Synthesis and characterization of tetracarbonylmolybdenum(0) and pentacarbonyltungsten(0) complexes of TADDOL-derived, monodentate P-donor ligands

Article abstract of DOI:10.1016/j.jorganchem.2018.11.018

TADDOL-derived P-donor ligands are of interest as ligands in transition metal catalyzed transformations; however, few studies have been conducted on the steric and electronic properties of P-donor ligands derived from TADDOL. To gain more insight into these properties four tetracarbonylmolybdenum(0) and two pentacarbonyltungsten(0) complexes of monodentate P-donor ligands derived from TADDOL have been studied. These studies show that exchanging the chloro substituent on the phosphorus for OMe increases the donor ability of the ligand and that the cis-tetracarbonylmolybdenum(0) complex of the ligand having the OMe substituent spontaneously isomerizes in solution. X-ray crystallographic analyses indicate that the orientations of the 1,3,2-dioxaphosphepane ring and the aryl substituents are not always conserved, even within the same complex.

Full text of DOI:10.1016/j.jorganchem.2018.11.018

Accepted Manuscript
Synthesis and characterization of tetracarbonyl molybdenum and pentacarbonyl
tungsten complexes of TADDOL-derived, monodentate P-donor ligands
Ethan C. Cagle, Gary M. Gray
PII:
S0022-328X(18)30920-3
DOI:
https://doi.org/10.1016/j.jorganchem.2018.11.018
JOM 20638
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 15 October 2018
Revised Date: 9 November 2018
Accepted Date: 12 November 2018
Please cite this article as: E.C. Cagle, G.M. Gray, Synthesis and characterization of tetracarbonyl
molybdenum and pentacarbonyl tungsten complexes of TADDOL-derived, monodentate
P-donor ligands, Journal of Organometallic Chemistry (2019), doi: https://doi.org/10.1016/
j.jorganchem.2018.11.018.
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ACCEPTED MANUSCRIPT

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Synthesis and Characterization of Tetracarbonyl Molybdenum and Pentacarbonyl Tungsten
complexes of TADDOL-derived, Monodentate P-Donor Ligands
Ethan C. Cagle and Gary M. Gray
Abstract
TADDOL-derived P-donor ligands are of interest as ligands in transition metal catalyzed
transformations; however, few studies have been conducted on the steric and electronic
properties of P-donor ligands derived from TADDOL. To gain more insight into these properties
four tetracarbonylmolybdenum(0) and two pentacarbonyltungsten(0) complexes of
monodentate P-donor ligands derived from TADDOL have been studied. These studies show
that exchanging the chloro substituent on the phosphorus for OMe increases the donor ability
of the ligand and that the cis-tetracarbonylmolybdenum(0) complex of the ligand having the
OMe substituent spontaneously isomerizes in solution. X-ray crystallographic analyses indicate
that the orientations of the 1,3,2-dioxaphosphepane ring and the aryl substituents are not
always conserved, even within the same complex.
Introduction
Since the original reports of the synthesis of TADDOLs by Seebach and coworkers [1],
substituted TADDOLs have become important precursors to chiral organic molecules and chiral
ligands in transition metal catalysts [2-5]. The interest in the use of TADDOLs is due to multiple
factors: 1) TADDOL can easily be synthesized from the readily available chiral tartaric acid; 2)
multiple phosphorus donor ligands (phosphochlorodite esters, phosphites, phosphoramidites
and phosphonites) can easily be synthesized from the diol; 3) many derivatives of the TADDOL
can easily be achieved by modifying the aryl substituents or the acetal ring (Figure 1) [5].
Figure 1. Areas of modification to achieve various TADDOL-derived P-donor ligands.
Despite the successes of TADDOL-derived P-donor ligands in catalytic transformations,
the coordination chemistry of these ligands in transition metal complexes has not been

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extensively studied. This is particularly true for TADDOL-derived phosphite ligands. As of this
writing, the structure of only one coordination compound with a TADDOL-derived phosphite
has been determined.[4]
To better understand how TADDOL-derived phosphite ligands behave when coordinated
to transition metals in catalytic systems, the coordination geometries and electronic properties
of simple, monodentate phosphite ligands should be studied. In this paper, we present the
syntheses, and the NMR spectroscopic and X-ray crystallographic characterizations of cis- and
trans- Mo(CO) complexes with two TADDOL-derived monodentate P-donor ligands. The
4
1
electronic properties of the ligands were determined by measuring their | JWP| coupling
constants in their W(CO) complexes. A Rh(I) complex of the monodentate TADDOL-derived
5
phosphite ligand was also evaluated as a catalyst for the hydroformylation of styrene to provide
a baseline for future comparisons with catalysts having more complicated TADDOL-derived
phosphites.
Results and Discussion
Ligand Synthesis and NMR Characterization
The TADDOL-derived phosphochloridite ester (L1) was synthesized by a previously
published literature protocol [6]. Scheme 1 shows the reaction pathway for the conversion of
L1 into the monodentate TADDOL-derived phosphite ligand L2. The reagents and products
involved in these reactions are highly air-sensitive; therefore, Schlenk techniques were used.
Scheme 1. Synthesis of L2.
3
1
1
The P{ H} NMR spectrum of L2 displayed a singlet at 133.78 ppm that is shifted upfield
3
1
1
relative to the P{ H} NMR resonance of L1 (148.92 ppm). One peak is expected as the RR
chirality of the starting dimethyl 2,3-O-isopropylidene-L-tartrate is neither lost in the formation
1
of TADDOL nor in the formation of the P-donor ligands. The H NMR spectrum of L2 displays
four distinct regions. The aromatic region shows a complex second-order resonance due to the
multiple couplings within the aromatic rings between chemically and magnetically inequivalent
protons. The C-H protons in the acetal ring give rise to two broad doublets. This splitting
pattern appears to be due to coupling to the other acetal proton, which is magnetically

