Hemilabile β-aminophosphine ligands derived from 1,3,5-triaza-7- phosphaadamantane: Application in aqueous ruthenium catalyzed nitrile hydration

Article abstract of DOI:10.1021/ic301160x

A series of β-aminophosphines derived from 1,3,5-triaza-7- phosphaadamantane (PTA) are described. PTA-CHPhNHPh (1), PTA-CH(p-C ₆H₄OCH₃)NHPh (2), and PTA-CPh₂NHPh (3) were prepared in good yield (62-77%) by reaction of lithiated PTA with the corresponding imine followed by hydrolysis. Compounds 1 and 2 were synthesized as pairs of diastereomers which were separated by successive recrystallization from THF/hexane. Compounds 1-3 are somewhat soluble in water (S ₂₅^o = 4.8 (1), 4.9 (2), 2.7 (3) g/L). Upon coordination to Ru(II) arene centers both monodentate (κ¹-P) [RuCl ₂(η⁶-toluene)(1-3)] and bidentate (κ ²-P,N) [RuCl(η⁶-toluene)(1-3)]Cl coordination modes were observed. Ru(II) arene complexes 4-6 exhibited hemilabile behavior transitioning between κ¹-P and κ²-P,N coordination upon change in solvent or addition of a coordinating ligand such as Cl^- or CH₃CN. Complexes (4-6) were found to be active air stable catalysts for the aqueous phase hydration of various nitriles with TOF up to 285 h^-1 and TON of up to 97 000 observed.

Full text of DOI:10.1021/ic301160x

Article
pubs.acs.org/IC
Hemilabile β‑Aminophosphine Ligands Derived from 1,3,5-Triaza-7-
phosphaadamantane: Application in Aqueous Ruthenium Catalyzed
Nitrile Hydration
Wei-Chih Lee, Jeremiah M. Sears, Raphel A. Enow, Kelly Eads, Donald A. Krogstad,† and Brian J. Frost*
Department of Chemistry, University of Nevada, Reno, Nevada 89557-0216, United States
S
* Supporting Information
ABSTRACT: A series of β-aminophosphines derived from
1,3,5-triaza-7-phosphaadamantane (PTA) are described. PTA-
CHPhNHPh (1), PTA-CH(p-C6H4OCH3)NHPh (2), and
PTA-CPh2NHPh (3) were prepared in good yield (62−77%)
by reaction of lithiated PTA with the corresponding imine
followed by hydrolysis. Compounds 1 and 2 were synthesized
as pairs of diastereomers which were separated by successive
recrystallization from THF/hexane. Compounds 1−3 are somewhat soluble in water (S25o = 4.8 (1), 4.9 (2), 2.7 (3) g/L). Upon
coordination to Ru(II) arene centers both monodentate (κ1-P) [RuCl2(η6-toluene)(1−3)] and bidentate (κ2-P,N) [RuCl(η6-
toluene)(1−3)]Cl coordination modes were observed. Ru(II) arene complexes 4−6 exhibited hemilabile behavior transitioning
between κ1-P and κ2-P,N coordination upon change in solvent or addition of a coordinating ligand such as Cl− or CH3CN.
Complexes (4−6) were found to be active air stable catalysts for the aqueous phase hydration of various nitriles with TOF up to
285 h−1 and TON of up to 97 000 observed.
metal complexes of PTA have been used for a range of catalytic
transformations,42 e.g., hydrogenation of arenes43 and CO2/
bicarbonate,44 transfer hydrogenation of α,β-unsaturated
carbonyls,45,46 atom transfer radical addition,47,48 hydro-
formylation of 1-decene,49 and hydration.35,39,50,51 We recently
published details that [Ru(PTA)4Cl2] is a highly active and
recyclable catalyst for nitrile hydration.50 Cadierno and co-
workers previously reported that a series of ruthenium
complexes of PTA and derivatives, including [RuCl2(η6-
arene)(PTA)], were efficient catalysts for aqueous nitrile
hydration.51 The excellent efficiency was attributed to the
ability of PTA to serve as a hydrogen bond acceptor to activate
water.
INTRODUCTION
■
There has been a growing interest in the development of
aminophosphine ligands, many of which have shown good
catalytic performance for a broad range of organic trans-
formations,1−11 e.g., (transfer) hydrogenation,12−18 hydro-
formylation,19−21 and hydrosilylation.22−25 Aminophosphines
are potentially hemilabile ligands, especially if the amine group
is sufficiently bulky.3 Hemilabile κ2-P,N complexes of amino-
phosphines are of interest in catalysis since the labile amine
group can be displaced by substrate, allowing catalysis to
proceed, and can potentially increase catalyst lifetime.
Nitrile hydration is an atom economical method to convert
nitriles to amides. The mechanism is generally assumed to
involve coordination of the nitrile to the metal center,
necessitating an open coordination site.26 Water may or may
not coordinate to the metal prior to nucleophilic attack on the
nitrile carbon. Amide dissociation has been implicated in
catalyst deactivation or inhibition.26 Both the requirement of an
open coordination site and the need to remove coordinated
product make hemilabile ligands intriguing for nitrile hydration.
A variety of transition metal complexes have been utilized as
effective catalysts,26−29 for example, [Cp2Mo(OH)-
(H2O)]+,30,31 cis-Ru(acac)2(PPh2Py)2,32 and [PtH(PMe2OH)-
{(PMe2O)2H}.33 Ruthenium has become one of the most
highly explored metals for nitrile hydration with ruthenium
arene compounds as some of the most efficient and versatile
catalysts with high substrate tolerance for the hydration of
nitriles.26,34−40
Our group has been interested in upper-52,53 and lower-rim54
modifications of PTA maintaining the heterocyclic cage.
Functionalization of the upper rim has been demonstrated by
us and others through lithiation of PTA followed by reaction of
PTA-Li with various electrophiles including chlorodiphenyl-
phosphine,52 CO2,53 and aryl ketones and aldehydes, Scheme
1.53,55−57 Herein we continue this work with the synthesis of a
series of β-aminophosphines obtained through the addition of
imines (R1R2CNPh) to 1,3,5-triaza-7-phosphaadamantan-6-
yllithium (PTA-Li). These functionalized PTA derivatives were
coordinated to ruthenium arene centers, and their activity for
nitrile hydration is reported.
The air-stable and water-soluble aminophosphine 1,3,5-
triaza-7-phosphaadamantane (PTA) has received attention in
recent years mainly due to medicinal interest.41 Transition
Received: May 31, 2012
Published: January 28, 2013
© 2013 American Chemical Society
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Scheme 1
Table 1. 31P{1H} NMR Spectroscopy and Water Solubility
Data for a Series of PTA Derivatives
S25°C
g/L
a,b
31P{1H}
ligand
M mol/L
PTA67
−102.3 (−12.5)
−102.4, −105.9 (−2.9,
−5.7)
1.5
235
4.8
PTA-CHPhNHPh (1)
0.0142
PTA-CH(p-C6H4OMe)
NHPh (2)
−102.1, −105.9 (−2.9,
0.0133
4.9
−5.7)
PTA-CPh2NHPh (3)
−97.7 (−1.5)
−95.5 (−3.46)
−96.4 (−3.1)
0.0065
0.0174
0.0265
2.7
PTA-CPh2OH53
5.9
PTA-C(p-
10.6
C6H4OMe)2OH53
PTA-CH(p-C6H4OMe)
−102.6, −105.7 (−1.48,
−3.19)
0.0379
11.1
OH53
a
b
In CDCl3. Phosphine oxide chemical shift in parentheses.
PTA-Li even with dropwise addition of the imine at −78 °C.
The 31P{1H} NMR spectra of the crude products of 1 and 2
contained two singlets in ca. 1:1 ratio of RS/SR:RR/SS in
CDCl3 (−102.4 and −105.9 ppm for 1; −102.1 and −105.9
ppm for 2), Table 1. β-Aminophosphines 1 and 2 were isolated
as diastereomeric mixtures in 3.5:1 (1) and 2.1:1 (2) ratio of
RS/SR:RR/SS after a single recrystallization from THF and
hexane (1:10). Repeated recrystallization from a 1:10 solution
of THF/hexane resulted in the clean isolation of the RS/SR
diastereomer of 1 (−102.4 ppm, 27%) and 2 (−102.1 ppm,
30%). Peruzzini and co-workers have previously reported the
isolation of a single diastereomer for the oxide of PTA-
CHPhOH by recrystallization.55
RESULTS AND DISCUSSION
■
The β-phosphine alcohol derivatives of PTA previously
reported (Scheme 1, PTA-CRR′OH) coordinate to metals in
a monodentate fashion with some evidence of bidentate
coordination.53,55−57 We were interested in developing ligands
which would be able to coordinate metals in a bidentate fashion
ideally with hemilabile behavior. The β-aminophosphines
described below were designed to be able to weakly chelate a
metal center serving in a hemilabile manner.
