Studies with the rhenacarborane Cs[Re(CO)3(η5-7,8-C2B9H 11)]: Surprising reactivity with a range of metal ligand fragments

Article abstract of DOI:10.1021/om9905097

The rhenacarborane salt Cs[Re(CO)₃(η⁵-7,8-C₂B₉H ₁₁)] (1) has been synthesized in excellent yield using a new procedure. Treatment of CH₂Cl₂ solutions of 1 with [RuCl₂(PPh₃)₃] yields the exo-closo complex [Re(CO)₃(η⁵2,3,10-(μ-H) ₃-exo-{RuCl(PPh₃)₂}-7,8-C₂B ₉H₈)] (2a). In this molecule a [RuCl(PPh₃)1₂]⁺ moiety is exopolyhedrally bound via three B - H - Ru bonds to a closo-3,1,2-ReC₂B₉ system. An X-ray diffraction study revealed that one of these agostic interactions utilizes a β-B-H bond in the coordinating CCBBB face of the cage, while the source of the remaining two B - H - Ru bonds is in the 65 belt. The anion of salt 1 also binds exopolyhedral [Rh(PPh₃)₂]⁺ and [Rh{Fe(η-C₅H₄PPh₂)₂}] ⁺ fragments in the complexes [Re-(CO)₃(η⁵-5,10-(μ-H)_2-exo-(RhL ₂)-7,8-C₂B₉H₉)] (L₂ = (PPh₃)₂ (3a), {Fe(η-C₅H₄PPh₂)₂} (3b)). Reaction of 1 with the salts [M(CO)₂(THF)(η-C₅H₅)] [BF₄] (M = Fe, Ru) and [Fe(CO)₂(THF)-(η-C₅Me₅)][BF₄] gives the complexes [Re(CO)₃(η⁵-n-(μH)-exo-{M(CO) ₂(η-C₅R₅)}-7,8-C₂B ₉H₁₀)] (M = Fe, R = H, n = 10 (4a); M = Ru, R = H, n = 10 (4b); M = Fe, R = Me, n = 10 (4c), 9 (4d)) with isomers 4c and 4d formed as an inseparable mixture. An X-ray structural study on 4b revealed that there was no Re-Ru bond and that an exro-[Ru(CO)₂(η-C₅H₅)]⁺ fragment is bound to the rhenacarboranyl anion by a single unsupported B - H - Ru interaction with an unusually long B - Ru distance (2.695(13) A?). The compounds [ReM(μ-10-H-η⁵-7,8-C₂B₉H ₁₀)-(CO)₃(PPh₃)] (M = Cu (5a), Ag (5b)) were isolated from the reaction of 1 with sources of the fragments [M(PPh₃)]⁺ (M = Cu, Ag). X-ray structure determinations of both species 5 revealed the presence of direct Re - M (M = Cu, Ag) connectivities bridged by carborane β-B - H - M interactions. In solution the complexes 5 are highly dynamic on the NMR time scale, even at low ( - 90°C) temoeratures.

Full text of DOI:10.1021/om9905097

4982
Organometallics 1999, 18, 4982-4994
Stu d ies w ith th e Rh en a ca r bor a n e
Cs[Re(CO)3(η5-7,8-C2B9H11)]: Su r p r isin g Rea ctivity w ith a
Ra n ge of Meta l Liga n d F r a gm en ts†
Dianne D. Ellis, Paul A. J elliss, and F. Gordon A. Stone*
Department of Chemistry & Biochemistry, Baylor University, Waco, Texas 76798-7348
Received J uly 1, 1999
The rhenacarborane salt Cs[Re(CO)3(η5-7,8-C2B9H11)] (1) has been synthesized in excellent
yield using a new procedure. Treatment of CH2Cl2 solutions of 1 with [RuCl2(PPh3)3] yields
the exo-closo complex [Re(CO)3(η5-2,3,10-(µ-H)3-exo-{RuCl(PPh3)2}-7,8-C2B9H8)] (2a ). In this
molecule a [RuCl(PPh3)2]+ moiety is exopolyhedrally bound via three B-HFRu bonds to a
closo-3,1,2-ReC2B9 system. An X-ray diffraction study revealed that one of these agostic
interactions utilizes a â-B-H bond in the coordinating CCBBB face of the cage, while the
source of the remaining two B-HFRu bonds is in the B5 belt. The anion of salt 1 also binds
exopolyhedral [Rh(PPh3)2]+ and [Rh{Fe(η-C5H4PPh2)2}]+ fragments in the complexes [Re-
(CO)3(η5-5,10-(µ-H)2-exo-(RhL2)-7,8-C2B9H9)] (L2 ) (PPh3)2 (3a ), {Fe(η-C5H4PPh2)2} (3b)).
Reaction of 1 with the salts [M(CO)2(THF)(η-C5H5)][BF4] (M ) Fe, Ru) and [Fe(CO)2(THF)-
(η-C5Me5)][BF4] gives the complexes [Re(CO)3(η5-n-(µ-H)-exo-{M(CO)2(η-C5R5)}-7,8-C2B9H10)]
(M ) Fe, R ) H, n ) 10 (4a ); M ) Ru, R ) H, n ) 10 (4b); M ) Fe, R ) Me, n ) 10 (4c), 9
(4d )) with isomers 4c and 4d formed as an inseparable mixture. An X-ray structural study
on 4b revealed that there was no Re-Ru bond and that an exo-[Ru(CO)2(η-C5H5)]+ fragment
is bound to the rhenacarboranyl anion by a single unsupported B-HFRu interaction with
an unusually long B-Ru distance (2.695(13) Å). The compounds [ReM(µ-10-H-η5-7,8-C2B9H10)-
(CO)3(PPh3)] (M ) Cu (5a ), Ag (5b)) were isolated from the reaction of 1 with sources of the
fragments [M(PPh3)]+ (M ) Cu, Ag). X-ray structure determinations of both species 5 revealed
the presence of direct Re-M (M ) Cu, Ag) connectivities bridged by carborane â-B-HFM
interactions. In solution the complexes 5 are highly dynamic on the NMR time scale, even
at low (-90 °C) temperatures.
In tr od u ction
this salt to react either with strong acids (HBF4‚Et2O,
HCl(Et2O), CF3CO2H) or with sources of the fragment
[Au(PPh3)]+. Failure of [Au(PPh3)]+ to afford a Re-Au
species was especially surprising, as the gold reagent
reacts with several other anionic metallacarboranes
to form metal-metal bonds.4 However, recently the
monocarbon rhenacarborane [N(PPh3)2]2[Re(CO)3(η5-7-
CB10H11)] has been used as an effective precursor to
novel bimetallic complexes with Re-Pt, Re-Pd, Re-
Rh, and Re-Ir bonds,5 and this has prompted us to
reexamine the reactivity of compound 1. Despite the
negative results obtained in attempts to protonate and
aurate 1, we demonstrate herein that this reagent does
in fact display unusual reactivity toward mid- to late-
transition-metal reagents. Moreover, despite the ab-
sence of a reaction with [Au(PPh3)]+, we have used
reactions between 1 and [M(PPh3)]+ (M ) Cu, Ag) to
Studies on the synthesis and especially the reactivity
of metallacarborane complexes having closo-3,1,2-
MC2B9 and closo-2,1-MCB10 core structures has at-
tracted our attention in recent years for several reasons.
Thus, reactions where exopolyhedral metal-metal bonds
are formed have been a particularly productive topic for
investigation because many of the new di- and tri-
nuclear metal compounds obtained possess carborane
cages which function as nonspectator ligands.1 Several
years ago during a preliminary investigation2 of the
rhenacarborane Cs[Re(CO)3(η5-7,8-C2B9H11)] (1), first
synthesized by Hawthorne and Andrews,3 it came as
some surprise to us that there was no propensity for
† The compounds described in this paper have a rhenium atom
incorporated into a closo-1,2-dicarba-3-rhenadodecaborane structure.
However, to avoid a complicated nomenclature for the complexes
reported, and to relate them to the many known rhenium species with
η-coordinated cyclopentadienyl ligands, we treat the cages as nido-
11-vertex ligands with numbering as for an icosahedron from which
the 12th vertex has been removed.
(1) (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) J elliss,
P. A.; Stone, F. G. A. J . Organomet. Chem. 1995, 500, 307.
(2) Li, S.; Stone, F. G. A. Unpublished results.
(4) (a) Goldberg, J . E.; Stone, F. G. A. Polyhedron 1992, 11, 2841.
(b) Pilotti, M. U.; Stone, F. G. A.; Topalogˇlu, I. J . Chem. Soc., Dalton
Trans. 1991, 1355. (c) Carr, N.; Gimeno, M. C.; Goldberg, J . E.; Pilotti,
M. U.; Stone, F. G. A.; Topalogˇlu, I. J . Chem. Soc., Dalton Trans. 1990,
2253. (d) J effery, J . C.; J elliss, P. A.; Stone, F. G. A. J . Chem. Soc.,
Dalton Trans. 1994, 25. (e) Batten, S. A.; J effery, J . C.; J ones, P. L.;
Mullica, D. F.; Rudd, M. D.; Sappenfield, E. L.; Stone, F. G. A.; Wolf,
A. Inorg. Chem. 1997, 36, 2570.
(3) (a) Hawthorne, M. F.; Andrews, T. D. J . Am. Chem. Soc. 1965,
87, 2496. (b) Andrews, T. D.; Hawthorne, M. F.; Howe, D. V.; Pilling,
R. L.; Pitts, D.; Reintjes, M.; Warren, L. F., J r.; Wegner, P. A.; Young,
D. C. J . Am. Chem. Soc. 1968, 90, 879.
(5) (a) Blandford, I.; J effery, J . C.; J elliss, P. A.; Stone, F. G. A.
Organometallics 1998, 17, 1402. (b) J effery, J . C.; J elliss, P. A.; Rees,
L. H.; Stone, F. G. A. Organometallics 1998, 17, 2258.
10.1021/om9905097 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/28/1999

