Chemistry on a metallathiaborane cluster Part 4: Reactions of 11-vertex rhodathiaboranes with bidentate phosphines and their subsequent rearrangements

Article abstract of DOI:10.1016/S0022-328X(02)01329-3

The phosphine ligands on of the type [8,8-{η²-(CH₂)_n(PPh₂)₂}-8-{η¹-(CH₂) _n(PPh₂)₂}-nido-8,7-RhSB₉H₁₀] (II), in the case of

Full text of DOI:10.1016/S0022-328X(02)01329-3

Journal of Organometallic Chemistry 657 (2002) 40ꢁ47
/
www.elsevier.com/locate/jorganchem
Chemistry on a metallathiaborane cluster Part 4ꢀ: reactions of 11-
vertex rhodathiaboranes with bidentate phosphines and their
subsequent rearrangements
Oleg Volkov 1, Ramon Macias, Nigam P. Rath, Lawrence Barton *
Department of Chemistry, Center for Molecular Electronics, University of Missouri-St. Louis, St. Louis, MO 63121, USA
Received 3 September 2001; accepted 15 February 2002
Abstract
The phosphine ligands on [8,8-(PPh3)2-nido-8,7-RhSB9H10] (I) may be replaced by the bidentate phosphines, (CH2)n(PPh2)2, to
form species of the type [8,8-{h2-(CH2)n(PPh2)2}-8-{h1-(CH2)n(PPh2)2}-nido-8,7-RhSB9H10] (II), in the case of dppm (nꢀ
/1) and of
the type [8,8-{h2-(CH2)n(PPh2)2}-nido-8,7-RhSB9H10] (III), in the case of dppe (nꢀ
/
2) and dppp (nꢀ/3). It was originally thought
that the chemistry followed by dppm differed substantially but predictably from that of dppe and dppp. In fact the reactions are
more complex and mixed-ligand systems are accessible which provide insight into these reactions and rearrangement mechanisms.
Reactions involving the transfer of a metal bonded bidentate phosphine to the cage are observed for dppe and dppp but only for
dppm can a species of the type [1-PPh3-{1,3-(m-dppm)}-closo-1,2-RhSB9H8] (IV), which may be the key to the identification of the
intermediate in these reactions, be observed. We also observed the ultimate product in this series of reactions which appears to be a
mixture of isomers, [3-(h1-dppm)-1,1-(h2-dppm)-closo-1,2-RhSB9H8] (V) and [1-(h1-dppm)-1,3-(m-dppm)-closo-1,2-RhSB9H8] (VI).
Additional ligand exchange reactions can be effected so that such species as [3-(h1-dppm)-1,1-(h2-dppe)-closo-1,2-RhSB9H8] (VII)
may be isolated from IV. From these results, suggestions for possible reaction pathways are presented. # 2002 Published by
Elsevier Science B.V.
Keywords: Boranes; Metallaboranes; Thiaboranes; Rhodium; NMR spectroscopy; X-ray diffraction
1. Introduction
features associated with compound I. Structural and
calculational studies have suggested the presence of two
unusual ortho-CH. . .Rh agostic interactions [5] which, it
is suggested, account for its stability. I undergoes
interesting fluxional behavior in solution and is reactive
towards both electrophiles and nucleophiles [3]. In
particular, the reactions of I with Lewis bases, L, (where
The related pair of metallaheteroboranes, [9,9-
(PPh3)2-nido-9,7,8-RhC2B8H11] (VIII) [2] and [8,8-
(PPh3)2-nido-8,7-RhSB9H10] (I) [3], compounds which
are formally isoelectronic, are two electrons short of the
number notionally required to satisfy the polyhedral
skeletal electron pair theory [4]. The latter rhodathia-
borane, I, is stable, easily prepared, and had been the
more extensively studied of the two prior to our
LꢀCO, PMe2Ph or CH3CN) result in either addition of
/
the ligand, L, to the metal center or addition and
substitution, giving rise to species such as [8-L-8,8-
(PPh3)2-nido-8,7-RhSB9H10] (where LꢀCO [3b] or
/
previous work on this system [3,5ꢁ8]. There are novel
/
CH3CN [4]) and [8,8,8-(PMe2Ph)3-nido-8,7-RhSB9H10]
[6]. Refluxing [8-(CO)-8,8-(PPh3)2-nido-8,7-RhSB9H10]
in benzene leads to the formation of [1-(CO)-1,3-
(PPh3)2-closo-1,2-RhSB9H8], which when treated with
an excess of PMe2Ph, also in refluxing benzene, affords
ꢀ See Ref. [1].
* Corresponding author. Fax: ꢂ
E-mail address: lbarton@umsl.edu (L. Barton).
/1-314-516-5342.