Ligand Synthesis. Synthesis of ligands 1−3 was performed
by adding a THF solution of the corresponding imine to a cold
suspension of PTA-Li in THF followed by quenching with
water (Scheme 2). The ligands were isolated as pale yellow
The presence of −NHPh moieties in 1−3 was confirmed by
IR spectroscopy. A single IR absorption (υN−H) was observed in
the N−H stretching region of the infrared spectrum of 1 (3371
cm−1), 2 (3360 cm−1), and 3 (3323 cm−1) indicating the
presence of a secondary amine. The υN−H assignments were
confirmed by H/D exchange. Reaction of 3 with D2O in THF
Scheme 2
resulted in the disappearance of the absorbance at 3323 cm−1
58
and a new absorption at 2479 cm−1 corresponding to υN‑D
.
The solid-state structures of compounds 1−3 were
determined by single crystal X-ray diffraction. Crystals of 1
and 3 suitable for X-ray diffraction study were grown by slow
evaporation of a 1:1 CH2Cl2/CH3CN solution of 1 or 3.
Crystals of 2 were grown by slow evaporation of a 1:1 CH2Cl2/
MeOH solution of the single diastereomer of 2 (the
stereochemistry of the racemate was determined to be RC1/
powders in 62−77% yield and characterized by IR spectrosco-
1
py, ESI+ mass spectrometry, H, 13C{1H}, and 31P{1H} NMR
1
spectroscopy, and single-crystal X-ray analysis. H and 13C
resonances were assigned by analyzing 1H, 13C{1H}, 13C DEPT
(90° and 135°), COSY, HMQC, and HMBC spectral data of
1−3. The resulting β-aminophosphines are readily soluble in
common organic solvents, e.g., methanol, acetone, tetrahy-
drofuran, chloroform, dichloromethane, toluene, and acetoni-
trile. Compounds 1−3 are slightly less soluble in water (S25° =
2.7−4.9 g/L, Table 1) than the β-phosphino alcohols
previously reported by us (S25° = 5.9−11.1 g/L).53 Similar to
other upper-rim substituted PTA derivatives, compounds 1−3
are air-stable in the solid state; however, they oxidize slowly in
solution. The oxidation of 1−3 in CDCl3 was monitored by
31P{1H} NMR spectroscopy; after 6 weeks in solution ∼6%,
9%, and 4% of the phosphine oxides of 1, 2, and 3, respectively,
were observed.
S
C7 and SC1/RC7). Thermal ellipsoid representations for 1 and 3
are depicted in Figures 1 and 2, respectively (see Supporting
Figure 1. Thermal ellipsoid representation (50% probability) of PTA-
CHPhNHPh (1) along with the atomic numbering scheme. Hydrogen
atoms have been omitted except those attached to N4 and
stereocenters C1 and C7. Only the SC1/RC7 enantiomer is shown;
however, both SC1/RC7 and RC1/SC7 are present in the structure.
Treatment of PTA-Li with PhNCPh2 provided a racemic
mixture of 3 with a single 31P{1H} NMR resonance at −97.7
ppm in CDCl3. No diastereomeric selectivity was observed for
the addition of PhNCHC6H5 or PhNCHC6H4OCH3 to
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The ruthenium arene complexes 4−6 are soluble in chloroform,
dichloromethane, methanol, and acetonitrile but not soluble in
diethyl ether and hexane. Complex 6 is not water-soluble at
room temperature while complexes 4 and 5 are slightly water-
soluble (S25° = 6 mg/mL for 4 and 5 mg/mL for 5). As solids,
compounds 4−6 are stable in air; however, solutions of 4−6
slowly decompose in air over the course of weeks turning dark
brown/black.
As expected the β-aminophosphine ligands 1−3 are able to
coordinate to the Ru center in either a monodentate (κ1-P) or
bidentate (κ2-P,N) fashion with possible hemilabile behavior.
κ2-P,N coordination of 1 or 2 to the ruthenium arene center
results in an organometallic complex with three chiral centers:
the ruthenium center and the two on the ligand. The hemilabile
nature of the amine functionality allows for only two
diastereomeric pairs to be observed in the 31P NMR spectrum.
In polar solvents, such as water or methanol, complexes 4, 5,
and 6 exist, predominantly, as the cationic [(η6-toluene)RuCl-
(κ2-P,N-PTA-CR1R2NHPh)]Cl ([4]Cl, [5]Cl, and [6]Cl) with
a chelating κ2-P,N coordination of 1, 2, and 3, respectively,
Table 3. In methanol only 4 is found to have any κ1-P
Figure 2. Thermal ellipsoid representation (50% probability) of PTA-
CPh2NHPh (3) with the atomic numbering scheme. Hydrogen atoms
have been omitted except those attached to N4 and stereocenter C1.
Only the RC1 enantiomer is shown; however, both enantiomers (SC1
and RC1) are present in the structure.
Information for a thermal ellipsoid representation of 2). All
three structures contain both enantiomers in the respective unit
cell: RS/SR for 1 and 2, and R/S for 3. The C7−C1−P1 bond
angle in 1 and 2 are similar (110.19° and 111.83°, respectively)
while this angle in 3 is significantly larger at 119.32°. This
arises, presumably, from the increased steric bulk due to the
additional phenyl ring on C7. Table 2 contains selected bond
Table 3. Mole Fraction of κ1-P Coordination in 4a, 5a, 6a in
Various Solvents by 31P{1H} NMR Spectroscopy at 25 °C
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1−
3
solvent
4a
5a
6a
CD3OD
D2O
0.15
0.0
0.0
0.0
0.0
0.0
1
2
3
a
a
a
P1−C1
P2−C2
P3−C3
N1−C1
C1−C7
N4−C7
N1−C1−C7
C7−C1−P1
1.880(2)
1.860(2)
1.862(2)
1.480(2)
1.548(3)
1.460(2)
113.90(15)
110.19(13)
1.8830(12)
1.8662(12)
1.8608(13)
1.4767(16)
1.5460(15)
1.4487(16)
111.47(9)
111.83(8)
1.874(2)
1.878(3)
1.853(4)
1.481(3)
1.579(3)
1.466(3)
113.60(19)
119.32(16)
CD3CN
CDCl3
0.12 (0.16)
0.36
0.09 (0.14)
0.41
0.95 (0.96)
0.95
a
50 °C.
coordination present in solution as measured by 31P NMR
spectroscopy (∼15%). In less polar solvents, such as CH2Cl2 or
CHCl3, 4−6 exist as equilibrium mixtures of monodentate (κ1-
P) 4a−6a and bidentate (κ2-P,N), [4]Cl−[6]Cl, coordination
modes (Scheme 3 and Table 3). In CD3CN 4 and 5 exist
mainly as the κ2-P,N [4]Cl and [5]Cl whereas 6 is
predominately found in the κ1-P coordination mode (6a).
These results suggest hemilabile coordination of the nitrogen.
Variable temperature NMR spectroscopy in CD3OD or CDCl3
between 0 and 50 °C revealed little variation in the
coordination found for compounds 4−6. In CD3CN as the
temperature was raised from 25 to 50 °C the mole fraction of
κ1-P coordination increased slightly for 4 and 5, while largely
unchanged for 6 (Table 3).
lengths and angles. The amine proton in 2 forms a hydrogen
bond with an oxygen atom of one of the two cocrystallized
methanol molecules (N4···O2 = 2.9414(16) Å). Hydrogen
bonding is also observed between the two methanol molecules
(O2···O3 = 2.6942(18) Å) as well as between one of the lower-
rim nitrogen atoms on the PTA cage and the hydroxyl group of
methanol (O3···N3 = 2.7425(16) Å).59
Ruthenium Arene Complexes. Ruthenium arene com-
plexes of the β-aminophosphine ligands, PTA-CR1R2NHPh, 1
(R1 = H, R2 = C6H5), 2 (R1 = H, R2 = p-C6H4OMe), and 3 (R1
= R2 = C6H5) were prepared by reaction of [(η6-C6H5CH3)-
RuCl(μ-Cl)]2 with 2 equiv of the appropriate ligand (1−3) in
dichloromethane, Scheme 3. The resulting air stable complexes
4−6 were isolated as orange solids in greater than 85% yield.