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inequivalent, as well as long range coupling to the phosphorus. The -POCH protons give rise to
3
two separate doublets. This could be due to loss of the C symmetry because of the pyramidal
2
phosphorus and conformational equilibrium between different arrangements about the 1,3,2-
dioxaphosphepane Finally, the furthest upfield resonances are singlets due to the methyl
substituents on the acetal ring.
3
1
1
1
L1 and L2 hydrolyze when expose to air therefore P{ H} and H NMR spectra were used
to evaluate their purity. After the purity was determined, the ligands were used to synthesize
coordination complexes with tetracarbonylmolybdenum(0) and pentacarbonyltungsten(0)
metal centers. Additionally, L2 was used in the Rh(I) catalyzed hydroformylation of styrene.
Styrene Hydroformylation Catalyzed by the Rh(I) Complex of L2
Rhodium(I) complexes containing L2 were used as catalysts in the hydroformylation of
styrene (Scheme 2). The results for these reactions are given in Table 1 and are compared to
those obtained with an analogous P-donor ligand 2,2’-(C H O )POCH , L3. Two catalytic runs
1
2
8
2
3
were performed at each set of conditions in order to measure reproducibility. The activities and
regioselectivities were also measured under the same conditions in the absence of any P-donor
ligand to determine the effects of the ligands.
Scheme 2. Rh(I) catalyzed hydroformylation of styrene
Because the active catalyst forms in situ, the catalytically active species is not known.
n
Possibilities include RhH(CO)2+n(phosphite)2-n (n = 1, 0), HRh(CO) (n= 3,4), and rhodium
carbonyl clusters depending on the reactions conditions [7-9]. Martin and coworkers showed
that increasing the P-donor ligand concentration has no effect on the regioselectivity of the
reaction but drastically decreases the activity. This suggests that the active catalyst is formed at
low ratios of ligand to rhodium [10].
Catalytic runs at 80 °C and 20 atm of syn gas with L2 present in solution show increases in both
2
iso-selectivity and activity when compared to those with only Rh(CO) (acac) but show decreases
in both iso-selectivity and activity when compared to catalytic runs with the biphenol-derived P-
donor ligand (L3) in solution. These and previously reported results [10] suggest that the lower
steric hindrance around the P-donor atom in L3 leads to a higher iso-selectivivity and a more
active catalyst under this set of reaction conditions. The catalytic runs with L2 present in
solution showed a slight enantiomeric excess (3%) of the R enantiomer of the iso product.

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a
Table 1. Results of Styrene Hydroformylation Catalyzed by Rh(I) complexes of L2 or L3
Ligand
b
None
L2
L3[10]
80
Temperature (°C)
iso-selectivity (%)
ee (%)
45
81 (82)
-
80[10]
47 (47)
-
45
80
89 (89)
77 (78)
86 (86)
-
7 (6) [R] 3 (3) [R]
4
-1
k x 10 (s )
0.1 (0.1)
0.76 (0.88) 0.3 (0.1) 2.9 (2.9)
8.3 (8.2)
Completion (%)
100 (100)
100 (100) 100 (91) 100 (100) 100 (100)
a
Results for duplicate experiments are shown in parentheses. Conditions (all ratios are molar): solvent =
dichloromethane, CO/H2 = 1:1, P = 20 atm, substrate/Rh = 1000:1, ligand/Rh = 2.4:1. The pseudo-first-order rate
1
constant, k, was obtained from a first-order fit of pressure drop versus time using Graphical Analysis software. H
NMR was used to determine % iso after a pressure change was no longer observed. No hydrogenation was
b
observed. GC/MS was used to determine ee. The only pro-catalytic species present is Rh(CO)
2
(acac).
It is well established that decreasing the temperature in the hydroformylation of styrene
results in higher iso-selectivites and lower rates [11]. With this in mind, catalytic runs were
conducted with L2 in solution at 45 °C. While the catalyst with L2 showed an iso-selectivity near
9
0%, a marked improvement over catalytic solutions containing only Rh(CO) (acac) at the same
2
temperature, the reaction took more than 20 hours to reach completion. At the lower
temperatures, the enantiomeric excess increased slightly from 3% R to 7% R.
Model Complexes
Use in Studies of Coordination Geometries
During alkene hydroformylation, catalysts with Rh(I) metal centers exhibit numerous
coordination geometries. Because of this, it is beneficial to study ligands used in such reactions
in a variety of chemical environments that model the coordinate geometries observed in these
reactions. In addition, it is also possible to use coupling of NMR-active metal nuclei to
phosphorus to evaluate the effect of substituents on the donor ability of the ligand [12-18] and
the σ-character of the W-P bond [12,19].
Synthesis and Characterization of Molybdenum Model Complexes
4 2
The cis-Mo(CO) (L) (L= L1, L2) complexes were synthesized using the synthetic pathway
shown in Scheme 3 with dry DCM as the solvent. These reactions took no more than two hours.
Following each reaction, the mixture was evaporated to dryness, and the norbornadiene
byproduct was removed though diffusion recrystallization using DCM/methanol. Some
spontaneous cis/trans isomerization occurred during the purification of 2a.

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Scheme 3. Synthesis of 1a and 2a
To determine the trans:cis equilibrium ratios for each complex, solid mercury(II) chloride
8
31
1
was added to solutions of the complexes in THF-d . The P{ H} NMR spectra were then
obtained for each sample at regular intervals until an equilibrium had been established. Upon
addition of the HgCl , 2a immediately and completely transformed to trans-Mo(CO) (L2) (2b).
2
4
2
3
1
1
4 2
The isomerization of 1a to trans-Mo(CO) (L1) (1b), whose P{ H} NMR spectra are shown in
Figure 2, took 5.25 hours; reaching equilibrium at a 4:1 ratio of 1b to 1a. These reaction
mixtures were then filtered through silica gel to obtain pure 1b and 2b.
Figure 2. cis/trans isomerization reaction of 1a to 1b with catalytic HgCl
2
3
1
1
13
1
1
The complexes (1a-2b) were characterized by P{ H}, C{ H}, and H NMR
3
1
1
spectroscopy. The P{ H} NMR spectral data for all complexes in this study are summarized in
Table 2. All the resonances of the molybdenum complexes are singlets. That of 1a showed an
upfield shift of 5 ppm from that of L1, while that of 2a showed a downfield shift of nearly 26
ppm from that of L2. The very different coordination chemical shifts could be due to different
conformational changes about the phosphorus upon coordination to the Mo(0) center. The
resonances of the trans complexes, 1b and 2b, are downfield of resonances of the respective cis
complexes, 1a and 2a, with that of 2a exhibiting a much larger coordination chemical shift. It is