1
[1-(CO)-1-(PMe2Ph)-3-L-closo-1,2-RhSB9H8]
(where
Permanent address: Institute of Inorganic Chemistry, Russian
Academy of Sciences, 630090, Novosibirsk, Russia.
LꢀPMe2Ph or PPh3) [3b]. Other reaction patterns
/
0022-328X/02/$ - see front matter # 2002 Published by Elsevier Science B.V.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 3 2 9 - 3

O. Volkov et al. / Journal of Organometallic Chemistry 657 (2002) 40ꢁ
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47
41
such as terminal hydrogen substitution at the 9-position
by an OEt group [7] or metal incorporation to form 12-
vertex bimetallic species have also been reported [3b].
Our previous work on this system described a study of
the reactions of I with the bidentate bis(diphenylpho-
2. Experimental
2.1. General
sphino)alkanes, [(CH2)n(PPh2)2], where nꢀ1, 2 and 3,
/
Solvents used were reagent grade and were dried
before use. Some reactions were carried out using a
Schlenk line, a glove box and standard techniques for
handling air-sensitive compounds [9]. [8,8-(PPh3)2-nido-
8,7-RhSB9H10] (I) was prepared according to the
literature method [3b] from the reaction between
Cs[SB9H12] [10] and [RhCl(PPh3)3] [11]. PPh3 and
dppe were obtained from Aldrich and dppm was
obtained from Strem. NMR spectroscopy was carried
out on a Bruker ARX 500 spectrometer operating at
500.1 MHz for proton, 160.5 MHz for boron-11, and at
202.5 MHz for phosphorus-31. Chemical shifts are
(abbreviated as dppm, dppe and dppp, respectively) [1b].
Some of the results are illustrated in Scheme 1. It
appeared that the reactions with dppm differed from
those with dppe and dppp. For the former, the species
[8,8-(h2-dppm)-8-(h1-dppm)-nido-8,7-RhSB9H10] (II),
which contained both mono- and bidentate-dppm
ligands on Rh, was isolated, and although other species
clearly existed in the reaction mixture, we were unable to
isolate them. Derivative chemistry at the pendant PPh2
group in II was demonstrated by the formation of [8,8-
h2-{h2-(BH3)dppm}-nido-8,7-RhSB9H10] (IX) on reac-
tion with BH3×
THF [1a] and [8,8-h2-{(m-Cl)2Ru(h6-p-
/
reported in ppm for CD2Cl2 solutions to low field
1
(high frequency) of Et2O×
/
BF3 for 11B, of SiMe4 for H
cym)Ph2PCH2PPh2}-nido-8,7-RhSB9H10] on reaction
with [Ru(h6-p-cym)Cl2]2 [1c]. With dppe or dppp, the
analogue of II is not observed but species of the type
[8,8-(h2-dppp)-nido-8,7-RhSB9H10] (III) containing a
single bidentate ligand on Rh, and one containing two
and of 85% H3PO4 for 31P. Elemental analyses were
attempted by Atlantic Microlabs Inc., Norcross, GA.
NMR spectra were run on all samples sent for mass
spectra and crystal growth was generated from NMR
samples, after spectral analysis. The samples were
evaporated to dryness and then dissolved in the appro-
priate solvent for subsequent crystallization. The mass
spectra were measured in the FAB mode on a JEOL
MStation JMS-700 spectrometer using 3-nitrobenzyl
alcohol (3-NBA).
ligands,
H10] (X) one of them on the cage, as illustrated in
[8,8-(h2-dppp)-9-(h1-dppp)-nido-8,7-RhSB9-
Scheme 1, are precursors to closo-clusters of the type
(XI)
[1,1-(h2-dppp)-3-(h1-dppp)-closo-1,2-RhSB9H8]
and more complex linked clusters [1b]. In this paper,
we report additional progress in this area.
Scheme 1.

42
O. Volkov et al. / Journal of Organometallic Chemistry 657 (2002) 40ꢁ47
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2.2. Preparation of [1-(PPh3)-{1,3-(m-dppm)}-closo-
1,2-RhSB9H8] (IV)
(Calc. intensity)}: 1019, 21.43 (14.46); 1020, 46.52
(41.61); 1021, 80.47 (80.43); 1022, 100 (100); 1023,
81.95 (74.37); 1024, 45.93 (31.18); 1025, 21.94 (9.53).