The 31P{1H} NMR spectrum of 6 in CDCl3 (Figure 3a)
contains two singlets at +0.6 and −31.1 ppm indicative of [(η6-
toluene)RuCl2(PTA-CPh2NHPh)] (6a) and [(η6-toluene)-
RuCl(PTA-CPh2NHPh)]Cl ([6]Cl). Dissolving 6 in CD3OD
results in a single resonance at −0.4 ppm in the 31P{1H} NMR
spectrum indicating bidentate coordination of ligand 3 and
dissociation of a chloride (Figure 3b). Addition of 10 equiv of
NaCl to the CD3OD solution of 6 results in the reappearance
of a small singlet at −30.3 ppm indicating that 6a and [6]Cl are
indeed at equilibrium and that the nitrogen coordinates in a
hemilabile fashion (Figure 3c). In CD3CN 6 is mostly
coordinated κ1-P with a large broad peak at −31.0 ppm and
a small peak for κ2-P,N coordination at −0.5 ppm in the
31P{1H} NMR spectrum. Ion exchange of [6]Cl to [6]PF6
resulted in exclusive bidentate P,N-coordination (single
31P{1H} resonance at −0.7 ppm in CDCl3, Figure 3d).
Nitrogen coordination in [6]PF6 was confirmed by solid-state
Scheme 3
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Slow evaporation of a CH3CN solution of complex [5]Cl or
[6]PF6 over the course of a few days resulted in orange blocks
suitable for single crystal X-ray diffraction. The κ2-P,N
coordination in [5]Cl and [6]PF6 was confirmed by the X-
ray diffraction analysis, Figures 5 and 6. The Ru(II)
coordination sphere for [5]Cl and [6]PF6 each contain one
η6-arene ring, one chloride, one phosphorus, and one nitrogen
atoms. The Ru1−arenecentroid for [5]Cl and [6]PF6 is 1.701 and
1.711 Å, respectively. The Ru1−P1 distances for [5]Cl
(2.2833(7) Å) and [6]PF6 (2.2742(5) Å) are slightly shorter
than those observed for ruthenium arene complexes of κ1-P
PTA derivatives (2.3108(15)−2.3294(11) Å).53 The Ru1−N4
distances in [5]Cl (2.236(2) Å) and [6]PF6 (2.2206(15) Å) are
comparable to other β-aminophosphines complexes of
ruthenium with κ2-P,N coordination and secondary amines
(2.203−2.253 Å).12,61 Although only one enantiomer SRuSC1RC7
and SRuRC1 is shown for [5]Cl (Figure 5) and [6]PF6 (Figure
Figure 3. 31P{1H} NMR spectra: (a) [6]Cl and 6a in CDCl3, (b) [6]
Cl in CD3OD, (c) [6]Cl and 6a in CD3OD + 10 equiv of NaCl, (d)
[6]PF6 in CDCl3, (e) [6]Cl and 6a in CD3CN, (f) [6]PF6 and 6a in
CD3CN.
IR spectroscopy. The υNH in [6]PF6 (3154 cm−1) was found to
be 169 cm−1 lower than the υNH in the free ligand 3 (3323
cm−1) consistent with amine coordination to the metal
center.60 Dissolution of [(η6-toluene)RuCl(PTA-
CPh2NHPh)]PF6 ([6]PF6) in a coordinating solvent, such as
CD3CN, reveals the hemilabile nature of the β-aminophosphine
ligand. A mixture of monodentate (−30.7 ppm) and bidentate
(−0.6 ppm) coordination is observed by 31P{1H} NMR
spectroscopy along with two resonances at −26.1 and −26.8,
likely nitrile coordinated species, Figure 3f.
Figure 5. Thermal ellipsoid representation (50% probability) of [5]Cl
with the atomic numbering scheme. Hydrogen atoms have been
omitted except those bonded to the stereocenters or heteroatoms.
Only the SRuSC1RC7 enantiomer is shown; however, both SRuSC1RC7
and RRuRC1SC7 are present in the structure. Selected bond lengths (Å)
and angles (deg): Ru1−N4 2.236(2), Ru1−P1 2.2833(7), Ru1−Cl1
2.3979(8), Ru1−arenecentroid 1.701, N4−C7 1.517(3), N4−Ru1−P1
79.90(6), P1−Ru1−Cl1 87.93(3), N4−Ru1−Cl1 89.48(7).
In CD3OD only bidentate coordination is observed in the
31P{1H} NMR spectrum of 5 ([5]Cl; −10.6 and −17.4 ppm,
Figure 4b). Compound 4 in methanol contains ∼15% of the κ1-
6), both enantiomers are present in the unit cell (SSR/RRS for
[5]Cl; SR/RS for [6]PF6).62 The five-membered chelate ring
Figure 4. 31P{1H} NMR spectra: (a) [5]Cl and 5a in CDCl3, (b) [5]
Cl in CD3OD, (c) [5]Cl and 5a in CD3CN.
Figure 6. Thermal ellipsoid representation (50% probability) of the
cationic portion of [6]PF6 with the atomic numbering scheme.
Hydrogen atoms have been omitted except those bonded to the
P coordination mode ([4]Cl; −10.5 and −17.7 ppm; 4a; −30.4
ppm).59 Redissolution of [5]Cl in chlorinated solvents (CD2Cl2
or CDCl3) results in the appearance of an additional peak in the
31P{1H} NMR spectrum at −31.6 ppm for 5a (Figure 4a)
indicating both monodentate (5a, −31.6 ppm) and bidentate
([5]Cl, −10.3 and −19.6 ppm) coordination. Other ruthenium
κ1-P complexes of PTA and derivatives have contained
resonances in the −30 to −35 ppm region of the 31P NMR
spectrum.53
−
stereocenters or heteroatoms. The PF6 counterion has also been
omitted for clarity. Only the SRuRC1 enantiomer is shown; however,
both SRuRC1 and RRuSC1 are present in the structure. Selected bond
lengths (Å) and angles (deg): Ru1−N4 2.2206(15), Ru1−P1
2.2742(5), Ru1−Cl1 2.4051(4), Ru1−arenecentroid 1.711, N4−C7
1.559(2), N4−Ru1−P1 79.31(4), P1−Ru1−Cl1 85.083(16), N4−
Ru1−Cl1 80.30(4).
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(Ru1−P1−C1−C7−N4) has a slightly twisted conformation,
and the bite angle (N4−Ru1−P1) of the P,N chelate ring is
79.90(6)° and 79.31(4)° for [5]Cl or [6]PF6, respectively. A
weak hydrogen bond between Cl2 and the amine-N4 atoms
was observed for [5]Cl (N4···Cl2 = 3.345(3) Å).
co-workers reported higher performance with more sterically
demanding and electron-rich arenes (C6Me6 > 1,3,5-C6H3Me3
> p-cymene > C6H6) with a series of [RuCl2(η6-arene)(PTA)]
complexes.51 The indenyl complex [IndRu(PTA)(PPh3)Cl]
(Ind = η5-indenyl) exhibited the highest conversion (77%) and
TOF (0.83 h−1) among the cyclopentadienyl complexes (Table
4, entries 3−6). Presumably this is due to the indenyl effect, η5-
to η3-rearrangement, facilitating nitrile coordination to
ruthenium.
Aqueous Nitrile Hydration. While [RuCl2(η6-arene)-
(PTA)] was demonstrated as an efficient catalyst for aqueous
nitrile hydration,51 we were intrigued to explore if such
hydration efficiency could be retained or improved upon using
the functionalized PTA derivatives, 1−3, as ligands. In
particular, we envisioned that the hemilabile amine function-
ality could serve as a hydrogen-bond acceptor activating water
and could also help promote dissociation of the product amide
(at times considered the rate-determining step of nitrile
hydration).26 The structures of ruthenium arene complexes
(vide supra) reveal that the pendant amine group on ligands 1,
2, and 3 is capable of binding the metal center and is also close
enough to help activate water for nucleophilic attack. The
catalytic hydration of benzonitrile to benzamide by [4]Cl,
[5]Cl, and [6]Cl as well as other ruthenium complexes was
evaluated. A typical catalytic experiment was carried out by
mixing in air 5 mol % catalyst, 1 mmol nitrile, and 3 mL water
in a culture tube at 100 °C (Scheme 4). The reaction was
monitored by GC-MS at 7 and 24 h (Table 4).
Complex [6]Cl (95%, TOF = 2.7 h−1) was found to be much
more active than [4]Cl (53%, TOF = 1.5 h−1) or [5]Cl (60%,
TOF = 1.7 h−1) in the catalytic production of benzamide
(Table 4, entries 8−10). The activity seems to correlate with
the observation that 6 in acetonitrile is almost exclusively in the
κ1-P form (6a); however, 4 and 5 are observed mostly in the κ2-
P,N form in acetonitrile and other polar solvents such as water
and methanol. Ruthenium arene complexes with κ2-P,N
coordination have been shown to be less active than similar
κ1-P coordinated complexes.34 The more labile Ru−N bond in
[6]Cl, allowing nitrile coordination to ruthenium, may be
responsible for the increased activity. For comparison the κ1-P
coordinated complex [RuCl2(η6-toluene)(PTA)] did not
exhibit comparable efficiency (47%; Table 4, entry 7).
