Persistent Digermenes with Acyl and α-Chlorosilyl Functionalities

Abstract

We report the preparation of α-chlorosilyl- and acyl-substituted digermenes. Unlike the corresponding transient disilenes, these species with a Ge=Ge double bond show an unexpectedly low tendency for cyclization, but in turn are prone to thermal Ge=Ge bond cleavage. Triphenylsilyldigermene has been isolated as a crystalline model compound, and is the first fully characterized example of a neutral digermene with an A₂ GeGeAB substitution pattern. Spectroscopic and computational evidence prove the constitution of 1-adamantoyldigermene as a first persistent species with a heavy double bond conjugated with a carbonyl moiety.

Keywords: cycloaddition; digermenes; double bonds; germanium; isomerization.

Scheme 1

Small ring systems (E=Si, Ge) derived from [2+2] cycloadditions of disilenes or digermenes to ketones (I), alkenes (II), and acetylenes (III).

Scheme 2

Synthesis of cyclic silenes 3 a–c and 5 a–e (1 a: R=Tip=2,4,6‐iPr₃C₆H₂; 1 b: R=SiMetBu₂; 2 a, 3 a: R=Tip, R′=tBu; 2 b, 3 b: R=Tip, R′=1‐adamantyl; 2 c, 3 c: R=SiMetBu₂, R′=1‐adamantyl; 4 a, 5 a: R=Tip, R′=Ph; 4 b, 5 b: R=Tip, R′=SiMe₃; 4 c, 5 c: R=SiMetBu₂, R′=H; 4 d, 5 d: R= SiMetBu₂, R′=Ph; 4 e, 5 e: R=SiMetBu₂, R′=SiMe₃).8, 9

Scheme 3

Synthesis of α‐chlorosilyldisilenes 6 a,b and cyclotrisilanes 7 a,b (R=Tip; 6 a, 7 a: R′=Me; 6 b, 7 b: R′=Ph).12

Scheme 4

Previously reported synthesis of unsymmetrically substituted digermenes 9 a,b (R=Tip=2,4,6‐iPr₃C₆H₂; 9 a: SiR′₃=SiMe₃; 9 b: SiR′₃=SiMe₂Ph).13

Scheme 5

Synthesis of triphenylsilyl digermene 10 (R=Tip=2,4,6‐iPr₃C₆H₂).

Figure 1

Molecular structure of triphenylsilyl digermene 10 in the solid state (hydrogen atoms omitted for clarity; thermal ellipsoids drawn at 50 % probability). Selected bond lengths [Å] and angles [°]: Ge1−Ge2 2.3279(4), Ge1−Si 2.3984(8); Ge2−Ge1−Si 119.09(8), Σ°(Ge1) 346.53, Σ°(Ge2) 345.24, θ(Ge1) 23.7, θ(Ge2) 21.3, τ 13.6. Σ°(E) refers to the sum of angles around atom E.

Scheme 6

Synthesis of α‐chlorosilyl digermenes 11 a–c (R=Tip=2,4,6‐iPr₃C₆H₂; 11 a, 12 a: R′=R′′=Me; 11 b, 12 b: R′=Me, R′′=Ph; 11 c, 12 c: R′=R′′=Ph).

Scheme 7

Synthesis of acyl digermenes 13 a–c and trapping with methanol to afford 15 (R=Tip=2,4,6‐iPr₃C₆H₂; 13 a, 14 a: R′=tBu; 13 b, 14 b: R′=2‐methylbutan‐2‐yl; 13 c, 14 c, 15: R′=1‐adamantyl).

Figure 2

Selected Kohn–Sham orbitals of 13 c at the M06‐2X(D3)/def2‐SVP level of theory.

Figure 3

Molecular structure of acyldigermane 15 in the solid state (carbon‐bonded hydrogen atoms omitted for clarity; thermal ellipsoids drawn at 50 % probability). Selected bond lengths (Å) and angles (°): Ge1−Ge2 2.4694(5), Ge1−C1 2.041(3), C1−O1 1.215(3), Ge2−O2 1.8189(17); Ge1−C1−O1 118.7(2).

Scheme 8

Theoretically investigated cyclizations of α‐chlorosilyldimetallenes 6 a,b and 11 a,c as well as acyldimetallenes 2 a,c and 13 a,c (R=Tip=2,4,6‐iPr₃C₆H₂; 6 a, 7 a: E=Si, R′=Me; 6 b, 7 b: E=Si, R′=Ph; 11 a, 12 a: E=Ge, R′=Me; 11 c, 12 c: E=Ge, R′=Ph; 2 a, 3 a: E=Si, R′=tBu; 2 c, 3 c: E=Si, R′=1‐adamantyl; 13 a, 14 a: E=Ge, R′=tBu; 13 c, 14 c: E=Ge, R′=1‐adamantyl).