Large effects of ion pairing and protonic-hydridic bonding on the stereochemistry and basicity of crown-, azacrown-, and cryptand-222-potassium salts of anionic tetrahydride complexes of iridium(III)

Article abstract of DOI:10.1021/ic0255149

The compounds [K(Q)][IrH₄(PR₃)₂] (Q = 18-crown-6, R = Ph, ⁱPr, Cy; Q = aza-18-crown-6, R = ⁱPr; Q = 1,10-diaza-18-crown-6, R = Ph, ⁱPr, Cy; Q = cryptand-222, R = ⁱPr, Cy) were formed in the reactions of IrH₅-(PR₃)₂ with KH and Q. In solution, the stereochemistry of the salts of [IrH₄(PR₃)₂]^- is surprisingly sensitive to the countercation: either trans as the potassium cryptand-222 salts (R = Cy, ⁱPr) or exclusively cis (R = Cy, Ph) as the crown- and azacrown-potassium salts or a mixture of cis and trans (R = ⁱPr). There is IR evidence for protonichydridic bonding between the NH of the aza salts and the iridium hydride in solution. In single crystals of [K(18-crown-6)][cis-IrH₄(PR₃)₂] (R = Ph, ⁱPr) and [K(aza-18-crown-6)][cis-IrH₄(Pⁱ Pr₃)₂], the potassium bonds to three hydrides on a face of the iridium octahedron according to X-ray diffraction studies. Significantly, [K(1,10-diaza-18-crown-6)][transIrH₄(Pⁱ Pr₃)₂] crystallizes in a chain structure held together by protonic-hydridic bonds. In [K(1,10-diaza-18-crown-6)][cis-IrH₄(PPh₃)₂], the potassium bonds to two hydrides so that one NH can form an intra-ion-pair protonichydridic hydrogen bond while the other forms an inter-ion-pair NH···Hlr hydrogen bond to form chains through the lattice. Thus, there is a competition between the potassium and NH groups in forming bonds with the hydrides on iridium. The more basic PⁱP₃ complex has the lower N-H stretch in the IR spectrum because of stronger N-H···HIr hydrogen bonding. The trans complexes have very low Ir-H wavenumbers (1670-1680) due to the trans hydride ligands. The [K(cryptand)]⁺ salt of [trans-IrH₄(PⁱPr₃)₂]^- reacts with WH₆(PMe₂Ph)₃ (pKα^THF 42) to give an equilibrium (K_eq = 1.6) with IrH₅(PⁱPr₃)₂ and [WH₅(PMe₂Ph)₃]^- while the same reaction of WH₆(PMe₂Ph)₃ with the [K(18-crown-6)]⁺ salt of [cis-IrH₄(PⁱPr₃)₂]^- has a much larger equilibrium constant (K_eq = 150) to give IrH₅(Pⁱ-Pr₃)₂ and [WH₅(PMe₂Ph)₃]^-; therefore, the tetrahydride anion displays an unprecedented increase (about 100-fold) in basicity with a change from [K(crypt)]⁺ to [K(crown)]⁺ countercation and a change from trans to cis stereochemistry. The acidity of the pentahydrides decrease in THF as IrH₅(PⁱPr₃)₂/[K(crypt)] [trans-IrH₄(PⁱPr₃)₂] (pKα^THF = 42) > IrH₅-(PCy₃)₂/[K(crypt)][trans- IrH₄(PCy₃)₂] (pKα^THF = 43) > IrH₅(PⁱPr₃)₂/[K(crown)] [cis-IrH₄(PⁱPr₃)₂] (pKα^THF = 44) > IrH₅-(PCy₃)₂/[K(crown)][cis H₄(PCy₃)₂]. The loss of PCy₃ from IrH₅(PCy₃)₂ can result in mixed ligand complexes and H/D exchange with deuterated solvents. Reductive cleavage of P-Ph bonds is observed in some preparations of the PPh₃ complexes.

Full text of DOI:10.1021/ic0255149

Inorg. Chem. 2002, 41, 2995−3007
Large Effects of Ion Pairing and Protonic−Hydridic Bonding on the
Stereochemistry and Basicity of Crown-, Azacrown-, and
Cryptand-222-potassium Salts of Anionic Tetrahydride Complexes of
Iridium(III)
Shaun E. Landau, Kai E. Groh, Alan J. Lough, and Robert H. Morris*
DaVenport Laboratory, Department of Chemistry, UniVersity of Toronto, 80 St. George Street,
Toronto, Ontario, M5S 3H6 Canada
Received January 27, 2002
i
i
The compounds [K(Q)][IrH (PR ) ] (Q ) 18-crown-6, R ) Ph, Pr, Cy; Q ) aza-18-crown-6, R ) Pr; Q )
4
3 2
1,10-diaza-18-crown-6, R ) Ph, iPr, Cy; Q ) cryptand-222, R ) Pr, Cy) were formed in the reactions of IrH -
i
5
(PR ) with KH and Q. In solution, the stereochemistry of the salts of [IrH (PR ) ]- is surprisingly sensitive to the
3 2
4
3 2
countercation: either trans as the potassium cryptand-222 salts (R ) Cy, iPr) or exclusively cis (R ) Cy, Ph) as
the crown- and azacrown-potassium salts or a mixture of cis and trans (R ) iPr). There is IR evidence for protonic−
hydridic bonding between the NH of the aza salts and the iridium hydride in solution. In single crystals of [K(18-
i
crown-6)][cis-IrH (PR ) ] (R) Ph, iPr) and [K(aza-18-crown-6)][cis-IrH (PPr3)2], the potassium bonds to three hydrides
4
3 2
4
on a face of the iridium octahedron according to X-ray diffraction studies. Significantly, [K(1,10-diaza-18-crown-
i
6)][trans-IrH (PPr3)2] crystallizes in a chain structure held together by protonic−hydridic bonds. In [K(1,10-diaza-
4
18-crown-6)][cis-IrH (PPh ) ], the potassium bonds to two hydrides so that one NH can form an intra-ion-pair protonic−
4
3 2
hydridic hydrogen bond while the other forms an inter-ion-pair NH‚‚‚HIr hydrogen bond to form chains through the
lattice. Thus, there is a competition between the potassium and NH groups in forming bonds with the hydrides on
i
iridium. The more basic PR complex has the lower N−H stretch in the IR spectrum because of stronger
3
N−H‚‚‚HIr hydrogen bonding. The trans complexes have very low Ir−H wavenumbers (1670−1680) due to the
trans hydride ligands. The [K(cryptand)]+ salt of [trans-IrH (PPr3)2]- reacts with WH (PMe2Ph)3 (pKRTHF 42) to give
i
4
6
an equilibrium (K ) 1.6) with IrH (PPr3)2 and [WH (PMe2Ph)3]- while the same reaction of WH (PMe2Ph)3 with
i
eq
5
5
6
i
i
the [K(18-crown-6)]+ salt of [cis-IrH (PPr3)2]- has a much larger equilibrium constant (K ) 150) to give IrH (P-
4
eq
5
Pr3)2 and [WH (PMe2Ph)3]-; therefore, the tetrahydride anion displays an unprecedented increase (about 100-fold)
5
in basicity with a change from [K(crypt)]+ to [K(crown)]+ countercation and a change from trans to cis stereochemistry.
The acidity of the pentahydrides decrease in THF as IrH (PPr3)2/[K(crypt)][trans-IrH (PPr3)2] (pKRTHF ) 42) > IrH -
i
i
5
4
5
(PCy3)2/[K(crypt)][trans-IrH (PCy3)2] (pKRTHF ) 43) > IrH (PPr3)2/[K(crown)][cis-IrH (PPr3)2] (pKRTHF ) 44) > IrH -
i
i
4
5
4
5
(PCy3)2/[K(crown)][cis-IrH (PCy3)2]. The loss of PCy3 from IrH (PCy3)2 can result in mixed ligand complexes and
4
5
H/D exchange with deuterated solvents. Reductive cleavage of P−Ph bonds is observed in some preparations of
the PPh3 complexes.
Introduction
hydridic bonds.9b The strength of this bond is influenced by
the donor acidity and the basicity of the hydride ligand. Most
reports thus far involve neutral or cationic hydride complexes
Hydride ligands are known to form hydrogen bonds with
proton donors in solution and in the solid state.1-13 These
have been called dihydrogen, proton-hydride, or protonic-
(2) Lee, J. C.; Peris, E.; Rheingold, A. L.; Crabtree, R. H. J. Am. Chem.
Soc. 1994, 116, 11014-11019.
* To whom correspondence should be addressed. E-mail: rmorris@
chem.utoronto.ca.
(1) Stevens, R. C.; Bau, R.; Milstein, D.; Blum, O.; Koetzle, T. F. J. Chem.
Soc., Dalton Trans. 1990, 1429-1432.
(3) Lough, A. J.; Park, S.; Ramachandran, R.; Morris, R. H. J. Am. Chem.
Soc. 1994, 116, 8356-8357.
(4) Abdur-Rashid, K.; Gusev, D. G.; Landau, S. E.; Lough, A. J.; Morris,
R. H. J. Am. Chem. Soc. 1998, 120, 11826-11827.
10.1021/ic0255149 CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/02/2002
Inorganic Chemistry, Vol. 41, No. 11, 2002 2995

