Synthesis and Characterization of a Series of Diarylgermylenes and Dihalodigermenes Having Fused-Ring Bulky “Rind” Groups

Abstract

A series of diarylgermylenes, (Rind)2Ge: (1) [Rind = EMind (a), Eind (b), and MPind (c)], bearing the fused-ring bulky 1,1,3,3,5,5,7,7-octa-R-s-hydrindacen-4-yl (Rind) groups has been obtained as purple to blue crystals by the reaction of GeCl2·dioxane with 2 equiv. of (Rind)Li. A similar reaction using 1 equiv. of (Rind)Li affords the 1,2-dibromodigermenes, (Rind)BrGe=GeBr(Rind) (2) [Rind = Eind (b) and MPind (c)], as yellow to orange crystals. The ligand redistribution reaction between 1 and GeCl2·dioxane in toluene leads to the formation of the 1,2-dichlorodigermenes, (Rind)ClGe=GeCl(Rind) (3) [Rind = EMind (a), Eind (b), and MPind (c)]. The molecular structures of 1a, 1c, 2c, and 3c have been newly determined by X-ray crystallographic analysis. The 1,2-dihalodigermenes, (Rind)XGe=GeX(Rind) [X = Br (2) and Cl (3)], show a dimeric form with a Ge=Ge double bond in the solid state, but exist as a monomeric halogermylene, (Rind)XGe: [X = Br (4) and Cl (5)], in solution. The electronic properties of the Rind-based diarylgermylenes, dihalodigermenes, and halogermylenes have been experimentally and theoretically investigated.

A series of (E)-1,2-diaryldigermenes incorporating bulky Eind groups: structural characteristics and absorption properties

“…As shown in Scheme 1, the Eind-based 1,2-diaryldigermenes ( 2–5 ) were straightforwardly synthesized by the reaction of the 1,2-dibromodigermene, (Eind)BrGeGeBr(Eind) ( 1 ), which is known to exist as a bromogermylene, (Eind)BrGe, in solution with the dissociation of the GeGe double bond, 22 with two equivalents of aryllithiums (ArLi). 4 h After removal of the insoluble materials, the 1,2-diaryldigermenes 2–5 were obtained as yellow-orange to red crystalline solids in ca .…”

“…In addition, we sometimes met with difficulty to completely remove salts from the reaction mixtures, suggesting the formation of halogermylenoides, such as [Li + ][(Eind)ArGeBr] − , which caused the lowering of the yields. 22…”

“…All the digermene moieties have a trans -bent geometry; the trans -bent angles ( θ ) between the Ge–Ge vector and the C Eind –Ge–C Ar plane are 33.69(12)–39.30(13)° (entry 3), which are comparable to or larger than that of I (33.7°) 7,8 and smaller than that of 1 [43.29(4)°]. 22 These angles ( θ ) are much larger than those of the silicon analogues [1.81(7)°–19.12(12)°], 3,4 f , n in which the coplanar 1,2-diaryldisilene π-frameworks are attained by the perpendicularly-fixed Eind groups. Thus, the GeGe bonds have a flexible nature compared to the SiSi bonds in the 1,2-diarylditetrelene skeleton even with the installation of the rigid Eind groups.…”

“…The Ge atoms in 2–5 also tend to have a pyramidal form. The sums of the bond angles at the Ge atom (∑Ge = 339.5–346.1°) (entry 2) are between those in 1 (337.14°) 22 and I (348.35°) 7,8 and smaller than those in the 1,2-diaryldisilenes (∑Si = 355.5–359.9°). 3,4 f , n These structural features are ascribed to both the steric fitness of the Eind groups for the atomic sizes of the tetrels [covalent radius: Ge 1.20(4) Å vs. Si 1.11(2) Å] 24 and the strength of the π-bonding with the capacity for s-p hybridization at the tetrels.…”

“…( E )-1,2-Dibromo-1,2-bis(1,1,3,3,5,5,7,7-octaethyl- s -hydrindacen-4-yl)digermene ( 1 ) was prepared by the modified literature procedure. 22 All other chemicals and gases were used as received.…”