Synthesis, Molecular Structure, and Vibrational Spectra of mer-Tris(carbonyl)iridium(III) Fluorosulfate, mer-Ir(CO)3(SO3F)3

Article abstract of DOI:10.1021/ic9506769

Addition of carbon monoxide (0.5-2 atm) to iridium(III) fluorosulfate, Ir(SO₃F)₃, dissolved in HSO₃F over 4 days and at 60 °C, results in the quantitative formation of tris(carbonyl)iridium(III) fluorosulfate Ir(CO)₃(SO₃F)₃. Slow evaporation of the solvent produces single crystals of mer-Ir(CO)₃(SO₃F)₃. Crystal structure data for mer-Ir(CO)₃(SO₃F)₃: monoclinic, space group P2₁/c, Z = 4, a = 8.476(1) A?, b = 12.868(2) A?, c = 12.588 (1) A?, β = 108.24(1)°, V = 1304.0 A?³, T = 200 K, R_F = 0.022 for 2090 data (I_o ≥ 2.5σ(I_o)) and 200 variables. Vibrational spectra of the crystalline solid are consistent with a mer-isomer with CO stretching modes at 2249 (A₁), 2208 (B₁), and 2198 (A₁) cm^-1 in the IR spectrum. In solution of HSO₃F, additional CO stretching bands attributed to the fac-isomer are found in the FT-Raman and IR spectra at 2233 (A₁) and 2157 cm^-1 (E). Additional evidence for a mixture of fac- and mer-isomers comes from ¹⁹F NMR spectra. The vibrational spectra suggest strongly reduced iridium to CO π-back-bonding. The crystal structure reveals significant intra- and intermolecular contacts between the electropositive C atom of the CO groups and O or F atoms of the fluorosulfate groups. Hence mer-tris(carbonyl)iridium(III) fluorosulfate becomes the first thermally stable, structurally characterized, and predominantly σ-bonded carbonyl derivative of a metal in the +3 oxidation state.

Full text of DOI:10.1021/ic9506769

Inorg. Chem. 1996, 35, 1279-1285
1279
Synthesis, Molecular Structure, and Vibrational Spectra of mer-Tris(carbonyl)iridium(III)
Fluorosulfate, mer-Ir(CO)3(SO3F)3
Changqing Wang,† Andrew R. Lewis,† Raymond J. Batchelor,‡ Frederick W. B. Einstein,‡
Helge Willner,§ and Friedhelm Aubke*,†
Department of Chemistry, The University of British Columbia, Vancouver, BC, Canada V6T 1Z1,
Department of Chemistry, Simon Fraser University, Burnaby, BC, Canada V5A 1S6, and Institut fu¨r
Anorganische Chemie der Universita¨t, D-30167 Hannover, Callinstrasse 9, Germany
ReceiVed June 1, 1995X
Addition of carbon monoxide (0.5-2 atm) to iridium(III) fluorosulfate, Ir(SO3F)3, dissolved in HSO3F over 4
days and at 60 °C, results in the quantitative formation of tris(carbonyl)iridium(III) fluorosulfate Ir(CO)3(SO3F)3.
Slow evaporation of the solvent produces single crystals of mer-Ir(CO)3(SO3F)3. Crystal structure data for
mer-Ir(CO)3(SO3F)3: monoclinic, space group P21/c, Z ) 4, a ) 8.476(1) Å, b ) 12.868(2) Å, c ) 12.588 (1)
Å, â ) 108.24(1)°, V ) 1304.0 Å3, T ) 200 K, RF ) 0.022 for 2090 data (Io g 2.5σ(Io)) and 200 variables.
Vibrational spectra of the crystalline solid are consistent with a mer-isomer with CO stretching modes at 2249
(A1), 2208 (B1), and 2198 (A1) cm-1 in the IR spectrum. In solution of HSO3F, additional CO stretching bands
attributed to the fac-isomer are found in the FT-Raman and IR spectra at 2233 (A1) and 2157 cm-1 (E). Additional
evidence for a mixture of fac- and mer-isomers comes from 19F NMR spectra. The vibrational spectra suggest
strongly reduced iridium to CO π-back-bonding. The crystal structure reveals significant intra- and intermolecular
contacts between the electropositive C atom of the CO groups and O or F atoms of the fluorosulfate groups.
Hence mer-tris(carbonyl)iridium(III) fluorosulfate becomes the first thermally stable, structurally characterized,
and predominantly σ-bonded carbonyl derivative of a metal in the +3 oxidation state.
Introduction
(SO3F)3 according to the vibrational spectra. However slow
removal of HSO3F allows the growth of single crystals. The
subsequent molecular structure determination and vibrational
spectra of the crystals indicate conclusively that in the crystalline
solid only the meridional isomer is present and is apparently
less soluble in HSO3F than the fac-isomer. The opposite
We have recently reported on the synthesis of three noble
metal carbonyl fluorosulfates, Au(CO)SO3F,1 cis-Pt(CO)2-
2
(SO3F)2 and cis-Pd(CO)2(SO3F)2.2 The latter compound has
subsequently been structurally characterized by X-ray diffrac-
tion.3 Vibrational analysis suggests the presence of covalent
O-monodentate fluorosulfate groups and terminal CO groups
trans to the fluorosulfate ligands.1,2 However the νj(CO)
stretching modes are shifted to higher wavenumbers relative to
νj(CO(g)) (2143 cm-1) and are observed at 2196 cm-1 for
Au(CO)SO3F,1 2185 and 2219 cm-1 for cis-Pt(CO)2(SO3F)2,2
and 2208 and 2228 cm-1 for cis-Pd(CO)2(SO3F)2,2 which in
turn suggests substantially reduced π-back-donation.
4
observation has recently been reported for Ir(CO)3F3 in a
solution of anhydrous HF, where according to solution NMR
at -78 °C (19F and 13C) and the IR spectrum of the isolated
solid, the facial isomer is predominant. A fac-isomer is also
suggested for Ir(CO)3I3.5
Experimental Section
(i) Chemicals. Iridium metal powder, 60 mesh of 99.9% purity,
was obtained from the Ventron Corporation (Alfa Inorganics). Techni-
cal grade fluorosulfuric acid (Orange County Chemicals) was doubly
distilled at atmospheric pressure as described previously.6 Bis-
(fluorosulfuryl) peroxide, S2O6F2, was obtained by the catalytic
fluorination of SO3 in a procedure7 adopted from a previous report.8
Iridium(III) fluorosulfate, Ir(SO3F)3 is obtained by oxidation of iridium
metal with S2O6F2 in HSO3F at 120 to 140 °C. The earlier9 report is
substantially modified and details are described below. Carbon
monoxide (CP grade 99.5% purity) was obtained from Linde Gases
and passed through a glass trap cooled to 77 K, to retain moisture and
other impurities.