Landau et al.
that serve as proton acceptors, and these are not very basic
or hydridic.
Most of the known polyhydride complexes of iridium are
neutral with coordination numbers varying from five to
seven.14 However, some anionic hydride complexes of
iridium have been reported including [IrH6]3-,15,16 [IrH6]4-,17
and [IrH5].4-18 The present study involves the preparation
and characterization of the new and basic anionic hydride
i
complexes [IrH4(PR3)2]- (R ) Ph, Pr, Cy). The series of
phosphine ligands PPh3, PiPr3, and PCy3 provides increas-
ingly more basic and more crowded metal complexes that
can be tested as hydrogen bond acceptors toward the cations
[K(1,10-diaza-18-crown-6)]+ and [K(aza-18-crown-6)]+ as
some of us have also done for anionic rhenium polyhy-
drides.19 These complexes, regardless of their configuration
about the iridium atom, possess mutually trans hydride
ligands that are potentially good hydrogen-bond acceptors.
In some cases, the resulting interactions were found to direct
the formation of networks in the solid state.
In preliminary work, [K(1,10-diaza-18-crown-6)][trans-
IrH4(PiPr3)2] was found to form a chain structure held
together by 1.85 Å NH‚‚‚HIr bonds as shown schematically
in Figure 1.4 The X-ray diffraction data set was exceptionally
good and allowed the hydride positions to be clearly located
as evidenced by the electron density contour map for the
plane containing the iridium atom and hydride ligands
(Figure 2). The Ir(1)-H(1IR) bond lengths are 1.54(3) Å,
and the Ir(1)-H(2IR) bond lengths are 1.68(3) Å. The
observed H(1N)-H(2IR) separation was 2.07 Å which is
indicative of protonic-hydridic bonding. This observed
separation is probably greater than the true separation because
the observed N(1)-H(1N) bond length of 0.77(3) Å is likely
less than the true value as would be determined in a neutron
diffraction study because this bond is highly polarized with
the electrons being associated more with N than with H. By
increasing the length of the N(1)-H(1N) bond to a more
Figure 1. Chain structure of [K(1,10-diaza-18-crown-6)][IrH4(PiPr3)2].
PiPr3 carbon and hydrogen atoms and nonessential crown hydrogen atoms
have been omitted for clarity. The distances given are observed distances.
(5) Klooster, W. T.; Koetzle, T. F.; Siegbahn, P. E. M.; Richardson, T.
B.; Crabtree, R. H. J. Am. Chem. Soc. 1999, 121, 6337-6343.
(6) Messmer, A.; Jacobsen, H.; Berke, H. Chem.sEur. J. 1999, 5, 3341-
3349.
(7) Abdur-Rashid, K.; Gusev, D. G.; Lough, A. J.; Morris, R. H.
Organometallics 2000, 19, 834-843.
(8) Belkova, N. V.; Shubina, E. S.; Gutsul, E. I.; Epstein, L. M.; Eremenko,
I. L.; Nefedov, S. E. J. Organomet. Chem. 2000, 610, 58-70.
(9) (a) Custelcean, R.; Jackson, J. E. J. Am. Chem. Soc. 2000, 122, 5251-
5257. (b) Custelcean, R.; Jackson, J. E. Chem. ReV. 2001, 101, 1963-
1980.
(10) Bakhmutov, V. I.; Bakhmutova, E. V.; Belkova, N. V.; Bianchini,
C.; Epstein, L. M.; Masi, D.; Peruzzini, M.; Shubina, E. S.; Vorontsov,
E. V.; Zanobini, F. Can. J. Chem. 2001, 79, 479-489.
(11) Belkova, N. V.; Ionidis, A. V.; Epstein, L. M.; Shubina, E. S.;
Gruendemann, S.; Golubev, N. S.; Limbach, H. H. Eur. J. Inorg. Chem.
2001, 1753-1761.
Figure 2. [K(1,10-diaza-18-crown-6)][IrH4(PiPr3)2] electron contour map.
Gradient ) 0.1 e/Å3.
typical length of 1.00 Å, an H(1N)-H(2IR) separation of
1.85 Å is obtained. This corrected separation is within the
typical range observed for protonic-hydridic bonds (between
1.7 and 2.1 Å). On the other hand, [K(18-crown-6)][cis-
IrH4(PiPr3)2] exists in the crystalline state as ion pairs with
potassium-hydride interactions.4
This study explores the dependence of structure and
reactivity of these ion pairs with potassium-hydride or
protonic-hydridic bonds as a function of the phosphine
ligands present.
(12) Fan, H.-J.; Hall, M. B. J. Am. Chem. Soc. 2001, 123, 3828-3829.
(13) Hinman, J. G.; Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Inorg.
Chem. 2001, 40, 2480-2481.
(14) Hlatky, G. G.; Crabtree, R. H. Coord. Chem. ReV. 1985, 65, 1-48.
(15) Graefe, A. F.; Robeson, R. K. J. Inorg. Nucl. Chem. 1967, 29, 2917.
(16) Bronger, W.; Gehlen, M.; Aufferman, G. J. Alloys Compds. 1991,
176, 255-262.
(17) Varma, S. K.; Chang, F. C.; Magee, C. B. Inorg. Chem. 1972, 11,
400.
(18) Moyer, R. O.; Stanitski, C.; Tanaka, J.; Kay, M. I.; Kleinberg, R. J.
Solid-State Chem. 1971, 3, 541.
(19) Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Can. J. Chem. 2001,
79, 964-976.
2996 Inorganic Chemistry, Vol. 41, No. 11, 2002

Ion Pairing and Protonic-Hydridic Bonding
NMR (CDCl3), δ: 3.10 (m, 6H, CH), 1.34 (m, 36H, CH3), -49.31
Experimental Section
2
(t, J(HP) ) 11.4, 1H, IrH).24,25 31P{1H} NMR (CDCl3), δ: 32.9
General Procedures. Unless otherwise stated, all manipulations
and reactions were carried out under an atmosphere of prepurified
argon or nitrogen using standard Schlenk and glovebox techniques.
All solvents were thoroughly dried over the appropriate drying
agents and made free of oxygen and nitrogen by distillation under
argon. THF, Et2O, toluene, and hexanes were refluxed over sodium
wire with benzophenone indicator. CH2Cl2 was refluxed over CaH2.
iPrOH and EtOH were refluxed over iodine-activated magnesium
turnings. Acetone was refluxed over anhydrous CaSO4. THF-d8,
C6D6, CD2Cl2, and CDCl3 were obtained from Cambridge Isotopes
Laboratories. These deuterated solvents were degassed by freeze-
pump-thaw (3 cycles) and dried over molecular sieves.
All 1H and 31P NMR spectra were acquired on a Varian Gemini
300 MHz spectrometer running at 300 MHz for H and 121 MHz
for 31P. These instruments were used to acquire both H and 31P
NMR spectra in deuterated and nondeuterated solvents. For the
acquisition of 1H NMR spectra of samples in nondeuterated
solvents, the following criteria were essential: deactivation of
deuterium locking, minimization of pulse width, and minimization
of gain. For good quality spectra, a double precision Fourier
transform and a high sample concentration were desirable. The
acquisition of 31P NMR spectra for samples in nondeuterated
(s).24,25 IR (Nujol), cm-1: 2228 (IrH).
Preparation of IrHCl2(PPh3)3 (2). A 20 mL portion of PrOH
i
was added to a flask containing IrCl3‚3H2O (0.746 g, 2.50 mmol)
and PPh3 (3.981 g, 15.18 mmol). The resulting mixture was refluxed
for 1.5-3 days. After 1.5 days, mainly or exclusively cis,mer-2
can be isolated. After 3 days, a mixture of cis,mer-2 and trans,mer-2
is isolated. During the first 48 h, the mixture changed from green-
brown to yellow. The mixture was allowed to return to room
temperature and extracted with Et2O (3 × 20 mL; each extract was
carefully decanted off, filtered to recover any product, and finally
discarded). The yellow product was collected by filtration, washed
with 3 × 5 mL of Et2O, and dried under vacuum. Yield 95%.
1
cis,mer-2. H NMR (CD2Cl2), δ: 7.6-6.8 (m, 45H, phenyl H),
1
-19.13 (d of t, 2J(HPA) ) 12.4 Hz, 2J(HPB) ) 17.5 Hz, IrH). 31P-
1
{1H} NMR (CD2Cl2), δ: -2.1 (d, 2J(PP) ) 16.1 Hz, 2P, PA), -8.3
2
1
(t, J(PP) ) 16.1 Hz, 1P, PB). trans,mer-2. H NMR (CD2Cl2), δ:
-14.00 (d of t, 2J(HPtrans) ) 160.1 Hz, 2J(HPcis) ) 16.4 Hz, IrH).
31P{1H} NMR (CD2Cl2), δ: -7.5 (d, J(PP) ) 13.4 Hz, 2P, Pcis),
2
-29.7 (t, J(PP) ) 13.4 Hz, 1P, Ptrans). IR (Nujol), cm-1: 2200
2
(IrH). Anal. Calcd for C54H46Cl2IrP3: C, 61.71; H, 4.42%. Found:
C, 61.90; H, 4.54%.
Preparation of IrH5(PiPr3)2 (3). THF (30 mL) was added to a
mixture of IrHCl2(PiPr3)2 (0.370 g, 0.633 mmol) and NaOH (2.7
g, 67.5 mmol) under 1 atm H2. The resulting mixture was stirred
for 3 h over which time it gradually changed from purple to
colorless. All volatiles were removed under vacuum, and the white
residue was collected and washed on a frit with 5 × 5 mL of
distilled, degassed H2O. The white product was finally dried under
vacuum for several hours. Yield 84%. 1H NMR (THF-d8), δ: 1.80
1
solvents required only the deactivation of deuterium locking. H
NMR spectra were indirectly referenced to TMS via solvent peaks,
and 31P spectra were referenced to external 85% H3PO4.
CAUTION must be exercised when heating samples sealed in
NMR tubes as excessively high pressures may result in explosion
of tubes. The solution component should be only partially immersed
in an oil bath maintained at a temperature slightly above the normal
boiling point of the solvent. In most cases, immersing only 1 cm
of the tube is sufficient to heat the contents to reflux and adequately
mix the contents by convection.
2
(m, 6H, CH), 1.12 (m, 36H, CH3), -11.29 (t, J(HP) ) 12.3 Hz,
1
5H, IrH). H NMR (C6D6), δ: 1.70 (m, 6H, CH), 1.12 (m, 36H,
CH3), -10.85 (t, 2J(HP) ) 12.2 Hz, 5H, IrH). 31P{1H} NMR (THF-
d8), δ: 46.2 (s). 31P{1H} NMR (C6D6), δ: 45.6 (s).26 IR (Nujol),
cm-1: 1950 (IrH). Anal. Calcd for C18H47IrP3: C, 41.75; H, 9.17%.
Found: C, 41.42; H, 9.33%.
Infrared spectra were acquired on a Nicolet Magna-IR spec-
trometer 550 or a Perkin-Elmer Paragon 500 FT-IR spectrometer.
IrH5(PCy3)2,20 IrH3(PPh3)3,21 and ReH7(PCy3)2 were prepared
22
by literature methods. IrCl3 was obtained in various hydrated forms
from Johnson Matthey Chemicals (approximately IrCl3‚3H2O),
Strem Chemicals, and Pressure Chemicals. 18-Crown-6, 1,10-diaza-
18-crown-6, 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexa-
cosane (cryptand-222, also known as Kryptofix-222), and KH were
purchased from Aldrich Chemical Co. The KH obtained was in
the form of a suspension in mineral oil; the salt was isolated by
filtration and washing with hexanes under a nitrogen atmosphere.
PPh3 was obtained from BDH. PCy3 and HPPh2 were obtained from
Organometallics. PiPr3 was obtained from Strem. High purity N2
gas, Ar gas, and H2 gas were obtained from BOC Gases Canada.
Preparation of IrHCl2(PiPr3)2 (1). A literature method23 was
Preparation of IrH5(PPh3)2 (4). A mixture of THF (40 mL),
IrHCl2(PPh3)3 (2.110 g, mixture of cis,mer and trans,mer isomers,
2.008 mmol), and KH (0.815 g, 20.3 mmol) was maintained at a
temperature of 100 °C under 75 atm H2 with stirring for 3 days in
an autoclave. The mixture was returned to room temperature, and
all solids were removed by filtration and washed with THF (3 × 3
mL). The red filtrate and washings were combined and evaporated
to dryness under reduced pressure. The residue was collected and
washed on a frit with 3 × 10 mL of distilled, degassed H2O which
resulted in a color change from orange to white. The solids were
finally washed with THF (3 × 5 mL) and dried under vacuum.
Yield 60%. IR (Nujol), cm-1: 1950 (IrH).
Preparation of [K(18-crown-6)][PPh2]. A mixture of KH (0.050
g, 1.2 mmol), 18-crown-6 (0.316 g, 1.20 mmol), HPPh2 (0.224 g,
1.20 mmol), and THF (5 mL) was stirred for 5 h. The solids were
removed by filtration, and 20 mL of hexanes was added to the
orange filtrate to precipitate the orange product. The product was
collected by filtration, washed with 3 × 3 mL of hexanes, and dried
under vacuum. Yield 90%. 31P NMR (THF), δ: -0.707 (s).
Observation of [K(18-crown-6)][fac-IrH3(PPh3)2(PPh2)]. An
NMR tube was charged with IrH3(PPh3)3 (0.014 g, 0.014 mmol),
i
improved slightly. A 7 mL portion of PrOH was added to a flask
containing IrCl3‚3H2O (1.108 g, 3.71 mmol) and PiPr3 (1.779 g,
11.12 mmol). The resulting mixture was refluxed under Ar for 24
h over which time the color changed from yellow to brown to red.
The mixture was allowed to return to room temperature, and the
purple solids were collected by filtration. The product was washed
with 3 × 3 mL of iPrOH and dried under vacuum. Yield 85%. 1H
(20) Brinkmann, S.; Morris, R. H.; Ramachandran, R.; Park, S. Inorg. Synth.
1998, 32, 303-308.
(21) Park, S.; Lough, A. J.; Morris, R. H. Inorg. Chem. 1996, 35, 3001-
3006.
(22) Zeiher, E. H. K.; DeWit, D. G.; Caulton, K. G. J. Am. Chem. Soc.
1984, 106, 7006-7011.
(23) Simpson, R. D.; Marshall, W. J.; Farischon, A. A.; Roe, D. C.; Grushin,
V. V. Inorg. Chem. 1999, 38, 4171-4173.
(24) Grushin, V. V.; Vymenits, A. B.; Vol’pin, M. E. J. Organomet. Chem.
1990, 382, 185-189.
(25) Werner, H.; Wolf, J.; Ho¨hn, A. J. Organomet. Chem. 1985, 287, 395-
407.
(26) Garlaschelli, L.; Khan, S. I.; Bau, R.; Longoni, G.; Koetzle, T. F. J.
Am. Chem. Soc. 1985, 107, 7212-7213.
Inorganic Chemistry, Vol. 41, No. 11, 2002 2997

