Experiments and density functional calculations were used to quantify the impact of the Pd-Ti interaction in the cationic heterobimetallic Cl2Ti(N(t)BuPPh2)2Pd(η(3)-methallyl) catalyst 1 used for allylic aminations. The catalytic significance of the Pd-Ti interaction was evaluated computationally by examining the catalytic cycle for catalyst 1 with a conformation where the Pd-Ti interaction is intact versus one where the Pd-Ti interaction is severed. Studies were also performed on the relative reactivity of the cationic monometallic (CH2)2(N(t)BuPPh2)2Pd(η(3)-methallyl) catalyst 2 where the Ti from catalyst 1 was replaced by an ethylene group. These computational and experimental studies revealed that the Pd-Ti interaction lowers the activation barrier for turnover-limiting amine reductive addition and accelerates catalysis up to 10(5). The Pd-Ti distance in 1 is the result of the N(t)Bu groups enforcing a boat conformation that brings the two metals into close proximity, especially in the transition state. The turnover frequency of classic Pd π allyl complexes was compared to that of 1 to determine the impact of P-Pd-P coordination angle and ligand electronic properties on catalysis. These experiments identified that cationic (PPh3)2Pd(η(3)-CH2C(CH3)CH2) catalyst 3 performs similarly to 1 for allylic aminations with diethylamine. However, computations and experiment reveal that the apparent similarity in reactivity is due to very fast reaction kinetics. The higher reactivity of 1 versus 3 was confirmed in the reaction of methallyl chloride and 2,2,6,6-tetramethylpiperidine (TMP). Overall, experiments and calculations demonstrate that the Pd-Ti interaction induces and is responsible for significantly lower barriers and faster catalysis for allylic aminations.

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Phosphinoamide-scaffolded heterobimetallic palladium-titanium complexes are highly effective catalysts for allylic aminations of allylic chlorides with hindered secondary amine nucleophiles. Three titanium-containing ligands are shown to assemble active catalysts in situ and enable catalysis at room temperature. A variety of sterically bulky secondary amines are efficiently allylated in high yields with as little as 1 mol % palladium catalyst. Piperidine and pyrrolidine products are also efficiently generated via intramolecular aminations with hindered amine nucleophiles.

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Complexes. -This method is suitable for the interand intramolecular amination of allylic chlorides. The latter variant uses chlorides generated from the corresponding alcohols and yields the heterocyclic compounds (X) and (XII). -(WALKER, W. K.; ANDERSON, D. L.; STOKES, R. W.; SMITH, S. J.; MICHAELIS*, D. J.; Org. Lett. 17 (2015) 3, 752-755, http://dx.doi.org/10.1021/acs.orglett.5b00058 ; Dep. Chem. Biochem., Brigham Young Univ., Provo, UT 84602, USA; Eng.) -Mais 26-043