Electronically dissymmetric DIPHOS derivatives give higher n:i regioselectivity in rhodium-catalyzed hydroformylation than either of their symmetric counterparts

Article abstract of DOI:10.1021/ja982117h

Electronic effects on rhodium-catalyzed hydroformylation of 1-hexene with electronically dissymmetric DIPHOS derivatives [3,5- (CF₃)₂C₆H₃]₂PCH₂CH₂PPh₂ = [DIPHOS-(3,5-CF₃,H)] (1), [2- (CF₃)C₆H₄]₂-PCH₂CH₂PPh₂ = [DIPHOS-(2-CF₃,H)] (2), [3,5- (CF₃)₂C₆H₃]₂PCH₂CH₂P[2-(CH₃)C₆H₄]₂ = [DIPHOS-(3,5-CF₃,2-CH₃)] (3), and [2-(CF₃)C₆H₄]₂PCH₂CH₂P[2-(CH₃)C₆h₄]₂ = [DIPHOS-(2-CF₃,2- CH₃)] (4) were investigated. Two apical-equatorial chelate isomers were observed for model (diphosphine)Ir(CO)₂H complexes of dissymmetric diphosphines 1-4. In each case, the equatorial phosphine of the major isomer (96-60%) had electron-withdrawing aryl substituents. These dissymmetric DIPHOS derivatives were used to test the hypothesis that an electron- withdrawing substituent on an equatorial phosphine increases the hydroformylation n:i ratio while an electron-withdrawing substituent on an apical phosphine decreases the n:i ratio. In agreement with the predictions of this hypothesis, hydroformylation with the dissymmetric diphosphine ligand DIPHOS-(3,5-CF₃,H) (1), gave an n:i ratio of 4.2:1, higher than either of the symmetric ligands DIPHOS, 2.6:1, and DIPHOS-(3,5-CF₃), 1.3:1. Similar observations were made for hydroformylations with 2-4.

Full text of DOI:10.1021/ja982117h

J. Am. Chem. Soc. 1999, 121, 63-70
63
Electronically Dissymmetric DIPHOS Derivatives Give Higher n:i
Regioselectivity in Rhodium-Catalyzed Hydroformylation Than Either
of Their Symmetric Counterparts
Charles P. Casey,* Evelyn Lin Paulsen, Eckart W. Beuttenmueller, Bernd R. Proft,
Brock A. Matter, and Douglas R. Powell
Contribution from the Department of Chemistry, UniVersity of Wisconsin, Madison, Wisconsin 53706
ReceiVed June 18, 1998
Abstract: Electronic effects on rhodium-catalyzed hydroformylation of 1-hexene with electronically dissym-
metric DIPHOS derivatives [3,5-(CF3)2C6H3]2PCH2CH2PPh2 ) [DIPHOS-(3,5-CF3,H)] (1), [2-(CF3)C6H4]2-
PCH2CH2PPh2 ) [DIPHOS-(2-CF3,H)] (2), [3,5-(CF3)2C6H3]2PCH2CH2P[2-(CH3)C6H4]2 ) [DIPHOS-(3,5-
CF3,2-CH3)] (3), and [2-(CF3)C6H4]2PCH2CH2P[2-(CH3)C6H4]2 ) [DIPHOS-(2-CF3,2-CH3)] (4) were
investigated. Two apical-equatorial chelate isomers were observed for model (diphosphine)Ir(CO)2H complexes
of dissymmetric diphosphines 1-4. In each case, the equatorial phosphine of the major isomer (96-60%) had
electron-withdrawing aryl substituents. These dissymmetric DIPHOS derivatives were used to test the hypothesis
that an electron-withdrawing substituent on an equatorial phosphine increases the hydroformylation n:i ratio
while an electron-withdrawing substituent on an apical phosphine decreases the n:i ratio. In agreement with
the predictions of this hypothesis, hydroformylation with the dissymmetric diphosphine ligand DIPHOS-
(3,5-CF3,H) (1), gave an n:i ratio of 4.2:1, higher than either of the symmetric ligands DIPHOS, 2.6:1, and
DIPHOS-(3,5-CF3), 1.3:1. Similar observations were made for hydroformylations with 2-4.
The rhodium-phosphine-catalyzed hydroformylation reac-
tion,1 first reported by Wilkinson2 in the late 1960s and
implemented by Union Carbide3 in the late 1970s, remains one
of the most important homogeneously catalyzed processes.
Rhodium-phosphine catalysts operate at lower temperature and
pressure than earlier cobalt-based catalysts and afford the
opportunity to maximize regioselectivity with ancillary phos-
phine ligand variations. The development of highly regioselec-
tive catalyst systems continues to be a primary research aim.
Recently developed phosphorus chelates which give high
regioselectivity for high linear aldehydes include Texas-
Eastman’s 2,2′-bis[(diphenylphosphino)methyl]-1,1′-biphenyl
(BISBI) ligand4 and Union Carbide’s diphosphite chelates.5
Stanley has developed a unique binuclear rhodium catalyst that
gives high rates and selectivity.6 van Leeuwen has reported a
variety of diphosphite and diphosphine ligands that give high
n:i regioselectivity.7 Buchwald8 and Wink9 have obtained high
regioselectivities in hydroformylation of functionalized alkenes
using rhodium diphosphite systems. While a wide variety of
phosphine and phosphite ligands have been screened, no detailed
understanding of how phosphorus ligands control regioselectivity
or enantioselectivity has emerged.
Wilkinson’s dissociative hydroformylation mechanism (Scheme
1) suggests that aldehyde regioselectivity is determined in the
hydride addition step that converts a five-coordinate H(alkene)-
Rh(CO)L2 into either a primary or secondary four-coordinate
(alkyl)Rh(CO)L2. Monodentate phosphine ligands can occupy
two equatorial or one equatorial and one apical site of the key
five-coordinate H(alkene)Rh(CO)L2 intermediate. For L ) PPh3,
Brown’s NMR studies showed an 85:15 diequatorial:apical-
equatorial mixture of isomers of (PPh3)2Rh(CO)2H which are
in rapid equilibrium at room temperature.10
(1) (a) Parshall, G. W. Homogeneous Catalysis: The Applications and
Chemistry of Catalysis by Soluble Transition Metal Complexes; Wiley: New
York, 1980. (b) Tkatchenko, I. In ComprehensiVe Organometallic Chem-
istry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford,
1982; Vol. 8, pp 101-223. (c) Tolman, C. A.; Faller, J. W. In Homogeneous
Catalysis with Metal Phosphine Complexes; Pignolet, L. H., Ed.; Plenum:
New York, 1983; pp 81-109. (d) Pino, P.; Piacenti, F.; Bianchi, M. In
Organic Syntheses Via Metal Carbonyls; Wender, I., Pino, P., Eds.; Wiley-
Interscience: New York, 1977; Vol. 2, pp 136-197. (e) Consiglio, G.;
Pino, P. Top. Curr. Chem. 1982, 105, 77. (f) Beller, M.; Cornils, B.;
Frohning, C. D.; Kohlpaintner, C. W. J. Mol. Catal., A 1995, 104, 17-85.
(2) (a) Evans, D.; Osborn, J. A.; Wilkinson, G. J. Chem. Soc. A 1968,
3133. (b) Yagupsky, G.; Brown, C. K.; Wilkinson, G. J. Chem. Soc. A
1970, 1392. (c) Brown, C. K.; Wilkinson, G. J. Chem. Soc. A 1970, 2753.
(3) Pruett, R. L. Ann. N.Y. Acad. Sci. 1977, 295, 239.
(4) (a) Devon, T. J.; Phillips, G. W.; Puckette, T. A.; Stavinoha, J. L.;
Vanderbilt, J. J. (to Texas-Eastman). U.S. Patent 4,694,109, 1987; Chem
Abstr. 1988, 108, 7890. For closely related systems, see: (b) Devon, T. J.;
Phillips, G. W.; Puckette, T. A.; Stavinoha, J. L.; Vanderbilt, J. J. (to Texas-
Eastman) U.S. Patent 5,332,846, 1994; Chem Abstr. 1994, 121, 280,879.
(c) Bahrmann, H.; Lappe, P.; Herrmann, W. A.; Albanese, G. P.;
Manetsberger, R. B. (to Hoechst AG) DE Patent 4,333,307, 1995; Chem
Abstr. 1995, 123, 112,408.
