Competition between NH? HIr Intramolecular Proton - Hydride Interactions and NH?FBF3- or NH?O Intermolecular Hydrogen Bonds Involving [IrH(2-thiazolidinethione)4(PCy3)](BF4)2 and Related Complexes

Article abstract of DOI:10.1021/ic950997k

The reaction of IrH₅(PCy₃)₂ in acetone with 2 equiv of HBF₄ results in the formation of the air-stable complex [Ir(H)₂(PCy₃)₂(acetone)₂]BF ₄, 1. The reactio

Full text of DOI:10.1021/ic950997k

Inorg. Chem. 1996, 35, 1549-1555
1549
Competition between NH‚‚‚HIr Intramolecular Proton-Hydride Interactions and
-
NH‚‚‚FBF3 or NH‚‚‚O Intermolecular Hydrogen Bonds Involving
[IrH(2-thiazolidinethione)4(PCy3)](BF4)2 and Related Complexes
Wei Xu, Alan J. Lough, and Robert H. Morris*
Department of Chemistry, University of Toronto, 80 St. George Street,
Toronto, Ontario M5S 1A1, Canada
ReceiVed August 3, 1995X
The reaction of IrH5(PCy3)2 in acetone with 2 equiv of HBF4 results in the formation of the air-stable complex
[Ir(H)2(PCy3)2(acetone)2]BF4, 1. The reaction of 1 with an excess of 2-thiazolidinethione or 2-benzothiazolethione
in the presence of 2 equiv of HBF4 gives the complexes [Ir(H)(PCy3)(L)4](BF4)2 (2a, L ) 2-thiazolidinethione;
2b, L ) 2-benzothiazolethione). Complex 2a has an intramolecular NH‚‚‚H(Ir)‚‚‚HN interaction both in the
crystalline solid as determined by X-ray diffraction and in a CD2Cl2 solution as determined by the T1 method.
The dHH were determined to be 2.2 ( 0.1 Å in the solid state and 1.9 ( 0.1 Å in solution. The NH‚‚‚H(Ir)‚‚‚HN
-
interactions and NH‚‚‚F‚‚‚HN hydrogen bonds which involve FBF3 form a four-member ring in a butterfly
conformation. The nOe effect of the hydride on the NH proton is around 10%. A crystal of 2a is in the triclinic
space group P1h with a ) 11.426(3), b ) 11.922(3), c ) 19.734(4) Å, R ) 87.05(1)°, â ) 88.23(1)°, γ ) 75.50-
(1)°, V ) 2599(1) Å3, and Z ) 2 at T ) 173 K; full-matrix least-squares refinement on F2 was performed for
10 198 independent reflections; R[F2>2σ(F2)] ) 0.0480, Rw(F2) ) 0.099. The formation of the NH‚‚‚HIr proton-
-
hydride interaction is as favorable as the formation of intermolecular hydrogen bonds NH‚‚‚FBF3 or NH‚‚‚O
hydrogen bonds with OPPh3 or H2O in CD2Cl2. A similar NH‚‚‚HIr interaction also has been observed in the
complexes [Ir(H)2(PCy3)2(L)2]BF4 (3a, L ) 2-thiazolidinethione; 3b, L ) 2-benzothiazolethione) but not in the
complexes with L ) NH2NH2 (3c) and L ) NH3 (3d). Both the NH and IrH protons are deuterated when a
solution of 2 or 3 in C6D6 is exposed to 1 atm of D2 gas or D2O.
Introduction
interactions are favored over intramolecular IrCl‚‚‚HN interac-
tions in certain cases and that the ligand trans to the hydride
Recently intramolecular H‚‚‚H interactions of the new types
OH‚‚‚H(Ir) and NH‚‚‚H(Ir) have been reported.1-3 Such
hydride-proton interactions are thought to be important in the
heterolytic splitting of dihydrogen and the formation of inter-
mediate (dihydrogen)metal complexes.4,5 We report here a
study of the hydride-proton interactions NH‚‚‚H(Ir)‚‚‚HN and
IrH‚‚‚HN involving thiazolethione-type ligands and the crystal
structure of [IrH(2-thiazolidinethione)4(PCy3)](BF4)2‚CH2-
Cl2‚Et2O which contains three types of hydrogen-bonded units,
namely NH‚‚‚H(Ir)‚‚‚HN, NH‚‚‚F(B), and NH‚‚‚F(B)‚‚‚HN.
The strength of such proton-hydride interactions has been
addressed in a variety of ways. Stevens et al.1 noted that there
appears to be a 2.40(1) Å proton-hydride interaction (IrH‚‚‚HO)
in the complex cis-[Ir(H)(HO)(PMe3)4]PF6 in the crystal while
there is no analogous IrH‚‚‚HS interaction in the complex cis-
[Ir(H)(HS)(PMe3)4]PF6. Peris et al.3a have measured the barrier
to C-NH2 rotation when this group interacts with a hydride
ligand as an IrH‚‚‚HNH-C unit and compared it to intramo-
lecular IrX‚‚‚HN interactions. They found that IrH‚‚‚HN
can influence the strength of the proton-hydride interaction.3
We have found that the strong hydrogen-bond acceptor OPPh3
can disrupt the IrH‚‚‚HN bonding in [Ir(H‚‚‚HNC5H4S)2-
(PCy3)2]+ 2c but not in [Ir(H‚‚‚HNC5H4S)(NC5H4S)(PPh3)2]+.2a
In this paper we probe the strength of IrH‚‚‚HN interactions by
reaction with OPPh3.
