Heterobinuclear alkyl complexes of rhodium and iridium. Migratory insertion or Ir-to-Rh migration of a methyl group in reactions with small molecules

Article abstract of DOI:10.1021/om9505874

The reaction of [RhIr(CO)₃(dppm)₂] (dppm = Ph₂PCH₂PPh₂) with methyl triflate yields [RhIr(CH₃)(CO)₃(dppm)₂][CF₃SO ₃] (2), having the methyl group

Full text of DOI:10.1021/om9505874

1042
Organometallics 1996, 15, 1042-1054
Heter obin u clea r Alk yl Com p lexes of Rh od iu m a n d
Ir id iu m . Migr a tor y In ser tion or Ir -to-Rh Migr a tion of a
Meth yl Gr ou p in Rea ction s w ith Sm a ll Molecu les
Frederick H. Antwi-Nsiah, Okemona Oke, and Martin Cowie*
Department of Chemistry, The University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Received J uly 28, 1995X
The reaction of [RhIr(CO)3(dppm)2] (dppm ) Ph2PCH2PPh2) with methyl triflate yields
[RhIr(CH3)(CO)3(dppm)2][CF3SO3] (2), having the methyl group and two terminal carbonyls
on Ir and one carbonyl on Rh. An Ir f Rh dative bond is proposed, giving Rh+ a 16e square-
planar configuration. Reaction of 2 with hydrogen at ambient temperature yields [RhIrH-
(CO)2(µ-H)2(dppm)2]+ and methane. At 0 °C the intermediate [RhIrH(CH3)(CO)2(µ-
H)(dppm)2][CF3SO3] is observed which under H2 yields the trihydride species and CH4 upon
warming. Protonation of 2 with HCl and CF3SO3H yields [RhIr(CH3)(CO)2(µ-H)(µ-Cl)-
(dppm)2]+ and [RhIr(CH3)(CO)2(µ-H)(µ-CO)(dppm)2]+2, respectively. The reaction of 2 with
CO resulted in decomposition to several unidentified products. Reaction of 2 with CNtBu
yields the iminoacyl product [RhIr(CO)2(µ-tBuNdCMe)(dppm)2]+ via migratory insertion.
Two intermediates in the formation of the iminoacyl species were identified at low
temperature yielding some information about the subsequent migratory insertion. Although
the reaction of 2 with SO2 does not yield the SO2-insertion product, it does yield [RhIr(C(O)-
CH3)(CO)2(µ-SO2)(dppm)2]+, the product of methyl migration to Rh and migratory insertion
of the methyl to a carbonyl group. A mechanism is proposed on the basis of the
characterization of low-temperature intermediates. With ethylene, the substitution of one
carbonyl in 2 and migration of the methyl group to Rh occurs. The structures of [RhIr-
(CH3)(CO)3(dppm)2][CF3SO3]‚CH2Cl2 (2) and [RhIr(CO)2(µ-tBuNdCMe)(dppm)2][CF3SO3] (8)
have been determined by X-ray crystallography. Compound 2 has a trigonal bipyramidal
ligand arrangement at Ir with the methyl group opposite Rh. In addition the 18e Ir forms
a dative bond to Rh giving the latter a square planar geometry. Compound 8 has an “A-
frame” geometry in which the bridging iminoacyl group binds to Rh via nitrogen and to Ir
via carbon.
In tr od u ction
Rh/W9 combinations of metals have also been character-
ized and studied. Interestingly, in all the complexes
characterized, the alkyl group was found to be coordi-
nated to the unsaturated group 9 metal.
In this paper, methylation of the heterobinuclear
species [RhIr(CO)3(dppm)2] (1),6m in which both metals
are from group 9, is reported. It was of interest to
establish whether the methyl group would bind to Rh,
as in previous, related complexes6c,7-9 or whether bind-
ing to the heavier congener would be favored. It was
also of interest to determine the reactivity of an alkyl
group in a binuclear complex having a more labile Rh
center adjacent to a less labile third-row metal such as
Alkyl complexes of the Co-triad metals are known to
be involved as key intermediates in a variety of impor-
tant catalytic processes such as the carbonylation of
methanol,1 the hydrogenation of carbon monoxide,2 and
olefin hydrogenation, hydroformylation, and hydrosilyl-
ation.3 Although work on mononuclear alkyl complexes
of these metals has resulted in an improved under-
standing of the involvement of the metal-alkyl species
in catalysis,4 very little has been reported on binuclear
derivatives, in spite of continuing interest in utilizing
complexes containing adjacent metals as catalysts.5
Interest, within this research group, in utilizing
binuclear, dppm-bridged complexes of Rh and Ir as
models for transformations occurring at two or more
adjacent metal centers6 led to the investigation of alkyl
derivatives of such complexes. As part of this study,
the syntheses and reactivities of the complexes [MRe-
(CH3)(CO)4(dppm)2][CF3SO3] (M ) Rh, Ir) have been
reported,6c and more recently a series of related alkyl
compounds involving the Rh/Os,7 Rh/Mn,8 Rh/Mo,9 and
(5) (a) Balch, A. L. In Homogeneous Catalysis with Metal Phosphine
Complexes; Pignolet, L. H., Ed.; Plenum: New York, 1983. (b) Brown,
M. P.; Fisher, J . R.; Franklin, S. J .; Puddephatt, R. J .; Thomson, M.
A. In Catalytic Aspects of Metal Phosphine Complexes; Alyea, E. C.,
Meek, D. W., Eds.; Advances in Chemistry Series 196; American
Chemical Society: Washington, DC, 1982; p 231. (c) Poilblanc, R. Inorg.
Chim. Acta 1982, 62, 75. (d) Muetterties, E. L.; Krause, M. J . Angew.
Chem., Int. Ed. Eng. 1983, 22, 135. (e) Ertl, G. In Metal Clusters in
Catalysis; Gates, B. C., Guczi, L., Knozinger, H., Eds.; Elsevier: New
York, 1986; Chapter 11. (f) Levigne, G.; Kaesz, H. D. In ref 5e, Chapter
4. (g) Marko, L.; Vizi-Orosz, A. In ref 5e, Chapter 5. (h) Gelmini, L.;
Stephan, D. W. Organometallics 1988, 7, 849. (i) Casey, C. P. J .
Organomet. Chem. 1990, 400, 205. (j) Choukroun, R.; Dahan, F.;
Gervais, D.; Rifai, C. Organometallics 1990, 9, 1982. (k) Hostetler, M.
J .; Butts, M. D.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 2743.
(l) Garland, M. Organometallics 1993, 12, 535. (m) Stang, P. J .; Cao,
D. Organometallics 1993, 12, 996. (n) Kalck, P.; Serra, C.; Machet, C.;
Broussier, R.; Gautheron, B.; Delmas, G.; Trouve´, G.; Kubicki, M.
Organometallics 1993, 12, 1021. (o) Beers, O. C. P.; Elsevier, C. J .;
Smeets, W. J . J .; Spek, A. L. Organometallics 1993, 12, 3199. (p) Ball,
G. E.; Cullen, W. R.; Fryzuk, M. D.; Henderson, W. J .; J ames, B. R.;
MacFarlane, K. S. Inorg. Chem. 1994, 33, 1464.
X Abstract published in Advance ACS Abstracts, December 1, 1995.
(1) Forster, D. Adv. Organomet. Chem. 1979, 17, 255.
(2) Dombek, B. D. Adv. Catal. 1983, 32, 325.
(3) (a) J ames, B. R. Adv. Organomet. Chem. 1979, 17, 319. (b) Pruet,
R. L. Adv. Organomet. Chem. 1979, 17, 1. (c) Masters, C. Homogeneous
Transition-Metal Catalysis: A Gentle Art; Chapman and Hall: London,
1980. (d) Speier, J . L. Adv. Organomet. Chem. 1979, 17, 407.
(4) (a) Parshall, G. W.; Mrowca, J . J . Adv. Organomet. Chem. 1968,
7, 157. (b) Atwood, J . D. Coord. Chem. Rev. 1988, 83, 93.
0276-7333/96/2315-1042$12.00/0 © 1996 American Chemical Society

