Construction of metal butterflies on a metallacarborane scaffold. 2. Synthesis and structures of hetero-tri- and -tetrametallic clusters

Article abstract of DOI:10.1021/om060418r

Treatment of [N(PPh₃)₂][1,3,6-{Re(CO) ₃}-3,6-(μ-H)₂-1,1-(CO)₂-2-Ph-closo-1,2- IrCB₉H₇] (2a) with {Cu(PPh₃)}⁺ gives two types of polymetallic species: [1,4,7

Full text of DOI:10.1021/om060418r

4452
Organometallics 2006, 25, 4452-4461
Construction of Metal Butterflies on a Metallacarborane Scaffold. 2.
Synthesis and Structures of Hetero-tri- and -tetrametallic Clusters
Thomas D. McGrath,* Shaowu Du, Bruce E. Hodson, and F. Gordon A. Stone*
Department of Chemistry & Biochemistry, Baylor UniVersity, Waco, Texas 76798-7348
ReceiVed May 15, 2006
Treatment of [N(PPh3)2][1,3,6-{Re(CO)3}-3,6-(µ-H)2-1,1-(CO)2-2-Ph-closo-1,2-IrCB9H7] (2a) with {Cu-
(PPh3)}+ gives two types of polymetallic species: [1,4,7-{Cu(PPh3)}-1,5,6-{Re(CO)3}-4,5,6,7-(µ-H)4-
1,1-(CO)2-2-Ph-closo-1,2-IrCB9H5] (4a), containing a V-shaped Re-Ir-Cu trimetallic unit, and [1,3,6-
{Cu2(PPh3)2}-3,6-(µ-H)2-1,1-(CO)2-2-Ph-closo-1,2-IrCB9H7] (5a), containing an IrCu2 triangle. In contrast,
[N(PPh3)2][1,3,6-{Re(CO)3}-3,6-(µ-H)2-1,1-(CO)2-2-Ph-closo-1,2-RhCB9H7] (2b) with the same copper
cation essentially affords only the corresponding RhCu2 species 5b. Reaction of 2a with {Au(PPh3)}+
yields up to three types of polymetallic species, namely, [1,6-{Au2(PPh3)2}-6-(µ-H)-1,1-(CO)2-2-Ph-
closo-1,2-IrCB9H8] (7a), which contains an IrAu2 triangle and is thus related to compounds 5, [1,3,6-
{Au2(PPh3)2Re(CO)3}-6-(µ-H)-1,1-(CO)2-2-Ph-closo-1,2-IrCB9H7] (8a), in which there is an {Au2IrRe}
“butterfly” arrangement of metal atoms that is supported by the carborane, and the tetrametallic [1,3-
{Au3(PPh3)3}-1,1-(CO)2-2-Ph-closo-1,2-IrCB9H8] (9a), which contains an Au3 triangle bonded to the
iridacarborane. The parallel reaction of 2b with {Au(PPh3)}+ gives up to four polymetallic products:
these are compounds 7b, 8b, and 9b, the rhodium-containing analogues of 7a, 8a, and 9a, respectively,
along with the trimetallic [8,9,10-endo-{Au(PPh3)}-3,4,8-exo-{Re(CO)3}-3,4-(µ-H)2-8,8-(CO)2-7-Ph-nido-
8,7-RhCB9H7] (6b), which has a V-shaped Re-Rh-Au unit and a nido-structured rhodacarborane core.
these clusters add an additional metal center upon treatment
with a suitable cationic moiety.
Introduction
We have for some time been investigating the chemistry of
metal-monocarbollide complexes and, in particular, have taken
advantage of the often anionic nature of these species to prepare
bi- or polymetallic compounds by reaction with simple cationic
transition metal fragments.1 Although at first such studies were
essentially limited to 12-vertex {MCB10} species derived from
the corresponding long-known2 {CB10} carboranes, recent
developments in the synthesis of smaller monocarboranes3 have
allowed access to sub-icosahedral metal-monocarbollide com-
plexes and thence to their polymetallic derivatives. Among the
latter class, we have prepared {MCB9} (M ) Re,4 Mn,5 Mo6),
{Co2CB9},7 {MCB8} (M ) Fe,8 Co7), {FeCB7},9 and {M2CB7}
(M ) Fe,9 Co7) species and have demonstrated that many of
In the preceding paper,10 we focused on {MCB9} species, spe-
cifically [N(PPh3)2][NEt4][1,1,1-(CO)3-2-Ph-closo-1,2-MCB9H9]
(M ) Mn (1a), Re (1b); see Chart 1), and described their
reactions with sources of the cations {M′(CO)2}+ (M′ ) Ir, Rh)
to afford the bimetallic species [N(PPh3)2][1,3,6-{M(CO)3}-3,6-
(µ-H)2-1,1-(CO)2-2-Ph-closo-1,2-M′CB9H7] (M ) Re, M′ ) Ir
(2a), Rh (2b); M ) Mn, M′ ) Ir (2c), Rh (2d)). In these latter
products, the {M(CO)3} fragment, formerly a cluster vertex,
has assumed an exo-polyhedral role, while the incoming {M′-
(CO)2} units now occupy a site within the cluster. The metal-
lacarborane anions of compounds 2, as they retain a negative
charge, are attractive substrates for reaction with a further
transition metal monocation to obtain heterotrimetallic species.
Such reactions, using copper- and gold-phosphine cations, to
give tri- and even tetrametallic products, are the subject of this
report. A preliminary account has already been made of the
reaction of 2a with sources of {Cu(PPh3)}+ and {Au(PPh3)}+.11
(In that earlier report, the anion of 2a was incorrectly formulated
as a rhenacarborane bearing an exo-polyhedral iridium fragment,
and hence its copper and gold derivatives were also erroneously
described with rhenacarborane cores. The compounds discussed
herein have the correct metal atom assignments.10)
* To whom correspondence should be addressed. E-mail:
tom_mcgrath@baylor.edu; gordon_stone@baylor.edu.
(1) (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.
(2) (a) Hyatt, D. E.; Owen, D. A.; Todd, L. J. Inorg. Chem. 1966, 5,
1749. (b) Knoth, W. J. Am. Chem. Soc. 1967, 89, 1274.
(3) (a) 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. (b) St´ıbr, B.; Tok, O. L.; Milius,
W.; Bakardjiev, M.; Holub, J.; Hnyk, D.; Wrackmeyer, B. Angew. Chem.,
Int. Ed. 2002, 41, 2126. (c) Franken, A.; Kilner, C. A.; Thornton-Pett, M.;
Kennedy, J. D. Collect. Czech. Chem. Commun. 2002, 67, 869. (d) Jel´ınek,
T.; Thornton-Pett, M.; Kennedy, J. D. Collect. Czech. Chem. Commun. 2002,
67, 1035. (e) St´ıbr, B. Pure Appl. Chem. 2003, 75, 1295. (f) Brellochs, B.;
Backovsky, J.; St´ıbr, B.; Jel´ınek, T.; Holub, J.; Bakardjiev, M.; Hnyk, D.;
Hofmann, M.; C´ısarova´, I.; Wrackmeyer, B. Eur. J. Inorg. Chem. 2004,
3605.
(4) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Organometallics
2003, 22, 2842.
(5) (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.
(6) (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.
(7) Lu, X. L.; McGrath, T. D.; Stone, F. G. A. Organometallics 2006,
25, 2590.
(8) Franken, A.; McGrath, T. D.; Stone, F. G. A. Inorg. Chem. 2006,
45, 2669.
(9) Franken, A.; McGrath, T. D.; Stone, F. G. A. Organometallics 2005,
24, 5157.
(10) McGrath, T. D.; Du, S.; Hodson, B. E.; Lu, X. L.; Stone, F. G. A.
Organometallics 2006, 25, 4444.
(11) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Angew. Chem.,
Int. Ed. 2003, 42, 5728.
