Pnn ' & P2nn ' Ligands Via Reductive Amination With Phosphine Aldehydes: Synthesis And Base-Metal Coordination Chemistry

Novel PNN' & P2NN' ligands based on 2-aminopyridine (APyPNN-R) R = Ph (1a), Cy (1b), Bu-i (1c), 8-amino-quinoline (AQPNN-R) R = Ph (2a), Cy (2b), Bu-i (2c), Pr-i (2d), and 2-picolylamine (P2NN-R) R = Ph (3a), Cy (3b), Bu-i (3c), have been synthesized via a versatile, one-pot, single-step, reductive amination of tertiary phosphine acetaldehydes with the amine by reaction with STAB (where STAB is sodium(triacetoxy)boro-hydride). Ligands 1b and 1c bridge between paramagnetic Co(II) and form dimeric complexes Co2Cl4(APyPNN-R)(2) (4 and 5) when reacted with cobalt dichloride. Ligands 2a-c coordinate in a tridentate fashion forming chelate complexes MCl2(AQPNN-R) M = Co(II) (6-8), and, for 2d, the Fe(II) complex FeCl2(AQPNN-Pr-i) (9). A solution magnetic susceptibility value for 9 of 3.9 mu B is consistent with a monomer-dimer equilibrium. The synthesis of the dimeric complex [FeCl2(AQPNN-Ph)](2) (10) using 2a as well as solid state magnetic susceptibility measurements on 9 and 10 confirm this phenomenon. Ligand 3a coordinates to Fe(II) in an interesting tetradentate fashion despite bearing a tertiary amine moiety giving octahedral FeCl2(P2NN') (11). All of the metal complexes have been characterized by elemental analysis, paramagnetic H-1 NMR spectroscopy, solution magnetic susceptibility, and single crystal X-ray diffraction (XRD).