Luminescent Iridium(I) diethyldithiocarbamate complexes: Synthesis, structure, and reactivity including stereoselective hydrogen oxidative addition

Article abstract of DOI:10.1021/ja970208t

A series of neutral Ir(I) complexes IrLL'(Et₂dtc) (L = L' = CO PPh₃, P(OPh)₃; L = CO, L' = PPh₃; L + L' = 1,2-bis(diphenylphosphino)ethane, 1,5-cyclooctadiene, 1,2-bis(di(pentafluorophenyl)phosphino)ethane; Et₂- dtc = N,N'-diethyldithiocarbamate) has been synthesized and characterized by NMR, IR, and electronic spectroscopies. The complexes show spectra consistent with a four-coordinate structure. A distorted square planar coordination geometry is confirmed by a single crystal structure determination of Ir(CO)(PPh₃)(Et₂dtc) (₃). Yellow-orange crystals of 3 (C₂₄H₂₅IrNOPS₂) are monoclinic, space group P2₁/n (no. 14), with a 15.641(12) ?, b = 9.252(3) ? c = 17.119(14) ?,β = 111.42(3)°, V = 2395.00 ?³, Z = 4, and final R = 0.029 (R(w) = 0.031) for 3204 unique reflections. All of the complexes exhibit emission in the solid state and in frozen glass media at 77 K. Additionally, Ir(CO)-(PPh₃)(Et₂dtc), Ir(dppe)(Et₂dtc), and Ir(P(OPh)₃)₂(Et₂dtc) display emission in methylene chloride solutions at room temperature. The bis triphenylphosphite complex, Ir(P(OPh₃)₂)(Et₂dtc), undergoes intramolecular C-H activation in benzene solution to form the ortho-metalated product Ir(P(OPh)₂(OC₆H₄))(H)(P(OPh)₃)(Et₂dtc). A benzene solution of Ir(CO)(PPh₃)(Et₂dtc) reacts readily with H₂, forming several different dihydride products having the formula IrH₂(CO)(PPh₃)(Et₂dtc), including an isomer with a kinetic preference for formation of 170:1 as determined using parahydrogen induced polarization (PHIP) at 300 K. A method is described for observing the ¹³C resonance of the carbonyl ligand in submilligram samples of IrH₂(PPh₃)(CO)(Et₂dtc) in under 2 min. The ligand exchange reactions of the two parahydrogen active isomers are also examined. PHIP is also observed in H₂ oxidative addition to Ir((C₆F₅)₂-PCH₂CH₂P(C₆F₅)₂)(Et₂dtc). Benzene solutions of Ir(O₂)(PPh₃)(Et₂dtc) and Ir(dppe)(Et₂dtc) react with molecular oxygen to form the stable adducts Ir(O₂)(CO)(PPh₃)(Et₂dtc) and Ir(O₂)(dppe)(Et₂dtc), respectively, and both lose O₂ upon irradiation only. The complex Ir(CO)(PPh₃)(Et₂dtc) oxidatively adds CH₃I to form the trans addition product Ir(CH₃)(CO)(I)(PPh₃)(Et₂dtc).

Full text of DOI:10.1021/ja970208t

7716
J. Am. Chem. Soc. 1997, 119, 7716-7725
Luminescent Iridium(I) Diethyldithiocarbamate Complexes:
Synthesis, Structure, and Reactivity Including Stereoselective
Hydrogen Oxidative Addition
Gianfranco Suardi,§ Brian P. Cleary,§ Simon B. Duckett,*,† Christopher Sleigh,†
Melinda Rau,§ Earl W. Reed,§ Joost A. B. Lohman,‡ and Richard Eisenberg*,§
Contribution from the Department of Chemistry, UniVersity of Rochester, Rochester, New York
14627, Department of Chemistry, UniVersity of York, Heslington, York, Y01 5DD, UK, and
Bruker Spectrospin Limited, Banner Lane, CoVentry, CV4 9GH, UK
ReceiVed January 22, 1997X
Abstract: A series of neutral Ir(I) complexes IrLL′(Et2dtc) (L ) L′ ) CO PPh3, P(OPh)3; L ) CO, L′ ) PPh3; L
+ L′ ) 1,2-bis(diphenylphosphino)ethane, 1,5-cyclooctadiene, 1,2-bis(di(pentafluorophenyl)phosphino)ethane; Et2-
dtc ) N,N′-diethyldithiocarbamate) has been synthesized and characterized by NMR, IR, and electronic spectroscopies.
The complexes show spectra consistent with a four-coordinate structure. A distorted square planar coordination
geometry is confirmed by a single crystal structure determination of Ir(CO)(PPh3)(Et2dtc) (3). Yellow-orange crystals
of 3 (C24H25IrNOPS2) are monoclinic, space group P21/n (no. 14), with a ) 15.641(12) Å, b ) 9.252(3) Å, c )
17.119(14) Å, â ) 111.42(3)°, V ) 2395.00 Å3, Z ) 4, and final R ) 0.029 (Rw ) 0.031) for 3204 unique reflections.
All of the complexes exhibit emission in the solid state and in frozen glass media at 77 K. Additionally, Ir(CO)-
(PPh3)(Et2dtc), Ir(dppe)(Et2dtc), and Ir(P(OPh)3)2(Et2dtc) display emission in methylene chloride solutions at room
temperature. The bis triphenylphosphite complex, Ir(P(OPh3)2)(Et2dtc), undergoes intramolecular C-H activation
in benzene solution to form the ortho-metalated product Ir(P(OPh)2(OC6H4))(H)(P(OPh)3)(Et2dtc). A benzene solution
of Ir(CO)(PPh3)(Et2dtc) reacts readily with H2, forming several different dihydride products having the formula
IrH2(CO)(PPh3)(Et2dtc), including an isomer with a kinetic preference for formation of 170:1 as determined using
parahydrogen induced polarization (PHIP) at 300 K. A method is described for observing the 13C resonance of the
carbonyl ligand in submilligram samples of IrH2(PPh3)(CO)(Et2dtc) in under 2 min. The ligand exchange reactions
of the two parahydrogen active isomers are also examined. PHIP is also observed in H2 oxidative addition to Ir((C6F5)2-
PCH2CH2P(C6F5)2)(Et2dtc). Benzene solutions of Ir(CO)(PPh3)(Et2dtc) and Ir(dppe)(Et2dtc) react with molecular
oxygen to form the stable adducts Ir(O2)(CO)(PPh3)(Et2dtc) and Ir(O2)(dppe)(Et2dtc), respectively, and both lose O2
upon irradiation only. The complex Ir(CO)(PPh3)(Et2dtc) oxidatively adds CH3I to form the trans addition product
Ir(CH3)(CO)(I)(PPh3)(Et2dtc).
Introduction
series of investigations from our laboratory, the cis di(phosphine)
complexes IrX(CO)(dppe) where dppe ) bis(diphenylphosphi-
no)ethane were prepared, and the corresponding H2 oxidative
addition reaction examined with respect to the stereoselectivity
of the reaction.9,10 In that study, it was determined that oxidative
addition of H2 and related Y-H substrates (Y ) SiR3,
B(catecholate), halide) occur under kinetic control with a
stereochemistry determined by ligand and substrate electronic
effects.11,12 In the present paper, the range of substitution in
the Ir(I) coordination sphere is probed further with a monoan-
ionic chelating ligand that leads to a complex having properties
very similar to Vaska’s complex and a very high stereoselectivity
for hydrogen addition.
Interest in the chemistry of square planar platinum group
element complexes is predicated on a number of factors. On
the one hand, complexes of Rh(I), Ir(I), Pd(II), and Pt(II) have
been found to be catalytically active for a variety of reactions
including hydrogenation, hydroformylation, hydrosilation, car-
bonylation, and olefin polymerization. In this context, the
chemistry of Ir(I) systems has been extensively examined as
modeling key steps in catalytic reactions, notably substrate
activation by oxidative addition. The complex IrCl(CO)(PPh3)2
first reported by Vaska has been especially well investigated in
this regard, and its reaction with molecular hydrogen is viewed
as the quintessential example of a single step concerted oxidative
addition reaction proceeding by a three-center transition state
in which Ir-H bonds form concomitantly with H-H cleavage
to yield a cis dihydride product.1,2 Factors influencing the
course of this reaction have been probed extensively.3-8 In one
A different facet of interest in square planar complexes lies
in their excited state properties as manifested by luminescence.
