Resolution of Secondary Phosphanes Chiral at Phosphorus by Means of Palladium Metallacycles

First Application of Secondary Phosphines as Supporting Ligands for the Palladium-Catalyzed Heck Reaction: Efficient Activation of Aryl Chlorides

“…According to the results of Littke and Fu [3c] this should drastically decrease the activity of the catalyst and raises of course questions about the nature of the active palladium catalyst. Various explanations are possible: Even though mononuclear palladium complexes with secondary phosphine ligands are known, [7] palladium can also form phosphido-bridged di-and polynuclear compounds. [8] Moreover, it is well known that secondary phosphines react with aryl halides in the presence of palladium catalysts to form aryl phosphines.…”

Rhodium-Catalyzed Asymmetric Dehydrocoupling-Cyclophosphination of Supermesitylphosphines: Enantioselective Synthesis of a P-Stereogenic Benzophospholane via C–H Activation–Functionalization

“…The analogous cobalt catalyst was much faster (entry 3), but secondary phosphine 1 was formed without enantioselectivity with either metal, as shown by complexation to a chiral Pd-amine complex [see the SI for details, including comparison to results with the achiral Rh(dppf) catalyst (entry 4)] . This was not surprising, because the P-epimerization of P-stereogenic secondary phosphines catalyzed by trace acids has frustrated most previous attempts at their asymmetric synthesis . Attempted removal of acid by carrying out the catalytic reaction in the presence of added NaOSiMe 3 (Table , entry 2) did not provide any improvement …”

New principle for palladacycle resolution: diastereoselective monomer to dimer conversion

“…However, except in one case, 53 this methodology has been used only for the resolution of substrates (Q) with a soft donor atom(s)-mainly of monodentate phosphines-via neutral mononuclear intermediates of type [(C \ N)Pd(j 1 -Q)Cl]. [54][55][56][57][58][59][60][61][62] There are known also several instances of application of this approach to bidentate diphosphine ligands [63][64][65] (P \ P) with neutral binuclear complexes of type [{(C \ N)PdCl} 2 (l-P \ P)] as intermediates. Taking into account a rather tight bonding of soft phosphorus donor atom(s) with a soft palladium centre of a palladacycle, it would be hard to expect for these systems any decomplexation processes in the absence of serious steric hindrances.…”