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somewhat surprising that exchanging a chloro substituent for a methoxy substituent would
have such a large effect on the coordination chemical shifts.
3
1
Table 2. P NMR Chemical Shifts of Synthesized Compounds
Ligand
Free Ligand cis-Mo(CO) (L)2 trans-Mo(CO) (L)2
W(CO) (L)
4
4
5
1
10.89 (s), 110.89 (d,
L1
148.92 (s)
133.78 (s)
143.08 (s)
149.2 (s)
168.18 (s)
1
|
JWP| = 432.5 Hz)
132.89 (s), 132.91 (d,
L2
159.54 (s)
1
|
JWP| = 403.3 Hz)
1
3
1
The C{ H} NMR spectra of 1a and 2a display the multiplets common for cis and trans
metal carbonyls between 206-213 ppm. In both cases, the resonances of carbonyls cis to both
P-donor ligands are upfield of those for carbonyls trans to one of the P-donor ligands. The
1
3
1
C{ H} NMR spectra of 1b and 2b only display the multiplets for carbonyls cis to both P-donor
ligands.
1
The H NMR spectra for 1a-2b each show a downfield set of three doublets and an
upfield complex multiplet for the aromatic protons. The upfield multiplet exhibits splitting that
seems to be influenced by both by the coordination geometries of the P-donor ligands and the
nature of third substituent on the phosphorus. Two doublets upfield of the aromatic proton
resonances are due to the two protons of the acetal ring. The chemical shifts of these doublets
are also sensitive to both the coordination geometry of the Mo(CO) center and the nature of
4
third substituent on the phosphorus. Lastly, the protons for the acetal methyls give rise to two
singlets whose chemical shifts show the same sensitivity to the coordination geometry of the
Mo(CO) center and the nature of third substituent on the phosphorus as do those of the
4
resonances the acetal ring protons.
Synthesis and Characterization of Tungsten Model Complexes
5 2
The W(CO) (L) complexes (1c, 2c) were synthesized as show in Scheme 4 using dry THF
as the solvent. These reactions required up to 48 hours to reach completion.
3
1
1
13
1
1
Complexes 1c and 2c were characterized by P{ H}, C{ H}, and H NMR spectroscopy. The
3
1
1
P{ H} NMR spectra of the tungsten complexes 1c and 2c each displays a singlet with a
1
85
superimposed doublet due to the W isotope (I = ½). While the resonances of both complexes
are upfield of those of their respective free ligands, the resonance of 1c shows a great upfield
shift than does that of 2c.
1
3
1
The C{ H} NMR spectra of 1c and 2c show doublets for the carbonyls cis to both P-donor
ligands and for the carbonyl trans to the P-donor ligands. These doublets also have satellite
1
185
peaks due to the | JWC| coupling between the carbonyl carbons and the W isotope.

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Scheme 4. Synthesis of 1c and 2c
1
The H NMR spectra of 1c and 2c are similar to those of 1a and 2b; however, the
splitting patterns are less complex in 1c and 2c presumably due to the presence of only one P-
donor ligand.
1
The magnitudes of the | J | coupling constants allow the relative donor abilities of the
WP
P-donor ligands to be determined [12-18]. Based on the coupling constants in Table 2, replacing
the chloro group in L1 with the OMe group in L2 increases the donor ability of the ligand.
Likewise, the σ-character of the L1-W bond is slightly greater than is the σ-character of the L2-
W bond.
X-ray Crystal Structures of Model Complexes
X-ray quality crystals of most of the metal complexes synthesized in this research were
obtained. The details of the individual data collections are in Table S1. In each case, the X-ray
data confirmed the coordination geometry and agreed with NMR spectroscopic analyses. Select
bond lengths and angles are given in Tables 3-4 and the structural diagrams are shown in
Figures 3-7. All the structures were solved without issue.
Figure 3. Solid-state structure of 1a, Thermal ellipsoids are drawn at the 30% probability level,
hydrogen atoms and solvent are omitted for clarity.

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Figure 4. Solid-state structure of 1b, Thermal ellipsoids are drawn at the 30% probability level,
hydrogen atoms are omitted for clarity.
Figure 5. Solid-state structure of 2a, Thermal ellipsoids are drawn at the 30% probability level,
hydrogen atoms and solvent are omitted for clarity.

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Figure 6. Solid-state structure of 2b, Thermal ellipsoids are drawn at the 30% probability level,
hydrogen atoms and solvent are omitted for clarity.
Figure 7. Solid-state structure of 1c, Thermal ellipsoids are drawn at the 30% probability level,
hydrogen atoms and solvent are omitted for clarity.
Each of the molybdenum carbonyl complexes has a distorted octahedral metal center.
The largest distortion from the ideal angle is in the P-Mo-P bonds in 1a and 2a (99.29(5)° and
103.20(5)°, respectively) and in the C-Mo-P angles for the carbonyl ligands cis to both of the P-
donor ligands, which deviate significantly from the ideal 90°. None of the structures exhibited
significantly different C-O bond lengths for carbonyls cis to both the P-donor ligands and those
trans to one of the P-donor ligands as might be expected due to the different orbital

