Diverse reactivity of alkynes with the binuclear methyl and incipient methyl complexes [RhIr(CH3)(CO)3(Ph2PCH2PPh 2)2][CF3SO3] and [Ir2H(CO)3(μ-CH2)(Ph2PCH 2PPh2)2][CF3SO3]

Article abstract of DOI:10.1021/om9505118

The binuclear diiridium complex, [Ir₂H(CO)₃(μ-CH₂)(dppm)₂][CF ₃SO₃] (2), reacts with acetylene and phenylacetylene to give the alkyne- and vinylidene-bridged complexes, [Ir₂(CH₃)(CO)₃(μ-HC≡CR)(dppm) ₂][CF₃SO₃] and [Ir₂(CH₃)(CO)₃(μ-C=C(H)R)(dppm) ₂][CF₃SO₃] (R = H, Ph), respectively, in each case. At -78 °C in the acetylene reaction an intermediate acetylide-hydride, [Ir₂(H)(CH₃)(CO)₃(μ-C≡CH)(dppm) ₂)[CF₃SO₃], is observed, which transforms into the vinylidene product at higher temperature. The reaction of the related mixed-metal species [RhIr(CH₃)(CO)₃(dppm)₂][CF₃SO ₃] (1) with acetylene at -78 °C gives an acetylene-bridged intermediate analogous to that observed in the diiridium system, but warming to ambient temperature results in dissociation of the rhodium end of one of the diphosphines, which undergoes nucleophilic attack at the Rh end of the alkyne to yield [RhIr-(CH₃)(μ-η¹:η²:η ¹-HC=C(H)PPh₂CH₂PPh₂)(dppm)][CF ₃SO₃]. The reaction of 1 with phenylacetylene at -78 °C yields a methyl-hydrido-phenylacetylide intermediate analogous to that observed in diiridium-acetylene chemistry; however, upon warming reductive elimination of methane occurs to give the phenylacetylide-bridged species [RhIr(CO)₃(μ-C≡CPh)-(dppm)₂][CF ₃SO₃], which reacts with excess phenylacetylene to give the diacetylide-hydride product [RhIr(C≡CPh)(CO)₂(μ-H) (μ-C=CPh)(dppm)₂][CF₃SO₃]. Monitoring of the reaction at various temperatures by multinuclear NMR allows the characterization of the observed intermediates. Both compounds 1 and 2 react with dimethyl acetylenedicarboxylate (DMAD) to give the respective products [MIr(C(R)=C(CH₃)R)(CO)₃(dppm)₂][CF ₃SO₃] (M = Rh, Ir; R = CO₂Me) resulting from alkyne insertion into the metal-methyl bond. Also observed in the diiridium chemistry is the alkyne-bridged product [Ir₂(CH₃)(CO)₃(μ-DMAD)(dppm) ₂][CF₃-SO₃]. The structure of [RhIr(C≡CPh)(CO)₂(μ-H)(μ-C≡CPh)(dppm) ₂][CF₃SO₃] was determined by X-ray crystallography. This compound crystallizes with 2 equiv of CH₂Cl₂ in the monoclinic space group P2₁/c in a cell having a = 17.821(3) A?, b = 24.780(5) A?, c = 17.892(3) A?, β = 117.56(1)°, V = 7004(2) A?³, and Z = 4. On the basis of 8365 unique observations the structure has been refined to R = 0.064 and R_w = 0.083. Both acetylides are σ-bound to Ir in a mutually trans orientation, with one also engaging in a weak π-interaction with Rh. The hydride ligand bridges both metals on the face opposite the bridging acetylide group.

Full text of DOI:10.1021/om9505118

506
Organometallics 1996, 15, 506-520
Diver se Rea ctivity of Alk yn es w ith th e Bin u clea r Meth yl
a n d In cip ien t Meth yl Com p lexes
[Rh Ir (CH3)(CO)3(P h 2P CH2P P h 2)2][CF 3SO3] a n d
[Ir 2H(CO)3(µ-CH2)(P h 2P CH2P P h 2)2][CF 3SO3]
Frederick H. Antwi-Nsiah, Okemona Oke, and Martin Cowie*
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Received J uly 5, 1995X
The binuclear diiridium complex, [Ir2H(CO)3(µ-CH2)(dppm)2][CF3SO3] (2), reacts with
acetylene and phenylacetylene to give the alkyne- and vinylidene-bridged complexes,
[Ir2(CH3)(CO)3(µ-HCtCR)(dppm)2][CF3SO3] and [Ir2(CH3)(CO)3(µ-CdC(H)R)(dppm)2][CF3SO3]
(R ) H, Ph), respectively, in each case. At -78 °C in the acetylene reaction an intermediate
acetylide-hydride, [Ir2(H)(CH3)(CO)3(µ-CtCH)(dppm)2)[CF3SO3], is observed, which trans-
forms into the vinylidene product at higher temperature. The reaction of the related mixed-
metal species [RhIr(CH3)(CO)3(dppm)2][CF3SO3] (1) with acetylene at -78 °C gives an
acetylene-bridged intermediate analogous to that observed in the diiridium system, but
warming to ambient temperature results in dissociation of the rhodium end of one of the
diphosphines, which undergoes nucleophilic attack at the Rh end of the alkyne to yield [RhIr-
(CH3)(µ-η1:η2:η1-HCdC(H)PPh2CH2PPh2)(dppm)][CF3SO3]. The reaction of 1 with phenyl-
acetylene at -78 °C yields a methyl-hydrido-phenylacetylide intermediate analogous to
that observed in diiridium-acetylene chemistry; however, upon warming reductive elimina-
tion of methane occurs to give the phenylacetylide-bridged species [RhIr(CO)3(µ-CtCPh)-
(dppm)2][CF3SO3], which reacts with excess phenylacetylene to give the diacetylide-hydride
product [RhIr(CtCPh)(CO)2(µ-H) (µ-CtCPh)(dppm)2][CF3SO3]. Monitoring of the reaction
at various temperatures by multinuclear NMR allows the characterization of the observed
intermediates. Both compounds 1 and 2 react with dimethyl acetylenedicarboxylate (DMAD)
to give the respective products [MIr(C(R)dC(CH3)R)(CO)3(dppm)2][CF3SO3] (M ) Rh, Ir; R
) CO2Me) resulting from alkyne insertion into the metal-methyl bond. Also observed in
the diiridium chemistry is the alkyne-bridged product [Ir2(CH3)(CO)3(µ-DMAD)(dppm)2][CF3-
SO3]. The structure of [RhIr(CtCPh)(CO)2(µ-H)(µ-CtCPh)(dppm)2][CF3SO3] was determined
by X-ray crystallography. This compound crystallizes with 2 equiv of CH2Cl2 in the
monoclinic space group P21/c in a cell having a ) 17.821(3) Å, b ) 24.780(5) Å, c ) 17.892(3)
Å, â ) 117.56(1)°, V ) 7004(2) Å3, and Z ) 4. On the basis of 8365 unique observations the
structure has been refined to R ) 0.064 and Rw ) 0.083. Both acetylides are σ-bound to Ir
in a mutually trans orientation, with one also engaging in a weak π-interaction with Rh.
The hydride ligand bridges both metals on the face opposite the bridging acetylide group.
In tr od u ction
undergo migratory insertion reactions into metal-
carbon,9,10metal-hydride,1,11 or metal-heteroatom12
bonds. Although examples of alkyne insertions into
metal-hydride bonds are not as well-documented as
those involving olefins,11 they are nevertheless rather
common. In contrast, insertions of alkynes into metal-
alkyl or related bonds are not still common,9f,10 in spite
of their obvious significance in C-C-bond-forming pro-
cesses.
Binuclear complexes add an additional dimension to
the chemistry of alkynes since, in addition to reactivity
at either one of the metal centers, the involvement of
both metals is also possible. This is readily seen in the
two alkyne bridging modes that are possible, in which
the alkyne orients itself either parallel or perpendicular
to the metal-metal axis.13 The reactivity of bridging
alkyne groups continues to be a topic of interest14 in
efforts to determine the possible effects of adjacent
metals on the chemistry.
The alkyne molecule can display a wealth of chem-
istry in its reactions with transition metal complexes.1
Not only can it bind in the η2-fashion, in which it can
function as either a two- or a four-electron donor,1,2 but
it can also undergo a variety of transformations, yielding
acetylide3 or vinylidene4 ligands, as well as products of
alkyne condensation with substrates such as CO,5 CS2,6
olefins,7 or other alkyne molecules.8 Alkynes can also
X Abstract published in Advance ACS Abstracts, November 15, 1995.
(1) Davidson, J . L. Reactions of Coordinated Acetylenes. In Reactions
of Coordinated Ligands; Braterman, P. S., Eds.; Plenum Press: New
York, 1986; Vol. 1, p 825.
(2) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; p 156.
(3) (a) Werner, H.; Hohn, A.; Schulz, M. J . Chem. Soc., Dalton Trans.
1991, 777. (b) Bianchini, C.; Peruzzini, M.; Vacca, A.; Zanobini, F.
Organometallics 1991, 10, 3697. (c) Holton, J .; Lappert, M. F.; Pearce,
R.; Yarrow, P. I. W. Chem. Rev. 1983, 83, 135 and references cited
therein.
As part of an ongoing interest in alkyne reactivity at
two adjacent metals,15-17 we have been investigating the
migratory insertions of alkynes into metal-hydrogen16
(4) (a) Bruce, M. I. Chem. Rev. 1991, 91, 197 and references cited
therein. (b) Werner, H. Angew. Chem., Int. Ed. Engl. 1990, 29, 1077
and references cited therein.
0276-7333/96/2315-0506$12.00/0 © 1996 American Chemical Society

Reactivity of Alkynes with Rhodium and Iridium Complexes
Organometallics, Vol. 15, No. 2, 1996 507
or metal-carbon bonds, with the aim of yielding vinyl
complexes, and the transformations of alkyne molecules
to vinylidene ligands,17 again with the aim of effecting
carbon-hydrogen or carbon-carbon bond formation. As
part of this study, we undertook an investigation into
the reactivity of the related compounds, [RhIr(CH3)-
(CO)3(dppm)2][CF3SO3] (1) and [Ir2H(CO)3(µ-CH2)-
(dppm)2][CF3SO3] (2),18 with alkynes. Although at a
glance these compounds appear substantially different,
one being a methyl complex and the other being a
methylene-bridged hydride, they are in fact more closely
related than these ground state formulations suggest.
In compound 2 it has been shown that facile scrambling
of the hydride ligand and the methylene hydrogens
occurs via a labile methyl intermediate,18,19 which is
presumed to be rather similar to 1. It was reasoned
that in 1, and in the methyl intermediate involved in
the rearrangement of 2, the coordinative unsaturation
at one metal could serve as a site of alkyne coordination,
leading to species that might be capable of C-C-bond-
forming reactions. In addition, the diiridium species 2
presents the additional possibilities of alkyne insertions
involving the hydride or bridging methylene group.
In this paper we report the results of an investigation
into the reactivities of compounds 1 and 2 with a
number of alkyne molecules, demonstrating an interest-
ing diversity in reactivities that is alkyne- and metal-
dependent.
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Exp er im en ta l Section
Gen er a l Con sid er a tion s. All solvents were dried using
the appropriate drying agents, distilled before use, and stored
under argon. Deuterated solvents used for NMR experiments
were degassed and stored under argon over molecular sieves.
Reactions were carried out at room temperature unless
otherwise noted by using standard Schlenk procedures, and
compounds obtained as solids were purified by recrystalliza-
tion. A flow rate of ca. 0.2 mL s-1 was employed for all
reactions that involved purging a solution with a gas. Acety-
lene was obtained from Matheson, while 13C-labeled acetylene
was purchased from Cambridge Isotopes and 13CO (99%) was
supplied by Isotec Inc. All gases were used as received. The
hydrated rhodium(III) and iridium(III) chlorides were pur-
chased from Engelhard Scientific or Vancouver Island Precious
Metals, whereas dimethyl acetylenedicarboxylate (DMAD) and
phenylacetylene were obtained from Aldrich. The compounds
[RhIr(CH3)(CO)3(dppm)2][CF3SO3] (1) and [Ir2H(CO)3(µ-CH2)-
(dppm)2][CF3SO3] (2) were prepared as previously reported.18
Routine NMR spectra were recorded on a Bruker AM-400
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1
spectrometer at 400.1 MHz for H, 161.9 MHz for 31P{1H}, and
100.6 MHz for 13C{1H} spectra. The 13C{1H}{31P} NMR
experiments were obtained on a Bruker WH-200 spectrometer
operating at 50.32 MHz. All 13C NMR spectra were obtained
with use of 13C-enriched samples unless otherwise noted.
Infrared spectra were run on a Nicolet 7199 FT interferometer
or a Perkin-Elmer 883 IR spectrometer either as Nujol mulls
on KBr plates or as solutions in KCl cells with 0.5 mm path
lengths. Unless otherwise noted, IR spectra were carried out
on samples containing the isotopes in their natural abundance.
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preparation.