Several years ago, on the basis of Brown’s findings, we set
out to test the hypothesis that very different regioselectivities
(5) (a) Billig, E.; Abatjoglou, A. G.; Bryant, D. R. (to Union Carbide)
U.S. Patent 4,748,261 1988; 4,769,498, 1988. (b) For related work with
phosphine-phosphite chelates, see: Nozaki, K.; Sakai, N.; Nanno, T.;
Higashijima, T.; Mano, S.; Horiuchi, T.; Takaya, H. J. Am. Chem. Soc.
1997, 119, 4413.
(6) Broussard, M. E.; Juma, B.; Train, S. G.; Peng, W.-J.; Laneman, S.
A.; Stanley, G. G. Science 1993, 260, 1784.
(7) (a) van Rooy, A.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.;
Goubitz, K.; Fraanje, J.; Veldman, N.; Spek, A. L. Organometallics 1996,
15, 835. (b) Buisman, G. J. H.; Martin, M. E.; Vos, E. J.; Klootwijk, A.;
Kamer, P. C. J.; van Leeuwen, P. W. N. M. Tetrahedron: Asymmetry 1995,
6, 719. (c) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J. Organometallics 1995, 14,
3081.
(8) Cuny, G. D.; Buchwald S. L. J. Am. Chem. Soc. 1993, 115, 2066.
(9) Kwok, T. J.; Wink, D. J. Organometallics 1993, 12, 1954.
(10) Brown, J. W.; Kent, A. G. J. Chem. Soc., Perkin Trans. 2 1987,
1597.
10.1021/ja982117h CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/19/1998

64 J. Am. Chem. Soc., Vol. 121, No. 1, 1999
Casey et al.
Scheme 1
Figure 1. Effect of equatorial and apical electron-withdrawing groups
on n:i selectivity. For BISBI, the effect of electron-withdrawing groups
on each of the two equatorial phosphines increases the n:i selectivity
to give a net additive increase in n:i selectivity shown in the box. For
DIPHOS, the effect of electron-withdrawing groups on the equatorial
phosphine increases the n:i selectivity, but the effect of electron-
withdrawing substituents on the apical phosphine decreases the n:i
selectivity to a greater degree; the resulting net decrease in n:i selectivity
is shown in the box.
might be obtained from diequatorial diphosphine rhodium
complexes and from apical-equatorial diphosphine rhodium
complexes. The mode of chelation could be controlled by
employing chelating diphosphines with varying natural bite
angles.11 A strong correlation was found between regioselectivity
for n-aldehyde formation and natural bite angle.12 Chelates such
as BISBI with wide natural bite angles gave a much higher
percent n-aldehyde (ân ) 113°, n:i ) 66) than diphosphines
such as 1,2-bis(diphenylphosphino)ethane (DIPHOS) with nar-
row bite angles (ân ) 85°, n:i ) 2.6).13,14 Deuterioformylation
studies established that the predominant products were derived
from irreversible addition of a rhodium hydride to a complexed
alkene to give a rhodium alkyl intermediate that is committed
to aldehyde formation.15
of symmetrically substituted diphosphines with different che-
lation modes and varied the electronic environment at the
arylphosphino group.
We found that the added electron-withdrawing aryl substit-
uents of BISBI-(3,5-CF3) and T-BDCP-(3,5-CF3) ligand,
coordinated diequatorially on model five-coordinate metal
complexes, led to an increase in the linear to branched (n:i)
ratio. From the BISBI-(3,5-CF3) and T-BDCP-(3,5-CF3) data,
we were able to deduce that electron-withdrawing aryl substit-
uents in the equatorial position increased the n:i selectivity.
However, the DIPHOS-(3,5-CF3) ligand, which coordinates in
an apical-equatorial mode, showed a decrease in the n:i ratio
with electron-withdrawing aryl substituents. If electron-
withdrawing aryl substituents in the equatorial position increase
n:i selectivity, then in order to obtain a decrease in n:i selectivity
for the apical-equatorial chelated DIPHOS-(3,5-CF3), the
electron-withdrawing aryl substituents in the apical position must
act to decrease n:i selectivity. Our hypothesis then is that an
electron-withdrawing substituent on an equatorial phosphine
increases the n:i ratio while an electron-withdrawing substituent
on an apical phosphine decreases the n:i ratio (Figure 1).
A risky prediction of our hypothesis is that using the
dissymmetric DIPHOS derivative [3,5-(CF3)2C6H3]2PCH2CH2-
PPh2 ) [DIPHOS-(3,5-CF3,H)] could lead to greater n:i
selectivity than either of the related symmetric DIPHOS
derivatives [DIPHOS-(3,5-CF3) or DIPHOS]. This chelate is
designed to have an electron-withdrawing phosphine in the
equatorial position and an electron-donating phosphine in the
apical position. Here we report the synthesis and characterization
of [DIPHOS-(3,5-CF3,H)] and several other dissymmetric
DIPHOS derivatives as well as their chelation mode in model
(diphosphine)Ir(CO)2H complexes. It was determined that
hydroformylation n:i selectivity with these derivatives is indeed
greater than either of their related symmetric DIPHOS deriva-
tives, supporting our hypothesis.
The correlation between regioselectivity and chelation mode
suggests that diequatorial diphosphines such as BISBI and
apical-equatorial chelating diphosphines such as DIPHOS have
significantly different steric and/or electronic properties. We first
considered the steric differences between diequatorial and
apical-equatorial chelates as a possible explanation for regio-
selectivity. Molecular mechanics calculations were employed
to explore whether selectivity arose from steric differences
between the transition states leading to the primary and
secondary alkylrhodium intermediates.15 Unfortunately these
models predicted higher n:i regioselectivity for DIPHOS
(predicted 35:1, observed 2.6:1) than for BISBI (predicted
25:1, observed 66:1), contrary to our observations. These
estimates of steric effects incorrectly suggested that DIPHOS
should be more selective than BISBI, which is in fact the
opposite of the trend observed.
Since steric arguments failed to give a satisfactory explanation
for the much higher n:i aldehyde ratios observed, next we
focused on investigating electronic effects.16 We tested a series
Results
(11) Casey, C. P.; Whiteker, G. T. Isr. J. Chem. 1990, 30, 299.
(12) Casey, C. P.; Whiteker, G. T.; Melville, M. G.; Petrovich, L. M.;
Gavney, J. A., Jr.; Powell, D. R. J. Am. Chem. Soc. 1992, 114, 5535.
(13) van Leeuwen also observed an increase in linear aldehyde regio-
selectivity with increasing bite angle.7c In a series of bidentate chelating
phosphines containing xanthene-like ligand backbones, the bite angle was
varied from 102° to 131°, with minimal change in the steric or electronic
properties of the ligand. The resulting n:i ratio increased from 6.7 to 80.5
in the hydroformylation of 1-octene at 80 °C.
Synthesis of Electronically Dissymmetric DIPHOS De-
rivatives. Electronically dissymmetric DIPHOS derivatives
containing both an electron-donating aryl substituent (H or
o-CH3) and an electron-withdrawing aryl substituent [o-CF3 or
bis-m-(CF3)2] were synthesized by the base-catalyzed addition17
of a secondary arylphosphine16 to a diarylvinylphosphine16 in
moderate yields (16-61%) (Scheme 2, Figure 2). The reaction
of electron-rich arylphosphines with electron-poor vinylphos-
phines gave the desired ligands. In some cases, the reverse
(14) Earlier we reported a 2.1:1 n:i ratio for DIPHOS,12 which is the
ratio seen early in the reaction. For consistency, we are now reporting ratios
obtained after 120-250 turnovers (20-50% conversion) for all ligands.
(15) Casey, C. P.; Petrovich, L. M. J. Am. Chem. Soc. 1995, 117, 6007.
(16) Casey, C. P.; Paulsen, E. L.; Beuttenmueller, E. W.; Proft, B. R.;
Petrovich, L. M.; Matter, B. A.; Powell, D. R. J. Am. Chem. Soc. 1997,
119, 11817.
(17) (a) Clark, P. W.; Mulraney, B. J. J. Organomet. Chem. 1981, 217,
51. (b) Chatt, J.; Hussain, W.; Leigh, G. J.; Ali, H. M.; Pickett, C. J.; Rankin,
D. A. J. Chem. Soc., Dalton Trans. 1985, 1131.

Electronically Dissymmetric DIPHOS DeriVatiVes
J. Am. Chem. Soc., Vol. 121, No. 1, 1999 65
of (diphosphine)Ir(CO)2H: one diequatorial isomer (ee) and two
apical-equatorial isomers (ae-1, ae-2.) The parent diphosphine
DIPHOS has a calculated natural bite angle of 84.5°, thus
making apical-equatorial (ae) chelation strongly preferred.