10.1021/om060418r CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/17/2006

Metal Butterflies on a Metallacarborane Scaffold. 2
Organometallics, Vol. 25, No. 19, 2006 4453
Chart 1
Chart 2
Crystals of 4a were extremely difficult to obtain, and although
one was available for an X-ray diffraction study, it was only of
modest quality and weakly diffracting and so an accurate
structural determination was not possible. However, a very
preliminary experiment (see Supporting Information) did con-
firm the heavy-atom structure to be that represented by the
structure shown in Chart 2. The central iridacarborane core is
flanked by {Re(CO)3} and {Cu(PPh3)} moieties, which are
attached via Ir-Re and Ir-Cu bonds, respectively; it is
additionally deduced that each of these exo-polyhedral units is
also supported by two agostic-type bridges. Notably, the rhenium
fragment has migrated over to a site adjacent to the one occupied
in the precursor 2a. Thus, both exo-polyhedral units are now
All of compounds 2, however, are unstable in solution, and
the manganese species 2c and 2d are very particularly so. The
only observed decomposition products are [N(PPh3)2][1,3-{M-
(CO)4}-3-(µ-H)-1,1-(CO)2-2-Ph-closo-1,2-M′CB9H8] (M ) Re,
M′ ) Ir (3a), Rh (3b); M ) Mn, M′ ) Ir (3c), Rh (3d)), formed
following CO scavenging.10 Unfortunately, the decomposition
process appears to be very significantly accelerated by the
presence of impuritiessincluding added reagentssand in con-
sequence we have hitherto been unable to isolate any trimetallic
products from reactions of manganese-containing 2c and 2d with
either {Cu(PPh3)}+ or {Au(PPh3)}+. Although some of 3a and
3b are also always obtained in the same reactions with 2a and
2b, the substrate Re-Ir and Re-Rh bimetallics are sufficiently
stable that they may be converted to heteropolymetallic species,
as we now discuss.
anchored via R- and â-BH groups in the CBBBBB face that is
η6-bonded to iridium (cf. â- and γ-BH units for the {Re(CO)3}
in 2a). This is additionally interesting in that it is the only
instance of such R-BH coordination that we have observed thus
far in these or related {metal-CB9} systems.
Spectroscopic data for compound 4a (Tables 1-3) are
consistent with an asymmetric solid-state structure and were
useful in confirming the proposed architecture. Thus, the 11B-
{1H} NMR spectrum shows nine separate resonances, while the
31P{1H} NMR spectrum shows a broad resonance for the
1
copper-bound phosphine at δ 9.2. In the H NMR spectrum,
two broad, high-field quartet resonances are seen (δ -6.73 and
-9.18) that are assigned to hydrogens involved in the B-HFRe
agostic-type bonds,12 with no signals attributable to the B-HFCu
units. Peaks are seldom observed for the latter moieties as a
result of broadening by the adjacent quadrupolar B and Cu
nuclei and by fluxional processes that are rapid on the NMR
time scale.13 The 13C{1H} NMR spectrum of 4a shows as
expected five separate signals for the different CO ligands, with
the Re-bound groups resonating at δ 192.9, 192.5, and 189.4
and those bound to Ir at δ 176.4 and 168.0.
Results and Discussion
Reaction of 2a with the source of {Cu(PPh3)}+ gave the
desired heterotrimetallic species, namely, [1,4,7-{Cu(PPh3)}-
1,5,6-{Re(CO)3}-4,5,6,7-(µ-H)4-1,1-(CO)2-2-Ph-closo-1,2-Ir-
CB9H5] (4a) (see Chart 2). However, formation of the analogous
product 4b from reaction of 2b with the copper reagent was
only transiently observed (deduced from IR and 11B NMR
spectroscopy of the reaction mixture). Compound 4b appears
to be formed in extremely low and variable amounts, and its
formation is further compromised by significant conversion of
2b to 3b. Thus the copper reagent is effectively in excess, a
situation that favors the formation of compound 5b (see below).
(12) Brew, S. A.; Stone, F. G. A. AdV. Organomet. Chem. 1993, 35, 135.
(13) (a) Jeffrey, J. C.; Ruiz, M. A.; Sherwood, P.; Stone, F. G. A. J.
Chem. Soc., Dalton Trans. 1989, 1845. (b) Carr, N.; Gimeno, M. C.;
Goldberg, J. E.; Pilotti, M. U.; Stone, F. G. A.; Topaloglu, I. J. Chem.
Soc., Dalton Trans. 1990, 2253. (c) Jeffery, J. C.; Jelliss, P. A.; Stone, F.
G. A. J. Chem. Soc., Dalton Trans. 1993, 1073. (d) Jeffery, J. C.; Jelliss,
P. A.; Rees, L. H.; Stone, F. G. A. Organometallics 1998, 17, 2258.

4454 Organometallics, Vol. 25, No. 19, 2006
McGrath et al.
heterotrimetallic Re-Ir-Au species that could have a structure
related to that of compound 4a. However, from 2b and {Au-
(PPh3)}+ a product 6b, initially presumed structurally analogous
to 4b, was obtained.
Characterizing data for compound 6b are given in Tables
1
1-3. From the H NMR spectrum, it was evident that only a
single phosphine unit was present and, as for 4a, there are two
broad quartet resonances for B-HFRe linkages, at δ -6.32
and -7.14, but no peaks for B-HFAu groups. The 13C{1H}
NMR spectrum confirmed the presence of five different CO
ligands, with the three Re-bound groups resonating at δ 193.6,
192.8, and 187.8, while the Rh-CO units appear as doublets
at δ 185.4 and 179.9 (J(RhC) ) 71 and 70 Hz, respectively).
Similarly, the 11B{1H} NMR spectrum also suggests an asym-
metric structure, with peaks in the ratio 1:2:1:2:1:1:1, while the
single gold-bound PPh3 ligand resonates at δ 50.9 in the 31P-
{1H} NMR spectrum.
All of the above data suggested that 6b had a structure closely
related to that of 4a, as might be expected. Nevertheless, an
X-ray diffraction study on the gold species was merited for
confirmation of this, particularly as the gold center was
anticipated not to show the pseudo-tetrahedral coordination seen
for copper in 4a. This experiment, however, revealed complex
6b to have the molecular structure shown in Figure 2, and the
compound is, in fact, [8,9,10-endo-{Au(PPh3)}-3,4,8-exo-{Re-
(CO)3}-3,4-(µ-H)2-8,8-(CO)2-7-Ph-nido-8,7-RhCB9H7] (see also
Scheme 1). The {RhCB9} core of this species clearly has a nido-
11-vertex structure, with the {Re(CO)3} fragment in an exo-
polyhedral site, as expected, but with the {Au(PPh3)} moiety
occupying a site that is endo-polyhedral with respect to the open
Figure 1. Structure of 5a showing the crystallographic labeling
scheme. In this and subsequent figures, thermal ellipsoids are shown
with 40% probability and for clarity only chemically significant
H atoms are shown and phenyl rings are omitted. Selected dis-
tances (Å) and angles (deg) are as follows: Ir-Cu(1) 2.6799(3),
Ir-Cu(2) 2.6047(3), Ir-C(2) 2.1525(18), Ir-B(3) 2.246(2),
Ir-B(4) 2.420(2), Ir-B(5) 2.395(2), Ir-B(6) 2.427(2), Ir-B(7)
2.394(2), B(3)‚‚‚Cu(1) 2.137(2), B(3)‚‚‚Cu(2) 2.084(2),
B(6)‚‚‚Cu(1) 2.223(2), B(7)‚‚‚Cu(2) 2.564(3), Cu(1)-Cu(2)
2.9051(5); Cu(2)-Ir-Cu(1) 66.678(11), Ir-Cu(1)-Cu(2)
55.421(8), Ir-Cu(2)-Cu(1) 57.901(9).