In the past ten years, there have been a large number of reports
describing emissive d8 complexes of Rh(I), Ir(I), and Pt(II) with
† University of York.
(7) Sargent, A. L.; Hall, M. B.; Guest, M. F. J. Am. Chem. Soc. 1992,
114, 517-522.
‡ Bruker Spectrospin Limited.
§ University of Rochester.
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(9) Johnson, C. E.; Fisher, B. J.; Eisenberg, R. J. Am. Chem. Soc. 1983,
105, 7772-7774.
X Abstract published in AdVance ACS Abstracts, July 15, 1997.
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3160.
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6540.
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(6) Jean, Y.; Lledos, A. NouV. J. Chim. 1986, 10, 635-641.
S0002-7863(97)00208-4 CCC: $14.00 © 1997 American Chemical Society

Luminescent Iridium(I) Diethyldithiocarbamate Complexes
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7717
chelating diphosphine,13-18 diolefin,19 and diimine ligands.20-33
In 1983, our laboratory reported the synthesis and characteriza-
tion of a series of luminescent square planar complexes of
general formula [MLL′(mnt)]- (M ) Rh, Ir; L, L′ ) CO, PR3,
P(OR)3; mnt ) maleonitriledithiolate).34 These complexes
exhibited highly structured emission and excitation spectra in
the solid state and in frozen solution. From the similarity of
the vibronic structure among Ir and Rh complexes, the shifts in
emission maxima as a function of electron donating ability of
L and L′, and the observed lifetimes, the emissive transition
As a logical extension in the investigation of luminescent
square planar complexes containing sulfur donor ligands, we
have undertaken an investigation of neutral Ir(I) complexes
having the uninegative chelating ligand N,N′-diethyldithiocar-
bamate (Et2dtc). While the chemistry and electrochemistry of
dithiocarbamates of Rh(I) and Rh(III) have been studied
extensively,35-46 there are relatively few Ir(III) dithiocarbamate
complexes that have been described and virtually no Ir(I)
systems.47,48 In the present study, we describe a new series of
square planar Ir(I) complexes having the general formula
Ir(L)(L′)(Et2dtc) (L ) L′ ) CO, P(OPh)3, PPh3; L + L′ ) 1,2-
bis(diphenylphosphino)ethane, 1,2-bis(di(pentafluorophenyl)-
phosphino)ethane; L ) CO, L′ ) PPh3). The synthesis and
characterization of these complexes are reported as well as the
single crystal X-ray structure determination of Ir(CO)(PPh3)-
(Et2dtc). All of the complexes are luminescent in rigid media
at 77 K, and several are found to emit in fluid solution at
ambient temperature, representing the first time this has been
seen for four-coordinate Ir(I) systems. Additionally, in con-
nection with our interest in Ir(I) complexes for bond activation
and catalysis, we have investigated the reactivity of some of
these compounds with H2, O2, and methyl iodide. With regard
to the first of these, we have employed parahydrogen induced
polarization (PHIP) to probe the kinetic selectivity of oxidative
addition and monitor the mechanism of interconversion between
product isomers. PHIP is a sensitive and definitive method for
determining pairwise hydrogen addition reactions and has
recently been used in conjunction with 2-D HMQC experiments
to assign structures and dynamics of metal hydrides.
3
was assigned as arising from a (d-π*mnt) excited state.
More recently, we have synthesized a series of Pt(diimine)-
(dithiolate) complexes (diimine ) bipyridine, o-phenanthroline,
or alkylated derivative; dithiolate ) mnt, toluenedithiolate
(tdt) or 1-(ethoxycarbonyl)-1-cyanoethylene-2,2-dithiolate
(ecda)).20-28,30,31 It was observed that the absorption spectra
of all complexes exhibited solvatochromic behavior, while the
emission spectra were dependent upon the dithiolate ligand.
Specifically, emission bands from mnt complexes were struc-
tured, while tdt and ecda analogs possessed essentially feature-
less emission. Based on emission behavior as a function of
temperature for these systems, mnt and tdt complexes were
assigned as having a single emitting state, while the ecda
complexes showed evidence of multiple emitting states. Dif-
ferent emitting states were thus assigned to Pt(II) diimine
complexes of mnt and the other dithiolates with the mnt systems
having a 3(Pt(d)/S(p)-π*dithiolate) emissive state, and the tdt and
ecda complexes possessing a 3(Pt(d)/S(p)-π*diimine) lowest energy
excited state. The difference in the emitting states was thought
to arise from the difference in the π* dithiolate energies for
mnt, tdt, and ecda relative to the lowest unoccupied π* levels
of the diimine.
Experimental Section
Materials and Methods. Reactions and sample preparations were
conducted in a nitrogen filled glovebox or under the appropriate gas
using a high vacuum line or Schlenk line. All solvents were reagent
grade or better and were dried and degassed by accepted methods.49
Hydrogen (99.99%, Air Products) and carbon monoxide (99.3%, Air
Products) were used as received. The following compounds were used
as received: 1,2-bis(diphenylphosphino)ethane (dppe), triphenylphos-
phine (PPh3) (Aldrich), triphenylphosphite (P(OPh)3) (Strem), methyl
iodide (Aldrich), 1,2-bis(di(pentafluorophenyl)phosphino)ethane (Strem),
sodium N,N′-diethyldithiocarbamate trihydrate (NaEt2dtc‚3H2O) (East-
man). The EPA mixed solvent used for some of the emission
measurements was prepared from five parts diethyl ether (Baker
Photrex), five parts isopentane (Aldrich spectophotometric grade), and
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Suardi et al.
two parts ethanol (Baker Photrex). Elemental analyses were performed
by Desert Analytics Laboratory, Tucson, AZ.
to 77 K over a paramagnetic catalyst and then transferred to the
resealable NMR tube.
IrH2(PPh3)2(Et2dtc), 10a,b. Hydrogen gas was admitted to a
pressure of 2 atm to a resealable NMR tube containing a frozen solution
of Ir(PPh3)2(Et2dtc) in toluene-d8. After warming the sample to 300 K
in the probe, a 1H NMR spectrum revealed the presence of 10a. After
15 min at 300 K, 10b was formed.
IrH2(dpfpe)(Et2dtc), 11. Hydrogen gas enriched in the para spin
state was admitted up to a pressure of 3 atm to a resealable NMR tube
containing a frozen solution of Ir(dpfpe)(Et2dtc) in benzene-d6. After
warming the sample to 342 K in the probe, the 1H NMR spectrum was
recorded. This spectrum showed the presence of 11 as the sole hydride
containing product.
Ir(CO)(O2)(PPh3)(Et2dtc), 12. Molecular oxygen was bubbled
through a yellow methylene chloride solution of 3 (0.075 g; 0.083
mmol) for ca. 10 min and then stirred an additional 1 h under an atm
of O2. Solution reduction to 2 mL followed by the addition of 35 mL
of deaerated pentane yielded 0.056 g (71%) of 12 as a bright yellow
powder.
Ir(COD)(Et2dtc), 1. [Ir(COD)Cl]2 (0.500 g, 0.744 mmol) and NaEt2-
dtc‚3H2O (0.336 g, 1.490 mmol) were dissolved in 50 mL of 1:1 (v/v)
CH2Cl2-acetone, and the solution was stirred for 2 h. Filtration of
NaCl through a 5 cm MgSO4/SiO2 column resulted in a yellow-orange
solution which was concentrated under vacuum to about 10 mL. The
solution was set aside at -20 °C for 3 h. The yellow-orange crystalline
precipitate was collected by filtration and washed with cold hexane to
give 0.560 g (84%) of Ir(COD)(Et2dtc). Anal. Calcd for IrC13H22-
NS2: C, 34.74; H, 4.94. Found: C, 34.82; H, 4.94.
