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Inorganic Chemistry Communications 10 (2007) 125–128

Macropolyhedral boron-containing cluster chemistry:The reaction of syn-B18H22 with SMe2 and I2 in monoglyme:

Structure of [7-(SMe2)-syn-B18H20] q

Tomas Jelınek a,b, Bohumir Gruner a, Ivana Cısarova c, Bohumil Stıbr a, John D. Kennedy b,*

a The Institute of Inorganic Chemistry of the Academy of Sciences of the Czech Republic, 25068 Rez-u-Prahy, Czech Republicb The School of Chemistry of the University of Leeds, Leeds LS2 9JT, England, United Kingdom

c The Faculty of Natural Sciences of Charles University, Hlavova 2030, 12842 Prague 2, Czech Republic

Received 9 August 2006; accepted 29 September 2006Available online 6 October 2006

Abstract

The reaction of B10H14 with two-electron ligands L to give L2B10H12 is not mimicked by B18H22. Instead, an oxidizing agent isrequired to introduce a ligand onto the {B18} skeleton: thus deprotonation of syn-B18H22 in monoglyme followed by treatment withI2 and SMe2 gives [7-(SMe2)-syn-B18H20] (41%).q

� 2006 Elsevier B.V. All rights reserved.

Keywords: Borane cluster; Macropolyhedral; Ligand addition; X-ray structure; Oxidative addition of ligand; Ligand-borane complex; Fused clusters

The development of boron cluster chemistry significantlybeyond a cluster size limit of approximately 12–14 boronatoms [1] requires the development of fused-cluster ‘macro-polyhedral’ chemistry [2–4]. In many fused cluster species,although the architectures and electronic structures of theindividual subclusters are closely related to the architecturesand electronic structures of their single-cluster analogues,the reaction chemistry is often quite different to that of theirsingle-cluster analogues [5,6]. The two isomers of B18H22 arefused cluster nido 10-vertex: nido 10-vertex species, and theconstitutions, geometries and electronic structures of thenido 10-vertex subclusters closely relate to those of the 10-vertex single-cluster model nido-B10H14 [7,8]. A well-known

1387-7003/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.inoche.2006.09.020

q A IUPAC nomenclature for the new species 2 would be 7-(dimethyl-sulphide)-nido-decaborano-<50,6 0:5,6>-nido-decaborane. This article wasfreely submitted for publication without royalty. By acceptance of thispaper, the publisher and/or recipient acknowledges the right of theauthors to retain non-exclusive, royalty-free license in and to anycopyright covering this paper, along with the right to reproduce all orpart of the copyrighted paper.

* Corresponding author. Fax: +44 113 343 6401.E-mail address: j.d.kennedy@leeds.ac.uk (J.D. Kennedy).

reaction of nido-B10H14 is its very ready quantitative reac-tion with two-electron ligands L to give arachno speciesL2B10H12 (Eq. (1)) [9–11]. Under the same conditions, how-ever, the B18H22 isomers either (a) do not react, or (b) a sim-ple deprotonation occurs with stronger bases (Eq. (2)). Wenow report preliminary results, using the syn isomer ofB18H22 (compound 1, schematic connectivity as in I), thatshow that a ligand can be attached to the B18H22 clusterby the concomitant use of an oxidising agent, in this case ele-mental iodine. In principle a stoichiometry as in Eq. (3) suf-fices, but in practice we find that an initial deprotonation ofB18H22 by KH to give [B18H21]� gives a better result (Eq.(4)). The overall method has similarities to those reportedpreviously for the addition of single ligands to single-clusterspecies [12–14], in which oxidizing agents include aldehydesand anhydrous FeCl3 as well as elemental iodine

B10H14 þ 2L! L2B10H12 þH2 ð1ÞB18H22 þ L! LHþ þ ½B18H21�� ð2ÞB18H22 þ Lþ I2 ! LB18H20 þ 2HI ð3Þ½B18H21�� þ Lþ I2 ! LB18H20 þHIþ I� ð4Þ

