;R al ,R al ;R) has been determined by X-ray diffraction. The catalytic performance of the palladium complexes has been evaluated in asymmetric allylic alkylation and amination reactions with the benchmark substrate. The influence of the nature and absolute configuration of both the terminal and bridging fragments of the bis(diamidophosphite) ligands on the asymmetric induction is discussed. The best results in terms of enantioselectivity were obtained with 1c-(R;R al ;R), affording enantiomeric excesses up to 85% in both alkylation and amination reactions. A large match−mismatch effect between the absolute configurations of stereocenters of ligand c has been observed in the allylic amination process. Preliminary results in the rhodiumcatalyzed asymmetric hydroformylation of styrene by using bis(diamidophosphite) ligands a, b, and c disclosed in all cases low enantiomeric discrimination for the branched aldehyde. Both for the allylic alkylation and for the hydroformylation reaction, a related monodentate diamidophosphite d, derived from (R)-N,N′-dimethyl-1,1′-binaphthyldiamine and (S)-borneol, was also tested. Palladium complexes of this monodentate ligand showed fairly good enantioselectivity in allylic alkylation, but with very low rate, while the rhodium complex of d rendered better enantioselectivity (37% ee) than the bidentate ligands a−c in the hydroformylation of styrene.

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