508 Organometallics, Vol. 15, No. 2, 1996
Antwi-Nsiah et al.
Spectroscopic parameters for the compounds prepared are
found in Table 1. Elemental analyses were performed by the
microanalytical service within the department.
orange again. The orange product was obtained in 70% yield.
Anal. Calcd for IrRhClSP4F3O5C69.5H56: C, 55.10; H, 3.72; Cl,
2.34. Found: C, 54.38; H, 3.70; Cl, 2.00.
P r ep a r a t ion of Com p ou n d s. (a ) [Ir 2(CH 3)(CO)3(µ-
CdCH2)(dppm )2][CF3SO3] (4). The compound [Ir2(H)(CO)3(µ-
CH2)(dppm)2][CF3SO3] (2) (60 mg, 0.043 mmol) was dissolved
in 7 mL of CH2Cl2 in a round-bottomed flask. The solution
was then cooled to -78 °C by immersing the flask in a dry
ice/acetone bath. Acetylene was then passed through the
solution for 1 min, after which time the mixture was stirred
under a static atmosphere of the gas for 30 min at -78 °C
and then warmed to room temperature. After the solution was
stirred for 2 h at this temperature, during which time the
color changed from orange to yellow, the solvent was removed
under vacuum and the solid was recrystallized from CH2Cl2/
Et2O, yielding a yellow product in 84% yield. Anal. Calcd for
Ir2SP4F3O4C59H49: C, 47.96; H, 3.46. Found: C, 47.76; H, 3.36.
(b) [Ir 2(H)(CH3)(CO)3(µ-η1:η2-CtCH)(d p p m )2][CF 3SO3]
(5). Excess acetylene (20 mL) was added, by means of a gas-
tight syringe, to a solution of compound 2 (30 mg, 0.021 mmol)
in 0.6 mL of CD2Cl2 at -78 °C in an NMR tube capped with a
rubber septum. NMR spectra obtained at -80 or -40 °C
showed the presence of compound 5, which was not isolated
as a solid.
(c) [Ir 2(CH3)(CO)3(µ-P h C2H)(d p p m )2][CF3SO3] (7). Com-
pound 2 (60 mg, 0.043 mmol) was dissolved in 10 mL of CH2-
Cl2. After the solution was cooled to -78 °C, 1 equiv (4.7 µL,
0.043 mmol) of phenylacetylene was added. The orange
mixture was stirred for 1 h at that temperature. It was then
warmed to room temperature and stirred for another 1 h,
during which time the color slowly changed to brown. The
solvent was then removed under vacuum, and the residue was
recrystallized from CH2Cl2/Et2O to give a brown product (76%
yield). Anal. Calcd for Ir2SP4F3O6C63H53: C, 50.32; H, 3.55.
Found: C, 49.52; H, 3.36.
(d) [Rh Ir (CH3)(CO)3(µ-C2H2)(dppm )2][CF3SO3] (9). Com-
pound 1 (30 mg, 0.023 mmol) was dissolved in 0.6 mL of CD2-
Cl2 in an NMR tube capped by a rubber septum and then
cooled to -78 °C. Excess acetylene (ca. 20 mL) was then slowly
added to the solution by means of a gas-tight syringe. Warm-
ing the sample to -40 °C yielded compound 9, which was
characterized by its NMR spectra (compound 9 was not
isolated as a solid).
(e)[Rh Ir (CH3)(CO)3(d p p m )(HCdC(H)P (P h 2)CH2P P h 2)]-
[CF 3SO3] (10). Acetylene was passed through a solution of
compound 1 (60 mg, 0.046 mmol) in 10 mL of CH2Cl2, which
had been cooled to -78 °C, for 1 min. The solution was stirred
under a static atmosphere of the gas at this temperature for
about 10 min and then warmed to room temperature. To
obtain NMR spectra, the reaction was carried out in CD2Cl2
solution under the same conditions, and the spectra were
obtained after keeping the solution at room temperature for
about 5 min. Attempts to precipitate the product as a solid
resulted in several decomposition products.
(h ) [Rh Ir (RCdC(CH3)R)(CO)3(d p p m )2][CF 3SO3] (R )
CO2Me) (16). Compound 1 (60 mg, 0.046 mmol) was dissolved
in 5 mL of CH2Cl2, and 1 equiv (5.6 µL, 0.046 mmol) of DMAD
was added. The solution was then stirred for 1 h, after which
time the solvent was removed under vacuum. The residue was
then recrystallized from CH2Cl2/Et2O, giving a yellow product
(75% yield). Anal. Calcd for IrRhSP4F3O10C61H53: C, 50.38;
H, 3.67. Found: C, 49.42; H, 3.44.
R ea ct ion of Com p ou n d 2 w it h Acet ylen e a t R oom
Tem p er a tu r e. The procedure was the same as that used for
the preparation of compound 4 as stated earlier, except that
the entire reaction was carried out at room temperature for 1
h, yielding a mixture of compound 4 and [Ir2(CH3)(CO)3(µ-
C2H2)(dppm)2][CF3SO3] (3) as products.
Rea ction of Com p ou n d 2 w ith P h en yla cetylen e a t
Room Tem p er a tu r e. The procedure was the same as that
used for the preparation of compound 7 as stated earlier,
except that the entire reaction was carried out at room
temperature for 1 h, yielding a mixture of compound 7 and
[Ir2(CH3)(CO)3(µ-CdC(H)Ph)(dppm)2][CF3SO3] (8) as products.
Rea ction of Com p ou n d 2 w ith DMAD. The procedure
was the same as that used for the preparation of compound
16, except that compound 2 was used instead of compound 1
and the mixture was stirred for 2 h instead of 1 h. A mixture
of the compounds [Ir2(RCdC(CH3)R)(CO)3(dppm)2][CF3SO3] (R
) CO2Me) (17) and [Ir2(CH3)(CO)3(µ-DMAD)(dppm)2][CF3SO3]
(18) was obtained, as shown by the NMR spectra. The reaction
was repeated using a procedure similar to that employed for
the preparation of compound 7, except that DMAD was used
instead of phenylacetylene and the color of the solution
changed from orange to yellow. This reaction yielded the same
products as those obtained from the reaction carried out at
room temperature.
Rea ction of Com p ou n d 4 w ith P Me3. To a solution of
compound 4 (60 mg, 0.042 mmol) dissolved in 5 mL of THF
was added a solution of 1 equiv of PMe3 (42.0 µL of a 1 M
solution in THF) in 5 mL of THF. The solution was then
stirred for 2 h, during which time its color changed to lighter
yellow. The solvent was then removed under vacuum, and the
yellow solid was recrystallized from CH2Cl2/Et2O. The NMR
spectra showed that the product was the compound [Ir2-
(CH3)(CO)2(PMe3)(µ-CdCH2)(dppm)2][CF3SO3] (6).
Ch a r a cter iza tion of In ter m ed ia tes in th e Rea ction of
Com p ou n d 1 w ith Excess P h en yla cetylen e. Compound
1 (30 mg, 0.023 mmol) was dissolved in 0.6 mL of CD2Cl2 in
an NMR tube, capped with a rubber septum, and cooled to
-78 °C. Phenylacetylene (7.5 µL, 0.069 mmol) was then
added, and NMR spectra of the reaction mixture were obtained
at temperatures starting from -80 to +25 °C by warming the
probe to the desired temperature, with the sample in place,
and allowing the sample to stand for 20 min before recording
the spectra.
X-r a y Da ta Collection . Orange crystals of [RhIr(CtCPh)2-
(CO)2(µ-H)(dppm)2][CF3SO3]‚2CH2Cl2 (12) were obtained by
slow diffusion of ether into a concentrated CH2Cl2 solution of
the compound. Several suitable crystals were mounted and
flame-sealed in glass capillaries under solvent vapor to
minimize decomposition or deterioration due to solvent loss.
Data were collected on an Enraf-Nonius CAD4 diffractometer
by using graphite-monochromated Mo KR radiation. Unit cell
parameters were obtained from a least-squares refinement of
the setting angles of 25 reflections in the range 20.0° e 2θ e
24.0°. The monoclinic diffraction symmetry and the systematic
absences (h0l, l ) odd; 0k0, k ) odd) were consistent with the
space group P21/c.
(f) [R h Ir (µ-η1:η2-CtCP h )(CO)3(d p p m )2][CF 3SO3]‚1/2-
CH2Cl2 (11). To a solution of compound 1 (60 mg, 0.046
mmol) in 10 mL of CH2Cl2 was added 1 equiv (5.0 µL, 0.046
mmol) of phenylacetylene. The mixture was stirred for 2 h
under a slow stream of argon, during which time the color
changed from orange to red. The solvent volume was then
reduced to about 5 mL, and the red solid was precipitated
and washed with ether. The solid was collected and dried
under a stream of argon. After recrystallization from CH2-
Cl2/Et2O, the product was dried again under an argon
stream and then under vacuum (75% yield). Anal. Calcd for
IrRhClSP4F3O6C62.5H50: C, 52.06; H, 3.50. Found: C, 52.12;
H, 3.61.
(g) [Rh Ir (CtCP h )2(CO)2(µ-H)(dppm )2][CF3SO3]‚1/2CH2Cl2
(12). The procedure for preparing compound 12 was the same
as that described for compound 11, except that an excess (ca.
3 equiv) instead of 1 equiv of phenylacetylene was used, and
the solution color changed from orange to yellow and then to
Intensity data were collected at 22 °C by using the θ/2θ scan
technique to a maximum 2θ ) 50.0°, collecting reflections with
indices of the form +h, +k, (l. Backgrounds were scanned
for 25% of the peak width on either side of the peak scan. Three