Experimental Section
All preparations were carried out under a dry argon atmosphere using
Schlenk techniques. Benzene, diethyl ether, and hexanes were dried
over and distilled from sodium. Acetone was dried over potassium
carbonate. Dichloromethane was distilled from calcium hydride. Deu-
terated solvents were dried over Linde type 4Å molecular sieves and
degassed prior to use. Tricyclohexylphosphine, triphenylphosphine,
an 85% solution of HBF4‚Et2O complex, 2-thiazolidinethione, and
2-benzothiazolethione were used as purchased from Aldrich Chemical
Co. Inc. The complex IrH5(PCy3)2 was prepared as described else-
where.6
NMR spectra were recorded on Varian Unity-400 (400 MHz for
1H, 61.4 MHz for 2H) and Varian Gemini 300 (300 MHz for 1H, 282.3
MHz for 19F, 121.4 MHz for 31P) spectrometers. All 31P NMR spectra
were recorded with proton decoupling. 31P NMR chemical shifts were
measured relative to 85% H3PO4 as an external reference, and 19F NMR
chemical shifts were measured relative to CFCl3 as an external
reference. 1H chemical shifts were measured relative to partially
deuterated solvent peaks but are reported relative to tetramethylsilane.
2H chemical shifts were referenced to natural-abundance deuterated
solvent peaks. T1 measurements were made at 400 or 300 MHz, as
specified, using the inversion recovery method. The temperatures of
the probes were calibrated with the temperature dependence of the
chemical shifts of MeOH. Microanalyses were performed by Guelph
Chemical Laboratories Ltd., Ontario, Canada.
X Abstract published in AdVance ACS Abstracts, February 15, 1996.
(1) Stevens, R. C.; Bau, R.; Milstein, D.; Blum, O.; Koetzle, T. F. J. Chem.
Soc., Dalton Trans. 1990, 1429.
(2) (a) Park S.; Lough, A. J.; Morris, R. H. Inorg. Chem., in press. (b)
Park, S.; Ramachandran, R.; Lough, A. J.; Morris, R. H. J. Chem.
Soc., Chem. Commun. 1994, 2201-2202. (c) Lough, A. J.; Park S.;
Ramachandran, R.; Morris, R. H. J. Am. Chem. Soc. 1994, 116, 8356-
8357.
(3) (a) Peris, E.; Lee, J. C., Jr.; Rambo, J. R.; Eisenstein, O.; Crabtree, R.
H. J. Am. Chem. Soc. 1995, 117, 3485. (b) Lee, J. C.; Peris, E.;
Rheingold, A. L.; Crabtree, R. H. J. Am. Chem. Soc. 1994, 116,
11014-11019.
(4) (a) Jessop, P. G.; Morris, R. H. Inorg. Chem. 1993, 32, 2236-2237.
(b) Schlaf, M.; Lough, A. J.; Morris, R. H. Organometallics 1993,
12, 3808-3809.
(5) Jessop, P. G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155.
(6) Brinkmann, S.; Ramachandran, R.; Morris, R. H. In preparation.
0020-1669/96/1335-1549$12.00/0 © 1996 American Chemical Society

1550 Inorganic Chemistry, Vol. 35, No. 6, 1996
Xu et al.
Preparation of [Ir(H)2(PCy3)2(acetone)2]BF4, 1. IrH5(PCy3)2 (1
g, 1.32 mmol) was suspended in acetone (20 mL) in a Schlenk flask
under argon. An Et2O solution of ca. 2 equiv of HBF4 (85% ethyl
ether complex, 0.4 mL, 2.6 mmol) was added slowly (ca. 5 min) to the
solution at room temperature. After completion of the addition, the
solution was stirred for a further 10 min. The solvent was then partially
removed under vacuum. Hexane (30 mL) was added to the mixture to
produce a white powder. The white powder was filtered off, washed
with n-hexane several times, and dried under vacuum. The yield was
90% (1.1 g). NMR (CD2Cl2, δ). 31P{1H} 38.2 (s); 19F{1H} -148.8
Table 1. Crystal Data for 2a
empirical formula: C30H54IrN4PS8B2F8‚CH2Cl2‚C4H10O
fw
1283.09
P1h
11.426(3)
11.922(3)
19.734(4)
2599(1)
1.640
crystal system
λ, Å
R, deg
â, deg
γ, deg
Z
triclinic
0.71073
87.05(1)
88.23(1)
75.50(1)
2
173(2)
5.32-52.00
0.099
space group
a, Å
b, Å
c, Å
V, Å3
D
calcd, mg m-3
T, K
µ(Mo KR), mm-1
3.086
0.0480
2θ, deg
1
2
b
Ra
R2w
(s, br); H -31.3 (t, 2H, JPH ) 16.1 Hz, Ir-H), 1.2-2.1 (m, 66H,
P(C6H11)3), 2.1 (s, 12H, C3H6O). Anal. Calc for C42H80BF4-
IrO2P2‚0.1HBF4, 1: C, 52.2; H, 8.3. Found: C, 51.9; H, 8.3.