Heterobinuclear Alkyl Complexes of Rh and Ir
Organometallics, Vol. 15, No. 3, 1996 1043
Ta ble 1. Sp ectr oscop ic Da ta for th e Com p ou n d sa
NMR
δ(1H)e,f
compd
IR,b,c cm-1
δ(31P{1H})d
δ(13C{1H})e
1
1
[RhIr(CH3)(CO)3(dppm)2]-
[CF3SO3] (2)
[RhIr(CH3)(H)(µ-H)(CO)2 -
(dppm)2][CF3SO3] (3)
1986 (s), 1971 (vs),
1912 (vs)
29.8 (dm, J Rh-P
)
4.33 (m, 4H), -0.08 (t, 3H)
183.7 (dt, 1C, J Rh-C ) 75.0 Hz),
120.0 Hz), -5.5 (m)
187.9 (t, 2C)
1
1
25.7 (dm, J Rh-P
)
4.42 (m, 2H), 4.07 (m, 2H),
187.5 (dt, 1C, J Rh-C ) 75.1 Hz),
110.3 Hz), -1.1 (m)
-0.16 (t, 3H), -10.02
174.4 (t, 1C)
1
(m, 1H, J Rh-H ) 15 Hz),
1
-12.47 (m, 1H, J Rh-H
)
24 Hz, 2J P(Rh)-H ) 11.2 Hz)
4.43 (m, 4H), -10.2 (bm, 1H)
1
1
[RhIr(CO)3(µ-H)(dppm)2]-
[CF3SO3] (5)
22.7 (dm, J Rh-P
)
186.2 (dt, 1C, J Rh-C ) 79 Hz),
113.3 Hz), -4.8 (m)
179.4 (b, 2C)
1
1
[RhIr(CH3)(CO)2(µ-H)(µ-Cl)-
1982 (s), 1932 (s)
22.1 (dm, J Rh-P
)
4.40 (m, 2H), 3.83 (m, 2H),
-0.25 (t, 3H), -9.50
189.3 (dt, 1C, J Rh-C ) 84.5 Hz),
(dppm)2][CF3SO3] (6)g
111.0 Hz), -4.4 (m)
164.4 (t, 1C)
(m, 1H, 1J Rh-H ) 22.0 Hz)
4.93 (m, 2H), 4.20 (m, 2H),
0.67 (t, 3H), -10.08 (bm, 1H)
1
1
[RhIr(CH3)(CO)2(µ-CO)-
2000 (s), 1977 (vs),
1864 (med)
28.0 (dm, J Rh-P
)
199.9 (dtt, 1C, J Rh-C ) 26.2 Hz),
(µ-H)(dppm)2][CF3SO3]2 (7)g
98.3 Hz), -11.3 (m)
186.0 (dt, 1C, 1J Rh-C
)
76.5 Hz), 165.6 (m, 1C)
1
1
[RhIr(CO)2(µ-C(CH3)d
NtBu)(dppm)2][CF3SO3] (8)
[RhIr(CH3)(CO)3(tBuNC)-
(dppm)2][CF3SO3] (9)
1964 (vs), 1945 (s)
15.4 (dm, J Rh-P
)
4.10 (m, 2H), 2.95 (m, 2H),
0.82 (s, 3H), 0.80 (s, 9H)
5.48 (m, 2H), 5.13 (m, 2H),
0.92 (s, 9H), -1.18 (t, 3H)
5.15 (m, 2H), 4.86 (m, 2H),
0.93 (s, 9H), 0.22 (t, 3H)
195.0 (dt, 1C, J Rh-C ) 65.4 Hz),
132.6 Hz), 4.7 (m)
191.3 (t, 1C)
1
1
10.5 (dm, J Rh-P
)
181.3 (dt, J Rh-C ) 74 Hz), 181.9
1
138.5 Hz), -16.7 (m)
(dt, J Rh-C ) 77 Hz), 176.3 (t)
1
1
[RhIr(CH3)(CO)2(tBuNC)-
(dppm)2][CF3SO3] (10)
[RhIr(CH3)(CO)2(C2H4)-
(dppm)2][CF3SO3] (11)
[RhIr(CH3)(CO)3(SO2)-
(dppm)2][CF3SO3] (12)
11.9 (dm, J Rh-P
)
180.2 (dt, 1C, J Rh-C ) 68.5 Hz),
140.9 Hz), -20.6 (m)
233.3 (b, 1C)
1
1
1985 (s)i
32.6 (dm, J Rh-P
)
3.32 (m, 4H), 0.75 (t, 4H), 0.35 204.7 (dm, 2C, J Rh-C ) 20.0 Hz)
2
141.1 Hz), 5.4 (m)
(td, 3H, J Rh-H ) 3.0 Hz)
20.9 (m),k -1.8 (m)
4.85 (m, 2H), 3.45 (m, 2H),
0.33 (t, 3H)
194.9 (dt, 1C, J Rh-C ) 56.3 Hz),
178.4 (t, 1C), 175.2 (dt, 1C,
1J Rh-C ) 63.4 Hz)
1
1
[RhIr(CH3)(CO)2(µ-SO2)-
(dppm)2][CF3SO3] (13)
[RhIr(CO)2(COCH3)(µ-SO2)-
(dppm)2][CF3SO3] (14)g
37.7 (dm, J Rh-P
)
4.12 (m, 2H), 3.50 (m, 2H), 1.08 180.6 (dt, 1C), 170.3 (dt, 1C,
2
138.2 Hz), -0.8 (m)
(td, J Rh-H ) 3.7 Hz, 3H)
4.18 (m, 2H), 3.40 (m, 2H),
1.15 (s, 3H)
2J C-C ) 13.6 Hz)
1
1
2030 (s), 1986 (vs),
1640 (m), 1055 (m)j
27.4 (dm, J Rh-P
)
255.5 (d, 1C, J Rh-C ) 34.2 Hz),
156.6 Hz), -1.2 (m)
172.7 (dt, 1C), 168.7 (dt, 1C,
2J C-C ) 12.6 Hz)
a
Abbreviations used: med ) medium, st ) strong, vs ) very strong, s ) singlet, d ) doublet, t ) triplet, m ) multiplet, dt ) doublet
of triplets, dm ) doublet of multiplets, bs ) broad singlet, b ) broad. Nujol mull on KBr disk unless otherwise stated. c Values are for
b
ν(CO). Vs 85% H3PO4, -40 °C in CD2Cl2 unless otherwise stated. e Vs TMS, -40 °C in CD2Cl2 solvent unless otherwise stated. f Resonances
d
g
h
i
for phenyl protons appear as multiplets in the range δ 6.9-8.1 for all compounds. NMR data at 25 °C. NMR data at -80 °C. IR in
j
k
CH2Cl2. ν(SO) second SO stretch obscured by triflate anion stretches. Magnitude of Rh-P coupling could not be determined because
of the nature of the multiplet.
employed for all reactions which involved purging a solution
with a gas. Prepurified argon, ethylene, and hydrogen were
purchased from Linde. Carbon monoxide, sulfur dioxide, and
hydrogen chloride gas were all purchased from Matheson. 13CO
(99%) was supplied by Isotec Inc. All gases were used as
received. Hydrated rhodium(III) chloride was purchased from
Engelhard Scientific, whereas triflic acid, methyl triflate, tert-
butyl isocyanide, trimethylphosphine, and triphenyl phosphite
were obtained from Aldrich. The compound [RhIr(CO)3-
(dppm)2] (1)6m was prepared as previously reported.
The NMR spectra were recorded on a Bruker AM-400
spectrometer at 400.1 MHz for 1H, at 161.9 MHz for 31P{1H}
and at 100.6 MHz for 13C{1H} spectra. The 13C{1H}{31P} NMR
spectra were obtained on a Bruker WH-200 spectrometer
operating at 50.32 MHz. All 13C{1H} NMR spectra were
obtained using 13CO-enriched samples unless otherwise stated.
Infrared spectra were obtained on a Nicolet 7199 Fourier
transform or a Perkin-Elmer 883 IR spectrometer, either as
Nujol mulls on KBr plates or as solutions in KCl cells with
0.5 mm-window path lengths. Carbonyl stretches reported are
for nonisotopically enriched samples. Spectroscopic param-
eters for the compounds prepared are found in Table 1.
Elemental analyses were performed by the microanalytical
service within the department.
P r ep a r a t ion of Com p ou n d s. (a ) [R h Ir (CH 3)(CO)3-
(d p p m )2][CF 3SO3] (2). The compound [RhIr(CO)3(dppm)2] (1)
(200 mg, 0.174 mmol) was dissolved in 20 mL of benzene, to
which was added 1 equiv (19.7 µL, 0.174 mmol) of methyl
triflate. The solution was stirred for 3 h during which time
the orange solution became cloudy and a brown solid precipi-
tated. The volume of the solvent was reduced to about 5 mL,
and precipitation was completed by adding 30 mL of diethyl
ether. The brown solid was collected and washed with three
10 mL portions of Et2O and dried under an argon stream and
then in vacuo (70-77% yield). Anal. Calcd for IrRhSP4-
F3O6C55H47: C, 50.35; H, 3.61. Found: C, 50.17; H, 3.83.
(b) [Rh Ir (CO)3(µ-H)(d p p m )2][CF 3SO3] (5). A 55 mg
amount of [RhIrCH3(CO)3(dppm)2][CF3SO3] (2) was dissolved
Ir, which should in turn be more prone to oxidative
addition. Methylation of the above RhIr complex was
also undertaken to provide comparisons with the related
studies on the dirhodium10 and diiridium analogues.11,12
A preliminary report of some of this work has ap-
peared.11
Exp er im en ta l Section
Gen er a l Com m en ts. All solvents were dried (using the
appropriate drying agents) and distilled before use and were
stored under argon. Deuterated solvents used for NMR
experiments were degassed and stored under argon over
molecular sieves. Reactions were carried out at room tem-
perature (unless otherwise stated) by using standard Schlenk
procedures, and compounds, that were isolated as solids were
purified by recrystallization. A flow rate of ca. 0.2 mL s-1 was
(6) For recent examples see: (a) Xiao, J .; Cowie, M. Organometallics
1993, 12, 463. (b) McDonald, R.; Cowie, M. Inorg. Chem. 1993, 32, 1671.
(c) Xiao, J .; Santarsiero, B. D.; Vaartstra, B. A.; Cowie, M. J . Am. Chem.
Soc. 1993, 115, 3212. (d) J enkins, J . A.; Cowie, M. Organometallics
1992, 11, 2774. (e) Vaartstra, B. A.; Xiao, J .; J enkins, J . A.; Verhagen,
R.; Cowie, M. Organometallics 1991, 10, 2708. (f) Antonelli, D. M.;
Cowie, M. Organometallics 1991, 10, 2550. (g) Antonelli, D. M.; Cowie,
M. Organometallics 1991, 10, 2173. (h) Hilts, R. W.; Franchuk, R. A.;
Cowie, M. Organometallics 1991, 10, 1297. (i) Hilts, R. W.; Franchuk,
R. A.; Cowie, M. Organometallics 1991, 10, 304. (j) McDonald, R.;
Cowie, M. Organometallics 1990, 9, 2468. (k) Antonelli, D. M.; Cowie,
M. Inorg. Chem. 1990, 29, 4039. (l) Antonelli, D. M.; Cowie, M. Inorg.
Chem. 1990, 29, 3339. (m) McDonald, R.; Cowie, M. Inorg. Chem. 1990,
29, 1564. (n) Vaartstra, B. A.; Cowie, M. Organometallics 1990, 9, 1594.
(o) Vaartstra, B. A.; Cowie, M. Inorg. Chem. 1989, 28, 3138. (p)
Vaartstra, B. A.; Cowie, M. Organometallics 1989, 8, 2388.
(7) Sterenberg, B. T.; Hilts, R. W.; Moro, G.; McDonald, R.; Cowie,
M. J . Am. Chem. Soc. 1995, 117, 245.
(8) (a) Wang, L.-S.; Cowie, M. Can. J . Chem. 1995, 73, 1058. (b)
Wang, L.-S.; Cowie, M. Organometallics 1995, 14, 2374.
(9) Graham, T.; Van Gastel, F.; Cowie, M. Unpublished work.
(10) Shafiq, F.; Kramarz, K. W.; Eisenberg, R. Inorg. Chim. Acta
1993, 213, 111.
(11) Antwi-Nsiah, F.; Cowie, M. Organometallics 1992, 11, 3157.
(12) Antwi-Nsiah, F. H.; Torkelson, J . R.; Cowie, M. Manuscript in
preparation.

1044 Organometallics, Vol. 15, No. 3, 1996
Antwi-Nsiah et al.
in 0.6 mL of CD2Cl2 in an NMR tube at 0 °C under N2. An
atmosphere of H2 was flushed through the solution briefly (ca.
2 min), and the reaction system was allowed to stand at 0 °C
for 1 h, after which the solution was cooled to -78 °C and the
H2 atmosphere was removed. An atmosphere of dinitrogen
was introduced, and the temperature was then warmed slowly
to ambient conditions. The 1H and 13C NMR spectra were
taken immediately.
(c) [Rh Ir (CH3)(CO)2(µ-H)(µ-Cl)(d p p m )2][CF 3SO3] (6).
Compound 2 (100 mg, 0.076 mmol) was dissolved in 20 mL of
CH2Cl2. Slightly more than 1 equiv of HCl (in the form of 10
mg of N,N-dimethylacetamide‚HCl, 0.081 mmol) in 10 mL of
CH2Cl2 was added, causing an immediate color change from
orange to light yellow. The solution was stirred for 2 h during
which time the color slowly darkened to a deeper yellow. The
solvent was removed under vacuum, and the orange solid was
recrystallized from CH2Cl2/Et2O giving a 60% yield. Anal.
Calcd for IrRhClSP4F3O5C54H48: C, 49.12; H, 3.66; Cl, 2.68.
Found: C, 48.38; H, 3.43; Cl, 3.93. Analytical results are
variable owing to loss of the CH2Cl2 of crystallization. The
above results, obtained over a short time span, to ensure
consistent results among the different elements, agree well
with the calculated values if 0.25 equiv of CH2Cl2 is assumed
(calcd: C, 48.56; H, 3.64; Cl, 3.96).
(d ) [Rh Ir (CH3)(CO)3(µ-H)(d p p m )2][CF 3SO3]2 (7). To a
solution of 2 (100 mg, 0.076 mmol) in 10 mL of CH2Cl2 was
added 1 equiv (6.7 µL, 0.076 mmol) of CF3SO3H, causing the
dark orange solution to change to a yellow color instantly. After
the solution was stirred for 1 h, the solvent volume was
reduced to ca. 5 mL and the yellow solid was precipitated by
the addition of 15 mL of Et2O. The solid was then collected,
washed with Et2O, and dried under an argon stream. It was
then recrystallized from CH2Cl2/Et2O, dried again under an
argon stream, and then under vacuo (67% yield). Anal. Calcd
for IrRhS2P4F6O9C56H48: C, 46.11; H, 3.30.Found: C, 45.49;
H, 2.96.
temperatures showed only incomplete reaction. [RhIr(CH3)-
(H)(µ-H)(CO)2(dppm)2][CF3SO3] (3) was the only species other
than 2 and 4 observed.
(b) Rea ction of Com p ou n d 2 w ith tBu NC. The proce-
t
dure in (a) was duplicated except that 1 equiv of neat BuNC
(2.6 µL, 0.023 mmol) was syringed into the solution at -78 °C
in a dry ice-acetone bath. The orange solution darkened
immediately and so was taken immediately for NMR charac-
terization. At temperatures below -40 °C several intermedi-
ates were observed which could not be identified owing to their
low concentrations and overlapping signals. At -40 °C the
major species was shown to be [RhIr(CH3)(CO)3(tBuNC)-
(dppm)2][CF3SO3] (9). Upon warming of the sample in the
NMR probe to 0 °C, a second species [RhIr(CH3)(CO)2(tBuNC)-
(dppm)2][CF3SO3] (10) was identified. This species trans-
formed to 8 upon further warming.
(c) R ea ct ion of Com p ou n d 2 w it h Su lfu r Dioxid e.
Compound 2 (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 ca. -60 °C by immersing it in a dry ice/chloroform
mixture. Sulfur dioxide gas was passed through the solution
for 1 min, and NMR spectra of this solution were obtained
immediately afterward at -40 °C. The spectra showed the
presence of [RhIr(CH3)(CO)3(SO2)(dppm)2][CF3SO3] (12). The
sample was allowed to warm to room temperature and was
maintained at this temperature for another 10 min. The NMR
spectra of the solution, obtained afterward at -40 °C, showed
the presence of [RhIr(CH3)(CO)2(µ-SO2)(dppm)2][CF3SO3] (13).
Alternatively, compound 13 was obtained by passing SO2 gas
through a solution of 2 (30 mg, 0.023 mmol) in 0.6 mL of CD2-
Cl2, until the solution color changed from orange to red (ca. 1
min). The solution was then transferred quickly to a rubber
septum-capped NMR tube under nitrogen, and the reaction
was quenched by immersing the tube in a dry ice/chloroform
bath until the NMR spectra were obtained shortly afterward.
X-r a y Da ta Collection . (a ) [Rh Ir (CH3)(CO)3(d p p m )2]-
[CF 3SO3].CH2Cl2 (2). Orange crystals of 2 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
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 (0k0, k ) odd) were consistent with the space groups
P21 or P21/ m; the noncentrosymmetric space group was
established by successful refinement of the structure.
(e) [Rh Ir (CO)2(µ-C(CH3)dNtBu )(d p p m )2][CF 3SO3] (8).
To a solution of 2 (80 mg, 0.016 mmol) in 10 mL of CH2Cl2
t
was added 1 equiv (6.9 µL, 0.061 mmol) of BuNC. The color
of the solution changed from orange to brown then to purple.
After the solution was stirred for 3 h, the solvent was removed
under vacuum giving a purple solid. Diethyl ether was layered
over a CH2Cl2 solution of the purple solid and allowed to diffuse
slowly giving purple crystals of the product in about 2 days
(67% yield). Anal. Calcd for IrRhSP4F3O5NC59H56: C, 51.83;
H, 4.13; N, 1.02. Found: C, 51.09; H, 4.03; N, 1.13.
(f) [Rh Ir (CH3)(CO)2(C2H4)(d p p m )2][CF 3SO3] (11). Eth-
ylene was passed through a 5 mL CH2Cl2 solution of 2 (80 mg,
0.061 mmol) for ca. 1 min. The solution was then stirred under
a static atmosphere of the gas for 18 h. To obtain NMR
spectra, the reaction was carried out in CD2Cl2 solution under
an ethylene atmosphere. The solid product was not isolated
in this reaction.
(g) [R h Ir (CO)2(COCH 3)(µ-SO2)(d p p m )2][CF 3SO3] (14).
Compound 2 (80 mg, 0.061 mmol) was dissolved in 5 mL of
CH2Cl2. Sulfur dioxide gas was then passed through the
solution for about 1 min. The color of the solution changed
instantly from orange to dark brown and then to red. The
mixture was then stirred under a static atmosphere of the gas
for 1.5 h, after which time the product was precipitated,
washed with ether, and dried under an argon stream. The
solid was then recrystallized from CH2Cl2/Et2O and dried again
under a stream of argon (84% yield). Anal. Calcd for IrRh-
S2P4F3O8C55H47: C, 48.01; H, 3.44; S, 4.66. Found: C, 48.30;
H, 3.86; S, 4.58.
Ch a r a cter iza tion of Low -Tem p er a tu r e In ter m ed ia tes.
(a ) Rea ction of Com p ou n d 2 w ith H2. In an NMR tube 30
mg (0.023 mmol) of 2 was dissolved in 0.6 mL of CD2Cl2 under
an N2 atmosphere, and the solution was cooled in an ice/salt
bath. Dihydrogen was passed through the solution for ca. 3
min, and the mixture was allowed to stand for 2 h at this
temperature, after which the NMR spectra were obtained at
0 °C. Observation of the solution at earlier times or at lower
Intensity data were collected at 22 °C 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
reflections were chosen as intensity standards, being remea-
sured 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 applied. A
total of 6760 unique reflections were measured and processed
13
in the usual way, using a value of 0.04 for p to downweight
intense reflections; 6248 of these were considered to be
2
observed (Fo g 3σ(Fo2)) and were used in subsequent calcula-
tions. Absorption corrections were applied to the data using
the method of Walker and Stuart.14,15
(b) [Rh Ir (CO)2(µ-C(CH3)dNtBu )(d p p m )2][CF 3SO3] (8).
Diffusion of ether into a concentrated CH2Cl2 solution of 8
yielded purple crystals of the complex, several of which were
mounted and flame sealed in glass capillaries under solvent
(13) Doedens, R. J .; Ibers, J . A. Inorg. Chem. 1967, 6, 204.
(14) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A: Found
Crystallogr. 1983, A39, 158.
(15) Programs used were those of the Enraf-Nonius Structure
Determination Package by B. A. Frenz, in addition to local programs
by R. G. Ball.

