Oxidative-addition of organic monochloro derivatives to dinuclear rhodium complexes: mechanistic considerations

Article abstract of DOI:10.1021/om0003133

The addition of RCH₂Cl to the complex [{Rh(μ-Pz)(CNBu^t)₂}₂] (Pz = pyrazolate, 1) occurs under mild conditions to yield the bis(alkyl)rhodium(III) complexes [{Rh(μ-Pz)(η¹-CH₂R)-(CNBu^t)₂}₂ (μ-Cl)]Cl (R = Ph, CHqqCH₂, CO₂Me, COMe). These reactions proceed through two separate steps, as evidenced by the observation of the intermediate mixed-valence complex [(CNBu^t)₂Rh^I(μ-Pz)₂Rh^III (η¹-CH₂Ph)(Cl)(CNBu^t)₂] resulting from the trans-addition of PhCH₂Cl at a single metal center in 1. Similar Rh(I)-Rh(III) complexes [(cod)Rh(μ-Pz)₂Rh(η¹-CH₂R)(Cl) (CNBu^t)₂] (R = Ph (7), CHqqCH₂, CO₂Me) result from the addition of RCH₂Cl to the mixed-ligand complex [(cod)Rh(μ-Pz)₂Rh(CNBu^t)₂] (6). These exist in benzene and toluene as two interconverting conformers, differentiated by the location of the RCH₂ group either between the two metals in the pocket of the complexes (endo conformer) or at the trans position (exo conformer). An intramolecular boat-to-boat inversion accounts for this exchange. The thermodynamic parameters for complex 7 were ΔH^? = 16.2 kcal·mol^-1, ΔS^? = 4.9 eu, and ΔG₂₉₃^? = 14.9 kcal·mol^-1. Primary alkyl bromides RCH₂Br react with 1 and with 6 to give the Rh(III) complexes [{Rh(μ-Pz)(η¹-CH₂R)(CNBu^t)₂}₂ (μ-Br)]Br (R = Ph, CO₂Me) and the mixed-valence complex [(cod)Rh(μ-Pz)₂(η¹-CH₂Ph)(Br) (CNBu^t)₂]. However, the secondary alkyl bromide PhCH(Me)Br reacts with 1 and with 6 to give the dirhodium(II) complexes [LFBCRh(μ-Pz)(Br)(CNBu^t)₂}₂] and [(cod)(Br)Rh(μ-Pz)₂Rh(Br)(CNBu^t)₂], respectively, along with 2,3-diphenylbutane and traces of styrene and ethylbenzene, suggesting free-radical pathways for these reactions. The thermal decomposition of the bis(alkyl)chloro complexes gives free isobutene and the cyanide complexes [(CNBu^t)₂(η¹-CH₂R)Rh(μ-Pz)₂(μ-Cl)Rh (η¹-CH₂R)(CN)(CNBu^t)] (R = Ph, COMe, CO₂Me). Decomposition of the bis(alkyl)bromo derivatives occurs under sunlight irradiation and anaerobic conditions to give bibenzyl, cis- and trans-stilbene, and toluene.

Full text of DOI:10.1021/om0003133

4968
Organometallics 2000, 19, 4968-4976
Oxid a tive-Ad d ition of Or ga n ic Mon och lor o Der iva tives
to Din u clea r Rh od iu m Com p lexes: Mech a n istic
Con sid er a tion s
Cristina Tejel, Miguel A. Ciriano,* Andrew J . Edwards, Fernando J . Lahoz, and
Luis A. Oro*
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain
Received April 13, 2000
The addition of RCH2Cl to the complex [{Rh(µ-Pz)(CNBut)2}2] (Pz ) pyrazolate, 1) occurs
under mild conditions to yield the bis(alkyl)rhodium(III) complexes [{Rh(µ-Pz)(η1-CH2R)-
(CNBut)2}2(µ-Cl)]Cl (R ) Ph, CHdCH2, CO2Me, COMe). These reactions proceed through
two separate steps, as evidenced by the observation of the intermediate mixed-valence
complex [(CNBut)2RhI(µ-Pz)2RhIII(η1-CH2Ph)(Cl)(CNBut)2] resulting from the trans-addition
of PhCH2Cl at a single metal center in 1. Similar Rh(I)-Rh(III) complexes [(cod)Rh(µ-Pz)2Rh-
(η1-CH2R)(Cl)(CNBut)2] (R ) Ph (7), CHdCH2, CO2Me) result from the addition of RCH2Cl
to the mixed-ligand complex [(cod)Rh(µ-Pz)2Rh(CNBut)2] (6). These exist in benzene and
toluene as two interconverting conformers, differentiated by the location of the RCH2 group
either between the two metals in the pocket of the complexes (endo conformer) or at the
trans position (exo conformer). An intramolecular boat-to-boat inversion accounts for this
exchange. The thermodynamic parameters for complex 7 were ∆Hq ) 16.2 kcal‚mol-1, ∆Sq
q
) 4.9 eu, and ∆G293 ) 14.9 kcal‚mol-1. Primary alkyl bromides RCH2Br react with 1 and
with 6 to give the Rh(III) complexes [{Rh(µ-Pz)(η1-CH2R)(CNBut)2}2(µ-Br)]Br (R ) Ph, CO2-
Me) and the mixed-valence complex [(cod)Rh(µ-Pz)2Rh(η1-CH2Ph)(Br)(CNBut)2]. However,
the secondary alkyl bromide PhCH(Me)Br reacts with 1 and with 6 to give the dirhodium-
(II) complexes [{Rh(µ-Pz)(Br)(CNBut)2}2] and [(cod)(Br)Rh(µ-Pz)2Rh(Br)(CNBut)2], respec-
tively, along with 2,3-diphenylbutane and traces of styrene and ethylbenzene, suggesting
free-radical pathways for these reactions. The thermal decomposition of the bis(alkyl)chloro
complexes gives free isobutene and the cyanide complexes [(CNBut)2(η1-CH2R)Rh(µ-Pz)2(µ-
Cl)Rh(η1-CH2R)(CN)(CNBut)] (R ) Ph, COMe, CO2Me). Decomposition of the bis(alkyl)bromo
derivatives occurs under sunlight irradiation and anaerobic conditions to give bibenzyl, cis-
and trans-stilbene, and toluene.
In tr od u ction
are less common by far. A few mononuclear complexes
are capable of cleaving alkyl C-Cl bonds by a conven-
tional two-fragment, two-electron oxidative-addition
reaction. Some examples are phosphino complexes of
palladium,8 platinum,9 and rhodium10 in low-oxidation
state, cyclometalated complexes of platinum,11b and
cyclopentadienyl derivatives of iridium.12
The oxidative-addition of alkyl halides to metal
complexes is a general synthetic method for metal-
carbon σ bonds.1 Most of the reported studies deal with
alkyl iodides and bromides and rhodium,2 iridium,3
palladium,4 platinum,5 and gold6 complexes. In particu-
lar, the addition of MeI to carbonyl rhodium complexes
has been studied with mechanistic detail, since it is the
key step in the catalyzed carbonylation of methanol on
an industrial scale.7 However, oxidative-addition reac-
tions of the less reactive alkyl chlorides to metal centers
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10.1021/om0003133 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 10/26/2000

Addition of Monochloro Derivatives to Rh Complexes
Organometallics, Vol. 19, No. 24, 2000 4969
Sch em e 1. Rea ction s of th e Com p lexes 1 a n d 6, Sh ow in g th e P r op osed In ter m ed ia tes A a n d B, a n d th e
Equ ilibr ia betw een Con for m er s
There is a no clear picture of the mechanism of the
oxidative-addition of C-X bonds to metal complexes,
since several pathways seem to be operative: an SN2
mechanism,1c,11 a concerted cis-addition, in which the
metal inserts into the C-X bond,2e and mechanisms
involving free alkyl radical intermediates.13 In particu-
lar, paramagnetic organometallic intermediates have
been detected in reactions of anionic iron(0) complexes
with organic halides,14 and halogen abstraction from RX
by a metal-centered radical has been reported.15 How-
ever, recent theoretical studies of the oxidative-addition
of MeX (X ) Cl, I) to Pd, Rh, and Ir complexes suggest
that the preferred pathway is SN2, either frontside16 or
backside.17 Moreover, kinetic studies on the oxidative-
addition of a wide range of alkyl halides to a Rh(I)
complex suggest a general SN2-like mechanism.18
and a thermal addition of dichloromethane to dinuclear
rhodium complexes with P-donor ligands has been
recently reported.21 The general picture to date is that
highly nucleophilic metal centers are required to over-
come the relative inertness of the C-Cl bond toward
reactions with metal complexes. An additional feature
shown by dinuclear complexes is that cooperative effects
between the metal center may facilitate C-Cl activa-
tions.22 In this paper we focus our attention on the four-
electron oxidative-addition reactions of monohaloalkyl
compounds to dinuclear rhodium complexes.
