Anionic iridium monohydrides

Full text of DOI:10.1021/ic990068j

Inorg. Chem. 1999, 38, 4171-4173
4171
Table 1. Selected Crystallographic Data for 1‚Me2CO and 2
Anionic Iridium Monohydrides
1‚Me2CO
2
Robert D. Simpson, William J. Marshall,
Amy A. Farischon, D. Christopher Roe, and
Vladimir V. Grushin*
empirical formula
fw
crystal size, mm
crystal system
space group
temp, K
a, Å
C37H85I3IrNOP2
1194.94
C54H73Cl3IrNP4
1158.64
0.17 × 0.18 × 0.21 0.22 × 0.35 × 0.37
triclinic
P1h
triclinic
P1h
173
Central Research and Development,
E. I. DuPont de Nemours & Co., Inc.,† Experimental Station,
Wilmington, Delaware 19880-0328
173
12.946(1)
16.178(1)
12.396(1)
106.26(1)
92.12(1)
96.58(1)
2469.5
2
1.607
46.37
Rigaku RU 300
3.2-50.0
ω
no
26 136
14.164(1)
19.729(1)
9.614(1)
96.93(1)
91.06(1)
89.26(1)
2666.3
2
1.443
27.98
Rigaku RU 300
3.5-48.2
ω
b, Å
c, Å
ReceiVed January 11, 1999
R, deg
â, deg
γ, deg
Introduction
volume, Å3
Z
Of all the transition metals, iridium forms the largest number
of hydrido complexes.1,2 Hundreds of various neutral and
cationic iridium hydrides have been isolated and reliably
characterized. At the same time, very little is known about
anionic hydrido complexes of iridium.3 Although a few mono-
nuclear polyhydridoiridates,4,5 anionic cluster hydrides,6 and two
π-acid-stabilized [HIrL5]3- (L ) CN or SnCl3) trianions7 have
been reported, simplest members of the family, i.e., mononuclear
monohydridoiridate monoanions remain unknown. In this note,
we report the synthesis of such complexes, the first remarkably
electron-rich, yet air-stable mononuclear anionic iridium hy-
drides, their X-ray structures, and solution behavior.
calcd density, g cm-1
µ(Mo), cm-1
diffractometer
2θ range, deg
scan type
abs corr
no
27 814
6098
no. of reflns collcd
no. of unique reflns used in 5603
refinement (I > 3σ(I))
no. of params refined
data-to-param ratio
R1, %a
410
13.54
3.5
571
10.63
3.2
Rw, %a
3.9
3.8
goodness of fit
2.05
2.23
Results and Discussion
a R ) ∑(||Fo| - |Fc||)/∑|Fo|; Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
2
While the green complex [(i-Pr3P)2Ir(H)I2] is virtually
insoluble in pure acetone, it readily dissolves in acetone
containing either NaI or Bu4NI, to produce stable orange-
tan solutions. When Bu4NI was the iodide source, brown-red
crystals of [Bu4N][(i-Pr3P)2Ir(H)I3]‚Me2CO (1‚Me2CO) were
isolated in 76% yield (eq 1). Similarly, bright yellow crystals
† Contribution No. 7887.
(1) Geoffroy, G. L.; Lehman, J. R. AdV. Inorg. Chem. Radiochem. 1977,
20, 189.
(2) For recent general reviews of classical and nonclassical transition metal
hydrides, see: (a) Transition Metal Hydrides; Dedieu, A., Ed.; VCH:
New York, 1992. (b) Jessop, P. G.; Morris, R. H. Coord. Chem. ReV.
1992, 121, 155. (c) Heinekey, D. M.; Oldham, W. J. Chem. ReV. 1993,
93, 913.
(3) Darensbourg, M. Y.; Ash, C. E. AdV. Organomet. Chem. 1987, 27, 1.
(4) Bronger, W.; Gehlen, M.; Aufferman, G. J. Alloys Compd. 1991, 176,
255. Kadir, K.; Noreus, D. J. Alloys Compd. 1994, 209, 213. Abdur-
Rashid, K.; Gusev, D. G.; Landau, S. E.; Lough, A. J.; Morris, R. H.
