Investigation of Nitrile Hydration Chemistry by Two Transition Metal Hydroxide Complexes: Mn-OH and Ni-OH Nitrile Insertion Chemistry

Article abstract of DOI:10.1021/acs.organomet.8b00687

Herein we describe the synthesis of a series of nickel complexes, including the formation of [(^iPrPN^HP)Ni(PMe₃)][BPh₄] (^iPrPN^HP = HN(CH₂CH₂(PiPr₂))₂). The ability of this phosphine complex to perform the 1,2-addition of H₂O to produce the Ni-OH species [(^iPrPN^HP)NiOH][BPh₄] has been investigated. The nucleophilicity of the hydroxide moiety of both [(^iPrPN^HP)NiOH][BPh₄] and the previously reported (^iPrPN^HP)MnOH(CO)₂ was investigated through the hydration of aryl and alkyl nitriles, leading to the formation of a number of metal carboxamide (RC(O)NH^-) bonds. This reactivity generated complexes with the general structures of [(^iPrPN^HP)Ni(NHC(O)R)][BPh₄] for nickel and (^iPrPN^HP)Mn(NHC(O)R)(CO)₂ for manganese. Under catalytic conditions, the hydration of nitriles using nickel complexes yielded only a single turnover. However, (^iPrPN^HP)MnOH(CO)₂ produced several turnovers, and the reaction conditions were probed for optimization.

Full text of DOI:10.1021/acs.organomet.8b00687

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Investigation of Nitrile Hydration Chemistry by Two Transition
Metal Hydroxide Complexes: Mn−OH and Ni−OH Nitrile Insertion
Chemistry
Nickolas H. Anderson, James M. Boncella,* and Aaron M. Tondreau*
Chemistry Division, Los Alamos National Laboratory, MS J514, Los Alamos, New Mexico 87545, United States
*
S Supporting Information
ABSTRACT: Herein we describe the synthesis of a series of
iPr
H
nickel complexes, including the formation of [( PN P)Ni-
iPr
H
(
PMe )][BPh ] ( PN P = HN(CH CH (PiPr )) ). The
3 4 2 2 2 2
ability of this phosphine complex to perform the 1,2-addition
iPr
H
of H O to produce the Ni−OH species [( PN P)NiOH]-
2
[
BPh ] has been investigated. The nucleophilicity of the
hydroxide moiety of both [( PN P)NiOH][BPh ] and the
4
iPr
H
4
iPr
H
previously reported ( PN P)MnOH(CO) was investigated
2
through the hydration of aryl and alkyl nitriles, leading to the
−
formation of a number of metal carboxamide (RC(O)NH )
bonds. This reactivity generated complexes with the general
iPr
H
structures of [( PN P)Ni(NHC(O)R)][BPh ] for nickel
4
iPr
H
and ( PN P)Mn(NHC(O)R)(CO) for manganese. Under
2
catalytic conditions, the hydration of nitriles using nickel complexes yielded only a single turnover. However,
iPr
H
(
PN P)MnOH(CO) produced several turnovers, and the reaction conditions were probed for optimization.
2
INTRODUCTION
elimination reaction, and the resultant Mn−OH complex has
■
1
the potential to participate in other stoichiometric or catalytic
Since its discovery, there have been numerous investigations
into the behavior of the PNP-Mn(I) system as a catalyst,
with a number of different applications being uncovered. Beller
4
−6,8−20
iPr
reaction chemistry.
Our prior work with water and manganese has led us to
explore the related 1,2-addition of water with other first row
transition metals supported by the same ligand scaffold,
and co-workers have used this system, starting with the
iPr
H
(
PN P)MnBr(CO) , for the hydrogenation of nitriles,
2
2
iPr
H
PN P. We have had little luck extending the chemistry to
ketones, and aldehydes in the presence of base. Our group
discovered the ability of the dehydrohalogenated complex
iron and cobalt, but the 1,2-addition of water to an analogous
nickel complex provided a second avenue to explore hydration
chemistry with another first row transition metal complex. This
report contains our investigations into the ability of the
iPr
(
PNP)Mn(CO)2 to accomplish the dehydrogenation of
3
formic acid to CO and H . Recently, Gauvin and co-workers
have shown that ( PNP)Mn(CO) is capable of performing
2
2
iPr
2
iPr
H
the acceptorless dehydrogenative coupling of alcohols to esters,
PN P ligand platform to form Ni−OH bonds via 1,2-
as well as isolating the 1,2-addition products of PhCH OH,
2
addition of H O. Prior precedent exists for the formation of
2
iPr
H
iPr
H
EtOH and H : ( PN P)Mn(OCH Ph)(CO) , ( PN P)Mn-
OEt)(CO) , and ( PN P)Mn(H)(CO) , respectively.
2
2
2
Ni−OH bonds (Scheme 1), some arising from surreptitious
iPr
H
4
(
21,22
2
2
water content and Ni−alkyl complexes,
as well as the
More recent progress on the use of this manganese system
for catalysis includes work by Jones on the dimerization of
purposeful formation of such species carried out through salt
metathesis by addition of a metal−hydroxide salt to the
5
ethanol with concomitant water elimination, as well as
23
24
24
starting Ni−X starting complex (X = F, Cl, Br, or
6
catalytic deuterium labeling of alcohols with D O. Pertinent
25−29
2
OTf).
Deprotonation of bound aquo-ligands has also
been performed in the formation Ni−OH complexes.
quite unique case, the Mindiola group reported the synthesis of
to this study, we have shown the ability of this system to
30,31
In a
reversibly activate H O via a 1,2-addition to generate a Mn−
2
iPr
H
7
hydroxide complex ( PN P)MnOH(CO) (5-Mn). This
2
a Ni−OH complex via the two-centered two electron oxidative
rare Mn−OH complex is unique, undergoing the aldehyde−
water shift reaction with aldehydes (transforming aldehydes to
Tol
addition of H O across two Ni(I) centers in [Ni(μ - PNP)] ,
2
2
2
Tol
Tol
forming equal amounts of the ( PNP)Ni−H and ( PNP)-
carboxylic acids with concurrent H release). A report by Liu
2
Tol
NiOH complexes (( PNP) = N[2-P(iPr) -4-methylphenyl] )
2
2
expands this work to provide a general catalytic scheme with
−
OH and alcohols at 160 °C to generate the corresponding
8
carboxylate and dihydrogen. The formation of the metal−
Received: September 18, 2018
hydroxide bond in 5-Mn is reversible via a 1,2-addition/
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00687
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Article
a
43
Scheme 1. Ni−OH Complexes and 1,2-Addition of H O
fashion similar to that of Arnold and co-workers, the
2
iPr
H
synthesis of [( PN P)NiCl][Cl] (1)was accomplished by the
slow addition of the PN P ligand to a slurried solution of
iPr
H
NiCl (DME) in THF, which slowly turned a light orange color
2
over the course of 1 h and was allowed to stir overnight
(
Scheme 2). After this time, precipitation of 1 was induced by
Scheme 2. Synthesis of Complexes 2−4
a
(
2
a−c) Notable and related Ni−OH complexes. (d) 1,2-Addition of
iPr
H O performed by ( PCP)Ni(PPh ) across a NiC bond.
