Synthesis, isolation, and characterization of trisodium tricarbonyliridate (3-), Na3[Ir(CO)3]. Initial studies on its derivative chemistry and structural characterizations of trans-[Ir(CO)3(EPh3)2]-, E = Ge, Sn, and trans-[Co(CO)3(SnPh3)2]-

Article abstract of DOI:10.1021/ic0105011

Reduction of Na[Ir(CO)₄] by sodium metal in (Me₂N)₃PO, followed by treatment with liquid ammonia, provided high yields (ca. 90%) of unsolvated Na₃[Ir(CO)₃], a thermally stable, pyrophoric orange solid. This substance contains iridium in its lowest known formal oxidation state of -3 and has been characterized by IR spectroscopy, elemental analyses, and derivative chemistry, i.e., by its conversion to the triphenylgermyl and triphenylstannyl complexes, trans-[Ir(CO)₃(EPh₃)₂]^-, E = Ge, Sn. Single-crystal X-ray structures of the tetraethylammonium salts of these species, as well as [Co(CO)₃(SnPh₃)₂]^-, confirm the trigonal bipyramidal nature of the anions, originally predicted on the basis of their IR spectra in the carbonyl stretching frequency region. These structural characterizations provide important additional evidence for the presence of metal tricarbonyl units in Na₃[M(CO)₃], M = Co, Ir.

Full text of DOI:10.1021/ic0105011

Inorg. Chem. 2001, 40, 5279-5284
5279
Synthesis, Isolation, and Characterization of Trisodium Tricarbonyliridate (3-),
Na3[Ir(CO)3]. Initial Studies on Its Derivative Chemistry and Structural Characterizations
of trans-[Ir(CO)3(EPh3)2]-, E ) Ge, Sn, and trans-[Co(CO)3(SnPh3)2]- †,1
Jessica M. Allen, William W. Brennessel, Carrie E. Buss, John E. Ellis,*,‡
Mikhail E. Minyaev, Maren Pink, Garry F. Warnock, Mark L. Winzenburg, and
Victor G. Young, Jr.
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455
ReceiVed May 14, 2001
Reduction of Na[Ir(CO)4] by sodium metal in (Me2N)3PO, followed by treatment with liquid ammonia, provided
high yields (ca. 90%) of unsolvated Na3[Ir(CO)3], a thermally stable, pyrophoric orange solid. This substance
contains iridium in its lowest known formal oxidation state of -3 and has been characterized by IR spectroscopy,
elemental analyses, and derivative chemistry, i.e., by its conversion to the triphenylgermyl and triphenylstannyl
complexes, trans-[Ir(CO)3(EPh3)2]-, E ) Ge, Sn. Single-crystal X-ray structures of the tetraethylammonium salts
of these species, as well as [Co(CO)3(SnPh3)2]-, confirm the trigonal bipyramidal nature of the anions, originally
predicted on the basis of their IR spectra in the carbonyl stretching frequency region. These structural
characterizations provide important additional evidence for the presence of metal tricarbonyl units in Na3[M(CO)3],
M ) Co, Ir.
Introduction
substantial interest since they contain transition metals in their
lowest known formal oxidation states,3 and for this reason they
have been referred to as “super-reduced” metal carbonyls.9 In
the original report on [Co(CO)3]3-, a formally analogous iridium
complex was also described,10 but no full account of the iridium
research has been available to date. The claimed existence of
[Ir(CO)3]3- was based mainly on IR spectral and derivative
studies, e.g., its reactions with Ph3ECl, E ) Ge, Sn, to provide
the respective [Ir(CO)3(EPh3)2]-.10 Recently, tetraethylammo-
nium salts of the latter, along with the related [Co(CO)3(SnPh3)2]-,
were characterized by single-crystal X-ray structural studies.
By this method, the presence of tricarbonylmetal units in these
derivatives and, by inference, in the analogous carbonylmetalate-
(3-) precursors was established for the first time. In this article
we describe these structural studies along with the first full
account of the synthesis, isolation, and characterization of Na3-
[Ir(CO)3], the only known Ir(III-) species.
Metal carbonyl anions are important precursors to a tremen-
dous variety of organometallic, inorganic, and organic species.2
They are also of interest as the first compounds to contain
transition metals in negative formal oxidation states,3 i.e.,
[Co(CO)4]- and [Fe(CO)4]2-, which were originally reported
more than 60 years ago.4 These anions have been shown to
mimic halides, e.g., I-, and chalcogenides, e.g., S2-, respec-
tively, in many of their chemical reactivity patterns.5 The
existence of main group atomic trianion salts, e.g., Na3P,
suggested that electronically equivalent or isolobal metal
carbonyl trianions should also be capable of existence.6 About
25 years ago the first compounds of this class, i.e., Na3[M(CO)4]
) Mn, Re, were obtained via reductions of the respective
pentacarbonylmetalates(1-) of these elements.7 Soon afterward,
tricarbonylcobaltate(3-), along with several others containing
3d, 4d, and 5d elements, were reported.8 These species are of
Experimental Section
† Dedicated to Professor Alan Davison, F.R.S., of MIT on the occasion
of his 65th birthday.
General Procedures and Starting Materials. All operations were
performed under an atmosphere of 99.9% argon or 99.5% carbon
monoxide, further purified by passage through columns of activated
BASF catalyst and molecular sieves. Also, the CO was passed through
a column of Ascarite, which is a trade name for a self-indicating sodium
hydroxide nonfibrous silicate formulation, for the quantitative absorption
of CO2. Similar products used by microanalysts should provide
satisfactory results. All connections involving the gas purification
systems were made of glass, metal, or other materials impermeable to
air.11 Solutions were transferred via stainless steel double-ended needles
(cannulas) whenever possible. Standard Schlenk techniques were
‡ E-mail: ellis@chem.umn.edu.
(1) Highly Reduced Organometallics. 55. Part 54: Ellis, J. E.; Warnock,
G. W. In Synthetic Methods of Organometallic and Inorganic
Chemistry (Herrman/Brauer); Hermann, W. A., Ed.; G. Thieme:
Stuttgart, 2000; Vol. 9, pp 141-152. Part 53: Barybin, M. V.; Young,
V. G.; Ellis, J. E. J. Am. Chem. Soc. 2000, 122, 4678.
(2) Calderazzo, F. Carbonyl complexes of the Transition Metals. In
Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; J. Wiley:
Chichester, 1994; Vol. 2.
