New Highly Active Heteroscorpionate-Containing Lutetium Catalysts for the Hydroamination of Aminoalkenes: Isolation and Structural Characterization of a Dipyrrolidinide–Lutetium Complex

The reactions of the hybrid scorpionate/cyclopentadiene
compounds,
as a mixture of regioisomers1-[2,2-bis­(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene
and 2-[2,2-bis­(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene
(bpzcpH) and 1-[2,2-bis­(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl]-1,3-cyclopentadiene and 2-[2,2-bis­(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl]-1,3-cyclopentadiene (bpztcpH)with
[Lu­(CH2SiMe3)3(thf)2]
proceed in very high yields to give the free solvent neutral heteroscorpionate
dialkyl lutetium complexes [Lu­(CH2SiMe3)2(bpzcp)] (1) and chiral [Lu­(CH2SiMe3)2(bpztcp)] (2). The structures in
solution of 1 and 2 were investigated by
VT NMR spectroscopy, and a fluxional behavior corresponding to an
exchange between the alkyl groups was observed. The lutetium complex
[Lu­(CH2SiMe3)2(bpztcp)­(thf)] (3) was isolated as an enantiomerically enriched complex. Supramolecular
CH−π interactions between molecules in crystals of 3 have been identified in its X-ray molecular analysis, and
they explain the formation of a conglomerate among molecules of 3. Complexes 1–3 are efficient
catalysts for the intramolecular hydroamination of aminoalkenes, giving
TOF values of up to 475 h–1 at 90 °C for 2,2-diphenyl-pent-4-enylamine
(4) by using complex 3 as catalyst. Enantioselectivities
up tp 70% ee were achieved in the cyclization of the 1,2-disubstituted
olefin 6 with the high enantiopurity complex 3. The hydroamination reactions show apparently zero-order rate dependence
on substrate concentration and first-order rate dependence on catalyst
concentration. Additionally, bicyclization of 2-allyl-2-methylpent-4-enylamine
(10) was achieved at 60 and 100 °C, giving exo,exo-2,4,6-trimethyl-1-azabicyclo­[2.2.1]­heptane
(12). The protonolysis reaction of complex [Lu­(CH2SiMe3)2(bpztcp)] (2) with
2 equiv of 2,2-diphenyl-pent-4-enylamine (4) yielded
a dipyrrolidinide lutetium complex [Lu­(NC4H5-2-Me-4,4-Ph2)2(bpztcp)] (13)
as a mixture of two diastereoisomers. The structures of the complexes
were determined by spectroscopic methods, and the X-ray crystal structures
of 3 and 13 were also established.

以区域异构体混合物形式存在的杂合蝎型配体（scorpionate）/环戊二烯（cyclopentadiene）类化合物——即1-[2,2-双(3,5-二甲基吡唑-1-基)-1,1-二苯乙基]-1,3-环戊二烯与2-[2,2-双(3,5-二甲基吡唑-1-基)-1,1-二苯乙基]-1,3-环戊二烯（记为bpzcpH），以及1-[2,2-双(3,5-二甲基吡唑-1-基)-1-叔丁基乙基]-1,3-环戊二烯与2-[2,2-双(3,5-二甲基吡唑-1-基)-1-叔丁基乙基]-1,3-环戊二烯（记为bpztcpH）——与配合物[Lu(CH₂SiMe₃)₃(thf)₂]（三(三甲基硅基甲基)合三(四氢呋喃（thf）)镥）反应，可获得极高收率的无游离溶剂中性异蝎型配体（heteroscorpionate）二烷基镥配合物[Lu(CH₂SiMe₃)₂(bpzcp)]（1）与手性配合物[Lu(CH₂SiMe₃)₂(bpztcp)]（2）。采用变温核磁共振（VT NMR）光谱对配合物1和2的溶液结构进行了表征，观测到对应于烷基配体间交换的动态流变行为。配合物[Lu(CH₂SiMe₃)₂(bpztcp)(thf)]（3）以对映体富集的形式被分离得到。通过X射线分子结构分析，在配合物3的晶体中识别出分子间存在的超分子CH-π相互作用，该相互作用阐明了3的分子形成团聚体的原因。配合物1~3均为氨基烯烃分子内氢胺化反应的高效催化剂，以配合物3为催化剂时，针对2,2-二苯基-4-戊烯胺（4）的反应在90℃下可获得最高达475 h⁻¹的转换频率（TOF）值。采用高对映体纯的配合物3催化1,2-二取代烯烃6的环化反应时，可获得最高达70%对映体过量值（ee）的对映选择性。该氢胺化反应表现出对底物浓度的零级速率依赖性，以及对催化剂浓度的一级速率依赖性。此外，在60℃与100℃下均可实现2-烯丙基-2-甲基-4-戊烯胺（10）的双环化反应，得到外,外-2,4,6-三甲基-1-氮杂双环[2.2.1]庚烷（12）。配合物[Lu(CH₂SiMe₃)₂(bpztcp)]（2）与2当量的2,2-二苯基-4-戊烯胺（4）发生质子解反应，生成由两种非对映异构体组成的二吡咯烷基镥配合物[Lu(NC₄H₅-2-Me-4,4-Ph₂)₂(bpztcp)]（13）。所有配合物的结构均通过光谱手段得以表征，配合物3与13的X射线晶体结构也已解析完成。