Steric and electronic parameters characterizing bulky and electron-rich dialkylbiarylphosphines

Article abstract of DOI:10.1021/om101174x

The steric and electronic properties of several sterically demanding tertiary phosphines (dicyclohexylphosphino)biphenyl (2a), 2- dicyclohexylphosphino-2′-methylbiphenyl (2b), 2-dicyclohexylphosphino- 2′,6′-dimethoxybiphenyl (2c), 2-dicyclohexylphosphino-2′, 4′,6′-triisopropylbiphenyl (2d), 2-diphenylphosphino-2′-(N,N- dimethylamino)biphenyl (2e), 2-di-tert-butylphosphino-2′-(N,N- dimethylamino)biphenyl (2f), and di(cyclohexyl)phenylphosphine (2g) have been studied by synthesizing and characterizing iridium complexes of types [IrCl(cod)(L)] (L = 2a-d) and cis-[IrCl(CO)₂(L)] (L = 2a-d and 2g). The infrared stretching frequencies of the carbonyl complexes permit an estimation of the ligand donor properties (basicity) and suggest that the donor properties of ligands 2a-d reside between that of 2g and PCy₃. The crystal structures of several [IrCl(cod)(L)] (L = 2a-d) and cis-[IrCl(CO) ₂(L)] (L = 2a-d and 2g) complexes are reported and used to quantify the ligand steric parameter.

Full text of DOI:10.1021/om101174x

ARTICLE
pubs.acs.org/Organometallics
Steric and Electronic Parameters Characterizing Bulky and
Electron-Rich Dialkylbiarylphosphines
Olivier Diebolt,†,‡ George C. Fortman,† Hervꢀe Clavier,†,‡,§ Alexandra M. Z. Slawin,†
Eduardo C. Escudero-Adꢀan,‡ Jordi Benet-Buchholz,‡ and Steven P. Nolan*,†,‡
†School of Chemistry, University of St-Andrews, St-Andrews KY16 9ST, U.K.
‡Institute of Chemical Research of Catalonia (ICIQ), Avenida Països Catalans 16, 43007, Spain
S Supporting Information
b
ABSTRACT: The steric and electronic properties of several
sterically demanding tertiary phosphines (dicyclohexylphos-
phino)biphenyl (2a), 2-dicyclohexylphosphino-20-methylbi-
phenyl (2b), 2-dicyclohexylphosphino-20,60-dimethoxybiphenyl
(2c), 2-dicyclohexylphosphino-20,40,60-triisopropylbiphenyl
(2d), 2-diphenylphosphino-20-(N,N-dimethylamino)biphenyl
(2e), 2-di-tert-butylphosphino-20-(N,N-dimethylamino)biphenyl
(2f), and di(cyclohexyl)phenylphosphine (2g) have been studied
by synthesizing and characterizing iridium complexes of types
[IrCl(cod)(L)] (L = 2a-d) and cis-[IrCl(CO)2(L)] (L = 2a-d and 2g). The infrared stretching frequencies of the carbonyl complexes
permit an estimation of the ligand donor properties (basicity) and suggest that the donor properties of ligands 2a-d reside between that of
2g and PCy3. The crystal structures of several [IrCl(cod)(L)] (L = 2a-d) and cis-[IrCl(CO)2(L)] (L = 2a-d and 2g) complexes are
reported and used to quantify the ligand steric parameter.
’ INTRODUCTION
of catalytic efficiency, to date there has been no quantification of
the influence of the nature of the R group on the basicity of the
phosphine ligand itself.
It is of great interest to study the properties of these ligands in
order to better understand their activity in homogeneous cata-
lysis. Recently our group has published work concerning the
bonding enthalpies of a series of phosphines, which included the
Buchwald phosphines, to the Au-Cl moiety as shown in eq 1.21
Tertiary phosphines continue to play a major role as ancillary
ligands in catalysis. As is a common theme in chemistry and other
sciences, the simpler systems are studied and then expanded
upon into more unique and specialized systems. In the case of
tertiary phosphines, the symmetrical aryl and alkyl ligands such as
PCy3, PPh3, and PiPr3 were first rigorously studied and then
modified. One salient example is found in the work of Buchwald,
whose replacement of one R group in PR3 structures with a biaryl
group has resulted in a plethora of catalytically active organo-
metallic complexes.
The Buchwald group synthesized monodentate biphenyldia-
kyl phosphines in 1998.1 They have found applications in
numerous fields of homogeneous catalysis.1-6 This is especially
true of palladium-catalyzed carbon-carbon,7-13 carbon-
nitrogen,14,15 and carbon-oxygen16-18 bond-forming pro-
cesses. The synthetic route leading to this ligand family allows
modulation of the nature of the substituents appended to the
architectural core and therefore permits fine-tuning of ligand
steric and electronic parameters. The flexibility of their
syntheses19 allows for a vast range of substitution and, thusly, a
considerable array of their properties in catalysis (Figure 1).
Tuning the R groups also permits a potential decrease in the
reactivity of the ligand toward molecular oxygen.7 In addition,
the R1, R2, and R3 substituents influence the size of the ligand but
also allow arene coordination with the metal and can promote
reductive elimination processes.20Although studies have been
compiled on the effects of changing these R groups as a function
CH Cl f
2
½AuðthtÞClꢀ þ PR3
½AuðPR3ÞClꢀ þ tht þ ΔHrxn
ð1Þ
30 °C
It was deduced that the ΔHrxn was predominately influenced by
the electron-donating abilities of the phosphine ligand. In the
present contribution, we hope to extend this study of phosphine
ligands on a very fundamental level.
Pioneered by the work of Tolman,13,22,23 the electronic and
steric properties of tertiary phosphines are now known to have a
crucial impact on homogeneous catalysis. Their quantitative
measurement is not trivial, and Tolman described two param-
eters:23 (1) the electronic parameter ν (or TEP), gauged by the
infrared CO stretching frequencies of the [Ni(CO)3(L)]
(L being the ligand of interest) complex; (2) the steric parameter
θ (or cone angle), which allows for the quantification of the steric
hindrance around the metal center. Although ν and θ do not fully
Received: December 15, 2010
Published: February 14, 2011
r
2011 American Chemical Society
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Figure 1. General structure of the biaryl-containing tertiary
phosphines.
describe the ligand behavior, they give an overview of their
important properties.
As mentioned above, Tolman chose to use [Ni(CO)3(L)] to
examine the electronic parameter of L. Unfortunately, the
starting material used in the synthesis of the nickel complexes,
[Ni(CO)4], is extremely toxic and volatile. Moreover, in special
cases, the reaction between [Ni(CO)4] and very bulky ligands L
can lead to substitution of two carbonyl groups and the formation
of three-coordinate [Ni(CO)2L].24,25 In these cases, the Tolman
electronic parameter (TEP) cannot be measured.
Alternatives to this nickel method have been investigated.