Heterobinuclear Alkyl Complexes of Rh and Ir
Organometallics, Vol. 15, No. 3, 1996 1045
Ta ble 2. Cr ysta llogr a p h ic Da ta for
Ch a r t 1
[Rh Ir (CH3)(CO)3(d p p m )2][CF 3SO3].CH2Cl2 (2) a n d
[Rh Ir (CO)2(µ-C(CH3)dNtBu )(d p p m )2][CF 3SO3] (8)
compd
2
8
formula
fw
cryst shape
C56H49Cl2F3IrO6P4RhS C59H56Cl2F3IrNO5P4RhS
1396.99
monoclinic prism
1367.18
monoclinic prism
0.44 × 0.32 × 0.30
P21/n (nonstandard
setting of P21/c, No. 14)
-65
cryst dimens, mm 0.48 × 0.38 × 0.32
space group
P21 (No. 4)
temp, °C
22
radiation (λ, Å)
unit cell params
a, Å
b, Å
c, Å
graphite-monochromated Mo KR (0.710 69)
10.482(7)
12.708(2)
24.237(3)
20.328(2)
98.87(2)
6186(2)
4
25.435(5)
11.391(3)
114.07(3)
2773(4)
2
â, deg
V, Å3
whereas the two half-occupancy oxygens of the third disordered
carbonyl are superimposed so that only one full occupancy O(3)
is resolved. There was no apparent disorder involving the
Z
F(calcd), g cm-3
linear abs coeff
(µ), cm-1
1.673
29.329
1.468
25.823
phosphine groups, which appeared to be well behaved.
A
range of transm
factors
0.901-1.094
0.913-1.037
similar kind of disorder was observed in the X-ray structure
determination of [RhMn(CO)3(µ-CO3)(dppm)2].6g
max 2θ, deg
scan type
scan rate, deg/min
50.0
θ/2θ
50.0
θ/2θ
All non-hydrogen atoms of the complex cation and anion
were located. In addition, one molecule of CH2Cl2 per formula
unit of complex was also located. Full matrix least-squares
refinements proceeded so as to minimize the function ∑w(|Fï|
- |Fc|)2, where w ) 4Fo2/σ2(Fo2). Atomic scattering factors16,17
and anomalous dispersion terms18 were taken from the usual
tabulations. Hydrogen atoms, with the exception of the
methylene chloride hydrogens, were included as fixed contri-
butions but not refined. Their idealized positions were cal-
culated 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’s of their attached C atoms.
The final model, with 660 parameters refined, converged
to values of R ) 0.041 and Rw ) 0.056. Since the space group
P21 is chiral, refinement of the structure in the opposite hand
was also carried out, but this yielded significantly poorer
residuals (R ) 0.047 and Rw ) 0.067), suggesting that the
original solution was the right one. In the final difference
Fourier map the 10 highest residuals (1.8-1.1 e/Å3) were found
to be in the vicinity of the metal and carbonyl groups. A typical
carbon atom in an earlier synthesis had an electron density
of ca. 5.9 e/Å3. The positional and isotropic thermal param-
eters of the non-hydrogen atoms of 2 are given in Table 3.
(b) [Rh Ir (CO)2(µ-C(CH3)dNtBu )(d p p m )2][CF 3SO3] (8).
The structure was solved in the space group P21/n using
standard Patterson and Fourier techniques. Refinement
proceeded as described for compound 2. All non-hydrogen
atoms were ultimately located. Hydrogen atoms, as well as
the carbon atom of the triflate anion, were included as fixed
contributions as described earlier.
The triflate anion was found to be badly behaved. Although
the SO3 moiety was located and refined well, the CF3 moiety
did not refine well. These atoms were located in the Fourier
maps, but the carbon atom invariably refined toward the
fluorine atom positions. This carbon atom was fixed at its
observed position and was not refined. The thermal param-
eters for the fluorines were very high, consistent with the
smeared out electron density observed in their positions on
Fourier maps. The final model, with 362 parameters refined,
converged to values of R ) 0.072 and Rw ) 0.072. In the final
difference Fourier map, the 10 highest residuals (1.6-1.0 e/Å3)
were found to be in the vicinity of the phenyl rings, the
carbonyl groups, the triflate anion, and the dppm methylene
groups. A typical carbon atom in an earlier synthesis had an
tot. unique reflcns 6760 (h,(k,(l)
11 042 (+h,+k,l)
3029 (Fo2 g 3s(Fo
362
tot. observns (NO) 6248 (Fo2 g 3s(Fo2))
2
final no. params
varied (NV)
660
error in obs of unit 2.119
weight (GOF)a
1.570
Rb
Rw
0.040
0.055
0.072
0.072
c
a
GOF ) [∑w(|Fï| - |Fc|)2/(NO - NV)]1/2 where w ) 4Fo2/σ2(Fo2).
R ) ∑||Fï| - |Fc||/∑|Fï|. c Rw ) [∑w(| Fï| - |Fc| )2/∑w Fo
] .
b
2 1/2
vapor to minimize decomposition or deterioration due to
solvent loss. Data collection and the derivation of unit-cell
parameters proceeded in a manner similar to that above,
except that data collection was carried out at a different
temperature. The monoclinic diffraction symmetry and the
systematic absences (h0l, h + l ) odd; 0k0, k ) odd), were
consistent with the space group P21/n.
Intensity data were collected at -65 °C using the θ/2θ scan
technique to a maximum 2θ ) 50.0°, collecting reflections with
indices of the form +h,+k,(l. Of 11 042 unique reflections
measured, 3029 were considered to be observed and were used
in subsequent calculations, with absorption corrections applied
as above. See Table 2 for crystal data and more information
on X-ray data collection for both compounds.
Str u ctu r e Solu tion a n d Refin em en t. (a ) [Rh Ir (CH3)-
(CO)3(d p p m )2] [CF 3SO3]‚CH2Cl2 (2). The structure of 2 was
solved in the space group P21 using standard Patterson and
Fourier techniques. Although location of all atoms was
straightforward, initial refinements resulted in unusually high
thermal parameters for the atoms of the carbonyl groups and
the methyl carbon atom. In addition the isotropic thermal
parameter for Ir was unusually high and that of Rh was
unusually low. A difference Fourier calculation at this stage
showed the presence of superimposed methyl and carbonyl
groups. This together with the anomalous thermal parameters
for the metals led to the model shown (Chart 1) in which two
of the molecules, represented as A and B in the diagram (the
dppm ligands are omitted for clarity), are disordered in
approximately a 60:40 ratio (determined from the relative peak
intensities of the ordered and disordered atoms and by
refinement of the occupancy factors of the disordered carbonyl
oxygen atoms). The two molecules, A and B, are superimposed
such that they have the metal atom positions overlapping. This
is represented as C, in which Rr and Ih indicate the disordered
Rh and Ir positions with Rr being 60% Rh and Ih being 60%
Ir. The solid lines connect atoms of the major rotomer whereas
the dashed lines show the minor one. The disordered atoms
are either unprimed or primed, with the former having the
higher occupancy. Two positions are resolved for the half-
occupancy oxygen atoms O(2) and O(2)′ of the second carbonyl,
(16) Cromer, D. T.; Waber, J . T. International Tables for Crystal-
lography; Kynoch Press: Birmingham, England, 1974; Vol. IV, Table
2.2A.
(17) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J . Chem. Phys.
1965, 42, 3175.
(18) Cromer, D. T.; Liberman, D. J . Chem. Phys. 1970, 53, 1891.