(ii) Instrumentation. Infrared spectra were recorded on a Bomen
MB 102 Fourier transform spectrometer. Solid samples were pressed
as thin films between AgBr or AgCl (Harshaw Chemicals) windows.
FT-Raman spectra were recorded on Bruker FRA 106 FT-Raman
accessory mounted on an IFS 66v FT-IR optical bench.
The molecular structure of cis-Pd(CO)2(SO3F)23 confirms our
conclusion based on vibrational spectra and reveals in addition
a number of significant intra- and intermolecular contacts
between the carbon atom of the CO group and oxygen atoms
of the fluorosulfate groups, which appear to stabilize the
structure.
We have now extended our synthetic approach to iridium
and report here the synthesis of tris(carbonyl)iridium(III)
fluorosulfate, Ir(CO)3(SO3F)3. Vibrational and 19F-NMR spectra
in HSO3F solution suggest the initial formation of an isomeric
mixture of the facial and meridional forms with the latter the
major constituent. Polycrystalline samples, formed by rapid
solvent removal are again a mixture of mer- and fac-Ir(CO)3-
* Author to whom correspondence should be addressed.
† The University of British Columbia.
‡ Simon Fraser University.
(4) Brewer, S. A.; Holloway, J. H.; Hope, E. G.; Watson, P. G. J. Chem.
Soc. Chem. Commun. 1992, 1577.
(5) Malatesta, L.; Naldini, L.; Cariati, F. J. Chem. Soc. 1964, 961.
(6) Barr, J.; Gillespie, R. J.; Thompson, R. C. Inorg. Chem. 1964, 3, 1149.
(7) Zhang, D.; Wang, C.; Mistry, F.; Powell, B.; Aubke, F. J. Fluorine
Chem., in press.
§ Universita¨t Hannover.
X Abstract published in AdVance ACS Abstracts, February 1, 1996.
(1) Willner, H.; Aubke, F. Inorg. Chem. 1990, 29, 2195.
(2) Hwang, G.; Wang, C.; Bodenbinder, M.; Willner, H.; Aubke, F. J.
Fluorine Chem. 1994, 66, 159.
(3) Wang, C.; Willner, H.; Bodenbinder, M.; Batchelor, R. J.; Einstein,
F. W. B.; Aubke, F. Inorg. Chem. 1994, 33, 3521.
(8) Cady, G. H.; Shreeve, J. M. Inorg. Synth. 1976, 7, 124.
(9) Lee, K. C.; Aubke, F. J. Fluorine Chem. 1982, 19, 501.
0020-1669/96/1335-1279$12.00/0 © 1996 American Chemical Society

1280 Inorganic Chemistry, Vol. 35, No. 5, 1996
Wang et al.
Table 1. Crystallographic Data for the Structure Determination of
mer-Ir(CO)3(SO3F)3 at 200 K
formula IrS3F3O12C3 cryst syst
monoclinic
P21/c
2.921
0.70930
107.6
fw
573.42
8.476(1)
12.868(2)
12.588(1)
108.24 (1)
1304.0
4
space group
a (Å)a
b (Å)
c (Å)
â (deg)
V (Å)3
Z
Fc(g cm-3
)
λ(Mo KR1) (Å)
µ(Mo KR) (cm-1
)
min-max 2θ (deg) 4-50
transmb
0.453-1.0
cryst dimems (mm) 0.20 × 0.34 × 0.36
c
d
RF
0.022
RwF
0.024
a Cell dimensions were determined from 25 reflections (38°e2θe50°).
b The data were corrected empirically for the effects of absorption.c RF
d
) ∑|(|Fo| - |Fc|)|/∑|Fo|, for 2090 data (Io g 2.5σ(Io)). RwF
)
2
[∑(w(|Fo| - |Fc|)2)/∑(wFo )]1/2 for 2090 data (Io g 2.5σ(Io)); w ) 1.
graphite monochromatized Mo KR radiation. Intensity standards (two
every hour) showed (3% variations in intensity but no net decay. The
data were corrected for the effects of absorption by the product of an
empirical correction10 and 2θ-dependent correction for a sphere of radius
0.1 mm. Data reduction included corrections for intensity scale
variation and for Lorentz and polarization effects.
The structure was solved from the Patterson map by the heavy atom
method. The final full-matrix least squares refinement of 200
parameters, using 2090 data (Io g 2.5σ(Io)), included coordinates and
anisotropical thermal parameters for all atoms and an extinction
parameter.11 The refinement converged at RF ) 0.022 and RwF ) 0.024,
using unit weights.
The programs used for the structure determination were from the
NRCVAX Crystal Structure System12 and CRYSTALS.13 Complex
scattering factors for neutral atoms14 were used in the calculation of
structure factors. Computations were carried out on a MicroVAX-II
and on 80486-processor-based personal computers. Crystallographic
details are summarized in Table 1. Final fractional atomic coordinates
are listed in Table 2.
Figure 1. Two-part reactor used in the syntheses of Ir(SO3F)3 and
Ir(CO)3(SO3F)3.
19F-NMR spectra were obtained on a Varian XL-300 FT multinuclear
spectrometer operating at 282.231 MHz. About 10 mg of crystalline
mer-Ir(CO)3(SO3F)3 was dissolved in 0.5 mL of HSO3F. CFCl3 was
used as external reference. The spectrum was acquired without a lock.