Ir(CO)2(Et2dtc), 2. A solution of Ir(COD)(Et2dtc) (0.073 g, 0.164
mmol) in 10 mL of CH2Cl2 was stirred for 10 min under a slow flow
of CO. The red-orange solution was concentrated under vacuum to
ca. 2 mL, and addition of 10 mL of degassed hexane afforded
precipitation of a deep green-purple powder which was subsequently
collected by filtration and washed with hexane to give 0.057 g (88%)
of Ir(CO)2(Et2dtc). Anal. Calcd for IrC7H10NO2S2: C, 21.16; H, 2.54.
Found: C, 21.39; H, 2.56.
Ir(O2)(dppe)(Et2dtc), 13. Molecular oxygen was bubbled through
a yellow-orange methylene chloride solution of 6 (0.075 g; 0.083 mmol)
for ca. 10 min and then stirred an additional 1 h under an atm of O2.
Solution reduction to 2 mL followed by the addition of 35 mL of
deareated pentane yielded 0.079 g (73%) of a yellow solid.
Ir(CH3)(CO)(I)(PPh3)(Et2dtc), 14. To a 20 mL acetone solution
of Ir(CO)(PPh3)(Et2dtc) (0.150 g, 0.237 mmol) was added 74 µL of
CH3I (0.168 g, 1.189 mmol). The yellow-orange solution was stirred
for about 30 min. Upon concentration and addition of isopropyl alcohol,
a yellow-tan powder precipitate was collected by filtration and washed
with ether to give 0.162 g (88%) of Ir(CH3)(CO)(I)(PPh3)(Et2dtc).
Spectroscopic Characterization. Most NMR samples were pre-
pared using resealable NMR tubes fitted with J Young Teflon valves
(Brunfeldt) and high vacuum line adapters. Otherwise, samples were
placed in NMR tubes with high vacuum line adapters and flame sealed
after solvent transfer. 1H NMR spectra were recorded using either a
Bruker AMX-400 or a Bruker AMX-500 spectrometer at 400.13 or
500.13 MHz, respectively, and 31P{1H} NMR spectra were recorded
using either a Bruker AMX-400 or a Bruker AMX-500 spectrometer
at 161.98 or 202.404 MHz, respectively. 13C NMR spectra were
recorded using a Bruker AMX-500 spectrometer at 125.1 MHz. 1H
NMR chemical shifts are reported in ppm downfield of tetramethylsilane
Ir(CO)(PPh3)(Et2dtc), 3. A solution of Ir(COD)(Et2dtc) (0.090 g,
0.203 mmol) in 30 mL of methylene chloride was stirred for 10 min
under a slow flow of CO. To this red-orange solution was added 0.058
g (0.222 mmol) of PPh3. The solution turned yellow, while gas
evolution was observed. Upon concentration and addition of hexanes,
a yellow crystalline precipitate formed. The solid was collected by
filtration and washed with hexanes to give 0.100 g (78%) of Ir(CO)-
(PPh3)(Et2dtc). m/z: 731 M+. Anal. Calcd for IrC24H25NOPS2: C,
45.64; H, 3.86. Found: C, 45.64; H, 3.99.
Ir(PPh3)2(Et2dtc), 4. To a solution of Ir(COD)(Et2dtc) (0.060 g,
0.135 mmol) in 30 mL of acetone was added 0.077 g of PPh3 (0.294
mmol). The resultant red-orange solution was stirred for 1 h at room
temperature and concentrated to 5 mL under vacuum. Upon addition
of ether (10 mL), a powdery red precipitate formed that was collected
by filtration and washed with ether to give 0.102 g (87%) of
Ir(PPh3)2(Et2dtc). Anal. Calcd for IrC41H40NP2S2: C, 56.80; H, 4.77.
Found: C, 56.79; H, 4.66.
Ir(P(OPh)3)2(Et2dtc), 5. To a solution of Ir(COD)(Et2dtc) (0.100
g, 0.225 mmol) in 20 mL of CH2Cl2 was added 130 µL of P(OPh)3
(0.153 g, 0.496 mmol). The resultant pale yellow solution was stirred
for 20 min at room temperature and concentrated to 5 mL under
vacuum. Upon addition of ether (10 mL), a yellow precipitate formed
that was collected by filtration and washed with ether to give 0.168 g
(78%) of Ir(P(OPh)3)2(Et2dtc). Anal. Calcd for IrC41H40NP2O6S2: C,
51.19; H, 4.19. Found: C, 50.98; H, 4.04.
1
but measured from residual H signal in the deuterated solvents. 31P-
{1H} NMR spectra are reported in ppm downfield of an external 85%
solution of phosphoric acid. Infrared spectra were recorded from KBr
pellet samples using a Mattson Galaxy 6020 FT IR spectrometer.
Absorption spectra were recorded on a Hitachi U-2000 UV-visible
spectrophotometer. Room temperature and low temperature emission
measurements were performed on a Spex Fluorolog fluorescence
spectrophotometer using a quartz dewar. Room temperature emission
spectra were recorded in methylene chloride or butyronitrile. Low
temperature emission and excitation spectra were recorded in EPA and
butyronitrile glasses or in a KBr matrix. Mass spectra were collected
using electron impaction ionization on a VG autospectrometer.
Electrochemical Characterization. Electrochemical measurements
were made at (20 ( 1) °C in degassed acetonitrile using a Princeton
Applied Research (PAR) 173 potentiostat with a 179 and 175 sweep
generator and a Houston 200 xy recorder. Cyclic voltammograms were
measured using a single-compartment three electrode cell containing a
glassy-carbon working electrode, a platinum wire auxiliary electrode,
and a Ag wire quasi-reference electrode. Tetrabutylammonium hexaflu-
orophosphate (TBAPF6, 0.1 M) was used as the supporting electrolyte.
Solutions were prepared in a nitrogen filled glovebox, and a continuous
stream of nitrogen was passed over the solution while measurements
were being performed. All oxidation and reduction waves are reported
vs NHE based on using the ferrocene/ferrocenium couple (0.400 V) as
an internal standard.
Ir(dppe)(Et2dtc), 6. To a solution of Ir(COD)(Et2dtc) (0.100 g,
0.225 mmol) in 20 mL of acetone was added dppe (0.099 g, 0.247
mmol). The resultant orange solution was stirred for 1 h at room
temperature and concentrated to 5 mL under vacuum. Upon addition
of 10 mL of hexane, an orange powdery precipitate formed that was
collected by filtration and washed with hexane to give 0.125 g (78%)
of Ir(dppe)(Et2dtc). m/z: 739 M+.
Ir(dpfpe)(Et2dtc), 7. To a solution of Ir(COD)(Et2dtc) (0.075 g,
0.168 mmol) in 20 mL of acetone, dpfpe (0.130 g, 0.172 mmol) was
added. The resultant yellow-orange solution was stirred for 1 h at room
temperature and concentrated under vacuum. Upon addition of 10 mL
of hexane, a powdery yellow-orange precipitate formed that was
collected by filtration and washed with ether to give 0.160 g (85%) of
Ir(dpfpe)(Et2dtc).
Ir(P(OPh)2(OC6H4))(H)(P(OPh)3(Et2dtc), 8. A benzene-d6 solution
of complex 5 was allowed to stand under nitrogen for several hours.
NMR resonances characteristic for complex 5 were quantitatively
replaced by those of 8.
IrH2(CO)(PPh3)(Et2dtc), 9a-c. Hydrogen gas was admitted to a
pressure of 2 atm to a resealable NMR tube containing a frozen solution
of Ir(CO)(PPh3)(Et2dtc) in benzene-d6. After warming the sample to
Crystal Structure Determination of Ir(CO)(PPh3)(Et2dtc), 3. A
crystal suitable for X-ray diffraction was grown by slow diffusion of
diethyl ether to a saturated acetone solution of the complex at -30 °C.