Among them, carbonyl complexes of Rh, Cr, Mo, and W have
been considered.26-34 Finally, the iridium system cis-[IrCl-
(CO)2L] was found to be the most general.35,36 The reactions
take place in good yields, and the starting dimer [Ir(μ-Cl)(cod)]2
(1)37 (cod = 1,5-cyclooctadiene) is easily manipulated and
generally less toxic. Its reaction with a coordinating ligand L
(L generally is a 2 e- donor) leads to the monomeric species
[IrCl(cod)L], which reacts with carbon monoxide to form the
dicarbonyl species cis-[IrCl(CO)2L]. We wish to broaden the
scope of phosphines for which this fundamental knowledge of
steric and electronic parameters is known to the Buchwald
phosphines by utilizing a similar strategy.
Figure 2. Tertiary phosphines used in this study.
Scheme 1. Synthesis of [IrCl(cod)L] Complexes
Herein, we report the synthesis of [IrCl(cod)L] and cis-[IrCl-
(CO)2L] complexes where L is a series of unsymmetrical tertiary
phosphines. Measurement of the carbonyl stretching frequencies
of the latter complexes allowed for the first estimation of the
electronic parameters associated with the Buchwald phosphines.
Additionally, X-ray diffraction data on single crystals, for the
above-mentioned complexes, are reported and allowed for a
quantitative comparison of the steric bulk of these ligands.
temperature for 3 h (Scheme 1) and resulted in the square-planar
d8 Ir(I) complexes [IrCl(cod)L]. Unfortunately, the phosphine 2f
did not react with the starting dimer. Reactions with this ligand
conducted overnight at 80 °C led to the recovery of the unreacted
starting materials. The steric bulk conferred by the two tert-butyl
groups may impede this reaction. Of note, 2b reacted slowly with
[Ir(μ-Cl)(cod)]2 at room temperature, and the mixture had to be
stirred at 60 °C to afford complete conversion. The obtained
complex 3b is highly unsymmetrical in NMR, giving four different
signals in 1H and 13C for the CH of the cyclooctadiene. Moreover,
the 31P shift appeared very broad at room temperature, which
suggests hindered rotation about the Ir-P bond in solution.
Single crystals suitable for X-ray analysis were grown by slow
evaporation of solvents at room temperature from saturated
solutions containing the complex.38 The resulting structural
solutions are displayed in Figure 3. Unfortunately, repeated
attempts to crystallize complex 3e failed. The iridium atom
adopts a square-planar geometry around the metal center in all
structures obtained. Selected bond lengths and angles are given
in Tables 1 and 2 respectively.
’ RESULTS AND DISCUSSION
To gauge the influence of the substitution around the ligands,
the phosphines depicted in Figure 2 were selected. Phosphines
2a-d bear two cyclohexyl groups, their dissimilarity residing in
the substitution around the second aryl moiety, R1, R2, and R3.
Phosphines 2e and 2f, bearing phenyl and tert-butyl substituents,
would permit observation of the influence of the group R. Of
note, several unsuccessful attempts to synthesize [Ni(CO)3(L)]
complexes with the Buchwald ligand series were conducted.
These ligands simply appear to be too sterically demanding and
do not afford simple products amenable to facile characterization.
Therefore the selection of the iridium system appears to be the
judicious choice. Finally, to permit a comparison, the steric and
electronic properties of PCy2Ph (2g), as a model complex, were
also investigated.
Synthesis of [IrCl(cod)L] Complexes. The ligands shown in
Figure 2 were reacted with [Ir(μ-Cl)(cod)]2 (1) in THF at room
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Figure 4. ORTEP representation showing weak Ir---H anagostic inter-
action in complex 3a.
to direct the second phenyl ring away from the metal center,
whereas the complexes with less substituted biphenyls (3a and
3b) appear to direct the second phenyl ring toward the metal.
The common thread appears to be ortho substitution of the
pendant aryl ring. Indeed, there appears to be a weak Ir---H
anagostic interaction in these complexes. Complexes 3a and 3b
contain Ir---H distances41 of 2.640 and 2.710 Å, where the H
atom donor is the C-H that is ortho on the pendant aryl ring of
the phosphine. As shown in Figure 4, the H atom appears to align
along the z-axis, which is perpendicular to the coordination plane
of the metal center.
For complexes 3c and 3d the shortest Ir---H distances are
3.383 and 3.047 Å, respectively. Here the H atom is one-bonded
to a cyclohexyl ring. These M---H distances are just beyond the
generally accepted distance for an anagostic interaction.42 This
highlights the effects of the substitution on the second aryl group
of the biphenyl moiety on general molecular orientation (at least
in the solid state). This possible coordination mode, although
weak, may be a way to stabilize coordination complexes and help
explain the unique reactivities displayed by complexes bearing
members of this ligand family. It cannot, however, be discredited
that these conformations are solely due to the steric bulk of the
Buchwald ligands. The larger phosphines, 2c and 2d, may indeed
adopt an orientation in which the biaryl ring faces away from the
metal simply to reduce steric interactions with the metal center.
In this case the apparent anagostic M---H interactions would be
secondary in nature.
Figure 3. ORTEP representation of [IrCl(cod)L] (3a-d). Hydrogens
are omitted for clarity.
Table 1. Selected Bond Lengths (Å) for the [IrCl(cod)L]
Complexes
complex
Ir-P (Å)
Ir-Cl
Ir-cod (av)a
Ir-cod (av)b
3a
3b
3c
3d
2.3562(4)
2.3577(3)
2.3335(5)
2.346(1)
2.3521(6)
2.3625(3)
2.3676(5)
2.359(1)
2.123(2)
2.121(2)
2.117(2)
2.116(6)
2.184(2)
2.182(2)
2.178(3)
2.178(8)
a COD cis to phosphine. b COD trans to phosphine.
Table 2. Selected Angles (deg) for the [IrCl(cod)L]
Complexes
complex
P-Ir-Cl
P-Ir-Ccis-cod (av)
P-Ir-Ctrans-cod (av)
3a
3b
3c
3d
92.504(17)
93.682(10)
90.335(17)
89.64(5)
92.50(5)
92.83(4)
95.03(6)
96.2(1)
161.26(5)
161.3(4)
161.5(1)
161.3(2)
The Ir-P bond distances are similar in all complexes and fall
within the range 2.33-2.36 Å. As expected, the CH2dCH2 trans
to the Cl is slightly closer to the metal center than the CH2dCH2
trans to the phosphine. This is assuredly due to the π-basicity of
the Cl ligand as opposed to the weakly π-acidic phosphine.
Consequently, this would result in greater back-donation and a
slightly higher bond order for the Ir-COD for the side trans to
the chlorine ligand. Similar in character, structures of
[IrCl(cod)(PEt3)]39 and [IrCl(cod)(PBz3)]40 have previously
been published. No significant deviations from the norm appear
to be present for the PR2R0 complexes presented herein.
Synthesis of cis-[IrCl(CO)2L] Complexes. Dichloromethane
solutions of [IrCl(cod)L] placed under 1 atm of CO for 1 h
resulted in clean substitution of the cyclooctadiene to form the
corresponding greenish complexes 4a-d and 4g, cis-[IrCl-
(CO)2L] (see Scheme 2). Surprisingly, most of these dicarbonyl
complexes are not stable toward air and need to be handled under
inert atmosphere. Unfortunately, the carbonylation of 3e led to
the formation of two unknown products. Attempts to isolate
these products by crystallization or flash chromatography led to
product decomposition.