3
3
2
(
Scheme 1b). Borovik reported that addition of H O to
2
solutions of deprotonated bipodal ((bis[N-(tert-butylureayla-
to)-N-ethyl)]methylamine) and tripodal ureate (tris[(N-(tert-
butylureaylato)-N-ethyl)]amine) ligand−Ni complexes, as well
as the tripodal sulfonamide based (N,N′,N″-[2,2′,2″-nitrilotris-
the addition of hexane, and the resultant powder was collected
1
31
by filtration. Analysis of 1 by H and P NMR spectroscopy
confirmed its formation. Complex 1 displays four resonances
1
31
for the iPr-CH in the H NMR spectrum; the P NMR
3
(
ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamido)) li-
spectrum contains a single resonance at 54.2 ppm indicative of
chemically equivalent phosphorus atoms. X-ray quality single
crystals of 1 were isolated by slow evaporation of a dilute THF
solution over an extended period of time and the solid-state
structure is displayed in Figure S1.
gand−Ni system can result in the formation of both 4- and 5-
coordinate ligand hydroxide complexes in a pseudo-1,4-
3
3,34
addition type fashion.
1,2-Addition of H O across
2
metal−ligand bonds is described in a single report from the
iPr
iPr
Piers group, where the starting ( PCP)Ni(PPh ) (( PCP) =
Addition of 1 equiv of potassium tert-butoxide (tBuOK) to a
stirring C H F slurry of 1 results in immediate dissolution of
3
(
bis(2-(di-iso-propylphosphino)phenyl)methene)) is treated
6
5
with H O, resulting in protonation of the carbene ligand
the orange starting material and formation of a dark green
colored solution. Following a short workup, a dark green
2
concomitant with formation of the Ni−OH species (Scheme
3
5
iPr
1
d).
powder identified as ( PNP)NiCl (2) was isolated in excellent
1
31
While several Ni−OH complexes have been synthesized,
yields (85−93%) (Scheme 2). H and P NMR spectroscopic
analysis confirmed the formation of 2. This species displays
two resonances for the isopropyl methyl groups at 1.12 and
reports on their reactivity with respect to their nucleophilicity
26
is sparse, with only a handful of reports studying CO and
2
3
6,37
1
CO
insertion. In addition to studying the formation of
1.34 ppm in the H NMR spectrum, with a single isopropyl
Ni−OH complexes, we wished to probe the nucleophilicity of
both the Ni−OH and Mn−OH species with the respect to
attack on nitriles, which could lead to nitrile hydration. The
hydration of nitriles is a high volume catalytic transformation
in industrial use, with the hydration of acrylonitrile to
methine resonance centered at 2.52 ppm. The single resonance
3
1
in the P NMR spectrum suggests a C symmetric complex.
2v
Structural characterization of 2 was accomplished by cooling a
concentrated hexane solution to −34 °C and its molecular
structure is displayed in Figure S4.
38
acrylamide being carried out on the multiton scale. To our
While we note that 2 would appear to be capable of
knowledge, there are only two Ni−OH complexes proven
performing the 1,2-addition of H O, as is the primary objective
2
3
9,40
capable of catalyzing this transformation,
and no
of this project, attempts at such resulted in an inseparable
milieu of products, possibly a consequence of chloride
dissociation and anion scrambling, with 1 being isolated
from the reaction mixture. The cationic Ni complex
complexes of Mn have been reported for nitrile hydration.
Most of the homogeneous catalysts that are known for nitrile
hydration employ precious metals (Ru, Os, Rh, Ir, Pd,
3
7,41,42
iPr
Pt),
and as such, investigating base metals for this
[( PNP)Ni(PMe )][BPh ], (3), was sought because a neutral
3
4
transformation can ameliorate economic and environmental
concerns. The synthesis of the nickel−hydroxide species is
highlighted, and the related hydration chemistry of nitriles
using this nickel−hydroxide complex is described. Further-
more, the nitrile hydration chemistry catalyzed by known 5-
Mn is also described. This report expands the known reactivity
of a pair of first row transition metal hydroxide complexes, and
allows for a direct comparison between nickel and manganese
in nitrile hydration reactivity.
leaving group, like PMe , would likely cause fewer side
reactions than the anionic chloride. Synthesis of 3 was readily
accomplished via the addition of PMe3 to an equimolar
3
solution of 2 and NaBPh (Scheme 2). The addition of the
4
coordinating ligand is accompanied by an immediate color
change of the solution from dark green to purple along with
the eventual precipitation of NaCl over the course of 1 h.
Complex 3 was isolated as a dark purple powder in excellent
yields. Synthesis of 3 was also accomplished via the addition of
iPr
H
Results and Discussion. In order to obtain a direct
tBuOK to a solution of the dicationic complex [( PN P)Ni-
(PMe )][BPh ] (4), which was synthesized by the addition of
comparison between the reactivity of nickel and manganese,
3
4 2
iPr
the synthesis of a molecular analogue of the ( PNP)Mn-
1 equiv of PMe and 2 equiv of NaBPh to 1 (Scheme 2).
3
4
iPr
(
CO)2 complex, i.e., a “( PNP)Ni” species capable of
Synthetic details as well as structural and spectroscopic
performing the 1,2-addition of H O was undertaken. In
characterization of 4 can be found in Figures S11 and 12.
2
B
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Article
1
Analysis of 3 by H NMR spectroscopy reveals the presence
Analysis of a single crystal of 5-Ni by X-ray diffraction
(Figure 2), grown by slow diffusion of hexane into THF,
31
of the BPh ion and the P NMR spectrum confirms the
4
coordination of PMe to the Ni center, displaying a sharp
3
triplet resonance at 21.61 ppm with a doublet resonance for
iPr
the PNP ligand at 83.50 ppm. Structural characterization of 3
was accomplished by analysis of a dark purple crystal of 3 by
single crystal X-ray diffraction (Figure 1). The square planar Ni
iPr
H
Figure 2. Molecular structure of [( PN P)Ni(OH)][BPh ] (5-Ni)
4
with thermal ellipsoids depicted at 50% probability. Hydrogen atoms,
outer sphere BPh anion, and H-bound THF molecule have been
4
omitted for clarity.
iPr
H
+
confirmed its formation with a single [( PN P)Ni(OH)]
−
fragment, one [BPh ] , and a single inner sphere THF in the
4
iPr
Figure 1. Molecular structure of [( PNP)Ni(PMe )][BPh ] (3)
3
4
asymmetric unit cell. The inner sphere THF is hydrogen
with ellipsoids depicted at 50% probability. Hydrogen atoms and the
iPr
H
bound to the N−H proton of the PN P backbone with a
O(2)−H(1) distance of ∼1.96 Å. The Ni−P and Ni−N
distances seen in 3 compare nicely to those observed in 1 and
outer sphere BPh have been omitted for clarity.
