Synthesis of iron P-N-P' and P-NH-P asymmetric hydrogenation catalysts

Article abstract of DOI:10.1021/om5008083

Complexes of the type mer,trans-[Fe(P-N-P)(CO)₂Br]BF₄ are known to be precatalysts for the asymmetric direct hydrogenation of ketones and imines. Employing related ligand scaffolds, we successfully generated and tested the series of three new precatalysts [Fe(PCy₂CH₂CH-NCH(R)CH₂PPh₂)(CO)₂Br]BF₄ with chirality derived from (S)-amino alcohols with phenyl, benzyl, and isopropyl substituents (R), yielding fairly active and selective systems. For the reduction of acetophenone to (S)-1-phenylethanol turnover frequencies up to 920 h^-1 and up to 74% enantiomeric excess at 50 °C and 5-25 atm of H₂ were obtained. We found, however, that placing these large groups R next to nitrogen was found to be deleterious to catalytic activity. Extending the scope of the ligand structure, we then developed a series of six P-N-P and five P-NH-P systems starting with o-diphenylphosphinobenzaldehyde and the phosphine-amines PPh₂CHR¹CHR²NH₂ (R¹ = H, Ph, CH₂Ph, iPr with R² = H or R¹ = Me, Ph with R² = Ph) as well as their corresponding [Fe(P-N-P)(NCMe)₃][BF₄]₂ and [Fe(P-NH-P)(NCMe)₃][BF₄]₂ complexes, which were not catalytically active. Finally, we made the new achiral iron complex mer,cis-Fe(PPh₂(o-C₆H₄)CHNCH₂CH₂PPh₂)(CO)Br₂, which was active for the direct hydrogenation of acetophenone, achieving turnover frequencies of 800 h^-1 at 50°C and 25 atm of H₂.

Full text of DOI:10.1021/om5008083

Article
pubs.acs.org/Organometallics
Synthesis of Iron P‑N-P′ and P‑NH-P′ Asymmetric Hydrogenation
Catalysts
Jessica F. Sonnenberg, Alan J. Lough, and Robert H. Morris*
Davenport Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada
S
* Supporting Information
ABSTRACT: Complexes of the type mer,trans-[Fe(P-N-
P′)(CO)2Br]BF4 are known to be precatalysts for the
asymmetric direct hydrogenation of ketones and imines.
Employing related ligand scaffolds, we successfully generated
and tested the series of three new precatalysts [Fe-
(PCy2CH2CHNCH(R)CH2PPh2)(CO)2Br]BF4 with chir-
ality derived from (S)-amino alcohols with phenyl, benzyl, and isopropyl substituents (R), yielding fairly active and selective
systems. For the reduction of acetophenone to (S)-1-phenylethanol turnover frequencies up to 920 h−1 and up to 74%
enantiomeric excess at 50 °C and 5−25 atm of H2 were obtained. We found, however, that placing these large groups R next to
nitrogen was found to be deleterious to catalytic activity. Extending the scope of the ligand structure, we then developed a series
of six P-N-P and five P-NH-P′ systems starting with o-diphenylphosphinobenzaldehyde and the phosphine-amines
PPh2CHR1CHR2NH2 (R1 = H, Ph, CH2Ph, iPr with R2 = H or R1 = Me, Ph with R2 = Ph) as well as their corresponding
[Fe(P-N-P′)(NCMe)3][BF4]2 and [Fe(P-NH-P′)(NCMe)3][BF4]2 complexes, which were not catalytically active. Finally, we
made the new achiral iron complex mer,cis-Fe(PPh2(o-C6H4)CHNCH2CH2PPh2)(CO)Br2, which was active for the direct
hydrogenation of acetophenone, achieving turnover frequencies of 800 h−1 at 50 °C and 25 atm of H2.
graphically characterized by Chakraborty et al. in their study
of the dehydrogenation and hydrogenation of N-heterocycles.23
Prior to the aforementioned work with the P-N-P systems,
Casey and Guan developed a Shvo-type system using iron
capable of hydrogenating aldehydes and ketones, via an outer-
sphere (bifunctional) mechanism, at modest temperatures and
pressures.24,25 This ligand scaffold was then used by Berkessel
in conjunction with a chiral phosphorus ligand26 and by Beller
in conjunction with a chiral phosphonic acid27 to yield alcohols
and amines in modest to high enantiomeric excess (ee),
respectively. Our group has also developed a series of iron-(P-
N-N-P) systems, also shown in Figure 1, capable of
hydrogenating ketones with TOFs up to 1000 h−1 and ee
values up to 76% at 50 °C and 25 atm of H2.11 The most
efficient direct hydrogenation catalyst known to date was
developed by Noyori et al. and is a ruthenium-based catalyst
containing a chiral, bidentate phosphorus ligand (BINAP) and
a chiral diamine ligand.28,29 The catalyst, upon activation with
base to generate a reactive hydride complex, is capable of
achieving a total turnover number (TON) of up to 100,000 and
an ee of 99% at ambient temperature and 8 atm of H2. The
catalyst operates via a bifunctional, outer-sphere mechanism
that takes advantage of the “N-H effect”, whereby the Ru-
hydride and ligand N-H add directly to the substrate polar
double bond, resulting in a metal amido intermediate that then
heterolytically splits H2.30−33 Under basic conditions using
KOtBu an alternative pathway may involve an anionic
INTRODUCTION
■
The synthesis of enantiopure alcohols and amines is of
significant importance to the pharmaceutical, fragrance, and
fine chemical industries and is typically achieved via the
hydrogenation of ketones and imines, respectively, using
precious metal catalysts.1,2 There has been tremendous interest
recently in developing greener catalysts based on period 4
transition metals to replace iridium, ruthenium, and rhodium
catalysts, as they are much cheaper, more earth abundant, and
less toxic.3−5 Our group has been primarily focused on the
development and mechanistic investigation of iron carbonyl P-
N-N-P catalysts for asymmetric transfer hydrogenation
(ATH);6−17 however, we often encountered problems with
product racemization due to equilibration. We therefore sought
to develop asymmetric direct hydrogenation systems that could
use hydrogen gas to prevent reversibility.
Recently, Milstein et al. reported iron systems with tridentate
P-N-P ligands capable of directly hydrogenating polar double
bonds using H2(g).18,19 These complexes, shown in Figure 1,
achieved turnover frequencies (TOF) up to 430 h−1 at 40 °C
and 4.1 atm of H2. Beller and co-workers also used a similar
ligand system on iron for the release of H2 gas from methanol
and water with TOFs up to 720 h−1.20 He also recently detailed
the use of the same system for the hydrogenation of esters,21 as
did Chakraborty et al., who characterized a reactive dihydride
intermediate.22 In their hydrogen evolution paper, Beller and
co-workers hypothesized that the system goes through reactive
amide-hydride species, which can be generated from a Fe(P-
NH-P)(CO)(H)(OR) complex using base. This type of Fe(P-
N-P)H(CO) amide structure has been recently crystallo-
Received: August 6, 2014
© XXXX American Chemical Society
A
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Figure 1. Catalysts used for the direct hydrogenation of polar double bonds.
Scheme 1. Synthesis of [Fe(P-N-P′)(CO)2Br]BF4 Precatalysts 1a−f
hydridoamido complex stabilized by potassium that transfers
the hydride without participation of an NH group.34 We were
interested in developing a new series of direct hydrogenation
catalysts based on iron that would be chiral, would be able to
potentially take advantage of the N−H effect, and would
employ pincer ligands.35
Combining these key structural features, we developed a P-
N-P′ ligand scaffold that incorporated chiral centers, yielding
highly active and enantioselective direct hydrogenation catalysts
based on iron that could operate under mild conditions.36 The
precatalysts could be generated using a template method
employing air-stable phosphonium dimers,10 chiral PN ligands,
and FeBr2 under a CO(g) atmosphere, followed by silver-
assisted ligand exchange37 to cleanly generate mer,trans-
[Fe(Br)(CO)2(P-CHN-P′)][BF4] (where P-CHN-P′ =
R2PCH2CHNCH2CH2PPh2 and R = iPr (1a), Cy (1b) or P-
CHN-P′ = (S,S)-Cy2PCH2CHNCH(Me)CH(Ph)PPh2
(1c)). For the direct hydrogenation of acetophenone at 50
°C and 5 atm of H2, achiral catalysts 1a,b achieved turnover
frequencies (TOF) of 1980 h−1, and the chiral catalyst (S,S)-1c
achieved a TOF of 1980 h−1 with an ee value of 80% (S). The
precatalysts must be activated prior to use in catalysis;
precatalysts are first treated with LiAlH4 in THF under an
inert atmosphere followed by addition of alcohol, typically tert-
amyl alcohol (tAmOH), to generate Fe(P-NH-P′)(H)(OR)-
(CO).36 These species are further treated with base and
hydrogen in a Parr reactor to generate the catalytically active
Fe(P-NH-P′)(H)2(CO) species currently under investigation
in our group.
Keeping this activation process in mind, we were interested
in developing a new series of catalysts that employed a cheaper
and more variable chiral center(s). It was previously established
that when both P and P′ are PPh2 groups there is no activity.
Therefore, ligands with a PCy2 substituent were targeted in the
current work. We explored the effect on direct hydrogenation
activity and selectivity of changing the ligand sterics and
chirality (number and type of chiral centers) using alternative
PN ligands, the effect of changing the ligand structure and
B
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Scheme 2. Synthetic Pathway for the Formation of Chiral PN Complexes 2d−f
flexibility using o-phenylene linkers on the achiral side of the
ligand, and the effect of incorporating an N-H functionality into
the ligand backbone.
RESULTS AND DISCUSSION
■
Modifying the Catalyst Chirality. As outlined in Scheme
1, the precatalysts are formed using an iron-templated Schiff
base condensation reaction of a phosphonium dimer10,38 and a
chiral PN ligand under a CO(g) headspace,13 followed by
halide abstraction and carbonyl ligand substitution using AgBF4
also under CO(g)37 to yield the trans-[Fe(P-N-P′)(CO)2Br]-
[BF4] catalysts. Unlike the Milstein system discussed previously
(Figure 1),18 where a trans-Fe(P-N-P)(CO)Br2 complex could
be isolated and used to form the reactive iron hydride species, a
mixture of cis- and trans-bromide species were isolated using
our P-N-P′ template approach. To avoid the two-isomer
problem, we applied the approach developed by Kirchner and
co-workers.37 His group also isolated a mixture of isomers using
his P-N-P ligands on iron39,40 but found that the use of AgBF4
allowed for the clean formation of a trans-CO dicarbonyl
complex as the sole isomer. This selectivity was shown to arise
from the addition of CO to the coordinatively unsaturated
[Fe(P-N-P)(CO)Br]+ complex (formed from the loss of one
Br− to Ag+) to selectively form the dicarbonyl complex trans-
[Fe(P-N-P)(CO)2Br]+.
The chirality in the previously developed complex 1c was
derived from (S,S)-phenylpropanolamine, or norephedrine,
which is a controlled substance and expensive. We therefore
turned our attention to amino acids as a potential source of
chirality, as they are more cost efficient. The synthesis of chiral
PN ligands from amino acids is well-known,41−46 and we chose
to study valine, phenylglycine, and phenylalanine as sources of
iPr, Ph, and CH2Ph chiral groups, respectively. The steps for
the formation of chiral PN ligands from amino acids are shown
in Scheme 2 and given in detail in the Supporting Information.
The amino acid is first reduced with LiAlH4 to yield the amino
alcohol, followed by protection of the nitrogen with a BOC
group to prevent unwanted side reactions. The alcohol is then
tosylated to allow for a facile substitution with potassium
diphenylphosphide. The last step involves the removal of the
BOC protecting group with strong acid to give the chiral PN
compound with overall yields of 20−30% from the amino
alcohol.
Figure 2. Molecular structure (thermal ellipsoids at 30% probability)
of precatalyst 1d. Hydrogen atoms of Ph and Cy groups are removed
for clarity, as is the BF4 counterion. Selected bond lengths (Å) and
angles (deg): Fe(1)−P(1), 2.245(2); Fe(1)−P(2), 2.277(2); Fe(1)−
N(1), 1.998(5); Fe(1)−Br(1), 2.4732(14); N(1)−C(2), 1.286(8);
N(1)−C(3), 1.511(7), O(1)−C(11), 1.126(11); O(2)−C(12),
1.044(8); P(2)−Fe(1)−P(1), 170.25(7); C(11)−Fe(1)−C(12),
172.5(4).
