Reactions of the Binuclear Complexes [MIr(CO)3(Ph2PCH2PPh2)2] (M = Rh, Ir) with Alkyl Halides: Dramatic Reactivity Differences as a Function of Metal Combination and Alkyl Halide

Article abstract of DOI:10.1021/om990845n

Reactions of [Ir₂(CO)₃(dppm)₂] (1; dppm = Ph₂PCH₂PPh₂) with CH₃I and C_H3OCH₂I give the oxidative-addition products [Ir₂(R)(I)(CO)(μ-CO)(dppm)₂] (R = CH₃ (3), CH₂OCH₃ (4)). The X-ray structure determination of 4·CH₂Cl₂ shows that the alkyl group is the sole terminal ligand on one metal while the iodo and a carbonyl are terminally bound to the adjacent metal. The mixed-metal analogue [RhIr(CO)₃(dppm)₂] (2) does not react with CH₃I but reacts with CH₃OCH₂I to give [RhIr(CH₂OCH₃)(I)(CO)(μ-CO)(dppm)₂] (5). Reaction of 3 or 5 with methyl triflate results in iodide abstraction to yield the known compound [Ir₂(CH₃)(CO)(μ-CO)(dppm)₂][CF ₃SO₃] and [RhIr(CH₂OCH₃)(CO)(μ-CO)(dppm)₂][CF ₃SO₃] (8), respectively. In the mixed-metal compound iodide removal results in migration of the methoxymethyl group from Rh to Ir. Iodide abstraction from 4 results in a double C-H bond activation to yield the methoxycarbyne-bridged [Ir₂(H)₂(CO)₂(μ-COCH₃)(dppm) ₂][CF₃SO₃] (6). In the reactions of 4 and 5 with methyl triflate some methoxide abstraction also occurs, yielding the methylene-bridged products [MIr(CO)₂(μ-CH₂)(μ-I)(dppm)₂][CF ₃SO₃] (M = Ir (7), Rh (9)) as minor products in between 15 and 30% yield. The reactions of [MIr(CO)₃(dppm)₂] (M = Ir (1), Rh (2)) with CH₂I₂ and ICH₂CN yield [MIr(CO)₂(μ-I)(μ-CO)(Ph₂PCHPPh₂)(dppm)] (M = Ir (10), Rh (11)) together with CH₃I and CH₃CN, respectively, by hydrogen abstraction from one of the dppm ligands and iodine atom coordination at the metals. Reactions of 1 with allyl bromide and benzyl bromide yield the bromo analogue [Ir₂(CO)₂(μ-Br)(μ-CO)(Ph₂-PCHPPh ₂)(dppm)₂] (12). The X-ray structure of 10-THF has been determined and shows a planar Ir-P-C(H)-P-Ir moiety, short P-C bonds (1.72(2) A?), and a 122(1)° angle at carbon of the Ph₂PC(H)PPh₂ ligand, as expected for sp² hybridization and partial multiple-bond character in the P-C bonds.

Full text of DOI:10.1021/om990845n

854
Organometallics 2000, 19, 854-864
Rea ction s of th e Bin u clea r Com p lexes
[MIr (CO)3(P h 2P CH2P P h 2)2] (M ) Rh , Ir ) w ith Alk yl
Ha lid es: Dr a m a tic Rea ctivity Differ en ces a s a F u n ction
of Meta l Com bin a tion a n d Alk yl Ha lid e
J effrey R. Torkelson, Okemona Oke, J ohn Muritu, Robert McDonald,† and
Martin Cowie*,‡
Chemistry Department, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Received October 22, 1999
Reactions of [Ir2(CO)3(dppm)2] (1; dppm ) Ph2PCH2PPh2) with CH3I and CH3OCH2I give
the oxidative-addition products [Ir2(R)(I)(CO)(µ-CO)(dppm)2] (R ) CH3 (3), CH2OCH3 (4)).
The X-ray structure determination of 4‚CH2Cl2 shows that the alkyl group is the sole terminal
ligand on one metal while the iodo and a carbonyl are terminally bound to the adjacent
metal. The mixed-metal analogue [RhIr(CO)3(dppm)2] (2) does not react with CH3I but reacts
with CH3OCH2I to give [RhIr(CH2OCH3)(I)(CO)(µ-CO)(dppm)2] (5). Reaction of 3 or 5 with
methyl triflate results in iodide abstraction to yield the known compound [Ir2(CH3)(CO)(µ-
CO)(dppm)2][CF3SO3] and [RhIr(CH2OCH3)(CO)(µ-CO)(dppm)2][CF3SO3] (8), respectively. In
the mixed-metal compound iodide removal results in migration of the methoxymethyl group
from Rh to Ir. Iodide abstraction from 4 results in a double C-H bond activation to yield
the methoxycarbyne-bridged [Ir2(H)2(CO)2(µ-COCH3)(dppm)2][CF3SO3] (6). In the reactions
of 4 and 5 with methyl triflate some methoxide abstraction also occurs, yielding the
methylene-bridged products [MIr(CO)2(µ-CH2)(µ-I)(dppm)2][CF3SO3] (M ) Ir (7), Rh (9)) as
minor products in between 15 and 30% yield. The reactions of [MIr(CO)3(dppm)2] (M ) Ir
(1), Rh (2)) with CH2I2 and ICH2CN yield [MIr(CO)2(µ-I)(µ-CO)(Ph2PCHPPh2)(dppm)] (M )
Ir (10), Rh (11)) together with CH3I and CH3CN, respectively, by hydrogen abstraction from
one of the dppm ligands and iodine atom coordination at the metals. Reactions of 1 with
allyl bromide and benzyl bromide yield the bromo analogue [Ir2(CO)2(µ-Br)(µ-CO)(Ph2-
PCHPPh2)(dppm)2] (12). The X-ray structure of 10‚THF has been determined and shows a
planar Ir-P-C(H)-P-Ir moiety, short P-C bonds (1.72(2) Å), and a 122(1)° angle at carbon
of the Ph2PC(H)PPh2 ligand, as expected for sp2 hybridization and partial multiple-bond
character in the P-C bonds.
In tr od u ction
of binuclear alkyl complexes by the oxidative addition
of alkyl halides to binuclear diiridium and rhodium-
iridium complexes. Oxidative-addition reactions of alkyl
halides are of fundamental interest and have been much
studied, particularly in the case of low-valent, late
transition metals.2 Furthermore, the addition of methyl
iodide to late-metal complexes is of enormous practical
significance since it represents one of the key steps in
the industrial conversion of methanol into acetic acid.3-5
Although the majority of acetic acid production is based
on a rhodium-based catalyst,3-5 which has been identi-
fied as possibly the most successful example of an
industrial process catalyzed by a metal complex,5 BP
Chemicals has recently introduced a related iridium-
As part of an ongoing interest in the synthesis and
reactivity of binuclear complexes containing hydrocarbyl
fragments,1 we have initiated a study into the synthesis
* Corresponding author. Tel: +1 780-492-5581. Fax: +1 780-492-
8231.
† Faculty Service Officer, Structure Determination Laboratory.
‡ McCalla Research Professor, 1999-2000.
(1) See for example: (a) Sterenberg, B. T.; Hilts, R. W.; Moro, G.;
McDonald, R.; Cowie, M. J . Am. Chem. Soc. 1995, 117, 245. (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. (e) Antwi-Nsiah, F. H.; Oke, O.; Cowie, M.
Organometallics 1996, 15, 506. (f) Antwi-Nsiah, F. H.; Oke, O.; Cowie,
M. Organometallics 1996, 15, 1042. (g) George, D. S. A.; McDonald,
R.; Cowie, M. Can. J . Chem. 1996, 74, 2289. (h) Sterenberg, B. T.;
McDonald, R.; Cowie, M. Organometallics 1997, 16, 2297. (i) Antwi-
Nsiah, F. H.; Torkelson, J . R.; Cowie, M. Inorg. Chim. Acta 1997, 259,
213. (j) Torkelson, J . R.; McDonald, R.; Cowie, M. J . Am. Chem. Soc.
1998, 120, 4047. (k) George, D. S. A.; McDonald, R.; Cowie, M.
Organometallics 1998, 17, 2553. (l) Trepanier, S. J .; Sterenberg, B.
T.; McDonald, R.; Cowie, M. J . Am. Chem. Soc. 1999, 121, 2613. (m)
Torkelson, J . R.; Antwi-Nsiah, F. H.; McDonald, R.; Cowie, M.; Pruis,
J . G.; J alkanen, K. J .; DeKock, R. L. J . Am. Chem. Soc. 1999, 121,
3666. (n) Oke, O.; McDonald, R.; Cowie, M. Organometallics 1999, 18,
1624. (o) Graham, T. W.; VanGastel, F.; McDonald, R.; Cowie, M.
Organometallics 1999, 18, 2177. (p) Torkelson, J . R.; McDonald, R.;
Cowie, M. Organometallics 1999, 18, 4134.
(2) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; Chapter 5.
(3) (a) Paulik, F. E.; Roth, J . F. Chem. Commun. 1968, 1578. (b)
Roth, J . F.; Craddock, J . H.; Hershman, A.; Paulik, F. E. Chem.
Technol. 1971, 600. (c) Robinson, K. K.; Hershman, A.; Craddock, J .
H.; Roth, J . F. J . Catal. 1972, 27, 389. (d) Paulik, F. E.; Hershman,
A.; Knox, W. R.; Roth, J . F., Monsanto Company. US Pat. 3769329,
1973.
(4) Dekleva, T. W.; Forster, D. Adv. Catal. 1986, 34, 81.
(5) Maitlis, P. M.; Haynes, A.; Sunley, G. J .; Howard, M. J . J . Chem.
Soc., Dalton Trans. 1996, 2187.
