N-H cleavage as a route to new pincer complexes of high-valent rhenium

Article abstract of DOI:10.1039/C6DT03640F

A novel PNN-type pincer ligand has been accessed via imine reduction with LiAlH₄ to provide the phosphine diamino proligand, PN^HN^H (1). The ligand, 1, as well as PN^HP can be metallated directly, via N-H cleavage, with L₂ReOX₂(OEt) precursors to access six-coordinate (PNP)ReOCl₂ (2) and (PNN^H)ReOX₂ (3-Cl, X = Cl; 3-Br, X = Br) in good yield. 3-Cl and 3-Br undergo dehydrohalogenation upon treatment with NEt₃, furnishing the five-coordinate phosphine/diamido PNN-type compounds (PNN)ReOX (4-Cl, X = Cl; 4-Br, X = Br) in excellent yield, presenting as a mixture of rotameric diasteromers. The reversibility of this deprotonation, and the coordinative unsaturation of 4-Cl is shown in reactions with HCl_(aq) and PMe₃ providing 3-Cl and 4-PMe₃, respectively. Treatment of 4-Cl with AgOAc, AgOTf, or NaHBEt₃ lead to formation of (PNN)ReO(OAc) (4-OAc), (PNN)ReO(OTf) (4-OTf), and (PNN)ReO(H) (4-H), all isolated in excellent yields in varying diasteromeric ratios. The nature of the isomerism was analyzed based on solid-state structural studies and solution NMR data.

Full text of DOI:10.1039/C6DT03640F

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N-H Cleavage as a Route to New Pincer Complexes of High-Valent
Rhenium
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Alex J. Kosanovich, Wei-Chun Shih, Rodrigo Ramírez-Contreras, Oleg. V. Ozerov.*
www.rsc.org/
4
A novel PNN-type pincer ligand has been accessed via imine reduction with LiAlH to provide the phosphine diamino
H
H
H
2 2
proligand, PN N (1). The ligand, 1, as well as PN P can be metallated directly, via N-H cleavage, with L ReOX (OEt)
H
precursors to access six-coordinate (PNP)ReOCl
undergo dehydrohalogenation upon treatment with NEt
compounds (PNN)ReOX (4-Cl, X = Cl; 4-Br, X = Br) in excellent yield, presenting as a mixture of rotameric diasteromers. The
reversibility of this deprotonation, and the coordinative unsaturation of 4-Cl is shown in reactions with HCl(aq) and PMe
providing 3-Cl and 4-PMe , respectively. Treatment of 4-Cl with AgOAc, AgOTf, or NaHBEt lead to formation of
PNN)ReO(OAc) (4-OAc), (PNN)ReO(OTf) (4-OTf), and (PNN)ReO(H) (4-H), all isolated in excellent yields in varying
2
(2) and (PNN )ReOX
2
( 3-Cl, X = Cl; 3-Br, X = Br) in good yield. 3-Cl and 3-Br
3
, furnishing the five-coordinate phosphine/diamido PNN-type
3
3
3
(
diasteromeric ratios. The nature of the isomerism was analyzed based on solid-state structural studies and solution NMR
data.
Previous Work
F
Introduction.
F
F
F
Pincer ligands are tridentate and tend to coordinate to
transition metals in meridional fashion, engendering significant
thermal stability and geometric rigidity. As a result of these
attractive features, they have been utilized in the study of
multiple, challenging reactions of both catalytic and
N
P
P
N Re
P
P
O
F
F
Cl
Cl
Si
Si
CO
CO
N
Re
N
X
N
Re
P
N
ReH
4
P
F
1
,2
F
stoichiometric interest.
We became interested in the
F
chemistry of high-valent rhenium supported by pincers, and
3
recently reported a Re system accessed via C-H activation at
F
Schrock, Ison
{[5,5]-NNN}2-
Milstein
Schneider
{[5,5]-PNP}
Caulton
-
Re(V) of a pincer ligand that can be referred to as a {[5,5]-PCP}
4
using the Fryzuk notation. Given the wide variety of available
{[5,5]-PNP}
-
-
{[5,5]-PNP}
-
This Work
tridentate ligands, Fryzuk's notation can be used to conveniently
describe pincer frameworks based on the size of the two chelate
rings, the donor atoms involved, as well as the overall charge (as
used in Scheme 1).
H
NMes
P
P
NMes
i
-
H+
N
N
N
+
+ H
i
P Pr
2
P Pr
2
{
[5,5]-PNP}-
{[5,6]-PNN}-
{[5,6]-PNN}2-
Scheme 1. (Top) Various nitrogenous pincer ligands
previously utilized to support reactive rhenium fragments.
(
Bottom) Pincer ligands utilized in this study.
Much of the previous chemistry done with pincer-
supported Re(V) has involved either neutral, mono-, or
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5
H
dianionic pincers with nitrogenous donors (Scheme 1-top).
The Caulton group explored reactivity of Re in C-H activation
and formation of metal-carbon multiple bonds using the
i
NMes
P Pr
O
2
PNH
PNHNH,Mes
( )
1
X
P
N Re
X
N Re Cl
3 2 2
(PPh ) ReOX (OEt)
-
2 PPh
- EtOH
3
- 2 PPh
- EtOH
3
O
i
6
Cl
i
P Pr
2
Fryzuk-type amido/bis(phosphine) PNP ligand. Schneider and
P Pr
2
X = Cl
X = Cl, Br
3-X
(PNNH)ReOX
2
2
(58%)
co-workers reported dinitrogen splitting in a Re system
supported with a dialkylamido/bis(phosphine) PNP ligand.
Milstein et al. explored reversible activation of unsaturated
organic molecules by low-valent Re complexes supported by a
(
PNP)ReOCl
2
3
-Cl, X = Cl, 88%;
3-Br, X = Br, 45%
H
H H
Scheme 3. Metalation of PN P and PN N (1) via aminolysis of Re(V)-alkoxide
7
precursors
dearomatized pyridine/bis(phosphine) PNP ligand. The work
8
of the Ison group examined the insertion reactivity of CO
X-ray diffractometry studies on dark green, single crystals
using
a dianionic amine/bis(amido) NNN pincer first
established the molecular structures of (PNP)ReOCl
H
PNN )ReOCl (3-Cl) in the solid state (Figures 1 and 2). Both
2
(
2) and
9
introduced into Re chemistry by Schrock. Re complexes of
(
2
-
[5,5]-NNO} , of {(5,6)-PNN} , and of {(6,6)-NNN} pincers have
-
-
{
structures feature cis-chlorides, meridionally disposed pincer
1
0-12
also been reported.
Most of these examples include Re-
ligands, and short Re-O distances consistent with triply
15
bonded, terminal Re-oxo moieties.