Resu lts a n d Discu ssion
Rea ction s w ith Alk yl Ch lor id es. The dinuclear
complex [{Rh(µ-Pz)(CNBut)2}2] (Pz ) pyrazolate, 1) adds
a variety of alkyl monochloro derivatives (RCH2Cl)
under very mild conditions in the dark to give [{Rh(µ-
Pz)(η1-CH2R)(CNBut)2}2(µ-Cl)]Cl (R ) Ph (2); CHdCH2
(3); CO2Me (4); COMe (5)) in high isolated yield (Scheme
1). Noteworthy, complexes 2-5 were obtained as a
single stereoisomer. The C2v symmetry of this stereoi-
somer, deduced from the NMR spectra, is consistent
with a structure formed by two face-sharing octahedra
with two pyrazolate and one chloride bridging ligand.
Moreover, the proximity between the methlylene group
and the H3,5 protons of the pyrazolate ligands is
unambiguously detected through NOE experiments.
The above addition reactions, completed in a few
minutes, involve the oxidation of both metallic centers.
Direct evidence that the reactions occur in two separate
steps was provided by monitoring the reaction of PhCH2-
Regarding the chemistry of dinuclear complexes,
photoinduced C-Cl activation reactions have been
reported for dinuclear gold19 and iridium20 complexes,
(8) (a) Machnitzki, P.; Stelzer, O.; Sheldrick, W. S.; Landgrafe, C.
J . Organomet. Chem. 1998, 554, 207. (b) Leoni, P. Organometallics
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K.; Priermeier, T.; Scherer, W. J . Organomet. Chem. 1993, 461, 51.
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(9) Ghilardi, C. A.; Midollini, S.; Moneti, S.; Orlandini, A.; Scapacci,
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H. F.; Ernsting, J . M.; Kranenburg, M.; Kooijman, H.; Vedman, N.;
Spek, A. L.; van Leeuwen, P. W. N. M.; Vrieze, K. Organometallics
1997, 16, 887, and references therein. (c) Nishiyama, H.; Horihata,
M.; Hirai, T.; Wakamatsu, S.; Itoh, K. Organometallics 1991, 10, 2706.
(d) Fennis, P. J .; Budzelaar, P. H. M.; Frijns, J . H. G.; Orpen, A. G. J .
Organomet. Chem. 1990, 393, 287. (e) Yoshida, T.; Adachi, T.; Ueda,
T. Pure Appl. Chem. 1990, 62, 1127. (f) Marder, T. B.; Fultz, W. C.;
Calabrese, J . C.; Harlow, R. L.; Milstein, D. J . Chem. Soc., Chem.
Commun. 1987, 1543. (g) Burns, E. G.; Chu, S. S. C.; de Meester, P.;
Lattman, M. Organometallics 1986, 5, 2383.
1
Cl with 1 by H NMR. On mixing equimolar amounts
of 1 and PhCH2Cl, one could observe the intermediate
A (Scheme 1), which was found to be the mixed-valence
(11) (a) Oro, L. A.; Sola, E.; Lo´pez, J . A.; Torres, F.; Elduque, A.;
Lahoz, F. J . Inorg. Chem. Commun. 1998, 1, 64. (b) von Zelewsky, A.;
Suckling, A. P.; Stoeckli-Evans, H. Inorg. Chem. 1993, 32, 4585.
(12) Le Bras, J .; Amouri, H.; Vaissermann, J . J . Organomet. Chem.
1997, 548, 305.
(13) (a) Hall, T. L.; Lappert, M. F.; Lednor, P. W. J . Chem. Soc.,
Dalton Trans. 1980, 1448. (b) Labinger, J . A.; Osborn, J . A.; Coville,
N. J . Inorg. Chem. 1980, 19, 3236.
(19) Li, D.; Che, C.-M.; Kwong, H.-L.; Yam, V. W.-W. J . Chem. Soc.,
Dalton Trans. 1992, 3325.
(20) (a) Ciriano, M. A.; Pe´rez-Torrente, J .; Oro, L. A. J . Organomet.
Chem. 1993, 445, 273. (b) Caspar, J . V.; Gray, H. B. J . Am. Chem.
Soc. 1984, 106, 3029.
(21) (a) Brunet, J .-J .; Couillens, X.; Daran, J .-C.; Diallo, O.; Lepetit,
C.; Neibecker, D. Eur. J . Inorg. Chem. 1998, 349. (b) Ball, G. E.; Cullen,
W. R.; Fryzuk, M. D.; J ames, B. R.; Rettig, S. J . Organometallics 1991,
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(14) Hill, D. H.; Parvaez, M. A.; Sen, A. J . Am. Chem. Soc. 1994,
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(15) Huber, T. A.; Macartney, D. H.; Baird, M. C. Organometallics
1993, 12, 4715.
(16) Bickelhaupt, F. M.; Ziegler, T.; Schleyer, P. V. R. Organome-
tallics 1995, 14, 2288.
(17) Griffin, T. R.; Cook, D. B.; Haynes, A.; Pearson, J . M.; Monti,
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(18) Collman, J . P.; Brauman, J . I.; Madonik, A. M. Organometallics
1986, 5, 310.
(22) (a) Tejel, C.; Ciriano, M. A.; Lo´pez, J . A.; Lahoz, F. J .; Oro, L.
A. Organometallics 1998, 17, 1449. (b) Sola, E.; Bakhmutov, V. I.;
Torres, F.; Elduque, A.; Lo´pez, J . A.; Lahoz, F. J .; Werner, H.; Oro, L.
A. Organometallics 1998, 17, 683. (c) Oro, L. A.; Ciriano, M. A.; Tejel.
C. Pure Appl. Chem. 1998, 70, 779. (d) Tejel, C.; Ciriano, M. A.; Oro,
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1992, 2123.

4970 Organometallics, Vol. 19, No. 24, 2000
Tejel et al.
F igu r e 1. Selected regions of the 1H NMR spectrum in
C6D6 from the reaction mixture of [{Rh(µ-Pz)(CNBut)2}2]
(1) with PhCH2Cl showing resonances for 1 (O), [{Rh(µ-
Pz)(η1-CH2Ph)(CNBut)2}2(µ-Cl)]Cl (b), the intermediate
[(CNBut)2RhI(µ-Pz)2RhIII(η1-CH2Ph)(Cl)(CNBut)2] (*), and
PhCH2Cl ()).
complex [(CNBut)2RhI(µ-Pz)2RhIII(η1-CH2Ph)(Cl)(CNBut)2]
resulting from the trans-addition of the chloroalkane to
a single metal center. Characterization of A relies on
the Cs symmetry of the complex, shown by the 1H NMR
spectrum (Figure 1), the unusually low chemical shift
for the methylene group (at δ ) 5.76), the lack of NOE
between the Pz and the CH2Ph protons since they are
distant, and its preparation through a different route
(vide infra). Addition of 1 molar equiv of PhCH2Cl to
[(CNBut)2RhI(µ-Pz)2RhIII(η1-CH2Ph)(Cl)(CNBut)2] in the
NMR tube gave quantitatively 2.
Further evidence for this stepwise addition involving
single metal centers comes from such additions to the
mixed-ligand complex [(cod)Rh(µ-Pz)2Rh(CNBut)2] (6),
which contains a less active “Rh(cod)” moiety. Complex
6 reacted with equimolar amounts of RCH2Cl to give
the neutral mixed-valence complexes [(cod)Rh(µ-Pz)2Rh-
(η1-CH2R)(Cl)(CNBut)2] (R ) Ph (7); CHdCH2 (8); CO2-
Me (9)). These reactions involve the addition of the
RCH2Cl at the more nucleophilic rhodium atom with
isocyanide ligands, confirmed by the shift of ν(CN) by
ca. 115 cm-1 to higher frequencies, while the chemical
shifts and coupling constants of the cod ligand in the
13C{1H} NMR spectra remained similar to those found
in 6.
Con for m a tion a l Equ ilibr ia for Mixed -Va len ce
Rh (I)-Rh (III) Com p lexes. Complexes 7-9 exist as an
apparently single species in acetone-d6 and CDCl3
solution. NOE experiments at low temperature in CDCl3
(Figure 2) conclusively established that the RCH2 group
is inside the pocket (endo position) of the complexes 7-9.
However, they exist as a mixture of two species in C6D6.
