Sulfur-carbon bond formation and bond cleavage in alkynyl-bridged heterobinuclear complexes of rhodium and iridium

Article abstract of DOI:10.1016/S0020-1693(99)00605-2

The phenylacetylide-bridged heterobinuclear complexes [Rhlr(CO)₂(μ-η¹:η²-C₂Ph)(dppm)₂][X] (X = BF₄, SO₃CF₃; dppm = Ph₂PCH₂PPh₂) (1) react with carbon disulfide to give several products. At temperatures between -60 and -80°C the first product, [RhIr(CO)(η²-CS₂(μ-CO)(μ-η¹:η²-C₂Ph)(dppm)₂][X] (2), is the result of CS₂ coordination at Ir. Upon warming, two products are formed as a result of condensation of two CS₂ groups. In [RhIr(CO)(μ-η¹:η³-CC(Ph)SCSCS₂(μ-CO)(dppm)₂][X] (3), the resulting C₂S₄ fragment has also condensed at the β-carbon of the acetylide group to give a heteroatom-substituted vinylidene group. The other identified product, [RhIr(CO)(C₂S₄)(μ-C₂Ph)(μ-CO)(dppm)₂][X] (4), is very similar to 3 apart from the absence of coupling of the C₂S₄ moiety and the acetylide group. Compound 3 appears to be formed independently of 4, but also slowly transforms into 4 by cleavage of a C-S bond. The reaction of 1 with (n)BuNCS at - 80°C yields [RhIr(CO)(η²-SCN(n)Bu)(μ-CCPh)(μ-CO)(dppm)₂][X] (5), analogous to 2, and upon warming this rearranges to the isothiocyanate-bridged product [RhIr(CCPh)(CO)₂(μ-SCN(n)Bu)(dppm)₂][X] (6). Compound 6 undergoes S-C bond cleavage to yield [RhIr(CCPh)(CO)(CN(n)Bu)(μ-S)(μ-CO)(dppm)₂][X] (7), slowly at ambient temperature or within hours under reflux. Although no simple adducts analogous to 5 and 6 were observed with (t)BuNCS, refluxing 1 in the presence of an excess of this substrate yields [RhIr(CCPh)(CO)(CN(t)Bu)₂(μ-S)₂(dppm)₂][X] (9) as the major product along with smaller amounts of [RhIr(CCPh)(CO)(CN(t)Bu)(μ-S)(μ-CO)(dppm)₂,][X] (8), analogous to compound 7. Refluxing 1 in the presence of excess (n)BuNCS also yields some of the bis-n-butylisocyanide product, analogous to 9. The X-ray structures of compounds 3 (SO₃CF₃^- salt), 7 (BF₄^- salt) and 9 (BF₄^- salt) are reported. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00605-2

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 300–302 (2000) 353–368
Sulfur–carbon bond formation and bond cleavage in
alkynyl-bridged heterobinuclear complexes of rhodium and iridium
Darren S.A. George, Robert W. Hilts 1, Robert McDonald 2, Martin Cowie *,3
Chemistry Department, Uni6ersity of Alberta, Edmonton, Alta, Canada T6G 2G2
Received 13 September 1999; accepted 7 December 1999
Abstract
The phenylacetylide-bridged heterobinuclear complexes [RhIr(CO)2(m-h1:h2-C2Ph)(dppm)2][X] (X=BF4, SO3CF3; dppm=
Ph2PCH2PPh2) (1) react with carbon disulfide to give several products. At temperatures between −60 and −80°C the first
product, [RhIr(CO)(h2-CS2)(m-CO)(m-h1:h2-C2Ph)(dppm)2][X] (2), is the result of CS2 coordination at Ir. Upon warming, two
products are formed as a result of condensation of two CS2 groups. In [RhIr(CO)(m-h1:h3-CC(Ph)SCSCS2)(m-CO)(dppm)2][X] (3),
the resulting C2S4 fragment has also condensed at the b-carbon of the acetylide group to give a heteroatom-substituted vinylidene
group. The other identified product, [RhIr(CO)(C2S4)(m-C2Ph)(m-CO)(dppm)2][X] (4), is very similar to 3 apart from the absence
of coupling of the C2S4 moiety and the acetylide group. Compound 3 appears to be formed independently of 4, but also slowly
transforms into 4 by cleavage of a CꢀS bond. The reaction of 1 with nBuNCS at −80°C yields [RhIr(CO)(h2-SCNnBu)(m-
CCPh)(m-CO)(dppm)2][X] (5), analogous to 2, and upon warming this rearranges to the isothiocyanate-bridged product
[RhIr(CCPh)(CO)2(m-SCNnBu)(dppm)2][X] (6). Compound 6 undergoes SꢀC bond cleavage to yield [RhIr(CCPh)(CO)(CNnBu)(m-
S)(m-CO)(dppm)2][X] (7), slowly at ambient temperature or within hours under reflux. Although no simple adducts analogous to
5 and 6 were observed with tBuNCS, refluxing 1 in the presence of an excess of this substrate yields [RhIr(CCPh)(CO)(CNtBu)2(m-
S)2(dppm)2][X] (9) as the major product along with smaller amounts of [RhIr(CCPh)(CO)(CNtBu)(m-S)(m-CO)(dppm)2][X] (8),
n
analogous to compound 7. Refluxing 1 in the presence of excess BuNCS also yields some of the bis-n-butylisocyanide product,
analogous to 9. The X-ray structures of compounds 3 (SO3CF3− salt), 7 (BF4− salt) and 9 (BF4− salt) are reported. © 2000
Elsevier Science S.A. All rights reserved.
Keywords: Sulfur–carbon bond formation; Bond cleavage; Alkynyl-bridged heterobinuclear complexes; Rhodium; Iridium
1. Introduction
interest is in determining how p coordination to the
second metal (Rh in this case) can influence the reactiv-
ity of the alkynyl group.
As part of an ongoing study into the influence of two
adjacent metals on the reactivity of coordinated hydro-
carbyl groups [1], we have been investigating the reac-
tivity of the alkynyl group in the heterobinuclear
complexes [RhIr(CO)2(m2-h1:h2-C2Ph)(dppm)2][X] (X=
BF4 (1a), SO3CF3 (1b); dppm=Ph2PCH2PPh2) [2,3], in
which the alkynyl group is s-bound to Ir while in-
volved in a p interaction with Rh, as shown in A. Our
Previous work had shown that whereas a terminally
bound alkynyl group is susceptible to electrophilic at-
tack at the b-position [4], the m2-h1:h2-alkynyl group is
susceptible to nucleophilic attack, at either the a- or
b-carbon [5]. We were interested in extending this study
to include metal-mediated processes whereby transfer of
a metal-bound group to the alkynyl moiety could be
induced. Our investigations on compound 1 have
demonstrated that in all reactions studied, both nucleo-
philes [2] and electrophiles [3] attack at the metal
* Corresponding author. Tel.: +1-780-492 5581; fax +1-780-492
8231.
E-mail address: martin.cowie@ualberta.ca (M. Cowie)
1 Present address: Grant MacEwan Community College, Edmon-
ton, Alta, Canada.
2 Faculty Service Officer, Structure Determination Laboratory.
3 McCalla Research Professor, 1999–2000.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 9 9 ) 0 0 6 0 5 - 2

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D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
2. Experimental
(usually Ir), and in a number of cases subsequent
migration of the added ligand to the b-carbon of the
bridging alkynyl group occurs yielding bridging vinyli-
dene products. In the case in which the migrating group
was an allyl, the migration to an alkynyl moiety repre-
sented the only documented example, and was one of
the very few in which migration of a hydrocarbyl group
of any sort to the b-position had been observed [6]. We
sought to extend this chemistry into heteroatom-con-
taining substrates in order to determine if heteroatom-
containing vinylidene compounds would result, either
from direct attack at the alkynyl b-carbon, as has been
observed [5], or by a metal-mediated process. Sulfur-
containing heteroallenes (thiacumulenes), SꢁCꢁX (X=
S, NR), were chosen since allenes themselves had been
shown to coordinate to 1 [2], and also because of the
wide range of reactivities previously demonstrated for
these groups [7–10], including a tendency to couple
with unsaturated organic ligands [8], or to undergo
self-condensation reactions in which two [9–11] or
three [12] of these units combined.
All solvents were distilled over appropriate drying
agents (sodium/benzophenone for THF, ether, benzene,
and pentane; phosphorus pentoxide for halogenated
solvents) before use. Reactions were carried out at
ambient temperature using standard Schlenk techniques
(under either dinitrogen or argon) unless otherwise
stated. Prepurified dinitrogen, argon and carbon
monoxide were purchased from Praxair Products and
were used as received. Ammonium hexachloroiri-
date(IV) and potassium hexachlororhodate(III) were
obtained from Vancouver Island Precious Metals; hy-
drated rhodium trichloride was purchased from Colo-
nial Metals. Deuterated solvents (obtained from
Cambridge Isotope Laboratories) were distilled and
stored over molecular sieves. Spectrograde carbon
disulfide was obtained from Matheson, Coleman & Bell
Co. and was distilled and stored under nitrogen prior to
use. 13C-labelled carbon disulfide was purchased from
MSD Isotopes. n-Butyl isothiocyanate and t-butyl
isothiocyanate were purchased from Eastman Kodak
and used as received. The compounds [RhIr(CO)2(m2-
h1:h2-C2Ph)(dppm)2][X] (X=BF4 (1a), SO3CF3 (1b);
dppm=Ph2PCH2PPh2) were prepared as previously de-
scribed [2,3].
When only a single thiacumulene molecule is in-
volved the coordination modes shown in structures
B–F (where M and M% may be identical or different
metals) have been observed [13,14].
NMR spectra were obtained on either a Bruker 400
MHz spectrometer (operating at 100.614 MHz for 13C,
161.978 MHz for 31P, and 376.503 MHz for 19F) or a
Bruker 200 MHz spectrometer (operating at 50.323
MHz for 13C, and 81.015 MHz for 31P). Infrared spec-
tra were run on either a Perkin–Elmer model 1600
FTIR or a Nicolet Magna-IR 750 spectrometer as
either solids (Nujol mulls on KBr disks) or solutions
(KCl cell with 0.5 mm window path length). Elemental
analyses were conducted by the microanalytical service
within the department. Spectroscopic data for all com-
pounds are given in Table 1.
Although shown for a single metal, coordination mode
B can also occur at one metal of a multinuclear frag-
ment. When the condensation of two thiacumulenes at
one or more metal centers occurs, structures such as
those shown in G–J have been reported [9–11]. As
noted, incorporation of a third thiacumulene is also
possible [12] as is condensation with unsaturated or-
ganic substrates [8].
2.1. Preparation of compounds
2.1.1. [RhIr(CO)(v-p1:p3-CC(Ph)SCSCS2)-
(v-CO)(dppm)2][BF4]·2CH2Cl2 (3a)
An NMR tube was charged with compound 1a (21.8
mg, 16.7 mmol), 0.4 ml of CD2Cl2, and carbon disulfide
(100 ml, 1.66 mmol). This was allowed to stand for 1
week, forming a black solution, which was shown by
31P{1H} NMR spectroscopy to contain several com-
pounds, including [RhIr(CO)3(CCPh)(dppm)2][BF4],
compound 4, and a number of unidentified products.
The supernatant was removed with a syringe, leaving a
quantity of dark-yellow crystals of 3, which were
washed four times with 0.5 ml aliquots of CH2Cl2 and
dried under vacuum. Yield: 6.4 mg (24%). Anal. Calc.
for C64H53O2P4RhIrBCl4F4S4: C, 47.16; H, 3.28; S,
7.87; Cl, 8.70. Found: C, 47.66; H, 2.97; S, 7.67; Cl,
8.47%.
The reaction of thiacumulenes with the alkynyl-con-
taining mixed-metal fragment of compound 1 suggested
a potentially rich chemistry, and certainly alkynyl com-
pounds have already demonstrated interesting reactivity
with thiacumulenes [8b,e,f] as well as with the related
CO2 molecule [15]. Our initial results in the reactions of
the alkynyl-bridged 1 with selected thiacumulenes are
presented herein.