2
Table 1. Comparative 31P{1H} NMR Shifts, JPP Coupling
Constants, and IR Major v(CO) Stretches for Precatalysts
1b−f
31P{1H} NMR shift
2JPP coupling constant
IR ν(CO)
b
a
precatalyst
(ppm)
(Hz)
(cm‑1)
1b
1c
1d
1e
1f
70.8 (d), 45.7 (d)
69.2 (d), 67.8 (d)
66.8 (d), 39.4 (d)
64.2 (d), 42.6 (d)
85.0
81.0
81.6
82.1
81.6
2005
2000
2009
2004
2006
63.3 (d), 46.3 (d)
a
b
Solvent THF-d8. KBr disk.
couplings are within the range 81−85 Hz for the trans-31P
nuclei of the P-N-P′ ligand, indicative of the mer conformation
of the pincer ligand about the catalyst, as observed in the crystal
structures of 1a−c36 and 1d. Relevant bond lengths and angles
for 1d are given in Figure 2 and are quite similar to the values
obtained in previous systems. In the pincer ligand, N(1)−C(2)
and N(1)−C(3) bond lengths of 1.286(11) and 1.511(7) Å,
respectively, demonstrate that the ligand does contain an imine
group. The P−Fe−P bond angle is 170.25(7)°, and the CO−
Fe−CO bond angle is 172.5(4)°, indicative of a slightly
distorted octahedral complex.
With the three new chiral PN-ligands (S)-2d−f, we followed
the procedure outlined in Scheme 1 to generate precatalysts
(S)-1d−f. All three new complexes were fully characterized by
NMR, MS, elemental analysis, and IR and, in the case of 1d, by
single-crystal X-ray diffraction (Figure 2). The new complexes
are structurally similar to the previously reported precatalysts
1b,c, with 31P{1H} NMR shifts, 2JPP coupling constants, and IR
ν(CO) stretching frequencies, in wavenumbers, shown in Table
1. All major carbonyl IR stretching frequencies are within the
Catalytic Asymmetric Hydrogenation of Acetophe-
none. Table 2 gives the catalytic activity of these new iron(II)
2
range 2000−2010 cm−1 for the trans-CO ligands, and all JPP
C
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diphenylethylenediamine (dpen) backbone in our ATH Fe-(P-
N-N-P) catalysts,6,15,47 we were interested in developing PN
ligands bearing this type of functionality. Using commercially
available (1R,2S)-2-amino-1,2-diphenylethanol, the aminophos-
phine compound (1S,2S)-2-(diphenylphosphino)-1,2-dipheny-
lethanamine (2g) can be synthesized in an overall 37% yield by
employing the process previously developed by Guo et al.48 and
depicted in Scheme 3. To summarize, the amine is first
protected with a BOC group to prevent unwanted side
reactions with the primary amine functionality, followed by
cyclization using thionyl chloride to form a sulfamidite. This
could then be oxidized to the sulfamidate using a catalytic
amount of RuCl3·nH2O and sodium periodate. Then, using
potassium diphenylphosphide, the sulfamidate can be ring
opened in an SN2 fashion, reversing the chirality of the nearest
chiral center, to yield the BOC-protected PN ligand, which can
be readily deprotected under strongly acidic conditions.
Table 2. Catalytic Activity and Selectivity for the Asymmetric
Hydrogenation of Acetophenone to 1-Phenylethanol at 50
°C
precatalyst pressure of H2 (atm) TOF (h‑1)
ee (%)
ref
1a
5
5
1980
1980
1980
920
n/a
ref 36
1b
n/a
ref 36
(S,S)-1c
(S)-1d
(S)-1e
(S)-1f
8a
5
80 (S)
55 (S)
13 (S)
ref 36
5
this work
this work
this work
this work
5
460
a
a
25
25
250
74 (S)
800
n/a
a
H2 pressure 20 atm.
With (S,S)-2g in hand, we attempted to synthesize the
corresponding trans-[Fe(P-N-P′)(CO)2Br]+ complex using the
method detailed in Scheme 1. Unfortunately, the synthesis was
not as straightforward as was previously described, likely due to
significant steric and electronic changes when the diphenyl
backbone is used. Using a wide range of reaction solvents
(THF, MeOH, acetone), temperatures (0 °C, room temper-
ature, and 70 °C reflux), and orders of reagent addition, we
were not able to synthesize the desired complex but rather
isolated brown powders. Upon crystallization and analysis using
single-crystal X-ray diffraction, we were able to identify the
major product of our reaction attempts as cis-[Fe(PN)2(CO)-
Br][BF4] (3), as shown in Figure 3.
Interested in the potential reactivity of this complex, we
devised an alternative route to the clean and efficient synthesis
of 3, depicted in Scheme 4. Using 2 equiv of 2g with FeBr2
under a CO(g) atmosphere, followed by salt metathesis with
NaBPh4, we were able to isolate the BPh4 salt of 3 as a clean
brown powder that could be characterized by NMR, MS, IR
and, upon recrystallization, by single-crystal X-ray diffraction.
Complex 3 exhibited a much lower ν(CO) at 1944 cm−1 in
comparison to those of 1b−f at 2000−2010 cm−1 (Table 1),
indicative of a more electron rich iron(II) containing only one
π-acidic CO ligand. The 31P{1H} NMR spectrum exhibited two
doublets at 84.6 and 76.6 ppm with 2JPP = 145.8 Hz, larger than
the 81−85 Hz observed for 1a−f but still indicative of trans-
phosphorus donors as observed in the X-ray structure. The P−
Fe−P bond angle is 172.20(5)°, slightly greater than the
corresponding angles 168.38(4) and 167.40(5)° in 1b and 1a,
respectively, while the Fe−P and Fe−N bond lengths are
similar. As would be expected from the IR ν(CO) difference,
the C−O bond of the carbonyl in 3 is longer than that of 1b
and 1a: 1.17(1) Å in 3 versus 1.144(6) Å in 1a or 1.104(4) and
1.132(4) Å in 1b, indicative of more electronic back-donation
into the carbonyl antibonding orbital in the new system.
complexes for the direct hydrogenation of acetophenone to
chiral 1-phenylethanol using the previously established
activation methodology (LiAlH4, tAmOH, base). As reported
earlier, achiral complexes 1a,b with no substituents on the
ligand backbone were as active as the complex (S,S)-1c with the
methyl group next to nitrogen and the phenyl group next to
phosphorus, which provided (S)-1-phenylethanol in 80% ee.
Under the same conditions complexes 1d−f with larger
substituents next to nitrogen (phenyl, benzyl, isopropyl,
respectively) were less active. There is strong evidence that
this imine nitrogen is converted to an amine in the catalytically
active hydride complex Fe(CO)(H)2(PPh2-NH-PCy2); restrict-
ing access to this amino group by adding steric bulk nearby may
hinder the participation of the nitrogen in the bifunctional
reduction of the ketone. Complex 1f with a large isopropyl
group next to nitrogen was significantly less active, achieving a
TOF of 250 and an ee of 74% at much higher pressures of 20
atm of H2. The ee values ranging from 13 to 74% for (S)-1-
phenylethanol produced by using 1d−f with one substituent on
the carbon of the Fe−P−C−C−N ring were lower than that
using (S,S)-1c with two. This might be explained by a greater
flexibility of the five-membered ring and/or freer movement of
the PPh2 group. The preliminary calculated structure of
Fe(CO)(H)2(PPh2CHPhCHMeNHCH2CH2PCy2), which is
thought to be the active catalyst and is under active
investigation in our group, shows that the phenyl group on
the carbon next to phosphorus locks the movement of the PPh2
group, thus enhancing the enantioselectivity.
Synthesis of Fe Complexes Bearing Multiple Stereo-
genic Centers. This significant influence on both activity and
selectivity observed on going from two chiral centers to one
prompted us to investigate other possible PN ligands bearing
two chiral centers. Given our tremendous success with the
Scheme 3. Synthetic Pathway for the Formation of the Chiral PN Compound (S,S)-2g
D
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counterpart.8 It is interesting that, unlike Noyori’s system which
contained NH2 groups, iron systems appear to be negatively
affected by the presence of the NH2 group. We are currently
unsure as to why this is occurring; however, it likely has to do
with the varied electronics of the system, specifically the basicity
of the nitrogen group.
Changing the Catalyst Structure Using 6,5-(P-N-P′)
Ligands. Given that catalysis and enantioselectivity appeared
to be strongly influenced by the structure and flexibility of the
P-N-P′ pincer ligand, we chose to explore a new class of ligands
on iron with a more flexible ligand architecture. Our group has
previously developed three generations of iron-(P-N-N-P)
catalysts for use in hydrogenation.6,10,11 All catalyst ligands are
formed via the condensation of a diamine with phosphine-
aldehydes, much like the formation of the P-N-P′ ligands
previously discussed. In the first-generation TH systems, o-
phenylene linkers were utilized, making a 6,5,6-ring system
around iron, which gave the ligand the flexibility to bend up and
form ferraaziridine and ferraaziridinido species.7,16 In the
second- and third-generation P-N-N-P catalysts, much like
the P-N-P′ systems discussed here, phosphonium dimers were
used to generate smaller phosphine-aldehydes in situ, which
gave rise to 5,5,5-ring systems on iron.6,10 These 5,5,5-systems
were rigid and prevented the folding of the ligand during TH
catalysis.8,49 Another interesting feature of the ligands in the
different generations was the fact that the 6,5,6-(P-N-N-P)
ligands could be made without the presence of iron, unlike the
5,5,5-systems that required iron as a template. This made the
reduction of the imine functionalities to amines feasible with
the 6,5,6-system, allowing for the introduction of an N-H
functionality.50−52
Figure 3. Molecular structure (thermal ellipsoids at 30% probability)
of cis-[Fe(PN)2(CO)Br]BF4 (3). Hydrogen atoms of Ph groups and
the BF4 anion are removed for clarity. Selected bond lengths (Å) and
angles (deg): Fe(1)−P(1), 2.2701(9); Fe(1)−P(1a), 2.2702(9);
Fe(1)−N(1), 2.045(3); Fe(1)−N(1a), 2.045(3); Fe(1)−Br(1),
2.4514(16); Fe(1)−C(3), 1.764(12); O(1)−C(3), 1.169(12); P(1)−
Fe(1)−P(1a), 172.20(5); N(1)−Fe(1)−N(1a), 92.10(18); P(1)−
Fe(1)−N(1), 83.27(10).
Scheme 4. Synthesis of cis-[Fe(PN)2(CO)Br][BPh4] (3)
Combining these concepts, we sought to develop a new
generation of P-N-P′ ligands using larger and more flexible o-
phenylene linkers, as well as a related series of P-NH-P′ ligands,
all of which were to be tested for hydrogenation as iron
catalysts. To synthesize the 6,5-(P-N-P′) ligands, we applied a
methodology similar to that previously developed for the
synthesis of P-N-N-P ligands:11,50−53 the condensation of o-
(diphenylphosphino)benzaldehyde with PN ligands 2 in the
presence of a drying agent, as shown in Scheme 5. Upon
Still intent on generating the corresponding [Fe(P-N-
P′)(CO)2Br]+ complex with the 1,2-diphenylethylene back-
bone, we attempted to react 3 with phosphine-aldehyde and
CO(g) under varying conditions to generate the desired
complex. We were still unable, however, to generate the target
precatalyst. Given the presence of two chiral centers to provide
structural rigidity, we hypothesize that, if such a precatalyst
could be formed, it is likely that it would be quite selective for
direct hydrogenation of polar double bonds, and therefore
further attempts to synthesize this elusive complex are still
underway.
Scheme 5. Condensation Reaction of Phosphine-Aldehyde
with 2 To Generate Enantiopure P-N-P′ Ligands 4
Although 3 does not possess the initially desired structure,
we were interested in whether it could be catalytically active
under reaction conditions similar to those employed with 1a−f.