Both species have an identical formulation by NMR,
possess a symmetry plane between the two pyrazolate
ligands, and are mixed-valence Rh(I)-Rh(III) com-
plexes, judging from the 13C{1H} NMR chemical shifts
and coupling constants of the cod carbons. The unique
difference between them is the location of the alkyl
group on the octahedral rhodium center; the species A1
contain the RCH2 group at the endo position, while it
is placed at the exo position in the species B1 (Scheme
1). Thus, the A1 species give NOE results in toluene-d8
at low temperature similar to those described for the
solutions in CDCl3, while the B1 species show an
F igu r e 2. NOE difference spectra in CDCl3 at -50 °C of
[(cod)Rh(µ-Pz)2Rh(η1-CH2CHdCH2)(Cl)(CNBut)2] (8) on ir-
radiation at (a) the -CH2 group, (b) H5, (c) normal
spectrum.
enhancement of the H3 protons of the Pz ligands only
upon irradiation of the RCH2 group. Therefore, the
mixed-valence Rh(I)-Rh(III) complexes 7-9 exist in
benzene and toluene solution as the endo and exo
conformers (A1 and B1), respectively. The species A1
and B1 interconvert, which produced line broadening
in the NMR spectra in benzene at room temperature.
Accordingly, the coalescence of all pairs of resonances
and a full picture for the exchange were observed on
raising the temperature.
The activation parameters for this process, ∆Hq
)
16.2 kcal‚mol-1, ∆Sq ) 4.9 eu, and ∆G293 ) 14.9
kcal‚mol-1, were obtained from the line shape analysis23
of the variable-temperature 1H NMR spectra of complex
7 in toluene-d8 (Figure 3). The small value of ∆Sq along
with the lack of line broadening effects upon dilution
corroborates the intramolecular nature of the process.
In addition, these parameters are similar to those
found24 for the boat-boat inversion of the “Rh(N-
N)2Rh” six-membered ring undergone by the precursor
6. All these data provide evidence that the interconver-
sion A1/B1 proceeds through such a process. The exo
conformers of 7-9 and complexes 2-5 show the chemi-
cal shifts of the CH2 protons at high field at ca. 3-4
ppm, while it is at low field at ca. 6 ppm for the endo
conformers. Thus, the chemical shift is a good diagnostic
parameter to distinguish between these positions.
Addition of 2 molar equiv of CNBut to complex 7
resulted in the replacement of cod to give the complex
[(CNBut)2Rh(µ-Pz)2Rh(η1-CH2Ph)(Cl)(CNBut)2] (A). Al-
though the endo and exo conformers were formed at the
q
(23) Budzelaar, P. H. M. gNMR Software version 3.6; Cherwell
Scientific Publ. Ltd.: Oxford, U.K., 1995.
(24) Tejel, C.; Villoro, J . M.; Ciriano, M. A.; Lo´pez, J . A.; Eguiza´bal,
E.; Lahoz, F. J .; Bakhmutov, V. I.; Oro, L. A. Organometallics 1996,
15, 2967.

Addition of Monochloro Derivatives to Rh Complexes
Organometallics, Vol. 19, No. 24, 2000 4971
Sch em e 2
steric hindrance imposed on the R-carbon. Thus, while
MeCO2CH2Cl reacts with 1 to give 4, the R-methyl-
substituted MeCO2CH(Me)Cl is unreactive. These mixed-
valence compounds could also result from an alternative
and completely different mechanism. Thus, the transfer
of one electron from 1 or 6 to RCl (ii, Scheme 2) would
afford these products by coupling between the organic
and inorganic radicals. However, the reduction poten-
tials of the halo derivatives are too low to be reached
by complex 1, as shown by cyclic voltammetry measure-
ments on 1.25 Finally, a halide abstraction mechanism
involving the interaction between 1 and R-X to break
the C-X bond homolytically into two radicals (iii,
Scheme 2) also can be ruled out, since neither side-
reactions nor C-C coupling products are detected in
these reactions in the dark.
The second step of the reactions of 1 with alkyl
chlorides occurs at the “RhI(CNBut)2” active center
remaining in the intermediates [(CNBut)2RhI(µ-Pz)2-
RhIII(R)(Cl)(CNBut)2] to give the isolated products 2-5
(Scheme 1). The stereoselectivity shown in these reac-
tions, resulting in a single isomer, should not be
accidental but a consequence of how the second step
proceeds. Both conformers, A and B, are able to undergo
nucleophilic attack on the alkyl halide. However, the
bridging framework and the structure found for the
products result straightforwardly if this step occurs on
the minor conformer B. The most simple and reasonable
proposal is that this addition takes place preferentially
on the minor isomer followed by the conformational
equilibrium A/B to account for the stereoselectivity of
these reactions.
Rea ction s w ith Alk yl Br om id es. The influence of
the substrate and the reaction conditions on the reaction
mechanism is exemplified by the reactions of alkyl
bromides with 1 and 6. Complex 1 reacted with the
primary alkyl bromides RCH2Br (R ) Ph, CO2Me) to
give the Rh(III) complexes [{Rh(µ-Pz)(η1-CH2R)(CN-
But)2}2(µ-Br)]Br (R ) Ph (10), CO2Me (11)). In a similar
way, complex 6 reacted with PhCH2Br to give the
mixed-valence complex [(cod)Rh(µ-Pz)2Rh(η1-CH2Ph)-
(Br)(CNBut)2] (12). In general, the reactions proceed
more rapidly and they are noticeably more sensitive to
sunlight than those carried out with the analogous
chlorides. Complexes 10 and 11 were obtained as pure
samples only when working under strict darkness;
otherwise, both complexes appeared to be contaminated
F igu r e 3. Simulated (left) versus experimental (right)
variable-temperature H NMR spectra in the region of the
pyrazolate ligands for the interconversion of the conformers
of complex 7 in toluene-d8, and the corresponding Eyring
plot.
1
beginning of the reaction, as shown by the chemical
shifts for the CH2Ph groups (5.77 (A), 4.31 (B), Scheme
1) in benzene-d6, the equilibrium shifted to give the
conformer A within 10 min.
The formation of complexes 7-9 starting from 6
indicated a close relation between the nucleophility of
the rhodium center and the reactivity with primary
alkyl chlorides, suggesting an SN2 profile for these
reactions (i, Scheme 2). In addition, attempts to add the
secondary MeCO2CH(Me)Cl and tertiary ButCl alkyl
chlorides to 1 were unsuccessful. Both are particularly
inappropriate for SN2 type reactions because of the
(25) Tejel, C.; Ciriano, M. A.; Lo´pez, J . A.; Lahoz, F. J .; Oro, L. A.
Organometallics 1997, 16, 4718.

4972 Organometallics, Vol. 19, No. 24, 2000
Tejel et al.
Sch em e 3. Sp on ta n eou s Extr u sion of Isobu ten e
fr om a n Isocya n id e Liga n d Lea d in g to Cya n id e
Com p lexes
Moreover, similar results from the reactions between
the mixed-ligand complex 6 and alkyl bromides confirm
these hypotheses. Thus, while the trans-addition of the
primary alkyl bromide at a single metal center occurs
in the reaction with PhCH2Br, the dirhodium(II) com-
plex [(cod)(Br)Rh(µ-Pz)2Rh(Br)(CNBut)2] (14) and 2,3-
diphenylbutane result by bromine abstraction from the
secondary alkyl bromide PhCH(Me)Br by 6. Further-
more, these results show that the nucleophilicity of the
metal center is the driving force for the reactions with
primary bromides, while for the reactions with the
secondary bromides a distinct reaction pathway involv-
ing the two metal centers is operative.
with variable amounts of the golden Rh(II) compound
[{Rh(µ-Pz)(Br)(CNBut)2}2] (13). Therefore, the reactions
of 1 and 6 with primary RCH2Br substrates conform in
general to the SN2 pathway (i, Scheme 2), above
proposed for the reactions with alkyl chlorides, if
precautions to avoid free-radical initiators (light and
oxygen) are taken. Complex 13 arises, probably, from a
bromine abstraction reaction (iii, Scheme 3), which
suggests the participation of two competitive reaction
pathways: the SN2 mechanism versus the radical
bromine abstraction. A decisive test for this hypothesis
is obtained from the results of the reaction of 1 and 6
with the substrate probe PhCH(Me)Br. Complex 1
reacted with PhCH(Me)Br under sunlight exposure and
more slowly in the dark to give 13 in quantitative yield.
Examination of the crystallization liquors revealed the
formation of mainly an equimolar mixture of the two
pairs of diastereoisomers of 2,3-diphenylbutane in al-
most quantitative yield, contaminated with traces of
styrene and ethylbenzene.
