A 10-vertex iron - Dicarbollide system formed by insertion of Fe(CO) 4J into 8-vertex [closo-1-CB7H8]_: Synthesis and reactivity studies

Article abstract of DOI:10.1021/om700865s

Reaction of [NBu₄ⁿ][closo-1-CB₇H ₈] with [Fe₂(CO)₉] in refluxing THF (tetrahydrofuran) gives the neutral ferradicarborane [2,2,2-(CO) ₃-1-OH-closo-2,1, 10-FeC₂B₇H₈] (3), which, upon treatment with PEt₃ in the presence of Me₃NO, yields [2,2-(CO)₂-2-PEt₃-1-OH-closo-2,1,10-Fe ₂B₇H₈] (4). In 3 and 4 the 10-vertex (FeC ₂B₇] cluster has two carbon vertices in antipodal, four-connected positions and the iron atom in a five-coordinate site adjacent to a carbon vertex that bears an OH substituent. Treatment of 4 in THF with NaH and then R-X (X = Br, I) affords [2,2-(CO)₂-2-PEt₃-1-OR- closo-2,1,10-FeC₂B₇H₈] (R = Me (5), CH ₂CH=CH₂ (6), CH₂C=CH (7), CH₂CCMe (8)). The pendant allyl group in 6 becomes η²-bonded to the iron center upon treatment with Me₃NO in CH₂Cl₂, giving [2-CO-2-PEt₃-1,2-η²OCH₂CH=CH ₂-closo-2,1, 10-FeC₂B₇H₈] (9), which then with CNXyl (Xyl = C₆H₃Me₂-2,6) in the presence Of PEt₃ gives [2,2-(CNXyl)₂-2-PEt ₃-1-OCH₂CH=CH₂-closo-2,1,10-FeC ₂B₇H₈] (10). Reaction between compound 7 and [Co₂(CO)₈] in petroleum ether yields [2,2-(CO) ₂-2-PEt₃-l-{OCH₂-(μ- η²η²-CCH)Co₂(CO)₆}-closo-2, 1, 10-FeC₂B₇H₈] (12), in which a [C ₂Co₂} tetrahedron is linked to the 10-vertex (FeC ₂B₇} cluster by an -OCH₂- bridge. Heating compound 7 with [CO(CO)₂(η-C₅H₅)] in refluxing toluene gives the complex [2,2-(CO)₂-2-PEt ₃-1,4-μ-(OC(H)=C(Me)-B}-closo-2,1, 10-FeC₂B ₇H₇] (13a), which contains a 5-membered ring that involves one carbon vertex and an adjacent boron atom. Compound 13a yields [2-CO-2,2-(PEt₃)₂-1,4-μ-(OC(H)=C(Me)-B}-closo-2,1,10- FeC₂B₇H₇] (13b) upon addition of further PEt₃ in the presence of Me₃NO. Treatment of compounds 7 and 8 with PEt₃ in CH₂Cl₂ and in the presence of Me₃NO affords the zwitterionic ylide species [2-CO-2-PEt ₃-1,2-μ-{OCH₂C(=C(R′)PEt₃} }-closo-2,1,10-FeC₂B₇H₈] (R′ = H (15), Me (17), respectively). In the latter pair, an -OCH₂C{=C(R′) PEt₃J group bonded to a cage carbon atom is also directly σ-bonded (at the β-position) to the adjacent iron vertex, forming a 5-membered ring. The novel structural features of compounds 4, 10, 12, 13, 15, and 17 have been confirmed by single-crystal X-ray diffraction studies.

Full text of DOI:10.1021/om700865s

908
Organometallics 2008, 27, 908–917
A 10-Vertex Iron-Dicarbollide System Formed by Insertion of
{Fe(CO)4} into 8-Vertex [closo-1-CB7H8]-: Synthesis and Reactivity
Studies
Andreas Franken, Thomas D. McGrath,* and F. Gordon A. Stone
Department of Chemistry & Biochemistry, Baylor UniVersity, Waco, Texas 76798-7348
ReceiVed August 29, 2007
Reaction of [NBun ][closo-1-CB7H8] with [Fe2(CO)9] in refluxing THF (tetrahydrofuran) gives the
4
neutral ferradicarborane [2,2,2-(CO)3-1-OH-closo-2,1,10-FeC2B7H8] (3), which, upon treatment with PEt3
in the presence of Me3NO, yields [2,2-(CO)2-2-PEt3-1-OH-closo-2,1,10-FeC2B7H8] (4). In 3 and 4 the
10-vertex {FeC2B7} cluster has two carbon vertices in antipodal, four-connected positions and the iron
atom in a five-coordinate site adjacent to a carbon vertex that bears an OH substituent. Treatment of 4
in THF with NaH and then R-X (X ) Br, I) affords [2,2-(CO)2-2-PEt3-1-OR-closo-2,1,10-FeC2B7H8]
(R ) Me (5), CH2CHdCH2 (6), CH2CtCH (7), CH2CtCMe (8)). The pendant allyl group in 6 becomes
η2-bonded to the iron center upon treatment with Me3NO in CH2Cl2, giving [2-CO-2-PEt3-1,2-σ:η2-
OCH2CHdCH2-closo-2,1,10-FeC2B7H8] (9), which then with CNXyl (Xyl ) C6H3Me2-2,6) in the presence
of PEt3 gives [2,2-(CNXyl)2-2-PEt3-1-OCH2CHdCH2-closo-2,1,10-FeC2B7H8] (10). Reaction between
compound 7 and [Co2(CO)8] in petroleum ether yields [2,2-(CO)2-2-PEt3-1-{OCH2-(µ-η2:η2-CtCH)Co2-
(CO)6}-closo-2,1,10-FeC2B7H8] (12), in which a {C2Co2} tetrahedron is linked to the 10-vertex {FeC2B7}
cluster by an -OCH2- bridge. Heating compound 7 with [Co(CO)2(η-C5H5)] in refluxing toluene gives
the complex [2,2-(CO)2-2-PEt3-1,4-µ-{OC(H)dC(Me)-B}-closo-2,1,10-FeC2B7H7] (13a), which contains
a 5-membered ring that involves one carbon vertex and an adjacent boron atom. Compound 13a yields
[2-CO-2,2-(PEt3)2-1,4-µ-{OC(H)dC(Me)-B}-closo-2,1,10-FeC2B7H7] (13b) upon addition of further PEt3
in the presence of Me3NO. Treatment of compounds 7 and 8 with PEt3 in CH2Cl2 and in the presence of
Me3NO affords the zwitterionic ylide species [2-CO-2-PEt3-1,2-µ-{OCH2C{dC(R′)PEt3}}-closo-2,1,10-
FeC2B7H8] (R′ ) H (15), Me (17), respectively). In the latter pair, an -OCH2C{dC(R′)PEt3} group
bonded to a cage carbon atom is also directly σ-bonded (at the ꢀ-position) to the adjacent iron vertex,
forming a 5-membered ring. The novel structural features of compounds 4, 10, 12, 13, 15, and 17 have
been confirmed by single-crystal X-ray diffraction studies.
7–10 vertices.4,5 We have exploited the potential of this
Introduction
breakthrough to prepare a number of metal-monocarbollide
In metallacarborane chemistry there has traditionally been a
disparity between the number of complexes of monocarbollide
versus dicarbollide ligands, with the latter far outweighing the
former.1 The primary reason for this was the relatively limited
availability of monocarbon carboranes compared to their di-
carbon cousins,2 as there were few simple and high-yielding
routes to the monocarboranes from commercially available
starting materials such as B10H14. In attempting to redress the
monocarbollide/dicarbollide imbalance, we had been limited
essentially to 12-vertex {MCB10} species, as the {CB10}
carboranes were by far the most readily accessible.3 Recently,
however, there has been a resurgence in monocarborane
chemistry, initiated by Brellochs,4 which has led to straight-
forward procedures for the synthesis of monocarboranes with
species in the 9–11-vertex range,6–13 several of which have
displayed chemistry not seen in their larger cluster relatives. In
one such system 9- and 10-vertex {FeCB7} and {Fe2CB7}
species were synthesized, but a trace third product defied
(5) (a) Stíbr, B.; Tok, O. L.; Milius, W.; Bakardjiev, M.; Holub, J.; Hnyk,
D.; Wrackmeyer, B. Angew. Chem., Int. Ed. 2002, 41, 2126. (b) Franken,
A.; Kilner, C. A.; Thornton-Pett, M.; Kennedy, J. D. Collect. Czech. Chem.