Unfortunately, under pressures of up to 25 atm of H2 and
temperatures of up to 50 °C we saw no conversion of ketones
or imines to their corresponding alcohols or amines. Given the
structural similarities of our new iron system to our [Fe(P-N-
N-P)(CO)Br]+ TH catalysts,6,10,12 we were also interested in
testing the hydrogenation of ketones or imines using isopropyl
alcohol as the proton and hydride source. Unfortunately, the
system using base and isopropyl alcohol was inactive for TH
catalysis. It is worth pointing out that, with the tetradentate
system, a variant of the catalyst was made where there were
amine linkages, [Fe(P-NH-NH-P)(CO)Br]+; however, this
system was found to be significantly less active than its diimine
workup, this preparation yielded a wide variety of chiral P-N-P′
ligands 4, in yields varying from 46 to 75%. All of the
compounds were characterized by NMR, MS, and elemental
1
analysis. In the NMR, H chemical shifts for the imine ranged
from 8.4 to 9.0 ppm, and all species showed two sharp singlets
in the 31P NMR. 4a has peaks at −13.2 and −19.5 ppm, 4c at
−8.1 and −14.5 ppm, 4d at −12.8 and −22.9 ppm, 4e at −14.1
and −23.1 ppm, 4f at −13.3 and −22.0 ppm, and 4g at −7.2
E
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Scheme 6. Reduction of P-N-P′ Ligands 4 To Form Chiral P-NH-P′ Ligands 5
Scheme 7. Synthesis of [Fe(P-N-P′)(NCMe)3][BF4]2 (6) and [Fe(P-NH-P′)(NCMe)3][BF4]2 (7) from P-N-P′ (4) and P-NH-P′
(5), Respectively
and −15.4 ppm. The achiral ligand 4a was synthesized and
characterized previously by Bluhm et al.,54 who also made a
large series of structurally similar achiral ligands containing P,
N, S, and O donor groups. All of these pincer ligands were used
in the synthesis of Cr(“Y′N′Z”)Cl3 systems, such as Cr(P-N-
P)Cl3; these complexes in turn were used for the oligomeriza-
tion and polymerization of ethylene, as well as for the selective
formation of 1-hexene. Similar achiral P-N-N ligands have also
been developed, where in place of the diphenylphosphine
moiety of the PN ligand Wehman et al. used a pyridine group,
which allowed for the synthesis of stable Pd(II) and Pd(0) P-N-
N complexes.55 Kawamura et al. reported the synthesis of a
chiral P-N-P ligand derived from valine that is similar to 4f
which contained a 3,5-di-tert-butylphenylene linker in place of
our unfunctionalized phenylene linker.56 They used this ligand
with copper in the asymmetric 1,4-addition of diethylzinc to 2-
cyclohexen-1-one; however, the ee of the resulting ketone was
only moderate and the activity was quite low.
The next stage of our investigation was the synthesis of the
corresponding series of P-NH-P′ ligands 5, as depicted in
Scheme 6. It was previously reported that the P-N-N-P ligands
could be reduced in the presence of NaBH4 to yield the
corresponding P-NH-NH-P ligands, and we therefore tested
NaBH4 first.8,50−52 This was effective for the achiral system 5a,
as was also reported by Bluhm,54 who tested the chromium
complex as discussed previously. The use of NaBH4 was also
effective for the generation of 5c, with the Me/Ph PN
backbone; however, 5d−f could not be effectively reduced.
Under similar reaction conditions and times, 4d−f was less than
half reduced to 5d−f, and prolonged exposure gradually led to
decomposition and some ligand oxidation (some phosphine
oxides were detected). To form 5d−f, LiAlH4 was used, which
allowed for the clean reduction of the imine bond in those
cases. Therefore, the imine bonds of the ligands with a single
chiral center with a large substituent next to nitrogen are more
difficult to reduce, once again supporting the observation that
these systems have significantly different behavior than the
achiral and norphedrine derivatives. The P-NH-P′ ligands were
1
fully characterized by NMR, MS, and elemental analysis. H
NMR showed the disappearance of the imine proton, and
31P{1H} spectra once again exhibited two sharp singlets for the
inequivalent phosphorus atoms. 5a has peaks at −16.1 and
−20.6 ppm, 5c at −11.2 and −16.2 ppm, 5d at −16.4 and
−23.5 ppm, 5e at −16.0 and −23.4 ppm, and 5f at −16.1 and
−22.2 ppm. With the exception of the achiral P-NH-P′ ligand
developed by Bluhm,54 this is a new and novel series of ligands.
Structurally similar P-N-N ligands bearing an N-H group have
been developed and studied extensively by Clarke et al. for the
direct and transfer hydrogenation of ketones using ruthe-
nium.57−59 They have also investigated the effect of varying the
substituents on phosphorus,60 much like our group has done
with our P-N-N-P ligands,13,14 to improve the ee of the
hydrogenation reactions. Furthermore, they explored the role
of the N-H group in catalysis by designing a series of P-NR-
NR′2 ligands61 and found these to be less active in ketone
hydrogenation than their P-NH-NH2 counterparts, indicating
the importance of the N-H group in the ligand structure.
Following the successful synthesis and characterization of a
new library of P-N-P′ and P-NH-P′ ligands, we then
investigated their coordination to iron. This was initially
probed using [Fe(H2O)6][BF4]2 in MeCN under ambient
conditions and an inert atmosphere to generate the
corresponding [Fe(P-N-P′)(NCMe)3][BF4]2 (6) and [Fe(P-
NH-P′)(NCMe)3][BF4]2 (7) complexes, as depicted in
Scheme 7. The reactions were very clean, and most were
nearly quantitative, with yields ranging from 83 to 99%. The
complexes with imine functionalities 6 were isolated as deep
red powders, and the complexes with the N−H ligand 7 were
isolated as bright pink-purple powders.
All of the new complexes were characterized using NMR,
MS, and elemental analysis techniques, and 6a,e were
characterized crystallographically as depicted in Figures 4 and
5, respectively. The 1H NMR spectra of 6 have singlets for the
imine proton in the range of 7.9−8.8 ppm, which are no longer
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doublets for the complexes with a single chiral center exhibited
a slight roofing effect (second-order patterning). The achiral
complexes, on the other hand, demonstrated extreme second-
order patterns. The crystal structures of 6a,e were quite similar
in terms of common bond lengths and angles. The imine CN
bond length for both was 1.279−1.291 Å, indicative of a C−N
double bond, in comparison to the other side of the ligand,
which had C−N bonds with lengths of 1.485−1.495 Å,
indicative of a C−N single bond.
Following the development of a new library of chiral and
achiral iron-(P-N-P′) and iron-(P-NH-P′) complexes, we tested
6 and 7 for various types of catalysis. Unfortunately, neither
series of complexes was active for the direct or transfer
hydrogenation of ketones or activated imines. Direct hydro-
genation trials were conducted at 50 °C and 25 atm of H2,
employing the previously developed LiAlH4/tAmOH/KOtBu
activation process. A simplified process employing only KOtBu
was tested as well. Transfer hydrogenation was tested in an
argon glovebox at 28 °C in iPrOH using KOtBu. Unfortunately,
the hydrogenation of ketones to alcohols and imines to amines
was not successful under any of the conditions explored. Given
the success of our previously developed [Fe(P-N-N-P)-
(NCMe)2][BF4]2 systems to dehydrogenate ammonia−bor-
ane,62 we also tested the achiral complexes 6a and 7a for the
catalytic release of H2. Unfortunately, these systems were once
again inactive in the presence of base. Although straightforward
to synthesize and handle, these systems appear to be too stable
to be catalytically active for the transformations we have
explored, and a more complete investigation into potential
applications of these systems is still required.
Figure 4. Molecular structure (thermal ellipsoids at 30% probability)
of precatalyst 6a. Hydrogen atoms of Ph groups and BF4 anion are
removed for clarity. Selected bond lengths (Å) and angles (deg):
Fe(1)−P(1), 2.2732(8); Fe(1)−P(2), 2.3044(8); Fe(1)−N(1),
1.9724(19); Fe(1)−N(2), 1.922(2); Fe(1)−N(3), 1.932(2); Fe(1)−
N(4), 1.907(2); N(1)−C(7), 1.279(3); N(1)−C(8), 1.485(3), P(2)−
Fe(1)−P(1), 173.82(3); N(1)−Fe(1)−P(1), 89.82(6); N(1)−Fe(1)−
P(2), 84.76(6).
The next phase of our investigation was to explore the newly
developed ligand scaffolds using FeBr2 and CO(g), as has been
previously discussed. Beginning with the achiral imine ligand
4a, we investigated potential routes for synthesizing Fe(P-N-
P′)(CO)Br2 complexes. Stirring 4a and 1 equiv of FeBr2 under
N2 for 45 min, followed by rapid freezing of the reaction
solution with liquid nitrogen and atmosphere evacuation, along
with subsequent introduction of CO(g) and thawing, led to the
clean formation of Fe(P-N-P′)(CO)Br2 (8a) in 85% yield as a
red-orange powder. The complex 8a could also be synthesized
using a template reaction with FeBr2, 2a, and o-
(diphenylphosphino)benzaldehyde; however, the product was
more difficult to extract and purify because unidentified side
products were also forming. The structure of 8a was confirmed
by X-ray crystallography, as shown in Figure 6, and the complex
was fully characterized using NMR, IR, MS, and elemental
1
analysis. The imine proton was seen in the H NMR spectrum
at 8.36 ppm, and this was also confirmed by the crystal
structure, which had C(2)−N(1) and C(3)−N(1) bond
lengths of 1.489(3) and 1.283(3) Å corresponding to the C−
N and CN bonds of the ligand backbone, respectively. In the
IR spectrum of 8a, the carbonyl stretching frequency was 1961
cm−1, much lower than that of 1a−f (2000−2010 cm−1),
indicating a more electron rich iron center in comparison to
that in the trans-dicarbonyl species. The inequivalent
phosphorus atoms of the ligand appear as doublets in the
31P{1H} NMR spectrum at 44.0 and 39.6 ppm with 2JPP = 216.9
Hz, indicative of trans-phosphorus donors. This implies a mer
geometry for the ligand, as observed in the crystal structure,
yielding the overall geometry of mer,cis-Fe(P-N-P′)(CO)Br2
Figure 5. Molecular structure (thermal ellipsoids at 30% probability)
of precatalyst 6e. Hydrogen atoms of Ph groups and BF4 anion are
removed for clarity. Selected bond lengths (Å) and angles (deg):
Fe(1)−P(1), 2.2867(11); Fe(1)−P(2), 2.2558(11); Fe(1)−N(1),
1.976(3); Fe(1)−N(2), 1.896(4); Fe(1)−N(3), 1.928(4); Fe(1)−
N(4), 1.925(3); N(1)−C(3), 1.291(5); N(1)−C(2), 1.495(5), P(2)−
Fe(1)−P(1), 173.44(4); N(1)−Fe(1)−P(1), 84.32(9); N(1)−Fe(1)−
P(2), 89.12(9).
present in 7. 31P{1H} NMR spectra of these species proved to
be quite useful for their characterization, as they exhibited two
doublets in the 40−70 ppm range with 2JPP values in the range
2
138−152 Hz. Complex 6 had slightly larger JPP values in the
range 149−152 Hz, versus 7, which were in the range 138−142
Hz. In the 31P{1H} NMR spectra, complexes with two chiral
centers exhibited distinctly different doublets, whereas the
(bromides cis). Also observed in the 31P{1H} NMR spectrum
2
was a second set of doublets at 64.8 and 57.8 ppm with JPP
=
184 Hz. This was identified as the trans-Br species from the
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of which were paramagnetic, as evidenced by the highly
broadened NMR spectra. Confirming the presence of para-
magnetic species, Fe(PPh2C6H4CHNCHiPrCH2PPh2)Br2 crys-
tallized out of the reaction mixture while attempting to
synthesize 8f and was characterized crystallographically, as
shown in Figure 7. The complex is trigonal bipyramidal with a
Figure 6. Molecular structure (thermal ellipsoids at 30% probability)
of precatalyst 8a. Hydrogen atoms of Ph groups are removed for
clarity. Selected bond lengths (Å) and angles (deg): Fe(1)−P(1),
2.2668(8); Fe(1)−P(2), 2.2653(8); Fe(1)−N(1), 1.987(2); Fe(1)−
Br(1), 2.4821(5); Fe(1)−Br(2), 2.4787(5); Fe(1)−C(10), 1.776(4);
N(1)−C(2), 1.489(3); N(1)−C(3), 1.283(3), O(1)−C(10),
1.097(5); P(2)−Fe(1)−P(1), 174.36(3); C(10)−Fe(1)−Br(1),
178.20(10); Br(2)−Fe(1)−Br(1), 96.518(18).