Presumably, the lower efficiency was due to catalyst
decomposition; a black oily precipitate was observed during
and after hydration. Catalyst degradation was observed in [6]Cl
catalyzed nitrile hydration with small amounts of both
benzophenone and aniline observed by GC-MS. Catalyst
decomposition was not observed, by GC-MS, for benzonitrile
hydration by [4]Cl or [5]Cl. However, in all cases a black oily
precipitate was observed following catalysis, unlike the clear
solutions we observed in nitrile hydration catalyzed by
[RuCl2PTA4].
Scheme 4
Table 4. Catalytic Hydration of Benzonitrile by Various Ru
a
Compounds in Water in the Presence of Air
b
c
entry
catalyst
% conv
TOF (h−1
)
1
[RuCl2(η6-toluene)]2
0
0
Catalyst lifetime and activity were explored by looking at
turnover number (TON) and turnover frequency (TOF)67 for
the hydration of benzonitrile to benzamide at various catalyst
loadings from 5 mol % to 0.001 mol %, Table 5. Interestingly
the TOF of the catalyst increased significantly as the catalyst
loading was reduced. This is consistent with what we have
previously reported for nitrile hydration catalyzed by
[RuCl2PTA4].50 TONs up to 97 000 were observed along
2
RuCl3·3H2O
(54)
2(6)
6(20)
0.45
0.06
0.17
0.69
0.83
1.3
3
[CpRu(PTA)(PPh3)Cl]
[CpRu(PTA)2Cl]
[Cp*Ru(PTA)2Cl]
[IndRu(PTA)(PPh3)Cl]
[RuCl2(η6-toluene)(PTA)]
[4]Cl
4
5
24(57)
29(77)
47(96)
53(80)
60(79)
95(97)
99
6
7
8
1.5
9
[5]Cl
1.7
10
11
[6]Cl
2.7
Table 5. Effect of Catalyst Loading on TON and TOF for
50
d
a
59
,
RuCl2PTA4
2.8
Benzonitrile Hydration Catalyzed by [6]Cl or [6]PF6
a
Conditions: 1 mmol nitrile, 5 mol % cat., 3 mL H2O, 100 °C, in air.
b
c
entry
1
catalyst (mol %)
time (h)
conv
TON
TOF (h−1
)
b
c
GC yields of amide after 7 h (24 h yield in parentheses). TOF = mol
d
product/(mol cat.-h) determined after 7 h. TOF up to 30 h−1 were
observed for this catalyst.
5
7
95
78
74
44
92
89
94
98
73
97
56
97
19
2.7
d
2
5
7
16
2.2
3
1
7
74
10.6
6.3
d
4
1
7
44
Hydration did not proceed in the absence of a catalyst or in
the presence of [RuCl2(η6-toluene)] (Table 4, entry 1).
RuCl3·3H2O showed a 54% conversion after 24 h (entry
2).63 [CpRu(PTA)(PPh3)Cl] and [CpRu(PTA)2Cl] (Cp = η5-
cyclopentadienyl) showed poor activity for the hydration of
benzonitrile with conversions of 2−6% after 7 h and 6−20%
after 24 h (Table 4, entries 3−4). It is not surprising that
[CpRu(PTA)(PPh3)Cl] and [CpRu(PTA)2Cl] were not active,
as it has been reported that CpRu phosphine complexes
hydrate terminal alkynes in the presence of nitriles.64−66 The
more electron-rich Cp*Ru(PTA)2Cl complex (Cp* = η5-
pentamethylcyclopentadienyl) exhibited improved activity
compared to CpRu(PTA)2Cl (entries 4−5). Cadierno and
e
5
f
1
7
92
13.1
12.7
7.8
6
1
7
89
7
8
1
12
24
24
100
160
340
94
1
98
4.1
g
9
1
73
3.0
10
11
12
0.1
0.01
0.001
970
5600
97 000
9.7
35
285
a
b
Conditions: 1 mmol nitrile, 3 mL H2O, 100 °C, in air. Determined
c
d
by GC. mol product/(mol catalyst-h). Reaction run with ∼0.5 mL
Hg. Reaction run with 10 mol % NaCl. Reaction run with 25 mol %
NaCl. 6[PF6].
e
f
g
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Inorganic Chemistry
Article
a
with TOF up to 285 h−1 making [6]Cl an active and long-lived
nitrile hydration catalyst, more active than the highly recyclable
[RuCl2PTA4] where TON of up to 22 000 and TOF of up to
30 h−1 were observed.50 To test the effect of chloride we looked
at the activity of [6]PF6 (TOF = 3.0 h−1, Table 5, entry 9) and
found it to be slightly less active than [6]Cl (TOF = 4.1 h−1,
Table 5, entry 8). This difference in activity is ascribed to the
difference in coordination of [6]Cl (>95% κ1-P) and [6]PF6
(∼50:50 κ1-P:κ2-P,N) in acetonitrile.59 At 1 mol % catalyst a
slight enhancement (TOF up to 13.1 h−1) in rate was observed
when 10 mol % NaCl was added to the reaction (Table 5, entry
5). When 25 mol % Cl− was added, a slightly lower conversion
and TOF was observed (12.7 h−1 89% at 7 h entry 6). The
addition of mercury had a slight inhibitory effect on catalysis
(Table 5, entries 2 and 4, with additional data available in
Supporting Information). These mercury experiments are far
from conclusive, but do suggest a combination of heteroge-
neous and homogeneous mechanisms.
Table 6. Hydration of Various Nitriles Catalyzed by [6]Cl
Catalyst Scope. The catalytic activity of [6]Cl was further
explored and extended to the hydration of various aromatic,
aliphatic, and vinyl nitriles (Table 6). All nitriles, with the
exception of acrylonitrile, were converted to their correspond-
ing amides with 47−99% conversion in 24 h as determined by
GC-MS (isolated yields ranged from 36% to 85%). Substituted
benzonitriles were successfully converted to the corresponding
amides with those containing electron-withdrawing groups
(entries 7−9) obtained in better conversion compared to
benzonitriles with electron-donating groups (entries 2−6).
Hydration of o-tolunitrile (entry 2) was found to be less
efficient compared to that of m- or p-tolunitrile (entries 3−4)
attributed to the steric hindrance of o-tolunitriles. Hydration of
heteroaromatics has been reported to be more challenging due
to the strong coordinating ability of the heteroatom to the
metal. Picolinamide can be obtained in a moderate conversion
(47% after 24 h) by hydrating 2-cyanopyridine (entry 10).
Aliphatic nitriles (entries 11−14) were also hydrated to the
corresponding amides in 24 h. Transformation of 4-
methylbenzyl cyanide to the amide reached a 93% conversion
in 24 h (entry 11). Heptyl cyanide was converted to octamide
in a moderate conversion (42% after 7 h, entry 12). The bulky
pivalonitrile was converted into pivalamide with a 79%
conversion after 24 h (entry 13). The hydration of acrylonitrile
did not result in a clean reaction as evidenced by GC-MS
analysis.59
In summary, the insertion of imines into the C−Li bond of
PTA-Li has provided access to a series of β-aminophosphine
ligands (1−3). These ligands function as hemilabile ligands to
ruthenium with both κ1-P and κ2-P,N coordination modes
observed depending on solvent and counterion. Presumably
due to the presence of the hemilabile amine functionality a
ruthenium arene complex of ligand 3 was a highly active
catalyst for the hydration of nitriles in water with tolerance for
air. Although some catalyst decomposition was observed during
hydration, 6 showed excellent efficiency for aqueous nitrile
hydration with tolerance toward a variety of functional groups
and air. It is unclear, at this point, if the high activity is due to
activation of water by the pendant amine or if the amine is
helping push the product amide off of the metal center. As the
hemilabile nature of ligand 3 appears important for catalytic
hydration, studies are currently underway focused on the role of
the pendant amine and the hemilabile nature of ligands 1−3.
a
Conditions: nitrile (1 mmol), [6]Cl (5 mol %), H2O (3 mL), 100 °C,
b
in air. GC yields of amide after 7 h (24 h yield in parentheses).
c
d
Isolated by column chromatography. TOF calculated using %
e
conversion at 7 h. 0.2 mL DME was added to help with solubility.
f
The hydration of acrylonitrile did not result in a clean reaction as
evidenced by GC-MS analysis (see Supporting Information).