The crystals were found to be moderately oxygen sensitive. A yellow-
orange prism (dimension 0.30 mm × 0.26 mm × 0.24 mm) was
mounted on a glass fiber using epoxy. The goniometer head was
1
342 K in the probe and waiting for a total of 20 min, the H NMR
spectrum was recorded. This spectrum showed the presence of 9a.
1
After 20 h at room temperature, the H NMR spectrum revealed the
presence of the different isomers 9a-c. For the PHIP experiments,
hydrogen enriched in the para spin state was prepared by cooling H2

Luminescent Iridium(I) Diethyldithiocarbamate Complexes
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7719
Scheme 1a
Table 1. Crystallographic Data for Ir(CO)(PPh3)(Et2dtc), 3
chemical formula
formula weight
crystal system
space group
Z
a, Å
b, Å
IrC24H25NOPS2
626.8
monoclinic
P21/n (no. 14)
4
15.641(11)
9.252(3)
17.119(14)
111.42(3)
2395.0
1.749
0.029
0.031
1.045
c, Å
â, deg
V, Å3
F
calc , g/cm3
R(Fo)
Rw(Fo)
GOF
Table 2. Selected Intramolecular Bond Distancesa and Bond
Anglesb for Ir(CO)(PPh3)(Et2dtc), 3
atoms
distance
atoms
angle
IR-S1
IR-S2
IR-P1
IR-C6
S1-C1
S2-C1
P1-C7
P1-C13
P1-C19
O1-C6
N1-C1
N1-C2
N1-C4
C2-C3
C4-C5
2.372(3)
2.384(3)
2.252(3)
1.79(1)
1.70(1)
1.75(1)
1.831(9)
1.83(1)
1.831(8)
1.17(1)
1.30(1)
1.46(1)
1.50(1)
1.52(1)
1.48(1)
S1-IR-S2
S1-IR-P1
S1-IR-C6
S2-IR-P1
S2-IR-C6
P1-IR-C6
IR-S1-C1
IR-S2-C1
C1-N1-C2
C1-N1-C4
C2-N1-C4
S1-C1-S2
S1-C1-N1
S2-C1-N1
IR-C6-O1
73.95(9)
173.54(9)
97.0(3)
99.59(9)
170.9(3)
89.5(3)
a Conditions: (a) CO, CH2Cl2; (b) CO, 1.1 equiv of PPh3, acetone;
(c) 2.1 equiv of PPh3, acetone; (d) 2.1 equiv of P(OPh)3, CH2Cl2; (e)
1.1 equiv of dppe (dppe ) 1,2-bis(diphenylphosphino)ethane), acetone;
(f) 1.1 equiv of dpfpe (dpfpe ) 1,2-bis(di(pentafluorophenyl)phos-
phino)ethane), acetone.
87.8(3)
86.3(3)
Table 3. Selected Infrared Spectral Data for Ir(L)(L′)(Et2dtc)
124.4(8)
119.5(8)
116.1(7)
111.9(5)
125.5(7)
122.6(7)
178(1)
Complexesa
complex
νCO
νC-N
νO-O
1
2
3
4
5
6
7
12
13
14
Ir(COD)(Et2dtc)
Ir(CO)2(Et2dtc)
Ir(CO)(PPh3)(Et2dtc)
Ir(PPh3)2(Et2dtc)
Ir(P(OPh)3)2(Et2dtc)
Ir(dppe)(Et2dtc)
1514
1521
1525
1499
1489
1507
1518
1517
1520
1515
2037, 1972
1958
a Distances are in Å. b Angles are in deg. Estimated standard
deviations in the least significant figure are given in parentheses.
Ir(dpfpe)(Et2dtc)
mounted on an Enraf-Nonius CAD4 diffractometer with graphite
monochromated Mo KR radiation operating in the ω/2θ scan mode.
The crystal was found to be monoclinic, space group P21/n, with cell
dimensions a ) 15.641(12) Å, b ) 9.252(3) Å, c ) 17.119(14) Å, â
) 111.42(3)°. Heavy atom methods were employed to locate the
iridium atom. The remaining non-hydrogen atoms were located using
cycles of difference Fourier maps and least square refinements. An
empirical absorption correction using the program DIFABS was
applied.50 In the last refinement all non-hydrogen atoms were described
with anisotropic thermal parameters. Hydrogen atoms were placed at
calculated positions around the diethyldithiocarbamate ligand and
around the phenyl rings. Neutral atom scattering factors were taken
from Cromer and Waber.51 Anomalous dispersion effects were included
in Fcalc; the values ∆f′ and ∆f′′ were those of Cromer.52 All calculations
were performed using TEXSAN software.53 Tables of abbreviated
crystallographic data and selected bond lengths and angles are presented
in Tables 1 and 2, respectively. The Supporting Information contains
full crystallographic data, positional parameters for all atoms, final
anisotropic thermal parameters, and complete tabulations of bond
distances and angles. (See paragraph regarding Supporting Information
at the end of paper.)
Ir(O2)(CO)(PPh3)(Et2dtc)
Ir(O2)(dppe)(Et2dtc)
Ir(CH3)(CO)(I)(PPh3)(Et2dtc)
1994
2025
843
818
a All spectra obtained from KBr pellets with bands given in
wavenumbers (cm-1).
new Ir(I) dithiocarbamate complexes investigated in the present
work are shown in Scheme 1. All of the complexes are obtained
in high yield as analytically pure solids and are characterized
by IR and 1H and 31P NMR spectroscopic data as presented in
Tables 3 and 4, respectively.
A common feature in the infrared spectra of all of the
complexes is a stretch around 1500-1520 cm-1 corresponding
to a νCN of the Et2dtc ligand, while a dominant feature of all of
Results and Discussion
1
the H NMR spectra are the resonances corresponding to the
Synthesis and Characterization of Complexes. The com-
plex Ir(COD)(Et2dtc) (1) is prepared by reacting [Ir(µ-Cl)-
(COD)]2 with the Na+ salt of N,N′-diethyldithiocarbamate in
acetone/dichloromethane according to eq 1. All of the other
ethyl protons of the Et2dtc ligand. For complex 1, the
coordinated COD ligand is readily identified by the resonances
arising from the two sets of methylene protons and the vinylic
protons of bound diolefin. Substitution of COD proceeds readily
under CO leading to complex 2 which exhibits two νCO at 2037
and 1972 cm-1 consistent with a cis dicarbonyl arrangement
about a four-coordinate Ir(I) center.54,55 Complex 2 is orange
(50) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A29, 158-166.
(51) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, England, 1974; Vol.
IV, p Table 2.2A.
(52) Cromer, D. T. International Tables for X-ray Crystallography; The
Kynoch Press: Birmingham, England, 1974; Vol. IV, p Table 2.3.1.
(53) TEXSAN-TEXRAY Structure Analysis Package; Molecular Struc-
ture Corporation: 1985.
(54) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th
ed.; John Wiley and Sons, Inc.: New York, NY, 1988; p 1455.
(55) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals; John Wiley and Sons: New York, NY, 1988.

7720 J. Am. Chem. Soc., Vol. 119, No. 33, 1997
Suardi et al.
