Masuda Jason D, Martin David, Lyon-Saunier Celine, Baceiredo Antoine, Gornitzka Heinz, Donnadieu Bruno, Bertrand Guy
UCR-CNRS Joint Research Chemistry Laboratory (UMI 2957), Department of Chemistry, University of California, Riverside, CA 92521-0403, USA.
Chem Asian J. 2007 Jan 8;2(1):178-87. doi: 10.1002/asia.200600300.
The conjugate acids (PHCH+s) of P-heterocyclic carbenes (PHCs) are prepared by formal [3+2] cycloaddition of a 1,3-diphosphaallyl or 1,3-phosphinophosphenium cation with various nitriles. The effect of the phosphorus substituent on the fate of the cyclization and on that of the counteranion and base in the subsequent deprotonation reaction are reported. Two PHCs that are indefinitely stable in the solid state are described. In solution, one of them, made from acetonitrile, undergoes a facile [3+2] cycloreversion, whereas the other, based on dimethyl cyanamide, is stable, presumably owing to its zwitterionic structure, which involves a tricoordinate pentavalent phosphorus atom. The reactivity of PHCs is strongly driven by the high electrophilicity of the phosphorus centers, as demonstrated by their reactivity with water and benzaldehyde. Although both PHCs reported in this paper are direct analogues of the least-basic NHCs, their basicity is comparable to those of the more strongly basic NHCs (as determined by comparison of the carbonyl stretching frequencies of their corresponding cis-[RhCl-(CO)2(L)] complexes).
通过1,3 - 二磷烯丙基或1,3 - 磷代磷烯鎓阳离子与各种腈的形式上的[3 + 2]环加成反应制备了P - 杂环卡宾（PHC）的共轭酸（PHCH⁺）。报道了磷取代基对环化反应结果以及后续去质子化反应中抗衡阴离子和碱的影响。描述了两种在固态下无限稳定的PHC。在溶液中，其中一种由乙腈制备，经历了容易的[3 + 2]环反转，而另一种基于二甲基氰胺，是稳定的，推测是由于其两性离子结构，其中涉及一个三配位的五价磷原子。PHC的反应性强烈地受到磷中心的高亲电性的驱动，这通过它们与水和苯甲醛的反应性得到证明。尽管本文报道的两种PHC都是碱性最弱的NHC的直接类似物，但它们的碱性与碱性更强的NHC相当（通过比较其相应的顺式 - [RhCl(CO)₂(L)]配合物的羰基伸缩频率来确定）。