(iii)The Synthesis of Ir(CO)3(SO3F)3. Iridium metal was oxidized,
initially to Ir(SO3F)4, by reaction with a large excess of S2O6F2 in
HSO3F at ∼120 °C over several weeks as described previously.9 To
ensure complete oxidation of iridium a two-part reactor, shown in Figure
1, was employed. In a typical reaction 0.0976 g of metal powder was
added Via a funnel through the stopcock to part A of the reactor. About
2.5 mL each of HSO3F and S2O6F2 were added by distillation in Vacuo
to part A. The reaction mixture was heated to 120 °C with vigorous
magnetic stirring for 16 h. Some of the metal was consumed at this
stage to give a dark brown solution. The mixture was allowed to cool
to room temperature and the unreacted metal settled out over a period
of 30 min with stirring discontinued. The supernatant brown solution
was decanted into part B. The volatile materials (HSO3F and S2O6F2)
were distilled back onto the unreacted metal by heating part B to 60
°C. Some more (∼1 mL) S2O6F2 was added at this point and the
oxidation reaction was continued for another 24 h. The procedure was
repeated four more times until all metal powder appeared to have been
consumed. The dark brown solution in part B was heated to 140 °C
for 12 more hours to ensure complete oxidation. At this stage the color
of the solution changed to a deep blue-purple due to a decomposition
of Ir(SO3F)4 to Ir(SO3F)3.9 The solution was then transferred by
decanting to reactor arm A for the carbonylation reaction.
The refined anisotropic atomic displacement parameters were
analyzed in a manner analogous to that previously described for the
3,15,16
structure of cis-Pd(CO)2(SO3F)2
and yielded very similar results.
The estimated ranges of corrections (always positive) to the bond lengths
are given in the footnote to Table 3.
Results and Discussion
2
Like Au(CO)SO3F1 and cis-M(CO)2(SO3F)2 , M ) Pd or Pt,
tris(carbonyl)iridium(III) fluorosulfate, Ir(CO)3(SO3F)3, is formed
from a binary fluorosulfate precursor in fluorosulfuric acid by
a reaction with gaseous CO according to:
All volatile materials (O2, S2O5F2, S2O6F2, SiF4, and HSO3F) were
removed in Vacuo and about 3 mL of HSO3F was added to produce a
deep blue solution. At this stage CO gas (∼2 atm) was admitted to
the reactor and the solution was heated to 60 °C for about 4 days. The
color of the solution changed gradually from blue to violet, then to
brown, and to black. Finally a bright yellow solution resulted, and no
color change was noted on further heating.
Ir(SO3F)3 + 3CO 60 °C, 2atm8 Ir(CO)3(SO3F)3
(1)
4 d, HSO3F
From the bright yellow solution, pale yellow, almost colorless crystals
and a deep yellow solution were obtained after the removal of most
volatiles. Recrystallization from HSO3F produced single crystals
suitable for an X-ray diffraction study. The total yield of crystalline
material isolated and identified as mer-Ir(CO)3(SO3F)3 was estimated
to be ∼70%.
There are three important differences to the earlier formation
reactions:
(i) The oxidation state of iridium remains +3 while
2
Au(CO)SO3F,1 cis-Pt(CO)2(SO3F)2,2 or cis-Pd(CO)2(SO3F)2
(10) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(11) Larson, A. C. In Crystallographic Computing; Ahemed, F. R., Ed.;
Munksgaard: Copenhagen, 1970; p 293.
(12) Gabe, E. J.; LePage, Y.; Charland, J-P.; Lee, F. L.; White, P. S.
NRCVAXsAn Interactive Program System or Structure Analysis. J.
Appl. Crystallogr. 1989, 22, 384.
(13) Watkin, D. J.; Carruthers, J. R.; Betteridge, P. W. CRYSTALS.
Chemical Crystallographic Laboratory, University of Oxford, Oxford,
England, 1984.
(14) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1975; Vol. IV, p 99.
(15) Shomaker, V.; Trueblood, K. N. Acta Crystallogr. 1968, B24, 63.
(16) Trueblood, K. N. Acta Crystallogr. 1978, A34, 950.
Crystalline mer-Ir(CO)3(SO3F)3 is an almost colorless, pale yellow
material. Heating in a sealed capillary results in melting, gas evolution
and a color change to light brown at 150 °C. Anal. Calcd for
C3O12F3S3Ir: C, 6.28; S, 16.77; H, 0. Found: C, 5.7; S, 18.25; H, 0.1.
No weight loss due to CO release is noted when the sample is kept in
Vacuo for several days.
(iv) X-ray Crystallography. Under a dry nitrogen atmosphere, a
suitable fragment was cleaved from a colorless crystal and was gently
wedged in a capillary tube with a trace of fluorocarbon grease as
adhesive. The tube was hot-wire sealed in the glovebox. Data were
recorded at 200 K with an Enraf Nonius CAD4F diffractometer
equipped with an in-house modified low-temperature attachment using

mer-Tris(carbonyl)iridium(III) Fluorosulfate
Inorganic Chemistry, Vol. 35, No. 5, 1996 1281
Table 2. Fractional Atomic Coordinates and Equivalent Isotropic
Displacement Parameters (Å)2 for mer-Ir(CO)3(SO3F)3 at 200 K
(ii) Reductive carbonylation reactions in superacids are
usually found to be very fast, and proceed easily at 25 °C within
a few hours, particularly in the case of the reduction of the gold1
and palladium2 precursors. Formation of Ir(CO)3(SO3F)3 is very
slow and requires heating to 60 °C over 4 days. The reaction
is easily followed by the color changes: the deep blue color of
Ir(SO3F)39 dissolved in HSO3F gradually changes to dark brown
and finally to pale yellow-orange. While there is no precise
structural information available for either solid Ir(SO3F)3 or its
solution in HSO3F, the observed weak temperature independent
paramagnetism of the former9 is consistent with a d6 low spin
configuration in an approximately octahedral environment. The
compound is hence expected to be substitutionally inert.