126 T. Jelınek et al. / Inorganic Chemistry Communications 10 (2007) 125–128

Thus, syn-B18H22 (compound 1) (200 mg; 910 lmol) inanhydrous monoglyme (20 ml) was treated with NaH(60% suspension in mineral oil; 100 mg), stirred at ca.20 �C for 1 h, and then filtered. The filtrate was stirred withSMe2 (50 ml) and elemental I2 (260 mg; 1.04 mmol) for10 h at ca. 20 �C, and then heated at reflux for 12 h. Theresulting mixture was then evaporated in vacuo at ambienttemperature, the viscous residuum treated with CHCl3(20 ml) and filtered. Column chromatography on silica,using CHCl3 as the liquid phase, thence yielded a main(pale yellow) fraction, which had RF 0.54 by analyticalTLC on silica (Silufol, Kavalier, Prague; CHCl3). The vol-atile components were removed in vacuo at ca. 20 �C, andthe residual solid rechromatographed by preparative TLCon silica-gel G (Fluka, Type GF254, 1 mm layers) withpure benzene as liquid phase. The fraction with RF 0.38(benzene) was isolated and evaporated in vacuo, and puri-fied by diffusion crystallisation between hexane and a solu-tion in CH2Cl2 contained in a 5 mm o.d. NMR tube. Thisresulted in pale yellow crystals, which are characterised as[7-(SMe2)-syn-B18H20] (compound 2; Fig. 1) (104 mg,366 lmol; 41%), m.p. 192–193 �C; UV–VIS kmax(CH2Cl2)258 and 352 nm; (m/z)max 280, [12C2

1H2611B18

32S]+ requires280. The product was readily identified by NMR spectros-copy [15] and single-crystal X-ray diffraction analysis [16](Fig. 1; schematic connectivity as in II). Note that, in sche-

Fig. 1. Crystallographically determined molecular structure of [7-(SMe2)-syn-B18H20] (compound 2) [16]. Selected interatomic distances (in A) are asfollows: B(5/5 0)–B(6/6 0) 1.788(2), B(6)–B(7) 1.656(2), B(7)–B(8) 1.810(2),B(8)–B(9) 1.795(3), B(9)–B(10) 1.773(3), B(10)–B(5) 2.019(2), B(6 0)–B(70)1.789(2), B(7 0)–B(8 0) 1.969(2), B(8 0)–B(9 0) 1.787(2), B(9 0)–B(10 0) 1.773(2)and B(10 0)–B(50) 1.964(2); B(7)–S(1) is 1.8770(16), S(1)–C(1) is 1.795(2)and S(1)–C(2) is 1.788(2). Angles (in �) at S(8) are C(1)C(2) 101.1(1),C(1)B(7) 103.3(1) and C(2)B(7) 108.8(1).

matics I and II, large open circles represent {BH(exo)}units, small black circles represent bridging hydrogenatoms, and the symbols B represent boron atoms.

Compound 2 is seen to have the nido 10-vertex: nido 10-vertex geometry of the syn-B18H22 precursor species 1; inparticular, the nido character of both subclusters is retained.This contrasts with the ligand reaction with the nido 10-ver-tex single-cluster model B10H14, albeit without an oxidizingagent present (Eq. (1)), that results in an arachno species. In2 one subcluster (the one with primed numbering) is as incompound 1, and is essentially unperturbed in comparisonto 1; e.g. the characteristically longer nido-decaboranyl‘gunwale’ distances, at 1.964(2), and 1.969(2) A in 2, arepresent (compare 1.956(3)–2.002(3) A in 1 [7]). Theligand-substituted subcluster has the ligand at the B(7) posi-tion, next to the intercluster B(5/5 0)–B(6/6 0) interclusterfusion; the adjacent gunwale distance B(7)–B(8) is corre-spondingly shorter, at 1.810(2) A, similar to the value of1.830(3) A for the corresponding distance B(5)–B(10) inits single-cluster model 5-(SMe2)B10H12 [4], with the othergunwale remaining ‘long’ at 2.019(2) A. The distanceinvolved in the intercluster linkage, B(5/5 0)–B(6/6 0) at1.788(2) A, is within normal cluster interboron distancerange; that in compound 1 is 1.794(2) A [7]. Similaritiesbetween 1 and 2 are also manifest in NMR cluster shieldingpatterns. Compared to syn-B18H22 1, the overall cluster 11BNMR shielding pattern for the ligand species 2 is very sim-ilar, the principal perturbations being at the B(2), B(3), B(6/6 0) and B(8) sites adjacent to the substituted B(7) site, withshielding differences of ca. �9 , +6, �12 and +13 ppmrespectively relative to syn-B18H22. Interestingly, the substi-tuted B(7) site itself is not dramatically shifted, occurring atca. 7 ppm to lower shielding in 2 compared to 1.