1046 Organometallics, Vol. 15, No. 3, 1996
Antwi-Nsiah et al.
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 Cor e Atom s of [Rh Ir (CH3)(CO)3(d p p m )2]-
[CF 3SO3]‚CH2Cl2 (2)a
Sch em e 1
atom
x
y
z
B,b Å2
Ir
Rh
0.20140(4)
0.35373(5)
0.1539(2)
0.3001(2)
0.2529(2)
0.4012(2)
0.570(2)
-0.016(3)
0.501(1)
0.531(2)
0.0326(8)
0.494(2)
0.075(1)
0.388(2)
0.470(2)
0.090(2)
0.141(3)
0.098(3)
0.451(3)
0.2655(8)
0.2913(8)
0.00000
0.02892(2)
-0.0847(1)
-0.0479(1)
0.0775(1)
0.1131(1)
0.0549(9)
-0.025(1)
-0.0365(5)
-0.0346(8)
0.0662(4)
0.0462(8)
-0.0163(6)
-0.0217(8)
-0.010(1)
0.0405(6)
0.051(1)
-0.09826(4)
0.15216(4)
-0.0479(2)
0.2311(2)
-0.1782(2)
0.1011(2)
0.414(2)
-0.363(2)
0.018(1)
0.047(2)
0.022(1)
2.39(1)*
2.36(1)*
2.40(6)*
2.49(6)*
2.54(6)*
2.53(6)*
10.1(6)
8.0(7)
4.6(3)
4.3(4)
7.8(3)*
5.0(4)
0.1(2)
4.1(4)
3.7(5)
3.2(3)
4.1(6)
8.4(7)
4.1(6)
2.5(2)*
3.0(2)*
P(1)
P(2)
P(3)
P(4)
O(1)
O(1)′
O(2)
O(2)′
O(3)
C(1)
C(1)′
C(2)
C(2)′
C(3)
C(3)′
C(4)
C(4)′
C(5)
C(6)
0.320(2)
-0.277(1)
-0.048(2)
0.084(2)
-0.030(1)
0.071(2)
-0.291(3)
0.337(2)
0.1172(8)
-0.0648(8)
-0.031(1)
0.054(1)
-0.1024(4)
0.1318(4)
H)(dppm)2][BF4],6m respectively, by apparent electro-
philic attack at the metal-metal bond. On the basis of
these results, the reaction of compound 1 with the
electrophile CH3+ (in the form of methyl triflate (MeOTf))
was attempted, in efforts to obtain a CH3-bridged
analogue of these hydrido-bridged species. However,
unlike the protonations, reaction of 1 with methyl
triflate does not yield the targeted methyl-bridged
species but instead gives [RhIr(CH3)(CO)3(dppm)2][CF3-
SO3] (2), having the methyl group terminally bound to
Ir (see Scheme 1). Although initial attack may occur
at the Rh-Ir bond, this cannot be confirmed, since even
at low temperature only 2 was observed. It should be
noted, however, that protonation and alkylation of an
analogous RhOs complex appear to occur at a site on
the saturated Os center remote from Rh7 and not at the
Rh-Os bond, suggesting that electrophilic attack occurs
directly at the saturated Ir center in compound 1 also.
a
Phenyl carbons and atoms of the triflate anion and the solvent
molecule are given in the Supporting Information. Numbers in
parentheses are estimated standard deviations in the least
significant digits in this and all subsequent tables. The atoms
labeled Rh and Ir are actually a 60:40 mix of Rh/Ir and Ir/Rh,
respectively, owing to disorder (see Experimental Section). Primed
atoms have 40% occupancy and are related to the unprimed (60%
b
occupancy) atoms by the rotational disorder. Starred B values
are for atoms refined anisotropically. B values for the anisotro-
pically refined atoms are given in the form of the equivalent
isotropic Gaussian displacement parameter defined as 4/3[a2â11
b2â22 + c2â33 + ab(cos γ)â12 + ac(cos â)â13 + bc(cos R)â23].
+
Ta ble 4. P osition a l a n d Th er m a l P a r a m eter s for
th e Cor e Atom s of [Rh Ir (CO)2(µ-C(CH3)dNtBu )-
(d p p m )2][CF 3SO3] (8)a
atom
x
y
z
B,b Å2
Ir
Rh
0.1047(1)
0.3106(2)
0.0581(6)
0.2640(6)
0.1430(6)
0.3439(6)
-0.007(1)
0.355(2)
0.314(2)
0.032(2)
0.336(2)
0.207(2)
0.215(2)
0.422(2)
0.452(3)
0.415(2)
0.507(2)
0.177(2)
0.278(2)
0.92373(4)
0.93613(8)
0.8438(3)
0.8599(3)
0.9921(3)
1.0134(3)
0.9988(7)
1.0006(7)
0.8860(7)
0.967(1)
0.977(1)
0.843(1)
0.878(1)
0.858(1)
0.874(1)
0.798(1)
0.876(1)
0.8119(9)
1.009(1)
0.26515(6)
0.3533(1)
0.3154(4)
0.4115(4)
0.1942(3)
0.2933(4)
0.3452(9)
0.4787(9)
0.2675(9)
0.308(1)
0.429(1)
0.172(1)
0.229(1)
0.254(1)
0.193(2)
0.263(1)
0.308(1)
0.362(1)
0.207(1)
2.29(2)*
2.38(6)*
2.8(2)*
2.9(2)*
2.5(2)*
2.7(2)*
4.0(6)*
5.0(7)*
2.2(6)*
3.5(7)
3.2(6)
3.7(7)
3.0(6)
3.4(7)
P(1)
P(2)
P(3)
P(4)
O(1)
O(2)
N
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
1
The H NMR spectrum of 2 shows the methyl reso-
nance as a triplet at δ -0.08, and selective 31P-decoupling
experiments confirm that the methyl protons are coupled
to only the phosphorus nuclei on Ir. The absence of Rh
coupling to the methyl protons also supports the model
in which the methyl group is bound to Ir but is equivocal
since such coupling is only 2-4 Hz, at most, in related
Rh-bound methyl species (vide infra).6f,7-9 The 13C{1H}
NMR spectrum of a 13CO-enriched sample, which shows
a doublet of triplets at δ 183.7 (1J Rh-C ) 75.0 Hz) and a
triplet at δ 187.9, with relative intensities 1:2, respec-
tively, indicates that compound 2 has one terminal
carbonyl group on Rh and two on Ir. Taken together
the NMR spectroscopic data clearly establish the struc-
ture of 2, having one terminal carbonyl group bound to
Rh and the methyl group as well as two terminal
carbonyl groups bound to Ir.
5.8(9)
4.8(8)
4.1(7)
1.7(5)
2.7(6)
a
Phenyl carbons and atoms of the triflate anion are given in
b
the Supporting Information. Starred B values are for atoms
refined anisotropically. B values for the anisotropically refined
atoms are given in the form of the equivalent isotropic Gaussian
displacement parameter defined as 4/3[a2â11 + b2â22 + c2â33
ab(cos γ)â12 + ac(cos â)â13 + bc(cos R)â23].
+
This proposed structure is confirmed by the X-ray
structure determination. The asymmetric unit of com-
pound 2 contains the complex cation, a triflate anion,
and one molecule of CH2Cl2 solvent. The geometries of
the triflate anion and the solvent molecule are as
expected, and there are no unusual contacts involving
the solvent and the ions. A perspective drawing of the
cation of this compound is shown in Figure 1. Although
as noted earlier, the non-phosphine components of the
electron density of ca. 3.5 e/Å3. The positional and isotropic
thermal parameters of the non-hydrogen atoms are given in
Table 4.
Resu lts a n d Discu ssion
(a ) P r ep a r a tion a n d Ch a r a cter iza tion of [Rh Ir -
(CH3)(CO)3(d p p m )2][CF 3SO3] (2). Earlier work in
this research group and by Eisenberg and co-workers
had shown that protonation of the complexes [Ir2(CO)3-
(dppm)2], [Rh2(CO)3(dppm)2], and their heterobinuclear
analogue, [RhIr(CO)3(dppm)2] (1), yielded the hydrido-
bridged complexes, [Ir2(CO)2(µ-CO)(µ-H)(dppm)2][BF4],19
[Rh2(CO)2(µ-CO)(µ-H)(dppm)2][BF4],20 and [RhIr(CO)3(µ-
(19) Sutherland, B. R.; Cowie, M. Organometallics 1985, 4, 1637.
(20) (a) Kubiak, C. P.; Woodcock, C.; Eisenberg, R. Inorg. Chem.
1982, 21, 2119. (b) Kubiak, C. P.; Eisenberg, R. J . Am. Chem. Soc.
1980, 102, 3637.

Heterobinuclear Alkyl Complexes of Rh and Ir
Organometallics, Vol. 15, No. 3, 1996 1047
Ta ble 6. Selected An gles (d eg) in
[Rh Ir (CH3)(CO)3(d p p m )2][CF 3SO3]‚CH2Cl2 (2)a
Rh-Ir-P(1)
94.95(5)
92.74(5)
173.7(4)
70.7(5)
68.2(4)
173.2(7)
170.17(7)
86.4(4)
87.6(5)
99.6(4)
81.0(7)
86.6(4)
89.2(5)
88.9(4)
90.7(7)
138.8(6)
103.5(8)
117.8(8)
92.56(5)
94.73(5)
167.9(6)
69.1(6)
63.5(6)
174.8(8)
170.22(7)
91.0(5)
90.8(6)
90.5(6)
88.0(7)
83.1(5)
97.9(6)
86.9(6)
84.1(7)
132.6(9)
C(2)′-Rh-C(4)′
C(3)′-Rh-C(4)′
Ir-P(1)-C(5)
116(1)
111(1)
Rh-Ir-P(3)
Rh-Ir-C(1)′
Rh-Ir-C(2)
Rh-Ir-C(3)
Rh-Ir-C(4)
111.6(2)
118.7(3)
112.6(2)
103.8(3)
105.3(4)
103.5(4)
112.0(2)
117.8(3)
113.1(3)
101.6(3)
107.6(3)
103.6(4)
112.7(2)
118.3(2)
113.5(3)
100.5(3)
106.3(4)
104.1(4)
112.8(3)
113.9(2)
117.1(3)
104.2(4)
103.3(3)
104.3(4)
178(2)
Ir-P(1)-C(11)
Ir-P(1)-C(21)
C(5)-P(1)-C(11)
C(5)-P(1)-C(21)
C(11)-P(1)-C(21)
Rh-P(2)-C(5)
Rh-P(2)-C(31)
Rh-P(2)-C(41)
C(5)-P(2)-C(31)
C(5)-P(2)-C(41)
C(31)-P(2)-C(41)
Ir-P(3)-C(6)
Ir-P(3)-C(51)
Ir-P(3)-C(61)
C(6)-P(3)-C(51)
C(6)-P(3)-C(61)
C(51)-P(3)-C(61)
Rh-P(4)-C(6)
Rh-P(4)-C(71)
Rh-P(4)-C(81)
C(6)-P(4)-C(71)
C(6)-P(4)-C(81)
C(71)-P(4)-C(81)
Rh-C(1)-O(1)
Ir-C(1)′-O(1)′
Ir-C(2)-O(2)
P(1)-Ir-P(3)
P(1)-Ir-C(1)′
P(1)-Ir-C(2)
P(1)-Ir-C(3)
P(1)-Ir-C(4)
P(3)-Ir-C(1)′
P(3)-Ir-C(2)
P(3)-Ir-C(3)
P(3)-Ir-C(4)
C(2)-Ir-C(3)
C(2)-Ir-C(4)
C(3)-Ir-C(4)
Ir-Rh-P(2)
Ir-Rh-P(4)
Ir-Rh-C(1)
Ir-Rh-C(2)′
Ir-Rh-C(3)′
Ir-Rh-C(4)′
P(2)-Rh-P(4)
P(2)-Rh-C(1)
P(2)-Rh-C(2)′
P(2)-Rh-C(3)′
P(2)-Rh-C(4)′
P(4)-Rh-C(1)
P(4)-Rh-C(2)′
P(4)-Rh-C(3)′
P(4)-Rh-C(4)′
C(2)′-Rh-C(3)′
F igu r e 1. Perspective view of the [RhIr(CH3)(CO)3-
(dppm)2]+ cation, showing the numbering scheme. Thermal
ellipsoids are shown at the 20% level except for the methyl
and methylene hydrogens, which are shown artificially
small, and the phenyl hydrogens, which are omitted. The
carbonyl and methyl groups are disordered in a 60:40 mix;
only the major contributor is shown.
163(2)
178(1)
176((2)
174((1)
113.9(4)
113.6(4)
Rh-C(2)′-O(2)′
Ir-C(3)-O(3)
P(1)-C(5)-P(2)
P(3)-C(6)-P(4)
Ta ble 5. Selected Dista n ces (Å) in
[Rh Ir (CH3)(CO)3(d p p m )2][CF 3SO3]‚CH2Cl2 (2)a
(a) Bonded Distances
a
Labeling as in footnotes of Table 5.
Ir-Rh
2.743(1)
2.336(2)
2.327(2)
1.97(1)
1.88(2)
1.94(1)
2.16(3)
2.316(2)
2.326(2)
1.93(2)
1.96(2)
2.11(2)
2.04(3)
1.820(8)
1.782(8)
1.834(8)
P(2)-C(5)
P(2)-C(31)
P(2)-C(41)
P(3)-C(6)
P(3)-C(51)
P(3)-C(61)
P(4)-C(6)
P(4)-C(71)
P(4)-C(81)
O(1)-C(1)
O(1)′-C(1)′
O(2)-C(2)
O(2)′-C(2)′
O(3)-C(3)
O(3)-C(3)′
1.831(8)
1.827(7)
1.820(8)
1.821(9)
1.819(8)
1.803(8)
1.830(8)
1.813(8)
1.816(8)
1.06(2)b
1.07(3)
Ir-P(1)
Rh has a distorted square-planar geometry as expected
for Rh(1+) species, while Ir has a distorted trigonal-
bipyramidal geometry (ignoring the metal-metal bond).
The discussion of the nature of the metal-metal inter-
action requires a concomitant consideration of metal
oxidation states. If the positive charge is considered to
be localized on Ir, then the oxidation-state assignment
is Ir(2+)/Rh(0), and this d7/d9 system would require a
conventional metal-metal bond to give a diamagnetic
compound. The other possibility places the positive
charge on Rh, yielding d8/d8, Ir(1+)/Rh(1+) centers. In
this situation, the Ir has an 18-electron configuration
and the trigonal-bipyramidal geometry observed is as
expected. However, the Rh center has only 14 valence
electrons and requires an Ir f Rh dative bond to give a
square-planar 16-electron configuration at this atom.
We favor this latter view. The Ir f Rh dative bond
would utilize filled nonbonding dxy or dx -y orbitals on
Ir and would require no rehybridization of the trigonal-
bipyramidal Ir center, whereas the Ir(2+)/Rh(0) system,
having a normal covalent bond, would result in rehy-
bridization of Ir to give an octahedral geometry at this
metal. In addition, the carbonyl stretches, which are
all lower than 1990 cm-1, are more consistent with Ir-
(1+). The Rh-Ir distance (2.743(1) Å), which is signifi-
cantly shorter than the intraligand P(1)-P(2) and P(3)-
P(4) distances (3.060(3) and 3.055(3) Å, respectively),
indicates substantial attraction of the adjacent metal
centers and is therefore consistent with some form of
metal-metal bond. This distance is similar to that
observed in the precursor, [RhIr(CO)3(dppm)2] (2.7722(7)
Å),6m which was also proposed to have a dative bond,
in this case between an 18e Ir(1-) center and the 14e
Ir-P(3)
Ir-C(1)′
Ir-C(2)
Ir-C(3)
Ir-C(4)
Rh-P(2)
Rh-P(4)
Rh-C(1)
Rh-C(2)′
Rh-C(3)′
Rh-C(4)′
P(1)-C(5)
P(1)-C(11)
P(1)-C(21)
1.15(2)
1.09(2)b
1.20(1)
1.11(2)
(b) Nonbonded Distances
Rh-C(2)
Rh-C(3)
2.77(1)
2.71(1)
P(1)-P(2)
P(3)-P(4)
3.060(3)
3.055(3)
a
The atoms labeled Rh and Ir are actually a 60:40 mix of Rh/Ir
and Ir/Rh, respectively, owing to disorder (see Experimental
Section). Primed atoms have 40% occupancy and are related to
the unprimed (60% occupancy) atoms by the rotational disorder.
O(2) is disordered over two positions (O(2), O(2)′) whereas there
is only one position resolved for O(3), although it is probably two
closely spaced, unresolved, half-occupancy oxygen atoms.
2
2
b
cation are disordered in a 60:40 ratio, only the molecule
having the larger occupancy is shown. In Tables 5 and
6 the parameters involving both disordered molecules
are shown, with the atoms of the minor species being
primed; however, only the parameters of the major
species are discussed, since they are more reliable.
Owing to the disorder, there will be some uncertainty
in the metal-ligand parameters; nevertheless, the
crystal structure does confirm the gross overall struc-
ture of compound 2. As is observed in most other
binuclear dppm-bridged systems,21 the diphosphine
groups are oriented trans to each other about the metal
centers and are cis to the ligands in the equatorial plane.
(21) Puddephatt, R. J . Chem. Soc. Rev. 1983, 12, 99.