Commun. 2002, 67, 869. (c) Jelínek, T.; Thornton-Pett, M.; Kennedy, J. D.
Collect. Czech. Chem. Commun. 2002, 67, 1035. (d) Stíbr, B. Pure Appl.
Chem. 2003, 75, 1295. (e) Brellochs, B.; Backovsky, J.; Stíbr, B.; Jelínek,
T.; Holub, J.; Bakardjiev, M.; Hnyk, D.; Hofmann, M.; Císarová, I.;
Wrackmeyer, B. Eur. J. Inorg. Chem. 2004, 3605.
(6) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Organometallics
2003, 22, 2842.
(7) (a) Du, S.; Farley, R. D.; Harvey, J. N.; Jeffery, J. C.; Kautz, J. A.;
Maher, J. P.; McGrath, T. D.; Murphy, D. M.; Riis-Johannessen, T.; Stone,
F. G. A. Chem. Commun. 2003, 1846. (b) Du, S.; Jeffery, J. C.; Kautz,
J. A.; Lu, X. L.; McGrath, T. D.; Miller, T. A.; Riis-Johannessen, T.; Stone,
F. G. A. Inorg. Chem. 2005, 44, 2815.
(1) Grimes, R. N. In ComprehensiVe Organometallic Chemistry; Wilkin-
son, G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon Press: Oxford, U.K.,
1982; Vol. 1, Section 5.5. Grimes, R. N. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon
Press: Oxford, U.K., 1995; Vol. 1, Chapter 9.
(8) (a) Lei, P.; McGrath, T. D.; Stone, F. G. A. Chem. Commun. 2005,
3706. (b) Lei, P.; McGrath, T. D.; Stone, F. G. A. Organometallics 2006,
25, 2011.
(2) Stíbr, B. Chem. ReV. 1992, 92, 225.
(3) (a) McGrath, T. D.; Stone, F. G. A. J. Organomet. Chem. 2004,
689, 3891. (b) McGrath, T. D.; Stone, F. G. A. AdV. Organomet. Chem.
2005, 53, 1.
(9) Franken, A.; McGrath, T. D.; Stone, F. G. A. Organometallics 2005,
24, 5157.
(10) Franken, A.; McGrath, T. D.; Stone, F. G. A. Inorg. Chem. 2006,
45, 2669.
(4) Brellochs, B. In Contemporary Boron Chemistry; Davidson, M. G.,
Hughes, A. K., Marder, T. B., Wade, K., Eds.; Royal Society of Chemistry:
Cambridge, U.K., 2000; p 212.
(11) Lu, X. L.; McGrath, T. D.; Stone, F. G. A. Organometallics 2006,
25, 2590.
10.1021/om700865s CCC: $40.75
2008 American Chemical Society
Publication on Web 02/15/2008

A 10-Vertex Iron-Dicarbollide System
Organometallics, Vol. 27, No. 5, 2008 909
Chart 1
Chart 2
identification for some time. We now report upon the charac-
terization and reactivity of this last species, ironically an
iron-dicarbollide cluster. Aspects of this work have already
been communicated.14
CO ligand in 3, forming [2,2-(CO)2-2-PEt3-1-OH-closo-2,1,10-
FeC2B7H8] (4). This treatment had the fortunate attendant benefit
that it destroyed iron carbonyl hydride contaminants (apparently
forming [Fe3(CO)12]); addition of small quantities of CF3SO3H
to crude 3 similarly facilitated workup. In the case of 4, the
presence of the metal-bound phosphine donor reduced the acidity
of the cage-OH moiety by destabilizing the conjugate base,
allowing straightforward chromatographic purification. An X-ray
diffraction experiment upon 414 then confirmed the {closo-
2,1,10-FeC2B7} architecture of this compound and hence of its
parent 3.
The structural study showed that both of the cluster carbon
vertices are in antipodal, four-connected sites, as would be
expected,1,15 and the iron center is five-connected, also as
anticipated. A most notable feature of the molecule is the
terminal OH function that is bound to the carbon vertex adjacent
to iron. This functional group is involved in hydrogen bonding
to an adjacent molecule in the crystal, so that the two form
weakly hydrogen bonded pairs as discussed previously.14
It is apparent that during formation of 3 a CO molecule has
inserted into the carborane at the same time as the iron center,
or else immediately before or after that event. The mechanism
of such a reaction is not clear but it presumably involves an
{Fe(CO)4} fragment: the yields of 3 being much higher from
[Fe2(CO)9] than from either [Fe(CO)5] or [Fe3(CO)12] might
suggest that the {Fe(CO)4} fragment forms more readily from
the first reagent.16 Initial interaction between the carborane and
the iron moiety would be necessary to bring a metal-bound
carbonyl into proximity with the cage, so that the CO ligand is
activated toward cage insertion. At this point, for example,
protonation of an {Fe-CO} unit would afford the carbyne
{FetCOH}, which might readily penetrate the carborane to give
the observed product; alternatively the hydroxyl oxygen might
only become protonated by scavenging upon workup.
Results and Discussion
Synthesis and Derivatization of Ccage-OH-Substituted
{FeC2B7} Clusters. We have recently reported upon the reaction
of [NBun ][closo-1-CB7H8] with [Fe3(CO)12], in which {Fe-
4
(CO)3} fragments sequentially insert into the carborane to form
the anionic mono- and diiron monocarbollide complexes [7,7,7-
(CO)3-closo-7,1-FeCB7H8]- (1) and then [6,6,6,10,10,10-(CO)6-
closo-6,10,1-Fe2CB7H8]- (2), respectively (see Chart 1).9 The
same two anionic complexes are also formed when [Fe(CO)5]
is used as the iron reagent, but yields are inferior and there is
greater product contamination; use of [Fe2(CO)9] gave only
small quantities of 1 and 2. However, such reactions involving
this last, diiron carbonyl complex afforded a third ferracarborane
species, compound 3, in apparently good yields, as judged by
11B NMR analysis of the reaction mixture. It was also observed
that the same product was formed in the syntheses of 1 and 2
from the other iron carbonyls, but only in trace amounts (<5%).
Although the precise constitution of compound 3 eluded us
for some time, it was ultimately identified as the 10-vertex
iron-dicarbollide cluster [2,2,2-(CO)3-1-OH-closo-2,1,10-
FeC2B7H8] (see Chart 2) following an X-ray diffraction analysis
upon crystals of a derivative (compound 4 below).14 Chromato-
graphic purification of 3 was difficult, as a consequence of the
acidic cage-OH group, and this, combined with its contamination
by higher nuclearity iron carbonyl hydride byproducts, seriously
hindered its characterization. However, we found that addition
of Me3NO and PEt3 resulted in substitution of one Fe-bound
(12) (a) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Angew.
Chem., Int. Ed. 2003, 42, 5728. (b) McGrath, T. D.; Du, S.; Hodson, B. E.;
Lu, X. L.; Stone, F. G. A. Organometallics 2006, 25, 4444. (c) McGrath,
T. D.; Du, S.; Hodson, B. E.; Stone, F. G. A. Organometallics 2006, 25,
4452.
(15) (a) Williams, R. E. AdV. Inorg. Chem. Radiochem. 1976, 18, 67.
(b) Ott, J. J.; Gimarc, B. M. J. Am. Chem. Soc. 1986, 108, 4303.
(16) Shriver, D. F.; Whitmire, K. H. In ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon
Press: Oxford, U.K., 1982; Vol. 4, Section 31.1.
(13) Franken, A.; McGrath, T. D.; Stone, F. G. A. J. Am. Chem. Soc.
2006, 128, 16169.
(14) Franken, A.; Lei, P.; McGrath, T. D.; Stone, F. G. A. Chem.
Commun. 2006, 3423.

910 Organometallics, Vol. 27, No. 5, 2008
Franken et al.