Landau et al.
[K(18-crown-6)][PPh2] (0.007 g, 0.014 mmol), and C6D6 (0.65 mL).
The tube was flame-sealed, and the contents were gently refluxed
for 12 h. 1H NMR (C6D6), δ: -11.89 (2nd order, 2H, HAA′ pattern),
-14.09 (d of t of t, J(HAA′HB) ) 5.1 Hz, J(HBPY) ) 54.4 Hz,
2J(HBPXX′) ) 14.7 Hz, 1H, HB pattern). 31P{1H} NMR (C6D6), δ:
10.1 (d, 2J(PXX′PY) ) 14.9 Hz, 2P, PXX′ pattern), -9.5 (t, 2J(PXX′PY)
) 14.9 Hz, 1P, PY pattern, PPh2).
3252 (NH), 1926 (IrH), 1707 (IrH). IR (THF), cm-1: 3232 (NH),
1975 (IrH), 1693 (IrH).
A single crystal was grown by diffusion of hexanes into a solution
of the salt in THF. The colorless crystal was analyzed by single-
crystal X-ray diffraction.
2
2
Preparation of [K(1,10-diaza-18-crown-6)][IrH4(PiPr3)2] ([K(di-
aza)]6). A mixture of KH (0.127 g, 3.17 mmol), IrH5(PiPr3)2 (0.152
g, 0.294 mmol), and THF (1.5 mL) was stirred for 12 h. The solids
were removed by filtration, and the filtrate was slowly added with
stirring to a solution of 1,10-diaza-18-crown-6 (0.092 g, 0.35 mmol)
in THF (5 mL). The resulting solution was stored at -30 °C, and
the colorless, crystalline product was collected after 2 days. The
product was washed with hexanes (3 × 1.5 mL) and then dried
Observation of K[IrH4(PiPr3)2] (K6). A mixture of THF (0.65
mL) or C6D6 (0.65 mL), KH (0.010 g, 0.25 mmol), and IrH5-
(PiPr3)2 (0.015 g, 0.026 mmol) was sealed in an NMR tube under
1 atm N2. The mixture was gently refluxed for 12 h and then
examined by 1H and 31P{1H} NMR spectroscopy. 1H NMR (THF),
δ: -14.95 (t of t, 2J(HH) ) 4.9 Hz, 2J(HP) ) 13.4 Hz, 2H, cis-6),
2
1
-15.51 (2nd order, 2H, HAA′ of cis-6), -15.74 (t, J(HP) ) 17.2
under vacuum. Yield 54%. H NMR (THF-d8), δ: 3.58 (m, 16H,
1
3
Hz, 4H, trans-6). H NMR (C6D6), δ: 1.89 (m, CH, [cis-IrD4-
CH2), 2.75 (m, 8H, CH2 R to N), 2.14 (qi, J(HH) ) 7.3 Hz, 2H,
(PiPr3)2]-), 1.28 (m, CH3, [cis-IrD4(PiPr3)2]-). 31P{1H} NMR (THF),
δ: 60.2 (s, trans-6), 39.9 (s, cis-6). 31P{1H} NMR (C6D6), δ: 40.4
(s, cis-6). No trans isomer was observed for the reaction done in
C6D6, and H/D exchange between the solvent and hydride ligands
of the complex did not permit the determination of upfield 1H NMR
chemical shifts.
NH), 1.80 (m, 6H, CH), 1.18 (m, 36H, CH3), -14.63 (t of t, 2J(HH)
) 4.9 Hz, 2J(HP) ) 13.4 Hz, 2H, HA of A2BB′XX′ pattern of cis-
2
6), -15.56 (BB′, 2H, cis-6), -15.60 (t, J(HP) ) 17.2 Hz, IrH,
1
trans-6). H NMR (C6D6), δ: 3.57-2.0 (extremely broad reso-
2
2
nances, 26H, crown H), -14.09 (t of t, J(HH) ) 5.1 Hz, J(HP)
) 13.3 Hz, 2H, HA of cis-6), -15.27 (BB′, 2H, cis-6). 31P{1H}
NMR (THF-d8), δ: 65.7 (s, trans-6), 42.6 (s, cis-6). 31P{1H} NMR
(C6D6), δ: 40.7 (s, cis-6). IR (Nujol), cm-1: 3148 (NH), 1680 (IrH).
IR (THF), cm-1: 3300 (NH), 3227 (NH), 1970 (IrH), 1694 (IrH).
A colorless crystal suitable for structural determination by single-
crystal X-ray diffraction was grown by a small-scale preparation.
IrH5(PiPr3)2 (0.023 g, 0.044 mmol), KH (0.010 g, 0.25 mmol), diaza-
18-crown-6 (0.017 g, 0.065 mmol), and 0.6 mL THF were combined
in an NMR tube, and the mixture was shaken vigorously for 5 min.
The solid contents were allowed to settle, and over 24 h, crystals
grew from the solution component of the reaction mixture.
Preparation of [K(cryptand-222)][IrH4(PiPr3)2] ([K(crypt)]6).
THF (5 mL), IrH5(PiPr3)2 (252 mg, 0.49 mmol), KH (98 mg, 2.45
mmol), and cryptand-222 (190 mg, 0.5 mmol) were combined in a
flask, and the resulting mixture was stirred for 3 h. The solids were
then removed by filtration, and hexanes (25 mL) were slowly added
with stirring to precipitate the white product. The product was
collected by filtration, washed with hexanes (2 × 3 mL), and dried
under vacuum. Yield 33%. 1H NMR (C6D6), δ: 3.32 (m, 12H, crypt
H), 3.23 (m, 12H, crypt H), 2.28 (m, 6H, CH), 2.19 (m, 12H, crypt
Preparation of [K(18-crown-6)][IrH4(PiPr3)2] ([K(crown)]6).
THF (5 mL), IrH5(PiPr3)2 (0.296 g, 0.572 mmol), KH (0.105 g,
2.62 mmol), and 18-crown-6 (0.160 g, 0.604 mmol) were combined
in a flask, and the resulting mixture was stirred for 3 h. The solids
were then removed by filtration, and hexanes (25 mL) were slowly
added with stirring to precipitate the white product. In some cases,
where the product did not precipitate immediately from solution,
cooling overnight at -30 °C resulted in the formation of colorless
crystals. The product was collected by filtration, washed with
hexanes (2 × 3 mL), and dried under vacuum. Yield 70%. 1H NMR
(C6D6), δ: 3.25 (m, 24H, crown H), 2.17 (m, 6H, CH), 1.57 (m,
36H, CH3), -14.23 (t of t, 2J(HAHB) ) 4.9 Hz, 2J(HP) ) 13.4 Hz,
2
2H, HA of A2BB′XX′ pattern of cis-6), -15.04 (t, J(HP) ) 16.7
Hz, 4H, IrH, trans-6), -15.12 (BB, 2H, cis-6). 1H NMR (THF), δ:
2
2
-14.79 (t of t, J(HH) ) 4.9 Hz, J(HP) ) 13.4 Hz, 2H, HA of
cis-6), -15.45 (BB′, 2J(HBHB′) ) (3.5 Hz, 2J(HBPX′) ) 2J(HB′PX)
2
2
) (121.5 Hz, J(HBPX) ) J(HB′PX′) ) (24.8 Hz, the signs of
the coupling constants may all be reversed, 2H, cis-6), -15.62 (t,
2J(HP) ) 17.4 Hz, 4H, IrH, trans-6). 31P{1H} NMR (C6D6), δ:
60.1 (s, trans-6), 42.1 (s, cis -6). 31P{1H} NMR (THF), δ: 65.7 (s,
trans-6), 42.6 (s, cis-6). IR (Nujol), cm-1: 1922 (IrH), 1698
(IrH). IR (THF), cm-1: 1965 (IrH), 1688 (IrH). Anal. Calcd for
C30H70IrKO6P2: C, 43.93; H, 8.62%. Found: C, 43.81; H,
8.91%.
2
H), 1.45 (m, 36H, CH3), -15.02 (t, J(HP) ) 17.5 Hz, 4H, IrH).
31P{1H} NMR (C6D6), δ: 66.5 (s). IR (Nujol), cm-1: 1953 w (IrH
of IrH5L2 impurity), 1673 s (IrH).
Observation of [K(18-crown-6)][cis-IrH4(PCy3)2] ([K(crown)]-
7). A mixture of THF (3 mL), KH (0.028 g, 0.70 mmol), IrH5-
(PCy3)2 (0.058 g, 0.076 mmol), and 18-crown-6 (0.035 g, 0.13
mmol) was stirred under an atmosphere of N2 for 24 h. The reaction
mixture in THF was analyzed by 31P{1H} NMR spectroscopy (δ):
28.5 (s). The reaction mixture was filtered and the filtrate
characterized by IR spectroscopy: 1960 cm-1 (IrH), 1680 cm-1
(IrH). The reaction mixture was evaporated to dryness under
reduced pressure, and the gray residue was analyzed by IR
spectroscopy (Nujol): 1986 cm-1 (IrH), 1697 cm-1 (IrH). The
For the X-ray structure determination of [K(18-crown-6)][IrH4-
(PiPr3)2], a crystal was grown by layering of hexanes above a THF
solution of the salt. A well-formed, colorless crystal was obtained
in one week.
Preparation of [K(aza-18-crown-6)][cis-IrH4(PiPr3)2] ([K-
(aza)]6). THF (3 mL) was added to a mixture of IrH5(PiPr3)2 (0.157
g, 0.303 mmol), KH (0.043 g, 1.07 mmol), and aza-18-crown-6
(0.092 g, 0.349 mmol), and the resulting mixture was stirred under
N2 for 4 h. The solids were removed by filtration, and the filtrate
was concentrated to 1.5 mL under reduced pressure. A 20 mL
portion of hexanes was slowly added to the brown filtrate with
stirring to precipitate the white product. The product was collected
by filtration, washed with hexanes (2 × 1 mL), and dried under
1
residue was also extracted with C6D6 for H and 31P{1H} NMR
analysis. 1H NMR (C6D6), δ: 3.3 (s, 24H, crown H), 1.0-2.5 (m,
66H, PCy3), -14.04 (t of t, 2J(HH) ) 4.5, 2J(HP) ) 13.5,
2H, HA), -15.43 (BB′, 2H, IrH). 31P{1H} NMR (C6D6), δ: 28.3
(s).
1
vacuum. Yield 89%. H NMR (C6D6), δ: 4.2-2.8 (br, crown H),
Preparation of [K(cryptand-222)][IrH4(PCy3)2] ([K(crypt)]7).
THF (5 mL), IrH5(PCy3)2 (300 mg, 0.40 mmol), KH (80 mg, 2.0
mmol), and cryptand-222 (151 mg, 0.41 mmol) were combined in
a flask, and the resulting mixture was stirred for 3 h. The solids
were then removed by filtration, and hexanes (25 mL) were slowly
3.08 (br s, crown H), 3.02 (br s, crown H), 2.59 (br s, crown H),
2
2.15 (m, 6H, CH), 1.56 (m, 36H, CH3), -14.10 (t of t, J(HH) )
5.1 Hz, 2J(HP) ) 13.3 Hz, 2H, HA of A2BB′XX′ pattern), -15.27
(BB′, 2H). 31P{1H} NMR (C6D6), δ: 40.8 (s). IR (Nujol), cm-1
:
2998 Inorganic Chemistry, Vol. 41, No. 11, 2002