31P NMR chemical shifts differ, as expected, as a function of
the ligand and range between 19.7 and 40.9 ppm (see Table 3). In
contrast, the 13C signals corresponding to the carbonyl are very
similar. The carbonyl carbon cis to the phosphine (trans to the
Interestingly for the Buchwald ligand series, each tertiary
phosphine adopts a different spatial conformation. The com-
plexes containing more substituted biphenyls (3c and 3d) tend
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Cl) retained a chemical shift at approximately 169 ppm and
2JCP = 12 Hz, while the carbon in trans position displayed a
chemical shift at ca. 178 ppm and 2JCP = 115 Hz.
Single crystals suitable for X-ray analysis of 4a-d and 4g were
obtained by slow evaporation of solvents from saturated solu-
tions. ORTEP diagrams of the XRD data are shown in Figure 5,
and selected bond lengths and angles are given in Tables 4 and 5.
Compared to the cod complexes, the Ir-P bond is slightly longer
for complexes 4a-d and 4g. Metal to CO back-donation is
stronger than in the cod complexes, and thus there is less
donation into the P-C σ* orbitals, which in turns causes the
Ir-P bond distance to increase. Also lack of the spatial restriction
introduced by the chelating cod ligand allows the bond angles to
approach the classical 90° found in square-planar complexes.
Additionally, the orientation of the biphenyl ring is the same as
that found in the cod complexes. That is, the more substituted
biphenyls are positioned away from the phosphorus and metal
center, whereas the biphenyls with less substitution are directed
toward the metal. Despite the fact that the shortest Ir---H
distances are more uniform for complexes 4a-d (2.918-2.946
Å) than for 3a-d (2.640-3.383 Å), the H atoms closest to the
metal center are the same as those in the cod complexes. That is,
for complexes 4a and 4b, the H is attached to the pendant aryl
ring, while for complexes 4c and 4d the H is bonded to a
cyclohexyl ring. Again, it must be stated that the orientation of
the biaryl rings may be solely due to ligand size. The larger ligands
2c and 2d may twist away from the metal center in an attempt to
reduce steric pressure about the metal center.
Scheme 2. Synthesis of cis-[IrCl(CO)2L] Complexes
Table 3. Selected Chemical Shifts (ppm) of the cis-[IrCl-
(CO)2L] Complexes
complex
δ
31P δ C(cis-CO) (2JCP, Hz) δ C(trans-CO) (2JCP, Hz)
4a
4b
4c
4d
4g
29.3
168.9 (12.1)
168.8 (12.2)
168.8 (12.4)
169.4 (11.8)
168.7 (12.4)
178.1 (115.1)
178.3 (115.1)
178.2 (115.1)
178.1 (114.7)
178.8 (115.7)
32.8
29.9
40.9
19.7
Comparison of metrical parameters between complexes 4a-d
and 4g highlights no significant variation in bond angles or
lengths about the Ir metal center as a function of the pendant aryl
ring. There does not, however, appear to be any weak Ir---H
Figure 5. ORTEP representation of cis-[IrCl(CO)2L] complexes 4a-d and 4g. Hydrogens are omitted for clarity.
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Table 4. Selected Bond Lengths (Å) for cis-[IrCl(CO)2L] Complexes 4a-d and 4g
complex
Ir-P (Å)
Ir-Cl
Ir-COa
1.828(8)
Ir-COb
1.896(8)
4a
4b
4cc
4d
4g
2.380(2)
2.348(2)
2.365(1)
2.328(1)
1.826(3)
1.883(3)
2.385(3), 2.389(3)
2.373(1)
2.359(3), 2.328(3)
2.347(1)
1.85(1), 1.82(1)
1.856(4)
1.88(1), 1.86(1)
1.900(4)
2.373(2)
2.355(2)
1.855(8)
1.899(9)
a CO cis to phosphine. b CO trans to phosphine. c Complex contains two independent molecules within the unit cell.
Table 5. Selected Angles (deg) for cis-[IrCl(CO)2L] Com-
plexes 4a-d and 4g
Table 6
ligand
νCO, cm-1
av νCO, cm-1
TEP, cm-1a
complex
P-Ir-Cl
P-Ir-COa
P-Ir-COb
COa-Ir-COb
b
PPh3
2002, 2085
1991, 2075
1986, 2077
1989, 2073
1987, 2070
1984, 2072
1986, 2069
1985, 2070
2067, 1981
2065, 1981
2043.5
2033.0
2031.5
2031.0
2028.5
2028.0
2027.5
2027.5
2023.9
2023.0
2068.9
2058.0
2059.2
2056.3
2054.1
2056.4
2053.3
2053.3
2051.5
2049.6
4a
87.15(6)
87.81(11)
90.4(1),
89.8(1)
91.8(2)
92.07(9)
89.9(3),
89.3(4)
91.9(1)
90.3(2)
176.9(2)
174.19(9)
178.7(4),
174.8(5)
174.9(1)
173.1(3)
91.4(3)
91.5(1)
88.8(5),
94.4(6)
91.0(2)
90.7(4)
PCy2Ph (2g)
PiPr3
b
4b
4cc
Cy-JohnPhos (2a)
S-Phos(2c)
b
4d
4g
88.33(3)
PCy3
90.09(7)
Me-Phos (2b)
X-Phos(2d)
IPrc
a CO cis to phosphine. b CO trans to phosphine. c Complex contains two
independent molecules within the unit cell.
ICyc
anagostic interaction in 4g. The closest Ir---H distance for
complex 4g is 3.110 Å.
a TEP values in italics calculated from linear regression derived in ref 36a.
b νCO for [IrCl(CO)2(L)] from ref 35. TEP values from ref 23. c νCO for
[IrCl(CO)2(L)] from ref 36a. TEP values from ref 25.
To date, only one other related structure has been reported.
Schumann et al. published the structure of cis-[IrCl(CO)2-
(PtBu3)] in 1979.43 The Ir-P bond length of cis-[IrCl(CO)2-
frequencies. The TEP can be calculated using the correlation
shown in eq 2.
t
ꢀ
(P Bu3)] is slightly longer (2.43(1) Å) than that of structures of
the carbonyl complexes reported herein (2.365(1)-2.385(3)
Å). Most strikingly, the bond angles about the Ir metal center are
somewhat more perturbed in cis-[IrCl(CO)2(PtBu3)] (P-Ir-
Cl = 94.8(5)o; P-Ir-cisCO = 98.2(15)o) than in complexes 4a-
d and 4g, suggesting that the unsymmetrical phosphine ligands
studied herein are not as sterically demanding as the PtBu3 ligand.
Infrared Spectroscopy and Derived Electron Donor Prop-
erty. Measurement of the characteristic νCO stretching frequen-
cies of the cis-[IrCl(CO)2(PR3)] complexes by FT-IR
spectroscopy was performed. As expected, two bands of similar
intensity (as typical of cis-CO in square-planar complexes) in the
carbonyl region were observed. Complexes 4a-d displayed
similar stretches in the ranges 1980-1989 and 2069-
2073 cm-1, slightly lower than that of complex 4g, where
νCO = 1991 and 2075 cm-1 were recorded. It is well known
that changes in carbonyl stretching frequency are related to the
electron-donating/withdrawing abilities of other ligands bound
to the metal center. As such, we compared the carbonyl stretch-
ing frequencies of complexes 4a-d and 4g to other
[IrCl(CO)2(L)] complexes (Table 6).
