Magnesiated and Calciated N‐Mesityl Diphenylphosphinic Amides

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Metalation of N‐mesityl‐P,P‐diphenylphosphinic amide (1) in THF at room temperature with MgBu2 and [(thf)2Ca{N(SiMe3)2}2] yields [(thf)nM{Ph2P(=O)–N–Mes}2{Ph2P(=O)–NH–Mes}2] [M/n = Mg/0 (2), Ca/2 (3)] regardless of the applied stoichiometry. These complexes are stabilized by weak intramolecular N–H···N hydrogen bridges. In both complexes only one NMR signal set is observed, however, for the magnesium complex 2 the 1H NMR chemical shift of the hydrogen bridge shifts toward higher field with increasing temperature. For the calcium congener 3 two resonance sets are observed at low temperature, allowing to determine an energy barrier of 52.4 kJ mol–1 for the proton exchange between adjacent nitrogen bases.