Synthetic, structural, chemical, and electrochemical studies of the metallatricarbadecaboranyl analogues of ferrocene, ruthenocene, and osmocene and the observation of a reversible η6-η4 tricarbadecaboranyl coordination that is analogous to the η5-η3 cyclopentadienyl ring-slippage process

Article abstract of DOI:10.1021/om020757u

The synthetic, structural, chemical and electrochemical studies of the metallatricarbadecaboranyl analogues of ferrocene, ruthenocene and osmocene were presented. The electrochemical studies revealed that tricarbadecaboranyl compounds showed reversible one-electron oxidation and two successive one-electron reductions. The reduction values indicated a stabilization energy in excess of the comparative electronic effect.

Full text of DOI:10.1021/om020757u

5078
Organometallics 2002, 21, 5078-5090
Syn th etic, Str u ctu r a l, Ch em ica l, a n d Electr och em ica l
Stu d ies of th e Meta lla tr ica r ba d eca bor a n yl An a logu es of
F er r ocen e, Ru th en ocen e, a n d Osm ocen e a n d th e
Obser va tion of a Rever sible η6-η4 Tr ica r ba d eca bor a n yl
Coor d in a tion th a t Is An a logou s to th e η5-η3
Cyclop en ta d ien yl Rin g-Slip p a ge P r ocess
Bhaskar M. Ramachandran,1 Sabrina M. Trupia,2 William E. Geiger,*,2
Patrick J . Carroll,1 and Larry G. Sneddon*,1
Departments of Chemistry, University of Pennsylvania, Philadelphia,
Pennsylvania 19104-6323, and University of Vermont,
Burlington, Vermont 05405
Received September 12, 2002
-
The tricarbadecaboranyl anions, 6-R-nido-5,6,9-C3B7H9 (R ) CH3 or C6H5), have been
employed to produce a series of metallatricarbadecaboranyl analogues of the group VIII
metallocenes, (η5-C5H5)2M, M ) Fe, Ru, and Os, including 1-(η5-C5Me5)-2-Me-closo-1,2,3,4-
RuC3B7H9 (3), commo-Ru-(2-Me-closo-1,2,3,4-RuC3B7H9)2 (4), commo-Os-(4′-Me-closo-1′,2′,3′,4′-
OsC3B7H9)(2-Me-closo-1,2,3,4-OsC3B7H9) (5), commo-Os-(2-Me-closo-1,2,3,4-OsC3B7H9)2 (6),
1-(η5-C5H5)-2-Ph-closo-1,2,3,4-FeC3B7H9 (7), and 1-(η5-C5Me5)-2-Ph-closo-1,2,3,4-RuC3B7H9
(8). In the mixed ligand complexes 3, 7, and 8, formal Fe2+ and Ru2+ ions are sandwiched
between the tricarbadecaboranyl and cyclopentadienyl monoanionic ligands, while in
complexes 4, 5, and 6 the Ru2+ and Os2+ ions are sandwiched between two tricarbadecabo-
ranyl ligands. In all complexes, the metals are η6-coordinated to the puckered six-membered
face of the tricarbadecaboranyl cage. Reaction of 7 with Cr(CO)6 resulted in the formation
of the arene-substituted complex 1-(η5-C5H5)-2-[(η6-C6H5)Cr(CO)3]-closo-1,2,3,4-FeC3B7H9 (9).
Complexes 3 and 7 were also found to undergo reversible cage-slippages between the η6-η4
coordination modes during the association-dissociation reactions of these complexes with
tert-butylisocyanide to produce 8-(η5-C5Me5)-8-(CNBut)-9-Me-nido-8,7,9,10-RuC3B7H9 (10) and
8-(η5-C5H5)-8-(CNBut)-9-Ph-nido-8,7,9,10-FeC3B7H9 (11), respectively. This reversible η6-
η4 coordination is analogous to the η5-η3 ring-slippage process that is proposed to occur in
related reactions of cyclopentadienyl-metal complexes. Electrochemical studies revealed that
the tricarbadecaboranyl compounds undergo reversible one-electron oxidations and two
successive one-electron reductions. Comparison of oxidation E1/2 values for Cp and RC3B7H9
analogues indicates a comparative electronic effect of +0.44 V for the tricarbadecaboranyl
group. Reduction E1/2 values indicate a stabilization energy of 1.2-1.7 V in excess of the
comparative electronic effect. It is likely that the overall ligand-induced stabilization of low
metal oxidation states arises in part from redox-induced hapticity changes of the tricarba-
decaboranyl ligand. Formal M0 dianions are detected that have no precedence in the
metallocenes.
In tr od u ction
We have previously demonstrated3 that, because of
their equivalent charges and formal electron-donating
abilities, the coordination properties of the tricarbade-
caboranyl, 6-Me-nido-5,6,9-C3B7H9-,4 and the cyclopen-
tadienide monoanions (Figure 1) are in many ways
similar, but that metallatricarbadecaboranyl complexes
have significantly greater oxidative, chemical, thermal,
and hydrolytic stabilities than their metallocene coun-
terparts. For example, we recently reported3g the forma-
tion of a series of vanadatricarbadecaboranyl analogues,
F igu r e 1. Comparison of the structures of the cyclopen-
tadienyl and tricarbadecaboranyl anions.
i.e., (Me-C3B7H9)2V, of vanadocene (η5-C5H5)2V, that are,
unlike vanadocene, both air- and water-stable. In this
paper we report the synthetic, structural, chemical, and
(1) University of Pennsylvania.
(2) University of Vermont.
10.1021/om020757u CCC: $22.00 © 2002 American Chemical Society
Publication on Web 10/15/2002