2
oxo complexes in the +5 oxidation state where a low-spin d
configuration is ensured in part by the strong triple bond
between Re and oxygen engaging the two formally vacant dπ
orbitals. Looking to expand upon the chemistry of pincer-
IR spectroscopy
corroborated the presence of Re-oxo moieties in
-1
2
(νRe≡O = 940
-1
cm ) and 3-X
(
3-Cl, X = Cl, νRe≡O = 963 cm ; 3-Br, X = Br, νRe≡O
=
-1
62 cm ). The Re-N1amido distances in both structures are
9
supported, high-valent rhenium, we targeted
a pincer
comparable, while the Re-N2 distance in the structure of
H
PNN )ReOCl (3-Cl) is over 0.2 Å longer. Together with the
2
framework with access to variable modes of protonation. To
this end, we report the synthesis of Re(V) oxo complexes of
(
pyramidalization at N2, these indicate a neutral amine bound
to Re. This notion is supported by the observation of the N-H
-1
stretch by IR spectroscopy in 3-X (X = Cl, 3214 cm ; X = Br,
-
5,6-(PNN)} ligands (Scheme 1-bottom). For comparison, we
/2-
{
-
also report a complex of the {5,5-(PNP)} ligand.
-
1
3
189 cm ). The X-ray structure solution for (PNP)ReOCl
contains crystallographic two-fold axis of symmetry,
however, this is owing to disorder along the O1/Re1/Cl1 axis.
2
(2)
a
Results and Discussion.
Synthesis and Metalation of Diarylamido Ligands
Each individual molecule of
in the solid state.
2
, as well as of 3-Cl is C
1
-symmetric
1
3
H imine
Imine reduction of the previously reported PN N
with
, as a free-flowing
white powder in 65% yield upon workup (Scheme 2). gave
rise to a single resonance by P{ H} NMR spectroscopy (δ -
H
H
4
LiAlH produced the PN N proligand, 1
1
3
1
1
1
13
1
1
s
4.5 ppm) and to C -symmetric H and C{ H} NMR spectra in
solution at ambient temperature.
MesHN
MesN
i
i
PPr2
1) LiAlH4
2) H2O
P Pr2
H
H
N
N
=
Mes
1
PNNimine
PNHNH,Mes
iPr
H H
Scheme 2. Synthesis of PN N proligand
It was envisaged that a Re(V) alkoxide might serve as a
convenient precursor for metalation of an N-H containing
pincer ligand via aminolysis of the Re-OR bond. Gratifyingly,
1
4
treatment of
3 2 2
1 with (PPh ) ReOX (OEt) (X = Cl, Br) in toluene
for 12 h at ambient temperature led to quantitative expulsion
1
31
1
of free PPh
3
and EtOH ( H and P{ H} NMR evidence observed
) with clean formation of the metallated products,
3-X), isolated in moderate to excellent yields (3-
Cl, X = Cl, 88%; 3-Br, X = Br, 45%) (Scheme 3-right). In a similar
fashion, (PNP)ReOCl ) was synthesized and isolated in 58%
yield via reaction of PN P with (PPh
albeit at 110 C. (Scheme 2-left).
H
Figure 1. ORTEP drawing (50% probability ellipsoids) of (PNN )ReOCl
2
(3-Cl). H atoms
in toluene-d
8
H
are omitted for clarity. Selected distance (Å) and angles (deg): Re1-N1, 1.984(2);Re1-
N2, 2.2126(2); Re1-O1, 1.684(2); P1-Re1-N2, 155.62(6)
(
2
PNN )ReOX (
2
(2
H
3 2 2
) ReOCl (OEt) in toluene,
°
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P
P
Cl
Cl
N Re Cl
T
N Re Cl
O
O
P
P
up/down
rotamer
down/up
rotamer
2
Scheme 4. Two different rotamers/enantiomers possible for (PNP)ReOCl (2)
2
Figure 2. ORTEP drawing (50% probability ellipsoids) of (PNP)ReOCl (2). O1/Re1/Cl1
disorder and H atoms are omitted for clarity. Selected distance (Å) and angles (deg):
Re1-N1, 2.028(4); Re1-O1, 1.67(2); P1-Re1-P2, 155.79(3).
3
Ambient temperature P{ H} NMR spectra of (PNP)ReOCl
1
1
2
2
(2) feature two broad resonances at δ 34.1 (br d, JP-P = 174 Hz)
2
and 27.2 ppm (br d,
JP-P = 174 Hz), consistent with the
inequivalent phosphorus environments indicated by the X-ray
1
6
31
1
structure.
revealed coalescence to
observations are consistent with rapid interconversion of two
degenerate -symmetric structures, resulting in time-
averaged C
A
P{ H} NMR spectrum collected at 80
°C
a
single resonance. These
C
1
Close contact
1
7
s
symmetry at 80 °C. We propose that the nature
leading to ring current
of the interconversion lies in the “flipping” of the two aromatic
rings of the diarylamido backbone past each other (Scheme 4).
We have previously described such “flipping” being slow on
the NMR time scale for certain complexes of the diarylamido-
imine
13,18
based PNN
pincer.
In PNP complexes, this “flipping” is
displayed lowered symmetry
typically fast, although (PNP)AlCl
2
1
9
presumably for this reason.
The two interconverting rotamers in (PNP)ReOCl
enantiomers, i.e., species of degenerate energy that give rise
N
O
2
(
2) are
H
N
Re
Cl
H
to identical NMR spectra. Similar rotamerism in (PNN )ReOCl
3-Cl) would give rise to diastereomers distinguishable by NMR
2
(
Cl P
spectroscopy. The molecule of 3-X possesses chiral centers at
N2 and at Re itself, with multiple theoretically possible
H
Scheme 5. Alternative view of (PNN )ReOCl
2
(3-Cl) and representative schematic of
2
0
diasteromers. Yet, only one diastereomer of C
-symmetry is
H
1
observed proximity of benzylic methyl protons with PNN ligand's aromatic backbone,
observed by NMR spectroscopy, with a specific feature in leading to ring current effects.
accord with the solid-state structure. One of the singlet
H
1
Dehydrohalogenation of (PNN )ReOX
2
methyl H NMR resonances is shifted considerably upfield (X =
Cl, δ 1.27 ppm; X = Br, δ 1.23 ppm). We ascribe this to one of
the ortho-methyl groups of the mesityl ring being affected by
the ring current of one of the other aromatic rings, based on
the positioning of an ortho-methyl directly above an aromatic
H
Reaction of (PNN )ReOX
triethylamine in toluene at 70 ˚C for 10 min led to precipitation
of [HNEt ][X] and quantitative conversion to (PNN)ReOX (4-X
2
(3-X) (X = Cl, Br) with
3
31
)
1
1
(
H and P{ H} NMR evidence), isolated as dark green powders
Scheme 6). These materials consist of a mixture of C
2
1
ring in the solid-state structure of 3-Cl (Scheme 5).
(
1
-
Observation of separate ortho-methyl resonances by NMR
spectroscopy also indicates that rotation about the N-CMes
bond is slow on the NMR time scale.
symmetric diastereomers in a roughly 3:1 ratio, as evidenced
by solution NMR studies. IR spectra confirm the terminal
-1
-1
rhenium-oxo (4-Cl, X = Cl, 962, 970 cm ; 4-Br, X = Br, 968 cm )
and show no N-H stretching modes. Both 3-X and 4-X
complexes
are
air-stable.
Dehydrohalogenation
of
H
PNN )ReOCl (3-Cl) was reversed by treatment of a sample of
(
2
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9
(
PNN)ReOCl (4-Cl) in C
6
D
6
with concentrated HCl(aq) (Scheme detected for the corresponding X groups: two different
F
6).
