Solvent Dependence of the Reaction of η5-C5 Me5Ir(Co)2 with Aryldiazonium Ions. Synthesis and Characterization of Mono- and Diiridium Carbonyl Complexes Including the X-ray Structures of [{η5-C5Me5Ir(Co)} 2(1-η 1-1,2-η2-p-C6H 4OMe)]BF4

Article abstract of DOI:10.1021/ic960993v

Reaction of Cp*Ir(CO)₂ (3, CP* = η⁵-C₅Me₅) with [N²Ar][BF₄] (Ar = p-C₆H₄OMe) in acetone at -78°C affords the nitrogen extrusion product [Cp*Ir(CO)₂(Ar)][BF₄] (5), but in dichloromethane it yields a dinuclear product [Cp*(CO)₂Ir-Ir(Cl)(CO)Cp*][BF₄] (6). By carrying out this very reaction in ethanol solution, a nitrogen-retained product [Cp*Ir(CO)(OEt)(NHNAr)][BF₄] (7) is obtained, containing an aryldiazene ligand. Deprotonation of 7 gives quantitatively the neutral doubly-bent aryldiazenido complex Cp*Ir(CO)(OEt)(N₂Ar) (8). The IR v(CO) absorptions measured for the dinuclear compound 6 indicate no bridging carbonly, but a ¹³C NMR study in solution shows that 6 is stereochemically nonrigid at ambient temperature; its three carbonyl ligands are all involved in a fast exchange process, and this process is frozen at -86 °C. Exchange of the CO groups via a terminalbridging- terminal process accompained by rotation about the Ir-Ir axis is suggested. The molecular structure of 6 in the solid state has been established by single crystal X-ray crystallographic analysis and is consistent with the solution spectra. By reaction of [N₂Ar][BF₄] with the dinuclear complex [Cp*Ir(CO)]₂ (4) in acetone, the complex [{Cp*Ir(CO)}₂(1-η¹-1,2-η ²-p-C₆H₄OMe)][BF₄] (9) with a rare σ,π-bridging aryl group has been obtained and crystallyzed. The molecular structure containing an asymmetric bridging aryl group is established for 9 in the solid state by a single crystal X-ray crystallogaphic analysis. However, the identical ¹H NMR features observed at ambient temperuture and -90 °C in solutin (i.e., a singlet resonance for the two Cp* ligands and a symmetric AA'BB' pattern for the p-C₆H₄OMe) indicate a static or time-averaged symmetrical molecular geometry for 9. Compound 6 crystallizes in the monoclinic space group P2₁/c with a = 10.583(2) A?, b = 14.256(3) A?, c =16.818(4) A?, β = 95.91 (2)°, V = 2523.9 A?³, and Z = 4. Refinement yielded R_F = 0.033 for 3299 observed reflection (I_o ≥ 2.5σ(I_o)) of 4427 unique reflections. Compound 9 crystallizes in the monoclinic space group P2₁/n with a = 11.695(2) A?, b = 19.911(3) A?, c = 12.539(2) A?, β = 96.54(1)°, V = 2900,8 A?³, and Z = 4, Refinement yielded R_F = 0.025 and R_WF = 0.035 for 3444 observed reflections (I_o ≥ 2.5σ(I_o) of 4526 unique reflections.

Full text of DOI:10.1021/ic960993v

Inorg. Chem. 1997, 36, 1237-1246
1237
Solvent Dependence of the Reaction of (η5-C5Me5)Ir(CO)2 with Aryldiazonium Ions.
Synthesis and Characterization of Mono- and Diiridium Carbonyl Complexes Including the
X-ray Structures of [{(η5-C5Me5)Ir(CO)}2(1-η1-1,2-η2-p-C6H4OMe)][BF4] and
[(η5-C5Me5)(CO)2Ir-Ir(CO)(Cl)(η5-C5Me5)][BF4]
Xiaoqian Yan, Raymond J. Batchelor, Frederick W. B. Einstein, Xiaoheng Zhang,
Ruby Nagelkerke, and Derek Sutton*
Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
ReceiVed August 14, 1996X
Reaction of Cp*Ir(CO)2 (3, Cp* ) η5-C5Me5) with [N2Ar][BF4] (Ar ) p-C6H4OMe) in acetone at -78 °C affords
the nitrogen extrusion product [Cp*Ir(CO)2(Ar)][BF4] (5), but in dichloromethane it yields a dinuclear product
[Cp*(CO)2Ir-Ir(Cl)(CO)Cp*][BF4] (6). By carrying out this very reaction in ethanol solution, a nitrogen-retained
product [Cp*Ir(CO)(OEt)(NHNAr)][BF4] (7) is obtained, containing an aryldiazene ligand. Deprotonation of 7
gives quantitatively the neutral doubly-bent aryldiazenido complex Cp*Ir(CO)(OEt)(N2Ar) (8). The IR ν(CO)
absorptions measured for the dinuclear compound 6 indicate no bridging carbonyl, but a 13C NMR study in
solution shows that 6 is stereochemically nonrigid at ambient temperature; its three carbonyl ligands are all involved
in a fast exchange process, and this process is frozen at -86 °C. Exchange of the CO groups via a terminal-
bridging-terminal process accompanied by rotation about the Ir-Ir axis is suggested. The molecular structure
of 6 in the solid state has been established by single crystal X-ray crystallographic analysis and is consistent with
the solution spectra. By reaction of [N2Ar][BF4] with the dinuclear complex [Cp*Ir(CO)]2 (4) in acetone, the
complex [{Cp*Ir(CO)}2(1-η1-1,2-η2-p-C6H4OMe)][BF4] (9) with a rare σ,π-bridging aryl group has been obtained
and crystallized. The molecular structure containing an asymmetric bridging aryl group is established for 9 in
the solid state by a single crystal X-ray crystallographic analysis. However, the identical 1H NMR features observed
at ambient temperature and -90 °C in solution (i.e., a singlet resonance for the two Cp* ligands and a symmetric
AA′BB′ pattern for the p-C6H4OMe) indicate a static or time-averaged symmetrical molecular geometry for 9.
Compound 6 crystallizes in the monoclinic space group P21/c with a ) 10.583(2) Å, b ) 14.256(3) Å, c )
16.818(4) Å, â ) 95.91 (2)°, V ) 2523.9 Å3, and Z ) 4. Refinement yielded RF ) 0.027 and RwF ) 0.033 for
3299 observed reflections (Io g 2.5σ(Io)) of 4427 unique reflections. Compound 9 crystallizes in the monoclinic
space group P21/n with a ) 11.695(2) Å, b ) 19.911(3) Å, c ) 12.539(2) Å, â ) 96.54(1)°, V ) 2900.8 Å3, and
Z ) 4. Refinement yielded RF ) 0.025 and RwF ) 0.035 for 3444 observed reflections (Io g 2.5σ(Io)) of 4526
unique reflections.
Introduction
However, with a synthetic point of view, we are more
interested in how the stabilities and reactivities of an aryl-
diazenido ligand in a given complex are influenced by a
systematic change of the natures of the metal and the ligands
present in the complex. In this latter regard, our recent research
efforts, both in the experimental arena and in the theoretical
domain, have therefore been directed at investigating the effects
exerted on the aryldiazenido ligand by different ancillary ligands
L in a complex with a general formula [Cp*Ir(L)(p-N2C6H4-
OMe)]n (n ) 0, or +1).4-6 Experimentally, we have to date
demonstrated that the singly-bent aryldiazenido fragment Cp*Ir-
(p-N2C6H4OMe) prefers to bind a weak π-acid as the ancillary
ligand L,5 and when a π-base ligand is used for L, no stable
analogous two-legged piano stool molecule can be obtained.
Especially, in the latter case, when the π-basicity of L is strong
enough, e.g., iodide, a novel asymmetric bis(aryldiazenido)-
bridged diiridium complex is obtained, which is believed to be
formed through a doubly-bent aryldiazenido intermediate species
Since the first transition metal complex containing a stable
aryldiazenido ligand, CpMo(CO)2(N2Ph), was reported by King
and Bisnette in 1964,1 numerous such compounds have been
synthesized and an interesting range of coordination geometries
for the N2Ar ligand has been established from their crystal-
lographic studies.1b,2 With the wealth of the structural chemistry
displayed by these compounds, an understanding of the elec-
tronic interactions engendering the different geometries of the
aryldiazenido ligand is naturally appealing. A valuable theoreti-
cal contribution to this has been made by Hoffmann et al. by
using N2H as the modeling ligand, whereby a general correlation
of the geometric preference of a diazenido ligand to the
electronic structure of the complex has been elucidated.3
X Abstract published in AdVance ACS Abstracts, February 1, 1997.
(1) (a) King, R. B.; Bisnette, M. B. J. Am. Chem. Soc. 1964, 86, 5695.
(b) King, R. B. J. Organomet. Chem. 1995, 500, 187.
(2) See: (a) Zollinger, H. Diazo Chemistry II; VCH: New York, 1995;
p 421. (b) Sutton, D. Chem. ReV. 1993, 93, 995. (c) Johnson, B. F.
G.; Haymore, B. L.; Dilworth, J. R. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon Press: Oxford, England, 1987; Vol. 2, p 130. (d) Niemeyer,
H. M. In The Chemistry of Diazonium and Diazo Groups; Patai, S.,
Ed.; Wiley: New York, 1978; Vol. 1, Chapter 7. (e) Bruce, M. I.;
Goodall, B. L. In The Chemistry of Hydrazo, Azo, and Azoxy Groups;
Patai, S., Ed.; Wiley: Chichester, England, 1975; Part 1, Chapter 9.
(f) Sutton, D. Chem. Soc. ReV. 1975, 4, 443.
(3) Dubois, D. L.; Hoffmann, R. NouV. J. Chim. 1977, 1, 479.
(4) Yan, X. Ph.D. Thesis, Simon Fraser University, 1993.
(5) (a) Yan, X.; Einstein, F. W. B.; Sutton, D. Can. J. Chem. 1995, 73,
939. (b) Einstein, F. W. B.; Yan, X.; Sutton, D. J. Chem. Soc., Chem.
Commun. 1990, 1446. (c) Kim, G. C.; Batchelor, R. J.; Yan, X.;
Einstein, F. W. B.; Sutton, D. Inorg. Chem. 1995, 34, 6163.
(6) Yan, X.; Batchelor, R. J.; Einstein, F. W. B.; Sutton, D. Inorg. Chem.
1996, 35, 7818.