Figure 2. Starting materials for dissymmetric DIPHOS derivatives
1-4.
The two apical-equatorial isomers, ae-1 and ae-2, undergo
rapid interconversion by a series of Berry pseudorotations,
giving averaged NMR signals at room temperature.20 The NMR
spectra for the individual isomers can be observed at low
temperature, where interconversion is slow on the NMR time
scale. 31P chemical shifts of the isomers can be assigned by
comparison of shifts in dissymmetric complexes with the
corresponding shifts for the symmetric complexes, while
selectively hydride coupled 31P spectra can be used to determine
the site of phosphine binding (Table 1). Apical bound phos-
phines show a large P-H coupling constant to the apical hydride
in the range of 90-110 Hz. The equatorial P-H coupling is
usually around -15 Hz which can result in 31P resonance
broadening for equatorial bound phosphines (Table 1).
Scheme 2
combination failed. For example, (2-CF3C6H4)2PH and (C6H5)2P-
(CHdCH2) did not give DIPHOS-(2-CF3,H) (2).
Synthesis of Iridium Complexes as Models of Catalytic
Species. The nature of the catalytic rhodium hydride alkene
intermediate is important in understanding aldehyde regio-
selectivity. Insertion of the rhodium hydride into the terminal
or internal alkene carbon-hydrogen bond is the regioselectivity-
determining step for aldehyde formation. However, this catalytic
rhodium hydride alkene intermediate has never been directly
observed due to rapid hydride insertion to give a rhodium alkyl
species. The similar chelating diphosphine rhodium dicarbonyl
hydride where the alkene is replaced by a carbonyl is a suitable
model; however, it was not employed because in many cases
such complexes are unstable relative to loss of hydrogen and
dimer formation.18 Therefore, diphosphine iridium dicarbonyl
hydride complexes were used to determine the diphosphine
chelate geometry in a five-coordinate metal complex. Iridium
is a good model for rhodium complexes because it has similar
coordination geometries and iridium bond lengths are only
1-2% longer than related rhodium bond lengths.
[DIPHOS-(3,5-CF3,H)]Ir(CO)2H (5). The 1H and 31P NMR
spectra of 5 at -94 °C revealed the presence of two isomers in
a 94:6 ratio (Figure 3). The major isomer had 31P NMR
resonances at δ 38.7 and 31.6 ppm and a hydride resonance in
1
the H NMR spectrum at δ -11.21 (dd, JHP ) 91.5, -14.5
Hz). The minor isomer had 31P resonances at δ 36.7 and 34.0
ppm and a hydride resonance at δ -11.12 (dd, JHP ) 100, -15
Hz). The observation of one large trans JHP coupling and one
small cis JHP coupling established that each isomer had apical-
equatorial diphosphine coordination. In the hydride-coupled 31
P
NMR spectrum of the major isomer, the resonance at δ 31.6
had a large coupling to a trans hydride (JHP ) 87 Hz). In the
hydride-coupled 31P NMR spectrum of the minor isomer, the
resonance at δ 36.7 also had a large coupling to a trans hydride
(JHP ) 87 Hz).
The structural assignments of isomers 5a and 5b were made
by comparison of chemical shifts with analogous symmetric
DIPHOS iridium complexes (Figure 3, Table 1). For the major
isomer, the δ 31.6 chemical shift of the apical phosphorus trans
to hydride (JHP ) 87 Hz) is the same as the δ 31.6 (JHP ) 85
Hz) chemical shift of the apical phosphorus of (DIPHOS)Ir-
(CO)2H and the δ 38.7 chemical shift of its equatorial
phosphorus cis to hydride (JHP ) 9.5 Hz) is similar to the δ
39.2 (br s) of the equatorial phosphine of (DIPHOS-3,5-CF3)-
Ir(CO)2H. This establishes the structure of the major isomer as
5a with the electron-withdrawing PAr2 group in an equatorial
position. Similarly, for the minor isomer, the δ 36.7 chemical
(20) We agree with van Leeuwen’s suggestion20a,b that equilibration of
isomers such as ae-1 and ae-2 does not occur via a Berry pseudorotation
involving pivoting about the equatorial phosphine; such a pseudorotation
would proceed through an unstable intermediate with both an unfavorable
equatorial hydride and a small bite angle chelate spanning equatorial sites.
However, a series of Berry pseudorotations involving succesive pivoting
about CO, H, and CO avoids diequatorial diphosphines and appears likely,
even though it requires an intermediate with an equatorial hydride ligand.
We cannot exclude a one-step Meakin mechanism20c for phosphine
interchange. The transition state for Berry pseudorotation is a square-based
pyramid that we believe would be more stable than the transition state for
a Meakin mechansm which resembles an edge-protonated tetrahedron. (a)
Buisman, G. J. H.; van der Veen, L. A.; Kamer, P. C. J.; van Leeuwen, P.
W. N. M. Organometallics 1997, 16, 5681-5687. (b) Castellanos-Pa´ez,
A.; Castillo´n, S.; Claver, C.; van Leeuwen, P. W. N. M.; de Lange, W. G.
J. Organometallics 1998, 17, 2543-2552. (c) Meakin, P.; Muetterties, E.
L.; Jesson, J. P. J. Am. Chem. Soc. 1972, 94, 5271.
(Diphosphine)Ir(CO)2H complexes were prepared from diphos-
phines 2-4 (Scheme 3). The NaBH4 addition to (diphosphine)-
Ir(CO)I complexes gave the trihydrides, fac-(diphosphine)Ir-
(CO)H3. Subsequent photolysis under CO gave the desired
(diphosphine)Ir(CO)2H complexes.19
Scheme 3
An alternative method was necessary for (DIPHOS-3,5-
CF3,H)Ir(CO)2H (5). The (DIPHOS-3,5-CF3,H)Ir(CO)I complex
which is normally precipitated out with the addition of ethanol
remained soluble, and therefore could not be separated from
unreacted starting materials. Therefore, the dicarbonyl complex
was synthesized directly by reaction with Ir(acac)(CO)2 under
1 atm of 1:1 CO:H2.
Coordination Geometry of (Diphosphine)Ir(CO)2H Com-
plexes. These model compounds are particularly important in
understanding the mode of chelation for dissymmetric com-
plexes. For a dissymmetric diphosphine, there are three isomers
(18) For example, attempts to synthesize (T-BDCP)Rh(CO)2H led to
[(T-BDCP)Rh]2(µ-CO)2.12
(19) (a) Fisher, B. J.; Eisenberg, R. Organometallics 1983, 2, 764. (b)
Fisher, B. J.; Eisenberg, R. Inorg. Chem. 1984, 23, 3216.

66 J. Am. Chem. Soc., Vol. 121, No. 1, 1999
Casey et al.
1
Table 1. Low-Temperature 31P (Selectively Hydride Coupled) and H Hydride NMR Chemical Shifts for (Diphosphine)Ir(CO)2H Complexes
major
equatorial P
major
apical P
minor
equatorial P
minor
apical P
major
hydride
minor
hydride
diphosphine
Symmetrica
DIPHOS
33.6
(t, J ) 12)
39.2
(br s)
26.9
(br s)
37.6
31.6
-11.20
(dd, J ) 85, -10)
37.4
(br d, J ) 103)
25.4
(br d, J ) 83)
33.0
(br d, J ) 104)
(dd, J ) 92, -13)
-10.97
DIPHOS-(3,5-CF3)
DIPHOS-(2-CH3)
DIPHOS-(2-CF3)
(dd, J ) 101, -14)
-11.38
(dd, J ) 98, -16)
-11.41
(br s)
(dd, J ) 105, -14)
Unsymmetric
34.0
DIPHOS-(3,5-CF3,H) (5)
DIPHOS-(2-CF3,H) (6)
38.7
31.6
36.7
(br d, J ) 87)
3,5-CF3
-11.21
-11.12
(t, J ) 9.5) (dd, J ) 87, 9)
3,5-CF3
40.5
(s)
2-CF3
(br s)
H
31.2
(s)
H
(dd, J ) 91.5, -14.5) (dd, J ) 100, -14)
H
34.0
(d, J ) 92)
H
33.4
-10.69
-11.70
(dd, J ) 108, -14)
(br d, J ) 104) (dd, J ) 94, -13.5)
2-CF3
DIPHOS-(3,5-CF3,2-CH3) (8) 36.1
24.3
26.0
38.8
-11.67
-10.56
(br s)
(dd, J ) 84, 11)
2-CH3
26.2
(d, J ) 98)
2-CH3
(br s)
2-CH3
27.5
(br s)
2-CH3
(d, J ) 93)
3,5-CF3
34.