Table 1. Analytical and Physical Dataa
anal./%c
compd
ν
max(CO)b/cm-1
C
H
[2,2,2-(CO)3-1-OH-closo-2,1,10-FeC2B7H8] (3)
[2,2-(CO)2-2-PEt3-1-OH-closo-2,1,10-FeC2B7H8] (4)
[2,2-(CO)2-2-PEt3-1-OMe-closo-2,1,10-FeC2B7H8] (5)
[2,2-(CO)2-2-PEt3-1-OCH2CHdCH2-closo-2,1,10-FeC2B7H8] (6)
[2,2-(CO)2-2-PEt3-1-OCH2CtCH-closo-2,1,10-FeC2B7H8] (7)
[2,2-(CO)2-2-PEt3-1-OCH2CtCMe-closo-2,1,10-FeC2B7H8] (8)
[2-CO-2-PEt3-1,2-σ:η2-OCH2CHdCH2-closo-2,1,10-FeC2B7H8] (9)
[2,2-(CNXyl)2-2-PEt3-1-OCH2CHdCH2-closo-2,1,10-FeC2B7H8] (10)
[2,2-(CO)2-2-PEt3-1-{OCH2-(µ-η2:η2-CtCH)Co2(CO)6}-closo-
2,1,10-FeC2B7H8] (12)
[2,2-(CO)2-2-PEt3-1,4-µ-{OC(H)dC(Me)-B}-closo-2,1,10-FeC2B7H7]
(13a)
[2-CO-2,2-(PEt3)2-1,4-µ-{OC(H)dC(Me)-B}-closo-2,1,10-FeC2B7H7]
(13b)
[2-CO-2-PEt3-1,2-µ-{OCH2C{dC(H)PEt3}}-closo-2,1,10-FeC2B7H8]
(15)
[2-CO-2-PEt3-1,2-µ-{OCH2C{dC(Me)PEt3}}-closo-2,1,10-FeC2B7H8]
(17)
2092 s, 2042 s
2019 s, 1971 s
2015 s, 1967 s
2015 s, 1968 s
2018 s, 1970 s
2017 s, 1969 s
1964 s
22.8 (22.7)
33.8 (33.9)
36.0 (35.8)
39.8 (39.5)
40.0 (39.8)
41.1 (41.3)
39.4 (39.3)
58.3 (57.9)
33.7 (33.6)
3.4 (3.4)
6.6 (6.8)
7.3 (7.1)
7.1 (7.2)
6.6 (6.7)
6.7 (6.9)
7.5 (7.7)
7.6 (7.7)
3.7 (3.9)
2095 m, 2056 m, 2027 s, 1969 s
2018 s, 1970 s
1926 s
39.5 (39.8)
44.6 (44.8)
44.9 (44.8)
45.7 (45.9)
6.9 (6.7)
8.5 (8.6)
8.6 (8.6)
8.8 (8.7)
1906 s
1889 s
a All compounds are yellow, except compound 10, which is orange, and compounds 12, 15, and 17, which are red. b Measured in CH2Cl2; a broad,
medium-intensity band observed at ca. 2500–2550 cm-1 in the spectra of all compounds is due to B-H absorptions. In addition, for compound 10,
ν
max(CN) 2088 s, 2043 s cm-1 c Calculated values are given in parentheses. In addition, for compound 10: % N, 4.7 (4.7).
.
Previous reports of carbon vertex incorporation via CO
the {CH} units give rise to broad signals at δ 80.4 (3) and 78.5
(4), whereas the {COH} groups resonate far downfield at δ
177.3 (3) and 184.5 (4).
insertion into a boron cluster have been limited and include the
reaction of Na[nido-B10H13] with [M(CO)6] (M ) Cr, Mo, W)
under photochemical conditions17and the formation of iridac-
arboranes from a complex reaction between [IrCl(CO)(PPh3)2]
The cage carbon bound hydroxyl group in both compounds
3 and 4 can readily be deprotonated by treatment with NaH in
THF. In comparison to the spectra for their parents, the infrared
spectra of the resulting anions showed a lowering in their CO
stretching frequencies by tens of wavenumbers, as is to be
expected upon anion formation. (For example, THF solutions
of compound 4 turn darker yellow-orange upon deprotonation,
with νmax(CO) 1978 and 1927 cm-1, and the 11B{1H} NMR
chemical shift range also moves to lower frequency by 5–10
ppm: δ ca. +3 to -27.) Unfortunately, it was not possible to
isolate and fully characterize these deprotonated species, as they
were quite easily reprotonated by proton abstraction from
solvents. However, in situ deprotonation followed by addition
of a suitable organohalide reagent was a successful strategy for
the introduction of other functional groups at the cage C-O
terminus. Compound 4, whose yield is superior and whose
isolation and purification are much more straightforward, was
the substrate of choice for these reactions.
and [closo-B10H10]2- 18
. In our laboratories we have also recently
shown that a carbonyl-molybdenum-monocarbollide trianion
affords a molybdenum-dicarbollide cluster upon protonation
in the presence of CO.8b However, the reaction forming
compound 3 from [closo-1-CB7H8]- and iron carbonyls is
unique in that it apparently has some generality with other
transition-metal–carbonyl reagents: the corresponding {2,2,2-
(CO)3-1-OH-2,1,10-MC2B7H8} species are also known for M
) Ru, Mn, Re.14
The assumed structural similarity of compounds 3 and 4 is
supported by the close similarity of much of their spectroscopic
data (Tables 1-3). Both species show a 1:2:2:2 pattern of
resonances in their 11B{1H} NMR spectra, consistent with the
observed molecular Cs symmetry, but whereas the chemical shift
range for 3 is δ +14.5 to -22.1, the range for 4 is +8.3 to
-22.4. This may be a consequence of the increased electron
density upon the metal following CO f PEt3 substitution, but
it can be dangerous to read too much into such shifts.19 In their
1H NMR spectra, broad signals are seen for the cage {CH} units
at δ 6.16 (3) and 6.00 (4), typical for a four-connected {CH}
vertex in 10-vertex clusters,10,20 while the hydroxyl hydrogens
resonate at δ 3.68 (3) and 3.69 (4) in the same spectra.
Correspondingly, the two distinct types of cage carbon atom
appear at very different positions in the 13C{1H} NMR spectra:
Thus, reaction of 4 with NaH in THF followed by filtration
to remove excess NaH and then addition of MeI afforded the
cage-OMe species [2,2-(CO)2-2-PEt3-1-OMe-closo-2,1,10-
FeC2B7H8] (5). A similar protocol using various bromo reagents
RBr gave the analogous compounds [2,2-(CO)2-2-PEt3-1-OR-
closo-2,1,10-FeC2B7H8] (R ) CH2CHdCH2 (6), CH2CtCH (7),
CH2CtCMe (8)), all in good yields. Data characterizing
compounds 5–8 (see Chart 2) are given in Tables 1-3. All four
species are straightforward derivatives of compound 4, showing
very similar NMR data for the {FeC2B7H8} cage and the CO
(17) Wegner, P. A.; Guggenberger, L. J.; Muetterties, E. L. J. Am. Chem.
Soc. 1970, 92, 3473. See also: Schultz, R. V.; Sato, F.; Todd, L. J. J.
Organomet. Chem. 1977, 125, 115. Fontaine, X. L. R.; Greenwood, N. N.;
Kennedy, J. D.; MacKinnon, P. I.; Macpherson, I. J. Chem. Soc., Dalton
Trans. 1987, 2385.
1
and PEt3 ligands. In addition, signals are seen in the H and
13C{1H} NMR spectra, corresponding to the various substituents
attached via the cluster-bound oxygen. These occur in the
expected positions and merit little further comment.
(18) (a) Crook, J. E.; Greenwood, N. N.; Kennedy, J. D.; McDonald,
W. S. J. Chem. Soc., Chem. Commun. 1981, 933. (b) Crook, J. E.;
Greenwood, N. N.; Kennedy, J. D.; McDonald, W. S. J. Chem. Soc., Chem.
Commun. 1983, 83.
The presence of the strong donor PEt3 bound to the iron center
in compounds 4–8 results in a relatively high electron density
at the metal center, evidenced by the rather low CO stretching
frequencies (Table 1), so that substitution of a further CO ligand
by donor groups such as PEt3 and CNBut was neither expected
nor observed, even in the presence of Me3NO. On the other
hand, it was hoped that the unsaturated organic moieties in
(19) See, for example: Hermánek, S. Chem. ReV. 1992, 92, 325.
(20) See also, for example: (a) Stíbr, B.; Kennedy, J. D.; Thornton-
Pett, M.; Dradáková, E. Collect. Czech. Chem. Commun. 1992, 57, 1439.
(b) Evans, W. E.; Dunks, G. B.; Hawthorne, M. F. J. Am. Chem. Soc. 1973,
95, 4565. (c) Briguglio, J. J.; Sneddon, L. G. Organometallics 1986, 5,
327.