S0020-1669(96)00993-7 CCC: $14.00 © 1997 American Chemical Society

1238 Inorganic Chemistry, Vol. 36, No. 6, 1997
Yan et al.
with a formal 16e metal center.5c,6 On the other hand, these
experimental facts have been successfully rationalized, and in
some cases predicted, by the theoretical considerations derived
from a combination of symmetry arguments and EHMO
calculations carried out on the N2Ph+ ligand.4-7 From this, it
was further anticipated that when L is a strong π-acid such as
CO or CN-, both L and the aryldiazenido ligand in the chosen
system would have a strong tendency to mutually labilize each
other, which might essentially lead to dissociation of one, or
even both, of these two ligands in the system.4,6
of the fragment ions were matched with that simulated by computer
for the species in question, and in all cases the m/z value quoted is that
for the most intense peak. Microanalyses for C, H, and N were
performed by Mr. M.-K. Yang of the Microanalytical Laboratory of
Simon Fraser University.
The [p-N2C6H4OMe][BF4] was prepared by the standard procedure
using p-methoxyaniline (Aldrich) and sodium nitrite and purified
periodically by recrystallization from acetone and diethyl ether. The
diazonium salt substituted with 15N at the terminal nitrogen (NR) was
prepared by using Na15NO2 (95% 15N, MSD Isotopes) and was
employed for the syntheses of 15N-labeled compounds. [Cp*IrCl2]2,
Cp*Ir(CO)Cl2, and Cp*Ir(CO)2 (3) were synthesized by the Maitlis
method.11 The known complex [Cp*Ir(CO)]2 (4)10 was made in high
yield by four different methods detailed below. The syntheses of
[Cp*Ir(C2H4)(p-N2C6H4OMe)][BF4] (2), as well as its isotopomer
[Cp*Ir(C2H4)(p-15NRNC6H4OMe)][BF4] (2a), have been reported
previously.4,5a
In this work, we report experimental efforts that have
attempted to test this theoretical prediction. Specifically,
attempted synthesis of the unknown complex [Cp*Ir(CO)(p-
N2C6H4OMe)][BF4] (1), where the carbonyl is a strong π-acid,
has been the main target. As possible synthetic routes to 1, we
have examined (i) reactions of [Cp*Ir(C2H4)(p-N2C6H4OMe)]-
[BF4] (2) with carbon monoxide under different reaction
conditions, (ii) reactions of Cp*Ir(CO)2 (3) directly with
[p-N2C6H4OMe][BF4] under different reaction conditions, and
(iii) reactions of [Cp*Ir(CO)]2 (4) with [p-N2C6H4OMe][BF4].
Despite these different synthetic strategies and numerous
attempts, we have had no success in obtaining 1 to date.
On the other hand, the results that have emerged from these
attempts are nevertheless interesting and informative. For
example, a strong solvent dependence has been observed for
the reaction of 3 with [p-N2C6H4OMe][BF4], in which the N2-
extrusion products [Cp*Ir(CO)2(p-C6H4OMe)][BF4] (5) and
[Cp*(CO)2Ir-Ir(Cl)(CO)Cp*][BF4] (6)8,9 were obtained in
acetone and CH2Cl2, separately, but a N2-retained aryldiazene
complex [Cp*Ir(CO)(OEt)(p-NHNC6H4OMe)][BF4] (7) was
obtained in ethanol. Furthermore, reaction of 4 with [p-N2C6H4-
OMe][BF4] afforded an interesting N2-elimination product
[Cp*2Ir2(CO)2(1-η1-1,2-η2-p-C6H4OMe)][BF4] (9), which X-ray
crystallographic analysis shows to possess a rare bridging aryl
group in the solid state. Several new facile synthetic routes to
the known compound 410 were developed during this work and
are reported.
Four Convenient Synthetic Routes to [Cp*Ir(CO)]2 (4).10 Method
1. Cp*Ir(CO)Cl2 (100 mg, 0.234 mmol) and excess predried anhydrous
Na2CO3 (≈500 mg) in 10 mL ethanol were refluxed for about 2 h with
vigorous stirring. During the reaction, the orange yellow suspension
of Cp*Ir(CO)Cl2 slowly disappeared, and a brownish slurry was
gradually produced. After the reaction mixture was cooled to room
temperature, the solvent was removed under reduced pressure, the
residue was extracted with CH2Cl2 (ca. 20 mL) and filtered through a
Celite filter. Evaporating the dark green CH2Cl2 extract to dryness
afforded the desired product quantitatively as a brownish powder. The
product was recrystallized from CH2Cl2/hexanes with a typical yield
>80%. IR: ν(CO) 1676 cm-1 (CH2Cl2). 1H NMR(CDCl3): δ 1.79
(s, Cp*). EIMS (m/z): 710 (M+), 680 (M+ - CO - 2H), 648 (M+
-
2CO - 6H), 463 ([Cp*2Ir]+).
Method 2. A reaction similar to method 1, but using a 2:1 molar
ratio of Cp*Ir(CO)2 and [Cp*IrCl2]2 under reflux with Na2CO3 for 3 h,
gave 4 in 92% yield.
Method 3. To a Schlenk tube containing a solution of Cp*Ir(CO)-
Cl2 (100 mg, 0.234 mmol) in anhydrous ethanol (20 mL) was added
excess zinc dust (≈500 mg). This mixture was degassed twice and
then stirred vigorously overnight (ca. 14 h) at room temperature. When
Cp*Ir(CO)Cl2 had completely disappeared (monitored by IR), the
solution was pumped to dryness, and the residue was extracted with
CH2Cl2 (3 × 5 mL). Removal of the solvent from the combined
extraction solution in Vacuo gave 4, generally in >90% yield.
Method 4. A reaction similar to method 3, but using a 2:1 molar
ratio of Cp*Ir(CO)2 and [Cp*IrCl2]2, also gave 4 in high yield.
Reaction of Cp*Ir(CO)2 with [p-N2C6H4OMe][BF4] in
AcetonesFormation of [Cp*Ir(CO)2(p-C6H4OMe)][BF4] (5). To a
vigorously stirred, yellow solution of Cp*Ir(CO)2 (3) (20 mg, 0.052
mmol) in acetone (2 mL) at -78 °C (dry ice/ethanol bath) was added
an acetone solution (∼1 mL) of [p-N2C6H4OMe][BF4] (12 mg, 0.052
mmol) dropwise along the wall of the Schlenk tube. The addition of
the diazonium solution should be slow enough to ensure that this
solution cools significantly before it mixes with the bulk reaction
solution. The color of the reaction solution first changed from yellow
to bright red and then to dark brown in a few seconds as the addition
proceeded. After the addition was complete, the reaction mixture was
stirred for another hour at the same temperature, and then 10 mL of
diethyl ether was slowly added with vigorous stirring. A dark brown
precipitate formed upon the addition of the diethyl ether. After the
precipitate settled, the supernatant solution was carefully removed by
pipet and the solid residue was washed three times with cold ether.
Still at -78 °C, the dark brown precipitate was dried in Vacuo, leaving
[Cp*Ir(CO)2(p-C6H4OMe)][BF4] (5) as the product in 80% yield. IR:
ν(CO) 2114 (m), 2074 (m) cm-1 (acetone). 1H NMR (CDCl3): δ 2.19
(s, 15H, C5(CH3)5), 3.80 (s, 3H, OCH3), 6.95 (q, AA′BB′ pattern, 4H,
C6H4). FABMS (m/z): 491 (M+), 463 (M+ - CO), 433 (M+ - CO -
OCH2), 405 (M+ - 2CO - OCH2). Anal. Calcd: C, 39.50; H, 3.84.
Found: C,39.81; H, 3.85.
Experimental Section
All reactions and manipulations were conducted under anhydrous
and anaerobic conditions using typical Schlenk-tube techniques under
nitrogen. All solvents were dried and freshly distilled under nitrogen
by the appropriate procedures.
Infrared spectra for solutions were measured in CaF2 cells, and solid
samples were measured either as KBr pellets or as a thin film on a
KBr disk by using a Bomem Michelson 120 FTIR instrument. Some
of the routine 1H NMR spectra were recorded at 100 MHz by using a
Bruker SY-100 spectrometer. The remaining 1H NMR and 15N NMR
spectra were obtained in the NMR service of Simon Fraser University
by Mrs. M. Tracey on a Bruker AMX-400 instrument at operating
frequencies of 400.1 and 40.5 MHz for 1H, and 15N, respectively.
Chemical shifts (δ) are reported in parts per million, downfield positive,
relative to tetramethylsilane (TMS) for 1H and relative to external
nitromethane for 15N spectra. Coupling constants are reported in hertz.
Fast atom bombardment (FAB) or electron impact (EI) mass spectra
were obtained by Mr. G. Owen on a Hewlett-Packard Model 5985 GC-
MS spectrometer equipped with a fast atom bombardment probe (xenon
source, Phrasor Scientific, Inc., accessory) and utilized samples
dispersed or dissolved in thioglycerol. The pattern of the envelopes
(7) (a) Cusanelli, A.; Batchelor, R. J.; Einstein, F. W. B.; Sutton, D.
Organometallics 1994, 13, 5096. (b) Garcia-Minsal, A.; Sutton, D.,
Organometallics 1996, 15, 332.
(8) Einstein, F. W. B.; Jones, R. H.; Zhang, X.; Yan, X.; Nagelkerke, R.;
Sutton, D. J. Chem. Soc., Chem. Commun. 1989, 1424.
(9) Cotton, F. A.; Poli, R. Inorg. Chem. 1987, 26, 590.
(10) Ball, R. G.; Graham, W. A. G.; Heinekey, D. M.; Hoyano, J. K.;
McMaster, A. D.; Mattson, B. M.; Michel, S. T. Inorg. Chem. 1990,
29, 2023.
Reaction of Cp*Ir(CO)2 with [p-N2C6H4OMe][BF4] in
CH2Cl2sFormation of [Cp*(CO)2Ir-Ir(Cl)(CO)Cp*][BF4] (6). To
(11) (a) Kang, J. W.; Moseley, K.; Maitlis, P. M. J. Am. Chem. Soc. 1969,
91, 5970. (b) Kang, K. W.; Maitlis, P. M. J. Organomet. Chem. 1971,
26, 393.

Solvent Dependence of (η5-C5Me5)Ir(CO)2 Reactions
Inorganic Chemistry, Vol. 36, No. 6, 1997 1239
a yellow solution of Cp*Ir(CO)2 (3) (100 mg, 0.26 mmol) in 3 mL of
CH2Cl2 at room temperature was directly added solid [p-N2C6H4OMe]-
[BF4] (30 mg, 0.13 mmol), and the reaction mixture was stirred
vigorously. The color of the reaction mixture changed from yellow to
greenish. To completely dissolve the [p-N2C6H4OMe][BF4] could take
about 1 h. Gas effervescence was obvious initially but gradually
diminished over 1 h as all aryldiazonium salt dissolved. After another
3-4 h of stirring, a large amount of fine yellow powder formed. The
IR spectrum of the solution after ca. 6 h showed that 3 was completely
consumed. The solution was concentrated under reduced pressure to
ca. 1.5 mL, and excess hexane was added to complete precipitation of
the yellow powder. The supernatant solution was carefully removed
by pipet, and the yellow solid residue was washed twice with diethyl
ether, affording the analytically pure product [Cp*(CO)2Ir-Ir(Cl)(CO)-
Cp*][BF4] (6) (85%). IR: ν(CO) 2058 (m), 2017 (s, br) cm-1 (CH2-
Cl2). 1H NMR (CDCl3): δ 1.94 (s, 15H, C5(CH3)5), 2.23 (s, 15H,
C5(CH3)5). 13C{1H} NMR (CDCl3): δ 10.17, 10.39 and 103.05, 106.67
(C5(CH3)5), 171.37 (CO). FABMS (m/z): 775 (M+), 745 (M+ - CO
- 2H), 717 (M+ - 2CO - 2H). Anal. Calcd: C, 31.98; H, 3.50.