Ion Pairing and Protonic-Hydridic Bonding
added with stirring to precipitate the white product. The product
A crystal suitable for structural determination by single-crystal
X-ray diffraction was grown by vapor diffusion of Et2O into a THF
solution of the salt.
was collected by filtration, washed with hexanes (2 × 3 mL), and
1
dried under vacuum. Yield 33%. H NMR (C6D6), δ: 3.23 (m,
12H, crypt H), 2.82 (m, 12H, crypt H), 2.63-2.06 (m, 66H, CH),
Reaction of ([K(crown)]6) with ReH7(PCy3)2. An NMR tube
2
27
1.83 (m, 12H, crypt H), -14.71 (t, J(HP) ) 17.5 Hz, 4H, IrH).
was charged with ReH7(PCy3)2 (0.016 g, 0.021 mmol), [K(18-
31P{1H} NMR (C6D6), δ: 51.76 (s). IR (Nujol), cm-1: 1953, 1935
w (IrH of IrH5L2 impurity), 1680 s (IrH).
crown-6)][IrH4(PiPr3)2] (0.016 g, 0.020 mmol), and THF (0.65 mL).
The tube was flame sealed, and the solution was analyzed by NMR
1
2
after 1 h. H NMR (THF), δ: -7.09 (t, J(HP) ) 18.8 Hz, ReH7-
(PCy3)2), -9.69 (t, 2J(HP) ) 16.4 Hz, [ReH6(PCy3)2]- 19,27), -11.34
(t, 2J(HP) ) 12.3 Hz, IrH5(PiPr3)2). 31P{1H} NMR (THF), δ: 57.9
(s, [ReH6(PCy3)2]-), 48.4 (s, ReH7(PCy3)2), 46.3 (s, IrH5(PiPr3)2).
Reaction between ([K(crown)]6) and WH6(PMe2Ph)3. An
NMR tube was charged with WH6(PMe2Ph)3 (14.7 mg, 0.024
mmol), [K(18-crown-6)][IrH4(PiPr3)2] (20 mg, 0.024 mmol), and
THF-d8 (0.65 mL). The tube was sealed, and the solution was
Observation of [K(1,10-diaza-18-crown-6)][cis-IrH4(PCy3)2]
([K(diaza)]7). A mixture of THF (3 mL), KH (0.028 g, 0.70 mmol),
IrH5(PCy3)2 (0.065 g, 0.086 mmol), and diaza-18-crown-6 (0.029
g, 0.11 mmol) was stirred under an atmosphere of N2 for 24 h.
The reaction mixture in THF was analyzed by 31P{1H} NMR
spectroscopy (δ): 28.5 (s, PXX′ pattern). For IR characterization of
the THF solution, the reaction mixture was filtered, and the gray
to brown filtrate was analyzed: 3300 cm-1 (NH), 3228 cm-1 (NH),
1965 cm-1 (IrH), 1685 cm-1 (IrH). For the solid-state IR charac-
terization, the filtrate was evaporated to dryness under reduced
pressure, and the residue was ground with Nujol: 3289 cm-1 (NH),
3222 cm-1 (NH), 1957 cm-1 (IrH), 1668 cm-1 (IrH).
1
1
analyzed by H NMR after 1 h. H NMR (THF-d8), δ: -2.4 (q,
2J(HP) ) 36.0 Hz, WH6(PMe2Ph)3, 6H, I ) 67.6), -4.6 (m,
2
[WH5(PMe2Ph)3]-, 5H, I ) 65.9), -11.3 (t, J(HP) ) 12.3 Hz,
IrH5(PiPr3)2, 5H, I ) 100), -14.7 (tt, [cis-IrH4(PiPr3)2]-, 2H, I )
0.3), -15.5 (m, [cis-IrH4(PiPr3)2]-, 2H, I ) 0.3), -15.6 (t, [trans-
IrH4(PiPr3)2]-, 4H, I ) 0.3). A small amount of mer-IrH3-
(PiPr3)2(PMe2Ph) was also produced: -13.1 (d qrt, 2H), -15.6 (dtd,
1H).
Observation of [K(18-crown-6)][cis-IrHD3(PCy3)2]. A solution
of [K(18-crown-6)][IrH4(PCy3)2] (0.012 g, mmol) dissolved in C6D6
(0.65 mL) was gently refluxed in a flame-sealed NMR tube for 12
h and then examined by 1H NMR spectroscopy. 1H NMR (C6D6),
2
Reaction between ([K(crypt)]6) and WH6(PMe2Ph)3. An NMR
tube was charged with WH6(PMe2Ph)3 (13 mg, 0.02 mmol),
[K(crypt)][trans-IrH4(PiPr3)2] (20 mg, 0.02 mmol), and THF (0.65
mL). The tube was sealed, and the solution was analyzed by
quantitative 31P NMR after 1 and 24 h. The reaction was complete
in less than 1 h. 31P NMR (THF), δ: 66.77 (s, [trans-IrH4(PiPr3)2]-,
I ) 15.62), 46.0 (s, IrH5(PiPr3)2, I ) 22.22), 0.0 (t, 1J(WP) ) 84.5
δ: -13.95 (t, J(HP) ) 13.5 Hz, 1H, H trans to D), -15.40 (d of
d, 2J(HPtrans) ) 120 Hz, 2J(HPcis) ) 26 Hz, 1H, H trans to P). The
sample was contaminated with approximately 20% IrH5(PCy3)2 as
1
evidenced by H NMR spectroscopy. The same reaction carried
out in the presence of excess KH resulted in little or no H/D
exchange over the same time period.
Preparation of [K(18-crown-6)][IrH4(PPh3)2] ([K(crown)]5).
A mixture of IrH5(PPh3)2 (0.119 g, 0.165 mmol), THF (1.5 mL),
KH (0.027 g, 0.67 mmol), and 18-crown-6 (0.065 g, 0.25 mmol)
was stirred for 12 h under an atmosphere of N2. The resulting
mixture was pale orange indicating the presence of PPh2-. However,
its 31P{1H} NMR spectrum consisted of just a single resonance
(26.3 ppm) corresponding to the desired product. All solids were
removed by filtration, and the colorless to pale yellow product was
crystallized from the filtrate by vapor diffusion of Et2O. 1H NMR
(C6D6), δ: 7.97 (m, 12H, phenyl H), 6.98 (m, 18H, phenyl H),
1
Hz, [WH5(PMe2Ph)3]-, I ) 31.29), -3.151 (t, J(WP) ) 37.3,
WH6(PMe2Ph)3, I ) 30.87).
Determination of the ∆pK Value between IrH5(PiPr3)2 and
IrH5(PCy3)2. (a) An NMR tube was charged with IrH5(PCy3)2
(0.016 g, 0.020 mmol), [K(18-crown-6)][IrH4(PiPr3)2] (0.016 g,
0.020 mmol), and THF (0.65 mL). The tube was flame-sealed and
warmed (50 °C) for 4 h while the contents were occasionally shaken
to dissolve suspended complex. The solution was cooled to room
temperature, and the 31P{1H, inverse-gated decoupled} NMR
spectrum was recorded (THF), δ: 65.5 (s, [trans-IrH4(PiPr3)2]-, I
) 140), 46.0 (s, IrH5(PiPr3)2, I ) 195), 42.2 (s, [cis-IrH4(PiPr3)2]-,
I ) 361), 32.5 (s, IrH5(PCy3)2, I ) 75), 28.5 (s, [cis-IrH4(PCy3)2]-,
I ) 243). The equilibrium constant was determined to be 0.6. (b)
A solution of [K(crypt)][trans-IrH4(PCy3)2] (20 mg, 0.02 mmol)
and IrH5(PiPr3)2 (9 mg, 0.02 mmol) in THF-d8 was prepared in a
similar fashion at room temperature. The tube was sealed, and the
solution was analyzed quantitatively by 31P NMR after 3 and 24 h.
There were negligible differences in the two spectra. 31P NMR
(THF-d8) δ: 63.42 (s, [trans-IrH4(PiPr3)2]-, I ) 62.15), 48.36 (s,
[trans-IrH4(PCy3)2]-, I ) 4.96), 43.52 (s, IrH5(PiPr3)2, I )19.88),
43.52 (s, IrH5(PCy3)2, I )13.01). The equilibrium constant was
determined to be 8.2.
2
2
3.28 (s, 24H, crown H), -11.88 (t of t, J(HH) ) 5.1 Hz, J(HP)
) 13.2 Hz, 2H, HA of A2BB′XX′ pattern), -12.30 (BB′, 2H). 31P-
{1H} NMR (C6D6), δ: 26.1 (s). 31P{1H} NMR (THF), δ: 26.3 (s).
IR (Nujol), cm-1: 2010 (IrH), 1716 (IrH). IR (THF), cm-1: 2005
(IrH), 1713 (IrH). Anal. Calcd for C48H58IrKO6P2: C, 56.28; H,
5.72%. Found: C, 56.0; H, 5.71%.
For X-ray structural characterization, a colorless crystal was
grown by vapor diffusion of Et2O into a THF solution of the
salt.
Preparation of [K(1,10-diaza-18-crown-6)][IrH4(PPh3)2] ([K(di-
aza)]5). The preparation of [K(18-crown-6)][IrH4(PPh3)2] was
followed substituting diaza-18-crown-6 (0.048 g, 0.18 mmol) for
18-crown-6. The quantities of other reagents used were as fol-
lows: THF (1.5 mL), KH (0.025 g, 0.62 mmol). As was the case
for the preparation of [K(18-crown-6)][IrH4(PPh3)2], the 31P{1H}
NMR spectrum for the orange reaction mixture consisted of a single
Observation of IrH5(PCy3)(PiPr3) and K[IrH4(PCy3)(PiPr3)].
A mixture of IrH5(PCy3)2 (0.015 g, 0.018 mmol), K[IrH4(PiPr3)2]
(0.015 g, 0.027 mmol), and THF (0.65 mL) was sealed in an NMR
tube under an atmosphere of N2. The mixture was gently refluxed
for 2 days and then analyzed by 31P{1H} NMR spectroscopy. The
complexes were not isolated from solution. 31P{1H} NMR (THF),
1
resonance at 25.6 ppm. Yield 68%. H NMR (C6D6), δ: 7.95 (m,
phenyl H), 7.00 (s, phenyl H), 6.98 (s, phenyl H), 3.30 (br s, crown
H), 3.15 (br s, crown H), 2.29 (br s, crown H), -11.79 (t of t,
2J(HH) ) 5.0 Hz, 2J(HP) ) 13.2 Hz, 2H, HA of A2BB′XX′ pattern),
-12.41 (BB′). 31P{1H} NMR (C6D6), δ: 25.6 (s). 31P{1H} NMR
(THF), δ: 25.6 (s). IR (Nujol), cm-1: 3198 (NH), 1974 (IrH), 1712
(IrH). IR (THF), cm-1: 3299 (NH), 3205 (NH), 1999 (IrH), 1714
(IrH).
2
δ: 59.9 (s, [trans-6 46.2 (d, J(PP) ) 319 Hz, PiPr3 resonance of
2
trans-IrH5(PiPr3)(PCy3)), 46.0 (s, 3), 40.6 (d, J(PP) ) 12 Hz, Pi-
(27) Abdur-Rashid, K.; Fong, T. P.; Greaves, B.; Gusev, D. G.; Hinman,
J. G.; Landau, S. E.; Morris, R. H. J. Am. Chem. Soc. 2000, 122,
9155-9171.
Inorganic Chemistry, Vol. 41, No. 11, 2002 2999

