N-Thiophosphorylated and N-Phosphorylated Iminophosphoranes [R3P=N-P(X)R2; X = O, S] as Models for Dendrimers: Synthesis, Reactivity and Crystal Structures

Several R3P=N-P(X)Rʹ2 and Fe[C5H4Ph2P=N-P(X)Rʹ2]2 derivatives (X = S, O) are readily obtained from Staudinger reactions between phosphanes and N3-P(X)Rʹ2. The P=N-P=X groups are easily alkylated on the X atom with methyl or isopropyl triflates. The alkylation induces a lengthening of the P-X bond, as shown by X-ray diffraction studies. This corresponds to a weakening of the P-X bond which can be cleaved with P(NMe2)3 to yield [P=N-P:] linkages. The presence of tricoordinated phosphorus atoms opens the way to a versatile reactivity, including the reaction with alkyl iodides and functionalized azides. These molecules are good models for screening which types of reagents and reactions could be used with macromolecules possessing also P=N-P=X linkages, such as dendrimers.