Reactivity of Alkynes with Rhodium and Iridium Complexes
Organometallics, Vol. 15, No. 2, 1996 509
reflections were chosen as intensity standards and were re-
measured at 120 min intervals of X-ray exposure time. There
was no significant systematic decrease in the intensities of
these standards; thus, no decomposition correction was ap-
plied. A total of 12 976 unique reflections was measured and
processed in the usual way using a value of 0.04 for p20 to
downweight intense reflections; of these, 8365 were considered
bridges the two metals parallel to the metal-metal
axis,15c,e,i,28 and contrasts with the lower values of ca.
1425 cm-1 reported for [Rh2(CO)2(µ-η2:η2-PhC2H)(dppm)2]
and [Rh2(CO)2(µ-η2:η2-PhC2Ph)(dppm)2], in which the
alkyne bridges the metals perpendicular to the metal-
metal bond.29 The 13C{1H} NMR spectrum of compound
3, prepared by using acetylene that was 13C-enriched
at both positions, shows two doublets of multiplets at δ
160.7 and 147.1 (1J C-C ) 50.8 Hz) due to the two carbon
nuclei of the coordinated acetylene. These chemical
shifts are close to those in related systems in which the
alkyne bridges in an orientation parallel to the metal-
metal axis,17 suggesting such a bridging mode in
compound 3. The 1H NMR spectrum of this 13C-
enriched sample shows the proton resonances of the
bridging acetylene as two doublets of multiplets (1J C-H
≈ 160 Hz for each of the protons). In a sample of
compound 3 in which all of the carbon nuclei of the
bridging acetylene and CO ligands were 13C-enriched,
each of the carbonyl resonances at δ 194.4 and 181.3
shows strong coupling (21.0 Hz) to one of the carbon
nuclei of the coordinated acetylene, suggesting a trans
arrangement of the carbon atoms of the acetylene and
two of the CO ligands,29a as shown in Scheme 1.
2
to be observed [Fo g 3σ(Fo2)] and were used in subsequent
calculations. Absorption corrections were applied to the data
by using the method of Walker and Stuart.21,22 See Table 2
for crystal data and further information on X-ray data collec-
tion.
Str u ctu r e Solu tion a n d Refin em en t. The structure was
solved in the space group P21/c by using standard Patterson
and Fourier techniques. Full-matrix, least-squares refine-
2
ments minimized the function ∑w(|Fo| - |Fc|)2, where w ) 4Fo
/
σ2(Fo2). All non-hydrogen atoms ultimately were located. In
addition, two molecules of CH2Cl2 per formula unit of complex
were also located. Atomic scattering factors23,24 and anomalous
dispersion terms25 were taken from the usual tabulations.
Hydrogen atoms, with the exception of the methylene chloride
hydrogens, were included as fixed contributions but not
refined. Their idealized positions were calculated from the
geometries about the attached carbon atoms, using a C-H
bond length of 0.95 Å, and they were assigned thermal
parameters 20% greater than the equivalent isotropic B values
of their attached C atoms.
The 1H NMR spectrum of compound 4 shows the
methyl resonance as a triplet at δ -0.55 and the
vinylidene proton resonances as singlets at δ 6.40 and
5.72. The 13C{1H} NMR spectrum of a 13CO-enriched
sample shows a broad resonance at δ 181.2 and triplets
at δ 175.1 and 172.3, indicating the presence of three
CO ligands in compound 4. Although none of these
resonances is at low enough field to unequivocally
indicate the presence of a symmetrically bridging car-
bonyl ligand, the CO stretch at 1790 cm-1 in the IR
spectrum suggests the presence of some form of bridging
carbonyl ligand, presumably that giving rise to the
broad, low-field resonance at δ 181.2. However, since
this resonance is broad and the 31P resonances for 4 are
quite close, as shown in Table 1, 13C{31P}{1H} NMR
experiments (using the 13CO-enriched sample) do not
give much information about the nature of the bridging
interaction. The 13C{1H} NMR spectrum of 4, prepared
using 13C-enriched acetylene, shows a doublet of quin-
tets at δ 198.4 and a doublet at δ 123.5 (1J C-C ) 67.0
Hz), due to the R- and â-carbon atoms of the bridging
vinylidene ligand. In the 1H NMR spectrum of this
sample, the vinylidene proton resonances appear as
doublets (1J C-H ) 160 Hz for each of the protons).
Although the carbon resonance at δ 198.4 is unusually
high-field for a vinylidene R-carbon, it is very close to
that of another vinylidene-bridged compound, [Ir2I2-
(CO)2(µ-CdCH2)(dppm)2] (δ 194.3), previously charac-
terized by an X-ray structure determination.17a In
addition, the bridging vinylidene formulation for 4, as
shown in Scheme 1, is substantiated by 13C{31P}{1H}
The final model, with 575 parameters refined, converged
to values of R ) 0.064 and Rw ) 0.083. In the final difference
Fourier map, the 10 highest residuals (1.7-1.2 e/Å3) were
found in the vicinity of the metal atoms, phenyl rings, and
solvent molecules. A typical carbon atom in an earlier
synthesis had an electron density of ca. 5.0 e/Å3. The
positional and isotropic thermal parameters of the non-
hydrogen atoms are given in Table 3.
Resu lts a n d Com p ou n d Ch a r a cter iza tion
The reaction of [Ir2(H)(CO)3(µ-CH2)(dppm)2][CF3SO3]
(2) with acetylene at ambient temperature gives a
mixture of the alkyne- and vinylidene-bridged products
[Ir2(CH3)(CO)3(µ-HC2H)(dppm)2][CF3SO3] (3) and [Ir2-
(CH3)(CO)3(µ-CdCH2)(dppm)2][CF3SO3] (4), respectively,
1
in a typical ratio of about 1.7:1. The H NMR spectrum
of the mixture shows the methyl resonance of 3 as a
broad signal at δ -0.14 and the proton resonances of
the coordinated acetylene as multiplets at δ 10.25 and
9.15, in the appropriate ratios. The 13C{1H} NMR
spectrum of a 13CO-enriched sample shows broad reso-
nances for 3 at δ 198.7 and 181.3 and a triplet at δ 194.4,
and the IR spectrum26 shows CO stretches at 2007,
1970, and 1911 cm-1, suggesting the presence of three
terminally bound CO ligands. Also in the IR spectrum,
the peak at 1632 cm-1 is assigned to the CtC stretch
of the coordinated acetylene.27 This is within the range
of 1530-1642 cm-1 observed in closely related dppm-
bridged binuclear complexes, in which the alkyne
(20) Doedens, R. J .; Ibers, J . A. Inorg. Chem. 1967, 6, 204.
(21) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A: Found
Crystallogr. 1983, A39, 158.
(22) Programs used were those of the Enraf-Nonius Structure
Determination Package by B. A. Frenz, adapted for use on the SUN
SPARC station 1+ by R. G. Ball, in addition to local programs by R. G.
Ball.
(23) Cromer, D. T.; Waber, J . T. International Tables for Crystal-
lography; Kynoch Press: Birmingham, England, 1974; Vol. IV, Table
2.2A.
(24) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J . Chem. Phys.
1965, 42, 3175.
(27) Compounds such as 3, with an alkyne bridging two metals
parallel to the metal-metal axis, are sometimes referred to as
dimetalated olefin compound, in which case reference is made to the
CdC stretch.
(28) See, for example: (a) Vaartstra, B. A. Ph.D. Thesis, University
of Alberta, Edmonton, AB, 1989. (b) Mague, J . T. Organometallics 1986,
5, 918. (c) Mague, J . T.; Klein, C. L.; Majeste, R. J .; Stevens, E. D.
Organometallics 1984, 3, 1860. (d) Cowie, M.; Dickson, R. S.; Hames
B. W. Organometallics 1984, 3, 1879. (e) Puddephatt, R. J .; Thomson,
M. A. Inorg. Chem. 1982, 21, 725. (f) Puddephatt, R. J .; Thomson, M.
A. Inorg. Chim. Acta 1980, 45, L281.
(25) Cromer, D. T.; Liberman, D. J . Chem. Phys. 1970, 53, 1891.
(26) IR spectra are of samples with natural abundance carbon.
(29) (a) Berry, D. H.; Eisenberg, R. Organometallics 1987, 6, 1796.
(b) Berry, D. H.; Eisenberg, R. J . Am. Chem. Soc. 1985, 107, 7181.

510 Organometallics, Vol. 15, No. 2, 1996
Antwi-Nsiah et al.
Sch em e 1
experiments (using the sample prepared with 13C-
enriched acetylene) that indicate that the R-carbon
shows essentially equal coupling to all four phosphorus
nuclei, whereas the â-carbon shows no phosphorus
coupling. In this experiment, decoupling of either
phosphorus resonance leads to the collapse of the signal
at δ 198.4 into a doublet of triplets, while it collapses
into a doublet upon broadband 31P decoupling. The
signal at δ 123.5 remains a doublet in all of these
decoupling experiments, as expected. In samples that
are 13C-enriched at both the carbonyl and vinylidene
carbon atoms, the carbonyl resonance at δ 175.1 shows
strong coupling (23.3 Hz) to the vinylidene R-carbon
nucleus, while the carbonyl resonance at δ 172.3 shows
weaker coupling (13.0 Hz) to the same vinylidene carbon
nucleus. This suggests a trans arrangement of the
vinylidene R-carbon and one of the terminal CO ligands
and an orientation with respect to the other terminal
CO ligand that deviates significantly from trans.17a The
of multiplets at δ 127.2 and 102.4 (1J C-C ) 55.3 Hz),
which are assigned to the acetylide â- and R-carbons,
respectively. These resonances are in a range similar
to those of other acetylides.30-32 Appropriate 13C{1H}-
{31P} NMR experiments show that the acetylide reso-
nances are actually doublets of triplets of triplets,
indicating that both acetylide 13C nuclei couple to the
phosphorus nuclei bound to both metals. However, the
R-carbon shows stronger coupling to the phosphorus
nuclei that are bound to the Ir bearing the methyl ligand
than to the other set, while the â-carbon nucleus shows
stronger coupling to the phosphorus nuclei on the other
Ir. This suggests a σ,π-mode of coordination for the
acetylide. The assignment of the R- and â-carbon
resonances is based on the stronger P-C coupling that
is assumed to occur with the σ-bound R-carbon. The
proposed σ,π-coordination mode is consistent with the
magnitude of the C-C coupling, which is close to that
of the coordinated alkyne in compound 3 and other
related compounds and substantially less than that
expected for a triple bond.17a It is also consistent with
the low-field signal of the acetylide hydrogen noted
1
13C{31P}{1H} and H{31P} NMR experiments show that
the CO ligand that is trans to the vinylidene R-carbon
is bound to the same metal as the methyl group, while
the carbonyl group that shows a weaker coupling to the
R-carbon is bound to the other metal, together with the
third CO ligand.
1
earlier. The H NMR spectrum of the sample having
the 13C-enriched ligand shows the acetylide proton
resonance as a broad doublet (1J C-H ≈ 160 Hz). A trans
orientation of the methyl and hydride ligands is pro-
posed as the factor inhibiting methane loss, which does
not occur upon warming 5; instead, hydrogen transfer
to the â-carbon of the acetylide ligand occurs to give the
vinylidene-bridged product 4.
When the reaction of compound 2 with acetylene is
carried out at -78 °C, a hydrido-acetylide intermediate,
[Ir2(H)(CH3)(CO)3(µ-η1:η2-CtCH)(dppm)2][CF3SO3] (5),
is observed, which is converted quantitatively to the
vinylidene product 4 upon warming to room tempera-
ture. (In all schemes, intermediates observed only at
low temperatures are highlighted within a box enclo-
sure.) The 1H NMR spectrum of compound 5 shows the
acetylide proton resonance as a broad signal at δ 8.06,
the methyl resonance as a triplet at δ -0.40, and the
hydride resonance as a multiplet at δ -9.83. Selective
31P decoupling experiments show that the methyl group
and the hydride are terminally bound to the same metal.
The 13C{1H} NMR spectrum of a 13CO-enriched sample
shows broad resonances at δ 181.8 and 179.1, as well
as a triplet at δ 154.7, suggesting the presence of three
terminal CO ligands, and the 13C{1H} NMR spectrum
of a sample prepared using 13C2H2 shows two doublets
Attempts to induce C-C coupling via migratory
insertion of the vinylidene and methyl groups in com-
pound 4 by reaction with PMe3 instead resulted in
the substitution of a CO by PMe3 to give [Ir2-
(CH3)(CO)2(PMe3)(µ-CdCH2)(dppm)2][CF3SO3] (6). The
(30) Werner, H.; Hohn, A.; Schulz, M. J . Chem. Soc., Dalton Trans.
1991, 777.
(31) Garcia Alonso, F. J .; Riera, V.; Ruiz, M. A.; Tiripicchio, A.;
Tiripicchio-Camellini, M. Organometallics 1992, 11, 370.
(32) (a) Berenguer, J . R.; Falvello, L. R.; Lalinde, E.; Tomas, M.
Organometallics 1993, 12, 6. (b) Matsuzaka, H.; Hirayama, Y.; Nishio,
M.; Mizobe, Y.; Hidai, M. Organometallics 1993, 12, 36. (c) Touchard,
D.; Haquette, P.; Pirio, N.; Toupet, L.; Dixneuf, P. H. Organometallics
1993, 12, 3132.