(d, J ) 101)
2-CF3
(dd, J ) 94, -14)
(dd, J ) 100, -14)
3,5-CF3
39.2
(br s)
DIPHOS-(2-CF3,2-CH3) (9)
-11.22
(dd, J ) 98, -15)
-11.45
(dd, J ) 111, -17)
2-CF3
a For complete characterization see ref 16.
brating mixture of 5a and 5b, the observed coupling constants
are the weighted average of the coupling constants of the two
isomers and can be used to compute the mole fraction of 5a
and 5b present:
(JPH at 25 °C) ) ø5a(JPH in 5a at -94 °C) +
ø5b(JPH in 5b at -94 °C) (1)
Figure 3. [DIPHOS-(3,5-CF3,H)]Ir(CO)2H (5) is an equilibrium
mixture of two isomers.
For the PPh2 group, the +75 Hz room-temperature coupling
constant for the equilibrating mixture of 5a and 5b, the 91.5
Hz for the low-temperature JPH of 5a, and the -14 Hz for the
low-temperature JPH of 5b were inserted into eq 1 to give mole
fractions ø5a ) 0.844 and ø5b ) 0.156.22 Similarly, the coupling
constants for the PAr2 group provided an independent measure-
ment of ø5a ) 0.825 and ø5b ) 0.175 when the average room-
temperature coupling constant of the PAr2 group (+5.5 Hz) and
the low-temperature coupling constants for 5a (-14.5 Hz) and
5b (100 Hz) were inserted into eq 1.23 The average of these
two independent measurements corresponds-to-a ratio of 5a:
5b of 83:17 at room temperature (∆G° ) 0.94 kcal mol-1). At
-94 °C, this ratio was 94:6 (∆G° ) 0.97 kcal mol-1) (Table
2).
Additional (Diphosphine)Ir(CO)2H Complexes. The re-
maining three complexes, [DIPHOS-(2-CF3,H)]Ir(CO)2H (6),
[DIPHOS-(3,5-CF3,2-CH3)]Ir(CO)2H (8), and [DIPHOS-(2-
CF3,2-CH3)]Ir(CO)2H (9), were characterized similarly to
complex 5 above. Selectively hydride-coupled 31P spectra were
used to determine the site of phosphine binding, and 31P
chemical shifts of the isomers were assigned by comparison of
shifts in dissymmetric complexes with the corresponding shifts
for the symmetric complexes (Table 1). Ratios of isomers at
low temperature were obtained by integration and ratios at room
temperature by eq 1 (Table 2).24-26
shift of the apical phosphorus trans to hydride (JHP ) 87 Hz) is
similar to the δ 37.4 (JHP ) 103 Hz) chemical shift of the apical
phosphorus of (DIPHOS-3,5-CF3)Ir(CO)2H and the δ 34.0 (br
s) chemical shift of its equatorial phosphorus cis to hydride is
similar to the δ 33.6 (d, JHP ) 12 Hz) of the equatorial
phosphine of (DIPHOS)Ir(CO)2H. This establishes the structure
of the minor isomer as 5b with the electron-withdrawing PAr2
group in an apical position.
The electron-withdrawing substituted diarylphosphine prefers
the equatorial position as shown in the major isomer 5a. A
similar bias toward coordination of phosphines with electron-
withdrawing groups in the equatorial position was responsible
for an increase in the ratio of diequatorial to apical-equatorial
isomers for T-BDCP-(3,5-CF3) (ae:ee ) 10:90) relative to
T-BDCP (ae:ee ) 63:37).16 Hoffmann’s molecular orbital
analysis of ligand electronic site preferences in five-coordinate
d8 ML5 complexes21 also supports these observations, suggesting
that weaker σ-donor ligands should prefer the equatorial position
while stronger σ-donor ligands should prefer the apical position.
At room temperature, 5a and 5b undergo rapid interconver-
sion and average resonances are observed in the NMR spectra.
The hydride resonances average to give a doublet of doublets
at δ -11.2 with average coupling constants of 75 and 5.5 Hz
to the two different phosphines. The 31P NMR spectrum shows
averaged signals at δ 39.6 (d, JPP ) 9 Hz) and 32.5 (d, JPP
9 Hz) which were assigned to the averaged PAr2 resonance and
the averaged PPh2 resonance, respectively.
The JPH coupling constants of individual isomers 5a and 5b
should be nearly temperature independent. In a rapidly equili-
)
(22) There are two possible solutions to each equation because the sign
of JRT is unknown. The solution of eq 1 gives øA ) 0.844 for +75 Hz or
øA ) -0.578 for -75 Hz. The reasonable solution with 0 e øA e 1 is
picked.
(23) In this case both solutions are reasonable, øA ) 0.825 or øA ) 0.921.
The solution most similar to øA ) 0.844, obtained in the previous calculation,
was selected.
(21) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365.

Electronically Dissymmetric DIPHOS DeriVatiVes
J. Am. Chem. Soc., Vol. 121, No. 1, 1999 67
Table 2. Isomer Ratios for Complexes 5-8 at Low Temperature and Room Temperature
major hydride at
low temp
minor hydride at
low temp
low temp
isomer ratio
hydride at
room temp
room temp
isomer ratio
diphosphine
DIPHOS-(3,5-CF3,H) (5)
-11.21
-11.12
94:6
-11.20
83:17
(dd, J ) 91.5, -14.5)
-10.69
(dd, J ) 100, -14)
-11.70
(dd, J ) 75, 5.5)
-11.18
DIPHOS-(2-CF3,H) (6)
67:33
96:4
65:3524
88:1225
68:3226
(dd, J ) 94, -13.5)
-11.67
(dd, J ) 108, -14)
-10.56
(dd, J ) 57, 31)
-11.58
DIPHOS-(3,5-CF3,2-CH3) (8)
DIPHOS-(2-CF3,2-CH3) (9)
(dd, J ) 94, -14)
-11.22
(dd, J ) 100, -14)
-11.45
(dd, J ) 82, 0)
-11.39
60:40
(dd, J ) 98, -15)
(dd, J ) 111, -17)
(dd, J ) 62, 27)
Table 3. Regiochemistry of Hydroformylation of 1-Hexene with Rhodium Diphosphine Catalysts
Ir complex ratio
aldehyde
n:ib
regiochemistry
turnover
ratec
diphosphine
ae-1:ae-2a
% n
Symmetric Chelates
DIPHOS
100:0
100:0
100:0
100:0
2.6:1 ( 0.1
1.3:1 ( 0.1
3.0:1 ( 0.1
2.6:1 ( 0.1
71.9 ( 0.3
56.9 ( 0.9
75.2 ( 0.5
72.1 ( 0.3
3.5 ( 0.1
4.3 ( 0.1
4.0 ( 0.2
0.40 ( 0.01
DIPHOS-(3,5-CF3)
DIPHOS-(2-CH3)
DIPHOS-(2-CF3)
Dissymmetric Chelates
DIPHOS-(3,5-CF3,H) (1)
DIPHOS-(2-CF3,H) (2)
DIPHOS-(3,5-CF3,2-CH3) (3)
DIPHOS-(2-CF3,2-CH3) (4)
83:17
65:35
88:12
68:32
4.2:1 ( 0.1
2.9:1 ( 0.1
3.3:1 ( 0.1
3.8:1 ( 0.1
80.8 ( 0.3
74.1 ( 0.5
76.9 ( 0.6
79.1 ( 0.2
2.5 ( 0.1
3.8 ( 0.2
4.7 ( 0.1
2.7 ( 0.1
a Ratio of ae-1:ae-2 isomers of (diphosphine)Ir(CO)2H at room temperature. b Moles of heptanal:moles of 2-methylhexanal. c Turnover rate )
[moles of aldehyde] × [moles of Rh]-1 h-1
.