The reluctance of the B18H22 isomers to undergo reac-tions analogous to that of B10H14 in the very facile processof Eq. (1) is of interest and merits comment. The B10H14

reaction engenders an arachno 10-vertex species L2B10H12

via an overall two-electron cluster reduction. Althoughthe loss of dihydrogen is a two-electron cluster oxidation,

T. Jelınek et al. / Inorganic Chemistry Communications 10 (2007) 125–128 127

the addition of two two-electron ligands results in a nettwo-electron gain. The ligand addition to B18H22, by con-trast, needs an oxidising agent to remove two electrons,and only one two-electron ligand is added, to giveLB18H20. Consequently, there is no net electron gain orloss, and the nido 10-vertex: nido 10-vertex character ofthe original syn-B18H22 cluster skeleton is retained. Theconstraints of the two-boron intercluster conjunction pre-sumably inhibit a molecular flexibility that permits the sin-gle-cluster reaction to proceed so readily. Here it may benoted that substantial cluster rearrangement has been iden-tified in the reaction of the substituted single-cluster nido

decaborane 1,2,4-Cl3B10H11 with SMe2 to give the arachno

species [6,9-(SMe2)2-1,2,7-Cl3B10H9] [9], and also that nido-B10H14 itself is known to scramble all its boron sites underbasic conditions [17]. An important general principle hereis that this inhibitory effect is likely to be quite general incomparative macropolyhedral reaction chemistry. Anothermanifestation of this inhibitory effect in this present reac-tion may be that in [7-(SMe2)-syn-B18H20] the ligand isfound at a ‘gunwale’ site of the decaboranyl ‘boat’, whereasin the formation of L2B10H12 the ligands are found at the6,9 ‘prow’ positions [8].

It is anticipated that the reaction is quite general. Wehave demonstrated it here using SMe2 and the syn isomerof B18H22 as a model system, but it is probably genericallyapplicable to other macropolyhedral species, as well asbeing equally useful for single-cluster work. Preliminaryresults suggest that other oxidising agents such as CuI2

and FeCl3 may also be used, but that choice of solvent iscritical: for example use of CH2Cl2 rather than monoglymegives a mixture of several products: we hope to be able toreport on this further work later, as well as any generalapplicability to other ligands.

Acknowledgement

Contribution no. 107 from the Rez-Leeds Anglo-CzechPolyhedral Collaboration (ACPC). We thank the GrantAgency of the Czech Republic (Grant no. 203/05/2646),the Grant Agency of the Academy of Sciences of the CzechRepublic (Grant no. IAA400320601), and the Ministry ofEducation of the Czech Republic (Project no. LC 523)for support, the Royal Society, the Academy of Sciencesof the Czech Republic, and the Royal Society of Chemistryfor assistance with travel, and the EPSRC (UK) for previ-ous contributions towards instrumentation.

Appendix A. Supplementary material

CCDC 616629 contains the supplementary crystallo-graphic data for this paper. These data can be obtained freeof charge via http://www.ccdc.cam.ac.uk/conts/retriev-ing.html, or from the Cambridge Crystallographic DataCentre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.Supplementary data associated with this article can be

found, in the online version, at doi:10.1016/j.inoche.2006.09.020.

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[2] J.D. Kennedy, in: W. Siebert (Ed.), Advances in Boron Chemistry,Royal Society of Chemistry, Cambridge, 1997, pp. 451–462.

