Isolation and Reactivity of a Digerma Analogue of Vinyllithiums: a Lithium Digermenide

Abstract

The versatile reactivity of disilenides, heavier analogues of vinyl anions, opened the door to novel heavier group 14 structure motifs with residual functionalities in the periphery around the SiSi moiety. The corresponding germanium analogue, digermenide Tip 2 GeGe(Tip)Li•dme 2 (Tip = 2,4,6-triisopropylphenyl, dme = 1,2-dimethoxyethane), has now been obtained from the reduction of Tip 2 GeCl 2 with 3.3 equiv of Li powder and a catalytic amount of naphthalene in dme at −70 °C. The lithium digermenide was characterized by NMR spectroscopy, UV/vis spectroscopy, X-ray diffraction, and DFT calculations. As proof of principle for its suitability for the nucleophilic transfer of the GeGe motif, the reaction with chlorosilanes leads to the unsymmetrically substituted digermenes Tip 2 GeGe(Tip)SiR 3 .

Persistent Digermenes with Acyl and α‐Chlorosilyl Functionalities

“…[13] The longest wavelengtha bsorption in the UV/Vis spectrum is located in the typical regionf or heaviera lkene homologuesa tl max = 426 nm (e = 20 845 Lmol À1 cm À1 )a nd is thus slightly blue-shifted compared to the value reported for digermenide 8 (l max = 435 nm). [13] The longest wavelengtha bsorption in the UV/Vis spectrum is located in the typical regionf or heaviera lkene homologuesa tl max = 426 nm (e = 20 845 Lmol À1 cm À1 )a nd is thus slightly blue-shifted compared to the value reported for digermenide 8 (l max = 435 nm).…”

“…[13] The longest wavelengtha bsorption in the UV/Vis spectrum is located in the typical regionf or heaviera lkene homologuesa tl max = 426 nm (e = 20 845 Lmol À1 cm À1 )a nd is thus slightly blue-shifted compared to the value reported for digermenide 8 (l max = 435 nm). [13,15,16] In agreement with the increased trans bending, the GeÀGe distance of 2.3279(4) is elongated compared to those in both 8 (2.284 ) and Tip 2 Ge=GeTip 2 (2.213 ). The trans-bent angles q (defined as the angle between the R-E-R' plane normal andt he E-E bond vector) in 10 [q(Ge1) = 23.78; q(Ge2) = 21.38]a re substantially larger than those in 8 [q-(GeTipLi) = 12.88, q(GeTip 2 ) = 7.18]o rt he symmetrically substituted Tip 2 Ge=GeTip 2 [q(GeTip 2 ) = 128].…”

“…[13] Single-crystal X-ray diffraction analysisc onfirmed the constitution of 10 as as ilyl-substituted digermene ( Figure 1). [13,15,16] The Ge1ÀSi bond of 2.3984(8) is slightly shorter than those in persilyl-substituted digermenes (iPr 2 MeSi) 2 Ge=Ge(SiMeiPr 2 ) 2 (2.400 )a nd (iPr 3 Si) 2 Ge=Ge(SiiPr 3 ) 2 (2.427 ). In contrast, the twist angle t (defined as the angle between the R-E-R' plane normals) of 10 (t = 13.68)i ss imilar to that in Tip 2 Ge=GeTip 2 (t = 148)a nd thus smaller than that in 8 (t = 19.98).…”

“…The identicalc hemical environment of the two methyl groups virtually excludes a three-membered Si 2 Ge ring as the presence of the asymmetric Ge center in the hypothetical heavy cyclopropane 12 a would cause diastereotopic splitting of the corresponding signals. [12,13] The slightly lower field 29 Si NMR shift of 11 a compared to 6a can be rationalized in terms of the highere lectronegativity of germanium compared to silicon.T he UV/Vis spectrum of af reshly prepared and filtered solution shows the longest-wavelength absorption at l max = 435 nm (e = 11 110Lmol À1 cm À1 ), close to the values for silyldisilenes and digermenes( 7b:4 27 nm, [12] 10:4 26 nm), strongly supportingt he presence of an uncompromised Ge= Ge moiety.B ased on the accumulateds pectroscopic evidence, we are confidenti na ssigning the connectivity of a-chlorosilyldigermene 11 a to the main product of the reaction of digermenide 8 with Me 2 SiCl 2 (Scheme 6). [11] Consistent evidencei sp rovided by the 13 CNMR spectrum of 11 a,w ith twelve signals between 153.1 and 122.0 ppm that satisfyingly match,i nn umber and chemical shifts, the corresponding signals of silyl disilene 6a,w hile being in stark contrast to the eighteen signals in this range for cyclotrisilane 7a.…”

“…[13] Single-crystal X-ray diffraction data for the resulting unsymmetrically substituted digermenes 9a,b could only be obtained for ap artially hydrolyzed sample of 9b,w hich were of limited value in terms of the determination of pertinent bonding parameters. [13] Single-crystal X-ray diffraction data for the resulting unsymmetrically substituted digermenes 9a,b could only be obtained for ap artially hydrolyzed sample of 9b,w hich were of limited value in terms of the determination of pertinent bonding parameters.…”