NMR resonances for (PNN)ReO(OTf) (4-OTf) (δ -73.1 and -73.6
1
ppm), two different H NMR singlets for the acetate groups in
NMes
N Re
(
PNN)ReO(OAc) (4-OAc) (δ 2.84 and 1.53 ppm), and two
Toluene
NEt3
H
X
different doublets for the hydrides in (PNN)ReO(H) (4-H) (δ
2
8.22, J = 17.4 Hz, and δ 3.94, J = 14.5 Hz). The downfield
P-H P-H
(
PNN )ReOX2
2
O
i
+
HCl(aq)
PPr2
chemical shift of these Re hydrides is unusual, but appears to
22
be typical for hydrides cis to a triply bound oxo ligand. Re(V)
X = Cl
3
-X
4-X
(
PNN)ReO(X)
oxo/hydride complexes have been implicated in schemes of
2
catalytic reduction.
Major : Minor
-Cl, X = Cl, 75:25 (80%)
3
4
Additional support for these
4
-Br, X = Br, 78:22 (92%)
formulations comes from IR spectroscopy where bands
corresponding to the various element-oxygen stretches were
observed for each compound, a band corresponding to triflate
H
2
Scheme 6. Reversible deprotonation of (PNN )ReOX (3-X) to give (PNN)ReO(X) (4-X).
-1
(
1154 cm ) in (PNN)ReO(OTf)
(4-OTf), and
1
a
band
Reaction with PMe
Illustrating the unsaturated nature of (PNN)ReOCl (4-Cl),
addition of PMe in C led to a color change from dark green
to purple, as C -symmetric (PNN)ReOCl(PMe ) (4-PMe ) was
formed in a 68:32 isomeric ratio (Scheme 7). 4-PMe was
3
-
corresponding to acetate (1653 cm ) in (PNN)ReO(OAc) (4-
OAc). Separate bands for each isomer could not be observed
presumably because of close overlap.
3
6 6
D
1
3
3
3
isolated in 85% yield as a dark purple powder. Two rhenium-
-
oxo stretches were evident in its IR spectrum (957 and 945 cm
1
).
Scheme 8. Chloride metathesis reactions with (PNN)ReOCl.
Structural and isomerism analysis
We were able to obtain single crystals of (PNN)ReOCl (4-Cl
)
Scheme 7. Reaction of (PNN)ReOCl (4-Cl) with PMe
PMe ) in isomeric ratios. One possible isomer is shown.
3
to form (PNN)ReOCl(PMe
3
) (4- (dark-green) and (PNN)ReO(OTf) (4-OTf) (dark-red) that were
3
suitable for an X-ray diffraction study. Both structures feature
short Re≡O bonds. All the Re-N distances in the two structures
fall into the ca. 1.95-2.00 Å range, consistent with two amide
donors on Re. The mutual disposition of donor atoms
3
1
1
Each isomer displays two resonances in its P{ H} NMR
spectrum (major: δ 4.4 (PNN) and -50.2 (PMe ) ppm; minor: δ
.3 (PNN) and -49.2 (PMe ) ppm). The lack of perceptible P-P
3
0
3
(accounting for the Cl/OTf change) is approximately the same
coupling points to cis-disposition of the two phosphorus
in both structures. The resulting five-coordinate environment
about Re cannot be accurately described by idealized square
donors in both isomers. We cannot be certain of which ligand
3
is trans to the oxo in 4-PMe , but favour it being the chloride
pyramidal or trigonal bipyramidal geometries (the
24
τ
for thermodynamic reasons as the weakest trans-influence
parameter is 0.33 for (PNN)ReOCl (4-Cl) and 0.66 for
PNN)ReO(OTf)) (4-OTf). The triflate O of 4-OTf is at a ca. 90
ligand in the molecule (as shown in Scheme 7, other
(
°
possibilities include oxo trans to PMe
3
or the central Namido).
The close similarity of the P NMR chemical shifts for the
PMe group suggests that PMe is trans to the same donor
angle to the Re-oxo bond, but all other donor atoms in both
molecules bend away from the oxo to a greater degree
3
1
3
3
(
Element-Re-O angles of ca. 103-130°). The largest of these
are the angles between the Re-oxo and the Re-N(Mes) bonds
ca. 131 in 4-OTf and ca. 117 in 4-Cl). Such bending away of
atom in both isomers and thus the isomerism is not due to
changes in the mutual disposition of ligands about the Re
center.
(
°
°
a π-donating amido ligand may be reflective of maximizing π-
donation to the otherwise unsaturated Re center. An analogy
could be drawn to the Y-shaped distortions in five-coordinate
Chloride metathesis Reactivity of (PNN)ReOCl
Treatment of (PNN)ReOCl (4-Cl) with AgOTf, AgOAc, or
6
25
2
complexes of d metal centers. Although Re here is d , the
formally empty d orbitals are effectively unavailable because
of strong π-bonding in the Re≡O fragment.
NaHBEt
3
allowed isolation of the respective (PNN)ReOX
π
chloride metathesis products (X = OTf, OAc, H) in excellent
yield upon workup (Scheme 8). Each of these new products
was isolated as a mixture of two diastereomers distinct by
NMR spectroscopy. In each case, two singlets were present in
3
1
1
the P{ H} spectrum and two different resonances were
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1
1.1-1.5 ppm) H
displays an anomalously upfield shifted (to
δ
NMR resonance for a benzylic methyl group. Thus, we
propose that the observed pairs of isomers correspond to the
two rotameric diastereomers (Scheme 9) arising from slow
“
flipping” of the rings of the diarylamido backbone and that
the isomers displaying upfield shifted benzylic methyl
resonances correspond to the conformation observed in the
solid-state structures of 4-Cl and 4-OTf. Interestingly, these
isomers are the minor isomers for all (PNN)Re(O)(X) except X =
OAc. Unfortunately, all of our attempts to obtain an X-ray
quality crystal of the other type of isomer have been
unsuccessful.
We have considered diastereomerism arising from
different arrangements of donor atoms about Re. However,
given the very strong trans-influence of the oxo ligand
disfavoring the positioning of a ligand strictly trans to it in five-
coordinate structures and the inherent constraints of the PNN
ligand, that seems unlikely.
Figure 3. ORTEP drawing (50% probability ellipsoids) of (PNN)ReOCl (4-Cl). H atoms are
omitted for clarity. Selected distance (Å) and angles (deg): Re1-N1, 1.955(3); Re1-N2,
1
.997(4); Re1-O1, 1.684(3); P1-Re1-N2, 80.3(1); N1-Re1-N2, 87.1(1); O1-Re1-N1,
17.1(1); O1-Re1-N2,103.4(1); P1-Re1-O1, 106.6(1); P1-Re1-N1, 136.2(1); Cl1-Re1-N2,
54.1(1)
Mes
Mes
O
1
1
N
N Re
P
N
N Re
P
O
X
T
X
up/down
rotamer
down/up
rotamer
Scheme 9. Representation of different possible rotameric diastereomers envisioned for
the PNN-type framework.
Conclusions
In conclusion, we have presented a series of new synthetic
methods for the metalation of a PNP and PNN-type pincer
ligand via N-H aminolysis of a rhenium-alkoxide bond. The
newly synthesized PNN ligand allows for variable modes of
reversible protonation, and the formation and stabilization of
unsaturated, high-valent Re(V). Complexes of the dianioninc
PNN ligand exist as pairs of diasteromers which are thought to
arise from the restricted motion of the diarylamido backbone.
