Reactions of chalcogens and borane with phosphazane macrocycles assembled from diethanolamine and P2N2 building blocks

Abstract

Phosphazanes of the type [ClP(μ-NR)]₂ are excellent building blocks for the formation of a range of macrocycles. The condensation reaction of the bifunctional linkers, N-substituted diethanolamine with cyclodiphosphazane, [ClP(μ-N^tBu)]₂ leads to the formation of dimeric macrocycles, [{P(μ-N^tBu)}₂{O(CH₂)₂N(R)(CH₂)₂O}]₂; (R = Me (1), Ph (2)). Furthermore, the P^III centres of 1 and 2 were oxidized with chalcogens (O, S, and Se) to afford the corresponding P^V macrocycles – [{(O)P(μ-N^tBu)}₂{O(CH₂)₂N(R)(CH₂)₂O}]₂ (R = Me (3), Ph (4)); [{(S)P(μ-N^tBu)}₂{O(CH₂)₂N(R)(CH₂)₂O}]₂ (R = Me (5), Ph (6)) and [{(Se)P(μ-N^tBu)}₂{O(CH₂)₂N(R)(CH₂)₂O}]₂ (R = Me (7), Ph (8)). An investigation of the Lewis basic behavior of the dimeric macrocycles 1 and 2 was performed by treating them with BH₃·SMe₂, which resulted in Lewis adduct formation, incorporating a total of six BH₃ molecules in the macrocyclic skeleton of 1, [{(BH₃)P(μ-N^tBu)}₂{O(CH₂)₂N(BH₃)(Me)(CH₂)₂O}]₂ (9) and four BH₃ molecules in the macrocyclic skeleton of 2, [{(BH₃)P(μ-N^tBu)}₂{O(CH₂)₂N(Ph)(CH₂)₂O}]₂ (10). Compounds 9 and 10 constitute the first examples of the Lewis adduct of a P₂N₂ macrocycle with a main group Lewis acid. All the new compounds have been fully characterized using multinuclear NMR, HRMS, and single-crystal X-ray diffraction (compounds 1–3, 8 and 9).