Reactivity of Alkynes with Rhodium and Iridium Complexes
Organometallics, Vol. 15, No. 2, 1996 511

512 Organometallics, Vol. 15, No. 2, 1996
Antwi-Nsiah et al.
Ta ble 2. Cr ysta llogr a p h ic Da ta for
[Rh Ir (CtCP h )2(CO)2(µ-H)(d p p m )2][CF 3SO3]‚2CH2Cl2
(12)
Ta ble 3. P osition a l a n d Th er m a l P a r a m eter s for
th e Atom s of
[Rh Ir (CtCP h )2(CO)2(µ-H)(d p p m )2][CF 3SO3]‚2CH2Cl2
(12)a
formula
formula weight
crystal shape
crystal dimensions (mm)
space group
temperature (°C)
radiation (λ, Å)
C71H59Cl4F3IrO5P4RhS
1642.14
monoclinic prism
0.39 × 0.47 × 0.62
P21/c (No. 14)
22
atom
Ir
Rh
P(1)
P(2)
P(3)
P(4)
O(1)
O(4)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
x
y
z
B (Å2)b
0.24240(2)
0.25265(5)
0.0983(2)
0.1071(2)
0.3900(2)
0.3966(2)
0.2204(6)
0.2728(6)
0.2273(7)
0.2420(6)
0.2376(6)
0.2631(7)
0.2417(6)
0.2450(6)
0.0557(6)
0.4330(6)
0.2321(6)
0.2663(9)
0.261(1)
0.222(1)
0.188(1)
0.1955(9)
0.2554(6)
0.2811(8)
0.291(1)
0.273(1)
0.247(1)
0.2389(9)
0.15084(2)
0.24799(4)
0.1483(1)
0.2550(1)
0.1508(1)
0.2575(1)
0.1164(4)
0.2845(4)
0.1331(5)
0.0690(4)
0.0214(4)
0.2701(5)
0.2323(4)
0.2809(5)
0.2165(5)
0.2182(4)
-0.0361(4)
-0.0616(5)
-0.1156(7)
-0.1451(6)
-0.1225(6)
-0.0689(6)
0.3365(4)
0.3414(5)
0.3895(7)
0.4336(6)
0.4296(5)
0.3807(6)
0.26946(2)
0.37922(5)
0.2297(2)
0.3192(2)
0.3387(2)
0.4269(2)
0.0946(5)
0.5454(5)
0.1573(8)
0.2826(6)
0.2758(6)
0.4781(7)
0.2520(5)
0.2429(6)
0.2210(6)
0.3632(6)
0.2632(7)
0.2173(8)
0.206(1)
0.241(1)
0.279(1)
0.293(1)
0.2181(6)
0.1565(8)
0.1279(8)
0.162(1)
0.220(1)
0.2482(9)
2.59(1)*
2.72(2)*
3.01(8)*
2.97(8)*
2.70(7)*
2.83(8)*
6.2(3)*
6.2(3)*
4.1(4)*
3.0(3)*
3.1(3)*
3.8(3)
2.9(3)*
3.6(3)*
2.8(3)*
2.7(3)*
3.5(3)*
6.1(5)*
8.7(6)*
9.7(8)*
9.3(8)*
6.2(5)*
2.7(3)*
5.2(4)*
7.3(5)*
8.7(6)*
8.4(6)*
7.4(5)*
graphite-monochromated
Mo KR (0.710 69)
unit cell parameters
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
17.821(3)
24.780(5)
17.892(3)
117.56(1)
7004(2)
4
F(calcd) (g cm-3
linear absorption coefficient (µ)
(cm-1
)
1.557
24.497
)
C(8)
range of transmission factors
detector aperture (mm)
0.884-1.095
C(91)
C(92)
C(93)
C(94)
C(95)
C(96)
C(101)
C(102)
C(103)
C(104)
C(105)
C(106)
(3.00 + tan θ) wide × 4.00
high
take-off angle (deg)
maximum 2θ (deg)
crystal-detector distance (mm)
scan type
3.0
50.0
173
θ/2θ
scan rate (deg/min)
scan width (deg)
between 1.43 and 6.71
0.60 + 0.347 tan θ
12 976 (+h, +k, (l)
total unique reflections
total observations (NO)
final no. params varied (NV)
error in obs of unit weight (GOF)a
Rb
2
8365 (Fo g 3σ(Fo2))
575
2.544
0.064
0.083
a
Numbers in parentheses are estimated standard deviations
in the least significant digits in this and all subsequent tables.
b Starred B values are for atoms refined anisotropically. Displace-
ment parameters for the anisotropically refined atoms are given
in the form of the equivalent isotropic Gaussian diplacement
c
Rw
a
GOF ) [∑ω(|Fo| - |Fc|)2/(NO - NV)]1/2, where ω ) 4Fo2/σ2(Fo2).
R ) ∑||Fo| - |Fc||/∑ |Fo|. c Rw ) [∑ω(|Fo| - |Fc|)2/∑ωFo
] .
b
2 1/2
parameter, defined as 4/3[a2â11 + b2â22 + c2â33 + ab(cos γ)â12
+
spectroscopic data for compound 6, given in Table 1,
are consistent with the assigned structure shown in
Scheme 1.
ac(cos â)â13 + bc(cos R)â23]. Atoms of the triflate anion, the solvent
molecules, and the phenyl groups of the dppm ligands are given
as supporting information.
The reaction of compound 2 with phenylacetylene also
occurs readily, yielding a mixture of the alkyne- and
phenylvinylidene-bridged products [Ir2(CH3)(CO)3(µ-
PhC2H)(dppm)2][CF3SO3] (7) and [Ir2(CH3)(CO)3(µ-
CdC(H)Ph)(dppm)2][CF3SO3] (8), which are analogous
to those obtained in the reaction with acetylene. Their
structural assignments (see Scheme 2) are largely based
on their NMR data, which resemble those of 3 and 4.
The 1H NMR spectrum of compound 7 shows the proton
resonance of the coordinated alkyne as a multiplet at δ
9.51 and the methyl resonance as a broad signal at δ
0.02. The 13C{1H} NMR spectrum33 shows two broad
carbonyl resonances at δ 198.7 and 182.9, as well as a
triplet at δ 191.5, and the IR spectrum shows CO
stretches at 2011, 1970, and 1785 cm-1, suggesting that
one CO ligand is semibridging. The peak at 1640 cm-1
in the IR spectrum is assigned to the CtC stretch of
the coordinated phenylacetylene and is consistent with
the alkyne lying parallel to the metal-metal axis. The
orientation of the alkyne, in terms of which metal the
phenyl substituent is closer to, is assigned on the basis
of steric arguments, with the bulky phenyl group lying
closer to the less cluttered metal. This could not be
determined from the NMR spectra; even NOE experi-
ments did not yield information on this orientation.
The 1H NMR spectrum of compound 8 shows the
methyl resonance as a triplet at δ -0.58, but does not
Sch em e 2
show the vinylidene proton resonance, which is presum-
ably obscured by the phenyl resonances. The 13C{1H}
NMR spectrum shows a broad resonance at δ 182.9 and
two triplets at δ 179.6 and 168.0 for the three carbonyls,
while the IR spectrum shows CO stretches at 1960,
(33) 13C{1H} NMR spectra are of 13CO-enriched samples, unless
otherwise stated.

