Reactivity of the heterobinuclear phenylacetylide-bridged A-frame [RhIr(CO)2(μ-CCPh)(Ph2PCH2PPh 2)2][O3SCF3] with small molecules

Article abstract of DOI:10.1021/om970946q

The compound [RhIr(CO)₂(μ-CCPh)(dppm)₂][O₃SCF ₃] (2, dppm = Ph₂PCH₂PPh₂) is an "A-frame" species in which the bridging phenylacetylide group is σ-bound to iridium and functioning as a π donor to rhodium. Compound 2 reacts with CO and SO₂ to give the carbonyland sulfur dioxide-bridged products [RhIr(CO)₂(μ-CCPh)(μ-L)(dPPm)₂][O ₃SCF₃] (L = CO (1), SO₂ (5)), respectively. Reaction of 2 with a hydride source yields [RhIr(H)(CO)₂(μ-CCPh)-(dppm)₂] (6), having the hydride terminally bound to iridium, and this product rearranges at room temperature to give the phenylvinylidene complex [RhIr(CO)₂(μ-CC(H)Ph)(dppm)₂] (7). Phosphines, olefins, and alkynes also bind terminally to iridium, yielding [RhIr(L)(CO)₂-(μ-CCPh)(dPPm)₂][O₃SCF ₃] (L = PR₃, olefin, alkyne). In the case of dimethyl acetylenedicarboxylate, rearrangement of the initial alkyne adduct occurs to give the alkyne-bridged product [RhIr(CO)₂(μ-CCPh)(μ-CH₃O ₂CC≡CCO₂CH₃)(dppm)₂][O ₃SCF₃] (18). In addition, the initial adducts of terminal alkynes also rearrange by an oxidative addition reaction to give the bis(acetylide) hydride species [RhIr(CCPh)(CO)₂(μ-H)(μ-CCR)(dppm)₂][O ₃SCF₃] (R = Ph (19), CH₃ (2O)). Compound 2 also undergoes oxidative addition with dihydrogen to give [RhIr(H)-(CO)₂(μ-H)(μ-CCPh)(dPPm)₂][O ₃SCF₃] (21), in which the terminal (on Ir) and the bridging hydrides are in the A-frame pocket. It appears that SO₂ and H₂ attack on the inside of the A-frame pocket, whereas all other substrates attack on the outside of the pocket, at iridium.

Full text of DOI:10.1021/om970946q

Organometallics 1998, 17, 2553-2566
2553
Rea ctivity of th e Heter obin u clea r
P h en yla cetylid e-Br id ged A-F r a m e
[Rh Ir (CO)2(µ-CCP h )(P h 2P CH2P P h 2)2][O3SCF 3] w ith Sm a ll
Molecu les
Darren S. A. George, Robert McDonald,† and Martin Cowie*
Department of Chemistry, University of Alberta, Edmonton, AB, Canada T6G 2G2
Received October 30, 1997
The compound [RhIr(CO)2(µ-CCPh)(dppm)2][O3SCF3] (2, dppm ) Ph2PCH2PPh2) is an “A-
frame” species in which the bridging phenylacetylide group is σ-bound to iridium and func-
tioning as a π donor to rhodium. Compound 2 reacts with CO and SO2 to give the carbonyl-
and sulfur dioxide-bridged products [RhIr(CO)2(µ-CCPh)(µ-L)(dppm)2][O3SCF3] (L ) CO (1),
SO2 (5)), respectively. Reaction of 2 with a hydride source yields [RhIr(H)(CO)2(µ-CCPh)-
(dppm)2] (6), having the hydride terminally bound to iridium, and this product rearranges
at room temperature to give the phenylvinylidene complex [RhIr(CO)2(µ-CC(H)Ph)(dppm)2]
(7). Phosphines, olefins, and alkynes also bind terminally to iridium, yielding [RhIr(L)(CO)2-
(µ-CCPh)(dppm)2][O3SCF3] (L ) PR3, olefin, alkyne). In the case of dimethyl acetylenedicar-
boxylate, rearrangement of the initial alkyne adduct occurs to give the alkyne-bridged product
[RhIr(CO)2(µ-CCPh)(µ-CH3O2CCtCCO2CH3)(dppm)2][O3SCF3] (18). In addition, the initial
adducts of terminal alkynes also rearrange by an oxidative addition reaction to give the
bis(acetylide) hydride species [RhIr(CCPh)(CO)2(µ-H)(µ-CCR)(dppm)2][O3SCF3] (R ) Ph (19),
CH3 (20)). Compound 2 also undergoes oxidative addition with dihydrogen to give [RhIr(H)-
(CO)2(µ-H)(µ-CCPh)(dppm)2][O3SCF3] (21), in which the terminal (on Ir) and the bridging
hydrides are in the A-frame pocket. It appears that SO2 and H2 attack on the inside of the
A-frame pocket, whereas all other substrates attack on the outside of the pocket, at iridium.
In tr od u ction
can somehow interact in a cooperative manner when
activating organic substrates. Binuclear complexes of
this type are members of the so-called “A-frame”5 series,
in which the metals are bridged by a single ligand in
addition to the diphosphine groups, which are mutually
trans on each metal.
We have recently begun an investigation of binuclear
complexes containing the acetylide or alkynyl ligand
(-CtCR), for which a variety of organic transformations
has been demonstrated, including cycloaddition,6 carbon-
Our understanding of organometallic processes, par-
ticularly involving late transition metals, in both stoi-
chiometric and catalytic reactions, has benefited greatly
from studies of d8, square planar complexes such as
RhCl(PPh3)3 and IrCl(CO)(PPh3)2.1 One series of analo-
gous complexes, in which the chloro ligand is replaced
by an anionic organic group, such as an alkyl, aryl, or
related group, presents an interesting extension to the
chemistry. Not only can the electronic influence of this
group give rise to interesting reactivity changes at the
metal,1g,2 but C-C bond formation is also possible
through migratory insertion reactions involving carbon-
containing substrates and the anionic, organic ligand.3
Our interest in the above systems, involving ligands
such as alkyl, aryl, and alkenyl groups,4 has centered
on binuclear complexes in which the adjacent metals
(3) (a) Kein, W. J . Organomet. Chem. 1969, 19, 161. (b) English, A.
D.; Herskovitz, J . J . Am. Chem. Soc. 1977, 99, 1648. (c) Calabrese, J .
C.; Roe, D. C.; Thorn, D. L.; Tulip, T. H. Organometallics 1984, 3, 1223.
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Deutsch, D. A.; Eisenberg, R. J . Am. Chem. Soc. 1991, 113, 5090. (f)
Foo, T.; Bergman, R. G. Organometallics 1992, 11, 1811. (g) Kramarz,
K. W.; Eisenberg, R. Organometallics 1992, 11, 1997. (h) Cleary, B.
P.; Eisenberg, R. Organometallics 1992, 11, 2335. (i) Shafiq, F.;
Kramarz, K. W.; Eisenberg, R. Inorg. Chim. Acta 1993, 213, 111.
(4) (a) Antonelli, D. M.; Cowie, M. Organometallics 1991, 10, 2550.
(b) Antwi-Nsiah, F. R.; Cowie, M. Organometallics 1992, 11, 3157. (c)
Sterenberg, B. T.; Hilts, R. W.; Moro, G.; McDonald, R.; Cowie, M. J .
Am. Chem. Soc. 1995, 117, 245. (d) Wang, L.-S.; Cowie, M. Organo-
metallics 1995, 14, 2374. (e) Wang, L.-S.; Cowie, M. Organometallics
1995, 14, 3040. (f) Wang, L.-S.; Cowie, M. Can. J . Chem. 1995, 73,
1058. (g) Antwi-Nsiah, F. H.; Oke, O.; Cowie, M. Organometallics 1996,
15, 506. (h) Antwi-Nsiah, F. H.; Oke, O.; Cowie, M. Organometallics
1996, 15, 1042. (i) Sterenberg, B. T.; Cowie, M. Organometallics 1997,
16, 2297. (j) Graham, T. W.; Van Gastel, F.; Cowie, M. Manuscript in
preparation. (k) Torkelson, J . R.; Antwi-Nsiah, F. H.; Cowie, M.; Pruis,
J . G.; J alkanen, K. J .; DeKock, R. Manuscript in preparation. (m) Oke,
O.; Cowie, M. Manuscript in preparation.
* To whom correspondence should be addressed. Fax: (403)-492-
8231. E-mail: martin.cowie@ualberta.ca.
† Faculty Service Officer, Structure Determination Laboratory.
(1) (a) 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. (b) J ardine, F. H.;
Osborn, J . A.; Wilkinson, G. J . Chem. Soc. A 1967, 1574. (c) Collman,
J . P. Acc. Chem. Res. 1968, 1, 136. (d) Collman, J . P. Adv. Organomet.
Chem. 1968, 7, 53. (e) Vaska, L. Acc. Chem. Res. 1968, 1, 335. (f)
Halpern, J . Inorg. Chim. Acta 1981, 50, 11. (g) Atwood, J . D. Coord.
Chem. Rev. 1988, 83, 93.
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metallics 1985, 4, 1162. (b) Walter, R. H.; J ohnson, B. F. G. J . Chem.
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S0276-7333(97)00946-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/16/1998