J. Am. Chem. Soc. 1998, 120, 11826.
(5) (a) Deprotonation of [Cp*IrH4], [Cp*Ir(PMe3)H2], and [Cp*Ir(SiMe3)-
H3] with strong bases produces highly reactive species which have
been used as synthons of anionic hydrides. See: Gilbert, T. M.;
Bergman, R. G. J. Am. Chem. Soc. 1985, 107, 3502, 6391. Gilbert, T.
M.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1985, 107,
3508. McGhee, W. D.; Bergman, R. G. J. Am. Chem. Soc. 1985, 107,
3388. (b) Very recently, it was demonstrated that deprotonation of
[Cp*Ir(PMe3)H2] with t-BuLi resulted in the formation of [Cp*Ir-
(PMe3)(H)(Li)], from which no lithium decoordination occurred in
THF, DME, or benzene, even in the presence of 12-crown-4. See:
Peterson, T. H.; Golden, J. T.; Bergman, R. G. Organometallics 1999,
18, 2005.
(6) Ciani, G.; Manassero, M.; Albano, V. G.; Canziani, F.; Giordano, G.;
Martinengo, S.; Chini, P. J. Organomet. Chem. 1978, 150, C17. Bau,
R.; Chiang, M. Y.; Wei, C.-Y.; Garlaschelli, L.; Martinengo, S.;
Koetzle, T. F. Inorg. Chem. 1984, 23, 4758. Ceriotti, A.; Pergola, R.
D.; Garlaschelli, L.; Laschi, F.; Manassero, M.; Masciocchi, N.;
Sansoni, M.; Zanello, P. Inorg. Chem. 1991, 30, 3349. Beringhelli,
T.; Ciani, G.; D’Alfonso, G.; Garlaschelli, L.; Moret, M.; Sironi, A.
J. Chem. Soc., Dalton Trans. 1992, 1865. Pergola, R. D.; Cea, F.;
Garlaschelli, L.; Masciocchi, N.; Sansoni, M. J. Chem. Soc., Dalton
Trans. 1994, 1501.
of [PPN][(i-Pr3P)2Ir(H)Cl3], 2, were isolated in 85% yield upon
dissolving deep-purple [(i-Pr3P)2Ir(H)Cl2] in an acetone solution
of PPN Cl. Given the unique set of electron-rich ligands on the
metal, both 1 and 2 are remarkably air-stable in the solid state,
showing no sign of decomposition for months. When exposed
to air, solutions of 1 or 2 decompose over the course of hours
at room temperature.
Single-crystal X-ray diffraction of 1 and 2 (Table 1) showed
mer-trans octahedral structures for both anions (Figures 1 and
2). No bonding contacts were observed between 1 and the
cocrystallized acetone molecule. The Ir-H bond distances of
1.56(4) Å for 1 and 1.46(4) Å for 2 are close to the average
value of 1.6 Å obtained from X-ray and ND studies of neutral
hydrido iridium complexes.8 In comparison with the Ir-X bonds
that are mutually trans, the Ir-X bond trans to the hydride is
remarkably elongated (by 0.14 and 0.19 Å for X ) I and Cl,
respectively) due to the strong trans-influence of the H. This
(7) Krogmann, K.; Binder, W. Angew. Chem., Int. Ed. Engl. 1967, 6, 881.
Whitesides, G. M.; Maglio, G. J. Am. Chem. Soc. 1969, 91, 4980.
Mockford, M. J.; Griffith, W. P. J. Chem. Soc., Dalton Trans. 1985,
717. Yamakawa, T.; Shinoda, S.; Saito, Y.; Moriyama, H.; Pregosin,
P. S. Magn. Reson. Chem. 1985, 23, 202.
(8) Bau, R.; Teller, R. G.; Kirtley, S. W.; Koetzle, T. F. Acc. Chem. Res.
