| Summary: | Deprotonation of a bis(amino)phosphane H<sub>2</sub>L = PhP(HNBtd)<sub>2</sub> bearing a heterocyclic Btd = 2,1,3-benzothiadiazol-4-yl substituents at nitrogen atoms by silylamides LiNTms<sub>2</sub> and Y(NTms<sub>2</sub>)<sub>3</sub> (Tms = trimethylsilylamide) results in lithium and yttrium complexes with the deprotonated HL<sup>–</sup> and L<sup>2–</sup> forms as κ<sup>2</sup>-N and κ<sup>4</sup>-N chelating ligands. A binuclear complex [LiHL]<sub>2</sub> was crystallized from Et<sub>2</sub>O, and was shown to reversibly dissociate in thf (tetrahydrofuran) with the NH<i><sub>(soln)</sub></i>–PH<i><sub>(crystal)</sub></i> tautomeric shift; the compound [Li<sub>2</sub>L] was spectroscopically characterized. Yttrium readily forms stable bis-ligand complexes [YL<sub>2</sub>]<sup>–</sup> and [YL(HL)]. In the latter, the H atom in HL resides on phosphorus; the coordination sphere remains accessible to another ligands, and it was crystallized as [{YL(HL)}<sub>2</sub>(µ-dioxane)] species (YN<sub>8</sub>O coordination). In the former complex, the coordination sphere was saturated (YN<sub>8</sub>) by closer bound ligands; it was crystallized as a salt with [Li(thf)<sub>4</sub>]<sup>+</sup>. The monoligand complex could not be cleanly obtained in a 1:1 reaction of H<sub>2</sub>L and Y(NTms<sub>2</sub>)<sub>3</sub>, and was only crystallographically characterized as a dimer [YL(NTms)<sub>2</sub>]<sub>2</sub>. Partial oxidation of the central P atom with the formation of phosphine-oxide ligands PhP(O)(NBtd)<sup>2–</sup> was observed. They co-crystallize in the same position as non-oxidized ligands in [YL<sub>2</sub>]<sup>–</sup> and [YL(NTms<sub>2</sub>)]<sub>2</sub> species and participate in bonding between two units in the latter. TD-DFT calculations reveal that main transitions in the visible region of electronic spectra correspond to the charge transfer bands mostly associated with the orbitals located on Btd fragments.
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