Figure 7. Molecular structure (thermal ellipsoids at 30% probability)
of Fe(P-N-P′)Br2(iPr). Hydrogen atoms of Ph groups are removed for
clarity. Selected bond lengths (Å) and angles (deg): Fe(1)−P(1),
2.620(4); Fe(1)−P(2), 2.500(3); Fe(1)−N(1), 2.249(10); Fe(1)−
Br(1), 2.453(2); Fe(1)−Br(2), 2.377(2); N(1)−C(2), 1.482(16);
N(1)−C(6), 1.298(17), P(2)−Fe(1)−P(1), 158.78(13); Br(2)−
Fe(1)−Br(1), 122.25(10); N(1)−Fe(1)−P(1), 78.1(3); N(1)−
Fe(1)−P(2), 80.8(3).
crystal structure, present in 8% on the basis of the cis Br/CO
disorder.
With 8a in hand, we tested the direct hydrogenation of
ketones using the LiAlH4/tAmOH/KOtBu process previously
developed. At 50 °C and 5 atm of H2 catalysis was slow and
irreproducible. At 50 °C and 25 atm of H2, catalysis with the
ratio 8a:KOtBu:acetophenone = 1:13:500 was 80% complete in
30 min and 98% complete in 1 h, yielding a TOF of 800 h−1.
This is lower than the those for the corresponding achiral
precatalysts 1a,b, which exhibited TOFs of 1980 h−1 under the
milder H2 pressure of 5 atm. However, 8a has diphenylphos-
phine groups on both sides of the P-N-P′ ligand, unlike 1a,b,
which have a diphenylphosphine group on one side and
required an alkyl-substituted phosphorus donor on the other
side. For the achiral 5,5-P-N-P′ iron complex, when both
phosphorus donors were diphenylphosphine groups, the
precatalyst was completely inactive,36 indicating that the
incorporation of the o-phenylene linker to generate a 6,5-(P-
N-P′) system may have positively influenced reactivity as
targeted.
much narrower P−Fe−P angle of 158.78(13)° versus the 170−
175° range seen with the previously characterized octahedral
Fe(P-N-P) complexes. The Fe−Br bonds have lengths
comparable to those of the previous complexes. However, the
Fe−N and two Fe−P bonds are much longer: Fe(1)−N(1) at
2.249(10) Å versus 1.97−2.04 Å and Fe(1)−P(1) and Fe(1)−
P(2) at 2.620(4) and 2.500(3) Å versus 2.25−2.30 Å. This
indicates a more weakly and loosely bound ligand in this case,
explaining why they decompose so readily. This is also
consistent with a paramagnetic species. The imine moiety is
maintained in the complex with C(6)−N(1) and C(2)−N(1)
bonds of 1.298(17) and 1.482(16) Å for the CN and C−N
bonds, respectively.
Although previous investigations demonstrated that the
various complexes 1d−f with one stereogenic center yielded
lower ee values than the complex with two centers, 1c, we were
interested in synthesizing and testing the complete series with
the o-phenylene linker, as was done with 8a, to determine
whether the same trends were maintained on changing the
ligand structure and flexibility. Unfortunately, we ran into
difficulties attempting to coordinate our presynthesized chiral
P-N-P′ and P-NH-P′ ligands to FeBr2. Following various
methodologies, we were unable to cleanly isolate Fe(P-N-
P′)(CO)Br2 or [Fe(P-N-P′)(CO)2Br]+ complexes bearing the
new chiral ligands developed. Using in situ 31P{1H} NMR of
reaction solutions under a CO(g) headspace, we were able to
detect a pair of doublets, indicating that a single iron species
was forming; however, upon workup, decomposition occurred.
Investigating this decomposition, we learned that the iron
species were unstable when no longer under a CO(g)
atmosphere, leading to the formation of several species, some
CONCLUSIONS
■
Following the successful development of a highly active
asymmetric direct hydrogenation catalyst based on iron, we
further expanded the range of available precatalysts by
synthesizing a series of enantiopure PN ligands derived from
amino acids. These were condensed with phosphonium dimers
and used to synthesize mer,trans-[Fe(P-N-P′)(CO)2Br][BF4]
complexes 1d−f derived from (S)-phenylglycine, (S)-phenyl-
alanine, and (S)-valine, respectively, which were shown to be
catalytically active for the direct hydrogenation of ketones
under mild conditions. The new systems were slower and less
enantioselective than the original catalyst, which contained a
PN ligand derived from (S,S)-norephedrine (1c). Under
comparable conditions the TOF values for acetophenone
hydrogenation decreased in the order 1a−c (1980 h−1) > 1d
(920 h−1) > 1e (460 h−1) > 1f (250 h−1) while the ee values of
H
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anions, as previously reported in the literature.63 These complexes are
denoted with ** following the elemental analysis results.
the (S)-1-phenylethanol produced decreased in the order 1c
(80%) > 1f (74%) > 1d (55%) > 1e (13%). Thus, it seems that
for activity a CHMe or CH2 group next to nitrogen is optimum
while for enantioselectivity a CHPh group next to PPh2 is best.
Given the subtle interplay of ligand rigidity, and the
involvement of an N−H in the ligand backbone in the reaction
mechanism, we developed a new series of P-N-P′ and P-NH-P′
ligands with an o-phenylene linker on one side of the ligand to
significantly increase ligand flexibility. This new library of
ligands was coordinated to iron to make the series of complexes
[Fe(P-N-P′)(NCMe)3][BF4]2 (6) and [Fe(P-NH-P′)-
(NCMe)3][BF4]2 (7), which were shown to be quite stable
but inactive toward hydrogenation (direct or transfer) and
ammonia−borane dehydrogenation. Finally, we coordinated
our achiral P-N-P′ ligand 4a to FeBr2 under CO(g) to generate
the new precatalyst mer,cis-Fe(P-N-P′)(CO)Br2, which was
active for the direct hydrogenation of acetophenone with a
TOF value of 800 h−1 at 50 °C and 25 atm of H2.
Unfortunately, the chiral variants of this system decomposed
on removal from a CO(g) atmosphere. Judging from the
success of the use of the complexes FeH(X)(CO)-
(PiPr2CH2CH2NHCH2CH2PiPr2) in ester and imine hydro-
genation,22,23 a future direction will be to incorporate alkyl
groups on both phosphorus donors of our more active 5,5-
systems.
Catalysis. Hydrogenation Studies. In an argon-filled glovebox, a
vial was charged with precatalyst (0.006 mmol) and 3 mL of THF. To
this solution was added 0.05 mL of LiAlH4 (1.0 M in THF), and the
solution immediately changed from pink to dark brown. After the
solution was stirred for 5 min, 2-methyl-2-butanol (0.5 mL) was added
and the solution was stirred for an additional 10 min. The solution was
transferred to a syringe equipped with a 12 in. needle. The same vial
was then charged with acetophenone (0.35 mL, 3.0 mmol) and 3 mL
of THF. The solution was taken up into the same syringe that already
contained the precatalyst solution and stoppered. In a second syringe
equipped with a 12 in. needle, a solution of base (0.08 mmol) in 3 mL
of THF was taken up and stoppered. Both syringes were removed
from the glovebox and injected into Parr reactors heated to 50 °C and
pressurized to 5 atm H2(g) against a flow of hydrogen. At set times,
small amounts of sample were removed from the reactor using a
needle and syringe under a flow of hydrogen and injected into the gas
chromatograph for analysis.
Transfer Hydrogenation Catalysis. In a vial containing precatalyst
(0.007 mmol) and KOtBu (6 mg, 0.054 mmol), isopropyl alcohol (6
mL, 78 mmol) and acetophenone (0.5 mL, 4.3 mmol) were added at
28 °C, in an argon -filled glovebox. Solutions were stirred vigorously,
and samples were taken from the mixture, quenched by exposure to
air, and analyzed by gas chromatography. All of the catalytic results
were reproduced to ensure consistency.
Ammonia−Borane Dehydrogenation Catalysis. In an argon-filled
glovebox, precatalyst (0.007 mmol) and ammonia−borane (AB; 10
mg, 0.32 mmol) were placed in a 25 mL two-neck round-bottom flask
which was sealed with a rubber septum and a 10 mL dry-addition flask
containing KOtBu (8 mg, 0.071 mmol). The sealed system was
removed from the glovebox and submerged in a 24 °C water bath
before 5 mL of THF was added to the flask and the mixture was stirred
for 10 min. A cannula needle was used to pierce the septum, and an
upturned 50 mL buret filled with water was used to measure the
evolution of gas. To start the reaction, the dry-addition flask was tilted,
and base was added to the reaction mixture, which was stirred
vigorously. Hydrogen production was measured in terms of volume
displacement of water in the buret as a measure of time. All catalytic
results were reproduced to ensure consistency (C:B:S = 1:10:45).
Synthesis. Synthesis of mer,trans-[Fe(Br)(CO)2(P-N-P′)][BF4]
Precatalysts 1d−f. General Synthesis. In a nitrogen-filled glovebox,
dicyclohexylphosphonium dimer (0.05 g, 0.078 mmol) and potassium
tert-butoxide (0.018 g, 0.16 mmol) were stirred in 8 mL of THF for 10
min to yield a cloudy white solution. To this solution were added the
PN ligand 2d−f (0.16 mmol) and FeBr2 (0.05 g, 0.23 mmol), yielding
a pale yellow solution, and the flask was transferred to a Schlenk line
and put under a CO(g) atmosphere. Immediately upon exposure the
solution turned purple. The solution was stirred under CO(g) (∼2
atm) for 5 h to yield a deep red-purple solution. The solution was
dried under reduced pressure, transferred to a nitrogen-filled glovebox,
and redissolved in 8 mL of DCM. The solution was filtered through
Celite, transferred back to the Schlenk line, and exposed to a CO(g)
atmosphere. AgBF4 (0.033 g, 17 mmol) in 2 mL of THF was injected
into the solution, and the mixture was stirred for 30 min. The solvent
was removed under reduced pressure, and the flask was transferred
back into a nitrogen-filled glovebox. The residue was redissolved in 5
mL of DCM, filtered through Celite, and concentrated to ∼1 mL
under reduced pressure. A 5 mL portion of pentane was added to
crash out the product as a deep purple powder, which was
subsequently washed with diethyl ether and dried under reduced
pressure.
EXPERIMENTAL SECTION
■
General Considerations. All procedures and manipulations were
performed under an argon or nitrogen atmosphere using standard
Schlenk line and glovebox techniques unless stated otherwise. The
reagents and amino acids were purchased from Sigma-Aldrich, and the
chiral diphenyl amino alcohol was purchased from ACE Synthesis. The
phosphonium dimer [PCy2CHOHCH2−]2Br2 and the PN compounds
2d−g were published as described elsewhere,41−46,48 and the series of
steps required for the generation of the PN ligands illustrated in
Schemes 2 and 3 are briefly summarized in the Supporting
Information. All solvents were degassed and dried using standard
procedures prior to all manipulations and reactions unless stated
otherwise. Deuterated solvents were purchased from Cambridge
Isotope Laboratories or Sigma-Aldrich, degassed, and dried over
activated molecular sieves prior to use. All other reagents were
purchased from commercial sources and utilized without further
purification. NMR spectra were recorded at ambient temperature and
pressure using a Varian Gemini 400 MHz spectrometer (400 MHz for
1H, 100 MHz for 13C, 376 MHz for 19F, and 161 MHz for 31P) or an
Agilent DD2 600 MHz spectrometer (600 MHz for 1H, 151 MHz for
13C, 564 MHz for 19F, and 243 MHz for 31P) unless stated otherwise.
1
The H and 13C NMR were measured relative to partially deuterated
solvent peaks but are reported relative to tetramethylsilane (TMS). All
31P chemical shifts were measured relative to 85% phosphoric acid as
an external reference. Gas chromatography was done on a PerkinElmer
Clarus 400 chromatograph equipped with a chiral column (CP
Chirasil-Dex CB 25 m × 2.5 mm) to determine substrate conversion
and enantiopurity. Hydrogen gas was used as the mobile phase, and
the oven temperature was set at 130 °C. Retention times for
phenylethanol are 7.58 and 8.03 min, and that for acetophenone is
4.56 min. All of the hydrogenation reactions were performed in a 50
mL stainless steel Parr hydrogenation reactor at constant temperatures
and pressures. The temperature was maintained at 50 °C using a
constant-temperature water bath and was purged of oxygen by flushing
the reactor several times with 5 atm of H2(g). The elemental analyses
were performed on a PerkinElmer 2400 CHN elemental analyzer.