Table 4. 1H and 31P NMR Spectral Data for Ir(L)(L′)(Et2dtc) Complexesa
1H NMRb
complex
Ir(COD)(Et2dtc)
Ir(CO)2(Et2dtc)
Et2dtc
others ligands
31P{1H} NMRb
1
2
3
0.67 t (7.2); 2.99 q (7.2)
0.48 t (7.2); 2.71 q (7.2)
0.52 t (7.2); 0.67 t (7.2);
2.84 q (7.2); 3.01 q (7.2)
0.60 t (7.2); 2.98 q (7.2)
0.42 t (7.2); 2.74 q (7.2)
0.74 t (7.2); 3.15 q (7.2)
0.56 t (7.2); 2.95 q (7.2)
0.59 t (7.2); 0.84 t (7.2);
2.78 m; 3.01 m
1.46 m; 2.21 m; 4.32 m
Ir(CO)(PPh3)(Et2dtc)
7.02 m; 7.88 m
21.61 s
4
5
6
7
8
Ir(PPh3)2(Et2dtc)
Ir(P(OPh)3)2(Et2dtc)
Ir(dppe)(Et2dtc)
Ir(dpfpe)(Et2dtc)
Ir(P(OPh)2(OC6H4))(H)(P(OPh)3)(Et2dtc)
6.93 m; 7.91 m
23.40 s
93.81 s
45.98 s
10.74 s
88.60 d (21.8);
112.40 d (21.8)
15.56 s
6.86 m; 7.04 m; 7.56 m
1.88 m; 7.04 m; 8.00 m
2.31 m
-16.02 dd (17.1; 24.9);
6.70-8.40 m
7.73 m; 7.04 m; -6.11
dd (20.1, 3.1); -15.70
dd (19.2, 3.1)
9a
IrH2(CO)(PPh3)(Et2dtc)
3.12 m; 0.75 t (7.2); 0.72 t (7.2)
9b
IrH2(CO)(PPh3)(Et2dtc)
0.538 t (7.1); 0.55 t (7.1)
-7.74 dd (166.5, 3.9);
-14.76 dd (10.9, 4.4)
-16.52 d (18.6)
7.75 m; 6.95 m; -9.21 ddd
(157.6, 22.6, 3.7); -17.35
ddd (18.0, 14.0, 3.7)
8.01 m; 7.07 m; -18.44 t (16.8)
2.18 m; 2.49 m; 3.11 m; 3.25 m;
-5.92 m; -16.89 m
6.99 m; 7.74 m
4.59 s
9c
10a
IrH2(CO)(PPh3)(Et2dtc)
IrH2(PPh3)2(Et2dtc)
0.63 t (7.1)
0.70 t (7.0); 3.03 q (7.0)
13.03 s
9.61 d (6.9);
-18.3 d (6.9)
10b
11
IrH2(PPh3)2(Et2dtc)
IrH2(dpfpe)(Et2dtc)
0.65 t (7.0); 2.81 q (7.0)
0.57 t (7.1); 0.74 t (7.1);
2.64 spt (7.14); 2.96 m; 3.11 m
0.55 t (7.2); 0.56 t (7.2);
2.68-3.02 m
0.33 t; 0.48 t; 2.84 m;
2.61 m; 2.37 m
0.62 t (7.2); 0.69 t (7.2); 2.88 m
17.8 s
7.86 m; 0.34 m
12
13
14
Ir(CO)(O2)(PPh3)(Et2dtc)
Ir(O2)(dppe)(Et2dtc)
2.40 s
2.13 m; 8.17-6.92 m
32.44 s; 14.00 s
Ir(CH3)(CO)(I)(PPh3)(Et2dtc)
1.65 d (4.1); 7.02 m; 7.87 m
-1.17 s
a 400 MHz, C6D6 solutions. b 500 MHz, C6D5CD3. c Chemical shift values are reported in ppm, coupling constant in parentheses are in Hz.
Abbreviations: s, singlet; d, doublet;t, triplet; q, quartet; m, multiplet; spt, septet.
in fluid solution and dark purple as a solid. The dark purple
color is indicative of stacking in the solid state as has been
observed before for certain Ir(I) systems such as Ir(CO)3Cl,56
Ir(CO)2(acac) (acac ) acetylacetonato),57 and [IrCl(PF3)2]2.58
The mixed carbonyl phosphine complex 3 is synthesized by
either reacting 2 with PPh3 or reacting 1 with CO in the presence
of ca. 1 equiv of PPh3. Infrared and 31P NMR spectroscopic
data reveal the presence of both CO and PPh3 coordinated to
Ir(I). The room temperature 1H NMR spectrum of a sample of
3 that is carefully prepared to have no excess PPh3 displays
two inequivalent methyl resonances and two inequivalent
methylene resonances for the ethyl groups of the Et2dtc ligand
(see Table 4). With trace amounts of PPh3 present, an ambient
temperature 1H NMR spectrum of 3 exhibits two broad
Figure 1. ORTEP drawing of Ir(CO)(PPh3)(Et2dtc) (3). Thermal
resonances for the ethyl groups of the Et2dtc ligand. Each of
ellipsoids are shown at 50% probability.
the broad signals decoalesces and sharpens at -50 °C, appearing
as two triplets and two quartets for the two inequivalent ethyl
groups, while at 100 °C the methyl signals appear as one triplet.
The observed dynamic behavior is consistent with exchange via
transient formation of Ir(PPh3)2(CO)(Et2dtc) and facile C-N
bond rotation within that species.
A single crystal X-ray analysis of Ir(CO)(PPh3)(Et2dtc) (3)
confirms the coordination geometry of the complex assigned
results in a S1-Ir-S2 bond angle of 74°, appreciably less than
the idealized 90° value.
The syntheses of complexes 4-7 are relatively routine
substitution reactions. All of the NMR data for these complexes
are consistent with products having mirror symmetry in which
any conformational effects are averaged out at room temperature.
The chelating di(phosphines) dppe and dpfpe of 6 and 7 have
multiplet resonances ca. 2 ppm indicating the equivalence of
from the spectroscopic data, although it reveals considerable
distortion from perfect planarity. A perspective drawing of
the four methylene protons in each complex. The 31P NMR
complex 3 is shown in Figure 1, and important bond distances
resonances of complexes 4-7 are all singlets. A benzene
solution of the bis(triphenylphosphite) complex Ir(P(OPh)3)2-
(Et2dtc) (5) is not stable and yields the ortho-metalated species
and angles are tabulated in Table 2. The Ir-S bond distances
of 2.372(3) Å for S1 and 2.384(3) Å for S2 indicate a slight
structural trans effect, while the similarity of S1-C1 and S2-
C1 bond lengths indicate that the -1 charge of the dithiocar-
bamate is delocalized over both sulfur atoms. The Et2dtc chelate
(8). The 1H NMR spectrum of a benzene solution of 8 displays
the hydride resonance at -16.02 ppm as a doublet of doublets
(2JH-P ) 17.1, 24.9 Hz) with coupling from two cis phosphorus
nuclei. The 31P{1H} NMR spectrum shows two doublets (2JP-P
) 21.8 Hz) at 88.60 and 112.40 ppm consistent with cis
phosphorus nuclei. Based on the NMR spectra, the stereo-
chemistry of 8 can be assigned unambiguously as that shown
below.
(56) Ries, A. H.; Hagley, V. S.; Peterson, S. W. J. Am. Chem. Soc. 1977,
99, 4184.
(57) Pitt, C. J.; Monteith, L. K.; Ballard, L. F.; Collman, J. P.; Morrow,
J. C.; Roper, W. R.; Ulku, D. J. Am. Chem. Soc. 1966, 88, 4286.
(58) Hitchcock, P. B.; Morton, S.; Nixon, J. F. J. Chem. Soc., Chem.
Commun. 1984, 603-604.

Luminescent Iridium(I) Diethyldithiocarbamate Complexes
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7721
Table 5. Room Temperature Electronic Spectral and
Electrochemical Data for Ir(L)(L′)(Et2dtc) Complexesa
oxc
×103
ꢀmax
(M-1 cm-1
Ep
complex
nm
cm-1
)
(V)
1
Ir(COD)(Et2dtc)
406
446
492
379
406
400
445
365
451
310
397
345
431
319
407
24.6
22.4
20.3
26.4
24.6
25.0
22.5
27.4
22.2
32.2
25.2
29.0
23.2
31.3
24.6
1084
1246
344
0.986
2
3
4
5
6
7
Ir(CO)2(Et2dtc)
3100
1950
3050
1350
6980
3240
11050
2630
6500
2700
11080
3540
1.111
0.966
Ir(CO)(PPh3)(Et2dtc)
Ir(PPh3)2(Et2dtc)b
Ir(P(OPh)3)2(Et2dtc)b
Ir(dppe)(Et2dtc)c
Ir(dpfpe)(Et2dtc)b
Electronic Spectra of Complexes. Dilute solutions of Ir(I)
Et2dtc complexes are yellow in color, and their absorption
spectra reveal maxima around 400 nm as given in Table 5. From
the magnitude of the extinction coefficient, ꢀ, the transition is
charge transfer in character. A general trend emerges from
Table 5 for the Ir(Et2dtc)(diphosphine) complexes; the more
electron withdrawing triphenylphosphite and dpfpe ligands result
in absorbances that are higher energy than their triphenylphos-
phine and dppe counterparts. This simple correlation, however,
cannot be extended to include those complexes containing CO
and COD ligands.