a R ) ∑(|Fo| - |Fc|)/∑|Fo|. R2w ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo )2]}1/2
.
b
2
Preparation of [Ir(H)(PCy3)(L)4](BF4)2 (2a, L ) 2-Thiazolidine-
thione; 2b, L ) 2-Benzothiazolethione). A mixture of [Ir(H)2(PCy3)2-
(acetone)2]BF4, 1 (0.2 g, 0.21 mmol), L (excess, ≈1 mmol) and Et2O
solution of ca. 2 equiv of HBF4 (85% diethylether complex, 0.65 mL,
0.42 mmol) in toluene (10 mL) were stirred under Ar for 2 h. Small
amounts of insoluble impurities were filtered off. Then Et2O (20 mL)
was layered on the top of the solution. This was cooled in a refrigerator
overnight. The next day, the resulting yellow crystalline 2 was filtered
and washed with n-hexane several times and dried under vacuum. NMR
(CD2Cl2, δ) for [Ir(H)(PCy3)(2-thiazolidinethione)4](BF4)2, 2a (yellow
solid, yield 70%): 31P{1H} 29.4 (s); 19F{1H} -149.6 (s, 6F), -149.5
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2a
Ir-H(Ir)
1.44(6)
2.10(10)
0.79(8)
0.92(9)
2.27(8)
2.16(8)
2.351(2)
2.499(2)
Ir-P
2.326(2)
2.27(9)
0.83(7)
0.75(7)
2.15(8)
2.343(2)
2.434(2)
H(Ir)‚‚‚H(N1)
N(1)-H(1A)
N(3)-H(3A)
F(2)‚‚‚H(N1)
F(8)‚‚‚H(N4)
Ir-S(2)
H(Ir)‚‚‚H(N2)
N(2)-H(2A)
N(4)-H(4A)
F(2)‚‚‚H(N2)
Ir-S(1)
Ir-S(4)
Ir-S(3)
H(N1)‚‚‚H(Ir)‚‚‚H(N2) 105(4)
H(N1)‚‚‚F(2)‚‚‚H(N2) 103(4)
1
2
(s, 2F); H -18.7 (d, H, JHH ) 16.8 Hz, Ir-H), 1.1-2.5 (m, 33H,
Ir-H(Ir)‚‚‚H(N1)
H(Ir)-Ir-P
116(4)
83(3)
Ir-H(Ir)‚‚‚H(N2)
H(Ir)-Ir-S(1)
114(4)
93(3)
97(3)
3
P(C6H11)3), 3.7 (m, 8H, -SCH2CH2N-), 4.33 (t, 4H, JHH ) 8 Hz,
3
-SCH2CH2N-), 4.22 (t, 2H, JHH ) 8 Hz, -SCH2CH2N-), 4.20 (t,
P-Ir-S(1)
91.80(6) H(Ir)-Ir-S(2)
90.91(6) S(1)-Ir-S(2)
79(3)
3
2H, JHH ) 8 Hz, -SCH2CH2N-), 8.95, 8.94 (br, 2s, 2H, NH), 9.23
P-Ir-S(2)
170.35(6)
61.70(5)
88.82(6)
101.42(6)
84.22(6)
63(2)
(br, s, 2H, NH‚‚‚H-Ir). Anal. Calc for C30H54B2F8IrN4PS8‚2C7H8‚C4-
H10O, 2a: C, 41.7; H, 5.8; N 4.1. Found: C, 41.5; H, 6.2, N, 4.2.
NMR (CD2Cl2, δ) for [Ir(H)(PCy3)(2-benzothiazolethione)4](BF4)2, 2b
H(Ir)-Ir-S(4)
S(1)-Ir-S(4)
H(Ir)-Ir-S(3)
S(1)-Ir-S(3)
S(4)-Ir-S(3)
P-Ir-S(4)
91.51(6) S(2)-Ir-S(4)
175(3)
P-Ir-S(3)
1
2
(yellow solid, yield 66%): 31P{1H} 28.7 (s); H -19.8 (d, H, JHH
)
86.16(6) S(2)-Ir-S(3)
96.76(6) Ir-H(Ir)-P
17 Hz, Ir-H), 1.1-2.5 (m, 33H, P(C6H11)3), 7-8 (m, 16H, Ar H),
8.55, 8.45 (br, 2s, 2H, NH), 8.6 (br, s, 2H, NH‚‚‚H-Ir). Anal. Calc
for C46H54B2F8IrN4PS8, 2b: C, 42.0; H, 4.1; N 4.26. Found: C, 41.6;
H, 5.1; N, 3.3.
monochromated Mo KR radiation (λ ) 0.710 73 Å). The ω-scan
technique was applied using variable scan speeds (6-60°/min in ω).
