3090 limation at 80" onto a 0' cold finger; 46 mg (92%) of 2-(v-C5H5)-2- eluted with hexane gradually enriched with dichloromethane. Co-l,6-GB7H, was obtained. The bands that were separated were, in order of elution, 4-(v-CsHb)Rearrangement of 2-(ll-CsHa)-2-Co-1,6-C2&H~. A solution of' 4-Co-1,l3-C2BloHl2 (trace), 4-(&bH5)-4-Co-1,8-C2B10H12 (0.158 50 mg of 2-(q-CbH5)-2-Co-1,6-C2B~Hg in 5 ml of decane was heated g, 60%), and 4-(17-CbHS)-4-Co-1,7-CzB1~HI2 (0.101 g, 37%). If the at the reflux temperature for 4 hr. Column chromatography of rearrangement were performed in benzene at the reflux temperature the reaction mixture on silica gel eluted with hexane afforded a for 24 hr, only one band, consisting of 4-(q-CsH5)-4-Co-l,13yellow band. The solvent was removed and a yellow solid was CPBIOHI~ (71 %), was isolated. sublimed at 70" to a 0" probe. 2-(~-C&15)-2-Co-l,10-C~B7H9, 38 Kinetic Methods. Kinetic runs at temperatures less than 60" mg (76%), was isolated. were carried out in a constant temperature water bath. Others were carried out in an apparatus where a chamber containing the Rearrangement of 2-(o-CsH5)-2-Co-l,7-Cz&Hg. A 40-mg sample sample solution was suspended in a reservoir of refluxing liquid. of 2-(~-CsH5)-2-Co-1,7-C2B1H, was heated for 15 min in 5 ml of A constant temperature of ~ t 0 . 0 5 "could be maintained within the hexadecane at the reflux temperature. Column chromatography sample chamber. removed the hexadecane and the rearrangement product was eluted Kinetic data for the rearrangement of 2-(q-C:H&2-Co-6,9and further purified by thick-layer chromatography. The product C2B,Hgto 2-(~-CjH5)-2-Co-1 ,6-CzB7Hgwere obtained by monitorwas sublimed at 70" to a 0" cold finger yielding 20 mg (50%) of ing the increase in absorbance at 504 nm. In all other runs, ali24 v-CsH5)-2-Co-I,1 O-CZB~H,. quots were withdrawn from the samples at appropriate time interRearrangement of 2-(rl-CsH5)-2-Co-3,1O-C~B7Hg.. A 100-mg vals and injected into a high-pressure liquid chromatograph.28 sample of ~ - ( & ~ H ~ ) - ~ - C ~ - ~ , I O - was C Z Bheated , H ~ in 7 ml of reThe absorbance of reactant and product was determined using a fluxing hexadecane for 5 hr. Column chromatography followed 280-nm uv detector and a strip-chart recorder. Individual peak by sublimation at 70" to a -78" probe yielded 85 mg (85%) of areas were measured with a planimeter and, after corrections were 2-(?-CsHi,)-2-Co-l,lO-C2B7Hg. made for differences in extinction coefficients at 280 nm, the conRearrangement of 2-(11-CsH5)-2-Co-4,5-C2BsHs. A solid sample centration of each component was calculated. Plots of the log of was placed in an nmr tube which of 2-(7pC5H5)-2-Co-4,5-CZB& the concentration of the reactants as a function of time gave firstwas then immersed in cyclooctane at the reflux temperature for 5 order rate constants. Activation parameters were calculated from hr. CDClowas added to the tube, and the lH and llB nmr spectra plots of In k 1;s. l/Tusing three temperatures for each reaction. identified the product as 2-(11-CsH5)-2-Co-4,6-C~BsH88. Rearrangement of ~ - ( T & H ~ ) - ~ - C O - ~ , ~ - C ~ BAK , H 0,268-g ,~. Acknowledgment. This work was s u p p o r t e d by the sample of 4-(~-C5H5)-4-Co-1,7-C2BloH1~ was added to 20 ml of National Science Foundation Grant GP-36451X. hexane and heated to the reflux temperature for 15 hr. The products were separated by column chromatography using silica gel (28) W. J. Evansand M. F. Hawthorne, J . Chromatogr., 88,187 (1974).