D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
355
Table 1
Spectral data a for compounds
d
Compound
NMR
IR (cm−1
)
l(31P{1H}) b
l(13C{1H}) c
l(1H) c
[RhIr(CO)(CS2)(m-CCPh)(m-CO)- 19.2 (dm, 1JRhP=89.9 Hz), 239.5 (b, CS2),
3.95 (m, 2H, PCH2P)
3.00 (m, 2H, PCH2P) e
(dppm)2][BF4] (2)
−15.0 (m) e
194.5 (dm, RhꢀCO,
1JRhC=83.7 Hz, 2JPC=15.5
Hz),
190.6 (dm, m-CO, 1JRhC=22.9
Hz, 2JPC=4.6 Hz) e
[RhIr(CO)(m-CC(Ph)SCSCS2)-
(m-CO)(dppm)2][BF4] (3a)
24.6 (dm, 1JRhP=142 Hz),
−7.2 (m) f
3.62 (m, PCH2P),
3.71(m, PCH2P) f
2019, 1832
[RhIr(CO)(m-CC(Ph)SCSCS2)-
(m-CO)(dppm)2][SO3CF3] (3b) −7.2 (m)
24.6 (dm, 1JRhP=143 Hz),f
3.55 (m, 2H, PCH2P) f, 1986, 1834
3.72 (m, 2H, PCH2P)
[RhIr(CO)(SCSCS2)(m-CCPh)-
(m-CO)(dppm)2][BF4] (4)
23.8 (dm, 1JRhP=144.6 Hz), 274.0 (m, Ir=CS2),
3.75 (m, 2H, PCH2P), 1986, 1841
2.85 (m, 2H, PCH2P)
−7.9 (m)
233.8 (s, S2CS),
193.3 (dt, RhꢀCO, 1JRhC=57.4
Hz, 2JPC=16.2 Hz),
197.9 (dt, m-CO, 1JRhC=14.8
Hz, 2JPC=8.0 Hz)
[RhIr(CO)2(SCNnBu)(m-CCPh)- 20.6 (dm, 1JRhP=88.2 Hz) e,
(dppm)2][BF4] (5) −25.4 (m)
[RhIr(CCPh)(CO)2(m-SCNnBu)- 19.0 (dm, 1JRhP=142.1 Hz), 188.5 (dt, RhꢀCO,
3.90 (m, 2H, PCH2P) e,
3.10 (m, 2H, PCH2P)
5.05 (m, 2H, PCH2P), 2018g, 1996, 1984
4.05 (m, 2H, PCH2P),
3.35 (m, 2H, NCH2),
(dppm)2][BF4] (6)
−35.0 (m)
1JRhC=73.1 Hz,
2JPC=13.5 Hz),
154.6 (t, IrꢀCO,
2JPC=4.1 Hz),
1.25 (m, 2H, CH2),
0.95 (m, 2H, CH2),
140.5 (t, IrꢀC(S)NR,
2JPC=17.1 Hz),
108.7 (s, IrꢀCꢂCPh),
55.3 (t, IrꢀCꢂCPh,
2JPC=14.2 Hz),
45.3 (s, NCH2),
0.65 (t, 3H, CH3)
30.1 (s, NCH2CH2),
19.7 (s, CH2CH2CH3),
13.1 (s, CH3)
[RhIr(CCPh)(CO)2(CNnBu)(m-S)- 17.9 (dm, 1JRhP=124.6 Hz), 195.1 (dt, IrꢀCO,
5.30 (m, 2H, PCH2P), 2126g, 1985, 1825
2.60 (m, 2H, PCH2P),
2.40 (m, 2H, NCH2),
(dppm)2][BF4] (7)
−23.0 (m)
1JRhC=18.4 Hz,
2JPC=8.4 Hz),
188.8 (dt, RhꢀCO,
1JRhC=69.7 Hz,
2JPC=14.1 Hz),
108.3 (s, IrꢀCꢂCPh),
69.0 (t, IrꢀCꢂCPh,
2JPC=11.2 Hz),
43.8 (s, NCH2),
0.80 (m, 2H, CH2),
0.70 (m, 2H, CH2),
0.60 (t, 3H, CH3)
30.1 (s, NCH2CH2),
19.4 (s, CH2CH2CH3),
13.3 (s, CH3)
h
[RhIr(CCPh)(CO)2(CNtBu)(m-S)- 17.0 (dm, 1JRhP=128 Hz),
(dppm)][BF4] (8)
−27.3 (m)
[RhIr(CCPh)(CO)(CNtBu)2-
(m-S)2(dppm)2][BF4] (9)
1.15 (dm, 1JRhP=95 Hz),
−33.6 (m)
5.58 (m, 2H, PCH2P), 2199g, 2178g,
4.10 (m, 2H, PCH2P), 2119, 2031
0.95 (s, 9H, CH3),
0.69 (s, 9H, CH3)
h
[RhIr(CCPh)(CO)(CNnBu)2-
(m-S)2(dppm)2][BF4] (10)
2.29 (dm, 1JRhP=92.7 Hz),
−32.05 (m)
a Abbreviations used: NMR, m=multiplet, dm=doublet of multiplets, s=singlet; d=doublet, t=triplet, q=quartet, dt=doublet of triplets,
ddt=doublet of doublets of triplets, dtt=doublet of triplets of triplets, ddm=doublet of doublets of multiplets, b=broad; IR, w=weak,
m=medium, s=strong, b=broad.
b Vs. 85% H3PO4 in CD2Cl2 at 23°C unless otherwise stated.
c Vs. TMS in CD2Cl2 at 25 °C unless otherwise stated.
d Nujol mull on KBr discs unless otherwise noted, wCO unless otherwise noted.
e −80°C.
f CD3OD solution, 23°C.
g wCN
.
h 1H NMR resonances not identified owing to overlaps with other species in solution (see text for explanation).