TEP ¼ 0:847 ꢁ ðνCOaverageÞ þ 336
ð2Þ
The results are shown in Table 6. It was found that the electronic
parameters of the biaryl-containing phosphines fall between
2054 and 2056 cm-1. The estimated TEPs suggest a slightly
different ordering of electron-donating ability but in general still
imply a higher basicity than PCy2Ph and very similar to that of
PCy3. It should be stated, however, that these derived TEP values
are estimations at best, and the direct comparison of Ir complexes
and the primary data they furnish should be a better gauge of
their electronic parameter.44 The high electron-donating ability
of the biaryl phosphines correlate well with catalytic perfor-
mance, as is observed for the facile oxidative addition of aryl
chlorides at room temperature for palladium catalysts bearing
strong σ-donating ligands.45
Steric Parameter. The second parameter described by Tol-
man is the cone angle (θ). It is defined as a “cylindrical cone from
the center of the P atom, which just touches the van der Waals
radii of the outermost atoms of the model”.23 The phosphine
ligands 2 are nonsymmetrical, and the corresponding symme-
trical phosphines bearing three biaryl substituents (which would
allow the calculation of θ) have not been reported. As an
alternative, a computational method has been developed by
Cavallo et al. that should be useful in the present system.46
The parameter %Vbur is defined as the amount of the volume of a
sphere centered on the metal occupied by atoms of a ligand. The
putative metal atom was positioned at 2.334 Å (the shortest bond
length of all the structures obtained in this study; that of complex
3c) from the phosphorus atom, and the radius of the sphere was
chosen as 3.5 Å. The calculated values for the complexes reported
herein and of other relevant ligands are shown in Figure 6.47
From Table 6 it can be seen that all of the Buchwald family
phosphines investigated appear to be more electron donating
than PCy2Ph. Of the set, Cy-JohnPhos appears to be the least
donating, while X-Phos ≈ Me-Phos are the most donating. The
carbonyl stretches of 4b-d suggest that S-Phos, Me-Phos, and
X-Phos are very similar in basicity to PCy3. These biaryl
phosphines are less donating than the N-heterocyclic carbenes
(NHCs) ICy and IPr.36a
A method initially developed by Crabtree35 and later refined
by our group36a allows for the determination of the Tolman
electronic parameter (TEP) by correlation of the CO stretching
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Table 7. Calculated %Vbur Valuesb for Ligands 2a-d Using
[AuCl(L)]c and [IrCl(CO)2Cl] Complexesa
[AuCl(L)]c
2.28 Å
[IrCl(CO)2(L)]
ligand
2.00 Å
2.00 Å
2.28 Å
2a
2b
2c
2d
2g
51.0
53.6
53.7
57.4
38.0
46.7
49.3
49.7
53.1
32.7
40.2
40.6
38.0
38.9
36.8
35.0
35.4
32.6
33.4
31.6
a The M-L distances of 2.00 and 2.28 Å were used to achieve
consistency with ref 48. b Values calculated using ref 46b. c Values
obtained from ref 48.
NHC = ICy, IMes, IAd, and IPr. Of the NHCs only the extremely
bulky IAd ligand is of a similar size as the biarylphosphines
examined here.
Interestingly, the %Vbur of ligands 2a-d appears to be heavily
dependent upon the metal center. For example, X-Phos was
calculated to have a %Vbur of 57.4-53.1% for [Au(X-Phos)Cl].48
For complex 4d, using the same values for M-L distance as those
used for the gold calculation, we obtained values of 38.9 and
33.5% for %Vbur. Shown in Table 7 is a comparison of %Vbur of
ligands 2a-d in the complexes [IrCl(CO)2(L)] and [AuCl(L)].
The buried volume for all of the biaryl phosphines varies by more
than 10% depending on whether the system is [AuCl(L)] or
[IrCl(CO)2Cl].
Conversely, the %Vbur for PCy2Ph (2g) varies by less than
1.5%. This exemplifies a possible fluctionality of these biaryl
ligands. These ligands can apply different steric pressures on the
metal center depending upon the steric environment about the
coordination sphere of the metal. Ligand flexibility has been
shown to enhance catalytic activity,49 and this may help explain
why these biaryl-containing phosphines have repeatedly been
shown to be excellent ligands in catalytic systems.
Figure 6. Selected %Vbur (%) calculated with Ir-P = 2.334 Å. Values in
bold are based on the [Ir(Cl)(cod)L] X-ray structures, and values in
italics are based on [Ir(Cl)(CO)2L] X-ray structures. Calculated using
ref 46b. aValue based on XRD data from ref 43. bValues based on XRD
obtained from ref 36a.
Upon examination of these data, the first observation is that all
biaryl phosphines are relatively bulky (2a-d and 2g), the %Vbur
being in the range 29-35%. Values determined from structures
of [Ir(Cl)(cod)L] and cis-[Ir(Cl)(CO)2L] were found to vary by
no more than 1.2%. Surprisingly, increasing the substitution
(from 2a to 2d) decreases the steric factor. This may be the result
of the aforementioned availability of the ortho H on the pendant
aryl ring and subsequent weak Ir---H anagostic interaction.
Indeed, the phosphines 2a and 2b have a %Vbur 35.0/33.8 and
34.1/34.4% (cod/(CO)2 complexes), respectively, whereas the
substituted phosphines 2c and 2d have a lower buried volume
value of approximately 31%. From the crystal structures in
Figures 3 and 5, it can be stated that the more highly substituted
biphenyl ligands shift the substituted ring away from the metal,
whereas the second phenyl ring is angled toward the Ir center in
the structures of 3a/b and 4a/b. Of the carbonyl complexes
examined, PCy2Ph (2g) possesses the lowest %Vbur (30.6%).
This is in line with the obvious difference of the lack of the
pendant aryl group and additionally consistent with the lack of
any significant Ir---H anagostic interaction in complex 4g.
The structure of cis-[IrCl(CO)2(PtBu3)] has been reported.43
Using the same bond distance (2.334 Å), a value of 34.9% was
calculated for the buried volume of PtBu3 in this iridium
environment. This value is nearly identical to the one calculated
for 2a. One advantage of the %Vbur calculation over Tolman’s
cone angle is that it allows for a direct comparison between
NHCs and phosphines. Again, using the bond distance of 2.334
Å, values were calculated for the reported structures36 of
[IrCl(cod)(NHC)] and cis-[IrCl(CO)2(NHC)], where
’ CONCLUSION
New iridium complexes bearing biaryl phosphine ligands
[IrCl(cod)L] 3a-e and 3g have been successfully synthesized
and characterized. Only the very bulky phosphine 2f did not react
with the dimer 1. Placed under one atmosphere of carbon
monoxide, 3a-d and 3g gave the dicarbonyl complexes cis-[IrCl-
(CO)2(L)] 4a-d and 4g. The carbonyl stretching frequencies of
these complexes suggest that IPr > X-Phos ≈ Me-Phos ≈ PCy3
≈ S-Phos > Cy-DavePhos > PCy2Ph . PPh3 in terms of
electron-donating ability. The characterization of the complexes
by XRD allowed for the calculation of %Vbur of these ligands in
the square-planar environment. For the square-planar Ir systems
studied here, some Buchwald phosphine ligand family members
were found to have relatively medial %Vbur (29-35%). It was
shown that increasing the substitution on the pendant aryl
moiety caused a decrease in ligand %Vbur that may arise from
weak M---H anagostic interactions between the ortho C-H
pendant aryl moiety and metal center. Most interestingly was a
substantial (>10%) change in %Vbur for ligands 2a-d between
different metal complexes. This large change demonstrates that
the biaryl phosphines are indeed flexible, and this important
structural feature may help explain the attractive catalytic beha-
vior of complexes that incorporate these ligands.