Complexes 3, 5, and 6 exhibit luminescence in fluid solution
at ambient temperature. Excitation of methylene chloride
solutions of these complexes near 450 nm leads to broad and
featureless emissions centered near 500 nm. Representative
electronic and luminescence spectra are shown in Figure 2 for
a dilute butyronitrile solution of Ir(CO)(PPh3)(Et2dtc). This
represents the first example of luminescence from a four-
coordinate Ir(I) complex in fluid solution. Like four-coordinate
d8 dithiolate complexes of Ir(I) and Pt(II) that have been reported
recently,13,14,19-28,31,34,59-61 all of the Et2dtc complexes are
photoluminescent in rigid media at 77 K. The spectra of the
Ir(I) dithiocarbamate complexes, however, show a concentration
dependence with low energy bands appearing with increasing
concentration. The origin of absorption and emission from these
complexes is currently under investigation and will be described
in a future report.
0.490
0.965
0.857
1.362
0.544
0.823
0.932
a Electronic spectra recorded in chloroform unless otherwise noted.
b Electronic spectrum recorded in methylene chloride. c Recorded in
acetonitrile; values are vs NHE based on the Fc/Fc+ couple at 0.400 v
as an internal standard.
Electrochemical Characterization of Complexes. The
electrochemical properties of complexes 1-7 were investigated
in the range of 1.5 to -1.2 V, and the results show irreversible
oxidation waves in the cyclic voltammograms with peak
potentials given in Table 5. The voltammograms for each
compound were recorded using the same experimental param-
eters, and, therefore, some empirical conclusions may be drawn.
The dicarbonyl complex Ir(CO)2(Et2dtc) has the highest peak
oxidation potential of 1.111 V, reflecting the strong π-acid
character of the carbonyl ligands. The oxidation is shifted to
less positive potentials for Ir(CO)(PPh3)(Et2dtc) and Ir(PPh3)2(Et2-
dtc) which display peak potentials of 0.966 and 0.490 V,
respectively. The peak potential observed for Ir(dppe)(Et2dtc)
(0.544 V) is similar to that seen for Ir(PPh3)2(Et2dtc) and is
consistent with the P2S2 donor set for each. The complex
Ir(P(OPh)3)2(Et2dtc) has an oxidation peak potential of 0.857
V which is higher than that of the PPh3 analog, as expected
based on the electron donating ability of P(OPh)3 vs PPh3. A
similar rationale can be used to account for the increase in peak
potential from 0.544 to 0.932 V for Ir(dppe)(Et2dtc) and Ir-
(dpfpe)(Et2dtc), respectively. The results presented here show
that as the ligand donor ability is changed systematically, the
oxidation peak potential is altered in a consistent way. Specif-
ically, the better the electron donation of ligand L + L′, the
more easily oxidized is the complex. This observation is
Figure 2. Ambient temperature absorption and luminescence spectra
of a 8.2 × 10-5 M butyronitrile solution of Ir(CO)(PPh3)(Et2dtc) (3).
a ) absorption spectrum; c ) excitation spectrum monitoring emission
at 530 nm; b ) emission spectrum with excitation at 425 nm.
consistent to a good extent with changes in the lowest energy
absorbance of the different complexes (see Table 5). Similar
behavior has been observed also for IrLL′(mnt)2- complexes
and indicates that the highest occupied orbital in these complexes
has significant metal character which in turn is altered by the
donicity of L + L′.62
Reactions with Hydrogen. The oxidative addition of H2 to
three of the Ir(Et2dtc) complexes has been investigated. When
Ir(CO)(PPh3)(Et2dtc) (3) in C6D6 is placed under H2 at 323 K,
rapid reaction takes place leading to the formation of three
dihydride complexes within 10 min, eq 2 and Figure 3a. From
the coupling patterns of the hydride resonances, it is possible
to assign the structure of each dihydride product unequivocally.
Complex 9a possesses hydride resonances at -6.11 and -15.70
ppm with similar 2JH-P for each hydride corresponding to a fac
arrangement of the phosphine and hydride ligands; only the
structure shown as 9a has this arrangement with inequivalence
of the two hydrides. Complex 9b, on the other hand, has one
hydride trans to phosphorus leading to the observed splitting
pattern with 2JH-P of 166.5 Hz for the resonance at -7.74 ppm.
(59) Bevilacqua, J. M.; Zuleta, J. A.; Eisenberg, R. Inorg. Chem. 1993,
32, 3689-3693.
(60) Bradley, P.; Johnson, C. E.; Eisenberg, R. J. Chem. Soc., Chem.
Commun. 1988, 255-257.
(61) Bradley, P.; Suardi, G.; Zipp, A. P.; Eisenberg, R. J. Am. Chem.
Soc. 1994, 116, 2859-2868.
(62) Megehee, E. G.; Johnson, C. E.; Eisenberg, R. Inorg. Chem. 1989,
28, 2423.

7722 J. Am. Chem. Soc., Vol. 119, No. 33, 1997
Suardi et al.
hydrogen enriched in the para spin state lead to enhanced
resonances of the product hydrides. For the reaction of 3 with
p-H2 at 298 K, a 40-fold enhancement of hydride resonances
was seen mainly in complex 9a with a kinetic selectivity for
9a over 9b of ca. 170:1 (Figure 3b). This kinetic selectivity
corresponds to a ∆∆Gq for hydrogen oxidative addition of 3.3
kcal/mol. The addition of H2 to form 9a occurs over the S-Ir-
CO axis of 3 with the CO and S donors moving to positions cis
to each other and trans to the hydride ligands. The observed
kinetic selectivity to form 9a is larger than that observed for
H2 addition over the P-Ir-CO axis of Ir(CO)X(dppe) (X )
Cl, Br, and I).9,10
The basis of the stereoselectivity in H2 oxidative addition
has been much discussed.3-8,72,73 As with the kinetic isomer
of H2 addition to Ir(CO)X(dppe), isomer 9a corresponds to
addition with H2 over the axis of the starting square planar
complex that contains the CO ligand.9,10 As the addition
proceeds, the entering H2 molecule, the CO moiety, and the
ligand initially trans to it move into positions corresponding to
the equatorial sites of a trigonal bipyramid intermediate. The
CO ligand in this site can through backbonding reduce the
2
repulsive interaction between the filled Ir dz orbital and the
filled σb function of the H2 molecule. This repulsive interaction
has been cited as the major contributor to the activation barrier
for H2 oxidative addition to d8 complexes.7 Based on the results
for H2 addition to 3 and the previous report of H2 addition to
Ir(CO)X(dppe), it seems evident that the carbonyl ligand
properly located in the reaction intermediate reduces the
activation barrier effectively, leading to the observed stereo-
selectivity of oxidative addition.
Figure 3. (a) Hydride region of the 1H NMR spectrum for the addition
of H2 to Ir(CO)(PPh3)(Et2dtc) (3). A ) complex 9a; B ) complex 9b;
C ) complex 9c. (b) Hydride region of the 1H NMR spectrum for the
addition of para-enriched H2 to Ir(CO)(PPh3)(Et2dtc) (3). A ) complex
9a; B ) complex 9b. Kinetic selectivity shown is approximately 170:1
favoring 9a.
