WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, UK.
Dalton Trans. 2011 Nov 28;40(44):11945-54. doi: 10.1039/c1dt11430a. Epub 2011 Oct 6.
Towards a systematic development of the zinc chemistry of the important five-membered nitrogen heterocycle pyrrole, this work reports the synthesis and characterisation of five crystalline zinc-pyrrolyl complexes. Pyrrolyl in this context means where conversion of the N-H bond to an N-zinc bond has occurred. Two neutral complexes, [(t)BuZn(NC(4)H(4))(TMEDA)·HNC(4)H(4)] 1 and [Zn(NC(4)H(4))(2)(TMEDA)] 2, containing one and two pyrrolyl ligands, respectively, were synthesised by reacting di-t-butylzinc with different amounts of pyrrole in the presence of TMEDA (TMEDA is N,N,N',N'-tetramethylethylenediamine). X-ray crystallographic studies established that both adopt mononuclear structures with the salient feature of the former the presence of an additional parent protonated pyrrole molecule which engages its anionic counterpart in N-H…πC-C interactions. Employing a similar synthetic approach but adding n-butylsodium to the reaction mixture in attempts to form ate derivatives delivered three distinct sodium zincate (anionic zinc) compounds in [{(THF)(2)·NaZn(THF)(NC(4)H(4))(3)}(∞)] 3, [{(TMEDA)·Na}(2)Zn(NC(4)H(4))(4)] 4, and [{(PMDETA)·Na}(2)Zn(NC(4)H(4))(4)] 5 (PMDETA is N,N,N',N'',N''-pentamethyldiethylenetriamine). From their crystal structures, the 1 : 1, Na:Zn complex 3 can be classified as a lower-order zincate having three pyrrolyl ligands bound to zinc in a polymeric chain arrangement, while the 2 : 1, Na:Zn complexes 4 and 5 are molecular higher-order zincates having Zn centres fully saturated by four pyrrolyl ligands. Discussion of the structures of 1-5 focuses on the interplay of σ-bonding and π-bonding between the pyrrolyl ligands and the metal centres. Revealingly, the zinc-free sodiopyrrole complex [{(PMDETA)·Na(NC(4)H(4))}(2)] 6, made and characterised for comparison, shows that on its own sodium prefers the former type of bonding, but is forced to switch to the latter type when combined with the stronger Lewis acid zinc in the zincate compositions. Complexes 1-6 have also been characterised in solution by NMR spectroscopy.
为了系统地发展五元氮杂环吡咯的锌化学，本工作报道了五个结晶锌吡咯配合物的合成和表征。在这种情况下，吡咯是指 N-H 键转化为 N-锌键的过程。两个中性配合物，[(t)BuZn(NC(4)H(4))(TMEDA)·HNC(4)H(4)]1 和 [Zn(NC(4)H(4))(2)(TMEDA)]2，分别含有一个和两个吡咯配体，是通过在 TMEDA（TMEDA 是 N,N,N',N'-四甲基乙二胺）存在下，用不同量的吡咯与二丁基锌反应合成的。X 射线晶体结构研究表明，这两种配合物都采用单核结构，前者的显著特征是存在额外的母体质子化吡咯分子，它与阴离子对应物通过 N-H…πC-C 相互作用结合。采用类似的合成方法，但在反应混合物中加入正丁基钠，试图形成烷氧基衍生物，得到三种不同的钠锌酸盐（阴离子锌）化合物，在 [{(THF)(2)·NaZn(THF)(NC(4)H(4))(3)}(∞)]3、[{(TMEDA)·Na}(2)Zn(NC(4)H(4))(4)]4 和 [{(PMDETA)·Na}(2)Zn(NC(4)H(4))(4)]5（PMDETA 是 N,N,N',N'',N''-五甲基二亚乙基三胺）中。从它们的晶体结构可以看出，1:1、Na:Zn 配合物 3 可以归类为低阶锌酸盐，其中三个吡咯配体以聚合物链排列方式与锌结合，而 2:1、Na:Zn 配合物 4 和 5 是分子高阶锌酸盐，其中 Zn 中心完全由四个吡咯配体饱和。讨论 1-5 的结构重点在于吡咯配体和金属中心之间的 σ 键和 π 键的相互作用。显然，不含锌的钠吡咯配合物 [{(PMDETA)·Na(NC(4)H(4))}(2)]6，为了比较而合成并进行了表征，表明钠本身更喜欢前一种类型的键合，但在与锌酸盐组成中的更强路易斯酸锌结合时，被迫切换到后一种类型。配合物 1-6 也通过 NMR 光谱在溶液中进行了表征。