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Organometallics
ARTICLE
’ EXPERIMENTAL SECTION
resulting solid added with cold hexane. The resulting suspension was
filtered and washed with cold hexane, leading to 211 mg (94%) of a
yellow, microcrystalline solid. 1H NMR (CD2Cl2): δ(ppm) 0.62-0.85
(m, CH2, 2H), 1.02-1.22 (m, CH2, 4H), 1.30-1.86 (m, CH2, 16H),
1.94-2.27 (m, CH2, 6H), 2.55 (q, 2JHH = 10.5 Hz, CH-Cy, 2H), 2.99 (br
s, CH-cod, 2H), 3.71 (s, CH3, 6H), 4.69 (br s, CH-cod, 2H), 6.68 (d,
2JHH = 8.4 Hz, Ph-H, 2H), 6.92-6.99 (m, Ph-H, 1H), 7.35-7.45 (m,
Ph-H, 3H), 7.66-7.75 (m, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm)
26.5 (s, CH2), 27.6 (d, JCP = 11.3 Hz, CH2), 28.2 (d, JCP = 11.7 Hz,
General Considerations. All reactions were carried out using
standard Schlenk techniques under an atmosphere of dry argon or in an
MBraun glovebox containing dry argon and less than 1 ppm oxygen.
Ligands 2a-g were purchased from Sigma-Aldrich Chemicals. [IrCl-
(cod)]2 was graciously donated from Umicore. [IrCl(cod)(PCy2Ph)]
was prepared following literature procedures.50 NMR solvents were
dried over molecular sieves and degassed with argon before use. 1H, 13C,
and 31P NMR spectra were recorded on a Bruker 400 or 300 MHz
spectrometer at ambient temperature. IR spectra were recorded on a
FTIR Bruker Tensor 27 with an ATR cell in CH2Cl2.
CH2), 29.5 (m, CH2), 31.0 (m, CH2), 33.2 (m, CH2), 34.7 (d, 1JCP
=
26.5 Hz, CH-Cy), 55.5 (s, CH3), 88.3 (d, 1JCP = 13.8 Hz, CH-Cy), 104.0
(s, Ph-CH), 125.0 (d, JCP = 12.1 Hz, CH-Ph), 126.3 (d, JCP = 31.0 Hz,
Synthesis of [IrCl(cod)(2a)] (3a). In a glovebox, a round-bottom
flask was charged with [Ir(μ-Cl)(COD)]2 (200 mg, 0.298 mmol), 2a
(210 mg, 0.600 mmol), and dry toluene (10 mL). The solution was
stirred at room temperature for 3 h, while the product precipitated. The
solvent was evaporated, and 20 mL of acetone was added. The resulting
suspension was filtered and washed with acetone, leading to 387 mg
(94%) of a yellow microcrystalline product. 1H NMR (CDCl3): δ(ppm)
0.92-1.14 (m, CH2, 6H), 1.18-1.33 (m, CH2, 2H), 1.38-1.71 (m,
CH2, 14H), 1.93-2.17 (m, CH2, 6H), 2.47-2.57 (m, CH-Cy, 2H), 2.74
(br s, CH-cod, 2H), 4.74-4.79 (m, CH-cod, 2H), 7.15-7.21 (m, Ph-H,
2H), 7.30-7.38 (m, Ph-H, 6H), 7.83-7.89 (m, Ph-H, 1H). 13C NMR
(CD2Cl2): δ(ppm) 26.4 (s, CH2), 27.9 (d, J = 9.7 Hz, CH2), 29.1 (s,
CH2), 30.5 (d, J = 5.1 Hz, CH2), 31.7 (s, CH2), 33.6 (s, CH2), 36.0 (d, J =
23.1 Hz, CH-Cy), 53.4 (s, CH-cod), 87.2 (s, CH-cod), 87.4 (s, CH-cod),
126.2 (d, J = 7.3 Hz, CH-Ph), 127.2 (d, J = 34.1 Hz, C-Ph), 127.9 (s, CH-
Ph), 128.0 (s, CH-Ph), 129.1 (s, CH-Ph), 130.1 (s, CH-Ph), 132.1 (d, J =
5.9 Hz, CH-Ph), 132.6 (d, J = 6.9 Hz, CH-Ph), 141.8 (s, Ph-C), 145.9 (d,
J = 6.7 Hz, CH-Ph). 31P NMR (CD2Cl2): δ(ppm) 18.71. Anal. Calcd for
C32H43ClIrP (MW 686.33): C, 56.00; H, 6.31. Found: C, 56.30; H, 6.32.
Synthesis of [IrCl(cod)(2b)] (3b). In a glovebox, a round-
bottom flask was charged with [Ir(COD)Cl]2 (200 mg, 0.298 mmol),
2b (217 mg, 0.600 mmol), and dry toluene (3 mL). The solution was
stirred at 60 °C for 8 h. After this time, the volatiles were evaporated, and
the resulting orange solid was dissolved in 3 mL of acetone. To this
solution was added 15 mL of tert-butylmethyl ether to precipitate the
product. Isolation by filtration leads to 319 mg (77%) of a yellow
microcrystalline solid. 1H NMR (CD2Cl2): δ(ppm) 0.72 (m, CH2, 1H),
0.86-1.21 (m, CH2, 6H), 1.27-1.37 (m, CH2, 1H), 1.44-1.82 (m,
CH2, 14H), 1.89-2.35 (m, CH2, 11H) (this multiplet contains a singlet
integrating for three protons corresponding to CH3), 2.71 (pseudosept,
J = 3.5 Hz, CH-cod, 1H), 2.89-2.97 (m, CH-cod, 1H), 4.59
(pseudosept, J = 3.7 Hz, CH-cod, 1H), 4.68 (pseudosept, J = 3.6 Hz,
CH-cod, 1H), 6.97-7.03 (m, Ph-H, 1H), 7.05-7.14 (m, Ph-H, 2H),
7.14-7.24 (m, Ph-H, 3H), 7.25-7.35 (m, Ph-H, 2H), 7.53-7.51 (m,
Ph-H, 1H), 7.75 (br d, J = 6.8 Hz, CH-Ph, 1H). 13C NMR (CD2Cl2):
δ(ppm) 20.8 (s, CH3), 26.6 (d, J = 4.8 Hz, CH2), 27.8 (d, J = 11.1 Hz,
CH2), 27.9 (d, J = 13.8 Hz, CH2), 28.0 (d, J = 11.1 Hz, CH2), 28.1 (d,
J = 9.3 Hz, CH2), 29.0 (br s, CH2), 29.7 (br s, CH2), 30.7 (br s, CH2),
30.9 (d, J = 1.5 Hz, CH2), 32.8 (d, J = 4.7 Hz, CH2), 33.0 (d, J = 2.8 Hz,
CH2), 34.2 (d, J = 3..2 Hz, CH2), 34.6 (d, J = 25.2 Hz, CH-Cy), 36.7 (d,
J = 23.7 Hz, CH-Cy), 53.0 (s, CH-cod), 55.2 (s, CH-cod), 87.8 (d, J =
14.0 Hz, CH-cod), 88.0 (d, J = 12.3 Hz, CH-COD), 125.5 (s, CH-Ph),
125.7 (d, J = 10.1 Hz, CH-Ph), 128.3 (s, CH-Ph), 129.1 (br s, CH-Ph),
129.0 (br d, J = 1.7 Hz, CH-Ph), 131.0 (br d, J = 3.2 Hz, CH-Ph), 133.2
(d, J = 6.3 Hz, CH-Ph), 135.9 (br d, J = 14.6 Hz, CH-Ph), 136.1 (s, C-
Ph), 141.4 (s, C-Ph), 145.0 (br s, C-Ph). 31P NMR (CD2Cl2): δ(ppm)
28.52 (br s). Anal. Calcd for C38H57ClIrPO (2 þ TBME) (MW
788.50): C, 57.88; H, 7.29. Found: C, 57.84; H, 6.69.