In addition to compound 4a, reaction of 2a with {Cu(PPh3)}+
also gave another type of trimetallic product; a similar species
was obtained from 2b and the same copper reagent. These were
the dicopper complexes [1,3,6-{Cu2(PPh3)2}-3,6-(µ-H)2-1,1-
(CO)2-2-Ph-closo-1,2-M′CB9H7] (M′ ) Ir (5a), Rh (5b)) (see
Chart 2), which were identified by an X-ray diffraction study
on 5a. The structure so obtained is shown in Figure 1. As can
be seen, the iridacarborane core supports a dicopper unit, so
that overall an {IrCu2} metal triangle is present (Ir-Cu(1) )
2.6799(3), Ir-Cu(2) ) 2.6047(3), Cu(1)-Cu(2) ) 2.9051(5)
Å). The structure of this trimetallic assembly contrasts with the
V-shaped unit in compound 4a and that in the previously
reported dicopper derivative of 1b.4
RhCBBB face of the {nido-8,7-RhCB9} cluster. The rhenium
center is attached to the cage via an Rh-Re bond (Rh(1)-
Re(1) ) 2.8333(8) Å) and two B-HFRe agostic-type interac-
tions that involve B(3) and B(4) in the upper pentagonal
B5 belt (Re(1)‚‚‚B(3) ) 2.383(8), Re(1)-H(3) ) 2.05(7),
Re(1)‚‚‚B(4) ) 2.372(8), Re(1)-H(4) ) 1.87(7) Å). In contrast,
the gold unit is approximately η3-bound to three atoms in the
RhCBBB ring: there is a bond to the rhodium vertex (Rh(1)-
Au(1) ) 2.8206(7) Å) and two adjacent boron atoms (Au(1)-
B(9) ) 2.439(9), Au(1)-B(10) ) 2.222(10) Å). This bonding
for the gold fragment is reminiscent of that in several other,
simpler gold complexes of nido-11-vertex carboranes.14-17
The NMR data for compounds 5 (Tables 2 and 3) are at odds
with the structure determined crystallographically, as they appear
to show mirror symmetry in solution. A 1:1:1:2:2:2 pattern of
intensities is seen (with one coincidence for 5b) in their 11B-
{1H} spectra, while their 31P{1H} spectra show only a single
broad resonance at δ 9.2 (5a) and 9.5 (5b). This would be
consistent with time-averaged symmetry and suggests that the
copper fragments are fluxional over the surface of the metal-
lacarborane core.13 Such processes might involve breaking of
the Cu-Cu connectivity to give an intermediate with a V-shaped
trimetal unit (cf. compounds 4) or else a migration of the entire
{Cu2(PPh3)2} unit. As with 4, however, these mechanisms are
rapid on the NMR time scale, even at low temperature:13 they
could not be arrested upon cooling, and so two separate 31P
resonances were not obtained. Such processes also preclude the
On the basis of electron-counting rules18-20 and by analogy
with other compounds presented herein, the {(CO)2RhCB9-
H9Ph}2- cluster of 6b would be expected to have a closo
structure, and thus its observed nido character was surprising.
However, there are a large number of precedents for 11-vertex
metallaheteroboranes of the later transition metals having nido
structures despite a formal closo electron count, examples of
which include the {L2PtB10}, {L2RhC2B8}, and {L2RhSB9}
systems.21-24 Indeed, among the rhodathiaborane species [8,8-
L2-nido-8,7-RhSB9H10] it has been shown that these compounds
(14) Hamilton, E. J. M.; Welch, A. J. Polyhedron 1990, 9, 2407.
(15) Hamilton, E. J. M.; Welch, A. J. Acta Crystallogr. 1990, C46, 1228.
(16) Jeffery, J. C.; Jelliss, P. A.; Stone, F. G. A. Inorg. Chem. 1993, 32,
3382.
(17) Jeffery, J. C.; Jelliss, P. A.; Stone, F. G. A. J. Chem. Soc., Dalton
Trans. 1993, 1073.
(18) Wade, K. AdV. Inorg. Chem. Radiochem. 1976, 18, 1.
(19) Williams, R. E. AdV. Inorg. Chem. Radiochem. 1976, 18, 67.
(20) Mingos, D. M. P. Acc. Chem. Res. 1984, 17, 311.
(21) Boocock, S. K.; Greenwood, N. N.; Kennedy, J. D.; McDonald,
W. S.; Staves, J. J. Chem. Soc., Dalton Trans. 1981, 2573.
(22) Lu, P.; Knobler, C. B.; Hawthorne, M. F. Acta Crystallogr. 1984,
C40, 1704.
1
observation of signals for the B-HFCu units in the H NMR
spectrum as noted for 4.
In contrast with the reactions of 2a and 2b with the {Cu-
(PPh3)}+ fragment, reactions of the same metallacarboranes with
a source of {Au(PPh3)}+ proceed somewhat differently, and
up to four polymetallic products may be formed. With 2a and
the gold reagent, no evidence was seen of an “expected”

Metal Butterflies on a Metallacarborane Scaffold. 2
Table 1. Analytical and Physical Data
Organometallics, Vol. 25, No. 19, 2006 4455
anal.c (%)
compd
color
yield/%a
12
ν
max(CO)b/cm-1
C
H
[1,4,7-{Cu(PPh3)}-1,5,6-{Re(CO)3}-4,5,6,7-(µ-H)4-
1,1-(CO)2-2-Ph-closo-1,2-IrCB9H5] (4a)
[1,3,6-{Cu2(PPh3)2}-3,6-(µ-H)2-1,1-(CO)2-2-Ph-
closo-1,2-IrCB9H7] (5a)
[1,3,6-{Cu2(PPh3)2}-3,6-(µ-H)2-1,1-(CO)2-2-Ph-
closo-1,2-RhCB9H7] (5b)
[8,9,10-endo-{Au(PPh3)}-3,4,8-exo-{Re(CO)3}-3,4-
(µ-H)2-8,8-(CO)2-7-Ph-nido-8,7-RhCB9H7] (6b)
[1,6-{Au2(PPh3)2}-6-(µ-H)-1,1-(CO)2-2-Ph-closo-
1,2-IrCB9H8] (7a)
[1,6-{Au2(PPh3)2}-6-(µ-H)-1,1-(CO)2-2-Ph-closo-
1,2-RhCB9H8] (7b)
[1,3,6-{Au2(PPh3)2Re(CO)3}-6-(µ-H)-1,1-(CO)2-
2-Ph-closo-1,2-IrCB9H7] (8a)
[1,3,6-{Au2(PPh3)2Re(CO)3}-6-(µ-H)-1,1-(CO)2-
2-Ph-closo-1,2-RhCB9H7] (8b)
[1,3-{Au3(PPh3)3}-1,1-(CO)2-2-Ph-closo-1,2-
IrCB9H8] (9a)
[1,3-{Au3(PPh3)3}-1,1-(CO)2-2-Ph-closo-1,2-
RhCB9H8] (9b)
pale yellow
2067 s, 2035 s, 2019 s,
1944 br s
2023 s, 1974 s
37.4 (37.8)d
3.5 (3.7)
yellow
orange
red-orange
yellow
orange
orange
red
41
22
9
48.2 (48.0)e
48.3 (48.0)f
33.0 (33.2)
39.1 (38.9)e
41.6 (41.6)e
35.1 (35.3)
36.2 (36.2)g
40.3 (40.3)g
42.9 (43.0)e
4.1 (4.0)
3.9 (4.1)
2.7 (2.7)
3.2 (3.2)
2.9 (3.4)
2.7 (2.7)
2.8 (2.8)
3.2 (3.2)
3.4 (3.4)
2021 s, 1960 s
2087 s, 2048 s, 2038 vs,
1943 br vs
2044 s, 2000 s
39
7
2053 s, 2011 s
16
7
2051 s, 2009 vs, 1929 s,
1915 br s
2058 s, 2013 vs, 1927 s,
1918 br s
2017 s, 1969 s
yellow
yellow
13
5
2027 s, 1983 s
a Yields based on available 2a or 2b (see text). b Measured in CH2Cl2; in addition, the spectra of all compounds show a broad, medium-intensity band
ca. 2500-2550 cm-1 due to B-H absorptions. c Calculated values are given in parentheses. d Cocrystallized with 1.0 molar equiv of C5H12. e Cocrystallized
with 0.5 molar equiv of CH2Cl2. f Cocrystallized with 2.0 molar equiv of CH2Cl2. g Cocrystallized with 1.0 molar equiv of CH2Cl2.