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D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
2.1.2. [RhIr(CO)(v-p1:p3-CC(Ph)SCSCS2)(v-
CO)(dppm)2][CF3SO3]·1.5CH2Cl2 (3b)
C66H60O2P4Cl2RhIrBNF4S: C, 52.57; H, 4.01; N, 0.93;
Cl, 4.70. Found: C, 52.45; H, 3.75; N, 0.93; Cl, 4.81%.
A 10 mm NMR tube was charged with compound 1b
(100 mg, 73.1 mmol), 2.0 ml of CH2Cl2 and carbon
disulfide (300 ml, 4.98 mmol). This mixture was allowed
to stand undisturbed for 10 days. Gradually dark-yel-
low crystals formed on the inside wall of the tube. The
crystals were separated from the supernatant, washed
twice with 10 ml of CH2Cl2 and dried overnight under
dynamic vacuum. Yield: 57 mg (47%). Anal. Calc. for
C64.75H52.5O5P4Cl3.5RhIrF3S5: C, 46.54; H, 3.17; S, 9.59;
Cl, 7.43. Found: C, 46.40; H, 3.22; S, 10.48; Cl, 7.75%.
2.1.6. [RhIr(CO)(v-S)2(CCPh)(tBuNC)2-
(dppm)2][BF4]·0.5CH2Cl2 (9)
Neat t-butyl isothiocyanate (97 ml, 766 mmol) was
added by microliter syringe to a flask containing com-
pound 1a (100 mg, 76.5 mmol) dissolved in 13 ml of
acetonitrile. The mixture was heated at reflux for 4 h,
during which time the solution changed color from
purple–red to orange. Two products were observed in
the 31P{1H} NMR spectra. The minor product [RhIr(C-
CPh)(CO)2(CNtBu)(m-S)(dppm)2][BF4] (8) was present
in between 2 and 14% and was identified only on the
basis of its 31P{1H} NMR spectrum that closely resem-
bled that of 7. The other product 9 was subsequently
isolated upon allowing the solution mixture to cool to
ambient temperature and removing the solvent under
vacuum, affording an orange–red solid. Recrystalliza-
tion of the residue from (1:4) CH2Cl2–Et2O gave
2.1.3. [RhIr(SCSCS2)(CO)(v-CCPh)-
(v-CO)(dppm)2][BF4] (4)
A solution of compound 1a (119.2 mg, 91.2 mmol) in
25 ml of 1,2-dichloroethane was heated to gentle reflux
and treated with CS2 (2.00 ml, 33.2 mmol), yielding a
dark-brown solution. Heating was continued for 2 h,
and the solvent volume reduced under vacuum to 5 ml.
Addition of ether (10 ml) and pentane (25 ml) afforded
a brown precipitate, which was washed twice with 10
ml aliquots of ether. The brown solid was then recrys-
tallized from 2 ml of CH2Cl2 and 15 ml of ether,
washed three times with 10 ml of ether, and dried in
vacuo. Yield: 106.6 mg (80%).
[RhIr(CO)(m-S)2(CCPh)(tBuNC)2(dppm)2][BF4]
0.5CH2Cl2 (0.044 g, 37% Yield) as dark-orange crystals.
Anal. Calc. for C69.5H68N2OClP4RhIrS2BF4: C, 53.76;
H, 4.41; N, 1.80. Found: C, 53.86; H, 4.08; N, 1.75%.
(9)·
2.2. Low temperature reaction of 1a with CS2
2.1.4. [RhIr(CCPh)(CO)2(v-p1:p1-SCNnBu)-
(dppm)2][BF4] (6)
An NMR tube was charged with compound 1a (19.4
mg, 14.1 mmol) and 0.4 ml of CD2Cl2. The tube was
sealed with a rubber septum, and cooled to −78°C in
a dry ice–acetone bath. Carbon disulfide (50 ml, 830
mmol) was added, causing a slow color change to
orange. NMR spectroscopy at −80°C showed essen-
tially quantitative conversion to [RhIr(CO)(h2-CS2)(m-
CCPh)(m-CO)(dppm)2][BF4] (2). Upon warming to
−20°C, the solution turned reddishꢀpurple, and was
shown by 31P{1H} NMR spectroscopy to have reverted
completely to 1a.
Compound 1a (100.0 mg, 76.5 mmol) was placed in a
flask with 5 ml of CH2Cl2. Excess n-butyl isothio-
cyanate (10.0 ml, 82.9 mmol) was added via syringe,
causing a slow color change from purple–red to or-
ange. The solution was then stirred for 30 min, after
which the solvent was removed under vacuum, and the
orange residue was recrystallized twice from 2 ml of
THF and 25 ml of Et2O. The product was washed with
three 5 ml aliquots of ether, then dried under nitrogen.
Yield: 72.0 mg (66%). A satisfactory elemental analysis
of this compound could not be obtained due to facile
loss of the isothiocyanate ligand under vacuum.
2.3. Low-temperature reactions of 1a with SCNnBu or
SCNtBu
2.1.5. [RhIr(CCPh)(CO)2(CNnBu)(v-S)-
(dppm)2][BF4]·CH2Cl2 (7)
An NMR tube containing 50 mg (0.0383 mmol) of 1a
and 0.60 ml of CD2Cl2 was fitted with a rubber septum,
flushed with nitrogen and cooled to −78°C in a dry
ice–acetone bath. The appropriate isothiocyanate
(#4.6 ml, #0.038 mmol) was added. In the case of
SCNnBu the color of the solution changed to orange,
whereas no change was evident with addition of
SCNtBu. For the former reaction, NMR spectroscopy
at −80°C showed resonances attributed to [RhIr-
Compound 1a (40.0 mg, 30.6 mmol) was placed in a
flask with 5 ml of THF, and heated to reflux. Excess
n-butyl isothiocyanate (10.0 ml, 82.9 mmol) was added
via syringe, causing a color change from purple–red to
brown. After 30 min of reflux, the solution volume was
reduced to 2 ml under a steady stream of nitrogen, was
cooled and 15 ml of ether was added to precipitate a
solid. The orange solid was dried, recrystallized from 3
ml of CH2Cl2 and 15 ml of Et2O, washed twice with 10
ml of ether, then dried, first under nitrogen, then under
vacuum. Yield: 21.1 mg (46%). Anal. Calc for
(CO)(h2-SCNnBu)(m-CCPh)(m-CO)(dppm)2][BF4]
(5)
together with those of 1a, in a 1:2 ratio. This new
product persisted upon warming to −60°C, but had
completely disappeared by −40°C, having been re-

D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
357
Table 2
Crystal data and data collection details for compounds
Compound
3b·1.75CH2Cl2
7·CH2Cl2
9·1.5CH2Cl2
Formula
C64.75H52.5Cl3.5F3IrO5P4RhS5
0.37×0.18×0.14
1669.92
monoclinic
P21/c
C66H60BCl2F4IrNO2P4RhS
0.46×0.40×0.18
1507.91
monoclinic
P21/n
C70.25H69.5BCl2.5F4IrN2OP4RhS2
0.26×0.06×0.06
1616.32
monoclinic
P21/c
Crystal size (mm)
Formula weight
Crystal system
Space group
Unit cell dimensions
,
a (A)
23.994(1)
24.475(1)
22.3045(9)
93.6401(9)
13072(1)
8
15.904(1)
24.410(2)
16.679(1)
104.015(1)
6282.3(7)
4
17.1292(7)
14.7762(7)
29.090(1)
103.707(1)
7153.2(5)
4
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
Dcalc (Mg M−3
Diffractometer
)
1.698
1.594
1.501
Bruker P4/RA/SMART 1000 CCD Bruker P4/RA/SMART 1000 CCD Bruker P4/RA/SMART 1000 CCD
,
Radiation (u) (A)
graphite-monochromated Mo Ka
(0.71073)
51.50
2.745
193
graphite-monochromated Mo Ka
(0.71073)
51.50
2.656
193
graphite-monochromated Mo Ka
(0.71073)
51.40
2.384
193
2q max (°)
v (mm−1
T (K)
)
Independent reflections
Observed reflections (I\2|(I)) 19 676
Parameters refined
Goodness-of-fit
R1 (Fo2]2|(Fo2))
wR2 (all data)
24 851
11 962
10 518
748
13 603
6690
770
1570
1.046
0.0343
0.0912
2.16, −1.84
1.037
0.877
0.0366
0.0946
2.53, −1.57
0.0517
0.1160
1.68, −0.61
Largest difference peak, hole
−3
,
(e A
)
placed by signals for 6. By −20°C all of the starting
material 1a had also disappeared, leaving only signals
for 6. In the case of SCNtBu addition, no product was
observed over the temperature range between −80 and
20°C; only 1a and free SCNtBu were observed.
2.5. X-ray data collection
2.5.1. Compound 3b
Golden–yellow crystals of [RhIr(CO)(m-h1:h3-CC-
(Ph)SCSCS2)(m-CO)(dppm)2][CF3SO3]·1.75CH2Cl2 (3b)
were obtained from slow evaporation of a CH2Cl2
solution of the compound. Data were collected on a
Bruker P4/RA/SMART 1000 CCD diffractometer
using Mo Ka radiation at −80°C 4. Unit cell parame-
ters were obtained from a least-squares refinement of
the setting angles of 8192 reflections from the data
collection. The systematic absences indicated the space
group to be P21/c (no. 14). The data were corrected for
absorption through use of the sadabs procedure (see
Table 2 for a summary of crystal data and X-ray data
collection information for compounds 3b, 7 and 9).
n
2.4. Reaction of 1a with excess BuNCS under reflux
To a sample of 100 mg (0.0766 mmol) of 1a in 35 ml
n
of THF was added 0.046 ml (0.383 mmol) of BuNCS.
This mixture was refluxed for 4 h, during which time
the color changed from red to orange–yellow. The
solution was allowed to cool to room temperature and
the solvent was then removed under vacuum, affording
a tarry orange residue. The orange product was washed
with 2×20 ml of Et2O and kept under vacuum
overnight. A total of 0.093 g of orange solid was
collected. This orange solid was dissolved in 0.6 ml of
CD2Cl2 and the resulting clear orange solution was
analyzed by 31P{1H} and 1H NMR spectroscopy. In
the 31P{1H} NMR spectrum of the reaction mixture
four species predominated. The compounds [RhIr-
(CCPh)(CO)(CNnBu)2(m-S)2(dppm)2][BF4] (10) (31P
NMR: l 2.29 (1JRhP=92.7 Hz, l 32.05), 7 and two
unidentified species (31P NMR: l 19.33 (1JRhP=129.6
Hz), l −21.52; 2.35 (1JRhP=91.6 Hz), l −34.56) were
present in the respective ratios 1:2.00:1.85:0.58.
2.5.2. Compound 7
Yellow–orange crystals of [RhIr(CCPh)(CO)-
(CNnBu)(m-S)(m-CO)(dppm)2][BF4]·CH2Cl2 (7) were ob-
tained from slow diffusion of Et2O into a CH2Cl2
solution of the compound. Data were collected as
for 3b, with unit cell parameters obtained from a
least-squares refinement of the setting angles of 7586
4 Programs for diffractometer operation, data collection, data re-
duction and absorption corrections were those supplied by Bruker.

