Guanidinate Early-Transition-Metal Complexes: Efficient and Selective Hydroaminoalkylation of Alkenes

The influence of a series of N,N-chelating guanidinate ligands on the reactivity of in situ generated tantalum complexes for the intermolecular hydroaminoalkylation of amines has been explored. Increased conversion was observed with the sodium salt of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBDNa) paired with the tantalum precursor Ta(CH2SiMe3)3Cl2 at 110 °C. Terminal alkenes underwent hydroaminoalkylation with a variety of secondary amine substrates to give substituted secondary amine products. Mono- and bis(guanidinate) tantalum complexes were prepared, and their structures were investigated. Importantly, the guanidinate ligand could be alkylated in the β position using Ta(NMe2)5 as a precatalyst to give the linear regioisomer as the major product, and this substituted ligand gave improved hydroaminoalkylation conversion in comparison to the parent ligand.