1979, 12, 176. Teller, R. G.; Bau, R. Struct. Bonding (Berlin) 1981,
44, 1. Koetzle, T. F. Trans. Am. Crystallogr. Assoc. 1995, 31, 57.
Bau, R.; Drabnis, M. H. Inorg. Chim. Acta 1997, 259, 27.
10.1021/ic990068j CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/17/1999

4172 Inorganic Chemistry, Vol. 38, No. 18, 1999
Notes
Scheme 1
Figure 1. ORTEP drawing for the anion of 1, [(i-Pr3P)2Ir(H)I3]-,
showing the atom-labeling scheme. Hydrogen atoms, except Ir-H, are
omitted for clarity. Selected bond distances (Å) and angles (deg): Ir-
(1)-H(1), 1.558(42); Ir(1)-I(1), 2.8345(5); Ir(1)-I(2), 2.6946(5); Ir-
(1)-I(3), 2.6930(5); Ir(1)-P(1), 2.383(1); Ir(1)-P(2), 2.379(1); I(1)-
Ir(1)-I(2), 89.43(1); I(1)-Ir(1)-I(3), 93.88(1); I(1)-Ir(1)-P(1), 97.39(1);
I(1)-Ir(1)-P(2), 97.58(1); I(2)-Ir(1)-H(10), 85(2); I(3)-Ir(1)-H(10),
91(2); P(1)-Ir(1)-H(10), 80(1); P(2)-Ir(1)-H(10), 86(1).
three singlet resonances from 1, A, and B at -19.9, -1.0, and
-5.2 ppm, respectively, the ratio being ca. 60:3:1. Magnetization
transfer experiments (31P NMR) demonstrated that at -80 and
even at -90 °C, species A and B were in rapid exchange with
one another, whereas neither one exchanged with 1. At -70
°C, however, 1 was already involved in slow exchange with
both A and B.10 Importantly, the characteristic hydrido resonance
of the pentacoordinate hydride [(i-Pr3P)2Ir(H)I2] (at -47.5 ppm
1
in the H NMR spectrum) was not observed in spectra of [(i-
Pr3P)2Ir(H)I3]- in acetone-d6, acquired over the temperature
range of +20 to -90 °C. Saturating this solution of 1 with [(i-
Pr3P)2Ir(H)I2] (<1 equiv dissolved) did not lead to the appear-
ance of the resonance at -47.5 ppm but rather increased the
population of A/B.
Ligand exchange processes in solutions of 1 and 2 slowed
considerably in the presence of excess halide. When 8-15 equiv
of I- and Cl-, respectively, was added to solutions of 1 and 2,
the octahedral anions became inert on the NMR time scale at
room temperature.11,12 Neither A/B nor any Ir complexes other
than 1 and 2 were detected in these halide-enriched solutions.
Scheme 1 provides a rationale for the observed solution behavior
of 1, proposing that the pentacoordinate neutral hydride may
catalyze the halide exchange via the formation of a halogen-
bridged Ir dimer intermediate. The proposal of two conformers
of the dimer (e.g., from hindered rotation around the Ir-P, Ir-
(µ-X), and/or C-P bonds) would account for the observation
of the two species, A and B, whose proton resonances average
at -50 °C and above. In the presence of excess iodide, the
catalytic role of [(i-Pr3P)2Ir(H)I2] is eliminated as the equilibrium
is shifted to [(i-Pr3P)2Ir(H)I3]-. It is to be stressed that although
excess halide favors the formation of 1 and 2 thermodynamically
(Scheme 1), it should not affect kinetics of Ir-Hal ionization
that proceeds via the dissociative mechanism.13
Figure 2. ORTEP drawing for the anion of 2, [(i-Pr3P)2Ir(H)Cl3]-,
showing the atom-labeling scheme. Hydrogen atoms, except Ir-H, are
omitted for clarity. Selected bond distances (Å) and angles (deg): Ir-
(1)-H(1), 1.459(40); Ir(1)-Cl(1), 2.564(1); Ir(1)-Cl(2), 2.379(1); Ir-
(1)-Cl(3), 2.373(1); Ir(1)-P(1), 2.348(1); Ir(1)-P(2), 2.348(1); Cl(1)-
Ir(1)-Cl(2), 90.97(3); Cl(1)-Ir(1)-Cl(3), 92.14(4); Cl(1)-Ir(1)-P(1),
96.36(4); Cl(1)-Ir(1)-P(2), 95.72(4); Cl(2)-Ir(1)-H(10), 89(1); Cl-
(3)-Ir(1)-H(10), 87(1); P(1)-Ir(1)-H(10), 85(1); P(2)-Ir(1)-H(10),
83(1).
