Synthesis, characterization and reactivity of a series of alkaline earth and rare earth iminophosphoranomethanide complexes

Herein we report the use of the methanide ligand {CH(SiMe3)P(Ph)2=NSiMe3}– (NPC-H) in the stabilization of alkaline earth and rare earth complexes. Protonolysis of the proligand with nBu2Mg or dibenzyl precursors [M(CH2Ph)2(THF)x] (M = Ca–Ba, Eu, Yb) afforded bis-methanide complexes [M(NPC-H)2(THF)x] (1-M·(THF)x; M = Mg, Eu, Yb, x = 0; M = Ca, x = 0, 1; M = Sr, x = 0, 2; M = Ba, x = 2). The same reaction protocol with SmⅡ afforded oxidation product [Sm(NPC-H)3] (2-Sm) reproducibly, which could also be obtained via salt metathesis reaction between [{K(NPC-H)}2] and SmI3(THF)3.5. This salt metathesis methodology was also extended to [REI3(THF)x] (RE = Y, La, Pr), affording tris-methanides, [RE(NPC-H)3] (2-RE; RE = Y, La, Pr). 1-M and 2-RE were characterized by multinuclear NMR, IR spectroscopy, elemental analysis, UV-vis-NIR spectroscopy and single crystal X-ray diffraction; additionally, reactivity of 1-Yb, 2-Y and 2-La as potential synthetic precursors was probed with HN(SiMe3)2 and HOC6H3tBu2-2,6. NMR studies of the 1-M family reveal some underlying changes in the M–C bond character and bonding parameters in the ligand. We also report the first 171Yb{1H} NMR chemical shift (1046.5 ppm) of an ytterbium complex with an iminophosphoranomethanide ligand. Finally, the electronic structure of 1-Eu was studied by means of electron paramagnetic resonance and ab initio calculations.