(3) Beck, W. Angew. Chem., Int. Ed., Engl. 1991, 30, 168.
(4) (a) [Fe(CO)4]2-: Hock, H.; Stuhlmann, H. Chem. Ber. 1929, 62, 431.
Hieber, W.; Leutert, F. Z. Anorg. Allg. Chem. 1932, 204, 145. (b)
[Co(CO)4]-: Hieber, W.; Schulten H. Z. Anorg. Allg. Chem. 1937,
232, 17, 29.
(5) Ellis, J. E. J. Chem. Educ. 1976, 53, 2.
(6) Ellis, J. E. J. Organomet. Chem. 1975, 86, 1.
(7) (a) Ellis, J. E.; Faltynek, R. A. J. Chem. Soc., Chem. Commun. 1975,
966. (b) Warnock, G. F.; Moodie, L. C.; Ellis, J. E. J. Am. Chem.
Soc. 1989, 111, 2131.
(9) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; Wiley: New York, 1999; p 694.
(10) Ellis, J. E.; Barger, P. T.; Winzenburg, M. L. J. Chem. Soc., Chem.
Commun. 1977, 686.
(11) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-SensitiVe
(8) Ellis, J. E. AdV. Organomet. Chem. 1990, 31, 1.
Compounds, 2nd ed.; Wiley-Interscience: New York, 1986.
10.1021/ic0105011 CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/30/2001

5280 Inorganic Chemistry, Vol. 40, No. 20, 2001
Allen et al.
employed with a double-manifold vacuum line.11-14 Unless otherwise
stated below, all starting materials were obtained from commercial
sources and freed from oxygen and moisture before use and all reaction
mixtures were stirred with glass-covered magnetic stir bars. The
preparation of [Et4N][Co(CO)3(SnPh3)2] was carried out as previously
described.10 Solvents were freed of impurities by standard procedures.11
Liquid ammonia was distilled from sodium metal. Hexamethylphos-
phoramide (HMPA) was twice distilled in vacuo, first from calcium
hydride and then from a small piece of sodium, which first dissolved
at room temperature to provide a homogeneous deep blue solution.
(CAUTION: HMPA should be handled with extreme care as it is a
potential carcinogen!) HMPA solutions of Na3[Ir(CO)3] for infrared
spectra were very difficult to obtain free of oxidation products and
were prepared in a Vacuum Atmosphere Corporation drybox and
transferred into sealed CaF2 solution cells that had been previously
purged with dilute blue solutions of Na in HMPA to remove absorbed
moisture, oxygen, and other potential oxidants. Infrared spectra were
recorded on a Perkin-Elmer 283 grating spectrometer or a Mattson 6021
FTIR spectrometer with samples in 0.1 mm sealed NaCl or CaF2 cells.
Nujol (mineral oil) mulls of air-sensitive solids were prepared in an
argon-filled drybox. NMR samples were sealed in 5 mm tubes and
were run on Varian Unity-300, Nicolet NT-300 WB, or IBM NR-300
AF spectrometers. Melting points are uncorrected and were obtained
in sealed capillaries on a Thomas-Hoover unimetal apparatus. Mi-
croanalyses were carried out by H. Melissa and G. Reuter Analytical
Laboratories, Engelskirchen, Germany.
3.01. IR (mineral oil mull) ν(CO): 1908 sh, 1893 vs cm-1. IR (THF
solution) ν(CO): 1891 vs cm-1. Crystalline 2 is stable in air for brief
periods but should be stored under anaerobic conditions. Unlike 1, solid
2 appears to be stable indefinitely at room temperature. Solutions of 2
in THF are very air sensitive.
Na3[Ir(CO)3] (3). Colorless 1 (0.66 g, 2.0 mmol, assuming 1 is
unsolvated) was combined with sodium sand (0.15 g, 6.5 mmol) in a
round-bottom flask. Freshly distilled HMPA (15 mL) was added, and
the reaction mixture was stirred under dynamic vacuum (ca. 0.01 Torr)
for 12 h at 20 °C. The resulting dark yellow solution was then frozen
at -78 °C, and anhydrous ammonia (60 mL) was added via cannula.
The mixture was stirred at reflux (ca. -33 °C) until the solvents had
completely mixed. A yellow-orange precipitate in a deep yellow-red
solution was present after 2 h. The reaction mixture was cooled to -78
°C and filtered at -78 °C using a previously described jacketed filtration
unit.17a After the solid was washed thoroughly with liquid ammonia (4
× 50 mL), it was dried in vacuo at room temperature to provide 0.63
g (90% yield based on unsolvated 1) of orange powder, which provided
satisfactory analysis for unsolvated 3. Anal. Calcd for C3IrNa3O3 (%):
C, 10.44; H, 0.00; Na, 19.98. Found (%): C, 10.17; H, 0.15; Na, 19.84.
IR (mineral oil mull) ν(CO): 1805 w sh, 1642 vs (br) cm-1. IR (HMPA)
ν(CO): 1666 vs (br) cm-1. No N-H or C-H absorptions were present
in fluorolube mull spectra of 3. Compound 3 was exceedingly air
sensitive and observed to slowly darken without melting between 200
and 300 °C under an inert atmosphere.