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overlap.[20,21] With exception for 1b, the Mo-P bond lengths are also within the average
determined by Mogul 2.440(17).[22]
Table 3. Select bond distances of metal (1a-2b M = Mo, 1c M = W) complexes (Å).
(
Å)
1a
1b
-
2a
2b
1c
C–M [trans-CO to Pdonor] 2.01(1)
C–M [cis-CO to Pdonor] 2.05(1)
C–O [trans-CO to Pdonor] 1.14(1)
C–O [cis-CO to Pdonor] 1.13(1)
M–P 2.443(1)
2.01(1)
2.04(1)
1.13(1)
1.13(1)
-
2.018(5)
2.05(1)
1.126(7)
1.13(2)
2.05(1)
-
2.04(1)
-
1.13(1)
2.394(1)
1.13(1)
2.458(1) 2.404(1) 2.430(1)
Table 4. Select bond angles (°) of molybdenum complexes.
(
°)
1a
1b
2a
2b
1c
P1-Mo-P2 99.29(5)
C(1)–Mo–P1 172.2(2)
C(1)–Mo–P2 86.7(2)
C(2)–Mo–P1 87.3(2)
C(2)–Mo–P2 172.8(2)
C(3)–Mo–P1 86.1(2)
C(3)–Mo–P2 91.6(2)
C(4)–Mo–P1 94.2(2)
C(4)–Mo–P2 86.9(2)
176.73(2)
90.42(8)
91.96(8)
90.81(7)
87.09(7)
88.46(7)
89.19(7)
93.05(7)
89.24(7)
-
103.20(5) 179.48(4)
-
171.0(2)
85.4(2)
84.7(2)
170.9(2)
85.5(2)
90.5(2)
88.8(2)
88.9(2)
-
91.5(1)
88.9(1)
87.5(2)
92.2(2)
90.5(1)
89.1(1)
91.4(2)
88.9(2)
-
176.3(1)
-
89.8(1)
-
90.2(2)
-
90.6(2)
-
C(5)–Mo–P1
-
87.4(1)
It is of interest to determine if each of the P-donor ligands exhibit similar conformations
within each complex and between the complexes. The most basic aspect of the ligand
conformation is the conformation of the 1,3,2-dioxaphosphepane ring. Figure 8 shows that the
seven torsion angles around the 1,3,2-dioxaphosphepane ring have similar orientations and the
angles, with the exception of one ligand in 1b, and that these torsion angles fall within a range
of about 20°. In the conserved conformation, the oxygen and nonbridgehead carbons are
planar or nearly planar. The phosphorus atom is above this plane while the bridgehead carbons
are twisted about this plane. This twist is due to the chirality of the starting alcohol and can also

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be seen in the structure of the previously synthesized trans-PdCl complex of a polyether
2
derived TADDOL ligand [4]. In the unique conformation (P1 of 2a), the ligand exhibits a more
symmetrical orientation with a pseudo-C rotation axis through the phosphorus and the
2
quaternary carbon in the acetal ring. It is interesting to note that the preferred conformation of
the 1,3,2-dioxaphosphepane ring is found in the structure of 1c, which is a
pentacarbonyltungsten(0) complex that contains only a single P-donor ligand that should
experience minimal intramolecular steric interactions.
Figure 8. a) Ligand from 1a with 1,3,2-dioxaphosphepane torsion angles numbered. b) the 1,3,2-
dioxaphosphepane torsion angles for all complexes.
A related aspect of the ligand conformation is the orientation of the phenyl rings
relative to the 1,3,2-dioxaphosphepane rings. These are determined by the torsion angles about
the bonds between the ipso-phenyl carbons and the 1,3,2-dioxaphosphepane rings. The torsion
angles reported in Table 5 are calculated using the adjacent 1,3,2-dioxaphosphepane ring
oxygen and the ortho-phenyl carbon that gives the smaller torsion angle. The torsions in 1a and
2a are equal in sign and similar in magnitude. This could be expected as the ligands in the cis
complexes are held in close proximity. However, in the trans complexes and in the
pentacarbonyltungsten(0) complex, the torsion angles of the aryl rings are not conserved. This
suggests that fewer orientations are possible when the ligands are adjacent to one another.
Table 5. Torsion angles (°) to the aryl rings in the molybdenum complexes (O-C -Cipso-Cortho).
q
(
°)
1a
58.1
4.2
2a
41.49
25.07
1b
34.86
39.45
2b
1c
Ar 1
Ar 2
Ar 3
Ar 4
Ar 5
Ar 6
Ar 7
Ar 8
-30.96 -42.9(5)
-46.13 -15.9(5)
-44.33 -46.17 -38.19 -46.46
-22.34 -25.01 -18.45 -19.71
26.8(5)
44.9(5)
46.28
38.61
-59.94
42.84
33.51
-50.3
-23.15 -19.93
-
-
-
-
-24.38
22.5
38.1
-40.51
-21.19
-24.53 -23.06
47.24

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A comparison of the conformations of the 1,3,2-dioxaphosphepane rings and aryl
4
groups in the TADDOL-derived P-donor ligands in the same Mo(CO) complexes is given by the
wireframe overlays of the ligands in Figure 9. These overlays indicate that the conformations of
the ligands are most conserved in 2a. The conformations of the ligands are also quite similar in
2b, but the methoxy and molybdenum exchange positions on the phosphorus. The greatest
differences in the ligand conformations are seen in 1b in which the different 1,3,2-
dioxaphosphepane ring conformations result in very different aryl ring conformations.
Figure 9. a) wireframe overlay of both ligands of 1a. b) wireframe overlay of both ligands of 1b.
c) wireframe overlay of both ligands of 2a. d) wireframe overlay of both ligands of 2b.
The fact that the ligand conformations are more similar in the cis complexes suggests
that a requirement for ligands designed to yield high enantioselectivities in the
hydroformylation of styrene would be backbones that hold the TADDOL-derived P-donor
groups in close proximity and restrict the conformational mobility of the 1,3,2-
dioxaphosphepane rings and their aryl substituents. This approach is seen in the TADDOL-
derived P-donor ligands with o-catechol-derived backbones reported by Breit and coworkers
[
3g].
To determine how the arrangement of the aryl rings affect the steric bulk of the
phosphorus donor ligands, cone angles (θ), were determined for each ligand (Table 6) [23-25] .
The complex with the smallest difference in cone angles is 2a (2.4°), which is expected given the
similarities in the conformations of the two ligands. The other complexes have cone angles that
differ by 10-15° with all the cone angles falling within a 20° range.