A 10-Vertex Iron-Dicarbollide System
Organometallics, Vol. 27, No. 5, 2008 911
13C/δc
Table 2. 1H and 13C NMR Dataa
compd
1H/δb
3
4
6.16 (br s, 1H, cage CH), 3.68 (br, 1H, OH)
6.00 (br s, 1H, cage CH), 3.69 (br, 1H, OH), 1.94 (m, 8H, PCH2),
1.22 (m, 12H, CH3)
6.12 (br s, 1H, cage CH), 4.98 (s, 3H, OCH3), 1.89 (m, 8H, PCH2),
1.16 (m, 12H, CH3)
6.25 (m, 1H, dCH), 6.12 (br s, 1H, cage CH), 5.47 (dd, J(HH)trans
) 18, J(HH)gem ) 1, 1H, dCH2), 5.30 (d, J(HH)cis ) 10, 1H,
dCH2), 4.76 (d, J(HH) ) 6, 2H, OCH2), 1.91 (m, 6H, PCH2), 1.18
(m, 9H, CH3)
204.3 (Fe-CO), 177.3 (br, cage COH), 80.4 (br, cage CH)
211.0 (d, J(PC) ) 25, Fe-CO), 184.5 (br, cage COH), 78.5 (br,
cage CH), 19.4 (d, J(PC) ) 28, PCH2), 7.4 (br, CH3)
211.1 (d, J(PC) ) 24, Fe-CO), 189.7 (br, cage CO), 81.1 (br, cage
C), 63.4 (OCH3), 19.3 (d, J(PC) ) 29, PCH2), 7.3 (br, CH3)
211.1 (d, J(PC) ) 24, Fe-CO), 188.0 (br, cage CO), 134.6 (dCH),
117.4 (dCH2), 81.0 (br, cage CH), 77.7 (OCH2), 19.3 (d, J(PC) )
29, PCH2), 7.6 (br, CH3)
5
6
7
6.17 (br s, 1H, cage CH), 4.87 (s, 2H, OCH2), 2.61 (s, 1H, tCH),
1.87 (m, 6H, PCH2), 1.27 (m, 9H, CH3)
210.8 (d, J(PC) ) 24, Fe-CO), 185.7 (br, cage CO), 82.0 (br, cage
CH), 79.5 (tCH), 74.7 (tCCH2), 63.2 (OCH2), 19.2 (d, J(PC) )
29, PCH2), 7.5 (br, CH3)
8
6.14 (br s, 1H, cage CH), 4.80 (s, 2H, OCH2), 1.86 (m, 6H, PCH2),
1.25 (s, 3H, tCCH3), 1.17 (m, 9H, PCH2CH3)
210.9 (d, J(PC) ) 25, Fe-CO), 186.5 (br, cage CO), 81.6 (br, cage
CH), 64.1 (OCH2), 74.9 (tCCH2), 83.0 (tCCH3), 19.3 (d, J(PC)
) 29, PCH2), 7.5 (br, PCH2CH3), 3.4 (tCCH3)
9
5.93 (br s, 1H, cage CH), 5.13 (d, J(HH)trans ) 14, 1H, dCH2) 4.89, 219.5 (d, J(PC) ) 36, Fe-CO), 198.2 (br, cage CO), 88.5 ()CH2 or
4.86 (m × 2, 1H × 2, OCH2), 3.62 (d, J(HH)cis ) 9, 1H, dCH2),
2.64 (dd, 1H, dCH), 1.71 (m, 6H, PCH2), 1.04 (m, 9H, CH3)
7.05 (br m, 6H, C6H3), 6.26 (m, 1H, dCH), 5.94 (br s, 1H, cage
CH), 5.39, 5.19 (d × 2, J(HH) ) 10, 1H + 1H, dCH2), 4.74 (m,
2H, OCH2), 2.42 (s, 12H, C6H3CH3), 1.90 (m, 6H, PCH2), 1.13 (m,
9H, PCH2CH3)
OCH2), 77.0 (dCH2 or OCH2), 74.3 (br, cage CH), 54.2 (d, J(PC)
) 6, dCH), 19.5 (d, J(PC) ) 29, PCH2), 8.7 (d, J(PC) ) 5, CH3)
182.0 (br, cage CO), 135.8 (dCH), 134.5–126.5 (C6H3), 130.2 (d,
J(PC) ) 11, CtN), 115.9 (dCH2), 79.5 (br, cage CH), 76.8
(OCH2), 25.6 (C6H3CH3), 18.9 (d, J(PC) ) 27, PCH2), 7.9 (br,
PCH2CH3)
10
12
6.24 (s, 1H, Co2CtCH), 6.19 (br s, 1H, cage CH), 5.46 (s, 2H,
OCH2), 1.94 (m, 6H, PCH2), 1.20 (m, 9H, CH3)
210.9 (d, J(PC) ) 24, Fe-CO), 199.6 (br, Co-CO), 187.0 (br, cage
CO), 90.6 (Co2CtCH), 82.2 (br, cage CH), 77.0 (OCH2), 73.2
(Co2CtCH), 19.4 (d, J(PC) ) 29, PCH2), 7.6 (br, CH3)
211.4 (d, J(PC) ) 23, Fe-CO), 183.9 (br, cage CO), 169.3 (dCH),
129.5 (vbr, dCCH3), 65.8 (br, cage CH), 19.2 (d, J(PC) ) 28,
PCH2), 12.0 (dCCH3), 7.4 (br, PCH2CH3)
215.7 (t, J(PC) ) 27, Fe-CO), 182.0 (br, cage CO), 167.4 (dCH),
127.9 (vbr, dCCH3), 66.4 (br, cage CH), 20.1 (d, J(PC) ) 25,
PCH2), 12.1 (dCCH3), 8.4 (br, PCH2CH3)
218.4 (d, J(PC) ) 32, Fe-CO), 194.0 (br, cage CO), 91.3 (dd,
J(PC) ) 14 and 1, dCFe), 89.0 (d, J(PC) ) 60, dCPEt3), 72.4
(br, OCH2), 51.8 (br, cage C), 17.8 (d, J(PC) ) 26, PCH2), 15.0
(d, J(PC) ) 51, PCH2), 7.9 (d, J(PC) ) 5, CH3), 5.9 (d, J(PC) )
5, CH3)
217.0 (d, J(PC) ) 32, Fe-CO), 193.2 (br, cage CO), 96.4 (d, J(PC)
) 46, dCPEt3), 91.1 (dd, J(PC) ) 17 and 3, dCFe), 70.4 (br,
cage C), 60.0 (br, OCH2), 25.9 (dd, J(PC) ) 21 and 2, dCCH3),
18.6 (d, J(PC) ) 24, PCH2), 15.2 (d, J(PC) ) 47, PCH2), 8.5 (d,
J(PC) ) 6, PCH2CH3), 6.2 (d, J(PC) ) 4, PCH2CH3)
13a
13b
15
8.00 (s, 1H, dCH), 5.46 (br s, 1H, cage CH), 1.87 (m, 6H, PCH2),
1.78 (s, 3H, dCCH3), 1.20 (m, 9H, PCH2CH3)
8.02 (s, 1H, dCH), 5.41 (br s, 1H, cage CH), 1.86 (m, 12H, PCH2),
1.81 (s, 3H, dCCH3), 1.17 (m, 18H, PCH2CH3)
ca. 5.8 (vbr, 1H, cage CH),d 5.62, 5.52 (m × 2, 1H × 2, OCH2),
5.36 (ddt, 2J(PH) ) 29, 4J(PH) ) 4, 4J(HH) ) 2, dCHPEt3), 2.02
(m, 6H, PCH2), 1.79, 1.62 (m × 2, 3H × 2, PCH2), 1.17 (m, 9H,
CH3), 0.98 (m, 9H, CH3)
17
ca. 5.9 (vbr, 1H, cage CH),d 5.64, 5.42 (m × 2, 1H × 2, OCH2),
2.24 (d, J(PH) ) 13, dCMe), 2.06 (m, 6H, PCH2), 1.79, 1.61 (m
× 2, 3H × 2, PCH2), 1.16 (m, 9H, CH3), 1.00 (m, 9H, CH3)
a Chemical shifts (δ) are given in ppm and coupling constants (J) in hertz; measurements were carried out at ambient temperatures in CD2Cl2.
b Resonances for terminal BH protons occur as broad unresolved signals in the range δ ca. -1 to +3. c 1H-decoupled chemical shifts are positive to
high frequency of SiMe4. d Tentative assignment.
