Reaction of nido-7,8-C2B9H13 with Dicobalt Octacarbonyl: Crystal Structures of the Complexes [Co2(CO) 2(η5-7,8-C2B9H11) 2],[Co2(CO)(PMe2Ph)(η5-7,8-C 2B9H11)2],

Article abstract of DOI:10.1021/ic960560s

The compounds [Co₂(CO)₈] and nido-7,8-C₂B₉H₁₃ react in CH₂Cl₂ to give a complex mixture of products consisting primarily of two isomers of the dicobalt species [Co₂(CO)₂(η⁵-7,8-C₂B ₉H₁₁)₂] (1), together with small amounts of a mononuclear cobalt compound [Co(CO)₂(η⁵-10-CO-7,8-C₂B₉H ₁₀)] (5) and a charge-compensated carborane nido-9-CO-7,8-C₂B₉H₁₁ (6). In solution, isomers 1a and 1b slowly equilibrate. However, column chromatography allows a clean separation of 1a from the mixture, and a single-crystal X-ray diffraction study revealed that each metal atom is ligated by a terminal CO molecule and in a pentahapto manner by a nido-C₂B₉H₁₁ cage framework. The two Co(CO)(η⁵-7,8-C₂B₉H₁₁) units are linked by a Co-Co bond [2.503(2) A?], which is supported by two three-center two-electron B-H → Co bonds. The latter employ B-H vertices in each cage which lie in α-sites with respect to the carbons in the CCBBB rings bonded to cobalt. Addition of PMe₂Ph to a CH₂Cl₂ solution of a mixture of the isomers 1, enriched in 1b, gave isomers of formulation [Co₂(CO)(PMe₂Ph)(η⁵-7,8-C₂B ₉H₁₁)₂] (2). Crystals of one isomer were suitable for X-ray diffraction. The molecule 2a has a structure similar to that of la but differs in that whereas one B-H → Co bridge involves a boron atom in an α-site of a CCBBB ring coordinated to cobalt, the other uses a boron atom in the β-site. Reaction between 1b and an excess of PMe₂Ph in CH₂Cl₂ gave the complex [CoCl(PMe₂Ph)₂(η⁵-7,8-C₂B ₉H₁₁)] (3), the structure of which was established by X-ray diffraction. Experiments indicated that 3 was formed through a paramagnetic Co^II species of formulation [Co(PMe₂Ph)₂(η⁵-7,8-C₂B ₉H₁₁)]. Addition of 2 molar equiv of CNBu^t to solutions of either la or 1b gave a mixture of two isomers of the complex [Co₂(CNBu^t)₂(η⁵-7,8-C ₂B₉H₁₁)₂] (4). NMR data for the new compounds are reported and discussed.

Full text of DOI:10.1021/ic960560s

Inorg. Chem. 1996, 35, 6561-6570
6561
Reaction of nido-7,8-C2B9H13 with Dicobalt Octacarbonyl: Crystal Structures of the
Complexes [Co2(CO)2(η5-7,8-C2B9H11)2], [Co2(CO)(PMe2Ph)(η5-7,8-C2B9H11)2], and
[CoCl(PMe2Ph)2(η5-7,8-C2B9H11)]†
Shelley L. Hendershot,‡ John C. Jeffery,§ Paul A. Jelliss,‡ Donald F. Mullica,‡
Eric L. Sappenfield,‡ and F. Gordon A. Stone*,‡
Department of Chemistry, Baylor University, Waco, Texas 76798-7348, and School of Chemistry,
University of Bristol, Bristol BS8 1TS, U.K.
ReceiVed May 16, 1996X
The compounds [Co2(CO)8] and nido-7,8-C2B9H13 react in CH2Cl2 to give a complex mixture of products consisting
primarily of two isomers of the dicobalt species [Co2(CO)2(η5-7,8-C2B9H11)2] (1), together with small amounts
of a mononuclear cobalt compound [Co(CO)2(η5-10-CO-7,8-C2B9H10)] (5) and a charge-compensated carborane
nido-9-CO-7,8-C2B9H11 (6). In solution, isomers 1a and 1b slowly equilibrate. However, column chromatography
allows a clean separation of 1a from the mixture, and a single-crystal X-ray diffraction study revealed that each
metal atom is ligated by a terminal CO molecule and in a pentahapto manner by a nido-C2B9H11 cage framework.
The two Co(CO)(η5-7,8-C2B9H11) units are linked by a Co-Co bond [2.503(2) Å], which is supported by two
three-center two-electron B-H F Co bonds. The latter employ B-H vertices in each cage which lie in R-sites
with respect to the carbons in the CCBBB rings bonded to cobalt. Addition of PMe2Ph to a CH2Cl2 solution of
a mixture of the isomers 1, enriched in 1b, gave isomers of formulation [Co2(CO)(PMe2Ph)(η5-7,8-C2B9H11)2]
(2). Crystals of one isomer were suitable for X-ray diffraction. The molecule 2a has a structure similar to that
of 1a but differs in that whereas one B-H F Co bridge involves a boron atom in an R-site of a CCBBB ring
coordinated to cobalt, the other uses a boron atom in the â-site. Reaction between 1b and an excess of PMe2Ph
in CH2Cl2 gave the complex [CoCl(PMe2Ph)2(η5-7,8-C2B9H11)] (3), the structure of which was established by
X-ray diffraction. Experiments indicated that 3 was formed through a paramagnetic CoII species of formulation
[Co(PMe2Ph)2(η5-7,8-C2B9H11)]. Addition of 2 molar equiv of CNBut to solutions of either 1a or 1b gave a
mixture of two isomers of the complex [Co2(CNBut)2(η5-7,8-C2B9H11)2] (4). NMR data for the new compounds
are reported and discussed.
Introduction
some 80% of all known organometallic complexes of the
transition elements containing cyclopentadienyl ligands,4 it is
We have recently shown that reactions under mild conditions
between [Ru3(CO)12] and the carboranes nido-7,8-R2-7,8-
C2B9H11 (R ) H1 or Me2) or nido-7-NH2But-7-CB10H123 afford
mono- or triruthenacarborane carbonyl complexes in good yield.
We have extended this methodology for preparing metallacar-
boranes by investigating the reaction between [Co2(CO)8] and
nido-7,8-C2B9H13 with the results described herein. Transition
element complexes having metal centers ligated in a pentahapto
manner by C2B9 or CB10 nido-icosahedral cage systems and in
which the metals are also coordinated exopolyhedrally by
carbonyl ligands are important because of their formal relation-
ship with metallacyclopentadienyl carbonyl complexes. Thus
the complex [Ru(CO)3(η5-7,8-C2B9H11)]1 is isolobal with the
very extensively studied species [Mn(CO)3(η5-C5H5)]. With
not surprising that the chemistry of the metallacyclopentadienyl
carbonyls is very extensive. In contrast, relatively little is known
about the reactivity patterns of their metallacarborane analogs.
This is partly due to a lack of suitable synthetic methods for
obtaining this class of compound. Hence the possibility of
obtaining metallacarboranes having carbonyl groups attached
to the metal vertices directly from reactions between metal
carbonyls and nido-carboranes is attractive.
Results and Discussion
The compounds [Co2(CO)8] and nido-7,8-C2B9H13 react in
CH2Cl2 at room temperature or below to afford a complicated
mixture of products. The major reaction products are two
isomers of formulation [Co2(CO)2(η5-7,8-C2B9H11)2] (1), which
equilibrate slowly in solution. These species were characterized
by microanalysis and IR and NMR spectroscopies (Tables 1
and 2). One isomer (1a) could be separated free of the other
by column chromatography, and crystals suitable for X-ray
diffraction were obtained. The second isomer 1b was never
isolated entirely free of 1a (Chart 1).
The molecular structure of 1a is shown in Figure 1, and
selected internuclear separations and angles are listed in Table
3. The molecule consists of two Co(CO)(η5-7,8-C2B9H11)
fragments joined by a Co-Co bond. The latter is supported
by two B-H F Co linkages. The two-electron three-center
† In the compounds described in this paper cobalt atoms and nido-C2B9
cages form closo-1,2-dicarba-3-cobaltadodecaborane structures. Use of this
numbering scheme leads to a complicated nomenclature for the metal
complexes reported; hence as in earlier papers we treat the cage as a nido
11-vertex ligand with numbering as for an icosahedron from which the 12th
vertex has been removed. This has the added convenience of relating the
metallacarborane complexes to similar species with η5-C5H5 ligands.
‡ Baylor University.
§ University of Bristol.
X Abstract published in AdVance ACS Abstracts, September 15, 1996.
(1) Anderson, S. A.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.
Organometallics 1995, 14, 3516; 1996, 15, 1676.
(2) Liao, Y.-H.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.
Organometallics 1996, in press.
(3) Lebedev, V. N.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.
Organometallics 1996, 15, 1669.
(4) Janiak, C.; Schumann, H. AdV. Organomet. Chem. 1991, 33, 291.
S0020-1669(96)00560-5 CCC: $12.00 © 1996 American Chemical Society

6562 Inorganic Chemistry, Vol. 35, No. 22, 1996
Table 1. Analytical and Physical Data
Hendershot et al.
anal.b
a
compd
color
brown
brown
red-brown
purple
brown
ν
max(CO) (cm-1
)
yield (%)
C
H
1a
1b
2a
3
4
5
[Co2(CO)2(η5-7,8-C2B9H11)2] R,R-isomer
[Co2(CO)2(η5-7,8-C2B9H11)2] R,â-isomer
[Co2(CO)(PMe2Ph)(η5-7,8-C2B9H11)2] R,â-isomer
[CoCl(PMe2Ph)2(η5-7,8-C2B9H11)]
2086 s, 2066 s
2088 s, 2070 s
2056 s, 2028 w*
20c
10c
59
63
64e
4
16.6 (16.4)
16.7 (16.4)
27.7 (28.5)
43.0 (43.0)
30.8f (30.6)
4.9 (5.1)
4.6 (5.1)
6.0 (6.1)
6.7 (6.6)
7.7 (7.3)
[Co2(CNBut)2(η5-7,8-C2B9H11)2] R,R- and R,â-isomers
2190 br,d 2180 br
[Co(CO)2(η5-10-CO-7,8-C2B9H10)]g
light brown
2156 br, 2040 s, 1990 s
2152 s
6
nido-9-CO-7,8-C2B9H11
colorlessh
5
22.7 (22.4)
6.4 (6.9)
a Measured in CH2Cl2 unless otherwise stated, all compounds show broad medium-intensity bands in their infrared spectra at ca. 2550 cm-1 due
to B-H absorptions. Peak marked with an asterisk is due to a minor isomer. b Calculated values are given in parentheses. c Approximate values,
because these two compounds always occur as a mixture, and because even repeated chromatography cannot remove traces of one from the other.
