Ru and Rh nanoparticles catalyze the selective H/D exchange in phosphines using D 2 as the deuterium source. The position of the deuterium incorporation is determined by the structure of the P-based substrates, while activity depends on the nature of the metal, the properties of the stabilizing agents, and the type of the substituent on phosphorus. The appropriate catalyst can thus be selected either for the exclusive H/D exchange in aromatic rings or also for alkyl substituents. The selectivity observed in each case provides relevant information on the coordination mode of the ligand. Density functional theory calculations provide insights into the H/D exchange mechanism and reveal a strong influence of the phosphine structure on the selectivity. The isotope exchange proceeds via C−H bond activation at nanoparticle edges. Phosphines with strong coordination through the phosphorus atom such as PPh 3 or PPh 2 Me show preferred deuteration at ortho positions of aromatic rings and at the methyl substituents. This selectivity is observed because the corresponding C−H moieties can interact with the nanoparticle surface while the phosphine is Pcoordinated, and the C−H activation results in stable metallacyclic intermediates. For weakly coordinating phosphines such as P(otolyl) 3 , the interaction with the nanoparticle can occur directly through phosphine substituents, and then, other deuteration patterns are observed.

Controlling the selectivity in palladium-catalyzed telomerization of nonsymmetric dienes represents a formidable challenge since up to 12 isomers can be obtained, and a general method for selective synthesis is still lacking. We select isoprene (2-methylbutadiene) as a representative and relevant example of a nonsymmetric diene. A combined experimental–computational study on a large set of phosphine-modified palladium catalysts and reaction conditions aiming to understand the factors governing the selectivity shows that it can be controlled by selecting the protic solvent pK a and by the ligand. Atomistic and kinetic simulations reveal that the solvent switches the selectivity-determining step as a function of pK a from C–C oxidative coupling at low pK a values (preference for telomer head-to-head) to protonation at high pK a values (preference for telomer tail-to-tail). The selectivity toward tail-to-head telomer can be directed in moderately acidic solvents by selection of the appropriate ligand, which exerts steric control of the protonation step. Thus, using Et2NH as a nucleophile, it was possible to synthesize 3 of the 4 main isomers in very high yields and selectivities and to provide a complete mechanistic picture of Pd-catalyzed telomerization of nonsymmetric dienes.

Treatment of the dinuclear compound [{Ti( 5 -C5Me5)Cl2}2(-O)] with allylmagnesium chloride provides the formation of the allyltitanium(III) derivative [{Ti( 5 -C5Me5)(-C3H5)}2(-O)] (1), structurally identified by single-crystal X-ray analysis. Density functional theory (DFT) calculations confirm that the electronic structure of 1 is a singlet state, and the molecular orbital analysis, along with the short Ti-Ti distance, reveal the presence of a metal-metal single bond between the two Ti(III) centers.Complex 1 reacts rapidly with organic azides, RN3 (R = Ph, SiMe3), to yield the allyl -imido derivatives3)] along with molecular nitrogen release. Reaction of 2 and 3 with H2 leads to the -imido propyl species [{Ti( 5 -C5Me5)(CH2CH2CH3)}2(-NR)(-O)] [R = Ph(4), SiMe3(5)]. Theoretical calculations were used to gain insight into the hydrogenation mechanism of complex 3 and rationalize the lower reactivity of 2.Initially, the -imido bridging group in these complexes activates the H2 molecule via addition to the Ti-N bonds. Subsequently, the titanium hydride intermediates induce a change in hapticity of the allyl ligands, and the nucleophilic attack of hydride to the allyl groups leads to metallacyclopropane intermediates. Finally, the proton transfer from the amido group to the metallacyclopropane moieties afford the propyl complexes 4 and 5.

The reaction of [TaCp R X 4 ] (Cp R = η 5 -C 5 Me 5 , η 5 -C 5 H 4 SiMe 3 , η 5 -C 5 HMe 4 ; X = Cl, Br) with SiH 3 Ph resulted in the formation of the dinuclear hydride tantalum(IV) compounds [(TaCp R X 2 ) 2 (μ-H) 2 ], structurally identified by single-crystal X-ray analyses. These species react with azobenzene to give the mononuclear imide complex [TaCp R X 2 (NPh)] along with the release of molecular hydrogen. Analogous reactions between the [{Ta(η 5 -C 5 Me 5 )X 2 } 2 (μ-H) 2 ] derivatives and the cyclic diazo reagent benzo[ c ]cinnoline afford the biphenyl-bridged (phenylimido)tantalum complexes [{Ta(η 5 -C 5 Me 5 )X 2 } 2 (μ-NC 6 H 4 C 6 H 4 N)] along with the release of molecular hydrogen. When the compounds [(TaCp R X 2 ) 2 (μ-H) 2 ] (Cp R = η 5 -C 5 H 4 SiMe 3 , η 5 -C 5 HMe 4 ; X = Cl, Br) were employed, we were able to trap the side-on-bound diazo derivatives [(TaCp R X) 2 {μ-(η 2 ,η 2 -NC 6 H 4 C 6 H 4 N)}] (Cp R = η 5 -C 5 H 4 SiMe 3 , η 5 -C 5 HMe 4 ; X = Cl, Br) as intermediates in the N=N bond cleavage process. DFT calculations provide insights into the N=N cleavage mechanism, in which the ditantalum(IV) fragment can promote two-electron reductions of the N=N bond at two different metal–metal bond splitting stages.