Synthesis and Structure of K+[iPrNCP]-, a 1-Aza-3λ3-phospha-3-allenide†

2-Isopropyl(trimethylsilyl)amino-1λ3-phosphaalkyne 1 reacts with potassium tert-butoxide to form potassium 1-isopropyl-1-aza-3λ3-phospha-3-allenide (2). This compound was structurally characterized as the corresponding 18-crown-6
ether complex 3. The molecular structure of 1 was also determined in order to compare the bonding situation in
the anion and the neutral λ3-phosphaalkyne. Compound 3 contains a nitrogen−carbon−phosphorus group for which
the parameters were shown by X-ray structural analysis and quantum chemical calculations to lie between the
extrema N−C⋮P and NCP, suggesting reactivity typical of an ambident anion. This is indeed the case, as
subsequent reaction of 2 with chlorotrimethylsilane at nitrogen regenerates the λ3-phosphaalkyne 1; with
chlorotriphenylsilane the new derivative 4 is formed. In contrast, chlorotrimethylstannane reacts at phosphorus,
giving the 1-aza-3λ3-phosphaallene isopropyliminomethylidene(trimethylstannyl)phosphane 5.

2-异丙基(三甲基基硅基)氨基-1λ3-磷酰炔烃1与叔丁氧基钾反应，生成钾1-异丙基-1-氮杂-3λ3-磷酰-3-丁二烯(2)。该化合物经结构表征为相应的18-冠-6醚复合物3。为了比较阴离子和中性λ3-磷酰炔烃的成键情况，还对1的分子结构进行了确定。复合物3中含有氮-碳-磷基团，其参数通过X射线结构分析和量子化学计算得出，介于N−C⋮P和NCP的极值之间，表明其具有类似双齿阴离子的反应活性。事实上，2与氯三甲基硅烷在氮原子处反应，再生λ3-磷酰炔烃1；与氯三苯基硅烷反应，则形成新的衍生物4。相比之下，氯三甲基锡烷在磷原子处反应，生成1-氮杂-3λ3-磷酰烯丙基异丙基氨基甲基二甲基锡磷烷5。