Landau et al.
Pr3 resonance of [cis-IrH4(PiPr3)(PCy3)]-), 39.8 (s, cis-6), 32.6 (s,
IrH5(PCy3)2), 32.4 (d, 2J(PP) ) 319 Hz, PCy3 resonance of trans-
IrH5(PiPr3)(PCy3)), 27.6 (s, 7), 25.7 (d, 2J(PP) ) 11 Hz, PCy3
resonance of [cis-IrH4(PiPr3)(PCy3)]-).
Table 1. Crystal Structure Data Acquisition and Solution Details
[K(diaza)]5‚
Et2O‚THF0.5
[K(crown)]5
[K(aza)]6
formula
fw
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
C48H58IrKO6P2 C54H74IrKN2O5.5P2 C30H71IrKNO5P2
Reaction of IrH5(PiPr3)2 with IrH5(PCy3)2. A solution of
IrH5(PiPr3)2 (0.009 g, 0.017 mmol) and IrH5(PCy3)2 (0.009 g, 0.012
mmol) in 0.65 mL of THF was sealed in an NMR tube under 1
atm of N2. The mixture was gently refluxed for 24 h and then
analyzed by 31P{1H} NMR spectroscopy. The complexes were not
isolated from the reaction mixture. 31P{1H} NMR (THF), δ: 46.3
(d, 2J(PP) ) 319 Hz, PiPr3 of trans-IrH5(PiPr3)(PCy3)), 46.1 (s, 3),
1024.18
triclinic
P1h
1132.39
monoclinic
C2/c
36.056(7)
14.394(3)
23.799(5)
90
121.11(3)
90
10575(4)
8
819.12
triclinic
P1h
10.3032(2)
21.5110(4)
23.1192(5)
64.927(1)
80.982(1)
84.862(1)
4582.2(2)
4
9.0778(3)
11.1705(2)
20.1852(5)
76.836(2)
81.083(2)
71.597(1)
1883.47(8)
2
2
32.7 (s, IrH5(PCy3)2), 32.5 (d, J(PP) ) 319 Hz, PCy3 of trans-
IrH5(PiPr3)(PCy3)).
Z
d
calc/Mg m-3
1.485
1.422
1.444
Reaction of IrH5(PCy3)2 with PiPr3. A mixture of IrH5(PCy3)2
(0.020 g, 0.026 mmol), PiPr3 (0.010 g, 0.062 mmol), and THF (0.65
mL) was sealed in an NMR tube under an atmosphere of N2. The
mixture was gently refluxed for 48 h and then analyzed by 1H and
31P{1H} NMR spectroscopy. The complexes were not isolated from
µ(Mo ΚR)/mm-1 3.121
2.712
3.774
T/K
110(1)
34034
17311
0.051
0.0356
0.0997
1.09
150(1)
14307
3889
101(1)
34296
9328
rflns
indep rflns
Rmerge
0.059
0.081
R1a [I > 2σ(I)]
wR2a (all data)
GOF
0.0289
0.0777
1.03
0.0346
0.0626
0.93
1
2
the reaction mixture. H NMR (THF), δ: -11.22 (t, J(HP) ) 12
2
Hz, IrH5(PCy3)2), -11.28 (t, J(HP) ) 12.3 Hz, 3), -11.35 (t,
2J(HP) ) 12.1 Hz, IrH5(PiPr3)(PCy3)). 31P{1H} NMR (THF), δ:
a R1)∑(Fo - Fc)/∑(Fo); wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
2
46.3 (d, J(PP) ) 319 Hz, PiPr3 of trans-IrH5(PiPr3)(PCy3)), 46.2
2
2
(s, 3), 32.7 (s, IrH5(PCy3)2), 32.5 (d, J(PP) ) 319 Hz, PCy3 of
Table 2. Selected Bond Lengths
trans-IrH5(PiPr3)(PCy3)), 20.2 (s, PiPr3), 10.5 (s, PCy3).
Bond length/Å
Preparation of trans,mer-IrH3(PCy3)2(PPh3). A mixture of
IrH5(PCy3)2 (0.302 g, 0.398 mmol), PPh3 (0.127 g, 0.484 mmol),
and THF (10 mL) was refluxed for 24 h under Ar. The resulting
brown mixture was filtered through Celite, and the yellow filtrate
was evaporated to dryness under reduced pressure. The residue was
stirred with 5 mL of Et2O, and the white solids were collected by
filtration. The white product was washed with Et2O (2 × 3 mL)
and dried under vacuum. Yield 56%. 1H NMR (C6D6), δ: 8.30 (t,
phenyl H), 7.18 (m, phenyl H), 7.05 (m, phenyl H), 2.03-1.03
[K(crown)]5
[K(diaza)]5‚Et2O‚THF0.5
[K(aza)]6
Ir(1)-P(1)
2.259(1)
2.265(1)
1.53(4)
1.53(4)
1.55(4)
1.68(4)
2.259(1)
2.2837(9)
1.64(5)
1.66(4)
1.54(4)
1.51(3)
2.2964(9)
2.2923(9)
1.66(4)
1.64(4)
1.56(4)
Ir(1)-P(2)
Ir(1)-H(1IR)
Ir(1)-H(2IR)
Ir(1)-H(3IR)
Ir(1)-H(4IR)
1.63(3)
Table 3. Selected Bond Angles
2
2
(m, PCy3), -11.96 (m, J(HH) not resolved, J(HPX) ) 15.1 Hz,
Bond angle/deg
2J(HPY) ) 15.2 Hz, 2H, H trans to H), -14.99 (d of t, 2J(HH) not
[K(diaza)]5‚
2
2
resolved, J(HPX) ) 23 Hz, J(HPY) ) 116.2 Hz, H trans to P).
[K(crown)]5
175(2)
Et2O‚THF0.5
[K(aza)]6
31P{1H} NMR (C6D6), δ: 24.1 (d, J(PP) ) 14.6 Hz, 2PCy3, PX
2
H(1IR)-Ir(1)-H(2IR)
H(1IR)-Ir(1)-H(3IR)
H(2IR)-Ir(1)-H(3IR)
H(1IR)-Ir(1)-H(4IR)
H(2IR)-Ir(1)-H(4IR)
H(3IR)-Ir(1)-H(4IR)
H(1IR)-Ir(1)-P(1)
H(2IR)-Ir(1)-P(1)
H(3IR)-Ir(1)-P(1)
H(4IR)-Ir(1)-P(1)
H(1IR)-Ir(1)-P(2)
H(2IR)-Ir(1)-P(2)
H(3IR)-Ir(1)-P(2)
H(4IR)-Ir(1)-P(2)
P(1)-Ir(1)-P(2)
171(2)
87(2)
173(2)
90(2)
85(2)
84(2)
91(2)
82(2)
93(1)
91(1)
84(1)
165(1)
93(1)
91(1)
166(1)
85(1)
109.34(3)
trans to PX), 19.7 (t, 2J(PP) ) 14.6 Hz, 1PPh3, PY). 31P{1H} NMR
85(2)
91(2)
95(2)
82(2)
87(2)
86(2)
97(2)
85(2)
2
2
(THF), δ: 24.4 (d, J(PP) ) 14.6 Hz, 2P, PX), 19.7 (t, J(PP) )
87(2)
86(2)
87(2)
78(2)
92(2)
94(1)
88(2)
165(1)
95(2)
14.7 Hz, 1P, PY). IR (THF), cm-1: 2090 (IrH), 1757 (IrH).
1
Variable-Temperature H NMR Study of [K(1,10-diaza-18-
crown-6)][IrH4(PiPr3)2]. A H NMR spectrum of a solution of
1
[K(1,10-diaza-18-crown-6)][IrH4(PiPr3)2] in THF-d8 was obtained
at several temperatures. The chemical shifts of the NH resonances
for some of these spectra are as follows: 2.14 (298 K, qi), 2.22
(273 K, qi), 2.29 (248 K, qi), 2.35 (223 K, br s), 2.43 (198 K, br
s). The chemical shift was found to vary linearly with tempera-
ture: δ/ppm ) -0.0028 T/K + 2.99.
X-ray Structural Determinations. All single-crystal X-ray
diffraction data were collected with a Nonius Kappa CCD diffrac-
tometer using graphite monochromated Mo KR radiation (λ )
0.71073 Å). A combination of 1° æ and ω (with κ offsets) scans
were used to collect sufficient data. The data frames were integrated
and scaled using the Denzo-SMN package. The structures were
solved and refined using the SHELXTL[\]PC V5.1 package.28
Refinement was by full-matrix least-squares on F2 using all data
(negative intensities included). Hydrogen atoms were included in
calculated positions, except for the hydride atoms which were
refined with isotropic thermal parameters. The structure data
acquisition and solution details are listed in Table 1. Selected bond
172(2)
98(2)
86(2)
90(1)
168(2)
91(1)
171(2)
84(2)
103.89(5)
103.91(4)
lengths and bond angles are listed in Tables 2 and 3, respectively.
For [K(crown)][IrH4(PPh3)2], only data for subunit A are given.
Results and Discussion
Preparation and Properties of IrHCl2(PiPr3)2 and
IrHCl2(PPh3)3. IrHCl2(PiPr3)2 (1) was prepared in 85% yield
by refluxing a mixture of IrCl3 and PiPr3 in PrOH.
i
Compound 1 is a dark purple solid soluble in CH2Cl2, CHCl3,
and THF. Other synthetic routes to 1 reported in the literature
require more steps and give yields of 64% or less. Compound
1 is reported to have a square pyramidal geometry with
mutually trans PiPr3 ligands and a hydride ligand occupying
the apical position.25
(28) Sheldrick, G. M. SHELXTL[\]PC V5.1; Bruker Analytical X-ray
Systems: Madison, WI, 1997.
3000 Inorganic Chemistry, Vol. 41, No. 11, 2002