Total yield of two isomers is ca. 30%. d Vmax(NC), measured in petroleum ether. e Yield 52% when prepared from 1b. f N 4.7 (5.1). g Microanalysis
unavailable. Positive-ion EI mass spectrum: m/z 275.08, [Co(CO)2(η5-10-CO-7,8-C2B9H10)]+ (calcd 275.08); 247.09 (-CO × 1); 219.09 (-CO
× 2); 190.10 (-CO × 3). h Solutions may be stained pale brown by trace impurities of 5.
Table 2. Hydrogen-1, Carbon-13, and Boron-11 NMR Dataa
compd
1H (δ)b
13C (δ)c
11B (δ)d
1a
-11.45 (q br, 2 H, B-H F Co, JBH ) 92),
3.38, 3.65 (s × 2, 4 H, CH)
196.0 (br, CO), 43.1 (vbr, CH) 15.4 (2 B, B-H F Co, JHB ) 92), 3.7 (2 B), -0.3
(2 B), -3.8 (2 B), -7.3 (2 B), -11.7 (2 B),
-16.9 (2 B), -17.5 (2 B), -18.7 (2 B)
1b
-12.98 (q br, 1 H, B-H F Co, JBH ) 79),
-11.39 (q br, 1 H, B-H F Co, JBH ) 91),
3.55, 3.62, 3.75, 3.96 (s × 4, 4 H, CH)
195.8, 193.5 (br, CO), 58.3,
55.3, 43.8, 37.5, (br, CH)
24.7 (1 B, B-H F Co, JHB ) 79), 16.6 (1 B,
B-H F Co, JHB ) 91), 3.5 (1 B), -0.5 (1 B),
-3.0 (1 B), -3.5 (1 B), -5.5 (1 B), -7.6 (1 B),
-9.4 (2 B), -11.5 (1 B), -11.9 (1 B), -13.7
(1 B), -14.7 (1 B), -16.4 (1 B), -17.6 (1 B),
-18.5 (1 B), -26.2 (1 B)
2ae
-15.01 (q br, 1 H, B-H F Co, JBH ) 79),
-10.47 (q br, 1 H, B-H F Co, JBH ) 85),
1.62, 1.76 (d × 2, 6 H, PMe, JPH ) 10, 10),
2.25, 2.33, 3.57, 3.88 (s × 4, 4 H, CH),
7.44-7.78 (m, 5 H, Ph)
198.0 (br, CO), 131.3-129.5
(Ph), 54.0, 54.2, 48.9, 34.5
(CH), 17.4, 12.0 (d × 2,
PMe, JPC ) 24, 26)
18.1 (1 B, B-H F Co, JHB ) 79), 14.9 (1 B,
B-H F Co, JHB ) 85), 14.3* (1 B, B-H F Co),
10.6* (1 B, B-H F Co, JHB ) 82), 0.0 (1 B),
-0.1 (1 B), -2.6 (2 B), -4.5 (2 B), -7.2 (1 B),
-9.3 (1 B), -11.1 (1 B), -13.3 (2 B), -15.9
(1 B), -19.5 (3 B), -26.2 (1 B)
3f
4
1.52 (AXX′, 6 H, PMe, N ) 5g), 1.91
(AXX′, 6 H, PMe, N ) 6g), 3.49 (s, 2 H, CH),
7.39-7.76 (m, 10 H, Ph)
138.8-128.9 (Ph), 53.1 (CH), 5.1 (1 B), -5.3 (3 B), -5.7 (2 B), -8.3 (1 B),
17.2 (AXX′, PMe, N ) 38g),
17.1 (AXX′, PMe, N ) 34g)
144.1,h,* 142.9 (br,
-16.5 (2 B)
-13.72h,* (q br, 1 H, B-H F Co, JBH ) 79),
-11.54 (q br, 2 H, B-H F Co, JBH ) 89),
1.48* (s, 9 H, Me), 1.54 (s, 18 H, Me), 1.57*
(s, 9 H, Me), 2.80 (s, 2 H, CH), 3.08* (s, 1 H,
CH), 3.31 (s, 2 H, CH), 3.49* (s br, 2 H, CH),
3.66* (s, 1 H, CH)
19.0* (1 B, B-H F Co, JHB ) 79), 13.0* (1 B,
B-H F Co, JHB ) 89), 12.3 (2 B, B-H F Co,
JHB ) 89), -2.2 (2 B), -4.1 (2 B), -6.8 (2 B),
-9.4 (2 B), -12.3 (2 B), -13.7* (1 B), -14.6*
(1 B), -15.4* (1 B), -19.5 (2 B), -20.4 (2 B),
-22.2 (2 B), -27.5* (1 B)
-4.1 (1 B), -11.1 (2 B), -15.7 (2 B), -17.1 (1 B),
-18.6 (2 B), -23.9 (1 B, BCO)
-0.1 (2 B), -14.2 (1 B), -17.3 (1 B), -18.4 (1 B),
-19.5 (1 B), -24.1 (1 B, B-H-B, JHB ) 40, 147),
-30.5 (1 B, BCO), -31.5 (1 B)
CNCMe3), 59.0, 58.9,*
58.8* (CNCMe3), 55.3,*
50.4,* 46.7, 40.8,* 36.1,
35.4* (CH), 30.4,* 30.3,*
30.2 (CNCMe3)
197.0 (br, CO), 172.0 (q br,
BCO, JBC ) 85), 44.0 (CH)
171.7 (q br, BCO, JBC ) 84),
57.5 (q br, CH, JBC ) 43),
46.6 (q br, CH, JBC ) 32)
5
6
3.43 (s, 2 H, CH)
-2.74 (br, 1 H, B-H-B), 2.81, 3.12
(s × 2, 2 H, CH)
a Chemical shifts in ppm, coupling constants in hertz, measurements in CD2Cl2 at room temperature. Peaks marked with an asterisk are due to
a minor isomer (see text). b Resonances for terminal BH protons occur as broad unresolved signals in the range δ ca. -2 to 3. c Hydrogen-1
decoupled, chemical shifts are positive to high frequency of SiMe4. d Hydrogen-1 decoupled, chemical shifts are positive to high frequency of
BF3‚Et2O (external). B-H F Co, BCO, and B-H-B assignments are made from fully coupled 11B spectra. Many peaks due to minor isomers
may be masked by peaks due to the major counterpart; only distinct peaks due to minor isomers are noted. e 31P{1H} NMR: δ 4.1 (br), with a weak
resonance at δ 7.4 attributed to an isomer, see text. f 31P{1H} NMR: δ 5.2 (br). g Insufficient resolution prevents full analysis of coupling constants;
N ) |JAX + JAX′|. h A second similar resonance should be observed for the minor isomer, but is presumably hidden by peak due to corresponding
nucleus in the major isomer.
bonds involve boron atoms, B(13) and B(23), respectively.
These atoms lie in the R-sites with respect to the carbons in the
The agostic B-H F Co linkages in 1a are very common
structural features for dimetal complexes in which a metal atom
M in an icosahedral closo-3,1,2-MC2B9 framework forms an
exopolyhedral bond to another metal center.8 Clear evidence
for the presence of the hydrogen atoms H(13) and H(23) in 1a
came from the NMR spectra, discussed later, but these atoms
were located and refined in the analysis of the diffraction data.
pentagonal CCBBB faces of the nido-C2B9 fragments ligating
the cobalt atoms. We therefore designate 1a as the R,R-isomer.
Each cobalt atom in 1a carries a CO group, which is terminally
bound (Co-C-O average angle ) 177.8°). Thus the dimetal
species is electronically saturated since it has 34 valence
electrons with each C2B9H11 cage formally contributing six
electrons to the system and the carbonyl ligands four electrons.
The Co-Co separation [2.503(2) Å] is similar to those found
in many polynuclear cobalt complexes5 and may be compared
with the Co-Co bond distances in the two isomers of [Co2(µ-
CO){µ-B10H8(SEt2)2}(CO)4] [average 2.489(2) Å]6 and in
[WCo2(µ3-CPh)(CO)8(η5-7,8-Me2-7,8-C2B9H9)] [2.502(3) Å].7
(5) Raithby, P. R. In Transition Metal Clusters; Johnson, B. F. G., Ed.;
Wiley: Chichester, 1980; Chapter 2.
(6) Schubert, D. M.; Knobler, C. B.; Wegner P. A.; Hawthorne, M. F. J.
Am. Chem. Soc. 1988, 110, 5219.
(7) Baumann, F.-E.; Howard, J. A. K.; Musgrove, R. J.; Sherwood, P.;
Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1988, 1891.
(8) (a) Stone, F. G. A. AdV. Organomet. Chem. 1990, 31, 53. (b) Brew,
S. A.; Stone, F. G. A. AdV. Organomet. Chem. 1993, 35, 135. (c)
Jelliss, P. A.; Stone, F. G. A. J. Organomet. Chem. 1995, 500, 307.

