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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Asymmetric niobium guanidinates as intermediates in the catalytic guanylation of amines
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Asymmetric niobium guanidinates as intermediates in the catalytic guanylation of amines

机译：不对称铌胍盐作为胺催化鸟嘌呤化的中间体

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摘要

The molecular structure of the guanidinate complex {NbBz_2(N ~tBu)[(4-BrC_6H_4)NC(NiPr)(NH ~iPr)]previously obtained by reaction of [NbBz_3(N ~tBu)] and the corresponding guanidine proligand, has been established by X-ray diffraction. The series of complexes {NbBz_2(N ~tBu)[(Ar)NC(N~iPr)(NH~iPr)]} (Ar = 4-BrC _6H_4, 4-~tBuC_6H_4, 4-MeOC_6H_4) and {[NbBz_2(N~tBu)] _2[(C_6H_4)(NC(N~iPr)(NH ~iPr))_2]} show a preferred asymmetric coordination of the guanidinate ligand by means of one alkylamino nitrogen and the arylimino nitrogen atom. Computational studies confirm this preference and the results suggest that electronic factors prevail over steric factors. In addition, reaction of complex [NbBz_3(N~tBu)] with {2-(~nbutyl)-1,3-diisopropylguanidine} did not give rise to the regioselective asymmetrical guanidinate. Instead, the complex {NbBz _2(N~tBu)[(~nBu)NC(N~iPr)(NH ~iPr)]} was obtained as a mixture of three isomers with symmetrical and asymmetrical coordination modes. Finally, the complex [NbBz _3(N~tBu)] was shown to be a suitable precatalyst for the guanylation reaction of a wide range of amines under mild conditions. Guanidinates are proposed as intermediates in the mechanism of this reaction. The molecular structure of the biguanidine {2,2′-(1,4-phenylene) bis(2′,3-diisopropylguanidine)} was also established by X-ray diffraction studies.
机译：鸟嘌呤酸酯络合物{NbBz_2（N〜tBu）[（4-BrC_6H_4）NC（NiPr）（NH〜iPr）]的分子结构先前是通过[NbBz_3（N〜tBu）]与相应的胍配体的反应获得的通过X射线衍射确定。一系列的络合物{NbBz_2（N〜tBu）[（Ar）NC（N〜iPr）（NH〜iPr）]}（Ar = 4-BrC _6H_4，4-〜tBuC_6H_4，4-MeOC_6H_4）和{[NbBz_2（ N_tBu）] _2 [（C_6H_4）（NC（N〜iPr）（NH〜iPr））_ 2]}显示通过一个烷基氨基氮和芳基氮原子对胍盐配体的优选不对称配位。计算研究证实了这种偏好，结果表明电子因素胜过空间因素。此外，配合物[NbBz_3（N〜tBu）]与{2-（〜正丁基）-1,3-二异丙基胍}的反应未产生区域选择性的不对称胍盐。取而代之的是，将复杂的{NbBz _2（N〜tBu）[（〜nBu）NC（N〜iPr）（NH〜iPr）]}作为对称和不对称配位模式的三种异构体的混合物获得。最后，显示出配合物[NbBz _3（N〜tBu）]是在温和条件下进行多种胺类鸟嘌呤化反应的合适的预催化剂。胍基盐被提议作为该反应机理的中间体。双胍{2,2'-（1,4-亚苯基）双（2'，3-二异丙基胍）}的分子结构也通过X射线衍射研究确定。

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