difference is consistent with the halide trans to the H being labile
in solution (see below).
Only one broad (∆ν1/2 ≈ 1500 Hz) line at -27 ppm was
1
observed in the hydride region of room temperature H NMR
spectra of 1 and its sodium analogue, Na+[(i-Pr3P)2Ir(H)I3]-
(generated in situ from NaI and [(i-Pr3P)2Ir(H)I2] (1:1) in
acetone-d6).9 Cooling this solution to -20 °C narrowed the
signal to ∆ν1/2 ) 80 Hz, and at -50 °C, this resonance
transformed into a sharp, well-resolved 1:2:1 triplet at -25.2
ppm with J ) 14.5 Hz, fully consistent with the mer-trans
octahedral structure determined in the solid state (Figures 1 and
2). A weak broad line at -36 ppm was also observed in the
-50 °C spectrum. Further cooling the sample to -80 °C
transformed this minor resonance into two broadened singlets
at -36.1 ppm (weak; species A; ∆ν1/2 ) 70 Hz) and -34.0
ppm (very weak; species B; ∆ν1/2 ) 50 Hz), with the triplet at
-25.2 ppm due to 1 remaining unchanged. In accord with this
1H NMR data, the 31P{1H} NMR spectrum at -80 °C exhibited
(10) Based on consideration of 31P T1’s “rapid” and “slow” exchange
designate rates that are on the order of 10 and 1 s-1, respectively.
Line broadening of A and B at -70 °C corresponds to exchange rates
of approximately 100 s-1
.
(11) (a) Spectral data for Na+[(i-Pr3P)2Ir(H)I3]- in acetone-d6 containing
1
NaI (8 equiv) at 20 °C. H NMR, δ: -25.2 (t, 1H, JP-H ) 14.5 Hz,
Ir-H); 1.4 (dd, 36H, J ) 6.6 and 13.2 Hz, CH3); 3.5 (br s, 6H, CH).
31P{1H} NMR, δ: -18.4 (s). Similar patterns were obtained for 1 in
the presence of extra Bu4NI. (b) Spectral data for 2 in CD2Cl2
containing PPN Cl (15 equiv) at 20 °C. 1H NMR, δ: -27.9 (t, 1H,
JP-H ) 14.5 Hz, Ir-H); 1.3 (dd, 36H, J ) 6.6 and 13.2 Hz, CH3); 2.8
(m, 6H, CH). 31P{1H} NMR, δ: 1.7 (s, Ir-P); 22.2 (s, PPN).
(12) (a) Under similar conditions, the iodo complex 1 is more inert than
its chloro analogue 2. This difference may be rationalized in terms of
(9) Similarly, broad lines were observed in 1H and 31P NMR spectra of 2
in acetone-d6 or CD2Cl2 at room temperature.
dπ-p filled/filled repulsions12b that are stronger for Cl than I. (b)
π
Caulton, K. G. New J. Chem. 1994, 18, 25.