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Table 6. Cone angles, θ, (°) about the Mo-Px bond of the molybdenum complexes.
(
°)
1
a
1b
1c
147.8
-
2a
2b
P1
P2
154.6
140.4
154.4
141.8
151.7
154.1
135.5
145.5
Conclusion
The first family of TADDOL-derived P-donor ligands coordinated to (CO) Mo(0) centers
4
3
1
1
13
1
1
have been prepared and have been characterized by P{ H}, C{ H}, and H NMR
spectroscopies and by X-ray crystallography. These results show that the orientation of the 7-
membered 1,3,2-dioxaphosphepane ring is conserved in all but one of the nine ligands
coordinated to Mo(0) centers. The ability of these ligands to exhibit different conformations
could affect the chirality transfer in catalysis to prochiral substrates. This suggests that better
chirality transfer could potentially be seen in ligands that have less conformational flexibility,
like bidentate bridging ligands. Also, the spontaneous cis/trans isomerization of 2a to 2b was
observed. An equilibrium ratio of 4:1 (1b:1a) was observed when HgCl was added to solution
2
containing 1a.
A Rh(I) complex of L2 was evaluated as a catalyst for the HF of styrene. This ligand showed
improved activity and regioselectivity over solutions that contained no ligand under all reaction
conditions tested. At 45 °C, these complexes showed an iso-selectivity of nearly 90%; however,
the lower temperature resulted in a diminished catalytic activity. The enantioselectivity of the
reaction increased as the temperature was lowered, but never rose above a 7% ee of the R
enantiomer. Backbones that lead to less conformational variability may lead to better chirality
transfer and therefore higher enantioselectivities.
Complexes with TADDOL-derived P-donor ligands coordinated to (CO) W(0) centers have
5
3
1
1
13
1
1
been prepared and have been characterized by P{ H}, C{ H}, and H NMR spectroscopies and
1
X-ray crystallography. The magnitudes of the | J | coupling constants in these complexes are
WP
useful in determining the relative donor abilities of the P-donor ligands and demonstrate that
L1 is a better donor than L2.
This study is the first to date that probes the coordination of TADDOL-derived phosphite
ligands to octahedral metal centers. Octahedral geometries are often observed in transition
metal catalyzed reactions. Due to this, it would be of continued interest to study bidentate
TADDOL-derived phosphite ligands coordinated to similar metal centers.

ACCEPTED MANUSCRIPT
Experimental
Materials and Methods. Tetrahydrofuran (THF) was initially dried over MgSO for at
4
2
least twelve hours, then distilled from CaH and finally distilled from Na/benzophenone. It was
stored over molecular sieves (3Å; 8-12 mesh) and used within a few hours. Toluene was dried
by distillation from Na and stored over molecular sieves (3Å; 8-12 mesh). Dichloromethane
(
DCM) was dried by distillation from CaH and stored over molecular sieves (3Å; 8-12 mesh).
2
Triethylamine was initially dried over KOH for a minimum of twelve hours, distilled from
Na/benzophenone, and stored over molecular sieves (3Å; 8-12 mesh). Other solvents were
reagent grade and were degassed using high-purity (99.998%) nitrogen before use. Literature
procedures were used to prepare cis-Mo(CO) (nbd) (nbd = norbornadiene) [26], W(CO) (ACN)
4
5
[
2
27] (ACN = acetonitrile), Rh(CO) (acac) (acac = acetylacenoate) [28], and L1 [6].
Characterization. NMR spectra were recorded on Bruker DRX-400, Avance-500, and
Avance-700 MHz spectrometers. Solutions of the complexes in deuterated solvents were
prepared under a stream of N gas, and all NMR experiments were performed at room
2
3
1
1
temperature. The P{ H} NMR spectra were referenced to external 85% H
3
PO
4
in a coaxial tube
1
3
1
1
that also contained CDCl , and the C{ H} and H NMR spectra were referenced to internal
3
1
13
1
1
4
SiMe (TMS). Some assignments were based on 2D NMR spectra ( H – C HSQC, H – H COSY).
Elemental analyses (C and H) were performed by Atlantic Microlabs, Inc.
C H O POCH (L2). A solution of 0.66 g (1.16 mmol) of L1 in 25.0 mL of dry THF was
3
1
28
4
3
added dropwise to a stirred solution of 0.05 mL (1.16 mmol) methanol and 0.17 mL (1.16 mmol)
of dry triethylamine in 25.0 mL of dry THF. After addition was completed, the dropping funnel
was washed with 10.0 mL of dry THF, and the reaction mixture was then stirred for two hours
at room temperature under a constant stream of N (g). The solution was then cannula
2
transferred to a dry 200 mL fritted funnel containing a mixture of Celite and basic alumina and
2
filtered via positive N pressure into a 100 mL Schlenk flask to remove the triethylammonium
chloride precipitate byproduct and any hydrolysis byproducts. The residue in the filter was next
washed with two 10 mL portions of dry THF. Removal of the solvent from the filtrate through
rotary evaporation and vacuum drying yielded 0.574 g (87.8%) of spectroscopically pure L2 as a
3
1
1
1
colorless solid. P{ H} NMR (chloroform-d): δ 133.78 (s). H NMR (chloroform-d): δ 7.55-7.51
3
(
m, 4H, Ar-CH), 7.46-7.45 (m, 2H, Ar-CH), 7.36-7.14 (m, 14H, Ar-CH), 5.07 (bd, 1H, | J | = 8 Hz,
HH
3
2
3
TADDOL-CH), 5.02 (bd, 1H, | JHH| =8 Hz, TADDOL-CH), 3.48 (d, 1.5H, | JHP| = 10 Hz, POCH ), 3.47
2
(
d, 1.5H, | J | = 10 Hz, POCH ), 0.91 (s, 3H, CCH ), 0.42 (s, 3H, CCH ).
HP 3 3 3
cis-Mo(CO) (C H O PCl) (1a). A solution of 0.40 g (0.75 mmol) of L1 and 0.10 g (0.37
4
31 28
4
2
mmol) cis-Mo(CO) (nbd) in 25.0 mL dry THF was stirred at room temperature under a nitrogen
4
atmosphere for 2 hours. Then, the THF was removed by rotary evaporation to yield a brown
solid. The solid product was triturated with 15.0 mL methanol and dried in vacuo overnight to
yield crude 1a as an off-white powder. Recrystallization from DCM/methanol yielded 0.22 g
(
46.6%) of analytically pure 1a in the form of colorless crystals. Anal. Calc for
3
1
1
C H O P MoCl ·0.3 CH Cl : C, 61.57; H, 4.40. Found: C, 61.52; H, 4.65. P{ H} NMR
6
6
56 12
2
2
2
2