a
atom
Ir
x
y
z
Ueq
0.27018(3)
0.590208(17)
0.255878(18) 0.0144
S(1)
S(2)
S(3)
F(1)
F(2)
F(3)
O(11)
O(12)
O(13)
O(21)
0.30798(20) 0.82664(13)
-0.09454(18) 0.57702(13)
0.62836(19) 0.62602(13)
0.19034(14)
0.09385(13)
0.42295(13)
0.1515(3)
0.1518(4)
0.4789(4)
0.2756(4)
0.0941(4)
0.2419(5)
0.1133(3)
-0.0209(4)
0.1541(5)
0.3994(3)
0.3252(4)
0.5075(4)
0.2543(4)
0.0899(4)
0.4071(4)
0.2527(5)
0.1522(5)
0.3553(5)
0.0242
0.0225
0.0224
0.0358
0.0391
0.0398
0.0252
0.0348
0.0400
0.0196
0.0311
0.0388
0.0206
0.0312
0.0325
0.0303
0.0275
0.0364
0.0225
0.0223
0.0232
0.1271(5)
-0.1670(5)
0.5951(6)
0.3019(6)
0.3323(7)
0.4043(7)
0.0791(5)
0.8666(3)
0.6620(4)
0.7269(4)
0.7482(3)
0.7825(4)
0.9121(4)
0.6182(3)
0.5833(4)
0.4857(5)
0.5711(3)
0.6577(4)
0.5721(4)
0.3563(4)
0.5740(4)
0.6191(5)
0.4407(5)
0.5804(5)
0.6057(5)
O(22) -0.1852(6)
O(23) -0.0968(6)
(iii) Evidence from vibrational and 13C-NMR spectra suggests
that homoleptic metal carbonyl cations like linear [Au(CO)2]+ 1
and square planar [M(CO)4]2+ (M ) Pt or Pd)2 form initially
in HSO3F solution. All three cations have subsequently been
obtained as [Sb2F11]- salts.21,22 Substitution of CO by SO3F-
in more concentrated solutions of the metal carbonyl cations in
HSO3F leads subsequently to Au(CO)SO3F1 and cis-M(CO)2-
O(31)
O(32)
O(33)
O(1)
O(2)
O(3)
C(1)
0.4632(5)
0.6633(6)
0.7489(6)
0.2278(6)
0.4756(6)
0.0458(6)
0.2427(7)
0.4074(7)
0.1283(8)
2
C(2)
C(3)
(SO3F)2 , M ) Pd or Pt. Consistent with the greater trans-
directing ability of CO,23a the cis-isomers of M(CO)2(SO3F)2,
M ) Pd or Pt, form exclusively.
a Ueq is the cube root of the product of the principal axes of the
mean squared atomic displacement ellipsoid.
There is so far no evidence in the vibrational and 13C-NMR
spectra for any homoleptic carbonyl cation of iridium as
precursor in solution. Consequently the molecular structure and
spectroscopic results, discussed below, point to the mer-isomer
of Ir(CO)3(SO3F)3 as the predominant form. Observation of a
trans-Ir(CO)2 moiety is consistent with the gradual, stepwise
addition of CO to a fluorosulfate species, rather than with a
substitution of CO by SO3F- as observed during the formation
of Au(CO)SO3F from [Au(CO)2]+ 1 and M(CO)2(SO3F)2 from
[M(CO)4]2+ 2 with M ) Pd or Pt. There is however, no
conclusive evidence regarding the nature of solvated Ir(SO3F)3
in HSO3F, to permit a more detailed discussion of the formation
reaction of mer-Ir(CO)3(SO3F)3.
Table 3. Selected Intramolecular Distances (Å) and Angles (deg)
for mer-Ir(CO)3(SO3F)3 at 200 K
Bond Distances
Ir-O(11)
2.055(4)a
2.038(4)a
2.038(4)a
1.937(7)b
2.006(6)b
1.999(6)b
1.487(5)c
1.411(5)d
1.402(5)e
1.544(4)f
1.108(8)o
S(2)-O(21)
S(2)-O(22)
S(2)-O(23)
S(2)-F(2)
S(3)-O(31)
S(3)-O(32)
S(3)-O(33)
S(3)-F(3)
O(1)-C(1)
O(2)-C(2)
1.511(4)c
1.410(5)g
1.402(6)h
1.545(5)i
1.512(4)c
1.413(5)j
1.406(5)k
1.545(5)l
1.094(8)m
1.114(8)n
Ir-O(21)
Ir-O(31)
Ir-C(1)
Ir-C(2)
Ir-C(3)
S(1)-O(11)
S(1)-O(12)
S(1)-O(13)
S(1)-F(1)
O(3)-C(3)
It is noted that Ir(CO)3I3 is also formed by the CO addition
to IrI3 at 100 °C and 250 atm of CO.5 For this compound two
bands in the CO stretching region of the IR-spectrum have been
reported, and this is consistent with a fac-isomer. The com-
pound is apparently of low thermal stability and loses CO
readily. Ir(CO)3F3, the other precedent for Ir(CO)3(SO3F)3, is
formed by fluorination of Ir4(CO)12 with a 6-fold excess of XeF2
in HF at -40 °C.4 19F- and 13C-NMR spectra suggest initial
formation of a mixture of mer- and fac-isomers. The pale
yellow solid isolated from solution is the fac-isomer.4 This is
consistent with the presence of fac-Ir(CO)3 moieties in the
precursor Ir4(CO)12.
Bond Angles
O(11)-Ir-O(21)
O(11)-Ir-O(31)
O(11)-Ir-C(1)
O(11)-Ir-C(2)
O(11)-Ir-C(3)
O(21)-Ir-O(31)
O(21)-Ir-C(1)
O(21)-Ir-C(2)
O(21)-Ir-C(3)
O(31)-Ir-C(1)
O(31)-Ir-C(2)
O(31)-Ir-C(3)
88.25(17)
88.49(17)
174.41(23)
93.46(23)
84.67(23)
176.74(17)
95.74(22)
84.30(20)
93.79(21)
87.52(22)
95.80(20)
86.00(21)
C(1)-Ir-C(2)
C(1)-Ir-C(3)
C(2)-Ir-C(3)
Ir-O(11)-S(1)
Ir-O(21)-S(2)
Ir-O(31)-S(3)
Ir-C(1)-O(1)
Ir-C(2)-O(2)
Ir-C(3)-O(3)
90.8(3)
91.2(3)
177.4(3)
128.1(3)
123.07(24)
123.68(25)
177.8(6)
176.1(5)
176.1(6)
a-o Thermal motion corrections using rigid body, segmented rigid
body or riding models indicate that the actual bond lengths should be
In the case of Ir(CO)3(SO3F)3 the mer-isomer is formed
predominantly. In addition mer-Ir(CO)3(SO3F)3 is less soluble
in HSO3F than the fac-isomer. Slow evaporation produces
crystals of mer-Ir(CO)3(SO3F)3 which are isolated by removing
the mother liquor by pipetting. The total yield is about 70%.
