HX elimination from Ir(H)2X(PBu2tPh)2 promoted by CO coordination: Assessment of X ligand influence

Article abstract of DOI:10.1039/a800525g

The coordinatively unsaturated complexes Ir(H)₂X(PBu₂^tPh)₂ [X = Cl, Br, I, N₃, N=C=NSiMe₃, NHC(O)CH₃, OC(O)CF₃, OSO₂CF₃, OC(O)CH₃, SPh, OPh, F] all react within the mixing time in arene solvents to bind carbon monoxide. Subsequent reactivity of these CO adducts reductively to eliminate HX is dependent on the magnitude of the inherent destabilization caused by filled-filled repulsions between the ligand p_π orbitals and metal d_π orbitals. This destabilization is not sufficient to promote the loss of HX when X = Cl, Br, I, N₃, N=C=NSiMe₃, NHC(O)CH₃ or OC(O)CF₃. When X = OC(O)CH₃ or SPh, metastable CO adducts are formed that ultimately lose HX. The complexes containing OPh or F quickly lose HX upon reaction with CO. The unusual iridium(I) complexes IrH(CO)₂(PBu₂^tPh) and IrH(CO)(PBu₂^tPh)₂ have been characterized by multinuclear NMR and IR spectroscopy. The reaction of Ir(H)₂(F)(PBu₂^tPh)₂ with CO in a glass vessel yields crystalline [Ir(H)₂(CO)₂(PBu₂^tPh) ₂][SiF₅] and [Ir(CO)₂(PBu₂^tPh)₂][SiF₅] · C₆D₆, both characterized by X-ray diffraction. The latter, although approximately square planar, has a C - Ir - C angle of only 162.7°. Crystallographic data (Pc at - 165°C) for [Ir(H)₂(CO)₂(PBu₂^tPh) ₂][SiF₅], a = 8.293(2), b = 12.462(5), c = 16.333(7) A?, β = 98.21(2)° with Z = 2. Crystallographic data (P2₁/n at - 172°C) for [Ir(CO)₂(PBu₂^tPh)₂][SiF₅] · C₆D₆, a = 13.041(7), b = 12.998(5), c = 22.553(13) A?, β = 97.50(2)° with Z = 4.

Full text of DOI:10.1039/a800525g

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HX elimination from Ir(H) X(PBut Ph) promoted by CO
2
2
2
coordination: assessment of X ligand inÑuence¤
Alan C. Cooper, John C. Bollinger, John C. Hu†man and Kenneth G. Caulton*
Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington,
IN 47405-4001, USA
The coordinatively unsaturated complexes Ir(H) X(PBut Ph) [X \ Cl, Br, I, N , NxCxNSiMe ,
2
2
2
3
3
NHC(O)CH , OC(O)CF , OSO CF , OC(O)CH , SPh, OPh, F] all react within the mixing time in arene
3
3
2
3
3
solvents to bind carbon monoxide. Subsequent reactivity of these CO adducts reductively to eliminate HX is
dependent on the magnitude of the inherent destabilization caused by Ðlled-Ðlled repulsions between the ligand
p orbitals and metal d orbitals. This destabilization is not sufficient to promote the loss of HX when X \ Cl,
Br, I, N , NxCxNSiMe , NHC(O)CH or OC(O)CF . When X \ OC(O)CH or SPh, metastable CO
adducts are formed that ultimately lose HX. The complexes containing OPh or F quickly lose HX upon
p
p
3
3
3
3
3
reaction with CO. The unusual iridium(I) complexes IrH(CO) (PBut Ph) and IrH(CO)(PBut Ph) have been
2
2
2
2
characterized by multinuclear NMR and IR spectroscopy. The reaction of Ir(H) (F)(PBut Ph) with CO in a
2
2
2
glass vessel yields crystalline [Ir(H) (CO) (PBut Ph) ][SiF ] and [Ir(CO) (PBut Ph) ][SiF ] É C D , both
2
2
2
2
5
2
2
2
5
6 6
characterized by X-ray di†raction. The latter, although approximately square planar, has a CwIrwC angle of
only 162.7¡. Crystallographic data (Pc at [165 ¡C) for [Ir(H) (CO) (PBut Ph) ][SiF ], a \ 8.293(2),
2
2
2
2
5
b \ 12.462(5), c \ 16.333(7) A, b \ 98.21(2)¡ with Z \ 2. Crystallographic data (P2 /n at [172 ¡C) for
1
[Ir(CO) (PBut Ph) ][SiF ] É C D , a \ 13.041(7), b \ 12.998(5), c \ 22.553(13) A, b \ 97.50(2)¡ with Z \ 4.
2
2
2
5
6 6
The synthesis and reactivity of iridium dihydride complexes of
ligand and another ligand (L@) to release free L@X.11 Therefore,
the relative net donating ability of an X ligand can be revealed
not only in the stabilization of coordinatively unsaturated
complexes/intermediates, but also in the destabilization (and
subsequent reactivity to remove such destabilization) of coor-
dinatively saturated complexes and the formation of strong
HwX bonds. Towards this end, the characterization of the
reactions of a number of Ir(H) X(PBut Ph) complexes with
the general formula Ir(H) XL (X \ halide or pseudohalide,
2
2
L \ bulky phosphine) have been extensively investigated since
the earliest reports of the synthesis of these complexes.1 These
coordinatively unsaturated complexes react with a variety of
Lewis bases2 and p-acid ligands including dihydrogen3 and
ethylene.4 Their reactivity towards alkynes has been used
recently to synthesize a number of new alkynyl and vinylidene
complexes.5 Studies have also shown that these complexes
may be used as catalysts or catalyst precursors for a number
of catalytic processes including hydrogenation.6
2
2
2
the strongly binding ligand, CO, have been performed. This
study has been enhanced by a recently developed synthetic
methodology that has been used to synthesize a large number
of new Ir(H) X(PBut Ph) encompassing a wide range of
While the investigations of the reactivity of these complexes
have been extensive, the inÑuence of the identity of the X
ligand on the reactivity has been overlooked in many cases. It
has been proposed7 that coordinatively unsaturated transition
metal complexes may be stabilized by donation of lone pair
electron density from halide and pseudohalide ligands, provid-
ed that there is e†ective d Èp orbital overlap between an
2
2
2
expected X ligand p-donor abilities.12
Experimental
p
p
empty d orbital and a Ðlled (nonbonding) p ligand orbital.
General procedures
p
p
Thus, the reactivity (Lewis acidity) of Ir(H) XL should be
2
2
All manipulations were carried out using standard Schlenk
and glovebox techniques under argon. Toluene, benzene and
THF were dried and deoxygenated over sodium or
potassiumÈbenzophenone and distilled under argon. C D
highly dependent on the ability of the X ligand to stabilize
coordinative unsaturation. Indeed, we have observed that the
rate of catalytic oleÐn isomerization activity of an Ir(H) XL
complex is dependent on the donating ability of the X ligand.8
However, the same properties of a ligand with strong “net
donating abilityÏ (i.e., combined r and p electron donation) to
stabilize coordinative unsaturation also serve to destabilize a
coordinatively saturated complex via Ðlled-Ðlled d Èp repul-
2
2
6
6
and C D were dried over sodium metal and vacuum distilled
7
8
before use in a glovebox. CDCl was dried over CaH and
3
2
vacuum distilled before use in a glovebox. 1H (referenced to
residual solvent impurity), 13CM1HN, 31PM1HN (referenced to
external 85% H PO ) and 19F (referenced to external CFCl )
NMR spectra were collected on Varian Gemini-300 and
Inova-400 spectrometers. Ethylene (CP grade, Air Products),
carbon monoxide (CP grade, Air Products) and 13C (99%
13C, Monsanto Research Corp.) were used without further
puriÐcation. Triethylamine (Aldrich) was degassed and dried
p
p
sions.7 This destabilization is often manifested as
a
3
4
3
unimolecular reaction to remove the destabilizing repulsive
interactions. These reactions can include ionization of the
complex to expel the X ligand to the outer coordination
sphere,9 insertion into the MwX bond to replace the p-donor
ligand X with a non-p-donating ligand,10 or for complexes in
a suitably high valence state, reductive elimination of the X
over
4 A molecular sieves. Lithium 2,2,6,6-tetramethyl-
piperidide was prepared by the reaction of 2,2,6,6-tetramethyl-
piperidine with BunLi in pentane at [78 ¡C. Compounds
1È38, 4È7, 15, 18È20,12 and 2127 were synthesized according to
literature procedures.