Reaction of C2B9H13 with Dicobalt Octacarbonyl
Inorganic Chemistry, Vol. 35, No. 22, 1996 6563
observed in 1a. The disposition of the carbon atoms in both
the cages of 1a is anti to the carbonyl groups. While it is
ostensibly possible to generate isomers by disposing these
carbon atoms syn to the carbonyl ligands in one or both cages,
there is no structural precedent for this in our work or in similar
dimeric metallacarborane structures where BR-H F M contacts
are formed.10
Successive chromatographic procedures yielded solutions of
sufficiently pure 1a and 1b to be able to record accurate IR
and NMR measurements for both complexes, and the data are
listed in Tables 1 and 2, respectively. The IR spectrum of 1a
shows two strong νmax(CO) peaks at 2086 and 2066 cm-1. The
11B{1H} NMR spectrum revealed a pattern of nine singlet
signals (each integrating to two boron nuclei) consistent with
two identical cages in a molecule with axial C2 molecular
symmetry, as found in the X-ray structure, with the C2 axis
lying perpendicular to the Co-Co bond. One of the signals (δ
15.4) becomes a doublet in the fully coupled spectrum, with a
diminished JHB coupling of 92 Hz, indicative of an agostic B-H
F Co system. Though this coupling lies at the high end of the
range expected for B-H F M groups,8b the presence of the
equivalent B-H F Co hydrogen atoms was confirmed by the
above-discussed X-ray results and also by the 1H NMR
spectrum, with the appearance of a broad quartet at δ -11.45
(JBH ) 92 Hz). The latter spectrum also showed two cage CH
resonances at δ 3.38 and 3.65, in accordance with the structure
and symmetry of the molecule. The 13C{1H} NMR spectrum
revealed, as expected, one resonance due to the CO nuclei at δ
196.0, but only one broad peak due to the CH carbon nuclei (δ
43.1), which must be due to partial overlap of two signals.
Figure 1. Molecular structure of the R,R-isomer [Co2(CO)2(η5-7,8-
C2B9H11)2] (1a) showing the crystallographic atom-labeling scheme.
Thermal ellipsoids are shown at the 40% probability level. Only the
agostic hydrogen atoms are shown for clarity.
Chart 1
The IR spectrum of complex 1b was almost identical with
that of 1a, with strong νmax(CO) absorptions at 2088 and 2070
cm-1. The complete lack of molecular symmetry manifests
itself in the 11B{1H} NMR spectrum as a collection of 17
distinguishable signals (one peak being due to fortuitous overlap
of two resonances). Two of these signals (δ 24.7 and 16.6)
were, as determined by deduction from the fully coupled
spectrum, due to inequivalent B-H F Co boron nuclei, with
JHB coupling constants of 79 and 91 Hz, respectively. Cor-
respondingly, in the 1H NMR spectrum, two broad quartets were
observed at δ -12.98 (JBH ) 79 Hz) and -11.39 (JBH ) 91
Hz). As expected, all four CH nuclei gave rise to separate
resonances (δ 3.55, 3.62, 3.75, and 3.96) and this was also the
case in the 13C{1H} NMR spectrum (δ 58.3, 55.3, 43.8, and
37.5). In this latter spectrum, two resonances are seen for the
inequivalent CO ligands at δ 195.8 and 193.5. There is little
doubt from these spectroscopic data that 1b is the R,â-isomer,
where one of the cages involves a Bâ-H F Co linkage and
where the cage carbon atoms in the R-system almost certainly
lie anti to the carbonyl groups.
It should be noted that, even allowing for some flexibility of
the molecules in solution in the form of a partial rotation or
“wiggling” about the Co-Co bond, the overall molecular
symmetry and, therefore, the number of signals expected in the
NMR spectra of 1a and 1b remains the same. Complete rotation
about the Co-Co bond could only be facilitated by breaking
the B-H F Co contacts, and this was indeed observed to be
happening, but at a very slow rate. If a solution of pure 1a
was left to stir in CH2Cl2 at room temperature, then the
formation of 1b was monitored over a period of 24-48 h, until
an equilibrium ratio of 5:2 (1a:1b) was achieved. Solutions
As expected, the atoms B(13) and B(23) unsymmetrically bridge
the Co-Co bond [Co(1)-B(13) ) 2.049(7) Å and Co(1)-B(23)
) 2.138(8) Å; Co(2)-B(13) ) 2.134(8) Å and Co(2)-B(23)
) 2.056(7) Å]. The cobalt atoms, the midpoints of the cage
C-C connectivities, and CO ligands do not all lie in a plane,
but adopt a more twisted configuration, as revealed by the C(1)-
Co(1)-Co(2)-C(2) dihedral angle of 56.1°. This is reminiscent
of the crystal structure of the complex [Ni2(CO)2(η5-2,7-Me2-
2,7-C2B9H9)2],9 which contains two Ni(CO)(η5-2,7-Me2-2,7-
C2B9H9) units linked by a long Ni‚‚‚Ni connectivity and two
agostic B-H F Ni groups in a very similar manner to that
(10) (a) Baker, R. T.; King, R. E.; Knobler, C. B.; O’Con, C. A.; Hawthorne,
M. F. J. Am. Chem. Soc. 1978, 100, 8266. (b) Behnken, P. E.; Marder,
T. B.; Baker, R. T.; Knobler, C. B.; Thomson, M. R.; Hawthorne, M.
F. J. Am. Chem. Soc. 1985, 107, 932.
(9) Carr, C.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A. Inorg.
Chem. 1994, 33, 1666.

6564 Inorganic Chemistry, Vol. 35, No. 22, 1996
Hendershot et al.
Table 3. Selected Internuclear Distances (Å) and Angles (deg) for [Co2(CO)2(η5-7,8-C2B9H11)2] R,R-Isomer (1a) with Estimated Standard
Deviations in Parentheses
Co(1)-C(1)
Co(1)-B(14)
Co(2)-C(2)
Co(2)-B(25)
C(2)-O(2)
1.784(7)
2.109(7)
1.779(7)
2.097(7)
1.124(9)
1.04(6)
Co(1)-C(12)
Co(1)-B(15)
Co(2)-C(22)
Co(2)-B(24)
Co(1)-H(23)
2.031(6)
2.112(7)
2.053(6)
2.101(7)
1.66(6)
Co(1)-B(13)
Co(1)-B(23)
Co(2)-B(23)
Co(2)-B(13)
Co(2)-H(13)
2.049(7)
2.138(8)
2.056(7)
2.134(8)
1.58(8)
Co(1)-C(11)
Co(1)-Co(2)
Co(2)-C(21)
C(1)-O(1)
2.090(6)
2.503(2)
2.082(7)
1.137(8)
0.88(8)
B(13)-H(13)
B(23)-H(23)
C(1)-Co(1)-C(12)
C(1)-Co(1)-C(11)
C(1)-Co(1)-B(14)
163.5(3)
C(1)-Co(1)-B(13)
C(12)-Co(1)-C(11)
C(12)-Co(1)-B(14)
C(1)-Co(1)-B(15)
C(11)-Co(1)-B(15)
C(12)-Co(1)-B(23)
B(14)-Co(1)-B(23)
C(12)-Co(1)-Co(2)
B(14)-Co(1)-Co(2)
C(2)-Co(2)-C(22)
C(2)-Co(2)-C(21)
C(2)-Co(2)-B(25)
C(21)-Co(2)-B(25)
B(23)-Co(2)-B(24)
C(2)-Co(2)-B(13)
C(21)-Co(2)-B(13)
C(2)-Co(2)-Co(1)
C(21)-Co(2)-Co(1)
B(13)-Co(2)-Co(1)
138.5(3)
C(12)-Co(1)-B(13)
49.4(3)
83.8(3)
51.6(3)
82.0(3)
50.6(3)
98.1(3)
173.9(3)
54.8(2)
134.2(2)
139.5(4)
45.7(3)
82.5(3)
94.4(3)
83.8(3)
98.8(3)
173.7(3)
89.4(2)
134.6(2)
177.2(7)
117.4(3)
93.4(3)
83.3(3)
87.4(3)
93.6(3)
130.4(3)
106.7(2)
134.6(2)
51.9(2)
49.9(3)
83.4(3)
87.6(3)
85.3(3)
51.1(3)
98.1(3)
135.0(3)
54.9(2)
83.8(2)
178.4(8)
46.1(3)
84.4(3)
84.0(3)
47.2(3)
99.4(3)
135.4(3)
89.3(2)
84.0(2)
163.4(3)
117.8(3)
84.4(3)
47.5(3)
51.5(3)
93.1(3)
130.0(3)
107.1(3)
134.1(2)
51.7(2)
B(13)-Co(1)-C(11)
B(13)-Co(1)-B(14)
C(12)-Co(1)-B(15)
B(14)-Co(1)-B(15)
B(13)-Co(1)-B(23)
B(15)-Co(1)-B(23)
B(13)-Co(1)-Co(2)
B(15)-Co(1)-Co(2)
C(2)-Co(2)-B(23)
C(22)-Co(2)-C(21)
C(22)-Co(2)-B(25)
C(2)-Co(2)-B(24)
C(21)-Co(2)-B(24)
C(22)-Co(2)-B(13)
B(25)-Co(2)-B(13)
C(22)-Co(2)-Co(1)
B(25)-Co(2)-Co(1)
O(1)-C(1)-Co(1)
C(11)-Co(1)-B(14)
B(13)-Co(1)-B(15)
C(1)-Co(1)-B(23)
C(11)-Co(1)-B(23)
C(1)-Co(1)-Co(2)
C(11)-Co(1)-Co(2)
B(23)-Co(1)-Co(2)
C(22)-Co(2)-B(23)
B(23)-Co(2)-C(21)
B(23)-Co(2)-B(25)
C(22)-Co(2)-B(24)
B(25)-Co(2)-B(24)
B(23)-Co(2)-B(13)
B(24)-Co(2)-B(13)
B(23)-Co(2)-Co(1)
B(24)-Co(2)-Co(1)
O(2)-C(2)-Co(2)
containing an initially high proportion of 1b took slightly less
time to equilibrate (<12 h). There are in theory a maximum
of six isomers of 1 which could form,10b but no others, in
particular a â,â-isomer, were observed, either after the workup
of the original preparation or after the solutions were stirred at
room temperature and above.
Such interconversion between BR-H F M and Bâ-H F M
systems has been observed in spectroscopic studies on solutions
of the complex [WIr(µ-CC6H4Me-4)(CO)2(PPh3)2(η5-7,8-Me2-
7,8-C2B9H9)].11 In this case an equilibrium exists between three
isomers, one where the closo-3,1,2-WC2B9 core utilizes a boron
atom in the R-site in the CCBBB coordinating face of the cage
to form a B-H F Ir bond, a second isomer using a boron in
the â-position, and a third isomer where no B-H F Ir group
is present. The intermediacy of the latter is believed to provide
the route between the other two, since in this isomer the η5-
7,8-Me2-7,8-C2B9H9 cage can rotate to allow either BR-H or
Bâ-H bonds to come into position for bonding to iridium. It is
this kind of interconversion that, as will be discussed later, can
have a significant influence on the reactivity pattern of the
compounds 1.