The mer-geometry is retained on redissolution in HSO3F as is
evident from the 19F-NMR spectrum, and isomerization in
HSO3F solution is not observed. The mother liquor has, after
separation from the crystals, a measureable concentration of fac-
a
b
c
greater by from 0.003-0.008 Å; 0.003-0.004 Å; 0.003-0.011 Å;
d0.009-0.013 Å; e0.011-0.020 Å; f0.014-0.016 Å; g0.010-0.010 Å;
i
j
k
h0.014-0.022 Å; 0.019-0.024 Å; 0.009-0.010 Å; 0.009-0.016 Å;
l0.015-0.020 Å; m0.005-0.018 Å; n0.003-0.010 Å; and o0.008-0.026
Å.
form in reductive carbonylation reactions17 from [Au(SO3F)3]2,18
Pt(SO3F)4,19 or PdIIPdIV(SO3F)6,20 respectively. The byproducts
of the reduction, CO2 and bis(fluorosulfuryl)oxide, S2O5F2, are
absent in the reaction described here.
(21) Willner, H.; Schaebs, J.; Hwang, G.; Mistry, F.; Jones, R.; Trotter, J.;
Aubke, F. J. Am. Chem. Soc. 1992, 114, 8972.
(17) Aubke, F.; Wang, C. Coord. Chem. ReV. 1994, 137, 483.
(18) Willner, H.; Rettig, S. J.; Trotter, J.; Aubke, F. Can. J. Chem. 1991,
69, 391.
(19) Lee, K. C.; Aubke, F. Inorg. Chem. 1984, 23, 2124.
(20) (a) Lee, K. C.; Aubke, F. Can. J. Chem. 1977, 55, 2473. (b) Lee, K.
C.; Aubke, F. Can. J. Chem. 1979, 57, 2058.
(22) Hwang, G.; Wang, C.; Bodenbinder, M.; Willner, H.; Aubke, F. Can.
J. Chem. 1993, 71, 1532.
(23) (a) Wilkins, R. G. Kinetics and Mechanism of Reactions of Transition
Metal Complexes, 2nd ed.; VCH: Weinheim, Germany, 1991 and
references therein. (b) Dudley, F. B.; Cady, G. H. J. Am. Chem. Soc.
1963, 85, 3375.

1282 Inorganic Chemistry, Vol. 35, No. 5, 1996
Wang et al.
Ir(CO)3(SO3F)3, best detected by its vibrational spectrum. It is
estimated that approximately 10-15% of the fac-isomer is
formed.
While the carbonylation of iridium(III) fluorosulfate to give
Ir(CO)3(SO3F)3 is slow but straightforward, the synthesis of
Ir(SO3F)3 by the oxidation of iridium metal with S2O6F2 in
HSO3F is troublesome and time consuming for three main
reasons.
(i) The system is chemically complex. At temperatures below
100 °C the reaction is very slow. At 130 °C the reaction
proceeds to give dark brown Ir(SO3F)4, which then decomposes
to blue Ir(SO3F)3, S2O5F2, and O2. Ir(SO3F)3 is then reoxidized
and the reaction sequence constitutes a catalytic decomposition
of S2O6F2 into O2 and S2O5F2. At 160 °C the decomposition
of S2O6F2 becomes very rapid. In addition fluorosulfate radicals
formed from S2O6F2 are reported23b to produce O2 and S2O5F2
by reaction with the glass wall at ∼120 °C. Hence the oxygen
produced must be removed every 24 h in order to avoid an
explosion, and a fresh portion of S2O6F2 is added from time to
time.9 It is estimated that an about 20- to 40-fold excess of
S2O6F2 over the amount required by stoichiometry is needed,
and the reaction takes several days to go to completion.9
(ii) At temperatures of ∼140 °C, fluorosulfuric acid, which
is used as a solvent will undergo self-dissociation according
to:
Figure 2. Molecular structure of mer-Ir(CO)3(SO3F)3 at 200 K. The
50% probability atomic displacement ellipsoids are shown.
chemistry. The lengths of chemically equivalent bonds are not
significantly different (see Table 3). Variations in chemically
inequivalent Ir-C, Ir-O, and S-O(Ir) bond lengths are all
consistent with the relative trans-influences23a of the ligands.
As expected from the spectroscopic results, the lengths of
the C-O bonds lie at the lower end of the range exhibited by
transition metal carbonyls.24 The relatively large errors in the
C-O bond lengths and uncertainties introduced by applying
thermal motion corrections (Table 3) preclude more meaningful
correlations with spectroscopic parameters.
HSO3F f SO3 + HF
(2)
This results in extensive glass attack and formation of SiF4. It
is thus not possible to follow the course of the reaction by
weighing. We have in the past,9 and here as well, not used
metal reactors (Monel-A or nickel) to avoid contamination by
other metal fluorosulfates.
(iii) The black-blue color of the product Ir(SO3F)3 makes it
difficult to judge whether all of the metal has been consumed.
In this study we have designed and used a reactor with a sidearm
(see Figure 1), which permits decanting of the supernatant liquid
after the remaining metal has settled to the bottom and
subsequent condensation of the oxidizer and solvent back into
the main reactor. In this manner pure Ir(SO3F)3 is eventually
obtained in a relatively short period of time in order to reduce
side reactions. To reduce the hazards, only small amounts of
Ir (∼100 mg) are used at a time.
3
As found for cis-Pd(CO)2(SO3F)2 there are a number of
intermolecular and unimposed intramolecular C-O contacts
(three and one respectively for C(1), two of each for C(2) and
one of each for C(3)) to terminal oxygen atoms of the
fluorosulfate groups in the range 2.722(8)-3.069(8) Å. C(3)
has in addition a weaker unimposed intramolecular contact with
F(2) of 3.056(7) Å. The respective sums of accepted van der
Waals radii are C + O ) 3.22 Å and C + F ) 3.17 Å.25 These
interactions are thought to be attractive in nature and to provide
a stabilizing influence analogous to those in cis-Pd(CO)2(SO3F)2.
In the square planar palladium structure each carbon atom has
five such contacts; however, the C-O distance ranges are
somewhat longer (C-O range ) 2.869(6)-3.172(6) Å and one
C-F ) 3.051(6) Å). This is a reasonable consequence of the
lower coordination number and square planar geometry at Pd
which would allow more secondary contacts to the CO groups
from neighbouring molecules.
The extramolecular C-O interactions in the structure of mer-
Ir(CO)3(SO3F)3 link the molecules into an extended three-
dimensional structure. There are also a few less severe non-
bonded O--O contacts (in the range 2.917(7)-3.010(8) Å) and
F-O contacts (2.880(7)-2.970(6) Å). These are marginally
shorter than the respective sums of accepted van der Waals
radii25 (O + O ) 3.04 Å and O + F ) 2.99 Å respectively)
and may be thought largely to be imposed as a result of the
attractive C-O and C-F interactions. There are no further
intermolecular separations significantly less than the sums of
appropriate pairs of van der Waals radii.