The intensities of 3 standard reflections measured every 97 reflections
showed no decay. Data were corrected for Lorentz, and polarization
effects. A semiempirical absorption correction (minimum and maxi-
mum corrections were 0.5998 and 0.8042) was carried out using
Preparation of [Ir(H)2(PCy3)2(L)2]BF4 (3a, L ) 2-Thiazolidine-
thione; 3b, L ) 2-Benzothiazolethione; 3c, L ) NH2NH2; 3d, L )
NH3). A mixture of [Ir(H)2(PCy3)2(acetone)2]BF4, 1 (0.2 g, 0.21 mmol),
and L (0.42 mmol) in CH2Cl2 (10 mL) was stirred in a Schlenk flask
under argon for 2 h. By an isolation procedure similar to that for 2,
yellow crystalline 3 was obtained. NMR (CD2Cl2, δ) for [Ir(H)2(PCy3)2-
(2-thiazolidinethione)2]BF4, 3a (yellow solid, yield 75%): 31P{1H} 22.0
a
SHELXA-90 (in SHELXL-93).7
The position of the Ir atom was determined from a Patterson map,
and the other non-hydrogen atoms were located from successive
difference Fourier maps. Non-hydrogen atoms were refined with
anisotropic thermal parameters by least-squares calculations to minimize
∑w(Fo2 - Fc2) where w ) 1/(σ2(Fo) + (0.0236P)2 + 3.877P) and P )
(Fo2 + 2Fc2)/3. Hydrogen atoms were included in calculated positions
(C-H ) 0.96 Å) with Uiso of 0.042(3) Å2 for ring hydrogens, 0.092-
(27) A2 for dichloromethane hydrogens, and 0.158(20) Å2 for the
hydrogens of the diethyl ether solvate. Hydrogen atoms bonded to Ir
and N were refined with isotropic thermal parameters. Crystal data,
data collection details, and least squares parameters are listed in Table
1. All calculations were performed, and diagrams were created on a
486-66 personal computer using SHELXL-93 and SHELXTL-PC V4.2.7
Atomic coordinates and other data concerning the crystal structures
are given in the Supporting Information. The structure of 2a, including
the crystallographic labeling scheme, is shown in Figure 1, and selected
bond distances and angles are listed in Table 2.
2
(s); 1H -19.04 (t, 2H, JPH ) 15 Hz, Ir-H), 1.0-2.1 (m, 66H,
P(C6H11)3), 3.6 (t, 4H, -SCH2CH2N-), 4.2 (t, 4H, -SCH2CH2N-),
11.0 (br, s, 2H, NH). Anal. Calc for C42H78BF4IrN2P2S4‚0.5CH2Cl2,
3a: C, 45.5; H, 7.2; N, 2.6. Found: C, 45.2; H, 5.6; N, 2.6. NMR
(CD2Cl2, δ) for [Ir(H)2(PCy3)2(2-benzothiazolethione)2]BF4, 3b (yellow
1
2
solid, yield 71%): 31P{1H} 16.2 (s); H -19.2 (t, 2H, JPH ) 15 Hz,
Ir-H), 1.0-2.1 (m, 66H, P(C6H11)3), 7.2-8.0 (m, 8H, Ar), 12.0 (br, s,
2H, NH). Anal. Calc for C50H78BF4IrN2P2S4, 3b: C, 51.1; H, 6.7; N,
2.4. Found: C, 51.2; H, 7.0; N 1.7. NMR (CD2Cl2, δ) for [Ir(H)2-
(PCy3)2(NH2NH2)2]BF4, 3c (yellow solid, yield 79%): 31P{1H} 16.5
(s); 1H -24.2 (t, 2H, 2JPH ) 15 Hz, Ir-H), 1.0-2.1 (m, 66H, P(C6H11)3),
3.6 (br, s, 4H, Ir-NH2NH2), 4.9 (br, s, 4H, Ir-NH2NH2). Anal. Calc
for C36H76BF4IrN4P2, 3c: C, 49.4; H, 8.5; N, 6.18. Found: C, 49.3;
H, 8.0; N, 5.6. NMR (CD2Cl2, δ) for [Ir(H)2(PCy3)2(NH3)2]BF4, 3d
1
2
(yellow solid, yield 77%): 31P{1H} 17.5 (s); H -21.9 (t, 2H, JPH
)
16 Hz, Ir-H), 1.0-2.1 (m, 66H, P(C6H11)3), 3.0 (br, s, 6H, NH3).
A Typical NH‚‚‚HIr Interception Experiment. A CD2Cl2 (1 mL)
solution of complex 2a (0.05 g) and OPPh3 (0.05 g) or H2O (0.005 g)
was placed in an NMR tube under Ar and was shaken and left for 0.5
h to reach equilibrium. (a) NMR (δ) of the solution with the OPPh3:
Results and Discussion
Preparation of the Complexes. Treatment of IrH5(PCy3)2
with 2 equiv of HBF4 in acetone gives a clear solution (see eq
1).8 The analytically pure, air-stable complex [Ir(H)2(PCy3)2-
1H -18.7 (d, HIr, JPH ) 16.8 Hz), -20.6 (d, HIr, JPH ) 19.2 Hz); 31
P
30.0 (s, br), 28.4 (s, OPPh3). (b) NMR (δ) of the solution with H2O:
1H -18.7 (d, HIr, JPH ) 16.5 Hz), -20.7 (d, HIr, JPH ) 18.8 Hz); 31
30.0 (s, br).
P
(7) (a) Sheldrick, G. M. SHELXL-93: Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1994. (b)
Sheldrick, G. M. SHELXTL PC; Siemens Analytical X-ray Instruments,
Inc.: Madison, WI, 1990.
(8) The method of protonation of IrH5(PPh3)2 to give [Ir(H)2(acetone)2-
(PPh3)2]+ has been reported: Hlatky, G. G.; Crabtree, R. H. Coord.