Metallatricarbadecaboranyl Analogues
Organometallics, Vol. 21, No. 23, 2002 5079
Ta ble 1. NMR Da ta
electrochemical studies of a series of new ferra-, ruth-
ena-, and osmatricarbadecaboranyl analogues of fer-
rocene, ruthenocene, and osmocene that again illustrate
the unique properties of the tricarbadecaboranyl ligand.
In addition, we also report the discovery of a reversible
cage-slippage of the tricarbadecaboranyl ligand between
η6-η4 coordination modes that occurs during the as-
sociation-dissociation reactions of several of these
complexes with tert-butylisocyanide.5 This process is
analogous to the η5-η3 ring-slippage that is proposed
to occur in related reactions of cyclopentadienyl-metal
complexes.6
compound nucleus
δ (mult, J (Hz), assignt)
123a
11Ba,b
2.6 (d, 158), 1.9 (d, 172),
-7.4 (d, 147),-10.6 (d, 147), -24.6 (d, 145),
-27.7 (d, 156),-32.2 (d, 157)
6.60 (br s, C3H), 3.85 (s, Cp), 2.57 (s, Me),
0.71 (s br, C4H)
3.5 (d, 185), 2.3 (d, 165), -6.4 (d, 148), -7.8
(d, 148), -27.4 (d, 126), -28.2 (2, d, 154)
4.78 (br s, C3H), 2.28 (s, Me), 1.35 (s, Cp*),
1.27 (br s, C4H)
9.2 (d, 163), 4.1 (d, 170), 1.9 (d, 154), -4.8
(d, 162), -22.6 (d, 184), -23.8 (d, 169),
-27.0 (d, 159)
1Ha,c
11Ba,b
1Ha,c
11Ba,b
3
4
5
1Ha,c
6.05 (s, C3H), 2.14 (s, Me), 1.73 (s, C4H)
10.1 (2, d, 162), 6.3 (2, d, 175), -10.1 (d,
134), -10.8 (d, 150), -11.9
11Ba,b
Exp er im en ta l Section
(d, 168), -13.4 (d, 164), -23.3 (d, 164),
-25.6 (d, 165), -27.9 (2, d, 165), -29.0 (d,
175), -30.1 (d, 171)
Gen er a l Syn th etic P r oced u r es a n d Ma ter ia ls. Unless
otherwise noted, all reactions and manipulations were per-
formed in dry glassware under a nitrogen or argon atmosphere
using the high-vacuum or inert-atmosphere techniques de-
scribed by Shriver.7 Li+(6-Me-nido-5,6,9-C3B7H9-) (1-)3a,g,4 and
Li+(6-Ph-nido-5,6,9-C3B7H9-) (2-)8 were prepared by the re-
ported methods. LiH, [Ru(1,5-C8H12)Cl2]x, (η5-C5H5)Fe(CO)2I,
Na2(OsCl6)‚4H2O, Cr(CO)6, dibutyl ether, tert-butylisocyanide,
benzonitrile, and (Cp*RuCl2)x polymer were purchased from
Strem or Aldrich and used as received. Spectrochemical grade
glyme, diethyl ether, tetrahydrofuran, toluene, acetonitrile,
dichloromethane, and hexanes were purchased from Fisher or
EM Science. Glyme and tetrahydrofuran were freshly distilled
from sodium-benzophenone ketyl prior to use. Acetonitrile was
dried over P2O5, transferred onto activated 4 Å molecular
sieves, and stored under vacuum. All other solvents were used
as received unless noted otherwise.
1Ha,c
11Bb,f
6.53 (s, CH), 5.37 (s, CH), 5.04 (s, CH), 2.08
(s, Me), 1.92 (s, CH), 0.76 (s, Me)
9.2 (d, 158), 5.8 (d, 164), -3.1 (d, 155),
-11.4 (d, 156), -27.2 (d, 162),
6
7
-28.1 (d, 147), -30.4 (d, 165)
1Hc,f
6.15 (s, C3H), 2.69 (s, Me), 1.51 (s, C4H)
4.5 (d, 151), 1.4 (d, 161), -9.6 (d, 129),
-10.3 (d, 132), -24.2 (d, 142),
11Ba,b
-27.4 (d, 156),-32.8 (d, 158)
1Ha,c
11Ba,b
1Ha,c
11Ba,b
8.49 (Ph), 7.26 (Ph), 6.79 (Ph), 6.74 (s,
C3H), 3.75 (s, Cp), 1.50 (s, C4H)
4.6 (d, 150), 2.8 (d, 191), -7.9 (2, d, 143),
-27.5 (2, d, 144), -29.1 (d, 163)
8.21 (Ph), 7.27 (Ph), 6.75 (Ph), 5.08 (s,
C3H), 2.17 (s, C4H), 1.19 (s, Cp*)
8.9 (d, 150), 6.6 (d, 157), -5.1 (d, 152), -6.0
(d, 143), -21.1 (d, 146), -22.9 (d, 163),
-30.5 (d, 158)
8
9
Preparative thin-layer chromatography was conducted on
0.5 mm (20 × 20) silica gel F-254 plates (Merck-5744). The
yields of all metallatricarbaborane products are calculated on
the basis of the starting metal reagents.
1Ha,c
11Bb,f
1Hc,f
6.78 (Ph), 6.23 (s, C3H), 4.68 (Ph), 4.53
(Ph), 4.49 (Ph), 4.31 (Ph), 3.67 (Cp), 1.41
(C4H)
P h ysica l Meth od s. The 11B NMR at 64.2 MHz and 1H
NMR at 200 MHz were obtained on a Bruker AC 200 Fourier
transform spectrometer equipped with appropriate decoupling
accessories. 11B NMR at 160.5 MHz, 13C NMR at 125.7 MHz,
10
11
-0.9 (d, 146), -3.5 (d, 140), -12.2 (d, 141),
-13.3 (d, ∼150), -14.6 (d, 137), -20.4
(d, 148), -33.9 (d, 131)
4.93 (br, s, C3H), 1.92 (s, Me), 1.70 (s, But),
1.67 (s, Cp*)
1
and H NMR at 500 MHz were obtained on a Bruker AM-500
13Cd,e,f 94.91 (s, C5 Me5), 94.54 (s, C3H), 66.24 (br,
s, C2H), 38.11 (br, s, C4H), 32.19 (s, Me),
31.01 (CNC{Me3}), 9.60 (s, C5Me5)
spectrometer equipped with the appropriate decoupling ac-
cessories. All 11B chemical shifts are referenced to BF3‚OEt2
(0.0 ppm), with a negative sign indicating an upfield shift. All
proton chemical shifts were measured relative to internal
11Ba,b
7.3 (d, 126), 4.4 (d, 144), 1.5 (d, 147), -6.1
(d, 140), -7.1 (d, 173), -12.1 (d, 140),
-21.9 (d, 130)
1Ha,c
7.33 (Ph), 7.03 (Ph), 6.94 (Ph), 4.09 (s, Cp),
(3) (a) Plumb, C. A.; Carroll, P. J .; Sneddon, L. G. Organometallics
1992, 11, 1665-1671. (b) Plumb, C. A.; Carroll, P. J .; Sneddon, L. G.
Organometallics 1992, 11, 1672-1680. (c) Barnum, B. A.; Carroll, P.
J .; Sneddon, L. G. Organometallics 1996, 15, 645-654. (d) Weinmann,
W.; Wolf, A.; Pritzkow, H.; Siebert, W.; Barnum, B. A.; Carroll, P. J .;
Sneddon, L. G. Organometallics 1995, 14, 1911-1919. (e) Barnum, B.
A.; Carroll, P. J .; Sneddon, L. G. Inorg. Chem. 1997, 36, 1327-1337.
(f) Mu¨ller, T.; Kadlecek, D. E.; Carroll, P. J .; Sneddon, L. G.; Siebert,
W. J . Organomet. Chem. 2000, 614-615, 125-130. (g) Wasczcak, M.
D.; Wang, Y.; Garg, A.; Geiger, W. E.; Kang, S. O.; Carroll, P. J .;
Sneddon, L. G. J . Am. Chem. Soc. 2001, 123, 2783-2790.
(4) Kang, S. O.; Furst, G. T.; Sneddon, L. G. Inorg. Chem. 1989, 28,
2339-2347.
2.21 (br, s, C10H), 1.14 (But)
13Ca,d,e 155.57 (C NC{Me3}), 126.26 (s, Ph), 83.37
(s, Cp), 81.32 (s, C3H), 53.92 (CNC {Me3}),
30.62 (CNC{Me3})
a
b
d
In C6D6. 160.5 MHz. c 500 MHz. 125.8 MHz. e Broad-band
decoupled. f In CD2Cl2.
residual protons from lock solvents (99.5% C6D6 and 99.9%
CD2Cl2), then referenced to (CH3)4Si (0.0 ppm). NMR data are
summarized in Table 1.
(5) Ramachandran, B. M.; Carroll, P. J .; Sneddon, L. G. J . Am.
Chem. Soc. 2000, 122, 11033-11034.
High- and low-resolution mass spectra were obtained on a
VG-ZAB-E high-resolution mass spectrometer. IR spectra were
obtained on a Perkin-Elmer System 2000 FTIR spectrometer.
Elemental analyses were done at the University of Pennsyl-
vania microanalysis facility. Melting points were determined
using a standard melting point apparatus and are uncorrected.
Electr och em ica l P r oced u r es. Electrochemical procedures
were generally as described previously3g and performed in
either CH2Cl2 or THF containing 0.1 M [NBu4][B(C6F5)4]. The
supporting electrolyte was prepared by metathesis of Li-
[B(C6F5)4] etherate (Boulder Scientific Co.) with [NBu4]Br in
methanol and recrystallized several times from CH2Cl2/OEt2.9
Although the experimental reference electrode was a Ag/AgCl
(6) For some examples see: (a) Basolo, F. New J . Chem. 1994, 18,
19-24, and references therein. (b) Basolo, F. Polyhedron 1990, 9,
1503-1535, and references therein. (c) O’Connor, J . M.; Casey, C. P.
Chem. Rev. 1987, 87, 307-318, and references therein. (d) Schuster-
Woldan, H. G.; Basolo, F. J . Am. Chem. Soc. 1966, 88, 1657-1663. (e)
Rerek, M. E.; Basolo, F. J . Am. Chem. Soc. 1984, 106, 5908-5912. (f)
Simanko, W.; Tesch, W.; Sapunov, V. N.; Mereiter, K.; Schmid, R.;
Kirchner, K.; Coddington, J .; Wherland, S. Organometallics 1998, 17,
5674-5688. (g) Calhorda, M. J .; Gamelas, C. A.; Roma˜o, C. C.; Veiros,
L. F. Eur. J . Inorg. Chem. 2000, 331-340.
(7) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-Sensitive
Compounds, 2nd ed.; Wiley: New York, 1986.
(8) Ramachandran, B. M.; Carroll, P. J .; Sneddon, L. G. In prepara-
tion.

5080 Organometallics, Vol. 21, No. 23, 2002
Ramachandran et al.
Ta ble 2. Cr ysta llogr a p h ic Da ta Collection a n d Str u ctu r e Refin em en t In for m a tion
4
5
6
7
formula
fw
RuC8B14H24
372.68
OsC8B14H24
461.81
OsC8B14H24
461.81
FeC14B7H19
318.81
cryst class
space group
Z
triclinic
P1h (#2)
2
triclinic
P1h (#2)
2
triclinic
P1h (#2)
2
triclinic
P1h (#2)
2
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
6.6631(5)
7.7448(7)
17.686(2)
78.034(9)
80.883(9)
71.114(8)
840.67(14)
9.13
10.706(3)
12.373(3)
6.828(2)
92.45(2)
94.08(2)
105.70(2)
866.7(4)
73.38
7.7980(6)
17.6859(11)
6.6743(4)
99.126(5)
109.228(4)
78.123(4)
846.41(10)
75.14
8.0188(3)
15.4779(7)
6.7169(2)
97.413(2)
107.522(3)
76.351(3)
771.02(5)
9.62
µ, cm-1
cryst size, mm
0.25 × 0.20 × 0.15
0.42 × 0.24 × 0.04
0.30 × 0.11 x 0.02
0.35 × 0.30 × 0.14
D
calc, g/cm3
1.472
1.770
1.812
1.373
F(000)
372
436
436
328
radiation
Mo KR
Mo KR
Mo KR
Mo KR
(λ ) 0.71069 Å)
5.74-54.9
-7 e h e 8;
-7 e k e 9;
-22 e l e 22
5439
(λ ) 0.71069 Å)
3.42-50.7
-12 e h e 12;
-14 e k e 14;
-7 e l e 8
4873
(λ ) 0.71069 Å)
5.6-55.02
-10 e h e 10;
-22 e k e 21;
-8 e l e 8
9073
(λ ) 0.71069 Å)
5.42-50.7
-9 e h e 9;
-21 e k e 19;
-12 e l e 11
6640
2θ range, deg
hkl collected
no. reflns measd
no. unique reflns
3199
2761
3539
2614
(Rint ) 0.0169)
2969 (F>4σ)
3199
(Rint ) 0.0417)
2386 (F>4σ)
2761
(Rint ) 0.0450)
3370 (F>4σ)
3539
(Rint ) 0.0247)
2482 (F>4σ)
2614
no. obsd reflns
no. reflns used in refinement
no. params
304
210
209
255
R indices (F>4σ)
R1 ) 0.0208
wR2 ) 0.0488
R1 ) 0.0236
wR2 ) 0.0495
1.017
R1 ) 0.0784
wR2 ) 0.1709
R1 ) 0.0904
wR2 ) 0.1818
1.123
R1 ) 0.0500
wR2 ) 0.1296
R1 ) 0.0529
wR2 ) 0.1372
1.073
R1 ) 0.0407
wR2 ) 0.1066
R1 ) 0.0433
wR2 ) 0.1105
1.040
R indices (all data)
GOF
final diff peaks, e/Å3
+0.394, -0.867
+2.604, -2.413
+2.007, -2.472
+0.359, -0.524
8
9
10
11
formula
fw
RuC19B7H29
434.16
FeCrC17B7H19O3
454.84
RuC19B7H36
455.23
N
FeC19B7H28
401.94
N
cryst class
space group
Z
triclinic
P1h (#2)
4
monoclinic
P21/n (#14)
8
triclinic
P1h (#2)
2
monoclinic
P21 (#4)
2
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
14.8296(2)
16.5710(1)
9.7056(1)
96.141(1)
97.725(1)
115.837(1)
2090.20(4)
7.51
14.6585(3)
13.7293(3)
20.0208(3)
9.9335(4)
13.4379(4)
9.6881(4)
104.997(3)
110.448(2)
76.334(3)
1155.16(7)
6.83
10.5638(10)
9.6335(5)
11.0574(10)
102.640(1)
113.370(3)
3931.55(13)
13.07
1033.0(2)
7.34
µ, cm-1
cryst size, mm
0.36 × 0.22 × 0.06
0.22 × 0.20 × 0.008
0.40 × 0.20 × 0.07
0.15 × 0.12 × 0.10
D
calc, g/cm3
1.380
1.537
1.309
1.292
F(000)
888
1840
472
420
radiation
Mo KR
Mo KR
Mo KR
Mo KR
(λ ) 0.71069 Å)
5.04-54.96
-19 e h e 19;
-16 e k e 16;
-23 e l e 24
21 788
(λ ) 0.71069 Å)
5.12-50.7
-16 e h e 17;
-16 e k e 16;
-23 e l e 24
28 993
(λ ) 0.71069 Å)
5.02-50.7
-11 e h e 11;
-16 e k e 16;
-11 e l e 11
9708
(λ ) 0.71069 Å)
5.84-50.7
-12 e h e 12;
-11e k e 11;
-13 e l e 13
7727
2θ range, deg
hkl collected
no. reflns measd
no. unique reflns
8818
6890
3919
3564
(Rint ) 0.0506)
8202 (F>4σ)
8818
(Rint ) 0.0499)
6206 (F>4σ)
6890
(Rint ) 0.0506)
3755 (F>4σ)
3919
(Rint ) 0.0531)
3351 (F>4σ)
3564
no. obsd reflns
no. reflns used in refinement
no. params
561
595
290
254
R indices (F>4σ)
R1 ) 0.0439
wR2 ) 0.1066
R1 ) 0.0480
wR2 ) 0.1105
1.121
R1 ) 0.0632
wR2 ) 0.1391
R1 ) 0.0728
wR2 ) 0.1442
1.189
R1 ) 0.0577
wR2 ) 0.1562
R1 ) 0.0594
wR2 ) 0.1583
1.094
R1 ) 0.0780
wR2 ) 0.2090
R1 ) 0.0824
wR2 ) 0.2143
1.100
R indices (all data)
GOF
final diff peaks, e/Å3
+0.587,-0.680
+0.305, -0.643
+0.855, -1.735
+1.380, -0.847
electrode, all potentials in this paper are referred to the
ferrocene/ferrocenium potential, which was determined in each
experiment at an appropriate point by using Cp2Fe as an
internal standard. Each process had diffusion-controlled be-
havior, and no electrode history problems were encountered
at either glassy carbon or platinum electrodes (of 2 mm
diameter). The potentiostat was a Princeton Applied Research
Model 273 system interfaced to a personal computer. Standard