10.1021/om990845n CCC: $19.00 © 2000 American Chemical Society
Publication on Web 01/29/2000

[MIr(CO)3(Ph2PCH2PPh2)2] (M ) Rh, Ir)
Organometallics, Vol. 19, No. 5, 2000 855
based catalyst system.6 Both systems continue to gener-
ate considerable interest.5,7,8
addition of the carbon-halide bond. We had shown that
the methyl complex [Ir2(CH3)(CO)2(dppm)2][CF3SO3]
underwent facile, and sometimes reversible, methyl
C-H bond cleavage upon addition of substrate mole-
cules,1j,m,p and we were interested in generating analo-
gous compounds in which one or more of the methyl
hydrogens were replaced by different substituents, to
determine the tendencies of these substituted methyl
groups to undergo C-H bond activation. Certainly a
recent study has suggested that C-H bond activation
should be enhanced by substituting a hydrogen by an
electron-withdrawing substituent.18
Although the initial interest in alkyl halide oxidative
additions concentrated on mononuclear complexes,2
there has been considerable subsequent interest in
multimetal systems, particularly binuclear ones.9-17
Even in a relatively simple binuclear complex the second
metal introduces additional reactivity possibilities, par-
ticularly if two different metals are involved. In homo-
binuclear systems, based for example on an Mn+/Mn+
core, the following reactivity patterns have been identi-
fied: (1) oxidative addition of one alkyl halide (RX) unit
to one metal to give an Mn+/M(n+2)+ product;12,13,14b (2)
addition of one RX unit across the dimetal framework
to give an M(n+1)+/M(n+1)+ core;9,10,14a,16a,b (3) addition of
In this study we report the reactions of [Ir2(CO)3-
(dppm)2] (1)19 and [RhIr(CO)3(dppm)2] (2)20 with various
alkyl halides.
two RX units (one to each metal) to give an M(n+2)+
M
/
Exp er im en ta l Section
(n+2)+ product;11,13,14b and (4) in the case in which the
Gen er a l Com m en ts. The compounds [Ir2(CO)3(dppm)2]19
and [RhIr(CO)3(dppm)2]20 were prepared as previously re-
ported. The elemental analyses attempted on purified samples
of a number of the diirdium compounds were unsatisfactory
due to some contamination by traces of the previously char-
acterized diiodo dicarbonyl species [Ir2(I)2(CO)(µ-CO)(dppm)2],21
the tricarbonyl iodide [Ir2(I)(CO)2(µ-CO)(dppm)2][I],21 or other
uncharacterized species that could not be removed. Charac-
terization for these compounds is based primarily on spectro-
scopic methods. The 31P{1H}, 13C{1H}, and 1H NMR and IR
spectroscopic data for all new compounds are given in Table
1.
organic substrate contains two C-X bonds, cleavage of
both C-X bonds to give an M(n+2)+/M(n+2)+ framework,
bridged by the resulting hydrocarbyl fragment.11,16c
In addition to the intrinsic interest in oxidative
addition to bimetallic frameworks, particularly those
having metals (Rh, Ir) used commercially in the acetic
acid synthesis, we also considered that addition of
substituted methyl halides (XCH2Y; X ) halide, Y )
substituent) could constitute a useful route to complexes
containing substituted methyl ligands, by oxidative
P r ep a r a tion of Com p ou n d s. (a ) [Ir 2(I)(CH3)(CO)(µ-
CO)(d p p m )2] (3). A 30 mg (0.025 mmol) sample of [Ir2(CO)3-
(dppm)2] (1) was dissolved in 20 mL of benzene, and 18.2 µL
(0.30 mmol) of CH3I was added. The mixture was stirred
overnight, resulting in a color change from orange to yellow.
The volume of benzene was reduced to about 2 mL, and the
yellow product precipitated by the slow addition of pentane.
Washing of the product by 10 mL of pentane and drying under
a slow stream of dinitrogen gave 24.3 mg of a mixture
consisting of 85% of 3 and 15% of the previously characterized
[Ir2(CO)2(µ-I)(µ-CO)(dppm)2][I].21 Recrystallization attempts
failed to separate these compounds, which were present in
every attempt to prepare 3, with the amount of impurity
ranging from 15 to 30% of the total product.
(6) Noted in: (a) Chem. Br. 1996, 32, 7. (b) Chem. Ind. (London)
1996, 483.
(7) (a) Haynes, A.; Mann, B. E.; Gulliver, D. J .; Morris, G. E.; Maitlis,
P. M. J . Am. Chem. Soc. 1991, 113, 8567. (b) Haynes, A.; Mann, B. E.;
Morris, G. E.; Maitlis, P. M. J . Am. Chem. Soc. 1993, 115, 4093. (c)
Ellis, P. R.; Pearson, J . M.; Haynes, A.; Adams, H.; Bailey, N. A.;
Maitlis, P. M. Organometallics 1994, 13, 3215. (d) Griffin, J . R.; Cook,
D. G.; Haynes, A.; Pearson, J . M.; Monti, D.; Morris, G. E. J . Am. Chem.
Soc. 1996, 118, 3029. (e) Baker, M. J .; Giles, M. F.; Orpen, A. G.; Taylor,
M. J .; Watt, R. J . J . Chem. Soc., Chem. Commun. 1995, 197. (f) Katti,
K. V.; Santarsiero, B. D.; Pinkerton, A. A.; Cavell, R. G. Inorg. Chem.
1993, 32, 5919. (g) Dilworth, J . R.; Miller, J . R.; Wheatley, N.; Baker,
M. J .; Sunley, J . G. J . Chem. Soc., Chem. Commun. 1995, 1579. (h)
Weston, W. S.; Gash, R. C.; Cole-Hamilton, D. J . J . Chem. Soc., Chem.
Commun. 1994, 745. (i) Simpson, M. C.; Payne, M. J .; Cole-Hamilton,
D. J . J . Chem. Soc., Dalton Trans. 1994, 2899. (j) Rankin, J .; Poole, A.
D.; Benyei, A. C.; Cole-Hamilton, D. J . J . Chem. Soc., Chem. Commun.
1997, 1835.
(b) Rea ction of 3 w ith Meth yl Tr ifla te. A 30 mg (0.023
mmol) sample of [Ir2I(CH3)(CO)2(dppm)2] (3) was dissolved in
10 mL of CH2Cl2, and 2.56 µL (0.023 mmol) of methyl triflate
was added via syringe, resulting in a color change from yellow
to red. The solution was stirred at ambient temperature for 1
h, after which the solvent volume was reduced to 1 mL and
the product precipitated by the slow addition of diethyl ether.
A red precipitate of the previously characterized [Ir2(CH3)(CO)-
(µ-CO)(dppm)2][CF3SO3]1m was identified by 31P{1H} and 1H
NMR spectra. Carrying out the reaction with the use of
[Ir2I(13CH3)(CO)2(dppm)2] (13C-3) and unlabeled methyl triflate
yielded [Ir2(13CH3)(CO)(µ-CO)(dppm)2][CF3SO3] and CH3I with
no 13C label incorporated into the iodomethane, whereas
reaction of unlabeled 3 with 13CH3OSO2CF3 resulted in no
13CH3 incorporation into the methyl complex, but formation
of 13CH3I, as identified by 13C{1H} NMR spectroscopy.
(c) [Ir 2(CH2OCH3)(I)(CO)(µ-CO)(d p p m )2] (4). Compound
1 (50 mg, 0.040 mmol) was dissolved in 10 mL of benzene, and
CH3OCH2I (3.6 µL, 0.040 mmol) was added by syringe.
(Caution: R-halo ether compounds are extremely toxic.) The
solution was stirred for 1 h, during which time the color
(8) (a) Pearson, J . M.; Haynes, A.; Morris, G. E.; Sunley, G. J .;
Maitlis, P. M. J . Chem. Soc., Chem. Commun. 1995, 1045. (b) Ghaffar,
T.; Adams, H.; Maitlis, P. M.; Sunley, G. J .; Baker, M. J .; Haynes, A.
Chem. Commun. 1998, 1023. (c) Haynes, A.; Pearson, J . M.; Vickers,
P. W.; Charmant, J . P. H.; Maitlis, P. M. Inorg. Chim. Acta 1998, 270,
382.
(9) Schmidbaur, H.; Franke, R. Inorg. Chim. Acta 1975, 13, 85.
(10) Fackler, J . P.; Basil, J . D. Organometallics 1982, 1, 871.
(11) Balch, A. L.; Hunt, C. T.; Lee, C.-L.; Olmstead, M. M.; Farr, J .
P. J . Am. Chem. Soc. 1981, 103, 3764.
(12) (a) Ling, S. S. M.; Puddephatt, R. J . J . Organomet. Chem. 1983,
255, C11. (b) Azam, K. A.; Brown, M. P.; Hill, R. H.; Puddephatt, R.
J .; Yavari, A. Organometallics 1984, 3, 7. (c) Ling, S. S. M.; J obe, I.
R.; Manojlovic´-Muir, L.; Muir, K. W.; Puddephatt, R. J . Organometal-
lics 1985, 4, 1198.
(13) Schenck, T. G.; Milne, C. R. C.; Sawyer, J . F.; Bosnich, B. Inorg.
Chem. 1985, 24, 2338.
(14) (a) Ciriano, M. A.; Viguri, F.; Oro, L. A.; Tiripicchio, A.;
Tiripicchio-Camellini, M. Angew. Chem., Int. Ed. Engl. 1987, 26, 444.
(b) Tejel, C.; Ciriano, M. A.; Edwards, A. J .; Lahoz, F. J .; Oro, L. A.
Organometallics 1997, 16, 45.
(15) Caspar, J . V.; Gray, H. B. J . Am. Chem. Soc. 1984, 106, 3029.
(16) (a) Coleman, A. W.; Eadie, D. T.; Stobart, S. R.; Zaworotko, M.
J .; Atwood, J . L. J . Am. Chem. Soc. 1982, 104, 922. (b) Atwood, J . L.;
Beveridge, K. A.; Bushnell, G. W.; Dixon, K. R.; Eadie, D. T.; Stobart,
S. R.; Zaworotko, M. J . Inorg. Chem. 1984, 23, 4050. (c) Brost, R. D.;
Stobart, S. R. J . Chem. Soc., Chem. Commun. 1989, 498. (d) Brost, R.