Direct Insertion of Transition Metals into Polyhedral Carboranes. Structurally Novel Mono-, Di-, and Trimetallic Small Cage Systems Vernon R. Miller, Larry G . Sneddon, Don C. Beer, and Russell N. Grimes"
Contribution from the Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901. Received December 18, 1973 Abstract: Metallocarboranes of iron, cobalt, a n d nickel have been prepared by the direct reaction of the small polyhedral carboranes 1,5-CzB3H5,1,6-C2B4H6,or 2,4-C2B5H7with organometallic reagents i n the gas phase o r in solution, without the use of a prior cage-opening step. The novel six-vertex cages (CO)sFeC2B3HSa n d (~&sHb)C O C Z B ~ H Sa s, well as the seven-vertex species (C0)6Fe2C2BaH5a n d (&6H6)2C02C2B3H5, were obtained from C2B3H5 a n d Fe(CO)5 or ( ~ - C , H , ) C O ( C O )in ~ the gas phase a t elevated temperatures. Reactions of these metal reagents or (s-CzH4)Ni[P(CsH&I2 with C2B4H6gave primarily seven-vertex monometallocarboranes containing a n MC2B4cage. The cobalt reagent and C2B5H7gave mono-, di-, a n d trimetallocarborane species, including two isomers of the novel ( T & , H ~ ) ~ C O ~ Csystem. ~ B ~ H ~Nickel a n d iron monometallocarboranes of seven or eight vertices were obtained f r o m C2B5H7by analogous processes. The direct reaction of 1, ~ - C Z B I ~aH n dI ~( + ~ H ~ ) C O (CO), a t 300" gave a mixture of cobaltacarboranes which were predominantly isomers of (q-C5H5)CoC2B9Hll. Molecular structures were assigned t o the new compounds o n the basis of 1lB a n d lH nmr spectra. Fine structure in the carborane CH iH nmr signals exhibited by several of the cobaltacarborane species was interpreted o n the basis of H-C-B-H proton-proton coupling.
f many reported syntheses metallocarbor0 anes,' nearly are variations on one or the other of two basic themes: insertion of a metal atom of
the
all
(1) into a neutral open-cage (nido) carborane, or ( 2 ) t h e opening of a closed polyhedral (closo) carborane framew o r k to create a n i d o - c a r b o r a n e anion f o l l o w e d by the incorporation of a m e t a l into the open face. The
(1) Recent reviews: (a) M. F. Hawthorne, Pure Appl. Chem., 33, 475 (1973); (b) M. F. Hawthorne and G. B. Dunks, Science, 178, 462 (1972); (c) F. R. Scholer and L. J. Todd, Prep. Inorg. React., 1 (1971); (d) R. N. Grimes, "Carboranes," Academic Press, New York, N. Y., 1970.
first method has b e e n useful i n l i m i t e d a p p l i c a t i o n s , e.g., the synthesis of small m e t a l t o c a r b o r a n e s from nido-2,3-C2B4Hs,2+ but cannot be c o n s i d e r e d a truly (2) L. G. Sneddon, D. C. Beer, and R. N. Grimes, J . Amer. Chem. SOC.,95,6623 (1973).
(3) R. N. Grimes, D. C. Beer, L. G. Sneddon, V. R. Miller, and R. Weiss, Inorg. Chem., in press. (4) D. C. Beer, V. R. Miller, L. G. Sneddon, R. N. Grimes, M. Mathew, and G. J. Palenik, J . Amer. Chem. SOC.,95, 3046 (1973). (5) L. G. Sneddon and R. N. Grimes, J. Amer. Chem. SOC.,94, 7161 (1972). (6) R. N. Grimes, W. J. Rademaker, M. L. Denniston, R. F. Bryan, and P. T. Greene, J. Amer. Chem. SOC.,94, 1865 (1972).