In summary, all the (diphosphine)Ir(CO)2H complexes are a
mixture of two equilibrating isomers. For the key [DIPHOS-
(3,5-CF3,H)]Ir(CO)2H complex (5) and for [DIPHOS-(3,5-
CF3,2-CH3)]Ir(CO)2H (8), which both have 3,5-CF3-substituted
arenes, the major isomers have the electron-withdrawing
substituted phosphine in the equatorial position, with isomer
ratios of 94:6 and 96:4, respectively. In the case of the
o-trifluoromethyl-substituted
arylphosphine
complexes,
[DIPHOS-(2-CF3,H)]Ir(CO)2H (6) and [DIPHOS-(2-CF3,2-
CH3)]Ir(CO)2H (9), with only one trifluoromethyl group per aryl,
the preference for the isomers with the electron-withdrawing
substituted phosphine in the equatorial position was less, with
isomer ratios of 67:33 and 60:40, respectively. Steric effects
are apparently insignificant, and the isomer preference is dictated
by the number of electron-withdrawing trifluoromethyl substit-
uents. In all cases, the major isomer has the electron-withdraw-
ing substituted phosphine in the equatorial position and the better
donor phosphine in the apical position. This is the preferred
orientation to test our hypothesis.
X-ray Structure Determination of [DIPHOS-(2-CF3,H)]-
Ir(CO)2H (6). Recrystallization of [DIPHOS-(2-CF3,H)]Ir-
(CO)2H (6) from pentane gave pale yellow plates, suitable for
X-ray structure determination.27 The X-ray crystal structure of
6 shows that the minor isomer 6b selectively crystallized from
the 2:1 mixture of 6a:6b in solution. 6b has a trigonal
bipyramidal structure, with the DIPHOS-(2-CF3,H) ligand
chelated in an apical-equatorial fashion, with bite angle
85.19(5)° [P(2)-Ir(1)-P(1)] (Figure 4). Similar Ir-P bond
Figure 4. ORTEP drawing of the X-ray crystal structure of [DIPHOS-
(2-CF3,H)]Ir(CO)2H (6b).
lengths were observed for equatorial Ir-PPh2 (2.310(2) Å) and
for apical Ir-P[C6H33,5-(CF3)2]2 (2.331(2) Å). Although the
hydride was not located directly, it is expected to occupy the
other apical site. The angles between the apical phosphine and
the equatorial carbonyls are 100.0° [C(1)-Ir(1)-P(2)] and 94.3°
[C(2)-Ir(1)-P(2)], indicating the carbonyls are bent slightly
toward the hydride ligand.
Catalytic Hydroformylation of 1-Hexene. As in our earlier
studies, hydroformylation of 1-hexene was carried out in
benzene solution at 36 °C under 6 atm of 1:1 H2:CO using 0.2
mol % 1:1 Rh(CO)2(acac):diphosphine catalyst. The production
of heptanal and 2-methylhexanal was monitored by gas chro-
matography utilizing toluene as an internal standard. The results
of the studies are summarized in Table 3. The turnover rate
and n:i ratios are reported after 120-250 turnovers (20-50%
conversion).
(24) Equation 1 for complex 6: (57 Hz ) ø6a(94 Hz) + (ø6b)(-14 Hz),
øA ) 0.657 or øA ) -0.398; and (31 Hz ) ø6a(-13.5 Hz) + (ø6b)(108
Hz), øA ) 0.634 or øA ) 1.144.
(25) Equation 1 for 8: (82 Hz ) øA(94 Hz) + (1 - øA)(-14 Hz), øA
) 0.889 or øA ) -0.630; and 0 Hz ) øA(-14 Hz) + (1 - øA)(100 Hz),
øA ) 0.877.
(26) Equation 1 for 9: (62 Hz ) øA(98 Hz) + (1 - øA)(-17 Hz), øA
) 0.687 or øA ) -0.391; and (27 Hz ) øA(-15 Hz) + (1 - øA)(111
Hz), øA ) 0.667 or øA ) 1.095.
Discussion
The key dissymmetric diphosphine ligand DIPHOS-(3,5-
CF3,H) (1) shows an n:i ratio of 4.2:1, higher than either of the
symmetric ligands DIPHOS, 2.6:1, and DIPHOS-(3,5-CF3),
(27) The DIPHOS-(2-CF3, H) ligand was further characterized by the
synthesis and X-ray crystal structure determination of the [DIPHOS-(2-
CF3, H)]Fe(CO)3 (7) complex. See the Supporting Information.

68 J. Am. Chem. Soc., Vol. 121, No. 1, 1999
Casey et al.
1.3:1. This observation of a significant synergistic effect with
electronically dissymmetric ligands supports our hypothesis that
electron-withdrawing groups in the equatorial position modestly
increase n:i regioselectivity but electron-withdrawing groups in
the apical position greatly decrease regioselectivity.
The increase in n:i selectivity for the dissymmetric diphos-
phine DIPHOS-(3,5-CF3,H) (1) is attributed to the presence
of an electron-withdrawing phosphine in an equatorial position
which enhances n:i selectivity and the absence of an electron-
withdrawing phosphine in the apical position which would have
decreased n:i selectivity. The major isomer (83%) of the iridium
model compound [DIPHOS-(3,5-CF3,H)]Ir(CO)2H (5) had the
electron-withdrawing phosphine in the equatorial position. While
it is unknown whether the two catalytic rhodium isomers react
at similar rates, the small difference in rates for the symmetric
diphosphines suggests that the two isomers of the dissymmetric
chelate probably react at comparable rates.28
The turnover rate for hydroformylation with 1 (2.5 turnovers
h-1) is slightly less than the rates with either of the symmetric
diphosphines DIPHOS (3.5 turnovers h-1) and DIPHOS-(3,5-
CF3) (4.3 turnovers h-1). While the rate differences are small,
we believe it is significant that the dissymmetric diphosphine
has a rate outside the range of the related symmetric diphos-
phines.
The other three dissymmetric ligands 2-4 also achieve n:i
ratios higher than the related symmetric complexes. DIPHOS-
(2-CF3,H) (2) gives an n:i ratio of 2.9:1, higher than either
DIPHOS at 2.6:1 or DIPHOS-(2-CF3) also at 2.6:1. Perhaps
the smaller increase in selectivity is due to a more similar isomer
ratio of 65:35. DIPHOS-(3,5-CF3,2-CH3) (3) gives an n:i ratio
of 3.3:1, higher than either DIPHOS-(2-CH3) at 3.0:1 or
DIPHOS-(3,5-CF3) at 1.3:1. And finally, DIPHOS-(2-CF3,2-
CH3) (4) also gives an increased n:i ratio of 3.8:1 compared to
its symmetric counterparts, DIPHOS-(2-CH3) at 3.0:1 and
DIPHOS-(2-CF3) at 2.6:1.
selectivity of rhodium-catalyzed hydroborations with pyrazole-
containing ferrocenylphosphine ligands.29 The combination of
electron-withdrawing 3,5-(CF3)2 groups on the arylphosophine
and electron donor groups on the pyrazole ring gave the highest
enantioselectivity (98.5% ee for hydroboration of styrene). The
opposite combination of CF3 groups on the pyrazole ring and
electron donor p-methoxy groups on the diarylphosphine gave
the lowest enantioselectivity (5% ee). RajanBabu and Casaln-
uovo have used electronically unsymmetrical bis-3,4-diarylphos-
phinite ligands based on an R-D-fructofuranoside for asymmetric
hydrocyanation.30 The highest enantioselectivities for hydro-
cyanation to give naproxen nitrile (95% ee) were obtained with
a dissymmetric bisdiarylphosphinite having a relatively electron-
rich Ph2P and an electron-poor [3,5-(CF3)2C6H3)]2P. Takaya
reported that the electronically dissymmetric phosphine-
phosphite ligand (BINAPHOS) gave unusually high enantio-
selectivity in hydroformylation.31 This ligand which has an
electron-withdrawing phosphite ligand and an electron-donating
phosphine gave 94% ee in the rhodium-catalyzed hydroformy-
lation of styrene.
Grubbs found opposite electronic effects for halide and
phosphine ligands on ruthenium metathesis catalysts. The fastest
rates were observed for ruthenium olefin metathesis catalysts
(PR3)2X2RudCHR containing sterically large electron-donating
phosphines (PCy3 > PiPr3 > PCy2Ph > PiPr2Ph > PPh3) and
small electron withdrawing halide ligands (Cl > Br > I).32 It
was suggested that the large electron-donating phosphines more
readily dissociate to open a coordination site and that the
electron-withdrawing halogens stabilize alkene binding.