4
center is similar to what was observed in complexes 2 and 4.
Deprotonation of 4 results in a shortening of the Ni−N bond
by ∼0.1 Å as is expected from the increased ionic character on
the amide nitrogen, similar to that noted for 2. Interestingly,
H
42
4
, which are typical for other PN P−Ni complexes. The Ni−
OH bond distances found in the literature vary widely, ranging
between 1.78−2.11 Å, depending upon the trans-influence of
6
−19
the ligand trans to the OH and the charge on the complex.
despite containing a strong trans N-donor, the Ni-PMe bond
3
The Ni−OH bond distance found for 5-Ni of 1.837(1) Å is
similar to other phosphine chelated terminal Ni−OH
complexes with neutral trans-donors.
in 3 does not display any significant increase in bond length
from what was observed in 4, (3: Ni−P 2.208(1) Å, 4: Ni−P
2
.195(1) Å).
With both the Ni−OH, 5-Ni, and Mn−OH, 5-Mn, in hand,
the competency of these complexes to perform the hydration
of nitriles was investigated. Solutions of both 5-Ni and 5-Mn
were treated with 1.1 equiv of acetonitrile (MeCN) for 30 min.
Analysis of the crude reaction mixtures revealed the formation
With the successful isolation of 3, the compound’s ability to
perform 1,2-addition of H O was probed. Addition of a 10%
2
H O/THF solution to a stirring solution of 3 results in a slow
2
color change from purple to red over the course of 3 h.
Removal of the solvent followed by crystallization resulted in
iPr
H
iPr
H
of orange [( PN P)Ni(NHC(O)Me)][BPh
4
] (6-Ni) and
(6-Mn). Performing
identical reactions using benzonitrile (PhCN) resulted in the
the isolation of [( PN P)Ni(OH)][BPh ] (5-Ni) in good
4
iPr
yield (Scheme 3). Analysis of 5-Ni by 31P NMR spectroscopy
yellow ( PNP)Mn(NHC(O)Me)(CO)
2
iPr
H
isolation of both [( PN P)Ni(NHC(O)Ph)][BPh ] (7-Ni)
and ( PNP)Mn(NHC(O)Ph)(CO) (7-Mn) (Scheme 4). All
4
Scheme 3. 1,2-Addition of H O with 3 and the Formation of
iPr
2
2
5-Ni
four amide complexes, 6-Ni, 6-Mn, 7-Ni, and 7-Mn, were also
synthesized by addition of 1 equiv of MeCONH2 or
PhCONH to a stirring THF solution of 3 or an ether
2
iPr
solution of ( PNP)Mn(CO) (Scheme 4).
2
Scheme 4. Synthetic Routes to Nickel and Manganese
Carboxamide Complexes from 5-Ni or 5-Mn or by 1,2-
Addition of the Carboxamide to the Metal−Amide
Precursors
confirms the loss of PMe with only a single resonance noted
3,
in the spectrum at 53.1 ppm. Unlike the recently reported 5-
Mn, shown to form from a nearly thermo-neutral reversible
7
1
,2-addition of water, the 1,2-addition of H O to 3 is not
2
reversible in solution at room temperature. Analysis of crystals
1
of 5-Ni by H NMR spectroscopy displays significant
broadening of the spectrum thought to arise from the
hydrogen-bound THF dissociation/association in solution, a
feature that is resolved at low temperature (−20 °C) (Figure
1
S16). Despite the broad nature of the room temperature H
NMR spectrum, the corresponding 31P and C NMR spectra
31
are sharp (see the Supporting Information).
C
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Figure 3. Molecular structures of (a) 6-Ni, (b) 7-Ni, (c) 6-Mn, (d) 7-Mn, and (e) 8-Mn displayed with ellipsoids at 50% probability level. Select H
atoms, outer sphere solvent molecules, and BPh ions have been excluded for clarity.
4
Ni−carboxamide complexes 6-Ni and 7-Ni were isolated as
orange/yellow powders that are easily crystallized by slow
diffusion of hexane into concentrated THF solutions. Analysis
In order to probe catalytic turnover for the hydration of
nitriles, THF-d solutions of both 7-Ni and 7-Mn were placed
8
in J. Young tubes and studied by variable-temperature NMR
spectroscopy. Even when heated to 55 °C, there was no
obvious release of the amide from either the Ni or Mn
complexes. In an attempt to assist with amide release, THF-d8
solutions of 7-Ni and 7-Mn were treated with a solution of
10% H O/THF-d , and these reaction mixtures were analyzed
1
of these complexes by H NMR spectroscopy reveals multiple
iPrCH3 and iPrCH resonances for both species. This
3
1
observation combined with the presence of a single
P
NMR resonance indicates top-bottom inequivalence in both 6-
Ni and 7-Ni. This structural motif is confirmed by single
crystal X-ray diffraction studies of these compounds (Figure
2
8
1
by H NMR spectroscopy. Analysis of the reaction mixture of
3
a,b).
7-Mn and H O revealed no observable 5-Mn in solution, even
when the solution was heated to 50 °C. The same was noted
2
Both 6-Ni and 7-Ni are cationic square planar complexes
with trans-phosphorus and trans-nitrogen donors, which
display typical Ni−P and Ni−N distances. Much like 5-Ni,
both amide species display hydrogen bonding interactions
between the amide N−H and a lattice-bound molecule of THF
in the case of 7-Ni and the amide carbonyl group of a
neighboring molecule in the lattice of 6-Ni (see the Supporting
Information).
from 7-Ni, even at elevated temperatures or with the addition
of PMe . This suggests that the nickel− and manganese−
3
carboxamide bond is more stable than the corresponding
metal−hydroxide bond. Addition of 1 equiv of PhCN to these
heated H O/THF solutions of 7-Mn and 7-Ni revealed
2
reactivity differences between these complexes. Analysis of the
solution of 7-Mn shows the presence of NH C(O)Ph in
2
Analysis of the Mn−amide complexes by 1H NMR
spectroscopy reveals complexes with top-bottom asymmetry,
1
solution, confirmed by H NMR spectroscopy, demonstrating
that Mn affords some turnover as a PhCN hydration catalyst.