Table 3. 11B and 31P NMR Dataa
c
compd
11B/δb
31P/δ
3
4
5
6
7
8
9
10
12
13a
13b
15
17
14.5, -0.3 (2B), -15.7 (2B), -22.1 (2B)
8.3, -1.0 (2B), -17.4 (2B), -22.4 (2B)
7.1, -1.0 (2B), -19.5 (2B), -22.2 (2B)
7.0, -1.1 (2B), -19.2 (2B), -22.1 (2B)
6.3, -1.0 (2B), -18.9 (2B), -22.0 (2B)
7.1, -0.9 (2B), -19.0 (2B), -22.0 (2B)
1.5, -2.2, -8.2, -16.8, -20.2 (2B), -22.3
3.6, -0.6 (2B), -20.6 (2B), -23.1 (2B)
7.7, -0.9 (2B), -19.3 (2B), -22.0 (2B)
14.4 (B(4)), 0.2 (2B), -17.0 (2B), -24.9 (2B)
11.3 (B(4)), -0.1 (2B), -19.4 (2B), -25.3 (2B)
-3.8, -5.8, -10.8, -13.1, -20.4, -23.9, -26.3
-2.6 (2B), -8.5, -13.1, -20.8, -24.2, -24.9
54.8
54.7
54.5
54.7
54.7
50.6
54.0
53.9
54.8
41.5
50.9 (FePEt3), 6.9 (dCPEt3)
53.0 (FePEt3), 15.5 (dCPEt3)
a Chemical shifts (δ) are given in ppm and coupling constants (J) in Hz,; measurements were carried out at ambient temperatures in CD2Cl2.
b 1H-decoupled chemical shifts are positive to high frequency of BF3 · Et2O (external); resonances are of unit integral except where indicated.
c 1H-decoupled chemical shifts are positive to high frequency of 85% H3PO4 (external).
compounds 6–8, since they are attached to a cage vertex adjacent
to the metal center, might be able to become π-bound to the
iron through formation of an intramolecular five- or six-
membered ring. Such a situation would be highly favorable,
and it was anticipated that this could be sufficient to overcome
the reluctance of the CO ligands toward substitution. Not
surprisingly, rather different results were found for the double-
bond compound versus the triple-bond systems, of which the
former is discussed first.
Reactions of the Ccage-O-Allyl Derivative 6. Treatment
of 6 with Me3NO in CH2Cl2 afforded, as hoped, the compound
[2-CO-2-PEt3-1,2-σ:η2-OCH2CH)CH2-closo-2,1,10-
FeC2B7H8] (9) (see Chart 2). Unfortunately, crystals suitable
for an X-ray diffraction structural study upon 9 were not

912 Organometallics, Vol. 27, No. 5, 2008
Franken et al.
Scheme 1. Proposed Mechanism for the Formation of
Compound 10
Figure 1. Structure of compound 10 showing the crystallographic
labeling scheme. In this and subsequent figures, thermal ellipsoids
are shown at the 40% probability level, phosphorus-bound ethyl
groups are omitted, and only chemically important H atoms are
shown. Selected distances (Å) and angles (deg): Fe(2)-C(1) )
1.961(3), Fe(2)-P(1) ) 2.2219(10), Fe(2)-C(11) ) 1.832(3),
Fe(2)-C(21) ) 1.821(4), C(1)-O(1) ) 1.409(4), O(1)-C(2) )
1.439(4), C(2)-C(3) ) 1.488(5), C(3)-C(4) ) 1.262(6); O(1)-
C(1)-Fe(2) ) 119.7(2), C(1)-O(1)-C(2) ) 117.2(3), O(1)-C(2)-
C(3) ) 108.8(3), C(4)-C(3)-C(2) ) 125.4(5).
role of the phosphine is believed to be that proposed in Scheme
1. Initial attack of PEt3 upon 9 results not in a lifting off of the
double bond but instead in formation of an ylide compound
(11) by addition of the phosphine to the terminal iron bound
dCH2 unit. There are several precedents for such reactions in
metallacarborane chemistry, more usually with B,M-σ:η2-vinylic
groups.21 Attack of CNXyl upon the molecule 11 can then result
in displacement of the organic ylide function and a CO molecule
to give the intermediate A, from which PEt3 loss forms the
observed product 10. In the light of this proposed mechanism,
it was of interest to see whether compound 11 itself could be
isolated (or at least detected) by treatment of 9 with PEt3 alone.
However, no such evidence could be obtained in preliminary
studies, and so the above mechanism must remain somewhat
tentative.
available, but coordination to iron of the dangling double bond
is nevertheless clear from the spectroscopic data (Tables 1-3).
In particular, the presence of only one CO ligand, indicating
substitution at iron, is evident in both IR and 13C{1H} NMR
spectra. Moreover, the three different ligands on iron confer
molecular asymmetry, and confirmation of this is provided by
the 11B{1H} NMR spectrum, which displays a 1:1:1:1:2:1 set
of resonances. Other NMR data are likewise consistent with
the proposed structure.
It was thought that the CdC bond η-coordinated to the metal
center in 9 would be quite readily displaced by addition of strong
donor ligands. Thus, treatment with CNXyl (Xyl ) C6H3Me2-
2,6) was expected to afford a species with an {Fe(CO)(CNXyl)
(PEt3)} center and a dangling -O-allyl function. However,
addition of an excess of the isocyanide to a CH2Cl2 solution of
9 did not result in any observable reaction, as judged by infrared
analysis of the mixture. Very surprisingly, though, upon addition
of PEt3 to this mixture, both the allyl group and the remaining
CO ligand were replaced by CNXyl groups to afford the
compound [2,2-(CNXyl)2-2-PEt3-1-OCH2CHdCH2-closo-2,1,10-
FeC2B7H8] (10), data for which are summarized in Tables 1-3.
A single-crystal X-ray diffraction experiment upon this com-
pound revealed the structure shown in Figure 1. This study
confirmed the presence of one PEt3 and two CNXyl substituents
bonded to the iron center and a pendant allyl group attached
via an oxygen atom to the cage carbon atom adjacent to the
iron center. Geometric parameters are within normal ranges and
merit little further comment. The NMR spectroscopic data for
compound 10 (Tables 2 and 3) are in complete agreement with
the solid-state picture.
Reactions of the Ccage-O-Alkynyl Derivatives 7 and 8.
In parallel with the above studies on the cage-O-allyl species
6, a number of experiments were also performed to examine
the reactivity of the pendant organic group in the cage-O-
propargyl derivative 7. Thus, for example, it has long been
known that carbon-carbon triple bonds can react with
[Co2(CO)8] to form a {C2Co2} “tetrahedron”;22 it was hoped
that from compound 7 a species could be obtained in which an
{FeC2B7} cluster and a {C2Co2} tetrahedron are linked via a
-OCH2- bridge. If successful, such a reaction would also verify
that the dangling propargyl group retains its acetylenic character
despite attachment to the cluster. This proved to be the case,
with treatment of 7 with [Co2(CO)8] in petroleum ether giving
the compound [2,2-(CO)2-2-PEt3-1-{OCH2-(µ-η2:η2-CtCH)Co2-
(CO)6}-closo-2,1,10-FeC2B7H8] (12) (see Scheme 2) in excellent
(21) Anderson, S.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.
Organometallics 1996, 15, 1676. Du, S.; Ellis, D. D.; Jelliss, P. A.; Kautz,
J. A.; Malget, J. A.; Stone, F. G. A. Organometallics 2000, 19, 1983.
(22) Dickson, R. S.; Fraser, P. J. AdV. Organomet. Chem. 1974, 12,
323. Kemmitt, R. D. W.; Russell, D. R. In ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon
Press: Oxford, U.K., 1982; Vol. 5, Section 34. (c) Sweany, R. L. In
ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F. G. A.,
Wilkinson, G., Eds.; Pergamon Press: Oxford, U.K., 1995; Vol. 8, Chap-
ter 1.