1048 Organometallics, Vol. 15, No. 3, 1996
Antwi-Nsiah et al.
Sch em e 2
Rh(1+) center. The distortion of the geometry around
each metal in 2 is caused by the two metals being drawn
together as a result of the strong dative interaction.
The assignment of the methyl group as being bound
to Ir is supported by the successful refinement of the
structure with a 60% and 40% occupancy for O(1) and
O(1)′ respectively, with O(1) on the end of the molecule
having 60% occupancy for Rh. This indicates that this
carbonyl group (C(1)O(1)), which is trans to the metal-
metal bond, is bound to Rh, placing the methyl group
on Ir. The essentially linear Ir-C-O linkages, as well
as the magnitude of the contacts between Rh and C(2)
and C(3) (2.77(1) and 2.71(1) Å, respectively), preclude
any significant semibridging interaction between Rh
and the carbonyls C(2)-O(2) and C(3)-O(3). This is
supported by the lack of Rh coupling for these carbonyl
resonances in the 13C NMR spectrum.
of 2 with hydrogen sources, in order to establish the role
of the different metals in the reductive elimination of
methane. Surprisingly, little has been established
about the natures of hydrido-alkyl intermediates in the
elimination of alkanes from adjacent metals. In a
related dipalladium system, methane evolution from
[Pd2H(CH3)(µ-Cl)(dppm)2]+ and methane and ethane
evolution from [Pd2(CH3)2(µ-H)(dppm)2]+ occurred under
mild conditions,24 whereas the related platinum com-
plexes [Pt2(CH3)2(µ-H)(dppm)2]+ and [Pt2H(CH3)(µ-H)-
(dppm)2] were found to be thermally stable to methane
loss.25 Although methane elimination was observed in
two dirhodium A-frames,10 [Rh2(CH3)(CO)(µ-CO)-
(dppm)2]+ and [Rh2(CO)2(µ-CH3CO)(dppm)2]+, upon re-
action with H2, the hydrido-methyl intermediates were
not observed. Similarly, the reductive elimination of
methane from the mixed-metal species [MRe(CH3)(CO)4-
(dppm)2]+ (M ) Rh, Ir) was found in a previous study
to occur readily upon reaction with H2, but no hydrido-
methyl intermediates were observed down to -80 °C.
A hydride-bridged methyl complex was observed at -60
°C upon reaction of the above IrRe compound with a
hydride source, and this species eliminated methane at
ambient temperature.6f
One of the interesting features of compound 2 is that
it has the methyl group bound to the saturated Ir metal.
Although this is not surprising, on the basis of the
presumed stronger Ir-CH3 bond compared to Rh-
CH3,22 it differs from all analogous alkyl complexes of
9
Rh/Re,6f Rh/Os,7 Rh/Mn8, Rh/Mo and Rh/W9 which
have the alkyl groups bound to the unsaturated Rh
metal. However the stronger Ir-CH3 bond cannot be
the sole reason for favoring the structure of 2 since the
isoelectronic species [RhOs(CH3)(CO)3(dppm)2]7 has a
Rh-bound methyl group, in spite of our assumption of a
greater Os-CH3 bond strength.23 In addition, facile
migration of the methyl group from Ir to Rh is later
described upon substitution of a carbonyl in 2 by other
π-acid ligands (vide infra).
(b) Rea ctivity Stu d ies. (i) Hyd r id o Meth yl Com -
p lexes. Having successfully prepared the “RhIr” meth-
yl species 2, we undertook an investigation of its
reactivity. Among the topics of interest was the reaction
Reaction of 2 with H2 at ambient temperature yields
the known trihydride species [RhIr(H)(CO)2(µ-H)2-
(dppm)2][CF3SO3] (4),6m through methane and CO evo-
lution, as shown in Scheme 2. If this reaction is carried
out at 0 °C, the dihydrido-methyl intermediate [RhIr-
(H)(CH3)(CO)2(µ-H)(dppm)2][CF3SO3] (3) is observed.
This species displays two hydride resonances (δ -10.02,
1
-12.47) and a methyl signal (δ -0.16) in the H NMR
spectrum.
Phosphorus decoupling experiments allow us to es-
tablish that the hydride ligand at higher field is
terminally bound to Rh, with a Rh-H coupling constant
1
of ca. 24 Hz, while the other is bridging, having J RhH
(22) Ziegler, T.; Tschinke, V.; Becke, A. J . Am. Chem. Soc. 1987,
109, 1351.
(24) Young, S. J .; Kellenberger, B.; Riebenspies, J . H.; Himmel, S.
E.; Manning, M.; Anderson, O. P.; Stille J . K. J . Am. Chem. Soc. 1988,
110, 5744.
(25) (a) Brown, M. P.; Cooper, S. J .; Frew, A.; Manijlovic´-Muir, L.;
Muir, K. W.; Puddephatt, R. J .; Thomson, M. A. J . Chem. Soc., Dalton
Trans. 1982, 299. (b) Azam, K. A.; Puddephatt, R. J . Organometallics
1983, 2, 1396.
(23) Although we have not seen comparisons of Rh-CH3 and Os-
CH3 bond strengths in analogous complexes, our assumptions are based
on extrapolations of the studies done. See for example ref 22 and:
Armentrout, P. B. Bonding Energetics in Organometallic Compounds;
Marks, T. J ., Ed.; American Chemical Society: Washington, DC, 1900;
Chapter 2.

Heterobinuclear Alkyl Complexes of Rh and Ir
Organometallics, Vol. 15, No. 3, 1996 1049
) 15 Hz; the methyl group is seen to be bound to Ir.
Only two carbonyl resonances are observed in the 13C-
{1H} NMR spectrum, with one CO bound to each metal.
This product has a geometry consistent with H2 attack
at the coordinatively unsaturated Rh center. However,
attempts to observe the initial product of H2 addition,
which is presumed to precede CO loss, failed, with no
reaction being noted at temperatures much lower than
0 °C; only 3 and 4 were observed on slowly warming
the sample under H2 from lower temperatures. It was
of interest to establish whether reductive elimination
of methane would occur from Ir or whether migration
of the methyl group to Rh would occur with elimination
occurring from this center. In the only alkyl intermedi-
ate observed, the methyl group remains bound to Ir,
with one hydrido ligand in a bridging position. This
geometry can readily give rise to methane loss via
transfer of the bridging hydride to iridium, followed by
reductive elimination from this metal. Although elimi-
nation should occur more readily from the second-row
metal, it appears in this case to be occurring from Ir.
This parallels a previous study on related RhOs com-
pounds,7 in which reductive elimination of methane also
occurred from the third-row metal (Os) in preference to
Rh.
doublet of triplets at δ 186.0 (1J Rh-C ) 76.5 Hz), and a
multiplet at δ 165.6 in the appropriate ratios, indicating
the presence of a bridging carbonyl group (the coupling
to Rh of 26.2 Hz is in the range expected for a bridging
carbonyl27 ) and a terminal carbonyl group each on Rh
and Ir.
Although the hydrido-methyl species 6 and 7 are
possible models for intermediates in methane elimina-
tion from adjacent metal centers, their subsequent
reductive elimination reactions were not pursued since
our interests lay in establishing the nature of the
intermediates preceding CH4 loss in order to gain
information about the functions of the different metals.
Under forcing conditions we would not be able to observe
and characterize such intermediates. However, in a
related study, the protonation of the analogous species,
[RhOs(CH3)(CO)3(dppm)2], as well as methylation of the
hydrido analogue, has yielded valuable insights into
reductive elimination from these metals.7
(ii) Rea ction of 2 w ith π-Acid Liga n d s. In an
attempt to induce migratory insertion of the methyl
group and concomitant C-C or C-X (X ) heteroatom)
bond formation, the reactions of compound 2 with
π-acceptor ligands such as carbon monoxide, tert-butyl
isocyanide, ethylene, and sulfur dioxide were attempted.
Reactions with alkynes were also investigated, but this
forms the basis of another paper.28
In the absence of excess H2, methane loss from 3
generates the previously reported,6m hydride-bridged
A-frame [RhIr(CO)3(µ-H)(dppm)2][CF3SO3] (5), having
1
In the reaction of compound 2 with CO a large
number of products resulted, and these were not char-
acterized. In this reaction mixture no species was
identified which could be formulated as an acetyl species
resulting from the expected migratory insertion of the
methyl and a carbonyl group.
scavenged the CO originally lost from 2. The H NMR
spectrum of this species shows the bridging hydride
resonance as a complex multiplet at δ -10.2, while the
13C{1H} NMR displays two carbonyl resonances in a 1:2
intensity ratio, with only one displaying coupling (79
Hz) to Rh. This monohydride species generates 4 upon
reaction with H2, with accompanying CO loss.
t
The reaction of 2 with BuNC occurs readily, yielding
[RhIr(CO)2(µ-tBuNdCMe)(dppm)2][CF3SO3] (8), the prod-
uct of isocyanide insertion into the Ir-methyl bond and
CO loss. This transformation is accompanied by move-
ment of the resulting iminoacyl group to the bridging
position, yielding the mixed-metal, iminoacyl analogue
of the dirhodium, acetyl-bridged species [Rh2(CO)2(µ-
CH3CO)(dppm)2]+.10 The 1H NMR spectrum of 8 shows
the methyl and tert-butyl resonances as singlets at δ
0.82 and 0.80, respectively. Formal insertion of the
tBuNC ligand into the Ir-CH3 bond has resulted in the
expected downfield shift for this methyl resonance, and
its appearance as a singlet results from its position one
atom further removed from Ir, such that coupling to the
phosphorus nuclei is no longer observed. The structure
shown in Scheme 3, having the iminoacyl nitrogen
bound to Rh rather than to Ir, could not be established
from the available spectroscopic data but has been
established crystallographically (vide infra). The 13C-
{1H} NMR spectrum of 8 shows two carbonyl resonances
as a doublet of triplets at δ 195.0 (1J Rh-C ) 65.4 Hz)
and a triplet at δ 191.3, while the IR spectrum shows
CO stretches at 1964 and 1945 cm-1, indicating that
there is one terminally bound carbonyl on each metal.
The absence of an absorption in the 2000-2190 cm-1
range (as expected for a CtN stretch29a) is consistent
with the insertion of the isocyanide ligand into the Ir-
CH3 bond, reducing the C-N bond order. The resulting
Related hydrido-methyl species can also be obtained
by protonation. For example, the reaction of 2 with 1
equiv of HCl gives [RhIr(CH3)(CO)2(µ-H)(µ-Cl)(dppm)2]-
[CF3SO3] (6). This product represents a rare example
involving Rh, in which a hydrido-methyl complex is
stable to methane elimination at room temperature to
the extent that it can be isolated as a solid.26 Although
the relative positions of the equatorial ligands are not
known, the failure of 6 to eliminate methane leads us
to assume that the hydride and methyl groups are not
adjacent. The hydride ligand is clearly bridging, as
shown by the multiplet at δ -9.50 in the 1H NMR
spectrum, which collapses to a doublet of triplets on
selectively decoupling each of the Rh-bound and Ir-
bound phosphorus resonances in turn and to a doublet
(1J Rh-H ) 22.0 Hz) upon broadband 31P-decoupling. As
in 3, the methyl group again remains coordinated to Ir
as demonstrated by the 1H{31P} NMR experiments. The
formation of 6 is accompanied by CO loss, as indicated
by its 13C{1H} NMR spectrum, which shows a doublet
of triplets at δ 189.3 (1J Rh-C ) 84.5 Hz) and an equal
intensity triplet at δ 164.4, indicating the presence of
only one CO ligand each on Rh and Ir. A similar
product, [RhIr(CH3)(CO)2(µ-H)(µ-CO)(dppm)2][CF3SO3]2
(7), is obtained on reacting 2 with CF3SO3H, except that
carbonyl loss does not occur and the bridging chloride
ligand in 6 is replaced by a bridging carbonyl. The 13C-
{1H} NMR spectrum of compound 7 shows a doublet of
triplets of triplets at δ 199.9 (1J Rh-C ) 26.2 Hz), a
(27) J enkins, J . A.; Cowie, M. Organometallics 1992, 11, 2767.
(28) (a) Antwi-Nsiah, F. H.; Oke, O.; Cowie, M. Organometallics
1996, 15, 506. (b) Antwi-Nsiah, F. H. Ph.D. Thesis, The University of
Alberta, Edmonton, 1994; Chapter 4.
(26) See also: Wang, C.; Ziller, J . W.; Flood, T. C. J . Am. Chem.
Soc. 1995, 117, 1647.