Analysis of the solution of 7-Ni reveals no turnover, with no
iPr
H
similar to the carboxylate ( PN P)Mn(RC(O) )(CO) (R =
2
2
3
H, Ph) complexes previously described. Each displays 4
isopropyl methyl resonances with equivalent isopropyl methine
resonances. The ligand N−H resonances for complexes 6-Mn
and 7-Mn appear very far downfield at 9.98 and 10.17 ppm,
respectively, suggesting a strong H-bonding interaction is
observed release of NH C(O)Ph.
2
Several possible explanations for this difference in reactivity
exist. The first regards the differing ionicity of the two
complexes: The cationic nature of 7-Ni would disfavor the
dissociation of the NHC(O)Ph ligand more than the neutral
manganese complex. Geometry can also play a large role in the
difference of reactivity. The trans configuration of the N−H of
the chelate and the formed carboxamide in the case of 7-Ni
inhibits facile hydrogen transfer from the amine backbone to
the carboxamide, which is needed for product release. The cis
conformation of the N−H and carboxamide in 7-Mn allows for
an easier elimination of the product. Most likely, a
combination of these factors plays a role in the difference in
reactivity observed between nickel and manganese.
4
4
present. Structural characterization was possible by cooling
dilute Et O solutions of 6-Mn, 7-Mn, and another amide
2
iPr
H
complex, ( PN P)Mn(NHC(O)o-Py)(CO) (8-Mn), to
2
yield pale yellow blocklike crystals for single-crystal XRD
analysis (Figure 3c−e). All Mn−amide complexes display
iPr
H
pseudo-octahedral Mn centers with a protonated PN P
ligand, two CO ligands, and a single NHC(O)R ligand. As was
1
suggested in the H NMR data, all complexes display
intramolecular hydrogen bonding interactions between the
iPr
H
carbonyl oxygen and the N−H on the backbone of the PN P
ligand. In 8-Mn, there is additional H-bonding between the
pyridyl nitrogen and proton of the amide group (Figure 3c−e).
With the knowledge that 5-Mn was capable of turning over
the hydration of PhCN, our investigation focused on the
reactivity of various nitriles with the Mn−OH bond. In order
D
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to ascertain whether or not the nucleophilic attack of the
hydroxide on the nitrile was the rate-limiting step of these
hydration reactions, competition studies were performed with
a variety of para-substituted aryl nitriles. A solution containing
Scheme 5. Possible Mechanisms of Nitrile Hydration by 5-
Mn
a
1
equiv of both PhCN and the para-substituted nitrile,
XC H −CN, (X = CF , Br, Me, OMe, and NMe ) was added
6
4
3
2
to a stirring solution containing 1 equiv of 5-Mn. The resulting
1
mixture was analyzed by H NMR spectroscopy, and the ratio
of the two product complexes was analyzed. Owing to the
single and irreversible nature of the insertion, the ratio of
products will give the relative rate of nitrile insertion into the
OH bond of 5-Mn, and the resulting Hammett plot is given in
Figure 4. There is a clear correlation between the electro-
a
iPr
(
a) Addition of nitrile to ( PNP)Mn(CO) does not lead to the
2
Figure 4. Competition experiment for the insertion of nitrile into the
Mn−OH bond, with relative insertion rates plotted versus the
Hammett parameter.
iPr
formation of ( PNP)Mn(MeCN)(CO) . (b) Mechanism whereby
2
the nitrile displaces the hydroxide, forming a closely associated
−
[Mn][OH] salt pair and a manganese-coordinated nitrile that is the
electrophile for [OH] nucleophilic attack. (c) Displacement of a
single arm of the PNP scaffold allows for the migratory insertion of
the nitrile into the metal hydroxide. (d) Proposed close-association
pathway for nitrile hydration assisted by H-bonding to ligand N−H.
philicity of the nitrile carbon and the relative rate of insertion.
All of the para-substituted arylamide-Mn complexes,
iPr
iPr
iPr
iPr
H
(
(
(
(
(
PN P)Mn(NHC(O)p-CF Ph)(CO) (7-Mn-CF ),
3 2 3
H
PN P)Mn(NHC(O)p-BrPh)(CO) (7-Mn-Br),
2
H
Mn by the nitrile could lead to the formation of a salt pair
PN P)Mn(NHC(O)p-MePh)(CO) (7-Mn-Me),
2
iPr
H
−
H
[( PN P)Mn(CO) (NCR)][OH] (Scheme 5b). The [OH]
PN P)Mn(NHC(O)p-OMePh)(CO) (7-Mn-OMe), and
2
2
iPr
H
ion would then perform nucleophilic attack on the metal
bound nitrile leading to carboxamide formation in a similar
PN P)Mn(NHC(O)p-NMe Ph)(CO) (7-Mn-NMe ),
2
2
2
were characterized spectroscopically (Supporting Informa-
1
manner. We have observed the formation of a nitrile bound
tion). A spectroscopic trend was observed in the H NMR
iPr
salt pair [( PNP)Mn(CO) RCN][X]; this was easily
spectra of these complexes, with the resonance of the ligand
N−H proton varying according to the nature of the para
substituent on the aryl carboxamide. The strengths of these
hydrogen bonds are proportional to the downfield shift of the
2
accomplished where X = Br. Upon addition of MeCN to
iPr
H
iPr
H
(
(
PN P)Mn(CO) Br, the desired salt pair [( PN P)Mn-
2
CO) MeCN][Br] (9) (Scheme 6a) formed and was
2
1
characterized by NMR spectroscopy and single crystal X-ray
proton resonance in the H NMR spectrum; the strongest
hydrogen bond is formed by the carboxamide with the most
a
Scheme 6. Synthesis and Benzonitrile Addition
electron-donating substituent, NMe (Figures S45 and S46).
2
From the results of the Hammett analysis, plausible
mechanisms involving the nucleophilic attack of Mn−OH on
a nitrile were postulated (Scheme 5). It is important to note
that no coordination of nitrile to form a six-coordinate Mn
complex was observed in this study. Even in independent
iPr
reactions between ( PNP)Mn(CO) and excess RCN with
2
benzonitrile as a solvent, there is no evidence to suggest
1
interaction between the two, as determined by H NMR
spectroscopy. This information is important, as the most
predominant mechanism found in the literature for the
hydration of nitriles involves the coordination of the nitrile
to the metal center, followed by nucleophilic attack by an outer
4
5
or inner sphere molecule hydroxide/water (Scheme 5a).
iPr
While we do not observe nitrile coordination to ( PNP)-
a
Mn(CO) it is possible that displacement of hydroxide in 5-
(a) Synthesis of 9. (b) Addition of benzonitrile to Mn-OBn.