D.; Fjeldsted, D. O. K.; Stobart, S. R. J . Chem. Soc., Chem. Commun.
1989, 488. (e) Brost, R. D.; Stobart, S. R. Inorg. Chem. 1989, 28, 4309.
(17) (a) El Amane, M.; Maisonnat, A.; Dahan, F.; Prince, R.;
Poilblanc, R. Organometallics 1985, 4, 773. (b) He, X.; Maisonnat, A.;
Dahan, F.; Poilblanc, R. Organometallics 1991, 10, 2443.
(18) Sakaki, S.; Biswas, B.; Sugimoto, M. Organometallics 1998, 17,
1278.
(19) Sutherland, B. R.; Cowie, M. Organometallics 1985, 4, 1637.
(20) McDonald, R.; Cowie, M. Inorg. Chem. 1990, 29, 1564.
(21) Vaartstra, B. A.; Xiao, J .; J enkins, J . A.; Verhagen, R.; Cowie,
M. Organometallics 1991, 10, 2708.

856 Organometallics, Vol. 19, No. 5, 2000
Torkelson et al.
Ta ble 1. Sp ectr oscop ic Da ta for Com p ou n d s
NMRc,d
δ (1H)f,g
compound
IR cm-1 a,b
δ (31P{1H})e
δ (13C)g
2
[Ir2(CH3)(I)(CO)(µ-CO)-
(dppm)2] (3)
1977(s),
1815(m)
20.9(m), -7.4(m)
4.60(m, 2H), 4.40(m, 2H),
-0.40(t, 3H, J PH ) 8.0
197.6(tt, CO, J PC ) 9.1, 4.3 Hz),
3
2
175.2(t, CO, J PC ) 13.0 Hz), 17.5
2
Hz)
(t, CH3, J PC ) 6.3 Hz)
3
[Ir2(CH2OCH3)(I)(CO)-
(µ-CO)(dppm)2] (4)
[RhIr(CH2OCH3)(I)(CO)-
(µ-CO)(dppm)2] (5)
1936(vs),
1732(s)
1932(s),
18.6(m), -6.4(m)
4.48(b, 4H), 3.30(t, J PH
)
199.8(b, CO), 175.8(b, CO)
4.4 Hz, 2H), 1.95(s, 3H)h
4.42(m, 2H), 4.20(m, 2H),
1
1
2
30.8 (dm, J RhP
)
212.7(dm, J RhC ) 40.1 Hz, J CC
) 6.0 Hz, CO), 179.5(m, CO)
3
1745(s) 163.7 Hz), -3.8(m)
2.93(td, 2H, J PH ) 6.9
2
Hz, J RhH ) 2.8 Hz), 2.02
(s, 3H)
2
[Ir2(H)2(CO)2(µ-COCH3)-
(dppm)2][CF3SO3] (6)
1975(vs)
-2.1(m), -4.6(m),
5.05(s, 3H), 4.81(m, 1H),
4.08(m, 1H), 3.22(m, 1H),
-11.12(m, 1H), -11.20(m,
1H)i
4.43(m, 2H), 3.98(m, 2H),
2.58(b, 2H), 2.27(s, 3H)
316.6(tt, J PC ) 55, 4 Hz,
-14.3(m), -18.1(m)i
COCH3), 173.5(b, 2CO), 77.5(t,
4J PC ) 10 Hz, COCH3)i
1
[RhIr(CH2OCH3)(CO)-
(µ-CO)(dppm)2][CF3SO3]
(8)
[Ir2(CO)2(µ-I)(µ-CO)-
(Ph2PCHPPh2)(dppm)]
(10)
[RhIr(CO)2(µ-I)(µ-CO)-
(Ph2PCHPPh2)(dppm)]
(11)
22.2-20.6 (second-
order multiplet)
182.5(bs, CO), 177.7(dt, J RhC
71.3 Hz, CO)
)
2
1948(vs)
1801(s)
-1.4(m), -10.1(m)
4.60(m, 1H), 4.23(m, 1H),
2.07(tt, J PH ) 10.0, 3.5 Hz,
1H)
4.60(m, 1H), 4.41(m, 1H),
2.03(tt, J PH ) 7.0, 3.3 Hz,
1H)
194.4(tt, J PC ) 12.2, 4.9 Hz, CO),
183.2(m, 2CO)
1
1
1953(bs),
1823(m)
25.3(dm, J RhP ) 124.0
204.3(dm, J RhC ) 38.0 Hz, CO),
1
1
Hz), 15.7(dm, J RhP
114.0 Hz), -6.1(m),
-12.7(m)
)
195.2(d, J RhC ) 71.1 Hz, CO),
182.0(bs, CO)
a
b
IR abbreviations: vs ) very strong, s ) strong, m ) medium, w ) weak, sh ) shoulder, b ) broad. Nujol mull or CH2Cl2 cast unless
otherwise stated. c NMR abbreviations: s ) singlet, t ) triplet, m ) multiplet, q ) quintet, b ) broad. NMR data at 25 °C in CD2Cl2
d
unless otherwise stated. e 31P chemical shifts referenced to external 85% H3PO4. f Chemical shifts for the phenyl hydrogens are not given.
g 1H and 13C chemical shifts referenced to TMS. -40 °C. -80 °C.
h
i
changed from orange to yellow. The volume was reduced to
ca. 3 mL, and a bright yellow powder was precipitated with
addition of pentane. The isolated solid was washed (2 × 10
mL pentane) and dried under argon and then in vacuo. Yield:
86%. Anal. Calcd for Ir2IP4O3C54H49: C, 46.95; H, 3.58; I, 9.19.
Found: C, 46.65; H, 3.34; I, 10.16.
(d ) [Rh Ir (CH2OCH3)(I)(CO)(µ-CO)(d p p m )2] (5). To a
slurry of 45 mg (0.039 mmol) of [RhIr(CO)3(dppm)2] (2) in 3
mL of toluene was added CH3OCH2I (3.3 µL, 0.039 mmol), and
the resulting mixture was then stirred. The suspension dis-
solved within 0.5 h, and after 1.5 h of stirring, the color of the
solution turned yellow from orange. A 10 mL portion of
pentane was added, causing the precipitation of a yellow solid
(36 mg, 71%). Anal. Calcd for IrRhIP4O3C54H49: C, 50.10; H,
3.78; I, 9.82. Found: C, 49.97; H, 4.07; I, 10.65.
(e) [Ir 2(H)2(CO)2(µ-COCH3)(d p p m )2][CF 3SO3] (6). Com-
pound 4 (31 mg, 0.022 mmol) was dissolved in 10 mL of
benzene, and CH3SO3CF3 (2.5 µL 0.022 mmol) was added,
causing an immediate color change from yellow to light red.
The solution was stirred for 1 h, during which time the color
changed to dark yellow. The solvent volume was reduced to
ca. 3 mL, and a yellow solid was obtained by addition of
pentane. The isolated solid was washed (2 × 10 mL pentane)
and dried under argon and then in vacuo. Yield: 78%. The
compound [Ir2(CO)2(µ-I)(µ-CH2)(dppm)2][CF3SO3] (7)22 was also
produced in the reaction in ca. 15% yield, as determined by
31P{1H} NMR of a reaction carried out in an NMR tube. These
products could not be separated, so were characterized by
NMR techniques. The minor product (7) was identified based
on a comparison of the spectral data with that of the previously
characterized compound.22
gradually allowed to warm to ambient temperature, causing
a change in the color of the solution from yellow to purple.
NMR analysis carried out immediately indicated the presence
of 8 together with 20-30% of [RhIr(CO)2(µ-I)(µ-CH2)(dppm)2]-
[CF3SO3] (9)23 in solution. Our failure to separate these
products precluded elemental analysis. The use of trimethyl-
silylmethyl triflate in the reaction with 5 gave a product
distribution similar to that described above.
(g) [Ir 2(CO)2(µ-I)(µ-CO)(P h 2P CHP P h 2)(dppm )] (10). Com-
pound 1 (30 mg, 0.024 mmol) was dissolved in 6 mL of THF,
and CH2I2 (2.0 µL, 0.025 mmol) was added. The solution
changed color over 0.5 h from orange to yellow and was stirred
an additional 0.5 h. The solvent was then removed, and the
residue was dissolved in 2 mL of CH2Cl2 and cooled to 0 °C. A
flocculent yellow precipitate was obtained upon addition of 20
mL of a 50:50 mixture of Et2O/hexane. The precipitate was
washed with the Et2O/hexane mixture (2 × 10 mL) and dried
under argon and then in vacuo. Yield: 75%.
(h ) Rea ction of [Ir 2(CO)3(d p p m )2] w ith ICH2CN. Com-
pound 1 (43.6 mg, 0.035 mmol) was dissolved in 7 mL of
benzene, and ICH2CN (2.6 µL, 0.036 mmol) was added. The
solution was stirred for 10 min, during which time the color
changed from orange to yellow. The solvent was then reduced
to ca. 2 mL, and a bright yellow powder was obtained upon
addition of 10 mL of pentane. The precipitate was washed with
pentane (2 × 10 mL) and dried under argon and then in vacuo.
NMR spectra run on the isolated sample showed the produc-
tion of compound 10. CH3CN was detected in a 1H NMR
spectrum run on the crude reaction mixture.
(i) [Rh Ir (CO)2(µ-I)(µ-CO)(P h 2P CHP P h 2)(d p p m )] (11). A
39 mg (0.034 mmol) sample of compound 2 was dissolved in 5
mL of benzene, CH2I2 (2.7 µL, 0.034 mmol) was added, and
the mixture was stirred for 1 h, during which time the color
of the solution changed from orange to dull yellow. The solvent
was removed in vacuo, and recrystallization from benzene/
pentane afforded a yellow microcrystalline solid (28 mg, 64%).