2554 Organometallics, Vol. 17, No. 12, 1998
George et al.
carbon bond formation,7 and transformations to vinyli-
denes8sthemselves useful precursors for further organic
transformations.9 The alkynyl ligand is isoelectronic
with the carbonyl group and displays some of the same
structural diversity10 of this ubiquitous group. At a
single metal center the alkynyl group binds in an η1-
fashion through the terminal carbon, whereas in multi-
nuclear systems a number of bridging modes are
possible. The common modes observed in a heterobi-
nuclear system (M * M′) are diagrammed as follows:
phosphorus pentoxide for halogenated solvents) before use.
Reactions were done 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, Inc., allene
was obtained from Canadian Liquid Air Ltd., and dihydrogen
was purchased from Linde. All gases were used as received.
Ammonium hexachloroiridate(IV) and potassium hexachlo-
rorhodate(III) were obtained from Vancouver Island Precious
Metals; hydrated rhodium trichloride was purchased from
Colonial Metals. The compounds [IrAgCl(CCPh)(CO)-
(dppm)2],12 [Rh2(CO)4Cl2],13 and [Rh2(COD)2Cl2]14 were pre-
pared by literature methods. Dimethyl acetylenedicarboxylate
(DMAD, obtained from Aldrich) and deuterated solvents
(obtained from Cambridge Isotope Laboratories) were distilled
and stored over molecular sieves. The previously reported4g
compound [RhIr(CO)3(CCPh)(dppm)2]Cl (1) was prepared by
a variation on Shaw’s method,12 as outlined below. All other
reagents were obtained from Aldrich and were used as
received.
In structure A, the alkynyl group is terminally bound
to either metal M or M′ and, to a first approximation,
resembles a mononuclear system. The direct involve-
ment of the second metal can occur as shown in the other
modes. In structure B, the alkynyl group functions as
a two-electron donor to the pair of metals, much as in a
symmetrically bridging carbonyl. When the alkynyl
group functions as an asymmetric bridge, as in C or D,
it behaves as a two-electron donor to one metal, via the
M-C σ bond, and as a two-electron donor to the other,
via the π-interaction. However, the above structural an-
alogy between -CtCR and CO should not be extended
too far into electronic effects, since it is generally accep-
ted that, unlike carbonyls, the alkynyl group has very
poor π-acceptor capabilities in the η1-binding mode.11
In this paper we present the first of our studies on
the chemistry of the phenylacetylide-bridged compound
[RhIr(CO)2(µ-CCPh)(dppm)2][O3SCF3] (2), in which we
concentrate on determining the roles of the different
metals in the reactivity of this species.
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 spectra were run on either a Perkin-
Elmer model 1600 FTIR or a Nicolet Magna-IR 750 spectrom-
eter 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 compounds is given
in Table 1.
(a ) P r ep a r a tion of [Rh Ir (CO)3(µ-η1:η2′-CCP h )(d p p m )2]-
[Cl] (1). A solid sample of [IrAgCl(CO)(CCPh)(dppm)2] (198.5
mg, 160.9 µmol) was placed in a flask with [Rh2(CO)4Cl2] (33
mg, 84.9 µmol) and 10 mL of CH2Cl2. The solution was stirred
for 1/2 h, during which time it changed from a red solution to
a brown suspension. Filtration resulted in a clear red solution.
The solvent was reduced to 2 mL under a stream of CO, and
the product precipitated by the addition of 20 mL of ether.
The resulting brown precipitate was then washed twice with
10 mL of ether and dried under nitrogen. It was shown by its
proton and phosphorus NMR spectra to be analogous to the
previously reported triflate salt.4g Yield: 193 mg (93%).
Exp er im en ta l Section
All solvents were distilled over appropriate drying agents
(sodium/benzophenone for THF, ether, benzene, and pentane;
(b) P r ep a r a tion of [Rh Ir (CO)2(µ-η1:η2′-CCP h )(d p p m )2]-
[O3SCF 3] (2). (Meth od 1). A solid sample of [IrAgCl(CO)-
(CCPh)(dppm)2] (0.97 g, 789.4 µmol) was placed in a flask with
(6) Bruce, M. I.; Hambley, T. W.; Liddell, M. J .; Snow, M. R.;
Swincer, A. G.; Tiekink, E. R. T. Organometallics 1990, 9, 96. (b)
Barrett, A. G. M.; Carpenter, N. E.; Mortier, J .; Sabat, M. Organome-
tallics 1990, 9, 151. (c) Bruce, M. I.; Duffy, D. N.; Liddell, M. J .; Tiekink,
E. R. T.; Nicholson, B. K. Organometallics 1992, 11, 1527. (d) Fischer,
H.; Leroux, F.; Roth, G.; Stumpf, R. Chem. Ber. 1996, 129, 1475. (e)
Fischer, H.; Leroux, F.; Roth, G.; Stumpf, R. Organometallics 1996,
15, 3723.
(7) McMullen, A. K.; Selegue, J . P.; Wang, J .-G. Organometallics
1991, 10, 3421. (b) Matsuzaka, H.; Hirayama, Y.; Nishio, M.; Mizobe,
Y.; Hidai, M. Organometallics 1993, 12, 36. (c) Barbaro, P.; Bianchini,
C.; Peruzzini, M.; Polo, A.; Zanobini, F.; Frediani, P. Inorg. Chim. Acta
1994, 220, 5. (d) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini, M.;
Zanobini, F. Organometallics 1994, 13, 4616. (e) Werner, H.; Scha¨fer,
M.; Wolf, J .; Peters, K.; von Schnering, H. G. Angew. Chem., Int. Ed.
Engl. 1995, 34, 191. (f) Albertin, G.; Antoniutti, S.; Bordignon, E.;
Cazzaro, F.; Ianelli, S.; Pelizzi, G. Organometallics 1995, 14, 4114. (g)
Yamamoto, Y.; Satoh, R.; Tanase, T. J . Chem. Soc., Dalton Trans. 1995,
307. (h) Klein, H.-F.; Heiden, M.; He, M.; J ung, T.; Ro¨hr, C. Organo-
metallics 1997, 16, 2003.
[Rh2(CO)4Cl2] (154 mg, 396.1 µmol) and 60 mL of CH2Cl2,
1
yielding a brown-red mixture which was stirred for
/ h,
2
followed by addition of 5 mL of a THF solution of AgO3SCF3
(215 mg, 836 µmol) via cannula. The solution was filtered after
a further 30 min of stirring, and then the solvent was removed
in vacuo. The resulting solid was dissolved in 5 mL of CH2-
Cl2 and 20 mL of THF, and the solution was refluxed for 2 h.
The solvent was reduced to 10 mL, and the product was
precipitated by the addition of ether (60 mL). The red product
was then washed three times with 10 mL aliquots of ether.
Yield: 0.97 g (90%). Calcd for C61H49O5P4RhIrF3S: C, 53.47;
H, 3.60. Found: C, 53.72; H, 3.58.
Meth od 2. A solid sample of [IrAgCl(CO)(CCPh)(dppm)2]
(1.50 g, 1.22 mmol) was placed in a flask with [Rh2(COD)2Cl2]
(267 mg, 608.1 µmol) and 30 mL of CH2Cl2. The resulting
brown-red mixture was stirred for 1 h, and then an atmosphere
of CO was placed over the solution. After a further 15 min of
stirring, 5 mL of a THF solution of AgO3SCF3 (310 mg, 1.207
mmol) was added via cannula. The solution was filtered after
a further 30 min of stirring, and then the solvent was removed
(8) (a) Elschenbroich, Ch.; Salzer, A. Organometallics: A Concise
Introduction; VCH Publishers: New York, 1989. (b) Esteruelas, M. A.;
Lahoz, F. J .; On˜ate, E.; Oro, L. A.; Rodr´ıguez, L. Organometallics 1993,
12, 4219. (c) Werner, H. J . Organomet. Chem. 1994, 475, 45. (d)
Edwards, A. J .; Esteruelas, M. A.; Lahoz, F. J .; Modrego, J .; Oro, L.
A.; Schrickel, J . Organometallics 1996, 15, 3556.
(9) Bruce, M. I. Chem. Rev. 1991, 91, 197.
(10) (a) Nast, R. Coord. Chem. Rev. 1982, 47, 89. (b) Lotz, S.; van
Rooyen, P. H.; Meyer, R. Adv. Organomet. Chem. 1995, 37, 219.
(11) (a) Lichtenberger, D. L.; Renshaw, S. K.; Bullock, R. M. J . Am.
Chem. Soc. 1993, 115, 3276. (b) Manna, J .; J ohn, K. D.; Hopkins, M.
D. Adv. Organomet. Chem. 1995, 38, 79.
(12) Hutton, A. T.; Pringle, P. G.; Shaw, B. L. Organometallics 1983,
2, 1889.
(13) McCleverty, J . A.; Wilkinson, G. Inorg. Synth. 1990, 28, 85.
(14) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88.

Reactivity of a Phenylacetylide-Bridged A-Frame
Organometallics, Vol. 17, No. 12, 1998 2555