EXPERIMENTAL SECTION
■
Materials and Methods. Unless otherwise noted all manipu-
lations were performed on a double-manifold Schlenk vacuum line
under nitrogen or in a nitrogen-filled glovebox. Solvents were freshly
distilled from standard drying reagents (Na/benzophenone for THF
and hexanes; Mg/I2 for methanol) or dried with activated molecular
sieves and degassed with nitrogen, prior to use. n-Butyllithium,
benzonitrile, o-tolunitrile, m-tolunitrile, p-tolunitrile, p-methoxybenzo-
nitrile, p-cyanophenol, p-nitrobenzonitrile, p-bromobenzonitrile, p-
cyanobenzaldehyde, 2-cyanopyridine, 4-methylbenzyl cyanide, heptyl
cyanide, pivalonitrile, acrylonitrile, and deuterated NMR solvents were
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Inorganic Chemistry
Article
3
obtained from commercial sources and used as received. Tetrakis-
(hydroxymethyl)phosphonium chloride was obtained from Cytec and
used without further purification. 1,3,5-Triaza-7-phosphaadamantane
(PTA),68 PTA-Li,52 N-benzylideneaniline (PhNCHPh),69 N-(4-
methoxybenzylidene)aniline (PhNCH(p-C6H4OCH3)),68 N-
(diphenylmethylene)aniline (PhNCPh2),68 and [(η6-C6H5CH3)-
RuCl2]270 were synthesized as reported in the literature. NMR spectra
were recorded on a Varian NMR System 400 spectrometer with
chemical shifts reported in ppm. 1H and 13C NMR spectra were
referenced to residual solvent relative to tetramethylsilane (TMS).
Phosphorus chemical shifts are relative to an external reference of 85%
H3PO4 in D2O with positive values downfield of the reference. IR
spectra were recorded on Perkin-Elmer 2000 FT-IR spectrometer as a
KBr pellet for solid samples. GC-MS analyses were obtained using a
Varian CP 3800 GC (DB5 column) equipped with a Saturn 2200 MS
and a CP 8410 autoinjector or an Agilent 7890A GC equipped with an
Agilent 5975C inert MSD with triple axis detector and an Agilent 7693
autosampler. X-ray crystallographic data were collected at 100( 1) K
on a Bruker APEX CCD diffractometer with Mo Kα radiation (λ =
0.710 73 Å) and a detector-to-crystal distance of 4.94 cm. Data
collection was optimized utilizing the APEX 2 software with 0.5°
rotation between frames. Data integration, correction for Lorentz and
polarization effects, and final cell refinement were performed using
SAINTPLUS and corrected for absorption using SADABS. The
structures were solved by direct methods and refined using SHELXTL,
version 6.10. All non-hydrogen atoms were refined anisotropically and
hydrogen atoms placed in calculated positions. Crystallographic data
and data collection parameters are listed in Table 2-S (see Supporting
Information).
NCH2N, RS/SR), 66.4 (d, JPC = 3.0 Hz, NCH2N, RR/SS), 64.4 (d,
1JPC = 21.7 Hz, PCHN, RS/SR), 64.3 (d, 1JPC = 19.5 Hz, PCHN, RR/
2
2
SS), 59.0 (d, JPC = 10.6 Hz, PCHCHN, RS/SR), 58.6 (d, JPC = 14.9
Hz, PCHCHN, RR/SS), 51.8 (d, JPC = 20.2 Hz, PCH2N, RS/SR),
1
1
1
51.0 (d, JPC = 20.9 Hz, PCH2N, RR/SS), 50.7 (d, JPC = 20.2 Hz,
1
PCH2N, RR/SS), 47.5 (d, JPC = 24.6 Hz, PCH2N, RR/SS), 47.1 (d,
1JPC = 24.6 Hz, PCH2N, RS/SR). 31P{1H} NMR (162 MHz, CDCl3): δ
−102.4 (s, RS/SR), −105.9 (s, minor). IR (KBr, cm−1): 3371 (υNH).
HRMS (ESI, CH3OH) m/z calcd for C19H23N4P: [M]+ 338.1660;
found 338.1651. Crystals suitable for X-ray diffraction were obtained
by slow evaporation of a 1:1 CH2Cl2/CH3CN solution of 1, resulting
in colorless blocks over the course of a few days. RS/SR enantiomers
were separated from the diastereomeric mixture by repeated
recrystallization from THF/hexane (1:10) as a yellow powder (948
mg, 27% yield). The 1H, 13C{1H}, and 31P{1H} NMR assignments and
spectra of pure RS/SR isomer are included in the Supporting
Information.
Synthesis of PTA-CH(p-C6H4OCH3)NHPh (2). A suspension of
PTA-Li (1.69 g, 10.4 mmol) in THF (40 mL) was cooled to −78 °C,
and a THF solution (20 mL) of N-(4-methoxybenzylidene)aniline
(2.23 g, 10.6 mmol) was added via cannula. The resulting mixture was
kept at −78 °C for 30 min, after which the solution was slowly warmed
to room temperature. After stirring for 1 h, an orange homogeneous
solution formed. Following 2 h of stirring, distilled water (3 mL) was
added to quench to the reaction, and the solvent was removed under
reduced pressure. The resulting residue was dissolved in water (30
mL) and extracted with dichloromethane (40 mL × 4). The combined
organic layers were dried with anhydrous potassium carbonate, filtered
through Celite, and evaporated to dryness under reduced pressure to
give a yellow oil. The yellow oil was taken up into THF (10 mL),
followed by adding hexanes (120 mL) under nitrogen. After being
placed in the freezer for 1 h, this mixture was filtered, washed with
hexane (10 mL × 3), and dried in vacuo to afford the desired product
as a white powder (2.39 g, 62% yield) isolated as a mixture of
diastereomers in a ∼2.1:1 ratio of RS/SR:RR/SS. 1H NMR (400 MHz,
CDCl3): δ 7.38 (d, JHH = 8.4 Hz, 2HRR/SS, Ar), 7.36 (d, JHH = 8.4 Hz,
2HRS/SR, Ar), 7.07 (t, JHH = 7.2 Hz, 2HRS/SR, Ar), 7.06 (t, JHH = 7.2 Hz,
2HRR/SS, Ar), 6.87 (d, JHH = 8.4 Hz, 2HRR/SS, Ar), 6.84 (d, JHH = 8.4
Caution! PTA-Li is a highly pyrophoric solid, igniting violently upon
exposure to air.
Synthesis of PTA-CHPhNHPh (1). A suspension of PTA-Li (1.64
g, 10.0 mmol) in THF (40 mL) was cooled to −78 °C, and a THF
solution (20 mL) of N-benzylideneaniline (1.83 g, 10.1 mmol) was
added via cannula. The resulting mixture was kept at −78 °C for 30
min, after which the solution was slowly warmed to room temperature.
After stirring for 1 h, an orange homogeneous solution formed.
Following 2 h of stirring, distilled water (3 mL) was added to quench
the reaction, and the solvent was removed under reduced pressure.