358
D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
reflections from the data collection. The systematic
absences indicated the space group to be P21/n (a
nonstandard setting of P21/c (no. 14)). Absorption
corrections were applied as for 3b.
2.6.3. Compound 9
The structure of 9 was solved using the dirdif-96
program, and refinement was completed using the pro-
gram SHELXL-93. The phenyl ring of the phenyl-
acetylide ligand was disordered over two closely spaced
positions with equal occupancy. The two half-occu-
pancy phenyl rings are labeled C91A–C96A and
C91B–C96B, respectively. An idealized geometry
2.5.3. Compound 9
Orange crystals of [RhIr(CꢂCPh)(CO)(CNtBu)2(m-
S)2(dppm)2][BF4]·1.5CH2Cl2 (9) were obtained from
slow evaporation of an acetonitrile solution of the
compound. Data were collected as for 3b, with unit cell
parameters obtained from a least-squares refinement of
the setting angles of 8192 reflections from the data
collection. The systematic absences indicated the space
group to be P21/c (no. 14). Absorption corrections were
applied as for 3b.
,
,
(ClꢀC=1.80 A; Cl···Cl=2.95 A) was imposed upon
the one of the solvent dichloromethane molecules, and
an idealized hexagonal geometry (with carbon–carbon
,
distance=1.39 A) was also imposed on both orienta-
tions of the disordered phenylacetylide phenyl ring. The
final model for 9 refined to values of R1(F)=0.0517
(for 6690 reflections with Fo2]2|(Fo2)) and wR2(F2)=
0.1160 (for all 13 603 independent reflections).
2.6. Structure solution and refinement
3. Results and compound characterization
2.6.1. Compound 3b
The structure of 3b was solved using the direct-meth-
ods program SHELXS-86, and refinement was completed
using the program SHELXL-93 [16] 5. The asymmetric
unit contained two independent molecules, which are
listed as molecules A and B in all related tabulations.
These molecules are essentially identical. Hydrogen
atoms were assigned positions based on the geometries
of their attached carbon atoms, and were given thermal
parameters 20% greater than those of the attached
carbons. Distance restraints were also applied to
achieve an idealized geometry within one of the solvent
Treatment of a solution of the phenylacetylide-
bridged [RhIr(CO)2(m-CCPh)(dppm)2][BF4] (1a) with
carbon disulfide results in the slow formation of a
number of compounds (see Scheme 1), from which
[RhIr(CO)(m-h1:h3-CC(Ph)SCSCS2)(m-CO)(dppm)2]
[BF4] (3a) can be isolated as dark-yellow crystals. Al-
though this compound is insoluble in many solvents
(e.g. CH2Cl2, CHCl3, THF, acetonitrile, toluene), it is
1
soluble enough in methanol to obtain 31P{1H} and H
NMR spectra, although not soluble enough for natural-
abundance 13C{1H} NMR data. Based upon the spec-
tral data available it is clear that the binuclear
,
,
CH2Cl2 molecules (ClꢀC=1.80 A; Cl···Cl=2.95 A).
The final model for 3b refined to values of R1(F)=
0.0343 (for 19 676 reflections with Fo2]2|(Fo2)) and
wR2(F2)=0.0912 (for all 24 851 independent
reflections) 6.
2.6.2. Compound 7
The structure of 7 was solved using the dirdif-96
program system [17], and refinement was completed
using the program SHELXL-93. The final model for 7
refined to values of R1(F)=0.0366 (for 10 518 reflec-
tions with Fo2]2|(Fo2)) and wR2(F2)=0.0946 (for all
11 962 independent reflections).
5 Refinement on Fo2 for all reflections (all of these having Fo2
]
−3|(Fo2)). Weighted R-factors wR2 and all GOFs S are based on Fo2;
conventional R-factors R1 are based on Fo, with Fo set to zero for
negative Fo2. The observed criterion of Fo2\2|(Fo2) is used only for
calculating R1, and is not relevant to the choice of reflections for
refinement. R-factors based on Fo2 are statistically about twice as
large as those based on Fo, and R-factors based on all data will be
even larger.
6 R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ; wR2=[Sw(Fo2−Fc2)2/Sw(Fo4)]1/2
.
Scheme 1.

D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
359
of two CS2 molecules. However, the connectivity of the
CS2 and alkynyl groups could not be determined from
the spectral data so an X-ray diffraction study was
undertaken. Fig. 1 shows the structure of 3b, clearly
showing that two units of carbon disulfide have con-
densed in a head-to-tail fashion on the iridium center
(as shown earlier for structure H or I), and this result-
ing C2S4 fragment has also added to the b-carbon of the
alkynyl ligand to give an extended fragment that com-
bines vinylidene (C(3)C(4)(Ph)S(1)), carbene (IrꢀC(5)),
and trithiocarbonate (C(6)S(2)S(3)S(4)) functionalities.
Carbon disulfide dimerization within the coordination
sphere of a transition metal has been previously re-
ported for several compounds, such as [CpRh(PMe3)-
(SC(S)SCS)] [9a], [Rh2Cl2(CO)(SC(S)SCS)(dppm)2] [9b],
and [Mo(SC(S)SCS)(PMe3)3(CH2ꢁCH2)] [9c]; however,
the additional coupling of a C2S4 moiety with the
alkynyl ligand appears to be unprecedented. The ob-
served transformation is not unlike those previously
reported [2,3], in which the formation of vinylidenes via
migration of moieties such as hydride or allyl ligands
from the metal centers to the b-carbon of the alkynyl
ligand of compound 1, was observed.
Fig. 1. Perspective view of the [RhIr(CO)(m-h1:h3-CC(Ph)SCSCS2)(m-
CO)(dppm)2]+ cation of 3b showing the atom labeling. Non-hydro-
gen atoms are represented by Gaussian ellipsoids at the 20%
probability level. Hydrogen atoms are shown with arbitrarily small
thermal parameters and are not shown for the phenyl groups.
Table 3
The complex has the usual trans-diphosphine ar-
rangement at both metals. At iridium the coordination
geometry is octahedral (ignoring the RhꢀIr bond), in
which the trans phosphines, bridging vinylidene, and
bridging carbonyl groups occupy four sites and the
C2S4 moiety occupies the two remaining sites, binding
through a carbon (C(5)) and a sulfur (S(3)) of this unit.
The fused tridentate ligand resulting from condensation
of the alkynyl group and the C2S4 fragment therefore
occupies three meridional sites at the iridium center,
resulting in two fused five-membered metallacycles. At
rhodium, the coordination is best described as a tetrag-
onal pyramid with the vinylidene, the terminal car-
bonyl, and the phosphines in the basal sites and the
bridging carbonyl in the lone axial site. Consistent with
this description, the phosphines are bent back away
from the bridging carbonyl, with resulting P(2)ꢀ
RhꢀP(4) angles of 163.35(4) and 155.88(4)°, in the two
independent molecules7. The C(2)ꢀRhꢀC(3) unit, on the
other hand, is essentially linear (171.9(2) and 175.9(2)°).
See Tables 3 and 4 for selected bond lengths and angles
for compound 3b.
,
Selected interatomic distances (A) in compound 3b
Molecule A
Molecule B
IrꢀRh
IrꢀS(3)
IrꢀP(1)
IrꢀP(3)
IrꢀC(1)
IrꢀC(3)
IrꢀC(5)
3.0079(4)
2.4526(12)
2.3579(12)
2.3540(12)
2.080(5)
2.065(5)
2.041(4)
2.3397(13)
2.3500(12)
2.138(5)
1.914(5)
2.029(4)
1.813(5)
1.660(5)
1.711(5)
1.785(5)
1.728(5)
1.636(5)
1.820(4)
1.829(4)
1.833(4)
1.832(4)
1.164(5)
1.132(6)
1.328(6)
1.477(6)
IrꢀRh
IrꢀS(3)
IrꢀP(1)
IrꢀP(3)
IrꢀC(1)
IrꢀC(3)
IrꢀC(5)
2.9422(4)
2.4294(11)
2.3679(12)
2.3741(12)
2.069(4)
2.054(4)
1.997(4)
2.3395(12)
2.3292(12)
2.137(4)
1.895(5)
2.032(4)
1.804(4)
1.690(4)
1.716(4)
1.776(5)
1.709(4)
1.634(4)
1.838(4)
1.842(4)
1.839(4)
1.837(4)
1.155(5)
1.151(5)
1.360(6)
1.480(6)
RhꢀP(2)
RhꢀP(4)
RhꢀC(1)
RhꢀC(2)
RhꢀC(3)
S(1)ꢀC(4)
S(1)ꢀC(5)
S(2)ꢀC(5)
S(2)ꢀC(6)
S(3)ꢀC(6)
S(4)ꢀC(6)
P(1)ꢀC(7)
P(2)ꢀC(7)
P(3)ꢀC(8)
P(4)ꢀC(8)
O(1)ꢀC(1)
O(2)ꢀC(2)
C(3)ꢀC(4)
C(4)ꢀC(91)
RhꢀP(2)
RhꢀP(4)
RhꢀC(1)
RhꢀC(2)
RhꢀC(3)
S(1)ꢀC(4)
S(1)ꢀC(5)
S(2)ꢀC(5)
S(2)ꢀC(6)
S(3)ꢀC(6)
S(4)ꢀC(6)
P(1)ꢀC(7)
P(2)ꢀC(7)
P(3)ꢀC(8)
P(4)ꢀC(8)
O(1)ꢀC(1)
O(2)ꢀC(2)
C(3)ꢀC(4)
C(4)ꢀC(91)
The bicyclic ligand system is close to planar, with
the largest deviation from the IrS(3)C(6)S(2)C(5)S(1)
,
C(4)C(3) least-squares plane being 0.055(3) A for C(4)
of molecule A. In such a metallacyclic ring system, the
bonding is not unambiguous. So although the
,
C(3)ꢀC(4) distance (1.328(6), 1.360(6) A) is consistent
framework is intact, having the conventional dppm-
bridged structure (by NMR), and that one carbonyl is
terminal with the other bridging (by IR). Furthermore,
the elemental analysis results indicate the incorporation
7 The two values given for each parameter for compound 3b are for
the two independent molecules, labeled A and B.