Reactivity of Cs[Re(CO)3(η5-7,8-C2B9H11)]
Organometallics, Vol. 18, No. 24, 1999 4983
Ta ble 1. An a lytica l a n d P h ysica l Da ta
anal./%b
compd
color yield/%
ν
max(CO)a /cm-1
C
H
2a
3a
[Re(CO)3(η5-2,3,10-(µ-H)3-exo-{RuCl(PPh3)2}-7,8-C2B9H8)]
[Re(CO)3(η5-5,10-(µ-H)2-exo-{Rh(PPh3)2}-7,8-C2B9H9)]
red
red
30
65
58
98
2024 vs, 1933 s br
2018 vs, 1923 s br
2019 vs, 1923 s br
2066 m, 2032 s,
2015 s, 1922 s br
2077 m, 2032 s,
46.3 (46.3) 3.9 (3.9)
c44.6 (45.2) 4.0 (3.9)
3bd [Re(CO)3(η5-5,10-(µ-H)2-exo-(Rh{Fe(η-C5H4PPh2)2})-7,8-C2B9H9)] red
4a
4b
[Re(CO)3(η5-10-(µ-H)-exo-{Fe(CO)2(η-C5H5)}-7,8-C2B9H10)]
[Re(CO)3(η5-10-(µ-H)-exo-{Ru(CO)2(η-C5H5)}-7,8-C2B9H10)]
orange
yellow
orange
24.9 (24.9) 2.7 (2.8)
23.1 (23.1) 2.6 (2.6)
f29.0 (29.4) 3.8 (3.8)
38.1 (37.9) 3.6 (3.6)
47
92
2015 s, 1920 s br
2047 m, 2014 s,
4c,d e [Re(CO)3(η5-n-(µ-H)-exo-{Fe(CO)2(η-C5Me5)}-7,8-C2B9H10)]
2005 sh,1917 s br
2027 vs, 1951 s, 1930 s
5a
5b
[ReCu(µ-10-H-η5-7,8-C2B9H10)(CO)3(PPh3)]
[ReAg(µ-10-H-η5-7,8-C2B9H10)(CO)3(PPh3)]
white
white
57
63
2024 vs, 1943 vs, 1924 vs g34.6 (34.6) 3.3 (3.3)
a
Measured in CH2Cl2; medium-intensity broad bands observed at ca. 2550 cm-1 in the spectra of all the compounds are due to B-H
absorptions. b Calculated values are given in parentheses. c Contains 1.0 mol equiv of CH2Cl2, confirmed by NMR. Unstable; microanalysis
d
unavailable. e Formed as an inseparable 1:1 mixture of isomers: n ) 10 (4c), 9 (4d ). f Contains 1.0 mol equiv of CH2Cl2, confirmed by
g
NMR. Contains 0.5 mol equiv of CH2Cl2, confirmed by X-ray structure.
Ch a r t 1
form rhenium-copper and -silver complexes with
metal-metal bonds.
Resu lts a n d Discu ssion
The original synthesis of complex 1 was reported over
30 years ago,3 and its X-ray structural characterization
was described soon after.6 By modifiying the original
procedure (see Experimental Section), we have improved
the yield of 1 from the reported 58% to over 90%,
making it an attractive starting material for the syn-
thesis of rhenacarborane complexes. A diffuse negative
charge distribution within the closo-3,1,2-ReC2B9 cage
is anticipated for the anion of 1, as was found with the
dianion [Re(CO)3(η5-7-CB10H11)]2- 5a
and this must at
,
least partially account for the low basicity at the metal
center. The initial agenda for studies with 1 involved
examining reactions with those transition-metal re-
agents which have successfully given adducts with the
-
carboranyl anions [nido-7,8-R2-7,8-C2B9H10
]
(R ) H,
alkyl, aryl) and [closo-1-CB11H12]-.
Recent work by Chizhevsky and co-workers7 has
shown that the carboranyl anion [nido-7,8-C2B9H12]- on
treatment with [RuCl2(PPh3)3] forms the adduct [2,3,-
10-(µ-H)3-exo-{RuCl(PPh3)2}-nido-7,8-C2B9H9] in which
the cage framework behaves as a tridentate ligand
toward the ruthenium center. With this in mind,
complex 1 was treated with 1 equiv of [RuCl2(PPh3)3],
affording the product [Re(CO)3(η5-2,3,10-(µ-H)3-exo-{Ru-
Cl(PPh3)2}-7,8-C2B9H8)] (2a ; Chart 1) in somewhat poor
yield (Table 1). Although spectroscopic data (Tables 2
and 3) were useful in elucidating the nature of 2a , its
relative novelty prompted us to carry out an X-ray
diffraction characterization. The pertinent bond lengths
and angles are given in Table 4, and the molecule is
shown in Figure 1. The absence of a Re-Ru bond is
immediately apparent, and the zwitterionic nature of
the molecule is realized: the anion of 1 is coordinated
with a [RuCl(PPh3)2]+ cation through the mediacy of
three B-HFRu bonds involving one B-H connectivity
protruding from the â-position of the lower coordinating
B5 belt (Ru-B(9) ) 2.379(3) Å, Ru-B(10) ) 2.462(3) Å).
This latter pair of interactions utilize both boron atoms
antipodal to each of the cage carbon vertexes and are
inequivalent. This might be attributed to subtle crystal
packing forces, as later discussion of the NMR spectra
will show that there is equivalence of the B5 belt
B-HFRu contacts in solution. The PPh3 ligands both
lie transoid to the B5 belt B-HFRu agostic moieties
(Ru-P(1) ) 2.3093(7) Å, Ru-P(2) ) 2.2870(8) Å, P(1)-
Ru-H(9) ) 169.7(8)°, P(2)-Ru-H(10) ) 171.2(7)°) while
the chloride ligand is transoid to the â-B(4)-H(4)FRu
system (Ru-Cl ) 2.3189(7) Å, Cl-Ru-H(4) ) 175.5-
(9)°). The binding of the [RuCl(PPh3)2]+ fragment to the
CCBBB belt (Ru-B(4) ) 2.310(3) Å) and two from the
(6) Zalkin, A.; Hopkins, T. E.; Templeton, D. H. Inorg. Chem. 1966,
5, 1189.
(7) Chizhevsky, I. T.; Lobanova, I. A.; Bregadze, V. I.; Petrovskii,
P. V.; Antonovich, V. A.; Polyakov, A. V.; Yanovskii, A. I.; Struchkov,
Y. T. Mendeleev Commun. 1991, 48.

4984 Organometallics, Vol. 18, No. 24, 1999
Ta ble 2. Hyd r ogen -1 a n d Ca r bon -13 NMR Da ta a
1H/δb
Ellis et al.
compd
13C/δc
2d
-15.56* [q br, 1 H, B-HFRu, J (BH) ) ca. 85], -14.84 [q br, 1 H,
B-HFRu, J (BH) ) ca. 80], -4.76* [q br, 1 H, B-HFRu,
J (BH) ) ca. 94], -4.63* [q br, 1 H, B-HFRu, J (BH) ) ca. 95],
-3.52 [dq br 2 H, B-HFRu, J (PH) ) ca. 30, J (BH) ) ca. 100],
2.91* (s br, 1 H, CH), 3.03 (s br, 2 H, CH), 3.09* (s br, 1 H, CH),
7.16-7.35 (m, 30 H, Ph)
194.6 (CO), 194.1* (CO), 137.8-128.2 (Ph),
33.1 (br, CH)
3a
3b
-5.34 (m br, 1 H, B-HFRh), 3.02 (s br, 2 H, CH),
7.14-7.36 (m, 30 H, Ph)
195.6 (CO), 135.5-128.3 (Ph), 33.8 (br, CH)
-5.56 [q br, 1 H, B-HFRh, J (BH) ) ca. 80],
2.97 (s br, 2 H, CH), 4.20, 4.32 (m × 2, 8 H, PC5H4),
7.16-7.72 (m, 20 H, Ph)
-19.67 [q br, 1 H, B-HFFe, J (BH) ) ca. 80],
2.92 (s br, 2 H, CH), 5.16 (s, 5 H, C5H5)
195.7 (CO), 137.9-128.5 (Ph), 76.4 [dd, C1(PC5H4),
J (PC) ) 62, 3], 76.3 [AXX′, C2(PC5H4), N ) 12e],
73.5 [AXX′, C3(PC5H4), N ) 8e], 33.9 (br, CH)
208.9 (FeCO), 196.1 (ReCO), 85.4 (C5H5),
33.3 (br, CH)
4a
4b
4cf
-12.92 [q br, 1 H, B-HFRu, J (BH) ) 75],
196.2 (ReCO), 194.3 (RuCO), 88.6 (C5H5),
33.4 (br, CH)
2.96 (s br, 2 H, CH), 5.48 (s, 5 H, C5H5)
-18.46 (m br, 2 H, B-HFFe), 1.81, 1.82 (s × 2, 30 H, C5Me5),
211.9 (FeCO × 2), 211.2, 211.1 (FeCO), 196.7,
196.4 (ReCO), 97.8, 97.3 (C5Me5), 34.6 (br, CH),
32.4 (br, CH × 2), 31.3 (br, CH), 10.0, 9.9 (C5Me5)
191.1 (CO), 134.1 [d, C2(Ph), J (PC) ) 15], 131.7 [d,
C4(Ph), J (PC) ) 2], 129.8 [d, C1(Ph), J (PC) ) 44],
129.7 [d, C3(Ph), J (PC) ) 10], 36.6 (br, CH)
191.8 (CO), 134.2 [d, C2(Ph), J (PC) ) 16], 131.9 [d,
C4(Ph), J (PC) ) 2], 129.8 [d, C3(Ph), J (PC) ) 11],
129.6 [d, C1(Ph), J (PC) ) 41], 36.2 (br, CH)
2.91 (s br, 2 H, CH), 2.94, 2.98 (s br × 2, 2 H, CH)
5a
5b
3.34 (s br, 2 H, CH), 7.48-7.55 (m, 15 H, Ph)
3.33 (s br, 2 H, CH), 7.49-7.56 (m, 15 H, Ph)
a
b
Chemical shifts (δ) in ppm, coupling constants (J ) in Hz, measurements at room temperature in CD2Cl2. Resonances for terminal
BH protons occur as broad unresolved signals in the range δ ca. -2 to 3. Resonances for cage CH and B-HFM protons are described as
broad, corresponding to approximate ν1/2 values of 10 and 300 Hz, respectively. c Hydrogen-1 decoupled, chemical shifts are positive to
high frequency of SiMe4. Resonances for cage CH groups are described as broad, corresponding to an approximate ν1/2 value of 20 Hz.
Composed of a 15:1 mixture of isomers (see text). Peaks marked with an asterisk are due to the minor isomer. e Insufficient resolution
d
prevents full analysis of coupling constants, N ) |J (AX) + J (AX′)|. f Composed of a 1:1 mixture of isomers (see text).
Ta ble 3. Bor on -11 a n d P h osp h or u s-31 NMR Da ta a
compd
11B/δb
31P/δc
2d
-5.6 (1 B), -10.2 (1 B), -12.3 [1 B, B-HFRu, J (HB) ) 76], -14.2* (1 B),
-16.1* [1 B, B-HFRu, J (HB) ) 85], -19.0* (1 B), -20.3 (4 B), -26.1 (2 B)
-10.1 (1 B), -14.3 (6 B), -23.3 (2 B)
57.4* [d, J (PP) ) 20], 53.5, 43.8* [d, J (PP) ) 20]
3a
3b
4a
45.0 [d, J (RhP) ) 187]
45.9 [d, J (RhP) ) 194]
-9.8 (1 B), -14.2 (6 B), -23.3 (2 B)
-7.2 (1 B), -11.3 (2 B), -14.5 (2 B), -20.0 (1 B), -22.9 [1 B, B-HFFe,
J (HB) ) 82], -23.7 (2 B)
-7.1 (1 B), -10.9 (2 B), -14.4 (2 B), -19.7 [1 B, B-HFRu, J (HB) ) 75],
-23.6 (3 B)
-7.1 (1 B), -8.3 (1 B), -11.2 (5 B), -15.1 (4 B), -20.3 (3 B), -23.9 (4 B)
-1.6 (1 B), -10.5 (2 B), -15.2 (3 B), -17.5 (1 B), -21.5 (2 B)
-1.5 (1 B), -10.0 (2 B), -15.2 (2 B), -18.6 (2 B), -22.3 (2 B)
4b
4ce
5a
5b
11.0
20.4 [d × 2, J (109AgP) ) 681, J (107AgP) ) 590]
a
b
Chemical shifts (δ) in ppm, coupling constants (J ) in Hz, measurements at room temperature in CD2Cl2. Hydrogen-1 decoupled,
chemical shifts are positive to high frequency of BF3‚OEt2 (external). The B-HFM assignments were made from fully coupled 11B spectra.
c Hydrogen-1 decoupled, chemical shifts are positive to high frequency of 85% H3PO4 (external). Composed of a 15:1 mixture of isomers
d
(see text). e Composed of a 1:1 mixture of isomers (see text). Peaks marked with an asterisk are due to the minor isomer.
rhenacarborane is thus strongly reminiscent of that
observed for this moiety in [2,3,10-(µ-H)3-exo-{RuCl-
(PPh3)2}-nido-7,8-C2B9H9].7 Similar tridentate bonding
of a carborane to a transition-metal species has also
been documented for the complex [7,8,12-(µ-H)3-exo-{Zr-
(Me)2(η-C5Me5)}-closo-1-CB11H9].8 Further examination
of the literature reveals that B-HFRu interactions are
in fact ubiquitous in metallaborane chemistry.9 Indeed,
a tridentate binding of a borane cage to a ruthenium
fragment was reported for the complex [1,2,3-(µ-H)3-exo-
{RuCl(PPh3)2}-7-NEt3-closo-B12H8] several years ago.10
However, employment of a closo-metallacarborane in
this tridentate role, namely that of 1, is unprecedented.
The Re(CO)3 unit of 2a is structurally unaffected by the
exopolyhedral ruthenium moiety, displaying a piano
stool arrangement with near-linear Re-C-O ligands
(average Re-C-O ) 177.0°).
In the IR spectrum there is a distinctive shift of
ν
max(CO) signals to higher frequency from those in the
starting material 1 (2005 and 1905 cm-1 in CH2Cl2) to
those in the product 2 (2024 and 1933 cm-1) (Table 1).
This simply reflects the formation of a charge-compen-
sated species from the anion of 1 but also is a good initial
indicator that an adduct has formed in this and other
reactions to be discussed presently. The 1H NMR
spectrum (Table 2) is highly informative with a low-
field broad quartet at δ -14.84 which has the diagnostic
coupling J (BH) ≈ 80 Hz.1b This may be assigned to the
â-B(4)-H(4)FRu proton. The remaining two B-HFRu
protons (H(9) and H(10)) give rise to a single but broad
doublet of quartets at δ -3.52 corresponding to two
protons. The quartet splitting (J (BH) ) 100 Hz) is large
for an agostic system but corresponds with the observa-
(8) Crowther, D. J .; Borkowski, S. I.; Swenson, D.; Meyer, T. Y.;
J ordan, R. F. Organometallics 1993, 12, 2897.
(9) (a) Kennedy, J . D. J . Chem. Soc., Dalton Trans. 1993, 2545 and
references cited therein. (b) Teixidor, F.; Vin˜as, C.; Casabo´, J .;
Romerosa, A. M.; Rius, J .; Miravitlles, C. Organometallics 1994, 13,
914. (c) Vin˜as, C.; Nun˜ez, R.; Teixidor, F.; Kiveka¨s, R.; Sillanpa¨a¨, R.
Organometallics 1996, 15, 3850.
(10) Elrington, M.; Greenwood, N. N.; Kennedy, J . D.; Thornton-
Pett, M. J . Chem. Soc., Dalton Trans. 1987, 451.