Figure 4. ORTEP drawing (50% probability ellipsoids) of (PNN)ReO(OTf) (4-OTf). H
atoms are omitted, and mirror image of original structure is shown for clarity and ease Solid-state structural studies support this notion. Future
of comparison. Selected distance (Å) and angles (deg): Re1-N1, 1.958(3); Re1-N2,
studies will focus on the reversible protonation of the amido
1
1
1
.949(3); Re1-O1, 1.698(3); P1-Re1-N2, 123.73(8); P1-Re1-O1, 105.68(9); O1-Re1-N2,
30.6(1); N1-Re1-O2, 164.5(1); P1-Re1-N1, 80.89(8); N1-Re1-N2, 86.70(1); Re1-N2-C16,
22.0(2).
sites and its potential role in new reactivity.
Experimental.
4
-Cl and 4-OTf possess analogous PNN conformations with
H
regard to the discussion of rotamers in (PNN )ReOCl
2
(
3-Cl
)
General Considerations. Unless otherwise stated, all
(vide supra). The aromatic ring attached to P is approximately experiments were carried out using standard glovebox and
coplanar with the P1-Re1-N2 plane, while the other ring of the Schlenk line techniques under a dry argon atmosphere.
diarylamido backbone is tilted towards the oxo ligand. This Triethylamine and C D were dried over NaK, benzophenone,
6
6
conformation is also analogous to that observed in 3-Cl. As in and 18-crown-6, distilled, and stored over molecular sieves in
the latter, one of the ortho-methyl groups of the mesityl is an argon glovebox prior to usage. Diethyl ether, pentane,
positioned over one of the diarylamido rings, although that toluene, and tetrahydrofuran (THF) were dried and
positioning is more pronounced in 4-OTf. This is consistent deoxygenated using a PureSolv MD-5 solvent purification
with the NMR observations for the pairs of isomers of system and were stored over molecular sieves in an argon-
(
PNN)ReOX (4-X) (X = Cl, OTf, OAc, H), as well as of filled glovebox. All other deuterated solvents were degassed
PNN)ReOCl(PMe ) (4-PMe – in each case, one of the isomers and stored over molecular sieves in an argon-filled glovebox.
(
3
3
)
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Ple Da s ae l tdo onn To rt aa nd sj ua s ct t mi o an r sg ins
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DOI: 10.1039/C6DT03640F
Journal Name
ARTICLE
H
26
H
PN N
imine 10
,
PN P,
PPh
(PPh
3
)
2
ReOCl
2
(OEt)
and resulting in a tan suspension. After ten minutes at room
2
7
(
3
)
2
ReOBr
2
(OEt)
were synthesized using reported temperature, the mixture took on a dark purple color and
literature procedures. All other chemical reagents were became homogeneous. The solution was then stirred in an oil
purchased from commercial suppliers and were used as bath at 110 ˚C for 12 h over which time the solution became
received. NMR spectra were recorded on a Varian iNova 500 dark green and solids were noted to precipitate. Cooling of the
3
1
1
13
1
19
(
P{ H} NMR, 202.276 MHz; C{ H} NMR, 125.670 MHz;
F
solution to room temperature resulted in the precipitation of
1
NMR, 470.385 MHz, H NMR, 499.678 MHz) spectrometer in dark solids that were collected by filtration, washed with
1
given solvents. Chemical shifts are reported in ppm (δ). P{ H} diethyl ether (10 mL) and dried in vacuo to provide the product
3
1
NMR spectra were referenced externally to an 85% phosphoric as an analytically pure, dark, semicrystalline powder. Yield: 750
1
acid standard at δ 0ppm. F NMR spectra were referenced mg (58%). Single crystals suitable for X-ray diffraction were
9
1
externally to 1,2-difluorobenzene at δ -139 ppm. C{ H} and grown over 72 h from slow evaporation of a concentrated
3
1
1
1
H NMR spectra were internally referenced to residual solvent CDCl
3 3
solution at room temperature. H NMR (500 MHz, CDCl ,
resonances. In reporting spectral data, the following 22 ˚C): δ 1.09 (br, 6H). 1.64 (br, 18H), 2.49 (s, 6H), 3.20 (br,
1
abbreviations were utilized: s = singlet; d = doublet; t = triplet; 2H), 7.19 (br, 4H), 7.34 (br, 2H). H NMR (500 MHz, toluene-d ,
8
dd = doublet of doublets; m = multiplet; br = broad. Infrared 80 ˚C): δ 0.93 (dvt, J = 14.6, 7.2 Hz, 6H), 1.47 (m, 12H), 1.60
spectra were collected on a Nicolet Nexus 470 FT-IR E.S.P. (dvt, J = 8.0 Hz, 6H), 2.27 (s, 6H), 2.44 (m, 2H), 3.10 (m, 2H),
spectrometer using KBr plates and Nujol oil. Elemental 6.82 (d, J = 8.4 Hz, 2H), 7.16 (br s, 2H), 7.22 (d, J = 8.4 Hz, 2H).
1
3
1
analyses were performed by CALI, Inc. (Parsippany, NJ, USA).
C{ H} NMR (126 MHz, CDCl
3
, 22 ˚C): δ 18.4 (br), 19.0 (br),
SAFETY NOTE: Although the following procedure for LiAlH
4
20.2, 27.6 (br), 117.9 (br), 130.9, 131.4, 133.4 (d, JP-C = 5.9 Hz),
3
1
1
2
3
reduction was quenched in open air, and no incidents occurred 165.1. P{ H} NMR (202 MHz, CDCl , 22 ˚C) δ 34.1 (br d, JP-P =
1
in our hands, on larger scales, an inert atmosphere quenching 174 Hz), 27.2 (br d, JP-P = 174 Hz). P{ H} NMR (202 MHz,
2
31
-1
and workup is highly recommended. Screened reaction toluene-d
conditions with THF as solvent and excess (>2 equiv.) of LiAlH Found (Calc): C: 44.59 (44.51); H: 5.63 (5.75).
led only to partial reduction of the imine moiety. Therefore, it
was found that thermolysis in toluene was necessary for this with magnetic stir bar was added (PPh
8
, 80 ˚C): δ 33.4 (br s). IR(KBr) = 940 cm . Elem. Anal
4
H
(PNN )ReOCl
2
(3-Cl) To a 20 mL scintillation vial equipped
ReOCl (OEt) (1.06 g,
) (0.58 g, 1.26 mmol), and 3 mL toluene.
(0.2 g, 0.436 mol), lithium aluminum The resultant suspension was stirred for 12 h, layered with ca.
3
)
2
2
H
H
transformation to proceed efficiently.