At first sight, it is perhaps somewhat surprising that the
addition of CNXyl to 9, giving 10, required an apparent
“activation” by addition of PEt3. Clearly the olefinic group in 9
is more strongly bonded to iron than initially was thought. The

A 10-Vertex Iron-Dicarbollide System
Organometallics, Vol. 27, No. 5, 2008 913
Scheme 2. Reactions of Compounds 7 and 8
yield. Definitive confirmation that the triple bond in 12 was
bonded to the two cobalt centers was provided by an X-ray
diffraction experiment, the result of which is shown in Figure
2. The acetylene moiety is bonded in the typical µ-η2:η2 mode,
and distances within the {C2Co2} tetrahedron are within normal
ranges,23 with C(12)-C(13) ) 1.325(4) Å and Co(1)-Co(2)
) 2.4715(4) Å. Spectroscopic data characterizing compound
12 (Tables 1-3) again are consistent with the observed structure,
with parameters attributed to the {C2Co2} tetrahedron also being
similar to those reported previously.24
In contrast with the reaction between acetylenes and
[Co2(CO)8] discussed above, the reagent [Co(CO)2(η-C5H5)] is
also known to react with CtC triple bonds, the process typically
resulting in acetylene oligomerization processes that include
cyclotrimerization or cyclopentadienone formation.22 It was
clearly of interest, therefore, to examine for similar reactivity
in the case of compound 7. Thus, thermolysis of 7 with
[Co(CO)2(η-C5H5)] (2 equiv) in refluxing toluene afforded a
single ferracarborane product, namely [2,2-(CO)2-2-PEt3-1,4-
µ-{OC(H)dC(Me)-B}-closo-2,1,10-FeC2B7H7] (13a; see Scheme
2). The exact nature of this species was not at first clear, and
single crystals suitable for a structural study were not readily
available. However, treatment of 13a in CH2Cl2 with
PEt3and Me3NO resulted in CO substitution and formation of
[2-CO-2,2-(PEt3)2-1,4-µ-{OC(H)dC(Me)-B}-closo-2,1,10-
FeC2B7H7] (13b; see Scheme 2), for which an X-ray diffraction
analysis was performed, and hence compounds 13 could be
identified.
deduced from that of compound 13b shown in Figure 3.
(Ultimately, crystals of 13a were also obtained, and its structure
confirmed by X-ray diffraction. The results of that experiment
are included as Supporting Information.) Molecules of 13b
consist of the same {closo-2,1,10-FeC2B7} framework as the
parent, but the metal center, of course, now bears two PEt3
ligands and only a single CO group. In addition, considerable
rearrangement of the erstwhile propargyl moiety is evident.
Thus, the formerly pendant {OCH2CtCH} unit now forms a
five-membered COC(H)dC(Me)B ring that involves a cage
carbon vertex and its directly bonded oxygen plus an adjacent
boron vertex (B(4)), with the terminal B-H hydride from that
boron now bonded to the exoskeletal ring. Distances within the
external part of the ring confirm that a double bond is localized
between C(2) and C(3).
A simple mechanism for the formation of compound 13a is
shown in Scheme 3. It is reasonably supposed that the first step
would be coordination of a {Co(CO)(η-C5H5)} fragment
(formed by CO elimination from the cobalt reagent)22 to the
dangling acetylenic moiety of the propargyl group, forming the
species B. From there, a thermally induced internal rearrange-
ment of the coordinated acetylene group gives the intermediate
C, from which insertion of this acetylene into a cluster B-H
bond would give the observed product 13a. Other, more
elaborate mechanisms are also possiblesincluding ones that
involve two cobalt centerssalthough many intermediates can
be excluded, as they do not lead to the COC(H)dC(Me)B ring
seen in the product.
Although compound 13a is not an acetylene oligomerization
product, it was nevertheless of great interest, its structure being
Spectroscopic data for compounds 13 (Tables 1-3) are
entirely consistent with the solid-state structure of 13b. Thus,
for example, the 11B{1H} NMR spectra indicate, as expected, a
mirror symmetric cage with four resonances in the ratio 1:2:2:2,
of which the highest frequency signal in each spectrumsthat
of unit integralsremains a singlet upon retention of proton
(23) Allen, F. H. Acta Crystallogr. 2002, B58, 388. Bruno, I.; Cole,
J. C.; Edgington, P. R.; Kessler, M.; Macrae, C. F.; McCabe, P.; Pearson,
J.; Taylor, R. Acta Crystallogr. 2002, B58, 389.
(24) Aime, S.; Milone, L.; Rossetti, R.; Stanghellini, P. L. Inorg. Chim.
Acta 1977, 22, 135.

914 Organometallics, Vol. 27, No. 5, 2008
Franken et al.
the 1H NMR spectrum, the dCH proton is seen at δ 8.00 (13a)
and 8.02 (13b), while the dCMe protons resonate at δ 1.78
(13a) and 1.81 (13b). In the 13C{1H} NMR spectrum, the two
olefinic carbons give rise to peaks at δ 169.3 (13a) and 167.4
(13b) (dCH), and at δ 129.5 (13a) and 127.9 (13b) (dC(Me)),
the signals for the latter carbons being significantly broadened
by the adjacent quadrupolar boron atom.
In addition to the above formation of a five-membered ring
involving a cluster boron atom, it was clearly also of interest
to establish whether the dangling triple bond in compound 7
could form an intramolecular bond to the iron center, similar
to the arrangement in compound 9. Thus, treatment of CH2Cl2
solutions of 7 with Me3NO was expected to afford [2-CO-2-
PEt3-1,2-σ:η2-OCH2CtCH-closo-2,1,10-FeC2B7H8] (14; see
Scheme 2). However, no reaction was evident, either as a color
change or by spectroscopic analysis of the reaction mixture.
Instead, treatment of the reaction mixture with PEt3 afforded a
deep red compound that was isolated and identified (see below)
as [2-CO-2-PEt3-1,2-µ-{OCH2C{dC(H)PEt3}}-closo-2,1,10-
FeC2B7H8] (15; Scheme 2). The observation of the ylide moiety
in 15 does support the intermediacy of 14: attack of PEt3 upon
the terminal carbon atom of the acetylene group would involve
activation through metal coordination.21 (Notably, also, com-
pounds 13b and 15 are structural isomers!) In parallel with this
reaction, similar treatment of complex 8 with PEt3 and Me3NO
also affords the zwitterionic species 17, presumed likewise to
form via the π-bound acetylene complex 16 (Scheme 2).
Figure 2. Structure of compound 12 showing the crystallographic
labeling scheme. Selected distances (Å) and angles (deg): Fe(1)-C(1)
) 1.968(2), Fe(1)-P(1) ) 2.2412(6), Fe(1)-C(21) ) 1.773(2),
Fe(1)-C(22) ) 1.773(3), C(1)-O(1) ) 1.401(3), O(1)-C(11) )
1.439(2), C(11)-C(12) ) 1.483(3), C(12)-C(13) ) 1.325(4),
Co(1)-Co(2) ) 2.4715(4), C(12)-Co(1) ) 1.960(2), C(12)-Co(2)
) 1.950(2), C(13)-Co(1) ) 1.946(3), C(13)-Co(2) ) 1.958(2);
O(1)-C(1)-Fe(1) ) 122.86(15), C(1)-O(1)-C(11) ) 115.03(17),
O(1)-C(11)-C(12) ) 106.83(18), C(13)-C(12)-C(11) ) 141.9(2),
C(11)-C(12)-Co(1) ) 133.44(17), C(11)-C(12)-Co(2) )
135.03(17), Co(1)-C(12)-Co(2) ) 78.39(9), Co(1)-C(13)-Co(2)
) 78.56(9).
Initial confirmation of the constitution of compounds 15 and
17 was via X-ray diffraction studies; the results for the latter
complex are deposited as Supporting Information. The structure
of one of the crystallographically independent molecules of
compound 15 is presented in Figure 4. Therein can be seen the
iron-bound ylide group FeCOCH2C{dC(H)PEt3}, the Fe-C σ
bond of which forms part of a five-membered ring. Distances
within this moiety are all consistent with the structure shown
in Scheme 2, and in particular with a CdC double bond being
located between C(3) and C(4) and a direct σ bond from C(3)
to the Fe center. Spectroscopic parameters for compounds 15
and 17 likewise also concur with the solid-state structure of
15.
Conclusion
The unusual synthesis of the 10-vertex dicarbon carbamet-
allaborane cluster in 3, starting from the monocarbon substrate
[closo-1-CB7H8]- plus [Fe2(CO)9], has been demonstrated.
Although the dicarbametallaboranes generally constitute the
largest class of metal-(hetero)borane cluster species,1 com-
pounds with fewer than 12 vertices remain relatively rare, and
the present work contributes several novel members to the latter
category. In 3 the second cluster carbon vertex evidently comes
from one of the iron-bound carbonyl ligands of the starting
substrate, and thus 3 and its derivatives all contain an oxygen
functionality directly bonded to that cage carbon atom. The
attachment of substituents to boron clusters is an area where
much current effort is focused. Of particular interest, therefore,
has been the introduction of a variety of organic functional
groups, bonded to the cluster surface via the Ccage-O moiety,
and this in turn has led to a variety of unusual species such as
those containing intramolecular 5-membered rings, exemplified
by compounds 13 and 15. The present compounds, of course,
represent only very simple derivatives of 3, and we are working
to expand upon these results in several directions.