[Et4N][Ir(CO)3(SnPh3)2] (4). Route a: From Ir4(CO)12. Ir4(CO)12
(0.57 g, 0.52 mmol) was reduced by excess sodium sand (0.l70 g, 30
mmol) in 10 mL of THF under an atmosphere of carbon monoxide as
described above in the synthesis of 1. Following filtration to remove
the excess sodium metal, all solvent was removed in vacuo. The
resulting colorless dry salt was then treated with sodium sand (0.142
g, 6.2 mmol, 3.0 equiv based on Ir4(CO)12) and stirred in 70 mL of
liquid ammonia for 3 h at -60 °C to give the usual yellow-orange
reaction mixture. Subsequently, solid Ph3SnCl (1.81 g, 4.70 mmol) was
added rapidly, via a bent Schlenk tube, to the reaction mixture. A white
suspension rapidly formed. After 1.5 h, solid [Et4N]Br (0.70 g. 3.3
mmol) was added and the reaction mixture was stirred for about 2 h at
-78 °C. Following evaporation of the liquid ammonia, the resulting
ivory solid was washed with diethyl ether (5 × 20 mL) to remove
traces of ammonia, dissolved in 20 mL of THF, and filtered through a
medium-porosity fritted disk. Addition of excess heptane to the filtrate
gave pale yellow crystals. Recrystallization from THF/absolute ethanol
afforded 1.06 g (46% based on Ir4(CO)12) of colorless needles of
satisfactorily pure 4, which began to decompose without melting at
about 160 °C. Anal. Calcd for C47H50IrNO3Sn2 (%): C, 51.07; H, 4.55;
N, 1.27. Found (%): C, 51.14; H, 4.65; N, 1.27. IR (mineral oil mull)
ν(CO): 1980 w, 1911 sh, 1901 s cm-1. IR (THF) ν(CO): 1924 vs,
1912 sh cm-1. 1H NMR (300 MHz, acetone-d6, 25 °C): δ ) 7.1 - 7.4
(m, 30 H, SnPh3), 3.1 (q, 8H, CH2 of Et4N), 1.2 (tt, 12 H, CH3 of
Et4N), ppm. Compound 4 appears to be stable indefinitely in the solid
state toward air oxidation at room temperature. It dissolves in CH2Cl2,
THF, N,N-dimethylformamide, CH3CN, acetone, and HMPA to provide
only slightly air sensitive solutions. For example, a THF solution of 4
was allowed to evaporate slowly in air to give long colorless needles
of pure 4.
Na[Ir(CO)4] (1). The method of Malatesta et al. was employed.15
Typically, Ir4(CO)12 (0.98 g, 0.89 mmol) was added to excess sodium
sand16 (1.20 g, 52 mmol) in a round-bottom flask. Tetrahydrofuran (20
mL) was transferred via cannula to the flask containing the reactants,
and the inert atmosphere was replaced with carbon monoxide at ambient
pressure. The reaction mixture slowly acquired a red hue as it was
stirred. After 24 h, a clear pale yellow solution of Na[Ir(CO)4] was
separated from muddy brown suspended solids via filtration. Removal
of solvent in vacuo provided 0.69 g (60% yield, if unsolvated, based
on Ir4(CO)12) of colorless powdery 1, which appeared to be essentially
free of THF, based on its fluorolube mull IR spectrum. IR (mineral oil
mull) ν(CO): 2018 w, 1938 sh, 1871 vs (br) cm-1. IR (THF solution)
ν(CO): 1892 vs, 1856 sh cm-1. The latter spectrum is in substantial
agreement with that originally reported by Malatesta and co-workers.15
The solid was of marginal thermal stability and darkened to a tan color
after several days at room temperature. Due to its thermal instability,
no satisfactory elemental analyses could be obtained, but it was
converted to a thermally stable [Ph4As]+ salt, vide infra.
[Ph4As][Ir(CO)4] (2). Reduction of Ir4(CO)12 (0.400 g, 0.362 mmol)
by excess 0.75% sodium amalgam (7.0 mL; 0.71 g, 31 mmol Na) in
THF (40 mL) was carried out with vigorous stirring under an
atmosphere of carbon monoxide. Three days were required before the
reduction was mostly complete, but IR spectra still showed the presence
of small amounts of less reduced carbonyl iridates. The resulting pale
brown solution of Na[Ir(CO)4] was separated from the excess sodium
amalgam via decantation and added to a solution of [Ph4As]Cl (0.66
g, 1.5 mmol) in 80 mL of water at 0 °C. The resulting brown solid
was isolated on a coarse porosity fritted disk, carefully washed with
20 mL of water, and dried in vacuo. Crystallization from THF/ether,
followed by washing with isopentane and drying in vacuo at room
temperature, afforded 0.52 g (52% yield based on Ir4(CO)12) of
homogeneous yellow crystalline 2 of satisfactory purity. Anal. Calcd
for C28H20AsIrO4 (%): C, 48.91; H, 2.93. Found (%): C, 48.81; H,
Route b: From Na[Ir(CO)4] (1). Freshly prepared 1, (0.25 g, 0.76
mmol) was reduced by a slight excess of sodium metal (0.0580 g, 2.52
mmol, 3.2 equiv) in 40 mL of liquid ammonia to rapidly produce a
slurry of yellow-orange solid, which was shown in other studies to be
an inseparable mixture of Na3[Ir(CO)3] and Na2C2O2. At -78 °C, a
solution of Ph3SnCl (0.95 g, 2.5 mmol, 3.2 equiv) in 10 mL of THF
was added via cannula. The remainder of the procedure was identical
to that of route a, except the product was recrystallized from acetone/
ether to provide 0.74 g (87% based on Na[Ir(CO)4]) of colorless
microcrystals that were identical to bona fide 4, obtained by route a.
[Et4N][Ir(CO)3(GePh3)2] (5). Ir4(CO)12 (0.50 g, 0.45 mmol) was
reacted with sodium sand (0.18 g, 7.8 mmol) in HMPA (20 mL) for 2
(12) Herzog, S.; Dehnert, J.; Luhder, K. In Technique of Inorganic
Chemistry; Johassen, H. B., Ed.; Wiley-Interscience: New York, 1968;
Vol. 7, pp 119-149.
(13) Kramer, G. W.,; Levy, A. B.; Midland, M. M. In Organic Synthesis
Via Boranes; Brown, H. C., Ed.; J. Wiley: New York, 1975; Chapter
9.
(14) Wayda, A. L., Darensbourg, M. Y., Eds. Experimental Organometallic
Chemistry; ACS Symposium Series 357; American Chemical Soci-
ety: Washington, DC, 1987.
(15) Angoletta, M.; Malatesta, L.; Caglio, G. J. Organomet. Chem. 1975,
94, 99.
(16) King, R. B. Organometallic Syntheses; Academic Press: New York,
1965; Vol. 1, pp 105-106.
(17) (a) See p 56, Figure 13 of ref 11. (b) SAINT, V6.1; Bruker Analytical
X-Ray Systems: Madison, WI, 1999. (c) An empirical correction for
absorption anisotropy: Blessing, R. Acta Crystallogr., Sect. A 1995,
51, 33.