1.26 mmol), PN N (1
H
H
PN N (1) PN N
H imine
hydride (0.017 g, 0.436 mol) and 10 mL of dry toluene were 15 mL pentane, and placed in a freezer at -35 ˚C. After 4 h, a
charged in a 50 mL Teflon taped culture tube equipped with a dark precipitate had formed and was isolated on a fine frit,
2
PTFE–coated stir bar The sealed culture tube was placed in an washed with 10 mL of a 2:1 pentane: Et O mixture, then again
oil bath and heated overnight to 120 °C with vigorous stirring. with 5 mL pentane, and dried under reduced pressure to
Within 1 h the yellow color of the suspension had turned into provide the product as a dark brown powder. Yield: 0.81 g
an intense neon orange color. The next morning it was (88%). Single crystals suitable for X-ray diffraction were grown
1
observed that the suspension had turned white. The cap was by slow evaporation of a concentrated toluene solution. H
3
removed and reaction was quenched with 1 mL of a 1.74 M NMR (500 MHz, CDCl ): δ 1.10 (dd, J = 15.4, 6.9 Hz, 3H), 1.27 (s,
solution of water in THF. The resulting suspension was filtered 3H), 1.33 (dd, J = 16.5, 6.8 Hz, 3H), 1.80 (dd, J = 18.2, 7.4 Hz,
through a short path of silica gel and the filtrate dried in vacuo 3H), 1.87 (dd, J = 15.7, 7.1 Hz, 3H), 2.25 (s, 3H), 2.41 (m, 1H),
to obtain a white solid. The product was dissolved in the 2.45 (s, 3H), 2.46 (s, 3H), 2.64 (s, 3H), 3.26 (m, 1H), 3.98 (dd, J =
minimum amount of hexanes and the solution placed 12.4 Hz, 2.9 Hz, 1H), 5.09 (dd, J = 12.4, 5.9 Hz, 1H), 6.70 (s, 1H),
overnight in a freezer set to −30 °C to obtain a white, 6.78 (d, J = 8.1 Hz, 1H), 6.92 (m, 1H), 7.03 (m, 2H), 7.10 (d, J =
crystalline solid that was pure by NMR. Yield: 130.5 mg (65%) 8.5 Hz, 1H), 7.24 (dd, J = 8.2, 1.9 Hz, 1H), 7.50 (m, 1H), 8.29 (br
1
3
3
13
1
H NMR (500 MHz, C
6
D
3
6
) δ 0.97 (dd, 6H, JP–H = 11.6 Hz, JH–H
=
d, J = 5.9 Hz, 1H). C{ H} NMR (126 MHz, CDCl
3
) : δ 18.79,
3
.9 Hz), 1.06 (dd, 6H, JP–H = 15.3 Hz, JP–H = 7.0 Hz), 1.95 (hd, 19.58, 19.80, 19.99, 20.27, 20.33, 20.38, 20.64, 21.16, 29.83 (d,
3
H, JP–H = 7.0 Hz, JP–H = 1.8 Hz), 2.14 (s, 3H), 2.15 (s, 3H), 2.20
6
2
3
JP-C = 36 Hz) 31.26 (d, JP-C = 25 Hz), 56.96, 118.19, 122.66,
3
s, 3H), 2.24 (s, 6H), 3.07 (t, 1H, JH–H = 6.7 Hz, benzylic NH), 129.76, 130.03, 131.66, 131.83, 131.97, 132.47, 133.05,
(
3
31
.06 (d, 2H, JH–H = 6.7 Hz), 6.76 (s, 2H), 6.92 (ddd, 2H, J = 6.9, 133.55, 134.48, 136.59, 141.75, 154.36. P{ H} NMR (202 MHz,
1
4
-1
6
3
.1, 1.8 Hz), 7.05 (d, 1H, J = 1.5 Hz), 7.19 (t, 1H, J = 2.3 Hz), 7.28 CDCl ): δ 37.4 (s). IR (KBr): 963 (VRe=O), 3214 (VN-H) cm . Elem.
(
dd, 1H, J = 8.3, 4.7 Hz), 7.38 (d, 1H, J = 8.1), 8.16 (d, 1H, J = 9.5 Anal. Found (Calc): C: 48.73 (49.18); H: 5.22 (5.50); N: 3.46
1
3
1
Hz, aromatic NH). C{ H} NMR (126 MHz, C
6
D
6
) δ 148.51, (3.82).
48.35, 144.09, 141.85, 133.69, 131.95, 131.47, 131.00, (PNN )ReOBr
30.86, 130.51, 129.91, 129.32, 128.90, 128.06, 122.55, with magnetic stir bar was added (PPh
H
1 (3-Br) To a 20 mL scintillation vial equipped
1 ReOBr (OEt) (364 mg,
1 ) (181 mg, 0.394 mmol), and 3 mL
2 ) δ toluene. The resultant suspension was stirred for 12 h, layered
−14.5. Elem. Anal. Found (Calc): C: 78.21 (78.22); H: 8.98 (8.97) with ca. 15 mL pentane, and placed in a freezer at -35 ˚C. After
PNP)ReOCl (2): To a Teflon taped culture tube equipped 4 h, a dark precipitate had formed and was isolated on a fine
with a magnetic stir bar was added (PPh
2
3
)
2
2
H
H
22.42, 118.94, 118.38, 51.81, 23.32, 20.97, 20.85,20.82, 0.391 mmol), PN N
(1
3
1
1
6 6
0.46, 20.31, 19.06, 18.99. P{ H} NMR (202 MHz, C D
(
2
3
)
2
ReOCl
2
(OEt) (1.56 g, frit, washed with 10 mL of a 2:1 pentane: Et
2
O mixture, then
H
1
.85 mmol), PN P (885 mg, 2.06 mmol), and 10 mL of toluene again with 5 mL pentane, and dried under reduced pressure to
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DOI: 10.1039/C6DT03640F
ARTICLE
provide the product as a dark brown powder. Yield: 145 mg (0.014 mL, 0.10 mmol). The solution was then heated at 80 ˚C
1
(
45%). H NMR (500 MHz, CDCl
H), 1.23 (s, 3H), 1.33 (dd, J = 16.6, 6.8 Hz, 3H), 1.91 (m products was observed by H and P{ H} NMR spectroscopy
H),2.26 (s, 3H), 2.43 (m, 1H), 2.46 (s, 3H), 2.47 (s, 3H), 2.66 (s, corresponding to deprotonated isomers of 4-Br and
H), 3.37 (m, 1H), 4.00 (dd, J = 12.4, 2.8 Hz, 1H), 5.21 (dd, J = concomitant formation of colorless solids (assumed to be