Similarly, complex 6 reacted with PhCH(Me)Br giving
the Rh(II) complex [(cod)(Br)Rh(µ-Pz)2Rh(Br)(CNBut)2]
(14), isolated as a red crystalline solid, and mainly 2,3-
diphenylbutane. Complex 14 was found to be diamag-
netic and possessing a symmetry plane that makes the
Pz ligands equivalent in the 1H and 13C{1H} NMR
spectra. Both metal centers were oxidized, as evidenced
by the chemical shifts and coupling constants in the 13C-
{1H} NMR spectrum for the olefinic cod carbons. There-
fore, complex 14 displays a Rh-Rh bond with the
bromide ligands trans to this metal-metal bond. The
formation of 2,3-diphenylbutane by a C-C coupling
reaction and, more significantly, the observation of
styrene and ethylbenzene as subproducts (eq 1) provide
evidence for the participation of radicals PhCH(Me)• in
the process.26As noted above, the steric hindrance shown
by the R-substituted alkyl chlorides disfavors SN2
pathways, while it enhances in this case the stability
of the possible radical PhCH(Me)•. Complex 13 should,
hence, be the result of the halogen abstraction from the
alkyl bromide, which generates the free radicals PhCH-
(Me)• and [{Rh(µ-Pz)(CNBut)2}2Br]•, followed by the
radical-chain propagation. Consequently, 2 molar equiv
of PhCH(Me)Br are required to complete the reaction,
as observed.
F u r t h er R ea ct ion s of t h e Alk yl R h od iu m (III)
Com p lexes. The sensitivity of the chloro complexes
2-5 to temperature, in particular of complex 2, prompted
us to study their stability. Complex 2 decomposes slowly
but cleanly at room temperature in CDCl3 to give a new
complex, 15, which has no symmetry and possesses only
three isocyanide ligands according to the 1H NMR
spectrum of the reaction mixture. Isobutene was the
second product of the reaction. This transformation,
completed at 323 K in ca. 3 h in the NMR cavity, was
reproduced in the laboratory to give the complex
[(CNBut )2(η1-CH2Ph)Rh(µ-Pz)2(µ-Cl)Rh(η1-CH2Ph)-
(CN)(CNBut)] (15). Complex 15 was isolated as a white
crystalline solid in moderate yield and fully character-
ized by spectroscopic methods and by X-ray diffraction
analyses (see below). The overall reaction involves a loss
of the Cl and But groups as HCl and (CH3)2CdCH2 from
2, leaving a cyanide ligand (Scheme 3). Related frag-
mentations27 in cationic complexes and rupture of an
isocyanide ligand producing an oxidative-addition of the
cyanide and alkyl groups to a low oxidation state metal
center have been reported previously.28 Although the
complexes 4 and 5 are thermally more stable than 2,
they undergo a similar transformation into the com-
plexes [(CNBut)2(η1-CH2R)Rh(µ-Pz)2(µ-Cl)Rh(η1-CH2R)-
(CN)(CNBut)] (R ) COMe, CO2Me) upon heating in the
darkness (1H NMR evidence).
The structure of complex 15 is shown in Figure 4
along with the atom-numbering scheme used. Selected
bond distances and angles are collected in Table 1. Both
metals exhibit slightly distorted octahedral geom-
etries: one rhodium center, Rh(1), completes its octa-
hedral environment with two CNBut ligands, each trans
to a bridging pyrazolate, and a benzyl group trans-
disposed to the bridging chloride. The Rh‚‚‚Rh inter-
metallic separation, 3.5594(8) Å, clearly indicates that
there is no metal-metal bonding interaction. Along the
metal-metal vector, the relative disposition of the
terminal ligands is such that the two benzyl groups are
eclipsed with respect to each other (C(1)-Rh(1)‚‚‚Rh-
(2)-C(12) 3.7(4)°); the Rh-C(benzyl) bond distances
(mean 2.098(6) Å) are similar to those reported in
related Rh(III)_η1-benzyl complexes as in [(η5-C5Me5)(η1-
CH2Ph)Rh(µ-CH2)2Rh(η4-C5Me5CH2Ph)] (2.11(2) Å)29
and [(tht)2(η1-CH2Ph)Rh(µ-Cl)3Rh(η1-CH2Ph)2(tht)] (tht
(27) (a) J ones, W. D.; Kosar, W. P. Organometallics 1986, 5, 1823.
(b) Terrick, S. M.; Walton, R. A. Inorg. Chem. 1985, 24, 3363.
(28) Werner, H.; Ho¨rlin, G.; J ones, W. D. J . Organomet. Chem. 1998,
562, 45, and references therein.
(29) Meanwell, N. J .; Smith, A. J .; Maitlis, P. M. J . Chem. Soc.,
Dalton Trans. 1986, 1419.
(26) March, J . Advanced Organic Chemistry, 4th ed.; J . Wiley: New
York, 1992.

Addition of Monochloro Derivatives to Rh Complexes
Organometallics, Vol. 19, No. 24, 2000 4973
Upon sunlight exposure, a colorless deoxygenated
CDCl3 solution of the bromo complex 10 becomes yellow
and then orange. The coupled product Ph-CH2-CH2-
Ph (50% relative to 10) is the major component along
with cis and trans stilbene (30%) and toluene (20%).
Uncharacterized rhodium products were observed at the
end of the reaction, although [{Rh(µ-Pz)(Br)(CNBut)2}2]
(13) appeared at the beginning. However, an indepen-
dent experiment showed the decomposition of 13 under
sunlight exposure. Attempts to obtain the cross-coupling
product Ph-CH2-CH2-CO2Me by irradiation of an
equimolar mixture of complexes 10 and 11 were unsuc-
cessful.
The formation of bibenzyl by a C-C coupling process
could be explained in terms of an intramolecular reduc-
tive elimination of the two PhCH2 fragments from 10
to give 13. Hovewer, the observation of stilbene and
toluene as products requires the participation of Ph-
F igu r e 4. Molecular structure of complex 15. For the
disordered atoms (methyl groups and the phenyl ring
C(31)-C(36)) only one group has been represented for
clarity. The thermal ellipsoids are at the 50% probability
level.
CH2 radicals in the process.26 Both pathways could
•
operate simultaneously in our case. Coupling reactions
involving the intermediacy of benzyl radicals have been
observed for the thermal reactions of PhCH2Br with
dinuclear ruthenium33 and mononuclear anionic iron
complexes14 and in photoinduced C-Cl activation by
dinuclear gold complexes.19
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lex 15
Rh(1)‚‚‚Rh(2)
Rh(1)-Cl
3.5594(8)
2.507(2)
2.067(6)
2.059(6)
2.099(8)
1.943(8)
1.941(8)
1.358(8)
1.138(9)
1.143(10)
Rh(2)-Cl
Rh(2)-N(6)
Rh(2)-N(8)
Rh(2)-C(12)
Rh(2)-C(13)
Rh(2)-C(18)
N(7)-N(8)
2.522(2)
2.094(6)
2.067(5)
2.096(8)
1.982(9)
1.920(8)
1.356(8)
1.114(10)
1.142(9)
Rh(1)-N(5)
Rh(1)-N(7)
Rh(1)-C(1)
Rh(1)-C(2)
Rh(1)-C(7)
N(5)-N(6)
N(1)-C(2)
N(2)-C(7)
When reproducing the above experiment, but using
a solution of 10 in CDCl3 under an oxygen atmosphere,
the major organic product was benzaldehyde, along with
small amounts of Ph-CHdN-But and But-NH-CO-
NH-But. The former results from the oxidation of the
N(3)-C(13)
N(4)-C(18)
Cl-Rh(1)-N(5)
Cl-Rh(1)-N(7)
Cl-Rh(1)-C(1)
Cl-Rh(1)-C(2)
Cl-Rh(1)-C(7)
N(5)-Rh(1)-N(7)
N(5)-Rh(1)-C(1)
87.46(14) Cl-Rh(2)-N(6)
87.59(14) Cl-Rh(2)-N(8)
174.55(18) Cl-Rh(2)-C(12)
92.00(19) Cl-Rh(2)-C(13)
89.8(2)
91.23(19) N(6)-Rh(2)-N(8)
87.4(2) N(6)-Rh(2)-C(12)
85.96(14)
86.86(13)
175.75(18)
94.11(19)
90.70(18)
90.73(19)
91.1(2)
•
Ph-CH2 fragments, a process also observed for light-
induced reactions of certain organopalladium deriva-
tives with oxygen.34 Free tert-butylamine, produced from
the decomposition of CNBut, is required to explain the
formation of the organic nitrogen compounds.35
Cl-Rh(2)-C(18)
N(5)-Rh(1)-C(2) 178.1(2)
N(6)-Rh(2)-C(13) 179.5(2)
Con clu d in g Rem a r k s
N(5)-Rh(1)-C(7)
N(7)-Rh(1)-C(1)
N(7)-Rh(1)-C(2)
89.8(2)
90.8(2)
90.5(2)
N(6)-Rh(2)-C(18)
N(8)-Rh(2)-C(12)
N(8)-Rh(2)-C(13)
N(8)-Rh(2)-C(18) 176.2(2)
C(12)-Rh(2)-C(13) 88.8(3)
C(12)-Rh(2)-C(18) 92.5(2)
C(13)-Rh(2)-C(18) 87.5(3)
Rh(2)-C(12)-C(41) 117.8(4)
Rh(2)-C(13)-N(3) 179.1(6)
Rh(2)-C(18)-N(4) 175.6(6)
92.0(2)
90.1(2)
89.8(3)
The results reported in this paper show the complex-
ity of the reactions of alkyl chlorides and bromides with
nucleophilic dinuclear rhodium complexes. Several path-
ways are operative depending on the substrate, and they
may compete depending on the reaction conditions. The
influence of light and oxygen on the type of products
resulting from these reactions requires a careful experi-
mental procedure to reproduce and compare results.