Reactivity of Cs[Re(CO)3(η5-7,8-C2B9H11)]
Organometallics, Vol. 18, No. 24, 1999 4985
Ta ble 4. Selected In ter n u clea r Dista n ces (Å) a n d An gles (d eg) for
[Re(CO)3(η5-2,3,10-(µ-H)3-exo-{Ru Cl(P P h 3)2}-7,8-C2B9H8)] (2a ) w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses
Re-C(3)
1.909(3)
2.333(3)
1.154(4)
2.379(3)
2.14(3)
Re-C(5)
1.920(4)
2.336(3)
1.149(3)
2.462(3)
2.2870(8)
1.837(3)
1.841(3)
Re-C(4)
Re-B(5)
C(5)-O(5)
H(4)-Ru
Ru-P(1)
P(1)-C(30)
1.937(3)
2.341(4)
1.148(4)
1.73(3)
2.3093(7)
1.848(3)
Re-C(2)
Re-B(3)
B(4)-Ru
H(9)-Ru
Ru-Cl
2.332(3)
2.347(3)
2.310(3)
1.94(3)
2.3819(7)
1.832(3)
Re-C(1)
Re-B(4)
C(3)-O(3)
B(9)-Ru
H(10)-Ru
P(1)-C(40)
P(2)-C(70)
C(4)-O(4)
B(10)-Ru
Ru-P(2)
P(1)-C(20)
P(2)-C(50)
1.831(3)
1.832(3)
P(2)-C(60)
C(3)-Re-C(5)
C(3)-Re-C(2)
C(3)-Re-C(1)
C(2)-Re-C(1)
C(4)-Re-B(4)
C(3)-Re-B(5)
C(2)-Re-B(5)
C(3)-Re-B(3)
C(2)-Re-B(3)
B(5)-Re-B(3)
O(5)-C(5)-Re
89.88(14)
150.38(13)
109.77(13)
40.88(11)
163.51(12)
85.87(13)
72.53(12)
151.77(12)
42.09(11)
77.36(12)
176.6(3)
H(9)-Ru-P(2)
H(9)-Ru-P(1)
H(4)-Ru-Cl
89.2(8)
169.7(8)
175.5(9)
91.49(3)
88.65(13)
119.74(13)
159.03(12)
106.91(12)
71.89(10)
136.39(12)
42.68(11)
C(5)-Re-B(3)
C(1)-Re-B(3)
O(3)-C(3)-Re
Ru-B(4)-Re
H(10)-Ru-P(2)
H(10)-Ru-P(1)
H(9)-Ru-Cl
86.94(13)
72.31(12)
176.8(3)
162.8(2)
171.2(7)
88.1(7)
C(5)-Re-B(4)
C(1)-Re-B(4)
C(4)-Re-B(5)
B(4)-Re-B(5)
C(4)-Re-B(3)
B(4)-Re-B(3)
O(4)-C(4)-Re
H(4)-Ru-P(2)
H(4)-Ru-P(1)
P(2)-Ru-P(1)
H(10)-Ru-Cl
95.97(12)
71.87(11)
133.80(13)
45.07(11)
119.33(12)
45.78(11)
177.2(3)
89.8(9)
P(2)-Ru-Cl
C(3)-Re-C(4)
C(5)-Re-C(2)
C(5)-Re-C(1)
C(3)-Re-B(4)
C(2)-Re-B(4)
C(5)-Re-B(5)
C(1)-Re-B(5)
80.6(7)
P(1)-Ru-Cl
93.71(3)
89.35(13)
91.91(12)
98.09(12)
C(5)-Re-C(4)
C(4)-Re-C(2)
C(4)-Re-C(1)
90.3(9)
99.54(3)
92.3(7)
2a . The resonance at δ -12.3 (1 B) becomes a doublet
(J (HB) ) 76 Hz) in the fully coupled 11B NMR spectrum,
while that at δ -26.1 (2 B) becomes a broader signal
1
with irresolvable H-11B coupling. The former must be
due to the â-boron atom B(4) in the CCBBB ring, while
the latter likely arises from the two B5 belt B(9,10) boron
atoms. These chemical shift values are located at
considerably higher field than is generally observed1b
for species displaying exopolyhedral B-HFM bonds,
and further discussion of this feature will be forthcom-
ing. The 11B and 11B{1H} NMR spectra also reveal weak
resonances due to the minor species 2b, though most
are obscured by larger peaks for 2a . Most notable for
2b, though, is a resonance at δ -16.1 which becomes a
doublet in the 11B NMR spectrum with J (HB) ) 85 Hz.
It is proposed that this signal, which correlates with the
1
F igu r e 1. Structure of [Re(CO)3(η5-2,3,10-(µ-H)3-exo-{Ru-
Cl(PPh3)2}-7,8-C2B9H8)] (2a ), showing the crystallographic
labeling scheme. Thermal ellipsoids are shown at the 40%
probability level. Only the agostic hydrogen and phenyl
ipso-carbon atoms are shown for clarity.
resonance at δ -15.56 (J (BH) ) 85 Hz) in the H NMR
spectrum, arises from the R-boron atom in the CCBBB
ring. Thus, the minor isomer 2b (Chart 1) employs three
inequivalent agostic B-HFRu interactions, one using
the R-boron atom in the CCBBB belt and the other two
from adjacent B5 belt boron atoms (i.e. B(3), B(8), and
B(9) if one employed the same crystallographic number-
ing scheme as in Figure 1 for 2a ). This is preferred over
tion in the X-ray structure that the B(9,10)-H(9,10)FRu
interactions are weaker than the B(4)-H(4)FRu bond.
This of course is a direct consequence of the stronger
trans influence of the PPh3 ligands compared with that
of chloride.9c The signal at δ -3.52 shows a further
discernible doublet splitting J (PH) ≈ 30 Hz, confirming
the transoid location of the B(9,10)-H(9,10)FRu pro-
tons with respect to the phosphines. With a resonance
at δ 3.03 for the cage CH groups, the Cs symmetry of
2a in solution is confirmed, with a mirror plane through
an alternative model invoking use of two CCBBB belt
boron atoms and one from the B5 ring, since this
arrangement would place the chlorine atom in close
proximity to the Re(CO)3 carbonyl ligands. The 13C{1H}
NMR spectrum of 2 displays a single sharp signal at δ
194.6 for the Re(CO)3 carbonyl carbon nuclei of 2a and
a further singlet resonance for this group at δ 194.1 for
2b. Thus, as for the parent complex 1, the Re(CO)3 unit
in both isomers of 2 is rapidly spinning relative to the
cage about an axis through the Re and apical boron
atoms, thereby rendering the CO ligands equivalent on
the NMR time scale.
1
the Re, Ru, Cl, and apical boron atoms. The H NMR
spectrum indicated the presence of the minor isomer 2b,
which is much less symmetrical, with three broad
quartets at δ -15.56, -4.76, and -4.63 (J (BH) ≈ 85,
94, and 95 Hz, respectively) and two signals arising from
the now inequivalent cage CH groups (δ 2.91 and 3.09).
The relative peak integrals suggest a ratio of sym-
metrical 2a to unsymmetrical 2b of 15:1. The 31P{1H}
NMR spectrum reflects the existence of 2a with equiva-
lent phosphine ligands (singlet at δ 53.5) and of 2b with
inequivalent PPh3 groups (doublets at δ 43.8 and 57.4,
J (PP) ) 20 Hz). The 11B{1H} NMR spectrum shows
principal peaks integrated in the ratio 1:1:1:4:2 due to
Our interpretation of the NMR data for 2 contrasts
with that given for the NMR data for the complex
[2,3,10-(µ-H)3-exo-{RuCl(PPh3)2}-nido-7,8-C2B9H9],7 which
in solution was believed to be undergoing a systematic
and reversible oxidative addition of the agostic B-HFRu
bonds to give various B-Ru-H moieties. We find no