2556 Organometallics, Vol. 17, No. 12, 1998
George et al.

Reactivity of a Phenylacetylide-Bridged A-Frame
Organometallics, Vol. 17, No. 12, 1998 2557
in vacuo, leaving a red residue which was redissolved in a
mixture of CH2Cl2 (10 mL) and THF (10 mL). Addition of
pentane (55 mL) precipitated the product, which was washed
with three 20-mL aliquots of pentane. The solid was dissolved
in 10 mL of CH2Cl2 and 40 mL of THF, and the solution was
refluxed for 2 h. The solvent was removed in vacuo, and the
product was recrystallized from CH2Cl2/ether (10:60 mL). The
red product was then washed three times with 10 mL aliquots
of ether. Yield: 1.34 g (80%).
(c) Rea ction of [Rh Ir (13CO)2(µ-η1:η2′-CCP h )(d p p m )2]-
[O3SCF 3] (2) w ith CO. An NMR tube was charged with
compound 2 (20.0 mg, 14.6 µmol) containing 13C-enriched
carbonyl ligands and 0.4 mL of CD2Cl2. The sample was cooled
to -80 °C in a dry ice-acetone bath, and an excess (≈2 mL,
80 µmol) of 12CO was added via gastight syringe, causing a
color change from red-purple to yellow. The 31P{1H} and 13C-
{1H} NMR spectra of this sample, run at -80 °C, showed
complete conversion of 2 to [RhIr(13CO)(CO)(µ-η1:η2′-CCPh)(µ-
13CO)(dppm)2][O3SCF3] (1), with the 12C-carbonyl occupying the
terminal position on iridium.
(d ) P r ep a r a tion of [Rh Ir (CO)2(P Me3)(µ-η1:η2′-CCP h )-
(d p p m )2][O3SCF 3] (3). Compound 2 (20.7 mg, 15.1 µmol) was
placed in a flask with 1 mL of CH2Cl2. Trimethylphosphine
(1.6 µL, 15.5 µmol) was added via syringe, causing a color
change from purple-red to orange. After the solution had
stirred for 30 min, the orange product was precipitated by
the addition of 10 mL of Et2O. This was washed with three
5 mL aliquots of ether and then dried, first under nitrogen
and then under vacuum. Yield: 14.7 mg (67%) Calcd for
solid was extracted into 5 mL of ether. This was filtered
through Celite, and the solvent was removed under vacuum.
No elemental analysis could be obtained for this compound,
due to its high air-sensitivity.
(i) P r ep a r a tion of [Rh Ir (CO)2(η2-CH2dCH2)(µ-η1:η2′-
CCP h )(d p p m )2][O3SCF 3] (8). An NMR tube was charged
with compound 2 (18 mg, 13.1 µmol) and 0.4 mL of CD2Cl2.
This was placed under an atmosphere of ethylene and cooled
to -80 °C, causing a rapid color change to yellow. NMR
spectroscopy showed complete conversion to 8; however, eth-
ylene was lost immediately upon warming, regenerating 2.
(j) P r ep a r a tion of [Rh Ir (CO)2(η2-CH2dCdCH2)(µ-η1:η2′-
CCP h )(d p p m )2][O3SCF 3] (9). An NMR tube was charged
with compound 2 (18 mg, 13.1 µmol) and 0.4 mL of CD2Cl2.
Allene was passed over this solution, causing a color change
1
to yellow. The H, 13C{1H}, and 31P{1H} NMR spectra of this
solution at -30 °C showed complete conversion to a mixture
of 9a ,b. This was not isolated in the solid state, due to facile
loss of allene.
(k ) P r ep a r a tion of [Rh Ir (CO)2(η2-CH2dCdC(CH3)2)(µ-
η1:η2′-CCP h )(d p p m )2][O3SCF 3] (10). A sample of compound
2 (75.0 mg, 54.7 µmol) was placed in a flask with 5 mL of CH2-
Cl2 and 5.4 µL (55.1 µmol) of dimethylallene, resulting in a
color change from red-purple to orange. This was stirred for
1/2 h and then precipitated by addition of 20 mL of pentane.
The resulting orange microcrystalline solid was washed twice
with 10 mL aliquots of pentane and dried under nitrogen. This
compound was not dried under vacuum, due to facile loss of
dimethylallene. The presence of 1 equiv of dichloromethane
of crystallization was confirmed by elemental analysis and by
X-ray structure determination. Yield: 73.9 mg (89%). Calcd
C
64H58O5P5RhIrF3S: C, 53.15; H, 4.04. Found: C, 52.89; H,
3.75.
(e) P r ep a r a tion of [Rh Ir (CO)2(P Me2P h )(µ-η1:η2′-CCP h )-
for
C67H59O5P4RhIrF3SCl2: C, 52.83; H, 3.90; Cl, 4.66.
Found: C, 52.65; H, 3.59; Cl, 4.39.
(d p p m )2][O3SCF 3] (4). Compound 2 (90.6 mg, 66.1 µmol) was
placed in a flask with 5 mL of THF. Phenyldimethylphosphine
(9.5 µL, 66.8 µmol) was added via syringe, causing a color
change from purple-red to brown, accompanied by the forma-
tion of a small amount of precipitate. After 30 min of stir-
ring, 25 mL of ether was added to complete precipitation.
The flocculent orange-brown solid was washed three times
with 5 mL of ether and then dried, first under nitrogen and
then under vacuum. Yield: 80.4 mg (81%) Calcd for
(l) P r ep a r a tion of [Rh Ir (CO)2(η2-CF 3CtCCF 3)(µ-η1:η2′-
CCP h )(d p p m )2][O3SCF 3] (11). A sample of compound 2
(40.0 mg, 29.2 µmol) was placed in a flask and dissolved in 4
mL of THF. Hexafluoro-2-butyne was passed over the solu-
tion, resulting in a change from red-purple to orange-brown.
After the solution was stirred for 1 h, the solvent was reduced
to 2 mL under a steady stream of nitrogen, and the product
precipitated by the addition of 15 mL of ether. The precipitate
was washed twice with 10 mL of ether and dried under
vacuum, giving a yellow microcrystalline powder. Yield: 30.5
mg (68%). Calcd for C65H49O5P4RhIrF9S: C, 50.95; H, 3.22.
Found: C, 50.85; H, 3.07.
C
69H60O5P5RhIrF3S: C, 54.95; H, 4.01. Found: C, 55.20; H,
3.87.
(f) P r ep a r a tion of [Rh Ir (CO)2(µ-SO2)(µ-η1:η2′-CCP h )-
(d p p m )2][O3SCF 3] (5). Compound 2 (30.7 mg, 22.4 µmol) was
placed in a flask with 2 mL of THF, and an atmosphere of
SO2 was placed over the solution, resulting in a color change
from red-purple to red-brown. After 15 min of stirring, 20 mL
of ether was added, resulting in the formation of a flocculent
orange precipitate. This was washed twice with 10 mL of
ether. Yield: 12 mg (37%). Calcd for C61H49P4O7S2F3RhIr: C,
51.09; H, 3.44; S, 4.47. Found: C, 51.03; H, 3.07; S, 4.70.
(g) R ea ct ion of [R h Ir (CO)2(µ-η1:η2′-CCP h )(d p p m )2]-
[O3SCF 3] w ith LiBH(Et)3. An NMR tube was charged with
compound 2 (20.1 mg, 14.7 µmol) and 0.5 mL of THF-d8. The
sample was cooled to -80 °C in a dry ice-acetone bath, and
superhydride (1.0 M solution of LiBH(Et)3 in THF; 15 µL, 15
µmol) was added via syringe, causing a color change to yellow
brown. The NMR spectra at -60 °C showed complete conver-
sion to 6a . Further warming to -20 °C resulted in almost
complete conversion to 6b, along with a small quantity of 7a .
Warming the sample to room temperature caused it to change
from brown to intense purple. The 31P{1H} NMR of this
sample showed a mixture of 7a ,b.
(m ) P r epar ation of [Rh Ir (CO)2(η2-CH3O2CCtCCO2CH3)-
(µ-η1:η2′-CCP h )(d p p m )2][O3SCF 3] (12). A sample of com-
pound 2 (60 mg, 43.8 µmol) was placed in a flask and dissolved
in 3 mL of CH2Cl2. This was cooled to 0 °C with an ice bath,
and dimethyl acetylenedicarboxylate (DMAD) (5.6 µL, 45.6
µmol) was added via syringe. The resulting orange-brown
solution was stirred for 30 min, and then 20 mL of ether was
added. The resulting light brown powder was washed twice
with 10 mL aliquots of ether and then dried, first under
nitrogen and then under vacuum. Yield: 47.3 mg (71%).
Calcd for C67H55O9P4RhIrF3S: C, 53.25; H, 3.60. Found: C,
52.98; H, 3.49.
(n ) P r epar ation of [Rh Ir (CO)2(η2-CH3CtCCO2CH2CH3)-
(µ-η1:η2′-CCP h )(d p p m )2][O3SCF 3] (13). An NMR tube was
charged with compound 2 (17.4 mg, 12.7 µmol) and 0.5 mL of
CD2Cl2, and ethyl 2-butynoate (1.5 µL, 12.9 µmol) was added.
Cooling to -40 °C gave an orange solution which was shown
by NMR spectroscopy to contain almost pure 13. This solution
reverted to 2 upon warming.
(h ) P r ep a r a tion of [Rh Ir (CO)2(µ-CCHP h )(d p p m )2] (7).
A sample of compound 2 was dissolved in THF and cooled to
-10 °C in a salt-ice bath. Superhydride (1 equiv) was added,
and the solution was allowed to slowly warm to room temper-
ature, causing a color change to intense purple. After the
solution was stirred for 1 h at room temperature, the solvent
was removed under a steady stream of nitrogen, and the purple
(o) P r ep a r a tion of [Rh Ir (CO)2(η2-HCtCP h )(µ-η1:η2′-
CCP h )(d p p m )2][O3SCF 3] (14). An NMR tube was charged
with compound 2 (18.4 mg, 13.4 µmol) and 0.5 mL of CD2Cl2.
The sample was cooled to -80 °C and treated with phenyl-
acetylene (1.6 mL, 14.6 µmol), forming an orange solution. This
solution was shown by NMR spectroscopy to contain pure 14.
Upon being warmed to -60 °C, this solution was converted