Moreover, the mechanism of the oxidative-addition of
alkyl halides to metal complexes cannot be generalized,
because the nature of the halide and subtle differences
of the organic chain may produce significant changes
in the reaction pathways.
N(7)-Rh(1)-C(7) 177.1(2)
C(1)-Rh(1)-C(2)
C(1)-Rh(1)-C(7)
C(2)-Rh(1)-C(7)
93.2(3)
91.9(3)
88.4(3)
Rh(1)-C(1)-C(31) 121.2(5)
Rh(1)-C(2)-N(1) 177.6(6)
Rh(1)-C(7)-N(2) 175.8(6)
Rh(1)-Cl-Rh(2)
90.13(5)
) tetrahydrothiophene) (mean 2.095(7) Å).30 The Rh-C
bond length for the terminal CN group (1.982(9) Å) is
slightly shorter than those previously reported in Rh-
(III) cyanide complexes (range 2.000(6)-2.047(4) Å),31
although in all these cases two relatively trans-disposed
terminal CN groups compete for the electron density of
the metal; the weaker trans influence of the bridging
pyrazolate group could rationalize the short Rh-C
separation observed in 15. Bridging pyrazolate ligands
show usual bond distances for rhodium-nitrogen con-
tacts of this type,2a,32 the Rh(2)-N(6) distance (trans to
the cyanide ligand) being slightly longer.
Exp er im en ta l Section
Gen er a l Com m en ts. All the reactions were carried out
under argon using standard Schlenk techniques and protected
from light with black photographic paper. The complexes [{Rh-
(32) Tejel, C.; Bordonaba, M.; Ciriano, M. A.; Edwards, A. J .; Clegg,
W.; Lahoz, F. J .; Oro, L. A. Inorg. Chem. 1999, 38, 1108.
(33) Takahashi, A.; Mizobe, Y.; Matsuzaka, H.; Dev, S.; Hidai, M.
J . Organomet. Chem. 1993, 456, 243.
(34) (a) McCrindle, R.; Ferguson, G.; McAlees, A. J .; Arsenault, G.
J .; Gupta, A.; J ennings, M. C. Organometallics 1995, 14, 2741. (b)
Vicente, J .; Arcas, A.; Bautista, D.; Shul’pin, G. B. J . Chem. Soc., Dalton
Trans. 1994, 1505.
(30) Hay-Motherwell, R. S.; Koschmieder, S. U.; Wilkinson, G.;
Hussain-Bates, B.; Hursthouse, M. B. J . Chem. Soc., Dalton Trans.
1991, 2821.
(31) (a) Lu, S. J .; Wei, F.-P.; Wang. X.-D.; Huang. L.-R. J . Orga-
nomet. Chem. 1996, 510, 7. (b) Odano, N.; Harada, K.; Urushiyama,
A. Bull. Chem. Soc. J pn. 1993, 66, 1991. (c) Yoshida, K.; Kitada, T.;
Odano, N.; Harada, K.; Urushiyama, A.; Nakahara, M. Bull. Chem.
Soc. J pn. 1991, 64, 895.
(35) Boschi, T.; Licoccia, S.; Paolesse, R.; Tagliatesta, P.; Pelizzi, G.;
Vitali, F. Organometallics 1989, 8, 330.

4974 Organometallics, Vol. 19, No. 24, 2000
Tejel et al.
1
(µ-Pz)(CNBut)2}2] (1) and [(cod)Rh(µ-Pz)2Rh(CNBut)2] (6) were
prepared according to literature methods.24 The alkyl halides
were distilled under argon prior to use. In general, the
products appear as pale yellow oils in dried solvents, which
become white microcrystals that contain water of hydration
upon addition of moist pentane. The formulas of the hydrates
are indicated with the analytical data, and the water of
crystallization was observed at 1.56 ppm in CDCl3 and at 2.81
and 2.84 ppm in acetone-d6 in their 1H NMR spectra. They
are light-sensitive and must be stored in the dark. Solvents
were dried and distilled under argon before use by standard
methods. Carbon, hydrogen, and nitrogen analyses were
performed in a Perkin-Elmer 2400 microanalyzer. IR spectra
were recorded with a Nicolet 550 spectrophotometer. Mass
spectra were recorded in a VG Autospec double-focusing mass
spectrometer operating in the FAB+ mode. Ions were produced
with a standard Cs+ gun at ca. 30 kV, and 3-nitrobenzyl alcohol
(NBA) was used as matrix. 1H and 13C{1H} NMR spectra were
recorded on a Bruker ARX 300 and on a Varian UNITY 300
spectrometer operating at 300.13 and 299.95 MHz for 1H,
respectively. Chemical shifts are reported in parts per million
and referenced to SiMe4 using the residual signal of the
deuterated solvent as reference. NOE experiments were car-
ried out using the standard NOE 1d pulse sequence on the
Varian spectrometer. Conductivities were measured in 4-5
× 10-4 M acetone solutions using a Philips PW 9501/01
conductimeter.
(CH3)3), 17.9 (d, J C-Rh ) 22 Hz, CH2). MS (FAB+, CH2Cl2,
m/z): 853, 100% (M+). ΛM (5.17 10-4 M in acetone): 113 S cm2
mol-1
.
[{Rh (µ-P z)(η1-CH2COMe)(CNBu t)2}2(µ-Cl)]Cl (5) was pre-
pared as described above for complex 2 starting from 1 (200
mg, 0.30 mmol) and MeCOCH2Cl (51 µL, 0.63 mmol) to render
pale yellow crystals. Yield: 240 mg (94%). Anal. Calcd for
C32H52N8O2Cl2Rh2‚2H2O: C, 43.01; H, 6.32; N, 12.54. Found:
C, 42.91; H, 6.30; N, 12.35. IR (CH2Cl2, cm-1): ν(CN) 2232 (s),
1
2210 (s); ν(CO) 1676 (s). H NMR (293 K, CDCl3): δ 7.74 (d,
2.2 Hz, 4H, H3,5Pz), 6.30 (t, 2H, H4Pz), 3.10 (d, J H-Rh ) 3.1
2
Hz, 4H, CH2), 2.25 (s, 6H, CH3CO), 1.51 (s, 36H, CNBut). 13C-
{1H} NMR (293 K, CDCl3): δ 213.3 (CO), 140.5 (C3,5Pz), 106.6
(C4Pz), 60.1 (C-(CH3)3), 30.4 (CH3CO), 30.1 (C-(CH3)3), 29.2
(d, 1J C-Rh ) 22 Hz, CH2). MS (FAB+, CH2Cl2, m/z): 821, 100%
(M+). ΛM (4.99 10-4 M in acetone): 111 S cm2 mol-1
.
