Synthesis and characterization of constrained-geometry half-sandwich sila- and germacarboranes derived from a trianionic C ðcageÞ -appended alkyloxo-C 2 B 9 -carborane ligand Yinghuai Zhu a,b,1 , John A. Maguire b , Narayan S. Hosmane a, * a Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA b Department of Chemistry, Southern Methodist University, Dallas, TX 75275, USA Received 18 January 2002; accepted 7 February 2002 Abstract The reaction of the ½nido-7-ðOCH 2 Þ-8-Me-7; 8-C 2 B 9 H 9  3 trianion with anhydrous MeMCl 3 (M ¼ Si, Ge) in 1:1 molar ratio in dry toluene, followed by re-crystallization from a solution of toluene/heptane, resulted in the formation of the corresponding novel half-sandwich constrained-geometry group 14 metallacarboranes, closo-1-M(Me)-2-(1-g 1 ðrÞ-OCH 2 )-3-Me-g 5 -2,3-C 2 B 9 H 9 [M ¼ Si (3), Ge (4)] in 48% and 56% yields, respectively. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Silacarborane; Germacarborane; Half-sandwich; C ðcageÞ -Alkyloxo; Constrained-geometry The potential applications of functionalized carbo- rane clusters in catalytic organic reactions have re- sulted in the reports of the syntheses and reactivities of a number of new metallacarboranes [1]. The reac- tion of group 14 metal halides with the dianion of nido-7,8-C 2 B 9 H 13 to form the corresponding half- sandwich complexes, closo-1-M-2,3-C 2 B 9 H 11 , or full- sandwich complexes of the type commo-3,3 0 - Mð3; 1; 2-C 2 B 9 H 11 Þ 2 (M ¼ Si, Ge, Sn, Pb) have been reported some years ago by Rudolph et al. [2] and Hawthorne and co-workers [3]. Our preliminary re- search in this area has shown that the trianionic li- gand ½nido-7-ðCH 2 NHÞ-7; 8-C 2 B 9 H 10  3 , prepared from the reaction of ½nido-7-ðCH 2 NH 2 Þ-7; 8-C 2 B 9 H 11   with two equivalents of n-BuLi, reacts with MCl 4 (M ¼ Ti, Zr) to give the corresponding half-sandwich metalla- carboranes [4]. These observations suggested the pos- sibility of using other constrained-geometry ligands, such as the ansa-alkyloxocarborane, to prepare a se- ries of C ðcageÞ -appended half-sandwich alkyloxometal- lacarboranes. Herein we report the syntheses and characterizations of two such metallacarboranes, con- taining the group 14 elements, silicon and germanium. The starting o-carborane derivative, closo-1-(CH 2 OH)-2-(Me)-1, 2-C 2 B 10 H 10 (1), was prepared from the reaction of the lithium salt of the monoanion, ½1-Me-1; 2-C 2 B 10 H 10   , with paraformaldehyde in an- hydrous ðC 2 H 5 Þ 2 O in 1:1 ratio, following the literature procedures [5]. Acidification of the product with aqueous hydrochloric acid resulted in an 83% yield (m.p. 268–269 °C) of 1 that was decapitated by KOH in refluxing absolute ethanol, to give the corresponding open-cage carborane, ½nido-7-ðCH 2 OHÞ -8-Me-7; 8-C 2 B 9 H 10   (2), as its potassium salt, in 91% yield [6]. The reaction pathway is shown in Scheme 1. Removal of the remaining bridging hydrogen on the open C 2 B 3 - face and that of the pendent hydroxymethyl group in 2 by the addition of two equivalents of n-BuLi in dry tetrahydrofuran (THF) at )78 °C resulted in the for- mation of a novel trianionic, constrained-geometry ansa-alkyloxocarborane ligand. The in situ generated trianionic ligand was further reacted with anhydrous MeMCl 3 (M ¼ Si, Ge), followed by re-crystallization from a toluene/heptane solution to produce the corre- Inorganic Chemistry Communications 5 (2002) 296–299 www.elsevier.com/locate/inoche * Corresponding author. Tel.: +1-815-753-3556; fax: +1-815-753- 4802. E-mail address: nhosmane@niu.edu (N.S. Hosmane). 1 On leave from Nankai University, People’s Republic of China. 1387-7003/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S1387-7003(02)00378-7