2
,
E
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a
diffraction (see the Supporting Information). Through
structural characterization we are able to note that while
bromide is displaced, it remains hydrogen bound to the NH of
the chelate. It should also be noted that there is an equilibrium
Scheme 7. Catalysis and Deprotonation Reactions
iPr
H
between 9 and ( PN P)Mn(CO) Br that is observed even in
2
MeCN-d , suggesting that the nitrile is easily displaced even
3
when the ligand backbone is protonated and has been
observed to revert back to the starting material in the solid-
state at room temperature overnight. While this lends support
for the mechanism proposed in Scheme 6b, the difference
between displacing a Br− and a −OH ion is quite substantial
given the hardness of the hydroxide ion. If the nitrile is
displacing the hydroxide, then we are unable to observe any
fleeting intermediates via variable-temperature NMR experi-
ments using 5-Mn. In an attempt to remedy this, we next
attempted an identical experiment with the known benzyl
iPr
H
alcoholate complex ( PN P)Mn(CO) OBn (Mn-OBn, OBn
2
4
a
=
OCH Ph) (Scheme 6b). No change in the NMR spectrum
(a) Catalysis for the hydration of nitriles. (b) Deprotonation of 7-
2
iPr
Mn leading to the formation of PNPMn(CO)2.
was observed upon addition of benzonitrile to a solution of
Mn-OBn. Although they do not rule out the mechanism in
Scheme 5b, these results conflict with its requirements,
specifically [OH] dissociation with concomitant coordination
of the nitrile to the metal.
exhibits some degree of decomposition, forming a solid
precipitate and extra signals in the P NMR spectrum are
−
31
observed. Under the more extreme conditions (>120 °C, >12
h) of several of the other catalytic studies regarding the use of
this manganese system as a catalyst, we find it hard to believe
no other instances of decomposition were observed, though
none were explicitly mentioned. In order to be certain 5-Mn
was the species involved in any catalytic transformation, the
conditions of the reactions were kept mild. This does not
change the catalytic outcomes of the other studies, but we are
uncomfortable claiming 5-Mn as the catalytically active species
under more forcing conditions.
Other proposed mechanisms involve coordination of both
nitrile and hydroxide/water to the metal center, with a
hydroxide migration to the nitrile to form the metal amide
4
6
(
Scheme 5c), a mechanism we disfavor for the requirement
of lability in the phosphorus arm of the PNP chelate, an
occurrence that has yet to be reported with the (PNP)Mn
system.
With no nitrile coordination observed with 5-Mn, we favor a
mechanism whereby the reaction proceeds through a
nucleophilic attack of the metal bound hydroxide on a closely
associated molecule of nitrile. This is likely promoted by
hydrogen bonding between the ligand N−H and the nitrile
For the sake of simplicity, only PhCN, NMe -PhCN, and
2
CF -PhCN were tested in order to observe the effect of a
3
broad range of electronic variability of the substrate on
catalysis. 5-Mn is capable of catalytically hydrolyzing nitriles to
amides, with the electronics of the substrate strongly affecting
turnover. Analysis of reaction solutions of PhCN only reveals
an 18% conversion to the amide over the course 24 h with an
additional 15% amide product bound to the Mn in the form of
7-Mn, equaling a total of 33% conversion (TON = 2.2).
iPr
H
nitrogen (Scheme 5d). The N−H on the PN P ligand has
been shown to form hydrogen bonds with molecules of THF
and H O in the crystal structures of many of the solid-state
2
structures reported here. More specifically, in the previously
reported crystal structure of 5-Mn, the ligand−NH displays H-
bonding to other water molecules inside the crystal lattice. We
suggest that this hydrogen bonding interaction is involved in
the mechanism to assist in orienting and activating the nitrile,
which promotes nucleophilic attack by the metal hydroxide
group. Similar hydrogen bonding networks have been
postulated in other mechanisms for nitrile hydration; however,
these mechanisms all involve metal bound nitrile and hydrogen
bound water to afford hydration. Determination of mecha-
nisms of nitrile hydration catalysts has been shown to be
extremely complex, often employing DFT calculations to
Hydrolysis of the electron-donating NMe -PhCN under
2
identical conditions results in roughly 26% total conversion
(TON = 1.7), while hydrolysis of the electron-withdrawing
CF −PhCN results in ∼59% total conversion (TON = 3.9).
3
This result suggests that the more electron-withdrawing the
amide, i.e., the better the leaving group, the greater the
conversion. This result is in agreement with the argument that
the catalysis is limited by the leaving ability of the amide.
It should be noted that at no point during our investigation
47−51
deconvolute varying reaction pathways.
Further work
of either 5-Ni or 5-Mn is the presence of RCO
H observed.
2
attempting to clarify the mechanism is ongoing, with
mechanism (d) being favored for the above reasons while
mechanism (b) remains plausible.
Interestingly, addition of base (LiCH SiMe , NaOtBu) to a
2
3
solution of 7-Mn results in the immediate color change of the
solution from yellow to red, indicating the reformation of
iPr
1
Next, the utility of 5-Mn as a nitrile hydration catalyst was
( PNP)Mn(CO) (Scheme 7b), which was confirmed by H
2
probed. To accomplish this, THF-d solutions containing 10%
NMR spectroscopy. However, when these bases are introduced
into a catalytic environment, they have no effect on the TON,
with nearly identical conversion to amide product as in its
absence under the same conditions.
8
wt. H O and 5-Mn were treated with just under 7 equiv of
2
appropriate nitrile (15 mol % 5-Mn), the solution was heated
to 50 °C inside a J. Young NMR tube, and the reactions were
1
analyzed by H NMR spectroscopy (Scheme 7a). It is
CONCLUSION
noteworthy that even at the relatively low temperature of 50
■
°
C after short reaction times in aqueous anaerobic conditions
in the presence of nitrile substrate, the manganese complex
We have been able to show that the PNP ligand scaffold is
capable of assisting in the formation of transition metal
F
DOI: 10.1021/acs.organomet.8b00687
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
hydroxide complexes, as seen previously by the formation of 5-
Mn and in this report with the formation of 5-Ni. These
nucleophilic transition metal hydroxide complexes are capable
of performing the hydrolysis of a wide range of nitriles, which
we suggest is assisted by the chemical noninnocence of the
solvent removed once more in vacuo leaving behind a dark green
powdery solid identified as ( PNHP)NiCl (2; yield 0.425 g, 93%).
iPr
Analysis for C H N P Cl Ni Calculated: C = 48.22%, H = 9.10%,
16 36
1
2
1
1
1
N = 3.51%. Found: C = 48.56%, H = 9.29%, N = 3.56%. H NMR
3
(
C D , 23 °C): 1.12 (quad, J = 6.8 Hz, 12H, iPrCH ), 1.34 (bs, 4H,
6 6 3
3
CH −P), 1.51 (quad, J = 6.8 Hz, 12H, iPrCH ), 2.04 (m, 4H, N−
H
2
3
PN P ligand; 1,2-addition of water across the metal-amide
31
1
CH ), 2.52 (m, 4H, iPrCH). P{ H} NMR (C D , 23 °C): 64.91.
