Dalton Transactions Oxidation of Germa - and Stanna -closo -dodecaborate Journal: Dalton Transactions Manuscript ID: DT-ART-01-2015-000099.R1 Article Type: Paper Date Submitted by the Author: 26-Jan-2015 Complete List of Authors: Wesemann, Lars; University of Tuebingen, Institut fur Anorganische Chemie Gädt, Torben; University of Tübingen, Dimmer, Lörg-Alexander; University of Tübingen, Fleischhauer, Sebastian; University of Tübingen, Frank, Anita; University of Tübingen, Nickl, Claudia; University of Tübingen, Wütz, Tobias; University of Tübingen, Eichele, Klaus; University of Tübingen, Page 1 of 8 Dalton Transactions Oxidation of Germa- and Stanna-closo -dodecaborate Torben Gädt, a Jörg-Alexander Dimmer, a Sebastian Fleischhauer, a Anita Frank, a Claudia Nickl, a Tobias Wütz, a Klaus Eichele, a and Lars Wesemann a* Table of contents entry 2– 2– Oxidation of group 14 heteroborates [GeB 11 H11 ] and [SnB 11 H11 ] yields a symmetrical dimer exhibiting a Ge–Ge bond or an unsymmetrical dimer bearing an Sn–B bond. Dalton Transactions Page 2 of 8 Journal Name RSC Publishing ARTICLE Oxidation of Germa- and Stanna-closo -dodecaborate [a] [a] [a] Cite this: DOI: 10.1039/x0xx00000x Torben Gädt, Jörg-Alexander Dimmer, Sebastian Fleischhauer, Anita Frank, [a] Claudia Nickl, [a] Tobias Wütz, [a] , Klaus Eichele, [a] and Lars Wesemann [a]* 2– 2– The oxidation of closo -heteroborates [GeB 11 H11 ] and [SnB 11 H11 ] is presented. Upon Received 00th January 2012, oxidation germa-closo -dodecaborate yields a symmetrical dimer exhibiting a Ge–Ge bond Accepted 00th January 2012 between two clusters. This dimer shows sulphur insertion into the Ge–Ge bond at room DOI: 10.1039/x0xx00000x temperature. In contrast, oxidation of the homologous tin cluster results in an unsymmetrical dimer bearing an Sn–B bond between two clusters. The Sn–B dimer is also the product of the www.rsc.org/ hydride abstraction reaction. In the presence of the donor ligand 2,2´-bipyridine, the oxidation 2– of closo -cluster [SnB 11 H11 ] leads to the Sn(IV)-half sandwich coordination compound [bipy- SnB 11 H11 ] which dissolves in DMSO to give the Sn(IV)-adduct [bipy(DMSO)-SnB 11 H11 ]. Introduction Heteroborane cluster chemistry is an active field of research and many interesting studies have been published in recent years. 1-10 In heteroborane clusters a BH vertex of a borane cluster skeleton is replaced by a main group element or a transition metal. Following the isolobal principle a BH unit can for example be substituted by a Ge atom or an anionic BH – unit by an N atom respectively. 11-13 In these cases the resulting heteroboranes do not have a substituent but a lone pair at the vertex of the heteroelement and therefore can potentially act as a Lewis base. For more than ten years we have been interested Chart 1 Two oxidation products of stanna-closo -dodecaborate in the chemistry of group 14 heteroborane clusters carrying an (Sn´= [SnB 11 H11 ]). unsubstituted group 14 element like germanium or tin.14 The monoheteroborane and diheteroborane clusters are the focus of In this heterocubane type structure three oxygen atoms coordinate at each tin vertex and the tin atom exhibits a very our investigations with respect to synthesis, ligand properties in 119 13-22 small isomeric Sn Mössbauer shift indicating the oxidation coordination chemistry and reactions with chalcogenes. 2- Besides their chemistry the NMR spectroscopical properties in state IV. In the case of the reaction of the cluster [SnB 11 H11 ] with iodine at –78°C we found oxidative addition of the solution and in the solid state were also explored. Furthermore 24 the Mössbauer spectroscopy results of the tin clusters and their halogen at the tin vertex of the cluster. In this manuscript we derivatives were published.23 Due to the low oxidation state II present oxidation chemistry of germa- and stanna-closo - 2– dodecaborate leading to unexpected Sn–B bond formation in of the group 14 elements in the clusters [GeB 11 H11 ] and 2– the case of the tin cluster. [SnB 11 H11 ] we started to study oxidation reactions of these closo -heteroborates. The oxidation of the stanna-closo - 2– dodecaborate [SnB 11 H11 ] with typical oxidation agents like Results and discussion hydrogen peroxide and iodine was investigated several years ago. 23, 24 The dianionic tin cluster [SnB H ]2- reacts with In order to investigate the oxidation of germa-closo - 11 11 2– hydrogen peroxide to give a tetrameric oxide