Conclusions
DIPHOS-(3,5-CF3,H) (1) shows a n:i ratio higher than either
of the symmetric ligands DIPHOS or DIPHOS-(3,5-CF3),
supporting our hypothesis that creating an electronically dis-
symmetric environment about our hydroformylation catalysts
enhances linear aldehyde selectivity. An electron-withdrawing
substituent on an equatorial phosphine increases the n:i ratio
while an electron-withdrawing substituent on an apical phos-
phine decreases the n:i ratio. Therefore, the best DIPHOS
catalysts place an electron-withdrawing substituted phosphine
in the equatorial position and an electron-donating substituted
phosphine in the apical position.
Experimental Section
General Procedures. See the Supporting Information. Ir(acac)-
(CO)2,33 Rh(CO)2(acac),34 (2-CH3C6H4)2PH,16 [3,5-(CF3)2C6H3]2P(CHd
CH2),16 and (2-CF3C6H4)2P(CHdCH2)16 were prepared as reported.
Analyzed mixtures of 1:1 CO:H2 were obtained from Matheson Gas
Products or Liquid Carbonic.
[3,5-(CF3)2C6H3]2PCH2CH2P(C6H5)2, DIPHOS-(3,5-CF3,H) (1).
Following a procedure similar to that used for 1-(diphenylphosphino)-
2-bis(m-fluorophenyl)phosphinoethane,35 a mixture of (C6H5)2PH (1.26
mL, 7.22 mmol), [3,5-(CF3)2C6H3]2 P(CHdCH2) (3.50 g, 7.22 mmol),
Figure 5. Electronically dissymmetric ligands and catalysts.
Enhanced product selectivity and more rapid rates for
electronically dissymmetric ligands have been observed previ-
ously (Figure 5). Togni studied electronic effects on enantio-
(29) (a) Schnyder, A.; Hintermann, L.; Togni, A. Angew. Chem., Int.
Ed. Engl. 1995, 34, 931. (b) Schnyder, A.; Togni, A.; Wiesli, U.
Organometallics 1997, 16, 255.
(28) If it is assumed that the ratio of [DIPHOS-(3,5-CF3, H)]Rh(CO)-
(alkene)H isomers is the same as the 83:17 ratio of isomers of iridium
complex 5, and that both isomers react at the same rate, the n:i ratio derived
from each of these rhodium isomers can be calculated. The 2.6:1 ratio seen
for DIPHOS was assumed to be perturbed to 1.3:1 by both equatorial and
apical phosphine substitution for DIPHOS-(3,5-CF3). The ratio for DIPHOS
was assumed to be perturbed by either an equatorial or an apical phosphine
substitution for the two different isomers of DIPHOS-(3,5-CF3,H) (1). The
n:i ratio for the major isomer of [DIPHOS-(3,5-CF3,H)]Rh(CO)(alkene)H
which has the electron-withdrawing aryl groups on the equatorial phosphine
was calculated to be 4.9 and the n:i ratio for the minor isomer with the
electron-withdrawing aryl groups on the apical phosphine was calculated
to be 0.7.
(30) RajanBabu, T. V.; Casalnuovo, A. L. J. Am. Chem. Soc. 1996, 118,
6325.
(31) (a) Horiuchi, T.; Ohta, T.; Nozaki, K.; Takaya, H. J. Chem. Soc.,
Chem. Commun. 1996, 155. (b) Sakai, N.; Mano, S.; Nozaki, K.; Takaya,
H. J. Am. Chem. Soc. 1993, 115, 7033.
(32) Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1997,
119, 3887.
(33) Roberto, D.; Cariati, E.; Psaro, R.; Ugo, R. Organometallics 1994,
12, 4227.
(34) Varshavskii, Y. S.; Cherkasova, T. G. Russ. J. Inorg. Chem. 1967,
12, 899.
(35) Kapoor, P. N.; Pathak, D. D.; Gaur, G; Kutty, M. J. Organomet.
Chem. 1984, 276, 167.

Electronically Dissymmetric DIPHOS DeriVatiVes
J. Am. Chem. Soc., Vol. 121, No. 1, 1999 69
and KO-t-Bu (0.3 g, 2.7 mmol) in THF (10 mL) was refluxed for 4 h.
Solvent was evaporated, and the resulting brown residue was recrystal-
lized twice from EtOH to give 1 (2.35 g, 49%) as a light cream solid:
mp 75-78 °C: 1H NMR (CD2Cl2, 300 MHz) δ 7.90 (br s, para Ar),
7.79 (br d, J ) 6 Hz, ortho Ar), 7.33-7.31 (m, Ph), 2.30-2.04 (m,
2.65-2.45 (CH2CH2), -11.20 (dd, JHP ) 75, 5.5 Hz, IrH); 13C{1H}
NMR (CD2Cl2, 125.7 MHz) δ 181.77 (dd, JCP ) 30, 6 Hz, CO), 139.75
(d, JCP ) 37 Hz, ipso), 134.34 (d, JCP ) 46 Hz, ipso′), 132.94 (br m),
132.7 (s), 132.57 (br d, JCP ) 13.7 Hz, ortho), 132.31 (d, JCP ) 11.8
Hz, ortho′), 131.19 (s, para Ph), 129.38 (br m), 129.09 (d, JCP ) 10.6
Hz, meta Ph), 126.1 (s), 124.96 (br s, para Ar), 123.36 (q, JCF ) 273
Hz, CF3), 32.46 (dd, JCP ) 34.2, 21.5 Hz, CH2), 31.51 (dd, JCP ) 31.2,
16.6 Hz, CH2′); 31P{1H} NMR (CD2Cl2, 202 MHz) δ 39.6 (d, JPP ) 9
Hz); 32.5 (d, JPP ) 9 Hz); 19F{1H} NMR (282 MHz, CD2Cl2) δ -63.2
CH2CH2); 13C{1H} NMR (CD2Cl2, 125.7 MHz) δ 141.94 (d, JCP
21.5 Hz, ipso), 137.94 (d, JCP ) 14 Hz, ipso′), 133.11 (br d, JCP
)
)
21.4 Hz, ortho Ar), 132.92 (d, JCP ) 18.6 Hz, ortho Ph), 132.29 (qd,
JCF ) 33.2 Hz, JCP ) 5.9 Hz, CCF3), 129.9 (d, JCP ) 6.8 Hz, meta
Ph), 129.38 (s, para Ph), 123.83 (br m, para Ar), 123.53 (q, JCF ) 273
Hz, CF3), 24.24 (t, JCP ) 16.6 Hz, CH2), 24.05 (t, JCP ) 15.6 Hz,
CH2′); 31P{1H} NMR (CD2Cl2, 121 MHz) δ -9.58 (d, JPP ) 39 Hz,
PAr2), -13.00 (d, JPP ) 39 Hz, PPh2); 19F{1H} NMR (CD2Cl2, 282
MHz) δ -63.2 (s); HRMS (EI) calcd (obsd) for C30H20F12P2 670.0849
(670.0846).
(s); IR (CH2Cl2) 1992 (νCO), 1941 (νCO), 2067 (νIr-H) cm-1
.
1H NMR (CD2Cl2, 500 MHz, -94 °C) δ 8.2-6.9 (m, Ar), 2.67-
2.37 (m, CH2CH2), -11.21 (dd, JHP ) 91.5, -14.5 Hz, IrH, 5a), -11.12
(dd, JHP ) 100, -14 Hz, IrH, 5b); the ratio of 5a:5b IrH resonances
was 94:6; 31P{1H} NMR (CD2Cl2, 202 MHz, -90 °C) (5a) δ 38.7 (d,
JPP ) 6 Hz), 31.6 (d, JPP ) 6 Hz); (5b) δ 36.6 (br s), 34.1 (br s); the
ratio of 5a:5b was 94:6; 31P{1H decoupled, except for the hydride
region} NMR (CD2Cl2, 202 MHz, -90 °C) (5a) δ 38.7 (t, JPH ) 9.5
Hz, JPP ) 9.5 Hz), 31.6 (dd, JPH) 87 Hz, JPP ) 9 Hz); (5b) δ 36.7 (br
d, JPH) 87 Hz), 34.0 (br s).
