Olivier Piechaczyk

Why Platinum Catalysts Involving Ligands with Large Bite Angle Are so Efficient in the Allylation of Amines: Design of a Highly Active Catalyst and Comprehensive Experimental and DFT Study

The platinum-catalyzed allylation of amines with allyl alcohols was studied experimentally and theoretically. The complexes [Pt(eta(3)-allyl)(dppe)]OTf (2) and [Pt(eta(3)-allyl)(DPP-Xantphos)]PF(6) (5) were synthesized and structurally characterized, and their reactivity toward amines was explored. The bicyclic aminopropyl complex [Pt(CH(2)CH(2)CH(2)NHBn-kappa-C,N)(dppe)]OTf (3) was obtained from the reaction of complex 2 with an excess of benzylamine, and this complex was shown to be a deactivated form of catalyst 2. On the other hand, reaction of complex 5 with benzylamine and allyl alcohol led to formation of the 16-VE platinum(0) complex [Pt(eta(2)-C(3)H(5)OH)(DPP-Xantphos)] (7), which was structurally characterized and appears to be a catalytic intermediate. A DFT study showed that the mechanism of the platinum-catalyzed allylation of amines with allyl alcohols differs from the palladium-catalyzed process, since it involves an associative ligand-exchange step involving formation of a tetracoordinate 18-VE complex. This DFT study also revealed that ligands with large bite angles disfavor the formation of platinum hydride complexes and therefore the formation of a bicyclic aminopropyl complex, which is a thermodynamic sink. Finally, a combination of 5 and a proton source was shown to efficiently catalyze the allylation of a broad variety of amines with allyl alcohols under mild conditions.

Protodesilylation of 2,6-disubstituted silyphosphinines. Experimental and theoretical study.

2,6-Disilylphosphinines react with HCl in ethereal solution to cleanly yield the corresponding 2,6-unsubstituted derivatives. DFT calculations allowed rationalization of the mechanism of this protodesilylation.

Bonding Mode of a Bifunctional P∼Si−H Ligand in the Ruthenium Complex “Ru(PPh2CH2OSiMe2H)3”

The phosphinosilane compound PPh 2CH 2OSiMe 2H is potentially a bifunctional P approximately Si-H ligand. By treatment with the Ru (II) precursor RuH 2(H 2) 2(PCy 3) 2, the complex Ru(PPh 2CH 2OSiMe 2H) 3 ( 2), resulting from the coordination of three ligands and the displacement of two PCy 3 and two dihydrogen ligands, was formed. The different bonding modes for each of the three bifunctional P approximately Si-H ligands are discussed on the basis of multinuclear NMR, X-ray diffraction, and density functional theory studies. One ligand acts as a monodentate phosphine ligand with a pendant Si-H group, whereas the two others act as bidentate ligands with different Si-H bond activations. Indeed, an intermediate structure between two arrested forms 2a and 2b can be proposed: a dihydrido(disilyl)ruthenium(IV) species (form 2a) resulting from two Si-H oxidative additions or a hydrido(silyl)ruthenium(II) species (form 2b) presenting an agostic Si-H bond and only one oxidative addition.