Metallatricarbadecaboranyl Analogues
Organometallics, Vol. 21, No. 23, 2002 5081
diagnostics10 were applied to voltammetric responses, details
of which are available elsewhere.11 The following potentials
of metallocene redox processes were used when comparing
their potentials to the E1/2 values of the tricarbadecaboranyl
compounds: Cp2Fe+/0 ) 0; Cp2Fe0/1- ) -3.4 V; Cp2Ru+/0 ) 0.41
to dryness. TLC separation (7:3 hexanes/CH2Cl2) gave a dark
blue band (Rf 0.55). For 7: 1-(η5-C5H5)-2-Ph-closo-1,2,3,4-
FeC3B7H9, yield 49% (0.156 g, 0.49 mmol); dark blue; mp 150
°C. Anal. Calcd: C, 52.74; H, 6.01. Found: C, 52.47; H, 5.78.
12
HRMS calcd for
C
1H1911B756Fe 320.1487, found 320.1507;
14
V; CpCp*Ru+/0 ) 0.11 V; Cp2Ru0/1- ) -3.9 V; CpCp*Ru0/1-
)
IR (KBr, cm-1) 3110 (m), 3063 (m), 2552 (s), 1419 (m), 1308
(m), 1260 (m), 1199 (m), 1116 (w), 939 (w), 838 (w), 738 (w),
668 (s).
-4.2 V (estimated; not reported); Cp2Os+/0 ) 0.25 V; Cp2Os0/1-
) -3.9 V (see Tables for literature sources).
1-(η5-C5Me5)-2-Me-closo-1,2,3,4-Ru C3B7H9 (3). A toluene
solution of 1- (1.5 mL of 0.5 M, 0.75 mmol) was added dropwise
to a stirring solution of [Cp*RuCl2]x (0.11 g, 0.37 mmol) in
glyme (35 mL). After stirring for 12 h at 50 °C, the dark brown
solution was exposed to air and filtered. The solvent was
vacuum evaporated from the filtrate to give a dark red residue,
which was then extracted with Et2O. TLC separation (7:3
hexanes/CH2Cl2) gave a single orange band (Rf 0.60). For 3:
1-(η5-C5Me5)-2-Me-closo-1,2,3,4-RuC3B7H9, yield 75% (0.10 g,
1-(η5-C5Me5)-2-P h -closo-1,2,3,4-Ru C3B7H9 (8). A toluene
solution of 2- (1.6 mL of 0.5 M, 0.80 mmol) was added dropwise
to a stirring solution of [Cp*RuCl2]x (0.12 g, 0.39 mmol) in
glyme (35 mL). After stirring for 12 h at 50 °C, the yellow-
orange solution was exposed to air and filtered through a silica
gel plug. The silica gel was washed with Et2O to extract any
remaining product. TLC separation (7:3 hexanes/CH2Cl2) gave
a single orange band (Rf 0.55). For 8: 1-(η5-C5Me5)-2-Ph-closo-
1,2,3,4-RuC3B7H9, yield 66% (0.112 g, 0.26 mmol); orange; mp
0.28 mmol); orange, mp 211 °C. Anal. Calcd: C, 45.19, H, 7.31.
179 °C. Anal. Calcd: C, 52.56, H, 6.73. Found: C, 53.29, H,
12
12
Found: C, 44.91; H, 7.32. HRMS calcd for
C
1H2711B7104Ru
6.87. HRMS calcd for
C
1H2911B7104Ru 438.1976, found
19
14
m/e 376.1819, found 376.1840; IR (KBr, cm-1) 2920 (m), 2571
(s), 1559 (w), 1472 (w), 1374 (w), 1028 (w), 967 (w), 790 (w),
727 (w), 668 (m).
438.1991; IR (KBr, cm-1) 2921 (s), 2546 (s), 1945 (m), 1494
(w), 1374 (w), 1160 (w), 1102 (m), 929 (m), 691 (m), 668 (s).
Rea ction of 2- w ith [Ru Cl2(cod )x]. A toluene solution of
2- (2.04 mL of 0.5 M, 1.02 mmol) was added dropwise to a
stirring solution of [RuCl2(cod)x] (0.143 g, 0.51 mmol) in glyme
(35 mL). After stirring for 12 h at reflux, the resulting dark
brown solution was worked up as reported above for the
reaction of 1- with [RuCl2(cod)x], but yielded no isolable
products.
com m o-Ru -(2-Me-closo-1,2,3,4-Ru C3B7H9)2 (4). A toluene
solution of 1- (2.04 mL of 0.5 M, 1.02 mmol) was added
dropwise to a stirring solution of [RuCl2(cod)x] (0.14 g, 0.51
mmol) in glyme (35 mL). After stirring for 12 h at reflux, the
red solution was exposed to air and filtered through a silica
gel plug. The silica gel was washed with diethyl ether to
extract any product. TLC separation (9:1 hexanes/toluene)
gave three bands with only the third dark red band (Rf 0.2)
obtained in sufficient amount for complete characterization.
For 4: commo-Ru-(2-Me-closo-1,2,3,4-RuC3B7H9)2, yield 8%
(0.02 g, 0.04 mmol); red; mp 110 °C. Anal. Calcd: C, 25.78, H,
Rea ction of 7 w ith Cr (CO)6: Syn th esis of 1-(η5-C5H5)-
2-[(η6-C6H5)Cr (CO)3]-closo-1,2,3,4-FeC3B7H9 (9). A 0.63 mmol
(0.202 g) sample of 7 was dissolved in a 10:1 mixture of dibutyl
ether/THF, and then an excess (1.39 g, 6.3 mmol) of Cr(CO)6
was added. After reflux for 36 h, the volatiles were vacuum
evaporated. TLC separation (CH2Cl2) gave a blue band of the
unreacted starting compound 7 (Rf 0.8) (0.074 g, 0.23 mmol,
37%) and a green band (Rf 0.5) of the product. For 9: 1-(η5-
C5H5)-2-[(η6-C6H5)Cr(CO)3]-closo-1,2,3,4-FeC3B7H9; yield 12%
6.49. Found: C, 26.28, H, 6.58. HRMS calcd for 12C8 H24
B -
14
1
11
104Ru 378.2236. Found: 378.2220. IR (KBr, cm-1) 3027 (s),
2998 (m), 2938 (s), 2861 (m), 2573 (s), 1852 (w), 1439 (s), 1376
(s), 1276 (m), 1099 (s), 967 (s), 931 (m), 865 (m), 838 (m), 791
(m), 725 (w), 696 (m), 645 (w).
(0.023 g, 0.05 mmol); green; mp 150 °C. Anal. Calcd: C, 44.89;
C -
1H19
17
12
com m o-Os-(4′-Me-closo-1′,2′,3′,4′-OsC3B7H9)(2-Me-closo-
1,2,3,4-OsC3B7H9) (5) a n d com m o-Os-(2-Me-closo-1,2,3,4-
OsC3B7H9)2 (6). A toluene solution of 1- (2.68 mL of 0.5 M,
1.34 mmol) was added dropwise to a stirring solution of Na2-
OsCl6‚4H2O (0.30 g, 0.67 mmol) in glyme (35 mL). After
stirring for 12 h at reflux, the reddish-brown solution was
exposed to air and filtered through a silica gel plug. The silica
gel was washed with CH2Cl2 to extract any product. TLC
separation (9:1 hexanes/toluene) gave two bands (overall yield
7.7%, 0.024 g, 0.05 mmol). For 5: commo-Os-(4′-Me-closo-
1′,2′,3′,4′-OsC3B7H9)(2-Me-closo-1,2,3,4-OsC3B7H9), (Rf 0.3),
H, 4.21. Found: C, 43.19; H, 4.67. HRMS calcd for
11B752Cr56Fe16O3 456.0740, found 456.0749; IR (KBr, cm-1) 3118
(s), 3067 (s), 3044 (m), 2633 (s), 2563 (s), 2504 (s), 2491 (s),
1965 (s), 1894 (s), 1872 (s), 1521 (m), 1504 (m), 1452 (s), 1425
(s), 1407 (m), 1363 (w), 1299 (m), 1216 (s), 1119 (s), 1060 (w),
1012 (m), 995 (m), 850 (s), 814 (m), 731 (m).
Rea ction of 3 w ith ter t-Bu tylisocya n id e: Syn th esis of
8-(η5-C5Me5)-8-(CNBu t)-9-Me-n id o-8,7,9,10-Ru C3B7H9 (10).
A 0.03 mmol (0.011 g) sample of 3 was dissolved in ∼3 mL of
glyme, and excess (1.0 mL, 8.9 mmol) tert-butylisocyanide was
added. An immediate color change from reddish-orange to
yellow was observed. Slow evaporation of the solution gave
X-ray quality yellow-colored crystals. For 10: nido-8-(η5-C5-
Me5)-8-(CNBut)-9-Me-nido-8,7,9,10-RuC3B7H9; yield 97% (0.013
g, 0.029 mmol); orange. Anal. Calcd: C, 50.13; H, 7.97; N, 3.08.
Found: C, 49.98; H, 8.14; N, 2.74. IR (KBr, cm-1) 3014 (s),
2983 (s), 2911 (s), 2855 (s), 2527(s), 2163 (s), 2069 (s), 1856
(m), 1460 (s), 1377 (s), 1259 (m), 1232 (s), 1085 (s), 1048 (s),
971 (s), 951 (m), 928 (w), 886 (m).
Rea ction of 7 w ith ter t-Bu tylisocya n id e: Syn th esis of
8-(η5-C5H5)-8-(CNBu t)-9-P h -n id o-8,7,9,10-F eC3B7H9 (11). A
0.03 mmol (0.010 g) sample of 7 was dissolved in ∼3 mL of
toluene, and excess (1.0 mL, 8.9 mmol) tert-butylisocyanide
was added. An immediate color change from blue-green to
brownish-red was observed. X-ray quality brownish-red colored
crystals were obtained by cooling the brownish-red solution
at 0 °C. For 11: 8-(η5-C5H5)-8-(CNBut)-9-Ph-nido-8,7,9,10-
FeC3B7H9; yield 63% (0.008 g, 0.019 mmol); brownish-red.
Anal. Calcd: C, 56.77; H, 7.02; N, 3.48. Found: C, 56.17; H,
7.06; N, 3.54. IR (KBr, cm-1) 3110 (s), 3087 (s), 2985 (s), 2870
(m), 2555 (s), 2166 (s), 2048 (m), 1961 (m), 1862 (m), 1494 (s),
1445 (s), 1370 (s), 1232 (w), 1199 (s), 1068 (m), 939 (s), 894
(m), 839 (s).
yield 2.3% (0.007 g); orange; mp 160 °C. Anal. Calcd: C, 20.81,
1
H, 5.24. Found: C, 20.58, H, 5.17. HRMS calcd for 12C8 H24
-
11
B
192Os 466.2793, found 466.2815; IR (KBr, cm-1) 3038 (m),
14
2937 (m), 2578 (s), 1477 (m), 1386 (m), 1276 (m), 1160 (w),
1102 (m), 921 (m), 720 (w), 668 (s), 649 (w). For 6: commo-
Os-(2-Me-closo-1,2,3,4-OsC3B7H9)2 (Rf 0.2); yield 5.4% (0.017
g); orange; mp 162 °C. Anal. Calcd: C, 20.81, H, 5.24. Found:
C, 21.04, H, 5.42. HRMS calcd for 12C8 H24
B
192Os 466.2793,
14
1
11
found 466.2815; IR (KBr, cm-1) 3031 (m), 2570 (s), 1413 (w),
1329 (w), 1160 (m), 1102 (m), 921 (s), 756 (w).
1-(η5-C5H5)-2-P h -closo-1,2,3,4-F eC3B7H9 (7). A toluene
solution of 2- (2.2 mL of 0.5 M, 1.10 mmol) was added dropwise
to a stirring solution of (η5-C5H5)Fe(CO)2I (0.304 g, 1.00 mmol)
in THF (35 mL). After stirring for 12 h at room temperature,
the bluish-green solution was exposed to air and filtered
through a silica gel plug, and the dark filtrate was evaporated
(9) LeSuer, R. J .; Geiger, W. E. Angew. Chem., Int. Ed. 2000, 39,
248-250.
(10) Geiger, W. E., Kissinger, P. T., Heineman, W. R., Eds. Labora-
tory Techniques In Electroanalytical Chemistry, 2nd ed.; Marcel
Dekker: New York, 1996; Chapter 23.
(11) Trupia, S. M. Ph.D. Thesis, University of Vermont, 2002.