ACCEPTED MANUSCRIPT
1
3
(
chloroform-d): δ 143.08 (s) . H NMR (chloroform-d): δ 7.58 (d,| J |= 8 Hz, 2H, ArCH), 7.56
HH
3
3
(
d| J |= 8 Hz, 2H, ArCH), 7.38 (d| J |= 8 Hz, 2H, ArCH), 7.34 (bs, 2H, ArCH), 7.28-7.09 (m,
HH HH
3
3
1
2H, ArCH), 5.94 (d,| J |= 8 Hz, 1H, TADDOL-CH), 4.97 (d,| J |= 8 Hz, 1H, TADDOL-CH), 1.29
HH HH
1
3
1
(
s, 3H, CH ), 0.22 (s, 3H, CH ). C{ H} NMR (chloroform-d): δ 211.77 (m, trans-CO), 205.90 (t,
3 3
2
|
J |= 15 Hz, cis-CO), 144.79 (bs, TADDOL C ), 144.37 (s, ArC ), 139.89 (bs, TADDOL C ), 139.40
CP q q q
(
s, ArC ), 129.18 (bs, Ar-CH), 129.03 (s, Ar-CH), 128.17 (s, Ar-CH), 127.89 (s, Ar-CH), 127.85 (s,
q
Ar-CH), 127.81 (s, Ar-CH), 127.79 (s, Ar-CH), 127.77 (s, Ar-CH), 127.52 (s, Ar-CH), 127.44 (s, Ar-
CH), 127.28 (s, Ar-CH), 127.04 (s, Ar-CH), 112.82 (s, C(CH ) ), 81.84 (s, TADDOL-CH), 79.19 (s,
3
2
TADDOL-CH), 27.64 (s, CH ), 25.23 (s, CH ).
3
3
cis-Mo(CO) (C H O POCH ) (2a). Using the procedure for 1a, 0.57 g (1.10 mmol) of L2
4
31 28
4
3 2
and 0.16 g (0.55 mmol) of Mo(CO)
4
(nbd) yielded 0.23 g (32.4%) of analytically pure 2a. Calcd for
3
1
1
C H O P Mo·0.5 CH Cl : C, 63.28; H, 4.86. Found: C, 63.09; H, 5.09. P{ H} NMR (chloroform-
6
8
62 14
2
2
2
3
3
3
d): δ 159.54 (s). δ 7.52 (d, | JHH|= 7 Hz, 2H, ArH), 7.44 (d, | JHH|= 8 Hz, 2H, ArH), 7.34 (d, | JHH|=
Hz, 2H, ArH), 7.29 (bs, 2H, ArH), 7.20-7.11 (m, 10H, ArH), 7.08-7.05 (m, 3H, ArH), 5.83 (dd,
7
3
4
3
4
| JHH|= 9 Hz, | JPH|= 2 Hz, 1H, TADDOL-CH), 4.73 (dd, | JHH|= 9 Hz, | JPH|= 2 Hz, 1H, TADDOL-
1
3
1
CH), 1.94-1.93 (m, 3H, POCH ), 1.31 (s, 3H, CCH ), 0.11 (s, 3H, CCH ). C{ H} NMR (chloroform-
3
3
3
2
d): δ 212.81 (m, trans-CO), 208.02 (t, | JCP|= 14 Hz, cis-CO), 146.13 (s, ArC
q
), 146.00 (bs,
TADDOL C ), 142.23 (s, ArC ), 140.90 (bs, TADDOL C ), 129.63 (s, Ar-CH), 128.76 (s, Ar-CH),
q
q
q
1
1
8
27.87 (s, Ar-CH), 127.52 (s, Ar-CH), 127.47 (s, Ar-CH), 127.44 (s, Ar-CH), 127.39 (s, Ar-CH),
27.39 (s, Ar-CH), 127.31 (s, Ar-CH), 127.18 (s, Ar-CH), 127.15 (s, Ar-CH), 111.83 (s, C(CH ) ),
3
2
2.06 (s, TADDOL-CH), 78.54 (s, TADDOL-CH), 52.09 (bs, POCH ) 27.91 (s, CH ), 25.24 (s, CH ).
3
3
3
trans-Mo(CO) (C H O PCl) (1b). A few crystals of HgCl were added to a stirred
4
31 28
4
2
2
3
1
1
solution of 0.07 g (0.13 mmol) of 1a in 20 mL of THF. The reaction was followed by P{ H} NMR
spectroscopy and, when an equilibrium between 1a and 1b had been established after 5.25
hours, the solution was filtered through silica gel. The THF was removed by from the filtrate by
rotary evaporation to yield crude 1b as an off-white powder. Recrystallization from
DCM/methanol yielded 0.021 g (31.05 %) of spectroscopically pure 1b as colorless crystals.
3
1
1
1
3
P{ H} NMR (chloroform-d): δ 149.20 (s) . H NMR (chloroform-d): δ 7.64 (d, | J |= 7 Hz, 2H,
HH
3
3
ArH), 7.58 (d, | JHH|= 7 Hz, 2H, ArH), 7.38 (d, | JHH|= 7 Hz, 2H, ArH), 7.31-7.28 (m, 7H, ArH),
3
4
7
.26-7.24 (m, 5H, ArH), 7.20-7.19 (m, 2H, ArH), 5.87 (dd, | J |= 8 Hz, | J |= 2 Hz, 1H, TADDOL-
HH PH
3
4
3 3
CH), 4.94 (dd, | JHH|= 8 Hz, | JPH|= 2 Hz, 1H, TADDOL-CH), 1.21 (s, 3H, CCH ), 0.22 (s, 3H, CCH ).
1
3
1
2
C{ H} NMR (chloroform-d): δ 205.76 (t, | J |= 13 Hz), cis-CO), 144.64 (m, TADDOL C ), 144.29
PC
q
(
s, ArC
q
), 140.22 (m, TADDOL C
q
), 139.74 (s, ArC
q
), 128.81 (s, Ar-CH), 128.23 (s, Ar-CH), 127.94 (t,
4
|
1
2
JCP|= 5 Hz, Ar-CH), 127.77 (s, Ar-CH), 127.73 (s, Ar-CH), 127.45 (s, Ar-CH), 127.24 (s, Ar-CH),
27.13 (s, Ar-CH), 112.95 (s, C(CH
3 2
) ), 81.69 (s, 1H, TADDOL-CH), 79.09 (s, 1H, TADDOL-CH),
7.56 (s, CH ), 25.41 (s, CH ).
3
3
4 28 4 3 2
trans-Mo(CO) (C31H O POCH ) (2b). Using the procedure for 1b, 0.05 g (0.10 mmol) of
3
1
1
2
a yielded 0.04 g (81.00%) of spectroscopically pure 2b. P{ H} NMR (chloroform-d): δ 168.18
1
3
3
(
s) . H NMR (chloroform-d): δ 7.79 (d, | JHH|= 8 Hz, 2H, ArH), 7.65 (d, | JHH|= 8 Hz, 2H, ArH),