[(cod )Rh (µ-P z)2Rh (η1-CH2P h )(Cl)(CNBu t)2] (7). PhCH2-
Cl (56 µL, 0.49 mmol) was added to a suspension of [(cod)Rh-
(µ-Pz)2Rh(CNBut)2] (6) (250 mg, 0.41 mmol) in pentane (15 mL)
and stirred overnight in the dark. The resulting suspension
was decanted and the residue washed with cold pentane and
dried under vacuum. Yield: 270 mg (89%). Anal. Calcd for
C
31H43N6ClRh2‚2H2O: C, 47.92; H, 5.58; N, 10.82. Found: C,
48.24; H, 5.71; N, 10.59. IR (CH2Cl2, cm-1): ν(CN) 2222 (s),
2199 (s). H NMR (223 K, CDCl3): δ 7.81 (d, 1.8 Hz, 2H, H3-
1
Pz), 7.36 (d, 2H, H5Pz), 7.29 (d, 7.0 Hz, 2H, HoPh), 7.20 (t, 7.0
Hz, 2H, HmPh), 7.16 (t, 1H, HpPh), 6.11 (t, 2H, H4Pz), 5.83 (d,
2J H-Rh ) 3.2 Hz, 2H, CH2), 4.13 and 3.96 (m, 2H + 2H, dCH
cod), 2.55 and 2.24 (m, 2H + 2H, H2Cexo cod), 1.82 and 1.68
(m, 2H + 2H, H2Cendo cod), 1.39 (s, 18H, CNBut). 13C{1H} NMR
(223 K CDCl3): δ 142.0 (C3Pz), 137.7 (C5Pz), 152.2, 128.3,
P r ep a r a tion of th e Com p lexes. [{Rh (µ-P z)(η1-CH2P h )-
(CNBu t)2}2(µ-Cl)]Cl (2). Neat PhCH2Cl (72 µL, 0.63 mmol)
was added to a solution of [{Rh(µ-Pz)(CNBut)2}2] (1) (200 mg,
0.30 mmol) in benzene (5 mL) in the dark. After 30 min the
solution was carefully layered with pentane (30 mL) to produce
white crystals of 2 overnight, which were filtered, washed with
cold pentane, and dried under vacuum. Yield: 248 mg (91%).
Anal. Calcd for C40H56N8Cl2Rh2‚2H2O: C, 49.96; H, 6.29; N,
11.65. Found: C, 49.52; H, 6.38; N, 11.96. IR (CH2Cl2, cm-1):
128.1, and 124.2 (Ph), 104.6 (C4Pz), 81.1 (d, J C-Rh ) 13 Hz,
1
dCH cod), 80.3 (d, 1J C-Rh ) 12 Hz, dCH cod), 57.9 (C-(CH3)3),
1
30.4 and 30.2 (H2C cod), 29.9 (C-(CH3)3), 29.4 (d, J C-Rh ) 23
Hz, CH2). MS (FAB+, CH2Cl2, m/z): 740, 5% (M+); 705, 90%
(M - Cl+); 649, 10% (M - CH2Ph+); 614, 100% (M - CH2Ph -
1
Cl+). ΛM (4.50 10-4 M in acetone): 3 S cm2 mol-1
.
ν(CN) 2226 (s), 2205 (s). H NMR (293 K, CDCl3): δ 7.72 (d,
2.2 Hz, 4H, H3,5Pz), 7.45 (d, 6.5 Hz, 4H, Hï Ph), 7.29 (t, 6.5
Hz, 4H, HmPh), 7.27 (t, 2H, HpPh), 6.40 (t, 2H, H4Pz), 3.96 (d,
2J H-Rh ) 3.2 Hz, 4H, CH2), 1.34 (s, 36H, CNBut). 13C{1H} NMR
(293 K, CDCl3): δ 140.0 (C3,5Pz), 149.3, 128.9, 128.8, and 125.8
(Ph), 106.2 (C4Pz), 59.2 (C-(CH3)3), 29.9 (C-(CH3)3), 28.8 (d,
1J C-Rh ) 21 Hz, CH2). MS (FAB+, CH2Cl2, m/z): 889, 100%
[(cod)Rh (µ-P z)2Rh (η1-CH2CHdCH2)(Cl)(CNBu t)2] (8) was
prepared as described above for complex 7 starting from 6 (100
mg, 0.16 mmol) and allyl chloride (17 µL, 0.20 mmol). Yield:
88 mg (80%). Anal. Calcd for C27H41N6ClRh2‚H2O: C, 45.74;
H, 6.11; N, 11.85. Found: C, 45.99; H, 5.61; N, 11.56. IR (CH2-
Cl2, cm-1): ν(CN) 2228 (s), 2201 (s). H NMR (223 K, CDCl3):
1
(M+). ΛM (4.79 10-4 M in acetone): 81 S cm2 mol-1
.
δ 7.79 (br s, 2H, H3Pz), 7.30 (br s, 2H, H5Pz), 6.29 (m, 1H,
CH2CHdCH2), 6.07 (br s, 2H, H4Pz), 5.22 (br d, 16.7, 1H, CH2-
[{Rh (µ-P z)(η1-CH2CHdCH2)(CNBu t)2}2(µ-Cl)]Cl (3) was
prepared and isolated as described above for complex 2 starting
from 1 (200 mg, 0.30 mmol) and allyl chloride (51 µL, 0.63
mmol) to yield white crystals. Yield: 217 mg (87%). Anal. Calcd
for C32H52N8Cl2Rh2‚2H2O: C, 46.61; H, 6.55; N, 13.00. Found:
3
2
CHdCH2), 5.05 (br t, J H-H and J H-Rh ) 5.8 Hz, 2H, CH2-
CHdCH2), 4.95 (dd, 9.7 and 2.3 Hz, 1H, CH2CHdCH2), 4.08
and 3.88 (m, 2H + 2H, dCH cod), 2.52 and 2.38 (m, 2H + 2H,
H2Cexo cod), 1.78 (m, 4H, H2Cendo cod), 1.53 (s, 18H, CNBut).
13C{1H} NMR (223 K CDCl3) (asigned form APT spectrum): δ
148.1 (CH2CHdCH2), 141.9 (C3Pz), 137.6 (C5Pz), 132.5 (d,
1J C-Rh ) 54 Hz, CN), 109.9 (CH2CHdCH2), 104.5 (C4Pz), 80.9
C, 44.44; H, 6.37; N, 13.21. IR (CH2Cl2, cm-1): ν(CN) 2224 (s),
1
2203 (s). H NMR (293 K, CDCl3): δ 7.48 (d, 2.1 Hz, 4H, H3,5
-
Pz), 6.26 (t, 2H, H4Pz), 6.23 (m, 2H, CH2CHdCH2), 5.30 (dd,
15.8 and 1.1 Hz, 2H, CH2CHdCH2), 5.08 (dd, 9.8 and 1.1 Hz,
1
1
(d, J C-Rh ) 13 Hz, dCH cod), 80.3 (d, J C-Rh ) 11 Hz, dCH
cod), 57.8 (C-(CH3)3), 30.4 and 30.2 (H2C cod), 30.0 (C-(CH3)3),
2H, CH2CHdCH2), 3.25 (dd, 3J H-H ) 8.5 and J H-Rh ) 2.5 Hz,
2
4H, CH2CHdCH2), 1.48 (s, 36H, CNBut). 13C{1H} NMR (293
K, CDCl3) (assigned from the APT spectrum): δ 146.3 (CH2CHd
CH2), 139.4 (C3,5Pz), 112.1(CH2CHdCH2), 106.1 (C4Pz), 59.1
(C-(CH3)3), 30.0 (C-(CH3)3), 28.2 (d, 1J C-Rh ) 21 Hz, CH2CHd
CH2). MS (FAB+, CH2Cl2, m/z): 789, 100% (M+). ΛM (4.77 10-4
28.4 (d, J C-Rh ) 21 Hz, CH2). MS (FAB+, CH2Cl2, m/z): 690,
1
7% (M+); 655, 95% (M - Cl+); 614, 100% (M - CH2CHdCH2
- Cl+).
[(cod )Rh (µ-P z)2Rh (η1-CH2CO2Me)(Cl)(CNBu t)2] (9) was
prepared as described above for complex 7 starting from 6 (100
mg, 0.16 mmol) and MeCO2CH2Cl (19 µL, 0.20 mmol). Yield:
88 mg (75%). Anal. Calcd for C27H41N6O2ClRh2‚H2O: C, 43.76;
H, 5.85; N, 11.34. Found: C, 43.46; H, 6.16; N, 10.97. IR (CH2-
M in acetone): 82 S cm2 mol-1
.
[{Rh (µ-P z)(η1-CH2CO2Me)(CNBu t)2}2(µ-Cl)]Cl (4) was
prepared and isolated as described above for complex 2 starting
from 1 (200 mg, 0.30 mmol) and MeCO2CH2Cl (59 µL, 0.63
mmol) to render white crystals. Yield: 217 mg (82%). Anal.
Calcd for C32H52N8O4Cl2Rh2‚2H2O: C, 42.35; H, 6.00; N, 12.35.
