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. 2023 Feb 16;29(10):e202203395.
doi: 10.1002/chem.202203395. Epub 2023 Jan 4.

Disproportionation and Ligand Lability in Low Oxidation State Boryl-Tin Chemistry

Xiongfei Zheng  1 , Agamemnon E Crumpton  1 , Andrey V Protchenko  1 , Andreas Heilmann  1 , Mathias A Ellwanger  1 , Simon Aldridge  1
Affiliations

Disproportionation and Ligand Lability in Low Oxidation State Boryl-Tin Chemistry

Xiongfei Zheng et al. Chemistry. .

Abstract

Boryltin compounds featuring the metal in the+1 or 0 oxidation states can be synthesized from the carbene-stabilized tin(II) bromide (boryl)Sn(NHC)Br (boryl={B(NDippCH)2 }; NHC=C{(Ni PrCMe)2 }) by the use of strong reducing agents. The formation of the mono-carbene stabilized distannyne and donor-free distannide systems (boryl)SnSn(IPrMe)(boryl) (2) and K2 [Sn2 (boryl)2 ] (3), using Mg(I) and K reducing agents mirrors related germanium chemistry. In contrast to their lighter congeners, however, systems of the type [Sn(boryl)]n are unstable with respect to disproportionation. Carbene abstraction from 2 using BPh3 , and two-electron oxidation of 3 both result in the formation of a 2 : 1 mixture of the Sn(II) compound Sn(boryl)2 , and the hexatin cluster, Sn6 (boryl)4 (4). A viable mechanism for this rearrangement is shown by quantum chemical studies to involve a vinylidene intermediate (analogous to the isolable germanium compound, (boryl)2 Ge=Ge), which undergoes facile atom transfer to generate Sn(boryl)2 and trinuclear [Sn3 (boryl)2 ]. The latter then dimerizes to give the observed hexametallic product 4, with independent studies showing that similar trigermanium species aggregate in analogous fashion.

Keywords: boryl ligand; cluster; germanium; sub-valent compounds; tin.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Systems of the stoichiometry (RE) n (E=group 14 element) relevant to the current study.
Figure 2
Figure 2
Molecular structures of {(HCDippN)2B}Sn(IPrMe)Br (1, upper), {(HCDippN)2B}SnSn(IPrMe){B(NDippCH)2} (2, centre) and K2[Sn2{B(NDipp CH)2}2] (3, lower) in the solid state as determined by X‐ray crystallography. Hydrogen atoms and solvate molecules omitted, and selected groups shown in wireframe format for clarity; thermal ellipsoids set at the 40 % probability level. Key bond lengths (Å) and angles (°): (for 1) Sn−B 2.295(5), Sn−C 2.307(5), 2.6325(8), B−Sn‐Br 98.1(1), B−Sn‐C 97.4(2), C−Sn‐Br 94.6(1); (for 2) Sn−Sn 2.581(1); Sn−B 2.243(7), 2.189(5); Sn−C 2.183(5); Sn‐Sn−B 109.1(2), 120.4(1); (for 3) Sn−Sn 2.749(1); Sn−B 2.288(3); Sn K 3.599(1), 3.575(1); Sn‐Sn−B 96.5(1).
Scheme 1
Scheme 1
Reduction of {(HCDippN)2B}Sn(IPrMe)Br (1) by potassium or magnesium reducing agents to give {(HCDippN)2B}SnSn(IPrMe){B(NDippCH)2} (2) or K2[Sn2{B(NDippCH)2}2] (3); oxidation of 3 or carbene abstraction from 2 to yield a mixture of the tin cluster Sn6{B(NDippCH)2}4 (4) and diborylstannylene Sn{B(NDippCH)2}2 via a formal disproportionation process. [B]={B(NDippCH)2}.
Figure 3
Figure 3
Molecular structures of Sn6{B(NDippCH)2}4 (4, upper) and Ge6{B(NDippCH)2}4 (6, lower) in the solid state as determined by X‐ray crystallography. Hydrogen atoms and solvate molecules omitted and selected groups shown in wireframe format for clarity; thermal ellipsoids set at the 40 % probability level. Key bond lengths (Å) and angles (°): (for 4) Sn−B 2.259(6), 2.269(6); Sn(B)‐Sn 2.841(1), 2.834(1); Sn−Sn 2.848(1), 2.831(1); (for 6) Ge−B 2.095(3), 2.105(3); Ge(B)‐Ge 2.500(1), 2.506(1); Ge−Ge 2.490(1), 2.468(1).
Figure 4
Figure 4
DFT calculated mechanism for the disproportionation of diboryldistannyne (formed by oxidation of 3 or NHC abstraction from 2) into diborylstannylene Sn{B(NDippCH)2}2 and tin cluster Sn6{B(NDippCH)2}4. [B]={B(NDippCH)2}.
Scheme 2
Scheme 2
Synthesis of Ge6{B(NDippCH)2}4 (6), the germanium analogue of Sn6{B(NDippCH)2}4 (4). [B]={B(NDippCH)2}.
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