11B-NMR (160.5 MHz, CD2Cl2, 25 8C): d 36.3 (d,
[8,8-(PPh3)2-nido-8,7-RhSB9H10] (I) (53 mg, 0.069
mmol) was added to a solution of [8,8-(h2-dppm)-8-
(h1-dppm)-nido-8,7-RhSB9H10] (II) (70 mg, 0.069
mmol) in CH2Cl2 (ca. 10 ml) under N2. The reaction
mixture was stirred at room temperature (r.t.) for 3
days. After this time, the solvent was reduced in volume
and the reaction mixture was applied to the Chromato-
tron (a radial chromatograph obtained from Harrison
Research, Palo Alto, CA) using a 25 cm diameter
circular plate coated with 0.1 cm of silica gel (EM
J(P,B)ꢀ
(v br, 3B), ꢃ
NMR (202.5 MHz, CD2Cl2, 25 8C): d 60.8 (d,
J(P,Rh)ꢀ144 Hz, 2P), 4.3 (v br, 1P), ꢃ25.8 (d,
J(P,P)ꢀ
35 Hz, 1P). 1H-NMR (500 MHz, CD2Cl2,
25 8C): 7.42ꢃ6.97 (m, 40H; C6H5), 2.99 (d,
J(P,H)ꢀ10 Hz, 2H; Ph2PCH2PPh2), 2.52ꢃ2.41 (m,
2H; Ph2PC2H4PPh2), 2.16 (m, 2H;
/
122 Hz, 1B), 27.1 (d, J(H,B)ꢀ
/
79 Hz, 1B), 1.2
/
16.3 (v br, 2B), ꢃ
/
27.4 (v br, 2B). 31P{1H}-
/
/
/
d
/
/
/
2.24ꢃ
/
Ph2PC2H4PPh2). Additional 1H{11B}-NMR (500
Science) using CH2Cl2ꢁhexane (3:2) mixture as the
/
MHz, CD2Cl2, 25 8C): d 3.93 (1H, BH), 2.74 (1H,
mobile phase. A red compound was isolated and
characterized as [1-(PPh3)-{1,3-(m-dppm)}-closo-1,2-
RhSB9H8] (IV) (0.075 g, 0.084 mmol; 61%). Single
crystals of this material were obtained by slow diffusion
of EtOH into CH2Cl2 solution. Anal. Calc. for
C43H45B9P3RhS: C, 58.23; H, 5.11. Found: C, 58.33;
H, 5.17%. HR-MS (FAB with 3-NBA) m/z Calc. for
C43H45B9P3RhS: 887.2412 [M]ꢂ ; Found: 887.2432. The
observed and calculated mass envelopes for the mea-
sured masses are, {m/q, observed intensity (Calc.
intensity)}: 884, 15.5 (15.22); 885, 56.7 (43.39); 886,
75.2 (82.57); 887, 100.00 (100.00); 888, 68.5 (70.72); 889,
35.6 (26.82); 890, 13.3 (7.58). 11B-NMR (160.5 MHz,
BH), 1.99 (2H, BH), 0.59 (2H, BH), ꢃ0.03 (2H,BH).
/
2.4. Preparation of the mixture of isomers [(dppm)2-
closo-1,2-RhSB9H8] (V) and (VI)
a) A solution of [8,8-(h2-dppm)-8-(h1-dppm)-nido-8,7-
RhSB9H10] (40 mg, 0.040 mmol) in CH2Cl2 (ca. 10
ml) was stirred under N2 for 7 days at r.t. After this
time a red compound was precipitated by addition
of pentane. Recrystallization in CH2Cl2ꢁhexane
/
gave rise to the isolation of a product, characterized
as a mixture of isomers of [(dppm)2-closo-1,2-
RhSB9H8] (0.026 g, 0.026 mmol; 65%).
CD2Cl2, 25 8C): d 34.9 (d, J(P,B)ꢀ
(d, J(H,B)ꢀ179 Hz, 1B), 5.4 (v br, 1B), ꢃ
20.0 (v br, 2B), ꢃ
29.4 (v br, 2B). 31P{1H}-NMR
(202.5 MHz, CD2Cl2, 25 8C): d 47.2 (dd, J(P,Rh)ꢀ135
Hz, J(P,P)ꢀ31 Hz, 1P), 45.8 (ddd, J(P,Rh)ꢀ172 Hz,
J(P,P)ꢀ96 Hz, J(P,P)ꢀ31 Hz, 1P), 17.1 (m, 1P). H-
NMR (500 MHz, CD2Cl2, 25 8C): d 7.70ꢃ6.97 (m,
10 Hz, 2H;
/
134 Hz, 1B), 20.8
b) dppm (0.052 g, 0.135 mmol) was added to a solution
of
/
/9.2 (v br, 2B),
[1-(PPh3)-{1,3-(m-dppm)}-closo-1,2-RhSB9H8]
ꢃ
/
/
(0.078 g, 0.088 mmol) in 15 ml CH2Cl2 under N2
and the reaction mixture was stirred at r.t. After 2 h
addition of 15 ml EtOH resulted in a precipitation
of a red product, which was recrystallized from
/
/
/
1
/
/
/
CH2Cl2ꢁhexane and characterized after drying in
/
35H; C6H5), 3.71 (t, J(P,H)ꢀ
/
vacuo as a mixture of isomers of [(dppm)2-closo-1,2-
RhSB9H8] (0.068 g, 0.067 mmol; 76%). HR-MS
(FAB with 3-NBA) m/z calc. for C50H52B9P4RhS:
1009.2702 [M]ꢂ; Found: 1009.2709. The mass
envelopes for the measured masses match quite
well with those calculated from the known isotopic
abundances of the constituent elements and are as
follows: {m/q, observed intensity (Calc. intensity)}:
991, 62.6 (32.4); 992, 87.7 (72.24); 993 (100.00)
100.00; 994, 92.6 (78.76); 995, 76.2 (31.3); 996, 48.1
(7.58). Anal. Calc. for C50H52B9P4RhS: C, 59.51; H,
5.19. Found: C, 59.52; H, 5.26%. NMR spectra of
the mixture of isomers: 11B-NMR (160.5 MHz,
CD2Cl2, 25 8C): d 26.9 (br, m, PB, 2B), 14.13 (br,
Ph2PCH2PPh2). Additional H{11B}-NMR (500 MHz,
CD2Cl2, 25 8C): d 3.60 (br, 2H, BH), 2.32 (2H, BH),
0.42 (v br, 4H, BH).