2558 Organometallics, Vol. 17, No. 12, 1998
George et al.
Ta ble 2. Cr ysta llogr a p h ic Exp er im en ta l Deta ils
to a 2:1 mixture of 14:2, and warming to -40 °C resulted in a
5:10:1 mixture of 14, 2, and the previously reported [RhIr-
(CO)2(CtCPh)(µ-H)(µ-η1:η2′-CCPh)(dppm)2][O3SCF3]4g (19). Fur-
ther warming gave complete conversion to 19.
A. Crystal Data
formula
fw
C67H59Cl2F3IrO5P4RhS
1523.09
(p ) P r ep a r a tion of [Rh Ir (CO)2(η2-HCtCCH3)(µ-η1:η2′-
CCP h )(d p p m )2][O3SCF 3] (15). An NMR tube was charged
with compound 2 (14.6 mg, 10.7 µmol) and 0.5 mL of CD2Cl2.
The sample was cooled to -80 °C and treated with propyne
(450 µL, 18 µmol). This solution was shown by NMR spec-
troscopy to contain about 10% of compound 15. Upon being
warmed to -60 °C, this compound was converted to 2, and
warming to 25 °C resulted in formation of [RhIr(CO)2(CtCPh)-
(µ-H)(µ-η1:η2′-CCCH3)(dppm)2][O3SCF3] (20).
cryst dimens (mm)
cryst syst
space group
unit cell paramsa
a (Å)
0.65 × 0.56 × 0.17
triclinic
P1h (No. 2)
12.3608(11)
15.4205(15)
18.966(2)
107.709(7)
96.972(7)
109.530(7)
3143.9(5)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
(q) P r ep a r a tion of [Rh Ir (CO)2(η2-C6H5CtCC6H5)(µ-η1:
η2′-CCP h )(dppm )2][O3SCF3] (16). An NMR tube was charged
with compound 2 (19.7 mg, 14.4 µmol), 0.5 mL of CD2Cl2, and
an excess of diphenylacetylene (5.0 mg, 28.1 µmol). Cooling
this solution to -80 °C resulted in an orange-red solution
which was shown by NMR to contain an 5:1 mixture of 16 and
2. The diphenylacetylene ligand was lost upon warming,
regenerating 2.
V (Å3)
Z
Fcalcd (g cm-3
)
1.609
2.655
µ (mm-1
)
B. Data Collection and Refinement Conditions
diffractometer
radiation [λ (Å)]
Siemens P4/RAb
graphite-monochromated Mo KR
(0.71073)
temp (°C)
scan type
data collcn 2θ limit (deg)
total no. of data collcd
-60
(r ) P r ep a r a tion of [Rh Ir (CO)2(CH3O2CCtCCO2CH3)(µ-
η1:η2′-CCP h )(d p p m )2][O3SCF 3] (17). A sample of compound
2 (89.9 mg, 65.6 µmol) was placed in a flask and dissolved in
10 mL of CH2Cl2. DMAD (9.1 µL, 74.0 µmol) was added via
syringe. The resulting orange-brown solution was stirred for
16 h, and then the solvent was reduced to 1 mL under a flow
of nitrogen. A 20 mL volume of ether was added to precipitate
the product, which was then recrystallized from 1 mL of CH2-
Cl2 and 20 mL ether, washed twice with 10 mL aliquots of
ether, and dried under vacuum. Yield: 58 mg (58%).
(s) P r ep a r a t ion of [R h Ir (CO)2(µ-η1:η1′-CH 3O2CCtC-
CO2CH3)(µ-η1:η2′-CCP h )(d p p m )2][O3SCF 3] (18). A sample
of compound 2 (99.3 mg, 72.5 µmol) was placed in a flask and
dissolved in 15 mL of THF. DMAD (8.9 µL, 72.4 µmol) was
added via syringe, and the resulting yellow solution was heated
to gentle reflux. After 1 h, the resulting red solution was
reduced in volume to 5 mL and cooled to room temperature.
Ether (15 mL) was added, causing the precipitation of 18 as
an orange powder, which was washed twice with 10 mL
aliquots of ether and dried under vacuum. Yield: 85 mg (78%).
Calcd for C67H55O9P4RhIrF3S: C, 53.25; H, 3.60. Found: C,
53.26; H, 3.73.
θ-2θ
50.0
10 949 (-13 e h e 14,
-16 e k e 16, 0 e l e 22)
10 612
no. of indepdt reflns
no. of obs (NO)
2
9512 (Fo g 2σ(Fo2))
structure solution method direct methods (SHELXS-86c)
refinement method
full-matrix least-squares on F2
(SHELXL-93d)
abs corr method
Gaussian integration (face-indexed)
range of transm factors
0.6752-0.4393
data/restraints/parameters 10553 [Fo g -3σ(Fo2)]/16e/799
2
2
goodness-of-fit (S)f
final R indicesg
1.197 [Fo g -3σ(Fo2)]
2
2
Fo > 2σ(Fo
)
R1 ) 0.0514, wR2 ) 0.1313
R1 ) 0.0612, wR2 ) 0.1505
3.130h and -0.950
all data
largest diff peak and hole
(e Å-3
)
a
Obtained from least-squares refinement of 36 reflections with
b
26.6° < 2θ < 29.1°. Programs for diffractometer operation and
data collection were those of the XSCANS system supplied by
Siemens. c Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-473.
d
Sheldrick, G. M. SHELXL-93. Program for crystal structure
(t) P r ep a r a tion of [Rh Ir (CO)2(CtCP h )(µ-H)(µ-η1:η2′-
CCCH3)(d p p m )2][O3SCF 3] (20). A sample of 2 (40.6 mg, 29.6
µmol) was dissolved in 3 mL of THF and placed under 1 atm
of propyne, causing a color change to brown. After the mixture
was stirred for 1 h, 15 mL of pentane was added, giving a
brown precipitate. This was redissolved in 1 mL of CH2Cl2
and precipitated by the addition of 10 mL of ether
and 10 mL of pentane. The brown solid was washed twice
with 10 mL of ether and dried. Yield: 29 mg (69%). Calcd
for C64H53O5P4RhIrF3S: C, 54.51; H, 3.79. Found: C, 54.31;
H, 3.55.
(u ) P r ep a r a tion of [Rh Ir (CO)2(H)(µ-η1:η2′-CCP h )(µ-H)-
(d p p m )2][O3SCF 3] (21). A sample of 2 (40 mg, 29.2 µmol)
was placed in a flask and dissolved in 3 mL of THF. Hydrogen
gas was passed over the solution for 15 min, causing the
solution color to change to brown. After 1 h of stirring, pentane
(15 mL) was slowly added, giving a yellow microcrystalline
precipitate. This was washed twice with 10 mL ether and
determination. University of Go¨ttingen, Germany, 1993. Refine-
ment on Fo2 for all reflections except for 59 having Fo2 < -3σ(Fo2).
Weighted R-factors wR2 and all goodnesses of fit S are based on
Fo2; conventional R-factors R1 are based on Fo, with Fo set to zero
2
2
for negative Fo
.
The observed criterion of Fo > 2σ(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. e Restraints were applied to enforce
idealized geometries within both positions of the disordered
dichloromethane molecule (d(Cl(1)-C(103)) ) d(Cl(2)-C(103)) )
d(Cl(3)-C(104)) ) d(Cl(4)-C(104)) ) 1.80 Å; d(Cl(1)‚‚‚Cl(2)) )
d(Cl(3)‚‚‚Cl(4)) ) 2.95 Å) and one of the orientations of the CF3
group of the disordered triflate anion (d(S(2)-C(102)) ) 1.80 Å;
d(F(104)-C(102)) ) d(F(105)-C(102)) ) d(F(106)-C(102)) ) 1.35
Å; d(F(104)‚‚‚F(105)) ) d(F(104)‚‚‚F(106)) ) d(F(105)‚‚‚F(106)) )
2.20 Å). Distance restraints were also applied to keep one of the
dichloromethane “molecules” (the one containing Cl(1), Cl(2) and
C(103)) in approximately the same region of space as one of the
CF3 group orientations (the one centered by C(102)): d(Cl(1)‚‚‚S(2))
) 2.75 Å; d(Cl(2)‚‚‚S(2)) ) 3.65 Å; d(S(2)‚‚‚C(103)) ) 2.30 Å;
d(C(102)‚‚‚C(103)) ) 0.90 Å (these distances were based on the
corresponding Cl(3)‚‚‚S(2), Cl(4)‚‚‚S(1), S(1)‚‚‚C(104) and
C(101)‚‚‚C(104) distances of the alternate triflate and dichlo-
dried under vacuum. Yield: 33.3 mg (83%). Calcd for C61H51
O5P4RhIrF3S: C, 53.40; H, 3.75. Found: C, 53.20; H, 3.54.
-
X-r a y Da ta Collection . Suitable crystals of compound 10
were grown by slow diffusion of pentane into a concentrated
CH2Cl2 solution of 10 (containing an excess of dimethylallene)
at 22 °C. Data were collected to a maximum 2θ ) 50° on a
Siemens P4/RA diffractometer using Mo KR radiation at -60
°C. Unit cell parameters were obtained from a least-squares
refinement of the setting angles of 54 reflections in the range
26.5° < 2θ < 29.1°. The cell parameters suggested either P1
2
romethane orientations). f S ) [∑w(Fo - Fc2)2/(n - p)]1/2 (n )
number of data; p ) number of parameters varied; w ) [σ2(Fo2) +
(0.0257P)2 + 39.5280P]-1, where P ) [Max(Fo2, 0) + 2Fc2]/3). R1
g
2
h
) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑w(Fo4)]1/2
.
The
largest residual peaks were found in the vicinity of the disordered
triflate ion and dichloromethane molecule and were without
chemical significance.