* E-mail: caulton=indiana.edu
¤ Non-SI unit used: atm B 105 Pa.
New J. Chem., 1998, Pages 473È480
473

View Article Online
Preparations and reactions
introduced. Upon mixing, the solution immediately became
colorless. 1H NMR (C D , 25 ¡C): 8.20 (m), 7.24È7.02 (m),
Ir(H) Cl(CO)(PBut Ph) (8). In a 100 mL Schlenk Ñask was
6
6
1.32 (vt, J \ 6.9 Hz), 1.28 (vt, J \ 6.9 Hz), [7.58 (td,
2
2
2
dissolved Ir(H) Cl(PBut Ph) (500 mg, 0.74 mmol) in 15 mL
PH
\ 18.3 Hz, J \ 6.0 Hz), [23.92 (td, J \ 14.4 Hz,
HH{ PH
\ 6.0 Hz). 31PM1HN NMR (C D , 25 ¡C): 54.3 (s). 19F
PH
J
J
2
2
2
THF. This solution was degassed three times (freezeÈpumpÈ
thaw method) and 1 atm CO introduced into the Ñask. Upon
stirring, the solution rapidly (\2 min) changed from orange
to colorless. The volatiles were removed in vacuo to yield an
o†-white solid (488 mg, 94%). 1H NMR (C D , 25 ¡C): 8.45
PH
HH{
6 6
NMR (C D , 25 ¡C): [77.2 (s). IR (C D ): m(CO) 1960 cm~1.
6
6
6 6
[Ir(H) (CO) (PBut Ph) ] [OSO CF ] (16). In 10 mL
2
2
2
2
2
3
toluene was dissolved Ir(H) (OSO CF )(PBut Ph) (100 mg,
6
6
2
2
3
2
2
(m), 7.20È7.01 (m), 1.49 (vt, J \ 7.2 Hz), 1.40 (vt, J \ 6.6
PH PH
Hz), [8.20 (td, J \ 18.0 Hz, J \ 5.7 Hz), [20.31 (td,
PH HH
\ 14.4 Hz, J \ 5.7 Hz). 31PM1HN NMR (C D , 25 ¡C):
HH{
53.6 (s). IR (C D ): m(CO) 1985 cm~1 .
0.128 mmol) to form a yellow solution. This solution was
transferred to a 100 mL Ñask where the solution was degassed
three times (freezeÈpumpÈthaw) and 1.5 atm CO introduced.
Upon stirring, a white precipitate began to form in the solu-
tion. After stirring for 30 min at room temperature, the pre-
cipitate was Ðltered away from the colorless mother liquor
and washed with toluene (2 ] 5 mL). The solid was dried in
vacuo to yield a white powder (97 mg, 90%). Anal. calcd for
J
PH
6 6
6
6
Ir(H) Br(CO)(PBut Ph) (9). In an NMR tube was dis-
2
2
2
2
2
solved Ir(H) Br(PBut Ph) (20 mg, 0.028 mmol) in 0.6 mL
2
C D to form an orange solution. This solution was degassed
three times (freezeÈpumpÈthaw) and 1 atm CO introduced.
6
6
C
H F IrO P S: C, 44.11; H, 5.74. Found: C, 44.21; H,
Upon mixing, the solution immediately became colorless. 1H
31 48 3
5 2
5.49%. 1H NMR (CDCl , 25 ¡C): 8.14 (m), 7.8È7.66 (m), 1.60
NMR (C D , 25 ¡C): 8.48 (m), 7.20È7.01 (m), 1.50 (vt, J
\
3
(vt, J \ 7.8 Hz), [10.9 (t, J \ 15.0 Hz). 13CM1HN NMR
6
6
PH
7.2 Hz), 1.41 (vt, J \ 6.6 Hz), [8.55 (td, J \ 18.0 Hz,
PH PH
\ 5.4 Hz), [19.31 (td, J \ 14.4 Hz, J \ 5.4 Hz).
PH HH{
31PM1HN NMR (C D , 25 ¡C): 48.4 (s). IR (C D ): m(CO) 1985
PH
3
PH
(CDCl , 25 ¡C): 170.9 (ddt, J \ 43.1 Hz, J \ 5.5 Hz,
J
CH
\ 5.5 Hz), 135.4 (vt, J \ 4.2 Hz), 132.3 (vt, J \ 7.0 Hz),
PC PC
129.3 (vt, J \ 2.8 Hz), 128.4 (br s), 120.8 (q, J \ 321 Hz),
CH{
J
HH{
cm~1.
Ir(H) I(CO)(PBut Ph) (10). In an NMR tube was dissolved
PC
6
6
6 6
PC
PC
CF
38.9 (vt, J \ 7.8 Hz), 30.6 (br s). 31PM1HN NMR (CDCl ,
3
25 ¡C): 57.3 (s). IR (CDCl ): m(CO) 2078, 2039 cm~1.
3
2
2
2
Ir(H) I(PBut Ph) (20 mg, 0.026 mmol) in 0.6 mL C D to
[Ir(H) (C H )(PBut Ph) ] [OSO CF ] (17). In an NMR
2
2
2
6 6
form an orange solution. This solution was degassed three
times (freezeÈpumpÈthaw) and 1 atm CO introduced. Upon
mixing, the solution immediately became colorless. 1H NMR
(C D , 25 ¡C): 8.38 (m), 7.19È7.01 (m), 1.51 (vt, J \ 7.2 Hz),
1.40 (vt, J \ 6.9 Hz), [9.95 (td, J \ 18.0 Hz, J \ 5.4
PH PH HH{
Hz), [17.56 (td, J \ 15.3 Hz, J \ 5.4 Hz). 31PM1HN
PH HH{
NMR (C D , 25 ¡C): 47.3 (s). IR (C D ): m(CO) 1985 cm~1.
2
2
4
2
2
2
3
3
tube was dissolved Ir(H) (OSO CF )(PBut Ph) (25 mg, 0.032
2
2
2
2
mmol) in 0.6 mL C D to form a yellow solution. This solu-
tion was degassed three times (freezeÈpumpÈthaw) and 1.5
6
6
atm C H introduced. Upon mixing, yellow precipitate began
6
6
PH
2
4
to form in the solution. After 30 min at room temperature, the
solution had become nearly colorless. 1H NMR assay
detected only dissolved C H . The C D was decanted and
6
6
6 6
2
4
6 6
CDCl (0.6 mL) added to dissolve the precipitate. 1H NMR
Ir(H) (N )(CO)(PBut Ph) (11). In an NMR tube was dis-
3
2
3
2
2
2
2
(CDCl , 25 ¡C): 8.05 (m), 7.59È7.42 (m), 3.90 (br s, 4H), 1.32
(vt, 36 H, J \ 6.9 Hz), [24.4 (br s, 2H). 31PM1HN NMR
solved Ir(H) (N )(PBut Ph) (20 mg, 0.029 mmol) in 0.6 mL
3
2
3
C D to form an orange solution. This solution was degassed
three times (freezeÈpumpÈthaw) and 1 atm CO introduced.