2.4, 6.2 Hz), 6.71 (s, 1H), 6.75 (d, J = 8.1 Hz, 1H), 6.90 (dd, J = HNEt Br) was observed. The solution was then filtered through
3
): δ 1.08 (dd, J = 15.5, 6.9 Hz, for 1 h over which time full conversion to a 75:25 mixture of
1
31
1
3
6
3
1
8
7
5
2
=
1
1
,
3
.5, 4.4 Hz, 1H), 7.04 (d, J = 1.0 Hz, 2H), 7.11 (d, J = 8.5 Hz, 1H), a pad of Celite and dried under reduced pressure to provide a
.24 (d, J = 1.7 Hz, 1H), 7.55 (dd, J = 8.7, 1.0 Hz, 1H), 8.60 (d, J = glutinous, dark green residue. The residue was washed with 5
1
3
1
.9 Hz). C{ H} NMR (126 MHz, CDCl
3
) : δ 18.96, 19.67, 20.01, mL of pentane and dried to give the desired product as a dark
0.39, 20.62, 20.66, 22.32, 31.36 (d, JP-C = 24.8 Hz), 31.69 (d, JPC green, free-flowing powder. Yield: 34 mg (92%). Major Isomer
1
36.5 Hz), 56.99, 115.39, 118.43, 122.55, 128.21, 129.02, (78%) H NMR (500 MHz, CDCl
3
): δ 0.69 (dd, J = 19.3, 7.0 Hz,
29.60, 129.81, 130.12, 131.63, 132.00, 132.31, 133.58, 3H), 1.23 (dd, J = 19.3, 6.9 Hz, 3H), 1.43 (dd, J = 14.0, 7.1 Hz,
1
34.80, 136.68, 142.06, 152.25, 154.05, 157.19. P{ H} NMR 3H), 1.63 (dd, J = 17.6, 6.9 Hz, 3H), 1.89 (s, 3H), 1.98 (s, 3H),
3
1
-1
(
202 MHz, CDCl
3
): δ 35.2 (s). 962 (VRe=O), 3189 (VN-H) cm
2.35 (s, 3H), 2.40 (s, 3H), 2.44 (s, 3H), 2.87 (m, 1H), 3.21 (m,
(
PNN)ReOCl (4-Cl) To a Teflon taped culture tube in 1H), 4.19 (dd, JH-H = 12.3, JH-P = 3.8 Hz, 1H), 4.32 (d, J = 12.3 Hz,
H
toluene was added (PNN )ReOCl
2
(3-Cl) (238 mg, 0.325 mmol) 1H), 6.94 (m, 3H), 7.08 (m, 1H), 7.16 (m, 2H), 7.28 (m, 1H), 7.46
3
and triethylamine (0.060 mL, 0.43 mmol). The solution was (dd, J = 8.6, 4.5 Hz, 1H). P{ H} NMR (202 MHz, CDCl
1
then heated at 80 ˚C for 1 h over which time full conversion to (s).Minor Isomer (22%) – H NMR (500 MHz, CDCl
1
1
3
): δ 60.7
3
): δ 0.67
1
31
1
a 75:25 mixture of products was observed by H and P{ H} (dd, J = 18.0, 7.0 Hz, 3H), 0.99 (dd, J = 18.2, 6.8 Hz, 3H), 1.14 (s,
NMR spectroscopy corresponding to deprotonated isomers of 3H), 1.43 (m, 3H), 1.57 (dd, J = 16.7, 7.0 Hz, 3H), 2.31 (s, 3H),
(
PNN)ReOCl, and concomitant formation of colorless solids 2.32 (s, 3H), 2.41 (s, 3H), 2.42 (s, 3H), 2.73 (m, 1H), 3.13(m,
assumed to be HNEt Cl) was observed. The solution was then 1H), 4.86 (d, J = 12.6 Hz, 1H), 5.39 (dd, J = 12.6, 9.1 Hz), The
through pad of expected remaining 7 aromatic resonances cannot be resolved
Celite and dried under reduced pressure to provide a due to presumed overlap with resonances corresponding to the
(
3
filtered
a
3
1
1
13
1
glutinous, dark green residue. The residue was washed with 2 major isomer. P{ H} NMR (202 MHz, CDCl
3
): δ 37.4 (s). C{ H}
mL of pentane and dried to give the desired product in NMR (126 MHz, CDCl ): δ 16.55 (JP-C = 5.3 Hz), 18.23, 18.49,
3
analytically pure form as a dark green, free-flowing powder. 19.06, 19.76, 19.82, 20.18, 20.39, 20.55, 20.76, 23.45 (d, J =
Yield: 180 mg (80%). Single crystals suitable for X-ray 29.6 Hz), 26.72 (d, J = 27.0 Hz), 64.92, 114.76, 115.67, 115.76,
diffraction were grown from a concentrated toluene solution 120.01, 120.16, 127.67, 127.98, 128.16, 128.19, 128.94,
1
layered with pentane. Major Isomer (75%) - H NMR (500 129.01, 130.65, 130.87, 130.93, 132.58, 133.22, 133.92,
MHz, CDCl
3
): δ 0.72 (dd, J = 19.0, 7.0 Hz, 3H), 1.24 (dd, J = 19.1, 134.28, 137.65, 149.31, 162.37, 169.93. IR (KBr): 968 (VRe=O
)
-1
6.9 Hz, 3H), 1.39 (dd, 14.1, 7.2 Hz, 3H), 1.58 (dd, J = 17.8, 6.9 cm .
Hz, 3H), 1.91 (s, 3H), 1.99 (s, 3H), 2.34 (s, 3H), 2.40 (s, 3H), 2.45
s, 3H), 2.86 (m, 1H), 3.06 (m, 1H), 4.27 (dd, JH-H = 12.4, JH-P
(PNN)ReOCl(PMe
3
) (4-PMe
3
): To a J. Young tube in C
6
D
6
3
(
=
was added (PNN)ReOCl (4-Cl) (15 mg, 0.022 mmol) and PMe
4
7
2
.1 Hz, 1H), 4.35 (d, J = 12.4 Hz, 1H), 6.95 (m, 4H), 7.17 (m, 2H), (0.003 mL, 0.03 mmol). Upon addition of PMe
3
3
the dark green
solution immediately became purple, as full conversion to the
1
1
3
.27 (m, 1H), 7.49 (dd, J = 8.5, 4.5 Hz, 1H). P{ H} NMR (CDCl ,
1
31
1
1
02 MHz): δ 60.2 (s) Minor Isomer (25%) - H NMR (500 MHz, adduct was noted by P{ H} NMR and H NMR spectroscopy.
): δ 0.66 ( m, 3H), 1.01 (dd, J = 18.2, 6.8 Hz, 3H), 1.18 (s, The solution was then filtered through Celite, dried under
H), 1.50 (dd, J = 16.9, 7.0 Hz, 3H), 2.30 (s, 3H), 2.31 (s, 3H), reduced pressure to provide a dark purple residue. The residue
CDCl
3
3
2
1
.36 (s, 3H), 2.43 (s, 3H), 2.52 (m, 1H), 2.72 (m, 1H), 4.89 (d, J = was then redissolved in pentane and filtered again.