As mentioned above, 1b was not obtained entirely free of
1a, and thus crystals for an X-ray diffraction study were not
obtained. However, treatment of mixtures enriched in 1b with
1 equiv of PMe2Ph gave isomers of formulation [Co2(CO)(PMe2-
Ph)(η5-7,8-C2B9H11)2] (2). Crystals of the major isomer (2a)
suitable for X-ray analysis were obtained after careful chroma-
tography and recrystallization, thus allowing establishment of
its molecular structure.
Figure 2. Molecular structure of the R,â-isomer [Co2(CO)(PMe2Ph)-
(η5-7,8-C2B9H11)2] (2a) showing the crystallographic atom-labeling
scheme. Thermal ellipsoids are shown at the 40% probability level.
Only the agostic hydrogen atoms are shown for clarity.
thus forming a BR-H F Co bond, while the other bridge
employs the boron atom B(24), hence forming a Bâ-H F Co
bond. This mode of unsymmetrical exopolyhedral B-H vertex
bridge-bonding by two η5-7,8-C2B9H11 groups across a metal-
metal bond has been previously seen in the dirhodium complex
[Rh2(PPh3)2(η5-7,8-C2B9H11)2].10 In both the latter rhodium
complex and in 2a the carbon atoms in the R-cage systems
occupy the usual positions anti to the carbonyl and phosphine
groups, respectively. The Co-Co bond in 2a [2.5480(9) Å] is
slightly longer than that in 1a but within the customary range
of such distances.5 Several complexes with Co-PMe2Ph groups
have been studied by X-ray crystallography, and the Co-P bond
distances are in the range 2.174-2.242 Å.12 The Co-P bond
of 2.269(1) Å in 2a is somewhat longer.
The molecular structure is shown in Figure 2, and selected
bond distances and angles are listed in Table 4. Apart from
the replacement of a CO ligand by a PMe2Ph molecule, the
structure of 2a is similar to that of 1a. It differs, however, in
the disposition of the two B-H F Co groups. Whereas in 1a
both groups involve boron atoms in the R-sites in the two
(12) (a) Werner, H.; Xiaolan, L.; Nu¨rnberg, O. Organometallics 1992, 11,
432. (b) Moldes, I.; Ros, J. R.; Mathieu, R.; Solans, X.; Font-Bard´ıa,
M. J. Organomet. Chem. 1992, 423, 65. (c) Zhou, Z.; Jablonski, C.;
Brisdon, J. Organometallics 1994, 13, 781. (d) Braunstein, P.; Rose´,
J.; Toussaint, D.; Ja¨a¨skela¨inen, S; Ahlgren, M.; Pakkanen, T. A.;
Pursiainen, J.; Toupet, L.; Grandjean, D. Organometallics 1994, 13,
2472. (e) Caffyn, A. J. M.; Martin, A.; Mays, M. J.; Raithby, P. R.;
Solan, G. A. J. Chem. Soc., Dalton Trans. 1994, 609.
CCBBB rings, in 2a one linkage involves the boron atom B(13),
(11) Jeffery, J. C.; Ruiz, M. A.; Sherwood, P.; Stone, F. G. A. J. Chem.
Soc., Dalton Trans. 1989, 1845.

Reaction of C2B9H13 with Dicobalt Octacarbonyl
Inorganic Chemistry, Vol. 35, No. 22, 1996 6565
Table 4. Selected Internuclear Distances (Å) and Angles (deg) for [Co2(CO)(PMe2Ph)(η5-7,8-C2B9H11)2] R,â-Isomer (2a) with Estimated
Standard Deviations in Parentheses
Co(1)-C(1)
Co(1)-B(15)
Co(2)-B(24)
Co(2)-C(22)
P(1)-C(31)
C(51)-C(52)
C(55)-C(56)
B(24)-H(2)
1.783(5)
2.121(5)
2.075(5)
2.105(4)
1.809(5)
1.407(6)
1.378(7)
1.24(4)
Co(1)-C(12)
Co(1)-B(14)
Co(2)-C(21)
Co(2)-B(13)
P(1)-C(41)
C(52)-C(53)
Co(1)-H(2)
2.020(4)
2.126(5)
2.075(4)
2.159(5)
1.821(5)
1.383(7)
1.59(4)
Co(1)-B(13)
Co(1)-B(24)
Co(2)-B(23)
Co(2)-P(1)
P(1)-C(51)
C(53)-C(54)
Co(2)-H(1)
2.046(5)
2.161(5)
2.101(5)
2.2691(14)
1.826(4)
1.387(8)
1.58(4)
Co(1)-C(11)
Co(1)-Co(2)
Co(2)-B(25)
C(1)-O(1)
C(51)-C(56)
C(54)-C(55)
B(13)-H(1)
2.102(4)
2.5480(9)
2.102(5)
1.132(5)
1.380(6)
1.375(8)
1.23(4)
C(1)-Co(1)-C(12)
C(1)-Co(1)-B(15)
C(1)-Co(1)-Co(2)
164.4(2)
C(1)-Co(1)-B(13)
C(1)-Co(1)-B(14)
C(12)-Co(1)-Co(2)
B(15)-Co(1)-Co(2)
B(24)-Co(2)-C(21)
B(23)-Co(2)-P(1)
B(13)-Co(2)-P(1)
B(23)-Co(2)-Co(1)
B(13)-Co(2)-Co(1)
B(18)-B(13)-Co(1)
C(12)-B(13)-Co(2)
B(14)-B(13)-Co(2)
B(28)-B(24)-Co(2)
B(29)-B(24)-Co(1)
B(23)-B(24)-Co(1)
C(31)-P(1)-Co(2)
139.4(2)
C(1)-Co(1)-C(11)
118.7(2)
97.1(2)
86.7(2)
106.3(2)
134.43(13)
51.48(13)
89.10(13)
112.38(12)
130.00(12)
134.51(12)
63.8(2)
96.0(2)
89.26(12)
135.52(14)
82.9(2)
C(1)-Co(1)-B(24)
B(13)-Co(1)-Co(2)
B(14)-Co(1)-Co(2)
B(24)-Co(2)-P(1)
B(25)-Co(2)-P(1)
B(24)-Co(2)-Co(1)
B(25)-Co(2)-Co(1)
P(1)-Co(2)-Co(1)
B(17)-B(13)-Co(1)
B(18)-B(13)-Co(2)
Co(1)-B(13)-Co(2)
B(25)-B(24)-Co(2)
B(28)-B(24)-Co(1)
Co(2)-B(24)-Co(1)
C(41)-P(1)-Co(2)
54.75(14)
84.58(14)
148.24(14)
101.45(14)
54.59(13)
82.75(13)
112.62(4)
117.1(3)
145.6(3)
74.5(2)
C(11)-Co(1)-Co(2)
B(24)-Co(1)-Co(2)
C(21)-Co(2)-P(1)
C(22)-Co(2)-P(1)
C(21)-Co(2)-Co(1)
C(22)-Co(2)-Co(1)
C(12)-B(13)-Co(1)
B(14)-B(13)-Co(1)
B(17)-B(13)-Co(2)
B(29)-B(24)-Co(2)
B(23)-B(24)-Co(2)
B(25)-B(24)-Co(1)
O(1)-C(1)-Co(1)
C(51)-P(1)-Co(2)
156.79(14)
96.33(14)
89.51(14)
50.70(13)
120.0(3)
111.2(3)
105.8(3)
118.3(3)
140.9(3)
111.4(3)
114.8(2)
66.8(2)
145.1(3)
118.7(3)
65.0(2)
101.8(3)
177.9(4)
111.90(14)
65.1(2)
150.1(3)
73.9(2)
120.0(2)
The IR and NMR spectroscopic data for 2 may now be
addressed. The IR spectrum revealed, as expected, one CO
absorption at 2056 cm-1 for 2a, with a small but discernible
peak at 2028 cm-1 arising from a minor isomer. The 11B{1H}
NMR spectrum (Table 2) showed the expected number of peaks
for the major product 2a, with resonances of note in the fully
coupled spectrum at δ 18.1 and 14.9 (JHB ) 79 and 85 Hz,
respectively), due to the inequivalent B-H F Co boron nuclei.
In addition, two weak signals arising from the minor isomer
were seen at δ 14.3 and 10.6 with only the higher field resonance
showing a discernible JHB coupling (82 Hz). Peaks due to the
minor isomer, apart from in the 31P{1H} NMR spectrum, were
not observed elsewhere because of its low concentration. This
latter spectrum was simple, displaying one large singlet for 2a
at δ 4.1, with a much weaker resonance at δ 7.4 for the minor
it would make no difference to which Co atom the PMe2Ph
ligand is attached. In both of these we suggest that the carbon
atoms in the R-cage ligands lie anti to the carbonyl and
phosphine ligands, as has been consistently observed in 1a, 2a,
and previous structural studies.10b Unfortunately we can only
speculate, as the NMR spectra for 2b and 2c would likely be
very similar due to both complexes lacking in any kind of
symmetry, and our studies have not allowed us to discriminate
between the two. Of course, in the reaction of PMe2Ph with
1a, where numerous products are formed, both 2b and 2c could
be present, and we cannot rule out the formation of species
where the R-system cage carbon atoms are syn to the carbonyl
and phosphine ligands.
Unlike the compounds 1 NMR spectroscopic studies of 2a
showed no tendency for it to equilibrate with its minor isomer(s)
in solution, and indeed, traces of the minor isomer detected in
the original preparation could be completely removed. There-
fore BR/â-H F Co interconversion does not appear to be a
significant process with the monosubstituted phosphine com-
plexes 2.
In an attempt to substitute the remaining CO ligand in 2a,
reaction of 1b with PMe2Ph was repeated employing 2 equiv
of the phosphine in CH2Cl2. However, only 2a was recovered
from this reaction in any quantity, and no disubstituted product
could be isolated. When the reaction was repeated in CH2Cl2
with a 5-fold excess of PMe2Ph, then the complex [CoCl(PMe2-
Ph)2(η5-7,8-C2B9H11)] (3) was formed. While there is a fairly
extensive family of compounds known of the type [Co(η5-C5R5)-
(η5-7,8-C2B9H9R′2)] and [Co(η5-C2B9H9R′R′′)2]n- (R ) H, Me;
R′, R′′ ) H, alkyl, aryl, halide, 2e- donor ligands; n ) 0, 1),13
very few mononuclear cobaltacarborane species containing other
inorganic ligands coordinated to the cobalt have been reported.
