Reactions of Tris(amino)phosphines with Arylsulfonyl Azides:  Product Dependency on Tris(amino)phosphine Structure

The Staudinger reaction of N(CH₂CH₂NR)₃P [R = Me (1), ⁱPr (2)] with 1 equiv of N₃SO₂C₆H₄Me-4 gave the ionic phosphazides [R = Me (3), R = ⁱPr (5a)], and the same reaction of 2 with N₃SO₂C₆H₂Me₃-2,4,6 gave the corresponding aryl sulfinite 5b. On the other hand, the reaction of 1 with 0.5 equiv of N₃SO₂Ar (Ar = C₆H₄Me-4) furnished the novel ionic phosphazide {[N(CH₂CH₂NMe)₃P]₂(μ-N₃)}[SO₂Ar] (6). Data that shed light on the mechanistic pathway leading to 3 were obtained by low temperature ³¹P NMR spectroscopy. A crystal and molecular structure analysis of the phosphazide sulfonate (4), obtained by atmospheric oxidation of 3, indicated an ionic structure, the cationic part of which is stabilized by a transannular P−N bond. A crystal and molecular structure analysis of 6 also indicated an ionic structure in which the cation features two untransannulated N(CH₂CH₂NMe)₃P cages bridged by an azido group in an η¹:μ:η¹ fashion. The reaction of P(NMe₂)₃ with N₃SO₂Ar (Ar = C₆H₄Me-4) in a 1:0.5 molar ratio furnished {[(Me₂N)₃P]₂(μ-N₃)}[SO₂Ar] (11) in quantitative yield. On the other hand, the same reaction involving a 1:1 molar ratio of P(NMe₂)₃ and N₃SO₂Ar produced a mixture of 11, [(Me₂N)₃PN₃][SO₂Ar] (12), and the iminophosphorane (Me₂N)₃PNSO₂Ar (10). In contrast, the bicyclic tris(amino)phosphines MeC(CH₂NMe)₃P (7) and OP(CH₂NMe)₃P (8) reacted with N₃SO₂Ar (Ar = C₆H₄Me-4) to give the iminophosphorane MeC(CH₂NMe)₃PNSO₂Ar (14) (structured by X-ray means) and OP(CH₂NMe)₃PNSO₂Ar (16) via the intermediate phosphazides MeC(CH₂NMe)₃PN₃SO₂Ar (13) and OP(CH₂NMe)₃PN₃SO₂Ar (15), respectively. The variety of products obtained from the reactions of arylsulfonyl azides with proazaphosphatranes (1 and 2), acyclic P(NMe₂)₃, bicyclic tris(amino)phosphines 7 and 8 are rationalized in terms of steric and basicity variations among the phosphorus reagents.