Figure 3. Structure of compound 13b showing the crystallographic
labeling scheme. Selected distances (Å) and angles (deg): Fe(1)-C(1)
) 1.941(5), Fe(1)-P(1) ) 2.2600(16), Fe(1)-P(2) ) 2.2765(17),
Fe(1)-C(11) ) 1.753(5), C(1)-O(1) ) 1.426(6), O(1)-C(2) )
1.380(6), C(2)-C(3) ) 1.340(8), C(3)-B(4) ) 1.544(8), C(3)-C(4)
) 1.510(8); O(1)-C(1)-Fe(1) ) 132.6(4), O(1)-C(1)-B(4) )
106.0(4), C(2)-O(1)-C(1) ) 108.3(4), C(3)-C(2)-O(1) ) 117.4(5),
C(2)-C(3)-C(4) ) 124.0(5), C(2)-C(3)-B(4) ) 106.9(5),
C(4)-C(3)-B(4) ) 129.1(5), C(3)-B(4)-C(1) ) 101.3(4).
coupling and therefore can be assigned to B(4), which bears
the exopolyhedral organic substituent. The C and H atoms of
the COC(H)dC(Me)B ring appear in diagnostic positions: in

A 10-Vertex Iron-Dicarbollide System
Organometallics, Vol. 27, No. 5, 2008 915
Scheme 3. Proposed Mechanism for the Formation of Compound 13a
added dropwise. After the mixture was stirred for 15 min, solvent
was removed under reduced pressure and the resulting green residue
was dissolved in CH2Cl2 (2 mL) and subjected to column chro-
matography as above, giving a fast-moving, deep green fraction
(identified as [Fe3(CO)12]) followed by a yellow fraction. The latter
was collected and solvent removed in vacuo to afford yellow
microcrystals of 3 (0.08 g, 52%).
Experimental Section
General Considerations. All reactions were carried out under
an atmosphere of dry nitrogen using standard Schlenk line
techniques. Solvents were stored over and distilled from appropriate
drying agents under nitrogen prior to use. Petroleum ether refers
to that fraction of boiling point 40–60 °C. Chromatography columns
(ca. 20 cm in length and ca. 2 cm in diameter) were packed with
silica gel (Acros, 60–200 mesh). NMR spectra were recorded at
the following frequencies (MHz): 1H, 360.13; 13C, 90.56; 11B,
115.5; 31P, 145.78. Elemental analyses were performed by Atlantic
Microlab, Inc., Norcross, GA, upon crystalline or microcrystalline
samples that had been dried overnight in vacuo. On occasion
residual solvent remained after drying, its presence and approximate
proportion confirmed by integrated 1H NMR spectroscopy, and this
was factored into the calculated microanalysis data. Sodium hydride,
supplied as a 60% suspension in mineral oil (Aldrich), was washed
with petroleum ether (2 × 10 mL) and dried in vacuo immediately
prior to use, and HCtCCH2Br was used as an 80% solution in
(ii) Similarly, a THF (15 mL) solution containing [NBun ][closo-
4
1-CB7H8] (0.20 g, ca. 0.6 mmol) and [Fe2(CO)9] (0.45 g, 1.2 mmol)
was heated to reflux for 18 h, and cooled, and then the volatiles
were removed under reduced pressure. The residue was dissolved
in neat CH2Cl2 (15 mL), PEt3 (0.9 mL, 5 mmol) and Me3NO (0.10
g, 1.33 mmol) were added, and the mixture was stirred at room
temperature for 2 h. Removal of solvent in vacuo yielded a brown
residue, which was dissolved in CH2Cl2/petroleum ether (3:2, 2
mL) and applied to a chromatography column. Eluting with the
same mixture gave a yellow fraction that was collected and
evaporated in vacuo to give yellow microcrystals of 4 (0.13 g, 61%).
toluene. The carborane salt [NBun ][closo-1-CB7H8] was synthe-
4
Synthesis of [2,2-(CO)2-2-PEt3-1-OR-closo-2,1,10-FeC2B7H8]
(R ) Me (5), CH2CHdCH2 (6), CH2CtCH (7), CH2CtCMe
(8)). (i) Compound 4 (ca. 0.18 g, 0.5 mmol) was dissolved in THF
(20 mL), the solution was added to NaH (0.2 g, 5 mmol), and the
mixture was stirred at ambient temperature for 15 min. Excess NaH
was removed by filtration, MeI (ca. 0.07 mL, 1 mmol) was added
to the filtrate, and the resultant mixture was stirred at ambient
temperature for 18 h. Volatiles were removed in vacuo, and the
residue was dissolved in CH2Cl2/petroleum ether (1:1, 2 mL) and
transferred to the top of a chromatography column. Elution with
the same mixture gave a yellow fraction, from which removal of
solvent in vacuo yielded yellow microcrystals of 5 (0.15 g, 84%).
sized according to the literature method;5e all other materials were
used as supplied.
Synthesis of [2,2-(CO)2-2-L-1-OH-closo-2,1,10-FeC2B7H8] (L
) CO (3), PEt3 (4)). (i) [NBun ][closo-1-CB7H8] (0.20 g, ca. 0.6
4
mmol) was dissolved in THF (15 mL), solid [Fe2(CO)9] (0.45 g,
1.2 mmol) was added, and the mixture was heated under reflux for
18 h. After the mixture was cooled to ambient temperature, volatiles
were removed under reduced pressure, the residue was dissolved
in neat CH2Cl2 (5 mL), and this solution was transferred to the top
of a short (10 cm) chromatography column. Elution with CH2Cl2
gave a deep red fraction that was collected, concentrated to 15 mL
by evaporation, and treated with CF3SO3H (0.25 mL, ca. 4 mmol),

916 Organometallics, Vol. 27, No. 5, 2008
Franken et al.
with CH2Cl2/petroleum ether gave a yellow fraction that contained a
small quantity of unreacted 9 (ca. 0.02 g, 8%).
Synthesis of [2,2-(CO)2-2-PEt3-1-{OCH2-(µ-η2:η2-CtCH)Co2-
(CO)6}-closo-2,1,10-FeC2B7H8] (12). To a solution of compound
7 (ca. 0.20 g, 0.5 mmol) in n-hexane (20 mL) was added [Co2(CO)8]
(0.17 g, 0.51 mmol), and the resulting mixture was stirred at ambient
temperature for 18 h. Volatile components were removed in vacuo,
and the residue was taken up in petroleum ether (2 mL) and applied
to a chromatography column. Elution with petroleum ether removed
unreacted [Co2(CO)8], and then elution with CH2Cl2/petroleum ether
(1:4) gave an orange fraction that was evaporated in vacuo to yield
yellow microcrystals of 12 (0.31 g, 91%).
Synthesis of [2-CO-2-PEt3-2-L-1,4-µ-{OC(H)dC(Me)-B}-
closo-2,1,10-FeC2B7H7] (L ) CO (13a), PEt3 (13b)). (i) Com-
pound 7 (ca. 0.19 g, 0.5 mmol) was dissolved in toluene (20 mL),
[Co(CO)2(η-C5H5)] (0.17 g, 1 mmol) was added, and the solution
was vigorously heated at reflux temperature for 18 h. After cooling
and removal of volatiles in vacuo, the residue was extracted into
petroleum ether (2 mL) and the solution transferred to a chroma-
tography column. Elution with the same solvent removed residual
cobalt species, and then elution with CH2Cl2/petroleum ether (1:4)
gave a yellow fraction. Removal of solvents from the latter yielded
yellow microcrystals of 13a (0.10 g, 53%).
(ii) Compound 13a (0.10 g, 0.25 mmol) was dissolved in CH2Cl2
(10 mL), and PEt3 (0.14 mL, 1.0 mmol) and Me3NO (ca. 0.8 g, 1
mmol) were added. The solution was stirred at room temperature and
evaporated to dryness, and the residue was taken up in CH2Cl2/
petroleum ether (1:4, 1 mL) and subjected to column chromatography.
Elution with the same solvent mixture gave a yellow fraction, from
which were obtained yellow microcrystals of 13b (0.08 g, 62%).
Synthesis of [2-CO-2-PEt3-1,2-µ-{OCH2C{dC(R)PEt3}}-closo-
2,1,10-FeC2B7H8] (R ) H (15), Me (17)). (i) To a solution of 7
(ca. 0.19 g, 0.5 mmol) in CH2Cl2 (20 mL) were added PEt3 (0.5
mL, 3.4 mmol) and Me3NO (0.1 g, 1.3 mmol), and the resulting
mixture was stirred for 24 h at room temperature. Volatiles were
removed in vacuo, the residue was dissolved in CH2Cl2 (2 mL),
and petroleum ether (8 mL) was added to precipitate a red solid.