1
2.3. Preparation of [3-(h1-dppm)-1,1-(h2-dppe)-closo-
1,2-RhSB9H8] (VII)
To a solution of [1-(PPh3)-{1,3-(m-dppm)}-closo-1,2-
RhSB9H8] (IV) (0.020 g, 0.023 mmol) in 5 ml CH2Cl2
was added dppe (0.013 g, 0.033 mmol) under N2. This
reaction mixture was stirred at r.t. for 1 h. A yellow
compound precipitated when EtOH was added, which
was characterized as [3-(h1-dppm)-1,1-(h2-dppe)-closo-
1,2-RhSB9H8] (VII) (0.021 g, 0.02 mmol; 87%). Crystals
suitable for X-ray analysis were grown by layering a
CH2Cl2 solution of the product with pentane. Anal.
Calc. for C51H54B9P4RhS: C, 59.87; H, 5.32. Found: C,
59.23; H, 5.36%. HR-MS (FAB with 3-NBA) m/z Calc.
2B), 9.51 (br, 2B) 6.91 (br, 2B), 2.49 (br, 3B), ꢃ
(br, 1B), ꢃ7.24 (br, 1B), ꢃ13.07 (d, J(H,B)ꢀ
Hz, 2B), 21.10 (d, J(H,B)ꢀ134 Hz, 3B).
1H{31P}-NMR (500 MHz, CD2Cl2, 25 8C): d
8.16ꢃ6.23 (m, C6H5), 3.95 (br d, J(H,H)$16 Hz,
Ph2PCH2PPh2), 3.60 (br d, J(H,H)$16 Hz,
Ph2PCH2PPh2), 3.16 (br s, Ph2PCH2PPh2), 2.89
(br d, J(H,H)$16 Hz, Ph2PCH2PPh2), 2.71 (br d,
/1.78
/
/
/
130
ꢃ
/
/
/
/
for C51H53B9P4RhS: 1022.2780 [M Ã
/
H]ꢂ; Found:
/
1022.2834. The observed and calculated mass envelopes
for the measured masses are {m/q, observed intensity
/

O. Volkov et al. / Journal of Organometallic Chemistry 657 (2002) 40ꢁ
/
47
43
J(H,H)$
(202.5 MHz, CD2Cl2, 25 8C): d 25.4{ddd(or 2
dd), J(P,Rh)ꢀ138 Hz, J(P,Rh)ꢀ141 Hz,
J(P,P)ꢀ30 Hz), 13.0 (br d, J(P,Rh)ꢀ132 Hz), ꢃ
32.2 (dd, J(P,Rh)ꢀ115 Hz), ꢃ34.7 (v br). Partial
/
16 Hz, Ph2PCH2PPh2). 31P{1H}-NMR
Table 2
˚
Selected bond distances (A) and angles (8) in [1-PPh3-{1,3-(m-dppm)}-
closo-1,2-RhSB9H8] (IV) and [3-(h1-dppm)-1,1-(h2-dppe)-closo-1,2-
RhSB9H8] (VII)
/
/
/
/
/
/
/
IV
VII
separation, see text, allowed two sets of signals to be
identified. Four major signals at: d 25.8 (dd,
˚
Bond distances (A)
Rh(1)ÃB(3)
Rh(1)ÃP(2)
Rh(1)ÃP(1)
Rh(1)ÃS(2)
Rh(1)ÃB(6)
Rh(1)ÃB(4)
Rh(1)ÃB(7)
S(2)ÃB(5)
S(2)ÃB(4)
B(3)ÃB(7)
B(3)ÃB(6)
B(4)ÃB(7)
B(5)ÃB(6)
B(3)ÃP(3)
2.078(2)
2.276(1)
2.326(1)
2.357(1)
2.380(2)
2.380(2)
2.442(2)
1.874(3)
2.001(3)
1.699(3)
1.736(4)
1.846(3)
1.850(4)
1.887(2)
2.107(3)
2.265(1)
2.260(1)
2.365(1)
2.379(4)
2.428(4)
2.364(4)
1.939(4)
1.939(4)
1.716(5)
1.717(5)
1.836(5)
1.841(5)
1.912(4)
J(P,Rh)ꢀ
