Organometallics 1996,14, 4463-4464
4463
Synthesis and Structural Characterization of the First Pentucurbon Metallacarborane Complex: nido-2-(q W5H5)Fe-7-CHs=7,8,9,10,12-C~B~H 10 Beverly A. Barnum, Patrick J. Carroll, and Larry G. Sneddon" Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323 Received August 11, 1995@ Summary: The reaction of the arachno-6-(CH3C(O)CH2)5,6,7-C3B7H11- tricarbaborane monoanion with CpFe(C0)d yields the first example of a metallacarborane complex containing five cage carbon atoms: n i d o - 2 4 ~ ~ C5Hs)Fe-7-CH3-7,8,9,10,12- C&HIO (1). A single-crystal X-ray study established that, in agreement with its 28skeletal-electron count, the cage adopts a nido-type structure based on a 13-vertex docosahedron missing one six-coordinate vertex. All five carbons are situated on the open six-membered face and exhibit carbon-carbon and boron-carbon distances in the normal ranges found in metallacarboranes. The development of polyhedral carborane chemistry has been dominated by studies of the dicarbon cage systems, since these are the most readily accessible carboranes. The more recent syntheses of carborane clusters with higher numbers of cage carbons, including tri-1,3and tetracarbon4 carboranes, as well as their derived metallacarborane complexes, have demonstrated that a continuum of carboranes with increasing carbon compositions should be achievable. However, although such species have been long anticipated, no neutral5 carboranes or metallacarboranes with greater than four cage carbons have been synthesized. In this communication, we report the synthesis and structural characterization of the first such higher-carbon boron cluster, the pentacarbon metallacarborane complex
crystalline solid in 13%isolated yield.6 An exact mass determination on the parent ion and the IlB NMR spectrum, which showed only six intensity 1 doublets, indicated that loss of a "BOH" unit from the starting carborane cage had occurred upon formation of the complex. The lH NMR spectrum showed, in addition to cyclopentadienyl and methyl resonances, four intensity 1 singlets with line widths and chemical shifts consistent with cage-carbon C-H resonances. A singlecrystal X-ray study confirmed that 1 was indeed a pentacarbon ferracarborane complex, with the structure shown in the ORTEP drawing in Figure l.7 Consistent with its 28-skeletal-electron count, the cage adopts an open nido-type structure, based on a 13-vertex docosahedron missing one six-connected vertex, similar to those found for other isoelectronic 12vertex cage systems, including 2-(v5-C5H5)Fe-1,7,8,9( C H ~ ) ~ C ~ B ~2,4-(~5-C5H5)2C~~-7,10,11,12-C~B6Hl~,g HS,' and 2-(v5-C5H5)Co-7,9,11,12-(CH3)&4B7H7.10 The sixmembered open face of the cage contains the five carbon atoms and one boron atom, with all four of the four~~~
~