Found: C, 32.08; H, 3.51.
Table 1. Crystallographic Data for the Structure Determination of
Complexes 6 and 9
complex
formula
cryst syst
space group
a (Å)
6
9
Ir2F4O3ClC23BH30
monoclinic
P21/c
10.583(2)
14.256(3)
16.818(4)
95.91(2)
4
Ir2F4O3C29BH37
monoclinic
P21/n
11.695(2)
19.911(3)
12.539(2)
96.54(1)
4
b (Å)
c (Å)
â (deg)
Z
V (Å3)
2523.9
2.266
10.66
2900.8
2.072
9.19
F (g/cm3)
µ(Mo KR) (mm-1
cryst size (mm)
l(Mo Ka1) (Å)
transmn
)
0.30 × 0.30 × 0.17
0.709 30
0.169-0.300
4-50
0.10 × 0.32 × 0.33
0.709 30
0.150-0.514
4-48
min - max 2θ (deg)
scan type
ω - 2θ
ω - 2θ
scan range (deg)
scan speed (deg/min)
1.00 + 0.35 tan θ
0.82-5.49
0.027
0.75 + 0.35 tan θ
0.70-5.50
0.025
a
Alternative Synthesis of 6. Gently bubbling CO into a suspension
of [Cp*IrCl2]2 (300 mg, 0.376 mmol) in 20 mL of freshly distilled
benzene changed the color of the reaction mixture completely to yellow
in ∼0.5 h. After another 2.5 h, CO was stopped, and Cp*Ir(CO)2 (288
mg, 0.753 mmol) and then AgBF4 (146 mg, 0.753 mmol) were added.
With the addition of AgBF4, the color of the solution immediately
changed to orange and a large amount of orange precipitate was formed.
Removal of the solvent in Vacuo gave an orange residue that was
redissolved into acetone. The grey precipitate of AgCl was removed
by filtration through Celite, and addition of excess diethyl ether to the
filtrate resulted in an orange precipitate. The supernatant solution was
carefully removed by pipet, and the orange precipitate was washed twice
with diethyl ether, affording the product 6 in 72% yield (310 mg). IR:
ν(CO) 2058 (m), 2017 (s, br) cm-1 (CH2Cl2).
Reaction of Cp*Ir(CO)2 with [p-N2C6H4OMe][BF4] in
EthanolsFormation of [Cp*Ir(CO)(OEt)(p-NHNC6H4OMe)][BF4]
(7), or 7a. To a solution of Cp*Ir(CO)2 (3) (20 mg, 0.052 mmol) in
ethanol (10 mL) was added solid [p-N2C6H4OMe][BF4] (11.5 mg,
0.052mmol) at room temperature. The color of the solution changed
from yellow to orange. IR spectra showed that absorptions (2015 and
1945 cm-1) due to Cp*Ir(CO)2 slowly decreased and a new band at
2058 cm-1 increased. After 1 h, the solvent was removed in Vacuo,
affording an orange-colored oily product. The complete characterization
of this compound was unsuccessful due to its very poor stability upon
complete removal of ethanol or after it was dissolved in other solvents.
IR: ν(CO) 2058 cm-1 (EtOH). 1H NMR (measured in less than 5
min after dissolving in acetone-d6): δ 1.12 (t, JH-H ) 7, 3H, MeCH2O),
1.96 (s, 15H, C5(CH3)5), 3.85 (s, 3H, OMe), 3.97 (b, m, 2H, MeCH2O),
RF
b
RwF
0.033
2.57
0.035
1.29
GOFc
b
a RF ) ∑(|Fo| - |Fc|)/∑|Fo| for observed data (Io g 2.5σ(Io)). RwF
2
) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2 for observed data (Io g 2.5σ(Io)). c GOF
) [∑w(|Fo| - |Fc|)2/(degrees of freedom).1/2
X-ray Structure Determination of [Cp*(CO)2Ir-Ir(Cl)(CO)Cp*]-
[BF4] (6).12 The crystallization of [Cp*(CO)2Ir-Ir(Cl)(CO)Cp*][BF4]
(6) was conducted with the slow diffusion of a large amount of diethyl
ether into a saturated CH2Cl2 solution of the complex. A suitable yellow
crystal was mounted on a glass fiber. Data were acquired using an
Enraf-Nonius CAD-4F diffractometer employing graphite monochro-
matized Mo KR radiation. Crystallographic data for 6 are summarized
in Table 1.
Anisotropic thermal motion, based on indications from the electron
density difference Fourier maps, was refined for Ir, Cl, O, and F atoms
in the structure, to yield physically reasonable values. All hydrogen
atom positions were assigned by calculation using a C-H distance of
0.96 Å and were input as fixed contributions in the subsquent
calculations; their idealized positions were recalculated between cycles
of refinement. Isotropic thermal parameters were assigned to these
hydrogen atoms, on the basis of those of their attached carbon atoms.
A weighting scheme based on counting statistics was used in the
final refinement, where the weight w was calculated from w ) [(σ-
2
(Fo))2 + 0.00035Fo ]-1. A final full matrix least-squares refinement
of 187 parameters, for 64 atoms, converged to RF ) 0.027 and RwF
)
0.033 with a maximum shift of less than 0.05 σ. In the final difference
Fourier map, the highest peak had an electron density 1.2(2) e/Å3 and
was located in the anion region at a distance of 0.38 Å from one F
atom.
7.10 (q, AA′BB′ pattern, 4H, C6H4). FABMS (m/z): 491 (M+
EtOH), 463 (M+ - EtOH - CO).
-
The 15NR-substituted complex 7a was synthesized analogously to
compound 7 by using [p-15NRNC6H4OMe][BF4]. 15N NMR (etha-
Scattering factors for neutral atoms were used in the calculation of
the structure factors, including anomalous dispersion terms for all non-
hydrogen atoms.13 All calculations were performed on a micro VAX-
II computer by using the NRC VAX Crystal Structure System.14
Preparation of [Cp*2Ir2(CO)2(1-η1-1,2-η2-p-C6H4OMe)][BF4] (9).
A solution of [p-N2C6H4OMe][BF4] (16 mg, 0.07 mmol) dissolved in
ca. 2 mL of acetone was added dropwise to a solution of [Cp*Ir(CO)]2
(4) (50 mg, 0.07 mmol) in 5 mL of acetone at -78 °C. The color of
the reaction solution changed immediately from deep green-yellow to
dark red. After stirring for 30 min, the IR spectrum of the solution
nol): δ -154 (d, J15
) 88, 15NR-H).
N-H
Preparation of Cp*Ir(CO)(OEt)(p-N2C6H4OMe) (8), or 8a. To
an orange solution of freshly synthesized 7 in situ in 5 mL of ethanol
was added ca. 0.2 mL (3 drops) of Et3N. The color of the reaction
solution changed immediately to red. The solvent was removed in
Vacuo, and an excess of hexanes was added to extract the neutral
product. After removing the insoluble [Et3NH][BF4] through a Celite
filter, the filtrate was then evaporated to dryness, resulting in a red
oily product 8 in ∼80% yield (based on the amount of Cp*Ir(CO)2
used). IR: ν(CO) 2025 (EtOH), 2029 cm-1 (hexanes). 1H NMR
(benzene-d6): δ 1.15 (t, JH-H ) 7, 3H, MeCH2O), 1.68 (s, 15H, C5-
showed only one broad absorption at 1964 cm-1
. The solvent was
then removed under reduced pressure, leaving a dark red foam.
Recrystallization of this dark red residue from CH2Cl2/hexanes at -10
°C yielded dark red crystals (<10% yield), suitable for X-ray
2
3
(CH3)5), 3.28 (s, 3H, OMe), 4.17 (dq, JH-H ) 10, JH-Me ) 7, 1H,
MeCH2O), 4.35 (dq, 2JH-H ) 10, 3JH-Me ) 7, 1H, MeCH2O), 6.83 (q,
AA′BB′ pattern, 4H, C6H4). EIMS (m/z): 536 (M+), 508 (M+ - CO),
491 (M+ - EtO), 463 (M+ - EtO - CO), 433 (M+ - EtO - CO -
OCH2). Anal. Calcd: C, 44.85; H, 5.08; N, 5.23. Found: C, 45.01;
H, 5.12; N, 5.41.
(12) Detailed X-ray single crystallographic analyses for 6 and 9 are given
in Supporting Information.
(13) International Tables for X-ray Crystallography, Kynoch Press: Bir-
mingham, England, 1975; Vol. IV, p 99.
(14) Gabe, E. J.; LePage, Y.; Charland, J.-P.; Lee, F. L.; White, P. S. J.
Appl. Crystallogr. 1989, 22, 384.
The 15NR-substituted complex 8a was synthesized analogously to
compound 8 by using 7a. 15N NMR (benzene-d6): δ 223.5 (s, 15NR).

1240 Inorganic Chemistry, Vol. 36, No. 6, 1997
Yan et al.
crystallographic analysis, covered by the dark red oil. 1H NMR spectra
of the crystals and the oil showed identical spectral features. IR: ν-
(CO) 1964 (s), 1990 (w, sh), cm-1 (acetone); 1964 (s), 1995 (w, sh)
cm-1 (ethanol), and 1968 (s), 1993 (w) cm-1 (CH2Cl2). 1H NMR
(CDCl3): δ 1.98 (s, 30H, Cp*), 3.85 (s, 3H, OMe), 6.52 d and 6.92 d
intensity, peaks at 1945, 2015 cm-1 due to Cp*Ir(CO)2 (3). After
removing the solvent in Vacuo, the H NMR spectrum of the residue
confirmed the presence of 3 and 7 but showed no signals due to the
starting material 2.
(d) Reaction of [Cp*Ir(CO)]2 (4) with 2 Equiv of [p-N2C6H4OMe]-
1
(4H, AA′BB′ pattern, C6H4). FABMS (m/z): 819 (M+), 789 (M+
-
[BF
4]. In a similar reaction to that described above for the synthesis
of 9, but using 2 equiv [p-N2C6H4OMe][BF4], compound 9, together
with some unreacted aryldiazonium salt, were found, as indicated by
CO), 763 (M+ - 2CO). Anal. Calcd: C, 38.50; H, 4.12. Found: C,
38.30; H, 4.00.