For this reason and because the presence of the chloride ligand
was not ascertained from the original NMR measurements,
single crystals of compound 3 were obtained and subjected to
X-ray analysis. The molecular structure is shown in Figure 3,
and selected bond distances and angles are listed in Table 5.
1
isomer. The H NMR spectrum shows two resonances due to
the B-H F Co protons at δ -15.01 and -10.47 with JBH
)
79 and 85 Hz, respectively. There were two doublet resonances
for the diastereotopic PMe groups (δ 1.62 and 1.76, both with
JPH ) 10 Hz) and four peaks for the CH protons (δ 2.25, 2.33,
3.57, and 3.88), in accordance with the lack of molecular
symmetry. The 13C{1H} NMR spectrum revealed a single
resonance due to the CO group (δ 198.0), and the remaining
signals are in agreement with the established structure.
Although the experimental procedure for the synthesis of 2a
from 1b produced small amounts (<10%) of a minor isomer,
2a was clearly the major product. The proportion of the minor
isomer was somewhat variable and depended on the chromato-
graphic procedure. Curiously, if the synthesis was attempted
using pure 1a, an intractable mixture of 2a, the minor isomer,
and other compounds was produced. The nature of this minor
isomer is uncertain, and we rule out multiple substitution by
PMe2Ph to give a complex with no CO ligands, as will be
discussed momentarily, particularly as this species appears to
display a CO band (2028 cm-1) in the IR spectrum. Two
possibilities present themselves, which are plausible on the basis
of the work discussed so far. The first is an R,â-isomer (2b)
with the same cage B-H F Co configuration as in 2a, but with
the PMe2Ph carried by the other Co atom. The second is an
R,R-isomer (2c), similar to 1a in its cage arrangements, where
(13) Grimes, R. In ComprehensiVe Organometallic Chemistry II; Abel, E.
W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford,
U.K., 1995; Vol. 1 (Housecroft, C. E., Ed.), Chapter 9.

6566 Inorganic Chemistry, Vol. 35, No. 22, 1996
Hendershot et al.
Table 5. Selected Internuclear Distances (Å) and Angles (deg) for [CoCl(PMe2Ph)2(η5-7,8-C2B9H11)] (3) with Estimated Standard Deviations
in Parentheses
Co-C(1)
Co-B(5)
P(1)-C(11)
P(2)-C(22)
2.077(5)
2.136(6)
1.820(5)
1.820(5)
Co-C(2)
2.092(5)
2.292(1)
1.817(5)
1.824(5)
Co-B(3)
Co-P(1)
P(1)-C(13)
2.157(6)
2.271(2)
1.821(5)
Co-B(4)
Co-P(2)
P(2)-C(21)
2.192(5)
2.262(2)
1.818(5)
Co-Cl(1)
P(1)-C(12)
P(2)-C(23)
C(1)-Co-C(2)
C(1)-Co-B(4)
C(1)-Co-B(5)
B(4)-Co-B(5)
B(3)-Co-Cl(1)
C(1)-Co-P(1)
B(4)-Co-P(1)
C(1)-Co-P(2)
B(4)-Co-P(2)
P(1)-Co-P(2)
C(11)-P(1)-C(12)
C(12)-P(1)-C(13)
C(21)-P(2)-C(22)
C(22)-P(2)-C(23)
45.5(2)
81.9(2)
47.7(2)
49.0(2)
115.9(2)
99.7(1)
108.1(2)
160.7(1)
91.3(2)
C(1)-Co-B(3)
C(2)-Co-B(4)
C(2)-Co-B(5)
C(1)-Co-Cl(1)
B(4)-Co-Cl(1)
C(2)-Co-P(1)
B(5)-Co-P(1)
C(2)-Co-P(2)
B(5)-Co-P(2)
Co-P(1)-C(11)
Co-P(1)-C(13)
Co-P(2)-C(21)
Co-P(2)-C(23)
80.4(2)
81.2(2)
80.5(2)
C(2)-Co-B(3)
46.2(2)
49.9(2)
83.8(2)
86.9(1)
136.7(2)
157.9(2)
86.2(1)
81.5(2)
86.6(1)
116.0(2)
99.8(2)
119.1(2)
101.8(2)
B(3)-Co-B(4)
B(3)-Co-B(5)
C(2)-Co-Cl(1)
B(5)-Co-Cl(1)
B(3)-Co-P(1)
Cl(1)-Co-P(1)
B(3)-Co-P(2)
Cl(1)-Co-P(2)
Co-P(1)-C(12)
C(11)-P(1)-C(13)
Co-P(2)-C(22)
C(21)-P(2)-C(23)
95.4(1)
165.7(2)
143.6(1)
80.3(2)
115.7(1)
136.1(2)
120.3(2)
111.5(2)
112.9(2)
117.5(2)
99.5(1)
101.0(2)
106.2(2)
101.7(3)
101.2(2)
Scheme 1
Figure 3. Molecular structure of [CoCl(PMe2Ph)2(η5-7,8-C2B9H11)]
(3) showing the crystallographic atom-labeling scheme. Thermal
ellipsoids are shown at the 40% probability level. Hydrogen atoms are
omitted for clarity.
produces an equilibrium mixture (Scheme 1) of a 34e-
diamagnetic Co2 species A and a mononuclear 17e- CoII moiety
B. The latter then readily abstracts a chlorine atom from the
solvent to give the product 3. If the reaction of PMe2Ph with
1b is repeated in THF, an extremely air-sensitive yellow-brown
solution is produced. A 31P{1H} NMR spectrum in THF-d8 of
the oily product from this reaction shows a very broad resonance
at δ ca. -37 (ν1/2 ) 1953 Hz) with a weaker less broad peak
at δ ca. 35 (ν1/2 ) 641 Hz) in 4:1 ratio, respectively. We
tentatively attribute the smaller signal to diamagnetic complex
A and the larger to paramagnetic species B. Furthermore, the
11B{1H} NMR spectrum is dominated by very broad peaks due
to complex B over a wide chemical shift range (δ -1.2, -82.9,
-86.1, and -134.5), consistent with previously reported 11B
NMR spectra of paramagnetic cobaltacarborane complexes.17
Smaller, sharper peaks also appear in the 11B{1H} NMR
spectrum of the mixture at δ -7.8, -11.9, -12.9, and -20.1,
which would be due to complex A. Because of the prevalence
in the NMR spectra of peaks due to species B, the room
temperature equilibrium in THF (Scheme 1) clearly lies well
to the right. Variable temperature 31P{1H} NMR spectra of the
A-B mixture in THF-d8 were therefore measured down to -90
°C. The spectrum at this temperature showed no resonance due
to species B, but a much stronger sharper peak was observed at
δ 35.3 (ν1/2 ) 147 Hz) attributable to complex A. This result
implies a reversal in the equilibrium position shown in Scheme
The cobalt is ligated in an η5 fashion by the CCBBB face of
the cage [Co-C(1) ) 2.077(5) Å, Co-C(2) ) 2.092(5) Å, Co-
B(3) ) 2.157(6) Å, Co-B(4) ) 2.192(5) Å, Co-B(5) ) 2.136-
(6) Å]. The Co-P bond lengths in 3 (average 2.267 Å) are
similar to the Co-P distance observed in complex 2a [2.269-
(1) Å] and are again perceptibly longer than those in the other
cobalt complexes containing PMe2Ph ligands.12 The Co-Cl
bond [2.292(1) Å] is only slightly longer than the mean Co-
Cl distance of 2.260 Å quoted for a range of six-coordinate
CoIII complexes.14
The NMR spectroscopic data for 3 are as expected and reflect
the presence in the molecule of a mirror plane that includes the
cobalt and chlorine atoms and the midpoint of the C-C
connectivity in the cage, with the PMe2Ph ligands sitting
symmetrically on either side of this plane. Thus the 31P{1H}
NMR spectrum shows just one signal at δ 5.2 for the equivalent
phosphorus nuclei, and the 1H NMR spectrum reveals one
resonance for the cage CH protons at δ 3.49. The latter
spectrum shows two virtual triplet signals for the PMe groups
(δ 1.52 and 1.91), as expected for Cs molecular symmetry in
solution.
Of interest in the formation of 3 is the origin of the chloride
ligand. It is almost certainly derived from the CH2Cl2 solvent
used, and examples where metallacarborane complexes have
abstracted chlorine atoms from CH2Cl2 are documented.15,16 We
believe that compound 1b and an excess of PMe2Ph in solution
(15) Baker, R. T.; Delaney, M. S.; King, R. E.; Knobler, C. B.; Long, J.
A.; Marder, T. B.; Paxson, T. E.; Teller, R. G.; Hawthorne, M. F. J.
Am. Chem. Soc. 1984, 106, 2965.
(16) Jeffery, J. C.; Stone, F. G. A.; Topalogˇlu, I. Polyhedron 1993, 12,
319.
(17) Wiersema, R. J.; Hawthorne, M. F. J. Am. Chem. Soc. 1974, 96, 761.
(14) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.