Chem. ReV. 1985, 65, 1 and references cited therein.
X-ray Crystal Structure Analysis of 2a. Crystals of 2a were
prepared by slow diffusion of diethyl ether into a CH2Cl2 (1.5 mL)
solution of complex 2a (200 mg) under 1 atm of Ar.
A pale yellow crystal was mounted on a glass fiber. Intensity data
were collected on a Siemens P4 diffractometer at 173 K, using graphite-

Intramolecular Proton-Hydride Interactions
Inorganic Chemistry, Vol. 35, No. 6, 1996 1551
(1)
(acetone)2]BF4 (1) crystallizes from the acetone solution in 2
h. A nearly quantitative yield can be achieved when 1 is
separated from a concentrated acetone solution by addition of
n-hexane. Other complexes of the type [Ir(H)2(PR3)2(L)2]BF4
(R ) Ph, Cy) are well known.9
When complex 1 was treated with an excess of 2-thiazoli-
dinethione or 2-benzothiazolethione in CH2Cl2 in the presence
of 2 equiv of HBF4 for 2 h, a clear yellow solution was obtained
(see eq 2). The yellow complexes [Ir(H)(PCy3)(L)4](BF4)2 (2a,
Figure 1. View of 2a showing the atomic labeling scheme. Thermal
ellipsoids are at the 50% probability level. For clarity, hydrogen atoms
are shown as small spheres.
(2)
L ) 2-thiazolidinethione; 2b, L ) 2-benzothiazolethione) can
be obtained by slowly diffusing diethyl ether into the solution
followed by washing with hexanes and drying under vacuum.
The analytical and spectroscopic data are consistent with the
proposed structure 2.
The addition of 2 equiv of L to a C6H6 solution of 1 at room
temperature under Ar atmosphere produces the complexes [Ir-
(H)2(PCy3)2(L)2]BF4 (3a, L ) 2-thiazolidinethione; 3b, L )
2-benzothiazolethione; 3c, L ) NH2NH2; 3d, L ) NH3) as
yellow solids after precipitation of the product from the solution
by addition of ethyl ether (see eq 3). The analytical and
spectroscopic data are consistent with the proposed structure 3.
Figure 2. Difference electron density map around the Ir and N centers
showing the positions of hydrogen atoms (calculated in the plane of
H(1Ir), H(1A), and H(2Aa) with contours every 0.1 e Å-3).
dinethione ligands coordinated to the iridium atom at cis
positions to the hydride are planar and embrace the Ir-H
hydride with close NH‚‚‚HIr contacts at an H‚‚‚H distance of
2.2 ( 0.1 Å. The hydride on iridium and the hydrogen on the
protonated nitrogens N1, N2 (Figure 2) and N4 are well-defined
in electron difference maps. Selected bond lengths and bond
angles are listed in Table 2.
(3)
One of the fluorine atoms (F2) of a BF4 anion forms two
weak hydrogen bonds (H‚‚‚F‚‚‚H) at distances of 2.15(8) and
2.27(8) Å with the two NH units which are interacting with
hydride. The NH‚‚‚H(Ir)‚‚‚HN interactions and NH‚‚‚F‚‚‚HN
hydrogen bonds form a four-membered ring in a butterfly
conformation (see Figure 1). A weaker interaction of this type
with H‚‚‚F distances of 2.4 Å is present in the structure of [IrH-
(‚‚‚HNC5H4S)2(NC5H4S)(PCy3)]BF4.2b The observation of a
bifurcated hydrogen bond IrH‚‚‚H(N)‚‚‚F(B) involving one NH
X-ray Diffraction Study of 2a at 173 K. The molecular
structure of 2a contains an iridium atom in a distorted octahedral
environment (Figure 1). The iridium atom is surrounded by
one PCy3 ligand, four 2-thiazolidinethione ligands bonded Via
sulfur atoms in a monodentate fashion, and a hydride ligand
cis to the PCy3 ligand. The phosphorus atom of the tricyclo-
hexylphosphine and the sulfur atom trans to it are slightly bent
toward the hydride. The H-N-C-S- units of two 2-thiazoli-
-
group has also been reported.2a The other BF4 anion in the
lattice forms a strong hydrogen bond with another free NH group
(F‚‚‚H distance of 2.16(8) Å). No close NH‚‚‚S contact is
observed in the structure, and hence there is no indication of
an NH‚‚‚S hydrogen bond. In the S-bonded 2-thiazolidinethione
ligand, the proton is located only on nitrogen and not on a sulfur.
The double-bond character is delocalized on both (S)C-N
and S-C(S) bonds, although a SdC(S) double bond is
drawn in the molecular structures of 2 and 3. Both bond
(9) (a) Crabtree, R. H.; Lavin, M.; Bonneviot, L. J. Am. Chem. Soc. 1986,
108, 4032. (b) Crabtree, R. H.; Mellea, M. F.; Mihelcic, J. M.; Sen,
A.; Chebolu, V. Inorg. Synth. 1989, 26, 122-126. (c) Luo, X.-L.;
Schulte, G. K.; Crabtree, R. H. Inorg. Chem. 1990, 29, 682.