C-Ph), 129.4 (d, JCP = 1.8 Hz, CH-Ph), 130.0 (s, CH-Ph), 134.0 (d, JCP
=
5.8 Hz, CH-Ph), 136.5 (d, JCP = 18.0 Hz, CH-Ph), 139.4 (s, C-Ph), 158.3
(s, C-Ph). 31P NMR (CD2Cl2) δ(ppm): 37.01. Anal. Calcd for
C33H45ClIrOP (MW 746.38): C, 54.71; H, 6.35. Found: C, 54.77; H,
6.43.
Synthesis of [IrCl(cod)(2d)] (3d). In a glovebox, a round-
bottom flask was charged with [Ir(COD)Cl]2 (100 mg, 0.149 mmol),
2d (142 mg, 0.298 mmol), and dry toluene (3 mL). The resulting
solution was stirred at room temperature for 3 h. The solvent was then
evaporated, and the resulting solid added with cold hexane. The
resulting suspension was filtered and washed with cold hexane, leading
to 175 mg (61%) of a yellow, microcrystalline solid. 1H NMR (CD2Cl2):
δ(ppm) 0.72-2.58 (m, CH2-cod; CH2-Cy, CH3-iPr, 47H), 2.66-2.85
(m, 3H), 2.98 (sept, 2JHH = 6.9 Hz, CH-iPr, 2H), 3.23 (m, 1H), 4.73 (m,
CH-COD, 1H), 7.08 (ddd, J = 7.6 Hz, J = 2.9 Hz, J = 1.7 Hz, Ph-H, 1H),
7.11 (s, Ph-H, 2H), 7.39 (tt, J = 7.5 Hz, J = 1.6 Hz, Ph-H, 1H), 7.47 (bt, J
= 7.6 Hz, Ph-H, 1H), 7.86-7.97 (m, Ph-H, 1H). 13C NMR (CD2Cl2):
δ(ppm) 22.4, 22.9, 24.2, 25.9, 26.5, 26.7, 27.1, 27.5, 27.9, 28.3, 28.5, 29.5,
30.5, 31.0, 31.3, 31.7, 32.8, 33.8, 34.8, 35.6, 36.4, 36.8, 88.2 (s, CH-cod),
88.3 (s, CH-cod), 121.1 (s, CH-Ph), 121.7 (s, CH-Ph), 125.1 (d, JPC
=
12.0 Hz, CH-Ph), 128.6 (d, JPC = 2.0 Hz, CH-Ph), 135.2 (d, JPC = 6.1 Hz,
CH-Ph), 136.9 (s, C-Ph), 144.0 (s, C-Ph), 147.0 (s, C-Ph), 149.3 (s, C-
Ph). 31P NMR (CD2Cl2): δ(ppm) 38.86. Anal. Calcd for C41H61ClIrP
(MW 812.57): C, 60.60; H, 7.57. Found: C, 60.28; H, 7.45.
Synthesis of [IrCl(cod)(2e)] (3e). In a glovebox, a round-bottom
flask was charged with [Ir(cod)Cl]2 (100 mg, 0.149 mmol), 2e (114 mg,
0.298 mmol), and dry toluene (3 mL). The resulting solution was stirred
at room temperature for 3 h. The solvent was then evaporated, and the
resulting solid added with cold hexane. The resulting suspension was
filtered and washed with cold hexane, leading to 139 mg (65%) of a
yellow microcrystalline solid. 1H NMR (CD2Cl2): δ(ppm) 8.14 (ddd,
J = 13.6 Hz, J = 7.6 Hz, J = 1.2 Hz, H-Ph), 7.78 (m, 2H, H-Ph), 7.49-
7.16 (m, 10H, H-Ph), 7.10 (m, 3H, H-Ph), 6.68 (dd, J = 8.1 Hz, J = 0.9
Hz, 1H, H-Ph), 5.08 (m, 1H, CH-cod), 4.98 (m, 1H, CH-cod), 2.88 (m,
1H, CH-cod), 2.59 (m, 1H, CH-cod), 2.31 (m, 2H, -CH2-cod), 2.20
(s, 8H, N-(CH3)2 and -CH2-cod), 1.91 (m, 1H, CH2-cod), 1.80 (m,
1H, -CH2-cod), 1.57 (m, 2H, CH2-cod). 13C NMR (CD2Cl2): δ(ppm)
150.5 (s, C-Ph), 146.6 (d, JCP = 2.2 Hz, C-Ph), 140.4 (s, CH-Ph), 140.2
(s, CH-Ph), 136.7 (d, JCP = 12.3 Hz, CH-Ph), 134.9 (d, JCP = 10.4 Hz,
CH-Ph), 133.1 (d, JCP = 6.6 Hz, CH-Ph), 132.8 (s, CH-Ph), 132.5 (d,
JCP = 2.2 Hz, C-Ph), 130.8 (m, CH-Ph), 130.7 (m, CH-Ph), 130.4 (m,
CH-Ph), 130.2 (m, CH-Ph), 130.0 (d, JCP = 2.3 Hz, CH-Ph), 129.8 (m,
CH-Ph), 129.5 (m, CH-Ph), 128.6 (s, CH-Ph), 127.4 (d, JCP = 9.9 Hz,
CH-Ph), 127.2 (d, JCP = 9.6 Hz, CH-Ph), 125.40 (d, JCP = 13.9 Hz, CH-
Ph), 119.9 (s, CH-Ph), 117.4 (s, CH-Ph), 91.6 (d, JCP = 13.9 Hz, CH-
cod), 91.0 (d, JCP = 14.4 Hz, CH-cod), 53.7 (br s, CH-cod), 52.8 (br s,
CH-cod), 42.8 (s, N-CH3), 33.9 (br s, CH2-cod), 33.07 (br s, CH2-cod),
30.2 (br s, CH2-cod), 29.3 (br s, CH2-cod). 31P NMR (CD2Cl2):
δ(ppm) 27.76. Anal. Calcd for C34H48ClIrNP (MW 717.30): C,
56.93; H, 5.06; N, 1.95. Found: 56.83; H, 5.16; N, 2.05.