2.8 Hz, 1H), 5.42 (dd, J = 12.8, 8.9 Hz, 1H), 6.78 (s, 1H). The Subsequent removal of solvent under reduced pressure
fourth isopropyl CH
3
and remaining 7 aromatic resonances provided the product as a free-flowing, dark purple powder in
cannot be resolved due to presumed overlap with resonances >97% purity (NMR evidence). Yield: 14 mg (85%). Major
3
1
1
1
2
corresponding to the minor isomer. P{ H} NMR (202 MHz, Isomer (68%): H NMR (500 MHz, C
6
D
6
): δ 1.05 (d, JP-H = 9.2
): δ 16.62, Hz, 9H), 1.20 (dd, J = 11.7, 5.6 Hz, 3H), 1.24 (dd, J = 13.7, 5.5
7.56, 17.96, 18.35, 18.68, 19.79, 20.31, 20.61 (d, JP-C = 19.6 Hz, 3H), 1.36 (dd, J = 11.6, 7.3 Hz, 3H), 1.51 (dd, J = 13.7, 7.2
Hz), 20.90 (d, JP-C = 29.8 Hz), 21.30 (d, JP-C = 23.7 Hz), 23.05 (d, Hz, 3H), 2.01 (s, 3H), 2.14 (m, 1H), 2.25 (s, 3H), 2.27 (s, 3H),
P-C = 29.2 Hz), 23.79 (d, JP-C = 23.6 Hz), 26.60 (d, JP-C = 26.5 Hz), 2.31 (s, 3H),2.84 (m, 1H), 2.85 (s, 3H), 4.67 (dd, J = 12.3, 3.3 Hz,
1
3
1
CDCl
3
): δ 39.1 (s)
C{ H} NMR (126 MHz, CDCl
3
1
J
6
1
1
1
1
4.72, 69.01, 114.58, 114.97, 116.17 (d, JP-C= 10.3 Hz), 119.78, 1H), 6.00 (dd, J = 12.3, 3.0 Hz, 1H), 6.74 (m, 1H), 6.84 (d, J = 1.8
20.12, 122.73 (d JP-C = 8.6 Hz), 125.42, 127.72, 127.87, 128.09, Hz, 1H), 6.88 (br, 1H), 6.91 (br, 1H), 7.0 (d, J = 8.1 Hz, 1H), 7.07
28.19, 129.10, 129.16, 129.43, 130.56, 130.80, 130.89, (td. J = 8.5, 2.0 Hz, 1H), 7.29 (dd, J = 8.4 , 4.4 Hz, 1H), 7.33 (dd, J
3
1
1
30.94, 131.42, 132.69, 133.14, 133.28, 133.44, 134.00, = 7.3, 2.0 Hz, 1H). P{ H} NMR (202 MHz, C
6
D
6
): δ 4.38 (s,
). Minor Isomer (32%): H NMR (500 MHz,
): δ 1.10 (d, J = 9.5 Hz, 9H), 1.08 (dd, J = 14.0, 5.7 Hz, 3H),
.1.16 (dd, J = 10, 7.2 Hz, 3H), 1.22 (s, 3H), 1.25 (dd, J = 16.7, 7.8
PNN)ReOBr(4-Br) To a J. Young tube in toluene was added Hz, 3H), 1.38 (dd, J = 15, 6.8 Hz, 3H), 2.18 (s, 3H), 2.23 (s, 3H),
i
1
2 3
34.05, 134.42, 137.55, 146.69 (m), 149.82, 160.78, 170.44 (d, P Pr ), -50.2 (s, PMe
-1
JP-C = 15.4 Hz). IR (KBr): 962(VRe=O), 970 (VRe=O) cm . Elem. Anal.
6 6
C D
Found (Calc): C: 51.60 (51.75); H: 5.64 (5.65); N: 3.81 (4.02).
(
H
2
(PNN )ReOBr (3-Br) (41 mg, 0.049 mmol) and triethylamine 2.34 (s, 3H), 2.41 (m, 1H), 2.50 (m, 1H), 2.57 (s, 3H), 4.78 (dd, J
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DOI: 10.1039/C6DT03640F
Journal Name
ARTICLE
3
1
1
=
6
1
12.3, 4.0 Hz, 1H), 5.75 (dd, J = 12.3, 7.1 Hz, 1H), 6.80 (s, H),
.94 (d, J = 1.9 Hz, 1H), 7.13 (m, 1H), 7.22 (dd, J = 8.6, 4.5 Hz, Isomer (78%) H NMR (500 MHz, C
H), 7.39 (d, J = 8.1 Hz, 1H). The expected remaining 3 Hz, 3H), 1.11 (m, 6H), 1.17 (dd, J = 17.5, 6.9 Hz, 3H), 1.30 (s,
P{ H} NMR spectroscopy. Yield: 28.8 mg (85%). Major
1
6 6
D ): δ 1.03 (dd, J = 16.2, 6.9
aromatic resonances were unable to be found and resolved due 3H), 1.79 (s, 3H), 1.82 (m, 1H), 2.09 (m, 1H), 2.15 (s, 3H), 2.22
to presumed overlap with resonances corresponding to the (s, 3H), 2.27 (s, 3H), 2.84 (s, 3H), 4.99 (dd, J = 13.2, 2.5 Hz), 5.83
3
1
1
i
6 6 2
major isomer. P{ H} NMR (202 MHz, C D ): δ 0.3 (s, P Pr ), - (dd, J = 13.2, 9.7 Hz), 6.77 (d, J = 12.0 Hz, 2H), 6.86 (m, 1H),
1
3
1
C{ H} NMR (126 MHz, C
4
1
2
3
1
9.2 (s, PMe
3
)
6
D
6
): δ 18.89, 18.94, 6.99 (m, 3H), 7.08 (dd, J = 8.3, 4.2 Hz, 1H), 7.42 (d, J = 8.3 Hz)
3
1
1
P{ H} NMR (202 MHz, C
9.14, 19.22 (d, J = 3.6 Hz), 19.43, 19.86 (m), 19.96(m), 20.17,
0.24, 20.34, 20.41, 20.59, 20.66, 22.29, 25.50 (d, J = 14.0 Hz),
6 6
D ): δ 27.9 (s). Minor Isomer (22%) -
1
6 6
H NMR (500 MHz, C D ): δ 0.53 (dd, J = 18.8, 7.0 Hz, 3H), 0.82
0.20 (d, J = 16.4 Hz), 67.66, 119.94, 128.78, 129.33, 129.85, (dd, J = 13.9, 7.1 Hz), 1.12 (s, 3H) 1.53 (s, 3H), 2.16 (s, 3H), 2.31
30.19, 130.82. 131.27, 134.06, 136.02, 151.03. IR (KBr): 957 (s, 3H), 2.43 (s, 3H), 2.49 (s, 3H), 4.75 (d, J = 13.9 Hz, 1H), 5.33
(
Re=O), 945 (Re=O)
.
(dd, J = 13.9, 6.1 Hz, 1H). Two expected resonances for the
PNN)ReO(OTf) (4-OTf): To a scintillation vial equipped isopropyl methyl (CH ) protons, and all eight aromatic protons
with a magnetic stir bar was added (PNN)ReOCl (4-Cl) (19.0 were unable to be found and resolved presumably due to
mg, 0.027 mmol) in 3 mL of a 2:1 CH Cl : Et O solution. To the overlap with signals corresponding to the major isomer in
stirring, dark green solution was added AgOTf (6.9 mg, 0.027 solution. P{ H} NMR (202 MHz, C
mmol) resulting in an immediate color change to dark red- (126 MHz, C ): δ 16.90, 17.10, 17.51, 17.88, 18.89, 19.16,
(
3
2
2
2
31
1
13
1
6 6
D ): δ 33.3 (s). C{ H} NMR
6 6
D
brown. The solution was allowed to stir for 12 h over which 19.79, 20.37, 20.53, 20.57, 20.78, 24.06 (d, J = 20.6 Hz), 69.23,
time a suspension had formed as AgCl precipitated out of 120.52, 126.91, 128.19, 129.49, 129.69, 129.92, 130.72,
solution. The solution was then filtered through a pad of Celite 131.84, 133.54, 134.87, 135.85, 136.56, 139.73,147.13, 154.91,
-1
and dried under reduced pressure to give a dark red-brown 175.03, 175.21, 178.28. IR (KBr):939 (VRe=O), 1653 (VC=O) cm
residue. The residue was then washed with pentane, and dried (PNN)ReO(H) (4-H): To a J. Young tube in C was added
under reduced pressure to provide 4-OTf as a 90:10 mixture of (PNN)ReOCl (4-Cl) (24 mg, 0.035 mmol) and a 1.0 M toluene
.