PH
6
6
(CDCl , 25 ¡C): 59.8 (s).
3
Upon mixing, the solution immediately became colorless. 1H
Reaction of Ir(H) [OC(O)CH ](PBut Ph) with CO. In an
NMR (C D , 25 ¡C): 8.30 (m), 7.22È7.03 (m), 1.40 (vt, J
\
2
3
2
2
3
NMR tube was dissolved Ir(H) [OC(O)CH ](PBut Ph) (25
6
6
PH
7.2 Hz), 1.34 (vt, J \ 6.9 Hz), [8.08 (td, J \ 18.0 Hz,
PH PH
\ 5.4 Hz), [20.2 (td, J \ 14.4 Hz, J \ 5.4 Hz).
PH HH{
31PM1HN NMR (C D , 25 ¡C): 59.4 (s). IR (C D ): m(CO) 1983
2
6
2
2
mg, 0.036 mmol) in 0.6 mL C D . This light yellow solution
J
6
was degassed three times (freezeÈpumpÈthaw) and 1.5 atm CO
introduced. Upon mixing, the solution immediately became
colorless. After 1 h at room temperature, the sample color had
changed back to yellow. 1H and 31PM1HN NMR assay
at 30 min showed signals consistent with two iridium
species in solution: Ir(H) [OC(O)CH ](CO)(PBut Ph) and
HH{
cm~1.
Ir(H) (NxCxNSiMe )(CO)(PBut Ph) (12). In an NMR
6
6
6 6
2
3
2
2
3
tube was dissolved Ir(H) (NxCxNSiMe )(PBut Ph) (20 mg,
0.027 mmol) in 0.6 mL C D to form an orange solution. This
2
6
2
2
2
3
2
2
6
IrH(CO) (PBut Ph) (in a ca. 1 : 1 ratio). NMR spectra for
solution was degassed three times (freezeÈpumpÈthaw) and 1
atm CO introduced. Upon mixing the solution immediately
became colorless. 1H NMR (C D , 25 ¡C): 8.39 (m), 7.19È6.99
2
2
Ir(H) [OC(O)CH ](CO)(PBut Ph) : 1H NMR (C D , 25 ¡C):
2
3
2
2
6 6
8.62 (m), 7.18È6.98 (m), 2.04 (s), 1.53 (vt, J \ 7.2 Hz), 1.43 (vt,
PH
6
6
J
\ 6.4 Hz), [7.85 (td, J \ 18.4 Hz, J \ 5.6 Hz),
(m), 1.32 (vt, J \ 7.2 Hz), 1.27 (vt, J \ 6.8 Hz), 0.31 (s),
PH
PH
HH
PH
[8.41 (td, J \ 18.0 Hz, J \ 5.6 Hz), [19.37 (td, J
PH HH{ PH
14.4 Hz, J \ 5.6 Hz). 31PM1HN NMR (C D , 25 ¡C): 48.5
HH{
(s). IR (C D ): m(CO) 1973 cm~1.
PH
[23.45 (td, J \ 15.2 Hz, J \ 5.6 Hz). 31PM1HN NMR
PH HH
(C D , 25 ¡C): 48.5 (s). Upon mixing for 18 h at room tem-
\
6
6
6
6
perature, the yellow color remained. 1H and 31PM1HN NMR
6
6
showed only signals for IrH(CO) (PBut Ph), free phosphine
2
2
Ir(H) [NHC(O)CH ](CO)(PBut Ph) (13). In an NMR
and CH COOH (in a 1 : 1 : 1 ratio). 1H NMR (C D , 25 ¡C):
2
3
2
2
3
6 6
tube was dissolved Ir(H) [NHC(O)CH ](PBut Ph) (15 mg,
11.8 (br s, CH COOH), 7.98 (m, free phosphine), 7.74 (m),
2
3
2
2
3
0.022 mmol) in 0.6 mL C D . This yellow solution was
7.14È6.98 (m), 1.52 (s, CH COOH), 1.18 (d, J \ 11.7 Hz, free
6
6
3
PH
degassed three times (freezeÈpumpÈthaw) and 1 atm CO intro-
duced. Upon mixing, the solution immediately became color-
less. 1H NMR (C D , 25 ¡C): 8.36 (m), 7.29È7.04 (m), 3.53 (br
phosphine), 1.08 (d, J \ 14.4 Hz), [11.41 (d, J \ 43.2 Hz).
PH
PH
31PM1HN NMR (C D , 25 ¡C): 57.9 (s), 40.0 (s, free phosphine).
6
6
IR (C D ): m(CO) 1966 cm~1.
6
6
6 6
s, 1H), 1.89 (s, 3H), 1.39 (vt, J \ 6.9 Hz), 1.36 (vt, J \ 6.6
PH
Hz), [10.2 (td, J \ 18.9 Hz, J \ 4.2 Hz), [18.3 (td,
PH HH{
\ 16.5 Hz, J \ 4.2 Hz). 31PM1HN NMR (C D , 25 ¡C):
HH{
53.3 (s). IR (C D ): m(CO) 1962 cm~1.
PH
Reaction of Ir(H) (SPh)(PBut Ph) with CO. In an NMR
2
2
2
2
tube was dissolved Ir(H) (SPh)(PBut Ph) (25 mg, 0.033 mmol)
J
2
2
PH
6 6
in 0.6 mL C D . This light yellow solution was degassed three
6
6
6
6
times (freezeÈpumpÈthaw) and 1.5 atm CO introduced. Upon
mixing, the solution immediately became colorless. After 1 h
at room temperature, the sample color had changed back to
yellow. 1H and 31PM1HN NMR assay at 1 h showed signals
consistent with two iridium species in solution:
Ir(H) [OC(O)CF ](CO)(PBut Ph) (14). In an NMR tube
2
3
2
2
3
2
was dissolved Ir(H) [OC(O)CF ](PBut Ph) (40 mg, 0.053
2
2
mmol) in 0.6 mL C D . This light yellow solution was
degassed three times (freezeÈpumpÈthaw) and 1.5 atm CO
6
6
474
New J. Chem., 1998, Pages 473È480

View Article Online
Ir(H) (SPh)(CO)(PBut Ph) and IrH(CO) (PBut Ph) (in a ca.
and [350 ppm. IR (C D ): m(CO) 2006(s), 1949(m), 1892(s)
2
2
2
2
2
6 6
1 : 1 ratio). NMR spectra for Ir(H) (SPh)(CO)(PBut Ph) : 1H
cm~1.
2
2
2
NMR (C D , 25 ¡C): 8.38 (m), 7.13È7.01 (m), 6.95È6.80 (m),
6
6
IrH(13CO)(PBut Ph) . In an NMR tube was dissolved
1.48 (vt, J \ 7.2 Hz), 1.37 (vt, J \ 6.4 Hz), [9.30 (td,
PH PH
\ 18.4 Hz, J \ 5.2 Hz), 16.38 (td, J \ 16.4 Hz, J
HH PH HH
2
2
Ir(H) Cl(PBut Ph) (25 mg, 0.037 mmol) in 0.6 mL THF-d .