(f) [Rh Ir (CH2OCH3)(CO)2(d p p m )2][CF 3SO3] (8). A 20 mg
(0.015 mmol) sample of [RhIr(CH2OCH3)(I)(CO)2(dppm)2] (5)
was dissolved in 0.5 mL of CD2Cl2 in an NMR tube at -78 °C.
Methyl triflate (1.8 µL, 0.015 mmol) was added; the mixture
was allowed to stand at this temperature for 0.5 h and then
(22) (a) Torkelson, J . R. Ph.D. Thesis, University of Alberta, 1998,
Chapter 5. (b) Torkelson, J . R.; Muritu, J .; McDonald, R.; Cowie, M.
(23) (a) Oke, O. Ph.D. Thesis, University of Alberta, 1999, Chapter
6. (b) Spectral parameters for compound 9: IR, ν(CO) 1958 cm-1; NMR,
1
Manuscript in preparation. (c) Spectral parameters for compound 7:
31P{1H} δ 21.5 (dm, J RhP ) 110.4 Hz), -5.8 (m); 1H δ 10.79 (qd, 2H),
3
1
IR, ν(CO) 1962 cm-1; NMR, 31P{1H} δ -7.9(s); 1H δ 10.01 (q, J PH
)
4.80 (m, 2H), 4.37 (m, 2H); 13C{1H} 191.9 (dt, J RhC ) 66.3 Hz, CO),
8.3 Hz, 2H), 5.02 (m, 2H), 4.19 (m, 2H).
183.5 (t, CO).

[MIr(CO)3(Ph2PCH2PPh2)2] (M ) Rh, Ir)
Organometallics, Vol. 19, No. 5, 2000 857
Ta ble 2. Cr ysta llogr a p h ic Da ta for Com p ou n d s 4 a n d 10
a
[Ir2(CH2OCH3)(I)(CO)(µ-CO) (dppm)2] (4)‚CH2Cl2
[Ir2(CO)2(µ-I)(µ-CO)(Ph2PCHPPh2)(dppm)](10)‚THF
a
formula
fw
C
54.7H50.25Cl2I1.15Ir2O2.85P4
C57H51IIr2O4P4
1435.16
1478.31
cryst dimens, mm
cryst syst
space group
a, Å
b, Å
c, Å
0.34 × 0.12 × 0.06
monoclinic
P21/c (No. 14)
20.0497 (9)
13.9589 (6)
20.9456 (8)
90.0
112.732 (3)
90.0
5406.7 (4)
4
0.42 × 0.24 × 0.03
triclinic
P1h (No. 2)
12.905 (2)
18.492 (3)
11.963 (2)
97.020 (14)
113.434 (12)
78.438 (12)
2563.5 (7)
2
R, deg
â, deg
γ, deg
V, Å3
Z
d
calcd, g cm-3
1.816
16.89
1.859
5.960
µ, mm-1
diffractometer
radiation (λ, Å)
Siemens P4/RAb
graphite-monochromated
Cu KR (1.54178)
-60
Enraf-Nonius CAD4c
graphite-monochromated
Mo KR (0.71073)
-50
T, °C
scan type
2θ (max), deg
no. of unique reflns
no. of observns
(NO)
θ-2θ
113.5
θ-2θ
50.0
7213
8964
2
2
5827 (Fo g 2σ(Fo2))
4784 (Fo g 2σ(Fo2))
range of abs corr
factors
0.4129-0.1633
1.255-0.844
residual density,
2.282 and -1.976
1.782 and -1.820
e/Å3
2
R1(Fo > 2σ(Fo2))d
0.0552
0.0725
0.0622
0.1784
wR2 (all data)
2
2
GOF(S)e
1.060 [Fo g -3σ(Fo2)]
1.015 [Fo g -3σ(Fo2)]
a
b
The sample crystallized as a mixture of 85% of compound 4 and 15% of [Ir2I2(CO)(µ-CO)(dppm)2]‚CH2Cl2. Programs for diffractometer
operation and data collection were those of the XSCANS system supplied by Siemens. c Programs for diffractometer operation and data
collection were those supplied by Enraf-Nonius. R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑w(Fo4)]1/2
.
e S ) [∑w(Fo - Fc2)2/(n -
d
2
2
p)]1/2 (n ) number of data; p ) number of parameters varied; w ) [σ2(Fo2) + (a0P)2 + a1P]-1 where P ) [max(Fo2, 0) + 2Fc2]/3). For 4 a0
) 0.0832, a1 ) 25.9490; for 10 a0 ) 0.0608, a1 ) 0.9018.
Microanalysis results for 11 were always low in percent carbon
and high in percent iodine due to the coproduction of between
15 and 25% of [RhIr(CO)2(µ-I)(µ-CO)(dppm)2][I]. A typical
result is given. Anal. Calcd for IrRhP8O3C53H43: C, 49.86; H,
3.37; I, 9.95. Found: C, 49.17; H, 3.34; I, 10.96.
structure. Absorption corrections to 10‚THF were applied by
the method of Walker and Stuart,24 whereas for 4‚CH2Cl2 the
crystal faces were indexed and measured, and an absorption
correction was carried out by Gaussian integration.
Str u ctu r e Solu tion a n d Refin em en t. For each structure,
the positions of the iridium and phosphorus atoms were found
using the direct-methods program SHELXS-86;25 the remain-
ing atoms were found using a succession of least-squares and
difference Fourier maps. Refinement of each structure pro-
ceeded using the program SHELXL-93.26 Hydrogen atom
positions were calculated by assuming idealized sp2 or sp3
geometries about their attached carbon atoms (as appropriate)
and were given thermal parameters 120% of the equivalent
isotropic displacement parameters of their attached carbons.
Further details of structure refinement (other than described
below) and final residual indices may be found in Table 2.
(j) Rea ction s of [Ir 2(CO)3(d p p m )2] w ith Ben zyl Br o-
m id e a n d Allyl Br om id e. A 30 mg (0.025 mmol) of [Ir2(CO)3-
(dppm)2] was dissolved in 0.6 mL of benzene-d6 in an NMR
tube, and 2.9 µL (0.025 mmol) of benzyl bromide (or 8.2 µL
(0.10 mmol) of allyl bromide) was added via syringe. In each
case the solution color changed from orange to yellow within
15 min. NMR spectroscopy showed three phosphine-containing
products in an approximate ratio 1:1:0.5. One species was
identified as [Ir2(CO)2(µ-Br)(µ-CO)(Ph2PCHPPh2)(dppm)] (12)
on the basis of its very similar NMR spectral parameters
compared to the iodo analogue 11. All attempts to separate
the three products failed, so compound 12 was never isolated
Although all of the non-hydrogen atoms of [Ir2(CH2OCH3)-
(I)(CO)(µ-CO)(dppm)2] (4)‚CH2Cl2 were located, the carbon and
oxygen atoms of the terminal methoxymethyl group (C(3),
O(3)) did not behave well in least-squares refinements. A
difference Fourier map at this stage located another peak near
C(3) and O(3), at approximately 2.7 Å from Ir(2). Successful
refinement of the structure was achieved by placing an iodide
in 15% occupancy at the peak site. The iodide ligand has
2
pure. NMR: 1H δ 4.72 (m, 1H), 4.32 (m, 1H), 2.10 (tt, J PH
)
4
8.0 Hz, J PH ) 4.3 Hz, 1H); 31P{1H} δ 5.5 (m), -5.0 (m).
X-r a y Da ta Collection . Crystals of each compound, suit-
able for X-ray diffraction, were grown via slow diffusion of
diethyl ether into a concentrated CH2Cl2 (4) or THF (10)
solution of the compound and were mounted and flame-sealed
in glass capillaries under solvent vapor to minimize decom-
position or deterioration due to solvent loss. For each com-
pound, three reflections were chosen as intensity standards
and were remeasured every 120 min of X-ray exposure time;
in no case was decay evident. Crystal parameters and details
of data collection are summarized in Table 2.
(24) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158-166.
(25) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(26) Sheldrick, G. M. SHELXL-93, Program for crystal structure
determination; University of Go¨ttingen, Germany, 1993. Refinement
2
2
on Fo for all reflections (all of these having Fo g -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 for negative Fo2. The
For compound 4‚CH2Cl2 the cell parameters and the sys-
tematic absences defined the space group as P21/c, whereas
for 10‚THF the cell parameters, the lack of absences, and the
diffraction symmetry suggested the space groups P1 or P1h, the
latter of which was established by successful refinement of 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 Fo are statistically about twice as large as those based on
2
2
Fo, and R-factors based on ALL data will be even larger.

858 Organometallics, Vol. 19, No. 5, 2000
Torkelson et al.
Sch em e 1
Sch em e 2
resulted from cocrystallization of the diiodo species [Ir2(I)2(CO)-
(µ-CO)(dppm)2],21 which frequently can be formed as a minor
impurity in the preparation of 4; its presence was confirmed
by NMR spectra of the dissolved crystals. Compound 4 and
[Ir2(I)2(CO)(µ-CO)(dppm)2] are isomorphous. The disorder was
resolved and all atoms were refined anisotropically, giving the
methoxy substituents (C(3), O(3), C(4)) an occupancy of 85%
and the iodide ligand (I(2)) an occupancy of 15%. All atoms
refined well, indicating that the two disordered molecules
superimpose almost exactly.
and producing the methoxymethyl iodide compound
[Ir2(CH2OCH3)(I)(CO)(µ-CO)(dppm)2] (4), as outlined in
Scheme 2. The 1H NMR spectrum of 4 at ambient
temperature shows the methylene protons of the meth-
oxymethyl ligand as a broad signal at δ 3.30, with the
methyl protons appearing as a singlet at δ 1.95. Cooling
the sample to -40 °C causes the broad methylene signal
to sharpen into a triplet, indicating terminal coordina-
tion on Ir, which is supported by selective 31P decoupling
experiments that show the methylene coupling to only
the phosphorus nuclei that give rise to the downfield
Location of all the atoms in compound 10 proceeded
smoothly.