[DIPHOS-(2-CF3,H)]Ir(CO)2H (6). Following a procedure similar
to that used for (DIPHOS)Ir(CO)2H,19 a solution of NaBH4 (170 mg,
4.54 mmol) in ethanol (20 mL) was added to a solution of [DIPHOS-
(2-CF3,H)]Ir(CO)I36 (400 mg, 0.454 mmol) in CH2Cl2 (10 mL). After
1 h, silica gel (1 g) and H2O (100 µL) were added. The light yellow
solution was filtered and evaporated to give [DIPHOS-(2-CF3,H)]Ir-
(CO)H337 as a white solid. A suspension of the white solid in benzene
in a quartz photolysis cell was purged with CO, and photolyzed for 3
h at 36 °C in a Rayonet photoreactor. Solvent was evaporated to give
6 as a yellow-orange oily solid that was then recrystallized from pentane
to give single crystals suitable for X-ray diffraction:38 1H NMR (500
MHz, CD2Cl2) δ 8.15-7.40 (m, Ar), 2.75-2.40 (m, CH2CH2), -11.18
(dd, JHP ) 57, 31 Hz, IrH); 31P{1H} NMR (202 MHz, CD2Cl2) δ 43.1
(br), 32.2 (br); 19F{1H} NMR (282 MHz, CD2Cl2) δ -55.3 (s); IR (CH2-
Cl2) 2049 (νIrH ), 1980 (νCO), 1929 (νCO) cm-1. Anal. Calcd for C30H23F6-
IrO2P2: C, 45.98; H, 2.96. Found: C, 45.67; H, 3.07.
(2-CF3C6H4)2PCH2CH2P(C6H5)2, DIPHOS-(2-CF3,H) (2). A solu-
tion of (2-CF3C6H4)2P(CHdCH2) (9.0 g, 25.8 mmol), (C6H5)2PH (4.6
mL, 26.4 mmol), and KO-t-Bu (0.2 g, 1.8 mmol) in THF (20 mL) was
refluxed for 2 h. Solvent was evaporated, and the resulting brown
residue was recrystallized from EtOH to give 2 (3.3 g, 23%) as a pale
yellow powder: mp 133-135 °C; 1H NMR (CD2Cl2, 300 MHz) δ 7.9-
7.3 (m, Ar), 2.07 (m, CH2CH2); 13C{1H} NMR (CD2Cl2, 125.7 MHz)
δ 138.52 (d, JCP ) 14.7 Hz, ipso), 136.68 (d, JCP ) 32.2 Hz, ipso′),
134.3 (qd, JCF ) 30.3 Hz, JCP ) 24.5 Hz, CCF3), 133.69 (s, Ar), 133.05
(d, JCP ) 18.6 Hz, ortho Ph), 132.10 (s, Ar), 129.38 (s, Ar), 129.14 (s,
para Ph), 128.85 (d, JCP ) 6.8 Hz, meta Ph), 127.09 (s, Ar), 124.68 (q,
JCF ) 273 Hz, CF3), 24.86 (t, JCP ) 17.6 Hz, CH2), 24.33 (dd, JCP
)
18.6, 14.7 Hz, CH2′); 31P{1H} NMR (CD2Cl2, 121 MHz) δ -12.3 (d,
JPP ) 33 Hz, PPh2), -22.8 (dsept, JPP ) 33 Hz, JPF ) 50 Hz, PAr2);
19F{1H} NMR (CD2Cl2, 282 MHz) δ -57.1 (d, JFP ) 50 Hz); EI mass
spectrum m/z (%) 534 (74) [M+], 550 (7) [MO+], 405 (100).
[3,5-(CF3)2C6H3]2PCH2CH2P(C6H4-2-CH3)2, DIPHOS-(3,5-CF3,2-
CH3) (3). A solution of (2-CH3C6H4)2PH (2.3 g, 10.8 mmol), [3,5-
(CF3)2C6H3]2P(CHdCH2) (5.3 g, 10.9 mmol), and KO-t-Bu (0.3 g, 2.7
mmol) in THF (20 mL) was refluxed for 4 h. Solvent was evaporated,
and the resulting brown residue was recrystallized twice from benzene:
MeOH to give 3 (4.6 g, 61%) as white fine crystalline needles: mp
1H NMR (500 MHz, CD2Cl2, -106 °C) δ 8.87-7.15 (m, Ar), 3.6-
2.5 (CH2CH2), -10.69 (dd, JHP ) 94, -13.5 Hz, IrH, 6a), -11.70
(dd, JHP ) 108, -14 Hz, IrH, 6b); the ratio of 6a:6b IrH resonances
was 67:33; 31P{1H} NMR (202 MHz, CD2Cl2, -98 °C) (6a) δ 40.5
(s), 34.0 (s); (6b) δ 33.4 (s), 31.2 (s); the ratio of 6a:6b was 67:33;
31P{1H decoupled, except for the hydride region} NMR (CD2Cl2, 202
MHz, -98 °C) (6a) δ 40.5 (s), 34.0 (d, JPH ) 92 Hz); (6b) δ 33.4 (d,
JPH ) 104 Hz), 31.2 (s).
1
131-132 °C; H NMR (CD2Cl2, 300 MHz) δ 7.89 (s, para, Ar), 7.79
(d, JPH ) 6.3 Hz, ortho, Ar), 7.10 (m, 4H, tol), 2.36 (s, CH3), 2.29 (m,
CH2CH2), 2.20 (m, CH2CH2); 13C{1H} NMR (CD2Cl2, 125.7 MHz) δ
142.9 (d, JCP ) 26 Hz, ipso), 141.1 (d, JCP ) 22.4 Hz, ipso′), 136.1 (d,
JCP ) 13.5 Hz, ortho Ar), 133.1 (d, JCP ) 18 Hz, ortho tol), 132.4 (qd,
JCF ) 33 Hz, JCP ) 5.4 Hz, CCF3), 131.2 (s), 130.7 (d, JCP ) 3.6 Hz),
129.2 (s), 126.6 (s), 123.9 (s, para tol), 123.6 (q, JCF ) 273 Hz, CF3),
24.5 (t, JCP ) 16 Hz, CH2), 22.8 (t, JCP ) 15 Hz, CH2′), 21.3 (d, JCP
[DIPHOS-(3,5-CF3,2-CH3)]Ir(CO)2H (8). A benzene solution of
36
[[DIPHOS-(3,5-CF3,2-CH3)]Ir(CO)H3 (150 mg, 0.163 mmol) in a
) 22 Hz, CH3); 31P{1H} NMR (CD2Cl2, 202 MHz) δ -9.7 (d, JPP
)
quartz photolysis cell purged with CO was photolyzed for 30 min at
36 °C. Solvent was evaporated to give 8 (60 mg, 39%) as a pale yellow
solid: 1H NMR (CD2Cl2, 300 MHz) δ 8.20-7.15 (m, Ar), 2.70-2.37
(m, CH2CH2), 2.06 (s, CH3), -11.58 (d, JHP ) 82 Hz, IrH); 31P{1H}
NMR (CD2Cl2, 121 MHz) δ 37.7 (d, JPP ) 11 Hz), 26.2 (d, JPP ) 11
Hz); 13C{1H} NMR (CD2Cl2, 75 MHz) δ 182.1 (d, JCP ) 32 Hz, CO),
140.6 (d, JCP ) 6 Hz, ipso), 140.0 (dd, JCP ) 37, 2 Hz, ipso′), 140-
123 (Ar), 123.4 (q, JCF ) 271 Hz, CF3), 24.4 (d, JCP ) 26 Hz, CH2),
23.3 (d, JCP ) 22 Hz, CH2′), 22.1 (d, JCP ) 7 Hz, CH3); 19F{1H} NMR
(CD2Cl2, 282 MHz) δ -63.2 (s); IR (CH2Cl2) 2028 (νIrH ), 1988 (νCO),
1938 (νCO) cm-1; EI mass spectrum m/z (%) 919 (0.6) [M - CO,H+],
918 (1.8) [M - 2Me+], 888 (1.5) [M - CO,H,2Me+], 214 (100)
[P(C6H4-2-CH3)2].
40 Hz, PAr2), -33.9 [d, JPP ) 40 Hz, P(o-Tol)2]; 19F{1H} NMR (282
MHz, CD2Cl2) δ -63.2 (s); EI mass spectrum m/z (%) 698 (100) [M+],
679 (14) [M - F+]. Anal. Calcd for C32H24F12P2: C, 55.03; H, 3.46.
Found: C, 54.80; H, 3.53.
