FULL PAPER DOI: 10.1002/ejic.200600701 Novel 1,2-Dicarba-closo-dodecaborane(12) Derivatives of Selenium Bernd Wrackmeyer,* [a] Zureima García Hernández, [a] Rhett Kempe, [a] and Max Herberhold [a] Keywords: Carboranes / Selenium / Platinum / Oxidative addition / NMR spectroscopy Lithiation of 1,2-dicarba-closo-dodecaborane(12) (1) followed by insertion of selenium into both C–Li bonds leads to the 1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion (3), which is converted by oxidative coupling into the cyclic eight-membered bis(diselane) 4 with annellated carborane moieties. Oxidative addition of 4 to ethenebis(triphenylphos- phane)platinum(0) gives the bis(triphenylphosphane)plati- num(II) complex 7, which contains a chelating 1,2-diselenol- Introduction An important aspect of the rich chemistry of 1,2-dicarba- closo-dodecaborane(12) (1) (“ortho-carborane”) is the varia- tion of substituents at the carbon atoms in the 1,2-posi- tions. [1,2] Most conveniently, this chemistry starts with me- tallation at the carbon atom(s), for example to form the dilithiated carborane 1,2-Li 2 -1,2-C 2 B 10 H 10 (2), followed by further transformations. [1,2] We and others became inter- ested in the 1,2-dichalcogenolato-1,2-dicarba-closo-dodeca- borane(12) anions [1,2-(1,2-C 2 B 10 H 10 )E 2 ] 2– (E = S, Se, Te) as chelating ligands, [3–10] and this chemistry has been fur- ther developed into various areas. [11–15] Tellurium deriva- tives are rarely studied since clean access to the anion [1,2- (1,2-C 2 B 10 H 10 )Te 2 ] 2– appears to be difficult. [16,17] However, the corresponding anions with sulfur or selenium are more readily accessible, and the anion containing selenium [1,2- (1,2-C 2 B 10 H 10 )Se 2 ] 2– (3) is particularly attractive consider- ing the useful NMR properties of 77 Se [18] (I = 1/2; natural abundance 7.58%; about three times more sensitive in NMR experiments than 13 C). In the present work, we re- port on observations of oxidative coupling of 3, or deriva- tives of 3, and cleavage of the resulting Se–Se bonds by oxidative addition to [Pt(PPh 3 ) 2 (CH 2 =CH 2 )]. Results and Discussion Formation of the anion [1,2-(1,2-C 2 B 10 H 10 )Se 2 ] 2– (3) and its conversion into the cyclic bis(diselane) 4 are shown in [a] Anorganische Chemie II, Universität Bayreuth, 95440 Bayreuth, Germany Fax: +49-921-552-157 E-mail: b.wrack@uni-bayreuth.de Eur. J. Inorg. Chem. 2007, 239–246 © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 239 ato-1,2-dicarba-closo-dodecaborane(12) ligand, by symmet- ric cleavage of the eight-membered ring in 4 and displace- ment of ethene. The molecular structures of 4 and 7 were determined by X-ray analysis. The solution-state structures of the new compounds are supported by multinuclear NMR data ( 1 H, 11 B, 13 C, 29 Si, 31 P, 77 Se, 195 Pt). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) Scheme 1. The reaction of 3 with an excess of Me 3 SiCl gave the disilylated derivative 5 in high yield along with a small amount of 1-Me 3 SiSe-1,2-C 2 B 10 H 11 (6) and unreacted car- borane 1, thus indicating the preferred conversion of 1 into 2, followed by double insertion of selenium into the C–Li bonds to give 3. In context with the chemistry of heterosub- stituted tropylium derivatives we have attempted to prepare a 1,2-bis(tropyliumseleno)-1,2-dicarba-closo-docecabor- ane(12) by cleavage of the Se–Si bonds. Surprisingly, the reaction of 5 with two equivalents of tropylium bromide, C 7 H 7 Br, gave 4 as the final product of a complex redox reaction together with the expected Me 3 SiBr and various organic compounds. The oxidative coupling of 3 with io- dine led directly to 4, as expected. Attempts to prepare a spirosilane from the reaction of 3 with SiCl 4 again gave 4 together with unidentified materials. The bis(diselane) 4 could be isolated as yellow crystals from benzene or toluene solutions and its molecular structure was determined by X- ray analysis (vide infra). Diselanes are known as reagents for oxidative addition reactions. [19] Thus, the reaction of [Pt(PPh 3 ) 2 (CH 2 =CH 2 )] with 4 was studied (Scheme 2). Monitoring of the reaction by 31 P NMR spectroscopy showed that the eight-membered ring in 4 was cleaved symmetrically to give the platinum(II) complex 7 in essentially quantitative yield. Orange crystals of 7 were isolated and studied by X-ray analysis (vide infra). Complexes of type 7 or their palladium analogues are po- tential catalysts of the cis-addition of the Se–Se bond to the CC bond in alkynes. [19c,19d] Addition of an excess of methyl iodide to a solution of 7 in dichloromethane led to cleavage of the Pt–Se bonds to give a mixture containing in the beginning cis-[PtI 2 - (PPh 3 ) 2 ], and the anionic complexes [PtI 3 (PPh 3 )] – and