ACCEPTED MANUSCRIPT
3
4
7
.45-7.43 (m, 4H, ArH), 7.35-7.17 (m, 12H, ArH), 5.87 (dd, | J |= 9 Hz, | J |= 2 Hz, 1H,
HH
PH
3
4
TADDOL-CH), 4.83 (dd, | J |= 9 Hz, | J |= 2 Hz, 1H, TADDOL-CH), 2.54-2.53 (m, 3H, OCH ),
HH
PH
3
1
3
1
2
1
.45 (s, 3H, CCH ), 0.18 (s, 3H, CCH ). C{ H} NMR (chloroform-d): δ 208.06 (t, | J |= 13 Hz),
3 3 PC
cis-CO), 146.99 (s, TADDOL C ), 145.87 (s, ArC ), 142.48 (s, TADDOL C ), 141.11 (s, ArC ), 129.37
q
q
q
q
(bs, Ar-CH), 128.27 (s, Ar-CH), 128.05 (s, Ar-CH), 127.51 (s, Ar-CH), 127.37 (s, Ar-CH), 127.32 (s,
Ar-CH), 127.29 (s, Ar-CH), 127.22 (s, Ar-CH), 127.20 (s, Ar-CH), 127.13 (s, Ar-CH), 126.87 (s, Ar-
CH), 111.63 (s, C(CH ) ), 82.69 (s, TADDOL-CH), 79.88 (s, TADDOL-CH), 52.52 (s, OCH ), 27.89 (s,
3
2
3
CCH ), 24.89 (s, CCH ).
3
3
5 28
W(CO) (C31H O
4
PCl) (1c). Solid W(CO)
5
(ACN) (0.16 g, 0.420 mmol)) was added to a
stirred solution of 0.22 g (0.420 mmol) of L1 in 50.0 mL of dry THF. After 48 hours, the solution
was decanted and filtered through a 2 cm pad of neutral alumina. THF was removed from the
filtrate by rotary evaporation to yield crude 1c as a yellow powder. Recrystallization from
DCM/hexanes yielded 0.36 g (98.4%) of analytically pure 1c as a yellow powder. Anal. Calcd for
3
1
1
(
C H ClO PW + 1.1 DCM): C, 47.72; H, 3.22. Found: C, 47.71; H, 3.59. P{ H} NMR (chloroform-
36 28 9
1
1
2
d): δ 110.89 (s), 110.89 (d, | JWP|= 433 Hz) . H NMR (chloroform-d): δ 7.66 (d, | JHH|= 8, 2H,
2
2
ArH), 7.62 (d, | J |= 8, 2H, ArH), 7.44 (d, | J |= 8, 2H, ArH), 7.38-7.28 (m, 14H, ArH), 5.91 (d,
HH
HH
2
2
3
| JPH|= 8, 1H, TADDOL CH), 5.08 (d, | JPH|= 8, 1H, TADDOL CH), 1.24 (s, 3H, CH ), 0.32 (s, 3H,
1
3
1
2
2
CH ) . C{ H} NMR (chloroform-d): δ 198.44 (d, | J |= 54 Hz, trans-CO), 198.44 (dd, | J |= 54
3
PC
PC
1
2
2
Hz, | J |= 142 Hz trans-CO), 195.09 (d, | J |= 11 Hz, cis-CO), 195.09 (dd, | J |= 11 Hz,
WC
PC
PC
1
2
2
|
J |= 127 Hz cis-CO), 144.01 (d, | J |= 7 Hz, TADDOL-C ), 143.68 (s, ArC ), 139.66 (d, | J |=
WC PC q q PC
7
Hz, TADDOL-C ), 139.20 (s, Ar-C ), 128.80 (s, Ar-CH), 128.42 (s, Ar-CH), 128.16 (s, Ar-CH),
q q
1
27.87 (s, Ar-CH), 127.61 (s, Ar-CH), 127.18 (s, Ar-CH), 127.10 (s, Ar-CH), 113.51 (s, C(CH ) ),
3 2
2
2
81.47 (d, TADDOL-CH, | J |= 4 Hz), 79.00 (d, TADDOL-CH, | J |= 6 Hz), 30.38 (s, CH ), 25.50 (s,
PC PC 3
CH3).
5 28
W(CO) (C31H O
4 3
POCH ) (2c). Using the procedure for 1c, 0.22 g (0.430 mmol) of L2 and
0
.10 g (0.430 mmol) of W(CO) (ACN) yielded 0.17 g (93.3 %) of analytically pure 2c. Anal. Calc
5
3
1
1
for (C37
H
31
O
10PW): C, 52.25; H, 3.67. Found: C, 52.28; H, 3.61. P{ H} NMR (chloroform-d): δ
1
1
3
1
7
4
0
32.91 (d, | J |=403 Hz), 132.90 (s) . H NMR (chloroform-d): δ 7.68 (d, | J |=8 Hz, 2H, ArH),
WP
HH
3
3
.59 (d, | JHH|=8 Hz, 2H, ArH), 7.43-7.20 (m, 16H, ArH), 5.80 (d, | JHH| =8 Hz, 1H, TADDOL-CH),
3
3
.88 (d, | J | =8 Hz, 1H, TADDOL-CH), 2.53 (d, | J | = 13 HZ, 3H, POCH ), 1.35 (s, 3H, CCH ),
HH
PH
3
3
1
3
1
2
.22 (s, 3H, CCH
3
). C{ H} NMR (chloroform-d): δ 198.30 (d, | JPC|= 41 Hz, trans-CO), 198.30
2
1
2
(
dd, | J |= 41 Hz, | J |= 140 Hz trans-CO), 195.55 (d, | J |= 11 Hz, cis-CO), 195.55 (dd,
PC
WC
PC
2
1
2
|
J
PC|= 11 Hz, | JWC|= 126 Hz cis-CO), 146.08 (s, Ar-C
q q
), 145.01 (d, | JPC|= 8 Hz, TADDOL-C ),
2
142.62 (s, Ar-C ), 142.07 (s, Ar-C ), 141.53 (s, ArC ), 140.31 (d, | J |= 7 Hz, TADDOL-C ), 128.36
q
q
q
PC
q
(s, Ar-CH), 128.27 (s, Ar-CH), 127.86 (s, Ar-CH), 127.77 (s, Ar-CH), 127.69 (s, Ar-CH), 127.65 (s,
Ar-CH), 127.59 (s, Ar-CH), 127.45 (s, Ar-CH), 127.37 (s, Ar-CH), 127.19 (s, Ar-CH), 127.17 (s, Ar-
CH), 127.15 (s, Ar-CH), 127.02 (s, Ar-CH), 126.90 (s, Ar-CH), 126.75 (s, Ar-CH), 112.39 (s,
3
3
C(CH ) ), 82.15 (d, | J |= 4 Hz, TADDOL-CH), 79.33 (d, | J |= 4 Hz, TADDOL-CH), 53.44 (d,
3
2
PC
PC
3
|
J |= 4 Hz, OCH ), 27.72 (s, CCH ), 25.11 (s, CCH ).
PC 3 3 3

