an isolable bis(silylene)-stabilized germylone and its ... · bph 3 could form a frustrated lewis...

Yuwen Wang,† Miriam Karni,‡ Shenglai Yao,† Yitzhak Apeloig,‡,* and Matthias Driess†,*

†Metalorganics and Inorganic Materials, Department of Chemistry, Technische Universität Berlin, Straße des 17, Juni 135, Sekr. C2, 10623 Berlin, Germany‡Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel

Introduction

Synthesis of Bis(NHSi)-Stabilized Germylone 3 and Its Electron Structure

Conclusion

An Isolable Bis(silylene)-Stabilized Germylone and Its Reactivity

In contrast to the easy access to the vast number of well-known zero-valent transition metal complexes,1 the synthesis of isolable zero-valent complexes of main group

elements, particularly the highly reactive heavy group 14 elements E0 (E = Si, Ge),2 is still challenging. Recently, supported by strong σ-donating ligands, the previously elusive

monatomic zero-valent germanium compounds,2 termed as germylone,3 become accessible. However, the germylone chemistry is still in its infancy due to the limited scope of

σ-donating ligands. Here, we report the synthesis of the first bis(N-heterocyclic silylene)-stabilized zero-valent silicon compound [SiII (Xant)SiII]Ge0 34,5 via the reduction of the

corresponding chlorosilyliumylidene chloride precursor {[SiII (Xant)SiII]SiCl}+Cl- 2. The electronic structure of 3, whose molecular structure is confirmed spectroscopically and

crystallographically, is investigated by Natural Bond Orbital (NBO) analysis, showing two perpendicular lone-pairs of electrons on the central Ge0 atom. Due to the electron-

rich character, 3 can coordinate with one or two Lewis acid AlBr3 and displays unusual reactivity toward borane and transition metal Ni(cod)2. In addition, the germylone and

BPh3 could form a frustrated Lewis pair (FLP) to cleave H2, representing, for the first time, that a metallylone could be applied in FLP chemistry.6

1. Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to Catalysis; University Science Books: Sausalito, CA, 2010.

2. (a) Yao, S.; Xiong, Y.; Driess, M. Acc. Chem. Res. 2017, 50, 2026–2037. (b) Majhi, P. K.; Sasamori, T. Chem. - Eur. J. 2018, 24, 9441–9455.

3. (a) Takagi, N.; Shimizu, T.; Frenking, G. Chem. - Eur. J. 2009, 15, 3448–3456. (b) Takagi, N.; Shimizu, T.; Frenking, G. Chem. - Eur. J. 2009, 15, 8593–8604.

4. Wang, Y.; Kostenko, A.; Yao, S.; Driess, M. J. Am. Chem. Soc. 2017, 139, 13499–13506.

5. Wang, Y.; Kostenko, A.; Hadlington, T. J.; Luecke, M.-P.; Yao, S.; Driess, M. J. Am. Chem. Soc. 2019, 141, 626−634.

6. Wang, Y.; Karni, M.; Yao, S.; Apeloig, Y.; Driess, M. J. Am. Chem. Soc. 2019, 141, 1655−1664.

The Reactivity of Germylone Toward Small Molecules

Utilizing the bis(NHSi)xanthene ligand 1 containing two donating NHSi, we have successfully synthesized the first bis(NHSi)-stabilized zero-valent Ge compound 3, which is

fully characterized and also theoretically investigated. Germylone 3 bears two lone pairs of electrons and thus can coordinate one or two AlBr3. Surprisingly, mixing germylone 3

with 9-BBN leads to the first silylene-stabilized boryl(silyl)germylene 6 with a heteroallylic B∙∙∙Ge∙∙∙Si π-conjugation. Because of the electron-rich Ge0 site, two molecules of 3

react with Ni(cod)2 undergoing reductive coupling of two Ge0 atoms on the Ni center to give the complex 7 bearing a three-membered GeI2NiII metallacycle. It is demonstrated

for the first time that metallylones can also act as Lewis donors to afford a frustrated Lewis pair (FLP). While 3 is inert towards H2, it could heterolytically split dihydrogen at 1

atm and room temperature in the presence of BPh3 to give the corresponding hydridogermyliumylidene hydroborate 8.

Figure 1. Molecular structure of compounds 2 and 3. H atoms are omitted for clarity.

Figure 2. A selection of B3LYP-D3(BJ)/6-311G(d,p) calculated orbitals of the germylone 3. LP: lone-pair orbital; BD:

bonding orbital; LV: formally vacant p-orbital. Occ is the occupancy of the orbital in electrons. Contour value = 0.03.

Two lone pairs of electrons on the zero-valent Ge atom

one σ-type lone-pair and one 3p(Ge) lone-pair

Figure 3. Molecular structure of compounds 4~8. H atoms are omitted (except H16 in compound 6; H90 and H91 in

compound 7) for clarity.

Reactivity Investigation

Synthesis of Germylone 3

References

Coordinate one

or two AlBr3

2-electron 3-center

B1∙∙∙Ge1∙∙∙Si1 allylic π-bond

GeI2NiII three-membered

metallacycle

Heterolytically split H2 with

the assistance of BPh3