5082 Organometallics, Vol. 21, No. 23, 2002
Ramachandran et al.
[(η5-C5Me5)RuCl2]x +
2Li+(6-Me-nido-5,6,9-C3B7H9)-
Rea ction of 4 w ith ter t-Bu tylisocya n id e. A 0.03 mmol
(0.011 g) sample of 4 was dissolved in ∼3 mL of glyme, and
excess (1.0 mL, 8.9 mmol) tert-butylisocyanide was added. No
color change was observed, and there was no change in the
11B NMR spectrum from that of the starting compound.
f
1-
1-(η5-C5Me5)-2-Me-closo-1,2,3,4-RuC3B7H9
+
Cr ysta llogr a p h ic Da ta . Single crystals of all compounds
were grown via slow solvent evaporation from dichloromethane
or a 50:50 hexanes/dichloromethane solutions in air.
3
2LiCl (2)
Collection a n d Red u ction of th e Da ta . Crystallographic
data and structure refinement information are summarized
in Table 2. X-ray intensity data were collected on a Rigaku
R-axis IIc area detector employing graphite-monochromated
Mo KR radiation at a temperature of 210 K. Indexing was
performed from a series of oscillation angles. A hemisphere of
data was collected using 0.5° oscillation angles for 4, 10° for 5
and 7, 5° for 6, 9, and 11, 4° for 8, and 6° for 10 and a crystal-
to-detector distance of 82 mm. Oscillation images were pro-
cessed using bioteX,12 producing a listing of unaveraged F and
σ(F) values that were then passed to the teXsan program
package13 for further processing and structure solution on a
Silicon Graphics Indigo R4000 computer. The intensity data
were corrected for Lorentz and polarization effects but not for
absorption.
2Li+(6-Me-nido-5,6,9-C B H )-
[RuCl2(cod)x] +
f
3
7
9
1-
commo-Ru-(2-Me-closo-1,2,3,4-RuC3B7H9)2
+
4
2LiCl (3)
Na2OsCl6‚4H2O +
4Li+(6-Me-nido-5,6,9-C3B7H9)- f
commo-Os-(4′-Me-closo-1′,2′,3′,4′-OsC3B7H9)
+
(2-Me-closo-1,2,3,4-OsC3B7H9)
5
commo-Os-(2-Me-closo-1,2,3,4-OsC3B7H9)2
+
Solu tion a n d Refin em en t of th e Str u ctu r es. The struc-
tures were solved by direct methods (SIR92).14 Refinements
were by full-matrix least squares based on F2 using SHELXL-
93.15 All reflections were used during refinement (values of
6
2NaCl + 4LiCl + 4H2O (4)
Likewise, the syntheses of the phenyltricarbadecabo-
ranyl analogues of ferrocene and ruthenocene were
achieved by the reactions given in eqs 5 and 6 employing
the new 6-Ph-nido-5,6,9-C3B7H9- anion.8
F2 that were experimentally negative were replaced by F2
0).
)
(η5-C5H5)Fe(CO2)I +
Resu lts a n d Discu ssion
Li+(6-Ph-nido-5,6,9-C3B7H9)-
Syn th eses a n d Str u ctu r a l Ch a r a cter iza tion s. As
illustrated in eq 1, we have previously shown3a,b that
ferratricarbadecaboranyl analogues of ferrocene, includ-
ing both bis-cage (Me-C3B7H9)2Fe and mixed-ligand (η5-
C5H5)Fe(Me-C3B7H9) complexes, can be prepared by the
reactions of the 6-Me-nido-5,6,9-C3B7H9- (1-) anion with
(η5-C5H5)Fe(CO)2I.
f
2-
1-(η5-C5H5)-2-Ph-closo-1,2,3,4-FeC3B7H9
+ LiI +
7
2CO (5)
[(η5-C5Me5)RuCl2]x +
2Li+(6-Ph-nido-5,6,9-C3B7H9)-
(η5-C5H5)Fe(CO)2I +
f
2-
Li+(6-Me-nido-5,6,9-C3B7H9)-
f
1-(η5-C5Me5)-2-Ph-closo-1,2,3,4-RuC3B7H9
+
1-
8
1-(η5-C5H5)-2-Me-closo-1,2,3,4-FeC3B7H9
+
2LiCl (6)
12
1-(η5-C5H5)-4-Me-closo-1,2,3,4-FeC3B7H9
Significant differences were observed in the reactions
employing the 6-Me-nido-5,6,9-C3B7H9- (1-) and 6-Ph-
nido-5,6,9-C3B7H9- (2-) anions. For example, 6-Me-nido-
+
13
commo-Fe-(5-Me-closo-1,2,3,5-C3B7H9)
-
+
5,6,9-C3B7H9 reactions usually result in some cage-
(4-Me-closo-1,2,3,4-C3B7H9)
carbon rearrangement to produce isomeric side products,
such as the 1-(η5-C5H5)-4-Me-closo-1,2,3,4-FeC3B7H9
(13) complex in eq 1, in which “methyl-migration” to the
4-cage carbon has occurred.16 However, in comparable
reactions employing the 6-Ph-nido-5,6,9-C3B7H9- anion,
no such isomerization occurs and only one isomer is
14
LiI + 2CO (1)
We have now used the reactions given in eqs 2-4 to
prepare methyltricarbadecaboranyl analogues of ru-
thenocene and osmocene.
-
produced. Likewise, in 6-Me-nido-5,6,9-C3B7H9 reac-
tions such as in eq 1, bis-cage, (Me-C3B7H9)2M, side
products are usually produced (for example, complex
14), but in the 6-Ph-nido-5,6,9-C3B7H9- reactions in eqs
5 and 6, no bis-cage (Ph-C3B7H9)2M, M ) Fe or Ru, were
observed. In fact, even reactions, such as shown in eq
7, intentionally designed to produce bis-cage complexes
(12) bioteX: A suite of Programs for the Collection, Reduction and
Interpretation of Imaging Plate Data; Molecular Structure Corporation,
1995.
(13) teXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corporation, 1985 & 1992.
(14) SIR92: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.;
Giacovazzo, C.; Guagliardi, A.; Polidoro, G. J . Appl. Crystallogr. 1994,
27, 435.
(15) Sheldrick, G. M. SHELXL-93: Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Germany, 1993.
(16) Plumb, C. A.; Sneddon, L. G. Organometallics 1992, 11, 1681-
1685.

