Synthesis, Structural Characterization, Reactivity, and Catalytic Properties of Copper(I) Complexes with a Series of Tetradentate Tripodal Tris(pyrazolylmethyl)amine Ligands

Novel
tris­(pyrazolylmethyl)­amine ligands TpaMe3, Tpa*,Br, and TpaBr3 have been synthesized and structurally characterized.
The coordination chemistries of these three new tetradentate tripodal
ligands and the already known Tpa and Tpa* have been explored using
different copper­(I) salts as starting materials. Cationic copper­(I)
complexes [TpaxCu]­PF6 (1–4) have been isolated from the reaction
of [Cu­(NCMe)4]­PF6 and 1 equiv of the ligand.
Complexes 2 (Tpax = Tpa*)
and 3 (Tpax = TpaMe3) have been characterized by X-ray studies. The former is a 1D helical
coordination polymer, and the latter is a tetranuclear helicate. In
both structures, the Tpax ligand adopts
a μ2:κ2:κ1-coordination
mode. However, in solution, all of the four complexes form fluxional
species. When CuI is used as the copper­(I) source, neutral compounds 5–8 have been obtained. Complexes 6–8 exhibit a 1:1 metal-to-ligand ratio,
whereas 5 presents 2:1 stoichiometry. Its solid-state
structure has been determined by X-ray diffraction, revealing its
3D polymeric nature. The polymer is composed by the assembly of [Tpa2Cu4I4] units, in which Cu4I4 presents a step-stair structure. The Tpa ligands bridge
the Cu4I4 clusters, adopting also a μ2:κ2:κ1-coordination mode.
As observed for the cationic derivatives, the NMR spectra of 5–8 show the equivalence of the three
pyrazolyl arms of the ligands in these complexes. The reactivities
of cationic copper­(I) derivatives 1–4 with PPh3 and CO have been explored. In all cases, 1:1
adducts [TpaxCuL]­PF6 [L = PPh3 (9–11), CO (12–15)] have been isolated. The crystal structure
of [Tpa*Cu­(PPh3)]­PF6 (9) has been
obtained, showing that the coordination geometry around copper­(I)
is trigonal-pyramidal with the apical position occupied by the tertiary
amine N atom. The Tpa* ligand binds the Cu center to three of its
four N atoms, with one pyrazolyl arm remaining uncoordinated. In solution,
the carbonyl adducts 13–15 exist
as a mixture of two isomers; the four- and five-coordinate species
can be distinguished by means of their IR νCO stretching
bands. Finally, the catalytic activities of complexes 1–4 have been demonstrated in carbene- and nitrene-transfer
reactions.

本研究合成并结构表征了三种新型三(吡唑基甲基)胺配体（tris(pyrazolylmethyl)amine ligands）：TpaMe3、Tpa*,Br及TpaBr3。以不同铜(I)盐为起始原料，探究了这三种新型四齿三脚架型配体（tetradentate tripodal ligands）以及已知配体Tpa和Tpa*的配位化学。通过[Cu(NCMe)4]PF6与1当量配体的反应，分离得到了阳离子型铜(I)配合物[TpaxCu]PF6（1~4）。
配合物2（Tpax=Tpa*）与3（Tpax=TpaMe3）经X射线衍射（X-ray studies）表征：前者为一维螺旋配位聚合物，后者为四核螺旋体。在两种结构中，Tpax配体均采用μ₂:κ₂:κ₁配位模式。但在溶液中，四种配合物均以流变型物种形式存在。
当以碘化亚铜（CuI）作为铜(I)源时，得到了中性配合物5~8。配合物6~8的金属与配体化学计量比为1:1，而配合物5的化学计量比为2:1。通过X射线衍射确定了配合物5的固态结构，结果显示其为三维聚合物结构，由[Tpa2Cu4I4]单元组装而成，其中Cu4I4簇呈现阶梯状结构。Tpa配体作为桥联配体连接Cu4I4簇，同样采用μ₂:κ₂:κ₁配位模式。
与阳离子衍生物一致，配合物5~8的核磁共振（NMR）光谱显示，其配体的三个吡唑基臂等价。此外，探究了阳离子型铜(I)衍生物1~4分别与三苯基膦（PPh3）和一氧化碳（CO）的反应性，所有反应均分离得到1:1加合物[TpaxCuL]PF6[L=PPh3（9~11）、CO（12~15）]。
配合物[Tpa*Cu(PPh3)]PF6（9）的晶体结构表明，铜(I)中心的配位几何为三角锥构型，顶点由叔胺氮原子占据。Tpa*配体仅通过其四个氮原子中的三个与铜中心配位，剩余一个吡唑基臂未参与配位。在溶液中，羰基加合物13~15以两种异构体的混合物形式存在，可通过其红外（IR）的νCO伸缩振动峰区分四配位和五配位物种。
最后，证实了配合物1~4在卡宾转移及氮宾转移反应中的催化活性。