1552 Inorganic Chemistry, Vol. 35, No. 6, 1996
Table 3. N-C and S-C Bond Distances of Complex 2a
Xu et al.
a:a N-C(S)
b:a N-C(C)
c:a S-C(S)
d:a S-C(S)
e:a S-C(C)
N1-C1
1.304(9)
1.293(9)
1.317(9)
1.294(8)
N1-C3
1.470(9)
1.449(9)
1.448(8)
1.466(9)
S1-C1
1.690(7)
1.701(7)
1.688(7)
1.702(7)
S5-C1
1.741(6)
1.740(7)
1.730(7)
1.727(7)
S5-C2
S6-C11
S7-C8
S8-C5
1.828(7)
1.829(7)
1.826(7)
1.797(7)
N2-C4
N3-C7
N4-C10
N2-C6
N3-C9
N4-C12
S2-C4
S3-C7
S4-C10
S6-C10
S7-C7
S8-C4
a The bond types refer to the structure above.
Table 4. Proton Minimum T1 Values (at 400 MHz) of Complexes 2 and 3 in CD2Cl2, Calculated NH‚‚‚HIr Distances, and nOe Enhancements
complex
T1(min)(IrH), s
T, K
dNH‚‚‚HIr, Å
T1(min)(NH‚‚‚H), s
T, K
nOe(NH‚‚‚H-Ir), %
2a
2b
3a
3b
3c
0.18 ( 0.01
0.19 ( 0.01
0.22 ( 0.01
0.23 ( 0.01
0.24 ( 0.01
233
243
213
213
213
1.9 ( 0.1
2.0 ( 0.1
2.0 ( 0.1a
2.1 ( 0.1a
0.23 ( 0.01
0.24 ( 0.01
0.24 ( 0.01
233
243
213
14.3
13.2
10
8.5
0
a The relaxation contributions of the four cyclohexyl protons at about 2.4 Å have been subtracted.
distances of N-C(S) and S-C(S) are considerably shorter
than the corresponding bond distances of N-C(C) and S-C(C)
(see Table 3). The Ir-S bond distances are also influenced by
the NH‚‚‚H(Ir)‚‚‚HN interactions. Sulfur atom S(3) which is
trans to the hydride and sulfur atom S(4) which is cis to the
hydride have significantly longer Ir-S bonds (2.499(2) and
2.434(2) Å, respectively) than the sulfur atoms of 2-thiazoli-
dinethione which have NH‚‚‚HIr interactions (2.343(2) and
2.351(2) Å, respectively). The trans influence of the hydride
causes Ir-S(3) to be the longest distance.
1
NMR Studies of Complexes 2. The H NMR study of
complexes 2 provides additional evidence for the existence of
the NHa‚‚‚H(Ir)‚‚‚HaN interaction in solution (refer to Scheme
1 for labeling of Ha, Hb, and Hc). The hydride of 2a has a very
short minimum T1 value of 0.18 s (at 400 MHz, 243 K), and
this implies a strong H‚‚‚H interaction. When the relaxation
contributions of the two cyclohexyl protons at about 2.3 Å are
subtracted from the hydride relaxation rate, the calculated
hydride to Ha distance is 1.9 ( 0.1 Å.10,11 Interestingly, the
protons bonded to nitrogen atoms have quite different minimum
T1 values. The two NHa protons with a resonance at 9.23 ppm
have a shorter minimum T1 value (0.23 s, at 400 MHz, 243 K)
than that of the other two NH protons (Hb, Hc) with resonances
at 8.94 and 8.95 ppm with the same T1(min) value (0.35 s, at
400 MHz, 243 K). The NHa protons are considered to have an
interaction with the hydride which leads to efficient dipole-
dipole relaxation. The NHa protons are close to three types of
dipolar nuclei: 14N, 19F, and 1H (hydride). When the contribu-
tions of the one 14N nucleus at 0.95 Å and one 19F nucleus at
2.2 Å to the rate of dipolar relaxation are subtracted, the
calculated (Ir)H to HN distance is 1.9 ( 0.1 Å, in agreement
with the distance calculated on the basis of the hydride T1(min)
value. This NH‚‚‚HIr distance estimated by the T1 method is
close to the H‚‚‚H distance revealed by the X-ray structural
analysis of 2.2 Å. The presence of the NH‚‚‚H(Ir)‚‚‚HN
interaction in solution was also confirmed by the nOe difference
experiments. By selective irradiation of the hydride resonance,
a 14% nOe enhancement of the NHa peak at 9.23 ppm was
Figure 3. Variable-temperature NMR study of 2a in CD2Cl2: (a) 19
F
NMR (282 MHz); (b) 1H NMR (300 MHz) in the hydride region (-17.5
to -19.0 ppm).
observed while there was less than a 3% nOe enhancement for
the NHb and NHc protons which have no close contact with the
hydride (see Table 4). Very similar results were obtained for
complex 2b (see Table 4).
(10) Desrosiers, P. J.; Cai, L.; Lin, Z.; Richards, R.; Halpern, J. J. Am.
Chem. Soc. 1991, 113, 4173-4184.
(11) Sudmeier, J. L.; Anderson, S. E.; Frye, J. S. Concepts Magn. Reson.
1990, 2, 197-212.