Table 2. 1H and 13C NMR Dataa
compd
1H/δ b
13C/δc
4a
7.59-7.48 (m, 17H, PPh and cage-C6H5),d 7.26 (m, 2H,
cage-C6H5), 7.22 (m, 1H, cage-C6H5), -6.73 (br q, J(BH) ≈
100, 1H, B-HFRe), -9.18 (br q, J(BH) ≈ 110, 1H, B-HFRe)
7.84 (m, 2H, cage-C6H5),d 7.45-7.12 (m, 33H, PPh and
cage-C6H5)
192.9, 192.5, 189.4 (Re-CO), 176.4, 168.0
(Ir-CO), 145.1, 134.1-128.9 (Ph), 47.8 (br, cage C)
5a
5b
6b
172.3 (CO), 149.1, 134.1-126.0 (Ph), 63.5
(br, cage C)
186.7 (br, CO), 149.3, 135.0-126.1 (Ph), 59.3
(br, cage C)
193.6, 192.8, 187.8 (Re-CO), 185.4 (d, J(RhC) )
71, Rh-CO), 179.9 (d, J(RhC) ) 70, Rh-CO),
149.4, 134.6-126.7 (Ph), 61.0 (br, cage C)
172.8 (CO), 148.4, 136.4-126.4 (Ph), 54.2
(br, cage C)
191.5 (d, J(RhC) ) 60, CO), 149.8, 134.6-126.2 (Ph),
74.5 (br, cage C)
198.0, 194.8, 192.6 (br × 3, Re-CO), 175.4, 171.0
(Ir-CO), 147.2, 135.4-126.8 (Ph), 56.1 (br, cage C)
197.1, 192.8, 190.4 (br × 3, Re-CO), 185.7, 182.2
(br × 2, Rh-CO), 147.7, 134.4-126.7 (Ph), 49.3
(br, cage C)
7.84 (m, 2H, cage-C6H5),d 7.51-7.33 (m, 30H, PPh),
7.27 (m, 2H, cage-C6H5), 7.15 (m, 1H, cage-C6H5)
7.62-7.51 (m, 16H, PPh and cage-C6H5), 7.45 (m, 2H,
cage-C6H5), 7.17 (m, 2H, cage-C6H5), -6.32 (br q, J(BH) ≈
100, 1H, B-HFRe), -7.14 (vbr q, J(BH) ≈ 100, 1H, B-HFRe)
7.93 (m, 2H, cage-C6H5),d 7.56-6.99 (m, 33H, PPh and
cage-C6H5)
7a
7b
8a
8b
7.84 (m, 2H, cage-C6H5),d 7.46-7.33 (m, 30H, PPh),
7.20 (m, 1H, cage-C6H5), 7.10 (m, 2H, cage-C6H5)
7.87 (m, 2H, cage-C6H5), 7.49-7.16 (m, 33H, PPh and
cage-C6H5), ca. -8.9 (vbr, 1H, B-HFRe)
7.88 (m, 2H, cage-C6H5), 7.48-7.18 (m, 33H, PPh and
cage-C6H5), ca. -7.9 (vbr, 1H, B-HFRe)
9a
9b
7.83 (m, 2H, cage-C6H5), 7.45-7.07 (m, 48H, PPh and
177.2 (CO), 150.4, 134.4-125.4 (Ph), 73.2 (br,
cage C)
cage-C6H5)
7.79 (m, 2H, cage-C6H5), 7.58-7.06 (m, 48H, PPh and
cage-C6H5)
182.5 (d, J(RhC) ) 54, CO), 149.7, 134.6-125.3
(Ph), 67.7 (br, cage C)e
a Chemical shifts (δ) in ppm, coupling constants (J) in hertz, measurements at ambient temperatures, except where indicated, 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 Signals for B-HFM′′ protons (M′′ ) Cu, Au) are not observed. e Tentative assignment.
reversibly undergo cage-closure reactions upon deprotonation.25
Similarly, closed-cage species are also found where the proton
is otherwise absent due to the presence instead of a boron-bound
two-electron-donor substituent.26 The proton so eliminated in
both types of complex occupied a bridging position in the open
face of the rhodathiaborane cluster, akin to the {Au(PPh3)}+
fragment in 6b: the gold-phosphine moiety is isolobal with
the proton,27 and hence a close parallel can be drawn between
the present case and the earlier rhodathiaboranes. In this respect,
the structure of compound 6b may also be compared with that
of [10,11-endo-{Au(PPh3)}-9-(η-C5H5)-nido-9,7,8-NiC2B8H10],
where the {Au(PPh3)} moiety also occupies an endo site over
the open face of an 11-vertex metallacarborane and of which
the {NiC2B8} core should also be closed (in electron-counting
terms) but has a nido structure.28 In the nickel system, however,
there is no Ni-Au bond (Ni‚‚‚Au > 3 Å), contrasting with the
Rh-Au connectivity present in compound 6b.
(23) (a) Ferguson, G.; Jennings, M. C.; Lough, A. J.; Coughlan, S.;
Spalding, T. R.; Kennedy, J. D.; Fontaine, X. L. R.; St´ıbr, B. J. Chem.
Soc., Chem. Commun. 1990, 891. (b) Adams, K. J.; McGrath, T. D.; Welch,
A. J. Acta Crystallogr. 1995, C51, 401. (c) Mac´ıas, R.; Rath, N. P.; Barton,
L. Organometallics 1999, 18, 3637.
(24) See also: Kennedy, J. D. In The Borane, Carborane, Carbocation
Continuum; Casanova, J., Ed.; Wiley: New York, 1998; p 85.
(25) Adams, K. J.; McGrath, T. D.; Thomas, Rh. Ll.; Weller, A. S.;
Welch, A. J. J. Organomet. Chem. 1997, 527, 283.
In addition to the “expected” trimetallic product exemplified
by 6b, the reactions of 2a and 2b with {Au(PPh3)}+ each also
(26) (a) Coughlan, S.; Spalding, T. R.; Ferguson, G.; Gallagher, J. F.;
Lough, A. J.; Fontaine, X. L. R.; Kennedy, J. D.; St´ıbr, B. J. Chem. Soc.,
Dalton Trans. 1992, 2865. (b) Volkov, O.; Mac´ıas, R.; Rath, N. P.; Barton,
L. J. Organomet. Chem. 2002, 657, 40.
(27) (a) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711. (b)
Stone, F. G. A. Angew. Chem., Int. Ed. Engl. 1984, 23, 89.
(28) Barker, G. K.; Godfrey, N. R.; Green, M.; Parge, H. E.; Stone, F.
G. A.; Welch, A. J. J. Chem. Soc., Chem. Commun. 1983, 277.

4456 Organometallics, Vol. 25, No. 19, 2006
McGrath et al.
Table 3. 11B and 31P NMR Dataa
compd
11B/δ b
31P/δ c
4a
38.4 (br), 6.9, 2.9, -9.4 (br), -13.9,
-16.8 (br), -22.5, -23.7, -32.0
7.6, ca. 6.3 (vbr), -7.1, -10.4 (br, 2B),
-28.8 (2B), -31.3 (2B)
9.2 (br)
5a
5b
6b
7a
7b
8a
8b
9a
9b
9.2 (br)
7.2 (2B), 2.8, -9.3 (2B), -26.5 (2B),
-30.9 (2B)
9.5 (br)
19.1 (br), 2.9 (2B), -6.6, -8.3 (2B),
-10.8, -12.8, -15.7
11.1, 9.2 (br), 0.5, -5.2 (br, 2B),
-27.6 (4B)
11.3, 7.4, 2.0, -3.5 (br, 2B), -18.0
(2B), -22.1 (2B)
37.9 (B(3)), 18.3, 8.6 (br), -5.6 (vbr),
-10.2 (br), -18.8 (br), -21.2 (2B), -33.6
46.9 (B(3)), 20.4, 9.1 (br), -1.1 (vbr),
-5.2 (vbr), -11.1, -13.1, -17.5, -30.2
21.3 (B(3)), 9.2, ca. 7.5 (br, sh), -9.4
(br, 2B), -23.6 (2B), -30.0 (2B)
27.3 (B(3)), 9.1 (2B), -5.8 (br, 2B),
-15.6 (2B), -24.5 (2B)
50.9
44.7
40.0
58.7 (br), 51.1 (br)
56.3 (br), 48.6 (br)
43.6 (br)
40.8 (br)
a Chemical shifts (δ) in ppm, coupling constants (J) in hertz, measure-
ments 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, and where peaks are broad the assigned
integrals are somewhat subjective. c 1H-decoupled chemical shifts are
positive to high frequency of 85% H3PO4 (external).