Found: C, 42.35; H, 5.76; N, 12.17. IR (CH2Cl2, cm-1): ν(CN)
Cl2, cm-1): ν(CN) 2233 (s), 2211 (s); ν(CO) 1706 (s). H NMR
1
(223 K, CDCl3): δ 7.78 (d, 1.9 Hz, 2H, H3Pz), 7.30 (d, 1.6 Hz,
2H, H5Pz), 6.08 (t, 2H, H4Pz), 4.53 (d, J H-Rh ) 3.2 Hz, 2H,
2
CH2), 4.08 and 3.93 (m, 2H + 2H, dCH cod), 3.66 (s, 3H, CH3-
OOC), 2.52 and 2.40 (m, 2H + 2H, H2Cexo cod), 1.78 (m, 4H,
H2Cendo cod), 1.56 (s, 18H, CNBut). 13C{1H} NMR (223 K
CDCl3): δ 181.5 (CO), 142.2 (C3Pz), 138.1 (C5Pz), 104.6 (C4-
Pz), 81.2 (d, J C-Rh ) 13 Hz, dCH cod), 80.6 (d, J C-Rh ) 11
Hz, dCH cod), 58.5 (C-(CH3)3), 50.7 (CH3OOC), 30.8 and 30.7
1
2235 (s), 2217 (s); ν(CO) 1713 (s). H NMR (293 K, CDCl3): δ
7.74 (d, 2.2 Hz, 4H, H3,5Pz), 6.35 (t, 2H, H4Pz), 3.75 (s, 6H,
2
CH3OOC), 2.87 (d, J H-Rh ) 3.2 Hz, 4H, CH2), 1.55 (s, 36H,
CNBut). 13C{1H} NMR (293 K, CDCl3): δ 179.5 (CO), 140.3
(C3,5Pz), 106.6 (C4Pz), 59.8 (C-(CH3)3), 51.2 (CH3CO2), 29.9 (C-
1
1

Addition of Monochloro Derivatives to Rh Complexes
Organometallics, Vol. 19, No. 24, 2000 4975
1
Ta ble 2. Cr ysta l Da ta a n d Da ta Collection a n d
Refin em en t for Com p lex 15
(H2C cod), 30.3 (C-(CH3)3), 17.7 (d, J C-Rh ) 21 Hz, CH2). MS
(FAB+, CH2Cl2, m/z): 723, 25% (M+); 687, 100% (M - Cl)+.
[{Rh (µ-P z)(η1-CH2P h )(CNBu t)2}2(µ-Br )]Br (10) was pre-
pared as described above for complex 2 starting from 1 (200
mg, 0.30 mmol) and PhCH2Br (78 µL, 0.63 mmol) to render
pale yellow crystals. Yield: 285 mg (92%). Anal. Calcd for
chem formula
fw
cryst size, mm
cryst syst
space group
a, Å
C36H47ClN8Rh2
833.09
0.49 × 0.36 × 0.39
monoclinic
P21/c (No. 14)
19.403(2)
9.1872(8)
24.055(2)
97.64(2)
4250.0(7)
4
1.302
C
32H52N8O4Br2Rh2‚2H2O: C, 45.73; H, 5.75; N, 10.66. Found:
C, 45.40; H, 5.46; N, 10.97. IR (CH2Cl2, cm-1): ν(CN) 2226 (s),
b, Å
c, Å
2203 (s). H NMR (293 K, CDCl3): δ 7.75 (d, 2.2 Hz, 4H, H3,5
-
1
Pz), 7.50 (d, 7.7 Hz, 4H, HoPh), 7.32 (m, 6H, Hm,p Ph), 6.42 (t,
â, deg
2H, H4Pz), 4.00 (d, J H-Rh ) 3.3 Hz, 4H, CH2), 1.41 (s, 36H,
2
V, Å3
CNBut). 13C{1H} NMR (293 K, CDCl3): δ 140.3 (C3,5Pz), 149.2,
128.9, 128.8 and 125.8 (Ph), 106.3 (C4Pz), 59.2 (C-(CH3)3), 29.9
(C-(CH3)3), 31.1 (d, 1J C-Rh ) 21 Hz, CH2). MS (FAB+, CH2Cl2,
m/z): 935, 100% (M+). ΛM (4.79 10-4 mol‚L-1 in acetone): 100
Z
D
calcd, g cm-3
µ, mm-1
0.871
no. of measd reflns
no. of unique reflns
min, max transm factora
no. data/restraints/params
R(F) (F2 g 2σ(F2))b
wR(F2) (all data)c
7859 (2θ e 50°)
7516 (Rint ) 0.0840)
0.675, 0.727
7516/0/407
0.0597
S cm2 mol-1
.
[{Rh (µ-P z)(η1-CH2CO2Me)(CNBu t)2}2(µ-Br )]Br (11) was
prepared as described above for complex 2 starting from 1 (100
mg, 0.15 mmol) and MeCO2CH2Br (31 µL, 0.31 mmol) to render
white crystals. Yield: 126 mg (86%). Anal. Calcd for C32H52N8O4-
Br2Rh2‚2H2O: C, 37.88; H, 5.56; N, 11.04. Found: C, 37.62;
H, 5,20; N, 11.25. IR (CH2Cl2, cm-1): ν(CN) 2234 (s), 2216 (s);
ν(CO) 1732 (s). 1H NMR (293 K, CDCl3): δ 7.69 (d, 2.1 Hz,
4H, H3,5Pz), 6.29 (t, 2H, H4Pz), 3.72 (s, 6H, CH3OOC), 2.87 (d,
2J H-Rh ) 3.2 Hz, 4H, CH2), 1.53 (s, 36H, CNBut). 13C{1H} NMR
(293 K, CDCl3): δ 179.4 (CO), 140.6 (C3,5Pz), 106.7 (C4Pz), 59.8
0.1666
a
An semiempirical ψ-scan absorption correction was applied.
R(F) ) ∑||Fo| - |Fc||/∑|Fo| for 5549 observed reflections. c wR(F2)
b
2
) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2; w-1 ) [σ2(Fo2) + (0.1064P)2
+
2.999P], where P ) [max(Fo2, 0) + 2Fc2)]/3.
CH cod), 3.29 and 2.66 (m, 2H+2H, H2Cexo cod), 2.33 and 2.25
(m, 2H + 2H, H2Cendo cod), 1.48 (s, 18H, CNBut). 13C{1H} NMR
(295 K CDCl3): δ 138.7 (C3Pz), 136.8 (C5Pz), 106.1 (C4Pz), 96.6
(d, 1J C-Rh ) 7 Hz, dCH cod), 92.4 (d, 1J C-Rh ) 8 Hz, dCH cod),
58.9 (C-(CH3)3), 32.7 and 30.5 (H2C cod), 30.4 (C-(CH3)3).
1
(C-(CH3)3), 51.3 (CH3OOC), 30.2 (C-(CH3)3), 20.1 (d, J C-Rh
) 22 Hz, CH2). MS (FAB+, CH2Cl2, m/z): 897, 100% (M+). ΛM
(4.92 10-4 mol‚L-1 in acetone): 91 S cm2 mol-1
.
[(cod)Rh (µ-P z)2Rh (η1-CH2P h )(Br )(CNBu t)2] (12) was pre-
pared as described above for complex 7 starting from 6 (100
mg, 0.16 mmol) and PhCH2Br (21.3 µL, 0.18 mmol). Yield: 108
mg (85%). Anal. Calcd for C31H43N6BrRh2‚2H2O: C, 45.33; H,
5.77; N, 10.23. Found: C, 45.24; H, 5.61; N, 10.17. IR (CH2-
Cl2, cm-1): ν(CN) 2222 (s), 2202 (s). 1H NMR (232 K, acetone-
d6): δ 7.88 (d, 2.0 Hz, 2H, H3Pz), 7.46 (d, 2H, H5Pz), 7.29 (m,
4H, Ho,mPh), 7.16 (m, 1H, HpPh), 6.06 (t, 2H, H4Pz), 5.85 (d,
2J H-Rh ) 3.2 Hz, 2H, CH2), 4.30 and 3.89 (m, 2H + 2H, dCH
cod), 2.54 and 2.24 (m, 2H + 2H, H2Cexo cod), 1.85 and 1.72
(m, 2H + 2H, H2Cendo cod), 1.42 (s, 18H, CNBut). MS (FAB+,
CH2Cl2, m/z): 785, 7% (M+); 705, 97% (M - Br+); 614, 100%
(M - CH2Ph-Br+). ΛM (4.45 10-4 M in acetone): 3.5 S cm2
[(CNBu t)2(η1-CH2P h )Rh (µ-P z)2(µ-Cl)Rh (η1-CH2P h )(CN)-
(CNBu t)] (15). To a solution of 1 (100 mg, 0.15 mmol) in ethyl
acetate (8 mL) was added neat PhCH2Cl (36 µL, 0.31 mmol)
and the resulting solution carefully layered with diethyl ether
(20 mL). White prismatic crystals of 2 were formed in 2 days,
which redissolved to render white crystals of 15 in 2 weeks.