Metallatricarbadecaboranyl Analogues
Organometallics, Vol. 21, No. 23, 2002 5083
-
from the 6-Ph-nido-5,6,9-C3B7H9 anion were unsuc-
cessful.
[RuCl2(cod)x] +
2Li+(6-Ph-nido-5,6,9-C3B7H9)-
f no reaction (7)
2-
The inability to form bis-cage complexes containing
-
the 6-Ph-nido-5,6,9-C3B7H9 ligand is most probably a
result of the unfavorable steric interactions between the
phenyl substituents of the two cages. As will be reported
elsewhere,8 we have used this feature to advantage in
achieving the high yield syntheses of a series of half-
sandwich complexes that were unattainable using the
F igu r e 2. ORTEP drawing of the structure of 1-(η5-C5H5)-
2-Ph-closo-1,2,3,4-FeC3B7H9 (7).
-
6-Me-nido-5,6,9-C3B7H9 anion. The absence of both
cage-isomerization and bis-cage side products in the
-
reactions with the 6-Ph-nido-5,6,9-C3B7H9 results in
these reactions being more selective than the corre-
sponding reactions with 6-Me-nido-5,6,9-C3B7H9-. Thus,
-
reactions with the 6-Ph-nido-5,6,9-C3B7H9 anion pro-
vide a more efficient route to metallatricarbadecabora-
nyl complexes than those reactions employing the 6-Me-
-
nido-5,6,9-C3B7H9 anion.
All complexes resulting from the reactions in eqs 1-6
were isolated as air-stable solids and were easily puri-
fied by TLC. The compositions of all compounds were
established by mass spectrometry and/or elemental
analyses. The proposed structures are strongly sup-
ported by their NMR data, with the structures of
compounds 4, 5, 6, 7, and 8 being further confirmed by
crystallographic determinations.
The 11B NMR spectra (Table 1) of the mixed-ligand
complexes, 1-(η5-C5Me5)-2-Me-closo-1,2,3,4-RuC3B7H9
(3), 1-(η5-C5H5)-2-Ph-closo-1,2,3,4-FeC3B7H9 (7), and
1-(η5-C5Me5)-2-Ph-closo-1,2,3,4-RuC3B7H9 (8), are each
consistent with C1 cage symmetries and are very similar
to that previously reported for 1-(η5-C5H5)-2-Me-closo-
F igu r e 3. ORTEP drawing of the structure of 1-(η5-C5-
Me5)-2-Ph-closo-1,2,3,4-RuC3B7H9 (8).
Ta ble 3. In tr a m olecu la r Dista n ces (Å) in
Com p ou n d s 12, 7, 8, a n d 9 (M ) F e for 12, 7, 9 a n d
M ) Ru for 8)
1
1,2,3,4-FeC3B7H9 (12).3a The H NMR spectra for com-
pounds 3, 7, and 8 are likewise similar to that of 12,
each showing, in addition to the appropriate Me or Ph
resonances, two C-H resonances with one occurring at
a low-field shift (∼6.8 to 4.8 ppm) characteristic of the
proton attached to the low-coordinate C3 carbon, which
is adjacent to the metal, and the other at a high-field
shift (>2.2 ppm) characteristic of the C4-H proton.
In agreement with the spectroscopic data, the crystal-
lographic determinations of 1-(η5-C5H5)-2-Ph-closo-
1,2,3,4-FeC3B7H9 (7) (Figure 2) and 1-(η5-C5Me5)-2-Ph-
closo-1,2,3,4-RuC3B7H9 (8) (Figure 3) confirm that the
metal atoms in these complexes, as in 12, are η6-
coordinated to the puckered six-membered face of the
tricarbadecaboranyl cage with the Me or Ph groups
bonded to the C2 cage carbon adjacent to the metal.
Thus, these complexes, as well as 12 and 1-(η5-C5Me5)-
2-Me-closo-1,2,3,4-RuC3B7H9 (3), can be considered as
mixed ligand analogues of ferrocene and ruthenocene
in which formal Fe2+ and Ru2+ ions are sandwiched
between the tricarbadecaboranyl and cyclopentadienyl
monoanionic ligands. From a cluster point of view,17 the
bond
12
7
8a
9a
M-C2
1.970(3)
1.951(3)
2.227(3)
2.264(3)
2.276(3)
2.241(3)
1.681
1.560(4)
1.817(5)
1.564(4)
1.574(4)
1.775(5)
1.508(3)
1.982(3)
1.955(3)
2.258(3)
2.239(3)
2.253(3)
2.275(3)
1.695(3)
1.502(4)
1.750(4)
1.576(4)
1.578(4)
1.841(5)
1.593(4)
2.111(3)
2.073(4)
2.355(4)
2.339(5)
2.352(5)
2.358(4)
1.829(2)
1.509(6)
1.781(7)
1.570(7)
1.578(8)
1.833(7)
1.577(6)
1.980(4)
1.952(5)
2.274(5)
2.217(5)
2.230(6)
2.285(6)
1.684(5)
1.496(6)
1.739(7)
1.557(9)
1.588(9)
1.854(8)
1.597(7)
M-C3
M-C4
M-B5
M-B6
M-B7
M-Cp/Cp*
C2-C4
C4-B7
B7-C3
C3-B6
B6-B5
B5-C2
a
The bond distances of only one of the two independent
molecules found in the asymmetric units of 8 and 9 are given, as
there were no significant differences.
11-vertex MC3B7H9 fragment has a closo skeletal elec-
tron count (24 skeletal electrons, with the CpFe and
Cp*Ru groups each donating 1 skeletal electron), and
it therefore adopts the octadecahedral structure nor-
mally observed for such systems.
Selected bond distances for 12, 7, 8, and 9 are
compared in Table 3. The metals are approximately
centered over the puckered six-membered open face,
with the closest metal-cage interactions being with the
(17) (a) Wade, K. Adv. Inorg. Chem. Radiochem. 1976, 18, 1-66.
(b) Williams, R. E. Adv. Inorg. Chem. Radiochem. 1976, 18, 67-142.
(c) Williams, R. E. Chem. Rev. 1992, 92, 117-201. (d) Williams, R. E.
In Electron Deficient Boron and Carbon Clusters; Olah, G. A., Wade,
K., Williams, R. E., Eds.; Wiley: New York, 1991.

5084 Organometallics, Vol. 21, No. 23, 2002
Ramachandran et al.
two carbons, C2 and C3, which are puckered out of the
ring. Longer and approximately equivalent bond lengths
are observed between the metals and the remaining four
atoms (C4, B5, B6, and B7) on the tricarbadecaboranyl
bonding face. The M-C2 and M-C3 bond lengths in 7
and 8 are significantly shorter than the M-C bond
lengths found to the ring-carbons in their respective
cyclopentadienyl (2.051(5)-2.069(3) Å) and pentameth-
ylcyclopentadienyl (2.158(4)-2.261(2) Å) ligands. As
pointed out previously,18 the orbitals on the open face
of even a planar polyhedral cluster are orientated more
directly toward the metal than in a cyclopentadienyl
ring. This enhances the overlap of the metal and ligand
orbitals and strengthens the bonding. In the case of the
tricarbadecaboranes, even stronger interactions could
be possible because the puckered ring structure allows
close approach of the metal to the C2 and C3 carbons.
Regardless of whether the substituent at the C2
carbon is a methyl or phenyl group, the M-C2 distance
is found to be considerably lengthened compared to the
M-C3 distance. For example, the Fe-C2 distances in
12 (1.970(3) Å) and 7 (1.982(3) Å) are considerably
longer than their corresponding Fe-C3 distances (1.951-
(3) and 1.955(3) Å, respectively).
F igu r e 4. ORTEP drawing of the structure of commo-Ru-
(2-Me-closo-1,2,3,4-RuC3B7H9)2 (4).
1
The 11B and H NMR spectra (Table 1) of the bis-cage
complexes commo-Ru-(2-Me-closo-1,2,3,4-RuC3B7H9)2 (4)
and commo-Os-(2-Me-closo-1,2,3,4-OsC3B7H9)2 (6) are
similar to those found for complexes 3, 7, 8, and 12,
indicating that the two cages in 4 and 6 are equivalent.
Thus, both complexes show only seven equal intensity
doublets in their 11B NMR spectra. Likewise, in their
1H NMR spectra, the complexes show only a single Me
resonance, as well as only two C-H resonances, one in
the low-field region (6.05 ppm, 4 and 6.15 ppm, 6)
characteristic of a C3-H proton and the other at high-
field (1.73 ppm, 4 and 1.51 ppm, 6) consistent with a
C4-H proton.3
fragment, like the (η5-C5Me5)M and (η5-C5H5)M (M )
Fe, Ru) groups in complexes 7 and 8, can donate one
skeletal electron to the second MeC3B7H9 cage. There-
fore, each (MeC3B7H9)M unit would be an 11-vertex, 24-
skeletal-electron system that should adopt the observed
closo-octadecahedral geometry in which the metal is
shared between the two cages.
As discussed3b previously, due to the fact that the
-
6-Me-nido-5,6,9-C3B7H9 anion exists as a racemic
mixture, when a bis-cage complex is formed, it may
contain two anion cages of the same enantiomeric type
or contain two different enantiomeric forms of the anion.
As can be seen in Figures 4 and 5, both complexes 4
and 6 contain a single enantiomeric form of the 6-Me-
The 11B and 1H NMR spectra of commo-Os-
(4′-Me-closo-1′,2′,3′,4′-OsC3B7H9)(2-Me-closo-1,2,3,4-
OsC3B7H9) (5) are much more complex, indicating that
the two cages of the complex are not equivalent. Thus,
the 11B NMR resolves 14 resonances in 2:2:1:1:1:1:1:1:
-
nido-5,6,9-C3B7H9 anion, and thus the two cages are
1
related by a C2-axis passing through the metal center.
The symmetry equivalence of the two cages thus results
in the simple NMR spectra observed for 4 and 6. As can
be seen in Figure 6, the structure of compound 5 is more
complex since the two cages are not symmetry equiva-
lent. Thus, the complex, unlike in 4 and 6, contains two
different enantiomeric forms of the anion. Furthermore,
in one of the cages (the top cage in Figure 6) the methyl
group that had originally been present at the C2′ carbon
has rearranged to the C4′ carbon position. The in-
equivalence of the two cages, as well as the observed
methyl rearrangement, is thus in complete accord with
the NMR data.
Selected bond distances for 4, 6, and 5 are presented
in Table 4. The metal ions are approximately centered
over the six-membered, puckered open faces of the two
cages. As was the case for complexes 7, 8, and 12, the
shortest metal-cage distances are between the metals
and the two carbons, C2 and C3, puckered out of the
six-membered face. While, as in the recently reported
bis-cage vanadatricarbaboranyl complexes,3g the planes
containing the three boron and one carbon (B5-B6-
B7-C4) atom on the six-membered open faces of each
2:1:1 ratios. The H NMR spectrum shows two separate
methyl resonances (one at low field, 2.08 ppm, and the
other at high field, 0.76 ppm), as well as three C-H
resonances at low field (6.53, 5.37, and 5.04 ppm) and
only one C-H at high field (1.92 ppm). The fact that in
the 1H NMR spectrum there are three low-field reso-
nances (C2-H and C3-H adjacent to the metal) and only
one high-field resonance (C4-H) suggests that a methyl
group has migrated from the C2 to the C4 position on
one of the two cages.16
As shown in Figures 4, 5, and 6, the structures of
compounds 4, 6, and 5 were confirmed by crystal-
lographic determinations and are in agreement with the
spectroscopic data discussed above. The complexes can
be considered analogues of ruthenocene and osmocene
in which the Ru2+ and Os2+ ions are sandwiched
-
between the two Me-C3B7H9 monoanions. From a
cluster point of view,17 a (Me-C3B7H9)M (M ) Ru or Os)
(18) (a) Hawthorne, M. F.; Young, D. C.; Andrews, T. D.; Howe, D.
V.; Pilling, R. L.; Pitts, A. D.; Reintjes, M.; Warren, J r., L. F.; Wegner,
P. A. J . Am. Chem. Soc. 1968, 90, 879-896. (b) Calhorda, M. J .; Mingos,
D. M. P.; Welch, A. J . Organomet. Chem. 1982, 228, 309-320. (c)
Mingos, D. M. P. J . Chem. Soc., Chem. Commun. 1977, 602-610.