Ion Pairing and Protonic-Hydridic Bonding
Scheme 1. Preparation of Some Triphenylphosphine Iridium Hydride
Complexes
Scheme 2. Preparation of the Triisopropylphosphine Complexes
by coordination and oxidative addition of H2. In the presence
of KH, 4 thus produced is deprotonated to give K[IrH4-
(PPh3)2]. The 16-electron transient species IrH3(PPh3)2 (not
observed) may also react directly with KH to yield K5.
The free PPh3 generated under these reaction conditions
may react with excess KH to produce KPPh2. A high H2
pressure is essential in order to minimize the side reaction
of the postulated IrH3(PPh3)2 intermediate with KPPh2 which
generates K[IrH3(PPh3)(PPh2)] (this reaction has been verified
independently). The formation of [IrH3(PPh3)(PPh2)]- by a
reaction of KH with IrH3(PPh3)3 has not been ruled out. The
K5 salt is not easily isolated from the dark red KPPh2
byproduct because these salts have similar solubilities.
Instead, the crude K5 is protonated with H2O, and the highly
insoluble IrH5(PPh3)2 produced is washed with copious
amounts of water and THF to remove all traces of KOH
and HPPh2. The IR IrH stretch (Nujol, 1950 cm-1) of the
isolated white IrH5(PPh3)2 agrees with previously reported
literature values for this complex. The complex is too
insoluble, even at 100 °C in toluene, to be characterized by
solution NMR spectroscopy.
IrHCl2(PPh3)3 (2) is a pale yellow, air-stable solid which
is quite soluble in CH2Cl2 and CHCl3 and less soluble in
THF and toluene. This compound has been reported several
times and has been obtained by various routes, but no NMR
data have been reported.29,30 These literature preparations
yield a product which is in some cases a mixture of cis,mer
and trans,mer isomers and in some cases a pure isomer.31
Reported here is the preparation of 2 in 95% yield (eq 1).
Depending on reflux time, the isolated product may be a
mixture of isomers or a pure isomer. Shorter reflux times
(1.5 days) yield a product which is enriched in or is
exclusively the cis,mer isomer. Another preparation with a
reflux time of 3 days afforded a product that was roughly a
1:1 mixture of the two isomers. On the basis of these
observations, one may conclude that the cis,mer isomer is
the kinetic product and the trans,mer isomer results by way
of slow isomerization.
Preparation and Properties of [IrH4(PiPr3)2]- Salts.
Treatment of 3 with KH in THF, benzene, or toluene results
in the generation of the new salt K[IrH4(PiPr3)2] (K6; Scheme
2). The reaction is fastest in THF and in all cases may be
aided by gentle heating. K6 produced in this way was
1
characterized in the reaction mixture by H and 31P NMR
spectroscopy and used in further preparations but was not
isolated from solution. [K(crown)]6, [K(aza)]6, and [K(crypt)]-
6 (crown ) 18-crown-6, aza ) aza-18-crown-6, crypt )
cryptand-222) were prepared by the treatment of 3 with KH
in THF in the presence of a slight excess of the appropriate
crown ether or cryptand (Scheme 2). [K(diaza)]6 (diaza )
1,10-diaza-18-crown-6), because of its poor solubility in
THF, was prepared by addition of a THF solution of diaza
to a freshly prepared THF solution of K6 which resulted in
the crystallization of the product (Scheme 2). Salts of 6 are
colorless and extremely water- and oxygen-sensitive. The
K+, [K(crown)]+, [K(aza)]+, and [K(crypt)]+ salts are soluble
in THF, benzene, and toluene. The [K(diaza)]+ salt is only
sparingly soluble in THF and even less soluble in benzene
and toluene. The X-ray crystal structures of [K(crown)]6 and
[K(diaza)]6 have been described briefly recently.4 The
structure of [K(aza)]6 will be described later.
Preparation and Properties of IrH5(PiPr3)2 and IrH5-
(PPh3)2. Pentagonal bipyramidal IrH5(PiPr3)2 (3)26 was
prepared in 84% by the method outlined in eq 2. Penta-
hydride 3 is a pale-yellow to colorless solid that is soluble
in most solvents with the exception of some alcohols and
water. Compound 3 is relatively air-stable in the solid state;
however, its solutions decompose readily when exposed to
air.
IrHCl2(PiPr3)2 + 3H2 + 2NaOH THF/H 8
2
IrH5(PiPr3)2 + 2NaCl + 2H2O (2)
IrH5(PPh3)2 (4) was prepared by the route outlined in
Scheme 1. Treatment of 2 with excess KH under 75 atm H2
pressure at 100 °C results in the generation of K[IrH4(PPh3)2]
(K5). This transformation proceeds via IrH3(PPh3)321 which
has been observed as an intermediate in some small scale
NMR tube preparations. In the proposed mechanism, dis-
sociation of 1 equiv of PPh3 from IrH3(PPh3)3 is followed
These salts were also prepared by the corresponding
reactions with IrHCl2(PiPr3)2 in place of IrH5(PiPr3)2 under
an atmosphere of H2. However, the spectra indicate that the
isolated products are contaminated with a complex suspected
to be a salt of [IrH6(PiPr3)]-. The presence of the latter in
(29) Vaska, L. J. Am. Chem. Soc. 1961, 83, 756.
(30) Vaska, L.; DiLuzio, J. W. J. Am. Chem. Soc. 1962, 84, 4989-4990.
(31) Mynott, R. J.; Trogu, E. F.; Venanzi, L. M. Inorg. Chim. Acta 1974,
8, 201-207.
1
C6D6 is signaled in the H NMR spectrum by a doublet at
-12.2 ppm (J(HP) ) 15.3 Hz). However, there were several
Inorganic Chemistry, Vol. 41, No. 11, 2002 3001

Landau et al.
unassigned resonances in the corresponding 31P{1H} NMR
spectra, and the concentration of this species was always
too low to identify its 31P{1H} resonance(s). Precedents for
such a structure are [IrH6(PCy3)]- (see later) and [ReH8-
(PPh3)]-.32 IrHCl2(PiPr3)2 is not a practical starting material
for the preparation of [K(diaza)]6 because this salt is not
easily extracted from the KCl and KH salts of the reaction
mixture.
treatment of 4 with KH in the presence of a slight excess of
the appropriate crown ether (eq 3, R ) Ph). These colorless,
water- and oxygen-sensitive salts are quite soluble in THF.
The [K(crown)]+ salt is also soluble in benzene; however,
the [K(diaza)]+ salt is less soluble in benzene but is more
soluble than the PiPr3 analogue.
Acidity of IrH5(PiPr3)2 and IrH5(PCy3)2. An attempt to
establish an acid-base equilibrium between ReH7(PCy3)2 and
Preparation and Properties of Salts of [IrH4(PCy3)2]-
(7). Treatment of IrH5(PCy3)2 with KH and Q (Q )
18-crown-6, diaza-18-crown-6 or cryptand-222) in THF
generates the new and very basic salts [K(Q)][IrH4(PCy3)2]
(eq 3, R ) Cy). However, only the crypt salt could be
isolated without contamination from IrH5(PCy3)2, and all
attempts to produce single crystals for structural determina-
tion resulted in the formation of a white, amorphous
precipitate. The salts of 7 are extremely water- and oxygen-
sensitive and are soluble in THF, benzene and toluene, with
the crypt salt being the least soluble. The 31P{1H} NMR
spectra for gray to brown reaction mixtures of the crown
and aza-crown salts [K(Q)][IrH4(PCy3)2] exhibit only a single
resonance which is attributed to [cis-IrH4(PCy3)2]- while a
colorless solution of the crypt salt exhibits a single resonance
due to [trans-IrH4(PCy3)2]-.
[K(crown)]6 resulted in the complete protonation of 6. From
THF
this experiment, it is concluded that the pKR
of IrH5-
(PiPr3)2/[K(crown)][cis-IrH4(PiPr3)2] is at least 2 units greater
THF
than that of ReH7(PCy3)2/[K(crown)][ReH6(PCy3)2] (pKR
) 41).27 The hydride WH6(PMe2Ph)3 (pKRTHF(WH6(PMe2-
Ph)3/[K(crypt)][WH5(PMe2Ph)3]) ) 42)33 is almost com-
pletely deprotonated by the 2:1 mixture of [K(crown)][cis-
IrH4(PiPr3)2] (eq 4) and [K(crown)][trans-IrH4(PiPr3)2] to
produce an equilibrium with a constant of 150.
WH6(PMe2Ph)3 + [K(crown)][cis-IrH4(PiPr3)2] h
[K(crown)][WH5(PMe2Ph)3] + IrH5(PiPr3)2 (4)
This gives the pKRTHF(IrH5(PiPr3)2/[K(crown)][cis-IrH4(Pi-
Pr3)2]) as 44 with the assumption that ion pair interactions
between the crown and tungsten hydrides are similar to that
for the iridium hydride. Surprisingly, the [K(crypt)]+ salt of
[trans-IrH4(PiPr3)2]- reacts with WH6(PMe2Ph)3 to give an
equilibrium with a constant of about 1.6 (eq 5). Ion pair
dissociation constants of the tungsten and iridium salts are
expected to be similar so that the pKRTHF(IrH5(PiPr3)2/
[K(crypt)][trans-IrH4(PiPr3)2]) is determined to be 42. This
ratio of about 102 in acid dissociation constant of the two
salts is an effect of ion pairing that is unprecedented as far
as we are aware. There is no spectroscopic evidence that
the stereochemistry and hence basicity of the reference
tungsten complexes are affected by the change in counter-
cation.
KH, Q, -H2
IrH5(PR3)2
8 [K(Q)][IrH4(PR3)2]
(3)
THF
Q ) 18-crown-6, diaza-18-crown-6, cryptand-222;
R ) Cy, iPr, Ph
These salts were also generated by the treatment of IrHCl2-
(PCy3)2 with KH and Q in THF under an atmosphere of H2.
As was similarly observed for the preparation of the
[IrH4(PiPr3)2]- salts, this reaction generates substantial
amounts of the new hydride salts [K(Q)][IrH6(PCy3)] in a
competing reaction (1H hydride (C6D6) at -12.16 ppm (d,
2J(HP) ) 15.5), 31P at 35.4 ppm (m with coupling to 6 H)).
The 31P{1H} NMR spectra of the reaction mixtures revealed
the presence of free PCy3.
WH6(PMe2Ph)3 + [K(crypt)][IrH4(PiPr3)2] h
[K(crypt)][WH5(PMe2Ph)3] + IrH5(PiPr3)2 (5)
Observation of [K(18-crown-6)][IrHD3(PCy3)2]. IrH5-
(PCy3)2 is known to undergo H atom exchange with aromatic
solvents such as benzene and toluene.14 To assess whether
this reactivity is also displayed by 7, a solution of [K(crown)]-
A question raised by these results is how can there also
be [K(crown)][trans-IrH4(PiPr3)2] present in equilibrium 4
(not shown) when the pKRTHF(IrH5(PiPr3)2/[trans-IrH4-
(PiPr3)2]-) is so much smaller than that of the cis isomer?
This might be explained by the fact that there is a difference
between the structure of the countercations of the cis and
trans isomers. A solvation of the [K(crown)]+ countercations
in THF that do not interact with the hydrides of the trans
isomer would produce ion pairs of the type [K(crown)(THF)2]-
[trans-IrH4(PiPr3)2]. The [K(crown)(THF)2]+ cation has been
observed in many crystal structures.33 Therefore, the analo-
gous reaction to eq 4 involving the trans isomer would result
in the favorable release of two THF molecules assuming that
the entropy gain and the formation of K-H-W interactions
more than overcomes the loss of the small K-THF bond
energies. In contrast, the cis isomer interacts via three
1
7 in C6D6 was refluxed for 12 h and then examined by H
NMR spectroscopy. The reaction mixture exhibited first-
order patterns for the two hydride positions in [cis-IrHD3-
(PCy3)2]- as well as for IrHD4(PCy3)2.
The same reaction carried out in the presence of an excess
of KH resulted in a severe decrease in the rate of H/D
scrambling. The presence of KH in the reaction mixture
served to deprotonate any acidic species in solution including
IrH5(PCy3)2. The reduced H/D scrambling rate indicates that
complex 7 and its isotopomers are not as reactive as IrH5-
(PCy3)2 and/or the process is mediated by IrH5(PCy3)2.
Preparation and Properties of [IrH4(PPh3)2]- Salts.
Pure [K(crown)]5 and [K(diaza)]5 were prepared by the
(32) Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 4126-
4133.
(33) Hinman, J. G.; Lough, A. J.; Morris, R. H. To be submitted.
3002 Inorganic Chemistry, Vol. 41, No. 11, 2002

