Benson Mark A, Zacchini Stefano, Boomishankar Ramamoorthy, Chan Yuri, Steiner Alexander
Department of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, U.K.
Inorg Chem. 2007 Aug 20;46(17):7097-108. doi: 10.1021/ic7009463. Epub 2007 Jul 10.
Phosphazenes (RNH)6P3N3 (R = n-propyl, isobutyl, isopropyl, cyclohexyl, tert-butyl, benzyl) are readily alkylated at ring N sites by alkyl halides forming N-alkyl phosphazenium cations. Alkylation of two ring N sites occurred after prolonged heating in the presence of methyl iodide or immediately at room temperature with methyl triflate yielding N,N'-dimethyl phosphazenium dications. Geminal dichloro derivatives Cl2(RNH)4P3N3 are methylated by methyl iodide at the ring N site adjacent to both P centers carrying four RNH groups. X-ray crystal structures showed that the alkylation of ring N sites leads to substantial elongation of the associated P-N bonds. Both N-alkyl and N,N'-dialkyl phosphazenium salts form complex supramolecular networks in the solid state via NH...X interactions. Systems carrying less-bulky RNH groups show additional NH...N bonds between N-alkyl phosphazenium ions. N-Alkyl phosphazenium halides form complexes with silver ions upon treatment with silver nitrate. Depending on the steric demand of RNH substituents, either one or both of the vacant ring N sites engage in coordination to silver ions. Treatment of (RNH)6P3N3 (R = isopropyl) with acetyl chloride and benzoyl chloride, respectively, yielded N-acyl phosphazenium ions. X-ray crystal structures revealed that elongation of P-N bonds adjacent to the acylated ring N site is more pronounced than it is in the case of N-alkylated species. Salts containing N-alkyl phosphazenium ions are stable toward water and other mild nucleophiles, while N,N'-dialkyl and N-acyl phosphazenium salts are readily hydrolyzed. The reaction of (RNH)6P3N3 with bromoacetic acid led to N-alkylation at one ring N site in addition to formation of an amide via condensation of an adjacent RNH substituent with the carboxylic acid group. The resulting bromide salt contains mono cations of composition (RNH)5P3N3CH2CONR in which a CH2-C(O) unit is embedded between a ring N and an exocyclic N site of the phosphazene.
磷腈（RNH）6P3N3（R = 正丙基、异丁基、异丙基、环己基、叔丁基、苄基）在环氮位点很容易被卤代烃烷基化，形成N - 烷基磷鎓阳离子。在碘甲烷存在下长时间加热后，或者在室温下立即用三氟甲磺酸甲酯处理，两个环氮位点都会发生烷基化，生成N，N'-二甲基磷鎓双阳离子。偕二氯衍生物Cl2（RNH）4P3N3在与两个带有四个RNH基团的磷中心相邻的环氮位点被碘甲烷甲基化。X射线晶体结构表明，环氮位点的烷基化会导致相关P - N键显著伸长。N - 烷基和N，N'-二烷基磷鎓盐在固态中通过NH...X相互作用形成复杂的超分子网络。带有体积较小的RNH基团的体系在N - 烷基磷鎓离子之间还存在额外的NH...N键。N - 烷基磷鎓卤化物在用硝酸银处理后会与银离子形成配合物。根据RNH取代基的空间需求，一个或两个空的环氮位点会与银离子配位。分别用乙酰氯和苯甲酰氯处理（RNH）6P3N3（R = 异丙基），得到N - 酰基磷鎓离子。X射线晶体结构表明，与酰化环氮位点相邻的P - N键的伸长比N - 烷基化物种的情况更明显。含有N - 烷基磷鎓离子的盐对水和其他温和亲核试剂稳定，而N，N'-二烷基和N - 酰基磷鎓盐很容易水解。（RNH）6P3N3与溴乙酸的反应除了通过相邻的RNH取代基与羧酸基团缩合形成酰胺外，还导致一个环氮位点发生N - 烷基化。所得的溴化物盐含有组成为（RNH）5P3N3CH2CONR的单阳离子，其中一个CH2 - C（O）单元嵌入在磷腈的一个环氮和一个环外氮位点之间。