4986 Organometallics, Vol. 18, No. 24, 1999
Ellis et al.
such evidence for a similar process in complex 2 and
propose that the minor isomer 2b can be simply gener-
ated from 2a by an effective lateral translation of the
exo-[RuCl(PPh3)2]+ fragment from one set of three
deltahedrally arranged B-H vertexes on the cage
surface to the adjacent set closer to the cage carbon
atoms.
The NMR data for 2 imply that there is no significant
dynamic behavior at ambient temperatures. This is in
contrast with the previously reported behavior of the
complexes [5,10-(µ-H)2-exo-{Rh(PPh3)2}-7,8-Me2-nido-
7,8-C2B9H8]11a and [10-endo-{Au(PPh3)}-5,10-(µ-H)2-exo-
{Rh(PPh3)2}-7,8-Me2-nido-7,8-C2B9H7],11b which have
exopolyhedral [Rh(PPh3)2]+ fragments bound via
B-HFRh interactions to carborane and auracarborane
cages, respectively. In these molecules the rhodium
fragments are dynamic with respect to the rest of the
cage, rapidly exchanging B-H bonds around the cage
surface at ambient temperatures. This prompted a study
of the formation of related rhodium complexes using 1.
Treatment of the salt 1 with [RhCl(PPh3)3] led to the
isolation of the compound [Re(CO)3(η5-5,10-(µ-H)2-exo-
{Rh(PPh3)2}-7,8-C2B9H9)] (3a ; Chart 1) in reasonable
yield (Table 1). The IR spectrum of the crude reaction
mixture was consistent with the partial formation of 3a ,
an adduct of the anion of 1, and a rhodium-bisphos-
phine fragment. However, the presence of a third PPh3
molecule, derived from [RhCl(PPh3)3], gave rise to an
equilibrium between 3a and the salt [Rh(PPh3)3][Re-
(CO)3(η5-7,8-C2B9H11)], a process also confirmed by NMR
spectroscopy. The additional PPh3 group was easily
removed by several washings of the residue with light
petroleum, leaving only product 3a . Despite the insta-
bility of solutions of 3a , which partially decomposed
after 3-5 days, it was possible to collect interpretable
NMR data (Tables 2 and 3).
F igu r e 2. 31P{1H} NMR spectrum of compound 3a in CD2-
Cl2 at -90 °C. Peaks labeled A and B are assigned to the
molecules similarly labeled in Scheme 1.
Sch em e 1. P a th w a ys in th e Dyn a m ic Beh a vior of
Com p lex 3a
The room-temperature 1H NMR spectrum of 3a shows
a broad resonance at δ 3.02 typical for the cage CH
groups, but also seen was a broad quartet at δ -5.34
integrated to one proton for a B-HFRh group but with
unresolved 11B-1H coupling. Similar observations were
made for the above-mentioned dynamic complexes [5,-
10-(µ-H)2-exo-{Rh(PPh3)2}-7,8-Me2-nido-7,8-C2B9H8] and
[10-endo-{Au(PPh3)}-5,10-(µ-H)2-exo-{Rh(PPh3)2}-7,8-
Me2-nido-7,8-C2B9H7].11 The 11B{1H} NMR spectrum
was regrettably unhelpful, comprising just three signals,
one of which was integrated to six boron nuclei, and
the 31P{1H} NMR spectrum contained a simple doublet
at δ 45.0 with a coupling (J (RhP) ) 187 Hz) typical for
a Rh(PR3)2 unit in a cis square-planar configuration.11
A variable-temperature NMR study was conducted, and
it was found that at low temperatures the dynamic
activity of 3a could be significantly suppressed. A 31P-
{1H} NMR spectrum measured at -90 °C in CD2Cl2
(Figure 2) showed peaks due to the major species A,
which appears to be an ABX system. The 103Rh-31P
coupling constants (190 and 182 Hz) for the now-
inequivalent phosphorus nuclei are discernible, but the
system may not have fully decoalesced to be able to
extract the J (PP) value. Thus, there may still be some
mobility in the molecule at -90 °C, the lowest temper-
ature attainable. This is supported by the 1H NMR
spectrum, also measured at -90 °C (Supporting Infor-
mation), which displays a very broad quartet at δ -5.32
and a singlet at δ 3.00 with a peak integral ratio of 1:2.
It is suggested that these peaks correspond to the
tautomers A (Scheme 1), where the [Rh(PPh3)2]+ frag-
ment is anchored to the anion of 1 by a â-B-HFRh
interaction. It is also bound to the B5 belt though a
second B-HFRh system involving one or other of the
two boron atoms antipodal to a cage carbon, similar to
that seen in the structures of [5,10-(µ-H)2-exo-{Rh-
(PPh3)2}-7,8-Me2-nido-7,8-C2B9H8] and [10-endo-{Au-
(PPh3)}-5,10-(µ-H)2-exo-{Rh(PPh3)2}-7,8-Me2-nido-7,8-
C2B9H7]. In CD2Cl2 solution at -90 °C there may still
be rapid exchange of these adjacent HC-antipodal B-H
bonds in the B5 belt; i.e., the rhodium atom is flipping
between these two B-H bonds. Thus, while the PPh3
ligands are inequivalent, a time-averaged mirror plane
of symmetry is generated in the molecule which encom-
passes the Re, Rh, the apical B, and both P atoms, which
is sufficient to render the cage CH groups equivalent
as observed. The minor species B is also present in
solution at -90 °C. This gives rise to two signals in the
(11) (a) Long, J . A.; Marder, T. B.; Behnken, P. E.; Hawthorne, M.
F. J . Am. Chem. Soc. 1984, 106, 2979. (b) J effery, J . C.; J elliss, P. A.;
Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1993, 1073.

Reactivity of Cs[Re(CO)3(η5-7,8-C2B9H11)]
Organometallics, Vol. 18, No. 24, 1999 4987
31P{1H} NMR spectrum measured at this temperature
(Figure 2): a broad doublet at δ 48.5 (J (RhP) ) 181 Hz)
and a much sharper doublet of doublets at δ 33.9
(J (RhP) ) 174 Hz, J (PP) ) 37 Hz). In the 1H NMR
spectrum at this temperature a broad quartet is seen
at δ -8.26 (B-HFRh) with a singlet at δ 3.16 (cage CH),
these signals integrated in the ratio 1:2. This is very
strong evidence for the species B (Scheme 1), which has
a Re-Rh bond. The broadness of the doublet at δ 48.5
in the 31P{1H} NMR spectrum can be accounted for by
assigning it to the PPh3 ligand which lies transoid to
the B-HFRh interaction. Such broadening has been
observed in similar molecules with a Pt(PR3)2 fragment
bonded in this manner and is attributed to the trans
location of the quadrupolar 11B nucleus.5a,12 The ratio
Ch a r t 2
1
of A to B is 4:1, as deduced from both the H and 31P-
{1H} NMR spectra at -90 °C. The fact that molecules
A and B can be observed at -90 °C implies that the
Re-Rh bond formation/fission process has been deceler-
ated to a rate slow enough on the NMR time scale to
distinguish between the two species. At room temper-
ature this process must be occurring rapidly enough that
only the single â-B-HFRh anchor can be observed in
1
the H NMR spectrum (δ -5.34, Table 2). The phospho-
rus nuclei are rendered equivalent most likely by virtue
of the intermediacy of the species C (Scheme 1), where
rapid rotation about the â-B-HFRh system occurs,
hence the observation of a lone doublet resonance in the
room-temperature 31P{1H} NMR spectrum (δ 45.0,
J (RhP) ) 187 Hz; Table 3). Complex C must be a long-
lived intermediate on the path between A and B but is
unlikely to be the ground-state structure. On the basis
of the prevalence of A at -90 °C and the previously
determined structures of [5,10-(µ-H)2-exo-{Rh(PPh3)2}-
7,8-Me2-nido-7,8-C2B9H8] and [10-endo-{Au(PPh3)}-5,-
10-(µ-H)2-exo-{Rh(PPh3)2}-7,8-Me2-nido-7,8-C2B9H7], the
molecule 3a shown in Chart 1 is the best representation.
In an attempt to form a more stable species in this
class which might give X-ray-quality crystals, compound
1 was reacted with a source of the cationic frag-
ment [Rh{Fe(η-C5H4PPh2)2}]+ to give the complex
[Re(CO)3(η5-5,10-(µ-H)2-exo-(Rh{Fe(η-C5H4PPh2)2})-7,8-
C2B9H9)] (3b; Chart 1). While it was possible to measure
spectroscopic data for 3b, it proved to be even less stable
than 3a . It does, however, represent an interesting
example of a metallacarborane incorporating first-,
second-, and third-row transition metals, with no direct
metal-metal bonds. The IR spectrum (Table 1) is
identical with that of 3a , and the 11B{1H} and 31P{1H}
NMR spectra (Tables 2 and 3) are extremely similar.
The 1H NMR spectrum revealed a diagnostic broad
quartet at δ -5.56, and this and the 13C{1H} NMR
spectrum displayed the expected resonances for the
equivalent η-C5H4PPh2 rings. It is reasonable to assume
that 3b is undergoing the same dynamic processes in
solution as 3a .
THF.13 Treatment of this iron salt with 1 gave [Re(CO)3-
(η5-10-(µ-H)-exo-{Fe(CO)2(η-C5H5)}-7,8-C2B9H10)] (4a ;
Chart 2) in excellent yield (Table 1). The IR spectrum
in the CO region (Table 1) with absorbances at 2015
and 1922 cm-1 (νmax(ReCO)) and at 2066 and 2032 cm-1
(νmax(FeCO)) clearly indicates that an adduct has formed
and that the iron center is still cationic in nature. An
interesting comparison may be made with the complex
[12-µ-H-exo-{Fe(CO)2(η-C5H5)}-closo-1-CB11H11] synthe-
sized by Reed and co-workers,14 where νmax(FeCO)
absorptions are observed at 2065 and 2026 cm-1 (KBr
disk). This complex was characterized by an X-ray
structural analysis, which revealed that the [closo-1-
-
CB11H12
]
anion was coordinated to the [Fe(CO)2(η-
C5H5)]+ fragment through the B-H bond antipodal to
the carbon vertex to give a zwitterionic species, having
the positive charge localized on the iron center and the
negative charge dispersed throughout the cage infra-
structure. Unfortunately, there are little reported NMR
data for this complex. The 1H NMR spectrum of 4a
displayed a broad high-field resonance at δ -19.67 with
an 11B-1H coupling that was barely observable (J (BH)
≈ 80 Hz). This coupling was more readily extracted from
the fully coupled 11B NMR spectrum, which showed a
doublet at δ -22.9 (J (HB) ) 82 Hz). The magnitude of
the coupling constant is typical for a B-HFM system,1b
1
but the chemical shifts for these signals in both the H
and 11B NMR spectra are much further upfield than
expected. It was noted above that a similar chemical
shift regime was recognized in the NMR spectra of
complex 2. The range of chemical shifts normally
encountered for these groups in complexes where there
The salt [Fe(CO)2(THF)(η-C5H5)][BF4] (THF ) tet-
rahydrofuran) is a useful synthon and is easily formed
by the reaction of [FeI(CO)2(η-C5H5)] with AgBF4 in
(12) (a) Goldberg, J . E.; Mullica, D. F.; Sappenfield, E. L.; Stone, F.
G. A. J . Chem. Soc., Dalton Trans. 1992, 2693. (b) Devore, D. D.;
Howard, J . A. K.; J effery, J . C.; Pilotti, M. U.; Stone, F. G. A. J . Chem.
Soc., Dalton Trans. 1989, 303. (c) Attfield, M. J .; Howard, J . A. K.;
J elfs, A. N. de M.; Nunn, C. M.; Stone, F. G. A. J . Chem. Soc., Dalton
Trans. 1987, 2219.
(13) Reger, D. L.; Coleman, C. J . Organomet. Chem. 1977, 131, 153.
(14) Liston, D. J .; Lee, Y. J .; Scheidt, W. R.; Reed, C. A. J . Am. Chem.
Soc. 1989, 111, 6643.