1
X-ray Structure Determination of [Cp*2Ir2(CO)2(1-η1-1,2-η2-p-
C6H4OMe)][BF4] (9).12 Crystals were obtained from CH2Cl2/hexane
at -15 °C. A red crystal of 9 was mounted in a Lindemann capilliary
tube using vacuum grease as adhesive. Intensity data (Mo KR/graphite
monochromator) were collected using an Enraf-Nonius CAD-4F
diffractometer. Data reduction included corrections for Lorentz and
polarization effects and intensity scale variations. Crystallographic data
for compound 9 are summarized in Table 1.
the IR and H NMR spectra, in the final dark tar residue.
Results and Discussion
Reactions of Cp*Ir(CO)2 with [p-N2C6H4OMe][BF4]. Pre-
viously, we have shown that Cp*Ir(C2H4)2 can readily react with
the aryldiazonium salt, [p-N2C6H4OMe][BF4], to produce the
corresponding aryldiazenido complex 2.5a,b Hence, its analogue
Cp*Ir(CO)2 (3) was initially thought to be a convenient entry
to [Cp*Ir(CO)(p-N2C6H4OMe)][BF4] (1). However, despite
numerous repetitions of this reaction under different conditions,
varying the reaction temperature, solvents, and the stoichiom-
etries of the starting materials, no [Cp*Ir(CO)(p-N2C6H4OMe)]-
[BF4] (1) was ever obtained. A dark red tar was usually
produced, which contained no nitrogen but otherwise gave
irreproducible microanalysis results. However, a few of these
attempts did produce reproducible products, and these are
discussed next.
Formation of the Nitrogen Extrusion Products 5 and 6.
Mixing equivalent quantities of 3 and [p-N2C6H4OMe][BF4] in
acetone at -78 °C gave a bright red solution, which may be
indicative of the coordination of the aryldiazenido ligand.1b,16
However, this highly colored species did not survive long and
the solution underwent a rapid further color change to dark red
in a few seconds. From the resulting solution, a dark brown
precipitate was isolated upon the addition of diethyl ether, which
was then characterized by spectroscopy and elemental analysis
as [Cp*Ir(CO)2(p-C6H4OMe)][BF4] (5), a nitrogen extrusion
product. It should be noted here that although the IR, 1H NMR,
and mass spectroscopic features observed for 5 could also
possibly be consistent with a product of formula [Cp*Ir(CO)-
(N2)(p-C6H4OMe)][BF4], a potential dinitrogen compound, the
absence of nitrogen revealed by elemental analysis rules this
out. The higher ν(CO)’s observed for 5, at 2074 and 2114 cm-1
in acetone, compared to those observed for Cp*Ir(CO)2 (3) (ν-
(CO) ) 1939, 2009 cm-1 in acetone) are consistent with the
higher oxidation state of the iridium in 5. Similar IR shifts to
higher wavenumbers for carbonyl ligands have been observed
for other Ir(III) derivatives.17
By way of contrast, reaction of 3 with 0.5 equiv of [p-N2C6H4-
OMe][BF4] in CH2Cl2 produces the diiridium complex [Cp*2-
Ir2(CO)3Cl][BF4] (6) in high yield. The solid state structure of
complex 6 has been unequivocally established by single crystal
X-ray crystallographic analysis (see Figure 1). The infrared
spectral features exhibited by 6 in solution are also consistent
with the molecular structure in the solid state. The observed
ν(CO) bands in CH2Cl2 fall within the terminal carbonyl range.
The absorption at 2058 cm-1 shows no unusual feature, but the
strong band at 2017 cm-1 is broad and asymmetric, likely
indicative of a superposition of two near-coincident peaks. The
most structurally interesting feature for this compound in
solution is that its 13C NMR spectrum at room temperature
shows only one signal, at δ 171.37 ppm, in the terminal carbonyl
range. This clearly indicates that 6 is nonrigid in solution at
room temperature, and the carbonyl ligands are rapidly ex-
changing on the NMR time scale. This has been further
The BF4- ion displayed considerable orientational disorder/thermal
motion and was ultimately modeled as three BF4- groups with refined
partial occupancies restrained to total one and subject to restraints which
imposed regular tetrahedral bonding about the boron sites. A single
isotropic thermal parameter was refined for all fluorine atoms and one
for boron. All hydrogen atoms were placed in calculated positions
(C-H, 0.95 Å) and were assigned isotropic thermal parameters
dependent on those for the corresponding carbon atoms. During
refinement, the phenyl hydrogen atom parameter shifts were linked
with those for the corresponding parameters of the carbon atoms to
which they were bound. Each CH3 group was refined as a rigid group
subject to restraints which maintained axial symmetry for the CCH3
fragment. A single parameter was refined for the isotropic thermal
motion of all methyl hydrogen atoms. Anisotropic thermal parameters
were refined for those ordered atoms which showed evidence of
significant anisotropic motion in electron density difference maps,
namely, iridium, oxygen atoms of the carbonyl groups, and the carbon
atoms of the Cp* ligands. An extinction coefficient was also refined.
Final full matrix least-squares refinement included 342 parameters for
3444 data (Io g 2.5σ(Io)) and 64 restraints. A weighting scheme, based
on counting statistics, was applied such that w(|Fo| - |Fc|)2 was near
constant as a function of both |Fo| and sin(θ/λ).
Complex scattering factors for neutral atoms13 were used in the
calculation of structure factors. The programs used for data reduction,
structure solution, and initial refinement were from the NRCVAX
Crystal Structure System.14 The program suite CRYSTALS15 was
employed in the final refinement of 9. All computations were carried
out on a MicroVAX-II computer.
Attempts To Synthesize [Cp*Ir(CO)(p-N2C6H4OMe)][BF4] (1) by
Four Methods: (a) Reaction of [Cp*Ir(C2H4)(p-N2C6H4OMe)][BF4]
(2) with Excess Carbon Monoxide in Acetone. In a typical reaction,
CO gas was bubbled through an acetone solution of [Cp*Ir(C2H4)(p-
N2C6H4OMe)][BF4] (2) (50 mg, 0.09 mmol) at room temperature. The
IR spectrum of the reaction solution showed that Cp*Ir(CO)2 (2) (ν-
(CO) ) 1939 and 2009 cm-1) was immediately formed as the major
product.
(b) Reaction of [Cp*Ir(C2H4)(p-N2C6H4OMe)][BF4] (2) with an
Equimolar Amount of Carbon Monoxide in Acetone. An acetone
solution of [Cp*Ir(C2H4)(p-N2C6H4OMe)][BF4] (2) in a Schlenk tube
equipped with a rubber serum stopper was injected with an equimolar
amount of carbon monoxide gas. After stirring overnight (ca. 10 h),
the IR spectrum of the solution showed that Cp*Ir(CO)2 (2) (ν(CO) )
1939 and 2009 cm-1) was the only observed product. After removing
the solvent in Vacuo, the 1H NMR spectrum of the residue in acetone-
d6 showed Cp*Ir(CO)2 (3) and unreacted compound 2 as the major
components.
(c) Reaction of [Cp*Ir(C2H4)(p-N2C6H4OMe)][BF4] (2) with
Excess Carbon Monoxide in Ethanol. Carbon monoxide was slowly
bubbled through an ethanol solution of [Cp*Ir(C2H4)(p-N2C6H4OMe)]-
[BF4] (2) for ca. 5 min. The color of the solution changed rapidly
from yellow to orange-yellow. The IR spectrum of this solution showed
a strong band at 2058 cm-1 due to compound 7 and two weak, equal
(15) Watkin, D. J.; Carruthers, J. R.; Betteridge, P. W. CRYSTALS;
Chemical Crystallography Laboratory, University of Oxford: Oxford,
England, 1984.
(16) Carroll, W. E.; Lalor, F. J., J. Organomet. Chem. 1980, 198, 189.
(17) Einstein, F. W. B.; Yan, X.; Zhang, X.; Sutton, D. J. Organomet.
Chem. 1992, 439, 221.

Solvent Dependence of (η5-C5Me5)Ir(CO)2 Reactions
Inorganic Chemistry, Vol. 36, No. 6, 1997 1241
Cp*Ir(CO)2 + [p-N2C6H4OMe]+ f
[Cp*Ir(CO)2]•+ + p-N2C6H4OMe• (1)
p-N2C6H4OMe•, generated in eq 1, would readily lose N2 to
give the radical [p-C6H4OMe]•. This can then recombine with
the cation radical [Cp*Ir(CO)2]+, in acetone, to yield the product
5 (eq 2). When the solvent is CH2Cl2, either p-N2C6H4OMe•
[Cp*Ir(CO)2]+• + [p-C6H4OMe]• f
[Cp*Ir(CO)2(p-C6H4OMe)]+
(2)
(5)
or p-C6H4OMe•, can react with solvent to generate Cl•, which
in turn could combine with [Cp*Ir(CO)2]•+ to form the 18e
cation [Cp*Ir(CO)2Cl]+ (eq 3). With excess of the nucleophile
Figure 1. Perspective view of the cation of 6 showing the atom
numbering scheme. Non-hydrogen atoms are represented by Gaussian
ellipsoids at the 50% probability level. Hydrogen atoms are not shown.
[Cp*Ir(CO)2]•+ + Cl• f [Cp*Ir(CO)2Cl]+
(3)
Scheme 1. Proposed Fluxional Process Interconverting CO
Groups in 6
(or electron-rich metal base) Cp*Ir(CO)2 present, a carbonyl
substitution reaction may then occur to give complex 6 (eq 4).
Cp*Ir(CO)2 + [Cp*Ir(CO)2Cl]+ f
[Cp*Ir(CO)2fCp*Ir(CO)Cl]+ + CO
(4)
(6)
So, in compound 6 the non-bridged metal-metal bond could
be formally considered as a donor-acceptor dative bond8,9
between Ir(I) and Ir(III). In this regard, compound 6 has also
been subsequently synthesized from Cp*Ir(CO)2 and Cp*Ir(CO)-
Cl2 in the presence of AgBF4. This alternative synthesis may
simply be viewed as proceeding by the formation of the
unsaturated (or solvated) 16-electron intermediate [Cp*Ir(CO)-
Cl]+ which is then attacked by the base Cp*Ir(CO)2 (eq 5).
confirmed by low temperature 13C NMR spectroscopy. At -86
°C the singlet at δ 171.37 ppm decoalesces to two singlet signals
at δ 173.0 and 168.2 ppm with an intensity ratio of 2:1. The
first is assigned to the two CO groups of the Cp*Ir(CO)2
fragment and the second to the CO of the Cp*Ir(CO)Cl
fragment. While the former are diastereotopic and should
ideally give separate resonances, their distance from the chiral
center may be the reason for the single resonance observed.
