N-thiophosphorylated and N-phosphorylated iminophosphoranes [R3P=N-P(X)R '(2); X = O, S] as models for dendrimers: Synthesis, reactivity and crystal structures

Several R3P=N-P(X)R'(2) and Fe[C5H4Ph2P=N-P(X)R'(2)](2) derivatives (X = S, O) are readily obtained from Staudinger reactions between phosphanes and N -3-P(X)R'(2). The P=N-P=X groups are easily alkylated on the X atom with me thyl or isopropyl triflates. The alkylation induces a lengthening of the P- X bond, as shown by X-ray diffraction studies. This corresponds to a weaken ing 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 funct ionalized azides. These molecules are good models for screening which types of reagents and reactions could be used with macromolecules possessing als o P=N-P=X linkages, such as dendrimers.