Reaction of C2B9H13 with Dicobalt Octacarbonyl
Inorganic Chemistry, Vol. 35, No. 22, 1996 6567
Table 6. Crystallographic Data
1a
2a
3
formula
Mr
T (K)
C6H22B18Co2O2
438.68
173
C13H33B18Co2OP
548.80
173
C18H33B9ClCoP2
503.1
292
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
15.842(7)
9.597(4)
12.946(4)
triclinic
P1h
monoclinic
P21/c
11.8998(13)
12.973(2)
16.470(3)
10.364(3)
12.073(3)
12.251(3)
103.901(12)
111.342(12)
104.563(11)
1284.9(6)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
91.35(3)
98.468(14)
1967.7(13)
4
1.481
1.685
872
2514.9(7)
4
1.329
0.919
d
calcd (g cm-3
)
1.418
1.362
556
µ(Mo KR) (mm-1
F(000) (e)
)
1040
cryst dimens (mm)
crystal color, shape
no. of reflcns measd
no. of independent reflcns
0.60 × 0.20 × 0.05
brown plate
8665
0.10 × 0.10 × 0.05
brown prism
4933
0.31 × 0.16 × 0.16
purple parallelepiped
2633
3436
3504
2333a
2θ range (deg)
reflcns limits
5.0-50.1
3.7-46.5
3.0-40.0
h
k
l
-17 to +18
-11 to +9
0 to +11
-8 to +11
-6 to +13
0 to +12
-15 to +15
-13 to +13
-15 to +15
refinement method
full-matrix least-squares
full-matrix least-squares
full-matrix least-squares
on observed F dataa
R ) 0.356 (R′ ) 0.400)d
g ) 0.0001e
on all F2 data
on all F2 data
final residuals
weighting factors
goodness of fit
wR2 ) 0.176b (R1 ) 0.065)c
a ) 0.0468; b )12.3838b
1.175
wR2 ) 0.096b (R1 ) 0.044)c
a ) 0.0000; b ) 3.8365b
1.226
1.83
final electron density diff features
1.03, -0.82
0.36, -0.31
0.80, -0.28
(max/min) (e Å-3
)
2
2
a 1948 observed reflections used in refinement with Fo > 4σ(Fo). b Structure was refined on Fo using all data: wR2 ) [∑[w(Fo - Fc2)2]/
∑w(Fo )2]1/2 where w-1 ) [σ2(Fo ) + a(P)2 + bP] and P ) [max(Fo ,0) + 2Fc2]/3. c The value in parentheses is given for comparison with refinements
2
2
2
2
based on Fo with a typical threshold of Fo > 4σ(Fo) and R1 ) ∑||Fo| - |Fc||/∑|Fo| and w-1 ) [σ2(Fo) + gFo ]. d R ) ∑||Fo| - |Fc||/∑|Fo|, R′ )
2
∑w1/2||Fo| - |Fc||/∑w1/2|Fo|. e Weighting scheme of the form where w-1 ) [σ2(Fo) + gFo ], where σ2(Fo) is the variance in Fo due to counting
statistics; g was chosen so as to minimize variation in ∑w(|Fo| - |Fc|)2 with |Fo|.
1, as one would expect since the process is a simple homolytic
bond fission/formation reaction. If a few drops of CCl4 are
added to the THF solution of A and B, the color turns
immediately purple and compound 3 is formed, identified by
its NMR spectra.
spectrum were as expected based on a C2 molecular symmetry
for 4a and no symmetry for 4b. The 13C{1H} NMR spectrum
clearly revealed a broad resonance due to the CNBut nuclei in
4a at δ 142.9. This chemical shift is somewhat lower than that
observed for the ligating isocyanide carbon atoms of the
complex [Co2(CNBut)8],18 which displays three signals (δ 229.0,
182.0, and 177.7) in a toluene-d8 solution at -90 °C. However,
the chemical shift observed for 4a is fairly similar in magnitude
to the analogous peaks in the 13C{1H} NMR spectra of the
complexes [M(CNBut)2(η5-7,8-Me2-7,8-C2B9H9)] (M ) Ni, δ
) 137.1; M ) Pt, δ ) 127.7).9 The minor isomer 4b shows
one peak due to a CNBut nucleus at δ 144.1; again it is believed
that a second peak may be hidden by the stronger signal due to
4a. All the remaining signals observed are in agreement with
the proposed structures for 4a and 4b. It is assumed that the
carbon atoms in the R-cage systems in 4a and 4b lie anti to the
CNBut ligands, similar to that found for 1a and 2a. Of course,
only structural analysis by X-ray diffraction could prove this
beyond doubt, but it was not possible to obtain X-ray quality
crystals of either isomer of 4.
Reaction of either 1a or 1b in CH2Cl2 with 2 equiv of CNBut
at room temperature, followed by column chromatography,
produced the complex [Co2(CNBut)2(η5-7,8-C2B9H11)2] (4) in
reasonable yield. While the IR spectrum of a petroleum ether
solution of 4 showed only two strong, broad νmax(NC) bands at
2190 and 2180 cm-1, it was evident from NMR spectroscopy
that the compound existed as an inseparable mixture of two
isomers, 4a and 4b. On the basis of NMR measurements of
this and other complexes discussed herein, we can confidently
assign the major component 4a as the R,R-isomer, akin to 1a,
and 4b as the R,â-complex, analogous to 1b. Furthermore, 4a
and 4b exist in CH2Cl2 solution in equilibrium in a 3:1 ratio,
respectively.
In a fully coupled 11B NMR spectrum, a doublet peak at δ
12.3 (JHB ) 89 Hz) corresponds to the equivalent B-H F Co
boron nuclei in 4a, with two smaller peaks at δ 19.0 and 13.0
(JHB ) 79 and 89 Hz, respectively) due to inequivalent B-H
F Co borons in 4b. All of the peaks expected for 4a were
accounted for in this spectrum, the remaining signals being
attributable to isomer 4b. Two of the three quartet resonances
expected for the B-H F Co protons in the isomer mixture were
That the reaction between either 1a or 1b and CNBut produces
a mixture of the isomers 4 at their equilibrium ratio within 1 h
of the start of the reaction is interesting, when one considers
that it was found that solutions of 1a or 1b only attained
equilibrium proportions at times g12 h. This observation may
provide some insight into the reaction mechanism. It is
proposed that formation of 4 progresses through initial associa-
1
observed in the H NMR spectrum. These occur at δ -11.54
(JBH ) 89 Hz) for 4a and at δ -13.72 (JBH ) 79 Hz) for 4b,
the other resonance for 4b probably being masked by the strong
signal due to 4a. The remaining signals in the 1H NMR
(18) Caroll, W. E.; Green, M.; Galas, A. M. R.; Murray, M.; Turney, T.
W.; Welch, A. J.; Woodward, P. J. Chem. Soc., Dalton Trans. 1980,
80.

6568 Inorganic Chemistry, Vol. 35, No. 22, 1996
Hendershot et al.
Scheme 2
Figure 4. 13C{1H} NMR spectrum showing the principal peaks for
the nido-carborane 6: (a) quartet at δ 171.7 due to the BCO carbon
nucleus, (b) signals at δ 57.5 and 46.6 due to cage CH carbon nuclei.
possible to obtain 5 in sufficient purity to procure an adequate
microanalysis, chiefly because it is formed as an oily solid with
unavoidable contamination by very small amounts of 6.
However, a positive-ion EI mass spectrum was obtained and
this clearly shows a parent molecular ion peak at m/z 275 and
peaks due to molecular ions resulting from consecutive loss of
three CO ligands at 247, 219, and 190, respectively.
tive steps (Scheme 2). This would involve addition of one or
both equivalents of CNBut to 1a or 1b to give molecules like
C and D, respectively, and would involve a lifting of the B-H
F Co contacts. Bands for CO groups appearing and then
diminishing in the IR spectrum in the range 2029-1937 cm-1
could correspond to such intermediate species. An opportunity
is thus provided for both cages to rotate freely and interconvert
the BR-H and Bâ-H bonds used in the formation of the agostic
B-H F Co contacts. Upon loss of CO, the complexes 4 are
generated in their thermodynamically stable ratio.
A variable temperature 11B{1H} NMR experiment was
conducted on a toluene-d8 solution of 4, measuring the spectra
at temperatures up to 90 °C to observe the effect on the
equilibrium between isomers 4a and 4b. Only minimal change
was observed when compared with room temperature CD2Cl2
solutions, there being a slight adjustment in the equilibrium
position, with the peaks due to each isomer remaining as distinct
as those recorded at ambient temperatures.
The nido-carborane 6 is a new member of the well-established
family of charge-compensated species of formulation nido-n-
L-7,8-C2B9H11 (n ) 9 or 10, L ) NEt3, NMe2Ph, NC5H5,
NC5H4CO2Me-4, NMe2COMe, THF, NCMe).19,20 In these
molecules a neutral donor molecule L has replaced hydride (H-)
on a boron vertex in the open pentagonal face of the cage. Such
species have been described as asymmetric (n ) 9) or symmetric
(n ) 10) according to the site occupied by the donor molecule
in the face.19c,21 The location of the proton in the face of the
symmetric cage systems apparently does not lower the sym-
metry, probably because in solution there is rapid exchange
between the two possible BR-Bâ(L) bridge sites. The function
of a CO molecule as a donor into a carborane cage is
comparatively rare, but has been observed before in the related
nido-icosahedral carborane nido-n-CO-7-NMe3-7-CB10H10 (n )
8 or 9).22 In this molecule the CO ligand could be bound to
either an R- or a â-site in the CB4 face of the cage. A band in
the IR spectrum of 6 at the relatively high frequency of 2152
cm-1 is in accord with the presence of the BCO group and is
similar to that observed for compound 5. On the basis of its
NMR spectra (Table 2), compound 6 is assigned an asymmetric
structure with the CO group attached to a boron atom in the
The compounds [Co(CO)2(η5-10-CO-7,8-C2B9H10)] (5) and
nido-9-CO-7,8-C2B9H11 (6) were minor products of the reaction
between [Co2(CO)8] and nido-7,8-C2B9H13. Both species were
never observed other than in poor yield, which is disappointing
because 5 is isolobal with the well-known reagent [Co(CO)2-
(η5-C5H5)]. The cage ligand in 5 is zwitterionic and formally
contributes five electrons to the metal. Such charge-compen-
sated metallacarboranes are well-known.19,20 The appearance
R-site in the CCBBB ring. The asymmetry is reflected in the
appearance of two resonances at δ 2.81 and 3.12 in the 1H NMR
spectrum for the cage CH protons. There is also a broad signal
at δ -2.74 that may be ascribed to the endo-B-H-B group.