Some complexes gave unsatisfactory carbon analyses but acceptable
hydrogen and nitrogen content because of a combustion problem due
to the tetrafluoroborate, hexafluorophosphate, and tetraphenylborate
1
1d: R1 = Ph, R2 = H. Yield: 110 mg, 86%. H NMR (400 MHz,
THF-d8): δ 8.15 (m, 2H, Ar-CH and P-Ar-CH), 8.01 (m, 2H, Ar-CH
and P-Ar-CH), 7.1−7.6 (m, Ar-CH and P-Ar-CH), 7.21 (NCH,
1
determined indirectly from H−1H COSY), 4.51 (t, 1H, N−CH, J =
11.6 Hz), 3.63 (CH2−PPh2, determined indirectly from 1H−1H
COSY), 3.58 (CH2-PCy2, determined indirectly from 1H−1H COSY),
1
3.39 (CH2−PCy2, determined indirectly from H−1H COSY), 3.13
(dd, 1H, CH2-PPh2, J = 5.1 and 13.1 Hz), and 0.9−2.6 (m, PCy-H)
I
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ppm. 31P{1H} NMR (161 MHz, THF-d8): δ 66.76 (d, 2JPP = 81.9 Hz),
4a: R1 = R2 = H. In a nitrogen-filled glovebox, 2a (0.6 g, 2.6 mmol)
was added to a solution of o-(diphenylphosphino)benzaldehyde (0.76
g, 2.6 mmol) and Na2SO4 (5 g, 35 mmol) in 30 mL of DCM. The
mixture was stirred for 24 h and then filtered through a frit and
concentrated to 2 mL. With rigorous stirring, 8 mL of cold ethanol was
added and the flask was sealed and stored at −30 °C for 48 h to yield a
white powder. The powder was filtered and washed with cold ethanol
and then dried under reduced pressure to yield pure P-N-P′ ligand.
Yield: 980 mg, 75%.
2
and 39.35 (d, JPP = 81.6 Hz) ppm. 13C{1H} NMR (100 MHz, THF-
d8): δ 181.6 (NCH), 128−133 (Ar-CH and P-Ar-CH), 74.1 (N-
CH), 38.5 (PCy-C), 36.1 (PCy2-CH2), 34.5 (PPh2-CH2), 25−29
(PCy-C), and 13.3 (PCy2-C) ppm. 19F{1H} NMR (356 MHz, THF-
d8): δ −153 ppm. Anal. Calcd for [FeC36H43P2NO2Br][BF4]: C, 53.6;
H, 5.40; N, 1.70. Found: C, 41.93; H, 4.98; N, 1.40.** MS (ESI, m/
z+): 720.1 [FeC36H43P2NO2Br]+. IR: v(CO) 2009.2 cm−1.
1e: R1 = CH2Ph, R2 = H. Yield: 110 mg, 84%. 1H NMR (400 MHz,
THF-d8): δ 8.13 (m, 1H, NCH), 7.74 (m, 1H, Ar-CH and P-Ar-
CH), 6.9−7.5 (m, 14H, Ar-CH and P-Ar-CH), 3.61 (N−CH,
determined indirectly from 1H−1H COSY), 3.30 (CH2−PCy2,
determined indirectly from 1H−1H COSY), 3.03 (CH2-PPh2,
determined indirectly from 1H−1H COSY), 2.86 ((CH2−PPh2,
determined indirectly from 1H−1H COSY), 1.33 (CH2-Ph, deter-
mined indirectly from 1H−1H COSY), and 0.8−2.5 (m, PCy-H) ppm.
4
1H NMR (400 MHz, CD2Cl2): δ 8.77 (d, 1H, HCN, JHH = 4.7
Hz), 7.8 (dd, 1H, Ar-CH, J = 3.9, 7.5 Hz), 7.1−7.4 (m, 22H, Ar-CH,
P-Ar-CH), 6.8 (dd, 1H, Ar-CH, J = 7.4, 4.6 Hz), 3.5 (t, 2H, N−CH2,
3
3JHH = 7.8 Hz), and 2.1 (t, 2H, P-CH2, JHH = 7.8 Hz) ppm. 31P{1H}
NMR (161 MHz, CD2Cl2): δ −13.2 (s), −19.5 (s) ppm. 13C{1H}
NMR (100 MHz, CD2Cl2): δ 159.5 (d, HCN, J = 20 Hz), 137−139
(Ar-C, P-Ar-C), 127−134 (Ar-C, P-Ar-C), 57.8 (d, N−CH2, J = 21.1
Hz), and 29.5 (d, P-CH2, J = 12.8 Hz) ppm. Anal. Calcd for
[C33H29P2N]: C, 79.0; H, 5.82; N, 2.79. Found: C, 77.83; H, 5.59; N,
2.81. MS (TOF-DART, m/z+): 502.185 [C33H30P2N]+. The complex
was made multiple times in an attempt to synthesize pure compound
(acceptable elemental analysis); however, silica grease impurities
2
31P{1H} NMR (161 MHz, THF-d8): δ 64.20 (d, JPP = 82.1 Hz), and
42.55 (d, 2JPP = 82.1 Hz) ppm. 13C{1H} NMR (100 MHz, THF-d8): δ
146.7 (NCH), 127−133 (Ar-CH and P-Ar-CH), 66.5 (N-CH), 41.1
(CH2-PPh2), 38.6 (CH2-PCy2), 26.9 (CH2-Ph), and 22−28 (PCy-C),
and 13.6 (PCy2-C) ppm. 19F{1H} NMR (356 MHz, THF-d8): δ
−153.3 ppm. Anal. Calcd for [FeC37H45P2NO2Br][BF4]: C, 54.2; H,
5.5; N, 1.7. Found: C, 47.35; H, 5.39; N, 1.83.** MS (ESI, m/z+):
734.1 [FeC37H45P2NO2Br]+and 676.1 [FeC35H45P2NBr]+ (loss of two
−CO). IR: ν(CO) 2004.4 cm−1.
1
(observed in H NMR) caused the carbon analyses to be low. The
compound could therefore not be isolated as 100% pure.
4c: R1 = Me, R2 = Ph. From 2c (0.1 g, 0.31 mmol), Yield: 120 mg,
1
4
65%. H NMR (400 MHz, CD2Cl2): δ 8.80 (d, 1H, HCN, JHH
=
1f: R1 = iPr, R2 = H. Used AgPF6 instead of AgBF4. Yield: 120 mg,
4.90 Hz), 7.6 (m, 2H, Ar-CH), 7.0−7.4 (m, 26H, Ar-CH, P-Ar-CH),
3
1
6.8 (m, 1H, Ar-CH), 3.72 (d, 1H, CH(Ph), JHH = 5.6 Hz), 3.63 (dq,
78%. H NMR (400 MHz, THF-d8): δ 8.16 (m, 1H, Ph−CH), 7.92
1H, CH(CH3), 3JHH = 5.6 and 6.1 Hz), and 0.95 (d, 3H, CH3, 3JHH
=
(m, 1H, Ph−CH), 7.05−7.68 (m, 9H, Ph−CH and NCH at 7.58−
determined indirectly for 1H−13C HSQC), 3.26 (m, 1H, N-C(iPr)H),
2.98 (m, 2H, CH2-PPh), 2.35 (m, 2H, CH2-PCy), 1.21 (iPr-CH,
determined indirectly for 1H−1H COSY), 0.75 (m, 6H, iPr-CH3), and
0.6−2.1 (m, PCy-H) ppm. 31P{1H} NMR (161 MHz, THF-d8): δ
63.28 (d, 2JPP = 81.6 Hz), 46.26 (d, 2JPP = 81.6 Hz), and −137.56 (m,
6.1 Hz) ppm. 31P{1H} NMR (161 MHz, CD2Cl2): δ −8.1 (s), −14.5
(s) ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ 157.7 (CN), 132−
134 (Ar-C, P-Ar-C), 126−130 (Ar-C, P-Ar-C), 68.6 (CH-Me), 51.3
(CH-Ph), and 19.8 (CH3) ppm. Anal. Calcd for [C40H35P2N]: C,
81.19; H, 5.96; N, 2.37. Found: C, 80.75; H, 5.10; N, 1.93. MS (TOF-
DART, m/z+): 592.232 [C40H36P2N]+.
−
PF6 ) ppm. 13C{1H} NMR (100 MHz, THF-d8): δ 163.19 (NCH),
4d: R1 = Ph, R2 = H. From 2d (0.15 g, 0.49 mmol), Yield: 150 mg,
129−135 (Ph−CH), 67.02 (N-C(iPr)H), 42.70 (CH2-PPh), 35.80
(PCy2-C), 32.52 (CH2-PCy), 20−30 (PCy2-C), 24.07 (iPr-CH), and
15.23 (iPr-CH3) ppm. 19F{1H} NMR (356 MHz, THF-d8): δ −64.13
1
4
55%. H NMR (400 MHz, CD2Cl2): δ 8.68 (d, 1H, NCH, JHH
=
4.6 Hz), 7.76 (ddd, 1H, Ar-CH, J = 1.5, 3.9, and 7.8 Hz), 7.05−7.32
−
(m, 27H, Ar-CH), 6.78 (ddd, 1H, Ar-CH, J = 1.3, 4.6, and 7.7 Hz),
(d, PF6 , J = 790 Hz) ppm. Anal. Calcd for [FeC37H45P2NO2Br][PF6]:
3
4.16 (quart., 1H, C(Ph)H, JHH = 7.8 Hz), and 2.41 (qd, 2H, CH2,
C, 47.73; H, 5.46; N, 1.69. Found: C, 40.09; H, 6.17; N, 1.80.** MS
(ESI, m/z+ ): 686.1 [FeC3 3 H4 5 P2 NO2 Br]+ and 628.2
[FeC31H45P2NBr]+ (loss of two −CO). IR: ν(CO) 2005.8 cm−1.
Synthesis of [Fe(PN)2(CO)(Br)]BPh4 (3). In a nitrogen-filled
glovebox, 2g (0.074 g, 0.19 mmol) and FeBr2 (0.028 g, 0.13 mmol)
were stirred in 4 mL of THF for 30 min and then transferred to a
Schlenk line and stirred under CO(g) (∼2 atm) for 2.5 h to yield a
deep brown solution. The solution was dried under reduced pressure
and transferred to a nitrogen-filled glovebox. The residue was
dissolved in ∼5 mL of DCM and filtered through Celite to remove
salts. The DCM solution was concentrated under reduced pressure to
∼1 mL, NaBPh4 (0.033 g, 0.096 mmol) in 5 mL of methanol was
added, and the mixture was stirred for 15 min to precipitate a pale
purple solid. The solid was collected, washed with cold methanol, and
dried under reduced pressure. Yield: 100 mg, 87%.
2JHH and JHH = 13.6 and 7.1 Hz) ppm. 31P{1H} NMR (161 MHz,
3
CD2Cl2): δ −12.8 (s), −22.9 (s) ppm. 13C{1H} NMR (100 MHz,
CD2Cl2): δ 158.8 (d, CN, J = 19.8 Hz), 126−135 (Ar-C and P-Ar-
C), 72.5 (d, CH, J = 16.4 Hz), and 53.4 (quint, CH2, J = 27.2 Hz)
ppm. Anal. Calcd for [C39H33P2N]: C, 81.1; H, 5.76; N, 2.43. Found:
C, 79.07 H 5.79; N, 2.36. MS (ESI, m/z+): 578.2 [C39H34P2N]+.
Complex was made multiple times in an attempt to synthesize pure
compound (acceptable EA) however silica grease impurities (observed
1
in H NMR) caused the carbon analyses to be low. The compound
could therefore not be isolated as 100% pure.
4e: R1 = CH2Ph, R2 = H. From 2e (0.27 g, 0.85 mmol), Yield: 230
mg, 46%. 1H NMR (400 MHz, CD2Cl2): δ 8.37 (d, 1H, NCH, 4JHH
= 4.7 Hz), 7.71 (ddd, 1H, Ar-CH, J = 1.6, 3.9, and 7.6 Hz), 7.15−7.45
(m, 25H, Ar-CH), 7.01 (dd, 2H, Ar-CH, J = 1.7 and 7.9 Hz), 6.86
(ddd, 1H, Ar-CH, J = 1.5, 4.5, and 7.6 Hz) 3.28 (m, 1H, CH) 2.99 (dd,
1H NMR (400 MHz, THF-d8): δ 6.6−8.1 (m, 40H, Ph-CH), 5.23
(m, 1H, C(Ph)H), 5.00 (m, 1H, C(Ph)H, correlates to 5.23 proton),
4.85 (m, 1H, C(Ph)H), 3.43 (m, 1H, C(Ph)H, correlates to 4.85
proton), 3.48 (broad s, 1H (should be 2H, likely solvent exchange),
NH2), and 2.66 (broad s, 2H, NH2) ppm. 31P{1H} NMR (161 MHz,
THF-d8): δ 84.62 (d, 2JPP = 145.8 Hz), and 76.58 (d, 2JPP = 145.8 Hz)
ppm. 13C{1H} NMR (100 MHz, THF-d8): δ 126−137 (Ph-C), 68.5
(C(Ph)H, correlates to 3.43 proton), 64.4 (C(Ph)H, correlates to 5.00
proton), 50.0 (C(Ph)H, correlates to 5.23 proton), 49.3 (C(Ph)H,
correlates to 4.85 proton) ppm. Anal. Calcd for [FeC53H48P2NOBr]-
[BPh4]: C, 74.23; H, 5.50; N, 2.25. Found: C, 64.66; H, 5.43; N,
2.36.** MS (ESI, m/z+): 927.2 [FeC53H48P2N2OBr]+, IR: ν(CO)
1943.6 cm−1.