J
\
2
2
2
8
PH
This orange solution was degassed three times (freezeÈpumpÈ
thaw) and 1.0 atm 13CO introduced into the tube. Upon
mixing, the solution rapidly became colorless. The solution
5.2 Hz). 31PM1HN NMR (C D , 25 ¡C): 48.5 (s). Upon mixing
6
6
for 18 h at room temperature, the yellow color remained. 1H
and 31PM1HN NMR show only signals for IrH(CO) (PBut Ph),
2
2
was frozen in liquid N and the headspace above the frozen
free phosphine and PhSH (in a 1 : 1 : 1 ratio). 1H NMR
(C D , 25 ¡C): 7.98 (m, free phosphine), 7.74 (m), 7.14È6.98
2
solution evacuated and Ðlled with argon. To the colorless
6
6
solution of Ir(H) Cl(13CO)(PBut Ph) was added lithium 2,2,6,
(m), 6.94 (m, PhSH), 6.82 (m, PhSH), 4.46 (br s, PhSH), 1.18 (d,
2
2
2
6-tetramethylpiperidide (5.5 mg, 0.037 mmol). Upon mixing
for 2 h, the homogeneous solution turned yellow and a Ðne
J
\ 11.7 Hz, free phosphine), 1.08 (d, J \ 14.4 Hz),
PH
PH
[11.41 (d, J \ 43 Hz). 31PM1HN NMR (C D , 25 ¡C): 57.9
(s), 40.0 (s, free phosphine). IR (C D ): m(CO) 1966 cm~1.
PH
6
6
precipitate was formed. 1H NMR (THF-d , 25 ¡C): 8.20 (m),
8
6
6
7.40È7.34 (m), 1.45 (vt, J \ 6.6 Hz), [0.73 (dt, J \ 28.2
PH
CH
Hz,
J
\ 23.7 Hz). 13CM1HN NMR (THF-d , 25 ¡C,
carbonyl): 192.45 (t, J \ 7.3 Hz). 31PM1HN NMR (THF-d ,
Reaction of Ir(H) (OPh)(PBut Ph) with CO. In an NMR
PH
8
2
2
2
tube was dissolved Ir(H) (OPh)(PBut Ph) (25 mg, 0.034
PC
25 ¡C): 79.3 (d, J \ 7.3 Hz).
PC
8
2
2
2
mmol) in 0.6 mL C D . This light yellow solution was
6
6
degassed three times (freezeÈpumpÈthaw) and 1.5 atm CO
introduced. Upon mixing, the solution immediately became
colorless. After \2 min at room temperature, the sample
color had changed back to yellow. 1H and 31PM1HN NMR
assay showed only signals for IrH(CO) (PBut Ph), free phos-
Reaction of IrH(CO)(PBut Ph) with CO. In an NMR tube
2
2
was dissolved IrH(CO)(PBut Ph) (15 mg, 0.023 mmol) in 0.6
2
2
mL C D . This orange solution was degassed three times
6
6
(freezeÈpumpÈthaw) and 1.5 atm CO introduced. Upon
mixing, the orange solution immediately became light yellow.
1H and 31PM1HN NMR assay showed only signals for
IrH(CO) (PBut Ph) and free phosphine. The sample was
degassed Ðve times (freezeÈpumpÈthaw) and the NMR tube
charged with argon. During the degassing process, the light
yellow color darkened to become orange. 1H and 31PM1HN
NMR assay after degassing showed only signals for
IrH(CO)(PBut Ph) .
2
2
phine and PhOH (in a 1 : 1 : 1 ratio). 1H NMR (C D , 25 ¡C):
7.98 (m, free phosphine), 7.74 (m), 7.14È6.98 (m), 6.71 (m,
6
6
PhOH), 6.56 (m, PhOH), 4.62 (br s, PhOH), 1.18 (d, J \ 11.7
2
2
PH
Hz, free phosphine), 1.08 (d, J \ 14.4 Hz), [11.41 (d, J
\
PH
PH
43 Hz). 31PM1HN NMR (C D , 25 ¡C): 57.9 (s), 40.0 (s, free
6
6
phosphine). IR (C D ): m(CO) 1966 cm~1.
6
6
IrH(13CO) (PBut Ph). In an NMR tube was dissolved
2
2
2
2
Ir(H) [OC(O)CH ](PBut Ph) (25 mg, 0.036 mmol) in 0.6 mL
2
3
2
2
Reaction of Ir(H) (F)(PBut Ph) with CO in a glass vessel.
C D . This light yellow solution was degassed three times
2
2
2
6
6
In a 50 mL Schlenk Ñask was dissolved Ir(H) (F)(PBut Ph)
(freezeÈpumpÈthaw) and 1.0 atm 13CO introduced. Upon
mixing, the solution immediately became colorless. After 4 h
at room temperature, the sample color had changed to yellow.
1H NMR (C D , 25 ¡C): 7.74 (m), 7.14È6.98 (m), 1.08 (d,
2
2
2
(200 mg, 0.3 mmol) in 10 mL C H . This orange solution was
6
6
degassed three times (freezeÈpumpÈthaw) and 1.0 atm CO
introduced. Upon stirring, the solution rapidly became color-
less. After \5 min at room temperature, the sample color had
changed back to yellow. This solution was allowed to stand
under a CO atmosphere overnight, forming a number of
colorless crystals in the Ñask. The presence of several red-
orange crystals was also noted. The crystals were separated
from the solution and washed with C H (2 ] 2 mL). The
6
6
J
\ 14.4 Hz), [11.41 (d, J \ 43 Hz). 13CM1HN NMR
PH
6
PH
(C D , 25 ¡C, carbonyl): 178.45 (d, J \ 2.3 Hz). 31PM1HN
6
PC
NMR (C D , 25 ¡C): 57.9 (t, J \ 2.3 Hz).
PC
6
6
Reaction of Ir(H) (F)(PBut Ph) with CO in a TeÑon-lined
2
2
2
NMR tube. In a TeÑon-lined NMR tube was dissolved
Ir(H) (F)(PBut Ph) (25 mg, 0.038 mmol) in 0.6 mL C D .
6
6
colorless and red-orange (air stable) crystals were manually
separated. A small number of the colorless crystals were dis-
solved in CDCl and established to be [Ir(H) (CO)
2
2
2
6 6
This orange solution was degassed three times (freezeÈpumpÈ
thaw) and 1.5 atm CO introduced. Upon mixing, the solution
immediately became colorless. After \2 min at room tem-
perature, the sample color had changed back to yellow. 1H
and 31PM1HN NMR assay showed only signals for
IrH(CO) (PBut Ph) and free phosphine. Free HF was unde-
3
2
2
(PBut Ph) ][SiF ] by 1H, 31PM1HN and 19F NMR. 1H NMR
2
2
5
(CDCl , 25 ¡C): 7.99 (m), 7.65È7.55 (m), 1.49 (vt, J \ 8.4 Hz),
PH
3
[11.02 (t, J \ 14.8 Hz). 31PM1HN NMR (CDCl , 25 ¡C):
PH
3
57.4 (s). 19F NMR (CDCl , 25 ¡C): [141.7 (s). One of the
3
2
2
red-orange crystals was dissolved in a minimal amount of
tected by 1H NMR. 1H NMR (C D , 25 ¡C): 7.98 (m, free
6
6
CDCl and assayed by 19F NMR. 19F NMR (CDCl , 25 ¡C):
phosphine), 7.74 (m), 7.14È6.98 (m), 1.18 (d, J \ 11.7 Hz, free
3
3
PH
[142.3 (s).
phosphine), 1.08 (d, J \ 14.4 Hz), [11.41 (d, J \ 43 Hz).
PH
6
PH
31PM1HN NMR (C D , 25 ¡C): 57.9 (s), 40.0 (s, free phosphine).
6
X-Ray structure determinations
Reaction of Ir(H) (F)(PBut Ph) with CO and NEt . In a
A small, well-formed crystal was selected and affixed to the
end of a glass Ðber using silicone grease. The mounted sample
was then transferred to the goniostat where it was cooled for
characterization (Table 1) and data collection. Standard inert
atmosphere handling techniques were used throughout the
investigation. Data were collected using a standard moving
crystal-moving detector technique with Ðxed background
counts at each extreme of the scan. Data were corrected for
Lorentz and polarization e†ects. The structure was solved by
direct methods (SHELXTL) and Fourier techniques.