4988 Organometallics, Vol. 18, No. 24, 1999
Ellis et al.
Ta ble 5. Selected In ter n u clea r Dista n ces (Å) a n d An gles (d eg) for
[Re(CO)3(η5-10-(µ-H)-exo-{Ru (CO)2(η-C5H5)}-7,8-C2B9H10)] (4b) w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses
Re-C(3)
Re-C(1)
Re-Ru
B(4)-H(4)
Ru-H(4)
Ru-C(20)
1.882(14)
2.316(10)
4.4147(11)
1.67(10)
1.80(12)
2.223(10)
Re-C(4)
Re-B(3)
C(3)-O(3)
B(4)-Ru
Ru-C(23)
Ru-C(22)
1.886(14)
2.343(12)
1.171(13)
2.695(13)
2.191(11)
2.225(11)
Re-C(5)
Re-B(5)
C(4)-O(4)
Ru-C(7)
Ru-C(24)
C(7)-O(7)
1.91(2)
2.365(12)
1.17(2)
1.884(12)
2.207(11)
1.133(13)
Re-C(2)
Re-B(4)
C(5)-O(5)
Ru-C(8)
Ru-C(21)
C(8)-O(8)
2.301(12)
2.397(12)
1.15(2)
1.925(13)
2.208(11)
1.102(13)
C(3)-Re-C(4)
C(3)-Re-C(2)
C(3)-Re-C(1)
C(2)-Re-C(1)
C(5)-Re-B(3)
C(5)-Re-B(5)
C(5)-Re-B(4)
O(5)-C(5)-Re
H(4)-Ru-C(7)
H(4)-Ru-C(23)
H(4)-Ru-C(24)
C(23)-Ru-C(24)
C(8)-Ru-C(21)
H(4)-Ru-C(20)
88.4(5)
109.2(4)
148.9(5)
40.4(4)
136.7(6)
118.0(6)
162.4(5)
176.5(14)
65(3)
166(3)
151(3)
37.3(4)
153.6(5)
120(3)
C(23)-Ru-C(20)
H(4)-Ru-C(22)
C(23)-Ru-C(22)
C(20)-Ru-C(22)
O(8)-C(8)-Ru
C(3)-Re-C(5)
C(4)-Re-C(2)
C(4)-Re-C(1)
C(3)-Re-B(3)
C(3)-Re-B(5)
C(3)-Re-B(4)
O(3)-C(3)-Re
H(4)-B(4)-Ru
H(4)-Ru-C(8)
62.0(4)
130(3)
C(7)-Ru-C(23)
C(7)-Ru-C(24)
H(4)-Ru-C(21)
C(23)-Ru-C(21)
C(7)-Ru-C(20)
C(24)-Ru-C(20)
C(7)-Ru-C(22)
C(24)-Ru-C(22)
H(4)-Ru-B(4)
C(4)-Re-C(5)
C(5)-Re-C(2)
C(5)-Re-C(1)
C(4)-Re-B(3)
C(4)-Re-B(5)
106.7(5)
143.8(5)
111(3)
61.7(4)
149.9(5)
36.3(4)
92.5(5)
61.1(5)
37(3)
90.5(7)
99.5(5)
91.1(5)
132.3(5)
88.2(5)
C(4)-Re-B(4)
O(4)-C(4)-Re
Re-B(4)-Ru
93.5(5)
177.6(13)
120.1(5)
91.0(5)
101.8(5)
93.1(5)
112.9(5)
61.1(4)
118.1(5)
37.0(4)
36.8(4)
61.4(4)
174.1(11)
88.5(6)
159.8(5)
122.7(4)
86.4(5)
153.4(5)
108.8(5)
175.9(11)
39(3)
C(7)-Ru-C(8)
C(8)-Ru-C(23)
C(8)-Ru-C(24)
C(7)-Ru-C(21)
C(24)-Ru-C(21)
C(8)-Ru-C(20)
C(21)-Ru-C(20)
C(8)-Ru-C(22)
C(21)-Ru-C(22)
O(7)-C(7)-Ru
137.0(5)
36.6(4)
176.7(11)
89(3)
complex 2 the longest such distance is 2.462(3) Å
(B(10)-Ru; Table 4), while that in the complex [RuW-
(µ-CC6H4Me-4)(CO)3(η-C5H5)(η5-7,8-Me2-7,8-C2B9H9)], in
which a carborane bridges a Ru-W bond via a B-HFRu
group, is 2.400(9) Å.15 The B(4)-Ru distance in 4b
(2.695(13) Å) is therefore extremely long, and the
absence of a bond between these two atoms is justified
in Figure 3. The proton H(4) was located in final
difference Fourier maps with the distances Ru-H(4) )
1.80(12) and B(4)-H(4) ) 1.67(10) Å. While it is realized
that even for high-quality structures (R1 < 0.05) values
for bond distances involving hydrogen atoms are con-
sidered tenuous at best, the B(4)-H(4) contact in 4b is
notably long. Thus, the B-H distance in the B-HFRu
linkage in [RuW(µ-CC6H4Me-4)(CO)3(η-C5H5)(η5-7,8-
Me2-7,8-C2B9H9)] is 1.33 Å, which is usual.15 Hence,
complex 4b almost has the appearance of a [RuH(CO)2-
(η-C5H5)] molecule loosely bound to a neutral [Re(CO)3-
(η5-7,8-C2B9H10)] species at the â-boron position in the
F igu r e 3. Structure of [Re(CO)3(η5-10-(µ-H)-exo-{Ru(CO)2-
(η-C5H5)}-7,8-C2B9H10)] (4b), showing the crystallographic
labeling scheme. Thermal ellipsoids are shown at the 40%
probability level. Only the agostic hydrogen atom is shown
for clarity.
CCBBB ring, though such a relatively exposed boron
vertex is difficult to envision. Indeed, 4b could be viewed
as a product of incipient hydride extraction, a process
that, upon completion, has precedence in several areas
of metallacarborane chemistry.16 The carbonyl ligands
of 4b are nearly linear (average Re-C-O ) 176.7°,
average Ru-C-O ) 175.4°), and the spatial arrange-
ments of ligands around the metal centers is unremark-
able, with both the carborane cage and cyclopentadienyl
ligands η5-coordinated to the rhenium and ruthenium
atoms, respectively.
is a core M(B-HFM′) architecture, i.e., a metal-metal
bond bridged by a single carborane B-H bond, are δ
-5 to -11 (1H) and δ 10-30 (11B).1b Thus, it seemed
likely that there was no Re-Fe bond in complex 4a , an
idea supported by the observation in the 13C{1H} NMR
spectrum of just two resonances due to CO ligands (δ
208.9 (FeCO × 2) and 196.1 (ReCO × 3)). It was not
possible to grow tractable crystals of 4a , but the
ruthenium analogue [Re(CO)3(η5-10-(µ-H)-exo-{Ru(CO)2-
(η-C5H5)}-7,8-C2B9H10)] (4b, Chart 2) was prepared and
suitable crystals harvested for a structure determina-
tion. Selected bond lengths and angles are given in
Table 5, and the molecule is shown in Figure 3.
The absence of a Re-Ru bond is confirmed, as is the
participation of the â-B-H bond in ligating the ruthe-
nium atom. The exact nature of B-HFM bonding and
the associated B-M distances might be expected to
reflect whether a B-HFM interaction is bridging a
metal-metal bond or is in fact an unsupported or
isolated group. Kennedy9a reports a range of Ru-B bond
distances for B-HFRu groups in a collection of many
ruthenaboranes, the longest of which is 2.484(12) Å. In
The NMR spectra of 4b are akin to those of 4a . In
particular, the fully coupled 11B NMR spectrum displays
1
a doublet at δ -19.7 (J (HB) ) 75 Hz), and the H NMR
spectrum has a broad quartet at δ -12.92 (J (BH) ) 75
Hz) due to the â-B-HFRu boron and proton nuclei,
respectively. In solutions of both 4a and 4b a mirror
plane can be generated by free rotation about the
(15) Green, M.; Howard, J . A. K.; J elfs, A. N. de M.; J ohnson, O.;
Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1987, 73.
(16) (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. (c)
Hendershot, S. L.; J effery, J . C.; J elliss, P. A.; Mullica, D. F.;
Sappenfield, E. L.; Stone, F. G. A. Inorg. Chem. 1996, 35, 6561.

Reactivity of Cs[Re(CO)3(η5-7,8-C2B9H11)]
Organometallics, Vol. 18, No. 24, 1999 4989
Sch em e 2a
B-HFM system, this being a consequence of the
involvement of the CCBBB â-boron atom as opposed to
one of the two possible R-borons in the CCBBB ring.
Kennedy has observed9a that there appears to be little
correlation between the 1H chemical shift values for
B-HFRu groups in metallaboranes and their Ru-B
distances or the ligand disposition about the ruthenium
atom. Where the possibility exists for a metal-metal
bond to form, as we might have imagined in complex
4b (or indeed 4a ), we believe it can be inferred from
the significantly high field signals in the 1H and 11B
NMR spectra emanating from these B-HFRu groups
that the [Re(CO)3] and [Ru(CO)2(η-C5H5)] fragments in
fact remain unconnected by a Re-Ru bond in solutions
of these compounds. Thus, the latter moiety functions
exclusively as an exopolyhedral group bound by a single
unsupported B-HFRu interaction. The bonding to the
carborane cage of the [Ru(CO)2(η-C5H5)] fragment in 4b
is, however, atypical when compared with previously
reported molecules with B-HFRu groups. Whether this
unorthodox bonding is extended to 4a such that an
[FeH(CO)2(η-C5H5)] molecule is stabilized by a [Re(CO)3-
(η5-7,8-C2B9H10)] unit remains speculative without firm
structural proof but is interesting when one recalls that
[FeH(CO)2(η-C5H5)] readily decomposes to give the
binuclear complex [Fe2(µ-CO)2(CO)2(η-C5H5)2] and H2.17
A variation on the synthetic methodology which
afforded 4a and 4b involved employing the salt [Fe-
(CO)2(THF)(η-C5Me5)][BF4], formed in situ from [FeI-
(CO)2(η-C5Me5)] and AgBF4 in THF, and reacting it with
1. The product isolated was an inseparable 1:1 mixture
of the two isomers [Re(CO)3(η5-n-(µ-H)-exo-{Fe(CO)2(η-
C5Me5)}-7,8-C2B9H10)] (n ) 10 (4c), 9 (4d ); Chart 2).
This was not immediately apparent from the IR spec-
trum (Table 1), which displays absorbances similar in
form to that for 4a , but shifted to lower frequency,
particularly the νmax(FeCO) peaks (2047 and 2014 cm-1).
This latter feature is no doubt due to the stronger donor
ability of the η-C5Me5 ligand compared with η-C5H5. A
broad quartet is observed in the 1H NMR spectrum
(Table 2) at δ -18.46, which is actually a composite of
two B-HFFe proton resonances, although a structure
similar to 4a is indicated. This is accompanied by the
appearance of two singlets for the η-C5Me5 ligands in
each isomer (δ 1.81 and 1.82) and, more importantly,
three cage CH resonances at δ 2.91, 2.94, and 2.98
integrated in the ratio 2:1:1. The former signal (δ 2.91)
arises from an isomer utilizing the â-boron atom in the
a
Loss of CO from the complexes 4 could afford products with
Re-Fe (or Ru) bonds, but this process was not observed.
diastereotopic with resonances at δ 2.94 and 2.98 (1H,
CH), at δ 34.6 and 31.3 (13C{1H}, CH), and at δ 211.2
and 211.1 (13C{1H}, FeCO). The 11B{1H} and 11B NMR
spectra of 4c,d contain broad overlapping peaks which
were unfortunately not as informative as those of 4a
and 4b.
It had been hoped that the compounds 4 would be
precursors to stable complexes with Re-M (M ) Fe, Ru)
bonds resulting from the loss of a CO ligand from the
iron or ruthenium centers. Solutions of these complexes
were heated in various solvents and also treated with
Me3NO under differing conditions in order to promote
ejection of a CO molecule as CO2, but no new Re-M-
bonded complexes could be identified (Scheme 2). In fact,
these procedures invariably led to the regeneration of
the anion of 1.
The ability of MI (M ) Cu, Ag) metal centers to extend
their coordination number beyond 2 is a feature more
frequently encountered than in AuI chemistry, due to
the higher energy of gold 6p orbitals, which may not be
included in the frontier set.18 This observation encour-
aged us to examine the reactivity of 1 with sources of
the fragments [M(PPh3)]+ (M ) Cu, Ag) in the hope that
where gold had failed, copper and/or silver might
succeed. Treatment of 1 with either [CuCl(PPh3)3], or
AgBF4 in the presence of 1 equiv of PPh3, gave the
complexes [ReM(µ-10-H-η5-7,8-C2B9H10)(CO)3(PPh3)] (M
) Cu (5a ), Ag (5b); Chart 2). Both products form as a
white powder or colorless crystals and have similar IR
spectra (Table 1) which clearly indicate the formation
of adducts. However, the information gleaned from the
NMR spectra gave little clue as to the exact structural
nature of these complexes. The H and 13C{1H} NMR
1
spectra were very straightforward with single reso-
nances for the cage CH (δ 3.34 (5a ), 3.33 (5b), 1H; δ 36.6
(5a ), 36.2 (5b), 13C{1H}) and CO (δ 191.1 (5a ), 191.8
(5b)) groups (Table 2). There were no indications in the
CCBBB coordinating cage face to form the B-HFFe
bridge. The symmetrical structure 4c results after
allowing for free rotation in solution of the [Fe(CO)2(η-
C5Me5)] fragment about the B-HFFe linkage and is
precisely analogous to 4a . This also gives rise to one
FeCO resonance in the 13C{1H} NMR spectrum at δ
211.9 and one CH signal at δ 32.4. The second isomer
4d lacks the mirror plane present in 4c. This is most
1
room-temperature H NMR spectra of these molecules
of any B-HFM interactions. The 31P{1H} NMR spectra
(Table 3) each showed simple resonances with a singlet
at δ 11.0 for 5a and a pair of doublets at δ 20.4 for 5b,
this with the customary 107Ag-31P and 109Ag-31P
couplings of 590 and 681 Hz, respectively.19 The 11B-
{1H} NMR spectra were similar but not identical, each
with a set of five signals (1:2:3:1:2 (5a ), 1:2:2:2:2 (5b))
for the BH groups, all of which displayed typical
likely due to the R-boron atom in the CCBBB coordinat-
ing cage face being employed in the exopolyhedral
linkage to the iron center. Thus, both the cage CH
groups and the FeCO carbonyl ligands are rendered
(18) (a) Evans, D. G.; Mingos, D. M. P. J . Organomet. Chem. 1982,
232, 171. (b) Hamilton, E. J .; Welch, A. J . Polyhedron 1990, 9, 2407.
(19) Muetterties, E. L.; Alegranti, C. W. J . Am. Chem. Soc. 1972,
94, 6386.
(17) Green, M. L. H.; Street, C. N.; Wilkinson, G. Z. Naturforsch.
1959, 14B, 738.