Journal of the American Chemical Society 1 96:lO 1 May 15, 1974
3091
Table I. 32.1-MHz llB "r Data Compd
Solvent
CCla 1,2,4-(CO)3FeCaB3Hs(I) CHnCla 1,2,3,5-(CO)eFe2CzB3Hs (11) 1,2,4-(&sH5)CoCzB,Hs (111) CHnClz 1,2,3,5-(&sH 5)zCoaCa&H 5 (IV) CDCli 1,2,4-[(CpH5)3P]~NiC~B4Hg (VIII) CHzClz ~ , ~ , ~ , ~ - ( ~ - C ~ H ~ ) Z(XI11 C O Z C Z B ~ H ~CDC13 2,3,8,1,6-(&jHj)3CosCzBsH7(XIII) CDCl, 2,3,4,1,10-(17-CsHj)aC03CzBj (XIV) H7 CDC13
6," ppm (1,Hz)
Re1 areas
-36.3 (197), -4.9 (190) -44.5(163), -17.1 (160), -13.8 (163) -16.1 (181), -2.7 (173) -48.7 (156), - 8 . 5 (150), - 7 . 6 (146) -3.2' -80.3 (139), + 2 . 9 (161), +12.3 (166) -50.0 (146), -20.3 (137), - 3 . 7 (137) -26.0 (153), + 3 . 7 (153), +11.3 (131)
1, 2 1, 1,b l b 1, 2 1, 1,b l b 1, 2, 2 1, 2, 2 2, 2, 1
a Chemical shifts relative t o externally referenced BF3.0(C2Hj)z. Spectra of 1-111 and VI11 were obtained on Varian HA-100 continuousBroad singlet with W I / *= 605 Hz. wave spectrometer; the others are Fourier transform spectra, Estimated from overlapped peaks.
general route inasmuch as few readily available nidocarboranes exist. The second approach, discovered and developed by Hawthorne and coworkers, has been widely employed in metallocarborane syntheses involving the CzB,-2H, polyhedral carborane series. The opening of the polyhedron is normally accomplished by electron transfer from sodium naphthalide in ethereal solvents, producing a nido dianion into which a metal ion can be inserted to complete the "polyhedral expansion."7 (An alternative technique, in which the cage is opened by removal of a boron atom by base attack,' is essentially limited to the icosahedral CzBloH12systems.) The polyhedral expansion method is quite general and has been applied by Hawthorne and coworkers to polyhedra from CzBloHlz down to CzBeHs incl~sive,7~ and in our laboratory to 2,4-C~BsH7~,~ and 1,6-CzB4H6.3 We have found, however, that in the case of these smaller carboranes this technique gives rise to exceedingly complex reactions which produce in many cases nonexpanded products in which the metal replaces boron instead of adding to the original cage. 2 , 3 , 8 Moreover, in the case of C2B4Hethe metallocarborane yields were low, while similar treatment of C2B3Hbin several attempts gave no isolable metallocarboranes. Since metallocarboranes which might be derived from the smallest polyhedral carboranes are of considerable interest from a structural and bonding viewpoint, we have explored alternate routes to such compounds and have found that organometallic reagents of iron, cobalt, and nickel react directly with the lower carboranes to give small metallocarboranes, often in surprisingly good yield. Such reactions avoid a preliminary cage-opening step, are in most cases conducted in the gas phase and are exceedingly simple in execution, and give generally more tractable and easily separable product mixtures than those obtained in the sodium naphthalide treatment. Furthermore, this method is found to work well even with the thermally stable 2,4C2B5H, and 1,2-C2BloH12systems, as well as with metallocarboranes themselves, and hence appears broadly applicable. The only prior examples of direct metal insertion into polyhedral carboranes of which we are aware are the gas-phase reaction of 2,4-C2B6H7 with Fe(CO)5, which we reported recently, and several reactions of closo-2,3-CzB9Hll with nickel group reagents, described by Spencer, Green, and Stone in a short communicat i ~ n . In ~ this paper we report the direct synthesis of lalb
