Synthesis, Structure, and Reactivity of [σ:η1:η5-(OCH2)(Me2NCH2)C2B9H9]Ti(NR2) (R = Me, Et)

Interaction of [Me3NH][7,8-CH2OCH2-7,8-C2B9H10] with M(NR2)4 gave the simple amine elimination products [η5-(CH2OCH2)C2B9H9]M(NMe2)2(NHMe2) (M = Zr (2a), Hf (2b)) or the unexpected C−O bond cleavage products [σ:η1:η5-(OCH2)(Me2NCH2)C2B9H9]Ti(NR2) (R = Me (3a), Et (3b)). The higher oxophilicity of the Ti center provides the driving force for the latter reactions. It is suggested that the C−O bond cleavage is prior to the amine elimination in the formation of 3a,b. This serves as a convenient and practical method for the preparation of constrained-geometry half-sandwich metallacarboranes with two different functional sidearms. Complex 3a can undergo a clean amine exchange reaction to produce new constrained-geometry titanacarborane amides. Reactions of 3a with unsaturated molecules CyNCNCy, SCS, Xyl−NC, PhC⋮N, BunNCS, Ph2CCO, and PhNCO gave monoinsertion products. They, except for [σ:η1:η5-(OCH2)(Me2NCH2)C2B9H9]Ti[η3-CyNC(NMe2)NCy] (7), do not react with amines. In sharp contrast, 7 can react readily with Me2NH to regenerate 3a and release guanidine, which leads to the discovery of new catalytic guanylation of amines. All new complexes were fully characterized by various spectroscopic techniques and elemental analyses. Most of them were further confirmed by single-crystal X-ray analyses.将[Me3NH][7,8-CH2OCH2-7,8-C2B9H10]与四(二烷基氨基)金属配合物M(NR2)4反应，可得到两类产物：一类为简单胺消除产物[η5-(CH2OCH2)C2B9H9]M(NMe2)2(NHMe2)（M=Zr(2a)，Hf(2b)），另一类为意外获得的C-O键断裂产物[σ:η1:η5-(OCH2)(Me2NCH2)C2B9H9]Ti(NR2)（R=Me(3a)，Et(3b)）。钛中心更高的亲氧性为这类C-O键断裂反应提供了驱动力。研究表明，在3a、3b的合成过程中，C-O键断裂步骤先于胺消除步骤。该方法为制备带有两种不同官能侧臂的受限几何半夹心金属碳硼烷提供了一条便捷实用的合成途径。配合物3a可发生无副反应的胺交换反应，生成新型受限几何钛杂碳硼烷酰胺类化合物。3a与多种不饱和分子（包括N,N'-二环己基碳二亚胺、二硫化碳、二甲苯基异氰、苯甲腈、正丁基异硫氰酸酯、二苯基烯酮以及苯基异氰酸酯）反应，均可得到单插入产物。除配合物[σ:η1:η5-(OCH2)(Me2NCH2)C2B9H9]Ti[η3-CyNC(NMe2)NCy]（7）外，其余产物均不与胺类试剂发生反应。与之形成鲜明对比的是，配合物7可与二甲胺快速反应，再生得到3a并释放胍类化合物，这一发现推动了胺类新型催化胍基化反应的开发。所有新合成的配合物均通过多种光谱表征技术及元素分析完成了完整表征，其中多数配合物进一步通过单晶X射线衍射分析得到了确认。