Notes
Inorganic Chemistry, Vol. 38, No. 18, 1999 4173
0.14 mmol) and Bu4N I (66 mg; 0.18 mmol) were dissolved in warm
acetone (1.5 mL). The resulting dark brown solution was left at room-
temperature overnight and then kept at -10 °C for 6 h. The solution
was separated from well-shaped brown-red crystals by a pipet, and the
crystals were quickly washed with cold acetone (2 × 0.5 mL) and dried
by a nitrogen flow. The yield of the 1:1 acetone solvate was 125 mg
(76%). Anal. Calcd for C37H85I3IrNOP2: C, 37.2; H, 7.2; I, 31.9; N,
1.2. Found: C, 37.1; H, 7.2; I, 31.3; N, 1.1.
[PPN][(i-Pr3P)2Ir(H)Cl3]. In air, [(i-Pr3P)2Ir(H)Cl2] (97 mg; 0.17
mmol) was added to a solution of PPN Cl (100 mg; 0.17 mmol) in
acetone (5 mL). As the purple complex dissolved, a bright yellow
precipitate began to form. After CH2Cl2 (3 mL) was added to dissolve
all solids, the resulting solution was treated with ether (10 mL) and
left for 2.5 h. The yellow precipitate was separated, washed with ether
(3 × 3 mL), and dried under vacuum. The yield was 163 mg (85%).
Anal. Calcd for C54H73Cl3IrNP4: C, 56.0; H, 6.3; Cl, 9.2. Found: C,
56.4; H, 6.2; Cl, 9.3.
Experimental Section
All reagents and solvents were purchased from Strem, Johnson
Matthey, and Aldrich Chemical Companies, and used as received.
[(i-Pr3P)2Ir(H)Cl2].16 Triisopropylphosphine (3.2 mL; 16.8 mmol)
was added to an O2-free mixture of IrCl3‚nH2O (53.64% Ir; 2.00 g; 5.6
mmol), concentrated HCl (5.5 mL), and i-PrOH (40 mL), and the
resulting suspension was refluxed under N2 for 4 h. After water (10
mL) was added, the mixture was refluxed for 15 more min, left at room
temperature overnight, and then worked up in air. The dark-purple
crystals were filtered off, thoroughly washed with 2-propanol, and dried
under vacuum. The yield was 2.40 g (74%; it may vary from 60 to
1
87%). H NMR (CD2Cl2, 20 °C), δ: -48.9 (t, 1H, JP-H ) 11.8 Hz,
Ir-H); 1.4 (dd, 36H, J ) 7.9 and 14.5 Hz, CH3); 3.1 (m, 6H, CH).
31P{1H} NMR (CD2Cl2, 20 °C), δ: 33.2 (s).
[(i-Pr3P)2Ir(H)I2]. A solution of [(i-Pr3P)2Ir(H)Cl2] (0.358 g; 0.6
mmol), NaI (3.00 g; 20 mmol), and acetone (12 mL) was kept at room
temperature for 5 days. As the exchange occurred,13 solid NaCl
precipitated out of the orange solution. After water (40 mL) was added,
the dark green solid was filtered off in air, washed with water, and
dried under vacuum. The yield was 0.453 g (96%). Anal. Calcd for
X-ray Diffraction Studies. The structures of 1‚Me2CO and 2 were
determined using a Rigaku RU 300 diffractometer and the teXsan
structure solution package.18 Crystal and data parameters for the
structure determinations may be found in Table 1. Because no reliable
absorption correction programs exist for image plates, data were not
corrected for absorption. Absorption was minimized however by
selecting crystals with shapes as isotropic as possible and by using a
large number of redundant data for averaging. The final refinement
was done using the Z-refinement package19 and converged at R1 )
3.5% and Rw ) 3.9% for 1‚Me2CO and R1 ) 3.2% and Rw ) 3.8% for
C18H43I2IrP2: C, 28.2; H, 5.6; Cl, 0.0; I, 33.1. Found: C, 27.9; H, 5.3;
1
Cl, 0.01; I, 32.1. H NMR (CD2Cl2, 20 °C), δ: -47.5 (t, 1H, JP-H
)
11.8 Hz, Ir-H); 1.4 (dd, 36H, J ) 6.6 and 13.2 Hz, CH3); 3.6 (m, 6H,
CH). 31P{1H} NMR (CD2Cl2, 20 °C), δ: 30.3 (s).