2
2
2
3
100 mL Schlenk Ñask was dissolved Ir(H) (F)(PBut Ph) (250
2
2
2
mg, 0.38 mmol) in 20 mL THF. To this orange solution was
added NEt (53 lL, 0.38 mmol). The solution was degassed
3
three times (freezeÈpumpÈthaw) and 1.0 atm CO introduced.
Upon stirring, the solution rapidly became colorless. After 5
min at room temperature, the solution color had changed
back to yellow. After stirring for 30 min, the volatiles were
removed in vacuo to yield a bright yellow solid that was dried
overnight. NMR and IR assay of the solid showed quantitat-
ive conversion to a single product with signals that were con-
sistent with the formula IrH(CO)(PBut Ph) .1H NMR (THF-
[Ir(H) (CO) (PBut Ph) ] [SiF ]. A systematic search of a
2
2
2
2
2
2
5
d , 25 ¡C): 8.20 (m), 7.40È7.34 (m), 1.45 (vt, J \ 6.6 Hz),
PH
[0.73 (t, J \ 23.7 Hz). 31PM1HN NMR (THF-d , 25 ¡C):
PH
79.3 (s). No 19F NMR resonances were detected between ]25
limited hemisphere of reciprocal space located a set of data
with monoclinic symmetry and systematic absences corre-
sponding to either the centrosymmetric space group P2/c or
8
8
New J. Chem., 1998, Pages 473È480
475

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Table 1 Crystallographic data for [Ir(H) (CO) (PBut Ph) ][SiF ] and [Ir(CO) (PBut Ph) ][SiF ] É C D
2
2
2
2
5
2
2
2
5
6 6
[Ir(H) (CO) (PBut Ph) ][SiF ]
[Ir(CO) (PBut Ph) ][SiF ] É C D
2
2
2
2
5
2
2
2
5
6 6
Formula
C
H
F IrO P Si
2 2
C
H
F IrO P Si
30 48 5
32 52 5 2 2
M
817.95
Monoclinic
Pc
894.05
Crystal system
Monoclinic
Space group
P2 /n
1
a/A
b/A
c/A
b/¡
8.293(2)
12.462(5)
16.333(7)
98.21(2)
1670.6
2
13.041(7)
12.998(5)
22.553(13)
97.50(2)
3790.12
4
U/A
Ž
3
Z
q
/g cm~3
1.626
[165
1.567
calcd
T /¡C
[172
k/A
0.710 69
Graphite
41.638
0.710 69
Monochromator
l/cm~1
Graphite
36.776
No. reÑections
total
3417
2935
0.039
0.042
5978
4703
0.0435
0.0408
independent
R(F )a
o
R (F )b
w
o
a R \ &pF o [ o F p/& o F o.
o
c
o
b R \ [&w(o F o [ o F o)2/&w o F o2]" where w \ 1/r2(o F o).
w
o
c
o
o
to the non-centrosymmetric space group Pc. Intensity sta-
tistics favored the non-centrosymmetric space group. Sub-
sequent solution and reÐnement of the structure conÐrmed the
proper space group to be Pc. Hydrogen atoms were placed at
calculated positions and reÐned with the use of a riding
model. Fluorine and lighter atoms were reÐned isotropically;
all heavier atoms were reÐned anisotropically. The SiF anion
5
is disordered over two orientations in a ratio of ca. 3 : 2. A
Ðnal di†erence Fourier map is relatively clean, with the largest
peak having an intensity of 1.71 e A
ence peaks are all located near the iridium and all other peaks
are lower than 0.75 e A~3.
Ž ~3. The four largest di†er-
Ž
[Ir(CO) (PBut Ph) ] [SiF ] Æ C D . A systematic search of
2
2
2
5
6 6
a limited hemisphere of reciprocal space was used to deter-
mine that the crystal possessed monoclinic symmetry with sys-
tematic absences corresponding to the unique space group
These reactions are readily observed by the loss of the yellow
to orange color (characteristic of coordinative unsaturation) of
solutions containing 1È7 upon exposure to an excess of CO,
ultimately forming colorless solutions.
The products have been characterized by 1H, 31PM1HN
NMR and IR spectroscopy (Table 2). These compounds are
stable for periods of [1 week in benzene solution under either
CO or argon atmosphere and do not lose CO under vacuum
in solution or in the solid state. The rates of reaction of these
compounds with CO appear to be remarkably similar given
that the acetate and acetamide ligands have been shown by IR
spectroscopy and X-ray crystallography to bind in an g2
fashion to the iridium center.12
P2 /n. A slight splitting was apparent within the crystal.
Hydrogen atoms were placed in Ðxed calculated positions for
the Ðnal cycles of reÐnement. A Ðnal di†erence Fourier map
1
featured three peaks of intensity 2.2 e A
of the Ir position. All remaining peaks were less than 1.0 e
Ž ~3 lying in the vicinity
A
Ž
~3.
CCDC reference number 440/033.
Results and Discussion
Reactions
Reaction of Ir(H) X(PBut Ph) complexes with CO to form
2
2
2
stable Ir(H) X(CO)(PBut Ph) . Iridium complexes Ir(H) X
Reaction of Ir(H) (OSO CF )(PBut Ph) with CO or
2
2
2
2
2
2
3
2
2
(PBut Ph) [X \ Cl, Br, I, N , NxCxNSiMe , NHC(O)CH ,
C H . Upon reaction of Ir(H) (OSO CF )(PBut Ph) (15)
2
2
3
3
3
2 4
2 2 3 2 2
OC(O)CF , 1È7] react within the mixing time in C D with
an excess of CO to form the coordinatively saturated com-
with an excess of CO in C D , the yellow solution rapidly
3
6
6
6 6
begins to precipitate a colorless solid. After mixing for 1 min,
the yellow color had faded to yield a colorless solution with a
pounds Ir(H) X(CO)(PBut Ph) (8È14, eqn. 1).
2
2
2
Table 2 Selected 1H, 31PM1HN NMR and IR data (in C D ) for compounds 8È14, Ir(H) X(CO)(PBut Ph)
6
6
2
2
2
X
dH
dH
dL
J
PHa/Hz
J
PHb/Hz
J
/Hz
m(CO)/cm~1
a
b
HH{
Cl
Br
I
[8.20
[8.55
[9.95
[8.08
[8.41
[10.20
[7.58
[20.31
[19.31
[17.56
[20.20
[19.37
[18.30
[23.92
53.6
48.4
47.3
59.4
48.5
53.3
54.3
18.0
18.0
18.0
18.0
18.0
18.9
18.3
14.4
14.4
15.3
14.4
14.4
16.5
14.4
5.7
5.4
5.4
5.4
5.6
4.2
6.0
1985
1985
1985
1983
1973
1962
1960
N
3
NCNSiMe
NHC(O)CH
O CCF
3
3
2
3
476
New J. Chem., 1998, Pages 473È480

View Article Online
large amount of colorless precipitate. 1H and 31PM1HN NMR
assay of this colorless solution fails to show any resonances. If
the C D is decanted and CDCl added, the precipitate
spectrum of IrH(CO) (PBut Ph), suggest that the complex is
n
2
trans-IrH(CO) (PBut Ph). The value of J (43 Hz) is signiÐ-
2
2
PH
cantly larger than that expected for the coupling of cis hydride
6
6
3
rapidly dissolves to form a colorless solution. 1H, 13CM1HN
and 31PM1HN NMR and IR spectroscopy show the formation
of a single product, [Ir(H) (CO) (PBut Ph) ][OSO CF ] (16).
and phosphine ligands [2J (cis) are 9È20 Hz in square
PH
planar trans-MH(CO)(PR ) ].13 However, this 2J (trans) is
3 2
PH
not as large as those observed for complexes such as fac-
Ir(H) (CO)(PPh ) (123 Hz).14 An explanation for the smaller
2
2
2
2
2
3
If the reaction of 15 and an excess of CO is performed in
3
3 2
CDCl , a rapid homogeneous reaction occurs to produce 16
2J in trans-IrH(CO) (PBut Ph) is that contraction of the
3
PH
2
2
in quantitative yield.
