Generation of Weakly Bound Al–N Lewis Pairs by Hydroalumination of Ynamines and the Activation of Small Molecules: Phenylethyne and Dicyclohexylcarbodiimide

Treatment of aminoalkynes (ynamines), Me3Si-CC-NR2 [NR2 = N­(CH2CH2)2NMe, N­(CHMe-CH2)2CH2], with dialkylaluminum
hydrides, H-AlR′2 (R′ = CH2tBu, iBu, tBu), afforded
by hydroalumination the corresponding alkenyl derivatives R′2Al-(Me3Si)­CC­(H)-NR2 (3 to 6) in which the opposite Lewis functionalities adopted
a cis-arrangement with the aluminum and nitrogen
atoms on the same side of the resulting CC double bonds. Intramolecular
Al–N interactions gave four-membered AlC2N heterocycles,
but ring strain may cause relatively long Al–N distances of
2.07 to 2.15 Å. These compounds represent a new type of Lewis
acid–base pairs, and we observed C–H bond activation
by opening of the Al–N bond upon treatment with H-CC-C6H5. Compound 7 was isolated, which
had the proton attached to nitrogen and the anionic ethynyl group
bonded to aluminum. The formation of 7 is reversible
in solution with an increasing dissociation into the starting compounds
at elevated temperatures. Two different structural motifs were obtained
upon reaction of the Lewis acid–base pairs with dicyclohexylcarbodiimide,
which inserted selectively into the bond between the aluminum and
the vinylic carbon atom. In the first compound (8) an
amidinato ligand was formed, which coordinated the metal atom by both
nitrogen atoms to give an AlCN2 heterocycle. A six-membered
heterocycle (9) resulted from the insertion of only one
CN double bond of the carbodiimide into the Al–C­(vinyl)
bond. 9 had an unchanged interaction of the metal atom
with the α-nitrogen atom of the former ynamine. The latter compound
may be considered an intermediate, and rearrangement to yield an amidinato
compound analogous to 8 was indeed observed with extended
reaction time.

将氨基炔烃（ynamines）Me₃Si-C≡C-NR₂ [NR₂ = N(CH₂CH₂)₂NMe、N(CHMe-CH₂)₂CH₂] 与二烷基氢化铝H-AlR'₂（R' = CH₂tBu、iBu、tBu）反应，通过氢铝化反应得到相应的烯基衍生物R'₂Al-(Me₃Si)C=C(H)-NR₂（产物3至6）。此类产物中，对立的路易斯官能团呈现顺式排布，铝原子与氮原子位于生成的C=C双键同侧。分子内的Al-N相互作用形成了四元AlC₂N杂环，但受环张力影响，Al-N键长处于2.07至2.15 Å的相对较长区间。该类化合物代表一类新型路易斯酸碱对，研究发现其与H-C≡C-C₆H₅反应时，Al-N键发生断裂并引发C-H键活化。我们分离得到产物7，其中质子连接于氮原子，阴离子乙炔基与铝原子键合。该转化在溶液中可逆，升高温度时会更多解离为起始原料。当这类路易斯酸碱对与二环己基碳二亚胺反应时，得到两种不同的结构基元：二环己基碳二亚胺选择性插入铝与乙烯基碳之间的化学键。在第一种产物（8）中，形成了脒基配体，该配体通过两个氮原子与金属原子配位，生成AlCN₂杂环。第二种产物（9）则是由二环己基碳二亚胺的一条C=N双键选择性插入Al-C(乙烯基)键得到的六元杂环，其金属原子与原炔胺的α-氮原子仍保持未变的相互作用。该产物可被视为反应中间体，延长反应时间后确实会发生重排，得到与8类似的脒基类化合物。