The resulting residue was dissolved in water (30 mL) and extracted
with dichloromethane (40 mL × 4). The combined organic layers
were dried with anhydrous potassium carbonate, filtered through
Celite, and evaporated to dryness under reduced pressure to give a
yellow oil. The yellow oil was taken up into THF (10 mL), followed
by adding hexanes (120 mL) under nitrogen. After being placed in the
freezer for 1 h, this mixture was filtered, washed with hexane (10 mL ×
3), and dried in vacuo to afford the desired product as a pale yellow
powder (2.13 g, 63% yield) isolated as a mixture of diastereomers in a
Hz, 2HRS/SR, Ar), 6.65 (t, JHH = 7.6 Hz, 1HRR/SS, Ar), 6.63 (t, JHH
=
8.40 Hz, 1HRS/SR, Ar), 6.55 (d, JHH = 8.8 Hz, 2HRR/SS, Ar), 6.53 (d, JHH
= 10.4 Hz, 2HRS/SR, Ar), 4.93−4.84 (br. m, NH), 4.87−4.83 (m,
1HRR/SS, NCH2N), 4.82−4.77 (m, 1HRS/SR, PCHCHN), 4.68−4.62
(m, 1HRR/SS, PCHCHN), 4.73−4.62 (m, 2HRS/SR + 2HRR/SS, NCH2N),
4.60−4.25 (m, 4HRS/SR + 3HRR/SS, NCH2N), 4.21−4.10 (m, 1HRS/SR
+
2HRR/SS, PCH2N), 4.09−3.99 (m, 1HRR/SS, PCH2N), 4.04−3.97 (m,
1HRS/SR, PCHN), 3.94−3.85 (m, 1HRS/SR + 1HRR/SS, PCH2N), 3.77 (s,
3HRR/SS, OCH3), 3.76 (s, 3HRS/SR, OCH3), 3.74−3.66 (m, 1HRS/SR
PCH2N), 3.65−3.60 (m, 1HRR/SS, PCHN), 3.59−3.51 (m, 1HRS/SR
,
,
1
∼3.5:1 ratio of RS/SR:RR/SS. H NMR (400 MHz, CDCl3): δ 7.48
PCH2N). 13C{1H} NMR (100 MHz, CDCl3): δ 159.2 (s, Ar, RR/SS),
159.0 (s, Ar, RS/SR), 148.2 (s, Ar, RR/SS), 146.9 (s, Ar, RS/SR), 133.5
(d, JHH = 7.2 Hz, 2HRR/SS, Ar), 7.45 (d, JHH = 7.2 Hz, 2HRS/SR, Ar),
7.33 (t, JHH = 7.2 Hz, 2HRR/SS, Ar), 7.30 (t, JHH = 7.2 Hz, 2HRS/SR, Ar),
3
3
(d, JPC = 2.3 Hz, Ar, RS/SR), 133.3 (d, JPC = 3.0 Hz, Ar, RR/SS),
7.26−7.20 (m, 1HRS/SR + 1HRR/SS, Ar), 7.07 (t, JHH = 7.6 Hz, 2HRS/SR
Ar), 7.05 (t, JHH = 7.6 Hz, 2HRR/SS, Ar), 6.65 (t, JHH = 7.6 Hz, 1HRR/SS
,
,
129.2 (d, 4JPC = 3.0 Hz, Ar, RR/SS), 129.1 (s, Ar, RS/SR), 129.0 (s, Ar,
4
RR/SS), 128.1 (d, JPC = 2.3 Hz, Ar, RS/SR), 117.8 (s, Ar, RR/SS),
Ar), 6.63 (t, JHH = 7.6 Hz, 1HRS/SR), 6.55 (d, JHH = 7.6 Hz, 2HRR/SS),
6.53 (d, JHH = 7.6 Hz, 2HRS/SR), 4.92−4.88 (br. m, NH), 4.88−4.86
(m, 1HRR/SS, NCH2N), 4.86−4.80 (m, 1HRS/SR, PCHCHN), 4.74−
4.61 (m, 2HRS/SR + 2HRR/SS, NCH2N; 1HRR/SS, PCHCHN), 4.60−4.25
117.5 (s, Ar, RS/SR), 114.0 (s, Ar, RR/SS), 113.9 (s, Ar, RS/SR), 113.9
(s, Ar, RR/SS), 113.6 (s, Ar, RS/SR), 77.3 (s, NCH2N, RS/SR), 76.0
(s, NCH2N, RR/SS), 74.3 (d, 3JPC = 2.3 Hz, NCH2N, RS/SR), 74.2 (d,
3JPC = 2.2 Hz, NCH2N, RR/SS), 67.3 (d, JPC = 3.0 Hz, NCH2N, RS/
3
(m, 4HRS/SR + 3HRR/SS, NCH2N), 4.21−4.07 (m, 1HRS/SR + 2HRR/SS
PCH2N), 4.09−3.99 (m, 1HRR/SS, PCH2N), 4.04−3.97 (m, 1HRS/SR
,
,
SR), 66.4 (d, 3JPC = 2.2 Hz, NCH2N, RR/SS), 64.5 (d, 1JPC = 18.7 Hz,
PCHN, RR/SS), 64.3 (d, 1JPC = 21.7 Hz, PCHN, RS/SR), 58.4 (d, 2JPC
PCHN), 3.94−3.85 (m, 1HRS/SR + 1HRR/SS, PCH2N), 3.74−3.66 (m,
1HRS/SR, PCH2N), 3.65−3.60 (m, 1HRR/SS, PCHN), 3.59−3.51 (m,
1HRS/SR, PCH2N). 13C{1H} NMR (100 MHz, CDCl3): 148.1 (s, Ar,
2
= 10.4 Hz, PCHCHN, RS/SR), 57.9 (d, JPC = 15.0 Hz, PCHCHN,
1
RR/SS), 55.2 (s, OCH3, RS/SR + RR/SS), 51.8 (d, JPC = 20.2 Hz,
1
3
PCH2N, RS/SR), 51.0 (d, JPC = 20.9 Hz, PCH2N, RR/SS), 47.4 (d,
RR/SS), 146.9 (s, Ar, RS/SR), 141.9 (d, JPC = 1.5 Hz, Ar, RS/SR),
1JPC = 24.6 Hz, PCH2N, RR/SS), 47.1 (d, 1JPC = 24.6 Hz, PCH2N, RS/
SR). 31P{1H} NMR (162 MHz, CDCl3): δ −102.1 (s, RS/SR), −105.9
(s, RR/SS). IR (KBr, cm−1): 3360 (υNH). HRMS (ESI, CH3OH) m/z
calcd for C20H25N4OP: [M]+ 368.1766; found 368.1766. RS/SR
enantiomers were separated from the diastereomeric mixture by
repeated recrystallizations from THF/hexane (1:10) as a yellow
141.5 (d, 3JPC = 2.2 Hz, Ar, RR/SS), 129.2 (s, Ar, RS/SR), 129.1 (s, Ar,
4
RR/SS), 128.6 (s, Ar, RS/SR), 128.5 (s, Ar, RR/SS), 128.2 (d, JPC
=
3.7 Hz, Ar, RR/SS), 127.9 (s, Ar, RR/SS), 127.6 (s, Ar, RS/SR), 127.1
(d, 4JPC = 2.3 Hz, Ar, RS/SR), 117.8 (s, Ar, RR/SS), 117.6 (s, Ar, RS/
SR), 114.0 (s, Ar, RR/SS), 113.6 (s, Ar, RS/SR), 77.3 (s, NCH2N, RS/
3
SR), 76.1 (s, NCH2N, RR/SS), 74.2 (d, JPC = 3.0 Hz, NCH2N, RS/
3
3
1
SR), 73.7 (d, JPC = 3.0 Hz, NCH2N, RR/SS), 67.4 (d, JPC = 3.7 Hz,
powder (1.10 g, 30% yield). The H, 13C{1H}, and 31P{1H} NMR
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Inorganic Chemistry
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assignments and spectra of pure RS/SR isomer are included in the
Supporting Information. Colorless crystals suitable for X-ray
diffraction were obtained as blocks by slow evaporation of a 1:1
CH2Cl2/CH3OH solution of PTA-CH(p-C6H4OCH3)NHPh (RS/SR
enantiomers) over the course of a few days.
(s, C6H5CH3), 80.22 (d, JPC = 5 Hz, PCHCHN), 79.82 (s, C6H5CH3),
3
3
75.12 (d, JPC = 5 Hz, NCH2N), 72.64 (d, JPC = 8 Hz, NCH2N),
3
65.88 (d, JPC = 8 Hz, NCH2N), 65.47 (d, JPC = 8 Hz, C6H5CH3),
64.14 (d, JPC = 21 Hz, PCHC), 51.66−51.44 (m, PCH2N), 50.68 (d,
1JPC = 15 Hz, PCH2N), 17.63 (s, C6H5CH3). 31P{1H} NMR (162
Synthesis of PTA-CPh2NHPh (3). A suspension of PTA-Li (1.64
g, 10.0 mmol) in THF (40 mL) was cooled to −78 °C, and a THF
solution (20 mL) of N-(diphenylmethylene)aniline (2.60 g, 10.1
mmol) was added via cannula. The resulting mixture was kept at −78
°C for 30 min, after which the solution was slowly warmed to room
temperature. After stirring for 1 h, an orange homogeneous solution
formed. Following 2 h of stirring, distilled water (3 mL) was added to
quench to the reaction, and the solvent was removed under reduced
pressure. The resulting residue was dissolved in water (30 mL) and
extracted with dichloromethane (40 mL × 4). The combined organic
layers were dried with anhydrous potassium carbonate, filtered
through Celite, and evaporated to dryness under reduced pressure
to give a yellow oil. The yellow oily crude product was taken up into
THF (10 mL), followed by adding hexanes (120 mL) under nitrogen.
After being placed in the freezer for 1 h, this mixture was filtered,
washed with hexane (10 mL × 3), and dried in vacuo to afford the
desired product as a pale yellow crystalline powder (3.18 g, 77% yield).