Intramolecular Proton-Hydride Interactions
Inorganic Chemistry, Vol. 35, No. 6, 1996 1553
Scheme 1
Although the NHb and NHc protons have longer minimum
T1 values than the NHa protons, the minimum T1 values of the
NHb and NHc protons are still shorter than would be expected
for an NH proton which is only relaxed by the one 14N nucleus
at 0.95 Å (minimum T1 value of ca. 0.6 s). The (B)F‚‚‚HN
hydrogen bond should have an important contribution to the
dipole-dipole relaxation of HN. After subtracting the contribu-
tions of the one 14N nucleus at 0.95 Å to the dipole-dipole
relaxation, the calculated NH‚‚‚F(B) distance is 2.2 ( 0.1 Å
which is the same as the distance revealed by the X-ray analysis
(2.16(8) Å). Therefore, the BF4 anions are associated with
these NH groups in solution.
-
The X-ray structure analysis of 2a reveals that the BF4 anions
form hydrogen bonds at two different sites. However the
variable-temperature 19F NMR study of 2a in CD2Cl2 solution
-
indicates that the BF4 anions which produce a sharp peak at
-149.6 ppm are apparently rapidly moving among all of the
possible hydrogen-bonding sites in solution at room temperature
(see Figure 3a). Even at -90 °C, the fluxional process of the
BF4- cannot be frozen out although some new small resonances
at -146.5 and -147.4 ppm begin to grow in. With decreasing
temperature, the 19F resonances become very broad. The
variable-temperature 1H NMR study of complex 2a in CD2Cl2
confirms that at least one exchange process is occurring. At
lower temperature (<-40 °C), the doublet at -18.7 ppm splits
into two doublets (see Figure 3b) probably due to the BF4- anion
forming hydrogen bonds at different NH sites (see Scheme 1).
The NH proton resonances at 9.23, 8.95, and 8.94 ppm also
shift with decreasing temperature and become broad multiplets
at -80°C. It is believed that the hydrogen bonds between the
-
BF4 anion and the NH protons of the 2-thiazolidinethione
ligands are more fully formed at low temperature as shown in
Scheme 1 to generate two or even more different hydride NMR
resonances and two or more sets of NH proton resonances.
The NH‚‚‚H(Ir)‚‚‚HN interaction in 2 is comparable in
strength to that of NH‚‚‚O hydrogen bonds. In the presence of
a better hydrogen-bond acceptor such as OPPh3, H2O, or THF,
the NH‚‚‚HIr interaction is partly intercepted (see Figure 4). A
new species with a hydride resonance at -20.6 ppm (d, JPH
)
19.2 Hz) appears, and its intensity increases with an increasing
ratio of OPPh3 to 2a. However, the NH‚‚‚(Ir)‚‚‚HN interaction
cannot be completely disrupted even in the presence of excess
OPPh3. That the pattern of the new hydride resonance at -20.6
ppm does not change with decreasing temperature (see Figure
4d) implies that all the NH interactions with the iridium hydride
-
and the fluorine of the BF4 anions have been replaced by
hydrogen bonds with OPPh3 (see structure A). The competition
Figure 4. 1H NMR spectra (400 MHz) of 2a in the hydride region
(-17.5 to -21.5 ppm) in CD2Cl2: (a) without OPPh3 at 0 °C; (b) with
OPPh3 at 0 °C; (c) with OPPh3 at -20 °C; (d) with OPPh3 at -80 °C.
A

1554 Inorganic Chemistry, Vol. 35, No. 6, 1996
Xu et al.
between the two types of hydrogen bonds, NH‚‚‚H(Ir)‚‚‚HN
and O‚‚‚HN reaches equilibrium at room temperature in a slow
exchange mode. At low temperature (-20 °C), the equilibrium
favors the formation of the O‚‚‚HN hydrogen bond (see Figure
4b,c). The pattern of the hydride resonance at -18.7 ppm still
changes with decreasing temperature to give several doublet
resonances of hydrides, apparently due to the formation of
complex hydrogen-bonded structures. The disappearance of the
nOe enhancement of the NH resonances when the new hydride
resonance at -20.6 ppm was irradiated and the longer minimum
T1 value (0.34 s, at 400 MHz, 273 K) of this hydride resonance
are strong evidence for the breaking of the NH‚‚‚HIr interac-
tions. Therefore, the intramolecular NH‚‚‚(Ir)‚‚‚HN interaction
has a stability similar to that of an intermolecular NH‚‚‚O
hydrogen bond which should be favored on the basis of enthalpy
of formation but disfavored on the basis of entropy. These
H‚‚‚H interactions are more stable than the interionic NH‚‚‚FBF3
hydrogen bonds. They are also favored over NH‚‚‚S intramo-
lecular hydrogen bonds which might have formed between the
thiazolidinethione moieties.
