orthoMetallated Acetophenone Imines as Ligands for Transition and Main Group Metals: Synthesis and Organometallic Reactivity and the Hydroamination of Allenes using a Palladium Allyl Triflate 3-Iminophosphine Precatalyst

orthoMetallated aryl imines have been used extensively as ligands for late transition metals such as palladium and iridium. Due to the lack of a direct synthetic pathway from the imine to the orthometallated imine, there are few examples of early metals utilizing orthometallated aryl imines as ligands. Early transition metals like titanium and zirconium are unable to undergo the necessary C-H activation step to form the orthometallated complex. In order to synthesize early metal complexes utilizing orthometallated imines, a new method was developed which activates the ortho-proton, via a regiospecific lithiation, prior to metal complexation. The inclusion of a methylenedioxy moiety directs the lithiation and stabilizes the product. A series of early transition metal complexes with orthometallated imines were produced and structurally characterized, using small molecule X-ray diffraction. Multiple metal complexes were synthesized by reacting a ortholithiated imine with early transition and main group metal synthons such as Ti(NtBu)Cl2py3, CpTi(NtBu)Clpy, HfCl4, EtMgBr, AlCl3, CuI, ZnCl2,and nBu3SnCl.

The synthesis of alicyclic 3-iminophosphine ligands was extended to include a new framework incorporating a cyclopentenyl backbone with a di-tert-butyl phosphine functionality (3IPtBu). The palladium complex [(3IPtBu)Pd(allyl)]OTf displayed excellent catalytic activity in the hydroamination of 3-methyl-1,2-butadiene(1,1-dimethylallene) with primary aryl amines anilines), selectively producing the branched allylic amine product (kinetic product) in high conversion at ambient temperature for non-halogenated substrates. Hydroamination using halogenated anilines was successful at 70 °C, providing moderate yields, with the formation of little or no linear product (thermodynamic product). Additionally, a subsequent aromatic amino Claisen rearrangement of selected allylic amine products, employing catalytic triflic acid, proved to be an effective atom-economical method for the production of ortho-allylic anilines in a high yielding two-step, one-pot synthesis.