1050 Organometallics, Vol. 15, No. 3, 1996
Antwi-Nsiah et al.
Sch em e 3
CdN stretch is probably obscured by the absorptions
due to the dppm phenyl groups and is not observed.
In an attempt to identify intermediates in the trans-
formation of 2 to 8, in order to elucidate the steps
t
involved, the reaction with BuNC was carried out at
-80 °C and slowly warmed while observing NMR
spectral changes (1H, 13C, and 31P). Between -80 and
-40 °C the major product observed is a tricarbonyl
species 9, shown in Scheme 3. Its 13C{1H} NMR
spectrum indicates that two carbonyls (overlapping at
δ 181.3 and 181.9) are bound to Rh (1J Rh-C ) 74 and 77
Hz, respectively) with only one (δ 176.3) on Ir. The
1
methyl group is shown, by H NMR with selective 31P-
decoupling, to be bound to Ir, and the protons of the
tert-butyl group are observed as a singlet at δ 0.92. In
t
the absence of 13C-labeled BuNC we were unable to
observe the resonance for the isocyanide carbon, so the
site of coordination of this group is unknown. It is
assumed to be bound to Ir, as shown, on the basis of
similarities to related mixed-metal species previously
characterized by us.6f,h The site of BuNC attack on
t
Figu r e 2. Perspective view of the [RhIr(CO)2(µ-C(CH3)dNt-
Bu)(dppm)2]+ cation, showing the numbering. Thermal
parameters are as in Figure 1.
compound 2 should be at the unsaturated Rh center;
however, such an adduct was not identified. At -80 °C
several unidentified intermediates were observed, but
their low concentration and the overlap of signals
prevented their identification. As the reaction mixture
is warmed to 0 °C, compound 9 disappears to be replaced
by [RhIr(CH3)(CO)2(tBuNC)(dppm)2][CF3SO3] (10), which
is shown by 13C{1H} NMR to be a dicarbonyl species,
to Rh; instead it appears that the coupling of the methyl
and isocyanide ligands occurs on Ir. The ease of this
migratory insertion, transforming 10 to 8, is in contrast
to the failure of the isoelectronic, tricarbonyl precursor
2 to undergo a similar migration involving one of the
carbonyls but is consistent with the greater tendency
for isocyanides to insert.29b
The coordination mode of the iminoacyl ligand was
established by an X-ray determination of compound 8,
which shows that this group bridges the metals such
that it is N-bound to Rh and C-bound to Ir. Figure 2
shows a perspective view of the complex cation. Rel-
evant bond lengths and angles are given in Tables 7 and
8. Within the cation, the diphosphine groups are
oriented approximately trans to each other about the
metal centers (P(1)-Ir-P(3) ) 167.4(2)° and P(2)-Rh-
P(4) ) 175.8(3)°) and are both cis to the other atoms
coordinated to the metal nuclei, resulting in a distorted
square-planar geometry about both metals. Formation
of the iminoacyl complex is accompanied by elongation
of the Rh-Ir separation from 2.743(1) Å in the precursor
complex 2 (vide supra) to 2.950(2) Å. Although this Rh-
Ir separation is intermediate between those in com-
1
having one CO (δ 180.2, J Rh-C ) 68.5 Hz) terminally
bound to Rh, and by 1H NMR to have the methyl group
still on Ir. The low-field 13C resonance for the second
carbonyl (δ 233.3) suggests a bridging mode, in which
interaction with Rh must be weak, since no resolvable
Rh coupling is observed in this slightly broadened
t
resonance (20 Hz at half-height). Again the BuNC
group is assumed to be bound to Ir, yielding a species
analogous to 2, apart from the proposed semibridging
carbonyl interaction in 10. Upon further warming, 10
transforms to the iminoacyl-bridged product 8. Al-
though migratory insertions are known to occur more
readily at Rh than Ir, we see no evidence for a rear-
rangement bringing the isocyanide and methyl groups
(29) (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, pp 148 and 372. (b)
Ibid., pp 377-378.

Heterobinuclear Alkyl Complexes of Rh and Ir
Organometallics, Vol. 15, No. 3, 1996 1051
Ta ble 7. Selected Dista n ces (Å) in
The insertion of an isocyanide ligand into a M-C σ
bond is well documented.31,33 Whether the resulting
iminoacyl group is bonded in a mono- or bidentate
manner depends ultimately on the electronic configu-
ration and the required coordination geometry of the
metals in the complex.33a In 8, coordination of the
nitrogen lone pair to Rh gives this metal the square-
planar geometry characteristic of Rh (1+). Compound
8 is very similar to [Pd2(µ-CH3NdCCH3)(CNCH3)2-
[Rh Ir (CO)2(µ-C(CH3)dNtBu )(d p p m )2][CF 3SO3] (8)
(a) Bonded Distances
Ir-P(1)
2.310(7)
2.297(6)
1.72(3)
2.02(2)
2.319(7)
2.310(7)
2.13(2)
1.82(2)
1.83(2)
1.80(2)
1.83(2)
1.80(2)
1.80(2)
1.84(2)
P(3)-C(10)
P(3)-C(51)
P(3)-C(61)
P(4)-C(10)
P(4)-C(71)
P(4)-C(81)
O(1)-C(1)
O(2)-C(2)
N-C(4)
1.75(2)
1.81(2)
1.83(2)
1.82(2)
1.76(2)
1.85(2)
1.23(3)
1.15(2)
1.39(2)
1.59(3)
1.43(3)
1.42(3)
1.47(3)
1.47(3)
Ir-P(3)
Ir-C(1)
Ir-C(4)
Rh-P(2)
Rh-P(4)
Rh-N
Rh-C(2)
P(1)-C(9)
P(1)-C(11)
P(1)-C(21)
P(2)-C(9)
P(2)-C(31)
P(2)-C(41)
(dppm)2]3+ 33c
which was obtained by the insertion of an
,
isocyanide into a Pd-CH3 bond. Other examples of
bridging iminoalkyl ligands,34 and closely related bridg-
ing formimidoyl35 ligands are known.
N-C(5)
C(3)-C(4)
C(5)-C6
C(5)-C(7)
C(5)-C(8)
The reaction of compound 2 with ethylene does not
result in insertion of the unsaturated ligand into the
Ir-methyl bond as was observed with tert-BuNC;
nevertheless, it gives an interesting species, resulting
from substitution of a carbonyl and the accompanying
migration of the methyl group from Ir to Rh to give
[RhIr(CH3)(CO)2(C2H4)(dppm)2][CF3SO3] (11). This spe-
cies is analogous to [RhOs(CH3)(CO)3(dppm)2],7 in hav-
ing the methyl group coordinated to the unsaturated Rh
rather than to the saturated metal center, as shown
earlier in Scheme 3. The four ethylene protons are
equivalent, giving rise to a triplet at δ 0.75, while the
methyl group resonance appears as a doublet of triplets
(b) Nonbonded Distances
Ir-Rh
2.950(2)
3.04(1)
P(3)-P(4)
3.04(1)
P(1)-P(2)
Ta ble 8. Selected An gles (d eg) in
[Rh Ir (CO)2(µ-C(CH3)dNtBu )(d p p m )2][CF 3SO3] (8)
(a) Bond Angles
P(1)-Ir-P(3)
P(1)-Ir-C(1)
P(1)-Ir-C(4)
P(3)-Ir-C(1)
P(3)-Ir-C(4)
C(1)-Ir-C(4)
P(2)-Rh-P(4)
P(2)-Rh-N
167.4(2)
95.1(8)
86.6(6)
93.7(8)
86.6(6)
168(1)
175.8(3)
90.1(5)
91.5(7)
90.1(5)
89.1(7)
168.6(9)
109.6(7)
114.5(7)
111.9(7)
111.5(7)
Rh-N-C(4)
114(1)
120(1)
125(2)
170(2)
177(2)
110(1)
131(2)
119(2)
113(2)
109(2)
108(2)
114(2)
108(2)
104(2)
114(1)
117(1)
Rh-N-C(5)
C(4)-N-C(5)
Ir-C(1)-O(1)
Rh-C(2)-O(2)
Ir-C(4)-N
Ir-C(4)-C(3)
N-C(4)-C(3)
N-C(5)-C(6)
N-C(5)-C(7)
N-C(5)-C(8)
C(6)-C(5)-C(7)
C(6)-C(5)-C(8)
C(7)-C(5)-C(8)
P(1)-C(9)-P(2)
P(3)-C(10)-P(4)
1
at δ 0.35 (2J Rh-H ) 3.0 Hz) in the H NMR spectrum.
Selective 31P-decoupling experiments confirm that the
ethylene protons are coupled to the Ir-bound phosphorus
nuclei whereas the methyl protons are coupled to the
phosphorus nuclei bound to Rh. Both carbonyls interact
with Rh as shown by their coupling of 20.0 Hz to this
metal and are assumed to be semibridging on the basis
that this coupling is less than in symmetrically-bridged
carbonyls. Ethylene adducts of dppm-bridged binuclear
complexes of Rh or Ir are extremely rare (to our
knowledge the complexes, [Ir2(CO)(C2H4)(µ-I)(µ-CO)-
(dppm)2][X] (X ) I, BF4),6e [Ir2(CH3)(CO)2(C2H4)(dppm)2]-
[BF4],11 and [Ir2(C2H4)(CO)2(µ-H)(dppm)2][BF4]36 are the
only other examples); thus, compound 11 and that
previously described for the diiridium analogue,11 both
of which have an accompanying alkyl group, are un-
usual. Furthermore, methyl migration from one transi-
tion metal to another, as was observed in the above
reaction with ethylene, is also rare, having been ob-
served in only a few cases.10,11,37 It should be recalled,
however, that alkyl transfer from a main-group to a
transition metal is common in alkyl-transfer reactions
of Grignard reagents, as well as other alkyl-transfer
reagents of aluminum, zinc, mercury, and tin,38 and
compounds in which a methyl group bridges aluminum
and a transition metal have been characterized.39 Such
methyl-bridged species can be viewed as models for
methyl-group transfer from one metal to another.
P(2)-Rh-C(2)
P(4)-Rh-N
P(4)-Rh-C(2)
N-Rh-C(2)
Ir-P(1)-C(9)
Rh-P(2)-C(9)
Ir-P(3)-C(10)
Rh-P(4)-C(10)
(b) Torsion Angles
P(1)-Ir-Rh-N
P(3)-Ir-Rh-N
87.2(6)
-82.9(6)
C(4)-Ir-Rh-P(4)
C(4)-Ir-Rh-P(2)
93.1(8)
-88.9 (8)
pound 2, which has a Rh-Ir bond, and that in [RhIr-
(H)2(CO)2(µ-Cl)(dppm)2][BF4] (3.0651(5)Å),6p which has
no Rh-Ir bond, it is suggested that there is no Rh-Ir
bond in 8, since this situation is more consistent with
electron counting, in which both metals are d8 square-
planar centers. This is also the view taken in the report
of the acetyl-bridged dirhodium analogue, which has an
almost identical metal-metal separation.10 The imi-
noacyl bridge lies in the equatorial plane, perpendicular
to the metal-phosphorus plane, and the Ir-C(4) and
Rh-N distances of 2.02(2) and 2.13(2) Å, respectively,
are within the expected range for Ir-C and Rh-N single
bonds. Also the C-C bonds within the iminoacyl ligand
are consistent with single bonds. The N-C(4) separa-
tion of 1.39(2) Å is longer than those of the bridging
iminoacyl ligands in [Os3(CO)10(µ-H)(µ-η2-C6H5CdNCH3)]
(1.278(10) Å)30 and [Fe2{η2-C(Mes)NtBu}2(µ-C(Mes)dNt-
Bu)2] (Mes ) 2,4,6-Me3C6H2; 1.295(10) Å)31 and is also
longer than a normal NdC bond (ca. 1.30 Å32). The
geometries around C(4) and N are trigonal planar, with
the Ir-C(4)-C(3) angle (131(2)°) slightly increased at
the expense of the Ir-C(4)-N angle (110(1)°), while the
tert-butyl group adopts a normal tetrahedral geometry.
The carbonyl geometries and distances are normal for
such terminally bound groups.
Sulfur dioxide is also known to insert into metal-
alkyl bonds. However, the mechanism is not of migra-
(33) (a) Werner, H. Angew. Chem., Int. Ed. Eng. 1990, 29, 1077. (b)
Singleton, E.; Oosthuizen, H. E. Adv. Organomet. Chem. 1983, 22, 209
and references therein. (c) Lee, C.; Hunt, C. T.; Balch, A. L. Organo-
metallics 1982, 1, 824. (d) Yamamoto, Y.; Yamazaki, H. Coord. Chem.
Rev. 1972, 8, 225.
(34) Yin, C. C.; Deeming, A. J . J . Organomet. Chem. 1977, 133, 123.
(35) (a) Alonso, F. J . G.; Sanz, M. G.; Riera, V. Organometallics 1992,
11, 801. (b) Adams, R. D.; Golembeski, N. M. J . Am. Chem. Soc. 1979,
101, 3637.
(30) Adams, R. D.; Golembeski, N. M. Inorg. Chem. 1978, 17, 1969.
(31) Klose, A.; Solari, E.; Ferguson, R.; Floriani, C.; Chiesi-Villa, A.;
Rizzoli, C. Organometallics 1993, 12, 2414.
(32) Allen, F. H.; Kernard, O.; Watson, D. G.; Brammer, L.; Orpen,
G. A.; Taylor, R. J . Chem. Soc., Perkin Trans. 2 1987, S1.
(36) (a) Antwi-Nsiah, F. H. Ph.D. Thesis, The University of Alberta,
Edmonton, 1994; Chapter 5. (b) Antwi-Nsiah, F. H.; Torkelson, J . R.;
Cowie, M. Manuscript in preparation.