Synthesis, Isolation, and Characterization of Na3[Ir(CO)3]
Inorganic Chemistry, Vol. 40, No. 20, 2001 5281
Table 1. Crystal Data, Data Collection, Solution, and Refinement for 4, 5, and 6 as CH2Cl2 Solvates
compd
4‚CH2Cl2
C48H54Cl2IrNO3Sn2
1191.39
block, colorless
0.12 × 0.12 × 0.12
monoclinic
Cc
23.933(2)
9.858(1)
20.785(2)
90.00
105.913(2)
90.00
4715.9(8)
4
1.678
4.019
5‚CH2Cl2
C48H52Cl2Ge2IrNO3
1099.19
block, colorless
0.17 × 0.16 × 0.05
monoclinic
Cc
23.722(3)
9.780(1)
20.679(2)
90.00
106.946(2)
90.00
4589.2(9)
4
1.591
4.351
6‚CH2Cl2
C48H52Cl2CoNO3Sn2
1058.12
block, colorless
0.10 × 0.10 × 0.08
monoclinic
Cc
23.804(1)
9.8380(5)
20.788(1)
90.00
106.819(1)
90.00
empirical formula
formula mass
cryst habit, color
cryst size, mm
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
ν, Å
4660.0(4)
4
1.508
1.570
2128
Z
F
calcd, g cm-3
µ(Mo KR), mm-1
F(000)
2328
2184
temp (K)
θ range (deg)
completeness to θ ) 27.51 (%)
index range
173(2)
1.77-27.51
98.9
-31 ) h ) 27
-12 ) k ) 12
-26 ) l ) 26
23708
173(2)
1.79-27.52
99.5
-30 ) h ) 27
-12 ) k ) 12
-26 ) l ) 26
20663
173(2)
1.79-27.48
99.6
-30 ) h ) 30
-12 ) k ) 12
-26 ) l ) 26
23428
rflns collected
unique rflns
9708
0.0321
9783
0.0408
10092
0.0434
R(int)a
obsd data
variables
9066
518
8993
518
8217
518
absolute structure param
weighting params -a, bb
GOF on F2 c
0.012(3)
0.0249, 4.4766
1.057
0.0278/0.0580
0.0320/0.0591
0.672/-0.537
0.004(5)
0.0378, 0.0000
1.024
0.0351/0.0733
0.0413/0.0759
1.548/-0.537
0.004(14)
0.0179, 0.0000
0.922
0.0330/0.0501
0.0501/0.0538
0.500/-0.401
R1/wR2 indices with I > 2σ(I)d,e
R1/wR2 indices (all data)
largest peaks and holes, e Å-3
a Rint ) ∑|Fo2 - Fc2 |/∑|Fo |. b Weighting scheme: w ) q/σ2(Fo ) + (aP)2 + bP and P ) (Fo2 - 2Fc2)/3. c GOF ) S ) ∑[w(Fo2 - Fc2)2]/(n -
2
2
p)1/2
.
d R1 ) ∑||Fo| - |Fc||/∑|Fo|. e wR2 ) [∑[w(|Fo | - |Fc2|)2]/∑w(Fo )2]1/2
.
2
2
h in vacuo (ca. 0.01 Torr) at room temperature. The final reaction
mixture was deep blue due to excess sodium. After 12 h at room
temperature, it had changed to a deep red color. Solid Ph3GeCl (1.00
g, 5.4 mmol) was added, and, after being stirred for 3 h at room
temperature, the reaction mixture was a paler red hue. Transfer of this
mixture to an excess of Et4N+ Br- (1.5 g, 7 mmol) in 100 mL of water
gave a gummy orange precipitate. After decanting the excess liquid
from the solid, the latter was dried in vacuo and dissolved in 15 mL of
THF. Following filtration, all but about 5 mL of THF was removed to
provide tan crystals in a deep red solution. Addition of excess absolute
ethanol caused the remaining product to precipitate. The resulting
product was washed with diethyl ether and dried in vacuo. Recrystal-
lization from THF/ether gave 0.67 g (36%) of silvery pale green
crystalline 5, which provided satisfactory elemental analyses and
decomposed without melting at about 145 °C. Anal. Calcd for C47H50-
Ge2IrNO3 (%): C, 55.65; H, 4.97; N, 1.38. Found (%): C, 55.90; H.
5.14, N, 1.00. IR (mineral oil mull) v(CO): 1982 w, 1914 sh, 1899 s
frames were collected with 0.30° steps in ω. For all structures, the
program SADABS was used to correct the data for absorption.17b Final
cell constants were calculated from 6621 (4), 4978 (5), and 8106 (6)
strong reflections after integration by the program SAINT 6.01.17c
All structures were solved by the Patterson method, refined by full-
matrix least squares minimization on F2 and Fourier techniques using
the SHELXTL-PLUS suite of programs (SHELXTL-Plus V 5.4, Bruker
Analytical X-Ray Systems, Madison, WI). All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms were placed in ideal
positions and refined as riding atoms with individual isotropic displace-
ment parameters. Crystal data, data collection, solution, and refinement
information for 4, 5, and 6 are shown in Table 1. Additional
crystallographic details are found in the Supporting Information.
Results and Discussion
Syntheses and Isolation of Na3[Ir(CO)3]. Original syntheses
of tricarbonyliridate(3-) involved the direct reduction of Ir4-
(CO)12 by solutions of sodium metal in liquid ammonia or
hexamethylphosphoramide (HMPA)10 (eq 1). All attempts to
1
cm-1; (THF) v(CO): 1930 vs, 1914 sh cm-1. H NMR: (300 MHz,
acetone-d6, 25 °C) δ ) 7.0 - 7.7 (m, 30 H, GePh3), 3.1 (q, 8 H, CH2
of Et4N), 1.2 (tt, 12 H, CH3 of Et4N) ppm. Compound 5, like 4, is also
stable indefinitely in air at room temperature in microcrystalline form.
It also has solubility properties similar to those of 4; however, solutions
of 5 in air deteriorate more rapidly than those of 4. Pure 4 is colorless,
but 4 is pale green when very slightly oxidized.
NH3 (-33 °C)
4Na [Ir(CO) ] + ...