1H NMR (400 MHz, CDCl3): δ 7.85 (d, JHH = 8.0 Hz, 2H, Ar), 7.77
(d, JHH = 7.2 Hz, 2H, Ar), 7.45−7.38 (m, 3H, Ar), 7.33−7.29 (m, 2H,
Ar), 7.25−7.22 (m, 1H, Ar), 6.89 (dd, JHH = 8.8 and 7.6 Hz, 2H), 6.52
(t, JHH = 7.2 Hz, 1H, Ar), 6.41 (br. s, 1H, NH), 6.23 (dd, JHH = 8.8 and
1.2 Hz, 2H, Ar), 4.88, 4.69 (AB quartet, J = 13.2 Hz, 2H, NCH2N),
4.50 (s, 1H, PCHN), 4.46, 4.33 (AB quartet, J = 13.2 Hz, 2H,
NCH2N), 4.08, 3.56 (AB quartet, J = 13.6 Hz, 2H, NCH2N), 4.00 (td,
J = 14.0 and 1.8 Hz, 1H, PCH2N), 3.83−3.74 (m, 1H, PCH2N), 3.53
(t, J = 14.0 Hz, 1H, PCH2N), 3.43−3.35 (m, 1H, PCH2N). 13C{1H}
NMR (100 MHz, CDCl3): δ 145.5 (d, JPC = 1.5 Hz, Ar), 142.4 (d, JPC
= 2.3 Hz, Ar), 138.4 (s, Ar), 130.6 (d, JPC = 7.5 Hz, Ar), 129.1 (s, Ar),
128.5 (s, Ar), 128.2 (s, Ar), 128.1 (s, Ar), 127.8 (s, Ar), 127.3 (s, Ar),
MHz, CD3OD): δ −10.39 (s), −17.24 (s), −29.91 (s). ESI-MS
(positive, CH3OH): m/z = 566.76 for [(η6-C6H5CH3)RuCl(PTA-
CHPhNHPh)]+. HRMS (ESI, CH3OH) m/z calcd for
C26H31ClN4PRu: [M − Cl]+ 561.1051; found 561.1039.
Synthesis of [(η6-C6H5CH3)RuCl(κ2-(P,N)PTA-CH(p-
C6H4OCH3)NHPh)]Cl ([5]Cl). [(η6-C6H5CH3)RuCl(μ-Cl)]2 (136
mg, 0.26 mmol) and PTA-CH(p-C6H4OCH3)NHPh (190 mg, 0.52
mmol) were stirred in CH2Cl2 (20 mL) overnight, during which time a
homogeneous mixture formed. The solution was filtered through
Celite, and the solvent was removed under reduced pressure. The
residue was dissolved in minimum CH2Cl2 (∼10 mL), and hexane (80
mL) was added to precipitate the product. The precipitate was filtered
and washed with hexane (5 mL × 2) to give an orange solid (280 mg,
1
89% yield). H NMR (400 MHz, CD3OD): 7.72 (d, 1H, JHH = 8 Hz,
Ar), 7.60−7.48 (m, 1H, Ar), 7.42 (t, 1H, JHH = 8 Hz, Ar), 7.28−6.98
(m, 6H, Ar), 5.98−5.88 (m, 1H, C6H5CH3), 5.50 (t, 1H, JHH = 4.0 Hz,
C6H5CH3), 5.30−5.10 (m, 2H, C6H5CH3), 5.05 (d, 1H, J = 8 Hz,
C6H5CH3), 5.00−4.69 (m, 3H, NCH2N; 1H, PCHCHN; 3H,
PCH2N), 4.59 (d, 2H, J = 12 Hz, NCH2N), 4.43−4.27 (m, 1H,
PCHN; 1H, PCH2N), 4.22 (d, 1H, J = 12 Hz, NCH2N), 3.33 (s, 3H,
OCH3), 2.07 (s, 3H, C6H5CH3). 13C{1H} NMR (100 MHz, CD3OD):
δ 150.5 (s, Ar), 136.0 (d, JPC = 12 Hz, Ar), 130.6 (d, JPC = 12 Hz, Ar),
130.0 (s, Ar), 129.9 (s, Ar), 128.7 (s, Ar), 127.5 (s, Ar), 122.1 (s, Ar),
121.8 (s, Ar), 111.6 (d, JPC = 4.5 Hz, C6H5CH3), 99.9 (d, JPC = 9.0 Hz,
C6H5CH3), 94.6 (d, JPC = 2.2 Hz, C6H5CH3), 81.7 (s, C6H5CH3), 81.6
(s, C6H5CH3), 81.2 (s, C6H5CH3), 76.6 (d, JPC = 4.5 Hz, NCH2N),
74.0 (d, JPC = 7.5 Hz, NCH2N), 67.3 (d, JPC = 7.4 Hz, NCH2N), 66.8
(d, JPC = 8.1 Hz, PCHCHN), 65.6 (d, JPC = 21.7 Hz, PCHN), 52.9 (d,
JPC = 12.7 Hz, PCH2N), 52.1 (d, JPC = 14.3 Hz, PCH2N), 19.2 (s,
C6H5CH3). 31P{1H} NMR (162 MHz, CD3OD): δ −10.6 (s), −17.4
(s). ESI-MS (positive, CH3OH): m/z = 597.42 for [(η6-C6H5CH3)-
RuCl(PTA-CH(p-C6H4OCH3)NHPh)]+. HRMS (ESI, MeOH) m/z
calcd for C27H33ClN4OPRu: [M − Cl]+ 591.1157; found 591.1141.
Orange crystals suitable for X-ray diffraction were obtained as plates by
slow evaporation of a MeOH solution of the complex over the course
of a few days.
3
116.6 (s, Ar), 115.4 (s, Ar), 79.4 (s, NCH2N), 74.6 (d, JPC = 2.3 Hz,
1
2
NCH2N), 72.5 (d, JPC = 26.9 Hz, PCHN), 67.2 (d, JPC = 11.3 Hz,
CPh2NHPh), 66.2 (d, 3JPC = 3.0 Hz, NCH2N), 53.4 (d, 1JPC = 20.2 Hz,
PCH2N), 47.8 (d, 1JPC = 25.4 Hz, PCH2N). 31P{1H} NMR (162 MHz,
CDCl3): δ −97.7 (s). IR (KBr, cm−1): 3323 (sharp, υNH). HRMS (ESI,
CH3OH) m/z calcd for C25H27N4P: [M]+ 414.1973; found 414.1981.
Colorless crystals suitable for X-ray diffraction were obtained as blocks
by slow evaporation of a mixed CH2Cl2/CH3OH solution of 3 over
the course of a few days.
Synthesis of [(η6-C6H5CH3)RuCl(κ2-(P,N)PTA-CPh2NHPh)]Cl
([6]Cl). [(η6-C6H5CH3)RuCl(μ-Cl)]2 (137 mg, 0.25 mmol) and
PTA-CPh2NHPh (211 mg, 0.51 mmol) were stirred in CH2Cl2 (20
mL) overnight, during which time a homogeneous mixture formed.
The solution was filtered through Celite, and the solvent was removed
under reduced pressure. The residue was dissolved in minimum of
CH2Cl2 (∼10 mL), and hexane (80 mL) was added to precipitate the
product. The precipitate was filtered and washed with hexane (5 mL ×
Synthesis of the Oxides of 1−3 (1a−3a). The phosphine oxides
(1a−3a) were obtained quantitatively by the addition of 0.2 mmol
30% H2O2 to a 1 mL D2O solution of 1−3 (0.1 mmol). 31P{1H} NMR
(162 MHz, CDCl3): δ 1a, −2.9 (s), −5.7 (s); 2a, −2.9 (s), −5.7 (s);
3a, −1.5 (s).