The latter was collected by filtration, washed with petroleum ether
(3 × 10 mL), and dried in vacuo, giving red microcrystals of 15
(0.15 g, 62%).
Figure 4. Structure of one of the crystallographically independent
molecules of compound 15 showing the crystallographic labeling
scheme. Selected distances (Å) and angles (deg): Fe(1)-C(1) )
1.927(3), Fe(1)-P(1) ) 2.2118(9), Fe(1)-C(11) ) 1.736(3),
Fe(1)-C(3) ) 1.961(3), C(1)-O(1) ) 1.409(3), O(1)-C(2) )
1.428(3), C(2)-C(3) ) 1.534(4), C(3)-C(4) ) 1.353(4), C(4)-P(2)
) 1.772(3); C(11)-Fe(1)-C(3) ) 97.51(13), C(3)-Fe(1)-P(1)
) 87.62(8), C(1)-Fe(1)-C(3) ) 79.93(12), O(1)-C(1)-Fe(1) )
117.40(18), C(1)-O(1)-C(2) ) 108.6(2), O(1)-C(2)-C(3) )
110.9(2), C(4)-C(3)-C(2) ) 118.1(3), C(4)-C(3)-Fe(1) )
128.3(2), C(2)-C(3)-Fe(1) ) 113.35(18), C(3)-C(4)-P(2) ) 128.5(3).
Further elution with CH2Cl2/petroleum ether (4:1) allowed recovery
of unreacted 4 (ca. 0.02 g, 10%).
(ii) Similarly, compound 4 (ca. 0.18 g, 0.5 mmol), NaH (60%)
(0.2 g, 5 mmol), and CH2dCHCH2Br (ca. 0.09 mL, 1 mmol)
yielded yellow microcrystals of 6 (0.15 g, 77%), along with
unreacted 4 (ca. 0.025 g, 14%).
(iii) By an analogous procedure, compound 4 (ca. 0.18 g, 0.5
mmol), NaH (0.2 g, 5 mmol), and HCtCCH2Br (ca. 0.1 mL, 1
mmol) gave yellow microcrystals of 7 (0.12 g, 65%) plus unreacted
4 (ca. 0.037 g, 21%).
(iv) Similarly, compound 4 (ca. 0.18 g, 0.5 mmol), NaH (0.2 g,
5 mmol), and MeCtCCH2Br (ca. 0.09 mL, 1 mmol) afforded
yellow microcrystals of 8 (0.12 g, 65%) followed by unreacted 4
(ca. 0.037 g, 21%).
(ii) Similarly, reaction of 8 (ca. 0.20 g, 0.5 mmol), PEt3 (0.5
mL, 3.4 mmol), and Me3NO (0.1 g, 1.3 mmol) gave red microc-
rystals of 17 (0.13 g, 54%).
X-Ray Crystallographic Structure Determinations. Experi-
mental data for 10, 12, 13b, and 15 are presented in Table 4. Details
of the structure determinations for 13a and 17 have been deposited
as Supporting Information. X-ray intensity data were collected at
110(2) K on a Bruker-Nonius X8 APEX CCD area-detector
diffractometer using Mo KR X-radiation. Several sets of narrow
data “frames” were collected at different values of θ, for various
initial values of ꢁ and ω, using 0.5° increments of ꢁ or ω. The
data frames were integrated using SAINT;25 the substantial
redundancy in data allowed an empirical absorption correction
(SADABS)25 to be applied, based on multiple measurements of
equivalent reflections.
Synthesis of [2-CO-2-PEt3-1,2-σ:η2-OCH2CHdCH2-closo-
2,1,10-FeC2B7H8] (9). Compound 6 (0.18 g, 0.5 mmol) was dissolved
in CH2Cl2 (20 mL), Me3NO (0.08 g, 1 mmol) was added, and the
mixture was stirred at room temperature for 48 h. After evaporation
in vacuo the residue was dissolved in CH2Cl2/petroleum ether (3:2, 2
mL) and transferred to the top of a chromatography column. Elution
with the same solvent mixture afforded a small quantity of unreacted
6 (0.01 g, 5%). Thereafter, elution with CH2Cl2/petroleum ether (4:1)
gave a yellow fraction, removal of solvent from which in vacuo yielded
yellow microcrystals of 9 (ca. 0.17 g, 92%).
Synthesis of [2,2-(CNXyl)2-2-PEt3-1-OCH2CHdCH2-closo-
2,1,10-FeC2B7H8] (10). Compound 9 (0.18 g, 0.5 mmol) was
dissolved in CH2Cl2 (20 mL), CNXyl (0.13 g, 1 mmol) and PEt3 (0.25
mL, 1.7 mmol) were added, and the mixture was stirred at ambient
temperature for 18 h. Solvent was evaporated in vacuo, and the residue
was dissolved in CH2Cl2/petroleum ether (3:2, 2 mL) and transferred
to the top of a chromatography column. Elution with the same mixture
gave an orange fraction that was collected and evaporated in vacuo to
obtain orange microcrystals of 10 (0.25 g, 84%). Thereafter, elution
All structures were solved using conventional direct methods25,26
and refined by full-matrix least squares on all F2 data using SHELXTL
version 6.12,26 with anisotropic thermal parameters assigned to all
non-H atoms. The locations of the cage-carbon atoms were verified
by examination of the appropriate internuclear distances and the
magnitudes of their isotropic thermal displacement parameters. Cluster
BH and CH hydrogens, with the exception of those in compound 13b,
were allowed positional refinement; all other H atoms were set riding
in calculated positions. All hydrogen atoms had fixed isotropic thermal
(25) APEX 2, Version 1.0; Bruker AXS, Madison, WI, 2003–2004.
(26) SHELXTL, Version 6.12; Bruker AXS, Madison, WI, 2001.

A 10-Vertex Iron-Dicarbollide System
Organometallics, Vol. 27, No. 5, 2008 917
Table 4. Crystallographic Data for Compounds 10, 12, 13b, and 15
10 · 0.5C5H12
31.5H52B7FeN2OP
637.24
12
13b
15 · 0.5CH2Cl2
formula
fw
space group
a, Å
b, Å
c, Å
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
C
C19H26B7Co2FeO9P
678.75
C18H41B7FeO2P2
482.97
C
18.5H42B7ClFeO2P2
525.43
j
j
j
P1
P21/n
P1
P1
13.040(3)
15.018(3)
18.379(4)
90
90.564(15)
90
3599.1(14)
4
1.176
0.490
43 480
8387
0.1194
7.5362(3)
8.3695(4)
23.0178(10)
84.158(2)
83.378(3)
83.582(2)
1427.28(11)
2
8.7786(6)
9.8596(7)
15.0003(11)
85.101(4)
79.204(3)
82.038(3)
1260.69(15)
2
12.2721(15)
14.7948(18)
17.112(2)
106.637(6)
107.820(6)
98.800(6)
2733.7(6)
4
2733.7(6)
0.781
41 181
12 351
0.0716
F
calcd, g cm-3
1.579
1.751
21 657
6868
1.272
0.738
µ(Mo KR), mm-1
no. of rflns measd
no. of indep rflns
Rint
15 898
4990
0.0469
0.0521
0.1900, 0.0930
0.1832, 0.0764
wR2, R1a (all data)
wR2, R1 (obsdb data)
0.1339, 0.1348
0.1065, 0.0574
0.0747, 0.0587
0.0674, 0.0373
0.1023, 0.0870
0.0863, 0.0482
2
2 2
a wR2 ) [∑{w(Fo - Fc ) }/∑w(Fo2)2]1/2; R1 ) ∑||Fo| - |Fc||/∑|Fo|. b Fo > 4σ(Fo).
parameters defined as Uiso(H) ) 1.2 × Uiso(parent), or Uiso(H) ) 1.5
Nonius X8 APEX diffractometer was purchased with funds
received from the National Science Foundation Major
Instrumentation Program (Grant No. CHE-0321214).
× Uiso(parent) for methyl groups.
Molecules of 10 cocrystallized each with a half-molecule of
n-pentane in the asymmetric fraction of the unit cell. The γ-CH2 unit
of the solvate lay at an inversion center, while the ꢀ-CH2 unit was
disordered over two positions, these being modeled as each being 50%
occupied. Two independent molecules of compound 15 cocrystallized
with one molecule of CH2Cl2 in the asymmetric unit. This solvate
was located in general space and refined without difficulty.
Supporting Information Available: Full details of the crystal
structure analyses in CIF format, including data for compounds
13a and 17. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. We thank the Robert A. Welch
Foundation and Baylor University for support. The Bruker-
OM700865S