Reactivity of Alkynes with Rhodium and Iridium Complexes
Organometallics, Vol. 15, No. 2, 1996 513
40.0 Hz). These resonances are assigned to H1 and H2,
respectively (see Scheme 3 for the numbering scheme;
acetylenic protons have the same number as their
attached carbon), on the basis of the coupling constants.
The magnitude of the P-H coupling displayed by the
latter resonance suggests that the unsaturated ligand
in 10 has a trans configuration of H2 and phosphorus,
as shown.35 The methyl resonance appears as a triplet
at δ 0.46, while the four dppm protons, which are all
inequivalent, give rise to multiplets at δ 4.12, 3.95, 3.72,
and 2.88. The 13C{1H} NMR spectrum of a 13CO-
enriched sample of compound 10 shows two doublets of
multiplets at δ 191.1 (1J Rh-C ) 45.1 Hz) and 186.4
(1J Rh-C ) 63.9 Hz) and a multiplet at δ 171.5. Although
the Rh-C coupling constant for the low-field resonance
is smaller than expected for a CO ligand that is
terminally bound to Rh, the IR spectrum of compound
10 shows stretches at 2056, 2017, and 1975 cm-1, none
of which is in the range typical for symmetrically
bridging or semibridging CO ligands. The possibility
that this coupling of 45.1 Hz was due to carbon-carbon
coupling between two CO ligands, as was proposed for
[RhIrI(CO)2(µ-CO)(µ-DMAD)(dppm)2][BF4],15i was re-
jected since neither of the other two CO resonances
shows coupling of this magnitude.
Sch em e 3
1920, and 1780 cm-1, indicating the presence of two
terminally bound CO ligands and a third one that is
presumed to be semibridging. The IR spectrum of 8 also
shows a low-intensity peak at 1655 cm-1, which is
assigned to the CdC stretch of the vinylidene. The
orientation of the vinylidene ligand shown, having the
hydrogen adjacent to the methyl group, again is pro-
posed on steric grounds.
The 13C{1H} NMR spectrum of 10, prepared using
13C-enriched acetylene, shows a doublet of multiplets
1
at δ 42.1 (1J C-C ) 36.5 Hz, J Rh-C ) 8.4 Hz) and a
doublet of doublets of multiplets at δ 33.1 (1J P-C ) 76.0
1
1
Hz, J C-C ) 36.5 Hz, J Rh-C ) 11.8 Hz). The latter
resonance is assigned to C1, the carbon atom of the
inserted acetylene that is directly bound to one of the
phosphorus atoms, because it shows a large P-C
coupling, while the former resonance is assigned to C2.
These 13C NMR chemical shift values for C1 and C2 are
close to those of the coordinated olefins in [Rh(C2H4)-
Cl(P(p-tolyl)3)2] (δ 44.6),36 [Rh(acac)(C2H4)2] (δ 39.6),37
[Pt(C2H4)(PPh3)2] (δ 36.3),37 and [Pt(C2H4)2(PMePh2)] (δ
36.3, 42.0),38 while the Rh-C coupling constants (for
both C1 and C2) compare well with values in the range
of 10-16 Hz observed for the olefinic carbon nuclei in
related Rh-olefin complexes.36,38,39 In the 31P{1H} NMR
spectrum of the 13C2H2-enriched sample of compound
10, the resonance at δ 29.9 shows an additional coupling
of 76.0 Hz, which is consistent with it being directly
bound to C1. Also, the 1H NMR spectrum of this sample
shows the resonances for H1 and H2 as a doublet of
triplets (1J C-H ) 131 Hz) and a doublet of doublets of
multiplets (1J C-H ≈ 148 Hz), respectively. These C-H
coupling constants are lower than those expected for sp2-
hybridized carbon atoms40,41 and suggest a change in
hybridization of the carbon atoms of the inserted
In contrast to the chemistry of compound 2 with
acetylene, the reaction with phenylacetylene at -78 °C,
followed by warming to room temperature, does not
yield the phenylvinylidene product 8. Instead, the
alkyne-bridged product 7 is obtained. When this reac-
tion is monitored by NMR at low temperature, only
compounds 2 and 7 are observed.
The closely related mixed-metal species, [RhIr-
(CH3)(CO)3(dppm)2][CF3SO3] (1), also reacts with acety-
lene, as shown in Scheme 3. But in this case, the
reaction proceeds very differently from that involving
2, yielding instead [RhIr(CH3)(CO)3(HCdC(H)P(Ph2)CH2-
PPh2)(dppm)][CF3SO3] (10), the unusual product of
formal insertion of acetylene into one of the Rh-P bonds
of 1. The 31P NMR spectrum of compound 10 shows a
pattern diagnostic of an ABCDX spin system in which
only one of the phosphorus nuclei shows strong coupling
to Rh, consistent with a direct Rh-P bond. This
spectrum displays a multiplet at δ 29.9 (showing a
maximum coupling of about 9 Hz), a doublet of doublets
at δ 18.1 for the Rh-bound P nucleus (1J Rh-P ) 152.0
(35) J ackman, L. M.; Sternhell, S. Applications of Nuclear Magnetic
Resonance Spectroscopy in Organic Chemistry, 2nd ed.; Pergamon
Press: Oxford, 1969; p 352.
(36) Tolman, C. A.; Meakin, P. Z.; Lindner, D. L.; J esson, J . P. J .
Am. Chem. Soc. 1974, 96, 2762.
(37) Thomas, J . L. Inorg. Chem. 1978, 17, 1507 and references cited
therein.
(38) Harrison, N. C.; Murray, M.; Spencer, J . L.; Stone, F. G. A. J .
Chem. Soc., Dalton Trans. 1978, 1337.
2
Hz, J P-P ) 48.0 Hz), and two doublets of doub-
lets at δ -11.7 (2J P-P ) 406.0 Hz, J P-P ) 9.3 Hz) and
2
2
-22.6 (2J P-P ) 406.0 Hz, J P-P ) 48.0 Hz). The last
two resonances are due to the phosphorus nuclei bound
to Ir, and the large coupling between them shows that
they maintain a trans orientation with respect to each
other.34 The H NMR spectrum of compound 10 shows
1
(39) See, for example: (a) Mann, B. E.; Taylor, B. F. 13C Data for
Organometallic Compounds; Academic Press: London, 1981; p 188.
(b) Bodner, G. M.; Storhoff, B. N.; Doddrell, D.; Todd, L. J . J . Chem.
Soc., Chem. Commun. 1970, 1530. (c) J esse, A. C.; Gijben, H. P.;
Stufkens, D. J .; Vrieze, K. Inorg. Chim. Acta 1978, 31, 203. (d)
Maisonnat, A.; Poilblanc, R. Inorg. Chim. Acta 1978, 29, 203.
(40) Kegley, S. E.; Pinhas, A. R. Problems and Solutions in Orga-
nometallic Chemistry; University Science Books: Mill Valley, CA, 1986;
p 11.
one proton resonance of the inserted acetylene as an
apparent triplet at δ 8.58 (3J H-H ≈ J P-H ≈ 6.5 Hz) and
2
the other as a doublet of multiplets at δ 5.60 (3J P-H
≈
(34) Mague, J . T.; Klein, C. L.; Majeste, R. J .; Stevens, E. D.
Organometallics 1984, 3, 1860.

514 Organometallics, Vol. 15, No. 2, 1996
Antwi-Nsiah et al.
acetylene in compound 10 toward sp3. Moreover, the
C-C coupling constant (1J C-C ) 36.5 Hz) is significantly
lower than that expected for carbon atoms linked by a
CdC double bond between sp2 carbons, such as those
of the coordinated alkynes (resulting in dimetalated
olefins) in compounds 3 and 9 (vide infra), and is close
to that of ethane (34.6 Hz).41 On the basis of these
observations, it is proposed that there is interaction of
the CdC bond of the inserted acetylene with Rh as
shown, reducing the CdC bond order. All of the NMR
data are consistent with the structure proposed for
compound 10, as shown in Scheme 3. In addition, this
structure is reminiscent of that determined for [CpRh-
(µ-η1:η2-HCdC(H)PMe3)(µ-CO)Os(CO)3],42 which re-
sulted from migration of a PMe3 ligand from Rh to a
bridging acetylene moiety, much as proposed here for
one of the dppm ligands (vide infra). Although formula-
tion of a structure for 10 is not unambiguous, we
favor one in which Rh has a tetrahedral ligand
geometry, reminiscent of a [Rh(CO)2(olefin)PR3]- frag-
ment, and Ir has an octahedral geometry. The sixth
coordination site at the latter metal is occupied by a
Rh-Ir bond. This geometry at Rh is not unlike that at
one of the metal centers in the related mixed-valence
species [MM′(CO)3(dppm)2] (M,M′ ) Rh, Ir),43 and is
favored over a square-planar geometry, for which model
building could not easily accommodate binding of Rh
to the olefinic fragment within the 6-membered irida-
cycle. Unfortunately, suitable single crystals of com-
pound 10 could not be obtained due to facile decompo-
sition.
Sch em e 4
protons). The 13C{1H} NMR spectrum of a 13CO-
enriched sample shows a doublet of multiplets at δ 210.2
(1J Rh-C ) 19.0 Hz), a doublet of triplets at δ 191.0
(1J Rh-C ) 55.3 Hz), and a triplet at δ 172.8, indicating
the presence of one semibridging carbonyl ligand (in-
ferred from the Rh-C coupling of 19 Hz18) and a
terminally bound carbonyl ligand each on Rh and Ir.
The transformation of 9 to 10 can be seen as resulting
from dissociation of the Rh-bound end of a diphosphine,
followed by nucleophilic attack by this phosphorus at
the Rh end of the bridged alkyne.
The reaction of compound 1 with phenylacetylene
again differs from any of the previous reactions of
compound 1 or 2 with acetylene or of 2 with pheny-
lacetylene. At room temperature, compound 1 reacts
with 1 equiv of phenylacetylene to give the monoacetyl-
ide product [RhIr(CO)3(µ-η1:η2-CtCPh)(dppm)2][CF3-
SO3] (11), accompanied by methane loss, whereas with
excess phenylacetylene it gives the diacetylide-hydride
product [RhIr(CtCPh)2(CO)2(µ-H)(dppm)2][CF3SO3] (12),
with the evolution of methane and CO (see Scheme 4).
The 1H NMR spectrum of compound 11 shows only
dppm methylene proton resonances as multiplets at δ
3.82 and 3.32, apart from the phenyl and solvent
resonances, which is consistent with the loss of methane
at some stage in the formation of this compound. The
13C{1H} NMR spectrum of a 13CO-enriched sample
shows a doublet of multiplets at δ 196.0 (1J Rh-C ) 22.1
Hz), a doublet of triplets at δ 194.6 (1J Rh-C ) 80.3 Hz),
and a triplet at δ 181.7, indicating the presence of a
bridging CO ligand and a terminally bound CO ligand
on each metal. The peak at 1825 cm-1 in the IR
spectrum is consistent with a bridging CO, while those
at 2000 and 1955 cm-1 arise from the two terminally
bound CO ligands. The presence of the acetylide ligand
is inferred from the disappearance of the methyl group
Although the final product in the reaction of acetylene
with compound 1 is vastly different from those obtained
in the reaction with compound 2, an analogous alkyne-
bridged intermediate [RhIr(CH3)(CO)3(µ-HC2H)(dppm)2]-
[CF3SO3] (9) is observed at -78 °C. This intermediate
is converted to 10 upon warming to room temperature.
Characterization of 9 by NMR was relatively straight-
forward. Its 1H NMR spectrum shows the proton
resonances of the coordinated acetylene as a doublet of
triplets at δ 9.12 (2J Rh-H ) 6.4 Hz) and a multiplet at δ
7.63 and the methyl resonance as a triplet at δ -1.00.
The 13C{1H} NMR spectrum of a sample prepared with
13C2H2 shows the carbon resonances of the coordinated
acetylene as a doublet of doublets of multiplets at δ
162.9 (1J Rh-C ) 20.6 Hz, 1J C-C ) 53.0 Hz) and a doublet
of multiplets at δ 147.0 (coupling to the phosphorus
nuclei was complex in both cases). Selective 31P decou-
pling experiments indicate that each carbon nucleus
shows larger coupling to a different set of phosphorus
nuclei. The chemical shifts of the carbon nuclei of the
coordinated acetylene in compound 9 are very close to
those of 3 (δ 160.7 and 147.1), and this observation,
together with the fact that only one of the carbon nuclei
of the coordinated acetylene in 9 shows coupling to Rh,
is consistent with the assignment of an acetylene ligand
1
bridging the two metals. The H NMR spectrum of this
sample shows the proton resonances of the coordinated
acetylene as a doublet of doublets of triplets and a
doublet of multiplets (1J C-H ≈ 152 Hz for each of the
(41) Friebolin, H. Basic One- and Two-Dimensional NMR Spectros-
copy; VCH Publishers: New York and Weinheim, Germany, 1991;
Chapter 10 (a) and p 89 (b).
(42) Takats, J .; Washington, J .; Santarsiero, B. D. Organometallics
1994, 13, 1078.
(43) (a) Woodcock, C.; Eisenberg, R. Inorg. Chem 1985, 24, 1285.
(b) McDonald, R; Cowie, M. Inorg. Chem. 1990, 29, 1564.