2
6
6
bond allows for the generation of the desired metal hydroxide.
The nucleophilicity of the resultant metal hydroxide is retained
in late transition metals and allows for further reactivity with
electrophiles. Despite the ability of these complexes to
catalytically hydrate nitriles, the carboxamide products severely
inhibit catalytic turnover at the metal center. In the case of the
Ni system, no turnover is observed, while in the case of PNP−
Mn, turnover is limited due to this extreme product inhibition.
To our knowledge, this is the first instance of Mn-catalyzed
nitrile hydration in the literature. We have also proposed a
mechanism for this manganese assisted nitrile hydration,
invoking a metal-bound hydroxide nucleophilic attack on the
carbon of a nitrile, assisted by a hydrogen bonding interaction
between the N−H of the supporting chelate and the nitrile.
Theoretical investigations and further kinetic experiments are
ongoing and will be reported in due course.
13
1
C{ H} NMR (C D , 23 °C): 17.40 (iPrCH ), 18.81 (iPrCH ),
6
6
3
3
2
1.67 (iPrCH), 23.22 (CH −P), 60.34 (CH −N).
2
2
iPr
Synthesis of [( PNP)Ni(PMe )][BPh ] (3) (CCDC: 1867732).
3
4
A 20 mL scintillation vial was charged with 0.300 g (0.755 mmol) of 2
in an inert atmosphere dry box and dissolved in 15 mL of C H F. To
6
5
this stirring solution was added 0.258 g (0.755 mmol) of NaBPh
this was added several drops of PMe , resulting in an immediate color
. To
4
3
change from dark green to dark purple. Following a 1 h reaction
period, the solution was filtered through a plug of Celite, washed with
1
0 mL of C H F, and the excess solvent removed under reduced
6 5
pressure leaving behind a dark purple powdery solid identified as
iPr
[( PNP)Ni(PMe )][BPh ] (3; yield 0.468 g, 82%). Analysis for
3 4
C H N P B Ni Calculated: C = 67.87%, H = 8.86%, N = 1.69%.
4
3
65
1
3
1
1
Found: C = 67.32%, H = 8.39%, N = 1.85%. CHN values calculated
1
as the THF adduct as found in the crystal structure. H NMR
3
(CDCl , 23 °C): 1.06 (d, J = 8 Hz, 9H, PMe ), 1.30 (m, 24H,
3
3
iPrCH ), 1.46 (m, 2H, N−CH ), 1.91 (bs, 4H, CH −P), 2.10 (m, 4H,
3
2
2
iPrCH), 2.94 (m, 2H, N−CH ), 6.94 (s, 4H, p-H−BPh ), 7.08 (s, 8H,
2
4
3
1
1
o-H−BPh ), 7.46 (s, 8H, m-H−BPh ). P{ H} NMR (CDCl , 23
C): 83.50 (iPr P), 21.61 (PMe ). C{ H} NMR (CDCl , 23 °C):
2 3 3
4
4
3
EXPERIMENTAL SECTION
■
13
1
°
All air- and moisture-sensitive manipulations were carried out using
standard Schlenk techniques or in an MBraun drybox containing a
purified nitrogen atmosphere. THF, diethyl ether, toluene, and N-
hexane were dried on molecular sieves and shaved sodium before use.
1
5
8.95 (iPrCH ), 20.51 (iPrCH ), 21.28 (iPrCH), 26.10 (CH −P),
3
3
2
9.26 (CH −N), 121.76 (Ar−BPh ), 125.58 (Ar−BPh ), 136.30
2
4
4
(Ar−BPh ).
4
iPr
H
Synthesis of [( PN P)Ni(OH)][BPh ] (5-Ni) (CCDC 1867734).
4
THF-d , CDCl , DMSO-d , and C D were purchased from
8
3
6
6
6
A 20 mL scintillation vial was charged with 0.300 g (0.755 mmol) of 3
Cambridge Isotope Laboratories and dried over 4 Å molecular sieves.
in an inert atmosphere drybox and dissolved in 15 mL of C H F. To
6
5
The reagents: NiCl (DME), NaBPh , tBuOK, PhCN, p-BrPhCN, p-
2
4
this stirring solution was added a slight excess 10 wt %/wt solution of
CF PhCN, p-TolCN, p-MeOPhCN, p-NH PhCN, p-Me NPhCN,
iPr
3
2
2
H O in THF (0.258 g, 0.755 mmol) identified as [( PNHP)Ni-
2
and MeCN were purchased from Sigma-Aldrich and were used as
(
OH)][BPh ] (5-Ni; yield 0.216 g, 78%). Analysis for
iPr
H
4
received. The bis[(2-diisopropylphosphino]ethyl)amine ( PN P)
ligand was purchased as a 10% weight solution in THF from Sigma-
C H N P B Ni Calculated: C = 68.60%, H = 8.35%, N = 2.00%.
4
3
65
1
3
1
1
Found: C = 66.58%, H = 8.30%, N = 4.72%. CHN values are
1
13
31
Aldrich and used as was received. H NMR, C NMR, and P NMR
spectra were recorded on a Bruker Advance 400 MHz spectrometer
iPr
consistent with the H O adduct: [( PNHP)Ni(OH)][BPh ]·H O
2
4
2
1
Calculated: C = 66.88%, H = 8.42%, N = 1.95%. H NMR (CDCl ,
1
3
operating at 400.132, 100.627, and 161.978 MHz, respectively. All H
2
3 °C): 1.16 (bs, 6H, iPrCH ), 1.29 (bs, 6H, iPrCH ), 1.40 (bs, 6H,
and 13C NMR chemical shifts are reported (in ppm) relative to SiMe
3
3
4
iPrCH ), 1.48 (m, 6H, iPrCH ), 1.76 (bs, 2H, N−CH ) 1.86 (bs, 4H,
1
13
3
3
2
using the H (residual in the deuterated solvents) and C chemical
shifts of the solvent as a secondary standard.