360
D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
Table 4
with a CꢀC double bond [18], and the C(4)ꢀS(1) dis-
Selected interatomic angles (°) in compound 3b
,
tance (1.813(5), 1.804(4) A) is consistent with a CꢀS
single bond, all other CꢀS bonds within the ring sys-
Molecule A
Molecule B
,
tems (between 1.660(5) and 1.785(5) A) are intermediate
RhꢀIrꢀS(3)
148.60(3)
89.41(3)
89.67(3)
RhꢀIrꢀS(3)
RhꢀIrꢀP(1)
RhꢀIrꢀP(3)
145.15(3)
89.28(3)
88.59(3)
46.56(12)
43.65(11)
128.09(12)
90.78(4)
between single and double, which is consistent
RhꢀIrꢀP(1)
with significant p delocalization. Similarly, the IrꢀC(5)
RhꢀIrꢀP(3)
,
distance (2.041(4), 1.997(4) A), although suggestive
RhꢀIrꢀC(1)
45.30(12) RhꢀIrꢀC(1)
42.25(12) RhꢀIrꢀC(3)
124.71(15) RhꢀIrꢀC(5)
of some carbene-like character (cf. [IrCl(h3-tBu2P-
RhꢀIrꢀC(3)
CH3CH2CCH2CH2PtBu2)], IrꢀC=2.006(4)
A
[19];
,
RhꢀIrꢀC(5)
[(HB(N2C3H(CH3)2)3Ir(H)(h2 -NH = C(CH3)C(CH3)],
S(3)ꢀIrꢀP(1)
S(3)ꢀIrꢀP(3)
S(3)ꢀIrꢀC(1)
S(3)ꢀIrꢀC(3)
S(3)ꢀIrꢀC(5)
P(1)ꢀIrꢀP(3)
P(1)ꢀIrꢀC(1)
P(1)ꢀIrꢀC(3)
P(1)ꢀIrꢀC(5)
P(3)ꢀIrꢀC(1)
P(3)ꢀIrꢀC(3)
P(3)ꢀIrꢀC(5)
C(1)ꢀIrꢀC(3)
C(1)ꢀIrꢀC(5)
C(3)ꢀIrꢀC(5)
IrꢀRhꢀP(2)
88.49(4)
91.50(4)
S(3)ꢀIrꢀP(1)
S(3)ꢀIrꢀP(3)
92.33(4)
,
IrꢀC=1.80(3) A [20]), appears more consistent with
103.35(13) S(3)ꢀIrꢀC(1)
168.88(13) S(3)ꢀIrꢀC(3)
86.66(15) S(3)ꢀIrꢀC(5)
98.60(12)
171.20(12)
86.76(12)
176.81(4)
90.79(12)
89.13(12)
89.82(13)
89.47(12)
87.69(12)
89.63(13)
90.20(16)
174.60(17)
84.44(17)
93.00(3)
delocalized bonding. The C(6)ꢀS(4) bond (1.636(5),
,
1.634(4) A), on the periphery of the metallacycle ap-
178.23(4)
P(1)ꢀIrꢀP(3)
pears normal for a double bond. As in a previous
allylvinylidene compound, in which the pendent h2-allyl
moiety induces strain into the metallacycle [3], the fused
C2S4 fragment pulls the vinylidene unit towards itself
resulting in IrꢀC(3)ꢀC(4) (122.2(3), 120.0(3)°) and
RhꢀC(3)ꢀC(4) (143.2(4), 147.8(3)°) angles that demon-
strate the asymmetry. The resulting RhꢀC(3) bond is
89.49(13) P(1)ꢀIrꢀC(1)
89.40(12) P(1)ꢀIrꢀC(3)
91.19(13) P(1)ꢀIrꢀC(5)
88.79(13) P(3)ꢀIrꢀC(1)
90.94(12) P(3)ꢀIrꢀC(3)
90.58(13) P(3)ꢀIrꢀC(5)
87.55(17) C(1)ꢀIrꢀC(3)
169.98(19) C(1)ꢀIrꢀC(5)
82.47(19) C(3)ꢀIrꢀC(5)
,
shorter (2.029(4), 2.032(4) A) than IrꢀC(3) (2.065(5),
,
91.43(3)
91.26(3)
IrꢀRhꢀP(2)
IrꢀRhꢀP(4)
2.054(4) A). This asymmetry is the opposite to that
IrꢀRhꢀP(4)
93.33(3)
observed in the semibridging carbonyl, which is more
IrꢀRhꢀC(1)
43.74(13) IrꢀRhꢀC(1)
144.87(16) IrꢀRhꢀC(2)
43.17(13) IrꢀRhꢀC(3)
44.68(12)
139.80(14)
44.24(12)
155.88(4)
99.93(12)
94.88(15)
85.32(12)
100.92(12)
95.21(15)
83.08(12)
95.12(18)
88.91(16)
175.86(18)
99.5(2)
,
tightly bound to Ir (IrꢀC(1)=2.080(5), 2.069(4) A than
to Rh (RhꢀC(1)=2.138(5), 2.137(4) A) and is tipped
towards Rh (compare IrꢀC(1)ꢀO(1)=146.5(4),
IrꢀRhꢀC(2)
,
IrꢀRhꢀC(3)
P(2)ꢀRhꢀP(4)
P(2)ꢀRhꢀC(1)
P(2)ꢀRhꢀC(2)
P(2)ꢀRhꢀC(3)
P(4)ꢀRhꢀC(1)
P(4)ꢀRhꢀC(2)
P(4)ꢀRhꢀC(3)
C(1)ꢀRhꢀC(2)
C(1)ꢀRhꢀC(3)
C(2)ꢀRhꢀC(3)
C(4)ꢀS(1)ꢀC(5)
C(5)ꢀS(2)ꢀC(6)
IrꢀS(3)ꢀC(6)
IrꢀP(1)ꢀC(7)
RhꢀP(2)ꢀC(7)
IrꢀP(3)ꢀC(8)
RhꢀP(4)ꢀC(8)
IrꢀC(1)ꢀRh
163.35(4)
P(2)ꢀRhꢀP(4)
96.79(13) P(2)ꢀRhꢀC(1)
93.56(15) P(2)ꢀRhꢀC(2)
85.10(13) P(2)ꢀRhꢀC(3)
96.51(13) P(4)ꢀRhꢀC(1)
93.66(16) P(4)ꢀRhꢀC(2)
85.65(13) P(4)ꢀRhꢀC(3)
147.3(4)° and RhꢀC(1)ꢀO(1)=122.6(4), 123.9(3)°).
Consistent with the delocalized bonding within the
metallacycles, there is a corresponding uncertainty in
the nature of the RhꢀIr bond. The observed distance
,
(3.0079(4), 2.9422(4) A) is certainly longer than ‘nor-
101.1(2)
C(1)ꢀRhꢀC(2)
86.91(18) C(1)ꢀRhꢀC(3)
mal’ single bonds between these metals, typically rang-
,
ing between 2.70 and 2.85 A [1g,2b,21], however it is
171.9(2)
100.0(2)
105.1(2)
C(2)ꢀRhꢀC(3)
C(4)ꢀS(1)ꢀC(5)
C(5)ꢀS(2)ꢀC(6)
shorter than the PꢀP distances within the dppm ligands
,
103.8(2)
(between 3.057(2) and 3.071(2) A) indicating some de-
103.98(18) IrꢀS(3)ꢀC(6)
110.88(15) IrꢀP(1)ꢀC(7)
112.98(15) RhꢀP(2)ꢀC(7)
110.13(15) IrꢀP(3)ꢀC(8)
112.74(15) RhꢀP(4)ꢀC(8)
90.97(18) IrꢀC(1)ꢀRh
103.94(16)
109.97(15)
111.53(14)
110.72(15)
112.73(15)
88.76(17)
147.3(4)
123.9(3)
173.5(4)
92.11(17)
120.0(3)
147.8(3)
116.3(3)
113.3(3)
130.4(4)
119.7(2)
125.1(2)
115.2(2)
120.4(3)
114.1(3)
gree of mutual attraction between the metals. The acute
RhꢀC(3)ꢀIr angle (94.6(2), 92.1(2)°), which is much
smaller than the 120° expected for an sp2 carbon, is also
consistent with some RhꢀIr bonding.
Compound 3, discussed above, is not the major
product of the reaction between 1 and CS2, forming in
only about 20% yield. The major product (in about
40% yield), shown in Scheme 1, is the dark brown
complex [RhIr(SCSCS2)(CO)(m-CCPh)(m-CO)(dppm)2]-
[BF4] (4), in which two molecules of carbon disulfide
have condensed in a head-to-tail fashion to form a C2S4
ligand, as in compound 3. Unlike compound 3, the
C2S4 fragment in 4 has apparently not coupled with the
alkynyl ligand. Compound 4 is also formed when a
sample of 3 is allowed to stand under CH2Cl2 over a
IrꢀC(1)ꢀO(1)
RhꢀC(1)ꢀO(1)
RhꢀC(2)ꢀO(2)
IrꢀC(3)ꢀRh
146.5(4)
122.6(4)
169.6(5)
IrꢀC(1)ꢀO(1)
RhꢀC(1)ꢀO(1)
RhꢀC(2)ꢀO(2)
94.57(18) IrꢀC(3)ꢀRh
IrꢀC(3)ꢀC(4)
RhꢀC(3)ꢀC(4)
S(1)ꢀC(4)ꢀC(3)
S(1)ꢀC(4)ꢀC(91)
C(3)ꢀC(4)ꢀC(91)
IrꢀC(5)ꢀS(1)
IrꢀC(5)ꢀS(2)
S(1)ꢀC(5)ꢀS(2)
S(2)ꢀC(6)ꢀS(3)
S(2)ꢀC(6)ꢀS(4)
S(3)ꢀC(6)ꢀS(4)
P(1)ꢀC(7)ꢀP(2)
P(3)ꢀC(8)ꢀP(4)
122.2(3)
143.2(4)
115.4(4)
114.7(4)
129.9(5)
119.9(3)
124.2(3)
115.9(3)
120.0(3)
113.1(3)
126.9(3)
114.1(2)
113.8(2)
IrꢀC(3)ꢀC(4)
RhꢀC(3)ꢀC(4)
S(1)ꢀC(4)ꢀC(3)
S(1)ꢀC(4)ꢀC(91)
C(3)ꢀC(4)ꢀC(91)
IrꢀC(5)ꢀS(1)
IrꢀC(5)ꢀS(2)
S(1)ꢀC(5)ꢀS(2)
S(2)ꢀC(6)ꢀS(3)
S(2)ꢀC(6)ꢀS(4)
S(3)ꢀC(6)ꢀS(4)
P(1)ꢀC(7)ꢀP(2)
P(3)ꢀC(8)ꢀP(4)
1
period of weeks. The 31P{1H} and H NMR spectra of
compound 4 are rather uninformative, except to suggest
a similarity to 3. However, the 13C{1H} NMR spectrum
of a 13CS2-enriched sample of this complex is informa-
tive and shows two signals in the region expected for a
condensed C2S4 ligand of the type shown. The first of
125.5(3)
112.4(2)
112.5(2)
C(4)ꢀC(91)ꢀC(92) 122.3(5)
C(4)ꢀC(91)ꢀC(96) 120.5(5)
C(4)ꢀC(91)ꢀC(92) 120.4(4)
C(4)ꢀC(91)ꢀC(96) 121.7(4)