Figure 2. Structure of compound 6b showing the crystallo-
graphic labeling scheme. Selected internuclear distances (Å)
and interbond angles (deg) are as follows: Rh(1)-Au(1)
2.8206(7), Rh(1)-Re(1) 2.8333(8), Rh(1)-B(3) 2.295(9),
Rh(1)-B(4) 2.275(9), Rh(1)-C(7) 2.188(7), Rh(1)-B(9)
2.287(8), Re(1)‚‚‚B(3) 2.383(8), Re(1)‚‚‚B(4) 2.372(8), Au(1)-B(9)
2.439(9),
Au(1)-B(10)
2.222(10);
Au(1)-Rh(1)-Re(1)
gave digold products, namely, [1,6-{Au2(PPh3)2}-6-(µ-H)-1,1-
(CO)2-2-Ph-closo-1,2-M′CB9H8] (M′ ) Ir (7a), Rh (7b)) (see
Scheme 1), which are akin to compounds 5. Spectroscopic data
for compounds 7 are listed in Tables 1-3. In their IR spectra,
only two CO bands are seen, consistent with loss of the exo-
polyhedral {Re(CO)3} fragment. Similarly, the 1H and 13C{1H}
NMR spectra are straightforward, showing only peaks for the
carborane and PPh3 groups (in the ratio 1:2) and only a single
150.08(2).
resonance for CO ligands (δ 172.8 (7a), 191.5 (7b; d, J(RhC)
) 60 Hz)). Similar to compounds 5, the 11B{1H} NMR spectra
of compounds 7 indicate mirror symmetry in solution, with both
having peaks in 1:1:1:2:2:2 intensity ratios (7a has one
coincidence); likewise, only a single 31P{1H} NMR signal (δ
44.7 (7a), 40.0 (7b)) is evident. This is again attributable to
Scheme 1. Possible Sequence of Formation of Gold-Phosphine Derivatives from Compounds 2a and 2b

Metal Butterflies on a Metallacarborane Scaffold. 2
Organometallics, Vol. 25, No. 19, 2006 4457
Figure 4. Structure of 8b showing the crystallographic labeling
scheme. Selected distances (Å) and angles (deg) are as follows:
Rh-C(2) 2.154(7), Rh-B(3) 2.206(9), Rh-B(4) 2.372(9), Rh-
B(5) 2.440(9), Rh-B(6) 2.344(9), Rh-B(7) 2.351(9), Rh-
Au(1) 2.9106(7), Rh-Re 2.9581(7), B(3)-Au(1) 2.229(8), B(3)-
Au(2) 2.301(9), B(3)‚‚‚Re 2.336(9), B(6)‚‚‚Re 2.329(8), Re-
Au(2) 2.8619(5), Re-Au(1) 2.9983(5), Au(1)-Au(2) 2.7859(4);
Au(1)-Rh-Re 61.439(16), Au(2)-Re-Rh 96.883(17), Au(2)-
Re-Au(1) 56.713(12), Rh-Re-Au(1) 58.499(15), Au(2)-Au(1)-
Rh 99.718(17), Au(2)-Au(1)-Re 59.176(11), Rh-Au(1)-Re
60.061(15), Au(1)-Au(2)-Re 64.111(12).
Figure 3. Structure of compound 7b showing the crystallographic
labeling scheme. Selected internuclear distances (Å) and interbond
angles (deg) are as follows: Rh(1)-C(2) 2.173(10), Rh(1)-B(3)
2.237(12), Rh(1)-B(4) 2.452(12), Rh(1)-B(5) 2.476(12), Rh(1)-
B(6) 2.467(12), Rh(1)-B(7) 2.334(12), Rh(1)-Au(1) 2.9723(9),
Rh(1)-Au(2) 2.6635(9), Au(1)-Au(2) 2.8335(6), Au(1)-H(6)
1.98(9), B(6)‚‚‚Au(1) 2.298(11), B(3)‚‚‚Au(1) 2.455(12), B(3)‚‚‚
Au(2) 2.945(12), C(11)‚‚‚Au(2) 2.701(10); Au(2)-Rh(1)-Au(1)
60.07(2), Au(2)-Au(1)-Rh(1) 54.552(19), Rh(1)-Au(2)-Au(1)
65.38(2).
moieties present. The nature of compounds 8 was ultimately
determined by X-ray diffraction studies,11 of which the structure
of the rhodium derivative 8b is shown in Figure 4.
migration of the exo-polyhedral moieties to give a structure with
time-averaged symmetry, as discussed above.
For comparison with compounds 5, and to definitively
confirm the architecture of compounds 7, an X-ray diffraction
study was undertaken on 7b, revealing the structure shown
in Figure 3. As expected, the molecule of 7b is similar
to compounds 5, in that it consists of a central {closo-1,2-
RhCB9} core, of which the Rh vertex and two exo-poly-
hedral {Au(PPh3)} units are involved in an {RhAu2} triangle
(Rh(1)-Au(1) 2.9723(9), Rh(1)-Au(2) 2.6635(9), Au(1)-
Au(2) 2.8335(6) Å). The molecule is asymmetric, and this
feature, like the structure of 5a, contrasts with the symmetry
implied by solution NMR spectra. One of the gold atoms
(Au(1)) is also involved in an agostic-type linkage with BH(6)
(Au(1)‚‚‚B(6) ) 2.298(11) Å) and a much longer interaction
with BH(3) (Au(1)‚‚‚B(3) ) 2.455(12) Å). However, the second
gold center (Au(2)) is not supported by any B-HFAu interac-
tions, but instead enjoys only the two metal-metal bonds and
a very long interaction with one of the rhodium-bound carbonyl
ligands (Au(2)‚‚‚C(11) ) 2.701(10) Å). Thus, the structure of
compounds 7 is somewhat different from that of compounds 5,
where the copper centers can be considered more intimately
bonded to the cage. This can be attributed to the known
preference of gold for a lower coordination number than
copper.29
Compounds 8 are the tetrametallic species [1,3,6-{Au2(PPh3)2-
Re(CO)3}-6-(µ-H)-1,1-(CO)2-2-Ph-closo-1,2-M′CB9H7] (M′ )
Ir (8a), Rh (8b)), in which {Re(CO)3} and {Au(PPh3)} moieties
are bonded to the cluster {M′(CO)2} vertex and to each other.
In addition, the Re-Au vector is bridged by a second
{Au(PPh3)} fragment, so that overall an {M′Au2Re} “butterfly”
has been assembled, starting from the rhenacarborane of
1b. Distances within this “butterfly” in 8b are Rh-Re )
2.9581(7), Rh-Au(1) ) 2.9106(7), Re-Au(1) ) 2.9983(5),
Re-Au(2) ) 2.8619(5), and Au(1)-Au(2) ) 2.7859(4) Å. The
exo-polyhedral rhenium center is additionally supported by a
B-HFRe agostic-type linkage (B(6)-Re ) 2.329(8), Re-H(6)
) 1.93(6) Å) that involves a â-BH vertex in the Rh-bound
CBBBBB belt. Notably, the adjacent γ-boron atom in this
CBBBBB belt lacks a terminal hydrogen atom and moreover
is in contact with all four of the metal atoms (B(3)-Rh )
2.206(9), B(3)-Au(1) ) 2.229(8), B(3)-Au(2) ) 2.301(9),
B(3)-Re ) 2.336(9) Å). As a result, the coordination around
this boron atom in the trigonal bipyramidal {BM′Au2Re} core
resembles that in transition metal boride clusters.30
The NMR spectra for compounds 8 (Tables 2 and 3) are
entirely consistent with the solid-state structure. Specifically,
their 11B{1H} NMR spectra shown nine separate resonances
(with one coincidence for 8a), as required by the lack of
molecular symmetry. The resonance for B(3), which lacks a
terminal hydrogen and is in contact with all four metal centers,
remains a singlet in the fully proton-coupled spectrum and
occurs at δ 37.9 for 8a and δ 46.9 for 8b. Despite the metal
boride structural analogy that was drawn above, the chemical
shift of this boron atom in compounds 8salthough it is rather
In addition to compounds 6 and 7, a third type of polymet-
allacarborane species of a novel structural class was isolated
from interaction of 2a or 2b with the {Au(PPh3)}+ source: these
species, compounds 8, are certainly the most interesting of the
products obtained. Initial spectroscopic analysis (Tables 1-3)
indicated the presence of Re and Au fragments in addition to
the irida- or rhoda-carborane core, and, significantly, both 31P
and 1H NMR data suggested there were two {Au(PPh3)}
(29) See, for example: Carvajal, M. A.; Novoa, J. J.; Alvarez, S. J. Am.