(impure product)
Ir4(CO)12 + 12Na
8
(1)
3
3
or HMPA (20 °C)
X-ray Structure Determinations of 4, 5, and [Et4N][Co(CO)3-
(SnPh3)2] (6). Heptane was slowly layered on nearly saturated solutions
of 4, 5, and 6 in CH2Cl2, at room temperature. After 1-2 days, X-ray
quality colorless block-shaped crystals had formed. A crystal of each
compound was placed on the tip of a 0.1 mm glass capillary and
mounted on a Siemens SMART Platform CCD diffractometer for data
collection (Mo KR radiation with λ ) 0.71073 Å was employed), which
was carried out at -100 °C. A randomly oriented region of reciprocal
space was surveyed to the extent of a full sphere (4) and 1.3 hemispheres
(5, 6) to a resolution of 0.77 Å (2θmax ) 55.0°). Major sections of
isolate satisfactorily pure salts of [Ir(CO)3]3- from these
reactions were unsuccessful. Invariably, the latter were con-
taminated by polynuclear carbonyliridates, which Malatesta and
co-workers showed, many years ago, to form via alkali metal
reductions of Ir4(CO)12, even when conducted under an atmo-
sphere of CO.15,18a
Subsequently, it was discovered that high yields of satisfac-
torily pure samples of unsolvated Na3[M(CO)4], M ) Mn, Re,

5282 Inorganic Chemistry, Vol. 40, No. 20, 2001
Allen et al.
were available by sodium metal reductions of the respective
Na[M(CO)5] in HMPA, followed by addition of excess liquid
ammonia7b (eq 2). For this reason, we investigated the analogous
determination will be essential to unambiguously establish the
nature of this unique iridium complex.
1H NMR spectra of approximately 0.1 M HMPA-d18 solutions
of freshly prepared Na3[Ir(CO)3] at room temperature almost
invariably showed a Very weak singlet at δ -15.2 ppm,
suggesting that most of the iridium species in solution was
nonhydridic in nature. Addition of 1 equiv of ethanol caused
the resonance at -15.2 ppm to dramatically increase in intensity.
Introduction of a second equivalent of ethanol caused the signal
at -15.2 ppm to disappear, and a new intense singlet at -12.3
was observed. Attempts to isolate the latter species as a pure
substance have not been successful to date. Infrared mineral
oil mull spectra in the ν(CO) region of an impure and thermally
Na[M(CO)5] + 3Na 1. HMPA (20 °C)8
(2)
Na3[M(CO)4]V + ...
98% (Mn), 88% (Re)
2. NH3 (-33 °C)
reduction of Na[Ir(CO)4], a thermally unstable and very air
sensitive colorless solid. Although [Ir(CO)4]- was reported by
Hieber in 1940,18a Malatesta and co-workers15,18b were the initial
group to characterize this substance and describe solutions of
Na[Ir(CO)4]. However, to the best of our knowledge, the first
details of its isolation are reported herein. Also, we describe its
metathesis with [Ph4As]Cl to produce a new thermally stable
and satisfactorily pure tetraphenylarsonium salt, [Ph4As][Ir-
(CO)4] (eq 3). The yield of the tetracarbonyliridate(1-) salt is
unstable Ph4As+ salt showed an intense band at 1880 cm-1
,
which is not coincident with that of bona fide [Ph4As][Ir(CO)4],
vide supra. Since the IR spectrum of the impure product in the
ν(CO) region exhibits a band pattern and intensity very similar
to those of trans-[Ir(CO)3(EPh3)2]-, E ) Ge, Sn, vide infra,
this salt is postulated to contain trans-[Ir(CO)3H2]- units.
However, it will be necessary to unambiguously determine the
composition of this species by 1H and 13C NMR spectra of the
99%-enriched 13CO-labeled complex before a definitive for-
mulation is possible.
Germylation and Stannylation of Na3[Ir(CO)3]: Synthesis
and Isolation of [Ir(CO)3(EPh3)2]-, E ) Ge, Sn. More than
40 years ago Hein established that carbonylmetalates react with
Ph3EX, E ) Ge, Sn, X ) Cl, Br, OH, to provide bi- or
polymetallic derivatives that are generally much less reactive
and consequently easier to handle and purify than the parent
metal carbonyl salts.21 This important derivatization method is
now recognized to be one of the best strategies in obtaining
initial evidence for the existence of highly reactive and/or
thermally unstable mononuclear homoleptic carbonyl,3 isocya-
nide,22 alkyne,23 or organophosphane24 metalates, as well as
related mixed-ligand versions thereof.25
As mentioned above, direct reduction of Ir4(CO)12 by 12 equiv
of sodium metal in liquid ammonia or HMPA invariably resulted
in unsatisfactory conversion to Na3[Ir(CO)3]. Reactions of these
solutions with 2 equiv of Ph3GeCl or Ph3SnCl, followed by
cation exchange with tetraethylammonium bromide and workup,
provided only 35-45% yields of colorless microcrystals of
satisfactorily pure [Et4N][Ir(CO)3(EPh3)2], E ) Sn 4 or Ge 5,
respectively. Compound 5 was only prepared by this procedure
in HMPA. In contrast, when Na[Ir(CO)4] was reduced by
sodium metal in liquid ammonia, followed by addition of 3 equiv
of Ph3SnCl and metathesis with Et4NBr, the isolated yield of 4
increased to 87% (eq 5). The latter procedure, or an analogous
one employing HMPA for reactants/products unstable in liquid
Ph4AsCl
1/4Ir4(CO)12 + Na/Hg + CO(1 atm) THF, 20 °C8 H O, 20 °C8
3 days
2
[Ph4As][Ir(CO)4]V + ...
(3)
52%
only moderate, ca. 52%, because the initial sodium amalgam
or sodium sand reductions of Ir4(CO)12 provided only about 60%
yields of Na[Ir(CO)4]. IR spectra of both the isolated Na+ and
[Ph4As]+ salts of [Ir(CO)4]- in the ν(CO) region are in good
agreement with that of the bis(triphenylphosphine)iminium salt,
[PPN][Ir(CO)4]. Martinengo and co-workers previously obtained
this thermally stable material in 75% isolated yield by a
reductive carbonylation of IrCl3(H2O)3.18c
Reduction of Na[Ir(CO)4] by sodium in HMPA at room
temperature, under a dynamic (ca. 0.01 Torr) vacuum, provided
after 12 h a dark yellow solution. Following precipitation with
excess liquid ammonia at -78 °C, a homogeneous, pyrophoric
orange powder was isolated. Satisfactorily pure and thermally
robust Na3[Ir(CO)3], dec g200 °C, was thereby obtained in 90%
yield based on unsolvated Na[Ir(CO)4] (eq 4). Mineral oil mull
IR spectra of Na3[Ir(CO)3] indicated that the product was
spectroscopically free of ammonia and HMPA, vide infra.
