Cyclogallanes and Metalloaromaticity. Synthesis and Molecular Structure of Dipotassium Tris((2,6-dimesitylphenyl)cyclogallene), K₂[(Mes₂C₆H₃)Ga]₃ (Mes = 2,4,6-Me₃C₆H₂):  A Structural and Theoretical Examination

Abstract

The cyclogallane dipotassium tris((2,6-dimesitylphenyl)cyclogallene), K 2 [(Mes 2 C 6 H 3 )Ga] 3 (Mes ) 2,4,6-Me 3 C 6 H 2 ), has been prepared by either of two distinct synthetic routes. Disproportionation of gallium(II) chloride, Ga 2 Cl 4 , in the presence of (2,6-dimesitylphenyl)lithium, (Mes 2 C 6 H 3 )Li, followed by potassium metal reduction in Et 2 O affords the title compound as large ruby red crystals. Alternatively, K 2 [(Mes 2 C 6 H 3 )Ga] 3 may readily be approached by direct alkali metal reduction of (Mes 2 C 6 H 3 )GaCl 2 . The title compound was characterized by 1 H and 13 C NMR, elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction. The cyclogallane resides about the planar Ga 3 triangle constituted by extremely short Ga-Ga bonds: 2.4260(5), 2.4317(5), and 2.4187(5) Å. Theoretical examination of the Ga 3 2anionic core in [GaH] 3 2-, Na 2 [GaH] 3 , and K 2 [GaH] 3 suggests a well-defined π-molecular orbital. Both experimental and theoretical results strongly support the cyclogallene dianion, [(Mes 2 C 6 H 3 )Ga] 3 2-, as a well-defined metalloaromatic systemsa metallic ring system exhibiting aromatic behavior.

Synthesis and Structure of the “Dialuminyne” Na2[Ar′AlAlAr′] and Na2[(Ar′′Al)3]: AlAl Bonding in Al2Na2 and Al3Na2 Clusters

“…Two of these absorbances are likely attributable to transitions from the HOMO (a u ) and the HOMOÀ1 (b u ) to the LUMO (a g ) while the highestenergy transition may involve the HOMO and the LUMO + 1 (a g ) levels. Compound 4, the "cycloaluminene", is isoelectronic to the recently reported cyclotrisilenylium ion [Si 3 R 2 R'] + (R = SitBu 3 , R' = SiMe 2 tBu) published by Sekiguchi and co-workers [37] and the previously described gallium salts M 2 [(GaAr'') 3 ] (9, M = Na [38] ; 10, M = K [39] ) of Robinson and co-workers. The structure of 4 bears a resemblance to that of 9 except that the AlÀAl bond length exceeds that of its gallium analogue 9 by about 0.08 and is about 0.30 larger than the SiÀSi bond lengths in the cyclotrisilenylium ion [Si 3 R 2 R'] + .…”

Recent developments and future prospects of all-metal aromatic compounds

“…The earlier ones belong to a family of group 13 three-membered rings and were investigated by Robinson et al [29][30][31][32] Dipotassium tris((2,6-dimesitylphenyl)cyclogallene), K 2 [Ga 3 R 3 ], with R = (Mes 2 C 6 H 3 ) and (Mes = 2,4,6-Me 3 C 6 H 2 ), was the first one synthesized (see Fig. 1).…”

2,6-Di(4-t-butylphenyl)phenyl-group 13 organometallic compounds

“…That the structure and bonding of a given compound may be dramatically tuned as a function of ligand steric loading has been a practical method to afford interesting organometallic compounds with intriguing properties. This concept is elegantly illustrated by cyclogallenes, M 2 [GaR] 3 (M = Na [4], K [5]; R = 2,6-Mes 2 C 6 H 3 ; Mes = 2,4,6-Me 3 C 6 H 2 ), metalloaromatic gallium ring systems [1,6]. Another notable example of this concept is the digallyne, Na 2 [RGa"GaR] (R = 2,6-(2,4,6-i-Pr 3 C 6 H 2 ) 2 C 6 H 3 ) [7].…”