Polyhedmn Vol. I, No. 1, pp. 11-82. 1982 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA az77-5387182/010017-&so3.03/0 Printed in Great Britain. Pergamon Press Ltd. zyxwvutsrq SYNTHESIS OF r-(ARENE)METALLOCARBORANES CONTAINING IRON AND RUTHENIUM. CRYSTAL STRUCTURE OF 3,l ,2-($-1,3$(CH,),C6H,)FeC2B,H1, TIMOTHY P. HANUSA, JOHN C. HUFFMAN and LEE J. TODD* Department of Chemistry, Indiana University, Bloomington, IN 47405, U.S.A. zyxwvutsrqponmlkjihgfedcbaZ (Received 8 June 1981) Abstract-The reaction of bis(arene)iron(II) salts (arene = mesitylene or hexamethylbenzene) or benzene- dichlororuthenium(I1)dimer with Tl[3,1,2-TlC$BsH,t] in THF produces neutral, air-stable r-(arene)(Fe, Ru)&B&, complexes in low or moderate yields. The metallocarboranes are formal analogues of [a-(arene)(Fe, Ru)“+(C,Hs)] species, and a single crystal X-ray structure of the title compound has established the doso sandwich geometry expected for the molecule on the basis of electron counting rules. The carborane cage was found to be disordered in the crystal but the essential features of the molecular geometry were not obscured. The mesitylene is symmetrically bound to the iron, and the Fe-arene (centroid) distance of 1.6OA is similar to that found in the previously-characterized [(CH&,C~]Fe*(CrHs) complex, despite the difference in the metal electronic configurations (d* vs d’) and the change from the B&H:, cage to &HJ-. Crystals of 3,1~-(8*-lSJ~CH3~C6H3FeC*B~H,, are orthorhombic, space group PnZta, with a = 12.638(4), b = 12.432(4), c = 9.686(3) A. INTRODUCTION The remarkable structural and electronic similarities be.- tween the cyclopentadienide anion (Cp-) and the five- membered open face of the undecahydro - dicarba - nido - undecaborate(2)dianion (B&H:;) have long been recognized.‘-3 Even though recent theoretical analyses have suggested that the carborane moiety is not a pure r-electron donor to transition metals,’ it can often sub- stitute isoelectronically for one or more a-cyclopen- tadienyl ligands in a metal complex. In some cases, the presence of the carborane cage enhances the thermal or hydrolytic stability of the complex: or stabilizes the metal in a higher formal oxidation state than that in a Cp analogue.* In recent years the study of mixed-sandwich transition metal compounds of the type [(arene)Fe”‘(Cp)] has provided numerous insights into the electronic and steric controls governing the synthesis and reactivity of metal- arene complexes.7-9 The increasing interest being expressed in such systems should logically extend to the related [(arene)M”+-C2B9H,,] (M = Fe, Ru, OS) species as well. No a--(arene)-carborane metal complexes con- taining “free” arene ligands have been reported in the literature,” however, although their likely existence was predicted soon after the discovery of the first metallo- carboranes.‘3 Whether only the requisite synthetic pro- cedures were lacking, or whether an inherent instability of such complexes precluded their isolation, was not apparent at the beginning of our studies. We have, however, been able to prepare several ?r- (arene)MC2B9H1, complexes containing iron and ruthenium, and have obtained crystals of 3,1,2-(n*-1,3,5- (CH3)3C6H3)FeC2B9H11 which were suitable for X-ray analysis. A low-temperature structural determination was then completed, both to contirm the close sandwich geometry anticipated for the complex, and to establish general structural parameters to be expected in this new class of metallocarboranes. *Author to whom correspondence should be addressed. EXPERIMENTAL Physical measurements Boron (“B) NMR spectra were obtained at 70.6 MHz with a Varian HR-220 spectrometer and were externally referenced to BF3G(C,HJh (positive values downfield). Proton NMR spectra were recorded on either a Varian HR-220 or a Varian TdOA spectrometer and were referenced to internal Me’Si. IR spectra were obtained as KBr disks using a Perkin-Elmer 283 spec- trometer. Low resolution mass spectral data were collected on a Varian CH-7 spectrometer. High resolution mass spectral data were obtained on a Hitachi Perk&Elmer RMH-2 spectrometer interfaced to a Kratos DSSOS data system at the University of Pennsylvania, Philadelphia, Pennsylvania. Melting points were determined in sealed, evacuated capillaries and are uncorrected. Elemental analysis was performed by Schwarzkopf Micro- analytical Laboratories, Woodside, New York. Materials All reactions were performed under an atmosphere of pre- purified nitrogen. Tetrahydrofuran (THF) was freshly distilled from sodium betuophenone ketyl. The bis(arene) iron salts.“.” benxenedichlororuthenium dim&,‘* and ‘Tl[3,1’2-TlCzB9H~,]17 were prepared according to literature methods. All other com- mercially-available reagents were used as received. Preparation of 3,1,% [ $1 JS-(CHJ)IC6HI]FeC2B9H11 To a slurry of bis(mesitylene)iron hexatktorophosphate, (l&5- (CH3)3C6H3)2Fe(PF&‘6 (1.99 g, 3.4 mmole) in dry tetrahydro- furan (50 mL) was added Tl[3,1,2-TICzBgHu] (0.61 g, 1.13 mmole) with stirring. The reaction mixture developed a dark red color within I5 set after the addition of the thallium salt. Stirring under nitrogen was continued for 5 hr at room temperature, after which the reaction was opened to the air and silica gel (0.5g, 60-200 mesh) added. The solvent was removed in uacuo and the solids chromatographed on a short (- 13cm) silica gel column packed under benzene. Elution with benzene produced an orange band; enrichment of the eluent with CH& and finally acetonitrile yielded a dark purple-red band. Removal of the solvent from the orange fraction yielded 3,12-[~*-1SJ_(CH,),C6HIIFeC2B9HII. Recrystallization from CH&/hexanes produced orange crystals (30 mg, 9%). m.p. 249 251”C(dec). The proton NMR spectrum (220MHz, CDCI,) con- tains sharp singlets at S 566(3H) and 2.40(9H), and a broad resonance at 6 3.4(2H).The IR spectrum includes absorptions at 3346(w), 2568(vs, br), 1539(w), 1455(m), 1377(m), 1305(w), POLY Vol. 1. No. I-F 77