Resu lts a n d Ch a r a cter iza tion of Com p ou n d s
The compound [Ir2(CO)3(dppm)2] (1) reacts with meth-
yl iodide, accompanied by carbonyl loss, to yield the
targeted oxidative-addition product [Ir2(CH3)(I)(CO)(µ-
CO)(dppm)2] (3), as shown in Scheme 1. Both the 13C-
{1H} and 1H NMR spectra show the methyl group
resonance as a triplet, indicating that it is terminally
bound to one iridium with coupling to the two adjacent
31P nuclei on this metal. Furthermore, the 13C{1H} NMR
data indicate that one carbonyl is terminally bound
while one is bridging. Although the available data do
not indicate the positioning of the iodo ligand, the
structure shown is proposed on the basis of the close
similarity in the 13C{1H} and 31P{1H} NMR spectra with
those of compound 4, the structure of which has been
determined (vide infra). Reaction of 3 with methyl
triflate leads to iodide abstraction (as methyl iodide) to
give the known compound [Ir2(CH3)(CO)(µ-CO)(dppm)2]-
[CF3SO3].1m The use of 13CH3-labeled methyl triflate
results in exclusive formation of 13CH3I and unlabeled
metal-containing product, indicating that the function
of the methyl triflate is merely to abstract the iodide
ion and that the original methyl group in 3 remains
coordinated to Ir. The use of silver salts to effect iodide
removal is not recommended with this series of com-
pounds, giving irreproducible mixtures of products. The
use of methyl triflate, on the other hand, works well,
as has been previously reported.1c,14b
1
signal in the 31P{1H} NMR spectrum. The H chemical
shifts observed correspond well to those observed for
other methoxymethyl compounds.27 At ambient tem-
perature the 31P{1H} NMR spectrum shows sharp
AA′BB′ signals at δ 18.6 and -6.4. The carbonyl bands
in the infrared spectrum appear at 1936 and 1732 cm-1
,
suggesting a terminal and bridging orientation, which
is supported by the carbonyl resonances in the 13C{1H}
NMR spectrum that appear as broad signals at δ 175.8
and 199.8, respectively. Confirmation of the proposed
structure for 4 in the solid state comes from the X-ray
structure determination, as shown in Figure 1. Selected
distances and angles are given in Table 3. This structure
is essentially identical to the previously characterized
diiodo compound [Ir2(I)2(CO)(µ-CO)(dppm)2],21 with one
of the iodo ligands being replaced by the methoxymethyl
ligand, and crystals of compound 4 are in fact contami-
nated with ca. 15% of this diiodo compound that is
isomorphous with the methoxymethyl species (see Ex-
perimental Section). As a result, the structure is disor-
dered, containing 85% of 4 with 15% of the superim-
posed diiodide. However, this disorder affected only the
superimposed methoxymethyl and iodo groups, which
refined well despite this disorder. The phosphines are
in a trans arrangement at each metal, with angles of
(27) (a) J olly, P. W.; Pettit, R. J . Am. Chem. Soc. 1966, 88, 5044. (b)
Brookhart, M.; Nelson, G. O. J . Am. Chem. Soc. 1977, 99, 6099. (c)
Brookhart, M.; Tucker, J . R.; Flood, T. C.; J ensen, J . J . Am. Chem.
Soc. 1980, 102, 1203. (d) Thorn, D. L.; Tulip, T. H. J . Am. Chem. Soc.
1981, 103, 5984. (e) Thorn, D. L. Organometallics 1982, 1, 879. (f)
Calabrese, J . C.; Roe, D. C.; Thorn, D. L.; Tulip, T. H. Organometallics
1984, 3, 1223.
Surprisingly perhaps, the mixed-metal analogue of 1,
namely, [RhIr(CO)3(dppm)2] (2), fails to react with CH3I
under the same conditions as noted for 1.
Compound 1 also reacts with the iodomethyl methyl
ether (CH3OCH2I) losing carbon monoxide in the process

[MIr(CO)3(Ph2PCH2PPh2)2] (M ) Rh, Ir)
Ta ble 3. Selected In ter a tom ic Dista n ces a n d An gles for Com p ou n d 4
(a) Distances (Å)
Organometallics, Vol. 19, No. 5, 2000 859
atom 1
atom 2
distance
atom 1
atom 2
distance
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(2)
Ir(2)
Ir(2)
I(1)
2.8527(7)
Ir(2)
Ir(2)
Ir(2)
O(1)
O(2)
O(3)
O(3)
P(4)
C(2)
C(3)
C(1)
C(2)
C(3)
C(4)
2.281(3)
1.924(12)
2.08(2)
1.13(2)
1.185(14)
1.39(2)
2.8025(10)
2.324(3)
2.328(3)
1.858(15)
2.061(13)
2.708(8)
2.299(3)
P(1)
P(3)
C(1)
C(2)
I(2)a
P(2)
1.37(2)
(b) Angles (deg)
atom 1
atom 2
atom 3
angle
atom 1
atom 2
atom 3
angle
Ir(2)
Ir(2)
Ir(2)
I(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(2)
Ir(2)
Ir(2)
I(1)
85.10(3)
154.6(4)
42.4(3)
120.3(4)
127.5(3)
173.86(10)
175.3(2)
46.2(4)
I(2)
Ir(2)
Ir(2)
Ir(2)
O(3)
C(1)
C(2)
C(2)
C(2)
C(3)
C(2)a
P(4)
C(3)
C(4)
O(1)
Ir(2)
O(2)
O(2)
O(3)
131.5(4)
167.54(11)
139.2(7)
112.8(15)
173.5(13)
91.4(5)
134.0(10)
134.6(10)
115.6(12)
C(1)
C(2)
C(1)
C(2)
P(3)
I(2)a
C(2)
C(3)
P(2)
C(2)
C(3)
Ir(1)
Ir(1)
Ir(1)
Ir(2)
Ir(2)
I(1)
P(1)
Ir(1)
Ir(1)
Ir(1)
174.4(6)
a
I(2) corresponds to the 15% superimposed [Ir2I2(CO)(µ-CO)(dppm)2] molecule that is disordered with compound 4.
Sch em e 3
F igu r e 1. Perspective view of [Ir2(CH2OCH3)(I)(CO)(µ-
CO)(dppm)2] (4). Thermal ellipsoids are shown at the 20%
probability level except for hydrogens, which are shown
artificially small. Phenyl hydrogens are omitted.
It is interesting that the carbonyls do not assume a
symmetrical arrangement with one on each metal as
found for trans-[IrCl(CO)(dppm)]2,28c but instead adopt
the unsymmetrical arrangement as observed for [Ir2-
(I)2(CO)(µ-CO)(dppm)2].21 Since this geometry does not
appear to be sterically driven, we assume that the
bridging carbonyl is necessary to make use of its better
π-accepting properties in this position.29
The mixed-metal analogue [RhIr(CO)3(dppm)2] (2)
also reacts with CH3OCH2I to give the oxidative-
addition product [RhIr(CH2OCH3)(I)(CO)(µ-CO)(dppm)2]
(5), which like the diiridium compound has also under-
gone loss of a carbonyl, as shown in Scheme 3. The
methoxymethyl group is bound to Rh, as shown in the
1H NMR spectrum, in which the methylene protons
appear as a triplet of doublets, with coupling to the two
173.9(1)° for P(1)-Ir(1)-P(3) and 167.5(1)° for P(2)-Ir-
(2)-P(4). The metal-metal separation of 2.8527(7) Å
corresponds to a normal Ir-Ir single bond.28 The car-
bonyls are mutually cis, with one in a terminal position
almost opposite the Ir-Ir bond and the other bridging
the two metals in an unsymmetrical fashion, being
slightly closer to Ir(2) than Ir(1) (1.92(1) vs 2.06(1) Å).
The iodo ligand of compound 4 is terminally bound to
the same metal as the terminal carbonyl and is on the
face opposite the bridging carbonyl. The methoxymethyl
group is the only terminal ligand on the adjacent metal,
falling opposite the metal-metal bond and having an
Ir(1)-Ir(2)-C(3) angle of 174.4(6)°, analogous to one of
the iodo groups in the diiodo species mentioned above.
(28) (a) Kubiak, C. P.; Woodcock, C.; Eisenberg, R. Inorg. Chem.
1980, 19, 2733. (b) Sutherland, B. R.; Cowie, M. Organometallics 1984,
3, 1869. (c) Sutherland, B. R.; Cowie, M. Inorg. Chem. 1984, 23, 2324.
(d) Sutherland, B. R.; Cowie, M. Organometallics 1985, 4, 1801. (e)
Xiao, J .; Cowie, M. Organometallics 1993, 12, 463.
(29) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; p 112.

860 Organometallics, Vol. 19, No. 5, 2000
Torkelson et al.
adjacent 31P nuclei (6.9 Hz) and to Rh (2.8 Hz). The
carbonyl region of the 13C{1H} NMR spectrum is similar
to that of 4, except for the 40 Hz coupling to Rh observed
for the bridging carbonyl in compound 5. A structure
for 5, much like that of 4, is therefore proposed.
phorus AB and CD signals that did not allow full
decoupling of one signal without affecting another.
Decoupling the high-field phosphorus resonances had
a larger effect on the hydride multiplet than decoupling
the low-field resonances, indicating a larger coupling of
the hydrides to the former. The two different couplings
are consistent with each hydride being trans to a similar
phosphorus nucleus, and therefore more strongly coupled
to them, and cis to the others, to which they display a
smaller coupling. Similar hydride signals have previ-
ously been observed for the cis-phosphine, silylene-
bridged dihydride complexes [Ir2(H)2(CO)2(µ-SiR2)-
(dppm)2].35 These silylene-bridged species contain
hydrides that have a trans-cis arrangement to the
dppm phosphines, and on the basis of spectral similari-
ties the structure shown in Scheme 2 is proposed for
compound 6.