In summary, the synthetic challenge in this study is not the
preparation of Ir(CO)3(SO3F)3 but rather the synthesis of the
starting material Ir(SO3F)3 in sufficient quantities. Attempts
to follow the original preparation9 are not successful, because
the recommended overall reaction time is far too long and the
synthesis is now completely modified.
A final comment concerns the microanalytical results reported
here. The difficulties in obtaining reasonable quantities of
Ir(SO3F)3 and subsequently It(CO)3(SO3F)3 discussed above
have made it necessary to use very small quantities of material
for product identification. The presence of very small amounts
of hydrogen (about 0.1%) detected during microanalysis sug-
gests that not all solvent (HSO3F) has been removed from the
sample used. If an approximate composition of Ir(CO)3-
(SO3F)3‚0.7 HSO3F is assumed the calculated values for C
(5.5%), S (18.16%) and H (0.11%), agree very well with the
found values of 5.7, 18.25, and 0.1% for C, S, and H,
respectively. There is no evidence for the presence of HSO3F
in samples used for vibrational spectroscopy, which have been
obtained in a different preparation.
Figure 3 depicts four complete molecules whose iridium
atoms lie within a common unit cell plus additional atoms to
show all the presumed attractive C-- and C-F contacts to one
molecule, the atomic coordinates of which are given in Table
2.
Molecular Structure of mer-Ir(CO)3(SO3F)3. The molec-
ular structure, depicted in Figure 2, shows that the coordination
about the iridium atom is octahedral with a meridional stereo-
(24) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor R. J. Chem. Soc., Dalton Trans. 1989, S1.
(25) Bondi, A. J. Phys. Chem. 1964, 68, 441.

mer-Tris(carbonyl)iridium(III) Fluorosulfate
Inorganic Chemistry, Vol. 35, No. 5, 1996 1283
Figure 3. Stereoscopic view of four complete molecules of mer-Ir(CO)3(SO3F)3 at 200 K, whose iridium atoms lie within a common unit cell, plus
other symmetry related atoms (4 C and 1 O) sufficient to depict all attractive secondary interactions (thin lines) to one molecule (right, upper). The
50% probability atomic displacement ellipsoids are shown.
a
Table 4. Vibrational Data for mer-Ir(CO)3(SO3F)3 and cis-Pt(CO)2(SO3F)2
mer-Ir(CO)3(SO3F)3
cis-Pt(CO)2(SO3F)2
IR
Raman
IR
Raman
approx. assignment
2249 (w)
2208 (s)
2198 (s)
2168, 2150 (vw)
1409 (s, sh)
1394 (vs)
2249 (vs)
2206 (w, sh)
2196 (s)
2219 (s)
2218 (vs)
2181 (s)
1395 (s)
1376 (m)
ν(12CO)
ν(12CO)
ν(12CO)
ν(13CO)
2185 (vs)
1397 (s)
1389 (s, sh)
1378 (vs)
∼1380 (m, sh)
ν
asym(SO3)
1362 (w, sh)
1230 (m, sh)
1209 (vs)
1034 (m, sh)
1026 (s)
ν
sym(SO3)
1213 (vs)
1030 (s)
1011 (s)
987 (vs)
932 (w, sh)
829 (s)
1215 (s)
1056 (m)
1024 (m)
1007
1212 (s)
1019 (s)
993 (m)
νSO‚‚‚M
νSF
1009 (vs)
825 (mw)
815 (mw)
799 (s)
815 (w)
792 (w)
818 (s)
802 (s)
658 (m, sh)
657 (ms)
656 (s)
ν(MO) +
δ(SO2)
643 (m, sh)
595 (s)
640 (s)
585 (m-w)
648 (m, sh)
589 (s, sh)
584 (s)
557 (ms)
551 (s)
476, 472 (ms)
436 (w)
411 (vw)
588 (mw)
580 (m)
565 (w)
δ
asym(SO3)
sym(SO3)
548 (m, sh)
530 (s)
554 (m)
543 (m, sh)
512 (m)
450 (ms)
403 (w)
276 (s)
δ
554 (w)
475 (w, sh)
462 (ms)
412 (w)
291 (m)
276 (vw)
175 (w)
δ(M-CO)?
ν(MO) + δ(SO3)
F(SO3F)
unassigned
torsion and
def modes
451 (vs)
151 (m)
138 (vw)
137 (s)
a Abbreviations: s ) strong, m ) medium, w ) weak, v ) very, br ) broad, sh ) shoulder, ν ) stretching mode, sym ) symmetric, asym )
asymmetrical, δ ) bonding mode, and F ) rocking.
In spite of differences in stereochemistry and oxidation states
of the two respective metals, the molecular structures of mer-
Ir(CO)3(SO3F)3 and of cis-Pd(CO)2(SO3F)2 show very strong
Å is quoted.24 To account for the long iridium to carbon bonds
strongly reduced Ir to CO π-back-donation, in particular in the
trans-Ir(CO)2 moiety, is suggested from the vibrational spectra
which will be discussed next.
-
similarities in bond distances and angles for both the M(CO)n
(M ) Ir, Pd; n ) 3 or 2) and the fluorosulfate moieties. Even
the metal-oxygen distances are comparable for both com-
pounds.
The iridium-carbon distances in the trans-Ir(CO)2 group are,
at 1.998(6) and 2.006(6) Å, identical within accuracy limits.
Both are measurably longer than the third Ir-C distance of
1.937(6) Å due to the weak trans-influence of the fluorosulfate
group. All three rank at the longer end of Ir-CO bonds to
terminal CO groups, where for 148 examples a qu value of 1.898
In summary, while the observed bond parameters with the
possible exception of the short C-O and the long Ir-CO bond
distances are not unusual, the molecular structure of mer-
Ir(CO)3(SO3F)3 is unique for three reasons: (i) mer-Ir(CO)3-
(SO3F)3 is the first structurally characterized example of a metal
carbonyl derivative of iridium(III) where π-back-donation is
significantly reduced (vide infra); (ii) this is only the third case,
3
after cis-Pd(CO)2(SO3F)2 and [Hg(CO)2][Sb2F11],26 where
secondary contacts involving the electropositive C atoms of the

1284 Inorganic Chemistry, Vol. 35, No. 5, 1996
Wang et al.