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Academic, New York and London, 1975, pp. 79–174, Chapter 3.[12] A.R. Siedle, G.M. Bodner, A.R. Garber, L.J. Todd, Inorg. Chem. 13

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[15] NMR Data for [8-(SMe2)-syn-B18H20] 2, CD3CN, 294–299 K,ordered as tentative assignment d(11B)/ppm [d(1H)/ppm of directlybound H atoms {apparent splitting arising from 1J(11B-1H)/Hz}]:B(6/60) +22.3 [conjuncto position, no directly bound H(exo)], BH(30)+11.8 [+3.39] {145}, BH(10) +8.5 [+3.63] {150}, BH(1) and BH(100)near coincident at ca. +6.3 [+3.20 and +3.10] {both ca. 145; absolutesplitting values uncertain, overlapping peaks}, B(10) +3.6 [+3.53]{150}, B(9 0) +0.8 [+3.14] {160}, BH(80) �0.1 [+3.00], B(7) �7.5[prochiral substituted position, no directly bound H(exo), SMe2 at+2.79 and +2.67], BH(9) �7.9 [+2.85] {165}, B(5/50) �10.6 [conjuncto

position, no directly bound H(exo)], BH(3) �11.9 [+2.51] {145},BH(8) �12.4 [+2.26] {splitting not resolved}, B(7 0) �14.3 [+2.57]{155 and 35}, BH(2) �17.4 [+0.09] {155}, BH(20) �24.0 [�0.87]{155}, BH(40) �41.1 [+0.26] {155} and BH(4) �42.6 [+0.36] {155};with d(1H)/ppm for (l-H) (60,7 0) +0.14, (l-H) (9,10) �1.27, (l-H)(90,10 0) �1.79, (l-H) (80,9 0) �2.27 and (l-H) (8,9) �3.20; assignmentsby {11B–11B} and 1H–{11B} correlation work.

[16] X-ray crystallography. [7-(SMe2)-syn-B18H20] 2, C4H26B18S, M =276.87, monoclinic, space group P21/n (no. 14), a = 10.227(1) A,

128 T. Jelınek et al. / Inorganic Chemistry Communications 10 (2007) 125–128

b = 13.911(1) A, c = 13.343(2) A, b = 112.33(1)�, V = 1755.9(3) A3

(by least squares from 25 automatically centred diffractions with26 6 2h 6 28�), T = 293(2) K, graphite-monochromated Mo Karadiation, k = 0.71073 A, Z = 4, Dc = 1.047 Mg m�3, F(000) = 576,l(Mo Ka) = 0.157 mm�1, colourless prism, from hexane-CH2Cl2,dimensions 0.6 · 0.5 · 0.4 mm, Enraf-Nonius CAD4-MACHIII dif-fractometer, h–2h scan, data collection range �12 6 h 6 +11,0 6 k 6 +16, 0 6 l 6 +15 (2hmax = 50�), variation of three periodi-cally measured standard diffractions 1.5%; 3083 unique diffractionswere measured (Rint 0.011) and used in all calculations. The data werecorrected for Lorentz-polarization effects; the absorption wasneglected. The structure was solved by direct methods [SIR92: A.Altomare, M.C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A.Guagliardi, G. Polidori, J. Appl. Crystallogr. 27 (1994) 435] andrefined by full-matrix least squares on F2 [SHELXL97: G.M.

Sheldrick, Program for Crystal Structure Refinement from Diffrac-tion Data, University of Gottingen, 1997]. The weighting schemew ¼ ½r2ðF 2

oÞ þ ðw1P Þ2 þ w2P ��1, where P ¼ ½maxðF 2o; 0Þ þ 2F 2

c �=3,w1 = 0.073, w2 = 0.2264 was applied. All non-hydrogen atoms wererefined anisotropically. The hydrogen atoms were found on differencemap and refined isotropically, except those of methyl moiety, whichwere fixed into idealised positions (riding model) and assignedtemperature factors Hiso(H) = 1.5 Ueq(pivot atom), Final R = 0.035,R 0 = 0.103 for 2615 observed diffractions [I > 2r(I)] and R = 0.046,R 0 = 0.110 for all data; 273 parameters, largest D/r = 0.000, goodnessof fit 1.031, extremes on the residual electron density map +0.220 and�0.205 e A�3. CCDC 616629.

[17] See, for example, together with references therein D.F. Gaines, in: S.Hermanek (Ed.), Boron Chemistry (IMEBORON VI), World Scien-tific, Singapore, 1988, pp. 118–145.