2,6-Di(4-t-butylphenyl)phenyl-group 13 organometallic compounds Brandon Quillian, Yuzhong Wang, Pingrong Wei, Adele Handy, Gregory H. Robinson * Department of Chemistry, The University of Georgia, Athens, GA 30602-2556, USA Received 19 April 2006; received in revised form 12 May 2006; accepted 12 May 2006 Available online 20 May 2006 Abstract Reaction of MX 3 (M = Al, Ga, In; X = Br, Cl) with RLi (R = 2,6-(4-t-BuC 6 H 4 ) 2 C 6 H 3 ) affords RGaCl 2 Æ OEt 2 , 1, RAlBr 2 Æ OEt 2 , 2, R 2 GaCl, 3, and R 3 In, 4. These sterically demanding compounds have been characterized by elemental analyses, 1 H NMR spectroscopy, and single crystal X-ray diffraction. The geometry about the metal centers in 1 and 2 is best described as distorted tetrahedral while the coordination about the gallium atom in 3 is distorted trigonal planar. Compound 4, with the indium atom in a trigonal planar environ- ment, is noteworthy as the first example of a tris(m-terphenyl)group 13 metal compound. The propeller arrangement of the three ligands in compound 4 serves to virtually encapsulate the metallic center. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Aluminum; Gallium; Group 13; Indium; Terphenyl ligand 1. Introduction Sterically demanding ligands have played a prominent role in the development of group 13 organometallic chem- istry. In particular, m-terphenyl ligands have been exten- sively utilized to stabilize low-valent, low-coordinate, organometallic group 13 compounds [1–3]. That the struc- ture and bonding of a given compound may be dramati- cally tuned as a function of ligand steric loading has been a practical method to afford interesting organometallic compounds with intriguing properties. This concept is ele- gantly 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 ), metal- loaromatic 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]. The digallyne and cyclogallenes are typically prepared by alkali metal reduc- tion of the respective RGaCl 2 (R = m-terphenyl) species. Surprisingly, efforts to evaluate the organometallic group 13 chemistry of less bulky m-terphenyl ligands have been limited. Herein, we report the syntheses and molecular structures of RGaCl 2 Æ OEt 2 , 1, RAlBr 2 Æ OEt 2 , 2,R 2 GaCl, 3, and R 3 In, 4 (R = 2,6-di(4-t-butylphenyl)phenyl, 2,6- (4-t-BuC 6 H 4 ) 2 C 6 H 3 ). The geometry about the metal centers in 1 and 2 is best described as distorted tetrahedral while the coordination about the gallium atom in 3 approaches distorted trigonal planar. Compound 4, with the indium atom in a trigonal planar environment, is noteworthy as a rare example of a tris-m-terphenyl-group 13 metal com- pound. The propeller arrangement of the three ligands in 4 serves to effectively shield the indium center. 2. Results and discussion Investigation of the 2,6-di(4-t-butylphenyl)phenyl ligand was undertaken in an effort to gain further insight into the significance of substitution at the ortho position of the outer phenyl rings, or the lack thereof, when employing ste- rically encumbered m-terphenyl-based ligands [8]. It has been shown that this ligand has the tendency for facile intramolecular C–H bond activation of the ortho position of the outer phenyl ring, which may serve as a mechanism to form an in situ generated bidentate ligand that provides robust steric protection for the metal center [9]. The 0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2006.05.024 * Corresponding author. Tel.: +1 706 542 1853; fax: +1 706 542 9454/ 1972. E-mail address: robinson@chem.uga.edu (G.H. Robinson). www.elsevier.com/locate/jorganchem Journal of Organometallic Chemistry 691 (2006) 3765–3770