Chem. Soc. 2004, 126, 1465.
(30) Housecroft, C. E. Coord. Chem. ReV. 1995, 143, 297.

4458 Organometallics, Vol. 25, No. 19, 2006
McGrath et al.
(Au(1)-B(3) 2.230(12), Au(2)-B(3) 2.253(11), Au(3)-B(3)
2.247(11) Å), similar to the situation in compounds 8: this boron
vertex likewise lacks a terminal hydrogen atom. How-
ever, although this boron atom is also directly bonded to the
fourth metal atom, namely, the rhodium vertex (Rh(1)-B(3)
) 2.245(10) Å), there is no connectivity between Rh(1) and
Au(2) (Rh(1)‚‚‚Au(2) is >3.3 Å), and this eliminates a closer
similarity to compounds 8.
Spectroscopic data for compounds 9 are listed in Tables 1-3.
These bear some similarity to those for compounds 7, with both
11B{1H} and 31P{1H} NMR spectra also indicating a symmetric
structure in solution. The former spectrum for each compound
showed a 1:1:1:2:2:2 intensity pattern (with one coincidence
for 9b) and with a rather deshielded12 resonance for B(3) (δ
21.3 (9a), 27.3 (9b)) that remains a singlet upon retention of
proton coupling. Surprisingly, the 31P{1H} NMR spectrum
showed only a single broad resonance (δ 43.6 (9a), 40.8 (9b))
for all three PPh3 ligands, with this showing some possible
Figure 5. Structure of compound 9b showing the crystallo-
graphic labeling scheme. Selected distances and angles are as
follows: Au(1)-Au(2) 2.8693(5), Au(2)-Au(3) 2.8046(5),
Au(1)-Au(3) 2.8025(6), Au(1)-Rh(1) 2.8145(9), Au(1)-
B(3) 2.230(12), Au(2)-B(3) 2.253(11), Au(3)-B(3) 2.247(11),
Au(2)‚‚‚B(6) 2.548(12), Rh(1)-C(2) 2.150(10), Rh(1)-B(3)
2.245(10), Rh(1)-B(4) 2.363(11), Rh(1)-B(5) 2.408(12), Rh(1)-
B(6) 2.438(11), Rh(1)-B(7) 2.320(11); Au(2)-Au(1)-Au(3)
59.259(13), Au(1)-Au(2)-Au(3) 59.185(14), Au(1)-Au(3)-
Au(2) 61.556(14), Au(3)-Au(1)-Rh(1) 102.74(2), Au(2)-Au(1)-
Rh(1) 72.195(19).
2
quartet structure due to unresolved J(BP) coupling to B(3). It
may be envisioned that the {Au3(PPh3)3} moiety can undergo
a “propeller” type of rotation with respect to the metallacarbo-
rane surface, which renders the three phosphines equivalent on
the NMR time scale, or there may be other, more elaborate
fluxional processes taking place. Notably, the related trigold
complex [10-exo-{Au2(PPh3)2}-10-endo-{Au(PPh3)}-7,8-Me2-
nido-7,8-C2B9H8], which contains a similar {Au3(PPh3)3} tri-
angle, also demonstrates fluxional behavior that makes all three
PPh3 groups equivalent and the overall structure symmetric.31
As is indicated in Scheme 1, it is thought that initial reaction
of compound 2a or 2b with {Au(PPh3)}+ results in either (i)
addition of the gold fragment, giving compounds of type 6, or
(ii) displacement of the {Re(CO)3}+ moiety and then coordina-
tion of two gold units, giving compounds 7. These suggestions
are supported by IR spectroscopic monitoring of the reaction
between 2b and the gold reagent, which at first shows growth
of bands attributable to 6b and 7b. Notably, reaction of
compound 1b with the same gold substrate also always yield
bis-{Au(PPh3)} species (regardless of reaction stoichiometry);4
it is, therefore, perhaps not surprising that anionic, monogold
species ({Au-IrCB9}- or {Au-RhCB9}-) that would be formal
precursors to compounds 7 are not observed in these systems.
As the reaction of 2b with {Au(PPh3)}+ proceeds, IR spectros-
copy indicates a decrease in the quantity of 6b present and a
concomitant increase in that of 8b. Similarly, compound 7b also
appears to partially convert to 9b, albeit much more slowly.
Moreover, solutions of pure samples of 6b and 7b with time
show the presence of 8b and 9b, respectively, as decomposition
products, and, as noted earlier, we have observed experimentally
that the former pair can be converted more rapidly to the latter
two by addition of further gold reagent. All of these observations
are consistent with paths (iii) in Scheme 1, namely, that
compounds 8 and 9 are formed from 6 and 7, respectively, by
loss of H+ and gain of {Au(PPh3)}+. Further support for this is
provided by the earlier observation31 that in a related system
the digold-carborane species [9-exo-{Au(PPh3)}-9-(µ-H)-10-
endo-{Au(PPh3)}-7,8-Me2-nido-7,8-C2B9H8] affords the trigold
complex [10-exo-{Au2(PPh3)2}-10-endo-{Au(PPh3)}-7,8-Me2-
nido-7,8-C2B9H8] upon deprotonation (NaH) and addition of
[AuCl(PPh3)]. The alternative possibility, namely, that com-
pounds 7 and 9 are formed from 6 and 8, respectively, by loss
of {Re(CO)3}+ and then coordination of {Au(PPh3)}+ (pathway
iv in Scheme 1), cannot entirely be excluded, but we found no
downfieldsis definitely more typical of a metallacarborane12
than a boride, where the boron atom experiences much greater
deshielding (typically, δ ≈ 100-200).30 In their 31P{1H} NMR
spectra, compounds 8 each show two separate, broad resonances
for the two different {Au(PPh3)} units, at δ 58.7 and 51.1 for
8a and δ 56.3 and 48.6 for 8b. Likewise, their 1H and 13C{1H}
NMR spectra show all the expected features: in particular five
different CO resonances and a single very broad, high-field
proton resonance (δ ca. -8.9 (8a) and -7.9 (8b)) for the sole
B-HFRe linkage in each molecule.
The fourth product type obtained from reaction of 2a or 2b
with the {Au(PPh3)}+ fragment is related to the above com-
pounds 8. These species are the trigold-irida- or -rhoda-
carborane complexes [1,3-{Au3(PPh3)3}-1,1-(CO)2-2-Ph-closo-
1,2-M′CB9H8] (M′ ) Ir (9a), Rh (9b)), which are typically
isolated only in very small quantities and only when the reaction
time is a day or more. This is hardly surprising, as the
stoichiometry of the reaction (the ratio of 2a or 2b to Au is
1:1) strongly disfavors their formation. However, compounds
9 are obtained in larger quantities when the above reactant
stoichiometry is 1:2 or when CH2Cl2 solutions of compounds 7
are allowed to decompose over several days; the former method
is, of course, the more satisfactory. Treatment of compounds 7
with further {Au(PPh3)}+ also affords compounds 9: we note
that this is analogous to the observation that 8b is formed from
6b under similar conditions. Compounds 9 were initially
identified via an X-ray diffraction experiment on 9b, of which
the results are shown in Figure 5. The structure of 9a has also
been determined and is essentially identical to that of 9b, and
is included as electronic Supporting Information only.
The molecule of 9b consists of a central {closo-1,2-RhCB9}
core, to which is bonded a triangular {Au3(PPh3)3} unit
(Au(1)-Au(2) 2.8693(5), Au(1)-Au(3) 2.8025(6), Au(2)-
Au(3) 2.8046(5) Å). One of the gold centers is directly bonded
to the cluster rhodium vertex (Au(1)-Rh(1) ) 2.8145(9) Å)
and all three of the gold atoms are in contact with B(3)
(31) Jeffrey, J. C.; Jelliss, P. A.; Stone, F. G. A. J. Chem. Soc., Dalton
Trans. 1994, 25.