Scheme 2
Scheme 3
NMR Studies of Complexes 3. The same NH‚‚‚HIr interac-
tions have been detected for complexes 3a and 3b in solution
(see diagram B for structure of 3b). The T1 and nOe studies
about 5%. After 12 h, about 100% of NH and 30% of (Ir)H
have been deuterated. 2H NMR experiments confirm that there
is deuteration of these two sites. The deuteration processes of
3a and 3b under D2 gas are much faster than that of 2. The
deuteration of 3a or 3b is finished in less than 10 min at the
NH sites and about 6 h at the (Ir)H sites. The NH proton is
deuterated much faster than the iridium hydride. In contrast,
the deuteration of 3c or 3d is much slower, although a partial
deuteration (∼20%) has been observed after a 24 h exposure
to D2 gas. Therefore, it is quite possible that the H/D exchange
of 2, 3a, and 3b with D2 results from the formation of an
intermediate dihydrogen complex by dissociation of one thione
ligand, probably the one trans to the hydride. The exchange
between acidic dideuterium and the active protons of amides
results in the deuteration of NH protons as shown in Scheme
2. Since the deuteration of the NH is much faster than that of
the hydride, the dideuterium is thought to coordinate trans to
the hydride. Otherwise the dideuterium and hydride exchange
would be expected to be very fast if the deuterium and hydride
were in cis positions.5
The NH‚‚‚H(Ir)‚‚‚HN interaction may be responsible for the
deuteration of the iridium hydride. Initially, the NH‚‚‚H-
(Ir)‚‚‚HN interaction generates a dihydrogen intermediate via
intramolecular proton transfer from NH to IrH. Then the
exchange between the two tautomers (see Scheme 3) leads to
deuteration of the hydride. This mechanism has been proposed
previously to explain the H/D exchange reactions of [Ir-
(H‚‚‚HNC5H4S)2(PCy3)2]BF4.2c
B
(see Table 4 for details) of 3a and 3b verify the existence of
the NH‚‚‚HIr interactions. The calculated NH‚‚‚HIr distances
by the minimum T1 method are listed in Table 4. Crystals of
these complexes lose solvent easily, making them unsuitable
for X-ray analysis. The observation of a partially resolved
splitting of 4 Hz in the hydride resonance of 3b may be due to
a coupling to H on nitrogen and indicates a close contact
between NH and hydride. A similar 1JNH‚‚‚HIr coupling constant
has been observed by Crabtree and co-workers.3 The NH‚‚‚-
HIr interaction in 3a or 3b is weaker than NH‚‚‚O hydrogen
bonds. In the presence of a better hydrogen-bond acceptor such
as OPPh3 or H2O, the NH‚‚‚HIr interaction is intercepted
completely. As in the case of complex 2a, the disappearance
of the nOe enhancement of the NH resonances when the hydride
of complex 3a was irradiated, the disappearance of the possible
coupling between the NH proton and the Ir-H resonance, and
the longer minimum T1 value (0.35 s at 400 MHz, 263 K) of
the hydride resonance are strong evidence for the intercep-
tion.
When the hydride resonance of complex 3c is irradiated in
CD2Cl2 at room temperature, no nOe enhancement of the NH
proton resonances is observed. Instead, CH proton resonances
of the PCy3 ligand are enhanced. When the terminal amine of
the hydrazine ligand is irradiated, a strong nOe enhancement is
observed on the NH2 coordinated to Ir. Therefore, there is no
intramolecular NH‚‚‚HIr interaction (see B) in 3c. Apparently,
the intramolecular NH‚‚‚N hydrogen bonds are stronger than
the intramolecular NH‚‚‚HIr interactions.
Conclusions
The intramolecular NH‚‚‚H(Ir)‚‚‚HN interaction with dHH
≈
1.9 is established to exist in complexes 2a ([IrH(2-thiazoli-
dinethione)4(PCy3)](BF4)2) and 2b. These NH‚‚‚HIr interactions
are as stable as intermolecular NH‚‚‚O hydrogen bonds in
solution and more stable than intermolecular NH‚‚‚F(B) hy-
-
drogen bonds to the BF4 anions. The deuteration of the NH
Hydrogen/Deuterium Exchange Reactions. When a solu-
tion of either complex 2a or 2b in CD2Cl2 is exposed to D2 (1
atm) or is mixed with D2O (excess) for 5 min, the intensities of
protons by reaction of 2a with D2 may result from the formation
of an acidic dideuterium intermediate formed after a thione
ligand dissociates whereas the deuteration of the iridium hydride
may proceed Via an exchange process between the ND groups
1
both the NH and IrH resonances in the H NMR decrease by

Intramolecular Proton-Hydride Interactions
Inorganic Chemistry, Vol. 35, No. 6, 1996 1555
and hydride in the intramolecular ND‚‚‚H(Ir)‚‚‚DN interaction.
The crystalline structure of 2a contains a novel four-membered
ring defined by the NH‚‚‚H(Ir)‚‚‚HN and NH‚‚‚F(B)‚‚‚NH
interactions.
Complexes 3a and 3b with these thione ligands also have
NH‚‚‚HIr contacts as indicated by T1(min) and nOe experiments.
Here again, the NH groups are deuterated upon reaction with
D2 at a greater rate than the hydride on iridium. The hydrazine
ligands in complex 3c preferentially form intramolecular NH‚‚‚N
hydrogen bonds over NH‚‚‚HIr interactions. As expected,
complex 3d with ammine ligands does not have an NH‚‚‚HIr
contact.
Acknowledgment. This work was supported by grants to
R.H.M. from the NSERC of Canada and the Petroleum Research
Fund, administered by the American Chemical Society, by a
loan of iridium salts from Johnson Matthey Ltd., and by an
NSERC postdoctoral fellowship to W.X.
Supporting Information Available: Tables giving a structure
determination summary, atomic coordinates and equivalent isotropic
displacement parameters, bond lengths, bond angles, anisotropic thermal
parameters, and hydrogen atom coordinates (9 pages). Ordering
information is given on any current masthead page.
IC950997K