1052 Organometallics, Vol. 15, No. 3, 1996
Antwi-Nsiah et al.
(COCH3)(CO)4(dppm)2][CF3SO3].6f In the IR spectrum
the acetyl C-O stretch appears at 1640 cm-1, and one
of the SO stretches of the SO2 group appears at 1055
cm-1; the second SO2 stretch is presumably obscured
by the triflate anion stretches. The spectroscopic data
do not unambiguously establish the binding mode of the
SO2 ligand; however, the high tendency for this ligand
to bridge late metals, the low SO stretch,41 and the
characterization of a closely related SO2-bridged diiri-
dium complex12 suggest a bridged mode for the SO2
group in this species also.
Sch em e 4
When the reaction of 2 with SO2 is started at ca. -60
°C, the intermediate, [RhIr(CH3)(CO)3(SO2)(dppm)2][CF3-
SO3] (12), is observed in solution. On standing at room
temperature for about 10 min, compound 12 is trans-
formed to a second intermediate, [RhIr(CH3)(CO)2(µ-
SO2)(dppm)2][CF3SO3] (13), which in turn is trans-
formed to the acetyl product, 14, after 1 h at room
temperature. In the 1H NMR spectrum of compound
12, the dppm-methylene resonances appear as multip-
lets at δ 4.85 and 3.45, while the methyl resonance
appears as a broad signal at δ 0.33. Selective 31P-
decoupling experiments show that the methyl group is
still bound to Ir, as decoupling the resonance due to the
Ir-bound phosphorus nuclei leads to the collapse of the
broad methyl resonance into a sharp singlet, while
decoupling the other 31P resonance has no effect. The
13C{1H} NMR spectrum shows doublets of triplets at δ
194.9 (1J Rh-C ) 56.3 Hz) and 175.2 (1J Rh-C ) 63.4 Hz),
as well as a triplet at δ 178.4, indicating the presence
of two terminal CO ligands on Rh and one on Ir. A
terminal coordination mode is proposed for the SO2
group in compound 12, on the basis that transfer of a
CO from Ir to Rh has occurred, which would leave Ir
electron deficient. A bridging SO2 is ruled out since it
would inhibit methyl transfer from Ir to Rh, accompa-
nied by CO transfer in the reverse direction, as is
observed in subsequent transformations (vide infra).
Although we have no spectroscopic data that would
allow us to establish whether the Ir-SO2 moiety is
planar or pyramidal,42 a pyramidal sulfur is assumed
on the basis of analogies with the known structures for
the closely related [MCl(CO)(SO2)(PPh3)2] (M ) Rh, Ir)
complexes.43 The structure shown for 12 in Scheme 4
also depicts a tetragonal pyramidal Ir center, in which
SO2 occupies the apical site, as was observed in the
above mononuclear analogues.
tory insertion, as observed with CO, but involves
electrophilic attack directly at the alkyl group.40 It was
therefore of interest to determine whether compound 2
would undergo SO2 insertion. Compound 2 does react
with SO2 at ambient temperature but not to give an
S-bound sulfinate, via SO2 insertion. Instead, the
reaction leads to the formation of the acetyl complex
[RhIr(CO)2(COCH3)(µ-SO2)(dppm)2][CF3SO3] (14) (see
Scheme 4). The 1H NMR spectrum of 14 shows the
resonance of the acetyl protons as a singlet at δ 1.15
and the 13C{1H} spectrum shows three carbonyl reso-
nances of equal intensity. Two doublets of triplets are
observed for the Ir-bound carbonyls at δ 172.7 and 168.7
with coupling to the two adjacent phosphorus nuclei and
to each other (12.6 Hz). This C-C coupling is less than
the values of 25 Hz observed between a carbon nucleus
of the bridging acetylene and a CO in [Ir2(I)(CO)2(µ-
HC2H)(dppm)2][I] (acetylenic and carbonyl carbons 13C-
enriched), in which a trans orientation of the alkyne and
this CO ligand was proposed,6a and between two mutu-
ally trans carbonyls in [RhOs(NCMe)(CO)3(µ-H)(dppm)2]-
[BF4]27 but is close to the 13 Hz observed between a CO
ligand and the vinylidene R carbon in [Ir2(CH3)(CO)3(µ-
CdCH2)(dppm)2][CF3SO3].28 It is therefore proposed
that these Ir-bound carbonyls in 14 deviate from an
exactly trans orientation. The third 13C resonance at δ
255.5 appears as a doublet (1J Rh-C ) 34.2 Hz) and is
assigned to the acetyl carbonyl, which is bound to Rh.
The chemical shift and magnitude of the Rh-C coupling
of this carbonyl group is similar to that of [RhRe-
The 1H NMR spectrum of compound 13 shows the
dppm methylene resonances as multiplets at δ 4.12 and
3.50, as well as the methyl resonance as a triplet of
doublets at δ 1.08 (2J Rh-H ) 3.7 Hz). The presence of
Rh coupling to the methyl protons indicates that the
methyl group has now migrated to Rh, as was observed
(37) (a) Schore, N. E.; Ilenda, C. S.; White, M. A.; Bryndza, H. E.;
Matturro, M. G.; Bergman, R. G. J . Am. Chem. Soc. 1984, 106, 7451.
(b) Krause, M. J .; Bergman, R. G. Organometallics 1986, 5, 2097. (c)
Ling, S. S. M.; Puddephatt, R. J . J . Organomet. Chem. 1983, 255, C11.
(38) Elschenbroich, Ch.; Salzer, A. Organometallics; VCH Publish-
ers: New York, 1989.
(39) (a) Holton, J .; Lappert, M. F.; Scollary, G. R.; Ballard, D. G.
H.; Pearce, R.; Atwood, J . L.; Hunter, W. E. J . Chem. Soc., Chem.
Commun. 1976, 425. (b) Holton, J .; Lappert, M. F.; Ballard, D. G. H.;
Pearce, R.; Atwood, J . L.; Hunter, W. E. J . Chem. Soc., Dalton Trans.
1979, 54. (c) Busch, M. A.; Harlow, R.; Watson, P. L. Inorg. Chim. Acta
1987, 140, 15 and references therein.
(40) (a) Mils, S. L.; Mils, D. L.; Bau, R.; Flood, T. C. J . Am. Chem.
Soc. 1978, 100, 7278. (b) Attig, T. G.; Teller, R. G.; Wu, S.-M.; Bau, R.;
Wojcicki, A. J . Am. Chem. Soc. 1979, 101, 619. (c) Wojcicki, A. Adv.
Organomet. Chem. 1974, 12, 31. (d) Wojcicki, A. Acc. Chem. Res. 1971,
4, 344.
(41) See, for example: (a) Uson, R.; Fornies, J .; Espinet, P.; Fortuno,
C. J . Chem. Soc., Dalton Trans. 1986, 1849. (b) Cowie, M.; Dickson,
R. S.; Hames B. W. Organometallics 1984, 3, 1879. (c) Kubas, G. J .
Inorg. Chem. 1979, 18, 182. (d) Dwight, S. K.; Cowie, M. Inorg. Chem.
1980, 19, 209. (e) Mingos, D. M. P. Transition Met. Chem. 1978, 3, 1.
(f) Balch, A. L.; Benner, L. S.; Olmstead, M. M. Inorg. Chem. 1979,
18, 2996. (g) Angoletta, M.; Malatesta, L.; Caglio, G. J . Chem. Soc.,
Dalton Trans. 1977, 2131. (h) Angoletta, M.; Bellon, P. L.; Manassero,
M.; Sansoni, M. J . Organomet. Chem. 1974, 81, C40. (i) Churchill, M.
R.; Krishan, L. K. Inorg. Chem. 1973, 12, 1650. (j) Churchill, M. R.;
DeBoer, B. G.; Kalra, K. L. Inorg. Chem. 1973, 12, 1646. (k) Churchill,
M. R.; DeBoer, B. G.; Kalra, K. L.; Reich-Rohrwig, P.; Wojcicki, A. J .
Chem. Soc., Chem. Commun. 1972, 981.
(42) (a) Ryan, R. R.; Eller, P. G. Inorg. Chem. 1976, 15, 494. (b)
Mingos, D. M. P. Transition Met. Chem. 1978, 3, 1.
(43) (a) Muir, K. W.; Ibers, J . A. Inorg. Chem. 1969, 8, 1921. (b)
LaPlaca, S. J .; Ibers, J . A. Inorg. Chem. 1966, 5, 405.