Reactivity of a Phenylacetylide-Bridged A-Frame
Organometallics, Vol. 17, No. 12, 1998 2559
Ta ble 3. Selected In ter a tom ic Dista n ces (Å)
Ta ble 4. Selected In ter a tom ic An gles (d eg)
Ir-Rh
2.8759(7)
2.351(2)
2.355(2)
1.984(9)
2.163(9)
2.049(8)
2.054(8)
2.329(2)
2.332(2)
2.374(9)
1.828(9)
2.271(8)
2.516(8)
P(1)-C(10)
P(2)-C(10)
P(3)-C(20)
P(4)-C(20)
O(1)-C(1)
O(2)-C(2)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(5)-C(7)
C(8)-C(9)
C(9)-C(91)
1.828(8)
1.830(9)
1.827(8)
1.840(8)
1.153(10)
1.158(11)
1.433(12)
1.335(13)
1.497(14)
1.514(13)
1.218(12)
1.447(12)
Rh-Ir-P(1)
Rh-Ir-P(3)
Rh-Ir-C(1)
Rh-Ir-C(3)
Rh-Ir-C(4)
Rh-Ir-C(8)
P(1)-Ir-P(3)
P(1)-Ir-C(1)
P(1)-Ir-C(3)
P(1)-Ir-C(4)
P(1)-Ir-C(8)
P(3)-Ir-C(1)
P(3)-Ir-C(3)
P(3)-Ir-C(4)
P(3)-Ir-C(8)
C(1)-Ir-C(3)
C(1)-Ir-C(4)
C(1)-Ir-C(8)
C(3)-Ir-C(4)
C(3)-Ir-C(8)
C(4)-Ir-C(8)
Ir-Rh-P(2)
Ir-Rh-P(4)
Ir-Rh-C(1)
Ir-Rh-C(2)
Ir-Rh-C(8)
Ir-Rh-C(9)
P(2)-Rh-P(4)
P(2)-Rh-C(1)
P(2)-Rh-C(2)
P(2)-Rh-C(8)
P(2)-Rh-C(9)
P(4)-Rh-C(1)
P(4)-Rh-C(2)
91.51(6)
90.73(5)
54.8(3)
161.4(2)
158.8(3)
51.6(2)
177.50(8)
90.0(2)
90.7(2)
88.3(3)
91.7(2)
92.2(2)
87.5(2)
89.2(2)
88.9(2)
106.7(4)
146.3(4)
106.5(3)
39.7(3)
146.7(3)
107.2(3)
92.34(6)
93.51(6)
43.1(2)
148.6(3)
45.2(2)
73.9(2)
169.81(8)
94.1(2)
88.6(3)
89.0(2)
90.6(2)
95.9(2)
90.8(3)
P(4)-Rh-C(8)
P(4)-Rh-C(9)
C(1)-Rh-C(2)
C(1)-Rh-C(8)
C(1)-Rh-C(9)
C(2)-Rh-C(8)
C(2)-Rh-C(9)
C(8)-Rh-C(9)
Ir-P(1)-C(10)
Rh-P(2)-C(10)
Ir-P(3)-C(20)
Rh-P(4)-C(20)
Ir-C(1)-Rh
Ir-C(1)-O(1)
Rh-C(1)-O(1)
Rh-C(2)-O(2)
Ir-C(3)-C(4)
Ir-C(4)-C(3)
Ir-C(4)-C(5)
89.2(2)
83.1(2)
105.6(4)
88.3(3)
116.9(3)
166.1(4)
137.4(4)
28.9(3)
110.4(3)
112.3(3)
112.0(3)
111.3(3)
82.1(3)
Ir-P(1)
Ir-P(3)
Ir-C(1)
Ir-C(3)
Ir-C(4)
Ir-C(8)
Rh-P(2)
Rh-P(4)
Rh-C(1)
Rh-C(2)
Rh-C(8)
Rh-C(9)
155.1(8)
122.8(7)
178.7(10)
65.9(5)
or P1h space groups; successful solution and refinement of the
structure confirmed P1h to be the correct choice. Three reflec-
tions were chosen as intensity standards and were remeasured
after every 200 reflections. There was no significant variation
in the intensities of either set of standards, so no correction
was applied. Absorption corrections were applied to the data.
See Table 2 for a summary of crystal data and X-ray collection
information.
The structure was solved by direct methods, using SHELXS-
86 to locate the Ir, Rh, and P atoms. All other atoms were
located after subsequent least-squares cycles and difference
Fourier syntheses. Refinement was completed using the
program SHELXS-93. All hydrogen atoms of the complex were
included as fixed contributions; their idealized positions were
generated from the geometries of the attached carbon atoms
and their thermal parameters set at 20% greater than the
isotropic thermal parameter of these carbons. The triflate
anion and the dichloromethane solvent molecule were found
to be disordered over a common region of space. Alternate
orientations of the triflate ion were present in an approximate
50:50 occupancy ratio, with these orientations sharing two
oxygen positions (O(101) and O(102)), with the two half-
occupancy CH2Cl2 molecules superimposed on the triflate ion
positions (specifically in the region of the triflate CF3 group).
All significant residual peaks on a final difference Fourier map
were in the vicinity of this anion/solvent disorder.
74.5(5)
143.4(7)
142.1(9)
123.9(9)
120.2(9)
115.9(9)
83.2(3)
167.6(7)
86.8(6)
64.3(5)
130.9(6)
161.7(9)
112.4(4)
112.6(4)
123.2(8)
117.8(8)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(4)-C(5)-C(7)
C(6)-C(5)-C(7)
Ir-C(8)-Rh
Ir-C(8)-C(9)
Rh-C(8)-C(9)
Rh-C(9)-C(8)
Rh-C(9)-C(91)
C(8)-C(9)-C(91)
P(1)-C(10)-P(2)
P(3)-C(20)-P(4)
C(9)-C(91)-C(92)
C(9)-C(91)-C(96)
is based on its NMR spectral parameters and on
analogies with the structurally characterized [Rh2(CO)2(µ-
C2 Bu)(dppm)2][ClO4].16 The 13C{1H} NMR spectrum
t
displays two resonances in a region typical of terminal
carbonyls (ca. δ 185), with only one of these displaying
coupling to Rh (81.1 Hz). Furthermore, the IR spectrum
shows two terminal carbonyl stretches. The alkynyl
carbons are observed at δ 106.0 and 107.9 in the 13C-
{1H} NMR spectrum, and the latter is identified as the
R-carbon, on the basis of the greater coupling to the Ir-
bound phosphines. Both alkynyl carbons display almost
equal coupling to Rh (5.1 and 5.7 Hz), consistent with
the bonding mode in which the alkynyl group is σ-bound
to Ir and side-on bound to Rh. In the alternate binding
modes in which the alkynyl could be either sym-
metrically bridging the metals or σ-bound to Rh and
π-bound to Ir, the Rh coupling to the R-carbon would
be expected to be significantly greater than that to the
â-carbon.
It has been shown that the dppm-bridged dirhodium
alkynyl-bridged species,15,16 along with the related spe-
cies [Rh2(µ-O2CCH3)(µ-η1:η2-CCR)(CO)2(PCy3)2],8b [Rh2(µ-
O2CCH3)(µ-η1:η2-CCPh)(COD)2],8b and [NBu4]2[(C6F5)2-
Pt(µ-η1:η2-CCPh)(µ-η2:η1-CCPh)Pt(C6F5)2],17 is fluxional,
having the alkynyl group moving from one metal to the
other in a “windshield-wiper” fashion. In contrast, the
heterobinuclear species 2 is static, as was also reported
for [RhPtCl(µ-CCCH3)(CO)(dppm)2][PF6].18 The 31P{1H}
and 13C{1H} NMR spectra of 2 are essentially invariant
from room temperature to -80 °C.
The final model for the complex refined to values of R1
)
0.0514 (for Fo g 2σ(Fo2)) and wR2 ) 0.1505 (on all data).
Atomic coordinates and displacement parameters are given in
the Supporting Information, and selected bond lengths and
angles are given in Tables 3 and 4, respectively.
2
Resu lts a n d Com p ou n d Ch a r a cter iza tion
The phenylacetylide-bridged, tricarbonyl complex
[RhIr(CO)2(µ-C2Ph)(µ-CO)(dppm)2][O3SCF3] (1), although
earlier obtained in our group by the reaction of the
tricarbonyl methyl complex [RhIr(CH3)(CO)3(dppm)2]-
[O3SCF3] with phenylacetylene,4g is more conveniently
prepared as the chloride salt, via the trans-metalation
method of Shaw,12 in which the AgCl moiety is displaced
from [IrAgCl(C2Ph)(CO)(dppm)2] by a “RhCl(CO)2” frag-
ment. In all subsequent chemistry, the chloride ion is
replaced by triflate in order to reduce the possibility of
anion coordination. Compound 1 is labile and readily
loses CO under reflux in CH2Cl2/THF to form [RhIr-
(CO)2(µ-C2Ph)(dppm)2][O3SCF3] (2), a mixed-metal ana-
logue of Grundy’s alkynyl-bridged compounds, [Rh2(CO)2-
(µ-C2R)(dppm)2][ClO4]15 (R ) H, Ph, Bu). Compound
2 is another member of a series of A-frame complexes
containing an anionic ligand at the bridgehead position
and terminal carbonyl groups.4 Characterization of 2
t
(16) Loeb, S. J .; Cowie, M. Organometallics 1985, 4, 852.
(17) Fornie´s, J .; Lalinde, E. J . Chem. Soc., Dalton Trans. 1996,
2587.
(15) Deraniyagala, S. P.; Grundy, K. R. Organometallics 1985, 4,
424.
(18) Hutton, A. T.; Shehanzadeh, B.; Shaw, B. L. J . Chem. Soc.,
Chem. Commun. 1984, 549.

2560 Organometallics, Vol. 17, No. 12, 1998
George et al.
Sch em e 1
Compound 2 presents a number of different sites of
attack for substrate molecules. As with other A-frame
complexes having coordinative unsaturation at both
metals, substrate attack can occur either on the inside
(i.e. between the metals) or on the outside of the
framework defined by the metals, the terminal carbo-
nyls, and the bridging ligand, diagrammed (dppm
ligands above and below the plane of the drawing are
omitted) as follows:
from within the “pocket” of the A-frame) cannot be ruled
out on the basis of the spectroscopy, the signal for the
iridium-bound carbonyl in the 13C{1H} NMR spectrum
of 4 (at δ 185.5) suggests that it is angled toward the
rhodium, since, in these adducts of 2, compounds in
which the carbonyl is angled away from the rhodium
have 13C{1H} NMR signals in the range δ 175-180,
whereas carbonyls aimed between metals have lower-
field chemical shifts, possibly resulting from a weak
bridging interaction with the second metal. Coordina-
tion of the bulky phosphine inside the pocket of the
A-frame also appears less likely due to unfavorable
steric interactions involving the dppm phenyl groups.
Coordination at iridium is expected for steric as well as
electronic reasons; not only is coordination at rhodium
disfavored owing to steric repulsion involving the phenyl
substituent of the bridging CtCPh group, but coordina-
tion at Ir is favored by the stronger Ir-P vs Rh-P bond.
Compound 3 is isoelectronic with the carbonyl adduct
(1) but differs in having only terminal carbonyl groups.
It is assumed that the carbonyl group remains terminal
on Ir to remove the excess electron density resulting
from σ-donation by the two dppm groups and the PR3
group (it should be recalled that the η1-acetylide is a
poor π-acceptor11). Compound 2 does not react with
PPh3, presumably owing to the bulk of this ligand.
Furthermore, since the two metals differ, attack at
rhodium will clearly be different from attack at iridium.
In addition, substrate attack (either nucleophilic or
electrophilic) can occur at the bridging alkynyl group.
We therefore undertook an investigation of the reactiv-
ity of 2 with a number of substrates to determine the
sites of reactivity in the molecule, with particular inter-
est in inducing transformations of the alkynyl group.
Carbon monoxide attacks compound 2 at the external
face of the A-frame, at iridium, giving compound 1
(Scheme 1). When 12CO is placed over a solution of
13CO-enriched 2 at low temperature (to inhibit rapid
scrambling of the carbonyls), the 12CO is found to occupy
only the terminal position on iridium as shown by the
13C{1H} NMR spectrum, which shows only signals for
the rhodium-bound and semibridging carbonyls, at δ
195.7 (1J RhC ) 80.0 Hz) and δ 198.7 (1J RhC ) 26.8 Hz),
respectively, consistent with that reported for 1.4g
Attack by PMe3 and PMe2Ph also appears to occur
on the outside of the A-frame, at iridium, to give 3 and
4, respectively, as shown in Scheme 1. Although the
phosphorus nucleus of the PR3 group couples to rhodium
and to the rhodium-bound carbonyl, the rhodium cou-
pling is quite small (J RhP ≈ 7 Hz), ruling out direct
phosphine coordination to this metal. While the other
possible isomer (resulting from attack of the phosphine
The reaction of 2 with phosphines is in contrast to
the reaction involving the dirhodium analogue [Rh2-
(CO)2(µ-C2H)(dppm)2][ClO4],15 which yielded phospho-
nium vinylidenes, in which the PR3 group coordinated
to the alkynyl â-carbon. This is certainly not the case
for compounds 3 and 4; for compound 4 the 13C chemical
shifts for CR and Câ of the phenylacetylide group are
inconsistent with those expected for a vinylidene (see
compounds 7a ,b for example), and neither signal dis-
plays significant coupling to the high-field phosphorus
nucleus, as would be expected for a phosphonium
vinylidene. Although the failure of the phosphines to
migrate from Ir to the alkynyl â-carbon, yielding a
phosphonium vinylidene, may be a consequence of a
stronger Ir-PR3 bond, the presence of the bulky phenyl
group on the alkynyl ligand of 2 would also be expected
to inhibit such a migration of the sterically demanding
PR3 ligands.