D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
361
these is an unresolved multiplet at l 274.0, which is
in the range expected for a thioacyl carbon [22], and
the second occurs at l 233.8. These are similar to the
values found in [Mo(SC(S)SCS)(PMe3)3(CH2CH2)] (l
292.3, 226.9) [9c] for the thioacyl and trithiocarbonate
carbons, respectively. Both carbons of the C2S4 frag-
ment show weak (4 Hz) coupling to each other in the
doubly-labeled compound, which is consistent with
coupling through more than one bond [23]. The car-
proximately 20% of the species in solution (by
31P{1H} NMR). We assume that the tricarbonyl
product is formed by reaction of 1a with CO lost in
the formation of this monocarbonyl species. Unfortu-
nately, the unidentified product decomposed during
attempts to isolate it, and could not be further char-
acterized. Although an attempt was made to observe
the 13CS2 signals for this compound, the reaction
mixture was not sufficiently clean to unambiguously
identify its signals, particularly in the presence of an
excess of labeled carbon disulfide.
bonyl region of this spectrum shows the presence of a
1
terminal, rhodium-bound carbonyl (l 193.3, JRhC
=
57 Hz) and an iridium-bound carbonyl which is
In an attempt to obtain information about the
mode of formation of these species, a large excess of
carbon disulfide was added to a sample of 1a at
−80°C, and the reaction monitored at low tempera-
ture by NMR spectroscopy. The initial product ap-
pears to be the CS2 adduct [RhIr(CO)(h2-CS2)-
(m-CCPh)(m-CO)(dppm)2][BF4] (2), in which the het-
eroallene has coordinated to iridium. This coordina-
tion is analogous to that found for the coordination
of allene and dimethylallene to 1 [2]. Unlike the al-
lene adduct, however, only one isomer is found for
compound 2. The 13C{1H} NMR spectrum of this
compound at −80°C shows the presence of one ter-
minal, rhodium-bound carbonyl (l 194.5, 1JRhC=83
Hz) and one bridging carbonyl (l 190.6, 1JRhC=23
Hz). The signal for the coordinated CS2 ligand ap-
pears as a broad singlet at l 239.5, which is strongly
shifted from free carbon disulfide (l 193.0). Although
carbon disulfide often bridges adjacent metal centers,
the CS2 ligand in 2 is thought to be terminally bound
to iridium, as a complex containing a bridging carbon
disulfide ligand would be expected to be spectroscopi-
cally similar to the isostructural isothiocyanate com-
plex 5 (vide infra). On the contrary, the 31P NMR
signals for 2 are separated from those of the isothio-
cyanate complex by nearly 20 ppm, but only a few
ppm shifted from the signals for the previous allene
adducts [2]. Upon warming, the CS2 ligand is lost,
regenerating 1a.
1
semibridging to rhodium (l 197.9, JRhC=15 Hz). In
the quadruply-labeled compound, made by the reac-
tion of [RhIr(13CO)2(m-CCPh)(dppm)2][BF4] with
13CS2, the iridium-bound carbonyl shows strong cou-
pling (34 Hz) to the thioacyl carbon, as well as
weaker coupling (:4 Hz) to the trithiocarbonate car-
bon. The magnitude of the carbonyl–thioacyl cou-
pling suggests that the two carbons are mutually
trans, as this is higher than expected for a normal
two-bond carbon–carbon coupling [23]. The alkynyl
carbons, which were not 13C-enriched, could not be
located in the 13C{1H} NMR spectrum.
The IR spectrum of this compound confirms the
presence of both terminal and bridging carbonyls.
The CꢀO stretching frequency of the rhodium-bound
carbonyl is significantly lower than that of 3 (1986
versus 2019 cm−1), indicating that the rhodium center
in 4 is much more electron-rich than that in com-
pound 3. This is consistent with the presence of a
vinylidene group in 3 being a much stronger p-acid
than the alkynyl group in 4, as previously noted [24].
An alternative structure, in which the thioacyl frag-
ment of the C2S4 moiety bridges the two metals (as
found previously in [Rh2Cl2(CO)(m-SCSCS2)(dppm)2]
[9b]) can be ruled out, since the iridium-bound
semibridging carbonyl could not, in this structure, be
trans to the thioacyl carbon, as required to generate
the large CꢀC coupling observed in the 13C{1H}
NMR spectrum. The proposed structure for 4 is also
consistent with its generation from 3. The conversion
of 3 to 4 requires the breaking of only one carbon–
sulfur bond, and appears more likely than the dra-
matic molecular rearrangement that would be
required to form the C2S4-bridged structure previously
observed in related systems [9b]. Unfortunately, crys-
tals of 4 suitable for an X-ray study could not be
obtained.
In light of the above transformations, it was of
interest to determine if other sulfur-containing sub-
strates would react with 1a in a similar fashion.
Isothiocyanates (RNꢁCꢁS) are nitrogen-containing
analogues of CS2, and often undergo similar reactions
[7,8,10–15]. Compound 1a reacts with n-butyl iso-
thiocyanate,
forming
[RhIr(CCPh)(CO)2(m-h1:h1-
SCNnBu)(dppm)2][BF4] (6), as shown in Scheme 2.
Both carbonyls are terminal, as shown by the
13C{1H} NMR spectra, in which one is clearly
rhodium-bound (l 188.5; 1JRhC=73 Hz), and the
other is bound to iridium (l 154.6). Although this
latter resonance is at rather high field for an iridium-
bound carbonyl that is also in the vicinity of the
adjacent rhodium center, as described previously [2],
Along with the two compounds described above,
addition of carbon disulfide to 1a also produces the
tricarbonyl phenylacetylide complex [RhIr(CO)2(m-
CCPh)(m-CO)(dppm)2][BF4] [25] and an equal amount
of an uncharacterized monocarbonyl complex
(13C{1H} NMR: l 169.1 (t)) that presumably also
contains CS2; each of these species is present as ap-

362
D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
Scheme 2.
sulfur–carbon bond. The 13C{1H} NMR spectrum of 7
shows that the alkynyl ligand remains terminally bound
to iridium (l 69.0 (t), Ca; l 108.3 (s), Cb), while one
carbonyl is rhodium-bound, appearing as a doublet of
triplets (l 188.8, 1JRhC=70 Hz), and the other (a
multiplet at l 195.1, showing significant coupling (18
Hz) to the rhodium center) is semibridging. This assign-
ment is supported by the IR spectrum, which shows
bands due to both bridging/semibridging (wCO=1825
cm−1) and terminal (wCO=1985 cm−1) carbonyls. The
the position of this carbonyl is supported by the facile
rearrangement of 6 to 7 (vide infra), the latter of which
has been structurally characterized by an X-ray study.
1
Both the H and 13C{1H} NMR spectra of 6 show the
presence of only one butyl group, suggesting that only
one isothiocyanate moiety reacts with 1a despite the
large excess used. The 13C{1H} NMR spectrum of 6
also shows that the alkynyl ligand is terminally bound
to iridium (Ca, l 55.3 (t); Cb, l 108.7 (s)). The displace-
ment of the alkynyl group from the bridging position
suggests that the isothiocyanate ligand has adopted
this site, giving a structure analogous to that of
[Rh2Cl2(CO)(m-SCNCO2Et)(dppm)2] [11d]. The 13C
NMR signal for the isothiocyanate carbon appears as a
triplet at l 140.5, and the lack of rhodium coupling
suggests that the isothiocyanate ligand is bound to
iridium through the carbon atom, and sulfur-bound to
the rhodium center.
IR spectrum also shows a strong band at 2126 cm−1
which is typical for a coordinated isocyanide [7a].
,
The structure of the isocyanide complex 7 was deter-
mined by X-ray crystallography, and is shown in Fig. 2.
Bond lengths and angles are given in Tables 5 and 6,
respectively. The n-butyl isothiocyanate ligand is shown
to have undergone oxidative carbon–sulfur bond cleav-
At −80°C the reaction of 1a with SCNnBu showed
the presence of an additional product [RhIr(CO)(h2-
SCNnBu)(m-CCPh)(m-CO)(dppm)2][BF4] (5) together
with the starting material. Although not completely
characterized, it appears clear that this product is the
analogue of the CS2 adduct (2), in which the SCNnBu
group is h2-bound to Ir. Consistent with this proposal
the resonances for the Rh-bound 31P nuclei are very
similar in the two compounds, with a significant differ-
ence at the Ir end owing to the binding of the different
groups (CS2 or SCNnBu). Warming the solution slightly
results in a smooth transformation from the h2-bound
complex (5) to the isothiocyanate-bridged complex (6).
The proposed arrangement of the isothiocyanate lig-
and in 6 is supported by the facile conversion of this
complex to the oxidative-addition product [RhIr-
(CCPh)(CO)(CNnBu)(m-S)(m-CO)(dppm)2][BF4]
(7),
Fig. 2. Perspective view of the [RhIr(CCPh)(CO)(CNnBu)(m-S)(m-
CO)(dppm)2]+ cation of 7 showing the atom labeling. Thermal
parameters shown as in Fig. 1.
which occurs slowly upon standing in solution or more
rapidly upon heating, through oxidative cleavage of the