Metallatricarbadecaboranyl Analogues
Organometallics, Vol. 21, No. 23, 2002 5085
Ta ble 4. In tr a m olecu la r Dista n ces (Å) in
Com p ou n d s 4, 5, a n d 6 (M ) Ru for 4 a n d Os for 5
a n d 6)
bond
4
5
6
M-C2
2.120(2)
2.116(2)
2.053(2)
2.060(2)
2.499(2)
2.494(2)
2.349(2)
2.354(2)
2.307(2)
2.296(2)
2.458(2)
2.467(2)
1.491(3)
1.494(3)
1.747(3)
1.747(3)
1.589(3)
1.588(3)
1.603(3)
1.610(3)
1.863(3)
1.867(3)
1.604(3)
1.605(3)
2.14(2)
2.06(2)
2.12(2)
2.09(2)
2.45(2)
2.43(2)
2.33(2)
2.24(3)
2.37(3)
2.35(2)
2.43(3)
2.42(3)
1.51(3)
1.46(3)
1.74(3)
1.67(4)
1.66(3)
1.64(4)
1.57(3)
1.63(3)
1.72(4)
1.72(4)
1.60(4)
1.65(3)
2.121(7)
2.114(7)
2.078(8)
2.075(8)
2.479(8)
2.478(9)
2.333(11)
2.332(10)
2.287(9)
2.313(10)
2.459(11)
2.469(11)
1.517(13)
1.501(12)
1.724(14)
1.738(14)
1.60(2)
1.593(14)
1.600(14)
1.628(14)
1.85(2)
1.83(2)
1.613(13)
1.623(14)
M-C2′
M-C3
M-C3′
M-C4
M-C4′
M-B5
M-B5′
M-B6
M-B6′
M-B7
M-B7′
C2-C4
C2′-C4′
C4-B7
C4′-B7′
B7-C3
B7′-C3′
C3-B6
C3′-B6′
B6-B5
B6′-B5′
B5-C2
B5′-C2′
F igu r e 5. ORTEP drawing of the structure of commo-Os-
(2-Me-closo-1,2,3,4-OsC3B7H9)2 (6).
tained by refluxing a mixture of 7 and Cr(CO)6 in the
mixed 10:1 dibutyl ether/THF solvent system which has
been employed in the synthesis of (η6-C6H6)Cr(CO)3.19,20
1-(η5-C5H5)-2-Ph-closo-1,2,3,4-FeC3B7H9
+
7
Cr(CO)6 f
1-(η5-C5H5)-2-[(η6-C6H5)Cr(CO)3]-
+
closo-1,2,3,4-FeC3B7H9
9
3CO (8)
Consistent with the withdrawing nature of the Cr-
(CO)3 group coordinated to the cage phenyl substituent,
the 11B NMR spectrum of 9 is nearly identical to that
of 7, but with the peak positions shifted slightly down-
1
field relative to those in 7. In the H NMR spectrum,
F igu r e 6. ORTEP drawing of the structure of commo-Os-
(4′-Me-closo-1′,2′,3′,4′-OsC3B7H 9)(2-Me-closo-1,2,3,4-
OsC3B7H9) (5).
the arene protons of 9 resonate at higher field than
those in 7 and fall into the normal range observed in
other (η6-arene)Cr(CO)3 complexes.21
As shown in Figure 7, a crystallographic determina-
tion of 9 showed that there are two independent
molecules in the unit cell, with the two molecules
differing in their relative orientations of the Cr(CO)3
group with respect to the phenyl ring. Unsubstituted
(η6-arene)Cr(CO)3 complexes have been found to exhibit
two different arene/carbonyl conformations, where the
carbonyl groups are oriented in the eclipsed or staggered
forms.21a,22 In the case of monosubstituted arene com-
plexes (η6-RC6H5)Cr(CO)3, the eclipsed conformation can
occur in either the syn or anti orientations. The confor-
mations of the (-η6-C6H5)Cr(CO)3 fragments found in the
of the two cages of complex 5 are reasonably parallel
(dihedral angle 6(3)°), those in 4 (dihedral angle 17.1-
(2)°) and 6 (dihedral angle 15.8(8)°) are not and are
tilted away from each other on the C2-Me side of the
cages. Unlike in the vanadatricarbaborane complexes,
the two cages in 4, 6, and 5 are not aligned ∼90° to one
another: 4, 50.48(7)°; 6, 49.8(2)°; and 5, 57.6(5)° (as
measured by the dihedral angle between the C2-C3-
B8-B9 and C2′-C3′-B8′-B9′ planes).
As noted earlier, the use of the 6-Ph-nido-5,6,9-
-
C3B7H9 anion has a number of advantages over the
6-Me-nido-5,6,9-C3B7H9- anion in terms of both higher
selectivity and yield of metallatricarbadecaboranyl prod-
ucts. The introduction of the phenyl substituent also
provides a new reactive site for further modification of
a complex. Indeed, as shown in eq 8, it was found that
the phenyl-coordinated complex 1-(η5-C5H5)-2-[(η6-C6H5)-
Cr(CO)3]-closo-1,2,3,4-FeC3B7H9 (9) was readily ob-
(19) Top, S.; J aouen, G. J . Organomet. Chem. 1979, 182, 381-392.
(20) Mahaffy, C. A. L.; Pauson, P. L. Inorg. Synth. 1979, 19, 154-
158.
(21) (a) Solladie-Cavallo, A. Polyhedron 1985, 6, 901-927. (b) Price,
J . T.; Sorensen, T. S. Can. J . Chem. 1968, 46, 515-522. (c) Emanuel,
R. V.; Randall, E. W. J . Chem. Soc. (A) 1969, 3002-3006.
(22) Muetterties, E. L.; Bleeke, J . R.; Wucherer, E. J .; Albright, T.
A. Chem. Rev. 1982, 82, 499-525.

5086 Organometallics, Vol. 21, No. 23, 2002
Ramachandran et al.
F igu r e 8. Expanded views of the anti-eclipsed and stag-
gered conformations of the (-η6-C6H5)Cr(CO)3 fragments of
the two independent molecules in the crystal structure of
1-(η5-C5H5)-2-[(η6-C6H5)Cr(CO)3]-closo-1,2,3,4-FeC3B7H9 (9).
Selected distances (Å) and angles (deg) for (-η6-C6H5)Cr-
(CO)3 fragments, structure A (anti-eclipsed): Cr-C18
1.830(6); Cr-C20 1.838(6); Cr-C22 1.830(6); C18-O19
1.162(6); C20-O21 1.158(7); C22-O23 1.166(6); C12-C13
1.415(7); C13-C14 1.415(7); C14-C15 1.397(11); C15-C16
1.389(11); C16-C17 1.415(8); C17-C12 1.412(7); Cr-ring
centroid 1.7074(7); C18-Cr-C22 88.5(2); C18-Cr-C20
88.3(3); C20-Cr-C22 88.3(2); structure B (staggered):
Cr′-C18′ 1.840(5); Cr′-C20′ 1.827(5); Cr′-C22′ 1.834(5);
C18′-O19′ 1.167(6); C20′-O21′ 1.166(6); C22′-O23′ 1.166-
(6); C12′-C13′ 1.436(6); C13′-C14′ 1.406(6); C14′-C15′
1.412(7); C15′-C16′ 1.386(7); C16′-C17′ 1.415(7); C17′-
C12′ 1.405(6); Cr′-ring centroid 1.7169(7); C18′-Cr′-C22′
90.8(2); C18′-Cr′-C20′ 88.4(2); C20′-Cr′-C22′ 86.6(2).
F igu r e 7. ORTEP drawings of the structures of the two
independent molecules in the crystal structure of 1-(η5-
C5H5)-2-[(η6-C6H5)Cr(CO)3]-closo-1,2,3,4-FeC3B7H9 (9).
two molecules of complex 9 are shown in Figure 8, where
it can be seen that molecule A has the anti conforma-
tion, in which the Cr-CO bonds overlap with the
phenyl-carbons at the ortho and para positions, while
in molecule B, the unit has adopted a staggered
conformation. The staggered structure adopted by mol-
ecule B is relatively uncommon for monosubstituted
arenes, but has, in fact, been observed in another
polyborane complex, nido-2,3-[(CO)3Cr(η6-C6H5)CH2]2-
2,3-C2B4H6.23
The intracage distances in 9 (Table 3) are quite
similar to those found in 7. Likewise, the bond lengths
and angles observed in the (-η6-C6H5)Cr(CO)3 fragments
(Figure 8 caption), as well as the observed CtO stretch-
ing frequencies (1965, 1894, 1872 cm-1), are consistent
with the values found in other (η6-RC6H5)Cr(CO)3
complexes.21a,22
compositions resulting from the association of 1 equiv
of the tert-butyl isocyanide.
1-(η5-C5Me5)-2-Me-closo-1,2,3,4-RuC3B7H9
+
3
CNBut h
8-(η5-C5Me5)-8-(CNBut)-9-Me-nido-
(9)
8,7,9,10-RuC3B7H9
10
1-(η5-C5H5)-2-Ph-closo-1,2,3,4-FeC3B7H9
Rever sible Ca ge-Slip p a ge Rea ction s. As shown in
eqs 9 and 10, addition of excess tert-butyl isocyanide to
glyme solutions of either 1-(η5-C5Me5)-2-Me-closo-1,2,3,4-
RuC3B7H9 (3) (reddish-orange) or 1-(η5-C5H5)-2-Ph-closo-
1,2,3,4-FeC3B7H9 (7) (blue) resulted in an immediate
color change characteristic of the formation of the 8-(η5-
C5Me5)-8-(CNBut)-9-Me-nido-8,7,9,10-RuC3B7H9 (10) (yel-
low) and 8-(η5-C5H5)-8-(CNBut)-9-Ph-nido-8,7,9,10-
FeC3B7H9 (11) (brownish-red) products, respectively.
Crystallization from the reaction solutions gave 97% and
62% isolated yields, respectively, of pure materials.
Elemental analyses are consistent with the indicated
+
7
CNBut h
8-(η5-C5H5)-8-(CNBut)-9-Ph-nido-8,7,9,10-FeC3B7H9
11
(10)
These reactions are reversible. Heating a toluene
solution of 10 at reflux under flowing N2 for 20 min
resulted in the quantitative formation of 3, while simply
dissolving pure 11 in glyme resulted in the formation
of an equilibrium mixture of 7 and 11. Heating the
solution to reflux under flowing N2 resulted in complete
conversion to 7.
(23) Spencer, J . T.; Pourian, M. R.; Butcher, R. Y.; Sinn, E.; Grimes,
R. N. Organometallics 1987, 6, 335-343.