Synthesis of [( PN P)NiCl][Cl] (1) (CCDC: 1867730). A 100
THF), 2.09−2.30 (bm, 4H, N−CH ), 3.75 (bs, 4H, iPrCH), 6.93 (s,
2
4
H, p-H−BPh ), 7.08 (s, 8H, o-H−BPh ), 7.49 (s, 8H, m-H−BPh ).
iPr
H
4
4
4
31
1
1
3
1
P{ H} NMR (CDCl , 23 °C): 53.11 (iPr P). C{ H} NMR
3
2
mL round-bottomed flask was charged with 0.474 g (3.70 mmol) of
(
2
CDCl , 23 °C): 17.64 (iPrCH ), 18.80 (iPrCH ), 20.54 (CH −P),
3
3
3
2
NiCl (DME) in an inert atmosphere drybox and dissolved in 50 mL
2
2.94 (iPrCH), 24.55 (iPrCH ), 25.75 (CH CH O), 54.97 (CH −N),
3
2
2
2
of THF. To this stirring solution was added 2.50 g (25 mL of 10 wt %
iPr
H
68.09 (CH
(
2
CH
2
O), 121.99 (Ar−BPh
4
), 125.86 (Ar−BPh
4
), 136.33
in THF) of PN P ligand, and the reaction mixture was left to stir
for 16 h. The reaction mixture slowly turned light orange color and
was precipitated from solution using hexane. Filtration of the solid
Ar−BPh ), 163.95 (Ar−BPh ).
General Synthesis for M−NHC(O)R Complexes. Solutions of
4
4
iPr
H
either 5-Ni or 5-Mn in diethyl ether were treated with the
corresponding nitrile and the solutions stirred 30 min. Following a
short workup (see the Supporting Information), complex was isolated
as a powder for analysis.
afforded 0.895 g (95% yield) of the solid identified as [( PN P)-
NiCl][Cl] (1). Analysis for C H N P Cl Ni Calculated: C =
1
6
37
1
2
2
1
4
3
4.18%, H = 8.57%, N = 3.22%. Found: C = 44.29%, H = 8.54%, N =
1
3
.22%. H NMR (CDCl , 23 °C): 1.40 (quad, J = 7.2 Hz, 6H,
3
iPr
H
3
3
[( PN P)Ni(NHC(O)Me)][BPh ] (6-Ni) (CCDC 1867735). Analysis
iPrCH ) 1.47 (quad, J = 7.0 Hz, 6H, iPrCH ) 1.53 (quad, J = 8.1
Hz, 6H, iPrCH ) 1.62 (quad, J = 8.0 Hz, 6H, iPrCH ), 2.24 (m, 6H,
4
3
3
3
for C H N P B Ni Calculated: C = 70.26%, H = 7.90%, N = 3.49%.
43 65
1
3
1
1
3
3
3
1
1
Found: C = 66.53%, H = 8.50%, N = 4.72%. CHN values are
N−CH ), 3.05 (m, 2H, iPrCH). P{ H} NMR (CDCl , 23 °C):
2
3
1
3
1
consistent with those of the NH C(O)Me adduct as seen in the
5
4.27. C{ H} NMR (CDCl , 23 °C): 17.83 (iPrCH ), 17.93
2
3
3
iPr
H
crystal structure: [( PN P)Ni(NHC(O)Me)][BPh ]·NH C(O)Me
Calculated: C = 66.02%, H = 8.31%, N = 5.25%. H NMR (CDCl ,
(iPrCH ) 18.82 (iPrCH ), 19.30 (iPrCH ), 20.42 (iPrCH), 23.42
4
2
3
3
3
1
(
iPrCH), 23.58 (CH −P), 24.22 (CH −P), 54.80 (CH −N).
3
2
2
2
iPr
23 °C): 1.25 (m, 12H, iPrCH ), 1.39 (m, 12H, iPrCH ), 1.52 (m, 4H,
Synthesis of ( PNP)NiCl (2) (CCDC: 1867731). A 20 mL
3
3
N−CH ), 1.76 (s, 3H, NHC(O)CH ), 2.01 (bs, 4H, CH −P), 2.14
scintillation vial was charged with 0.500 g (1.15 mmol) of 1 in an
2
3
2
(
4
m, 2H, iPrCH), 2.24 (m, 2H, iPrCH), 5.31 (bs, 2H, N−H), 6.93 (s,
inert atmosphere dry box and dissolved in 15 mL of C H F. To this
6
5
H, p-H−BPh ), 7.08 (s, 8H, o-H−BPh ), 7.49 (s, 8H, m-H−BPh ).
stirring slurry was added 0.122 g (1.15 mmol) of tBuOK resulting in
an immediate dissolution of the Ni product and a color change from
light orange to dark green. Following a 1 h reaction period, the
solution was filtered through a plug of Celite, washed with 10 mL of
C H F, and the excess solvent removed under reduced pressure. The
4
4
4
3
1
13
P NMR (CDCl
, 23 °C): 51.00 (iPr
), 18.82 (iPrCH
20.27 (iPrCH), 23.77 (iPrCH), 25.37 (CH −P), 53.62 (CH −N),
P). C NMR (CDCl , 23 °C):
2 3
3
17.69 (iPrCH
), 17.89 (iPrCH
), 19.31 (iPrCH ),
3 3
3
3
2
2
121.90 (Ar−BPh ), 125.74 (Ar−BPh ), 163.45 (Ar−BPh ), 177.21
(NHC(O)Ph). IR (Neat, 23 °C, cm ): 1663 (RC(O)NH).
6
5
4
4
4
−
1
dark green sticky solid was mobilized in 10 mL of hexane and the
G
DOI: 10.1021/acs.organomet.8b00687
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
iPr
H
[
( PN P)Ni(NHC(O)Ph)][BPh ] (7-Ni) (CCDC: 1867736). Analysis
iPrCH, MeCN), 1.86 (bm, 2H, CH −N), 1.50−1.23 (m, 24H, iPr−
4
2
3
1
1
13
1
for C H N P B Ni Calculated: C = 68.04%, H = 8.29%, N = 3.78%.
CHMe ). P{ H} NMR (C D , 23 °C): 72.44. C{ H} NMR
2 6 6
4
3
65
1
3
1
1
Found: C = 70.57%, H = 8.16%, N = 3.30%. CHN values are
consistent with THF adduct as seen in the crystal structure and NMR
(C D , 23 °C): 51.00 (CH −P), 29.63 (CH −N), 25.72 (iPr−
6
6
2
2
CHMe ), 25.40 (iPr−CHMe ), 20.73 (iPr−CHMe ), 18.86 (iPr−
2
2
2
1
−1
analysis. H NMR (CDCl , 23 °C): 1.29 (m, 12H, iPrCH ), 1.39 (m,
CHMe ), 17.46 (MeCN). IR (Neat, 23 °C, cm ): 2010 (MeCN),
3
3
2
6
4
H, iPrCH ), 1.44 (m, 6H, iPrCH ), 1.61 (m, 2H, N−CH ) 1.73 (bs,
1902 (Mn−CO), 1845 (Mn−CO).