Since two chemically different Cp* groups can be clearly
identified in both ambient temperature 1H and 13C NMR spectra,
it can be concluded that the chloro ligand is not likely involved
in the fluxional process. Consequently, we propose that the
exchange of the carbonyl ligands of 6 occurs in a terminal-
bridging-terminal fashion together with rotation relative to the
metal-metal bond axis. This is illustrated in Newman projec-
tions in Scheme 1.
Cp*Ir(CO)2 + Cp*Ir(CO)Cl2 +8
Ag
[Cp*Ir(CO)2fCp*Ir(CO)Cl]+ + AgCl
(5)
(6)
Reactions similar to the formation of 5 and 6 are known for
other transition metal complexes. For example, aryl complexes
resulted from reactions of [KCo{P(OMe))3}4]19a and
[CpFe(CO)2]- 19b with [N2Ar]+, and in a chlorinated solvent
the reaction of [Tp′Mo(CO)3]-, Tp′ ) BH(3, 5-dimethyl-
pyrazolyl)3,19c with [N2Ar]+ resulted in [Tp′Mo(CCl)(CO)2], a
product involving abstraction and coupling of a solvent-based
radical. This type of radical process, initiated by one electron-
transfer from the metal to N2Ar+, has, in fact, been known since
Formation of complexes 5 and, especially, 6 in the reactions
clearly indicates a radical process is involved. Ready one-
electron oxidation of Cp*Ir(CO)2 (3) has been previously
demonstrated by us in its reaction with [C(Ph)3]+, where the
diiridium dication [Cp*(CO)2Ir-Ir(CO)2Cp*]2+, formally a
product of one-electron oxidation followed by radical coupling,
was obtained.8 The aryldiazonium ion was also known to be
an excellent one-electron oxidizing agent long before it was
shown to act as a ligand.18 To account for this radical process,
a mechanism of one electron oxidation of Cp*Ir(CO)2 by the
aryldiazonium ion is suggested (eqs 1-4). The neutral radical,
(18) For leading articles on this aspect, see: (a) Connelly. N. G.; Geiger,
W. E. Chem. ReV. 1996, 96, 877. (b) Galli, C. Chem. ReV. 1988, 88,
765. (c) Miller, I. J.; Springall, H. D. A Shorter Sidgwick’s Organic
Chemistry of Nitrogen; Clarendon Press, Oxford, England, 1969. (d)
Zollinger, H. Angew. Chem., Int. Ed. Engl. 1978, 17, 141. (e) Bunnett,
J. F.; Yijima, C. J. Org. Chem. 1977, 42, 639. (f) Kornblum, N.;
Cooper, G. D.; Taylor, J. E. J. Am. Chem. Soc. 1950, 72, 3013. (g)
Waters, W. A. J. Chem. Soc. 1942, 266.
(19) (a) Muetterties, E. L.; Hirsekorn, F. J. J. Chem. Soc., Chem. Commun.
1973, 683. (b) Nesmeyanov, A. N.; Chapovskii, K. A.; Makarova, L.
G. IzV. Akad. Nauk. SSSR, Ser. Khim. 1965, 1310. (c) Lalor, F. J.;
Desmond, T. J.; Cotter, G. M.; Shanahan, C. A.; Ferguson, G.; Parvez,
M.; Ruhl, B. J. Chem. Soc., Dalton Trans. 1995, 1709.

1242 Inorganic Chemistry, Vol. 36, No. 6, 1997
Yan et al.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) for
[Cp*2Ir2(CO)3Cl][BF4] (6)
Ir-Ir distance to be found in similar bis(pentamethylcyclopen-
tadienyl)diiridium complexes. Complex [Cp*Ir(CO)2]2[BF4]2
synthesized in this laboratory has the longest Ir-Ir bond length
of 2.839(2) Å.8 Since 6 and [Cp*Ir(CO)2]2[BF4]2 are the only
two known examples containing an Ir-Ir single bond without
any bridging ligand, the long Ir-Ir single bonds observed in
these two compounds are thus most likely due to the lack of
supportive bridging ligands. The M-C and C-O distances in
this compound are comparable with those of the dication
complex.8
Bond Lengths
Ir(1)-Ir(2)
Ir(1)-C(1)
Ir(1)-C(2)
Ir(1)-C(11)
Ir(1)-C(12)
Ir(1)-C(13)
Ir(1)-C(14)
Ir(1)-C(15)
Ir(1)-Cp*(1)b
O(1)-C(1)
O(2)-C(2)
2.8266(6)
1.907(10)
1.901(11)
2.239(10)
2.235(10)
2.257(9)
2.241(10)
2.323(10)
1.904
Ir(1)-Ir(2)
2.855a
Ir(2)-Cl
2.3939(24)
1.849(10)
2.221(10)
2.206(10)
2.198(9)
2.301(9)
2.262(10)
1.879
Ir(2)-C(3)
Ir(2)-C(21)
Ir(2)-C(22)
Ir(2)-C(23)
Ir(2)-C(24)
Ir(2)-C(25)
Ir(2)-Cp*(2)b
O(3)-C(3)
Formation of the Nitrogen-Retained Products 7 and 8.
In ethanol solution, Cp*Ir(CO)2 reacted rapidly with an
equivalent amount of [p-N2C6H4OMe][BF4] at room temperature
to produce an orange-yellow solution, from which an oily
product could be obtained upon removal of the solvent. This
1.129(13)
1.119(13)
1.152(13)
Bond Angles
Ir(2)-Ir(1)-C(1)
Ir(2)-Ir(1)-C(2)
79.2(3) Ir(1)-Ir(2)-C(3)
85.3(3)
85.10(6)
85.3(3) Ir(1)-Ir(2)-Cl
orange oil was identified on the basis of IR, 1H NMR, and 15
N
Ir(2)-Ir(1)-Cp*(1)b 130.5
C(1)-Ir(1)-Cp*(1)b 126.6
C(2)-Ir(1)-Cp*(1)b 124.4
Ir(1)-Ir(2)-Cp*(2)b 133.2
C(3)-Ir(2)-Cp*(2)b 124.2
NMR spectroscopies as the aryldiazene complex [Cp*Ir(CO)-
(OEt)(p-NHNC6H4OMe)][BF4] (7), which was futher verified
by deprotonation of the compound to yield a much more stable
neutral aryldiazenido complex Cp*Ir(CO)(OEt)(p-N2C6H4OMe)
(8), containing a doubly bent aryldiazenido ligand (eqs 6 and
7).
Cl-Ir(2)-Cp*(2)b
118.6
99.0(3)
170.3(9)
C(1)-Ir(1)-C(2)
Ir(1)-C(1)-O(1)
Ir(1)-C(2)-O(2)
96.7(4) Cl-Ir(2)-C(3)
174.7(9) Ir(2)-C(3)-O(3)
173.2(9)
a Upper limit value corrected for thermal motion. b Cp* here signifies
the center of mass of the respective C5 rings.
EtOH
Cp*Ir(CO)2 + [N2Ar]+ -CO8 [Cp*Ir(CO)(OEt)(NHNAr)]+
the discovery of the Sandmeyer reaction in 1884.20 However,
despite the extensive use, and the significant success, of this
type of reaction in preparative organic chemistry,2a,d,e,18 the
mechanism involved, whether an outer-sphere18b,21 or an inner-
sphere electron transfer,18a is still under debate. To account
for this type of radical process in our system, a direct, or outer-
sphere, electron transfer from the complex to the aryldiazonium
ion appears unfavored. According to the Marcus theory,22 the
efficiency (or rate) of electron transfer in an outer-sphere
mechanism is directly related to the thermodynamic driving
force, i.e., reduction potential, of the reductant, but relative to
Cp*Ir(C2H4)2, the complex Cp*Ir(CO)2 has a lower metal-
centred HOMO in energy, due to its strong π-electron with-
drawing CO ligands, and hence it would be expected to be a
poorer reductant than Cp*Ir(C2H4)2. In other words, if the
radical decomposition was caused by a direct electron transfer
from Cp*Ir(CO)2 to the aryldiazonium ion, the same process
should also occur even more favorably when Cp*Ir(C2H4)2 is
used. This latter situation, however, contrasts with our experi-
mental observation that the reaction of Cp*Ir(C2H4)2 with
aryldiazonium ion resulted in [Cp*Ir(C2H4)(p-N2C6H4OMe)]-
[BF4], an obvious ligand substitution product.4,5a,b
Molecular Structure of 6. In the solid state, the crystal
structure of 6 consists of discrete cations [Cp*2Ir2(CO)3Cl]+ and
the counter ions [BF4]-, separated by the normal van der Waals
distances. There are no unusually short interionic contacts. The
structure of the cation of 6 is shown in Figure 1. The selected
interatomic distances and angles for 6 are listed in Table 2.
The two iridium atoms in the cation [Cp*2Ir2(CO)3Cl]+ are
both in the typical three-legged piano-stool coordination envi-
ronment by sharing a common leg as a metal-metal bond. The
Ir(1)-Ir(2) distance of 2.827(1) Å in 6 is the second longest
(7)
(6)
[Cp*Ir(CO)(OEt)(NHNAr)]+ + NEt3 f
(7)
Cp*Ir(CO)(OEt)(N2Ar) + [NHEt3]+
(7)
(8)
Ar ) p-C6H4OMe
Since complex 7 is not stable in the ethanol-free state, it has
been only partially characterized. The IR spectrum of 7 in EtOH
shows a strong absorption at 2058 cm-1 for ν(CO). The N-H
vibration was unobservable due to overlap with solvent O-H.
No ν(NN) band could be assigned, even when the 15N-enriched
sample was used. However, the 15N NMR spectrum of the 15NR-
enriched sample of 7a showed a doublet with a chemical shift
at δ -154 ppm and a coupling constant of 88 Hz. Both the
position of the resonance and the coupling constant indicate
the presence of a terminally coordinated aryldiazene ligand in
7.5a,23 The 1H NMR spectrum of this compound was measured
immediately after it was dissolved in acetone-d6. Except for
the proton directly bonded to NR, all other proton signals were
observed in the appropriate resonance range and with the correct
integration. Notably, the highest mass values (m/z: 489, 491)
observed in the FABMS spectrum of 7 were not those of the
parent, but the fragment from loss of EtOH, i.e., [Cp*Ir(CO)-
(p-N2C6H4OMe)]+ (ironically, the species we have been trying
to obtain by synthesis).
As a matter of contrast, the complex Cp*Ir(CO)(OEt)(p-
N2C6H4OMe) (8), obtained by deprotonation of 7 in situ, showed
a much higher stability either in solution or in the solid state.
The infrared spectra of 8 exhibited ν(CO) at 2025 cm-1 in
ethanol, which is 23 cm-1 lower than the corresponding ν(CO)
observed in its parent compound 7. This decrease in wave-
number, upon removal of the NR proton, clearly indicates the
sensitivity of the ν(CO) position to the NR lone pair electrons
of the aryldiazenido ligand in this three-legged piano-stool
structure. Correlations of this kind have been previously
(20) (a) Sandmeyer, T. Chem. Ber. 1884, 17, 1633. (b) Sandmeyer, T. Chem.
