Complexes of an Anionic Gallium(I) <i>N</i>-Heterocyclic Carbene Analogue with Group 14 Element(II) Fragments: Synthetic, Structural and Theoretical Studies

The reactions of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue, [K(tmeda)][:Ga{[N(Ar)C(H)]2}], Ar = C6H3Pri2-2,6, with the heavier group 14 alkene analogues, R2EER2, E = Ge or Sn, R = −CH(SiMe3)2, have been carried out. In 2:1 stoichiometries, these lead to the ionic [K(tmeda)][R2EGa{[N(Ar)C(H)]2}] complexes which exhibit long E−Ga bonds. The nature of these bonds has been probed by DFT calculations, and the complexes have been compared to neutral NHC adducts of group 14 dialkyls. The 4:1 reaction of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with R2SnSnR2 leads to the digallyl stannate complex, [K(tmeda)][RSn[Ga{[N(Ar)C(H)]2}]2], presumably via elimination of KR. In contrast, the reaction of the gallium heterocycle with PbR2 affords the digallane(4), [Ga{[N(Ar)C(H)]2}]2, via an oxidative coupling reaction. For sake of comparison, the reactions of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with Ar‘2EEAr‘2, E = Ge, Sn or Pb, Ar‘ = C6H2Pri3-2,4,6, were carried out and led to either no reaction (E = Ge), the formation of [K(tmeda)][Ar‘2SnGa{[N(Ar)C(H)]2}] (E = Sn), or the gallium(III) heterocycle, [Ar‘Ga{[N(Ar)C(H)]2}] (E = Pb). Salt elimination reactions between [K(tmeda)][:Ga{[N(Ar)C(H)]2}] and the guanidinato group 14 complexes [(Giso)ECl], E = Ge or Sn, Giso = [Pri2NC{N(Ar)}2]-, gave the neutral [(Giso)EGa{[N(Ar)C(H)]2}] complexes. All complexes have been characterized by NMR spectroscopy and X-ray crystallographic studies.本研究开展了阴离子型一价镓氮杂环卡宾（N-heterocyclic carbene, NHC）类似物[K(四甲基乙二胺, TMEDA)][:Ga{[N(Ar)C(H)]₂}]（其中Ar为2,6-二异丙基苯基C₆H₃Pri₂-2,6）与重第14族烯烃类似物R₂E=ER₂（E为锗Ge或锡Sn，R为−CH(SiMe₃)₂）的反应。当以2:1的化学计量比进行反应时，生成离子型[K(TMEDA)][R₂EGa{[N(Ar)C(H)]₂}]配合物，该类配合物展现出较长的E−Ga键。通过密度泛函理论（Density Functional Theory, DFT）计算对这类化学键的本质进行了探究，并将其与第14族二烷基化合物的中性NHC加合物进行了对比。 当[K(TMEDA)][:Ga{[N(Ar)C(H)]₂}]与R₂Sn=SnR₂以4:1的化学计量比反应时，经消除KR的过程，生成二镓基锡酸根配合物[K(TMEDA)][RSn[Ga{[N(Ar)C(H)]₂}]₂]。与之相反，该镓杂环与PbR₂的反应则通过氧化偶联过程生成二镓烷(4)配合物[Ga{[N(Ar)C(H)]₂}]₂。 为进行对比，本研究还开展了[K(TMEDA)][:Ga{[N(Ar)C(H)]₂}]与Ar’₂E=EAr’₂（E为Ge、Sn或Pb，Ar’为2,4,6-三异丙基苯基C₆H₂Pri₃-2,4,6）的反应：当E=Ge时未发生任何反应；E=Sn时生成[K(TMEDA)][Ar’₂SnGa{[N(Ar)C(H)]₂}]；E=Pb时则生成三价镓杂环配合物[Ar’Ga{[N(Ar)C(H)]₂}]。 通过[K(TMEDA)][:Ga{[N(Ar)C(H)]₂}]与胍基配位的第14族配合物[(Giso)ECl]（E为Ge或Sn，Giso为[Pri₂NC{N(Ar)}₂]⁻）之间的盐消除反应，得到中性配合物[(Giso)EGa{[N(Ar)C(H)]₂}]。所有配合物均通过核磁共振波谱法（NMR spectroscopy）与X射线晶体衍射研究进行了表征。