Metallatricarbadecaboranyl Analogues
Organometallics, Vol. 21, No. 23, 2002 5087
Ta ble 5. In tr a m olecu la r Dista n ces (Å) in
Com p ou n d s 10 a n d 11 (M ) Ru for 10 a n d F e for
11)
bond
10
11
M-C9
2.204(6)
2.218(5)
2.246(5)
2.273(6)
3.117(6)
3.152(7)
1.871(3)
1.632(8)
1.875(10)
1.605(9)
1.588(9)
1.639(10)
1.541(8)
2.102(8)
2.114(8)
2.175(9)
2.191(9)
3.020(8)
3.051(10)
1.736(1)
1.575(12)
1.861(13)
1.585(12)
1.606(12)
1.656(12)
1.537(11)
M-C7
M-B4
M-B3
M-C10
M-B11
M-Cp/Cp*
C9-B4
B4-B3
B3-C7
C7-B11
B11-C10
C10-C9
F igu r e 9. ORTEP drawing of the structure of 8-(η5-C5-
Me5)-8-(CNBut)-9-Me-nido-8,7,9,10-RuC3B7H9 (10).
F igu r e 11. Comparison of structures and bonding modes
of the tricarbadecaborane and cyclopentadienide mono-
anions.
B8-B9-C3 atoms were coplanar, but in 10 and 11 the
metals lie significantly out of the plane of the other four
atoms, so that the dihedral angles between the C7-M-
C9 and C7-B2-B5-C9 planes in 10 and 11 are 36.8-
(1)° and 36.3(3)°, respectively.
F igu r e 10. ORTEP drawing of the structure of 8-(η5-
C5H5)-8-(CNBut)-9-Ph-nido-8,7,9,10-FeC3B7H9 (11).
As we have previously discussed,3e,24 the change from
the η6- to η4-coordination mode corresponds to a conver-
sion of the tricarbadecaboranyl ligand from a six- to a
four-electron donor. As illustrated in Figure 11, an η4-
tricarbadecaboranyl ligand could therefore be considered
The metals in 3, 7, and 8, as in ruthenocene and
ferrocene, have formal 18-electron counts. Thus, unless
there is a change in the donor properties of either the
cyclopentadienyl or tricarbadecaboranyl ligands, the
metal coordination of a two-electron isocyanide ligand
would result in the formation of a 20-electron complex.
As shown in the ORTEP drawings in Figures 9 and 10,
crystallographic studies of 10 and 11 demonstrated that
upon isocyanide addition, the cyclopentadienyl rings
remain symmetrically bonded to the metals with only
a slight increase in the metal to ring-centroid distances
in 10 (1.871(3) Å) and 11 (1.736(1) Å) relative to their
values in 3 (1.829(2) Å) and 7 (1.695(3) Å), respectively
(Table 5). However, the coordination mode of the tri-
carbadecaboranyl ligand in 10 and 11 has changed from
η6 to η4. Thus, in 10 and 11, the ruthenium and iron
atoms are no longer centered over the six-membered
face, but instead, the metals have slipped to one side of
the cage. The metals are now centered above the C7-
B3-B4-C9 face with the bond lengths between the
metal and the four facial atoms being similar. Nonbond-
ing distances (>3.0 Å) are found between the metals and
the C10 and B11 cage atoms. In 7 and 8, the M-C2-
the electronic analogue of a metal-coordinated η3-C3H5
1-
allyl or a “slipped” η3-C5H51- ligand. Thus, the net result
of the addition of the two-electron isocyanide ligand to
complexes 3 and 7 is to convert the tricarbadecaboranyl
ligands to their η4-coordination modes, reducing their
electron donation to the metals to only four electrons
and thereby preserving the metal’s favorable 18-electron
count.25 From a skeletal-electron counting point of
view,17 this process simply corresponds to a cage-
opening of the metallatricarbadecaboranyl fragment
brought about by the addition of two electrons to the
(24) Weinmann, W.; Pritzkow, H.; Siebert, W.; Sneddon, L. G. Chem.
Ber./ Recl. 1997, 130, 329-333.
(25) Siebert has also shown that the diborolyl rings in the formal
16-electron complexes (η5-C5Me5)Ru(R3′C3B2R2) and (η5-C5H5)Fe-
(R3′C3B2R2) reversibly change their degree of folding upon the associa-
tion/dissociation reactions of the complexes with tert-butyl isocyanide
to form the 18-electron (η5-C5Me5)Ru(CNBut)(R3′C3B2R2) and (η5-C5H5)-
Fe(CNBut)(R3′C3B2R2) complexes. See: (a) Hettrich, R.; Kaschke, M.;
Wadepohl, H.; Weinmann, W.; Stephan, M.; Pritzkow, H.; Siebert, W.;
Hyla-Kryspin, I.; Gleiter, R. Chem. Eur. J . 1996, 2, 487-494. (b)
Mu¨ller, T.; Kaschke, M.; Strauch, M.; Ginsberg, A.; Pritzkow, H.;
Siebert, W. Eur. J . Inorg. Chem. 1999, 1685-1692.

5088 Organometallics, Vol. 21, No. 23, 2002
Ramachandran et al.
Ta ble 6. Rever sible Red ox P oten tia ls (V vs Cp 2F e0/+) of Releva n t Meta lla tr ica r ba d eca bor a n yl a n d
Cyclop en ta d ien yl Com p lexes in Non a qu eou s Solu tion s Con ta in in g 0.1 M [NBu 4][B(C6F 5)4]
compound
solvent
E1/2(0/1+)
E1/2(0/1-)
E1/2(1-/2-)
source
a
CpFe(MeC3B7H9), 12
CpFe(MeC3B7H9), 12
CpFe(PhC3B7H9), 7
CpFe(PhC3B7H9), 7
Cp*Ru(MeC3B7H9), 3
Cp*Ru(MeC3B7H9), 3
Cp*Ru(PhC3B7H9), 8
Cp*Ru(PhC3B7H9), 8
Ru(MeC3B7H9)2, 4
Os(MeC3B7H9)2, 6
Cp2Fe
CH2Cl2
THF
CH2Cl2
THF
CH2Cl2
THF
CH2Cl2
THF
CH2Cl2
THF
THF
CH2Cl2
THFa
CH2Cl2
THFa
0.39
ref 3g
ref 3g
-1.74
-1.64
-2.32
0.43
0.52
0.57
this work
this work
this work
this work
this work
this work
this work
this work
ref 32c
-2.79
-2.7 (irrev)b
-2.18
-1.33
-1.37
-3.4
-2.56
-1.5
-1.52
1.28
1.25 (irrev)b
0
0.41
Cp2Ru
Cp2Ru
Cp2Os
Cp2Os
this work, ref 33e
ref 34
-3.9d
-3.9d
0.36
ref 33c
ref 34
e
a
b
Supporting electrolyte was 0.1 M [NBu4][PF6]. For chemically irreversible systems, E1/2 is estimated from Ep at CV scan rate of 0.1
V/s. c Reduction of ferrocene at T ) 228 K. Value estimated from reduced temperature data in ref 32. e In experiments involving
d
[NBu4][B(C6H3(CF3)2)4] as supporting electrolyte, ref 33 reports Cp2Ru0/+ as 0.56 V and Cp2Os0/+ as 0.36 V vs ferrocene.
closo-M(R)C3B7H9 cage (24 skeletal electrons) frame-
works of 3 and 7 to form the nido-M(R)C3B7H9 cage (26
skeletal electrons) structures of 10 and 11.
No reaction was observed between tert-butylisocya-
nide and the commo-complex 4 (eq 11). Lack of reaction
probably results from the fact that, as can be seen in
the structure in Figure 4, the two tricarbadecaborane
ligands in 4 are oriented in such a fashion that they
wrap around the ruthenium and protect it from attack
by the tert-butylisocyanide.
ment further suggests that metallatricarbadecaboranyl
complexes may exhibit even greater reactivities than
their cyclopentadienyl counterparts for many transfor-
mations requiring the generation of a coordinatively
unsaturated metal center.
Electr och em ica l Stu d ies. When compared with
measured or estimated redox potentials of metallocene
analogues, the redox reactions of compounds 3, 4, 6, 7,
and 8 clearly show a tendency toward the thermody-
namic stabilization of metals in lower oxidation states.
Although this property has been noted previously,3g the
present data allow quantification of the tricarbadecabo-
ranyl electronic effect relative to that of the Cp ligand.
Before discussing that however, we first summarize
aspects of the chemical and electrochemical reversibili-
ties of the redox reactions.
All five of the electrochemically investigated com-
pounds give rise to three diffusion-controlled redox
processes comprised of one oxidation and two reductions
(Table 6). Each process has one-electron stoichiometry,
as determined indirectly by comparison of their CV peak
heights and ∆Ep values, and directly by coulometry (vide
infra). These electron-transfer reactions generally ap-
proach Nernstian behavior,27 implying relatively rapid
heterogeneous electron-transfer reactions and allowing
us to write eq 13 as a description of 4 and its analogues.
Exceptions to completely reversible behavior will be
discussed.
commo-Ru-(2-Me-closo-1,2,3,4-RuC3B7H9)2
+
4
CNBut f No Reaction (11)
Although not observed for ferrocene and ruthenocene,
reversible ring-slippage from η5 to η3 has been proposed,
as shown in the well-studied example6d,e in eq 12, to be
a key step in the substitution reactions of numerous
cyclopentadienyl complexes6 and some dicarbaboranyl
complexes.26
As discussed above for the tricarbadecaboranyl com-
plexes, cyclopentadienyl η5 to η3 ring-slippage both
provides an open coordination site for the incoming
ligand and avoids the formation of an unfavorable 20-
electron intermediate, thus providing a low-energy
pathway for the substitution reaction. Similar cyclo-
pentadienyl ring-slippages are thought to be critical
steps in many other important stoichiometric and
catalytic organometallic reactions.6 The η6 to η4 cage-
slippage reaction reported herein not only further
illustrates the similarities of the cyclopentadienyl and
tricarbadecaboranyl ligands but also demonstrates that
tricarbadecaboranyl cage-slippage is preferred over η5
to η3 cyclopentadienyl ring-slippage in these complexes.
The facile nature of the tricarbadecaboranyl rearrange-
-
-
-
4
+ y-e z 4 y+e z 4- y+e z 42-
(13)
Bulk electrolyses carried out on the oxidation of 3 at
room temperature and on the first reduction of 4 at 233
K confirmed the one-electron stoichiometries and showed
that the products (3+ and 4-, respectively) are reason-
ably persistent under these conditions. Regenerative
electrolyses (e.g., “back”-oxidation of electrochemically
generated 4-) gave back the starting materials in 90%
yield for 4 and 65% yield for 3.
Variations in reversibility were primarily found in the
cathodic reactions of these compounds. As demonstrated
in Figure 12A, the CV response for the mixed-sandwich
compound 8 reveals that the dianion 82- undergoes a
(26) See for example: Shen, J . K.; Zhang, S.; Basolo, F.; J ohnson,
S. E.; Hawthorne, M. F. Inorg. Chim. Acta 1995, 235, 89-97.
(27) Except where noted, values of |Epa - Epc| were very similar to
those observed for the Cp2Fe+/0 couple under similar conditions.