iron, cobalt, or nickel metallocarboranes from 1,5C2B3Hb,1,6-c&He, 2,4-CzBbH7,and 1,2-CZB10H12 and the structural characterization of several novel compounds obtained. General Procedure. All of the reactions involving cobalt apd iron reagents were conducted in the vapor phase without solvent, in an evacuated Pyrex "hotcold" reactor described in the Experimental Section. Reactions of ethylenebis(tripheny1phosphine)nickel were carried out in tetrahydrofuran (THF) solution at room temperature. In most instances, one or two major products were obtained, accompanied by minor or trace amounts of other compounds; of the latter species, only those considered structurally novel or otherwise significant were examined in detail. The new compounds were characterized from their llB and 'H nmr, infrared, and electronic spectra (Tables I-IV, respectively) and from high-resolution mass spectroscopic analysis as described in the Experimental. Table 11. 1 W M H z lH Nmr Data 7 -
Compd Solvent
I
CCla
I1
CC14
I11 IV
CDCl, CDCli
VI11 CDC18 XI CDCI, XI1 CDC13 XI11 CDC13 XIV
CDC13
CjHa
ppm (4Hz)Cage CH Other -2.97
-5.03 -5.07 -4.57
-4.82 -4.71 -4.87 -4.75 -4.751 -4.74j
-
-3.69 (185)b -2.49 (181)' -3.82(192)d - 2 . 5 5 (177)d -2.92 (166)d
-6.88 -4.37 -2.86 -8.29 -3.70 -5.08 -7.14' -3.23(3.4)f -8.63 -2.87 -10.65 (4.2)o -6.94 (4.4)h -15.81 (2.4)i -5.69
Re1 areas 2, 1 2 1, 2 1, 2 5 , 2, 3 5, 1 5, 1 1, 15 5, 1 10, 1 1 5, 1 10, 1 10, 1 5, 1
a Chemical shifts relative to (CH3)aSi. Except where otherwise indicated, H-"B quartets were weak and/or masked by H-C peaks. Spectra of 1-111 and VI11 were obtained on Varian HA-100 continuous-wave spectrometer ; all others are Fourier transform nmr spectra. H-B(6) quartet. H-B(3,5) quartet. d H-B quartets, not specifically assignable. * Phenyl resonance. f Quartet-like multiplet in relative intensities 1 :3:3:1 (see text). 0 Triplet-like multiplet. Quartet-like multiplet. Doublet. 2 CsH5 singlets were resolved on an expanded scale with a separation of 0.8 Hz.
(7) (a) W. J. Evans and M. F. Hawthorne, J . Chem. SOC., Chem. Dunks, and M. F. Haw-
Reactions of 1,5-C2B3Hs. The trigonal-bipyramidal carborane closo-l,5-dicarbapentaborane(5) reacted with excess iron pentacarbonyl at 230°, forming the orange liquids (C0)3FeC2B3Hb(I) and (CO)sFezC2B3H5(11) in 13 and 1.4% yield, respectively. It appeared probable
(8) V. R. Miller and R. N. Grimes, J . Amer. Chem. Soc., 95, 2830 (1973).
(9) J. L. Spencer, M. Green, and F. G. A. Stone, J. Chem. Soc., Chem. Commun., 1178 (1972).
Comniun., 611 (1972); (b) W. J. Evans, G. B. thorne, J . Amer. Chem. SOC.,95, 4565 (1973).
Grimes, et a/. 1 Metallocarboranes
3092 Table IV. Electronic Spectra, C H C N Solution Compd
I
3
m ILL
II
\
Figure 1. Reaction scheme for the gas-phase polyhedral expansion of 1,5-CzB3Hc Structures shown for metallocarborane products are proposed from spectroscopic data. An additional product of the cobalt reaction sequence is 1, ~ , ~ , ~ - ( T & H & C O Z C Z (V). B~HS Table 111. Infrared Absorptions, cm-l
I= 116
IIIC IVC VIIIc
XIIc
XIIIc
XIVc
3040 (w), 2590 (m), 2550 (m), 2095 (vs), 2085 (m), 2050 (vs), 2030 (vs), 2000 (s), 1970 (w),1260 (m) 3040 (w), 2590 (m), 2550 (m), 2095 (vs), 2085 (m), 2050 (vs), 2030 (vs), 2000 (s), 1970 (w), 1260 (m), 1095 (m), 1010 (m) 2617 (vs), 2590 (vs), 1820 (w), 1750 (w), 1660 (w), 1400 (w), 1115 (sh, m), 1095 (m),1045 (w), 1025 (w), 1000 (m), 965 (w), 730 (m) 2550 (s), 2510 (s), 1810 (w), 1720 (w),1600 (w), 1185 (w), 1130 (m), 1110 (m), 1005 (m), 805 (s) 3040 (m), 2550 (vs), 1970 (w), 1900 (w), 1820 (w), 1665 (w), 1590 (w), 1575 (w), 1480 (s), 1435 (s), 1310 (w), 1170 (m), 1095 (s), 1060 (m), 1030 (w), 1000 (m), 870 (m), 850 (w), 680 (w) 3925 (w), 3120 (w), 3080 (w), 2530 (vs), 1820 (w), 1743 (w), 1676 (w), 1601 (w), 1414 (m), 1252 (w), 1134 (s), 1115 (m), 1094 (m), 1076 (w), 1008 (m), 898 (w), 845 (s), 821 (s), 798 (s), 657 (w) 3925 (w), 3105 (w), 2460 (vs), 1816 (w), 1741 (w), 1662 (w), 1598 (w), 1415 (m), 1354 (w), 1116 (m), 1064 (s), 1030 (m), 1008 (m), 898 (w), 875 (m), 837 (s), 819 (vs), 804 (s) 3920 (w), 3105 (w), 2485 (s), 1720 (w), 1603 (w), 1414 (w), 1103 (m), 1011 (m), 958 (m), 910 (w), 868 (m), 838 (s), 813 (s), 799 (m)
a Gas phase, CH2C1,.
