Li Yahong, Shi Yanhui, Odom Aaron L
Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
J Am Chem Soc. 2004 Feb 18;126(6):1794-803. doi: 10.1021/ja038320g.
Treatment of Ti(NMe(2))(2)(dpma) (1) with aniline results in the protonation of the dimethylamido ligands, which are retained as dimethylamines, and generation of a titanium imido complex Ti(NPh)(NHMe(2))(2)(dpma) (2) in 94% yield. The monomeric imido 2 is converted to the reactive dimeric micro-imido Ti(NPh)(dpma) (3) on removal of the labile dimethylamine donors. The dimer 3 is converted to monomeric terminal imido complexes in the presence of added donors, e.g., 4,4'-di-tert-butyl-2,2'-bipyridine (Bu(t)-bpy) and DME. Compounds 1-3 exhibit the same rate constant for 1-phenylpropyne hydroamination by aniline and are all kinetically competent to be involved in the catalytic cycle. Attempts to use 1 as a catalyst for hydroaminations involving 1,1-dimethylhydrazine resulted in only a few turnovers under the best conditions. Consequently, the chemistry of 1 with hydrazines to generate hydrazido complexes was scrutinized for comparison with the imido species. Through these studies, titanium hydrazido complexes including Ti(eta(2)-NHNC(5)H(10))(2)(dpma) (5), Ti(eta(2)-NHNMe(2))(2)(dpma) (6), and Ti(micro:eta(1),eta(2)-NNMe(2))(dpma) (7) were characterized. In addition, a terminal hydrazido(2-) complex was available by addition of Bu(t)-bpy to 1 prior to 1,1-dimethylhydrazine addition, which provided Ti(eta(1)-NNMe(2))(Bu(t)-bpy)(dpma) (8). Compound 8 was structurally characterized and compared to Ti(NPh)(Bu(t)-bpy)(dpma) (4b), an imido derivative with the same ancillary ligand set. Compound 8 has a nucleophilic beta-nitrogen consistent with a hydrazido(2-) formulation, as determined by reaction with MeI to form the ammonium imido complex [Ti(NNMe(3))(Bu(t)-bpy)(dpma)]I (9). Analogous pyridinium imido complexes Ti(N-1-pyridinium)(Bu(t)-bpy)(dpma) (10) are available by addition of 1-aminopyridinium iodide to 1. From the investigations, some conclusions regarding the activity of titanium pyrrolyl complexes in hydroamination were drawn. The lack of conversion of the bis[micro-hydrazido(2-)] 7 to monomeric species in the presence of donor ligands is put forth as one explanation for the poor hydrazine hydroamination activity of 1. This problem was combated in the synthesis of Ti(NMe(2))(2)(dap)(2), which is an active catalyst for hydrazine hydroamination of alkynes.
用苯胺处理Ti(NMe(2))(2)(dpma) (1)会导致二甲基酰胺配体发生质子化，质子化后的二甲基酰胺以二甲胺形式保留下来，同时生成产率为94%的钛亚胺基配合物Ti(NPh)(NHMe(2))(2)(dpma) (2)。在除去不稳定的二甲胺供体后，单体亚胺基配合物2会转化为具有反应活性的二聚微亚胺基配合物Ti(NPh)(dpma) (3)。在加入供体（如4,4'-二叔丁基-2,2'-联吡啶（Bu(t)-bpy）和乙二醇二甲醚（DME））的情况下，二聚体3会转化为单体末端亚胺基配合物。化合物1 - 3对苯胺与1 - 苯基丙炔的氢胺化反应表现出相同的速率常数，并且在动力学上都有可能参与催化循环。尝试将1用作涉及1,1 - 二甲基肼的氢胺化反应的催化剂时，即使在最佳条件下也只能实现少量的催化循环。因此，对1与肼生成酰肼基配合物的化学反应进行了详细研究，以便与亚胺基物种进行比较研究。通过这些研究，表征了包括Ti(η(2)-NHNC(5)H(10))(2)(dpma) (5)、Ti(η(2)-NHNMe(2))(2)(dpma) (6)和Ti(μ:η(1),η(2)-NNMe(2))(dpma) (7)在内的钛酰肼基配合物。此外，在加入1,1 - 二甲基肼之前，先向1中加入Bu(t)-bpy，可以得到一种末端酰肼基(2 -)配合物，即Ti(η(1)-NNMe(2))(Bu(t)-bpy)(dpma) (8)。对化合物8进行了结构表征，并与具有相同辅助配体的亚胺基衍生物Ti(NPh)(Bu(t)-bpy)(dpma) (4b)进行了比较。通过与甲基碘反应形成铵亚胺基配合物[Ti(NNMe(3))(Bu(t)-bpy)(dpma)]I (9)，确定化合物8具有与酰肼基(2 -)结构相符的亲核β - 氮。通过向1中加入1 - 氨基吡啶碘化物，可以得到类似物吡啶鎓亚胺基配合物[Ti(N - 1 - 吡啶鎓)(Bu(t)-bpy)(dpma)]⁺ (10)。通过这些研究，得出了一些关于钛吡咯基配合物在氢胺化反应中活性的结论。在供体配体存在下，双[μ - 酰肼基(2 -)] 7无法转化为单体物种，这被认为是1对肼的氢胺化反应活性较差的一个原因。在合成Ti(NMe(2))(2)(dap)(2)时解决了这个问题，Ti(NMe(2))(2)(dap)(2)是一种用于炔烃肼氢胺化反应的活性催化剂。