Removal of the iodo ligands from 4 and 5, by addition
of methyl triflate, to yield the methoxymethyl analogues
of the methyl complexes [MIr(CH3)(CO)2(dppm)2][CF3-
SO3] (M ) Rh,1n Ir1m) has led to very different results.
Reaction of 4 with methyl triflate does result primarily
in iodide loss (as methyl iodide); however the anticipated
product was not obtained. Instead, iodide loss is ac-
companied by a double C-H activation of the meth-
oxymethyl ligand to give the methoxycarbyne-bridged
product [Ir2(H)2(CO)2(µ-COCH3)(dppm)2][CF3SO3] (6), as
shown in Scheme 2. Methyl triflate addition also
resulted in about 10-15% production of compound 7 (as
determined by 31P{1H} NMR) and dimethyl ether (by
1H NMR), through electrophilic attack at the methoxy
group (compound 7 has been previously characterized
and will be reported elsewhere).22 The 13C{1H} NMR
spectrum of compound 6 shows the characteristic car-
byne signal at low field (δ 316.6) as a pseudo triplet of
triplets (2J C-P ) 55, 4 Hz). Although this signal is at
slightly higher field than has been observed for meth-
oxycarbynes (δ 345-390),30-33 it falls into the range
typically observed for other carbyne signals (δ 200-
350).34 The larger P-C coupling constant indicates that
the carbyne is trans to one set of phosphines, while the
smaller value corresponds to cis coupling to the other
pair of phosphorus nuclei. At room temperature the 31P-
{1H} NMR spectrum for this compound shows broad
signals at δ -3.2 and -16.7, which sharpen upon cooling
to -80 °C, to a pattern consistent with an ABCD spin
system, having multiplets centered at δ -2.1, -4.6,
-14.3, and -18.1. Compound 6 is believed to have a
cis-phosphine orientation based on the large difference
in carbon-phosphorus coupling observed for the car-
byne carbon, the four multiplets observed for the phos-
phines at low temperatures, and the inequivalence of
1
The broadening of the 31P{1H} and H signals upon
warming suggests a fluxional process that averages the
four inequivalent phosphorus nuclei into two sets. The
fact that the three observed dppm methylene signals
do not change upon warming indicates that this flux-
ional process does not average the four inequivalent
methylene protons into two, further supporting the
proposed structure shown in Scheme 2, in which the
hydrides are eclipsed on adjacent metals. Such a process
can be rationalized by rotation of the methoxy group
around the C-OCH3 bond. The resonance representa-
tions of the bridging methoxycarbyne, shown below,
suggest partial π-character in the carbon-oxygen bond
that is presumed to be responsible for the hindered
rotation of the methoxy substituent that gives rise to
the limiting 31P{1H} and 1H NMR spectra at low
temperature. Note that in representation b, the orienta-
tion of the methyl group differentiates one Ir center from
the other, which together with the different 31P environ-
ments on each metal gives rise to four inequivalent 31P
environments. Rapid rotation about the C-O bond at
higher temperatures would give rise to only two 31P
environments and an AA′BB′ spin system. An identical
orientation of the bridging methoxycarbyne group was
observed in the solid-state structures of a related
diruthenium complex32 and an Ru3 cluster,31a and the
cluster complex also displayed fluxionality resulting
from restricted rotation about the carbyne-oxygen
bond. The partial C-O π-character proposed is also
supported by crystal structures of these methoxycar-
byne-bridged compounds,31a,32 in which the C-OMe
bond lengths of 1.245(7) and 1.299(8) Å were found to
be intermediate between a normal single and double
bond. Unfortunately we have not yet been able to
confirm the unusual structure proposed for 6 by X-ray
techniques owing to the failure to obtain X-ray quality
crystals.
1
the dppm protons that appear in the H NMR spectrum
as multiplets at δ 4.81, 4.08, 3.22, with the fourth signal
believed to be obscured by the phenyl protons. The
methyl group of the methoxy substituent appears at δ
5.05 as a singlet. At room temperature the 1H NMR
spectrum shows the hydrides as one broad and unre-
solved second-order multiplet, which sharpens into a
complex pattern at δ -11.16 upon cooling the sample
to -80 °C. Broad-band 31P decoupling resolves this
pattern into two broad singlets at δ -11.12 and -11.20.
1H NMR experiments with selective 31P decoupling were
attempted in order to elucidate the stereochemistry;
however these experiments were equivocal because of
the close proximity of the chemical shifts of the phos-
(30) (a) Hodali, H. A.; Shriver, D. F. Inorg. Chem. 1979, 18, 1236.
(b) Holt, E. M.; Whitmire, K. H.; Shriver, D. F. J . Organomet. Chem.
1981, 213, 125. (c) Kolis, J . W.; Basolo, F.; Shriver, D. F. J . Am. Chem.
Soc. 1982, 104, 5626. (d) Fong, R. H.; Hersh, W. H. Organometallics
1985, 4, 1468.
(31) (a) J ohnson, B. F. G.; Lewis, J .; Orpen, A. G.; Raithby, P. R.;
Suss, G. J . Organomet. Chem. 1979, 173, 187. (b) Gavens, P. D.; Mays,
M. J . J . Organomet. Chem. 1978, 162, 389.
(32) J ohnson, K. A.; Gladfelter, W. L. Organometallics 1990, 9, 2101.
(33) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Organo-
metallics 1999, 18, 634.
(34) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Apllications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; p 139.
Compound 6 is found to be rather unreactive. At-
tempts to convert the carbyne moiety into a carbene by
addition of nucleophiles gave no reaction; presumably,
the contribution from resonance structure b results in
(35) McDonald, R.; Cowie, M. Organometallics 1990, 9, 2468.

[MIr(CO)3(Ph2PCH2PPh2)2] (M ) Rh, Ir)
Organometallics, Vol. 19, No. 5, 2000 861
Sch em e 4
the carbyne carbon being less electrophilic. Similarly,
attempts to deprotonate one of the M-H moieties by
addition of base failed. Reaction of compound 6 with
trimethylsilyl triflate resulted in complete decomposi-
tion of the complex presumably by removal of the
methoxy group of the carbyne, leaving a highly reactive
“carbide” species, which reacted further. Attempts at
inducing reductive elimination of H2 from the complex
by refluxing in THF also left 6 unchanged.
The mixed-metal analogue [RhIr(CH2OCH3)(I)(CO)-
(µ-CO)(dppm)2] (5) reacts with methyl triflate in the
expected manner, resulting in loss of methyl iodide and
generation of the targeted methoxymethyl complex
[RhIr(CH2OCH3)(CO)(µ-CO)(dppm)2][CF3SO3] (8). As in
the reaction of the diiridium analogue, the analogous
methylene-bridged [RhIr(CO)2(µ-I)(µ-CH2)(dppm)2][CF3-
SO3] (9)23 was also obtained as a minor product (20-
30%) by abstraction of the methoxy group as dimethyl
ether. Both the 31P{1H} and 13C{1H} spectra of com-
pound 8 closely resemble those of the methyl analogue
[RhIr(CH3)(CO)(µ-CO)(dppm)2][CF3SO3];1n in particular
Ch a r t 1
1
the carbonyl resonances (δ 182.5(s), 177.7 (dt, J RhC
)
71 Hz)) differ from those of the methyl analogue by only
a couple of ppm. The lower field chemical shift of the
Ir-bound carbonyl, compared to that on Rh, suggests a
weak semibridging interaction of this group, although
the expected coupling to Rh is too small to be resolved.
In the methyl analogue, the semibridging carbonyl at δ
184.9 in the 13C{1H} NMR spectrum displayed a 7 Hz
coupling to Rh. Removal of the iodide ion is accompanied
by migration of the methoxymethyl group from Rh to
Ir.
larger coupling (129 vs 80 Hz) results from coupling
through the sp2 carbon of the methyne (PCHP) com-
pared to sp3 hybridization of the methylene carbon in
the PCH2P group. The derived coupling constants for
compounds 10 and 11 are summarized in Chart 1.
Confirmation of the proposed structure for 10 in the
solid state comes from the X-ray structure determina-
tion, a representation of which is shown in Figure 2,
with selected distances and angles given in Table 4. The
structure, having the iodo group on the face opposite
the bridging carbonyl, looks remarkably like the carbo-
nyl-bridged A-frames [Rh2(CO)2(µ-Cl)(µ-CO)(dppm)2]-
[BPh4],36 [Rh2(CO)2(µ-H)(µ-CO)(dppm)2][CH3C6H4SO3],37
[Ir2(CO)2(µ-S)(µ-CO)(dppm)2],28a and [Ir2(CO)2(µ-H)(µ-
CO)(dppm)2][BF4],38 apart from the subtle differences
resulting from hydrogen loss from one methylene unit
in the present compound. Loss of the hydrogen from C(4)
is clearly evident in a comparison of the geometry at
this atom compared with that at C(5). The P(1)-C(4)-
P(2) angle of 122.2(12)° for the Ph2PCHPPh2 group,
compared to the normal dppm angle of 112.7(10)° at
C(5), reflects the rehybridization of C(4) from sp3 to sp2.