Ber. 1884, 17, 2650. (c) Gattermann, L. Chem. Ber. 1890, 23, 1218.
(d) Groggins, P. H. Unit Processes in Organic Syntheses; McGraw-
Hill: New York, 1938; p 199. (e) Hodgson, H. H.; Foster, C. K. J.
Chem. Soc. 1942, 581. (f) Hodgson, H. H.; Birtwell, S.; Walker, J. J.
Chem. Soc. 1941, 770. (g) Hodgson, H. H.; Birtwell, S.; Walker, J. J.
Chem. Soc. 1942, 720.
(21) Bowden, W. L.; Brown, G. M.; Gupton, E. M.; Little, W. F.; Meyer,
T. J. Inorg. Chem. 1977, 16, 213.
(22) See reviews: (a) Marcus, R. A., Sutin, N. Biochim. Biophys. Acta
1985, 811, 265. (b) Marcus, R. A. Discuss. Faraday Soc. 1960, 29,
21.
(23) Haymore, B. L.; Hughes, M.; Mason, J.; Richards, R. L. J. Chem.
Soc., Dalton Trans. 1988, 2935.

Solvent Dependence of (η5-C5Me5)Ir(CO)2 Reactions
Inorganic Chemistry, Vol. 36, No. 6, 1997 1243
discussed in detail in terms of the electronic interactions
aryldiazenido ligand is trans to a carbonyl ligand and thus
competes for the same metal dπ-electrons.
1
involved in this type of complex.4-6 The H NMR spectrum
of 8 was recorded in C6D6. In addition to the resonances
corresponding to the protons in the Cp* and p-N2C6H4OMe
ligands, two well-resolved multiplets due to the two diaste-
reotopic methylene protons of the OEt group were also observed.
Most convincingly, the 15N NMR spectrum of 8a shows a far
downfield singlet at δ 224, indicating the presence of a doubly-
bent aryldiazenido ligand,23 which sharply contrasts with the
doublet observed at δ -154 ppm for the 15NR-labeled aryldia-
zene ligand of 7a.
Reaction of [Cp*Ir(CO)]2 with [p-N2C6H4OMe][BF4]. It
was at first thought that the reaction of [Cp*Ir(CO)]2 with
[p-N2C6H4OMe][BF4] might provide an alternative synthetic
route to [Cp*2Ir2(CO)2(η2-µ-p-N2C6H4OMe)][BF4],5b,6 that had
been synthesized in a rather low yield from the reaction of
[Cp*Ir(C2H4)(p-N2C6H4OMe)][BF4] (2) with Cp*Ir(CO)2 (3) in
ethanol.
Instead, treatment of a dark green acetone solution of [Cp*Ir-
(CO)]2 with [p-N2C6H4OMe][BF4] at -78 °C resulted in a dark
red solution, from which [Cp*2Ir2(CO)2(1-η1-1,2-η2-p-C6H4-
OMe)][BF4] (9), a nitrogen elimination product, was isolated
in a fairly good yield. Presumably similar to the formation of
5, the formation of compound 9 is also initiated by an addition
of aryldiazonium ion to the unsaturated metal-metal bond,
followed by a nitrogen extrusion from the adduct to give the
bridging aryl complex as the final product. A symmetrical
bridge-terminal transfer of the two carbonyl ligands to the two
metal centers must also be involved in this process. Chemistry
closely related to this has been seen in the reactions of
diazoalkanes with complexes containing an unsaturated metal-
metal bond, in which bridging carbene complexes are often
generated.24-26 However, to the best of our knowledge,
compound 9 is the first instance where the bridging aryl group
is introduced from an aryldiazonium ion.
Reactions of [Cp*Ir(C2H4)(p-N2C6H4OMe)][BF4] (2) with
Carbon Monoxide. Previously, we have shown that a simple
substitution of the labile ethylene ligand in compound 2 has
provided a convenient entry to a variety of aryldiazenido
complexes.5,6 Logically, a similar substitution of the ethylene
ligand of 2 by carbon monoxide was expected to lead to the
target complex [Cp*Ir(CO)(p-N2C6H4OMe)][BF4] (1). Hence,
2 was reacted first with excess carbon monoxide in acetone
solution at different temperatures, but always resulted in Cp*Ir-
(CO)2 as the only isolable organometallic species. The failure
to obtain an aryldiazenido derivative was thought possibly to
be due to the excess of carbon monoxide. Consequently, a
stoichiometrically controlled reaction was carried out, in which
equivalent amounts of 2 and carbon monoxide were used. After
a much longer reaction time, the IR and 1H NMR spectra again
revealed that, in addition to the unreacted 2, Cp*Ir(CO)2 was
the only detectable product. Hence, it is concluded that no stable
compound [Cp*Ir(CO)(p-N2C6H4OMe)][BF4] (1) can be formed
by this method.
Compound 9 is very soluble in polar solvents such as
chloroform, acetone, dichloromethane, and ethanol. However,
it is not very stable in solution at room temperature. It slowly
decomposes to [Cp*Ir(CO)]2, Cp*Ir(CO)2, and other unidentified
products. The elemental analysis for 9 immediately negated
the possibility of the presence of nitrogen in this compound.
The FABMS of 9 exhibits the appropriate molecular ion, as
well as the ions corresponding to a sequential loss of two CO
ligands. The IR spectrum of 9 in CH2Cl2 exhibits bands at 1968
and 1993 cm-1 (1964 and 1990 cm-1 in ethanol), with the band
at higher frequency much weaker than the lower one. Conse-
quently, these two bands were assigned to two terminal
carbonyls. The relative intensities and positions of the two
absorption bands indicated that the two carbonyls were, most
likely, separated with a large 2θ angle.27 The most chemically
interesting feature for 9 was its rather simple 1H NMR spectrum.
At room temperature the 100 MHz 1H NMR spectrum showed
a singlet at δ 1.95 attributed to Cp*, also a singlet at δ 3.85
and an AA′BB′ pattern in the aromatic proton range corre-
sponding to the p-C6H4OMe group. Integration of the signals
indicated a relationship of two Cp*’s and one p-C6H4OMe
ligand, in agreement with the molecular formula [Cp*2-
Ir2(CO)2(C6H4OMe)][BF4]. One single signal observed for the
two Cp* ligands indicated that they are either chemically
equivalent or undergoing exchange. In an attempt to distinguish
A similar reaction of 2 and CO in ethanol solution resulted
in [Cp*Ir(CO)(OEt)(p-NHNC6H4OMe)][BF4] (7) and Cp*Ir-
(CO)2 (3), instead of the target complex [Cp*Ir(CO)(p-N2C6H4-
OMe)][BF4] (1).
In the reactions of complex 2 with CO, the replacement of
ethylene by a CO ligand is evident. However, in acetone
solution these reactions apparently did not stop at the stage of
[Cp*Ir(CO)(p-N2C6H4OMe)][BF4] (1), the target complex, but
instead continued to give Cp*Ir(CO)2 (3), even when the
stoichiometric amount of CO was used. Cp*Ir(CO)2 (3) was
also produced by the reaction in ethanol. However, in addition
to it, a nitrogen-retained complex, [Cp*Ir(CO)(OEt)(p-NHNC6H4-
OMe)][BF4] (7), was formed. Complex 7 is clearly a form of
[Cp*Ir(CO)(p-N2C6H4OMe)][BF4] (1) stabilized by the solvent
ethanol, and its formation unequivocally shows that CO is
capable of being added without immediate loss of the N2Ar
ligand and points to the target complex [Cp*Ir(CO)(p-N2C6H4-
OMe)][BF4] (1) being an intermediate in the reaction pathway.
These observations, together with the repeated failures to obtain
1 by use of this reaction in the absence of EtOH indicate that
[Cp*Ir(CO)(p-N2C6H4OMe)][BF4] (1) itself must be either very
reactive or very unstable. This view is consistent with our
predictive argument that in such a system there is an unfavorable
electronic arrangement that leads to destabilization of a singly-
bent aryldiazenido ligand. Because of the critical role of
π-bonding in the stabilization of a singly-bent aryldiazenido
ligand in a late transition metal complex, sharing the same pair
of metal dπ-electrons with a trans-arranged strong π-acid, CO,
would significantly weaken the π-bonding between a singly-
bent aryldiazenido ligand and a late transition metal, such as
Ir(I).4,5a,6 A further note to this is that, while numerous carbonyl
aryldiazenido complexes of the late transition metals have been
synthesized and structurally characterized,2 to the best of our
knowledge, there has been no example of such a compound of
a late transition metal in the literature in which a singly-bent
1
these two possibilities, a low-temperature (-90 °C) H NMR
spectrum in a different solvent (CD2Cl2) was recorded on a
higher field (400 MHz) spectrometer. However, the features
displayed by the low-temperature 1H NMR spectrum were
identical to that observed at ambient temperature in CDCl3,
except for a slight broadening and slightly different chemical
shifts. It was then obvious that a single-crystal X-ray structural
analysis would be helpful to establish the molecular structure
(24) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1978, 17, 800.
(25) Brown, M. P.; Fisher, J. R.; Franklin, S. J.; Puddephatt, R. J.; Seddon,
K. R. J. Chem. Soc., Chem. Commun. 1978, 749.
(26) Herrmann, W. A.; Schweizer, I.; Creswick, M.; Bernal, I. J. Orga-
nomet. Chem. 1979, 165, C17.
(27) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
John Wiley & Sons: New York, 1988; p 1036.

1244 Inorganic Chemistry, Vol. 36, No. 6, 1997
Yan et al.