CwIrwC angles due to strong backbonding into the CO n*
orbitals by the electron-rich IrI (vide infra) causes a corre-
sponding decrease in the HwIrwP angle from 180¡ (the
In a similar reaction, treatment of 15 with an excess of
ethylene in C D results in the precipitation of a colorless
6
6
solid that may be dissolved in CDCl . 1H and 31PM1HN
geometry moves towards T symmetry), decreasing the magni-
3
d
NMR suggest that the product formed is [Ir(H) (C H )-
tude of the coupling between the hydride and phosphine
2
2 4
(PBut Ph) ][OSO CF ] (17).
ligands. Several complexes with the formula IrX(CO) (PR )
2
2
2
3
2
3
Thus, the reaction of 15 with CO is similar to the reactions
of 1È7 with CO, except the characteristics of the triÑate anion
facilitate the ionization of an Ir(H) (OSO CF )(CO)(PBut Ph)
have been reported recently,15 but they have been character-
ized as cis dicarbonyl compounds based upon the observation
of two CO stretches in the IR spectrum.
2
2
3
2
2
intermediate to form [Ir(H) (CO)(PtBut Ph) ][OSO CF ],
2
2
2
2
3
which quickly adds a second equivalent of CO to form the
Ðnal product, 16. While the coordination of the triÑate ligand
to the metal in 15 has not been conÐrmed by an X-ray di†rac-
tion study, the solubility of 15 in nonpolar C D suggests that
Reactions
of
Ir(H) (OPh)(PBut Ph)
and
Ir(H) -
2
2
2
2
(F)(PBut Ph) with CO. A solution of Ir(H) (OPh)(PBut Ph)
2
2
2
2
2
(20) in C D was allowed to react with an excess of CO in a
6
6
sealed NMR tube. The orange solution quickly changed color
to light yellow. The 1H and 31PM1HN NMR spectra, after 5
min at room temperature, show complete conversion of 20 to
IrH(CO) (PBut Ph). Equimolar amounts of PBut Ph and
6
6
it is a neutral species in which the triÑate ligand is coordinated
to the iridium. Therefore, ionization (and precipitation from
benzene) does not occur until after CO binding.
2
2
2
PhOH are also present in the solution.
A solution of Ir(H) (F)(PBut Ph) (21) in C D was allowed
Formation of “metastableÏ Ir(H) X(CO)(PtBut Ph) com-
2
2
2
2
2
2
6 6
plexes. Reaction of Ir(H) (X)(PtBut Ph) [X \ OC(O)CH (18)
to react with an excess of CO in a sealed NMR tube. Due to
the possibility of HF formation, this reaction was performed
using a TeÑon liner inside the NMR tube. Upon agitation, the
solution changed color from orange to colorless and quickly
(\2 min) back to yellow. 1H and 31PM1HN NMR spectra
recorded shortly after the appearance of the yellow color indi-
cate a quantitative conversion of 21 to IrH(CO) (PBut Ph)
2
2
2
3
or SPh (19)] with an excess of CO in C D results initially in
6
6
a colorless solution. However, after a period of 30 min to 1 h,
the colorless solution begins to turn yellow. 1H and 31PM1HN
NMR assay of these samples soon after the reappearance of
coloration shows the presence of two iridium species in solu-
tion: Ir(H) X(CO)(PBut Ph) and the same compound
2
2
2
2
2
(independent of X) with a single upÐeld 1H NMR resonance
at [11.4 ppm. This resonance is a doublet (J \ 43 Hz), sug-
and free phosphine. HF was not detected in the 1H NMR
spectrum. However, if the same reaction is performed without
the TeÑon liner in the NMR tube, visible etching of the inner
surface of the NMR tube is apparent, indicating a reaction of
the glass surface with HF.
gestive of
a monophosphine complex. Accordingly, the
31PM1HN NMR spectrum shows, in addition to a singlet
assigned to Ir(H) X(CO)(PBut Ph) , two signals of equal
2
2
2
intensity. One of these can be assigned, based upon the chemi-
cal shift, as free PBut Ph. The 1H NMR of these solutions also
Reaction of Ir(H) (F)(PBut Ph) with CO and NEt . In an
2
2
2
2
3
shows the presence of free HX in solution. These data suggest
e†ort to neutralize reactive HF in a larger scale reaction of 21
that HX elimination and loss of a phosphine occur from
with CO, NEt was employed as an HF scavenger. A 1 : 1
3
Ir(H) X(CO)(PBut Ph) to give a complex with the formula
mixture of 21 and NEt was stirred under 1 atm CO in THF.
2
2
2
3
IrH(CO) (PBut Ph) (eqn. 2).
Upon exposure to CO, this solution rapidly became colorless
n
2
and turned yellow over ca. 5 min. Removal of the volatiles in
vacuo yielded a bright yellow solid. 1H and 31PM1HN NMR
spectra show that this solid was not the expected
IrH(CO) (PBut Ph), but instead was IrH(CO)(PBut Ph) ,
2
2
2
2
formed in essentially quantitative yield. This compound has a
hydride resonance in the 1H NMR spectrum at [0.73 ppm
(triplet, J \ 24 Hz). This unusually low-Ðeld hydride chemi-
PH
cal shift is characteristic of H trans to CO.13,16 The triplet
splitting indicates the presence of two equivalent phosphine
ligands. Accordingly, the 31PM1HN NMR spectrum of this
solution shows only one signal, a singlet at 79.3 ppm. In order
to verify this assignment, IrH(CO)(PBut Ph) was prepared
If the reactions are allowed to proceed at room temperature
for [12 h, quantitative formation of this complex is observed;
IrH(CO) (PBut Ph), PBut Ph and HX are observed in a 1 : 1 : 1
n
2
2
ratio (by 1H integration). The rates of formation of
IrH(CO) (PBut Ph) from 18 and 19 are similar, with t \ 30
2
2
reaction
via
an
independent
route.
The
of
n
2
1@2
Ir(H) Cl(13CO)(PBut Ph) with one equivalent of lithium 2,2,6,
min for 18 and t \ 1 h for 19.
2
2
2
1@2
6-tetramethylpiperidide in THF-d results in the precipitation
8
Reaction of 18 with 13CO. In an e†ort to verify the number
of CO ligands present in the IrH(CO) (PBut Ph) product, the
of LiCl and quantitative formation of IrH(13CO)(PBut Ph) .
2
2
The 31PM1HN NMR spectrum displays a doublet due to coup-
ling with the 13CO ligand and the 13CM1HN NMR spectrum
n
2
reaction of 18 with 13CO was performed. The 31PM1HN NMR
spectrum of the reaction mixture shows that the resonance for
the coordinated PBut Ph of IrH(13CO) (PBut Ph) has triplet
shows a triplet (J \ 7.3 Hz) in the carbonyl region. The
PC
hydride is present in the 1H NMR spectrum as a doublet of
2
n
2
splitting (J \ 2.3 Hz), indicating the presence of two equiva-
triplets (J \ 28 Hz, J \ 24 Hz) at [0.73 ppm.