Ion Pairing and Protonic-Hydridic Bonding
hydrides with its nonsolvated [K(crown)] countercation on
the basis of the geometry of its crystal structure.4
A mixture of [K(crown)]6 and IrH5(PCy3)2 was warmed
to 50 °C and allowed to reach acid-base equilibrium and
then was analyzed by 31P{1H} NMR spectroscopy at room
temperature. Making use of the equilibrium constant (0.6),
it is estimated that the two complexes IrH5(PiPr3)2/[K(crown)]-
THF
6 and IrH5(PCy3)2/[K(crown)]7 have similar pKR
values
of about 44 with the PCy3 system being slightly less acidic.
Note that ReH7(PCy3)2/[K(crown)][ReH6(PCy3)2] is 2 units
more basic than ReH7(PiPr3)2/[K(crown)][ReH6(PiPr3)2].19
From the equilibrium constant of 8.2 for the reaction of
IrH5(PiPr3)2 and [K(crypt)]7, it is concluded that IrH5(PCy3)2/
THF
Figure 3. (a) Observed and (b) simulated upfield 300 MHz 1H NMR
spectra of [K(18-crown-6)][cis-IrH4(PiPr3)2] in THF. The large triplet at
-15.6 ppm in (a) is due to trans-[IrH4(PiPr3)2]-.
[K(crypt)]7 has a pKR
of about 43.
It was unexpected that the approximate pKa values for the
acid pentahydrides converting to the conjugate base cis-
tetrahydrides are about 2 units higher (44 vs 42) than those
for converting to the conjugate base trans-tetrahydrides.
The stabilization of the conjugate base cis-isomer from
Ir-H‚‚‚K interactions and reduced trans-H-Ir-H destabi-
lization must be overcome by interligand destabilizing
interactions in the cis form relative to the trans form.
Formation of Mixed Ligand Complexes. A mixture of
K6 and IrH5(PCy3)2 in refluxing THF was observed to
undergo a phosphine-exchange reaction to give some [cis-
IrH4(PCy3)(PiPr3)]-. Refluxing THF solutions of IrH5(PCy3)2
and IrH5(PiPr3)2 (1:1) afforded a mixture containing IrH5-
(PiPr3)(PCy3). There is no resonance for uncoordinated
phosphine in these reactions. However, it is likely that these
reactions proceed via phosphine dissociation. The reaction
of IrH5(PCy3)2 with PiPr3 yields IrH5(PCy3)(PiPr3) but no
IrH3(PCy3)2(PiPr3). The related reaction of IrH5(PCy3)2 with
PPh3 results in the formation of IrH3(PCy3)2(PPh3). The
dissociation of PCy3 from IrH5(PCy3)2 would explain its
property of exchanging hydride hydrogen with C6D6 deute-
rium; the reactive 16-electron intermediate IrH5(PCy3) is
likely to insert into a C-D bond to cause this reaction.
Solution Structure and NMR Properties of [IrH4(PR3)2]-
Figure 4. (a) Observed and (b) simulated hydride-coupled 121 MHz 31
NMR spectra of [K(18-crown-6)][cis-IrH4(PiPr3)2] in THF.
P
IrH4(PCy3)2]- have magnitudes and therefore coupling
constants similar to those for [cis-IrH4(PiPr3)2]-.
To check the validity of this simulation, the hydride-
coupled 31P NMR 6 resonance for the same sample of
[K(crown)]6 was also simulated with the same parameters
(Figure 4). There is reasonable agreement between the
observed and simulated spectra of the cis isomer.
For [IrH4(PiPr3)2]-, the [cis]/[trans] ratio is highly sensitive
to the nature of the solvent and the crown- or azacrown-
potassium cation. The [cis]/[trans] ratio in THF increases
from 2:1 to 8:1 on changing the cation from [K(crown)]+ to
[K(diaza)]+. This indicates that a combination of protonic-
hydridic bonding and increased potassium-hydride inter-
actions causes a stabilization of the cis isomer in an ion pair
structure that is similar to the one observed in the solid state
for [K(aza)][IrH4(PiPr3)2]. On changing the cation to K+, the
[cis]/[trans] ratio increases to 15:1, and this increase is
attributed to a strong interaction between the small and
electrophilic K+ cation and three facial hydride ligands. The
largest [cis]/[trans] ratios are observed for the [K(aza)]+ and
[K(diaza)]+ salts in toluene and benzene for which no trans
isomer is observed. Complex 6 exists exclusively as the cis
isomer with stronger ion pairing in this environment because
of the lower dielectric constant of toluene compared to THF.
(R ) Pr, Cy, Ph). The complexes [IrH4(PCy3)2]- and
i
[IrH4(PPh3)2]- as crown- and azacrown-potassium salts exist
in solution with an exclusive cis configuration about the
iridium atom while the complex [IrH4(PiPr3)2]- exists in
solution as an equilibrium mixture of cis and trans isomers.
Surprisingly, the cryptand-potassium salts of [IrH4(PCy3)2]-
and [IrH4(PiPr3)2]- exist exclusively in the trans form as
1
indicated by a binomial triplet resonance in the H NMR
spectrum.
The second-order HBB′ resonances for the three [cis-IrH4-
(PR3)2]- complexes are similar in appearance. This pattern
for [K(crown)]6 in THF was simulated, and the results are
2
illustrated in Figure 3. The J(HPtrans) value of 121.5 Hz
determined by simulation is comparable to the corresponding
value of 120 Hz observed for [K(crown)][cis-IrHD3(PCy3)2]
and simulated for IrH3(PPh3)3.21 The simulated second-order
2
| J(HPcis)| of 24.8 Hz is similar to the value of 26 Hz
observed for [K(crown)][IrHD3(PCy3)2] but significantly
greater than the value of 18 Hz simulated for IrH3(PPh3)3.
The second-order patterns for [cis-IrH4(PPh3)2]- and [cis-
Inorganic Chemistry, Vol. 41, No. 11, 2002 3003

Landau et al.
Table 4. IR Data (cm-1) for [K(Q)][IrH4(PR3)2] in THFa
Q ) 18-crown-6
Q ) diaza-18-crown-6
R
ν(H-IrP) ν(H-IrH)
ν(NH)
∆νb ν(H-IrP) ν(H-IrH)
Ph
iPr
Cy
2005
1965
1960
1713
1688
1680
3299, 3205 1, 95
3300, 3227 0, 73
3300, 3228 0, 72
2001
1970
1965
1716
1695
1685
a The frequencies of the H-IrP absorptions in THF solution are
imprecise, and this is in most part due to the presence of a strong solvent
absorption at approximately 2000 cm-1 b Decrease in ν(NH) from ν(NH)
.
) 3300 cm-1 for [K(1,10-diaza-18-crown-6)]BPh4.
At 298 K, both NH protons of [K(diaza)]6 in THF-d8
resonate at 2.14 ppm while they result in two vibrational
modes in the infrared spectrum (Table 4). One may infer
that the observed 1H NMR chemical shift for the NH protons
of [K(diaza)]6 is in fact that for an averaged environment.
With this in mind, an attempt was made to observe
1
inequivalent NH protons at low temperature by H NMR
Figure 5. X-ray structure of [K(18-crown-6)][IrH4(PPh3)2] (subunit A).
spectroscopy. The chemical shift of the NH resonance for a
solution of [K(diaza)]6 in THF-d8 was found to vary linearly
with temperature, but no decoalescence was observed down
to 167 K. This precluded the effective use of nOe and T1
measurements for the detection of close proton-hydride
contacts.
X-ray Structures of [K(18-crown-6)][IrH4(PiPr3)2] and
[K(18-crown-6)][IrH4(PPh3)2]. In solution, [IrH4(PiPr3)2]-
exists as an equilibrium mixture of cis and trans isomers
where in all cases the cis isomer predominates. A single-
crystal X-ray structural determination for [K(crown)]6
revealed that this salt crystallizes from THF solution with
the anion in the cis configuration. The structure was described
briefly.4 The hydride ligands were located and refined and
had Ir-H bond lengths ranging from 1.52(7) to 2.0(1) Å. A
typical iridium(III)-hydride distance is 1.60(2) Å.34 The
observed Ir-P bond lengths of 2.290(1) and 2.295(1) Å are
typical for PiPr3 complexes of iridium. The K atom completes
a distorted tetrahedron with three hydride ligands arranged
facially about the iridium atom. This arrangement is recurring
and will be subsequently referred to as the tripod arrange-
ment.
In terms of the spatial relationship between anion and
cation, the solid-state structure of [K(crown)]5 is essentially
the same as that of its PiPr3 counterpart. However, in this
case, there are two similar formula units, with only one
illustrated in Figure 5.
The Ir-H bond lengths range from 1.53(4) to 1.68(4) Å.
The Ir-P bond lengths of approximately 2.26 Å are shorter
than the bond lengths of 2.36(5) Å typically observed for
6-coordinate PPh3 complexes of iridium. The short Ir-P
bond lengths for this salt seem even more peculiar when
one realizes that the phosphine ligands are trans to hydride
ligands. However, the steric requirements of the hydride
ligands are quite small, and this allows for a close approach
of the phosphine ligands to the metal as the P-Ir-P angle
(104°) deviates from ideal octahedral geometry. The H-Ir-P
angles (H trans to P) are substantially less than 180° which
Figure 6. X-ray structure of [K(aza-18-crown-6)][IrH4(PiPr3)2].
may reduce the trans influence and result in shorter-than-
expected Ir-P bond lengths.
X-ray Structure of [K(1,10-diaza-18-crown-6)][IrH4-
(PiPr3)2]. Unlike [K(crown)]6, the related salt [K(diaza)]6
crystallizes with the anion in the trans configuration, Figure
1.4 It is clear that when the trans isomer with [K(diaza)]+
as the cation forms a chain of protonic-hydridic bonds in
the crystalline state, it is less soluble than the cis isomer
because the trans isomer is in lower concentration than the
cis one in THF solution ([trans]/[cis] ratio is 1:8).
X-ray Structure of [K(aza-18-crown-6)][IrH4(PiPr3)2].
The X-ray structure of [K(aza)]6 revealed a cis configuration
for the anion of this salt (Figure 6). This structure possesses
the tripod K+/hydride arrangement observed also for
[K(crown)]6. The X-ray data do not directly indicate the
presence of any NH‚‚‚HIr hydrogen bonds for [K(aza)]6
because the smallest observed NH‚‚‚HIr separation is
2.47(5) Å. The crown NH proton lies in the H(3IR)-Ir(1)-
H(4IR) plane and also very nearly bisects the H(3IR)-Ir-
(1)-H(4IR) angle. This is similar to the bifurcated interaction
arrangement observed for the ReH5(PPh3)2‚indole system,35
(35) Wessel, J.; Lee, J. C.; Peris, E.; Yap, G. P. A.; Fortin, J. B.; Ricci, J.
S.; Sini, G.; Albinati, A.; Koetzle, T. F.; Eisenstein, O.; Rheingold,
A. L.; Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1995, 34, 2507-
2509.
(34) Typical bond lengths for comparison are obtained from the following
review: Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.;
Watson, D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.
3004 Inorganic Chemistry, Vol. 41, No. 11, 2002

Ion Pairing and Protonic-Hydridic Bonding
Figure 7. X-ray structure of [K(1,10-diaza-18-crown-6)][IrH4(PPh3)2].
but the H‚‚‚H distances are much longer in the iridium salt.
However, if the N-H bond length is increased to 1.00 Å
and the Ir-H distances are increased to 1.65 Å, the corrected
H(4N)-H(2IR) and H(4N)-H(3IR) bond lengths are 2.3 and
2.6 Å, respectively. The 2.3 Å distance is indicative of an
NH‚‚‚HIr hydrogen bond and is consistent with the lowered
NH stretch of the IR spectrum.
Another interesting feature of the [K(aza)]6 structure is
the very short H(4A)-H(27A) separation of 2.1 Å (between
an isopropyl methine hydrogen and an aza methylene
hydrogen). This close contact likely impedes a closer
approach of the NH group to the hydride ligands.
X-ray Structure of [K(1,10-diaza-18-crown-6)][cis-IrH4-
(PPh3)2]. As in solution, the anion of [K(diaza)]5 adopts a
cis configuration about the iridium atom in the solid state
(Figure 7). The anions and cations form a chain by way of
alternating protonic-hydridic bonds and (K+)‚‚‚(H-) inter-
actions as illustrated in Figure 8. For this structure, the Ir-H
bond lengths range from 1.51(3) to 1.66(4) Å. The observed
H(4N)-H(3IR) separation is 2.50(6) Å if the observed N-H
bond length of 0.79(4) Å is considered. If the N(4)-H(4N)
bond is elongated to a more reasonable length of 1.00 Å,
one obtains a corrected H(4N)-H(3IR) distance of 2.33 Å
which is marginally indicative of protonic-hydridic bonding
within the ion pair. The importance of this interaction is
illustrated by the fact that the potassium atom of the cation
is displaced from the tripod arrangement observed for
Figure 8. Chain structure of [K(1,10-diaza-18-crown-6)][IrH4(PPh3)2].
Carbon and nonessential hydrogen atoms have been omitted for clarity.
IR Studies of Anionic Hydride Salts. In solution, the
configuration about the iridium atom for all of the
[IrH4(PR3)2]- salts studied is exclusively cis (R ) Ph, Cy)
i
or primarily cis (R ) Pr) except for the cryptate salt. In
each case, the cis arrangement results in two intense IrH
stretching absorptions. Typically, one of these has a fre-
quency of approximately 2000 cm-1 while the second may
be found at or near 1700 cm-1. Although these modes are
probably coupled, the higher mode can be associated with
hydride trans to phosphine, while the lower, to hydride trans
to hydride. This is consistent with the fact that the trans
tetrahydride salts in Nujol display only one intense H-IrH
mode in the region of 1670-1680 cm-1. [K(diaza)][trans-
IrH4(PiPr3)2] exhibits an H-IrH mode at 1680 cm-1 but no
H-IrP absorption. Similarly, the [K(crypt)][trans-IrH4-
(PiPr3)2] and [K(crypt)][trans-IrH4(PCy3)2] salts in Nujol have
strong H-IrH modes at 1673 and 1680 cm-1, respectively.
These complexes also give weak absorptions between 1960
and 1930 cm-1 that are very similar to those of the neutral
pentahydride species; these are probably produced during
i
[K(crown)][cis-IrH4(PR3)2] (R ) Ph, Pr) and [K(aza)][cis-
IrH4(PiPr3)2] to accommodate the NH‚‚‚HIr interaction. The
inter-ion-pair NH‚‚‚HIr interaction in [K(diaza)][cis-IrH4-
(PPh3)2] is characterized by an observed H(1N)-H(2IR)
separation of 2.08(6) Å. By increasing the N(1)-H(1N) bond
length from the observed value of 0.81(5) Å to a more
reasonable value of 1.00 Å, the corrected H(1N)-H(2IR)
separation is 1.91 Å. This separation is very similar to that
of 1.85 Å observed for [K(diaza)][trans-IrH4(PiPr3)2]. The
complex [K(diaza)][ReH6(PPh3)2] forms similar intra- and
inter-ion-pair protonic-hydridic bonds but instead of forming
a chain of ion pairs, it forms a ring of four linked ion pairs.19
Inorganic Chemistry, Vol. 41, No. 11, 2002 3005

