Asymmetric niobium guanidinates as intermediates in the catalytic guanylation of amines
作者:David Elorriaga、Fernando Carrillo-Hermosilla、Antonio Antiñolo、Francisco J. Suárez、Isabel López-Solera、Rafael Fernández-Galán、Elena Villaseñor
DOI:10.1039/c3dt50477h
日期:——
The molecular structure of the guanidinate complex NbBz2(NtBu)[(4-BrC6H4)NC(NiPr)(NHiPr)]}, previously obtained by reaction of [NbBz3(NtBu)] and the corresponding guanidine proligand, has been established by X-ray diffraction. The series of complexes NbBz2(NtBu)[(Ar)NC(NiPr)(NHiPr)]} (Ar = 4-BrC6H4, 4-tBuC6H4, 4-MeOC6H4) and [NbBz2(NtBu)]2[(C6H4)(NC(NiPr)(NHiPr))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 [NbBz3(NtBu)] with 2-(nbutyl)-1,3-diisopropylguanidine} did not give rise to the regioselective asymmetrical guanidinate. Instead, the complex NbBz2(NtBu)[(nBu)NC(NiPr)(NHiPr)]} was obtained as a mixture of three isomers with symmetrical and asymmetrical coordination modes. Finally, the complex [NbBz3(NtBu)] 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.
先前通过 [NbBz3(NtBu)] 与相应的胍配体反应获得的胍盐配合物 NbBz2(NtBu)[(4-BrC6H4)NC(NiPr)(NHiPr)]} 的分子结构已通过 X 确定射线衍射。系列配合物 NbBz2(NtBu)[(Ar)NC(NiPr)(NHiPr)]} (Ar = 4-BrC6H4, 4-tBuC6H4, 4-MeOC6H4) 和 [NbBz2(NtBu)]2[(C6H4) (NC(NiPr)(NHiPr)) 2]} 显示胍基配体通过一个烷基氨基氮和芳基亚氨基氮原子的优选不对称配位。计算研究证实了这种偏好,结果表明电子因素优于空间因素。此外,络合物[NbBz3(NtBu)]与2-(正丁基)-1,3-二异丙基胍}的反应没有产生区域选择性不对称胍盐。相反,复合物NbBz2(NtBu)[(nBu)NC(NiPr)(NHiPr)]}是作为具有对称和不对称配位模式的三种异构体的混合物获得的。最后,复合物[NbBz3(NtBu)]被证明是一种适合在温和条件下进行多种胺的鸟苷化反应的预催化剂。建议胍盐作为该反应机理中的中间体。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。