4990 Organometallics, Vol. 18, No. 24, 1999
Ellis et al.
Ta ble 6. Selected In ter n u clea r Dista n ces (Å) a n d An gles (d eg) for [ReCu (µ-10-H-η5-7,8-C2B9H10)(CO)3(P P h 3)]
(5a ) w ith Estim a ted Sta n d a r d Devia tion s in P a r en th eses
Re-C(3)
Re-C(2)
Re-Cu
1.927(3)
2.298(3)
2.6583(6)
2.169(3)
Re-C(4)
Re-B(5)
C(3)-O(3)
H(4)-Cu
1.927(3)
2.352(3)
1.147(3)
1.67(3)
Re-C(5)
Re-B(3)
C(4)-O(4)
Cu-P
1.945(3)
2.362(3)
1.154(3)
2.2051(8)
Re-C(1)
Re-B(4)
O(5)-C(5)
2.296(3)
2.381(3)
1.148(3)
B(4)-Cu
C(3)-Re-C(4)
C(3)-Re-C(1)
C(3)-Re-C(2)
C(3)-Re-B(5)
C(3)-Re-B(3)
B(5)-Re-B(3)
C(5)-Re-B(4)
C(5)-Re-Cu
B(5)-Re-Cu
95.53(12)
108.87(12)
150.26(12)
85.65(12)
150.89(11)
76.87(12)
164.89(11)
143.64(9)
81.29(8)
O(3)-C(3)-Re
Cu-B(4)-Re
H(4)-Cu-Re
C(3)-Re-C(5)
C(4)-Re-C(1)
C(4)-Re-C(2)
C(4)-Re-B(5)
C(4)-Re-B(3)
C(3)-Re-B(4)
174.7(3)
71.33(10)
92.3(10)
85.53(12)
155.49(12)
113.81(12)
145.98(11)
86.66(12)
106.27(12)
C(3)-Re-Cu
C(1)-Re-Cu
B(3)-Re-Cu
O(4)-C(4)-Re
H(4)-Cu-P
B(4)-Cu-Re
C(4)-Re-C(5)
C(5)-Re-C(1)
C(5)-Re-C(2)
76.71(8)
121.01(7)
77.74(8)
175.4(3)
129.5(10)
58.05(8)
84.71(12)
94.62(11)
92.20(11)
C(5)-Re-B(5)
C(5)-Re-B(3)
C(4)-Re-B(4)
C(4)-Re-Cu
C(2)-Re-Cu
B(4)-Re-Cu
O(5)-C(5)-Re
B(4)-Cu-P
129.18(12)
123.55(12)
103.09(11)
66.09(8)
118.61(7)
50.61(8)
178.4(3)
161.88(9)
137.25(3)
P-Cu-Re
Ta ble 7. Selected In ter n u clea r Dista n ces (Å) a n d An gles (d eg) for [ReAg(µ-10-H-η5-7,8-C2B9H10)(CO)3(P P h 3)]
(5b) w ith Estim a ted Sta n d a r d Devia tion s in P a r en th eses
Re-C(3)
Re-C(2)
Re-Ag
1.87(2)
Re-C(5)
Re-B(3)
C(3)-O(3)
H(4)-Ag
1.907(14)
2.335(14)
1.181(13)
1.78(9)
Re-C(4)
Re-B(5)
C(4)-O(4)
Ag-P
1.918(13)
2.337(13)
1.156(13)
2.373(3)
Re-C(1)
Re-B(4)
C(5)-O(5)
2.296(11)
2.443(14)
1.171(14)
2.316(11)
2.9344(12)
2.449(14)
B(4)-Ag
C(3)-Re-C(5)
C(3)-Re-C(1)
C(3)-Re-C(2)
C(5)-Re-B(3)
C(3)-Re-B(5)
C(3)-Re-B(4)
C(3)-Re-Ag
C(1)-Re-Ag
B(5)-Re-Ag
93.4(5)
122.2(5)
160.4(5)
90.6(5)
88.9(5)
94.6(5)
72.1(4)
124.2(3)
93.1(4)
O(4)-C(4)-Re
P-Ag-B(4)
178.4(12)
171.1(3)
150(3)
C(5)-Re-Ag
C(2)-Re-Ag
B(4)-Re-Ag
O(5)-C(5)-Re
P-Ag-Re
H(4)-Ag-Re
C(5)-Re-C(4)
C(4)-Re-C(1)
C(4)-Re-C(2)
70.2(4)
108.7(3)
53.2(3)
176.6(11)
134.74(8)
74(3)
85.9(5)
89.1(5)
100.1(5)
C(3)-Re-B(3)
C(4)-Re-B(5)
C(4)-Re-B(4)
C(4)-Re-Ag
B(3)-Re-Ag
O(3)-C(3)-Re
Re-B(4)-Ag
B(4)-Ag-Re
134.3(5)
112.7(5)
157.6(5)
146.3(4)
66.7(4)
175.4(11)
73.7(4)
53.0(3)
H(4)-Ag-P
C(3)-Re-C(4)
C(5)-Re-C(1)
C(5)-Re-C(2)
C(4)-Re-B(3)
C(5)-Re-B(5)
C(5)-Re-B(4)
86.6(5)
143.7(5)
105.3(5)
139.1(5)
161.3(5)
116.3(5)
F igu r e 5. Structure of [ReAg(µ-10-H-η5-7,8-C2B9H10)(CO)3-
(PPh3)] (5b), showing the crystallographic labeling scheme.
Thermal ellipsoids are shown at the 40% probability level.
Only the agostic hydrogen and phenyl ipso-carbon atoms
are shown for clarity.
F igu r e 4. Structure of [ReCu(µ-10-H-η5-7,8-C2B9H10)(CO)3-
(PPh3)] (5a ), showing the crystallographic labeling scheme.
Thermal ellipsoids are shown at the 40% probability level.
Only the agostic hydrogen and phenyl ipso-carbon atoms
are shown for clarity.
coupling in the fully coupled 11B NMR spectra as
expected for terminal hydrogen atoms (J (HB) ) 100-
160 Hz).
[Re2Cu(µ-PCy2)(CO)8(PPh3)] (average 2.673 Å).20c In the
Cambridge Crystallographic Data Centre there are just
two reports of X-ray diffractomeric studies for complexes
with Re-Ag bonds: [NEt3]5[{Re7AgC(CO)21}2Br], which
contains a Re3 face capped by an Ag atom (mean Re-
Because of this seemingly inadequate information,
X-ray crystal structure determinations were carried out
on both 5a and 5b. Selected bond lengths and angles
are given in Tables 6 (5a ) and 7 (5b), and the molecules
are displayed in Figures 4 (5a ) and 5 (5b). The im-
mediately apparent feature in each of these structures
is the presence of direct Re-Cu (2.6583(6) Å) and Re-
Ag (2.9344(12) Å) bonds. The Re-Cu distance is slightly
longer than those found in [Re2Cu(µ-H)(H)4(PMePh2)6]-
[PF6] (2.607(2) Å)20a and [Re2Cu2(µ-I)2(H)2(η-C5H5)4]
(2.599(3) Å)20b but comparable with those in the complex
Ag distance 2.882 Å),21a and [Ag{ReH7(PPhPri ) }2][PF6]
2 2
(Re-Ag ) 2.838(2) and 2.779(2) Å).21b In 5a and 5b both
(20) (a) Rhodes, L. F.; Huffman, J . C.; Caulton, K. G. J . Am. Chem.
Soc. 1983, 105, 5137. (b) Bel’skii, V. K.; Ishchenko, V. M.; Bulychev,
B. M.; Soloveichik, G. L. Polyhedron 1984, 3, 749. (c) Florke, U.; Haupt,
H.-J . Z. Kristallogr. 1992, 201, 323.
(21) (a) Beringhelli, T.; Ciani, G.; D’Alfonso, G.; Freni, M.; Sironi,
A. J . Organomet. Chem. 1985, 295, C7. (b) Connelly, N. G.; Howard,
J . A. K.; Spencer, J . L.; Woodley, P. K. J . Chem. Soc., Dalton Trans.
1984, 2003.