The 11B{1H} NMR spectrum is also indicative of asymmetry
displaying eight peaks, with the relative intensity of one
resonance (δ -0.1) corresponding to the fortuitous overlap of
two signals. Importantly, a fully coupled 11B NMR spectrum
revealed that the peak at δ -30.5 remained a singlet and thus
may be assigned to the BCO group. The 13C{1H} NMR
spectrum was particularly informative, and the principal peaks
are shown in Figure 4. In accordance with lack of symmetry
in the molecule, two resonances are observed for the cage CH
nuclei, one of these signals (δ 57.5) showing a fully resolved
11B-13C coupling of 43 Hz and the other (δ 46.6) a broader
less resolved coupling of ca. 32 Hz. Normally these peaks are
broad and weak, and since both these carbon atoms are each
bonded to three inequivalent boron atoms in the polyhedral cage
framework, the nature of this coupling is unclear. Possibly the
couplings are all of a very similar magnitude, especially so for
the quartet at δ 57.5. Most important, though, is the observation
of a quartet at δ 171.7 (JBC ) 84 Hz) for the BCO carbon
1
of only one resonance in the H NMR spectrum of 5 for the
cage CH protons (δ 3.43) is indicative of the structure shown,
with the CO group at the â-site in the CCBBB ring ligating the
metal atom. The observation in the 11B{1H} NMR spectrum
of six signals (1:2:2:1:2:1) is also in accord with a symmetrical
cage structure. The peak at δ -23.9 is assigned to the BCO
group since in a fully coupled 11B NMR spectrum it remains as
a singlet. A CO stretching band in the IR spectrum at 2156
cm-1 may be attributed to the BCO group, with strong bands
at 2040 and 1990 cm-1 arising from the cobalt carbonyl ligands.
The carbonyl carbon nuclei are clearly visible in the 13C{1H}
NMR spectrum, with a broad singlet at δ 197.0 and a broad
quartet at δ 172.0, the latter showing a 11B-13C coupling of 85
Hz, allowing it to be assigned to the BCO group. It was not
(19) (a) Wong E. H. S.; Hawthorne, M. F. Inorg. Chem. 1978, 17, 2863.
(b) King, R. E.; Miller, S. B.; Knobler, C. B.; Hawthorne, M. F. Inorg.
Chem. 1983, 22, 3548. (c) Kang, H. C.; Lee, S. S.; Knobler, C. B.;
Hawthorne, M. F. Inorg. Chem. 1991, 30, 2024. (d) Chizhevsky, I.
T.; Pisareva, I. V.; Petrovskii, P. V.; Bregadze, V. I.; Yanovsky, A.
I.; Struchkov, Yu T.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem.
1993, 32, 3393.
(21) Young, D. C.; Howe, D. V.; Hawthorne, M. F. J. Am. Chem. Soc.
(20) (a) Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.; Woollam, S.
F. Organometallics 1994, 13, 157. (b) Go´mez-Saso, M.; Mullica, D.
F.; Sappenfield, E. L.; Stone, F. G. A. Polyhedron 1996, 15, 793.
1969, 91, 859.
(22) Khan, S. A.; Morris, J. H.; Siddiqui, S. J. Chem. Soc., Dalton Trans.
1990, 2053.

Reaction of C2B9H13 with Dicobalt Octacarbonyl
Inorganic Chemistry, Vol. 35, No. 22, 1996 6569
Table 7. Atomic Positional Parameters (Fractional Coordinates ×
104) and Equivalent Isotropic Displacement Parameters (Å2 × 103)
for the Atoms of 1a
nucleus, which is very similar to that seen for the BCO group
in compound 5.
It is strongly believed that compound 6 derives from a cobalt
species [Co(CO)2(η5-9-CO-7,8-C2B9H10)] similar to complex 5.
This complex may then have decomposed, ejecting compound
6 possibly during chromatographic workup or even before. We
have frequently found that unstable cobaltacarborane species
can produce free cages among the decomposition products,
though this is the first time a CO ligand from a transition metal
moiety has been transferred directly to a C2B9 cage system.
Attempts to synthesize compound 6 using a more logical route
based on previous methods used to prepare compounds of the
type nido-n-L-7,8-C2B9H11 have so far been unsuccessful.
atom
x
y
z
U(eq)a
Co(1)
Co(2)
C(1)
O(1)
C(2)
3302(1)
1737(1)
3471(4)
3596(4)
1322(5)
1043(4)
4346(4)
3466(4)
2669(5)
3158(5)
4234(5)
4260(5)
3194(5)
2998(5)
3970(5)
4738(5)
3973(5)
885(5)
1853(4)
2463(5)
1734(5)
723(5)
1128(6)
2136(6)
2057(5)
974(5)
756(1)
987(1)
6460(1)
6628(1)
5456(6)
4795(5)
5400(6)
4635(5)
6999(5)
7542(5)
6666(5)
5422(5)
5702(6)
7587(6)
7368(6)
6012(5)
5409(6)
6397(6)
6573(5)
7744(5)
8134(5)
7267(5)
6258(6)
6600(6)
8767(6)
8465(6)
7294(6)
6864(6)
7789(7)
8208(6)
27(1)
28(1)
41(2)
63(2)
50(2)
77(2)
35(1)
33(1)
28(1)
33(2)
34(2)
38(2)
35(2)
34(2)
41(2)
40(2)
39(2)
43(2)
32(1)
31(2)
32(2)
40(2)
47(2)
38(2)
38(2)
39(2)
48(2)
46(2)
-479(8)
-1224(6)
1517(8)
1857(8)
1899(7)
2271(7)
2594(7)
2438(8)
1923(8)
3500(8)
3940(7)
4096(8)
3672(9)
3319(9)
4646(8)
388(8)
O(2)
C(11)
C(12)
B(13)
B(14)
B(15)
B(16)
B(17)
B(18)
B(19)
B(110)
B(111)
C(21)
C(22)
B(23)
B(24)
B(25)
B(26)
B(27)
B(28)
B(29)
B(210)
B(211)
Conclusions
The isomers 1 are as far as we are aware the first cobalta-
carborane carbonyl complexes to be isolated since an early report
of the existence of the unstable salt [NMe4][Co(CO)2(η5-7,8-
C2B9H11)].23 Although not structurally similar, the compounds
1 are isolobal with the cylopentadienylnickel carbonyl [Ni2(µ-
CO)2(η5-C5H5)2]. The reactions between 1 and PMe2Ph or
CNBut, which afford the species 2, 3, and 4, indicate that the
species 1 will serve as useful precursors to other complexes in
which a closo-3,1,2-CoC2B9 cage system is bonded via cobalt
to other ligands. Although the charge-compensated nido-
carborane 6 was only obtained in low yield, its existence is of
interest in the context of the rarity shown by CO as a donor
group to boron.
331(7)
-581(8)
-1145(8)
-418(9)
-672(9)
-1315(8)
-2280(8)
-2186(8)
-1181(9)
-2355(9)
408(6)
1227(6)
a Equivalent isotropic U defined as one-third of the trace of the
orthogonalized Uij tensor.
Experimental Section
General Considerations. Solvents were freshly distilled from
appropriate drying agents prior to use. Petroleum ether refers to that
fraction of boiling point 40-60 °C. All reactions were performed under
an atmosphere of dry nitrogen using Schlenk line techniques. Chro-
matography columns (ca. 15 cm in length and ca. 3 cm in diameter)
were packed with silica gel (Aldrich, 70-230 mesh). Celite pads used
for filtration were ca. 4 cm thick. The reagent nido-7,8-C2B9H13 was
prepared using a modified literature method.24 The NMR measurements
were recorded in CD2Cl2 at the following frequencies: 1H at 360.13
MHz, 13C{1H} at 90.6 MHz, 11B{1H} at 115.3 MHz, and 31P{1H} at
145.8 MHz.
matograph each fraction and repeat the crystallizations. Even this
procedure failed for 5 which persisted as an oily product.
Synthesis of [Co2(CO)(PMe2Ph)(η5-7,8-C2B9H11)2]. Compound 1b
(0.20 g, 0.46 mmol) in CH2Cl2 (20 mL) was treated dropwise with
PMe2Ph (65 µL, 0.46 mmol), and the mixture was stirred for 6 h.
Solvent was reduced in volume in vacuo to ca. 5 mL and the solution
chromatographed at -30 °C. Elution with CH2Cl2-petroleum ether
(1:1) removed a red-brown band, from which solvent was removed in
vacuo. The residue was crystallized from CH2Cl2-petroleum ether
(1:8, 10 mL) to yield [Co2(CO)(PMe2Ph)(η5-7,8-C2B9H11)2] (2a) (0.13
g).
Reaction between [Co2(CO)8] and nido-7,8-C2B9H13. (i) A 500
mL jacketed round-bottom flask fitted with a 500 mL dropping funnel
and a nitrogen bubbler was charged with a CH2Cl2 (150 mL) solution
of [Co2(CO)8] (2.00 g, 5.85 mmol) and cooled to 0 °C. A solution of
nido-7,8-C2B9H13 (1.60 g, 11.90 mmol) in CH2Cl2 (250 mL) was
syringed into the dropping funnel and then added dropwise (ca. 2-3
s-1). The mixture was slowly warmed to room temperature and stirred
for 24 h. After filtration through a Celite pad, the volume of the solvent
was reduced in vacuo to ca. 8 mL and the solution chromatographed
at -30 °C. Elution with petroleum ether yielded initially a dark brown
fraction containing 1b. A second dark brown band containing 1a was
next removed using a CH2Cl2-petroleum ether (1:9) mixture. Further
elution with CH2Cl2-light petroleum ether (2:3) gave a light brown
band of 5. Finally, a pale brown band containing 6 was eluted using
CH2Cl2-petroleum ether (1:1). Solvent was removed from each
fraction separately, and the complexes isolated by crystallizations from
CH2Cl2-petroleum ether or petroleum ether as follows: [Co2(CO)2-
(η5-7,8-C2B9H11)2] (1a) (0.51 g) from CH2Cl2-petroleum ether (1:9,
10 mL); [Co2(CO)2(η5-7,8-C2B9H11)2] (1b) (0.25 g) from CH2Cl2-
petroleum ether (1:9, 10 mL); [Co(CO)2(η5-10-CO-7,8-C2B9H10)] (5)
(0.13 g) from CH2Cl2-petroleum ether (1:9, 10 mL) at -78 °C; nido-
9-CO-7,8-C2B9H11 (6) (0.10 g) from petroleum ether (5 mL) at -78
°C. To achieve microanalytical purity, it was necessary to rechro-
Synthesis of [CoCl(PMe2Ph)2(η5-7,8-C2B9H11)]. A solution of 1b
(0.18 g, 0.41 mmol) in CH2Cl2 (10 mL) was treated with PMe2Ph (0.30
mL, 2.11 mmol) dropwise and the mixture stirred at room temperature
for 3 d. Solvent was removed in vacuo, and the residue was dissolved
in CH2Cl2 (5 mL) and chromatographed at -30 °C. Elution with a
CH2Cl2-petroleum ether mixture (2:3) removed a purple band. Solvent
was removed in vacuo, and crystallization of the product from CH2-
Cl2-petroleum ether (1:5, 12 mL) gave purple microcrystals of
[CoCl(PMe2Ph)2(η5-7,8-C2B9H11)] (3) (0.26 g).