J(P,Rh)ꢀ
J(P,Rh)ꢀ
34.7 (v br) were assigned to VI and a second set of
three signals at: d 44.3 (dd, J(P,Rh)ꢀ168 Hz,
133 Hz); ꢃ
/
140 Hz, J(P,P)ꢀ
146 Hz, J(P,P)ꢀ
132 Hz); ꢃ32.1 (br, d); ꢃ
/
30 Hz) and 25.1 (dd,
30 Hz); 13.0 (br d,
32.4 (br, d),ꢃ
/
/
/
/
/
/
/
J(P,P)ꢀ
/
89 Hz); 15.3 (br d, J(P,Rh)ꢀ
/
/
0.6 (v br) were assigned to V. H{11B}-NMR (500
MHz, CD3Cl, 25 8C): d 4.45 (1H, BH), 3.69 (1H,
BH), 3.50 (1H, BH), 3.15 (1H, BH), 2.84 (1H, BH),
2.17 (1H, BH), 1.93 (2H, BH).
1
Bond angles
Table 1
B(3)ÃRh(1)ÃP(2)
B(3)ÃRh(1)ÃP(1)
P(2)ÃRh(1)ÃP(1)
B(3)ÃRh(1)ÃS(2)
P(2)ÃRh(1)ÃS(2)
P(1)ÃRh(1)ÃS(2)
P(3)ÃB(3)ÃRh(1)
CH2ÃP(3)ÃB(3)
B(9)ÃB(3)ÃP(3)
B(9)ÃB(3)ÃRh(1)
P(3)ÃCH2ÃP(2)/P(4)
C(31)ÃP(2)ÃRh(1)
Rh(1)ÃP(2)ÃC(2)
Rh(1)ÃP(1)ÃC(1)
P(1)ÃC(1)ÃC(2)
87.72(6)
132.91(7)
98.598(19)
117.30(7)
129.36(2)
94.27(2)
113.88(10)
115.00(10)
84.00(3)
Crystal data and structure refinement for [1-PPh3-{1,3-(m-dppm)}-
closo-1,2-RhSB9H8] (IV)×EtOH and [1,1-(h2-dppe)-3-(h1-dppm)-clo-
so-1,2-RhSB9H8] (VII)
120.97(10)
110.88(3)
105.95(3)
136.61(18)
113.84(15)
112.8(2)
Compound nunber
IV
VII
118.54(12)
102.82(11)
123.58(16)
114.79(12)
110.59(11)
111.12(7)
Empirical formula
Formula weight
Temperature (K)
C45H51B9OP3RhS C51H54B9P4RhS
933.03
218(2)
0.71073
1023.08
223(2)
0.71073
˚
Wavelength (A)
110.3(2)
113.80(17)
Crystal system
Space group
Triclinic
¯
Triclinic
¯
ꢁ/
P
/
1
/
P
/ /
1
˚
ꢁ/
ꢁ/
ꢁ/
107.49(10)
110.39(10)
110.1(2)
a (A)
11.8312(2)
12.3952(2)
17.4196(3)
71.996(1)
84.696(1)
73.660(1)
2331.33(7)
2
10.4180(10)
14.7171(14)
16.3942(16)
82.010(7)
83.480(7)
87.340(7)
2471.9(4)
2
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
˚
V (A
2.5. X-ray diffraction [12]
ꢃ3
)
Z
Dcalc (Mg mꢃ3
)
1.329
0.548
1.375
0.554
Data sets were collected using a Bruker SMART CCD
area-detector diffractometer at ꢃ50 8C. The structures
were solved using direct methods and refined by full
Absorption coefficient
(mmꢃ1
Crystal size (mm)
/
)
0.34ꢄ0.28ꢄ0.26 0.28ꢄ0.18ꢄ0.10
960 1052
1.97ꢁ
¯
matrix least squares refinement to convergence in P1 for
/
F(000)
both IV and VII. The cage hydrogen atoms were located
and refined freely. All other hydrogen atoms were
treated using an appropriate riding model. Structural
data are given in Tables 1 and 2.