(3)(a) Stibr, B.; Holub, J.; Teixidor, F.; Virias, C. J . Chem. SOC., Chem. Commun. 1995, 795-796. (b) Shedlow, A. M.; Carroll, P. J.; Sneddon, L. G. Organometallics 1995, 14, 4046-4047. (c) For references to older tricarbaboranes, see footnotes 3-8 in ref 2b above. (4) (a) Grimes, R. N. Adv. Inorg. Chem. Radiochem. 1983,26, 55115 and references therein. (b) Grimes, R. N. Acc. Chem. Res. 1978, 420-427 and references therein. (5) The monoboron pentacarbon cation [l-RBC5(CH3)51' has been nid0-2-(~~-C5H5)Fe-7-CH3-7,8,9,10,12-C5B6H10 (1). synthesized and structurally characterized. See: (a) Jutzi, P.; Seufert, The complex was isolated along with the parent A. J . Organomet. Chem. 1978, 161, C5-C7. (b) Jutzi, P.; Seufert, A.; Buchner, W. Chem. Ber. 1979, 112, 2488-2493. (c) Dohmeier, C.; derivatives of two known ferratricarbaborane comKtippe, R.; Robl, C.; Schnockel, H. J. Organomet. Chem. 1995, 487, plexes,2 2 and 3, from the reaction of the arachno-6127-130. (6) Spectroscopic data: llB NMR (160.5 MHz, CDzC12) d 9.5 (d, B6, ( C H ~ C ( O ) C H Z ) - ~ , ~ , tricarbaborane ~ - C ~ B ~ H ~ ~monoJBH= 135 Hz), -1.6 (d, B3, JBH= 1531, -10.1 (d, B4, JBH= 161), anionlb,cwith CpFe(C0)zI as shown in eq 1. -18.4 (d, B11, JBH= 145), -21.8 (d, B5, JBH= 1441, -33.8 (d, B1, JBH = 143); two-dimensional llB-llB NMR established the connectivities Bl-B3. Bl-B4. Bl-B5. Bl-B6. B3-B4 (weak). B4-B5. B5-B6. B5K+(urachno-6-(CH3C(O)CHz)-5,6,7-C3B7Hll~) B11, B6-Bll (weak); 13C(lH} NhfR (50.3'MHz, CDzClz, -60 "C) h 94.8 (C7), 80.4 (Cp), 38.9 (cage-CH), 34.6 (cage-CHI, 29.5 (cage-CHI, 28.9 (q5-C5H5)Fe(C0)21 (cage-CH),18.0 (CH3);'H{"B} NMR (200 MHz, CD2Clz) b 4.52 (s,5H, CD).3.65 (br s, 1H, BH), 3.04 (br s. 1H. BH), 2.76 (s. 3 H. CH3), 2.66 nido-2-(q5-C5H5)Fe-7-CH3-7,8,9,10,12-C5B6Hlo -k (6r s, l H , CH), 2.12 (br s, l H , CH), 1.57 (br s, l H , BH), 1.38 (br s, l H , BH), 1.16 (br s, 2H, BH), 1.07 (br s, l H , CH), 0.88 (s, l H , CH); HRMS 1 (CI-) calcd for 1~Cl11Hl~11B~56Fel 272.1316, found 272.1318; mp 153 cZoso-1-(q5-C5H5)Fe-2,3,4-C3B7Hlo "C; IR (NaC1 windows, CC4) 3040 (m), 2975 (m), 2898 (w), 2840 (w), 2530 (8,br), 2295 (w), 1415 (w), 1370 (w), 1260 (s), 1115 (vw), 1080 2 1000 (w), 990 (sh), 985 (vw), (w), 1055 (vw,br), 1030 (w), 1018 (vw), commo-Fe-(2,3,4-C,B7H,,), (1) 925 (w) 855 (w), 840 (w), 740 (m, br). (7) Structural data: space group P1 (No. 2) a = 7.7398(6) 8, b = 3 12.9563(7) A, c = 6.8563(3) 8, v = 642.73(7) A3, = 2, and Dealcd= 1.404 g/cm3. The structure was solved by direct methods (SIR92). Refinement was by full-matrix least-squares techniques based on F to Separation by thin-layer chromatography (silica gel/ minimize the quantity ZW(lF,I with w = l/d(F). Non-hydrogen hexane-CHzClz (5:3),Rf 0.48)gave 1 as a red-pink atoms were refined anisotropically, and hydrogen atoms were refined isotropically, except for the cyclopentadienyl hydrogens, which were included as constant contributions to the structure factors and were Abstract published in Advance ACS Abstracts, September 15,1995. not refined. Refinement converged to R1 = 0.0327 and Rz = 0.0368. (1)(a) Kang, S. 0.; Furst, G. T.; Sneddon, L. G. Inorg. Chem. 1989, (8)Maxwell, W. M.; Bryan, R. F.; Grimes, R. N. J.Am. Chem. SOC. 28,2339-2347. (b) Su, K.; Barnum, B.; Carroll, P. J.; Sneddon, L. G. 1977,99,4008-4015. J . Am. Chem. SOC.1992, 114, 2730-2731. (c) Su, K.; Carroll, P. J.; (9) Wow, K.-S.; Bowser, J. R.; Pipal, J . R.; Grimes, R. N. J. Am. Sneddon, L. G. J . Am. Chem. SOC. 1993,115, 10004-10017. Chem. Soc~1978,100,5045-5051. (2) (a) Plumb, C. A.; Carroll, P. J.; Sneddon, L. G. Organometallics (lO)Maynard, R. B.; Sinn, E.; Grimes, R. N. Inorg. Chem. 1981, 1992, 11, 1666-1671. (b) Plumb, C. A,; Carroll, P. J.; Sneddon, L. G. 20, 1201-1206. Organometallics 1992, 11, 1672-1680.