Landau et al.
Table 5. Solid-State (cm-1) IR Data for [K(Q)][IrH4(PR3)2] in Nujol
Q ) 18-crown-6
Q ) diaza-18-crown-6
R
ν(H-IrP) ν(H-IrH)
ν(NH)
3198
3148
3289, 3222 -9, 58
∆νa
ν(H-IrP) ν(H-IrH)
Ph
iPr
Cy
2010
1922
1986
1716
1698
1697
82
132
1974
-
1712
1680
1668
1957
a Decrease in ν(NH) from ν(NH) ) 3280 cm-1 for [K(1,10-diaza-18-
crown-6)]BPh4.
the hydrogen-bonding interactions present in the case of
iridium.
Some solid-state IR data for the salts [K(Q)][IrH4(PR3)2]
are given in Table 5. [K(diaza)][BPh4] exhibits a single NH
stretching absorption at 3287 cm-1. The IR spectra of
samples in Nujol are quite distinct from the corresponding
ones for THF solutions. In Nujol, the [K(diaza)]+ salts of
both [IrH4(PiPr3)2]- and [IrH4(PPh3)2]- exhibit NH vibrations
perturbed by protonic-hydridic bonding. [K(diaza)][trans-
IrH4(PiPr3)2] exhibits only one NH absorption which is
consistent with its X-ray structure. The NH absorption of
[K(diaza)][cis-IrH4(PPh3)2] in Nujol is asymmetric and
appears to consist of two overlapping absorptions. This is
consistent with the X-ray-determined structure that has two
types of NH groups interacting with the hydride ligands of
the anions. The NH region for [K(diaza)][cis-IrH4(PCy3)2]
exhibits an absorption at 3289 cm-1 and a second absorption
of roughly equal intensity at 3222 cm-1. The first of these
is attributed to a cation NH group which is not interacting
with the anion, and the second is attributed to the second
cation NH group which is weakly interacting with the anion.
The salt [K(diaza)][trans-IrH4(PiPr3)2] causes the largest
reduction in the NH vibration (∆ν ) 132) in keeping with
the high basicity of this anion and the strong hydrogen bonds
(see Figure 1).
Figure 9. Solution IR spectrum of [K(1,10-diaza-18-crown-6)][IrH4-
(PiPr3)2] (NH region). The absorption at 3336 cm-1 is attributed to the
presence of diaza-18-crown-6 or [K(diaza)(THF)2]+.33
sample preparation by protonation of the anions with
adventitious water.
The solution IR spectroscopic properties of the [K(crown)]+
and [K(diaza)]+ salts of the three anionic hydride complexes
are given in Table 4. From these data, it is apparent that an
increase in phosphine basicity results in a reduction in the
frequency of both IrH absorptions. The presence of a
hydrogen-bond donor does not appear to significantly affect
the IrH stretching frequencies in solution, and so, any IrH
stretches for hydrogen-bonded hydride ligands were not
resolved from the non-hydrogen-bonded absorptions.
The position, intensity, and breadth of the NH absorptions
are quite sensitive to the nature of the anionic hydride
complexes (Table 4). For comparison, diaza-18-crown-6 has
an NH stretching frequency of approximately 3335 cm-1
while [K(diaza)][BPh4] in THF has an NH stretching
frequency of 3300 cm-1. All three of the iridium complex
[K(diaza)]+ salts in THF exhibit two or three IR NH
absorptions, one of which is in good agreement with that
observed for [K(diaza)][BPh4] and is thus attributed to an
NH group which is not interacting with any hydride ligands
(cf. Figure 9). In all cases, there is a second [K(diaza)]+
NH stretch that is shifted to lower frequency, broadened,
and considerably more intense than the absorption at 3300
cm-1. These features are typical of protonic-hydridic
hydrogen-bonded systems. The reduction in NH wavenumber
attributed to this interaction (∆ν in Table 4) increases as
PCy3 ) PiPr3 < PPh3. This is opposite to the trend expected
on the basis of the anion basicity: PPh3 < PiPr3 < PCy3
and opposite to the order observed for some rhenium anions
[ReH6L2]- where ∆ν and anion basicity both increased as
PPh3 < PiPr3 < PCy3.19 The interaction of the potassium
with the hydride tripod on iridium and the associated
interligand interactions appear to complicate the nature of
Conclusions
IrHCl2(PiPr3)2 and IrHCl2(PPh3)3 were prepared by reflux-
ing mixtures of IrCl3 and phosphine in iPrOH. IrHCl2(PPh3)3
may be a mixture of cis,mer and trans,mer isomers or it may
be exclusively cis,mer depending on reaction time.
i
IrHCl2(PR3)2 (R ) Pr, Cy) and IrHCl2(PPh3)3 have been
treated with KH and Q under H2 atmosphere to yield the
basic anionic hydride salts [K(Q)][IrH4(PR3)2] (Q )
i
18-crown-6, R ) Ph, Pr, Cy; Q ) aza-18-crown-6, R )
iPr; Q ) diaza-18-crown-6, R ) Ph, iPr, Cy). When R ) iPr
and Cy, the isolated products are usually contaminated with
the new salts [K(Q)][IrH6(PR3)]. When R ) Ph, the isolated
products are usually contaminated with [K(Q)][PPh2] and
the new salts [K(Q)][trans,mer-IrH3(PPh3)(PPh2)]. Alterna-
i
tively, the treatment of IrH5(PR3)2 (R ) Ph, Pr, Cy) with
KH and Q under a non-hydrogen atmosphere cleanly yields
[K(Q)][IrH4(PR3)2] although the crown and diaza-crown
[IrH4(PCy3)2]- salts could not be crystallized or isolated free
of IrH5(PCy3)2. The IrH5(PR3)2 (R ) iPr, Cy) precursors were
prepared by the treatment of IrHCl2(PR3)2 with NaOH under
H2 atmosphere. The IrH5(PPh3)2 precursor was prepared in
two steps: first, the preparation of crude K[IrH4(PPh3)2] from
3006 Inorganic Chemistry, Vol. 41, No. 11, 2002

Ion Pairing and Protonic-Hydridic Bonding
Scheme 3
IrHCl2(PPh3)3 and then its reaction with H2O. This route to
IrH5(PPh3)2 is far more efficient than previously reported
methods.
i
The salts [K(18-crown-6)][IrH4(PR3)2] (R ) Ph, Pr)
crystallize with the anion in a cis configuration. In these salts,
the potassium atom and three facially-arranged hydride
ligands form a tetrahedron. [K(aza-18-crown-6)][IrH4(PiPr3)2]
also crystallizes with a cis configuration about the iridium
atom and exhibits the potassium/hydride arrangement ob-
served for the [K(18-crown-6)]+ salts. There is IR and
structural evidence of significant protonic-hydridic interac-
tions in [K(aza-18-crown-6)][IrH4(PiPr3)2] although the ob-
served (X-ray) proton-hydride distance is greater than 2.4
Å.
The salt [K(1,10-diaza-18-crown-6)][IrH4(PPh3)2] crystal-
lizes with the anion in a cis configuration while the anion in
[K(1,10-diaza-18-crown-6)][IrH4(PiPr3)2] is trans. In the solid
state, both of these salts form extended chains with protonic-
hydridic hydrogen-bond links. The protonic-hydridic bonds
in [K(1,10-diaza-18-crown-6)][IrH4(PiPr3)2] are key to the
crystallization of this salt from THF with the anion in the
trans configuration because the [cis]/[trans] ratio is 8:1 for
this salt in THF. Thus, there is a competition between the
potassium and NH groups in forming bonds with the hydrides
on iridium.
explains why [K(crypt)]6 and [K(crypt)]7 are trans in the
absence of potassium-hydride interactions. However, a
fourth factor is the destabilization of isomers that have trans
hydride ligands in octahedral structures. This would disfavor
the formation of trans tetrahydride isomers (with two sets
of trans hydrides) over cis isomers (with one set). The fact
that the [K(crown)][IrH4(PCy3)2] and [K(diaza)][IrH4(PCy3)2]
salts are exclusively cis, when trans might be expected on
the basis of interligand repulsions, indicates that the fac-
hydrides in this particularly electron-rich cis complex are
excellent donors to potassium and in addition that the trans-
tetrahydride geometry is avoided.
The nature of the cation and hence the stereochemistry of
the anions [IrH4(PR3)2]- has a large influence on the basicity
THF
with respect to the acid WH6(PMe2Ph)3 and hence the pKR
value of the conjugate acids. The acidity decreases in THF
as IrH5(PiPr3)2/[K(crypt)][trans-IrH4(PiPr3)2] (pKRTHF ) 42)
> IrH5(PCy3)2/[K(crypt)][trans-IrH4(PCy3)2] (pKRTHF ) 43)
> IrH5(PiPr3)2/[K(crown)][cis-IrH4(PiPr3)2] (pKRTHF ) 44) >
IrH5(PCy3)2/[K(crown)][cis-IrH4(PCy3)2]. This is the first
example that we are aware of such a large counterion effect
on stereochemistry and acidity as summarized in Scheme 3.
There are at least four factors that are thought to influence
the stereochemistry of these tetrahydride complexes in THF
solution. The first and most important is the potassium-
hydride interactions in the ion pairs that favor the cis isomer
for [K(Q)]5, [K(Q)]7, K6, [K(crown)]6, [K(aza)]6, and
[K(diaza)]6. The cryptate salts that cannot make potassium-
hydride bonds are trans. On the basis of the [cis]/[trans]
ratios for the salts of 6, the Lewis acidity of the potassium
Acknowledgment. This research was funded by an
NSERC research grant to R.H.M. and an NSERC scholarship
to S.E.L. Dr. K. Abdur-Rashid and J. G. Hinman are thanked
for assistance with the project. Johnson Matthey PLC is
thanked for a loan of iridium salts.
cation decreases as K+ > [K(diaza)]+ > [K(aza)]+
>
[K(crown)]+ . [K(crypt)]+. A second factor is protonic-
hydridic bonding that would also contribute to a strengthen-
ing of the cation-anion interaction, an effect that would also
decrease as [K(diaza)]+ > [K(aza)]+ > [K(crown)]+. A third
factor is interligand repulsions in the anion, expected to
increase with the Tolman cone angle of the phosphine
ligand: PPh3 (145°) < PiPr3 (160°) < PCy3 (170°). This
Supporting Information Available: Crystallographic CIF file.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC0255149
Inorganic Chemistry, Vol. 41, No. 11, 2002 3007