PC
CH
PH
lent CO ligands in the product. Accordingly, the 13CM1HN
NMR spectrum shows only a single resonance in the carbonyl
region at 178.5 ppm (doublet, J \ 2.3 Hz). This data, coupled
with the observation of only one CO stretch in the solution IR
Reaction of IrH(CO)(PBut Ph) with CO. A solution of
2 2
IrH(CO)(PBut Ph) in C D was allowed to react with an
2
2
6 6
excess of CO, changing color from orange to light yellow
New J. Chem., 1998, Pages 473È480
477

View Article Online
upon mixing. 1H and 31PM1HN NMR assays show equimolar
IrH(CO) (PBut Ph) and PBut Ph in the solution. If this solu-
2
2
2
tion is degassed thoroughly, the solution color returns to
orange. 1H and 31PM1HN NMR spectra verify a complete
regeneration of IrH(CO)(PBut Ph) . These results, coupled
2
2
with the dependence of the identity of the IrI products of the
reactions of 21 and CO on the conditions employed (i.e.,
removal of volatiles in vacuo), suggest that the initial product
of the elimination of HX from Ir(H) X(CO)(PBut Ph) is
IrH(CO)(PBut Ph) . The mono-CO species reacts quickly with
an excess of CO to dissociate one phosphine and form
2
2
2
2
2
IrH(CO) (PBut Ph). While IrH(CO) (PBut Ph) appears to be
2
2
2
2
stable under a CO atmosphere, removing CO in vacuo in the
presence of free phosphine results in the loss of one CO ligand
and recoordination of phosphine.
Reaction of Ir(H) (F)(PtBut Ph) with CO in a glass vessel.
2
2
2
We have found that NEt is e†ective in scavenging HF
3
formed in the reaction of 21 with CO. If this reaction is per-
formed in a glass vessel without added base, the scavenging of
HF can occur via the following reaction: 5HF ] SiO
2
] 2H O ] H` ] SiF v .
2
5
In a glass Schlenk Ñask, a benzene solution of 21 was
allowed to stand overnight under a CO atmosphere. During
this time, a number of colorless and red-orange crystals
formed from the solution. The colorless crystals were
assayed by 1H and 31PM1HN NMR and found to have
spectra essentially identical to those of [Ir(H) (CO) -
2
2
(PBut Ph) ][OSO CF ] (16). In addition, the 19F NMR spec-
2
2
2
3
trum displayed a single resonance at [141.7 ppm. 19F NMR
assay of a red-orange crystal also showed a resonance at
ca. [142 ppm. This chemical shift is intermediate between
those of SiF ([163.6 ppm) and [SiF ]2~ ([127.0 ppm)17
Fig. 1 ORTEP drawing of Ir(H) (CO) (PBut Ph) `; hydride hydro-
2
2
2
2
4
6
gens were not located
and suggestive of the presence of a SiF anion in the crys-
5
talline products. Despite the similarity of SiF ~ to commonly
5
used, weakly coordinating anions such as BF ~ and PF ~,
IrH(CO) (PBut Ph). Eventual reaction of HF with the glass
4
6
2
2
the pentaÑuorosilicate anion has been rarely used as a weakly
coordinating counter ion.18 There has been only one struc-
tural determination of a cationic organometallic complex
with a pentaÑuorosilicate counter ion19 and very few structural
determinations of organic salts of the pentaÑuorosilicate
anion.20
surface produces HSiF , which can protonate IrH-
5
(CO) (PBut Ph) to yield an [Ir(H) (CO) (PBut Ph)][SiF ]
2
2
2
2
2
5
intermediate that should readily react with free PBut Ph
2
present in the solution (released in the primary reaction).
While the coordinatively saturated complex [Ir(H) -
2
(CO) (PBut Ph) ][SiF ] is not informative as to the coordi-
2
2
2
5
An X-ray crystal structure determination of the colorless
crystals (Fig. 1) conÐrms the assignment of the product as
[Ir(H) (CO) (PBut Ph) ][SiF ]. Selected bond distances and
angles are shown in Table 3. While the hydride ligands were
not located by X-ray di†raction, their positions may be
inferred as trans to the CO ligands in an octahedral geometry.
The carbonyl ligands are mutually cis [CwIrwC angle
97.1(5)¡] and the bulky phosphine ligands in the expected
nating ability of the SiF anion, the crystal structure
of a red-orange crystal from this reaction shows this com-
5
plex to be coordinatively unsaturated trans-[Ir(CO) -
2
2
2
2
5
2
(PBut Ph) ][SiF ] with a noncoordinating SiF anion and
2
2
5
5
one molecule of C D in the crystal lattice (Fig. 2).
6
6
The pentaÑuorosilicate anion is free from disorder and
adopts the expected trigonal bipyramidal geometry. The
PwIrwP and CwIrwC angles are both close to 180¡ (Table
4), indicating an approximate square-planar geometry for the
Ir cation. However, there is a signiÐcant narrowing of the
trans orientation. Unfortunately, the SiF anion exhibited
5
conformational disorder, ultimately being reÐned in two
orientations in a 3 : 2 ratio, preventing further investigation of
the anion. The formation of this complex from the reaction of
21 and CO in a glass vessel can be rationalized by the follow-
ing sequence of reactions: The primary Ir-containing product
of the reaction of 21 with CO, in the presence of HF, is
Table 4 Selected bond distances (A) and angles (deg.) for
[Ir(CO) (PBut Ph) ][SiF ] É C D
2
2
2
5
6 6
Ir(1)wP(6)
2.376(6)
2.378(6)
1.916(5)
2.526(7)
2.619(8)
Ir(1)wC(4)
C(2)wO(3)
C(4)wO(5)
F(37)wH(50)
1.8821(11)
1.125(7)
1.1629(26)
2.557(7)
Ir(1)wP(21)
Ir(1)wC(2)
Table 3 Selected bond distances (A) and angles (deg.) for
[Ir(H) (CO) (PBut Ph) ][SiF ]
F(37)wH(23)
F(41)wH(22)
2
2
2
2
5
Ir(1)wP(2)
2.406(3)
2.386(3)
1.910(13)
Ir(1)wC(34)
C(32)wO(33)
C(34)wO(35)
1.912(11)
1.17(2)
1.16(2)
SiwF(axial)
1.608(16)
1.611(14)
SiwF(equatorial)
1.557(18)
1.582(17)
1.608(20)
Ir(1)wP(17)
Ir(1)wC(32)
P(2)wIr(1)wP(17)
P(2)wIr(1)wC(32)
P(2)wIr(1)wC(34)
P(17)wIr(1)wC(32)
159.67(11)
102.3(3)
91.9(3)
P(17)wIr(1)wC(34)
Ir(1)wC(32)wO(33)
Ir(1)wC(34)wO(35)
C(32)wIr(1)wC(34)
100.7(3)
174.0(10)
177.6(10)
97.1(5)
P(6)wIr(1)wP(21)
P(6)wIr(1)wC(2)
P(6)wIr(1)wC(4)
P(21)wIr(1)wC(2)
173.70(11)
88.4(7)
91.7(6)
P(21)wIr(1)wC(4)
Ir(1)wC(2)wO(3)
Ir(1)wC(4)wO(5)
C(2)wIr(1)wC(4)
93.0(6)
176.3(13)
174.2(14)
162.7(8)
92.0(3)
88.4(8)
478
New J. Chem., 1998, Pages 473È480

View Article Online
to the metal via heteroatoms that have
a bond to
an electron-withdrawing acyl carbon. The triÑate ligand
has a strongly electron-withdrawing SO CF moiety on the
2
3
donating oxygen atom. The b-nitrogen atoms of the azide
ligand have a strong positive charge that serves to lower
the electron-donating ability of the a-nitrogen atom.
The initial reaction of Ir(H) [OC(O)CF ](PBut Ph) and
2
3
2
2
Ir(H) [OC(O)CH ](PBut Ph) with CO is the same, to form
2
3
2
2
Ir(H) (X)(CO)(PBut Ph) , but the enhanced donating power of
2
2
2
acetate vs. triÑuoroacetate promotes the elimination of acetic
acid from Ir(H) [OC(O)CH ](CO)(PBut Ph) . This is clearly
2
3
2
2
evidence of the powerful inÑuence of the CF group to with-
3
draw electron density from the acyl carbon, and ultimately the
oxygen that forms the IrwO bond. The factors that determine
whether HX elimination from Ir(H) X(CO)(PBut Ph) is exo-
2
2
2
thermic are not only the destabilization of the six-coordinate
species but also the driving force for formation of the HwX
bond. Relatively strong electron-donating substituents (CH
3
vs. CF ) contribute to the destabilization of the reactant by
3
increasing r and p donation, and favor HX formation (i.e., the
product is a weak acid). Thus, the donating ability of X inÑu-
ences both reactants and products to achieve reaction.