Figure 4. FT-IR spectrum of crystalline mer-Ir(CO)3(SO3F)3.
carbonyl groups and the O or F atoms3,26 of the SO3F3 groups
or the [Sb2F11]- anion are observed;26 (iii) with linear OC-
M-OSO2F configurations found for Au(CO)(SO3F)1 and cis-
Pd(CO)2(SO3F)23 the mer-geometry is unexpected and unusual.
In addition the structure determination is of high accuracy, and
thermal motion corrections are applied.
Vibrational Spectra. The FT-IR and FT-Raman band
positions observed for crystalline mer-Ir(CO)3(SO3F)3 are listed
in Table 4 together with estimated intensities, the corresponding
vibrational data for cis-Pt(CO)2(SO3F)2, which are very similar
2
to those of cis-Pd(CO)2(SO3F)2 , and an approximate assignment
of the bands.
The FT-IR spectrum of mer-Ir(CO)3(SO3F)3 is shown in
Figure 4. In Figure 5 we compare the CO-stretching regions
in the Raman spectrum of crystalline mer-Ir(CO)3(SO3F)3 to
the solution Raman spectrum of the mother liquor, removed
from the crystals by pipetting.
Figure 5. FT-Raman spectrum in the CO-stretching range of (a)
crystalline mer-Ir(CO)3(SO3F)3 and (b) a mixture of mer- and fac-
Ir(CO)3(SO3F)3 dissolved in HSO3F.
Except for some more extensive band splitting for mer-
Ir(CO)3(SO3F)3, particularly in the 1000-800 cm-1 region
(assigned to ν(SO‚‚‚M) and ν(SF), the vibrational spectra for
both compounds in the SO3F region are identical. Some small
variations in band positions in the 400-512 cm-1 range are
consistent with our proposed assignment2 of these bands as being
due to the metal carbonyl moieties of both compounds. While
Ir(CO)3 bands in the 400-500 cm-1 region are difficult to assign
and in some cases even more difficult to detect, a clear picture
is presented in the CO stretching frequency region. For mer-
Ir(CO)3(SO3F)3 three CO stretching modes are expected and
observed even though the band at 2206 cm-1, (assigned to a B2
mode) is poorly resolved in the Raman spectrum, while both
A1 modes at 2249 and 2196 cm-1 respectively are very intense.
Alternately the 2249 cm-1 band is weak in the IR spectrum.
This would suggest a νjav(CO) value of 2218 cm-1, about 75
wavenumbers higher than found for gaseous CO (2143 cm-1).27
A stretching force constant, fr of (19.9 ( 0.1) × 102 N m-1 is
obtained using the two mass model. We had previously reported
a fr value of 19.5 × 102 N m-1 21 for Au(CO)SO3F with νj(CO)
at 2196 cm-1 while for cis-Pt(CO)2(SO3F)2 νjav ) 2202 cm-1
and fr is (19.6 ( 0.1) × 102 N m-1. Hence it appears that for
the noble metal carbonyl fluorosulfates in the 5d-block the
strength of the CO bond gradually increases with increasing
formal charge of the metal. This in turn suggests gradually
decreasing π-back-donation as we progress from Au(CO)SO3F
through cis-Pt(CO)2(SO3F)2 to mer-Ir(CO)3(SO3F)3. If the two
bands at 2249 and 2208 cm-1 are attributed to the trans-Ir(CO)2
moiety and νj(CO) at 2198 cm-1 to CO trans to SO3F, two
stretching force constants, fr, of 20.0 × 102 and 19.5 × 102 N
m-1 are obtained.
There are reports of vibrational studies of iridium(III)
carbonyl derivatives27 and for complexes of the type IrCl3(CO)-
(PR3)2, R ) C2H5 or n-C4H9, νj(CO) is found between 2010
and 2090 cm-1 28
It appears that the phosphine ligands are
.
better σ-donors than CO which in turn results in enhanced
π-back-donation to CO and νj(CO) will now fall in the expected
range for terminal CO ligands.29a We have made similar
observations recently for various palladium(I) carbonyl com-
plexes with other π-acid ligands.29b
As can be seen in Figure 4, two additional νj(CO) stretching
modes are observed in the Raman spectrum of the mother liquor
in HSO3F solution. The two bands at 2233 (A1) and 2157 (E)
cm-1 with IR counterparts at 2232 (A1) and 2156 (E) cm-1 are
assigned, based on band intensities, to the fac-Ir(CO)3(SO3F)3.
These band positions correspond well to νj(CO) reported for
4
fac-Ir(CO)3F3 at 2213 and 2165 cm-1. The average νj(CO)
values for fac-Ir(CO)3(SO3F)3 and fac-Ir(CO)3F3 of 2183 and
2181 cm-1 respectively suggest CO bonds of comparable
strength and a stretching force constant of (19.2 ( 0.1) × 102
N m-1 is obtained. Finally for Ir(CO)3I3,5 assuming facial
symmetry and identical irreducible representations for the two
reported bands νjav(CO) is 2135 cm-1 and fr is 18.4 × 102 N
m-1, slightly lower than for gaseous CO (18.6 × 102 N m-1).
(26) Willner, H.; Bodenbinder, M.; Wang, C.; Aubke, F. J. Chem. Soc.
Chem. Commun. 1994, 1189. Bodenbinder, M.; Balzer-Jo¨llenbeck,
G.; Willner, H.; Batchelor, R. J.; Einstein, F. W. B.; Wang, C.; Aubke,
F. Inorg. Chem. 1995, 35, 82.
(27) Nakamoto, K. Infrared Spectra of Inorganic and Coordination
Compounds, 4th ed.; Wiley-Interscience: New York, 1986.
(28) Chatt, J.; Johnson, N. P.; Shaw, B. L. J. Chem. Soc. 1964, 1625.
(29) (a) Adams, D. M. Metal-Ligand and Related Vibrations, Edward
Arnold Publishers: London, 1967. (b) Wang, C.; Bodenbinder, M.;
Willner, H.; Rettig, S.; Trotter, J.; Aubke, F. Inorg. Chem. 1994, 33,
779.