Table 3. Selected Bond Distances (Å) and Angles (deg) for
[Cp*2Ir2(CO)2(1-η1-1,2-η2-p-C6H4OMe)][BF4] (9)
Bond Lengths
Ir(1)-C(1)
Ir(1)-C(2)
Ir(1)-C(8)
Ir(1)-Cp*1a
Ir(1)-C(11)
Ir(1)-C(12)
Ir(1)-C(13)
Ir(1)-C(14)
Ir(1)-C(15)
O(1)-C(8)
O(3)-C(4)
C(1)-C(2)
C(2)-C(3)
C(4)-C(5)
2.324(7)
2.394(7)
1.857(9)
1.902
Ir(2)-Ir(1)
Ir(2)-C(1)
Ir(2)-C(9)
Ir(2)-Cp*2 b
Ir(2)-C(21)
Ir(2)-C(22)
Ir(2)-C(23)
Ir(2)-C(24)
Ir(2)-C(25)
O(2)-C(9)
O(3)-C(7)
C(1)-C(6)
C(3)-C(4)
C(5)-C(6)
2.7294(5)
2.054(7)
1.858(9)
1.898
2.207(7)
2.251(8)
2.293(7)
2.272(8)
2.237(8)
1.127(9)
1.41(1)
2.192(7)
2.242(8)
2.331(8)
2.335(8)
2.197(7)
1.13(1)
1.367(9)
1.43(1)
1.40(1)
1.41(1)
1.43(1)
1.35(1)
1.35(1)
Bond Angles
47.1(2)
35.2(2)
91.2(3)
130.6
127.2
115.8
73.2(2)
81.9(3)
105.2(3)
148.7
120.9(5)
69.7(4)
113.7(7)
123.3(7)
119.6(7)
119.4(7)
121.5(8)
C(1)-Ir(1)-Ir(2)
C(2)-Ir(1)-C(1)
C(8)-Ir(1)-Ir(2)
Cp*1a-Ir(1)-Ir(2)
Cp*1a-Ir(1)-C(8)
Cp*1a-Ir(1)-C(2)
C(2)-Ir(1)-Ir(2)
C(8)-Ir(1)-C(1)
C(8)-Ir(1)-C(2)
Cp*1a-Ir(1)-C(1)
C(3)-C(2)-Ir(1)
C(1)-C(2)-Ir(1)
C(6)-C(1)-C(2)
C(3)-C(2)-C(1)
C(4)-C(3)-C(2)
C(5)-C(4)-C(3)
C(6)-C(5)-C(4)
C(1)-Ir(2)-Ir(1)
C(9)-Ir(2)-C(1)
C(9)-Ir(2)-Ir(1)
Cp*2b-Ir(2)-Ir(1)
Cp*2b-Ir(2)-C(9)
Cp*2b-Ir(2)-C(1)
C(2)-C(1)-Ir(1)
Ir(2)-C(1)-Ir(1)
C(2)-C(1)-Ir(2)
C(6)-C(1)-Ir(1)
C(6)-C(1)-Ir(2)
O(1)-C(8)-Ir(1)
O(2)-C(9)-Ir(2)
C(3)-C(4)-O(3)
C(5)-C(4)-O(3)
C(7)-O(3)-C(4)
C(5)-C(6)-C(1)
56.0(2)
88.8(3)
89.4(3)
134.4
127.5
136.1
75.1(4)
76.8(2)
122.5(5)
120.8(5)
123.8(5)
174.2(8)
174.3(8)
125.4(7)
115.2(7)
114.6(7)
122.4(7)
Figure 2. Perspective view of the cation of 9 showing the atom
numbering scheme. Non-hydrogen atoms are represented by Gaussian
ellipsoids at the 50% probability level. Hydrogen atoms are not shown.
of 9. After many various attempts, crystals suitable for X-ray
crystallographic study were obtained from CH2Cl2/hexane at
-10 °C.
Molecular Structure of 9 in the Solid State. The structure
of the cation of 9 in the crystal is shown in Figure 2. The
molecule consists of a binuclear bis(pentamethylcyclopentadi-
enyl) Ir-Ir structural frame, with two terminal carbonyls bonded
to two iridium centers separately, and a p-methoxyphenyl as a
bridging ligand between the two iridiums. There are no unusual
interionic distances in the crystal structure. The selected bond
distances and bond angles for compound 9 are listed in Table
3.
a The center of mass of Cp* 1. b The center of mass of Cp* 2.
Table 4. Least-Squares Plane for Aryl Group of
[Cp*2Ir2(CO)2(1-η1-1,2-η2-p-C6H4OMe)][BF4] (9).
Equation of the Plane
3.80(4)X + 7.45(6)Y +
10.356(23)Z ) 6.818(18)
Distances (Å) to the Plane from the Atoms in the Plane
The iridium-iridium bond distance of 2.7294(5) Å found in
9 is comparable to 2.723(4) Å found in the µ2-η2-bridging
aryldiazenido analogue, [Cp*2(CO)2Ir2(η2-µ-p-N2C6H4OMe)]-
[BF4],6 and 2.7166(2) Å found in [Cp2(CO)2Ir2](η2-µ-C6H4),29
indicating a metal-metal single bond. The bridging p-meth-
oxyphenyl ligand in 9 coordinates to Ir(2) by an apparent η1-
(or σ-) linkage from C(1) of the phenyl ring and to Ir(1) by
η2- (or π-) binding from C(1) and C(2) of the aromatic ring.
The C6 ring is planar (see Table 4), and the Ir(2) atom is
approximately coplanar with the C6 ring, with only a slight
deviation of 0.050(11) Å from the least-squares plane through
the six ring atoms. Furthermore, the bond angle C(2)-C(1)-
Ir(2) (122.5(5)°) is very close to the angle C(6)-C(1)-Ir(2)
(123.8(5)°). It is then clear that the ligand p-C6H4OMe is
σ-bonded to Ir(2), apparently through an sp2 hybridized atom
C(1). The Ir(2)-C(1) distance of 2.054(7) Å is similar to the
previously reported σ-bond lengths between iridium and phenyl
carbon. For example, Ir-C(phenyl) is 2.070(15) Å in Ir(C2H4)2-
(PPh3)PPh2C6H428 and Ir-C(phenylene) 2.045(3) Å in [Cp2(CO)2-
Ir2](η2-µ-C6H4).29 It should be also noted that as a result of
the σ-π coordination of the bridging p-C6H4OMe, the η2
coordination bond is not symmetric. The Ir(1)-C(2) distance
of 2.394(7) Å is slightly longer than Ir(1)-C(1) of 2.324(7) Å,
and the internal dihedral angle between plane C(1)-C(2)-Ir-
C(1)
C(3)
C(5)
-0.013(9)
-0.006(9)
0.007(10)
C(2)
C(4)
C(6)
0.016(9)
-0.007(10)
0.004(10)
ø2 for this plane
6.887
Distances (Å) to the Plane from the Atoms out of the Plane
Ir(1)
O(3)
-2.015(8)
0.015(11)
Ir(2)
C(7)
-0.050(11)
-0.020(15)
(1) and the C6-ring is not 90° but 116.2(3)°. The bonds Ir(1)-
Ir(2) and C(1)-C(2) make a torsional angle of -62.4(4)° for
Ir(1)-Ir(2)-C(1)-C(2). The bond angle C(2)-C(1)-C(6)
(113.7(7)°), compared to C(1)-C(2)-C(3) (123.3(7)°), presum-
ably reflects a larger stereochemical influence of the σ-bound
iridium atom at C(1) relative to that of the hydrogen atom at
C(2). In the phenyl ring, the bond lengths of C(3)-C(4) and
C(5)-C(6), both 1.35(1) Å, are marginally shorter than the other
intraring C-C bond distances, 1.40(1)-1.43(1) Å, but the
alternating pattern of these intraring C-C bond distances is
interesting. Note that the bond lengths of 1.35(1) Å are shorter
than the carbon-carbon bonds (1.39 Å) in benzene itself,30 and
very close to the bond length of an isolated CdC bond in ethene
(1.34 Å).31 So it is indicative that, as a consequence of the
π-bonding to iridium from C(1) and C(2), the aromaticity of
the phenyl ring is disrupted and an alternating multiple bond
character is produced in the ring.
(28) Perego, G.; Del Piero, G.; Clerici, M. G.; Perotti, E. J. Organomet.
Chem. 1973, 54, C51.
(29) Rausch, M. D.; Gastinger, R. G.; Gardner, S. A.; Brown, R. K.; Wood,
J. S. J. Am. Chem. Soc. 1977, 99, 7870.
(30) Wells, A. F. Structural Inorganic Chemistry, 5th ed., Clarendon
Press: Oxford, England, 1984; p 920.
(31) Wells, A. F. Structural Inorganic Chemistry, 4th ed., Clarendon
Press: Oxford, England, 1975; p 727.

Solvent Dependence of (η5-C5Me5)Ir(CO)2 Reactions
Inorganic Chemistry, Vol. 36, No. 6, 1997 1245
Scheme 2. Possible Fluxional Process for Compound 9 in
Solution
supra) indicates that little distortion of this framework would
be expected during the exchange process. In other words, by
only flipping the bridging aryl group without severe distortion
of the framework of the molecule, this exchange would be
energetically facile. This may provide an explanation for the
experimental observation that in the low-temperature NMR for
compound 9 no decoalescence was observed, even at -90 °C.
Notably, similar fluxionality for other σ-π-bridging ligands
has also been observed, for example (µ-σ-CH3CdCH2)(µ-EtS)-
Fe2(CO)6,34a (µ-η1,η3-CHdCdC(CH3)2(µ-t-BuS)Fe2(CO)6,34b
(µ-H)(µ-σ-π-CHdCH2)Re2(CO)7(PPh3),34c (µ-η1,η3-RCdCRC-
(O))M2(CO)(µ-CO)Cp2 (M ) Fe, Ru),34d {µ-EtCdCEt-
(CO2)}Fe2(CO)6,34e (L-L′)Fe2(CO)6 (L-L′ ) µ-C6H5CdCC6H5S
or µ-C6H4CH2NR),34f and (µ-H)(µ-σ-π-CHdCH2)Os3(CO)10.34g
Although the proposed mechanism above can give us a
satisfactory explanation for all of the experimental observations
for 9 in solution, we still lack evidence to rule out completely
the possibility of structure B being the only isomer present in
solution. This type of symmetrically bridged aryl ligand has
ample precedent in the literature.35
Furthermore, the difference of the bond orders between C(3)-
C(4) and C(4)-C(5) would be expected to have some effect
on the -OMe group at C(4). Notably, the bond angle C(3)-
C(4)-O(3) (125.4(7)°) is unusually much more obtuse than
C(5)-C(4)-O(3) (115.2(7)°).
Formation of [Cp*Ir(CO)]2 (4). Our interest in 4 was that
a stoichiometric reaction of it with 1, or 2, equiv of [p-N2C6H4-
OMe][BF4] might result in the known bridging aryldiazenido
complex [Cp*2Ir2(CO)2(η2-µ-p-N2C6H4OMe)][BF4], or the pos-
sible target complex [Cp*Ir(CO)(p-N2C6H4OMe)][BF4] (1).
Considering the exhausting long reaction time (1 week) at 180
°C, and very narrow optimal reaction conditions required by
the available literature method,10 an alternative route to com-
pound 4 was sought, and our efforts were rewarded by several
convenient methods for preparation of this compound. Complex
4 can be smoothly synthesized in excellent yield from readily
available precursors through procedures that consist essentially
of reduction and assembly steps, as shown in Scheme 3.
