Activation of Ge-H and Sn-H Bonds with N-Heterocyclic Carbenes and a Cyclic (Alkyl)(amino)carbene

Abstract

A study of the reactivity of several N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene (cAAC^Me ) with the group 14 hydrides GeH₂ Mes₂ and SnH₂ Me₂ (Me=CH₃ , Mes=1,3,5-(CH₃ )₃ C₆ H₂ ) is presented. The reaction of GeH₂ Mes₂ with cAAC^Me led to the insertion of cAAC^Me into one Ge-H bond to give cAAC^Me H-GeHMes₂ (1). If 1,3,4,5-tetramethyl-imidazolin-2-ylidene (Me₂ Im^Me ) was used as the carbene, NHC-mediated dehydrogenative coupling occurred, which led to the NHC-stabilized germylene Me₂ Im^Me ⋅GeMes₂ (2). The reaction of SnH₂ Me₂ with cAAC^Me also afforded the insertion product cAAC^Me H-SnHMe₂ (3), and reaction of two equivalents Me₂ Im^Me with SnH₂ Me₂ gave the NHC-stabilized stannylene Me₂ Im^Me ⋅SnMe₂ (4). If the sterically more demanding NHCs Me₂ Im^Me , 1,3-di-isopropyl-4,5-dimethyl-imidazolin-2-ylidene (iPr₂ Im^Me ) and 1,3-bis-(2,6-di-isopropylphenyl)-imidazolin-2-ylidene (Dipp₂ Im) were employed, selective formation of cyclic oligomers (SnMe₂ )_n (5; n=5-8) in high yield was observed. These cyclic oligomers were also obtained from the controlled decomposition of cAAC^Me H-SnHMe₂ (3).

Keywords: N-heterocyclic carbenes; cyclic alkyl(amino)carbenes; germanium; hydrides; tin.

Scheme 1

Previous work from our group on the reactivity of group 14 element hydrides with NHCs (iPr₂Im).

Figure 1

NHC‐mediated dehydrogenative Sn−Sn coupling.

Figure 2

Molecular structures free energy profile [kJ mol⁻¹] for the RER of Me₂Im^Me and EH₂Ph₂ (E=Si, Ge; TURBOMOLE, M06‐2x//def2‐TZVPP).

Scheme 2

Reaction of cAAC^Me and Me₂Im^Me with GeH₂Mes₂.

Figure 3

Molecular structures of cAAC^MeH−GeHMes₂ (1) and Me₂Im^Me ⋅ GeMes₂ (2), in the solid state. Hydrogen atoms and one enantiomer of the racemic mixture of 1 are omitted for clarity. Atomic displacement ellipsoids are set at 50 % probability, the Dipp substituent of 1 is shown as wire‐and‐stick model. Selected bond lengths [Å] and angles [°]: 1: Ge−C1, 2.026(2); Ge−C2, 1.989(2); Ge−C3, 1.997(2); C1−Ge−C2, 112.78(8); C2−Ge−C3, 107.06(8); C1−Ge−C3, 120.49(8); 2: Ge−C1, 2.051(2); Ge−C2, 2.029(2); Ge−C3, 2.036(2); C1−Ge−C2, 103.96(9); C2−Ge−C3, 110.82(10); C1−Ge−C3, 97.63(9); N−C1−Ge−C3: 124.2(2)°.

Scheme 3

Reaction of the NHCs Me₂Im^Me, iPr₂Im^Me, Dipp₂Im and cAAC^Me with SnH₂Me₂.

Figure 4

Molecular structure of cAAC^MeH−SnHMe₂ (3) in the solid state. Hydrogen atoms are omitted for clarity. Atomic displacement ellipsoids are set at 50 % probability, and the Dipp substituent is shown as a wire‐and‐stick model. Selected bond lengths [Å] and angles [°]: Sn−C1, 2.206(10); Sn−C2, 2.163(13); Sn−C3, 2.147(12); C1−Sn−C2, 104.9(5); C2−Sn−C3, 105.4(5); C1−Sn−C3, 116.9(4).