Transfer of parahydrogen induced polarization to 31P was also
achieved using the INEPT+ pulse sequence, as has been
described previously,68 leading to enhancement of the 31P
resonance for 9a. While isomer 9c is not be expected to exhibit
polarization because PHIP requires inequivalence of the added
hydrogens, it is also not anticipated to be a primary kinetic
product from a cis concerted addition owing to constraints of
the Et2dtc chelate ring. In such an H2 oxidative addition
reaction, the two ligands trans to the hydrides in the product
(and cis to each other) originate in the reactant as mutually trans,
but because of Et2dtc chelation, this is not possible in 9c. The
kinetic selectivity of the reaction was confirmed when the
reaction was carried out at 298 K rather than at 323 K; only
complex 9a was observed to form in the first 10 min. After 20
h at 298 K, however, a product distribution similar to that of
Figure 3a was found.
The minor component of the product mixture, complex 9c, has
two equivalent hydrides and a fac arrangement for the phosphine
and two hydrides; only the structure shown as 9c is consistent
with the observed resonances for that component. The 31P NMR
spectrum of the reaction solution supports the notion of only
three isomeric dihydride products from the reaction.
In light of recent studies that have used HMQC methods in
conjunction with parahydrogen induced polarization to see
heteronuclear resonances rapidly and efficiently,64,74,75 we have
carried out HMQC experiments to observe the 31P signals of
9a and 9b. The HMQC approach is superior to the INEPT+
polarization transfer experiment reported by us previously since
In order to address the kinetic selectivity of H2 oxidative
addition to 3 in light of the known stereoselectivity of oxidative
addition in the related IrX(CO)(dppe) system,9,10 experiments
involving parahydrogen induced polarization (PHIP) were
conducted.63-71 In PHIP, oxidative addition reactions using
1
it detects 31P indirectly through the H resonances, thereby
making optimal use of parahydrogen enhancements. As ex-
pected, the HMQC spectrum displays four cross peaks correlat-
ing the phosphorus signals of 9a and 9b at 15.6 and 4.6 ppm
with their respective hydride resonances, as shown in Figure
4a.
(63) Eisenberg, R. Acc. Chem. Res. 1991, 24, 110-116.
(64) Duckett, S. B.; Barlow, G. K.; Partridge, M. G.; Messerle, B. A. J.
Chem. Soc., Dalton Trans. 1995, 3427-3429.
(65) Duckett, S. B.; Newell, C. L.; Eisenberg, R. J. Am. Chem. Soc.
1994, 116, 10548-10556.
(66) Duckett, S. B.; Eisenberg, R.; Goldman, A. S. J. Chem. Soc., Chem.
Commun. 1993, 1185-1187.
(67) Duckett, S. B.; Eisenberg, R. J. Am. Chem. Soc. 1993, 115, 5292-
(71) Eisenschmid, T. C.; McDonald, J.; Eisenberg, R. J. Am. Chem. Soc.
1989, 111, 7267-7269.
5293.
(68) Duckett, S. B.; Newell, C. L.; Eisenberg, R. J. Am. Chem. Soc.
1993, 115, 1156-1157.
(72) Abu-Hasanayn, F.; Goldman, A. S.; Krough-Jespersen, K. J. Phys.
Chem. 1993, 97, 5890-5896.
(69) Eisenberg, R.; Eisenschmid, T. C.; Chinn, M. S.; Kirss, R. U. AdV.
Chem. Ser. 1992, 230, 47-74.
(73) Musaev, D. G.; Morokuma, K. J. Organomet. Chem. 1995, 504,
93-105.
(70) Eisenschmid, T. C.; Kirss, R. U.; Deutsch, P. P.; Hommeltoft, S.
I.; Eisenberg, R.; Bargon, J.; Lawler, R. G.; Balch, A. L. J. Am. Chem.
Soc. 1987, 109, 8089-8091.
(74) Bax, A.; Griffey, R. H.; Hawkins, B. L. J. Magn. Reson. 1983, 301.
(75) Duckett, S. B.; Mawby, R. J.; Partridge, M. P. J. Chem. Soc., Chem.
Commun. 1996, 383-384.

Luminescent Iridium(I) Diethyldithiocarbamate Complexes
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7723
Table 6. Relative Cross Peak Intensities for the Interconversion of
the Hydrides of IrH2(CO)(PPh3)(Et2dtc), 9b, as a Percent of the
Diagonal Peak Intensity
[PPh3]
% intensity
kobs (s-1
)
0
3
45
75
39
36
23
20
0.55
0.52
0.37
0.33
resonances. In this experiment, positive cross peaks reveal
chemical exchange between sites, while negative cross peaks
arise through NOE and connect nuclei that are close in space.
A toluene-d8 solution of complex 9a, with no added PPh3 at
353 K, displays NOE cross peaks between the two hydride
ligands and between the hydride ligands and the ortho phenyl
protons of bound PPh3, while exchange cross peaks are observed
correlating the hydride ligands to free H2. Only on warming
to 358 K does the corresponding NOESY spectrum with short
mixing times reveal exchange cross peaks between each hydride
ligand of 9a and each hydride ligand of 9b, indicative of a
nonstereospecific exchange process.
At 353 K, the hydride ligands of 9b show no correlation with
the corresponding ortho phenyl protons of coordinated PPh3 or
to free H2, although the two hydride ligands are observed to
undergo exchange with each other. Furthermore, for a given
mixing time, an increase in the concentration of free PPh3 from
zero to a 75-fold excess results in a progressive decrease in the
intensity of the intramolecular exchange peaks between the
hydride ligands of 9b. Standard methods were used to obtain
values of kobs (s-1) for this exchange process and are shown
for a variety of PPh3 concentrations in Table 6.77 The
concentration dependence of PPh3 vs cross peak intensity
suggests that the process interconverting the hydride ligands in
9b proceeds initially with phosphine dissociation. Additionally,
the observation of a hydride-hydride cross peak indicates that
the hydride ligands retain distinct magnetic identities in the
resultant 16 e- intermediate. In these experiments, the time
for which p-H2 enhancements are observable decreases as the
concentration of PPh3 is increased. At the same time, a new
dihydride species, IrH2(PPh3)2(Et2dtc) (10b), is observed to form
from 9, presumably via CO dissociation from 9 and PPh3
coordination to the unsaturated Ir(III) intermediate.
Figure 4. (a) The HMQC spectrum correlating the 31P signals of 9a
and 9b at 15.6 and 4.6 ppm with their respective hydride resonances.
1
(b) The H-13C gradient assisted correlation spectrum of 9a in neat
C6H6 displaying carbonyl (13C) and hydride (1H) regions.
1
Figure 5. Hydride region of the H NMR spectrum for the addition
of para-enriched H2 to Ir(dpfpe)(Et2dtc) (7). Signal centered at -5.92
ppm originates from hydride trans to phosphorus.
The HMQC experiment was also used in conjunction with a
z-field gradients to observe the natural abundance 13C resonance
of the carbonyl ligand in a submilligram sample of 9a in neat
C6H6. Figure 4b shows the 1H-13C gradients-assisted correlation
spectrum. The cross peak connecting the hydride, (1H) -6.1
ppm, and carbonyl carbon, (13C) 172 ppm, is observed clearly
in under 2 min. The advantages of using z-field gradients are
that it reduces the phase cycling requirements of the NMR
experiment, enabling two scans per increment to be used and
importantly in this case, it acts as a spectroscopic filter to remove
signals not involved in the 1H-13C-1H coherence pathway. The
latter establishes that p-H2 effects can be used to monitor
reactions in protio solvents.
The addition of H2 to a toluene-d8 solution of 4 results in the
formation of two dihydride containing complexes according to
eq 3. The complexes, IrH2(PPh3)2(Et2dtc) (10a and 10b) exist
Dipolar relaxation and the NOESY experiment can also be
used in conjunction with parahydrogen polarization to obtain
information about ligand exchange processes.76 A series of
NOESY spectra collected on toluene-d8 solutions of 3 and p-H2
with varying amounts of PPh3, mixing times of 500 or 300 ms
and total acquisition times of 20 min yielded cross peaks
resulting from magnetization transfer from p-H2 enhanced
in two forms: one with inequivalent hydrides (10a) and a second
with equivalent hydrides and trans phosphines (10b). The
(76) Sleigh, C. J.; Duckett, S. B.; Messerle, B. A. Chem. Commun. 1996,
2395-2396.