Corresponding reductions of Na[Rh(CO)4] also gave Na3[Rh-
(CO)3],8,19 but Na[Co(CO)4] was found to be totally inert toward
reduction in HMPA, under otherwise identical conditions.20
1. HMPA, 20 °C, 12 h
Na [Ir(CO) ]V + ...
8
Na[Ir(CO)4] + 3Na
3
3
2. NH3(l), -78 to -33 °C
90%
(4)
HMPA solution IR spectra of Na3[Ir(CO)3] in the ν(CO)
region consist of one intense, broad and symmetric absorption
centered at 1665 ((5) cm-1. The corresponding spectrum of
Na3[Rh(CO)3] in HMPA8 is virtually identical, indicating that
the iridate(3-) and rhodate(3-) are likely to have very similar
structures in solution. Mineral oil mull IR spectra of Na3[Ir-
(CO)3] in the ν(CO) region are nearly identical to those in
HMPA solution, which suggests that the environments of
[Ir(CO)3]3- in solution and in the solid state are similar. These
spectra are consistent with the presence of trigonal planar
[Ir(CO)3]3- units, for which only one IR active carbonyl
stretching frequency is expected. However a crystal structure
(21) Hein, F.; Kleinet, P.; Jehn, W. Naturwissenschaften 1957, 44, 34.
(22) (a) Warnock, G. F.; Cooper, N. F. Organometallics 1989, 8, 1826.
(b) Corella, J. A.; Thompson, R. L.; Cooper, N. J. Angew. Chem., Int.
Ed. Engl 1992, 31, 83. (c) Utz, T. L.; Leach, P. A.; Gieb, S. J.; Cooper,
N. J. Chem. Commun. 1997, 847.
(23) Maher, J. M.; Fox, J. R.; Foxman, B, M.; Cooper, N J. J. Am. Chem.
Soc. 1984, 106, 2347.
(24) (a) Klein, H.-F.; Ellrich, K.; Neugebauer, D.; Oramer, O.; Kru¨ger, K.
Z. Naturforsch. 1983, 38B, 303. (b) Mezailles, N,; Rosa, P.; Ricard,
L.; Mathey, F.; LeFloch, P. Organometallics 2000, 19, 2941.
(25) (a) Davison, A.; Ellis, J E. J. Organomet. Chem. 1972, 36, 113. (b)
Ellis, J. E.; Hayes, T. G.; Stevens, R. E. J. Organomet. Chem.1981,
216, 191. (c) Maher, J. M.; Beatty, R. P.; Cooper, N. J. Organome-
tallics 1982, 1, 215. (d) Ellis, J. E.; Rochfort, G. L. J. Organomet.
Chem. 1983, 250, 265. (e) Pfahl, K. M.; Ellis, J. E. Organometallics
1984, 3, 230. (f) Klein, H.-F.; Ellrich, K.; Lamac, S.; Lull, G.; Zsolnai,
L.; Huttner, G. Z. Naturforsch. 1985, 40B, 1377. (g) Leong, V. S.;
Cooper, N. J. Organometallics 1987, 6, 2000. (h) Leong V. S.; Cooper,
N. J. Organometallics 1988, 7, 2080. (i) Chen, Y. S.; Ellis, J. E. Inorg.
Chim. Acta 2000, 300-302, 675.
(18) (a) Hieber, W.; Lagaiiy, H. Z. Anorg. Allg. Chem. 1940, 245, 321. (b)
Malatesta, L.; Caglio, G.; Angoletta, M. Chem. Commun. 1970, 532.
(c) Garlaschelli, L.; Della Pergola, R.; Martinengo, S. Inorg. Synth.1990,
28, 211
(19) Ellis, J. E.; Winzenburg, M. L.; Warnock, G. W. To be submitted.
(20) Ellis, J. E.; Barger, P. T.; Winzenburg, M. L.; Warnock, G. W. J.
Organomet. Chem. 1990, 383, 521.

Synthesis, Isolation, and Characterization of Na3[Ir(CO)3]
Inorganic Chemistry, Vol. 40, No. 20, 2001 5283
1. NH3 (-33 °C)
Na[Ir(CO)4] + 3Na 2. Ph SnCl, Et NBr, THF8
3
4
[Et4N][Ir(CO)3(SnPh3)2]
87%
(5)
ammonia, would appear to be the method of choice for future
studies of the chemical properties of Na3[Ir(CO)3], which remain
very poorly explored. Compounds 4 and 5 are air stable
indefinitely at room temperature as microcrystalline solids. They
readily dissolve in polar solvents such as tetrahydrofuran,
dichloromethane, and acetonitrile to provide colorless solutions,
which only slowly deteriorate in air under ambient conditions.