Metal Butterflies on a Metallacarborane Scaffold. 2
Organometallics, Vol. 25, No. 19, 2006 4459
Scheme 2. Proposed10 Mechanism for the exo T endo
Vertex Exchange that Occurs in the Formation of
Compounds 2a
does indeed expel a manganese fragment.5b Moreover, it is
increasingly being suggested that established cluster stability
patterns may not always strictly apply, especially when multiple
metal vertexes are present. It should be remembered also that
species such as that in structure C are one bonding electron
pair short of the conventional closo electron count,18-20 and this
will certainly have an effect on their relative stabilities. Our
efforts continue in trying to understand the processes involved
in these and related reactions.
Conclusion
The surprising formation of compounds 2 from their precur-
sors 1, via exo T endo exchange of {metal-ligand} vertexes,
was described in the accompanying paper10 and is itself a
remarkable and highly significant observation in metallacarbo-
rane chemistry. However, those reactions notwithstanding,
arguably the most important aspect of the behavior of com-
pounds 2 is their reactions with copper- and gold-phosphine
cations reported herein, with several of the resulting products
revealing structures without close precedent in either metallac-
arborane or metal cluster chemistry. Moreover, we have
demonstrated the utility of monocarborane ligands to function
as scaffolds for the stepwise addition of different metal centers,
leading to a variety of heteropolymetallic products that culminate
in the “butterfly” species 8. There may also be other, as yet
undetected, products or intermediates present in all of these
reactions: their isolation and identification may help to shed
light upon the processes taking place. Clearly much work
remains to be done in order to fully understand the formation
of compounds 2 from compounds 1 and the subsequent synthesis
of the heteropolymetallic species reported herein. There is also
much further scope within this area, exploiting other combina-
tions of {metal-ligand} fragments and by employing the many
other new monocarboranes that have recently become available.3
a Key: (i) {M′(CO)2} exo-coordination; (ii) opening of {MCB9}
cluster and then {M′(CO)2} exo f endo migration; (iii) {M(CO)3} endo
f exo ejection and then {M′CB9} cluster closure.
evidence of this during monitoring of the reactions or by
deliberate addition of {Au(PPh3)}+ to the latter pair.
As a final aside, it may be noted that a closo T nido structural
change, similar to that which occurs with compound 6 (i.e.,
without the expected change in electron count), might also be
invoked as part of a possible explanation for the exo T endo
vertex exchange that occurs in the formation of compounds 2
from compounds 1. This process has been proposed10 to involve
a 12-vertex dimetallacarborane cluster as an intermediate. It is
reasonable to assume that the initial step of the latter reaction
is simple coordination of the {M′(CO)2}+ fragment to the
dianions A of compounds 1, giving the bimetallic MM′ species
B (see Scheme 2). There is ample precedent for the formation
of such structures in other, closely related reactions of com-
pounds 1.4,5b Were the rhena- or manga-carborane cores of B
to temporarily undergo some kind of closo f nido cage opening
following coordination of the exo-polyhedral {M′(CO)2} groups,
this could allow the latter to easily migrate from an exo- to an
endo-polyhedral site, giving intermediate C. Thereafter, expul-
sion of the {M(CO)3} vertex and then cage closure would afford
the observed products D, the anions of compounds 2, as
proposed earlier.10
Experimental Section
General Considerations. All reactions were performed under
an atmosphere of dry, oxygen-free dinitrogen using standard
Schlenk-line techniques. Solvents were stored over and freshly
distilled from appropriate drying agents prior to use. Petroleum ether
here refers to that fraction of boiling point 40-60 °C. Chroma-
tography columns (typically ca. 15 cm in length and ca. 2 cm in
diameter) were packed with silica gel (Acros, 60-200 mesh).
Filtrations through Celite typically employed a plug ca. 5 cm in
depth. Preparative thin-layer chromatography (TLC) was performed
on 20 × 20 cm glass plates (Uniplates with tapered thickness silica
gel GF254, Analtech). Elemental analyses were performed by
Atlantic Microlab, Inc., Norcross, GA, on crystalline or microc-
rystalline samples that had been dried overnight in vacuo. On
occasion residual solvent remained after drying, its presence and
1
approximate proportion confirmed by integrated H NMR spec-
troscopy, and this was factored into the calculated microanalysis
data. NMR spectra were recorded at the following frequencies
(MHz): 1H, 360.1; 13C, 90.6; 11B, 115.5; 31P, 145.8. Complexes
2a,10 2b,10 [CuCl(PPh3)]4,33 and [AuCl(PPh3)]34 were prepared by
literature methods. All other materials were used as received. For
purposes of comparison, product yields are quoted on the basis of
the starting compound 2a or 2b: in all reactions, up to 20% or
50% of compound 3a or 3b, respectively, is also formed as an
unavoidable side-product.
Such a mechanism, of course, is highly speculative and is
perhaps also somewhat surprising. Given the known stability
of closo-12-vertex species with respect to 11-vertex ones,32 it
might not be expected that the transformation C f D (Scheme
2) would be favorable. However, we have earlier reported that
a {PtMnCB9} cluster that is a direct analogue of structure C
(33) Jardine, F. H.; Rule, J.; Vohra, G. A. J. Chem. Soc. A 1970, 238.
(34) Bruce, M. I.; Nicholson, B. K.; Bin Shawkataly, O. Inorg. Synth.
1989, 26, 325.
(32) Schleyer, P. v. R.; Najafian, K.; Mebel, A. M. Inorg. Chem. 1998,
37, 6765.

4460 Organometallics, Vol. 25, No. 19, 2006
Table 4. Crystallographic Data for 5a, 6b, 7b, 8b, and 9b
McGrath et al.
5a‚(CH3)2CO
6b‚0.5CH2Cl2
7b‚0.5CH2Cl2
8b‚C5H12
9b
formula
C48H50B9Cu2IrO3P2
C
30.5H30AuB9ClO5-
C
45.5H45Au2B9-
ClO2P2Rh
1315.34
P21/n
C53H55Au2B9O5-
P2ReRh
1614.24
P21/n
18.6109(15)
17.0445(15)
19.674(2)
90
115.685(3)
90
5624.1(9)
4
1.906
7.736
65 525
15 647
0.1164
0.0942, 0.1279
0.0776, 0.0510
C63H58Au3B9-
O2P3Rh
1731.10
P21/c
18.7506(15)
12.7722(15)
25.442(2)
90
94.055(4)
90
6077.8(10)
4
1.892
7.608
40 134
12 169
0.1013
0.0838, 0.1069
0.0698, 0.0522
PReRh
1126.33
P1h
fw
1153.39
P21/c
16.9819(15)
14.8312(13)
19.6220(15)
90
91.699(5)
90
4939.9(7)
4
1.551
3.645
132 852
18 945
0.0383
space group
a, Å
b, Å
10.9430(12)
13.5989(14)
14.2374(18)
106.139(6)
109.551(6)
103.083(6)
1794.5(4)
2
2.084
8.054
23 821
7159
13.2293(7)
18.9707(10)
19.1492(11)
90
100.396(2)
90
4727.0(4)
4
1.848
6.699
38 586
10 730
0.0950
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
F
calcd, g cm-3
µ(Mo KR), mm-1
no. of rflns measd
no. of indep rflns
Rint
0.0633
0.0938, 0.0596
0.0842, 0.0392
wR2, R1a (all data)
wR2, R1 (obsdb data)
0.0627, 0.0400
0.0580, 0.0264
0.1184, 0.1224
0.1022, 0.0618
2
2
2
a wR2 ) [∑{w(Fo - Fc )2}/∑w(Fo )2]1/2; R1 ) ∑||Fo| - |Fc||/∑|Fo|. b Fo > 4σ(Fo).
Reaction of 2a or 2b with {Cu(PPh3)}+. (i) To compound 2a
(0.100 g, 0.08 mmol), [CuCl(PPh3)]4 (0.029 g, 0.02 mmol), and
Tl[PF6] (0.028 g, 0.08 mmol) was added CH2Cl2 (20 mL) and the
resultant mixture stirred overnight. The mixture was filtered (Celite),
and the filtrate was evaporated in vacuo. Column chromatography,
eluting first with CH2Cl2-petroleum ether (1:1), removed a pale
yellow band from which was obtained [1,4,7-{Cu(PPh3)}-1,5,6-
{Re(CO)3}-4,5,6,7-(µ-H)4-1,1-(CO)2-2-Ph-closo-1,2-IrCB9H5] (4a;
0.010 g) as pale yellow microcrystals after removal of solvent in
vacuo. Further elution with CH2Cl2-petroleum ether (2:1) gave a
yellow band, which afforded [1,3,6-{Cu2(PPh3)2}-3,6-(µ-H)2-1,1-
(CO)2-2-Ph-closo-1,2-IrCB9H7] (5a; 0.036 g) as a yellow, micro-
crystalline solid after evaporation in vacuo.