(77) Bodenhausen, G.; Ernst, R. R. J. Am. Chem. Soc. 1982, 104, 1304.

7724 J. Am. Chem. Soc., Vol. 119, No. 33, 1997
Suardi et al.
hydride trans to phosphorus of 10a is centered at -9.21 ppm
and possesses a large trans phosphorus coupling constant (2JH-P
of 156.6 Hz) and a smaller cis phosphorus coupling constant
(2JH-P of 22.6 Hz), while the hydride trans to sulfur appears as
a doublet of doublet of doublets at -17.35 ppm displaying two
cis phosphorus coupling constants and a small hydride coupling
2
2
constant (2JP-H ) 14.0, JP-H ) 18.0, JH-H ) 3.7 Hz). The
two equivalent hydrides of 10b appear at -18.44 ppm as a triplet
with a small JH-P of 16.8 Hz consistent with a cis hydride-
2
phosphorus disposition. When Ir(PPh3)2(Et2dtc), 4, reacts with
p-H2 at 300 K, enhanced resonances are seen for 10a, but the
size of the parahydrogen enhancement drops to zero as 10b is
formed. Complex 10b is not observed to lose H2 upon heating
to temperatures as high as 358 K.
Polarization is also seen in the 1H NMR resulting from
oxidative addition of para-enriched H2 to Ir(dpfpe)(Et2dtc) as
shown in Figure 5. The hydride trans to phosphorus is centered
at -5.92 ppm with a large 2JH-P of 219 Hz, while the hydride
trans to sulfur is shifted significantly to higher field appearing
as a multiplet at -16.88 ppm. The complicated splitting patterns
for both hydride ligands are interpreted as involving coupling
to the adjacent hydride, two phosphorus nuclei and fluorines in
the dpfpe ligand (see Table 4).
Reaction with Methyl Iodide. The addition of methyl iodide
to an acetone solution of Ir(CO)(PPh3)(Et2dtc) (3) yields
Ir(CH3)(CO)(I)(PPh3)(Et2dtc) (14) in 88% yield. The infrared
spectrum displays νCO at 2025 cm-1 consistent with the presence
of a terminal carbonyl ligand coordinated to Ir(III), while the
1H NMR spectrum shows the methyl ligand as a doublet with
3
a small JH-P of 4.1 Hz consistent with cis-methyl- and
triphenylphosphine ligands. Although the stereochemistry of
14 has not been unambiguously assigned, strong precedence
exists for trans oxidative addition of methyl iodide to other four-
coordinate complexes of Ir(I).80 Therefore, we assign the
stereochemistry of 14 to that shown in eq 6 with methyl and
iodide ligands having trans dispositions.
Reactions with Oxygen. Both Ir(CO)(PPh3)(Et2dtc) and
Ir(dppe)(Et2dtc) are found to react rapidly in solution with
molecular oxygen as shown in eqs 4 and 5, respectively. The
yellow color of the solution fades as the reaction proceeds,
indicating that oxidation to an Ir(III) species has occurred. The
resonances of the dithiocarbamate ligand observed in 1H NMR
spectra of the O2 adducts differ considerably from those of the
respective starting compounds. For Ir(O2)(CO)(PPh3)(Et2dtc)
(12), the dithiocarbamate methyl groups appear as two inequiva-
lent triplets while the methylene protons exhibit three distinct
multiplets in a ratio of 1:1:2 corresponding to four inequivalent
methylene protons (two signals have overlapping chemical
shifts). Given that solutions of 12 display distinct methyl and
methylene resonances we conclude that rotation around the C-N
bond in the Et2dtc ligand is slow on the NMR time scale. The
structure of 12 has not been unambiguously assigned with the
point of uncertainty being the relative disposition of the CO
and PPh3 ligands but is displayed in eq 4 based on 31P{1H}
NMR spectral comparison to that found for 9a and 9b. The
31P{1H} spectrum of Ir(O2)(dppe)(Et2dtc) (13) contains two
signals with unresolved cis phosphorus coupling. The oxygen
is bound most likely sideways to the Ir center in both complexes
in analogy with Vaska-type examples.78,79 Further characteriza-
tion of the O2 adducts comes from infrared spectroscopy which
shows bands at 843 and 818 cm-1 for Ir(O2)(CO)(PPh3)(Et2-
dtc) and Ir(O2)(dppe)(Et2dtc), respectively, consistent with η2-
O2. The O2 adducts are stable under vacuum. However, both
compounds lose O2 upon UV photolysis in solution. Some
starting material is formed, although there appears to be
considerable decomposition, the products of which have yet to
be identified.
6
Conclusions
The preparation of and characterization of neutral Ir (I) N,N′-
diethyldithiocarbamate complexes have been reported. The
complexes are easily prepared via substitution reactions from
Ir(COD)(Et2dtc) and form stable four-coordinate species as
determined spectroscopically and from a single crystal X-ray
diffraction study of Ir(CO)(PPh3)(Et2dtc). Remarkably, Ir(CO)-
(PPh3)(Et2dtc), Ir(dppe)(Et2dtc), and Ir(P(OPh)3)2(Et2dtc) are
luminescent in fluid solution, and all complexes are emissive
in low temperature glasses. Their luminescence behavior is
similar to that observed for Pt(II) dithiolate complexes although
the nature of the excited state is not clear at this time.
The complex Ir(CO)(PPh3)(Et2dtc) (3) exhibits great similarity
to Vaska’s complex, IrCl(CO)(PPh3)2, in terms of its reaction
chemistry. Complex 3 oxidatively adds H2 and MeI and readily
forms an adduct with O2 in solution and in the solid state.
Because of the cis nature of H2 oxidative addition and the
presence of the dithiocarbamate chelate, there are more
stereochemical consequences to the dihydride products
IrH2(CO)(PPh3)(Et2dtc) (9) than for the corresponding addition
product to IrCl(CO)(PPh3)2. It is found that H2 addition to
Ir(CO)(PPh3)(Et2dtc) occurs stereoselectively, as determined by
(78) Vaska, L. Science 1963, 140, 809-810.
(79) Vaska, L. Acc. Chem. Res. 1976, 9, 175-183.
(80) Chock, P. B.; Halpern, J. J. Am. Chem. Soc. 1966, 88, 3511-3514.

Luminescent Iridium(I) Diethyldithiocarbamate Complexes
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7725
exposure to para-enriched hydrogen, and displays a kinetic
preference for H2 addition over the S-Ir-CO axis. HMQC
experiments in conjunction with parahydrogen induced polariza-
tion reveal both 31P and natural abundance 13CO ligation in very
short acquisition times with submilligram samples. A NOESY
experiment reveals intermolecular phosphine exchange con-
comitant with hydride equilibration for one of the systems, 9b.
The O2 adducts Ir(O2)(CO)(PPh3)(Et2dtc) and Ir(O2)(dppe)(Et2-
dtc) form readily in fluid solution and the solid state. However,
they do not lose O2 thermally and must be photolyzed to liberate
oxygen.
for support of this research. G.S. also gratefully acknowledges
a fellowship from the Swiss National Science Foundation, and
M.R. thanks the Center for Photoinduced Charge Transfer
supported by the National Science Foundation for a summer
internship. We also thank Johnson Matthey/Alfa Aesar for a
generous loan of iridium salts. Assistance in these studies by
Dr. Jeremy Hill and Mr. Shawn Briglin is also acknowledged.
Supporting Information Available: Tables of data collec-
tion and refinement parameters, thermal parameters, atomic
positional parameters, and complete bond distances and angles
for non-hydrogen atoms for 3 (8 pages). See any current
masthead page for ordering and Internet access instructions.
Acknowledgment. We wish to thank the Department of
Energy, Division of Chemical Sciences (G.S., E.W.R., B.P.C.,
R.E.), NATO (S.B.D., R.E.), EPSRC (C.S.), NSF Grant CHE
94-09441 (S.B.D., R.E.), and the Royal Society (S.B.D., R.E.)
JA970208T