Synthesis of [IrCl(cod)(2c)] (3c). In a glovebox, a round-bottom
flask was charged with [Ir(cod)Cl]2 (100 mg, 0.149 mmol), 2c (122 mg,
0.298 mmol), and dry toluene (3 mL). The resulting solution was stirred
at room temperature for 3 h. The solvent was then evaporated, and the
Synthesis of cis-[IrCl(CO)2(2a)] (4a). A flask was charged with
3a (80 mg, 0.117 mmol) and dichloromethane (4 mL). A balloon filled
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Organometallics
ARTICLE
with CO was connected to the flask. The orange solution rapidly turned
yellow at room temperature. After 1 h, the solvent was evaporated and
the resulting solid was washed with hexane (2 ꢁ 3 mL), affording 62 mg
(84%) of a pale green powder. 1H NMR (CD2Cl2): δ(ppm) 0.97-1.16
(m, CH2-Cy, 6H), 1.21-1.36 (m, CH2-Cy, 2H), 1.39-1.53 (m, CH2-
Cy, 2H), 1.53-1.73 (m, CH2-Cy, 6H), 1.74-1.83 (m, CH2-Cy, 2H),
1.98-2.08 (m, CH2-Cy, 2H), 2.25 (m, CH-Cy, 2H), 7.15-7.19 (m,
CH-Ph, 1H), 7.30-7.47 (m, CH-Ph, 7H), 7.67-7.74 (m, CH-Ph, 1H).
13C NMR (CD2Cl2): δ(ppm) 26.5 (s, CH2-Cy), 27.5 (s, CH2-Cy), 27.7
(d, JCP = 2.1 Hz, CH2-Cy), 30.1 (d, JCP = 2.7 Hz, CH2-Cy), 31.3 (s, CH2-
Cy), 35.5 (d, JCP = 27.9 Hz, CH-Cy), 125.3 (d, JCP = 43.2 Hz, C-Ph),
127.1 (d, JCP = 9.1 Hz, CH-Ph), 128.3 (s, CH-Ph), 128.4 (s, CH-Ph),
130.2 (s, CH-Ph), 130.4 (d, JCP = 2.1 Hz, CH-Ph), 132.8 (d, JCP = 7.7 Hz,
CH-Ph), 136.0 (d, JCP = 8.5 Hz, CH-Ph), 141.8 (d, JCP = 2.7 Hz, C-Ph),
147.1 (d, JCP = 6.8 Hz, C-Ph), 168.9 (d, JCP = 12.1 Hz, cis-CO), 178.1 (d,
Synthesis of cis-[IrCl(CO)2(2d)] (4d). A flask was charged with
3d (80 mg, 0.098 mmol) and dichloromethane (4 mL). A balloon filled
with CO was connected to the flask. The color turnsed from orange to
yellow. After 2 h, the solvent was evaporated, and the resulting yellow
solid was washed with hexane (3 ꢁ 2 mL), leading to 66 mg (87%) of a
pale green solid. 1H NMR (CD2Cl2): δ(ppm) 0.80-0.89 (d, 2JHH = 6.5
Hz, CH3, 6H), 0.93-1.08 (m, CH2, 4H), 1.13-1.25 (m, CH2, 4H and
CH3, 12H), 1.35-1.76 (m, CH2, 12H), 2.40 (pseudo, 2JHH = 11.2 Hz,
CH-Cy, 2H), 2.52 (sept, 2JHH = 6.7 Hz, CH-iPr, 2H), 2.85 (sept, 2JHH
=
6.9 Hz, CH-iPr, 2H), 6.96-7.05 (m, Ph-H, 3H), 7.31-7.38 (m, Ph-H,
2H), 8.01-8.12 (m, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm) 22.6 (s,
CH3), 24.2 (s, CH3), 26.1 (s, CH), 26.1 (s, CH2-Cy), 27.2 (d, JCP = 13.0
Hz, CH2-Cy), 27.6 (d, JCP = 11.7 Hz, CH2-Cy), 30.9 (s, CH), 24.3 (d,
JCP = 26.6 Hz, CH-Cy), 34.8 (s, CH), 121.6 (s, CH-Ph), 126.0 (d, JCP
12.9 Hz, CH-Ph), 129.4 (d, JCP = 41.7 Hz, C-Ph), 129.6 (d, JCP = 2.1 Hz,
CH-Ph), 134.6 (d, JCP = 7.4 Hz, CH-Ph), 136.4 (s, C-Ph), 139.3 (d, JCP
=
J
CP = 115.1 Hz, trans-CO). 31P NMR (CD2Cl2): δ(ppm) 29.26. IR νCO
=
(CH2Cl2): 2069.5, 1985.6 cm-1. Anal. Calcd for C26H33ClIrO2P (8 þ
1/4 CH2Cl2) (MW 634.17): C, 47.99; H, 5.06. Found: C, 47.82; H, 4.99.
Synthesis of cis-[IrCl(CO)2(2b)] (4b). A flask was charged with
3b (80 mg, 0.114 mmol) and dichloromethane (4 mL). A balloon filled
with CO was connected to the flask. The orange solution rapidly turned
yellow. After 2 h, the solvent was evaporated and the resulting solid was
washed with hexane (3 ꢁ 2 mL), leading to 61 mg (83%) of a yellow
19.4 Hz, CH-Ph), 144.0 (s, C-Ph), 147.1 (s, C-Ph), 149.7 (s, C-Ph),
169.4 (d, JCP = 11.8 Hz, cis-CO), 178.1 (d, JCP = 114.7 Hz, trans-CO).
31P NMR (CD2Cl2): δ(ppm) 40.93. IR νCO (CH2Cl2): 2070.5, 1986.6
cm-1. Anal. Calcd for C35H51ClIrO2P (MW 762.42): C, 55.14; H, 6.74.
Found: C, 55.14; H, 6.58.
Synthesis of cis-[IrCl(CO)2(2g)] (4g). A flask was charged with
3g (215 mg, 0.352 mmol) and dichloromethane (6 mL). A balloon filled
with CO was connected to the flask. The orange solution rapidly turned
green at room temperature. After 1 h, the solvent was evaporated and the
resulting solid was washed with pentane (2 ꢁ 3 mL), affording 145 mg
(74%) of a pale green powder. 1H NMR (300 MHz, CD2Cl2): δ(ppm)
1.04-1.43 (m, CH2-Cy, 10H), 1.65-1.72 (m, CH2-Cy, 2H), 1.74-1.84
(m, CH2-Cy, 6H), 1.97-2.06 (m, CH2-Cy, 2H), 2.74-2.87 (m, CH2-
Cy, 2H), 7.47-7.57 (m, CH-Ph, 3H), 7.66-7.72 (m, CH-Ph, 2H). 13C
NMR (75 MHz; CD2Cl2): δ(ppm) 26.3 (s, CH2-Cy), 26.9 (s, CH2-Cy),
27.1 (d, JCP = 2.0 Hz, CH2-Cy), 28.1 (d, JCP = 2.1 Hz, CH2-Cy), 28.8 (d,
JCP = 1.6, CH2-Cy), 31.0 (d, JCP = 30.5 Hz, CH-Cy), 125.8 (d, JCP = 48.5
Hz C-Ph), 128.5 (d, JCP = 9.8 Hz, CH-Ph), 131.6 (d, JCP = 2.3 Hz CH-
Ph), 135.2 (d, JCP = 9.0 Hz CH-Ph), 168.7 (d, JCP = 12.4 Hz, cis-CO),
178.8 (d, JCP = 115.7 Hz, trans-CO). 31P NMR (121 MHz, CD2Cl2): δ
(ppm) 29.80. IR νCO (CH2Cl2): 2074.8, 1990.7 cm-1. Anal. Calcd
for C20H57ClIrO2P (MW 558.11): C, 43.04; H, 4.88. Found: C, 42.95;
H, 4.93.