Reactivity of a Phenylacetylide-Bridged A-Frame
Organometallics, Vol. 17, No. 12, 1998 2561
Sch em e 2
phosphorus nuclei (X represents Rh), when cooled to
-80 °C. This type of fluxionality has been previously
observed in related systems4m and has been attributed
to a twisting of the complex around the Rh-Ir axis;
apparently in the low-temperature limiting structure
the P-Rh-P vector is staggered with respect to the
P-Ir-P vector resulting in inequivalence of the two
phosphorus nuclei on a given metal. These phosphorus
nuclei become equivalent on a time average at higher
temperatures by the twisting process.
At 0 °C transformation of 6b to the two isomers of
the intensely colored vinylidene-bridged species (7a ,b)
occurs. Both isomers display CR for the vinylidene
ligand as multiplets in the region (δ 245-250) that has
been shown9 to be typical for such species; the appear-
ance of these signals rules out the possibility of hydride
migration onto the R-carbon of the alkynyl to give either
a parallel- or perpendicular-bound alkyne complex, since
these complexes typically give 13C NMR signals in the
range δ 120-150 and 60-100,4g,20 respectively. Unfor-
tunately, the â-carbon resonances are not observed and
are assumed to be obscured by those of the phenyl
carbons. The appearance of both isomers is not surpris-
ing since rotation of vinylidenes about the CdC axis,
both on single metal centers and when bridging metals,
In contrast to the previous reactions, attack of 2 by
SO2 appears to occur on the inside of the A-frame,
between the metals, yielding the SO2-bridged [RhIr-
(CO)2(µ-C2Ph)(µ-SO2)(dppm)2][O3SCF3] (5). Spectral iden-
tification of the binding mode of the SO2 ligand is not
straightforward. While the νSO of 1213, 1174, 1063, and
1042 cm-1 in the IR spectrum are consistent with a
bridging SO2 group, these data are also consistent with
terminal, pyramidal SO2 binding,19 as seen by the
similarity of the SO stretches in 5 with those of the
analogous mononuclear complex [Ir(CCPh)(CO)(PPh3)2-
(SO2)] (νSO ) 1196, 1181, 1050 cm-1).2b However, the
close similarity of the spectral parameters between 1
and 5 argues for analogous structures; furthermore, the
presence of only terminal carbonyls in 5 and the known
tendency for SO2 to bridge two metals suggest the
structure shown. It should also be noted that the high-
field chemical shift for the Ir-bound carbonyl (δ 177.1)
is consistent with the structure shown, as explained
earlier.
1
has been observed.9 The H NMR signal for the vinyl-
idene hydrogen was not observed for either isomer and
is presumably obscured by phenyl resonances which
appear in the same region of the spectrum. As reported
for the analogous dirhodium species,15 compound 7 is
very air-sensitive, oxidizing to an uncharacterized mix-
ture of compounds (including approximately 20% of 2)
upon exposure to traces of air.
Compound 2 also reacts with ethylene at low tem-
peratures, as shown in Scheme 3, forming the ethylene
adduct [RhIr(CO)2(C2H4)(µ-CCPh)(dppm)2][O3SCF3] (8),
in which the alkene is terminally bound to iridium, as
is found in the compounds [Ir2(CO)(C2H4)(µ-I)(µ-CO)-
(dppm)2][X] (X ) BF4, I).21 This adduct is very labile,
however, and readily loses ethylene at temperatures
higher than -40 °C. The characterization of 8 as having
a terminally bound ethylene and a semibridging CO is
based upon its NMR spectra. First, upon coordination
of the alkene, the 31P NMR signals for the rhodium-
bound phosphines change only slightly, while those for
the iridium-bound phosphines shift substantially up-
field, suggesting that the site of coordination is at
iridium. In the presence of a large excess of C2H4,
raising the temperature from -50 °C causes the Ir-
bound phosphorus resonance to broaden substantially,
until at 0 °C it has disappeared into the baseline,
offering additional support for reversible ethylene co-
ordination at Ir. Although the signal for the iridium-
bound carbonyl in the 13C{1H} NMR spectrum is broad
and shows no discernible coupling to phosphorus or to
rhodium, the chemical shift (δ 186.9) is consistent with
the carbonyl being angled toward rhodium. The 1H
NMR signals for the ethylene hydrogens are in the
expected range for an olefin complex; however, they are
Hydride attack on 2 also appears to occur on the
“outside” of the complex at Ir, much as was observed
with CO and phosphines, although at ambient temper-
ature migration of the hydride ligand to the â-position
of the alkynyl group occurs, yielding a vinylidene group.
The first product, [RhIr(H)(CO)2(µ-CCPh)(dppm)2] (6a ),
observed at -60 °C, is shown in Scheme 1. On the basis
1
of the H and 13C{1H} NMR spectra, the hydride and
one carbonyl ligand are shown to be terminally bound
to Ir (showing strong coupling to the iridium-bound
phosphines but none to rhodium) with one carbonyl
bound to Rh (showing strong coupling to rhodium). This
species is apparently static on the NMR time scale, but
as the temperature is raised to -20 °C, rearrangement
to another isomer (6b) occurs (see Scheme 2). This new
isomer is related to 6a by interchange of the hydride
and carbonyl ligand on Ir. Again the rearrangement of
the carbonyl from an “inside” to an “outside” site on
iridium is accompanied by an upfield shift in the 13C-
{1H} NMR spectrum (see Table 1). Compound 6b is
fluxional such that the AA′BB′X pattern observed in the
31P{1H} NMR spectrum at -20 °C transforms to an
ABCDX pattern, typical of four chemically inequivalent
(20) (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, 14, 3040. (d) Wang, L.-S.; Cowie, M. Can.
J . Chem. 1995, 73, 1058.
(21) Vaartstra, B. A.; Xiao, J .; J enkins, J . A.; Verhagen, R.; Cowie,
M. Organometallics 1991, 10, 2708.
(19) Kubas, G. J . Inorg. Chem. 1979, 18, 182.

2562 Organometallics, Vol. 17, No. 12, 1998
George et al.
Sch em e 3
broad and show no coupling, giving little useful struc-
tural information. Finally, the 13C{1H} and 31P{1H}
NMR spectra of this complex are very similar to the
structurally characterized dimethylallene adduct 10
(vide infra), which is shown to have the alkene bound
to iridium, on the “outside” of the complex.
More stable olefin adducts can be formed by the use
of cumulated alkenes. Allene reacts with 2 to give a
mixture of two isomers, which were identified on the
basis of their NMR spectra. These isomers are dia-
grammed in the plane of the “RhIr(C3H4)” moiety (dppm
ligands omitted), showing their relationship. While the
spectral data available are insufficient to unambigu-
ously assign the two geometries to the two isomers, the
major isomer has been given the designation 9a . The
F igu r e 1. Perspective view of the [RhIr(CO)(η2-H2CdC-
CMe2)(µ-CO)(µ:η1,η2-CCPh)(dppm)2]+ complex cation show-
ing the atom-labeling scheme. Non-hydrogen atoms are
represented by Gaussian ellipsoids at the 20% probability
level. Hydrogen atoms are shown with arbitrarily small
thermal parameters for the dimethylallene and dppm
methylene groups and are not shown for the phenyl
groups.
13C{1H} NMR signals for the iridium-bound carbonyls
of both isomers appear in the same region, and one
isomer shows coupling to rhodium (5 Hz) as expected
for a semibridging interaction (the signal for the car-
bonyl of 9b is broad and unresolved). These isomers
exchange rapidly at room temperature, showing very
broad signals in the 1H and 31P{1H} NMR spectra.
While it was initially thought that the mechanism of
this exchange might involve either an “allene roll”22 or
allene rotation about the Ir-olefin bond, spin saturation
transfer NMR experiments at 0 °C showed that the
dominant exchange pathway was between the coordi-
nated and free allene molecules, indicating a dissociative
mechanism. Exchange could not be observed by this
experiment at -20 °C. The presence of two isomers of
this sort is similar to that found in the isoelectronic [Ir2-
(CO)2(η2-C3H4)(µ-I)(dppm)2][O3SCF3].4e
tions in other systems.23 The methyl substituents on
the allene also increase the bulkiness of one end of the
ligand, so that only one isomer is sterically favorable,
having the noncoordinated double bond of the allene cis
to the alkynyl ligand. This compound was characterized
by an X-ray structure determination and has the
structure shown in Figure 1. The 13C{1H} NMR spec-
trum of this compound clearly shows the weak (6.3 Hz)
coupling of the iridium-bound carbonyl to rhodium,
indicating a semibridging interactionsa conclusion that
is supported by the IR spectrum (νCO ) 1882 cm-1) and
the X-ray structure.
The substituted cumulene, 1,1-dimethylallene, reacts
with 2 to form 10, which is more stable than the
unsubstituted allene adduct, consistent with observa-
The X-ray structure determination of 10 confirms the
geometry proposed for all olefin adducts of 2 having the
(22) Foxman, B.; Marten, D.; Rosan, A.; Raghu, S.; Rosenblum, M.
J . Am. Chem. Soc. 1977, 99, 2160.
(23) (a) Cooper, D. G.; Powell, J . Inorg. Chem. 1976, 15, 1959. (b)
Hughes, R. P.; Powell, J . J . Organomet. Chem. 1973, 60, 409.