Also consistent with the difference in rehybridization,
and the π-delocalization over the P(1)-C(4)-P(2) frag-
ment, are the shorter P-C bond lengths (P(1)-C(4) )
1.72(2) Å, P(2)-C(4) ) 1.72(2) Å vs P(3)-C(5) ) 1.82(2)
Å, P(4)-C(5) ) 1.81(2) Å). Bond lengths and angles of
the PCHP group compare well with those observed in
[Rh2(CO)2(µ-NHCH3)(Ph2PCHPPh2)(dppm)] that re-
sulted from deprotonation of one dppm group (P-C
Attempts to generate species containing either a
terminal iodomethyl group or a bridging methylene
group, through oxidative addition of a single C-I bond
or both C-I bonds of CH2I2, respectively, did not proceed
as anticipated in reactions of CH2I2 with either com-
pound 1 or 2. Instead, the compounds [MIr(CO)2(µ-I)-
(µ-CO)(Ph2PCHPPh2)(dppm)] (M ) Ir (10), Rh (11)),
resulting from hydrogen atom abstraction from one
dppm methylene group and iodine atom addition to the
metals, were obtained. In both cases the only organic
product observed was methyl iodide. Similarly, the
reactions of 1 and 2 with ICH2CN gave the same metal
complexes 10 and 11, together with acetonitrile, as
shown in Scheme 4. The NMR spectral data are very
similar for compounds 10 and 11, apart from the
appropriate Rh coupling observed for 11. For compound
10, three proton resonances, consistent with the loss of
1
one hydrogen, appear in the H NMR spectrum as two
multiplets at δ 4.60, 4.23 and a triplet of triplets at δ
2.07. The last signal is consistent with the methyne
hydrogen of the Ph2PCHPPh2 group, showing coupling
values of 10 and 3.5 Hz to phosphorus. The 31P{1H}
NMR spectrum of this compound differs from our usual
AA′BB′ spin systems due to the large coupling constants
(ca. 300 Hz) between the A and B phosphorus nuclei
owing to their trans alignment at the metals; in our
previous examples of AA′BB′ spin systems the PA and
PB nuclei are bound to different metals and are coupled
through the methylene unit with coupling constants of
ca. 80 Hz. The P-C-P coupling constants, obtained
from a simulation of the 31P{1H} NMR spectrum of 10,
are consistent with the formulation shown, in which the
(36) (a) Cowie, M.; Mague, J . T.; Sanger, A. R. J . Am. Chem. Soc.
1978, 100, 3628. (b) Cowie, M. Inorg. Chem. 1979, 18, 286.
(37) Kubiak, C. P.; Woodcock, C.; Eisenberg, R. Inorg. Chem. 1982,
21, 2119.

862 Organometallics, Vol. 19, No. 5, 2000
Torkelson et al.
Ta ble 4. Selected In ter a tom ic Dista n ces a n d An gles for Com p ou n d 10
(a) Distances (Å)
distance
atom 1
atom 2
atom 1
atom 2
distance
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(2)
Ir(2)
Ir(2)
Ir(2)
I
2.7828(11)
2.831(2)
2.352(5)
2.341(5)
1.85(2)
Ir(2)
Ir(2)
P(1)
P(2)
P(3)
P(4)
O(1)
O(2)
O(3)
C(2)
C(3)
C(4)
C(4)
C(5)
C(5)
C(1)
C(2)
C(3)
2.05(2)
1.84(2)
1.72(2)
1.72(2)
1.82(2)
1.81(2)
1.15(2)
1.18(2)
1.14(2)
P(1)
P(3)
C(1)
C(2)
I
2.04(2)
2.835(2)
2.351(5)
2.323(5)
P(2)
P(4)
(b) Angles (deg)
atom 1
atom 2
atom 3
angle
atom 1
atom 2
atom 3
angle
Ir(2)
Ir(2)
Ir(2)
I
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(1)
Ir(2)
Ir(2)
Ir(2)
Ir(2)
Ir(2)
Ir(2)
I
60.66(4)
165.2(7)
47.2(5)
134.1(7)
107.8(5)
173.1(2)
118.1(8)
60.51(4)
47.0(5)
165.1(6)
107.4(5)
134.4(6)
174.5(2)
C(2)
Ir(1)
Ir(1)
Ir(2)
Ir(1)
Ir(2)
Ir(1)
Ir(1)
Ir(1)
Ir(2)
Ir(2)
P(1)
P(3)
Ir(2)
I
C(3)
Ir(2)
C(4)
C(4)
C(5)
C(5)
O(1)
Ir(2)
O(2)
O(2)
O(3)
P(2)
P(4)
118.2(8)
58.83(3)
115.4(7)
115.2(7)
112.9(6)
112.2(6)
173.0(22)
85.9(7)
137.7(15)
136.3(15)
176.2(17)
122.2(12)
112.7(10)
C(1)
C(2)
C(1)
C(2)
P(3)
C(2)
I
C(2)
C(3)
C(2)
C(3)
P(4)
P(1)
P(2)
P(3)
P(4)
C(1)
C(2)
C(2)
C(2)
C(3)
C(4)
C(5)
I
P(1)
C(1)
Ir(1)
Ir(1)
Ir(1)
I
I
P(2)
In a preliminary attempt to probe the generality of
the assumed radical process that generates compounds
10 and 11, compound 1 was reacted under identical
conditions with allyl bromide and benzyl bromide. In
each case the same three products were obtained in the
approximate proportions 1:1:0.5. The 31P{1H} NMR
spectrum of the major product has resonances at δ 5.5
and -5.0 and appears very similar to that of 10, leading
us to propose that this product is [Ir2(CO)2(µ-Br)(µ-CO)-
(Ph2PCHPPh2)(dppm)] (12), the bromo analogue of 10.
Toluene has also been identified by 1H NMR in the
reaction of benzyl bromide, but propene could not be
detected in the allyl bromide reaction owing to the
excess of this reagent used. The other two metal-
containing products have not yet been identified.
Discu ssion
Oxid a tive Ad d ition s. Attempts to access binuclear
alkyl complexes involving the “Ir2(dppm)2” and the
“RhIr(dppm)2” frameworks, through oxidative addition
of alkyl halides to the respective low-valent metal
precursors, have succeeded with methyl iodide and
iodomethyl methyl ether, but have resulted in a number
of notable and unexpected failures, which will subse-
quently be discussed. The diiridium complex [Ir2(CO)3-
(dppm)2] (1) reacts readily with both CH3I and CH3-
OCH2I to give the targeted oxidative-addition products
[Ir2(R)(I)(CO)(µ-CO)(dppm)2] (R ) CH3 (3), CH2OCH3
(4)) (see Schemes 1 and 2), whereas the mixed-metal
RhIr analogue (2) reacts only with CH3OCH2I, yielding
[RhIr(CH2OCH3)(I)(CO)(µ-CO)(dppm)2] (5) (see Scheme
3). In all cases the structures of these oxidative-addition
products are essentially identical, having the alkyl
group on one metal and the iodo ligand on the other,
giving rise to M(+1)/Ir(+1) centers resulting from formal
oxidation of both metals. These compounds bear a
remarkable resemblance to the diiodo complexes [MIr-
(I)2(CO)(µ-CO)(dppm)2] (M ) Rh, Ir),21 which is not too
surprising since the methyl and iodo groups are thought
F igu r e 2. Perspective view of [Ir2(CO)2(µ-I)(µ-CO)(Ph2-
PCHPPh2)(dppm)] (10) in which only the ipso carbons of
the phenyl rings are shown. Thermal ellipsoids as for
Figure 1.
lengths of 1.738(8) and 1.736(8) Å; P-C-P angle of
119.3(4)°).39 Figure 2 clearly displays a nearly planar
arrangement of the Ir(1)-Ir(2)-P(2)-C(4)-P(1) ring
and can be compared to the Ir(1)-Ir(2)-P(4)-C(5)-P(3)
ring, in which the sp3-hybridized C(5) is distinctly out
of the plane of the other four atoms, as is normally
observed in dppm-bridged compounds.1 The planarity
in the case of the former presumably allows for more
favorable π-overlap with the p orbital of the PC(H)P
carbon.
Reaction of compounds 10 and 11 with HBF4‚OEt2
results in protonation at the CH group of the Ph2-
PCHPPh2 moiety, generating the previously character-
ized [MIr(CO)2(µ-I)(µ-CO)(dppm)2][BF4] (M ) Ir, Rh),21
and reaction of these cationic complexes with butyl-
lithium results in deprotonation of one dppm group to
regenerate 10 and 11.

[MIr(CO)3(Ph2PCH2PPh2)2] (M ) Rh, Ir)
Organometallics, Vol. 19, No. 5, 2000 863
to behave as electronically similar ligands40 and are also
sterically comparable.41 The failure of [RhIr(CO)3-
(dppm)2] (2) to react with CH3I is presumably due to
the lower nucleophilicity of Rh compared to Ir.42 Cer-
tainly the stability of the targeted [RhIr(CH3)(I)(CO)-
(µ-CO)(dppm)2] is not a problem, since this compound
has previously been synthesized by I- attack on [RhIr-
(CH3)(CO)(µ-CO)(dppm)2][CF3SO3].1n Iodide attack on
an intermediate, cationic methyl complex is generally
acknowledged as constituting the last step in the SN2
oxidative addition of CH3I to low-valent, late transition
metal complexes,2 suggesting that the unfavorable step,
resulting in the failure of 2 to react with methyl iodide,
is the initial nucleophilic attack. Substituting a hydro-
gen on methyl iodide by the electron-withdrawing
methoxy group43 to give ICH2OCH3 apparently in-
creases the electrophilicity of this alkyl halide group
enough to favor reaction with the RhIr precursor.