3
2
1H, CH-P, JHH and JHH = 4.9 and 13.3 Hz), 2.74 (dd, 1H, CH-P,
2
3
3JHH and JHH = 8.1 and 13.3 Hz), 2.33 (dd, 1H, CH-Ph, JHH = 5.1
and 13.6 Hz), and 2.13 (dd, 1H, CH-Ph, 3JHH = 8.1 and 13.6 Hz) ppm.
31P{1H} NMR (161 MHz, CD2Cl2): δ −14.1 (s), −23.1 (s) ppm.
13C{1H} NMR (100 MHz, CD2Cl2): δ 158.1 (d, CN, J = 19.3 Hz),
125−140 (Ar-C and P-Ar-C), 70.3 (d, CH, J = 14.1 Hz) 43.5 (d, CH2-
P, J = 9.0 Hz), and 34.5 (d, CH2-Ph, J = 12.8 Hz) ppm. Anal. Calcd for
[C40H35P2N]: C, 80.2; H, 5.96; N, 2.37. Found: C, 79.29; H, 6.18; N,
2.27. MS (ESI, m/z+): 592.2 [C40H36P2N]+.
4f: R1 = iPr, R2 = H. From 2f (0.1 g, 0.37 mmol), Yield: 100 mg,
1
4
50%. H NMR (400 MHz, CD2Cl2): δ 8.65 (d, 1H, HCN, JHH
=
4.77 Hz), 7.75 (ddd, 1H, Ar-CH, J = 1.4, 3.9, and 7.7 Hz), 7.70 (dd,
1H, Ar-CH, J = 3.3 and 5.7 Hz), 7.55 (dd, 1H, Ar-CH, J = 3.3 and 5.7
Hz), 7.2−7.4 (m, 20H, P-Ar-CH), 6.85 (ddd, 1H, Ar-CH, J = 1.4, 4.6,
Synthesis of P-N-P′ Ligands 4a,c−g. *As illustrated for 4a,
complete details for each system areavailable in the Supporting
Information.
3
and 7.7 Hz), 2.88 (m, 1H, N−C−H), 2.31 (dd, 1H, CH2, JHH and
J
dx.doi.org/10.1021/om5008083 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
1
2JHH = 4.3 and 13.8 Hz), 2.15 (dd, 1H, CH2, JHH and 2JHH = 8.9 and
(observed in H NMR) caused the carbon analyses to be low. The
compound could therefore not be isolated as 100% pure.
3
13.8 Hz), 1.82 (m, 1H, iPr-CH), and 0.73 (dd, 6H, iPr-CH3, JHH
=
5e: R1 = CH2Ph, R2 = H. From 4e (0.075 g, 0.13 mmol), Yield: 66
mg, 89%. 1H NMR (400 MHz, CD2Cl2): δ 7.0−7.3 (m, 26H, Ar-CH),
6.97 (m, 2H, Ar-CH), 6.74 (m, 1H, Ar-CH), 3.80 (d, 2H, N−CH2-Ph,
3JHH = 2.0 Hz), 2.76 (m, 1H, N−CH), 2.70 (m, 2H, CH2-P), 2.03 (d,
5.0, 6.7 Hz) ppm. 31P{1H} NMR (161 MHz, CD2Cl2): δ −13.3 (s),
−22.0 (s) ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ 158.5 (d, C
N, J = 19.8 Hz), 128−140 (Ar-C and P-Ar-C), 74.3 (d, N−C, J = 13
Hz), 33.6 (d, iPr-CH, J = 8.6 Hz), 32.7 (d, CH2, J = 13 Hz), 19.3 (s,
iPr-CH3), and 17.6 (s, iPr-CH3) ppm. Anal. Calcd for [C36H35P2N]:
C, 79.5; H, 6.49; N, 2.58. Found: C, 78.6; H, 7.04; N, 2.19. MS (ESI,
m/z+): 544.23 [C36H36P2N]+.
3
2H, CH2-Ph, JHH = 6.1 Hz), and 1.20 (br s, 1H, NH) ppm. 31P{1H}
NMR (161 MHz, CD2Cl2): δ −16.0 (s), −23.4 (s) ppm. 13C{1H}
NMR (100 MHz, CD2Cl2): δ 132−134 (Ar-C and P-Ar-C), 126−129
(Ar-C and P-Ar-C), 56.2 (N-CH), 49.0 (N-CH2-Ph) 41.2 (CH2-P),
and 33.3 (CH2-Ph) ppm. Anal. Calcd for [C40H37P2N]: C, 80.92; H,
6.28; N, 2.36. Found: due to the glassy nature of compound, sample
could not be extracted for elemental analysis. MS (ESI, m/z+): 594.2
[C40H38P2N]+.
4g: R1 = R2 = Ph. From 2g (0.15 g, 0.41 mmol), Yield: 151 mg,
1
4
58%. H NMR (400 MHz, CD2Cl2): δ 8.99 (d, 1H, NCH, JHH
=
5.6 Hz), 7.68 (td, 2H, Ar-CH, J = 1.7 and 7.7 Hz), 6.85−7.45 (m, 31H,
Ar-CH), 6.81 (ddd, 1H, Ar-CH, J = 1.4, 4.8, and 7.6 Hz), 4.83 (dd,
3
1H, N-CHPh, JHH = 5.8 and 8.2 Hz), and 4.22 (dd, 1H, P−CHPh,
5f: R1 = iPr, R2 = H. From 4f (0.133 g, 0.24 mmol), Yield: 120 mg,
3JHH and JHP = 5.5 and 8.2 Hz) ppm. 31P{1H} NMR (161 MHz,
3
1
90%. H NMR (400 MHz, CD2Cl2): δ 7.21−7.45 (m, 22H, Ph-CH),
CD2Cl2): δ −7.17 (s), −15.36 (s) ppm. 13C{1H} NMR (100 MHz,
CD2Cl2): δ 158.4 (CN), 133−135 (Ar-C and P-Ar-C), 126−131
(Ar-C and P-Ar-C), 78.9 (d, N-CHPh, J = 21.0 Hz), and 52.0 (d, P-
CHPh, J = 16.1 Hz) ppm. Anal. Calcd for [C45H37P2N]: C, 82.68; H,
5.70; N, 2.14. Found: C, 82.50; H, 6.16; N, 2.14. MS (ESI, m/z+):
654.2 [C45H38P2N]+.
7.15 (td, 1H, Ph-CH, J = 1.4 and 7.5 Hz), 6.86 (ddd, 1H, Ph−CH, J =
1.3, 4.5, and 7.7 Hz), 4.28 (m, 1H, N-CH2), 4.17 (m, 1H, N-CH2),
3.88 (m, 2H, CH2-P), 2.40 (m, 1H, N-CH), 1.95 (m, 1H, iPr-CH),
3
1.62 (br-m, 1H, NH), and 0.79 (dd, 6H, iPr-CH3, JHH = 6.8 and 3.7
Hz) ppm. 31P{1H} NMR (161 MHz, CD2Cl2): δ −16.09 (s), −22.15
(s) ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ 127−134 (Ph-C),
62.07 (N-CH2), 59.80 (N-CH), 49.89 (CH2-P) 20.31 (iPr-CH), and
17.10 (iPr-CH3) ppm. Anal. Calcd for [C36H37P2N]: C, 79.24; H, 6.84;
Synthesis of P-NH-P′ Ligands 5a,c−f. The synthesis is illustrated
for 5a; complete details for each system are available in the Supporting
Information.
1
N, 2.57, Anal. Calcd for [C36H37P2N]-2H2O (observed in H NMR,
5a: R1 = R2 = H. In a nitrogen-filled glovebox, 4a (0.055 g, 0.11
mmol) and NaBH4 (0.012 g, 0.31 mmol) were dissolved in 5 mL of
ethanol, sealed, and transferred to a Schlenk line. The solution was
refluxed under argon for 24 h, and then 8 mL of distilled water was
added to neutralize the excess NaBH4. The flask was then opened to
air, and the product was extracted with 20 mL of DCM. The aqueous
phase was further extracted with DCM (2 × 15 mL), and the
combined organics were washed with saturated NH4Cl solution (3 ×
15 mL) and water (3 × 15 mL), dried with Na2SO4, and dried under
reduced pressure to yield a clean, white powder. Yield: 54 mg, 97%.
1H NMR (400 MHz, CD2Cl2): δ 7.2−7.4 (m, 22H, Ar-CH), 7.15
(td, 1H, Ar-CH, J = 1.4 and 7.4 Hz), 6.78 (ddd, 1H, Ar-CH, J = 1.4,
from aqueous workup steps): C, 74.30; H, 7.10; N, 2.40. Found: C,
74.69; H, 7.81; N, 1.58. MS (ESI, m/z+): 546.2 [C36H38P2N]+.
Synthesis of [Fe(P-N-P′)(NCMe)3][BF4]2 (6a,c−g) and [Fe(P-NH-
P′)(NCMe)3][BF4]2 (7a,c−f). The synthesis is illustrated for 6a;
complete details for each system are available in the Supporting
Information.
6a: R1 = R2 = H. In a nitrogen-filled glovebox, 4a (0.097 g, 0.19
mmol) and [Fe(H2O)6][BF4]2 (0.065 g, 0.19 mmol) were stirred in 12
mL of acetonitrile for 16 h. The solution was then concentrated to 1.5
mL and washed with pentane (2 × 6 mL). The acetonitrile layer was
then dried to yield the pure product as a deep red solid. Yield: 160 mg,
98%.
1H NMR (400 MHz, CD3CN): δ 8.75 (s, 1H, NCH), 7.45−7.93
3
4.5, and 7.7 Hz), 3.8 (d, 2H, N-CH2-Ph, JHH = 1.8 Hz), 2.51 (quart,
(m, 23H, Ph-CH), 7.40 (m, 1H, Ph-CH), 3.84 (dt, 2H, N-CH2, 3JHH
=
2H, N-CH2, 3JHH = 8.1 Hz), 1.94 (t, 2H, P-CH2, 3JHH = 8.1 Hz), 1.28
(br-s, 1H, NH) ppm. 31P{1H} NMR (161 MHz, CD2Cl2): δ −16.1 (s),
−20.6 (s) ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ 128−135 (Ar-
C and P-Ar-C), 52.0 (N-CH2-Ph), 45.8 (N-CH2-CH2), and 28.7 (P-
CH2) ppm. Anal. Calcd for [C33H31P2N]: C, 78.71; H, 6.21; N, 2.78.
Found: C, 78.82; H, 6.66; N, 2.40. MS (ESI, m/z+): 504.2
[C33H32P2N]+.
14.0 and 6.8 Hz), 3.02 (dt, 2H, CH2-PPh2, 3JHH = 6.4 and 2.9 Hz), and
1.99 (s, NC−CH3/NC-CD3) ppm. 31P{1H} NMR (161 MHz,
CD3CN): δ extreme second order doublets centered at 54.94 ppm
(apparent coupling JPP = 151.7 Hz). 13C{1H} NMR (100 MHz,
2
CD3CN): δ 176.9 (NCH), 129−137 (Ar-C and P-Ar-C), 117.3
(NCMe), 67.8 (N-CH2), 22.7 (CH2-PPh2), and 0.77 (NC-CH3) ppm.
Anal. Calcd for [FeC39H38P2N4][BF4]2: C, 54.8; H, 4.5; N, 6.6. Found:
C, 54.22; H, 4.48; N, 6.59. MS (ESI, m/z+): 278.6 [Fe C33H29P2N]+2
(loss of three MeCN).