Reactivity of a Phenylacetylide-Bridged A-Frame
Organometallics, Vol. 17, No. 12, 1998 2563
Sch em e 4
olefin coordinated terminally to Ir. The dimethylallene
moiety is coordinated through the unsubstituted end of
the molecule with the methyl substituents on the side
of the complex adjacent to the bridging alkynyl group
and away from the semibridging carbonyl. Coordination
to Ir has resulted in the expected lengthening of the
C(3)-C(4) bond to 1.433(12) Å, compared to the uncom-
plexed C(4)-C(5) bond of 1.335(13) Å, and bending back
of the olefinic moiety (C(3)-C(4)-C(5) ) 142.1(9)°). The
rhodium-alkynyl distances of 2.271(8) Å (to CR) and
2.516(8) Å (to Câ) compare well to those found in the
related compounds [RhIr(CCPh)(µ-CCPh)(µ-H)(CO)2-
(dppm)2][O3SCF3] (19) (2.228(6) and 2.515(7) Å),4g [RhPt-
(dppm)2(CO)(CCCH3)Cl][PF6] (2.22(2) and 2.46(3) Å),18
and [Rh2(CO)2(µ-CCtBu)(dppm)2][ClO4] (2.209(6) and
2.616(6) Å).16 Further evidence for the binding of the
alkynyl ligand to rhodium is found in the Ir-C(8)-C(9)
angle of 167.6(7)°, in which the alkynyl group is pulled
toward the rhodium. At C(9) the phenyl substituent is
bent back away from the Rh as expected from the
π-back-donation to this group. The much shorter rhod-
ium-iridium distance in 10 (2.8759(7) Å) than in the
related 19 (Rh-Ir 3.0582(8) Å)4g is likely due to the
presence of the semibridging carbonyl in 10, which pulls
the metals closer together, and the absence of a bridging
hydride, which tends to lengthen the metal-metal
separation.
The semibridging carbonyl interaction is character-
ized by the substantially shorter Ir-C(1) vs Rh-C(1)
distance (1.984(9) Å vs 2.374(9) Å) and by the more
linear carbonyl angle involving Ir (Ir-C(1)-O(1) )
155.1(8)°) than Rh (Rh-C(1)-O(1) ) 122.8(7)°). As an
aside, it should be noted that both dppm methylene
groups are bent toward the bridging alkynyl group,
thereby allowing phenyl groups 2, 3, 6, and 8, which
are thrust into the region between the equatorial
ligands, to avoid the bulky phenylacetylide and the
methyl substituents on the dimethylallene ligand; if
either of these methylene groups were to bend in the
other direction, either phenyl groups 1 and 4 or phenyl
groups 5 and 7 would be thrust into the vicinities of
these methyl and phenyl substituents.
while compound 2 does not completely react with an
excess of propyne or diphenylacetylene (to form com-
pounds 15 and 16, respectively) at temperatures as low
as -80 °C, the adduct of ethyl 2-butynoate (13) only
loses the alkyne ligand at temperatures above -20 °C,
and strongly electron-withdrawing alkynes, hexafluo-
robutyne (HFB) and dimethyl acetylenedicarboxylate
(DMAD), give complexes (11 and 12) which are stable
toward ligand loss at room temperature.
The structural similarity of these complexes, both to
each other and to the alkene complexes, can be seen by
their IR and NMR spectra, which differ only slightly
with the identity of the ligands used. All show the
iridium-bound phosphines in the 31P{1H} NMR spectra
to be shielded by similar amounts by the presence of
the additional ligand, with the phosphines on rhodium
being only slightly affected by the added ligand. The
iridium-bound carbonyl, in almost all cases, appears in
the 13C{1H} NMR spectra slightly downfield from the
starting material, with small coupling (<15 Hz) to Rh,
indicating a semibridging geometry. For compounds 11
and 12, a carbonyl stretch appears in the IR spectra in
the 1860-1890 cm-1 region, consistent with a semibridg-
ing carbonyl. It is interesting to note that, in contrast
to the allene adduct 9, only one isomer is seen for the
unsymmetric alkynes PhCtCH and CH3CtCCO2CH2-
CH3. This is presumably due to the same steric effects
which permit only one isomer for the substituted allene
adduct 10.
The hexafluorobutyne complex (11) is particularly
informative, owing to the additional 19F NMR data
which show the trifluoromethyl signals as multiplets at
δ -52.59 and -52.67. Decoupling the iridium-bound
phosphines causes these multiplets to simplify to quar-
tets (5J FF ) 3.65 Hz), while decoupling the rhodium-
bound phosphines has no effect. This further suggests
that the alkyne is bound only to iridium. The 13C{1H}
NMR signals for the alkyne carbons (δ 92.9, 89.1) are
also consistent with the proposed structure. Complex
11 is also spectroscopically similar to the related
complex [RhIr(CO)(HFB)(µ-S)(µ-CO)(dppm)2] and to [Ir2-
(CO)(HFB)(µ-S)(µ-CO)(dppm)2], the latter of which was
shown by X-ray crystallography to have a structure very
similar to that proposed for 11.24 Surprisingly perhaps,
the HFB ligand is more labile in the sulfido-bridged
product than in 11.24 We had expected that the π-acidic
HFB would coordinate more strongly to the electron-
Compound 2 also reacts with a range of alkynes to
yield complexes of varying stability (see Scheme 4).
Complexes with electron-rich alkynes are unstable
toward loss of the alkyne ligand except at very low
temperatures. Increasing the π-acidity of the alkyne
by the addition of electron-withdrawing groups results
in much stronger coordination of the alkyne. Thus,
(24) Vaartstra, B. A.; Cowie, M. Organometallics 1989, 8, 2388.

2564 Organometallics, Vol. 17, No. 12, 1998
George et al.
Sch em e 5
rich [RhIr(CO)2(µ-S)(dppm)2], for which the carbonyl
stretches are at unusually low wavenumbers (νCO: 1932,
1906 cm-1).25
Terminal alkynes, such as phenylacetylene or pro-
pyne, react with 2, as shown in Scheme 5, to first give
the adducts 14 and 15, analogous to the HFB and
DMAD adducts (11 and 12). However, these rearrange
to the oxidative-addition products [RhIr(CCPh)(CO)2-
(µ-H)(µ-CCR)(dppm)2][O3SCF3] (19, R ) Ph; 20, R )
CH3), of which the bis(phenylacetylide) 19 was pre-
viously reported in the reaction of [RhIr(CH3)(CO)3-
(dppm)2][O3SCF3] with excess phenylacetylene and was
characterized crystallographically.4g The mixed bis-
(alkynyl) 20 shows very similar spectral characteristics,
both in the IR and the NMR spectra, to the bis-
(phenylacetylide) complex and is assumed to have an
analogous structure. Both complexes, for example, show
a signal for the bridging hydride in the 1H NMR
spectrum near δ -8, showing comparable coupling (≈9
Hz) to the iridium-bound phosphines and to rhodium,
as well as weaker coupling to the rhodium-bound
phosphines.
Oxidative addition of propyne to compound 2 can
result in two possible isomers: one in which the pro-
pynyl is terminal, while the phenylacetylide bridges the
metals, and one in which the phenylacetylide is terminal
and the propynyl ligand occupies the bridging position.
Addition of 13C-labeled propyne to 2 shows that only the
second isomer is observed, having the propynyl ligand
in the bridging position, with both the CR and Câ nuclei
showing coupling (4.6 and 4.7 Hz, respectively) to
rhodium. The signals for the phenylacetylide carbons
in the natural-abundance 13C{1H} NMR spectrum show
no coupling to rhodium.
The DMAD complex 12 differs from the other alkyne
adducts in that it is unstable toward rearrangement.
Upon standing in solution, 12 converts to complex 18,
having the DMAD ligand bridging the two metals in a
parallel fashion. This is shown by the infrared spectrum
of this compound, which shows νCdC ) 1592 cm-1
,
typical of an alkyne in this coordination mode, and the
13C{1H} NMR spectrum, which shows inequivalent
alkyne carbons, each having substantially different
coupling to the rhodium (23.1 Hz vs 7.2 Hz) and to the
phosphine ligands. This spectrum also suggests that
the phenylacetylide ligand is in its usual bridging
position, as shown by the coupling to rhodium (3-5 Hz)
of both alkynyl carbons. In addition, both carbonyls are
clearly terminal, as shown by their signals in the 13C-
{1H} NMR spectrum (as each carbonyl shows coupling
to only one set of phosphines, and only one shows
coupling to rhodium) and the IR spectrum (νCO ) 2034,
2009 cm-1).
In the rearrangement of 12 to 18, an intermediate
isomer 17 is observed. Unfortunately, the resonances
of the alkyne could not be located in the 13C{1H} NMR
spectrum, and further characterization was not possible
owing to its facile conversion to 18 even at low temper-
atures. This rearrangement is paralleled by the analo-
gous reaction of [RhIr(CO)2(µ-I)(dppm)2][BF4] with
DMAD,21 which also goes through at least one unchar-
acterized intermediate before yielding the alkyne-
bridged complex [[RhIr(CO)2(µ-I)(µ-DMAD)(dppm)2]-
[BF4]. The hexafluorobutyne adduct 11 does not
rearrange upon standing or with gentle reflux in dichlo-
romethane and slowly converts to 2 upon reflux in THF,
through dissociation of the alkyne. It is expected that
HFB would form a more stable complex with 2, due to
its greater π-acidity,26 so it remains unclear as to why
the DMAD adduct rearranges to the alkyne-bridged
species while HFB loss occurs in 11.
Reaction of 2 with dihydrogen also results in oxidative
addition, giving [RhIr(H)(CO)2(µ-CCPh)(µ-H)(dppm)2]-
[O3SCF3] (21), much as was observed in dihydrogen
addition to [RhIr(CO)2(µ-Cl)(dppm)2][BF4] and [RhIr-
(CO)2(µ-S)(dppm)2].25 The hydride ligands are believed
to be mutually cis, with no H-H coupling seen in the
1H{31P} NMR spectrum. The alkynyl ligand remains
in the bridging position, as indicated by the coupling to
rhodium seen in both alkynyl carbon signals in the 13C-
{1H} NMR spectrum.
(25) Vaartstra, B. A.; Cowie, M. Inorg. Chem. 1989, 28, 3138.
(26) Kosower, E. M. An Introduction to Physical Chemistry; Wiley:
New York, 1968; p 49.
Unlike the neutral monohydride 6, compound 21 does
not rearrange to form a vinylidene upon warming;