3
3
2
Catalytic Measurements. In a J. Young NMR tube, iPrPNPMn-
(CO) (0.014 g, 0.033 mmol) was dissolved in THF-d (0.280 g). To
H, CH -P), 2.17 (m, 2H, iPrCH), 2.27 (m, 2H, iPrCH), 6.94 (s, 4H,
2
p-H−BPh ), 7.09 (s, 8H, o-H−BPh ), 7.32 (m, 3H, p,m-NHC(O)-
4
4
2
8
3
1
1
Ph), 7.43 (d, 2H, o-NHC(O)Ph), 7.51 (s, 8H, m-H−BPh ). P{ H}
this was added a solution of 10 wt %/wt H O in THF-d mixture
4
2 8
1
3
1
NMR (CDCl , 23 °C): 51.51 (iPr P). C{ H} NMR (CDCl , 23
(0.220 g) and the corresponding nitrile (0.5 mmol). The NMR
spectrum of the starting reaction mixture was taken and the J. Young
tube was inserted into an oil bath preheated to 50 °C. The reaction
mixture was analyzed following a 16 h time period, and relative
integrations were used to determine percent conversion.
3
2
3
°
(
(
(
C): 17.74 (iPrCH ), 17.90 (iPrCH ), 18.82 (iPrCH ), 19.25
3 3 3
iPrCH ), 20.32 (iPrCH), 23.74 (iPrCH), 25.40 (CH −P), 53.80
3
2
CH −N), 121.76 (Ar−BPh ), 125.77 (Ar−BPh ), 126.26 (NHC-
2
4
4
O)Ph), 128.35 (NHC(O)Ph), 129.85 (NHC(O)Ph), 136.27 (Ar−
BPh ), 137.51 (NHC(O)Ph), 167.35 (Ar−BPh ), 174.20 (NHC(O)-
4
4
−
1
Ph). IR (Neat, 23 °C, cm ): 3189 (RC(O)NH), 1610 (RC(O)NH).
ASSOCIATED CONTENT
iPr
H
■
PN PMn(NHC(O)Me)(CO)2 (6-Mn) (CCDC: 1867737). Yield
0.109 g, 96%). Analysis: Calculated: C = 50.63%, H = 8.71%, N =
*
S
Supporting Information
(
5
1
.90%. Found: C = 50.90%, H = 8.88%, N = 5.91%. H NMR (THF-
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00687.
d , 23 °C): 9.98 (t, 1H, J = 10.8 Hz, N−H ), 3.24 (m, 2H, CH −
8
amide
2
P), 2.45 (m, 2H, CH −P), 2.38−2.20 (m, 6H, iPr−Me C−H, CH −
2
2
2
N), 1.70 (s, 3H, NH(O)CH ), 1.40−1.20 (m, 24H, iPr−CHMe ).
3
2
1H and 13C NMR spectroscopy and X-ray crystallog-
raphy data (PDF)
31
1
13
1
P{ H} NMR (THF-d , 23 °C): 88.98. C{ H} NMR (THF-d , 23
8
8
°
(
(
2
C): 182.21 (NHC(O)), 52.30 (CH −P), 27.36 (CH −N), 25.89
2
2
iPr−CHMe ), 24.66 (iPr−CHMe ), 19.71 (iPr−CHMe ), 19.53
2
2
2
iPr−CHMe ), 18.13 (iPr−CHMe ), 17.33 (iPr−CHMe ). IR (Neat,
Accession Codes
2
2
2
−
1
3 °C, cm ): 3324 (RC(O)NH), (1810 (Mn−CO), 1893 (Mn−
CCDC 1867730−1867740 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
CO), 1550 (RC(O)NH).
iPr
H
PN PMn(NHC(O)Ph)(CO)2 (7-Mn) (CCDC: 1867738). Yield
0.118 g, 92%). Analysis: Calculated: C = 55.97%, H = 8.08%, N =
(
5
2
1
.22%. Found: C = 56.23%, H = 7.83%, N = 5.19%. H NMR (C D ,
3 °C): 10.17 (t, 1H, J = 11.0 Hz, N−Hligand), 7.99 (d, 2H, J = 7.3 Hz,
o-ArH)), 7.18 (t, 2H, J = 7.3 Hz, m-ArH), 7.08 (t, 1H, J = 7.3 Hz, p-
6 6
ArH), 5.05 (s, 1H, NHamide), 2.93 (m, 2H, CH −P), 2.26−2.00 (m,
2
6
H, iPr−Me C−H, CH −P), 1.75 (m, 4H, CH −N), 1.39−1.17 (m,
AUTHOR INFORMATION
2
2
2
■
*
*
1
8H, iPr−CHMe ), 0.83 (dd, 6H, J = 7.0, 10.5 Hz, iPr−CHMe ).
2
2
Corresponding Authors
E-mail: boncella_j@lanl.gov.
E-mail: tondreau_a@lanl.gov.
3
1
1
13
1
P{ H} NMR (C D , 23 °C): 88.70. C{ H} NMR (C D , 23 °C):
6
6
6
6
79.05 (C(O)NH), 139.90 (Ar), 128.81 (Ar), 126.18 (Ar), 52.47
2
2
2
2
2
2
ORCID
−1
2
2
James M. Boncella: 0000-0001-8393-392X
Aaron M. Tondreau: 0000-0003-0440-5497
Funding
N.H.A. and A.M.T. would like to thank the Los Alamos
National Laboratory Directors’ Fellowship for funding during
this work and for partial support from Science Campaign 5.
iPr
H
PN PMn(NHC(O)Pyr)(CO)2 (8-Mn) (CCDC: 1867739). Yield
(
0.117 g, 90%). Analysis: Calculated: C = 53.63%, H = 7.88%, N =
1
7
2
.82%. Found: C = 53.68%, H = 7.67%, N = 7.99%. H NMR (C D ,
6
6
3 °C): 10.04 (t, 1H, J = 10.9 Hz, N−H ), 8.41 (d, 1H, J = 4.5 Hz,
Lig
Ar−H), 8.37 (d, 2H, J = 7.5 Hz, Ar−H), 7.28 (s, N−H
2
), 7.11 (t,
amide
Notes
H, J = 7.5 Hz, Ar−H), 6.60 (dd, 2H, J = 7.5, 4.5 Hz, Ar−H), 2.96
(
4
bm, 2H, CH −P), 2.21 (m, 6H, iPr−Me C−H, CH −P), 1.78 (m,
The authors declare no competing financial interest.
2
2
2
H, CH −N), 1.43−1.22 (m, 18H, iPr−CHMe ), 0.89 (dd, 6H, J =
2
2
31 13 1
1
0.7, 6.8, iPr−CHMe ). P NMR (C D , 23 °C): 88.65. C{ H}
2
6
6
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■
NMR (C D , 23 °C): 176.66 (Ar), 154.14 (Ar), 147.75 (Ar), 136.34
6
6
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1
=
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6
6
2
2
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Organometallics XXXX, XXX, XXX−XXX