5c: R1 = Me, R2 = Ph. From 4c (0.052 g, 0.088 mmol), Yield: 37
1
mg, 71%. H NMR (600 MHz, CD2Cl2): δ 7.57 (m, 2H, Ph−CH),
7.10−7.42 (m, 26H, Ph-CH), 6.85 (ddd, 1H, Ph-CH, J = 1.4, 4.5, and
6c: R1 = Me, R2 = Ph. From 4c (0.038 g, 0.063 mmol), Yield: 58
7.7 Hz), 3.96 (dd, 1H, N-CH2, 3JHH and 2JHH = 2.2 and 13.7 Hz), 3.87
1
mg, 97%. H NMR (400 MHz, CD3CN): δ 8.67 (s, 1H, NCH),
3
2
(dd, 1H, N-CH2, JHH and JHH = 2.4 and 13.7 Hz), 3.83 (m, 1H, P-
7.16−7.92 (m, 27H, Ar-CH and P-Ar-CH), 7.00 (d, 2H, Ar-CH and P-
Ar-CH, J = 7.45 Hz), 4.14 (1H, C(Me)H, overlapping, determined
indirectly using 1H−13C HSQC), 4.10 (1H, C(Ph)H, overlapping,
determined indirectly using 1H−13C HSQC), 1.29 (d, 3H, −CH3, 3JHH
= 4.71 Hz), 1.99 (s, 9H, CH3CN) ppm. 31P{1H} NMR (161 MHz,
CD3CN): δ 72.31 (d, 2JPP = 149.4 Hz), and 54.31 (d, 2JPP = 149.4 Hz)
ppm. 13C{1H} NMR (100 MHz, CD3CN): δ 175.5 (NCH), 127−
137 (Ar-C and P-Ar-C), 119.8 (NCMe), 73.38 (C(Me)H), 49.07
(C(Ph)H), 19.22 (−CH3), and 0.49 (NCCH3) ppm. Anal. Calcd for
[FeC46H44P2N4][BF4]2: C, 58.51; H, 4.70; N, 5.93. Found: C, 55.19;
H, 4.53; N, 4.93.** MS (DART, m/z+): 388.3 [FeC46H44P2N4]2+.
6d: R1 = Ph, R2 = H. From 4d (0.238 g, 0.41 mmol), Yield: 365 mg,
C(Ph)H), 2.77 (m, 1H, N-C(Me)H), 1.29 (br-s, 1H, NH), and 1.00
(d, 3H, CH3, JHH = 6.7 Hz) ppm. 31P{1H} NMR (161 MHz,
3
CD2Cl2): δ −11.15 (s), −16.15 (s) ppm. 13C{1H} NMR (150 MHz,
CD2Cl2): δ 126−135 (Ph−C), 53.39 (N−C(Me)H), 49.22 (N−CH2),
48.36 (P-C(Ph)H), and 17.16 (−CH3) ppm. Anal. Calcd for
[C33H31P2N]: C, 80.92; H, 6.28; N, 2.36 Found: C, 80.62; H, 6.31;
N, 2.34. MS (ESI, m/z+): 594.2 [C40H38P2N]+.
5d: R1 = Ph, R2 = H. From 4d (0.13 g, 0.23 mmol), Yield: 120 mg,
1
92%. H NMR (400 MHz, CD2Cl2): δ 7.15−7.45 (m, 28H, Ar-CH),
6.89 (m, 1H, Ar-CH), 3.71 (s, 2H, N−CH2-Ph), 3.62 (m, 1H, N-CH),
2.33 (d, 2H, CH2-PPh2, 3JHH = 7.1 Hz), and 1.29 (br s, 1H, NH) ppm.
31P{1H} NMR (161 MHz, CD2Cl2): δ −16.4 (s), −23.5 (s) ppm.
13C{1H} NMR (100 MHz, CD2Cl2): δ 132−134 (Ar-C and P-Ar-C),
127−129 (Ar-C and P-Ar-C), 60.0 (d, N-CH, J = 15.9 Hz), 50.1 (d, N-
CH2-Ph, J = 20.7 Hz), and 38.2 (d, CH2-PPh2, J = 14.3 Hz) ppm. Anal.
Calcd for [C39H35P2N]: C, 80.81; H, 6.09; N, 2.42. Found: C, 79.19;
H, 6.80; N, 2.26. MS (ESI, m/z+): 580.2 [C39H36P2N]+. The complex
was made multiple times in an attempt to synthesize pure compound
(acceptable elemental analysis); however, silica grease impurities
1
97%. H NMR (400 MHz, CD3CN): δ 7.92 (NCH, determined
1
indirectly via H−13C HSQC), 7.96 (m, 3H, Ar-CH and P-Ar-CH),
7.84 (m, 2H, Ar-CH and P-Ar-CH), 7.23−7.77 (m, 22H, Ar-CH and
P-Ar-CH), 7.16 (m, 2H, Ar-CH and P-Ar-CH), 4.72 (td, 1H, C(Ph)H,
3JHH = 3.4 and 11.5 Hz), 3.66 (ddd, 1H, CH2, JHH and JHH = 4.0,
13.0, and 14.7 Hz), 3.26 (ddd, 1H, CH2, 3JHH and 2JHH = 7.0, 12.5, and
14.6 Hz), 1.99 (s, 9H, CH3CN) ppm. 31P{1H} NMR (161 MHz,
CD3CN): δ 54.8 (d, 2JPP = 151 Hz), and 50.5 (d, 2JPP = 151 Hz) ppm
3
2
K
dx.doi.org/10.1021/om5008083 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(roofing doublets). 13C{1H} NMR (100 MHz, CD3CN): δ 176.8
(NCH), 129−137 (Ar-C and P-Ar-C), 120.8 (NCMe), 77.4 (N−
C(Ph)H), 27.4 (CH2), and 1.0 (NCCH3) ppm. Anal. Calcd for
[FeC45H42P2N4][BF4]2: C, 58.1; H, 4.6; N, 6.0. Found: C, 55.01; H,
4.26; N, 5.35.** MS (ESI, m/z+): 337 [C41H36P2N2]2+ (loss of two
MeCN), and 316.6 [C39H33P2N]2+ (loss of three MeCN).
2JPP = 138.4 Hz), and 43.31 (d, 2JPP = 138.4 Hz) ppm. 13C{1H} NMR
(125 MHz, CD3CN): δ 126−137 (Ph-C), 122.0 (NCMe), 62.50 (N-
C(Me)H), 52.78 (N-CH2), 50.50 (P-C(Ph)H), 17.11 (−CH3), and
1.31 (NC-CH3) ppm. Anal. Calcd for [FeC46H46P2N4][BF4]2 (extra
MeCN in solution, verified by NMR): C, 58.39; H, 5.00; N, 7.09.
Found: C, 48.80; H, 4.58; N, 7.85.** MS (ESI, m/z+): 656.2
[FeC40H37P2N][Li]+ (loss of three MeCN).
6e: R1 = CH2Ph, R2 = H. From 4e (0.086 g, 0.15 mmol), Yield: 136
mg, 96%. 1H NMR (400 MHz, CD3CN): δ 8.33 (d, 1H, NCH, 4JHH
= 5.4 Hz), 7.92 (t, 2H, Ph−CH, J = 8.0 Hz), 7.2−7.8 (m, 25H, Ph−
CH), 6.95 (d, 2H, Ph−CH, J = 4.8 Hz), 4.00 (m, 1H, N−CH), 3.27
(CH2-Ph, 1H, overlapping with 3.20 - determined indirectly from
1H−1H COSY), 3.20 (CH2-PPh2, 1H, overlapping with 3.27,
determined indirectly from 1H−1H COSY), 3.08 (dd, 1H, CH2-
7d: R1 = Ph, R2 = H. From 5d (0.075 g, 0.13 mmol), Yield: 114 mg,
1
99%. H NMR (600 MHz, CD3CN): δ 7.25−7.88 (m, 28H, Ph-CH),
3
6.76 (s, 1H, Ph-CH), 3.63 (t, 1H, P-CH2, JHH = 13.8 Hz), 3.46 (m,
1H, N-C(Ph)H), 3.15 (m, 1H, N-CH2), 2.94 (t, 1H, N-CH2), 2.77 (m,
1
1H, P-CH2), 2.00 (NH, determined indirectly using H−1H-COSY),
and 1.98 (s, NC-CH3/NC-CD3) ppm. 31P{1H} NMR (242 MHz,
CD3CN): δ 49.07 (d, 2JPP = 139.1 Hz), and 41.22 (d, 2JPP = 139.1 Hz)
ppm. 13C{1H} NMR (150 MHz, CD3CN): δ 126−133 (Ph-C), 120.4
(NCMe), 67.24 (N-C(Ph)H), 53.84 (N-CH2), 32.92 (P-CH2), and
0.68 (NC-CH3) ppm. Anal. Calcd for [FeC45H44P2N4][BF4]2: C,
57.98; H, 4.76; N, 6.01. Found: C, 54.66; H, 4.92; N, 6.04.** MS
(DART, m/z+): 380.2 [FeC45H44P2N4]2+.
3
2
PPh2, JHH and JHH = 7.7 and 14.0 Hz), 2.80 (m, 1H, CH2-Ph), and
2.00 (s, NC−CH3/NC-CD3) ppm. 31P{1H} NMR (161 MHz,
2
2
CD3CN): δ 54.7 (d, JPP = 151 Hz), and 51.7 (d, JPP = 151 Hz)
ppm (roofing doublets). 13C{1H} NMR (100 MHz, CD3CN): δ 176.1
(d, NCH, J = 5.4 Hz), 127−137 (Ar-C and P-Ar-C), 118.6
(NCMe), 76.1 (N-CH), 39.3 (CH2-PPh2), 27.8 (CH2-Ph), and 0.5
(NC−CH3) ppm. Anal. Calcd for [FeC46H44P2N4][BF4]2: C, 58.5; H,
4.7; N, 5.9. Found: C, 56.39; H, 5.0; N, 5.49.** MS (ESI, m/z+): 606.2
[FeC36H35P2N]Li+ (loss of three MeCN).
7e: R1 = CH2Ph, R2 = H. From 5e (0.025 g, 0.042 mmol), Yield: 38
1
mg, 95%. H NMR (600 MHz, CD3CN): δ 7.06−7.83 (m, 29H, Ph-
CH), 3.90 (m, 1H, N-CH2), 3.73 (m, 1H, P-CH2), 3.13 (m, 1H, CH2-
Ph), 3.02 (m, 1H, N-CH2), 2.71 (m, 1H, N-C(Bn)H), 2.60 (m, 1H, P-
CH2), 2.23 (m, 1H, Ph-CH2), 1.98 (s, NC-CH3/NC-CD3), 1.97 (NH,
determined indirectly using 1H−1H-COSY) ppm. 31P{1H} NMR (242
6f: R1 = iPr, R2 = H. From 4f (0.099 g, 0.18 mmol), Yield: 152 mg,
1
94%. H NMR (400 MHz, CD3CN): δ 8.58 (s, 1H, NCH), 7.96
(m, 2H, Ph−CH), 7.4−7.8 (m, 18H, Ph−CH), 7.30 (m, 4H, Ph-CH),
2
2
3.74 (dm, 1H, N-CH), 3.32 (m, 1H, CH2-PPh2), 2.84 (dd, 1H, CH2-
MHz, CD3CN): δ 48.82 (d, JPP = 139.9 Hz), and 41.38 (d, JPP
=
3
PPh2, JHH and 2JHH = 7.8 and 14.7 Hz), 1.94 (s, NC-CH3/NC-CD3),
139.9 Hz) ppm. 13C{1H} NMR (150 MHz, CD3CN): δ 126−133 (Ph-
C), 123.0 (NCMe), 63.78 (N-C(Bn)H), 52.72 (N-CH2), 37.87 (P-
CH2), 30.1 (Ph-CH2), and 1.06 (NC-CH3) ppm. Anal. Calcd for
[FeC46H46P2N4][BF4]2: C, 58.39; H, 4.90; N, 5.92. Found: C, 49.34;
H, 4.78; N, 5.56.** MS (ESI, m/z+): 656.2 [FeC40H37P2N][Li]+ (loss
of three MeCN).