Reactivity of Cs[Re(CO)3(η5-7,8-C2B9H11)]
Organometallics, Vol. 18, No. 24, 1999 4991
the Re-Cu and Re-Ag bonds are spanned by â-B-
HFM interactions (B(4)-Cu ) 2.169(3) Å and B(4)-
for the formation of metal-metal bonds. The existence
of these complexes is incidentally supportive of the
proposed Re-Rh-bonded species B in Scheme 1. We are
currently investigating reactions of 1 with platinum
complexes. Preliminary results show that Re-Pt bonds
are formed and exist in solution at ambient tempera-
tures. We have also demonstrated that the anion of 1
can function as a mono-, bi-, or tridentate ligand by
virtue of the coordination of the carborane B-H bonds
to exopolyhedral metal centers in complexes 4, 3, and
2, respectively. Despite earlier negative results, and
with some persistent probative effort, we have shown 1
to be as versatile a reagent as [N(PPh3)2]2[Re(CO)3(η5-
7-CB10H11)].5
Ag ) 2.449(14) Å) involving boron atoms in the CCBBB
coordinating face of the cage. Attachment of Cu(PPh3)
fragments to closo-3,1,2-MC2B9H11 structures by both
Cu-M and by either one or two B-HFCu bonds is well-
established,4e,22 whereas complexes with any kind of
B-HFAg contacts are comparatively scarce.22f,23 In fact
5b is the first complex isolated where a carborane ligand
η5-7,8-C2B9H11 bridges a metal-silver bond in such a
manner. The coordination spheres about the copper and
silver atoms are completed by the rhenium atom and
by the PPh3 ligand: Cu-P ) 2.2051(8) Å and Ag-P )
2.373(3) Å, which are both within accepted ranges for
M-P bonds of this nature.24 The PPh3 ligands lie
transoid to the B(4) boron atoms of the agostic systems
(B(4)-Cu-P ) 161.88(9)°, B(4)-Ag-P ) 171.1(3)°). The
perturbation of the Re(CO)3 group to accommodate the
M(PPh3) moieties appears to be slight, with the im-
mediately adjacent (O)C-Re-C(O) angles only margin-
ally widened (C(3)-Re-C(4) ) 95.53(12)°, average
C(3,4)-Re-C(5) ) 85.1° (5a ); C(3)-Re-C(5) ) 93.4(5)°,
average C(3,5)-Re-C(4) ) 86.3° (5b)). This would seem
to imply that the Re-M bonds primarily involve a
rhenium 5d-based orbital, previously from a nonbonding
set in the anion of 1. Therefore, the M(PPh3) units in 5
actually cause little electronic disruption to the Re(CO)3-
(η5-C2B3) core, requiring only slight steric accommoda-
tion. This is logically greater for Cu(PPh3) (ca. 2°) than
for Ag(PPh3) because a larger cone angle for Cu(PPh3)
derives from the smaller atomic radius for copper.
With the solid-state structures of 5a ,b firmly estab-
lished, the NMR spectroscopic data are clearly not in
accord with the results of the X-ray structure determi-
nations. Evidently in solution at ambient temperatures
5a ,b are highly dynamic. The NMR data can be ac-
counted for by a mechanism which includes Re-M
heterolytic fission and facile migration of the [M(PPh3)]+
fragments about the polyhedral cage surface, much like
that described for the [Rh(PPh3)2]+ unit in the complexes
[5,10-(µ-H)2-exo-{Rh(PPh3)2}-7,8-Me2-nido-7,8-C2B9H8]
and [10-endo-{Au(PPh3)}-5,10-(µ-H)2-exo-{Rh(PPh3)2}-
7,8-Me2-nido-7,8-C2B9H7].11 A representative structure
at any energy minimum along this dynamic profile
probably involves at least two B-HFligations to the
[M(PPh3)]+ cation, possibly three. Measurement of the
NMR spectra of both complexes 5 at -90 °C failed to
reveal any quenching of this mobility.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All experiments were conducted
under an atmosphere of dry nitrogen using Schlenk tube
techniques. Solvents were freshly distilled under nitrogen from
appropriate drying agents before use. Light petroleum refers
to that fraction of boiling point 40-60 °C. Chromatography
columns (ca. 20 cm in length and 2 cm in diameter, unless
otherwise stated) were packed with silica gel (Acros, 60-200
mesh). Celite pads used for filtration were ca. 3 cm in length
and 2 cm in diameter. The NMR measurements were recorded
at the following frequencies: 1H at 360.13 MHz, 13C at 90.56
MHz, 11B at 115.55 MHz, and 31P at 145.78 MHz. The salt
Cs[Re(CO)3(η5-7,8-C2B9H11)] (1) was synthesized using a modi-
fication of the procedure reported previously,3 and this is
detailed below. The reagents [NHMe3][nido-7,8-C2B9H12],25
[ReBr(CO)5],26 [RuCl2(PPh3)3],27 [RhCl(PPh3)3],28 [Fe(CO)2-
(THF)(η-C5H5)][BF4],13 and [CuCl(PPh3)3]29 were made as
previously described. The complexes [RuI(CO)2(η-C5H5)] and
[FeI(CO)2(η-C5Me5)] were prepared using the same procedure
as for [FeI(CO)2(η-C5H5)].30 Sodium hydride, supplied as a 60%
dispersion in oil by Aldrich, was weighed out, washed with
two portions of light petroleum (2 × 10 mL), and dried in vacuo
immediately prior to use. The compound [Fe(η-C5H4PPh2)2]
was purchased from Strem.
Im p r oved Syn th esis of Cs[Re(CO)3(η5-7,8-C2B9H11)].
The compound [NHMe3][nido-7,8-C2B9H12] (0.50 g, 2.58 mmol)
was dissolved in THF (20 mL) in a two-necked 100 mL round-
bottom flask fitted with a condenser which in turn was
connected to a Schlenk line. To this was carefully added a
suspension of NaH (0.52 g, 21.67 mmol) in THF (30 mL). After
the initial effervescence had subsided, the flask was stoppered
and the suspension was heated to reflux for ca. 12 h. Im-
mediately after this refluxing had commenced, the compound
[ReBr(CO)5] (1.00 g, 2.46 mmol) was placed in a second 250
mL two-necked round-bottom flask also fitted to a Schlenk line
via a condenser (or in a large reflux Schlenk tube) and
dissolved in THF (30 mL) and then heated to reflux, also for
ca. 12 h. After this period had elapsed (usually overnight), the
heat source was removed from the carborane/NaH suspension
and the mixture cooled to room temperature. Once cooled, the
stirring was ceased and the excess NaH allowed to settle. At
this point the heat source was removed from the rhenium
solution, though it should not be allowed to cool below ca. 55
°C. The solution of Na2[nido-7,8-C2B9H11] was taken up in a
syringe (being careful not to disturb the settled NaH) and
transferred to the [ReBr(CO)3(THF)2] solution with vigorous
Con clu sion
In the syntheses of the complexes 5 we have shown
that 1 can in limited circumstances be used as a synthon
(22) (a) Do, Y.; Knobler, C. B.; Hawthorne, M. F. J . Am. Chem. Soc.
1987, 109, 1853. (b) Kang, H. C.; Do, Y.; Knobler, C. B.; Hawthorne,
M. F. Inorg. Chem. 1988, 27, 1716. (c) Cabioch, J .-L.; Dossett, S. J .;
Hart, I. J .; Pilotti, M. U.; Stone, F. G. A. J . Chem. Soc., Dalton Trans.
1991, 519. (d) J effery, J . C.; Stone, F. G. A.; Topalogˇlu, I. J . Organomet.
Chem. 1993, 451, 205. (e) Ellis, D. D.; Couchman, S. M.; J effery, J . C.;
Malget, J . M.; Stone, F. G. A. Inorg. Chem. 1999, 38, 2981. (f) Ellis, D.
D.; Franken, A.; Stone, F. G. A. Organometallics 1999, 18, 2362.
(23) (a) Colquhoun, H. M.; Greenhough, T. J .; Wallbridge, M. G. H.
J . Chem. Soc., Dalton Trans. 1980, 192. (b) Shelly, K.; Finster, D. C.;
Lee, Y. J .; Scheidt, W. R.; Reed, C. A. J . Am. Chem. Soc. 1985, 107,
5955. (c) Eigenbrot, C. W.; Liston, D. J .; Reed, C. A.; Scheidt, W. R.
Inorg. Chem. 1987, 26, 2739. (d) Park, Y.-W., Kim, J .; Do, Y. Inorg.
Chem. 1994, 33, 1.
(25) Hawthorne, M. F.; Young, D. C.; Garrett, P. M.; Owen, D. A.;
Schwerin, S. G.; Tebbe, F. N.; Wegner, P. A. J . Am. Chem. Soc. 1968,
90, 862.
(26) Abel, E. W.; Wilkinson, G. J . Chem. Soc. 1959, 1501.
(27) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.
1970, 12, 238.
(28) Osborn, J . A.; Wilkinson, G. Inorg. Synth. 1967, 10, 67.
(29) Stephens, R. D. Inorg. Synth. 1979, 19, 87.
(30) Piper, T. S.; Wilkinson, G. J . Inorg. Nucl. Chem. 1956, 2, 28.
(24) Allen, F. H.; Brammer, L.; Kennard, O.; Orpen, A. G.; Taylor,
R.; Watson, D. G. J . Chem. Soc., Dalton Trans. 1989, S1.

4992 Organometallics, Vol. 18, No. 24, 1999
Ellis et al.
stirring. The resulting mixture was then refluxed for 5 h. After
this time it is cooled to room temperature and the THF
removed in vacuo. At this point it was no longer necessary to
maintain anaerobic conditions. The residue was dissolved in
water (50 mL) (some effervescence may occur) and then CsCl
(0.80 g, 4.75 mmol) added. The product Cs[Re(CO)3(η5-7,8-
C2B9H11)] (1; 1.20 g, 91%) precipitated rapidly from solution
as a creamy white solid and was collected by filtration and
then dried in vacuo overnight at 100 °C.
P r ep a r a tion of th e Com p ou n d [Re(CO)3(η5-2,3,10-(µ-
H)3-exo-{Ru Cl(P P h 3)2}-7,8-C2B9H8)]. The compounds 1 (0.05
g, 0.09 mmol) and [RuCl2(PPh3)3] (0.09 g, 0.09 mmol) were
dissolved in CH2Cl2 (10 mL), and the mixture was stirred for
1 h. Over this time the solution turned dark orange and a pale
precipitate formed. The suspension was filtered through Celite
to remove precipitated CsCl, and the solvent volume was
reduced in vacuo to ca. 5 mL. This solution was then chro-
matographed, and a red-orange band was eluted with neat
CH2Cl2. Removal of solvent in vacuo followed by crystallization
from CH2Cl2-light petroleum (10 mL, 2:3) gave red micro-
crystals of [Re(CO)3(η5-2,3,10-(µ-H)3-exo-{RuCl(PPh3)2}-7,8-
C2B9H8)] (2a ; 0.03 g). The major product 2a is inseparable from
its minor isomer 2b.
Syn th eses of th e Com p lexes [Re(CO)3{η5-5,10-(µ-H)2-
exo-(Rh L2)-7,8-C2B9H9}] (L2 ) (P P h 3)2, {F e(η-C5H4P P h 2)2}).
(i) To the compounds 1 (0.10 g, 0.19 mmol) and [RhCl(PPh3)3]
(0.17 g, 0.18 mmol) was added CH2Cl2 (15 mL) and the mixture
stirred for 1 h. Solvent was reduced in volume in vacuo to ca.
2 mL and light petroleum (15 mL) added. The suspension was
stirred for 1 h, after which time the solid was allowed to settle
and the supernatant liquid removed using a syringe. The
residue was washed with light petroleum (2 × 10 mL) and
then dissolved in CH2Cl2 (10 mL) and filtered through Celite.
Solvent was removed in vacuo and then CH2Cl2-light petro-
leum (5 mL, 2:3) introduced. This solution was then applied
to the top of a chromatography column cooled to -30 °C.
Elution with the same solvent mixture removed a red fraction
from which solvent was removed in vacuo. Crystallization from
CH2Cl2-light petroleum (10 mL, 1:4) yielded red microcrystals
of [Re(CO)3(η5-5,10-(µ-H)2-exo-{Rh(PPh3)2}-7,8-C2B9H9)] (3a ;
0.13 g).
(ii) The compounds [RhCl(PPh3)3] (0.10 g, 0.11 mmol) and
[Fe(η-C5H4PPh2)2] (0.06 g, 0.11 mmol) were treated together
with CH2Cl2 (10 mL) and stirred at room temperature for 1 h.
Reduction of the volume of solvent in vacuo to ca. 1 mL was
followed by addition of light petroleum (20 mL) and the
suspension stirred for 2 h. The precipitate of [RhCl{Fe(η-C5H4-
PPh2)2}(PPh3)] so formed was allowed to settle, and the
supernatant liquid was syringed off. The resulting residue was
dried in vacuo for 5 min. The salt 1 (0.06 g, 0.11 mmol) was
then added, followed by CH2Cl2 (10 mL), and the mixture
stirred at room temperature for 2 h. The volume of solvent
was reduced in volume in vacuo to ca. 2 mL, and light
petroleum (20 mL) was added and the suspension stirred for
30 min. The supernatant liquid was again removed with a
syringe from the settled precipitate, and the residue was
treated with CH2Cl2 (10 mL) and the solution filtered through
Celite. Solvent was removed in vacuo and CH2Cl2-light
petroleum (5 mL, 1:1) added. This solution was then chro-
matographed at -30 °C, and elution with the same solvent
mixture removed a red fraction. Solvent was removed in vacuo,
and crystallization from CH2Cl2-light petroleum (10 mL, 1:4)
gave red microcrystals of [Re(CO)3(η5-5,10-(µ-H)2-exo-(Rh{Fe-
(η-C5H4PPh2)2})-7,8-C2B9H9)] (3b; 0.07 g).
in vacuo. The residue was taken up in CH2Cl2-light petroleum
(5 mL, 1:1) and chromatographed, with the same solvent
mixture as eluent. An orange fraction was obtained, from
which solvent was removed in vacuo. The residue was crystal-
lized from CH2Cl2-light petroleum (10 mL, 1:4) to give orange
microcrystals of [Re(CO)3(η5-10-(µ-H)-exo-{Fe(CO)2(η-C5H5)}-
7,8-C2B9H10)] (4a ; 0.46 g).
(ii) The complex [RuI(CO)2(η-C5H5)] (0.19 g, 0.54 mmol) was
dissolved in THF (10 mL), and this mixture was treated with
AgBF4 (0.11 g, 0.57 mmol) and stirred for 30 min. The
suspension was filtered through Celite, and the THF was then
removed in vacuo. Compound 1 (0.30 g, 0.56 mmol) was added
to this residue, followed by CH2Cl2 (10 mL), and the reaction
mixture stirred for 2 h. Solvent was removed in vacuo and then
CH2Cl2-light petroleum (5 mL, 1:1) added. This solution was
chromatographed, with the same solvent mixture as eluent,
to afford a small orange fraction, which was discarded. Further
elution removed a yellow fraction. Solvent was removed in
vacuo, and crystallization from CH2Cl2-light petroleum (10
mL, 1:9) gave a yellow solid, which could be recrystallized at
-50 °C to give yellow microcrystals of [Re(CO)3(η5-10-(µ-H)-
exo-{Ru(CO)2(η-C5H5)}-7,8-C2B9H10)] (4b; 0.16 g).
(iii) Using a similar procedure, the compounds [FeI(CO)2-
(η-C5Me5)] (0.08 g, 0.21 mmol), 1 (0.10 g, 0.19 mmol), and
AgBF4 (0.04 g, 0.21 mmol) gave orange microcrystals of [Re-
(CO)3(η5-n-(µ-H)-exo-{Fe(CO)2(η-C5Me5)}-7,8-C2B9H10)] (n ) 10
(4c), 9 (4d ); 0.11 g), formed as an inseparable mixture of
isomers.
P r ep a r a tion of th e Com p lexes [ReM(µ-10-H-η5-7,8-
C2B9H10)(CO)3(P P h 3)] (M ) Cu , Ag). (i) The compounds 1
(0.10 g, 0.19 mmol) and [CuCl(PPh3)3] (0.17 g, 0.19 mmol) were
treated with CH2Cl2-THF (10 mL, 4:1), and the mixture was
stirred for 1 h. Solvent was reduced in volume in vacuo to ca.
3 mL and light petroleum (20 mL) added. After 30 min of
stirring the precipitate was allowed to settle and the super-
natant liquid syringed off. This washing was repeated twice.
The residue was then taken up in CH2Cl2-light petroleum (5
mL, 1:1) and the solution filtered through a silica gel plug (2
× 5 cm). As the desired product is colorless in solution, it is
necessary to ascertain its presence in the eluant with monitor-
ing by IR spectral measurements. Solvent was removed in
vacuo and the residue crystallized from CH2Cl2-light petro-
leum (10 mL, 1:4) to yield white microcrystals of [ReCu(µ-10-
H-η5-7,8-C2B9H10)(CO)3(PPh3)] (5a ; 0.08 g).
(ii) The compounds AgBF4 (0.06 g, 0.31 mmol) and PPh3
(0.08 g, 0.31 mmol) were treated with THF (10 mL), and the
solution was stirred for 20 min. In a second Schlenk tube, fitted
with a pressure-equalized dropping funnel, compound 1 (0.17
g, 0.32 mmol) was dissolved in THF and cooled to -80 °C. The
solution of [Ag(PPh3)(THF)][BF4] was transferred to the drop-
ping funnel and added over 15 min. The funnel was then
replaced by a stopper and the mixture, which becomes cloudy
with no coloration, was gradually warmed to room tempera-
ture. Solvent was removed in vacuo and the residue taken up
in CH2Cl2-light petroleum (5 mL, 1:1) and applied to a silica
gel plug (2 × 5 cm). The product solution is again colorless,
and it is necessary to monitor the eluant by consecutive IR
measurements. Solvent was removed in vacuo and the residue
crystallized from CH2Cl2-light petroleum (10 mL, 1:4) to give
white microcrystals of [ReAg(µ-10-H-η5-7,8-C2B9H10)(CO)3-
(PPh3)] (5b; 0.15 g).
Str u ctu r e Deter m in a tion s of Com p ou n d s 2a a n d 5a .
Crystals of 2a and 5a were grown by diffusion of light
petroleum into CH2Cl2 solutions of the complexes. All crystals
were mounted on glass fibers, and low-temperature data were
collected on a Siemens SMART CCD area-detector three-circle
diffractometer (Mo KR X-radiation, graphite monochromator,
λh ) 0.710 73 Å). For three or four settings of æ, narrow data
“frames” were collected for 0.3° increments in ω. For the
monoclinic complex 2a just over a hemisphere of data was
collected, while for the triclinic crystals 5a full spheres of data
Syn th eses of th e Com p lexes [Re(CO)3(η5-n -(µ-H)-exo-
{M(CO)2(η-C5R5)}-7,8-C2B9H10)] (M ) F e, R ) H, n ) 10;
M ) Ru , R ) H, n ) 10; M ) F e, R ) Me, n ) 9, 10). (i) The
salts 1 (0.43 g, 0.80 mmol) and [Fe(CO)2(THF)(η-C5H5)][BF4]
(0.27 g, 0.80 mmol) were treated with CH2Cl2 (10 mL), and
the mixture was stirred for 20 min. The mixture was then
filtered through Celite, following which solvent was removed