mer-Tris(carbonyl)iridium(III) Fluorosulfate
Inorganic Chemistry, Vol. 35, No. 5, 1996 1285
Summary and Conclusions
When mer-Ir(CO)3(SO3F)3 is redissolved in HSO3F two
Raman bands at 2253 and 2197 cm-1 are found, the latter with
a poorly resolved shoulder at ∼2205 cm-1. It appears that
isomerization in solution does not occur or does not occur
rapidly. For the same solution two 19F-NMR resonances due
to the solute are observed at 43.35 and 43.57 ppm of an
approximate peak area ratio of 1:2.
There is an alternative interpretation for the two bands at 2233
and 2157 cm-1 which are also observed in polycrystalline
samples. Both bands could be due to Ir(CO)2(SO3F)3, which
is a possible precursor in the formation of Ir(CO)3(SO3F)3 during
gradual CO addition. Since bands attributable to either bridging
SO3F groups or bridging CO are not observed, the precursor
would have to be a monomer. The coincidence of IR and
Raman bands would then suggest cis-Ir(CO)2(SO3F)3 as the sole
isomer, rather than an isomer mixture reflecting the trans-
directing ability of CO. Furthermore the broadness and low
Raman intensity of the band 2157 cm-1 is more consistent with
an E-mode in fac-Ir(CO)3(SO3F)3 than an A′ mode of cis-
Ir(CO)2(SO3F)3.
With the synthesis of mer-Ir(CO)3(SO3F)3 by CO addition
to Ir(SO3F)39 and its characterization by vibrational spectroscopy
and single-crystal X-ray diffraction described here, the range
of cationic metal carbonyls with significantly reduced π-back-
bonding is for the first time expanded from groups 11 (Ag(I)
and Au(I)) and 10 (Pd(II) and Pt(II)) to iridium(III) in group 9.
The sharp reduction in π-back-donation is evident from the long
Ir-C bonds, νjav(CO) of 2218 cm-1, and the stretching force
constant fr of 19.9 x 102 N m-1
.
Iridium is hence found to form cationic, uncharged32 and with
[Ir(CO)3]3- 33 also highly reduced carbonyl derivatives. As the
oxidation state of the metal ranges from +3 to -3, νj(CO) values
for terminal CO ligands range from a high of 2249 cm-1 for
the A1 mode in mer-Ir(CO)3(SO3F)3 to a low of 1642 cm-1 for
the [Ir(CO)3]3- anion.33
3
As observed previously for cis-Pd(CO)2(SO3F)2 significant
inter- and intramolecular SO-CO contacts appear to exert a
stabilizing influence on the structure of mer-Ir(CO)3(SO3F)3.
In addition bond parameters, such as bond lengths and bond
angles, for mer-Ir(CO)3(SO3F)3 and cis-Pd(CO)2(SO3F)23 com-
pare well, when the trans influence of CO and SO3F respectively
are taken into account. The only apparent difference between
both metal carbonyl fluorosulfates is the stereochemistry, which
is cis for Pd(CO)2(SO3F)2 and mer (or trans) for Ir(CO)3(SO3F)3.
This appears to be a consequence of the formation reaction:
cis-Pd(CO)2(SO3F)2 forms when two CO ligands in square
planar [Pd(CO)4]2+ are replaced by two SO3F- ions, while in
solvated Ir(SO3F)3 gradual addition of CO takes place. The
resulting geometries are hence in both cases a consequence of
the strong trans-directing ability of the CO group.
Thus it appears that CO bonding is slightly stronger in mer-
Ir(CO)3(SO3F)3 than in the fac-isomer. We have commented
in the preceding section on the difference in Ir-C bond length
due to the trans-influence exerted by the fluorosulfate group. It
may be argued that in the trans-Ir(CO)2-moiety there is more
competition for π-electron density from the metal while oxygen
of the fluorosulfate group functions as a weak π-donor toward
the iridium(III) center.
In compounds of the type IrCl3(CO)(PR3)2,28,29a R ) CH3 or
C4H9, where several geometrical isomers have been obtained
and studied by IR in CHCl3 as solvent, νj(CO) is always higher
by 30-40 wavenumbers when the CO group is trans to
phosphine compared to trans to chlorine. The CO stretching
frequencies for these compounds are observed in the region
between 2050 and 2100 cm-1
It is tempting to postulate the complete absence of π-back-
.
Acknowledgment. Financial support by the Natural Sciences
and Engineering Research Council of Canada (NSERC) and the
North Atlantic Treaty Organization (NATO) is gratefully
acknowledged. A.R.L. thanks the University of British Co-
lumbia for the award of a University Graduate Fellowship.
bonding in compounds with νj(CO) above 2200 cm-1 29,30
It is
.
our view30,31 that there still is residual π-back-donation, as long
as the stretching force constant fr stays below 21.3 × 102 N
m-1, the value for HCO+.2 The closest approach to a “no
π-back-bonding” situation is found for the [Hg(CO)2]2+ cation,
Supporting Information Available: Tables of supplementary
crystallographic data, anisotropic displacement parameters, selected
intramolecular torsion angles, distances, and angles, and unique
intermolecular and unimposed intramolecular secondary interaction
contact distances (6 pages). This material is contained in many libraries
on microfiche, immediately follows this article in the microfilm version
of this journal, and can be ordered from the ACS; see any current
masthead page for ordering information. For access on the World Wide
Web for journal subscribers (http://pubs.acs.org), files are presented
in Crystallographic Information Format (CIF).
reported by us recently,26 where fr is 21.0 + 0.1 × 102 N m-1
.
All other fr values reported here or elsewhere fall short.
The iridium(III) carbonyl derivatives discussed here4,5,28,29
clearly show, as phosphines or other π-acid ligands are replaced
by CO to give tris(carbonyl)-Ir(III) derivatives and as the
anionic ligands become harder and more electron withdrawing,
that metal CO bonding changes. π-back-donation decreases
gradually as νj(CO) increases to values well above 2143 cm-1
,
and the νj value of free CO25 and σ-bonding becomes predomi-
IC9506769
nant.
(30) Calderazzo, F. J. Organomet. Chem. 1990, 400, 303.
(31) Hurlburt, P. K.; Rack, J. J.; Luck, J. S.; Dec, S. F.; Webb, J. D.;
Andersen, O. P.; Strauss, S. H. J. Am. Chem. Soc. 1994, 116, 10003.
(32) Tripathi, S. C.; Srivastava, S. C.; Massi, R. P.; Shrimal, A. K. Inorg.
Chim. Acta 1976, 17, 257.
(33) Ellis, J. E., AdV. Organomet. Chem. 1990, 31, 1 and references therein.