u Range for data collection 1.79ꢁ
/30.00
/26.58
(8)
Index ranges
ꢃ165h 516,
ꢃ165k 517,
ꢃ245l 524
47 315
ꢃ125h 513,
ꢃ185k 518,
ꢃ205l 520
43 199
Reflections collected
Independent reflections
13 088
10 171
[Rintꢀ0.021] [Rintꢀ0.049]
0.8705 and 0.8355 0.9467 and 0.8604
3. Results and discussion
Max/min transmission
Data/restraints/parameters 13 088/46/592
Goodness-of-fit on F2
1.075
10 171/0/627
1.187
0.0527
Treatment of [8,8-(PPh3)2-nido-8,7-RhSB9H10] (I)
with a three-fold excess of dppm followed by chromato-
graphic workup allows the isolation of the yellow species
[8,8-(h2-dppm)-8-(h1-dppm)-nido-8,7-RhSB9H10] (II) in
ca. 50% yields. A minor impurity, always obtained in
this reaction, is a red species (described later as V and
VI) that eluded characterization [13]. It was not until we
Final R indices [I ꢀ2s(I)] 0.0368
R1
WR2 (all data)
0.1025
0.0868
Largest difference peak and 1.038 and ꢃ0.427 0.526 and ꢃ0.498
ꢃ3
˚
hole (e A
)

44
O. Volkov et al. / Journal of Organometallic Chemistry 657 (2002) 40ꢁ47
/
1H{11B} spectrum exhibits three resonances assigned to
BH nuclei in 2:2:4 ratio reflecting some overlap.
A close examination of the structure of IV reveals that
it is not a simple 11-vertex closo-structure. There is no
Rh(1)Ã
/
B(5) bond in the species. This renders an open
four-sided ‘face’ to the molecule reminiscent of the series
of iso-nido 11-vertex clusters which have been discov-
ered in recent years [14]. The difference between our
observed structure of IV and that for an idealized 11-
vertex cluster is illustrated in Scheme 2. The cage is quite
distorted in the vicinity of the open face S(2)Ã
B(6)ÃB(5). The non-bonded distance Rh(1)Ã
2.678(3) A, whereas if it were bonding it would be of
/
Rh(1)Ã
/
/
/B(5) is
˚
˚
the order 2.4ꢁ
described below. The stretching of the Rh(1)Ã
B(6) distance to
˚
3.178(3) A, whereas in VII, a normal octadecahedron,
˚
the distance is longer at 3.366(4) A. The confirmation of
/
2.5 A, as observed for compound VII
/B(5) axis
Fig. 1. A view of the molecular structure of IV with 50% thermal
ellipsoids. Only the ipso-carbon atoms on the phenyl groups and the
cage H atoms are included to aid clarity. Also missing is a molecule of
ethanol.
is reflected in the shortening of the S(2)Ã
/
IV as an iso-nido-species with an open square face, adds
to the number of examples of what may be considered
structurally to be ‘frozen’ intermediates or transition
states proposed [15] for the known fluxional process
which renders all the vertices in the closed 11-vertex
borane [B11H11]2ꢃ equivalent on the NMR time-scale
[16]. The process is thought to involve diamond-square-
diamond rearrangements and the square-faced species is
the transition state for such processes. Since the NMR
spectra of IV do not provide evidence for the structural
distortion in that they indicate a plane of symmetry in
the RhSB9 cage, the species must be fluxional in
solution. In previously described closo-species, such as
[1,1-(h2-dppe)-3-(h1-dppe)-closo-1,2-RhSB9H8] [8] the
plane including the two P atoms of the bidentate ligand
on Rh, and the Rh atom, is essentially perpendicular to
performed some ligand exchange experiments that clues
to the identity of the red compound became clearer to
us.
Stirring equimolar mixtures of [8,8-(PPh3)2-nido-8,7-
RhSB9H10] (I) and [8,8-(h2-dppm)-8-(h1-dppm)-nido-
8,7-RhSB9H10] (II) for 3 days in CH2Cl2 allowed the
isolation of a red species, identified as [1-(PPh3){1,3-(m-
dppm)}-closo-1,2-RhSB9H8] (IV). NMR spectra, and
elemental analysis are consistent with the formulation
and high-resolution mass spectrometry confirms it with
a divergence from the calculated value of 2.2 ppm.
Crystals suitable for an X-ray diffraction study were
grown from ethanolꢁCH2Cl2 and the structure is given
/
in Fig. 1. It consists of a closo-1,2-RhSB9 11-vertex
cluster with a PPh3 ligand on Rh and a dppm ligand
bridging the Rh atom and the closest B atom at position
3. Presumably, during the ligand exchange process
between the nido-species I and II, loss of H2 also occurs
resulting in the formation of closo-species IV. The 31P-
NMR spectrum exhibits the expected three signals.