Solution IR spectra of 4 and 5 in THF in the ν(CO) region
exhibit only one strong symmetrical absorption at 1924 and 1930
cm-1, respectively. Closely related neutral and cationic iridium
tricarbonyl complexes Ir(CO)3(PPh3)(SnPh3)26 and [Ir(CO)3-
(PMe2Ph)2]+ 27 also showed intense single absorptions at 1965
and 2000 cm-1, respectively, which indicated the presence of
trigonal bipyramidal species with carbonyls in trigonal positions,
in accord with Rossi and Hoffman’s conclusions.28 Structural
characterizations of [Ir(CO)3(PMe2Ph)2]+ 29 and [Ir(CO)3(PCy3)-
(SnPh3)30 confirmed the presence of trans-Ir(CO)3L2 units for
these formally d8 Ir(I) complexes. These results, along with the
1H NMR spectral data, provide strong evidence that solutions
of 4 and 5 contain trans-[Ir(CO)3(EPh3)2]- molecules, which
represent the first known five-coordinate carbonyliridates. On
the basis of the IR ν(CO) spectral data, 4 and 5 are best
formulated to possess two Ph3E- groups formally bound to d8
Ir(I) moieties. For comparison, the more electron rich four-
coordinate tricarbonyliridate complex, [Ir(CO)3(PPh3)]-, which
formally contains d10 Ir(I-), exhibits IR ν(CO) values of 1840
Figure 1. Molecular structure of trans-[Ir(CO)3(SnPh3)2]- (50%
thermal ellipsoids); hydrogens are omitted for clarity. See Table 2 for
selected bond distances and angles.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
trans-[M(CO)3(EPh3)2]1- in 4, 5 and 6
compd, M/E
4, Ir/Sn
5, Ir/Ge
6, Co/Sn
M-C(1)
M-C(2)
M-C(3)
M-C (av)
1.882(6)
1.891(6)
1.883(5)
1.885(6)
1.893(7)
1.894(6)
1.899(7)
1.895(7)
1.756(5)
1.748(5)
1.741(5)
1.748(8)
C(1)-O(1)
C(2)-O(2)
C(3)-O(3)
C-O (av)
1.180(7)
1.135(7)
1.164(6)
1.16(2)
1.161(8)
1.135(7)
1.117(7)
1.14(2)
1.155(5)
1.161(5)
1.162(5)
1.159(5)
M-E(1)
M-E(2)
2.6284(4)
2.6289(4)
2.4922(8)
2.4932(8)
2.4906(8)
2.4889(8)
and 1860 cm-1 26 which are shifted 70-90 cm-1 to lower energy
,
than those of 4 and 5.
E-C(Ph) (av)
2.17(1)
1.984(8)
2.169(5)
Structural Characterizations of [(C2H5)4N][Ir(CO)3(EPh3)2],
E ) Sn (4), Ge (5), and [(C2H5)4N][Co(CO)3(SnPh3)2] (6).
Salts 4, 5, and 6 crystallize in the space group Cc as colorless
dichloromethane solvates and have very similar unit cells, but
are not isomorphous. The asymmetric unit of each structure
contains one tetraethylammonium cation, one trans-[M(CO)3-
(EPh3)2]- unit, and one dichloromethane molecule. The tetra-
ethylammonium cations and CH2Cl2 groups are ordered, are well
separated from the anions, and show no unusual features.
Interatomic data for the latter are available in the Supporting
Information. Transition metals in the anions are in a nearly ideal
trigonal bipyramidal environment. For example, the M(CO)3
fragments are planar with all C-M-C angles close to 120°,
and the E-M-E units are nearly linear, with angles ranging
from 173 to 175°. The pyramidal triphenylstannyl and triph-
enylgermyl units in 4, 5, and 6 show no unusual features.
Interatomic data for the latter are also available in the Supporting
Information. Figure 1 shows the molecular structure of trans-
[Ir(CO)3(SnPh3)2]-. Selected interatomic data for the anions are
listed in Table 2. Average Ir-C and C-O distances in 4 and 5
are well within the usual range of values previously observed
for terminal carbonyl groups bound to low-valent iridium.29-31
However, and as expected, these values are far different from
M-C(1)-O(1)
M-C(2)-O(2)
M-C(3)-O(3)
M-C-O (av)
177.5(6)
178.2(6)
178.2(5)
178.0(6)
178.6(7)
179.4(7)
177.5(6)
178.5(9)
179.6(4)
179.8(5)
178.9(5)
179.4(5)
C(1)-M-C(2)
C(1)-M-C(3)
C(2)-M-C(3)
C-M-C (av)
118.5(2)
117.5(2)
124.0(2)
120(4)
119.7(2)
118.1(3)
122.2(3)
120(3)
119.7(2)
116.9(2)
123.5(2)
120(3)
E(1)-M-E(2)
173.47(1)
175.05(3)
174.39(3)
C(1)-M-E(1)
C(2)-M-E(1)
C(3)-M-E(1)
C(1)-M-E(2)
C(2)-M-E(2)
C(3)-M-E(2)
C-M-E (av)
92.0(2)
87.6(2)
90.1(2)
94.4(2)
90.2(2)
85.9(2)
90(3)
91.2(2)
88.9(2)
89.9(2)
93.5(2)
90.1(2)
86.5(2)
90(2)
92.1(2)
87.9(1)
90.1(1)
93.5(2)
90.1(1)
86.7(1)
90(3)
the average Ir-C and C-O distances of 2.02(2) and 1.08(2)
Å, respectively, found in [Ir(CO)5Cl]2+, in which the CO groups
are believed to function as essentially pure σ-donors to the
strongly electrophilic d6 Ir(III) center.32,33
The observed average Ir-Sn distance of 2.6286(4) Å in 4 is
unexceptional in comparison to corresponding values previously
reported for other triphenyltin iridium complexes. For example,
the shortest and longest such distances were in the d4 Ir(V)
complex, (C5Me5)Ir(H)3(SnPh3), 2.588 (1) Å,34 and the previ-
ously mentioned d8 Ir(I) species, Ir(CO)3(PCy3)(SnPh3), 2.6610-
(26) Collman, J. P.; Vastine, F. D.; Roper, W. R. J. Am. Chem. Soc. 1968,
90, 2282.
(27) Deeming, A. J.; Shaw, B. L. J. Chem. Soc. A 1970, 2705.
(28) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365.
(29) Raper, G.; McDonald, W. S. Acta Crystallogr., Sect. B 1973, 29, 2013.
(30) Esteruelas, M. A.; Lahoz, F. J.; Olivan, M.; Onate, E.; Oro, L. A.
Organometallics 1994, 13, 4246.
(31) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, J. Chem. Soc., Dalton Trans. 1989, S1.
(32) Bach, C.; Willner, H.; Wang, C.; Rettig, S. J.; Trotter, J.; Aubke, F.
Angew. Chem., Int. Ed. Engl. 1996, 35, 1974.
(33) Lupinetti, A. J.; Frenking, G.; Strauss, S. H. Angew. Chem., Int. Ed.
1998, 37, 2113.
(34) Gilbert, T. M.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc.
1985, 107, 3508.

5284 Inorganic Chemistry, Vol. 40, No. 20, 2001
Allen et al.