1
powder. H NMR (CD2Cl2): δ(ppm) 0.66-1.82 (m, CH2-Cy, 18H),
1.92-2.09 (m, CH2 and CH3), 2.10-2.23 (m, CH-Cy, 1H), 2.40-2.51
(m, CH-Cy, 1H), 7.06-7.11 (m, Ph-H, 1H), 7.13-7.32 (m, Ph-H, 4H),
7.35-7.44 (m, Ph-H, 2H), 7.77-7.87 (m, Ph-H, 1H). 13C NMR
(CD2Cl2): δ(ppm) 21.3 (s, CH3), 26.4 (d, JCP = 14.2 Hz, CH2-Cy),
27.2 (d, JCP = 13.9 Hz, CH2-Cy), 27.5 (d, JCP = 6.5 Hz, CH2-Cy), 27.6
(d, JCP = 7.0 Hz, CH2-Cy), 27.7 (d, JCP = 11.7 Hz, CH2-Cy), 29.1 (d,
JCP = 1.7 Hz, CH2-Cy), 30.7 (br s, CH2-Cy), 30.8 (br s, CH2-Cy), 32.3
(d, JCP = 2.6 Hz, CH2-Cy), 34.5 (d, JCP = 28.3 Hz, CH-Cy), 35.9 (d, JCP
=
27.6 Hz, CH-Cy), 125.4 (s, CH-Ph), 126.2 (d, JCP = 43.2 Hz, C-Ph),
126.7 (d, JCP = 10.4 Hz, CH-Ph), 128.7 (s, CH-Ph), 130.2 (s, CH-Ph),
130.4 (d, JCP = 2.2 Hz, CH-Ph), 131.3 (s, CH-Ph), 132.7 (d, JCP = 7.6 Hz,
CH-Ph), 137.2 (s, C-Ph), 137.6 (d, JCP = 12.1 Hz, CH-Ph), 141.0 (d,
JCP = 2.3 Hz, C-Ph), 146.1 (d, JCP = 5.2 Hz, C-Ph), 168.8 (d, JCP = 12.2
Hz, cis-CO), 178.3 (d, JCP = 115.1 Hz, trans-CO). 31P NMR (CD2Cl2):
δ(ppm) 32.76. IR νCO (CH2Cl2): 2070.0, 1986.1 cm-1. Anal. Calcd for
C27H35ClIrO2P (MW 650.21): C, 49.87; H, 5.43. Found: C, 50.06; H,
5.28.
’ ASSOCIATED CONTENT
Synthesis of cis-[IrCl(CO)2(2c)] (4c). A flask was charged with
3c (80 mg, 0.107 mmol) and dichloromethane (4 mL). A balloon filled
with CO was connected to the flask. Over 3 h, the orange solution turned
yellow, slightly green. The solvent was then evaporated and the solid was
washed with hexane. Drying the solid under vacuum led to 65 mg (88%)
S
Supporting Information. Crystallographic information
b
files (CIF) for all XRD structures. This material is available free of
charge via the Internet http://pubs.acs.org.
1
of a pale green product. H NMR (CD2Cl2): δ(ppm) 0.92-1.12 (m,
’ AUTHOR INFORMATION
CH2-Cy, 6H), 1.33-1.47 (m, CH2-Cy, 4H), 1.51-1.69 (m, CH2-Cy,
6H), 1.74-1.84 (m, CH2-Cy, 4H), 2.41 (qt, J = 9.7 Hz, J = 2.4 Hz, CH-
Cy, 2H), 3.58 (s, O-CH3, 6H), 6.56 (d, JHH = 8.4 Hz, Ph-H, 2H), 7.00
(ddd, J = 7.5 Hz, J = 3.6 Hz, J = 1.5 Hz, Ph-H, 1H), 7.28 (t, JHH = 8.4 Hz,
Ph-H, 1H), 7.34 (tt, J = 7.6 Hz, J = 1.4 Hz, Ph-H, 1H), 7.39 (tt, JHH = 7.4
Hz, JHH = 1.6 Hz, Ph-H, 1H), 7.78 (ddd, J = 11.4 Hz, J = 7.7 Hz, J = 1.1
Hz, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm) 26.5 (s, CH2-Cy), 27.6 (d,
Corresponding Author
*E-mail: snolan@st-andrews.ac.uk. Tel: þ 44 (0)1334 463698.
Fax: (þ44) 01334 463 763.
Present Addresses
§Universitꢀe Aix-Marseille, UMR CNRS 6263-Institut des
Sciences Molꢀeculaires de Marseille, Av. Escadrille Normandie
Niemen, 13397 Marseille Cedex 20, France.
J
PC = 11.5 Hz, CH2-Cy), 27.7 (d, JPC = 11.5 Hz, CH2-Cy), 30.0 (s, CH2-
Cy), 30.9 (s, CH2-Cy), 34.8 (d, JPC = 28.1 Hz, CH-Cy), 55.5 (s,
O-CH3), 104.1 (s, CH-Ph), 119.0 (d, JCP = 2.9 Hz, C-Ph), 126.2 (d, JCP
=
10.4 Hz, CH-Ph), 129.9 (d, JCP = 44.0 Hz, C-Ph), 130.0 (s, CH-Ph),
130.5 (d, JCP = 1.8 Hz, CH-Ph), 133.8 (d, JCP = 7.5 Hz, CH-Ph), 137.7
(d, JCP = 12.1 Hz, CH-Ph), 140.7 (d, JCP = 5.1 Hz, C-Ph), 158.4 (s, C-
Ph), 168.8 (d, JCP = 12.4 Hz, cis-CO), 178.2 (d, JCP = 115.1 Hz, trans-
CO). 31P NMR (CD2Cl2): δ(ppm) 29.88. IR νCO (CH2Cl2): 2069.1,
1985.7 cm-1. Anal. Calcd for C27H35ClIrO3P (MW 696.23): C, 48.30;
H, 5.36. Found: C, 48.14; H, 5.46.
’ ACKNOWLEDGMENT
We thank the ICREA, the ICIQ Foundation, the ERC
(Advanced Researcher Award FUNCAT to S.P.N.), and the
Ministerio de Educaciꢀon y Ciencia (Spain) for financial support.
We are grateful to Umicore AG for their generous gifts of materials.
S.P.N. is a Royal Society-Wolfson Research Merit Award holder.
1675
dx.doi.org/10.1021/om101174x |Organometallics 2011, 30, 1668–1676

Organometallics
ARTICLE
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