These are a doublet of doublets of doublets at 45.8
ppm assigned to the P atom from dppm on Rh, a
doublet of doublets at 47.2 ppm assigned to the PPh3
group on Rh and a single broad resonance assigned to
the P atom of the dppm ligand bounded to a cage boron
atom. The 11B spectrum exhibits the 1:1:1:2:2:2 pattern
expected for the symmetrical closo-RhSB9 cage and the
the plane described by the atoms S(2)Ã
/
Rh(1)Ã
/
B(3). In
the closo-species IV, however, the system is constrained
by the bridging dppm ligand and thus the angle between
the planes B(3)Ã
60.38, suggesting substantial strain in the molecule. Also
the angle between the planes P(3)ÃB(3)ÃRh(1) and
B(3) is 146.78, whereas if the dppm ligand
/
Rh(1)Ã
/
S(2) and P(2)Ã
/
Rh(1)Ã/P(1) is
/
/
C(31)Ã
/
P(3)Ã
/
were free at the distal end, the angle would be expected
to be close to 1808. Another measure of the extent of
strain in the system is the angle Rh(1)Ã
/
B(3)Ã/P(3) which
is 1188 whereas in related systems, for example III [1b]
and VII described below, such angles range from 129 to
1368. Clearly IV is a strained system and whether this
has anything to do with the distortion of the cage is not
clear, but it certainly is true that IV is the first example
of an iso-nido 11-vertex metallathiaborane.
We were somewhat surprised to observe the dppm
ligand bridging between the Rh atom and the boron
atom at position 3 in IV. We had thought that such
bridging might be an intermediate in the hypothetical
transfer of a second dppe or dppp ligand from here-
tofore unobserved dppe or dppp analogues of II to form
Scheme 2.

O. Volkov et al. / Journal of Organometallic Chemistry 657 (2002) 40ꢁ
/
47
45
the species X shown in Scheme 1. However, we rejected
the possibility of such an intermediate for the dppm
system in view of the ligand size and also the fact that we
observed no analogues of X in the case of dppm. We
surmised in a previous report that dppm analogues of
such species were not observed, because of the shorter
dppm ligand disfavoring such a transfer from the Rh in
the precursor II to the 9-position on the cage [1b].
Reaction of IV with dppm in CH2Cl2 at r.t. afforded the
red compound, which was observed as a minor impurity
in the reaction of [8,8-(PPh3)2-nido-8,7-RhSB9H10] (I)
with dppm, suggesting that perhaps latter species is an
analogue of IV with a dangling dppm moiety on Rh.
Transformation of II at r.t. over a period of 7 days also
afforded this red compound. Elemental analysis and
mass spectrometric data conform to a species with the
formula (dppm)2RhSB9H8. NMR spectroscopy sug-
gested a mixture but high-resolution mass spectrometry
and elemental analysis indicated a composition corre-
sponding to C50H52B9P4RhS; a RhSB9H8 cage with two
additional dppm ligands attached. The electron count
conforms to a closo-cluster, assuming that one of the
PPh2 groups is not coordinated to the cage. That would
be 12 skeletal electron pairs for an 11-vertex cluster [4].
Our experience suggested that we may have a mixture of
dppm)-closo-1,2-RhSB9H8] (VI) which is analogous to
IV.
One can propose a reaction scheme leading to species
for which analytical data conforms to that expected for
the red compound VꢁVI, as shown in Scheme 3. This
/
would involve the transfer of the dangling PPh2 group
on dppm to the cage to form T, a transition state
containing a very crowded 20 valence electron Rh atom
in an electron-rich cluster. Subsequent detachment of a
PPh2 group from Rh can go either to V? or VI?. This can
be followed by loss of H2 to afford species [1-(h1-dppm)-
1,3-(m-dppm)-closo-1,2-RhSB9H8] VI from VI? or [1,1-
(h2-dppm)-3-(h1-dppm)-closo-1,2-RhSB9H8] V from V?.
If species V and VI are not interchanging in a solution
equilibrium process, then different intermediates are
required and this possibility is where we identify the two
potential precursors to V and VI in Scheme 3, as V? and
VI?. Many attempts to solve the structure from diffrac-
tion patterns of the nice red crystals which were easy to
grow were unsuccessful. One attempt at purification
allowed isolation of one of the components in ca. 90%
purity which allowed tentative assignments of the
resonances in the 31P-NMR spectrum to each isomer.
An examination of the structures of V and VI given in
Scheme 3, indicates that there should be seven reso-
nances in the 31P-NMR spectrum. V should have three
resonances in 2:1:1 ratio and VI should have four
resonances in 1:1:1:1 ratio. We observe seven reso-
[1,1-(h2-dppm)-3-(h1-dppm)-closo-1,2-RhSB9H8]
which is analogous to XI and [1,1-(h2-dppm)-1,3-(m-
(V)
Scheme 3.