Considering that the synthetic procedure described in Scheme
3b involves two different precursor compounds, logically, it
could be used in the synthesis of unsymmetrical dinuclear
complexes by changing either the ligand or the metal center of
one precursor. Preliminary trials by using this strategy have
resulted in quantitative syntheses of the unsymmetrical com-
pounds Cp*2IrRh(µ-CO)2 from [Cp*RhCl2]2 and Cp*Ir(CO)2,
and Cp*CpIr2(µ-CO)2 from [Cp*IrCl2]2 and CpIr(CO)2.36
The success of the reduction-assembly method in syntheses
of the above symmetric and unsymmetrical dinuclear complexes
suggests it may have potentially wider utility. It is noticeable
that the literature preparative methods for these types of
Another interesting structural feature of 9 is that despite the
asymmetrically coordinated bridging aryl group, the molecular
framework of Cp*Ir(CO)-Cp*Ir(CO) approximates C2 sym-
metry. This is illustrated by the barely significant difference
in the molecular dimensions of the two Cp*Ir(CO) fragments,
e.g., Ir-CO distances: 1.857(9) Vs 1.858(9) Å; and angles of
Cp*(centroid)-Ir-CO, 127.2 Vs 127.5°, C(O)-Ir-Ir, 91.2(3)
Vs 89.4(3)°, and Cp*(centroid)-Ir-Ir, 130.6 Vs 134.4°. In other
words, the asymmetrical coordination of the aryl ring through
a simultaneous σ and π bonding to the two different iridium
atoms clearly does not cause any significant difference in the
configurations of the two Cp*Ir(CO) fragments.
It should be also pointed out here that although the 1-η1-1,2-
η2- bridging pattern has often been seen in complexes with a
bridging alkenyl or alkynyl ligand that contains an unconjugated
π bond,32 it is rare in a bridged aryl complex. Previously, only
two examples of 1-η1-1,2-η2-bridging aryl complexes have been
reported.33
Possible Molecular Structure of 9 in Solution. Evidently,
the unsymmetrical molecular structure of 9 in the solid state
revealed by its X-ray crystallographic analysis is discrepant with
the spectroscopic data obtained in solution. In order to confirm
that the crystals used for the X-ray crystallographic analysis
have the same chemical composition as that of the bulk samples
1
of 9, further IR and H NMR measurements were made on a
freshly prepared solution from the same group of crystals used
for X-ray structural analysis, and these were identical to the
previous ones. This, together with the absence of any short
intermolecular distance in the crystal lattice, strongly suggests
that a symmetrically bridged aryl ligand required by the
spectroscopic data of 9 in solution is most probably the time-
averaged result of a fast exchange process involved in the
molecule 9. Consequently, an exchange mechanism of the
bridging aryl ligand in 9 is proposed and shown in Scheme 2.
In this mechanism, the bridging aryl ring is rapidly flipping
its relative orientation from structure A, through B, to C and
Vice Versa. Furthermore, the closely related structure and
symmetry of Cp*Ir(CO)-Cp*Ir(CO) in A (or C) and B (Vide
(34) (a) Seyferth, D.; Archer, C. M.; Ruschke, D. P. Organometallics 1991,
10, 3363. (b) Seyferth, D.; Womack, G. B.; Archer, C. M.; Dewan, J.
C. Organometallics 1989, 8, 430. (c) Nubel, P. O.; Brown, T. L. J.
Am. Chem. Soc. 1984, 106, 3475. (d) Dyke, A. F.; Knox, S. A. R.;
Naish, P. J.; Taylor, G. E. J. Chem. Soc., Chem. Commun. 1980, 409.
(e) Aime, S.; Milone, L.; Sappa, E.; Tiripicchio, A.; Tiripicchio-
Camellini, M. J. Chem. Soc., Dalton Trans. 1979, 1155. (f) Hickey,
J. P.; Huffman, J. C.; Todd, L. Inorg. Chim. Acta 1978, 28, 77. (g)
Shapley, J. R.; Richter, S. I.; Tachikawa, M.; Keister, J. B. J.
Organomet. Chem. 1975, 94, C43.
(35) (a) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th
ed.; John Wiley & Sons, 1988, p 1125. (b) Evans, D. G.; Hughes, G.
R.; Mingos, D. M. P.; Bassett, J. M.; Welch, A. J. J. Chem. Soc.,
Chem. Commun. 1980, 1255. (c) Meyer, E. M.; Gambarotta, S.;
Floriani, C.; Chiesi-Villa, A.; Guastini, C. Organometallics 1989, 8,
1067. (d) Nobel, D.; van Koten, G.; Spek, A. L. Angew. Chem., Int.
Ed. Engl. 1989, 28, 209. (e) de Graaf, P. W. J.; Boersma, J.; van der
Kerk, G. J. M. J. Organomet. Chem. 1977, 127, 391. (f) Bradford, C.
W.; Nyholm, R. S.; Gainsford, G. J.; Guss, J. M.; Ireland, P. R.; Mason,
R. J. Chem. Soc., Chem. Commun. 1972, 87. (g) van Koten, G.;
Leusink, A. J.; Noltes, J. G. J. Organomet. Chem. 1974, 85, 105; 1973,
56, 379; 1974, 80, C56. (h) Schmidbaur, H.; Inoguchi, Y. Chem. Ber.
1980, 113, 1646. (i) Nesmeyanov, A. N.; Perevalova, E. G.; Granfberg,
K. I.; Lemenovskii, D. A.; Baukova, Y. V.; Afanassova, O. B. J.
Organomet. Chem. 1974, 65, 131.
(32) For leading review articles on this aspect, see: (a) Lotz, S.; van
Rooyen, P. H.; Meyer, R. AdV. Organomet. Chem. 1995, 37, 219. (b)
Holton, J.; Lappert, M.; Pearce, R.; Yarrow, P. I. W. Chem. ReV. 1983,
83, 135.
(33) (a) Pez, G. P.; Putnik, C. F.; Suib, S. L.; Stucky, G. D. J. Am. Chem.
Soc. 1979, 101, 6933. (b) Hoferkamp, L. A.; Rheinwald, G.; Stoeckli-
Evans, H.; Su¨ss-Fink, G. Organometallics 1996, 15, 704.

1246 Inorganic Chemistry, Vol. 36, No. 6, 1997
Scheme 3. Facile Synthetic Routes to Compound 4
Yan et al.
that were not reproducible or isolable. This is perhaps not
surprising since there are many instances in the literature in
which attempts to obtain aryldiazenido carbonyl complexes by
direct reaction of the aryldiazonium ion and metal carbonyl
derivatives have failed.39 Despite this, the results that have
emerged from these attempts are nevertheless interesting.
Several different products have been isolated from the reactions
of Cp*Ir(CO)2 and [p-N2C6H4OMe][BF4] in different reaction
media, i.e., formation of [Cp*Ir(CO)2(Ar)]+ in acetone, [Cp*Ir-
(CO)2 f Ir(CO)(Cl)Cp*]+ in CH2Cl2, and [Cp*Ir(CO)(OEt)-
(NHNAr)]+ in EtOH. Also the compound [Cp*2Ir2(CO)2(1-
η1-1,2-η2-p-C6H4OMe)][BF4] (9) with a rare σ,π-bridging aryl
ligand is obtained from the reaction of [Cp*Ir(CO)]2 and N2-
Ar+ and provides the first example of a bridging aryl group
generated from an aryldiazonium ion.
Acknowledgment. We thank the Natural Science and
Engineering Research Council of Canada for support of this
work by means of research, equipment, and infrastructure grants
to F.W.B.E. and D.S. and Johnson Matthey & Co. for a generous
loan of iridium trichloride.
dinuclear complexes of Co, Rh, or Ir usually always involve
vigorous reaction conditions, such as photolysis or thermolysis.
For example, Cp*2Co2(µ-CO)2 has been made by thermolysis
of Cp*Co(CO)2 in toluene for 24 h, or by photolysis in THF
for 4 days,37 Cp*2Rh2(µ-CO)2 has been synthesized by pyroliz-
ing Cp*Rh(CO)2 at high pressure,38 and as mentioned above,
Cp*2Ir2(µ-CO)2 was previously made by pyrolizing Cp*Ir(CO)2
at 180 °C for 1 week.10 Evidently, a further extension of the
method developed here to make these and other, both known
and unknown, dinuclear complexes will be useful, and a study
of this aspect is being undertaken.
Supporting Information Available: For compound 6, text giving
the detailed crystallographic analysis and listings of fractional atomic
coordinates and isotropic temperature factors for non-hydrogen atoms
(Table S1), anisotropic thermal parameters (Table S2), fractional atomic
coordinates and isotropic temperature factors for hydrogen atoms (Table
S3), and for compound 9, text giving the detailed crystallographic
analysis and listings of fractional atomic coordinates and isotropic or
equivalent isotropic temperature factors for non-hydrogen atoms (Table
S4), anisotropic thermal parameters (Table S5), fractional atomic
coordinates and isotropic temperature factors for hydrogen atoms (Table
S6) (10 pages). Ordering information is given on any current masthead
page.
Conclusion
The majority of the procedures in this study that were tried
in order to obtain the target complex [Cp*Ir(CO)(p-N2C6H4-
OMe)][BF4] (1) were frustrated by the formation of products
IC960993V
(36) Spectroscopic data for Cp*2IrRh(µ2-CO)2. IR: ν(CO) 1703 cm-1 (CH2-
Cl2). 1H NMR (CDCl3): δ 1.55 (s, 15H, Cp*), 1.88 (s, 15H, Cp*′).
EIMS (m/z): 622 (M+), 592 (M+ - CO - 2H), 564 (M+ - 2CO -
2H), 562 (M+ - 2CO - 4H), 560 (M+ - 2CO - 6H), 463 ([Cp*2-
Ir]+), 373 ([Cp*2Rh]+). Spectroscopic data for Cp*CpIr2(µ2-CO)2.
IR: ν(CO) 1695 cm-1 (CH2Cl2). 1H NMR (C6D6): δ 1.58 (s, 15H,
Cp*), 5.14 (s, 5H, Cp).
(37) Bailey, W. I., Jr.; Collins, D. M.; Cotton, F. A.; Baldwin, J. C.; Kaska,
W. C. J. Organomet. Chem. 1979, 165, 373.
(38) Nuttin, A.; Maitlis, P. M. J. Organomet. Chem. 1979, 166, C21.
(39) (a) King, R. B.; Bisnette, M. B. Inorg. Chem. 1966, 5, 300. (b) Carroll,
W. E.; Lalor, F. J. J. Organomet. Chem. 1973, 54, C37. (c) Schrauzer,
G. N. Chem. Ber. 1961, 94, 1891. (d) Clark, J. C.; Cookson, R. C. J.
Chem. Soc. 1962, 686. (e) Barrientos-Penna, C. F.; Einstein, F. W.
B.; Sutton, D.; Willis, A. C. Inorg. Chem. 1980, 19, 2740. (f)
Barrientos-Penna, C. F.; Gilchrist, A. B.; Klahn-Oliva, A. H.; Hanlan,
A. J. L.; Sutton, D. Organometallics 1985, 4, 478. (g) Connelly, N.
G.; Demidowicz, Z. J. Organomet. Chem. 1974, 73, C31.