Synthesis of [Co2(CNBut)2(η5-7,8-C2B9H11)2]. Compound 1a (or
1b) (0.20 g, 0.46 mmol) was dissolved in CH2Cl2 (20 mL), and CNBut
(110 µL, 0.97 mmol) was added dropwise. The mixture was stirred
for 1 h, after which the solution was reduced in volume in vacuo to ca.
5 mL and chromatographed at -30 °C. Elution with CH2Cl2-
petroleum ether (1:1) afforded a brown fraction. Removal of solvent
in vacuo and crystallization of the residue from CH2Cl2-petroleum
ether (1:8, 10 mL) gave [Co2(CNBut)2(η5-7,8-C2B9H11)2] (4) (0.16 g
from 1a, 0.13 g from 1b).
Crystal Structure Determinations and Refinements. Crystals of
1a, 2a, and 3 were grown by diffusion of petroleum ether into CH2Cl2
solutions of the complexes. Low-temperature data sets were collected
for 1a and 2a with the crystals mounted on a glass fiber. A crystal of
3a was mounted in a glass capillary with data collection carried out at
an ambient temperature.
(23) Hawthorne, M. F.; Ruhle, H. W. Inorg. Chem. 1969, 8, 176.
(24) (a) Hlatky, G. G.; Crowther, D. J. Inorg. Synth., in press. (b) Young,
D. A. T.; Wiersma, R. J.; Hawthorne, M. F. J. Am. Chem. Soc. 1971,
93, 5687.
Data for 1a and 2a were collected on a Siemens SMART CCD area-
detector three-circle diffractometer using Mo KR X-radiation, λ )

6570 Inorganic Chemistry, Vol. 35, No. 22, 1996
Hendershot et al.
Table 8. Atomic Positional Parameters (Fractional Coordinates ×
104) and Equivalent Isotropic Displacement Parameters (Å2 × 103)
for the Atoms of 2a
Table 9. Atomic Positional Parameters (Fractional Coordinates ×
104) and Equivalent Isotropic Displacement Parameters (Å2 × 103)
for the Atoms of 3
atom
x
y
z
U(eq)a
atom
x
y
z
U(eq)a
Co(1)
Co(2)
C(11)
C(12)
B(13)
B(14)
B(15)
B(16)
B(17)
B(18)
B(19)
B(110)
B(111)
C(21)
C(22)
B(23)
B(24)
B(25)
B(26)
B(27)
B(28)
B(29)
B(210)
B(211)
C(1)
2764(1)
4614(1)
1477(5)
2230(5)
4139(6)
4555(6)
2744(6)
1720(6)
3418(6)
4885(6)
4041(6)
2103(6)
3416(6)
4913(5)
4412(5)
2902(5)
2418(5)
3814(5)
4082(6)
2751(6)
1453(6)
2011(5)
3652(6)
2184(6)
2873(5)
2915(4)
6996(1)
7228(5)
8038(5)
8238(5)
8421(5)
9382(6)
10158(6)
9966(6)
9019(5)
2693(1)
2295(1)
3793(4)
3628(4)
3942(5)
4387(5)
4207(5)
4873(5)
4978(5)
5525(5)
5694(5)
5293(5)
6091(5)
670(4)
1217(4)
1568(5)
1114(4)
562(4)
-325(5)
233(5)
838(1)
2594(1)
780(4)
2102(4)
2632(5)
1465(5)
252(5)
2102(5)
3300(5)
2898(5)
1401(5)
958(5)
2570(5)
2651(4)
3686(4)
3053(5)
1390(4)
1175(5)
3233(5)
3449(5)
1960(5)
799(5)
1613(5)
2058(5)
-562(4)
-1470(3)
2887(1)
1467(4)
3652(4)
3915(4)
5158(4)
5990(5)
5607(6)
4388(6)
3555(5)
17(1)
16(1)
22(1)
21(1)
20(1)
22(1)
23(1)
26(1)
23(1)
23(1)
24(1)
27(1)
26(1)
21(1)
18(1)
19(1)
17(1)
20(1)
22(1)
23(1)
21(1)
18(1)
21(1)
22(1)
24(1)
38(1)
19(1)
31(1)
27(1)
22(1)
26(1)
36(1)
45(2)
45(2)
33(1)
Co
C(1)
C(2)
B(3)
B(4)
B(5)
B(6)
B(7)
2439(1)
1643(4)
2471(4)
3783(5)
3785(5)
2355(5)
2082(5)
3481(5)
4307(5)
3403(5)
2034(5)
3260(5)
1224(1)
1401(1)
800(4)
1810(1)
454(3)
285(4)
959(1)
1231(3)
550(3)
28(1)
36(2)
37(2)
37(2)
37(2)
36(2)
47(2)
44(2)
42(2)
44(2)
45(2)
49(2)
42(1)
31(1)
44(2)
49(2)
31(2)
43(2)
52(2)
56(3)
48(2)
41(2)
34(1)
52(2)
52(2)
34(2)
41(2)
55(3)
58(3)
51(2)
41(2)
726(4)
849(4)
1215(5)
1025(4)
-791(5)
-614(5)
-52(5)
125(5)
1894(3)
2088(3)
1059(4)
839(4)
B(8)
B(9)
1705(3)
2460(4)
2056(4)
1836(4)
-225(1)
1570(1)
1009(3)
2506(3)
1832(3)
2642(3)
2804(3)
2179(4)
1380(3)
1206(3)
476(1)
-572(3)
995(4)
401(3)
1040(3)
983(4)
291(4)
-343(4)
-289(3)
B(10)
B(11)
Cl(1)
P(1)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
P(2)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
-330(5)
-991(5)
2149(1)
2967(1)
4095(4)
3558(4)
2387(3)
2266(4)
1823(4)
1492(4)
1605(4)
2043(4)
2899(1)
2609(4)
2966(4)
4262(4)
4926(4)
5963(4)
6336(5)
5698(5)
4658(4)
2115(4)
108(4)
-93(5)
-1096(5)
-1906(5)
-1714(4)
-723(4)
3670(1)
3875(5)
5127(4)
3290(4)
3678(4)
3389(5)
2721(5)
2354(4)
2623(4)
134(5)
-502(4)
-767(5)
-1044(5)
1979(4)
1542(3)
3101(1)
2713(5)
4756(4)
2551(4)
2837(4)
2476(5)
1815(5)
1527(5)
1890(5)
O(1)
P(1)
C(31)
C(41)
C(51)
C(52)
C(53)
C(54)
C(55)
C(56)
a Equivalent isotropic U defined as one-third of the trace of the
orthogonalized Uij tensor.
an empirical absorption correction26 based on nine high-angle ψ scans
was carried out. The structure was solved by direct methods, which
located most of the non-hydrogen atoms, and successive Fourier
difference syntheses were used to locate all remaining non-hydrogen
atoms. Refinement was by full-matrix least squares on F using Siemens
SHELXTL-PC version 4.1,25c with anisotropic thermal parameters for
all non-hydrogen atoms. Methyl and phenyl hydrogen atoms were
included in calculated positions (C-H 0.96 Å) and constrained to ride
on their parent carbon atoms with fixed isotropic thermal parameters
(Uiso ) 0.08 Å2). Terminal B-H hydrogen atoms were also included
in calculated positions (B-H 1.10 Å, Uiso ) 0.06 Å2).27 All calculations
were performed on a VAX station. Atomic scattering factors were
taken from the usual source.28
a Equivalent isotropic U defined as one-third of the trace of the
orthogonalized Uij tensor.
0.710 73 Å. For three settings of φ, narrow data “frames” were
collected for 0.3° increments in ω. In both cases 1321 frames of data
were collected affording rather more than a hemisphere of data. The
substantial redundancy in data allows empirical absorption corrections
to be applied using multiple measurements of equivalent reflections.
Crystals of 2a were very small, and data frames were collected for 60
s per frame giving an overall data collection time of ca. 25 h. For 1a
data frames were collected for 20 s per frame. The data frames were
integrated using SAINT,25a and the structures were solved by conven-
tional direct methods. The structures were refined by full-matrix least
squares on all F2 data using Siemens SHELXTL version 5.03,25b and
with anisotropic thermal parameters for all non-hydrogen atoms. For
both 1a and 2a the agostic B-H F Co protons were located from
final electron density difference syntheses, and their positions were
refined. All other hydrogen atoms were included in calculated positions
and allowed to ride on the parent boron or carbon atoms with isotropic
thermal parameters (Uiso ) 1.2 × Uiso equiv of the parent atom except
for Me protons where Uiso ) 1.5 × Uiso equiv). All calculations were
carried out on Silicon Graphics Iris, Indigo, or Indy computers.
The data set for 3 was collected on an Enraf-Nonius CAD4-F
automated diffractometer operating in the ω-2θ scan mode, using
graphite-monochromated Mo KR X-radiation. Data were collected at
various scan speeds of 0.54-5.17° min-1 in ω with a scan range of
1.15° + 0.34 tan θ. No significant variations were observed in the
intensities of the monitored check reflections (<1%). All observed
data were corrected for Lorentz and polarization effects, after which
Final atomic positional parameters for non-hydrogen atoms with
equivalent isotropic thermal parameters for complexes 1a, 2a, and 3
are listed in Tables 7, 8, and 9, respectively.
Acknowledgment. We thank the Robert A. Welch Founda-
tion for support (Grants AA-1201 and 0668).
Supporting Information Available: Complete tables of atom
parameters, bond lengths and angles, and anisotropic thermal parameters
for 1a, 2a, and 3 (36 pages). Ordering information is given on any
current masthead page.
IC960560S
(26) Enraf-Nonius Vax Structure Determination Package; Enraf-Nonius:
Delft, The Netherlands, 1989.
(27) Sherwood, P. BHGEN, a program for the calculation of idealized
H-atom positions for a nido-icosahedral carborane cage; University
of Bristol, 1986.
(25) (a) SAINT; (b) SHELXTL, version 5.03; (c) SHELXTL-PC, version
4.1; Siemens X-ray Instruments, Madison, WI.
(28) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, U.K., 1974; Vol. 4.