46
O. Volkov et al. / Journal of Organometallic Chemistry 657 (2002) 40ꢁ47
/
nances, and on the basis of the isolation of VI in ꢀ
/
90%
This can arise from a possible mutual rearrangement of
pairs of species analogous to V and VI.
purity, we are able to assign the spectra and tentative
assignments are given in the Section 2. The 11B-NMR
spectrum of the mixture consists of nine resonances and
the relative areas are consistent with the presence of 18
boron atoms. The gross cage structures for V and VI are
expected to give very similar 11B-NMR spectra but given
what we observed for IV, it is not unreasonable to
expect that VI would also be distorted to the iso-nido
structure thus rendering asymmetry to this molecule,
leading to more than six signals. Clearly we do not have
the definitive answer to the identity of our ‘red’
compound but our tentative conclusions are consistent
with our observations.
An alternative possibility is that there is no such
intermolecular exchange between species types V and VI
but that in the case of addition of dppe to IV, initially
the PPh3 is replaced by the dppe ligand which would be
expected to become bidentate from considerations of the
chelate effect, and the greater stability of bidentate dppe
versus dppm. Also the PPh2 group on a dppe ligand is
more nucleophilic than one on a dppm ligand thus the
species VII is the expected thermodynamic product of
this reaction. In other words a dangling PPh2 group on
dppm is more favorable than one on dppe. Crystals of
VII grown from CH2Cl2ꢁpentane were amenable to a
/
single crystal X-ray diffraction study. The structure,
given in Fig. 2, confirms the conclusions drawn from the
other analytical data. Species VII is a conventional 11-
vertex closo-cluster with the dppe ligand essentially
Possible interchange between V and VI is confirmed
by the next experiment we performed. Adding a 50%
excess of dppe to a solution of IV in CH2Cl2, and
stirring for 1 h, allows the formation of the ligand
exchange product [1,1-(h2-dppe)-3-(h1-dppm)-closo-1,2-
RhSB9H8] (VII). VII is formed in 87% yield and
identified by elemental analysis, NMR spectroscopy
and mass spectrometry. What is interesting about this
system is that the dppe ligand, which has replaced the
PPh3 ligand is now bidentate at position-1 and the dppm
ligand is dangling. Thus the dppm and the dppe ligands
have effectively changed places as indicated in Scheme 4.
orthogonal to the B(3)Ã
between the two planes B(3)Ã
P(1)ÃP(2) being 92.68. Also the orientation of the
dangling dppm ligand on position 3 is as expected for
a species replacing an exo-hydrogen atom; the B(3)Ã
P(3) axis is in the plane of symmetry of the RhSB9
cage. The angle between the planes C(39)ÃP(3)ÃB(3)
and P(3)ÃB(3)ÃRh(1) is 171.78, reasonably close to the
/
Rh(1)Ã
/
S(2) plane; the angle
/
Rh(1)Ã
/
S(2) and Rh(1)Ã
/
/
/
/
/
/
/
ideal 1808. Some structural parameters for IV and VII
are given in Table 2, and apart from obvious differences
of the two cages and the distortion around the open face
of IV, they are quite similar.
In summary we have extended the chemistry of the
system [8,8-(PPh3)2-nido-8,7-RhSB9H10] (I) and in doing
so we now understand better the possible modes of
rearrangement for bidentate phosphine adducts of the
species. We have speculated on possible mechanisms for
some of these rearrangements and made some sugges-
tions about likely intermediates. We are extending this
chemistry and seek to identify species analogous to T in
Scheme 2 in order to provide evidence for the existence
of such species.
4. Supplementary material
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been depos-
itied with the Cambridge Crystallographic Cata Center:
Compound IV, CCDC no. 179102 and Compound VII,
CCDC no. 179101. Copies of the information may be
obtained free of charge from: The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (Fax: ꢂ44-
/
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Fig. 2. A view of the molecular structure of VII with 50% thermal
ellipsoids. Only the cage H atoms are included to aid clarity.

O. Volkov et al. / Journal of Organometallic Chemistry 657 (2002) 40ꢁ
/
47
47
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Acknowledgements
We acknowledge the NSF (grant Nos. CHE-
9727570), the Missouri Research Board and UM-St.
Louis for research grants to L.B., and the NSF and the
UM-St. Louis Center for Molecular Electronics and the
Missouri Research Board for funds which help purchase
the NMR, XRD and MS facilities.
[7] M. Murphy, T.R. Spalding, G. Ferguson, J.F. Gallagher, Acta
Crystallogr. Sect. C: Cryst. Struct. Commun. Sect. C 48 (1992)
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