The solid was filtered, washed with cold pentane, and dried
under vacuum. Yield: 84 mg (60%). Anal. Calcd for C36H47N8-
ClRh2‚H2O: C, 50.80; H, 5.80; N, 13.16. Found: C, 50.39; H,
5.28; N, 13.27. IR (CH2Cl2, cm-1): ν(CNBut) 2222 (s), 2201 (vs);
ν(CN) 2122 (w). 1H NMR (293 K, CDCl3): δ 8.01 (d, 2.1 Hz,
1H), 7.72 (d, 1.9 Hz, 1H), 7.68 (d, 2.0 Hz, 1H) and 7.63 (d, 2.0
Hz, 1H), (H3 and H5 Pz, Pz′), 7.81 (d, 7.1 Hz, 2H) and 7.49 (d,
7.0 Hz, 2H) (Ho Ph, Ph′), 7.27 (t, 7.0 Hz, 2H) and 7.21 (t, 7.1
Hz, 2H) (Hm Ph, Ph′), 7.14 (t, 7.19 Hz, 1H) and 7.11 (t, 7.3 Hz,
1H) (Hp Ph, Ph′), 6.30 (t, 1H) and 6.28 (t, 1H) (H4 Pz, Pz′),
mol-1
.
Rea ction of 1 w ith P h CH(Me)Br . Neat PhCH(Me)Br (44
µL, 0.31 mmol) was added to a solution of 1 (100 mg, 0.15
mmol) in benzene (7 mL). Fine orange needles and a yellow
solution were formed in the Schlenk tube after 15 min in the
dark. Hexane (30 mL) was added to complete the precipitation
of the solid characterized as [{Rh(µ-Pz)(Br)(CNBut)2}2] (13),
which was filtered and washed with 5 × 5 mL portions of
diethyl ether/hexane (1:1) and vacuum-dried. Yield: 123 mg
(90%). Anal. Calcd for C26H42N8Br2Rh2: C, 37.52; H, 5.09; N,
13.46. Found: C, 37.49; H, 5.02; N, 13.40. IR (CH2Cl2, cm-1):
2
2
4.35 (δA, J H-Rh ) 3.5 Hz, 1H) and 3.38 (δB, J H-Rh ) 3.6 Hz,
2
1H, J A-B ) 8.2 Hz) (CH2), 3.89 (δA, J H-Rh ) 3.4 Hz, 1H) and
3.86 (δB, 2J H-Rh ) 3.3 Hz, 1H, J A-B ) 9.1 Hz) (CH2′), 1.35, 1.31
and 1.05 (s, 27H, CNBut). 13C{1H} NMR (293 K, CDCl3): δ
151.9 and 150.7 (Ci Ph, Ph′), 140.8, 140.3, 138.8 and 138.7 (C3
and C5 Pz, Pz′), 131.8 (d, 1J C-Rh ) 47 Hz, NC-Rh), 129.7, 128.9,
128.5 and 128.1 (Co and Cm Ph, Ph′), 125.0 and 124.0 (Cp Ph,
Ph′), 105.3 and 105.0 (C4 Pz, Pz′), 59.7, 58.5 and 57.1
1
1
ν(CN) 2204 (s), 2178 (s). H NMR (293 K, CDCl3): δ 7.61 (d,
(C-(CH3)3), 30.0, 29.9, and 29.8 (C-(CH3)3), 27.7 (d, J C-Rh
)
1.8 Hz, 4H, H3,5Pz), 5.98 (t, 2H, H4Pz), 1.47 (s, 36H, CNBut).
MS (FAB+, CH2Cl2, m/z): 830, 7% (M+); 751, 100% (M - Br+).
The mother liquors were concentrated to ca. 3 mL and filtered
over Celite. Analysis of this solution by gas chromatography
coupled with mass spectrometry allowed the identification of
the following products (relative amounts): ethylbenzene (0.6%),
styrene (8.7%), 2,3-diphenylbutane (85.1%), acetophenone
(5.6%).
21 Hz) and 24.9 (d, J C-Rh ) 23 Hz) (CH2, CH2′). MS (FAB+,
1
CH2Cl2, m/z): 833, 75% (M + H+); 742, 100% (M - CH2Ph+).
Cr ysta l Str u ctu r e Deter m in a tion of Com p lex 15. A
summary of crystal data, intensity collection, and refinement
parameters is reported in Table 2. An irregular block white
crystal used for the X-ray analysis was glued to a glass fiber
and mounted on a Siemens-P4 diffractometer and irradiated
with graphite-monochromated Mo KR radiation (λ ) 0.71073
Å). Cell constants were obtained from the least-squares fit on
the setting angles of 25 reflections (20° e 2θ e 41°). A complete
set of independent reflections with 2θ up to 50° (-22 e h e
23, 0 e k e 10, and -28 e l e 1) was measured at room
temperature, 293(1) K, using the ω/2θ scan technique. Three
standard reflections were monitored every 100 measurements
throughout data collection as a check on crystal and instru-
ment stability; no decay was observed. Data were corrected
[(cod )(Br )Rh (µ-P z)2Rh (Br )(CNBu t)2] (14) was prepared
as described above for complex 13 starting from 6 (100 mg,
0.16 mmol) and PhCH(Me)Br (48 µL, 0.34 mmol) to render
red microcystals. Yield: 88 mg (70%). Anal. Calcd for C24H36N6-
Br2Rh2: C, 37.23; H, 4.69; N, 10.85 Found: C, 37.15; H, 4.50;
N, 10.73. IR (CH2Cl2, cm-1): ν(CN) 2207 (s), 2190 (s). 1H NMR
(295 K, CDCl3): δ 7.69 (d, 1.9 Hz, 2H, H3Pz), 7.66 (d, 1.7 Hz,
2H, H5Pz), 6.03 (t, 2H, H4Pz), 5.07 and 4.33 (m, 2H+2H, d

4976 Organometallics, Vol. 19, No. 24, 2000
Tejel et al.
for Lorentz and polarization effects. Reflections were also
corrected for absorption by a semiempirical method (Ψ-scan).36
The structure was solved by Patterson and subsequent
difference Fourier techniques (SHELXTL-PLUS)37 and refined
by full-matrix least-squares on F2 (SHELXL-97).38 J ust at the
isotropic model, the static disorder of all the terminal methyl
groups of the isocyanide ligands was apparent. Each disor-
dered tert-butyl group was modeled on the basis of two “Me3”
moieties related by a rotation around the N-C-Rh direction;
complementary occupancy factors were assumed. Anisotropic
thermal parameters were included for all remaining non-
hydrogen and nondisordered atoms. At this step, both benzyl
groups showed anomalous high anisotropic displacement
parameters, with greater values for the atoms more distant
from the metals. Eventually, a model of static disorder could
be established for one phenyl group based on two geometrically
constrained hexagonal rings (C(31a)-C(36a) and C(31b)-
C(36b)) with complementary occupancies. Dynamic disorder
was assumed for the second benzyl ligand (C(12), and C(41)-
C(46)). All hydrogen atoms were included in calculated posi-
tions and were refined with positional and thermal riding
parameters. The function minimized was ∑[w(Fo2 - Fc2)2]. The
calculated weighting scheme was 1/[σ2(Fo2) + (0.1064P)2
+
2.999P], where P ) [max(Fo2,0) + 2Fc2)]/3. All the refinements
converged to reasonable R factors (Table 2). The highest
residual electron density peaks, weaker than 1.21 e/Å3, were
situated in close proximity to the metal atoms and have no
chemical sense. Scattering factors were used as implemented
in the refinement program.38
Ack n ow led gm en t. We thank Direccio´n General de
Ensen˜anza Superior e Investigacio´n (DGES) for finan-
cial support (Projects PB95-221-C1 and PB94-1186) and
the EU Human Capital and Mobility Program (CT93-
0347) for a fellowship to A.J .E.
Su p p or tin g In for m a tion Ava ila ble: Full listings of
crystallographic data, complete atomic coordinates, isotropic
and anisotropic displacement parameters, and complete bond
distances and angles for complex 15. This material is available
free of charge via the Internet at http://pubs.acs.org.
(36) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(37) Sheldrick, G. M. SHELXTL-PLUS; Siemens Analytical X-ray
Instruments: Madison, WI, 1990.
(38) Sheldrick, G. M. SHELXL-97 Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
OM0003133