Metallatricarbadecaboranyl Analogues
Organometallics, Vol. 21, No. 23, 2002 5089
Ta ble 7. E1/2(0/1+) a n d E1/2(0/1-) Sh ifts (V) for
Tr ica r ba d eca bor a n yl Com p lexes Com p a r ed to
Id en tica l Cou p les of Meta llocen e An a logu es
compound ∆E1/2 (ox)a shift per ligb ∆E1/2 (red)c excess shiftd
12
7
3
8
4
0.39
0.43
0.41
0.46
0.87
0.39
0.43
0.41
0.46
0.435
1.66
1.76
1.88
2.02
2.57
2.53
1.22
1.32
1.44
1.58
1.69
1.65
6
∼1e
∼0.5e
a
E1/2(0/1+) for compound minus E1/2(0/1+) for analogous Cp2M.
b
c
lig ) RC3B7H9. E1/2(0/1-) for compound minus E1/2(0/1-) for
d
analogous Cp2M. ∆E1/2 (red) minus [m × (0.044 V)], where m is
number of RC3B7H9 ligands. e Estimated from peak potential of
irreversible oxidation of 6 in THF.
replacement of a Cp by RC3B7H9 is obtained by com-
parison of the ∆E1/2(0/1+) values in Table 6, where
∆E1/2(0/1+) ) [E1/2(0/1+) of (RC3B7H9)mCp2-mM) - E1/2
-
(0/1+) of (Cp2M)], m ) 1, 2. In each case, the neutral
compound is an 18-electron system which is not ex-
pected to undergo significant structural changes upon
one-electron oxidation. As shown in Table 7, the ∆E1/2
-
(0/1+) value for six RC3B7H9-containing compounds is
0.44 ( 0.04 V for each substitution of a Cp group by an
RC3B7H9 group.29 We therefore use the value of 0.44 V
as the comparative inductive effect of the RC3B7H9
group in the iron-group complexes.
For comparison, a comparative electronic effect of ca.
-0.25 V was obtained for the dicarbollide ligand,
[C2B9H11]
2-, when compared to Cp-,18a,30 the negative
sign being consistent in that case with the stabilization
of higher oxidation states by the more negatively
charged [C2B9H11]
2- ligand.18a Significantly, the -0.25
V dicarbollide comparative inductive effect successfully
accounted for trends in both the oxidations and reduc-
tions of neutral compounds,30 in contrast to the present
findings for tricarbadecaboranyl complexes. The ad-
ditional stabilization for the first reductions of the
tricarbadecaboranyl complexes is quantified by sub-
tracting the amount (0.44 × m)volt from the measured
shifts in E1/2(0/1-), where m is the number of RC3B7H9
ligands in the compound (see Table 7). For example,
compared to the reduction of ruthenocene (Cp2Ru0/1-),
the E1/2 of [(MeC3B7H9)2Ru]0/1-, 40/1-, is more positive
by 2.57 V. About 0.88 V of this value is accounted for
by the replacement of two Cp rings in Cp2Ru by
RC3B7H9 ligands in 4. This leaves an additional stabi-
lization (excess shift) of about 1.69 V, which must arise
from factors other than the comparative inductive effect.
Using this approach, one finds an additional stabiliza-
tion of 1.2-1.3 V for the two Fe compounds and 1.4-
1.7 V for the Ru and Os compounds (Table 7). Further-
more, these data suggest that the great bulk of the
additional stabilization is found in substitution of the
first Cp ligand by a RC3B7H9 group.
F igu r e 12. (A) Cyclic voltammogram of 2 mM 1-(η5-C5-
Me5)-2-Ph-closo-1,2,3,4-RuC3B7H9 (8) in CH2Cl2/0.1 M [NBu4]-
[B(C6F5)4] at d ) 2 mm glassy carbon electrode. Room
temperature, 0.2 V/s. (B) Cyclic voltammogram of 1 mM
commo-Ru-(2-Me-closo-1,2,3,4-RuC3B7H9)2 (4) in CH2Cl2/
0.1M [NBu4][B(C6F5)4] at d ) 2 mm glassy carbon electrode.
Room temperature, 0.2 V/s.
follow-up reaction to produce a product with an oxida-
tion wave at ca. -0.65 V. A similar result was found
for the second reduction of 3. The only indication of
electrochemical quasi-reversibility (i.e., a slow hetero-
geneous charge transfer) was observed in the second
reduction of the Ru bis-caged system 41-/2- (see second
cathodic wave in Figure 12B). The 41-/2- process exhib-
its effects from changes in solvent, temperature, and
scan rate, details of which are under investigation.
Perusal of the E1/2 values in Table 6 confirms that each
electron-transfer process of a mono- or bis-cage com-
pound is shifted positive compared to the equivalent
process of its metallocene analogue.28 It is readily
apparent, however, that the positive shifts for the first
reduction of the neutral compounds (i.e., the 0/1-
couple) are much greater than those seen for the
oxidation of the same compound (i.e., the 0/1+ couple).
This shows that the potential shifts of the cathodic
reactions cannot be ascribed to an electronic effect
analogous, for example, to the inductive effect observed
in the replacement of a C5H5 ligand by a C5Me5 ligand.
A measure of the comparative inductive effect upon
Among the chemical factors that might be considered
as contributing to the additional stabilization are (i)
medium effects such as solvation and ion-pairing; (ii)
changes in metal configurations or spin states, and (iii)
structural changes that are coupled to the electron-
transfer reactions. Given the results discussed above
(29) This value was adjusted by 0.3 V for compounds 3 and 8, which
contain Cp* groups.
(28) See Experimental Section for summary of metallocene poten-
tials.
(30) Geiger, W. E. In Metal Interactions with Boron Clusters; Grimes,
R. N., Ed.; Plenum Press: New York, 1982; p 239.

5090 Organometallics, Vol. 21, No. 23, 2002
Ramachandran et al.
demonstrating that the RC3B7H9 ligand can change
from a six-electron, η6- to a four-electron, η4-coordination
mode upon the addition of a two-electron donor (see
compounds 10 and 11), a redox-induced structural
change (i.e., possibility iii, specifically a slippage to lower
than η6-coordination) must be considered to be likely
in the reduced tricarbadecaboranyl-containing com-
plexes.
Much of the literature in which electrochemistry has
been used to probe η6/ η4 and η5/ η3 bonding changes has
been recently summarized.31 These papers emphasize
that heterogeneous electron-transfer rates are likely to
be less intricate probes of structural reorganizations
than are E1/2 effects. More detailed mechanistic studies,
including measurement of ks values, are therefore
planned for these and related ηn-RC3B7H9 compounds.
It should also be noted that the overall ligand-induced
stabilization of reduced forms of metal-tricarbadecabo-
ranyl complexes allows detection of formal metal oxida-
tion states which seem to have no precedent in their
metallocene analogues, namely, formal M0 complexes,
M ) Fe, Ru, Os, in the dianions of compounds 3, 4, 6,
7, and 8.
Ack n ow led gm en t. The National Science Founda-
tion supported the research carried out at the Universi-
ties of Pennsylvania (CHE 98-14252) and Vermont
(CHE 97-05763).
(31) (a) Stoll, M. E.; Baelanzoni, P.; Calhorda, M. J .; Drew, M. G.
B.; Felix, V.; Geiger, W. E.; Gamelas, C. A.; Gonzalves, I. S.; Roma˜o,
C. C.; Veiros, L. F. J . Am. Chem. Soc. 2001, 123, 10595-10606. (b)
Geiger, W. E. Acc. Chem. Res. 1995, 28, 351-357.
(32) Ito, N.; Saji, T.; Aoyagui, S. J . Organomet. Chem. 1983, 247,
301-305.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data for structure determinations of 4, 5, 6, 7, 8, 9,
10, and 11 (CIF). This material is available free of charge via
the Internet at http://pubs.acs.org.
(33) Hill, M. G.; Lamanna, W. G.; Mann, K. R. Inorg. Chem. 1991,
30, 4687-4690.
(34) Strelets, V. V. Coord. Chem. Rev. 1992, 114, 1-60.
OM020757U