Heterobinuclear Alkyl Complexes of Rh and Ir
Organometallics, Vol. 15, No. 3, 1996 1053
in the reaction of 2 with ethylene, and is in contrast to
the reaction of 2 with BuNC, previously noted, in which
logue 2 being a simple methyl complex. The dirhodium
species is in fact an acetyl-bridged compound, in which
migratory insertion of the methyl and one carbonyl has
occurred,10 while the diiridium species is a methylene-
bridged hydride, which has resulted from C-H activa-
tion of the methyl group.11,12 These differences reflect
the greater tendency for migratory insertions to occur
at Rh and for oxidative addition to occur on Ir.
t
the methyl group remained on Ir. This is confirmed in
the present case by selective 31P-decoupling experi-
ments. The 13C{1H} NMR spectrum shows two doublets
of triplets at δ 180.6 and 170.3 (2J C-C ) 13.6 Hz),
indicating the presence of only two CO ligands on Ir and
indicating that the transformation from 12 to 13 in-
volves CO loss. The 13.6 Hz coupling between the
carbonyl carbons again suggests an orientation that is
probably intermediate between exactly cis and trans,
as was proposed for 14. The change of the methyl
resonance from a triplet of doublets in 13 to a sharp
singlet in 14 is consistent with the assignment of the
latter as an acetyl complex in which four-bond coupling
between the methyl protons and the phosphorus nuclei
is not observed.
On the basis of the intermediates and the acetyl
product observed in the reaction of 2 with SO2, the
reaction pathway shown in Scheme 4 is proposed.
Apparently, there is migration of one CO ligand from
Ir to Rh accompanied by the coordination of SO2 to the
former metal to yield compound 12. This compound
then loses one CO ligand and undergoes CO migration
from Rh to Ir, concomitant with methyl migration from
Ir to Rh, and movement of the SO2 ligand into the more
favored bridging position41 to yield compound 13. The
latter species recoordinates CO, resulting in migratory
insertion to give the acetyl product, 14. No insertion
of the SO2 ligand into the Ir-methyl bond is observed
at any stage in this reaction. Apparently the methyl
group of 2 is not nucleophilic enough to result in direct
attack by the SO2 electrophile; instead attack at the
metal occurs ultimately yielding the acetyl product.
In spite of the stronger Ir-CH3 bond in 2, migration
of the methyl group to Rh occurs readily upon substitu-
tion of a carbonyl by either ethylene or sulfur dioxide.
This metal-to-metal migration of the methyl group
presumably passes via a methyl-bridged species, al-
though such an intermediate was not observed in this
study. Alkyl-bridged complexes have previously been
proposed in similar metal-to-metal migrations10,11,37 as
well as in C-H activation of an alkyl group by an
adjacent metal.10,37,44-49 In addition, a number of alkyl-
bridged complexes involving the d- and f-block metals
have now been characterized,44-46,48,50,51 in which sev-
eral binding modes have been identified. It is not clear
what factors (electronic and steric) are responsible for
migration of the methyl group from Ir to Rh, nor is it
clear under what conditions a methyl-bridged species
might be stable. We are currently continuing our
investigation of the factors involved in stabilizing alkyl-
bridged species, with interests in inducing C-H activa-
tion of this bridged alkyl, to give an alkylidene-bridged
hydride product, as we have observed in the related
diiridium system.11,12
Attempts to effect migratory insertion and concomi-
tant C-C bond formation did succeed in the reaction of
t
2 with BuNC. Although mechanistic information is not
available, the final product and the observed intermedi-
ates suggest that migratory insertion has occurred at
Ir. This presents an interesting contrast to the analo-
gous diiridium system for which migratory insertion of
Con clu sion s
+
Electrophilic attack of [RhIr(CO)3(dppm)2] by CH3
does not yield the targeted methyl-bridged species
analogous to the protonation product, [RhIr(CO)3(µ-H)-
(dppm)2]+. Instead, the product obtained, [RhIr(CH3)-
(CO)3(dppm)2][CF3SO3] (2), has the methyl group ter-
minally bound to the saturated Ir center. This is hardly
surprising in view of the stronger Ir-CH3 bond com-
pared to Rh-CH3 but is in contrast to all other
analogous compounds of Rh/Mo,9 Rh/W,9 Rh/Mn,8 Rh/
Re,6c and Rh/Os,7 which have the alkyl group terminally
bound to the unsaturated Rh. In this regard the most
enlightening contrast is between compound 2 and the
isoelectronic Rh/Os compound [RhOs(CH3)(CO)3(dppm)2],7
which has a Rh-bound methyl group in spite of an
expected stronger Os-CH3 bond.23 It is significant,
however, that 2 is a monocationic complex whereas the
Rh/Os species is neutral. As a result, both metals in 2
can have their favored +1 oxidation state (assuming
that with CH3 on Ir the positive charge is localized on
Rh or vice versa), whereas for the Rh/Os compound the
observed structure has a favored Rh+/Os0 formulation,
while a structure having CH3 on Os would yield a
lessfavorable Rh0/Os+ formulation. It may be that the
structure of the Rh/Os compound reflects the favored
oxidation states whereas for Rh/Ir the bond strengths
determine the structure.
(44) (a) Andersen, R. A.; J ones, R. A.; Wilkinson, G.; Hursthouse,
M. B.; Malik, K.M. A. J . Chem. Soc., Chem. Commun. 1977, 865. (b)
J ones, R. A.; Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. R.; Malik,
K. M. A. J . Chem. Soc., Dalton Trans. 1980, 1771. (c) Hursthouse, M.
B.; J ones, R. A.; Malik, K. M. A.; Wilkinson, G. J . Am. Chem. Soc.
1979, 101, 4128.
(45) (a) Calvert, R. B.; Shapley, J . R. J . Am. Chem. Soc. 1977, 99,
5225. (b) Calvert, R. B.; Shapley, J . R.; Schultz, A. J .; Williams, J . M.;
Suib, S. L.; Stucky, G. D. J . Am. Chem. Soc.. 1978, 100, 6240. (c)
Calvert, R. B.; Shapley, J . R. J . Am. Chem. Soc. 1978, 100, 7726.
(46) Park, J . W.; Mackenzie, P. B.; Schaeter, Grubbs, R. H. J . Am.
Chem. Soc. 1986, 108, 6402.
(47) Hostetler, M. J .; Bergman, R. G. J . Am. Chem. Soc. 1990, 112,
8621.
(48) Schmidt, G. F.; Muetterties, E. L.; Beno, M. A.; Williams, J .
M. Proc. Natl. Acad. Sci. U.S.A. 1981, 78, 1318.
(49) Goldberg, K. I.; Bergman, R. G. J . Am. Chem. Soc. 1988, 110,
4853.
(50) See for example: (a) Holton, J .; Lappert, M. F.; Ballard, D. G.
H.; Pearce, R.; Atwood, J . L.; Hunger, W.E. J . Chem. Soc., Chem.
Commun. 1976, 480. (b) Holton, J .; Lappert, M. F.; Ballard, D. G. H.;
Pearce, R.; Atwood, J . L.; Hunter, W. E. J . Chem. Soc., Dalton Trans.
1979, 54. (c) Dawkins, G. M.; Green, M.; Orpen, A. G.; Stone, F. G. A.
J . Chem. Soc., Chem. Commun. 1982, 41. (d) Casey, C. P.; Fagan, P.
J .; Miles, W. H. J . Am. Chem. Soc. 1982, 104, 1134. (e) Cree-Uchiyama,
M.; Shapley, J . R.; St. George, G. M. J . Am. Chem. Soc. 1986, 108,
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Chem. Soc., Dalton Trans. 1986, 173. (g) Waymouth, R. M.; Santar-
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Chem. Soc. 1986, 108, 1427. (h) Busch, M. A.; Harlow, R.; Watson, P.
L. Inorg. Chim. Acta 1987, 140, 15. (i) Kulzick, M. A.; Price, R. T.;
Andersen, R. A.; Muetterties, E. L. J . Organomet. Chem. 1987, 333,
105. (j) Dutta, T. K.; Vites, J . C.; J acobsen, G. B.; Fehlner, T. P.
Organometallics 1987, 6, 842. (k) Burns, C. J .; Andersen, R. A. J . Am.
Chem. Soc. 1987, 109, 5853. (l) Ozawa, F.; Park, J . W.; Mackenzie, P.
B.; Schaefer, W. P.; Henling, L. M.; Grubbs, R. H. J . Am. Chem. Soc.
1989, 111, 1319. (m) Reinking, M. K.; Fanwick, P. E.; Kubiak, C. P.
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Compound 2 is also the middle member of the series
of compounds having the formula [MM′(CH3)(CO)3-
(dppm)2]+ (M, M′ ) Rh, Ir). The three compounds are
dramatically different, with only the mixed-metal ana-

1054 Organometallics, Vol. 15, No. 3, 1996
Antwi-Nsiah et al.
tBuNC did not occur,12 suggesting a subtle involvement
of the adjacent Rh center which somehow helps labilize
the Ir. Another possibility, of course, is that the reaction
dioxide is capable of reacting as an electrophile.53 It
may be, therefore, that initial attack by this group
occurs at the saturated Ir center. If so, this would
parallel earlier suggestions of electrophilic attack of
either H+ or CH3+ at the saturated metals in compound
1 (vide infra) and in a series of isoelectronic rhodium-
osmium compounds.7
t
of 2 with BuNC proceeds via methyl migration to Rh,
followed by migratory insertion and migration of the
resulting iminoacyl group back to Ir. However, we see
no evidence to support this latter suggestion.
In the reactions of 2 with C2H4 and tBuNC the
coordinatively unsaturated Rh center is presumed to be
the initial site of attack, although no species corre-
sponding to attack at this site was observed. In
preliminary studies involving the reaction of 2 with
PMe3, an intermediate, having the phosphine bound to
Rh, has been observed at low temperature,52 supporting
the proposal of initial attack at Rh. This study is
currently ongoing.
It is anticipated that further work on alkyl complexes
of these and related mixed-metal species will continue
to shed light on the involvement of the different metals
in the fundamental processes relevant to catalysis.
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. Dr. Robert
McDonald is acknowledged for assistance with the X-ray
crystallography, and Lai Kong is thanked for help in
obtaining some of the variable-temperature NMR spec-
tra.
The reaction of 2 with SO2 may differ from the
reactions with C2H4, tert-BuNC, and PMe3, since sulfur
(51) (a) Andersen, R. A.; Carmona-Guzman, E.; Gibson, J . F.;
Wilkinson, G. J . Chem. Soc., Dalton Trans. 1976, 2204. (b) Davies, J .
I.; Howard, C. G.; Skapski, A. C.; Wilkinson, G. J . Chem. Soc., Chem.
Commun. 1982, 1077. (c) Howard, C. G.; Wilkinson, G.; Thornton-Pett,
M.; Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1983, 2025. (d)
Howard, C. G.; Girolami, G. S.; Wilkinson, G.; Thornton-Pett, M.;
Hursthouse, M. B. Ibid. 1983, 2631. (e) Girolami, G. S.; Howard, C.
G.; Wilkinson, G.; Davies, H. M.; Thornton-Pett, M.; Motevalli, M.;
Hursthouse, M. B. Ibid. 1985, 921. (f) Edwards, P. G.; Felix, F.; Mertis,
K.; Wilkinson, G. J . Chem. Soc., Dalton Trans. 1979, 361. (g) Edwards,
P. G.; Mertis, K.; Wilkinson, G.; Hursthouse, M. B.; Malik, K. M. A.
Ibid. 1980, 334. (h) Mertis, K.; Edwards, P. G.; Wilkinson, G.; Malik,
K. M. A.; Hursthouse, M. B. Ibid. 1981, 705. (i) Masters, A. F.; Mertis,
K.; Gibson, J . F.; Wilkinson, G. Nouv. J . Chem. 1977, 1, 389.
(52) Oke, O.; Antwi-Nsiah, F. H.; Cowie, M. Unpublished observa-
tions.
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
and thermal parameters for the phenyl groups, anion atoms,
and solvent atoms, anisotropic thermal parameters, bond
lengths and angles within the phenyl groups, anion, and
solvent molecules, and hydrogen positional and thermal
parameters (15 pages). Ordering information is given on any
current masthead page.
OM9505874
(53) Reich-Rohrwig, P.; Clark, A. C.; Downs, R. L.; Wojcicki, A. J .
Organomet. Chem. 1978, 145, 57.