1) afforded two bright yellow bands that yielded 7a (Rf ) 0.75;
0.011 g; 10%) and 9a (Rf ) 0.35; 0.019 g; 13%), both as
microcrystalline yellow solids.
(iii) Compound 2b (0.200 g, 0.17 mmol) and [AuCl(PPh3)] (0.085
g, 0.17 mmol) were dissolved in CH2Cl2 (20 mL), and finely ground
Tl[PF6] (0.062 g, 0.18 mmol) was added. The mixture was stirred
vigorously for 1 h and then evaporated in vacuo. The dark orange
residue was extracted with CH2Cl2-petroleum ether (1:1, 5 mL),
and the extract filtered (Celite) and applied to a chromatography
column. Elution first with CH2Cl2-petroleum ether (4:7) afforded
a golden yellow-orange band, which was collected and evapo-
rated in vacuo to afford orange microcrystals of [8,9,10-endo-{Au-
(PPh3)}-3,4,8-exo-{Re(CO)3}-3,4-(µ-H)2-8,8-(CO)2-7-Ph-nido-8,7-
RhCB9H7] (6b; 0.017 g). Further elution, using CH2Cl2-petroleum
ether (2:3), gave a red band that yielded, after removal of solvent
in vacuo, crimson microcrystals of [1,3,6-{Au2(PPh3)2Re(CO)3}-
6-(µ-H)-1,1-(CO)2-2-Ph-closo-1,2-RhCB9H7] (8b; 0.018 g). Finally,
elution with CH2Cl2-petroleum ether (1:1) gave a yellow fraction,
which was collected and evaporated in vacuo to give [1,6-{Au2-
(PPh3)2}-6-(µ-H)-1,1-(CO)2-2-Ph-closo-1,2-RhCB9H8] (7b; 0.012
g) as a yellow, microcrystalline solid.
(iv) Similarly, compound 2b (0.100 g, 0.09 mmol), [AuCl(PPh3)]
(0.085 g, 0.17 mmol), and Tl[PF6] (0.060 g, 0.17 mmol) were stirred
(16 h) in CH2Cl2 (20 mL). Evaporation of the reaction mixture
and then column chromatography, eluting with CH2Cl2-petroleum
ether (1:1), afforded only a single, broad yellow band, which was
collected and evaporated to dryness. The residue was purified by
preparative TLC, eluting with the same solvent mixture, to give
two yellow bands, which were collected and evaporated in vacuo
to give 7b (Rf ) 0.70; 0.008 g; 7%) and [1,3-{Au3(PPh3)3}-1,1-
(CO)2-2-Ph-closo-1,2-RhCB9H8] (9b; Rf ) 0.35; 0.007 g; 5%), both
as golden yellow microcrystalline solids.
X-ray Crystallographic Structure Determinations. Experi-
mental data for the structural studies discussed in the text are
presented in Table 4. Data for compounds 4a and 9a, and a revised
structure of 8a,11 are available as Supporting Information only.
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 φ and ω, using
0.5° increments of φ or ω. The data frames were integrated using
SAINT;35 the substantial redundancy in data allowed an empirical
absorption correction (SADABS)35 to be applied, based on multiple
measurements of equivalent reflections.
(ii) Compound 2b (0.200 g, 0.17 mmol) and [CuCl(PPh3)]4 (0.063
g, 0.04 mmol) were dissolved in CH2Cl2 (20 mL), and finely ground
Tl[PF6] (0.062 g, 0.18 mmol) was added. The mixture was stirred
vigorously for 1 h and then evaporated in vacuo. The dark orange
residue was extracted with CH2Cl2-petroleum ether (1:1, 5 mL),
and the extract filtered (Celite) and applied to a chromatography
column. Elution with CH2Cl2-petroleum ether (3:2) afforded a
golden yellow band that gave, after removal of solvent in vacuo,
crude [1,3,6-{Cu2(PPh3)2}-3,6-(µ-H)2-1,1-(CO)2-2-Ph-closo-1,2-
RhCB9H7] (5b). This was purified by further column chromatog-
raphy, eluting with the same solvent mixture, to give 5b (0.038 g)
as a yellow microcrystalline solid.
Reaction of 2a or 2b with {Au(PPh3)}+. (i) To compound 2a
(0.100 g, 0.08 mmol), [AuCl(PPh3)] (0.040 g, 0.08 mmol), and
Tl[PF6] (0.030 g, 0.08 mmol) was added CH2Cl2 (20 mL) and the
mixture stirred overnight. The mixture was filtered (Celite) and
solvent removed from the filtrate by evaporation in vacuo. The
residue was subjected to column chromatography, eluting first
with CH2Cl2-petroleum ether (1:1), to give an orange band that
was collected and evaporated in vacuo to furnish [1,3,6-{Au2(PPh3)2-
Re(CO)3}-6-(µ-H)-1,1-(CO)2-2-Ph-closo-1,2-IrCB9H7] (8a; 0.021
g) as orange microcrystals. Thereafter, elution with CH2Cl2-
petroleum ether (2:1) gave a yellow fraction from which was
likewise obtained [1,6-{Au2(PPh3)2}-6-(µ-H)-1,1-(CO)2-2-Ph-
closo-1,2-IrCB9H8] (7a; 0.042 g) as a yellow, microcrystalline
solid.
(ii) A similar reaction, employing 2a (0.100 g, 0.08 mmol),
[AuCl(PPh3)] (0.080 g, 0.16 mmol), and Tl[PF6] (0.060 g, 0.17
mmol), upon column chromatographic workup gave 8a (0.013 g;
10%) and then a yellow fraction containing a mixture of 7a and
[1,3-{Au3(PPh3)3}-1,1-(CO)2-2-Ph-closo-1,2-IrCB9H8] (9a). The
latter mixture was collected, evaporated, and then applied to
preparative TLC plates. Elution with CH2Cl2-petroleum ether (1:
(35) APEX 2, version 1.0; Bruker AXS: Madison, WI, 2003-2004.

Metal Butterflies on a Metallacarborane Scaffold. 2
Organometallics, Vol. 25, No. 19, 2006 4461
All structures were solved using conventional direct methods35,36
and refined by full-matrix least-squares on all F2 data using
SHELXTL version 6.12,36 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 hydrogens for compounds 5a, 6b, and 8b
were largely allowed positional refinement, and all other H atoms
were set riding in calculated positions, except for a few B-H units
that had to be restrained to sensible distances (1.12(5) Å; DFIX
card in SHELXL36). All hydrogens had fixed isotropic thermal
parameters defined as Uiso(H) ) 1.2Uiso(parent), or Uiso(H) )
1.5Uiso(parent) for methyl groups.
The asymmetric fraction of crystals of 5a contained one molecule
of acetone as solvate, and molecules of 8b cocrystallized with one
molecule of n-pentane as solvate, both of these solvates being in
general space. Crystals of 6b contained one-half molecule of CH2-
Cl2 solvate located at an inversion center. All of these solvates were
treated straightforwardly as above. The crystals of 7b also contained
one-half molecule of CH2Cl2 located at an inversion center, but in
this case the crystallographically independent chlorine atom was
disordered over two positions. The latter was refined in separate
parts with refining complementary occupancies that converge at
the approximate ratio 69:31. In addition, in 5a one of the phenyl
rings bonded to P(1) was disordered over two sites. These were
treated as two separate parts with refining complementary occupan-
cies, in the approximate ratio 61:39 at convergence.
Acknowledgment. We thank the Robert A. Welch Founda-
tion for support (Grant AA-0006) and Dr. Jason A. Kautz for
early crystallographic studies in this area. The Bruker-Nonius
X8 APEX diffractometer was purchased with funds received
from the National Science Foundation Major Instrumentation
Program (Grant CHE-0321214).
Supporting Information Available: Full details of the crystal
structure analyses (including data for compounds 4a, 8a, and 9a)
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(36) SHELXTL, version 6.12; Bruker AXS: Madison, WI, 2001.
OM060418R