Fig. 2 ORTEP drawing of Ir(CO) (PBut Ph) `, showing short con-
2
2
2
tacts with SiF ~ and C D in the solid lattice
5
6 6
A trend that has been observed previously is the decrease in
p-donating ability upon moving down the periodic table.
Among the halide group, the p-donating ability is found to
decrease in the following order: I \ Br \ Cl @ F.8,24,25 This
trend is also apparent among oxygen/sulfur donor ligands.
While Ir(H) (SPh)(PBut Ph) reacts with CO to form a meta-
CwIrwC angle (162.7¡) from 180¡. This deviation from rigor-
ous planarity may be indicative of strong backbonding into
the CO n* orbitals by the low-valent IrI, despite the 16 elec-
tron count at the metal. This phenomenon has been observed
for other unsaturated low-valent dicarbonyl and carbonyl/
nitrosyl complexes.21
2
2
2
stable Ir(H) (SPh)(CO)(PBut Ph) complex, the reaction of
2
2
2
Ir(H) (OPh)(PBut Ph) with CO forms Ir(H)(CO) (PBut Ph),
2
2
2
2
2
free phosphine and PhOH within two min at room tem-
perature. The Ñuoride ligand has long been considered to have
special properties among the group of halide ligands.26 The
strong p-donating ability of Ñuoride has been found to
promote reactivity that is not observed in the analogous com-
plexes with the heavier halide ligands.26 During the reaction
of Ir(H) (F)(PBut Ph) with CO, the strong donating ability of
While the SiF anion is found to have no interactions with
5
the metal, there are several contacts between aryl hydrogens
and Ñuorine atoms of the SiF anion (2.526È2.619 A) that are
5
close to the sum of the van der Waals radii of H and F (2.55
A).22 These contacts involve both the lattice benzene and the
phenyl group of one phosphine ligand and appear to be quite
weak as there is no perceptible lengthening of the SiwF bonds
of the Ñuorine atoms involved in the interactions (average
SiwF distance 1.593 A).23
2
2
2
Ñuoride distinguishes it from the heavier halides by promoting
the facile elimination of HF upon CO coordination.
Assessment of the relative X ligand donor abilities
Conclusions
The magnitude of X-dependent “p-stabilization of
unsaturationÏ in d6 RuH(X)(CO)(PBut Me) has been deter-
The coordinatively unsaturated complexes Ir(H) X(PBut Ph)
2
2
2
(X \ Cl, Br, I, N , NxCxNSiMe , NHC(O)CH ,
2
2
3 3 3
mined by analysis of the m(CO) values.24 The degree of stabili-
zation is found to vary according to the energy and spatial
distribution of the ligand nonbonding electrons and is ordered
as follows: H \ I \ Br \ CCPh \ Cl \ SPh \ OPh \
OC(O)CF , OSO CF , OC(O)CH , SPh, OPh, F) all react
3
2
3
3
within the mixing time with CO. Subsequent reactivity of
these CO adducts to eliminate HX is dependent on the magni-
tude of the inherent destabilization caused by Ðlled-Ðlled
repulsions between the ligand p orbitals and Ðlled d orbitals
NHPh \ OH \ OCH CF \ F \ OSiPh \ OSiMe
\
2
3
3
3
p
p
OEt. More recently, anisotropic frozen solution EPR spectra
and the formation of HX (i.e., the HwX bond strength). These
factors are not sufficient to promote the loss of HX when
X \ Cl, Br, I, N , NxCxNSiMe , NHC(O)CH ,
were analyzed to determine the p-donor series for X in
(Me C ) TiX as H \ I \ Br \ Cl \ N(Me)Ph \ F B OPh
5 5 2
3
3
3
\ OMe B NH B N(Me)H.25
OC(O)CF . When X \ OC(O)CH or SPh, metastable CO
2
3
3
In the present study, we seek to measure the same property
adducts are formed that ultimately lose HX. The iridium com-
plexes containing phenoxide or Ñuoride ligands quickly lose
HX upon reaction with CO. A coordination number of six
alone is not sufficient to promote the loss of HX, since the
acetamide and acetate complexes are six-coordinate before
CO addition due to the g2 binding modes of these ligands.
Apparently, a p-acid ligand like CO is needed to make the
hydrides of six-coordinate complexes more BrÔnsted acidic
(facilitating HX elimination) and also to stabilize the resulting
IrI product.
The qualitative ranking of donating ability of the X ligands
based upon the reaction of Ir(H) X(PBut Ph) with CO may
be summarized in the following order: [Cl, Br, I, N ,
NCNSiMe , NHC(O)CH , OC(O)CF , OSO CF ]
[OC(O)CH , SPh] \ [OPh, F]. This order of donating
ability, based upon reactivity, compares well with spectro-
of X ligands using the inherent destabilization created by
Ðlled-Ðlled d Èd repulsions in a coordinatively unsaturated
p
p
metal complex containing an X ligand capable of p-donation.
In this situation, nonbonding orbitals of the X ligand are
interacting with the Ðlled metal d orbitals of the saturated
p
complex. Our Ðndings show that Ir(H) X(PBut Ph) complex-
2
2
2
es containing X ligands expected to have relatively weak
donating ability can achieve coordinative saturation, via the
addition of a CO ligand, with no subsequent reaction to
release the Ðlled-Ðlled repulsions. The X ligands that fall into
this classiÐcation include Cl, Br, I, N , NxCxNSiMe ,
3
3
2
2
2
NHC(O)CH , OC(O)CF and OSO CF . While X ligands
3
3
2
3
3
with oxygen and nitrogen atom donors have been considered
to be among the strongest p-donors,24,25 the ligands used
here all experience an electron-withdrawing e†ect from
substituents. TriÑuoroacetate and acetamide both donate
\
3
3
3
3
2
3
scopic evaluations of donating ability published to date and
New J. Chem., 1998, Pages 473È480
479

View Article Online
Chem., 1986, 25, 1556. (c) R. G. Goel and R. C. Srivastava, Can. J.
Chem., 1983, 61, 1352.
includes X ligands that have not been evaluated in these pre-
vious studies.
14 J. F. Harrod and W. J. Yorke, Inorg Chem., 1981, 20, 1156.
15 (a) M. A. Esteruelas, F. J. Lahoz, M. Olivan, E. Onate and L. A.
Oro, Organometallics, 1994, 13, 4246. (b) M. A. Esteruelas, M.
Olivan and L. A. Oro, Organometallics, 1996, 15, 814. (c) W. Chen,
M. A. Esteruelas, M. Mart•n, M. Olivan and L. A. Oro,
Organomet. Chem., 1997, 534, 95.
Acknowledgements
This work was supported by the National Science Foundation
and the Petroleum Research Fund. We also thank Johnson
Matthey/Aesar for a generous loan of IrCl É 3H O.
16 R. H. Heyn, S. A. Macgregor, T. T. Nadasdi, M. Ogasawara, O.
Eisenstein and K. G. Caulton, Inorg. Chim. Acta, 1997, 259, 5.
17 F. A. Bovey, L. Jelinski and P. A. Mirau, in Nuclear Magnetic
Resonance Spectroscopy. Academic Press, San Diego, CA, 1984, p.
177.
3
2
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480
New J. Chem., 1998, Pages 473È480