K8[(OSnB 11 H11 )4] dodecaborate [GeB 11 H11 ] we reacted a sample of the salt 1 (Chart 1).23 with various oxidizing agents like hydrogen peroxide, iodine and ferrocenium hexafluorophosphate (Scheme 1). This journal is © The Royal Society of Chemistry 2013 J. Name ., 2013, 00 , 1-3 | 1 Page 3 of 8 Dalton Transactions ARTICLE Journal Name Scheme 1 Oxidation of germa-closo -dodecaborate, a: I 2, b: 2 product 3 was isolated as colourless crystals. In Figure 2 the [Cp 2Fe][PF 6]. structure of the dianion in the solid state together with selected interatomic distances and angles is shown. We were not able to characterize the product of the reaction of closo -cluster 1 with hydrogen peroxide. The 11 B NMR spectrum shows a new substance but due to the lack of crystalline material we cannot identify the composition of the product. However, in the case of the reaction with iodine or ferrocinium hexafluorophosphate the dimeric oxidation product 2 was formed quantitatively and isolated as colourless crystals (Scheme 1). The molecular structure together with selected interatomic distances is presented in Figure 1. 25 In the solid Scheme 2 Insertion of sulphur into the Ge–Ge bond of 2. state structure of 2 we found two independent dimeric germaborate salts with one dianion lying on a centre of symmetry. Therefore we can discuss two independent Ge–Ge distances. Fig. 2 Molecular structure of the sulphur insertion product 3 in the solid state (ellipsoids set at 50% probability). Tributylmethyl ammonium cations are omitted for the sake of clarity. Selected bond lengths [Å] and angles [°]: Ge1–B1 2.088(3), Ge1–B2 2.090(3), Ge1–B3 2.093(3), Ge1–B4 2.093(3), Ge1–B5 2.096(3), Ge1–S 2.178(1), Ge2–S 2.185(1), Fig. 1 Molecular structure of the oxidation product 2 in the Ge1–S–Ge2 105.05(3). solid state (ellipsoids set at 50% probability, distance in the second molecule in brackets). Tributylmethyl ammonium The observed Ge–S separations of 2.178(1) and 2.185(1) Å are cations are omitted for the sake of clarity. Selected bond slightly longer than the Ge–S bond characterized in the sulphur lengths [Å]: Ge1–B2 2.086(2), Ge1–B3 2.087(2), Ge1–B4 adduct [H B Ge–S] 2– of 2.102(1) Å. The found Ge–S–Ge 2.094(2), Ge1–B5 2.098(2), Ge1–B6 2.100(2), Ge1–Ge2 11 11 structural motive is known in the literature from a variety of 2.329(1) [2.340(1)]. cyclic Ge-S structures but should only be compared with molecules showing a related sulphur bridge between two To our surprise the observed Ge–Ge bond lengths of 2.329(1) germanium moieties. These examples show longer Ge–S bond [2.340(1)] Å are in the range of reported double bond values: lengths and a comparable Ge–S–Ge angle: [S(Ge{CH 2Ph} 3)2] 2.347(2) Å [Ge 2R4] [R = CH(SiMe 3)2], 2.3026(3) Å [Ar´HGe] 2 i 2.235(21) Å, 111.0°; [S–(GePh 3)2] 2.212(1), 2.261(1), 2.227(2), [Ar´= C 6H3-2,6(C 6H3-2,6- Pr 2)2], 2.3173(3) Å [Ge(R)C 6H3-2,6- 26-28 2.240(2) Å, 111.2(1), 110.7(1)°; Trip ] (R = Me, Et, Ph, Cl). For the interpretation of the 2 2 [{Ge(S)[N(SiMe )C(Ph)C(SiMe )(C H N- )]} S] 2.222(3), Ge–Ge bond length we use arguments of quantum chemical 3 3 5 4 2 2 2.226(3) Å, 101.4(1)°; [S(Ge{ButC(NAr)} ) ], (Ar = 2,6- investigations which were published in the case of the 2 2 iPr C H ) 2.2512(14), 2.2626(14) Å, 101.37(6)°; chalcogen compounds of stanna- and germa-closo - 2 6 3 23, 29 [S{Ge(NSiMe Ar)} ] (Ar = C H (CHPh ) Me-2,6,4) 2.2854(8), dodecaborate. The Ge–Ge bonding interaction is mainly a 3 2 6 2 2 2 2.2869(8) Å, 98.21(3)°. 30-34 single bond which might be enhanced as bonding and antibonding contributions of filled π and π* orbitals do not In analogy to the oxidation of the germanium cluster 1 the cancel exactly. As discussed in the chalcogen adducts, some of reaction of the homologous tin cluster [SnB H ]2– with the the π* orbitals might be slightly pushed away from the Ge atom 11 11 ferrocinium salt [Cp Fe][PF ] was also investigated. To our in the direction of the cluster skeleton. In this fashion the radial 2 6 surprise we did not isolate a homologous dimer showing a Sn– antibonding character of these orbitals is weakened and the 23, 29 Sn bond from this reaction. Instead a dimer exhibiting a Sn–B bond is strengthened. This type of delocalization of the bond was formed (Scheme 3). Dimer 5 was characterized by antibonding orbitals on the borane cluster skeleton could be the elemental analysis, mass spectrometry and heteronuclear NMR reason for the short Ge–Ge bond although electrostatic spectroscopy.