1.25 (m, 1H, iPr-CH), 0.87 (d, 3H, iPr-CH3, 3JHH = 6.2 Hz), and 0.00
3
(d, 3H, iPr-CH3, JH2H = 6.5 Hz) ppm. 31P{1H} NMR (161 MHz,
2
CD3CN): δ 53.8 (d, JPP = 151.6 Hz), and 57.3 (d, JPP = 151.6 Hz)
ppm. 13C{1H} NMR (100 MHz, CD3CN): δ 177.9 (NCH), 129−
138 (Ar-C and P-Ar-C), 121.0 (NCMe), 87.5 (N-CH), 30.0 (iPr-CH),
24.4 (CH2-PPh2), 19.2 (iPr-CH3), 18.1 (iPr-CH3), and 1.2 (NC-CH3)
ppm. Anal. Calcd for [FeC42H44P2N4][BF4]2: C, 58.9; H, 4.7; N, 5.9.
Found: C, 47.08; H, 4.44; N, 4.87.** MS (ESI, m/z+): 606.2
[FeC36H35P2N]Li+ (loss of three MeCN).
7f: R1 = iPr, R2 = H. From 5f (0.063 g, 0.12 mmol), Yield: 88 mg,
1
83%. H NMR (400 MHz, CD3CN): δ 7.22−7.86 (m, 24H, Ph-CH),
4.12 (m, 1H, N-CH(iPr)), 3.66 (m, 1H, N-CH2), 3.44 (m, 1H, P-
CH2), 2.84 (m, 1H, N-CH2), 2.13 (P-CH2, determined indirectly from
13C−1H HSQC), 1.99 (s, NC-CH3/NC-CD3), 1.43 (br s, 1H, NH),
1.19 (m, 1H, iPr-CH), and 0.77 (br m, 6H, iPr-CH3) ppm. 31P{1H}
6g: R1 = R2 = Ph. From 4g (0.038 g, 0.058 mmol), Yield: 55 mg,
1
96%. H NMR (400 MHz, CD3CN): δ 8.15 (s, 1H, NCH), 6.95−
7.80 (m, 34H, Ph−CH), 5.17 (dd, 1H, N-CH(Ph), 3JHH = 13.0 and 7.3
2
NMR (161 MHz, CD3CN): δ 49.55 (d, JPP = 139.8 Hz), and 41.25
3
2
(d, JPP = 139.8 Hz) ppm. 13C{1H} NMR (100 MHz, CD3CN): δ
Hz), 4.88 (dd, 1H, CH(Ph)-PPh2, JHH = 7.7 and 13.0 Hz), and 2.00
(s, 9H, NC−CH3) ppm. 31P{1H} NMR (161 MHz, CD3CN): δ 69.79
128−135 (Ar-C and P-Ar-C), 121.90 (NCMe), 62.01 (N-CH(iPr))
51.69 (N-CH2), 23.95 (P-CH2), 20.64 (iPr-CH), 12.55 (iPr-CH3), and
0.83 (NC-CH3) ppm. Anal. Calcd for [FeC42H46P2N4][BF4]2: C,
56.16; H, 5.16; N, 6.23. Found: C, 47.42; H, 4.38; N, 6.23.** MS (ESI,
m/z+): 362.2 [FeC42H46P2N4]2+and 608.2 [FeC36H37P2N]Li+.
Synthesis of Fe(P-N-P′)(CO)Br2 (8). In a nitrogen-filled glovebox, 4a
(0.05 g, 0.1 mmol) was added to a solution of FeBr2 (0.22 g, 0.1
mmol) in 5 mL of THF and the mixture was stirred at room
temperature for 45 min. The solution was then frozen using liquid
nitrogen, and the gases were removed under reduced pressure. A
carbon monoxide headspace was introduced, and the solution was
warmed to room temperature and stirred for an additional 2 h. The
solvent was removed under reduced pressure, and the crude product
was washed with ether and hexanes. The residue was dissolved in a
minimal amount of DCM, and the product was precipitated out with
cold pentane. The powder was filtered and washed with cold pentane
and then dried under reduced pressure to yield pure Fe-P-N-P′
product. Yield: 63 mg, 85%.
2
2
(d, JPP = 148.5 Hz), and 53.34 (d, JPP = 148.5 Hz). 13C{1H} NMR
(100 MHz, CD3CN): δ 177.9 (NCH), 127−137 (Ar-C and P-Ar-
C), 117.6 (NCMe), 81.7 (N−CH(Ph)), 46.6 (CH(Ph)-PPh2), and
0.34 (NC-CH3) ppm. Anal. Calcd for [FeC51H46P2N4][BF4]2: C,
60.87; H, 4.61; N, 5.57. Found: C, 59.57; H, 4.67; N, 5.07. MS (ESI,
m/z+): 415.2 [FeC51H46P2N4]+2.
7a: R1 = R2 = H. From 5a (0.103 g, 0.20 mmol), Yield: 167 mg,
98%. 1H NMR (400 MHz, CD3CN): δ 7.90 (m, 2H, Ph-CH), 7.80
(m, 2H, Ph-CH), 7.45−7.75 (m, 17H, Ph-CH), 7.37 (t, 1H, Ph-CH, J
= 8.3 Hz), 7.28 (m, 2H, Ph-CH), 3.54 (dd, 1H, Ph-CH2-NH, 3JHH and
4JHH = 13.0 and 3.8 Hz), 3.44 (t, 1H, CH2-PPh2, 3JHH = 14.6 Hz), 3.19
(m, 1H, Ph-CH2-NH), 3.10 (m, 1H, NH-CH2-CH2), 2.49 (m, 1H,
CH2-PPh2), 2.38 (m, 1H, NH), 2.32 (m, 1H, NH-CH2-CH2), and 1.99
(s, NC-CH3/NC-CD3) ppm. 31P{1H} NMR (161 MHz, CD3CN): δ
2
2
58.69 (d, JPP = 141.9 Hz), and 43.74 (d, JPP = 141.9 Hz) ppm.
13C{1H} NMR (100 MHz, CD3CN): δ 127−141 (Ar-C and P-Ar-C),
119.1 (NCMe), 57.3 (Ph-CH2-NH), 53.8 (HN-CH2-CH2), 24.2 (CH2-
PPh2), and 0.49 (NC-CH3) ppm. Anal. Calcd for [FeC39H40P2N4]-
[BF4]2: C, 54.7; H, 4.7; N, 6.5. Found: C, 53.22; H, 4.96; N, 6.27.**
MS (ESI, m/z+): 339.3 [FeC39H40P2N4]2+, 318.1 (loss of MeCN),
300.1 (loss of two MeCN), and 279.6 (loss of three MeCN).
7c: R1 = Me, R2 = Ph. From 5c (0.030 g, 0.050 mmol), Yield: 47
1H NMR (600 MHz, CD2Cl2): δ 8.36 (s, 1H, NCH), 8.25 (dd,
2H, Ph-CH, J = 7.7 and 10.0 Hz), 8.08 (m, 2H, Ph-CH), 8.03 (m, 2H,
Ph-CH), 7.31−7.65 (m, 17H, Ph-CH), 7.26 (t, 1H, Ph-CH, J = 8.1
Hz), 4.00 (m, 1H, N-CH2), 3.43 (m, 1H, N-CH2), 3.02 (m, 1H, P-
CH2), and 2.55 (m, 1H, P-CH2) ppm. 31P{1H} NMR (242 MHz,
1
2
2
mg, 99%. H NMR (500 MHz, CD3CN): δ 7.00−7.68 (m, 29H, Ph-
CD2Cl2): δ 44.01 (d, JPP = 216.9 Hz), 39.55 (d, JPP = 216.9 Hz)
ppm. 13C{1H} NMR (150 MHz, CD2Cl2): δ 173.7 (NCH),126−
137 (Ph-C), 71.5 (N-CH2), and 24.1 (P-CH2) ppm. Anal. Calcd for
[C34H29NP2OFeBr2]: C, 54.8; H, 3.92; N, 1.88. Found: C, 54.93; H,
4.19; N, 2.74. MS (TOF-ESI, m/z+): 636.0 [C33H29NP2FeBr]+ (loss of
CO, Br). IR: ν(CO) 1960.6 cm−1.
CH), 3.99 (dd, 1H, P-C(Ph)H, J = 7.7 and 12.2 Hz), 3.82 (dd, 1H, N-
4
3
CH2, JHH and JHH = 5.1 and 13.1 Hz), 3.04 (m, 1H, N-CH2), 2.88
(m, 1H, N-C(Me)H), 1.99 (s, NC−CH3/NC-CD3), 1.92 (NH,
1
determined indirectly using H−1H-COSY), and 1.17 (d, 3H, CH3,
3JHH = 5.8 Hz) ppm. 31P{1H} NMR (202 MHz, CD3CN): δ 74.30 (d,
L
dx.doi.org/10.1021/om5008083 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Note: synthesis yields a cis/trans mixture with a ratio of 8% trans on
the basis of the cis Br/CO disorder in the crystal structure. Minor trans
species also observable by 31P NMR at 64.8 and 57.8 ppm (doublets, J
= 184 Hz).
(22) Chakraborty, S.; Dai, H.; Bhattacharya, P.; Fairweather, N. T.;
Gibson, M. S.; Krause, J. A.; Guan, H. J. Am. Chem. Soc. 2014, 136,
7869.
(23) Chakraborty, S.; Brennessel, W. W.; Jones, W. D. J. Am. Chem.
Soc. 2014, 136, 8564.
(24) Casey, C. P.; Guan, H. J. Am. Chem. Soc. 2007, 129, 5816.
(25) Casey, C. P.; Guan, H. J. Am. Chem. Soc. 2009, 131, 2499.
ASSOCIATED CONTENT
■
S
* Supporting Information
(26) Berkessel, A.; Reichau, S.; von der Hoh, A.; Leconte, N.;
̈
Text, figures, tables, and CIF files giving detailed synthetic
routes and spectroscopic characterization data for all new
complexes, as well as crystal structure data. This material is
available free of charge via the Internet at http://pubs.acs.org.
Neudorfl, J. R.-M. Organometallics 2011, 30, 3880.
̈
(27) Zhou, S.; Fleischer, S.; Junge, K.; Beller, M. Angew. Chem., Int.
Ed. 2011, 50, 5120.
(28) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40, 40.
(29) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008.
(30) Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001,
66, 7931.
(31) Ikariya, T.; Murata, K.; Noyori, R. Org. Biomol. Chem. 2006, 4,
393.
(32) Hasanayn, F.; Morris, R. H. Inorg. Chem. 2012, 51, 10808.
(33) Zimmer-De Iuliis, M.; Morris, R. H. J. Am. Chem. Soc. 2009, 131,
11263.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for R.H.M.: Robert.Morris@utoronto.ca.
Notes
The authors declare no competing financial interest.
(34) Dub, P. A.; Henson, N. J.; Martin, R. L.; Gordon, J. C. J. Am.
Chem. Soc. 2014, 136, 3505.
ACKNOWLEDGMENTS
■
(35) Morales-Morales, D.; Jensen, C. The Chemistry of Pincer
Compounds; Elsevier: Amsterdam, The Netherlands, 2007.
(36) Lagaditis, P. O.; Sues, P. E.; Sonnenberg, J. F.; Wan, K. Y.;
Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2014, 136, 1367.
(37) Benito-Garagorri, D.; Alves, L. G. a.; Veiros, L. F.; Standfest-
Hauser, C. M.; Tanaka, S.; Mereiter, K.; Kirchner, K. Organometallics
2010, 29, 4932.
(38) Lagaditis, P. O.; Mikhailine, A. A.; Lough, A. J.; Morris, R. H.
Inorg. Chem. 2009, 49, 1094.
(39) Benito-Garagorri, D.; Puchberger, M.; Mereiter, K.; Kirchner, K.
Angew. Chem., Int. Ed. 2008, 47, 9142.
(40) Benito-Garagorri, D.; Alves, L. G.; Puchberger, M.; Mereiter, K.;
Veiros, L. F.; Calhorda, M. J.; Carvalho, M. D.; Ferreira, L. P.;
Godinho, M.; Kirchner, K. Organometallics 2009, 28, 6902.
(41) Saitoh, A.; Uda, T.; Morimoto, T. Tetrahedron: Asymmetry 1999,
10, 4501.
(42) Kawamura, K.; Fukuzawa, H.; Hayashi, M. Org. Lett. 2008, 10,
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(43) Xiao, H.; Chai, Z.; Zheng, C.-W.; Yang, Y.-Q.; Liu, W.; Zhang,
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(44) Veitía, M. S.-I.; Brun, P. L.; Jorda, P.; Falguier
We thank the NSERC for a Discovery grant to R.H.M. and a
Vanier Canada Graduate Scholarship for J.F.S. and the CFI and
OMR for a Leading Edge grant for the CSICOMP facility.
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