[Bu4N][(i-Pr3P)2Ir(H)I3]‚Me2CO. In air, [(i-Pr3P)2Ir(H)I2] (106 mg;
(13) Studying the Cl/I exchange between [(i-Pr3P)2Ir(H)Cl2] and NaI in
2
2, where Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2 with w proportional to
1
acetone by H and 31P NMR revealed that the reaction is first order
[σ2(I) + 0.0009I2]-1/2. Atomic scattering factors were taken from the
International Tables for X-ray Crystallography, Vol. IV, including
anomalous terms for Ir, P, Cl, and I.
in the Ir complex and zero order in NaI (k ) 2.1‚10-5 s-1 at 25 °C).
The displacement of Cl ligands is stepwise, as indicated by the
observation of two intermediates, [(i-Pr3P)2Ir(H)Cl2(I)]- and [(i-Pr3P)2-
Ir(H)ClI2]-. As the reaction occurs, resonances from [(i-Pr3P)2Ir(H)-
Cl2(I)]- (1H NMR, -26.1 ppm, t, JP-H ) 13.2 Hz; 31P NMR, -2.2
ppm) and [(i-Pr3P)2Ir(H)ClI2]- (1H NMR, -25.5 ppm, t, JP-H ) 14.5
Hz; 31P NMR, -10.1 ppm) can be observed. These lines gradually
disappear, being replaced by the signals from 1.11a The rate-limiting
step is the dissociation of an inert Cl- trans to I or Cl from the 18e
octahedral anion. Like the Finkelstein reaction,14 the Cl/I exchange is
driven to completion by the insolubility of NaCl in acetone.15
(14) Finkelstein, H. Chem. Ber. 1910, 43, 1528.
Acknowledgment. We thank Drs. David L. Thorn and
Nadine de Vries for a stimulating discussion.
Supporting Information Available: Full details of crystallographic
studies, ORTEP drawings of 1 and 2, tables of fractional coordinates
and isotropic thermal parameters, anisotropic thermal parameters,
interatomic distances, intramolecular angles, intramolecular nonbonding
distances, and selected intermolecular distances. This material is
available free of charge via the Internet at http://pubs.acs.org.
(15) (a) Six 31P NMR singlet resonances of different intensities (δ ) -1.2
to -7.3 ppm) were observed for six15b possible species [(i-Pr3P)2Ir-
(H)X3]- (X ) Cl, Br) formed from [(i-Pr3P)2Ir(H)Cl2] and Bu4N Br
(1: 10) upon equilibration in acetone after 4 days at room temperature.
The incomplete conversion to [(i-Pr3P)2Ir(H)Br3]- was because unlike
NaCl, the acetone-soluble Bu4N Cl stayed in solution, participating
in the exchange. (b) [(i-Pr3P)2Ir(H)Cl3]- (one isomer, 2), [(i-Pr3P)2-
Ir(H)Br3]- (one isomer), [(i-Pr3P)2Ir(H)Cl2Br]- (two isomers), and [(i-
Pr3P)2Ir(H)ClBr2]- (two isomers).
(16) Over the past decade, this procedure has been used many times by
one of us (VVG) and found to be simpler and more efficient than any
of the literature methods,17 affording the hydride which is carbonyl-
free.17c In the solid state, the complex does not decompose in air for
years. In solution, however, this hydride is only moderately air-stable.
IC990068J
(17) (a) Werner, H.; Wolf, J.; Ho¨hn, A. J. Organomet. Chem. 1985, 287,
395. (b) Grushin, V. V.; Vymenits, A. B.; Vol’pin, M. E. J. Organomet.
Chem. 1990, 382, 185. (c) Capitani, D.; Mura, P. Inorg. Chim. Acta
1997, 258, 169.
(18) Crystal Structure Analysis Package; Molecular Structure Corpora-
tion: The Woodlands, TX, 1985 and 1992.
(19) Calabrese, J. C. Crystal Structure Analysis Package; E. I. DuPont de
Nemours & Co.: Wilmington, DE, 1994.