In mixed-metal alkyl complexes the tendency of the
alkyl fragment to bind to one metal or the other is a
significant variable, since the binding site has important
implications regarding the subsequent reactivity of this
alkyl fragment. In these RhIr compounds we observe
an interesting migration of the alkyl group from one
metal to the other, depending upon the presence or
absence of the iodide ligand. Although the alkyl group
in [RhIr(CH2OCH3)(I)(CO)(µ-CO)(dppm)2] (5) is bound
to Rh, removal of the iodo ligand is accompanied by
migration of the methoxymethyl fragment to Ir. This
behavior mirrors that observed previously in which I-
addition to [RhIr(CH3)(CO)(µ-CO)(dppm)2]+ caused the
methyl group to migrate from Ir to Rh.1n Whether the
alkyl group binds to one metal or the other is not a
straightforward question and appears dependent upon
a number of factors including metal-alkyl and metal-
ancillary ligand bond strengths. We have also previously
noted1p that for monocationic “Rh(+1)Ir(+1)X” com-
plexes the anionic (X) ligand is invariably bound to Ir,
leaving the positive charge on the less electronegative
Rh.44
the methoxy group by electrophiles has been reported27
and seemed a promising route to methylene-bridged
complexes; and second, we were interested in the effect
of substituents on the R-carbon of an alkyl group on the
tendency of this alkyl group to undergo C-H bond
cleavage. In the first case, the generation of the meth-
ylene-bridged complexes 7 and 9 as minor products in
the reactions of [MIr(CH2OCH3)(I)(CO)(µ-CO)(dppm)2]
(M ) Ir (4), Rh (5)) with methyl triflate clearly demon-
strates the potential for this strategy. However, these
reactions are not discussed further here since they form
part of another study on methylene-bridged binuclear
complexes.22,23 The second objective, to investigate the
effect of substituents on an alkyl ligand on its tendency
to undergo C-H bond cleavage, was initiated by reports
in which the reactivity of C-H bonds appeared to be
promoted by the introduction of electron-withdrawing
substituents on the R-carbon.18,45 However, even with
this latter goal in mind we were unprepared for the
dramatic difference observed between the methyl com-
plex 3 and its methoxymethyl analogue 4. Whereas
iodide removal from 3 generates the expected methyl
complex [Ir2(CH3)(CO)(µ-CO)(dppm)2]+, the equivalent
reaction with 4 is accompanied by C-H bond cleavage
involving both hydrogens on the R-carbon, to give the
methoxycarbyne-bridged dihydride 6 (see Scheme 2). As
previously noted, replacement of one Ir by Rh causes a
dramatic drop in reactivity such that iodide removal
from the RhIr analogue 5 yields the cationic methoxy-
methyl complex 8. We remain puzzled by the extreme
ease of the double C-H bond activation in the diiridium
system, and the scope of this promotion of reactivity by
adjacent substituents will be further probed by the
incorporation of different substituents. Presumably, one
factor favoring the methoxycarbyne-bridged product is
the resonance stability gained through π-delocalization
involving the methoxy group, as noted earlier.
Hyd r ogen Atom Abstr a ction . In view of the above-
noted promotion of C-H bond cleavage by incorporation
of electronegative substituents on the R-carbon, we
looked at the incorporation of CH2CN and CH2I groups
into the Ir2 and RhIr complexes through the oxidative
addition of ICH2CN and CH2I2, respectively, with
compounds 1 and 2. Although CH2I2 is known to
undergo a double-oxidative addition to binuclear com-
plexes, generating methylene-bridged products,11,16c it
is also known to add across only one C-I bond, generat-
ing CH2I species14a,15,16c of the type targeted. It was our
anticipation that the Ir2 complex might give rise to the
double-oxidative addition, whereas the less reactive
RhIr analogue might give the targeted CH2I product.
Surprisingly, both substrates ICH2CN and CH2I2 react
with both compounds 1 and 2 to give the respective
products [MIr(CO)2(µ-I)(µ-CO)(Ph2PCHPPh2)(dppm)] (M
) Ir (10), Rh (11)) together with CH3CN and CH3I.
Although these reactions appear to be free-radical
processes, we observe no inhibition by the addition of
the radical inhibitors duroquinone, hydroquinone, or
9,10-dihydroanthracene or by addition of the radical
The iodomethyl complex 3 can also be generated from
I- addition to the previously characterized [Ir2(CH3)-
(CO)(µ-CO)(dppm)2]+. In this context it is interesting
that the addition of a number of neutral substrates (CO,
SO2, PR3, CNR) to this methyl-containing species re-
sulted in cleavage of one methyl C-H bond, yielding
the corresponding methylene-bridged, hydrido products.1m
We find it curious that addition of the anionic group
(I-) does not also lead to C-H bond cleavage, but
instead leaves the methyl group intact.
C-H Bon d Clea va ge of t h e Met h oxym et h yl
Gr ou p . Our interest in the chemistry of the methoxy-
methyl ligand arose from two ideas: first, removal of
(38) Sutherland, B. R.; Cowie, M. Can. J . Chem. 1986, 64, 464.
(39) Sharp, P. R.; Ge, Y.-W. J . Am. Chem. Soc. 1987, 109, 3796.
(40) Atwood, J . D. Coord. Chem. Rev. 1988, 83, 93.
(41) van der Waals radii are as follows: I, 1.95-2.12 Å; CH3, 2.00
Å. See: Huheey, J . E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemis-
try: Principles of Structure and Reactivity, 4th ed.; Harper Collins
College Publishers: San Francisco, CA, 1993; Chapter 8.
(42) (a) Henderson, S.; Henderson, R. A. Adv. Phys. Org. Chem.
1987, 23, 1. (b) Ellis, P. R.; Pearson, J . M.; Haynes, A.; Adams, H.;
Bailey, N. A.; Maitlis, P. M. Organometallics 1994, 13, 3215.
(43) March, J . Advanced Organic Chemistry: Reactions, Mecha-
nisms, and Structure, 4th ed.; J ohn Wiley & Sons: New York, 1992;
Chapter 1.
(45) (a) Yamamoto, Y.; Al-Masum, M.; Asao, N. J . Am. Chem. Soc.
1994, 116, 6019. (b) Murahashi, S.-I.; Hirano, T.; Yano, T. J . Am. Chem.
Soc. 1978, 100, 348. (c) Murahashi, S.-I.; Watanabe, T. J . Am. Chem.
Soc. 1979, 101, 7429. (d) Murahashi, S.-I.; Naota, T.; Taki, H.; Mizuno,
M.; Takaya, H.; Komiya, S.; Mizuno, Y.; Oyasato, N.; Hiraoka, M.;
Hirano, M.; Fukuoka, A. J . Am. Chem. Soc. 1995, 117, 12436. (e)
Murahashi, S.-I.; Naota, T. Bull. Chem. Soc. J pn. 1996, 69, 1805.
(44) Little, E. J .; J ones, M. M. J . Chem. Educ. 1960, 37, 231.

864 Organometallics, Vol. 19, No. 5, 2000
Torkelson et al.
scavenger di-tert-butylnitroxide. Similarly, these reac-
tions appeared unaffected when carried out in the dark.
The participation of radical processes in the oxidative
additions of alkyl halides to Rh(I) and Ir(I) is well
documented,7c,46,47 and the failure of duroquinone to
affect such processes has been noted and has been
rationalized in terms of caged radical species.7c In the
present study the alkyl halides for which a radical
process appears to be involved (CH2I2, ICH2CN, CH2d
CHCH2Br, and C6H5CH2Br) are those known to give rise
to more stable radicals by virtue either of resonance
stabilization or of stabilization by electron-withdrawing
groups.48,49 Certainly, polyhalomethanes CHnX4-n are
known to display a greater tendency to undergo radical
processes than the monohalo counterparts,47b,49 in agree-
ment with our observation of a radical-induced process
involving CH2I2.
the deactivating effect of substituting one Ir by the less
nucleophilic Rh. Our goal of activating C-H bonds in
alkyl ligands by substituting an R-hydrogen by a meth-
oxy substituent has been an overwhelming (if unex-
pected) success. Therefore, removal of the iodo ligand
from 4 is accompanied by activation of both C-H bonds
on the R-carbon, yielding the methoxycarbyne-bridged
dihydride [Ir2(H)2(CO)2(µ-COMe)(dppm)2][CF3SO3] (6).
Subsequent attempts to investigate the tendencies of
the CH2I and CH2CN ligands to undergo similar C-H
bond cleavage have not succeeded, owing to our failure
to obtain the targeted [MIr(CH2Y)(I)(CO)2(dppm)2] (M
) Rh, Ir; Y ) I, CN) products by oxidative addition of
CH2I2 and ICH2CN to the [MIr(CO)3(dppm)2] (M ) Rh,
Ir) precursors. These alkyl iodides react with the
precursor complexes by a free-radical process, resulting
in the unexpected hydrogen abstraction from one dppm
ligand and iodine atom addition to the metals yielding
[MIr(CO)2)(µ-I)(µ-CO)(Ph2PCHPPh2)(dppm)]. Further
studies are underway to probe the fascinating promotion
of C-H bond activation by electron-withdrawing sub-
stituents, and other routes to the target products [MIr-
(CH2Y)(I)(CO)2(dppm)2] are under investigation.
Con clu sion s
Oxidative addition of CH3I and CH3OCH2I is shown
to be a useful route for the preparations of the binuclear
alkyl complexes [Ir2(R)(I)(CO)(µ-CO)(dppm)2] (R ) CH3
(3), CH2OCH3 (4)) and [RhIr(CH2OCH3)(I)(CO)(µ-CO)-
(dppm)2] (5). The failure of this method to generate the
analogous mixed-metal methyl compound by oxidative
addition of CH3I to [RhIr(CO)3(dppm)2] demonstrates
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 for scholarships (to J .R.T.), and
NSERC for funding of the P4/RA diffractometer.
(46) Collman, J . P.; Brauman, J . I.; Madonik, A. M. Organometallics
1986, 5, 310.
(47) (a) Labinger, J . A.; Osborn, J . A. Inorg. Chem. 1980, 19, 3230.
(b) Labinger, J . A.; Osborn, J . A.; Coville, N. J . Inorg. Chem. 1980, 19,
3236. (c) J ensen, F. R.; Knickel, B. J . Am. Chem. Soc. 1971, 93, 6339.
(48) March, J . Advanced Organic Chemistry: Reactions, Mecha-
nisms, and Structure, 4th ed.; J ohn Wiley & Sons: New York, 1992;
Chapter 5.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
experimental details, atomic coordinates, interatomic distances
and angles, anisotropic thermal parameters, and hydrogen
parameters for compounds 4 and 10. This material is available
free of charge via the Internet at http://pubs.acs.org.
(49) Menapace, L. W.; Kuivila, H. G. J . Am. Chem. Soc. 1964, 86,
3047.
OM990845N