(2-CF3C6H4)2PCH2CH2P(C6H4-2-CH3)2, DIPHOS-(2-CF3,2-CH3)
(4). A solution of (2-CH3C6H4)2PH (1.20 g, 5.6 mmol), (2-CF3C6H4)2P-
(CHdCH2) (1.95 g, 5.6 mmol), and KO-t-Bu (0.2 g, 1.8 mmol) in THF
(15 mL) was refluxed for 20 h. Solvent was evaporated, and the
resulting brown residue was recrystallized twice from EtOH and then
from EtOH:CH2Cl2 to give 4 (0.51 g, 16%) as a light cream solid: mp
178-181 °C; 1H NMR (CD2Cl2, 300 MHz) δ 7.8-7.7 (m, 2H), 7.53-
7.43 (m, 4H), 7.28-7.00 (m, 10H), 2.38 (s, CH3), 2.07 (t, J ) 4.2 Hz,
CH2CH2); 13C{1H} NMR (CD2Cl2, 125.7 MHz) δ 142.78 (d, JCP
)
1H NMR (500 MHz, CD2Cl2, -110 °C) δ 8.7-6.9 (m, Ar); 3.2-
2.8 (m, CH2CH2); 2.06 (s, CH3, major isomer), 1.75 (s, CH3′, major
25.4 Hz, ipso); 136.80 (d, JCP ) 16.6 Hz, ipso′); 133.64, 132.10, 131.40,
130.42, 130.11, 129.34, 129.00, 128.93, 127.09, 126.42, 125.91, (Ar);
124.67 (q, JCF ) 275 Hz, CF3); 24.83 (t, JCP ) 16 Hz, CH2); 23.46 (t,
JCP ) 16 Hz, CH2′); 21.33 (d, JCP ) 21, CH3); 31P{1H} NMR (CD2Cl2,
121 MHz) δ -21.1 (dsept, JPP ) 33 Hz, JPF ) 49 Hz P[2-(CF3)C6H4]2),
isomer), -10.56 (dd, JHP ) 100, -14 Hz, IrH, 8b), -11.67 (dd, JHP
)
94, -14 Hz, IrH, 8a); the ratio of 8a:8b was 96:4; 31P{1H} NMR (CD2-
Cl2, 202 MHz, -106 °C) (8a) δ 36.1 (d, JPP ) 11 Hz), 24.3 (d, JPP)
11 Hz); (8b) δ 38.8 (br s), 26.0 (br s); the ratio of 8a:8b was 96:4.
31P{1H decoupled, except for the hydride region} NMR (CD2Cl2, 202
MHz, -110 °C) (8a) δ 36.1 (br s), 24.3 (dd, JPH ) 84 Hz, JPP ) 11
Hz); (8b) 38.8 (br d, JPH ) 93 Hz), 26.0 (br s).
-32.0 (d, J ) 33 Hz, P[2-(CH3)C6H4)2]); 19F{1H} NMR (CD2Cl2,
PP
282.16 MHz) δ -57.1 (d, JFP ) 50 Hz); HRMS (EI) calcd (obsd) for
C30H26F6P2 562.1414 (562.1416).
[DIPHOS-(3,5-CF3,H)]Ir(CO)2H (5). Ir(CO)2(acac) (2.9 mg, 8.4
µmol) and DIPHOS-(3,5-CF3,H) (1) (5.7 mg, 8.5 µmol) in CD2Cl2
were shaken in an NMR tube for 20 h under 1 atm of 1:1 CO:H2 to
give a solution of 5: 1H NMR (CD2Cl2, 500 MHz) δ 8.2-6.9 (m, Ar),
(36) See the Supporting Information for synthesis and characterization.
(37) See the Supporting Information for characterization.
(38) See the Supporting Information for X-ray data.

70 J. Am. Chem. Soc., Vol. 121, No. 1, 1999
Casey et al.
[DIPHOS-(2-CF3,2-CH3)]Ir(CO)2H (9). A benzene solution of
[DIPHOS-(2-CF3,2-CH3)]Ir(CO)H336 (50 mg, 0.064 mmol) was pho-
tolyzed in a quartz photolysis cell purged with CO for 30 min at 36
°C. Solvent was evaporated to give 9 (20 mg, 38%) as a brown oil:
1H NMR (CD2Cl2, 500 MHz) δ 8.16-7.00 (m, Ar), 2.74-2.52 (m,
CH2CH2), 2.01 (s, CH3), -11.39 (dd, JHP ) 62, 27 Hz, IrH); 31P{1H}
NMR (CD2Cl2, 121 MHz) δ 42.6 (br s), 27.9 (br s); 13C{1H} NMR
(CD2Cl2, 125.7 MHz) δ 184.1 (br s, CO), 140.7 (d, JCP ) 5.9 Hz, ipso),
135.3 (d, JCP ) 6.5 Hz, ipso′), 132.3 (d, JCP ) 6.3 Hz), 131.6 (d, JCP
H2) with toluene (0.20 mL, 1.9 mmol) added as an internal GC standard.
After 1 h of stirring at 36 ( 2 ° C, 1-hexene (2.50 mL, 0.020 mmol)
was added. Samples containing heptanal and 2-methylhexanal were
analyzed by temperature-programmed gas chromatography on an
HP5890A chromatograph interfaced to a HP3390A integrator using
an HP-1 10 m × 0.53 mm methyl silicone capillary column.
Acknowledgment. Financial support from the Department
of Energy, Office of Basic Energy Sciences, is gratefully
acknowledged. E.W.B. thanks the Fulbright commission for a
fellowship. B.R.P. thanks the Alexander von Humboldt Stiftung
for a von Lynene Fellowship. Grants from NSF (CHE-9105497)
and from the University of Wisconsin for the purchase of the
X-ray instruments and computers are acknowledged. We thank
Alpha Aesar for a loan of iridium compounds.
) 13 Hz), 130.9 (s), 130.7 (s), 129.0 (s) 128.7 (m), 126.28 (d, JCP
)
12.7 Hz), 124.5 (q, JCF ) 275 Hz, CF3), 33.6 (m, CH2), 33.3 (dd, JCP
) 33, 20 Hz, CH2′), 22.0 (d, JCP ) 7 Hz, CH3); 19F{1H} NMR (282
MHz, CD2Cl2) δ -55.5 (s); IR (CH2Cl2) 2049 (νIr-H), 1978 (νCO), 1926
(νCO) cm-1
.
1H NMR (500 MHz, CD2Cl2, -98 °C) δ 8.8-6.9 (m, Ar); 3.3-2.6
(m, CH2CH2); 1.99 (s, CH3, 9a), 1.85 (s, CH3, 9b), 1.80 (s, CH3′, 9b),
1.75 (s, CH3′, 9a), -11.22 (dd, JHP ) 98, -15 Hz, 9a), -11.45 (dd,
JHP ) 111, -17 Hz, 9b); the ratio of 9a:9b was 60:40. The observation
of more than one CH3 resonance for each isomer may be due to hindered
rotation about P-Ar bonds which gives rise to multiple rotomers, some
with inequivalent CH3 groups. 31P{1H decoupled, except for the hydride
region} NMR (CD2Cl2, 202 MHz, -98 °C) (9a) δ 39.2 (br s), 26.2 (d,
JPH ) 98 Hz); (9b) δ 34.9 (br d, JPH ) 101 Hz), 27.5 (br s).
Supporting Information Available: General experimental
methods and experimental details and characterization for 7,
[DIPHOS-(2-CF3,H)]Ir(CO)H3, [DIPHOS-(2-CF3,H)]Ir(CO)I,
[DIPHOS-(3,5-CF3,2-CH3)]Ir(CO)I, [DIPHOS-(2-CF3,2-CH3)]-
Ir(CO)I, [DIPHOS-(3,5-CF3,2-CH3)]Ir(CO)H3, and [DIPHOS-
(2-CF3,2-CH3)]Ir(CO)H3 and X-ray crystallographic data for 6
and 7 (26 pages, print/PDF). See any current masthead page
for ordering information and Web access instructions.
Catalytic Hydroformylation of 1-Hexene. Hydroformylation reac-
tions were performed as described earlier in a 90-mL Fischer-Porter
bottle equipped with a star-head magnetic stir bar.12 Rh(CO)2(acac)
(10 mg, 39 µmol) and a chelating diphosphine (39 µmol) were dissolved
in benzene (6.0 mL) under 70 psig of 1:1 CO:H2 (50.02% CO, 49.98%
JA982117H