D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
363
Table 5
Selected interatomic distances (A) in compound 7
terminal carbonyl ligand occupying the basal sites, and
the bridging carbonyl occupying the apical site. In this
case, however, the interaction between this carbonyl
and rhodium is stronger. The carbonyl is asymmetri-
cally bound as shown by the angles at C(2)
(RhꢀC(2)ꢀO(2)=125.7(3)°; IrꢀC(2)ꢀO(2)=144.6(3)°;
,
IrꢀRh
IrꢀS
2.9182(4)
2.4828(11)
2.3626(11)
2.3664(11)
1.988(5)
2.056(4)
2.019(4)
2.3513(11)
2.3399(11)
2.3291(12)
2.084(4)
P(2)ꢀC(6)
P(3)ꢀC(7)
P(4)ꢀC(7)
O(2)ꢀC(2)
O(5)ꢀC(5)
NꢀC(1)
1.835(4)
1.833(5)
1.839(5)
1.166(5)
1.136(6)
1.147(6)
1.444(6)
1.205(6)
1.445(7)
1.509(8)
1.517(8)
1.511(9)
IrꢀP(1)
IrꢀP(3)
IrꢀC(1)
IrꢀC(2)
IrꢀC(3)
RhꢀS
RhꢀP(2)
RhꢀP(4)
RhꢀC(2)
RhꢀC(5)
P(1)ꢀC(6)
,
although the asymmetry in the RhꢀC(2) (2.084(4) A)
,
and IrꢀC(2) (2.056(4) A) is not as pronounced as indi-
NꢀC(97)
cated by the angles. Consistent with a description of
C(2)O(2) as an asymmetrically bridged rather than a
semibridging carbonyl [26], the RhꢀIr distance
C(3)ꢀC(4)
C(4)ꢀC(91)
C(97)ꢀC(98)
C(98)ꢀC(99)
C(99)ꢀC(100)
,
(2.9182(4) A) is shorter than that in 3 and more consis-
1.874(5)
1.833(4)
tent with a normal RhꢀIr single bond. If C(2)O(2) were
considered as purely semibridging, it would be func-
tioning as a two-electron s-donor to Ir and as an
acceptor from Rh. In this formulation the 16- and
18-electron configurations at Rh(+1) and Ir(+3), re-
spectively, would require no metal–metal bond. All
parameters within the structure suggest a significant
component of metal–metal bonding, which necessitates
a description of the carbonyl as a conventional bridging
carbonyl, in which it functions as a one-electron donor
to each metal. The observed asymmetry can be ration-
alized as due to the more severe crowding about Ir.
Clearly however the transition between semibridging
CO (or a terminal CO on Ir) having no accompanying
RhꢀIr bond, and classical bridging CO with RhꢀIr
bond is not abrupt, but is gradual. The description of
the bonding in 7 is therefore most consistent with a
structure intermediate between the two extremes dis-
cussed above. Apparently the structures of 7 in solution
and in the solid state differ slightly. The 18 Hz coupling
of the bridging carbonyl to Rh in the 13C solution
NMR is more consistent with a semibridging than with
a conventional bridging arrangement (for which a value
near 30 Hz is expected).
Table 6
Selected interatomic angles (°) in compound 7
RhꢀIrꢀS
50.83(3)
90.01(3)
89.70(3)
132.50(13)
45.57(12)
140.72(13)
90.70(4)
SꢀRhꢀC(2)
SꢀRhꢀC(5)
99.73(12)
161.66(15)
159.74(4)
98.84(11)
95.71(14)
98.28(11)
92.36(14)
98.58(19)
74.21(3)
110.75(15)
114.33(14)
110.98(15)
113.41(15)
178.0(5)
177.6(4)
89.64(17)
144.6(3)
125.7(3)
167.7(4)
175.0(5)
173.5(5)
111.9(2)
111.4(2)
120.3(5)
121.7(5)
110.7(5)
114.3(5)
112.4(6)
RhꢀIrꢀP(1)
RhꢀIrꢀP(3)
RhꢀIrꢀC(1)
RhꢀIrꢀC(2)
RhꢀIrꢀC(3)
SꢀIrꢀP(1)
SꢀIrꢀP(3)
SꢀIrꢀC(1)
SꢀIrꢀC(2)
SꢀIrꢀC(3)
P(1)ꢀIrꢀP(3)
P(1)ꢀIrꢀC(1)
P(1)ꢀIrꢀC(2)
P(1)ꢀIrꢀC(3)
P(3)ꢀIrꢀC(1)
P(3)ꢀIrꢀC(2)
P(3)ꢀIrꢀC(3)
C(1)ꢀIrꢀC(2)
C(1)ꢀIrꢀC(3)
C(2)ꢀIrꢀC(3)
IrꢀRhꢀS
IrꢀRhꢀP(2)
IrꢀRhꢀP(4)
IrꢀRhꢀC(2)
IrꢀRhꢀC(5)
SꢀRhꢀP(2)
SꢀRhꢀP(4)
P(2)ꢀRhꢀP(4)
P(2)ꢀRhꢀC(2)
P(2)ꢀRhꢀC(5)
P(4)ꢀRhꢀC(2)
P(4)ꢀRhꢀC(5)
C(2)ꢀRhꢀC(5)
IrꢀSꢀRh
IrꢀP(1)ꢀC(6)
RhꢀP(2)ꢀC(6)
IrꢀP(3)ꢀC(7)
89.96(4)
81.67(13)
96.41(12)
168.42(13)
178.88(4)
91.70(13)
89.13(11)
90.10(13)
89.29(13)
89.89(11)
89.44(13)
177.92(17)
86.76(18)
95.15(17)
54.95(3)
RhꢀP(4)ꢀC(7)
C(1)ꢀNꢀC(97)
IrꢀC(1)ꢀN
IrꢀC(2)ꢀRh
IrꢀC(2)ꢀO(2)
RhꢀC(2)ꢀO(2)
IrꢀC(3)ꢀC(4)
C(3)ꢀC(4)ꢀC(91)
RhꢀC(5)ꢀO(5)
P(1)ꢀC(6)ꢀP(2)
P(3)ꢀC(7)ꢀP(4)
C(4)ꢀC(91)ꢀC(92)
C(4)ꢀC(91)ꢀC(96)
NꢀC(97)ꢀC(98)
C(97)ꢀC(98)ꢀC(99)
C(98)ꢀC(99)ꢀC(100)
92.02(3)
92.53(3)
44.78(12)
143.35(15)
82.31(4)
The presence of a bridging carbonyl in 7 is not
surprising, as the change in coordination number of
iridium from five (in compound 6) to six would force
the carbonyl into the vicinity of the rhodium center,
allowing bonding to take place. In addition, the formal
oxidation of the iridium and the presence of the p-
acidic isocyanide ligand will reduce the electron density
of this metal, making the iridium-bound carbonyl more
likely to accept electron density from rhodium.
84.20(4)
With t-butylisothiocyanate, no reaction is observed
under mild conditions (ambient and lower). However,
refluxing in acetonitrile does result in a reaction as
indicated by the dramatic color change from purple to
orange. 31P{1H} NMR monitoring of the solution
shows two products. The minor product, in between 2
and 14% spectroscopic yield is proposed to be [RhIr-
(CCPh)(CO)2(CNtBu)(m-S)(dppm)2][BF4] (8), based on
a comparison of its 31P{1H} spectral parameters with
those of the analogous n-butylisocyanide product (7),
although the small amounts of this product precluded a
age, resulting in the formation of a bridging sulfido
ligand and an n-butyl isocyanide ligand, which remain
mutually cis. The coordination geometries of the two
metal centers are much like those described for com-
pound 3. The ligands bound to iridium are arranged in
an octahedral manner, with the bridging sulfide, iso-
cyanide, and alkynyl ligands occupying the coordina-
tion sites occupied in 3 by the vinylidene/C2S4 moiety.
Likewise, rhodium adopts a square pyramidal configu-
ration, with the trans phosphines, bridging sulfide, and

364
D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
Table 8
complete characterization. The major product was
shown, on the basis of elemental analysis and spectral
results, to have resulted from incorporation of two
isothiocyanate molecules. The X-ray structure determi-
nation established that SꢀC bond cleavage has occurred
for both isothiocyanate molecules, yielding the bis-
sulfide-bridged product [RhIr(CCPh)(CO)(CNtBu)2(m-
S)2(dppm)2][BF4] (9), as shown in Fig. 3. In the IR
spectrum, the isocyanide groups show CN stretches at
2199 and 2178 cm−1, the terminal alkynyl CC stretch
appears at 2119 cm−1 and the lone carbonyl appears at
2031 cm−1, consistent with an Ir+3 formulation. In the
X-ray structure both metals are shown to have very
similar octahedral coordinations, which differ in having
both isocyanide ligands bound to Rh, while the car-
bonyl and alkynyl groups are bound terminally to Ir.
All parameters involving these groups are normal (see
Tables 7 and 8). The metals are not mutually bonded,
Selected interatomic angles (°) in compound 9
S(1)ꢀIrꢀS(2)
S(1)ꢀIrꢀP(1)
S(1)ꢀIrꢀP(3)
S(1)ꢀIrꢀC(1)
S(1)ꢀIrꢀC(2)
S(2)ꢀIrꢀP(1)
S(2)ꢀIrꢀP(3)
S(2)ꢀIrꢀC(1)
S(2)ꢀIrꢀC(2)
P(1)ꢀIrꢀP(3)
P(1)ꢀIrꢀC(1)
P(1)ꢀIrꢀC(2)
P(3)ꢀIrꢀC(1)
P(3)ꢀIrꢀC(2)
C(1)ꢀIrꢀC(2)
S(1)ꢀRhꢀS(2)
S(1)ꢀRhꢀP(2)
S(1)ꢀRhꢀP(4)
S(1)ꢀRhꢀC(4)
S(1)ꢀRhꢀC(5)
S(2)ꢀRhꢀP(2)
S(2)ꢀRhꢀP(4)
S(2)ꢀRhꢀC(4)
S(2)ꢀRhꢀC(5)
P(2)ꢀRhꢀP(4)
P(2)ꢀRhꢀC(4)
83.8(2)
90.2(2)
85.8(2)
91.0(8)
177.3(7)
83.2(2)
88.8(2)
173.9(8)
96.8(8)
171.4(2)
93.8(9)
92.5(7)
94.0(9)
91.5(7)
88.6(11)
85.4(2)
84.4(3)
89.9(2)
174.8(7)
86.3(8)
85.0(2)
83.4(2)
99.1(8)
171.4(8)
167.4(2)
93.4(8)
P(2)ꢀRhꢀC(5)ꢀ96.5(8)
P(4)ꢀRhꢀC(4)
P(4)ꢀRhꢀC(5)
C(4)ꢀRhꢀC(5)
IrꢀS(1)ꢀRh
IrꢀS(2)ꢀRh
IrꢀP(1)ꢀC(6)
RhꢀP(2)ꢀC(6)
IrꢀP(3)ꢀC(7)
96.5(8)
93.2(8)
94.3(8)
89.3(11)
95.3(2)
95.5(2)
111.9(9)
117.2(8)
115.2(8)
113.0(8)
177(3)
176(3)
178(3)
173(3)
168(3)
167(3)
25(2)
172(3)
178(2)
RhꢀP(4)ꢀC(7)
C(4)ꢀN(4)ꢀC(40)
C(5)ꢀN(5)ꢀC(50)
IrꢀC(1)ꢀO(1)
IrꢀC(2)ꢀC(3)
C(2)ꢀC(3)ꢀC(91A)
C(2)ꢀC(3)ꢀC(91B)
C(91A)ꢀC(3)ꢀC(91B)
RhꢀC(4)ꢀN(4)
RhꢀC(5)ꢀN(5)
,
as shown by the long RhꢀIr separation (3.550(2) A),
P(1)ꢀC(6)ꢀP(2)
P(3)ꢀC(7)ꢀP(4)
C(3)ꢀC(91A)ꢀC(92A)
C(3)ꢀC(91A)ꢀC(96A)
C(3)ꢀC(91B)ꢀC(92B)
C(3)ꢀC(91B)ꢀC(96B)
119.3(13)
120.1(13)
128(3)
112(3)
111(3)
which is even longer than the intraligand PꢀP separa-
,
tions (3.156(10) and 3.153(10) A). There is a slight
asymmetry in the binding of the bridging sulfide ligands
129(3)
,
(RhꢀS=2.383(7), 2.379(7) A; IrꢀS=2.422(6), 2.417(7)
,
A) with both of these groups being more strongly
bound to Rh.
4. Discussion
The reaction of carbon disulfide with the A-frame
complexes [RhIr(CO)2(m-CCPh)(dppm)2][X] (X=BF4
(1a), SO3CF3 (1b)) gives two interesting products result-
ing from condensation of two carbon disulfide
molecules at the iridium center. Although the formation
of a thioacyl/trithiocarbonate moiety has been previ-
ously observed in the reaction of CS2 with several
systems [9], the coupling of this C2S4 fragment with an
organic ligand (in this case an alkynyl ligand to yield 3)
is apparently unprecedented. The condensation of a
terminal phenyl acetylide with two equivalents of
phenylisothiocyanate has been reported [8f].
The first step in the reaction of 1 with CS2 appears to
be the formation of the CS2 adduct 2, which is formed
exclusively at −80°C. This product is spectrally very
similar to a series of olefin adducts of 1, the struc-
tures of which were established by the X-ray structure
determination of the dimethyl allene adduct [2].
Upon warming in the presence of CS2, 2 is con-
verted into other products, of which [RhIr(CO)2(m-
CC(Ph)SC(S)SCS)(dppm)2][X] (3) and [RhIr(CO)2(m-
Fig. 3. Perspective view of the [RhIr(CCPh)(CO)(CNtBu)2(m-
S)2(dppm)2]+ cation of 9. Thermal parameters as in Fig. 1.
Table 7
,
Selected interatomic distances (A) in compound 9
IrꢀS(1)
IrꢀS(2)
2.422(6)
2.417(7)
2.337(7)
2.344(7)
1.90(3)
P(1)ꢀC(6)
P(2)ꢀC(6)
P(3)ꢀC(7)
P(4)ꢀC(7)
O(1)ꢀC(1)
N(4)ꢀC(4)
N(4)ꢀC(40)
N(5)ꢀC(5)
N(5)ꢀC(50)
C(2)ꢀC(3)
C(3)ꢀC(91A)a
C(3)ꢀC(91B)a
1.83(2)
1.83(2)
1.83(2)
1.81(2)
1.14(3)
1.15(3)
1.49(4)
1.15(3)
1.52(4)
1.18(3)
1.49(4)
1.45(4)
IrꢀP(1)
IrꢀP(3)
IrꢀC(1)
IrꢀC(2)
RhꢀS(1)
RhꢀS(2)
RhꢀP(2)
RhꢀP(4)
RhꢀC(4)
RhꢀC(5)
2.04(3)
2.383(7)
2.379(7)
2.342(7)
2.351(7)
1.99(3)
1.99(3)
a See Section 2.6.3 for an explanation of phenyl group disorder.