Reactivity of a Phenylacetylide-Bridged A-Frame
Organometallics, Vol. 17, No. 12, 1998 2565
Sch em e 6
instead, dihydrogen elimination occurs upon heating,
regenerating 2 (along with some of the previously
characterized27 complex [RhIr(H)(CO)2(µ-H)2(dppm)2]+,
from reaction with excess hydrogen and loss of phenyl-
acetylene). Compound 21 can also be formed from
addition of strong acid to compound 6a at -80 °C.
Deprotonation of 21 with strong base (KOtBu) at room
temperature yields the vinylidene 7, presumably through
initial formation of 6b.
Discu ssion
The A-frame complex [RhIr(CO)2(µ-CCPh)(dppm)2]-
[O3SCF3] (2) is structurally analogous to the homobi-
nuclear species [Rh2(CO)2(µ-CCR)(dppm)2][ClO4] (R )
t
H, Ph, Bu),15 having the alkynyl group in an unsym-
metrical, σ,π-binding mode. However, unlike the dirhod-
ium analogues, the mixed-metal RhIr species is not
fluxional but instead has the phenylacetylide group
static and σ-bound to iridium and π-bound to rhodium.
In the dirhodium system, the alkynyl group was found
to move from one metal to the other in a windshield-
wiper motion. The failure of 2 to rearrange to a species
in which the alkynyl group is σ-bound to rhodium and
π-bound to iridium presumably results from the lower
stability of such a species, owing to the weaker Rh-C
vs Ir-C σ bond.
As alluded to earlier, A-frame complexes such as 2
have two substantially different sites for substrate
attack: either inside the A-frame pocket, between the
metals, or outside this pocket, at a single metal site
remote from the adjacent metal. When the two metals
are also different, as in 2, each of the inside or outside
sites can also be differentiated by the different metal.
With the exception of SO2 and H2, initial attack on 2
by all substrates investigated occurs on the outside of
the complex at iridium; even if subsequent rearrange-
ment occurs, an initial adduct having the substrate
bound at the outside site on Ir is observed. We suggest
that the preference for an outside site is based on less
steric crowding in this position, whereas the preference
for iridium is thermodynamic and based on stronger Ir-
substrate bonds. It is not clear why SO2 and H2
apparently attack inside the pocket of the A-frame,
between the metals. Although we cannot rule out
outside attack followed by a facile rearrangement such
that the initial adduct has too short a lifetime to be
observed, we argue against this since all other sub-
strates investigated show the adduct prior to rearrange-
ment. This dichotomy of SO2 attack at a site in the
A-frame pocket while other substrates attack the out-
side site has been previously proposed,28 and H2 attack
has previously been observed in the A-frame pocket in
related compounds.25
whether the acetylide group is the initial target or
whether attack at a metal occurs with subsequent
rearrangement. In the case of the RhIr complex 2,
attack by either H- or PR3 initially occurs at iridium,
to give [RhIr(H)(CO)2(µ-CCPh)(dppm)2] (6a ) or [RhIr-
(PR3)(CO)2(µ-CCPh)(dppm)2][O3SCF3] (PR3 ) PMe3 (3),
PPhMe2 (4)). The subsequent rearrangement of 6a to
the phenylvinylidene-bridged [RhIr(CO)2(µ-CCHPh)-
(dppm)2] (7) suggests a similar route for the dirhodium
system, although we would expect this rearrangement
to be more facile owing to the greater lability of rhodium
compared to iridium. The failure of the phosphine
adducts (3, 4) to rearrange to the phosphonium-
vinylidene analogues may result from steric interactions
involving the bulky phenyl substituent on the phenyl-
acetylide and the large phosphine ligands. In addition,
the stronger Ir-PR3 bond would inhibit such a migra-
tion.
Rearrangement of the hydride-phenylacetylide com-
plex 6a to the phenylvinylidene-bridged 7 proceeds via
the isomeric hydride 6b, which has resulted from
interchange of the hydride and Ir-bound carbonyl posi-
tion, such that the hydride ligand is now in the A-frame
pocket. In Scheme 6 we propose a mechanism for
rearrangement of 6b to 7. We believe that a pivotal
intermediate in this rearrangement is the species
diagrammed as 6d , in which the hydride ligand is
adjacent to the alkynyl â-carbon, facilitating migration
to this carbon. We suggest that this intermediate, in
which the hydride ligand is on the same face of the
complex as the alkynyl group, results from 6b by
movement of the hydride between the metals. This can
occur by replacement of the π interaction of the alkynyl
with rhodium by a bridging hydride interaction (6c); this
latter interaction maintains the electron count at each
metal, since the hydride bridge can be viewed as an
agostic interaction of the Ir-H bond with Rh. Having
the hydride-bridged intermediate 6c, twisting of the
equatorial ligand framework about the metal-phos-
phine bonds brings the hydride between the metals, as
has been proposed in a number of related systems.27,29
Movement of the alkynyl group back to the bridging site,
displacing the hydride bridge, generates 6d , which has
In addition to the coordination sites at the metal,
electrophilic or nucleophilic attack can also occur at the
bridging alkynyl group (either at the R- or â-carbons).
The dirhodium analogue [Rh2(CO)2(µ-CCH)(dppm)2]-
[ClO4], for example, is reported to undergo attack by
hydride and by phosphines to give the vinylidene-
bridged products resulting from coordination of these
nucleophiles at the acetylide â-carbon.15 It is not known
(29) (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) Antonelli, D. M.; Cowie, M. Inorg. Chem.
1990, 29, 4039.
(27) McDonald, R.; Cowie, M. Inorg. Chem. 1990, 29, 1564.
(28) (a) Cowie, M. Inorg. Chem. 1979, 18, 286. (b) Mague, J . T.;
Sanger, A. R. Inorg. Chem. 1979, 18, 2060.

2566 Organometallics, Vol. 17, No. 12, 1998
George et al.
an ideal structure to facilitate transfer of the hydride
to the â-carbon of the phenylacetylide. A similar
mechanism has been proposed for the formation of
vinylidenes from related diiridium alkynyl-hydride
complexes.4g
fluxional, via facile exchange of the terminal and
bridging alkynyl groups, there is no evidence of this.
Con clu d in g Rem a r k s
The DMAD adduct [RhIr(CO)2(DMAD)(µ-CCPh)-
(dppm)2][O3SCF3] (12), having the DMAD ligand bound
on the outside of the complex at Ir (see Scheme 4), also
rearranges in a manner not unlike that of 6a to give
the isomeric structure 18 in which the alkyne now
bridges the metals opposite the bridging alkynyl group.
This rearrangement is not unexpected since most other
binuclear alkyne complexes have the alkyne in bridging
sites.20 The failure of the analogous alkyne adducts
(13-16 and particularly the closely related HFB com-
plex 11) to rearrange presumably results from their
weaker binding which instead favors alkyne dissocia-
tion. In the rearrangement of 12 to 18 an intermediate
17 was observed; however, not enough spectral data
were accessible to allow us to establish its structure so
the mechanism of this rearrangement remains equivo-
cal.
The sites of attack by a number of small molecules
on the phenylacetylide-bridged A-frame, [RhIr(CO)2(µ-
CCPh)(dppm)2]+, have been determined. In most cases
the initially observed species have the added ligand
terminally bound to Ir on the “outside” of the A-frame
structure, remote from Rh. Only H2 and SO2 are
exceptions, with both apparently attacking in the A-
frame pocket between the metals. Although one of our
goals was to effect transformation of the acetylide group,
this has only been achieved in the present study with
the hydride group, in which hydride migration from Ir
to the â-carbon of the acetylide occurred yielding a
bridging phenylvinylidene group. A subsequent paper
will describe extensions of the above chemistry, in which
C-C bond formation, involving allyl group migration
to the â-carbon of the acetylide group, is observed.30
The reaction of 2 with terminal alkynes, as shown in
Scheme 5, incorporates a number of the rearrangements
proposed for other substrates. The first products have
the alkyne bound on the outside of the complex at Ir,
analogous to all initial olefin and alkyne adducts. We
then propose a rearrangement (either as for the DMAD
adduct rearrangement of 12 to 18 or via alkyne dis-
sociation and recoordination) to a species having the
alkyne on the inside of the complex, on Ir but adjacent
to Rh. Oxidative addition would yield the hydride-
bridged bis(acetylide) intermediate A, in which the
phenylacetylide group has remained in the bridging site.
This species rearranges to 20 in the propyne reaction,
having the propynyl group in the bridging position and
the phenylacetylide terminally bound to iridium. Al-
though it would appear that 19 and 20 should be
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada (NSERC)
and the University of Alberta for financial support of
the research and the NSERC for funding the P4/RA
diffractometer. We also thank Dr. J . M. Stryker for a
loan of 13C-labeled propyne.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
experimental details, atomic coordinates, interatomic dis-
tances, interatomic angles, anisotropic thermal parameters,
and hydrogen parameters for compound 10 (15 pages). Order-
ing information is given on any current masthead page.
OM970946Q
(30) George, D. S. A.; McDonald, R.; Cowie, M. Manuscript in
preparation.