Reactivity of Alkynes with Rhodium and Iridium Complexes
Organometallics, Vol. 15, No. 2, 1996 515
Ta ble 4. Selected Dista n ces (Å) in
[Rh Ir (CtCP h )2(CO)2(µ-H)(d p p m )2][CF 3SO3]‚2CH2Cl2
(12)
(a) Bonded
Ir-P(1)
2.326(2)
2.332(2)
1.95(1)
2.042(7)
2.041(8)
1.69a
2.310(2)
2.310(2)
1.778(8)
2.228(6)
2.515(7)
2.07a
1.830(7)
1.811(7)
1.827(8)
1.829(7)
P(2)-C(31)
P(2)-C(41)
P(3)-C(8)
P(3)-C(51)
P(3)-C(61)
P(4)-C(8)
P(4)-C(71)
P(4)-C(81)
O(1)-C(1)
O(4)-C(4)
C(2)-C(3)
C(3)-C(91)
C(5)-C(6)
C(6)-C(101)
1.822(8)
1.801(8)
1.805(7)
1.824(7)
1.815(8)
1.831(7)
1.818(8)
1.801(8)
1.15(1)
1.190(9)
1.185(9)
1.44(1)
1.22(1)
1.49(1)
Ir-P(3)
Ir-C(1)
Ir-C(2)
Ir-C(5)
Ir-H(1)
Rh-P(2)
Rh-P(4)
Rh-C(4)
Rh-C(5)
Rh-C(6)
Rh-H(1)
P(1)-C(7)
P(1)-C(11)
P(1)-C(21)
P(2)-C(7)
F igu r e 1. ORTEP diagram of the complex cation [RhIr-
(C2Ph)(CO)2(µ-H)(µ-C2Ph)(dppm)2]+ (12) showing the num-
bering scheme. Thermal parameters are shown at the 20%
level except for hydrogens, which are either omitted or
shown artificially small. Numbering of the phenyl carbons
starts at the ipso carbon and works sequentially around
the ring.
(b) Nonbonded
Ir-Rh
3.0582(8)
3.056(3)
P(3)-P(4)
3.053(3)
P(1)-P(2)
a
Ir-H(1) and Rh-H(1) distances are approximate since the
H(1) position was not refined.
of 1 and the formation of 12 upon reaction with an
additional equivalent of phenylacetylene (the acetylide
stretch could not be unambiguously assigned in the IR
spectrum of 11).
Ta ble 5. Selected An gles (d eg) in
[Rh Ir (CtCP h )2(CO)2(µ-H)(d p p m )2][CF 3SO3]‚2CH2Cl2
(12)
P(1)-Ir-P(3)
P(1)-Ir-C(1)
P(1)-Ir-C(2)
P(1)-Ir-C(5)
P(1)-Ir-H(1)
P(3)-Ir-C(1)
P(3)-Ir-C(2)
P(3)-Ir-C(5)
P(3)-Ir-H(1)
C(1)-Ir-C(2)
C(1)-Ir-C(5)
C(1)-Ir-H(1)
C(2)-Ir-C(5)
C(2)-Ir-H(1)
C(5)-Ir-H(1)
P(2)-Rh-P(4)
P(2)-Rh-C(4)
P(2)-Rh-C(5)
P(4)-Rh-C(4)
P(4)-Rh-C(5)
C(4)-Rh-C(5)
Ir-P(1)-C(7)
Ir-P(1)-C(11)
Ir-P(1)-C(21)
C(7)-P(1)-C(11)
C(7)-P(1)-C(21)
167.53(6) Rh-P(2)-C(31)
111.1(3)
120.5(2)
104.1(3)
103.9(3)
104.4(4)
112.1(2)
117.4(2)
114.9(2)
104.1(3)
104.0(3)
102.7(3)
111.7(2)
117.2(3)
113.2(3)
106.5(3)
104.5(3)
102.7(3)
171.7(8)
168.7(7)
176.9(9)
178.0(7)
91.4(3)
The 1H NMR spectrum of compound 12 shows the
hydride resonance as a multiplet at δ -8.70. Selective
and broadband 31P decoupling experiments show that
this signal is actually a doublet of triplets of triplets
94.1(2)
86.9(2)
93.0(2)
83a
97.5(2)
90.1(2)
90.4(2)
85a
Rh-P(2)-C(41)
C(7)-P(2)-C(31)
C(7)-P(2)-C(41)
C(31)-P(2)-C(41)
Ir-P(3)-C(8)
2
2
(1J Rh-H ) 12.7 Hz, J P(Ir)-H ) 12.0 Hz, J P(Rh)-H ) 3.3
Hz) and the magnitudes of the two P-H coupling
constants show that the hydride ligand couples more
strongly to the Ir-bound phosphorus nuclei than to those
bound to Rh. This observation, together with the
relatively small Rh-H coupling constant,44 suggests
that the hydride ligand interacts more strongly with Ir
than with Rh. The 13C{1H} NMR spectrum shows a
doublet of triplets at δ 191.1 (1J Rh-C ) 82.5 Hz) and a
triplet at δ 162.7, indicating the presence of a terminal
CO ligand each on Rh and Ir. The IR spectrum shows
CO stretches at 2015 and 1958 cm-1, as well as stretches
at 2134 and 2090 cm-1, assigned to the CtC stretches
of the two acetylide ligands. Although the NMR data
do not unambiguously establish the structure of com-
pound 12, the structure shown in Scheme 4 was
established by an X-ray structure determination.
Figure 1 shows a perspective view of the cation of
compound 12, with the dppm ligands bridging the metal
nuclei in a typical manner. Relevant bond lengths and
angles are given in Tables 4 and 5. While both
molecules of CH2Cl2 of crystallization are disordered,
the triflate anion is well-behaved. The diphosphine
groups are oriented approximately trans to each other
about the metal centers [P(1)-Ir-P(3) ) 167.53(6)° and
P(2)-Rh-P(4) ) 168.61(7)°] and are both cis to the
other atoms coordinated to the metal nuclei. The
geometry about Rh is tetragonal-pyramidal (with the
hydride ligand occupying the apical site), if the interac-
tion between this metal and the acetylide CtC bond is
considered to occupy one of the basal coordination sites,
while the CO and the two dppm phosphines occupy the
other sites. About Ir, the geometry is approximately
octahedral. The hydride ligand was not refined, but was
Ir-P(3)-C(51)
Ir-P(3)-C(61)
C(8)-P(3)-C(51)
C(8)-P(3)-C(61)
C(51)-P(3)-C(61)
Rh-P(4)-C(8)
83.6(3)
94.4(3)
177a
178.0(3)
Rh-P(4)-C(71)
Rh-P(4)-C(81)
C(8)-P(4)-C(71)
95a
87a
168.61(7) C(8)-P(4)-C(81)
91.0(2)
89.4(2)
90.8(3)
87.3(2)
172.1(3)
110.9(2)
113.8(3)
117.9(2)
103.8(3)
104.4(3)
C(71)-P(4)-C(81)
Ir-C(1)-O(1)
Ir-C(2)-C(3)
C(2)-C(3)-C(91)
Rh-C(4)-O(4)
Ir-C(5)-Rh
Ir-C(5)-C(6)
Rh-C(5)-C(6)
C(5)-C(6)-C(101) 167.4(7)
177.2(7)
88.7(5)
P(1)-C(7)-P(2)
P(3)-C(8)-P(4)
Rh-H(1)-Ir
113.3(4)
114.2(4)
109a
C(11)-P(1)-C(21) 104.7(3)
Rh-P(2)-C(7)
111.3(2)
a
Angles involving H(1) are approximate since this atom was
not refined.
fixed in the position obtained from the Fourier map;
therefore, no significance should be attached to the
derived Rh-H and Ir-H distances. The Ir-C(1) dis-
tance (1.95(1) Å), which is opposite H(1), is significantly
longer than the Rh-C(4) distance (1.778(8) Å), consis-
tent with the high trans influence of a hydride ligand,
but otherwise the geometries of these carbonyls are
normal. The Rh-Ir distance of 3.0582(8) Å is almost
exactly equal to the intraligand P-P separations [P(1)-
P(2) ) 3.056(3) Å, P(3)-P(4) ) 3.053(3) Å], suggesting
that there is no formal metal-metal bond. Instead, the
Ir-H(1) bond is viewed as functioning as an agostic
interaction with Rh, much as that observed in [RhIr-
(H)2(CO)2(µ-Cl)(dppm)2][BF4] (3.0651(5) Å), which also
was formulated as having no formal metal-metal
(44) Vaartstra, B. A.; Cowie, M. Inorg. Chem. 1989, 28, 3138.

516 Organometallics, Vol. 15, No. 2, 1996
Antwi-Nsiah et al.
bond.44 Both of the acetylide groups are σ-bound to Ir,
with Ir-C(2) and Ir-C(5) bond lengths of 2.042(7) and
2.041(8) Å, respectively. One of these mutually trans
groups is directed away from Rh, while the other
appears to interact weakly with this second metal. This
orientation of the two acetylides is similar to that found
in [Pt2(CtCPh)(µ-η1:η2-CtCPh)(µ-SiMe2)(PR3)2] (R )
cyclo-C6H11).45 The bending of the phenyl group on C(6)
away from Rh [C(5)-C(6)-C(101) ) 167.4(7)°], and the
proximity of the acetylide carbons to Rh [Rh-C(5) )
2.228(6) Å, Rh-C(6) ) 2.515(7) Å], suggest that there
is a π-interaction between Rh and the C(5)-C(6) acetyl-
ide bond. However, the small difference in the CtC
distances of the two acetylide ligands [C(2)-C(3) )
1.185(9) Å, C(5)-C(6) ) 1.22(1) Å] suggests that the
π-interaction of the latter is weak. A similar bending
of the phenyl group of one of the acetylide ligands was
observed in [Pt2(CtCPh)2(µ-η1:η2-CtCPh)(dppm)2]-
[ClO4].46 There is a slight bending of the Ir-C(2)-C(3)
moiety [Ir-C(2)-C(3) ) 168.7(7)°], probably due to
interactions with rings 2 and 5 of the dppm groups,
while the Ir-C(5)-C(6) moiety is almost linear (177.2-
(7)°). Bending of the same magnitude was observed in
the acetylide ligands of [Rh2(CO)2(µ-η1:η2-CtCtBu)-
(dppm)2][ClO4]47 and [Mn2(µ-H)(µ-η1:η2-CtCPh)(CO)6-
(µ-dppm)].31
When the reaction of compound 1 with phenylacety-
lene is started at -78 °C, and monitored by NMR while
gradually warming the reaction mixture, three ad-
ditional intermediates are observed (as shown in the
enclosure in Scheme 4). At -78 °C, the NMR spectra
of the reaction mixture, using 1 equiv of phenylacety-
lene, show the presence of 1 as the major compound,
together with [RhIr(CH3)(H)(CO)3(µ-η1:η2-CtCPh)-
(dppm)2][CF3SO3] (13) and a small amount of another
species, [RhIr(CH3)(CO)3(µ-HCtCPh)(dppm)2][CF3SO3]
(14). Increasing the temperature at a rate of ap-
proximately 15 °C h-1 results in increasing concentra-
tions of intermediates 13 and 14 at the expense of 1,
such that by -20 °C little of 1 remains, while the
acetylide-bridged species 11 and a new intermediate 15
also begin to appear. Further increases in temperature
result in the total disappearance of 1 and increasing
concentrations of 11 and 15, while 13 disappears
(compound 14 remains until 13 is depleted). Intermedi-
ate 15 is a minor species and is never present in greater
than 10% concentration. If more than 1 equiv of
phenylacetylene is present, the diacetylide product 12
also begins to appear near 0 °C.
presence of the hydride ligand. A trans orientation of
the hydride and methyl ligands is proposed as the factor
inhibiting methane loss in 13, however, the stereochem-
istry at Ir is not known with certainty. The proposed
µ-η1:η2-bonding mode of the acetylide in 11 and 13 is
based on analogies with several related compounds31,45-48
(also see compound 5).
The next species observed (14) is proposed to be a
1
phenylacetylene-bridged complex. The H NMR spec-
trum of compound 14 shows the alkyne proton reso-
nance as a triplet at δ 8.53 and also shows a broad
resonance at δ 0.27 due to the methyl protons. Selective
31P decoupling experiments show that the methyl group
is still bound to Ir and that the alkyne proton couples
to the phosphorus nuclei bound to Ir, suggesting the
alkyne orientation shown in which the large phenyl
substituent is close to the less congested Rh center. The
13C{1H} NMR spectrum of 14 shows a doublet of
multiplets at δ 200.6 (1J Rh-C ) 5.0 Hz), a doublet of
triplets at δ 193.8 (1J Rh-C ) 54.3 Hz), and a broad
resonance at δ 180.8, indicating the presence of a CO
ligand on Ir that interacts very weakly with Rh (inferred
from the small Rh-C coupling of 5 Hz), as well as a
terminally bound CO ligand each on Rh and Ir.
The final intermediate observed before conversion to
11 is complete is 15 and is formulated as the dicarbonyl
species [RhIr(H)(CH3)(CO)2(µ-CtCPh)(dppm)2)][CF3-
SO3], in which the methyl and hydrido groups are now
proposed to be mutually cis. Only two carbonyl reso-
nances are observed with only the low-field signal
showing Rh coupling (56 Hz), indicating that each CO
is terminally bound to a different metal. We cannot rule
out the possibility that a third carbonyl resonance is
buried under the signals for the more abundant prod-
ucts, but this seems unlikely since the spectra were
monitored over widely changing concentrations of all
1
species. The H NMR spectra clearly show the methyl
and hydrido groups as triplets at δ -0.52 and -8.75,
respectively, and selective 31P decoupling indicates that
they are both coordinated to Ir.
Although compounds 1 and 2 react quite differently
with the nonactivated alkynes, PhCtCH and HCtCH,
as described earlier, their reactions with the activated
alkyne, DMAD, yield similar products: [MIr(RCdC-
(CH3)R)(CO)3(dppm)2][CF3SO3] [R ) CO2Me; M ) Rh
(16), Ir (17)], in which the alkyne apparently has
inserted into the M-C(alkyl) bonds of the precursor
complexes (as shown in Schemes 5 and 6).
The 1H NMR spectrum of the RhIr compound 16
shows the dppm methylene proton resonances as mul-
tiplets at δ 4.35 and 3.65. It also shows three singlets
at δ 3.33, 2.22, and 0.81, which are assigned to the two
DMAD methyl groups and the methyl group that has
undergone migratory insertion. The shifting of the
methyl resonance from a triplet at δ -0.08 in compound
1 to a singlet at lower field (δ 0.81) in compound 16 is
consistent with the formal insertion of DMAD into the
Ir-CH3 bond. The 13C{1H} NMR spectrum shows two
doublets of triplets at δ 197.9 (1J Rh-C ) 4.0 Hz) and
194.4 (1J Rh-C ) 55.3 Hz) and a triplet at δ 176.8,
The 1H NMR spectrum of compound 13 shows the
hydride resonance as a triplet at δ -8.87 and the methyl
resonance as a triplet at δ 0.33. Selective 31P decoupling
experiments show that both the methyl and the hydride
ligands are bound to Ir, since they couple only to the
phosphorus nuclei bound to this metal. The 13C{1H}
NMR spectrum shows a doublet of triplets at δ 192.8
(1J Rh-C ) 80.5 Hz), a broad resonance at δ 193.1, and a
doublet of triplets at δ 186.0 (1J Rh-C ) 72 Hz) all having
equal intensities, indicating that there are two CO
ligands terminally bound to Rh and one terminally
bound to Ir in compound 13. The presence of the
acetylide ligand in this compound is inferred from the
(48) See, for example: (a) Esteruelas, M. A.; Lahuerta, O.; Modrego,
J .; Nurnberg, O.; Oro, L. A.; Rodriguez, L.; Sola, E.; Werner, H.
Organometallics 1993, 12, 266. (b) McEwan, D. M.; Markham, D. P.;
Pringle, P. G.; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1986, 1809.
(c) Hutton, A.; Langrick, C. R.; McEwan, D. M.; Pringle, P. G.; Shaw,
B. L. J . Chem. Soc., Dalton Trans. 1985, 2121.
(45) Ciriano, M.; Howard, J . A. K.; Spencer, L.; Stone, F. G. A. J .
Chem. Soc., Dalton Trans. 1979, 1749.
(46) Yam, V. W.; Chan, L.; Lai, T. Organometallics 1993, 12, 2197.
(47) Cowie, M.; Loeb, S. J . Organometallics 1985, 4, 852.