Reactivity of Cs[Re(CO)3(η5-7,8-C2B9H11)]
Organometallics, Vol. 18, No. 24, 1999 4993
Ta ble 8. Da ta for X-r a y Cr ysta l Str u ctu r e An a lyses
2a
4b
5a
5b
cryst dimens/mm
formula
Mr
0.20 × 0.15 × 0.15
0.20 × 0.18 × 0.10
C12 H16B9O5ReRu
624.81
0.40 × 0.40 × 0.40
C23H26B9CuO3PRe
728.44
0.33 × 0.26 × 0.15
C23H26AgB9O3PRe‚0.5CH2Cl2
815.23
C41 H41B9ClO3P2ReRu
1063.69
cryst color, shape
red prism
monoclinic
P21/n
yellow block
monoclinic
P21/c
colorless cube
triclinic
P1h
colorless block
monoclinic
C2/c
cryst syst
space group
T/K
173(2)
293(2)
173(2)
293(2)
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
19.4834(25)
12.3344(10)
19.7114(18)
14.461(2)
10.380(4)
14.694(2)
9.2246(20)
13.0494(13)
13.5816(16)
63.439(7)
84.281(14)
70.141(12)
1372.7(4)
2
1.762
5.264
704
3.4-55.0
13708
6182
0.03
24.5808(27)
8.8020(19)
28.1287(44)
115.095(8)
114.266(13)
102.190(11)
4289.8(8)
4
1.647
3.347
2088
4.0-55.0
27067
9806
2010.8(9)
4
2.064
6.785
1168
3.2-45.0
2737
2577
0.031
5949
8
Z
d
calcd/g cm-3
1.821
4.894
3128
3.4-45.0
3973
3869
0.038
µ(Mo KR)/mm-1
F(000)/e
2θ range/deg
no. of rflns measd
no. of indep rflns
R(int)
0.03
refln limits
h
k
l
-25 to +22
-16 to +13
-24 to +25
-15 to 0
0-12
-11 to +11
-16 to +16
-17 to +17
-26 to 0
0-9
-15 to +15
-29 to +30
final residuals
wR2a
0.052
0.025
0.091
0.039
0.037
0.019
0.095
0.048
R1b
weighting factorsa
a
b
0.0218
0.0
0.97
0.0451
0.0
1.076
0.0074
0.0
0.91
0.0272
3.8839
1.077
1.335, -0.670
goodness of fit on F2
final electron density diff
features (max/min)/e Å-3
0.818, -0.985
1.199, -1.130
0.845, -0.822
Structure was refined on Fo2 using all data: wR2 ) [∑[w(Fo2 - Fc2)2]/∑w(Fo2)2]1/2, where w-1 ) [σ2(Fo2) + (aP)2 + bP] and P ) [max(Fo2,0)
a
+ 2Fc2]/3. This value is given for comparison with refinements based on Fo with a typical threshold of Fo > 4σ(Fo) and R1 ) ∑||Fo| -
b
|Fc||/∑|Fo| and w-1 ) [σ2(Fo) + gFo2].
were collected. It was confirmed that crystal decay had not
taken place during the course of the data collections. The
substantial redundancy in data allows empirical absorption
corrections (SADABS31) to be applied using multiple measure-
ments of equivalent reflections. The data frames were inte-
grated using SAINT;31 structures were solved by conventional
direct methods and refined by full-matrix least squares on all
F2 data using Siemens SHELXTL version 5.03.31
For both structures the non-hydrogen atoms were refined
with anisotropic thermal parameters. Cage carbon atoms were
identified from the magnitudes of their anisotropic thermal
parameters and from a comparison of the bond lengths to
adjacent boron atoms. The agostic B-HFM hydrogen atoms
H(4), H(9), and H(10) in complex 2a and H(4) in complex 5a
were located from final difference Fourier syntheses, and their
positions and isotropic thermal parameters 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(parent atom)]).
All calculations were carried out on Silicon Graphics Iris,
Indigo, or Indy computers, and the experimental data are
summarized in Table 8.
unit cell dimensions were determined from the setting angle
values of 25 accurately centered reflections. The stability of
the crystals during the period of the data collections was
monitored by measuring the intensities of three standard
reflections every 2 h. Data were collected at the following scan
speeds: 4.13-5.17° min-1 in ω for 4b with a scan range of
(1.15 + 0.35 tan θ)°; and 5.17° min-1 in ω with a scan range of
(1.15 + 0.34 tan θ)° for 5b. The data were corrected for Lorentz,
polarization, and X-ray absorption effects, the last by a
semiempirical method based on azimuthal scans of ψ data of
several Euclerian angles (ø) near 90°.
Structures were solved by direct methods (4b) or conven-
tional heavy-atom methods (5b), and successive Fourier dif-
ference syntheses were used to locate all non-hydrogen atoms,
using the SHELXTL-PC package.31 Refinements were made
by full-matrix least squares on F2 data, using SHELXL-93,31
with anisotropic thermal parameters for all non-hydrogen
atoms. Cage carbon atoms were identified from the magnitudes
of their anisotropic thermal parameters and from a comparison
of the bond lengths to adjacent boron atoms. The hydride atom
H(4) in 4b and the agostic B-HFM hydrogen atom H(4) in
5b were located in final difference Fourier syntheses, their
coordinates freely refined, and isotropic thermal parameters
fixed with Uiso ) 0.05 Å2 for 4b and 1.2[Uiso(parent atom)] for
5b. All other hydrogen atoms were included in calculated
positions (C-H ) 0.96 Å and B-H ) 1.10 Å) and allowed to
ride on their parent boron or carbon atom with fixed isotropic
thermal parameters (Uiso ) 1.2[Uiso(parent atom)]). Atomic
scattering factors were taken from the usual source.32 All
Str u ctu r e Deter m in a tion s of Com p ou n d s 4b a n d 5b.
Crystals of 4b and 5b were grown by diffusion of light
petroleum into CH2Cl2 solutions of the complexes. Those of
5b grew with a half-molecule of CH2Cl2 in the asymmetric unit,
the carbon residing on a 2-fold axis. Diffracted intensities were
collected on an Enraf-Nonius CAD-4 operating in the ω-2θ
(4b) or ω (5b) scan mode, using graphite-monochromated Mo
KR X-radiation (λh ) 0.710 73 Å). For each structure, the final
(32) International Tables for X-ray Crystallography; Kynoch
Press: Birmingham, U.K., 1974; Vol. 4.
(31) Siemens X-ray Instruments, Madison, WI, 1995.

4994 Organometallics, Vol. 18, No. 24, 1999
Ellis et al.
calculations were carried out on Dell PC computers, and the
experimental data are summarized in Table 8.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates and U values, bond lengths and angles, and
anisotropic thermal parameters and ORTEP diagrams for 2a ,
4b, 5a , and 5b in CIF format and the 1H NMR spectrum of
3a measured at -90 °C. This material is available free of
charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. We thank the Robert A. Welch
Foundation for support (Grant AA-1201) and Dr. J . C.
J effery for the use of X-ray facilities by D.D.E. at the
University of Bristol, Bristol, U.K.
OM9905097