Synthesis of [(η6-C6H5CH3)RuCl(κ2-(P,N)PTA-CHPhNHPh)]Cl
([4]Cl). [(η6-C6H5CH3)RuCl(μ-Cl)]2 (106 mg, 0.2 mmol) and PTA-
CHPhNHPh (137 mg, 0.4 mmol) were stirred in CH2Cl2 (20 mL)
overnight, during which time a homogeneous solution formed. The
solution was filtered through Celite and evaporated to dryness under
reduced pressure. The resulting residue was dissolved in minimum
CH2Cl2, and hexane was added until an orange precipitate was
observed. The solution was placed in the freezer for one hour, and the
precipitate was filtered, washed with hexane, and dried in vacuo to give
1
2) to give an orange solid (306 mg, 90% yield). H and 13C NMR
spectra were obtained at 55 °C due to the slightly broadening
spectrum observed at room temperature. 1H NMR (400 MHz,
CD3OD, 55 °C): δ 8.68 (d, 1H, JHH = 8.4 Hz, Ar), 7.86 (t, 1H, JHH
7.8 Hz, Ar), 7.61 (t, 2H, JHH = 7.4 Hz, Ar), 7.33−7.12 (m, 8H, Ar),
6.92 (m, 2H, Ar), 6.76 (d, 1H, JHH = 8.0 Hz, Ar), 6.40 (d, 1H, JHH
=
=
7.6 Hz, Ar), 6.14−6.08 (m, 1H, C6H5CH3), 6.00 (t, 1H, J = 5.2 Hz,
C6H5CH3), 5.60 (t, 1H, J = 5.6 Hz, C6H5CH3), 5.35 (d, 1H, J = 6.0
Hz, C6H5CH3), 5.10 (d, 1H, J = 6.0 Hz, C6H5CH3), 5.01 (d, J = 10.8
Hz, 1H, PCHN), 4.99 (d, J = 15.2 Hz, 1H, PCH2N), 4.82 (d, J = 13.2
Hz, 1H, NCH2N), 4.71−4.63 (m, 2H, PCH2N; 2H, NCH2N), 4.46 (d,
J = 13.2 Hz, 1H, NCH2N), 4.37 (d, J = 15.2 Hz, 1H, PCH2N), 3.88 (d,
J = 13.6 Hz, 1H, NCH2N), 2.54 (d, J = 14.0 Hz, 1H, NCH2N), 2.00 (s,
3H, C6H5CH3). 13C{1H} NMR (100 MHz, CD3OD): δ 150.8 (d, JPC
= 1.5 Hz, Ar), 139.0 (s, Ar), 139.0 (s, Ar), 137.8 (s, Ar), 134.5 (s, Ar),
131.5 (s, Ar), 131.0 (s, Ar), 130.8 (s, Ar), 130.5 (s, Ar), 130.4 (s, Ar),
130.4 (s, Ar), 129.5 (s, Ar), 128.6 (s, Ar), 125.0 (s, Ar), 124.2 (s, Ar),
113.5 (d, JPC = 5.9 Hz, C6H5CH3), 101.3 (d, JPC = 8.2 Hz, C6H5CH3),
93.6 (d, JPC = 1.5 Hz, C6H5CH3), 82.8 (s, C6H5CH3), 82.4 (s,
C6H5CH3), 82.0 (s, C6H5CH3), 79.0 (d, JPC = 1.9 Hz, NCH2N), 77.9
1
a yellow orange solid (206 mg, 85% yield). H NMR (400 MHz,
CD3OD): δ 7.72 (d, J = 7 Hz, 1H, Ar), 7.62 (d, J = 6 Hz, 1H, Ar), 7.45
(dd, J = 11 and 7 Hz, 1H, Ar), 7.29−7.04 (m, 6H, Ar), 7.04−6.95 (m,
1H, Ar), 5.93−5.84 (m, 1H, C6H5CH3), 5.50−5.41 (m, 1H,
C6H5CH3), 5.22 (d, J = 6 Hz, 1H, C6H5CH3), 5.20−5.11 (m, 1H,
PCH2N), 5.08 (d, J = 6 Hz, 1H, C6H5CH3), 5.05−4.95 (m, 1H,
PCHCHN), 4.84−4.75 (m, 2H PCH2N; 1H NCH2N), 4.76−4.71 (m,
1H, C6H5CH3), 4.69 (s, 1H, NCH2N), 4.66−4.57 (m, 2H, NCH2N),
4.38 (dd, J = 19, 11 Hz, 2H, NCH2N; 1H PCH2N), 4.24 (d, J = 10 Hz,
1H, PCHN), 2.08 (apparent doublet, J = 1 Hz, 3H, C6H5CH3). 13C
NMR (100 MHz, CD3OD): δ 149.08 (s, Ar), 134.60−134.47 (m, Ar),
134.43 (s, Ar), 129.36 (s, Ar), 129.17−129.07 (m, Ar), 128.59 (m, Ar),
127.25 (s, Ar), 126.17 (s, Ar), 98.38 (d, JPC = 8 Hz, C6H5CH3), 93.26
(d, JPC = 3.7 Hz, CPh2), 74.7 (d, JPC = 4.5 Hz, NCH2N), 67.3 (d, JPC
=
1744
dx.doi.org/10.1021/ic301160x | Inorg. Chem. 2013, 52, 1737−1746

Inorganic Chemistry
Article
10.5 Hz, NCH2N), 67.0 (d, JPC = 20.9 Hz, PCHN), 54.3 (d, JPC = 18.0
Hz, PCH2N), 52.0 (d, JPC = 12.0 Hz, PCH2N), 19.2 (s, C6H5CH3).
31P{1H} NMR (162 MHz, CDCl3): δ 0.6 (s, minor), −16.4 (s, minor),
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699.
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−30.6 (s, major). 31P{1H} NMR (162 MHz, CD3OD): δ −0.4 (s). IR
(KBr, cm−1): 3308 (sharp, υNH). ESI-MS (positive, CH3OH): m/z =
643.23 for [(η6-C6H5CH3)RuCl(PTA-CPh2NHPh)]+. HRMS (ESI,
MeOH) m/z calcd for C32H35ClN4PRu: [M − Cl]+ 637.1364; found
637.1378.
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([6]PF6). [(η6-C6H5CH3)RuCl2(PTA-CPh2NHPh)] (342 mg, 0.5
mmol) and potassium hexafluorophosphate (95 mg, 0.51 mmol)
were stirred in CH2Cl2 (20 mL) for two days. The solution was filtered
through Celite to remove KCl, and the solvent was removed under
reduced pressure. The residue was dissolved in a minimum of CH2Cl2
(∼10 mL), and hexane (80 mL) was added to precipitate the product.
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give a yellow-orange solid (329 mg, 86% yield). 1H and 13C{1H} NMR
data are identical to [6]Cl in CD3OD. 31P{1H} NMR (162 MHz,
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CPh2NHPh)]+. Orange crystals suitable for X-ray diffraction were
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spectroscopic data with those reported in the literature. The retention
time/fragmentation observed by GC-MS was also compared to that of
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ASSOCIATED CONTENT
* Supporting Information
Detailed procedures for separation of the diastereomers of 1
and 2, additional catalytic results, crystallographic details (PDF
and CIF), and NMR spectra of all compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
Gobetto, R. Inorg. Chim. Acta 1994, 221, 109−116.
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2011, 40, 2348−2357.
■
S
́ ́ ́
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Lahoz, F. J.; Oro, L. A. Organometallics 2008, 27, 224−234.
(24) Gareau, D.; Sui-Seng, C.; Groux, L. F.; Brisse, F.; Zargarian, D.
Organometallics 2005, 24, 4003−4013.
(25) Thompson, S. M.; Stohr, F.; Sturmayr, D.; Kickelbick, G.;
̈
AUTHOR INFORMATION
Corresponding Author
*E-mail: Frost@unr.edu.
■
Schubert, U. J. Organomet. Chem. 2003, 686, 183−191.
(26) Ahmed, T. J.; Knapp, S. M. M.; Tyler, D. R. Coord. Chem. Rev.
2011, 255, 949−974.
(27) Kukushkin, V. Y.; Pombeiro, A. J. L. Inorg. Chim. Acta 2005,
358, 1−21.
Present Address
†Concordia College at Moorhead, 334F Ivers, Moorhead, MN,
56562.
(28) Kukushkin, V. Y.; Pombeiro, A. J. L. Chem. Rev. 2002, 102,
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Notes
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The authors declare no competing financial interest.
(30) Breno, K. L.; Ahmed, T. J.; Pluth, M. D.; Balzarek, C.; Tyler, D.
R. Coord. Chem. Rev. 2006, 250, 1141.
ACKNOWLEDGMENTS
■
(31) (a) Breno, K. L.; Pluth, M. D.; Tyler, D. R. Organometallics
2003, 22, 1203. (b) Breno, K. L.; Pluth, M. D.; Landorf, C. W.; Tyler,
D. R. Organometallics 2004, 23, 1738.
The authors thank the National Science Foundation CAREER
program (CHE-0645365) and the donors of the American
Chemical Society Petroleum Research Fund (PRF 43574-G3)
for support. K.E. thanks the NSF-REU program (CHE-
0552816) for summer support. The NSF is also acknowledged
for the X-ray and NMR facilities at UNR (CHE-0226402 and
CHE-0521191).
(32) Oshiki, T.; Yamashita, H.; Sawada, K.; Utsunomiya, M.;
Takahashi, K.; Takai, K. Organometallics 2005, 24, 6287.
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NOTE ADDED IN PROOF
■
After acceptance of this manuscript, Tyler and co-workers
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