Reactivity of Alkynes with Rhodium and Iridium Complexes
Organometallics, Vol. 15, No. 2, 1996 517
Sch em e 5
terminally bound and one semibridging CO ligand in
compound 17. The identification of one CO as semibridg-
ing is based on the low CO stretch in the IR spectrum
and the 13C chemical shift in the NMR spectrum that
is not unlike those of the terminal groups. Analogies
with compound 16 also support this assignment. The
CO stretch of the inserted DMAD ligand appears at
1695 cm-1 in the IR spectrum, while the band at 1642
cm-1 is assigned to the CdC stretch of the same ligand.
The similarities in the spectroscopic data for 16 and 17
support the assignment of similar structures to both
compounds.
In addition to compound 17, the reaction of 2 with
DMAD also gives [Ir2(CH3)(CO)3(µ-DMAD)(dppm)2][CF3-
SO3] (18), typically in about half the concentration of
1
compound 17. The H NMR spectrum of 18 shows the
dppm methylene proton resonances as multiplets at δ
4.78 and 4.25, the methyl resonances of the coordinated
DMAD as singlets at δ 3.45 and 2.13, and the metal-
bound methyl resonance as a triplet at δ -0.52. The
13C{1H} NMR spectrum shows triplets at δ 182.2, 175.9,
and 152.5 and the IR spectrum shows CO stretches at
2029, 2001, and 1982 cm-1, indicating the presence of
three terminal CO ligands. The IR spectrum also shows
Sch em e 6
the CO stretch of the coordinated DMAD at 1690 cm-1
,
and the band at 1635 cm-1 in this spectrum is assigned
to the CtC stretch of the same ligand. Compound 18
is analogous to the acetylene and phenylacetylene
adducts 3 and 7, described earlier. Although the
location of the methyl group in 18 is shown opposite the
bridging alkyne, we cannot rule out an arrangement like
that shown in 3 and 7, in which the methyl is adjacent
to the bridging alkyne.
Discu ssion
As indicated earlier, the methyl complex [RhIr-
(CH3)(CO)3(dppm)2][CF3SO3] (1) and the methylene-
bridged hydride species [Ir2H(CO)3(µ-CH2)(dppm)2][CF3-
SO3] (2) are more similar than they first appeared. The
latter, coordinatively saturated species can be viewed
as an incipient methyl complex since it has been
shown19 to be in equilibrium with the labile, coordina-
tively unsaturated methyl complex [Ir2(CH3)(CO)3-
(dppm)2][CF3SO3] (shown as I in Scheme 6), the simi-
larity of which to compound 1 is obvious. Due to the
unsaturation at one metal in this proposed species, it
was felt that reactions of 2 with small molecules would
proceed via attack at this unsaturated center. The
reactivities of 1 and 2 with acetylene, phenylacetylene,
and dimethyl acetylenedicarboxylate therefore were
investigated to compare the reactivities involving either
a RhIr or Ir2 core. In all cases it appears that our
assumption that 2 would react as a methyl complex,
much like 1, was justified, since all products obtained
are methyl species or, in one case, resulted from
methane elimination. Nevertheless, the two species do
show some interesting contrasts in reactivity that relate
to the replacement of one Ir center in 2 by Rh. With
the two terminal alkynes investigated, two basic types
of reactivity have been noted: reaction at the alkyne
triple bond yields the alkyne-bridged products, where-
as reaction at the alkyne C-H bond yields acety-
lide-hydride products. In each of these cases, the
ultimate product depends on the metal centers involved.
In the diiridium system, the alkyne-bridged products
indicating that there is one semibridging CO ligand
showing a very weak interaction with Rh, as well as a
terminally bound CO ligand each on Rh and Ir. The
IR spectrum of this product shows a peak at 1720 cm-1
,
which is consistent with the presence of a semibridging
CO ligand, as well as peaks at 2022 and 1995 cm-1 due
to the terminal CO ligands. In addition to these
stretches, bands at 1698 cm-1, due to the CO stretch of
the inserted DMAD, and at 1641 cm-1, assigned to the
CdC stretch of the same ligand, are observed.
1
The H NMR spectrum of the diiridium analogue 17
shows two multiplets at δ 4.43 and 3.60, representing
the dppm methylene proton resonances, as well as three
singlets at δ 3.27, 2.23, and 0.68, which are assigned to
the two methyl groups of the inserted DMAD and the
methyl group bound to the DMAD as a result of the
insertion. The 13C{1H} NMR spectrum shows a broad
resonance at δ 194.7 and two triplets at δ 192.0 and
179.5 while the IR spectrum shows stretches at 2015,
1998, and 1717 cm-1, indicating the presence of two