ACCEPTED MANUSCRIPT
Hydroformylation of Styrene. The hydroformylation reactions were carried out using a
Parr Series 4560 minireactor connected to a high-pressure gas burette that introduced gas to
the reactor at a constant pressure. The digitized reactor temperature, burette temperature,
and burette pressure were monitored using Agilent Benchlink Data Logger software on a PC
connected to an Agilent data acquisition switch unit. In a typical run, 9.0 mg (0.035 mmol) of
Rh(CO) (acac) and the appropriate amount of alkali metal salt, if used, were weighed and added
2
to a 50 mL Schlenk round bottom flask which was then sealed, evacuated, and filled with N . To
2
this flask was added the appropriate amounts of dry DCM and a stock solution containing a
known concentration of the appropriate ligand dissolved in dry DCM so that the mole ratio of
ligand:rhodium was 2.4:1 and the total volume was 22 mL. This solution was then added to the
reactor via cannula transfer under positive N pressure through the substrate inlet valve. The
2
reactor was then purged three times with a 1:1 H :CO (syngas) mixture, and then pressurized to
2
2
0 atm with syngas and heated to 80°C with mechanical stirring. The reactor was maintained
under these conditions for 45 min to allow for pre-catalyst equilibration and was then cooled to
38°C before pressure was slowly vented. Approximately 4.0 mL (35 mmol) of styrene was then
~
injected into the reactor through the substrate inlet valve, after which the reactor was again
pressurized to 20 atm with syngas and re-heated to 80°C with mechanical stirring.
The progress of the reaction was monitored using the Agilent software. The activity of
the catalyst was expressed in terms of a pseudo-first order rate constant (k). The pressure drop
-
kt
versus time data was fit to the natural exponential equation P = (P )e + P , where P is the
d
f
d
-1
pressure drop (P – P ), P is the final pressure, and k (s ) is the pseudo-first order rate constant,
f
i
f
using Graphical Analysis version 3.4 [29]. The regioselectivities (% iso) were determined from
1
integrations of the H NMR spectra of the reaction mixtures at the ends of the reactions.
Enantioselectivities were measured using a chiral Supelco β-DEX 225 column and a Shimadzu
GC/MS-QP5000 Spectrometer following the method developed by Whiteker and Klosin [30].
X-ray Data Collection and Solution
A suitable single crystal was mounted on a MicroLoop (MiTeGen, Inc.) after coating in
Paratone-N oil (Hampton Research Corp.). Data were collected at the specified temperature
with a Bruker CCD diffractometer (SMART APEX2) fitted with a low temperature device (Oxford
Cryostream). The diffractometer used graphite monochromated Cu Kα (λ = 1.54178 Å)
radiation with a detector distance of 5 cm. The program SAINT was used to collect and reduce
the data [31]. Unit cell constants are based upon the refinement of the XYZ-centroids found
using a standard indexing routine (APEX2) [32]. All data were corrected for Lorentz and
polarization effects, and were scaled using the numerical method SADABS [33]. The structure
was solved and refined using the Bruker SHELXTL Software Package [34]. Heavy atoms were
found using either Direct Methods or Pattersons, and the remainder of the non-hydrogen
2
atoms were located in difference Fourier maps. Full-matrix least-squares refinement on F was
performed on positional and anisotropic parameters for these atoms. Hydrogen atoms were
placed in calculated positions with the appropriate molecular geometry δ (C–H = 0.96 Å). The

ACCEPTED MANUSCRIPT
isotropic thermal parameter associated with each hydrogen atom was fixed equal to 1.2 times
the U of the atom to which it is bound. CCDC 1871695 (1a), 1871696 (1b), 1871697 (2a),
eq
1871698 (2b), 1877439 (1c) contains the supplementary crystallographic data for this paper.
The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/structures.
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ACCEPTED MANUSCRIPT
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Highlights
•
Synthesis of molybdenum and tungsten complexes with monodentate TADDOL-derived P-donor
ligands.
•
•
Cis-trans equilibria in Mo(CO)
4 2 2
(TADDOL-derived P-donor ligand) complexes catalyzed by HgCl .
Hydroformylation data suggests chirality transfer is poor with monodentate ligands.