D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
365
CCPh)(C2S4)(dppm)2][X] (4) are the only CS2-contain-
ing species characterized. Although 3 slowly converts
into 4 upon standing, this cannot be the sole source of
4 in the reaction of 1+CS2 since 3 and 4 appear
simultaneously in the reaction, at a rate much faster
than the 3 to 4 conversion. We suggest that 2 can react
in two ways as outlined in Scheme 3. It is known that
the uncoordinated sulfur of an h2-CS2 fragment is
nucleophilic and can react with an additional CS2
molecule. This would yield the C2S4 product 4. How-
ever, nucleophilic attack of a m-h1:h2-acetylide at the
b-carbon can also occur [2,5], in this case yielding an
intermediate such as K. Subsequent reaction of this
intermediate with additional CS2 could yield the
product 3. The slow conversion of 3 to 4 presumably
results from the strain within the vinylidene-containing
metallacycle, leading to cleavage of the sulfur–carbon
bond. The strain between the vinylidene and sulfur-con-
taining parts of the metallacycle is clearly demonstrated
by the structural parameters of this moiety (vide supra).
Although isothiocyanate molecules are closely related
to CS2 and can react analogously, the 1:1 isothio-
cyanate adduct that is analogous to the CS2 (2) and
olefin adducts [2] is not observed at ambient tempera-
ture. However, at temperatures between −60 and
−80°C the h2-SCNnBu complex (5) is observed in the
reaction mixture, and upon warming, this intermediate
rearranges to 6, in which the isothiocyanate ligand
bridges the metals, as shown in Scheme 4. Compound 6
can result from a merry-go-round migration of the
ligands, as shown, in which movement of the isothio-
cyanate to the bridging site on one face of the complex
is accompanied by movement of the alkynyl group
from the bridging site on the opposite face to a terminal
position on Ir. Analogous adducts of t-butylisothio-
cyanate, in which this group binds either to Ir (as in 5)
or bridging the two metals (as in 6), are not observed.
Presumably the bulky t-butyl substituent destabilizes
these adducts, by interactions with the dppm phenyl
groups.
Scheme 3.
Scheme 4.

366
D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
Over a period of a few days at ambient temperature
predominant routes. In the presence of a sulfur-ab-
stracting ligand, such as a phosphine, metal isocyanides
and the corresponding sulfide (for example, phosphine
sulfide) are obtained [27], or in the presence of excess
isothiocyanate an isocyanide is again one of the frag-
ments obtained, but in this case the other fragment is a
dithiocarbonimidato ligand [28]. We have been unable
to locate other examples in the literature in which SꢀC
bond cleavage in isothiocyanates was induced merely
by coordination to one or more metals. However, this
may be facilitated by coordination in a bridging mode,
since we have previously observed SꢀC bond cleavage
of isothiocyanates in diiridium complexes again yielding
sulfide-bridged isocyanide products [29].
(or more quickly upon heating) cleavage of the SꢀC
bond in 6 occurs to yield the n-butylisocyanide product
t
7. When BuNCS is used, only small amounts of the
single CꢀS bond-cleavage product (8) is obtained at
ambient temperature, even after several days. However,
refluxing compound 1 together with an excess of
tBuNCS yields two products; the minor one is 8, which
has resulted from CꢀS bond cleavage of one isothio-
cyanate molecule, and the major product which has
resulted from CO loss and SꢀC bond cleavage of two
isothiocyanate molecules. We suggest that under excess
SCNtBu, refluxing compound 8 results in CO expulsion
and replacement by a second SCNtBu molecule, giving
an unobserved intermediate, L. Subsequent SꢀC bond
cleavage yields a disulfide species, in which dissociation
of the first isocyanide ligand from Ir and recoordina-
tion at Rh apparently occurs, yielding 9. Compound 7,
the result of oxidative SꢀC bond cleavage of one n-
butyl isothiocyanate molecule can also be induced to
oxidatively add a second isothiocyanate molecule.
Therefore refluxing 1a for a longer period in the pres-
ence of a fivefold excess of nBuNCS yields the bis-
isocyanide product [RhIr(CCPh)(CO)(CNnBu)2(m-S)2-
(dppm)2][BF4] (10), however this has not yet been ob-
tained in a pure form, and two of the other major
products have not been identified.
Although isothiocyanates are known to condense at
metals, as observed with the (CS2)2 products 3 and 4,
this was not observed in the present chemistry. The
lower tendency of the isothiocyanate molecule to con-
dense than CS2 is presumably a function of the struc-
tural differences in these molecules. Two resonance
structures are of importance for the h2-thiaallene
molecule as shown in M and N. With X=NR the
carbon–nitrogen p overlap of these second-row ele-
ments is effective so structure M is favorable, whereas
for CS2 the carbon–sulfur p overlap is less effective
(one being second row while the other is third row)
leading to an increased contribution from structure N.
5. Conclusions
The acetylide-bridged A-frame complex [RhIr(CO)2-
(m-h1:h2-C2Ph)(dppm)2]+ reacts readily with CS2 and
the two isothiocyanates SCNR (R=nBu, tBu). Al-
though CS2 and SCNnBu react analogously at low
temperature, yielding the 1:1 adducts [RhIr(CO)(h2-
SCX)(m-C2Ph)(m-CO)(dppm)2]+ (X=S, NBu), their re-
activity differs appreciably at higher temperatures.
Whereas the CS2 adduct reacts with additional CS2
yielding two C2S4 products, the isothiocyanate ligand
apparently migrates from a terminal site on Ir to a
bridging site, followed by CꢀS bond cleavage to
give the sulfide-bridged, isocyanide products [RhIr-
(CCPh)(CO)(CNR)(m-S)(m-CO)(dppm)2]+, which upon
further refluxing can react with an additional mole-
cule of isothiocyanate to give the products [RhIr-
(CCPh)(CO)(CNBu)2(m-S)2(dppm)2]+, in which both
isothiocyanate molecules have been transformed to
isocyanides.
It was our goal to achieve coupling of the thiocumu-
lene molecules and the acetylide ligand, and this
was achieved only with CS2, yielding [RhIr(CO)(m-
h1:h3-CC(Ph)SCSCS2)(m-CO)(dppm)2]+. However, this
product is unstable and transforms to a related species
by cleavage of the CꢀS bond linking the acetylide and
the C2S4 groups, apparently to lower the strain within
the sulfur-containing, bridging macrocyclic group.
This binuclear system displays a number of extremely
facile CꢀS bond-forming and bond-cleavage processes.
This leads to a greater nucleophilicity of the bound CS2
and a greater tendency to condense with electrophilic
groups. In addition, the alkyl substituents on the iso-
thiocyanate molecules will hinder condensation reac-
tions for steric reasons so movement of the SCNR
moiety to the bridging site occurs more readily than
condensation with another SCNR molecule. Once in
the bridging site, SꢀC bond cleavage occurs leading to
the mono-sulfide products 7 (nBu) or 8 (tBu).
6. Supplementary material
Tables of X-ray experimental details, atomic coordi-
nates, interatomic distances and angles, anisotropic
thermal parameters, and hydrogen parameters for com-
pounds 3b, 7 and 9 (53 pages) are available from the
authors upon request.
Cleavage of the SꢀC bond of isothiocyanates has
previously been observed and appears to occur by two

D.S.A. George et al. / Inorganica Chimica Acta 300–302 (2000) 353–368
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Acknowledgements
We thank the Natural Sciences and Engineering Re-
search Council of Canada (NSERC) and the University
of Alberta for financial support of this research and
NSERC for support of the Bruker P4/RA/SMART
1000 CCD diffractometer.
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