Němec Vlastimil, Samsonov Maksim A, Růžičková Zdeňka, Vrána Jan, Růžička Aleš
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, CZ-532 10, Pardubice, Czech Republic.
Dalton Trans. 2025 Aug 5;54(31):11845-11856. doi: 10.1039/d5dt01182e.
Sterically crowded ligands form an integral part of contemporary coordination chemistry. The most common ones include bulky anilines, which are well accessible and modifiable. Ever increasing requirements to primary amines' steric protection leads to reaching the limits of amino-group shielding. In this work, the dissymmetrical aniline Art-Bu-NH (1) (Art-Bu = 2-C(4--Bu-CH)-4-Me-6-(CHPh)-CH) is designed and synthesized. Its shielding properties have been evaluated both theoretically and experimentally by the reaction with phosphorus trichloride and a base, giving monomeric chloro(imino)phosphine Art-Bu-NPCl (3). The same reactivity of extremely bulky anilines ArH-NH and ArMe-NH (ArH = 2,6-[C(Me)Ph]-CH; ArMe = 2,6-[C(Me)(3,5-Me-CH)]-CH) was tested. The products [2,6-R-4-PCl-CH]-NH (4H, 4Me) of C-H activation bearing NH and PCl groups simultaneously on the opposite sides of the central phenyl ring have been isolated alongside the desired products ArH-NH-PCl (5H) and ArMe-NH-PCl (5Me). Subsequent theoretical and experimental investigation has revealed that the electrophilic substitution by phosphorus trichloride is preferred over the reaction with the sterically encumbered anilide. When the reactions with phosphorus(III) compounds were conducted under forcing conditions, it was possible to isolate several imidophosphines, namely ArH-NPNMe (8H) and ArMe-NPNMe (8Me), but the steric shielding did not enable direct conversion to the chloro(imino)phosphines ArH-NPCl (9H) and ArMe-NPCl (9Me). For another comparison of steric hindrance, the reactions of ArH-NH, ArMe-NH and Art-Bu-NH with BCl and BH have been carried out. Regardless of the fact that symmetrical anilines with bulkier substituents have given mixtures of unidentified products, the reactions of dissymmetrical aniline yielded the dichloroamidoborane Art-Bu-NHBCl (10) and Art-Bu-NHBH (12) as the first evidence of a terminal NHBH group. The substituents in aniline 1 shield the amine group sufficiently, maintaining space for both the synthesis of amides and their subsequent reactivity.
空间位阻较大的配体是当代配位化学的重要组成部分。最常见的包括庞大的苯胺类，它们易于获取且可修饰。对伯胺空间保护的要求不断提高，导致氨基屏蔽达到极限。在本工作中，设计并合成了不对称苯胺Art-Bu-NH (1)（Art-Bu = 2-C(4--Bu-CH)-4-Me-6-(CHPh)-CH）。通过与三氯化磷和碱反应，从理论和实验两方面评估了其屏蔽性能，得到单体氯（亚氨基）膦Art-Bu-NPCl (3)。测试了空间位阻极大的苯胺ArH-NH和ArMe-NH（ArH = 2,6-[C(Me)Ph]-CH；ArMe = 2,6-[C(Me)(3,5-Me-CH)]-CH）的相同反应活性。在中心苯环相对两侧同时带有NH和PCl基团的C-H活化产物[2,6-R-4-PCl-CH]-NH (4H, 4Me)与所需产物ArH-NH-PCl (5H)和ArMe-NH-PCl (5Me)一同被分离出来。随后的理论和实验研究表明，三氯化磷的亲电取代反应优于与空间位阻较大的酰苯胺的反应。当在强制条件下与磷（III）化合物反应时，有可能分离出几种亚氨基膦，即ArH-NPNMe (8H)和ArMe-NPNMe (8Me)，但空间屏蔽无法直接转化为氯（亚氨基）膦ArH-NPCl (9H)和ArMe-NPCl (9Me)。为了进一步比较空间位阻，进行了ArH-NH、ArMe-NH和Art-Bu-NH与BCl和BH的反应。尽管带有更庞大取代基的对称苯胺反应生成了未鉴定产物的混合物，但不对称苯胺的反应生成了二氯氨基硼烷Art-Bu-NHBCl (10)和Art-Bu-NHBH (12)，这是末端NHBH基团的首个证据。苯胺1中的取代基充分屏蔽了胺基，为酰胺的合成及其后续反应活性都保留了空间。