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Q276-7333/95/2314-4463$Q9.QQlQ0 1995 American Chemical Society
Communications
4464 Organometallics, Vol. 14,No. 10, 1995
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CpFe(CO)21
d Figure 1. ORTEP drawing of the molecular structure of nido-%(~)~-CsH Fe-7-CH3-7,8,9,10,12-CaBsH10 (1). Selected bond lengths ( ) and angles (deg): C7-C8, 1.441(4);C8C9, 1.543(4);C9-Cl0, 1.525(4);C10-B11, 1.571(4);B11C12, 1.645(4);C7-Cl2, 1.423(4);C7-Fe2, 1.989(2);C8Fe2, 2.135(3);C12-Fe2, 2.106(3); B3-Fe2, 2.128(3); B6Fe2, 2.158(3); B1-Fe2, 2.165(4); C8-C7-C12, 117.2(2); C9-C10-B11, 121.33); C7-C8-C9, 120.8(2); C8-C9C10, 115.9(3); C10-B11-C12, 113.3(3); B l l - C l 2 4 7 , 117.0(3).
i
coordinate carbon atoms and one boron atom forming a plane. The unique three-coordinate methyl-substituted carbon atom, C7, is distorted out of this plane by 0.46 A. Given the high carbon content of the cage, deviation from the nonclassical bonding observed in the polyhedral boranes to a more classical organic structure might be expected; however, all of the intracage distances and angles are in the normal ranges observed in metallacarborane clusters. That all five cage carbon atoms are on the open face is consistent with the well-known preference of carbon atoms to occupy lower coordinate vertices in carborane clusters,ll and, indeed, no further carbon skeletal rearrangements for 1 were observed even upon heating a sample to 240 "C in uacuo. Consistent with the carbon bonding interactions with the iron atom, the distances between the three carbon atoms C7, C8, and C12 are somewhat shortened (C7C8, 1.441(4)A;C7-C12,1.423(4) A) compared to those between the non-metal-coordinated C9 and C10 carbon atoms (Cg-ClO, 1.525(4) A; C9-C8, 1.543(4) A. The iron atom occupies a six-coordinate position bound to three carbon atoms and three boron atoms. Again, five of the ring atoms form a plane with the C7 carbon atom distorted out of this plane 0.35A toward the iron atom. As a consequence, the Fe-C7 distance (1.989(2) A) is shortened relative to Fe-C8 (2.135(3) A) and Fe-C12 (2.106(3) A), as well as in comparison to the Fe-B1, -B3, and -B6 distances. The cyclopentadienyl ring and the C8-B3-Bl-B6-C12 plane are parallel (dihedral angle 3.1'1, with the iron atom sandwiched between the two planes (1.69 and 1.40 A, respectively). (11)Williams, R. E . Adu. Inorg. Chem. Radiochem. 1976,18, 67142.
1
Figure 2. Possible reaction sequence leading to the formation of nido-2-(~)~-C~HdFe-7-CH3-7,8,9,10,12-C5BsHlo (1). Although the mechanism for the formation of 1 is not yet known, a comparison of the compositions and structures of the starting arachno-6-(CH3C(O)CH2)5,6,7-C3B~Hll-anion and 1 suggests that the carbon atoms of the ketone side chain of the anion become incorporated into the final cage structure of 1. When the reaction was monitored by llB NMR, it was found that the arachno-6-(CH3C(O)CH2)-5,6,7-C3B7Hllanion readily converts to the nido-6-(CH3C(O)CHz)-5,6,9C3B7H9- anion. Subsequent reaction of the ketone oxygen with a boron atom on the open face of the cage of this anion, followed by cyclization of the carbon framework in the manner shown in Figure 2, could, in fact, generate the structure observed for 1 in a straightforward fashion. Such a process may be metal-promoted, since control reactions carried out in the absence of CpFe(C0)21showed no evidence of pentacarbon cage products. We are now investigating the detailed mechanism of this reaction, as well as the development of new routes for the synthesis of even higher-carbon carboranes and metallacarboranes that may provide more links between the polyhedral carboranes and classical carbon cage compounds. Acknowledgment. We thank the National Science Foundation for support of this work. SupportingInformation Available: Tables listing atomic coordinates,bond distances and angles, least-squaresplanes, and thermal parameters for 1 (10 pages). Ordering information is given on any current masthead page. OM950638X