(3) Å,30 respectively. To the best of our knowledge, no prior
examples of triphenylgermyl iridium complexes have been
structurally characterized, but the reported Ir-Ge distance of
2.484(2) Å in the trimethylgermyl Ir(III) species, Ir(CO)(H)2-
(PPh3)2(GeMe3),35 is only slightly shorter than the average Ge-
Ir distance of 2.4927(8) Å determined for 5. Two other
molecules containing Ir-Ge bonds have been structurally
characterized, but they contain Ge(N(SiMe3)2)2 or related
ligands36 that are sufficiently different sterically and electroni-
cally from simple trialkyl- or triarylgermyl units that compari-
sons of the Ge-Ir distances, which range from 2.325(3) to
2.466(2) Å, with those in 5 are not of any relevance to this
discussion. In conclusion, the structural data for the anions in
4 and 5 corroborate our prior formulations, based on elemental
analyses and solution spectroscopic data. Also, the interatomic
data for 4 and 5 appear to be entirely normal compared to those
of previously known mixed tin-iridium carbonyls, germanium-
iridium carbonyls, and related species.
To help confirm our prior claims on the formulation of
[Co(CO)3(SnPh3)2]- 10,20 and to provide additional evidence that
the carbonylcobaltate(3-) precursor, Na3[Co(CO)3], is indeed
a tricarbonyl complex, a structural characterization of 6 was
carried out. The basic architecture of the trans-[Co(CO)3-
(SnPh3)2]- units in 6 has been described earlier in the paper.
This section will provide details on important interatomic
distances. The average Co-C and C-O distances in 6, see Table
2, are unexceptional compared to corresponding values previ-
ously established for tricarbonylcobalt(I) complexes.31 The latter
include the trans-trigonal bipyramidal complexes Co(CO)3-
(PPh3)(GePh3),37 [Co(CO)3(SnCl3)2]- (7),38 Co(CO)3(PPh3)-
(SnMe3) (8),39 and Co(CO)3(AsPh3)(SnMe3) (9).39 The average
Co-Sn distance of 2.4898(8) Å in 6 is somewhat longer than
those reported for 7, 2.442(2) Å, which was described as being
“remarkably short”,38 and Co(CO)4SnCl3, 2.477(1) Å,40 but is
significantly shorter than the Co-Sn distances found in 8, 2.574-
(2) Å, and 9, 2.565(1) Å.39 All previously reported structures
containing triphenylstannyl-cobalt units have appreciably
longer Co-Sn distances than those in 6, including Co(η4-
anthracene)(PMe3)2(SnPh3),25f 2.546(2) Å, and Co(PMe3)3-
(SnPh3), 2.590(2)-2.598(2) Å,24a for three independent mol-
ecules in the unit cell. Very likely the triphenylstannyl units in
6 are able to approach the Co(I) center more closely for both
steric and electronic reasons; i.e., CO ligands are both smaller
and much better acceptors than the PMe3/anthracene units
present in the above mixed Co(PMe3)x(SnPh3) species.24a,25f
Concluding Remarks
Reduction of Na[Ir(CO)4] by sodium in hexamethylphos-
phoramide (HMPA) generates soluble Na3[Ir(CO)3]. Treatment
of this solution with excess liquid ammonia results in the
precipitation of high yields, ca. 90%, of a pyrophoric orange
solid, which proved to be satisfactorily pure unsolvated Na3-
[Ir(CO)3]. The latter is of interest as the only substance to contain
Ir(III-), the lowest known formal oxidation state of iridium.
IR spectra for this unusually electron rich carbonylmetalate show
a carbonyl stretching mode at very low energy, ca. 1665 cm-1
,
indicating that the metal-CO bonding in this species involves
substantial metal π donation to the carbonyl groups. In contrast,
the previously reported Ir(III) complex, [Ir(CO)6]3+, has an IR
ν(CO) value of 2254 cm-1, sufficiently far above that of gaseous
CO, 2143 cm-1, that the metal-CO bonding is believed to
involve only carbonyl σ donation to the metal center.32 Thus,
in proceeding from Na3[Ir(CO)3] to [Ir(CO)6][Sb2F11]332 the IR
ν(CO) value increases by nearly 600 cm-1! This may well be
the largest span of ν(CO) values known for terminal CO groups
in homoleptic complexes of any given metal.
Interactions of Na3[Ir(CO)3] with Ph3ECl, E ) Sn, Ge,
provided the respective mixed main group-transition metal
species trans-[Ir(CO)3(EPh3)2]-, the first five-coordinate anionic
iridium carbonyls. Beck and co-workers have also obtained the
unusual mixed rhenium-iridium hydride, (OC)5Re-Ir(CO)3H-
Re(CO)5, by the reaction of Na3[Ir(CO)3] with the highly
reactive cationic carbonyl, [(η2-C2H4)Re(CO)5]+ PF6- 40 To the
.
best of our knowledge, our present study and that of the Beck
group report on the only known reactions of Na3[Ir(CO)3].
However, these few examples suggest that the carbonyliridate-
(3-) should have a rich chemistry and be a useful precursor to
new classes of mixed main group element- and/or transition
metal-iridium carbonyl complexes.
Acknowledgment. This research was supported by the
National Science Foundation and donors of the Petroleum
Research Fund, administered by the American Chemical Society.
We are grateful for their support. Ms. Christine Lundby is also
greatly thanked for her expert and invaluable assistance in the
preparation of the manuscript.
(35) Bell, N. A.; Glockling, F.; Schneider, M. L.; Shearer, H. M. M.;
Wilbey, M. D. Acta Crystallogr., Sect. C 1984, 40, 625.
(36) Hawkins, S. M.; Hitchcock, P. B.; Lappert, M. F.; Rai, A. K. J. Chem.
Soc., Chem. Commun. 1986, 1689.
(37) Stalick, J. K.; Ibers, J. A. J. Organomet. Chem. 1970, 22, 213.
(38) Curnow, O. J.; Nicholson, B. K.; Severinsen, M. J. J. Organomet.
Chem. 1990, 388, 379.
Supporting Information Available: Details of crystallographic
analyses for 4, 5, and 6 in CIF format. This material is free of charge
via the Internet at http://pubs.acs.org.
(39) Loubser, C.; Dillen, J. L. M.; Lotz, S. Polyhedron 1991, 10, 2535.
(40) Breimar, J.; Robl, C.; Beck, W. J. Organomet. Chem. 1991, 411, 395.
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