518 Organometallics, Vol. 15, No. 2, 1996
Antwi-Nsiah et al.
[Ir2(CH3)(CO)3(µ-HCtCR)(dppm)2][CF3SO3] [R ) H (3),
Ph (7)] are stable and do not react further under the
relatively mild temperatures (ambient or subambient)
investigated. In this metal system, the presumed
acetylide-hydride intermediates (only observed for the
acetylene reaction at low temperatures) transform to the
vinylidene and phenylvinylidene products [Ir2(CH3)(CO)3-
(µ-CC(H)R)(dppm)2][CF3SO3] [R ) H (4), Ph (8)]. In
each case, reaction at -78 °C followed by slow warming
to ambient temperature yields only one product; how-
ever, interestingly, these products differ for the two
alkynes, yielding exclusively the vinylidene species 4
in the acetylene reaction but the alkyne-bridged 7 with
phenylacetylene. This was of some surprise to us since
we had initially assumed that oxidative addition of the
alkyne-H bond in phenylacetylene would occur more
readily than in acetylene, in which case formation of
the phenylvinylidene product should have a lower
kinetic barrier. It also seemed that coordination of the
more bulky phenylacetylene group through the CtC
bond should be less favored on steric grounds. Clearly
these ideas are not the determining factors since the
opposite occurs.
Although it is difficult to establish the exact stereo-
chemistry at a metal in these intermediates, the mobili-
ties of the hydride and acetylide groups can usually
generate the proposed acetylide-hydride precursor IV.
Even for compound 5 (Scheme 1), in which the hydride
and acetylide groups are suggested to be on opposite
faces of the complex, as shown by species II, the
necessary intermediate IV can be obtained from the
hydride-bridged species III via rotation about both P2-
Ir units, bringing the hydride ligand between the
metals. It should be recalled that an alternate, but
convenient, valence-bond representation of the 3-center,
2-electron M(µ-H)M interaction, as shown for III, is one
in which a terminal M-H bond on one metal forms an
agostic interaction with the second metal.52 In this
description, it becomes clear that the loss of the π-in-
teraction of the µ-η1:η2-acetylide group with the second
Ir center in II is compensated for by the agostic
interaction involving the Ir-H bond, forming the hy-
dride-bridged intermediate III while maintaining the
valence electron counts at both metals. It must also be
pointed out that the ancillary ligands, not shown in the
preceding generic scheme, can also migrate from metal
to metal. Such migrations, accompanied in some cases
by metal-metal bond formation or breakage, allows the
metals to maintain favorable electron counts. Interme-
diate IV can be generated from a number of other
geometries by variations of the preceding rearrange-
ments of the hydride and acetylide groups. By the same
token, complex 5, having the geometry shown, presum-
ably derives from an original species in which the
hydride and acetylide groups were adjacent on the same
face of the complex, following oxidative addition of the
alkyne, by movement of the hydride between the metals.
Although the RhIr system ultimately reacts very
differently with acetylene and phenylacetylene than the
Ir2 system, the initial products seen at -78 °C are
analogous to those noted earlier. The reaction of 1 with
acetylene at -78 °C first yields the acetylene-bridged
[RhIr(CH3)(CO)3(µ-HCtCH)(dppm)2][CF3SO3] (9), not
unlike the diiridium analogues 3 and 7. However, upon
warming, a much different product, [RhIr(CH3)(CO)3(µ-
η1:η2:η1-HCdC(H)PPh2CH2PPh2)(dppm)][CF3SO3] (10),
the apparent result of acetylene insertion into one of
the Rh-P bonds, is obtained. Formation of this product
can be rationalized by the greater lability at Rh, giving
rise to dissociation of the Rh-bound end of a diphosphine
with subsequent nucleophilic attack of this group at the
bridging alkyne and concomitant cleavage of the Rh-
alkyne bond (see Scheme 3). In the resulting product,
The transformation of a 1-alkyne into a vinylidene
group is shown, in this and other studies,49 to occur
readily in the presence of adjacent metal centers. We
propose that the facility of this transformation, at least
in related dppm-bridged complexes, results from the
abilities of the acetylide and hydride ligands in the
intermediates to function as either terminal or bridging
groups and from the mobilities of both of these groups
over the bimetallic core. The hydride ligand can readily
migrate from one metal to the other and from one face
of an M2P4 unit to the other,44,50 and the acetylide group
can also move from metal to metal in a “windshield
wiper” motion.51 It is proposed that a pivotal step in
the conversion of the acetylide and hydride groups to a
vinylidene group, in the presence of adjacent metals, is
the alignment of the hydride ligand adjacent to the
π-bound acetylide moiety, as shown for intermediate IV,
since such an orientation can facilitate transfer of the
hydride to the â-carbon atom in a concerted manner,
as diagrammed.
the 6-membered IrCdCPCP iridacycle has maintained
the original iridium-olefin σ-bond and the Ir-P bond
from the original dppm group, while being simulta-
neously π-bonded to Rh through the olefinic linkage. We
suggest that Rh has an 18-electron configuration on the
basis of a [Rh(CO)2(olefin)(PR3)]- formulation and that
donation of a pair of nonbonding Rh electrons to the Ir
(+3) center occurs, giving this metal an octahedral
geometry typical of this oxidation state. The proposal
that 10 results from the dissociation of one end of a
bridging diphosphine group (that bound to Rh) followed
by nucleophilic attack at a bridging acetylene unit is
unusual, but has precedent. As noted earlier, nucleo-
(49) (a) Xiao, J .; Cowie, M. Organometallics 1993, 12, 463. (b) Wang,
L.-S.; Cowie, M. Organometallics 1995, 14, 2374. (c) Wang, L.-S.; Cowie,
M. Organometallics 1995, in press. (d) Berry, D. H.; Eisenberg, R.
Organometallics 1987, 6, 1796.
(50) (a) Puddephatt, R. J .; Azam, K. A.; Hill, R. H.; Brown, M. P.;
Nelson, C. D.; Moulding, R. P.; Seddon, K. R.; Grossel, M. C. J . Am.
Chem. Soc. 1983, 105, 5642. (b) Antonelli, D. M.; Cowie, M. Organo-
metallics 1990, 9, 1818. (c) McDonald, R.; Cowie, M. Inorg. Chem. 1993,
32, 1671. (d) J enkins, J . A.; Cowie, M. Organometallics 1992, 11, 2767.
(51) Deraniyagala, S. P.; Grundy, K. R. Organometallics 1985, 3,
424.
(52) Brookhart, M.; Green, M. L. H.; Wong, L.-L. Prog. Inorg. Chem.
1988, 36, 1.

Reactivity of Alkynes with Rhodium and Iridium Complexes
Organometallics, Vol. 15, No. 2, 1996 519
philic attack of a monodentate PMe3 group on a bridging
acetylene ligand to yield a µ-η1:η2-hydrocarbyl moiety
has been reported,42 and even more closely related to
the present study, dissociation of one end of a bridging
diphosphine ligand in a phenylacetylene-bridged dico-
balt complex, followed by attack at the alkyne, has also
resulted in the formation of a bridging hydrocarbyl
unit,53 not unlike that reported for 10. The only other
example of attack of dppm on a coordinated alkyne, of
which we are aware, occurs in a mononuclear Ru
species, in which the free end of a dangling dppm ligand
apparently attacks an alkyne carbon of a coordinated
hexafluoro-2-butyne, followed by proton transfer from
dppm to the other acetylenic carbon.54
of the second-row metal.57 However, we see no evidence
of migration of the hydride or methyl groups to Rh
preceding the reductive elimination step. It instead
may be that the more labile Rh center serves to facilitate
rearrangements that allow these groups to attain a
mutually cis orientation on Ir, from which elimination
is possible.
One goal of this study was to induce migratory
insertion of an alkyne and a methyl group, leading to a
substituted vinyl moiety. This has been achieved for
both metal systems studied, but only with the strongly
electrophilic alkyne, dimethyl acetylenedicarboxylate;
other alkynes having strongly electron-withdrawing
substituents were not investigated. That insertion
occurs with DMAD but not with acetylene or pheny-
lacetylene possibly is not surprising since it has previ-
ously been noted that most alkyne insertions occur
with activated alkynes.10 It is unfortunate that no
intermediates were observed in this migratory insertion
since several questions arise about the mechanism.
Although one might expect alkyne attack to occur at the
unsaturated (Rh) center in the RhIr precursor 1, the
resulting alignment of the DMAD and methyl groups
is unsuitable for insertion, due to an intervening car-
bonyl group, and instead might be expected to generate
an alkyne-bridged product analogous to the diiridium
species 18. The absence of such a product suggests an
alternate site of alkyne coordination. Attack at a
saturated metal has been proposed via a dipolar path-
way, in which nucleophilic attack by the metal on the
electrophilic alkyne occurs.10 This being the case,
alkyne coordination on Ir at either site A or B would be
expected to generate the observed product, as shown in
Scheme 5.
In the related reaction of the diiridium precursor 2
with DMAD, two products are obtained as shown in
Scheme 6; in addition to the alkenyl product 17 result-
ing from migratory insertion, an alkyne-bridged product
was also obtained. As noted earlier, the reactive
intermediate in this diiridium species is presumed to
be a methyl complex, suggested to resemble intermedi-
ate I shown in Scheme 6. If, in this intermediate,
reaction occurs via a dipolar species resulting from
alkyne coordination at the saturated metal, the two
different products can be rationalized on the basis of
whether DMAD approaches from the front or the back
of the complex (routes A′ and B′). Alternately, even if
alkyne attack occurs at the unsaturated metal (routes
A and B), the same products might be expected on the
basis of the resulting positions of the methyl and alkyne
groups.
As in the reaction of 2 with acetylene to give the
acetylide-hydride species 5, compound 1 reacts with
phenylacetylene to give a phenylacetylide-hydride spe-
cies 13, which is observed at low temperature. This
species does not, however, yield a vinylidene species as
in the Ir2 system, but instead gives an alkyne-bridged
intermediate [RhIr(CH3)(CO)3(µ-HCtCPh)(dppm)2][CF3-
SO3] (14), which goes on to lose methane, yielding the
phenylacetylide-bridged species [RhIr(CO)3(µ-CtCPh)-
(dppm)2][CF3SO3] (11). The involvement of 14 as an
intermediate in methane elimination is puzzling, al-
though it may serve as a route to species 15 (preceding
reductive elimination) in which the hydride and methyl
groups are adjacent. As in the diiridium species 5, it is
proposed that the hydrido and methyl groups in 13 do
not have a cis disposition so do not eliminate readily.
Intermediate 14 undergoes a subsequent oxidative
addition of the alkyne-hydrogen bond accompanied by
CO loss to yield the new hydrido-methyl complex 15,
which is now assumed to have these groups mutually
cis, facilitating the reductive elimination of methane.
In the absence of excess phenylacetylene, methane loss
is followed by recoordination of the liberated CO to yield
11, whereas in the presence of excess phenylacetylene
oxidative addition of this substrate competes, yielding
12. In support of the dicarbonyl formulation for 15, the
generation of 12 at subambient temperatures appears
to occur more readily from 15 in the presence of
PhCtCH than from reaction of 11 with this alkyne.
Subsequent studies have shown55 that carbonyl loss
from 11 is necessary before oxidative addition of phe-
nylacetylene occurs.
The actual geometry at Ir in 13 is not known; however
the transformations of 1 (+PhCtCH) to 13 and of 13
to 14 are reasonable when it is recalled that movement
of a hydride ligand from one face of an MM′P4 unit to
the other is a facile process44,50 which, in combination
with the known ability of bridging acetylides to undergo
a windshield wiper movement from one metal to the
other,51 could easily give rise to such rearrangements.
We had considered that reductive elimination might be
occurring from Rh since this process might be expected
to be more facile from a second- rather than a third-
row metal, due to the stronger M-H and M-CH3 bonds
with the latter56 and due to the greater kinetic lability
Con clu sion s
Alkyne molecules display a rich chemistry with the
binuclear methyl complexes described, in which three
basic reactivities are initially observed. With all alkynes,
the common reactivity mode for late metal binuclear
complexes, leading to species having the alkyne group
bridging both metals, is again observed. In the second
reactivity type, 1-alkynes can oxidatively add to give
hydrido-acetylide species; and finally, the third reactiv-
ity is observed with DMAD, in which insertion of this
(53) Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1994,
13, 3767.
(54) (a) Mao, T., Bond, A. H., Rogers, R. D., Takats, J ., manuscript
in preparation. (b) Takats, J ., personal communication.
(55) George, D. A., Cowie, M., unpublished work.
(56) Ziegler, T.; Tschinke, V.; Becke, A. J . Am. Chem. Soc. 1987,
109, 1351.
(57) Shen, J .-K.; Tucker, D. S.; Basolo, F.; Hughes, R. P. J . Am.
Chem. Soc. 1993, 115, 11312 and references cited therein.

520 Organometallics, Vol. 15, No. 2, 1996
Antwi-Nsiah et al.
alkyne into the metal-alkyl bond occurs to give alkenyl
species. In all three reactivity modes, the diiridium
system is well-behaved, and only the hydrido-acetylide
species reacts further, in what is becoming a common
transformation in these binuclear systems,49 to give
vinylidene-bridged products. The unexpected subse-
quent reactivities occur when one iridium is substituted
by the more labile rhodium. In one case involving a
bridging acetylene ligand, the Rh center is directly
involved in the transformation, which results from
phosphine dissociation from this center followed by
nucleophilic attack at the coordinated acetylene, giving
an unusual unsaturated metallacycle involving iridium.
However, in the case in which the RhIr complex reacts
with phenylacetylene, subsequent reductive elimination
of methane from a hydrido-methyl-acetylide species
occurs. In this case there is no direct evidence of
methane elimination from Rh; instead, it may be that
the involvement of this more labile metal center may
result from its ability to facilitate rearrangements,
which in the present case allows the methyl and hydride
ligands to adopt a cis arrangement at Ir preceding
elimination.
Although reactivity of these 16-/18-electron binuclear
systems often appears to be initiated at the unsaturated
metal, the reactions with DMAD may occur at the
saturated metal, initiated by electron transfer from the
metal to the electrophilic alkyne. We also cannot rule
out facile carbonyl transfer from the saturated to the
unsaturated metal, exchanging the site of unsaturation
prior to reaction. Further work is required to obtain
detailed information (where possible) on the involve-
ment of the adjacent metals in the chemistry.
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada and the
University of Alberta for financial support and Mrs.
Gerty Aarts for assistance with some of the NMR
studies.
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
and thermal parameters for the dppm phenyl carbons, solvent
atoms, and atoms of the anion, anisotropic thermal param-
eters, idealized hydrogen parameters, and complete listings
of bond distances and angles (12 pages). Ordering information
is given on any current masthead page.
OM9505118