CCl, solution us. CCla.
CHzClz solution us.
that I1 was formed by the attack of Fe(CO)5 on I, and this was confirmed by allowing I to react with excess Fe(CO)5 at 250" for 12 hr. These reactions are depicted schematically in Figure l. The yield in the Journal of the American Chemical Society [ 96:IO
,,,A
mp (log e)
440 sh (2.11), 365 (2.47), 293 sh (3.30), 265 (4.33) IV 605 (2.35), 440 sh (2.84), 380 sh (3.16), 300 (3.84), 270 (4.03) V 670 sh (2.20), 555 (2.51), 371 (3.56), 303 (4.54) 405 (2.31), 265 (4.31) VI1 VI11 436 (2.86), 289 (4.22) X 373 (2.58), 304 (3.59), 260 sh (3.94), 234 (4.12) XI 630 sh (1.94), 525 sh (2.77), 434 (3.36), 375 sh (3.47), 350 sh (3.64), 298 sh (4.29), 280 (4.34), 238 (4.29) XI1 690 sh (2.34), 620 (2.39), 450 sh (3.06), 363 (3.85), 305 sh (3.88), 274 (4.22), 240 (4.32) XI11 700 sh (2.01), 5.90 sh (2.44), 490 sh (2.99), 414 (3.59, 274 (4.49) 560 sh (2.75), 495 sh (2.88), 440 sh XIV (3.12), 375 (3.61), 284 (4.25) 550 sh (2.06), 435 (3.00), 330 sh 3,5,1,7-(?-C~Hs)zCo*C~B~H~ (3.72), 292 (3.96), 263 sh (3.99, 240 (4.20) 111
first reaction is adversely affected by the decomposition of CzBZHs, which is unstable above 150". The llB and 'H spectra of I are consistent with an octahedral cage structure as depicted in Figure 1, and this species accordingly is designated l o 1,2,4-(C0)3FeCzBaHj. Alternative geometries having adjacent framework carbon atoms cannot be ruled out entirely but are considered unlikely since the original carborane has nonadjacent carbons (no case is known in which initially nonvicinal cage carbon atoms move together during metallocarborane synthesis, a particularly improbable occurrence at elevated temperatures since thermal isomerizations of carborane polyhedra tend to separate the carbonsld). Compound I and its analog (v-C5H5)CoCzB3H5 (uide infra) are the smallest known polyhedral metallocarboranes and are isoelectronic with the structurally l2 established octahedral systems 1,2- and 1,6-CzB4H611, and B6H6'-.'' In a formal sense, I is generated from CzB4H6by replacement of a BH unit with an Fe(C0)3 group, both being two-electron donors to the cage system. It is significant that I is also isoelectronic with a family of octahedral metal cluster molecules such as (CzH5)2CZCo4(C0)1~14 and with the recently discovered l 5 for which metalloboron compound (7pC5H5)2C02B4H6, an octahedral geometry containing a Co-Co bond has (10) Numbers preceding the formulas designate the locations of framework metal and carbon atoms in that order, and the heteroatoms of highest atomic number are given the lowest cage numbers. The IUPAC system of numbering for inorganic boron compounds is followed here: Pure Appl. Chem., 30,683 (1972). (11) R. A. Beaudet and R. L. Poynter, J. Chem. Phys., 53, 1899 (1970). (12) (a) G. L. McKown and R. A. Beaudet, Inorg. Chem., 10, 1350 (1971); (b) V. S. Mastryukov, 0. V. Dorofeeva, L. V. Vilkov, A. F. Zhigach, V. T. Laptev, and A. B. Petrunin, J . Chem. SOC., Chem. Commun., 276 (1973); (c) E. A. McNeill, I
