Highly active, chemo- and enantioselective Pt-SPO catalytic systems for the synthesis of aromatic carboxamides†
Platinum complexes modified with a chiral non-racemizing SPO preligand 1 have been applied in the hydration of aromatic nitriles. [Pt(1)3Cl]Cl formed readily from Pt(COD)Cl2. The chiral secondary phosphine oxide complex showed moderate activity in the hydration of para- and meta-substituted benzonitriles, but failed in converting the ortho-substituted derivatives. The hydride complex PtH(PR2OH)(PR2O–H⋯OR2P) (PR2OH = 1) formed from Pt(PPh3)4 and 1, and the cationic complex derived from [Pt(1)3Cl]Cl via direct chloride abstraction with AgNO3 were proven to be considerably more active, allowing us to extend the scope to the hydration of ortho-substituted aromatic nitriles, including axially chiral [1,1′-binaphthalene]-2,2′-dicarbonitrile. In the hydration of the racemic dinitrile, successful kinetic resolution has been achieved. The catalysts derived from non-racemizing 1 are the first chiral transition metal–SPO complexes that provide kinetic resolution in the hydration of a racemic chiral nitrile.