6 6
D
1
isomers in ca. 97% purity ( H NMR evidence). Yield: 21 mg solution of NaHBEt
96%). Single crystals suitable for X-ray diffraction were grown then rotated for ten minutes allowing formation of an emerald
from a concentrated THF solution layered with pentane. Major green, homogeneous solution. The solution was allowed to
3
(0.035 mL, 0.035 mmol). The solution was
(
1
6 6
Isomer (90%) – H NMR (500 MHz, C D ): δ 0.62 (J = 17.8, 7.0 react for 16 h, then filtered through Celite, and dried under
Hz, 3H), 1.01 (dd, J = 16.2, 7.1 Hz, 3H), 1.12 (dd, J = 18.1, 7.7 reduced pressure. The resultant residue was washed with a
Hz, 3H), 1.33 (dd, J = 20.3, 7.0 Hz, 3H), 1.95 (s, 3H), 2.09 (s, 3H), minimum of cold pentane and dried to provide the product as
1
.15 (s, 3H), 2.19 (s, 3H), 2.22 (s, 3H), 2.49 (m, 1H), 3.09 (m, a lime green solid determined to be >95% pure by H NMR
2
1
1
H), 3.86 (d, J = 12.4 Hz, 1H), 3.90 (d, J = 12.4 Hz, 1H), 6.66 (s, spectroscopy. Yield: 21 mg, (91%). Major Isomer (88%)
H
1
H), 6.86 (m, 4H), 7.01 (m, 2H), 7.29 (dd, J = 8.5, 4.3 Hz). F NMR (500 MHz, C
9
1
6
D
6
): δ 0.54 (dd, J = 17.5, 7.0 Hz, 3H), 0.90
3
1
1
6 6
NMR (407 MHz, C D ): δ -73.06 (s). P{ H} NMR (202 MHz, (dd, J = 17.5, 6.9 Hz, 3H), 0.98 (dd, J = 15.0, 7.0 Hz, 3H), 1.24
1
C
C
6
D
D
6
6
): δ 64.5 (s). Minor Isomer (10%)- H NMR (500 MHz, (dd, J = 17.8, 6.8 Hz, 3H), 2.01 (s, 3H), 2.07 (m, 2H), 2.13 (s, 3H),
): δ 0.73 (dd, J = 16.6, 6.8 Hz, 3H), 1.11 (s, 3H), 1.59 (dd, J = 2.31 (s, 3H), 2.32 (s, 3H), 2.50 (s, 3H), 4.36 (dd, J = 13.0, 4.4 Hz,
6
1
8.4, 7.4 Hz, 3H), 1.97 (s, 3H), 2.13 (s, 3H), 3.71 (d, J = 13.3 Hz, 1H), 4.57 (d, J = 13.0 Hz, 1H), 6.85 (m, 2H), 6.99 (br, 3H), 7.06
H), 5.30 (dd, J = 13.3, 6.3 Hz, 1H). Other expected resonances (m, 2H), 7.54 (dd, J = 8.9, 4.4 Hz, 1H), 8.22 (d, JP-H = 17.4 Hz, 1H,
1
3
1
1
were unable to be located and resolved due to presumed Re-H). P{ H} NMR (202 MHz, C
6
D
6
): δ 74.4 (s). Minor Isomer
): δ 0.57 (dd, J = 17.2, 7.1 Hz,
): δ -73.57. P{ H} NMR (202 MHz, 3H), 0.85 (dd, J = 12.6, 6.9 Hz, 3H), 1.51 (s, 3H), 2.14 (s, 3H),
): δ 42.2 (s). C{ H} NMR (126 MHz, C ): δ 17.29, 19.68, 2.15 (s, 3H), 2.28 (s, 3H), 2.75 (s, 3H), 3.94 (d, J = 14.5 Hz, 1H,
1
6 6
overlap with resonances corresponding to the major isomer. (12%) - H NMR (500 MHz, C D
1
9
31
1
6 6
F NMR (407 MHz, C D
1
3
1
C
6
D
6
6 6
D
2
1
1
1
0.24, 20.39, 26.30, 26.50, 26.54, 26.71, 62.98, 114.60, 117.96, Re-H), 4.82 (d, J = 13.0 Hz, 1H), 5.13 (dd, J = 13.0, 8.3 Hz,1H),
22.51, 128.56, 128.85, 129.03, 129.57, 130.37, 131.14, 7.51 (d, J = 8.1 Hz, 3H). Two isopropyl methyl signals were
31.29, 132.02, 134.19, 134.31, 134.89, 139.71, 151.07, observed but unable to be resolved due to significant overlap
56.57, 169.82. IR (KBr): 1195 (VOTf), 1154 (VOTf), 966 (VRe=O
)
with major isomer. No isopropyl methine signals were found
for the minor isomer, and no other aromatic signals were able
-1
cm .
(
PNN)ReO(OAc) (4-OAc): To a scintillation vial equipped to be resolved due to significant overlap with the resonances of
3
with a magnetic stir bar was added (PNN)ReOCl (4-Cl) (32.8 the major isomer. P{ H} NMR (202 MHz, C
1
1
6
D
6
) : δ 49.9 (s).
1
3
1
C{ H} (126 MHz, C D ): δ 19.58, 20.53, 23.62, 27.82, 61.86,
mg, 0.047 mmol) in 4 mL of a 1:1 CH
2
Cl
2
: Et
2
O solution. To the
6 6
stirring, dark green solution was added AgOAc (8.0 mg, 0.047 112.57, 112.94, 116.48, 119.75, 128.33, 128.54, 128.80,
mmol) resulting in immediate precipitation of white solids, 129.19, 129.30, 129.54, 129.74, 130.23, 130.47, 131.16,
presumed to be AgCl. After being allowed to stir for 16 h, 133.08, 134.29, 134.73, 135.30, 146.75, 166.12, 168.77. Anal.
2
another 1 mL of Et O was added resulting in further Found(Calcd): C: 54.18(54.44); H: 5.98 (6.09); N: 3.77 (4.23).
precipitation of solids. The resultant suspension was filtered
through a pad of Celite and dried under reduced pressure to
provide the product as a light, yellow-green powder in >95%
Acknowledgements
1
purity, determined to be a mixture of isomers by H and
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We are grateful to the Welch Foundation (Grant A-1717 to
Ple Da s ae l tdo onn To rt aa nd sj ua s ct t mi o an r sg ins
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DOI: 10.1039/C6DT03640F
ARTICLE
1
3
O.V.O.) for support of this research. A.J.K. acknowledges
support via the LSAMP NSF Fellowship (Award. No. HRD-
J. J. Davidson, J. C. DeMott, C. Douvris, C. M. Fafard, N.
Bhuvanesh, C.-H. Chen, D. E. Herbert, C. -I. Lee, B. J.
McCulloch, B. M. Foxman and O. V. Ozerov, Inorg. Chem.,
1406755). We would like to thank Dr. Vladimir I. Bakhmutov
2
015, 54, 2916-2935.
for providing insight regarding interpretation of NMR spectra. 14
We are grateful to David Kempe for helping with acquisition of
R. Rossi, A. Marchi, L. Magon, U. Casellato, S. Tamburini and R.
Graziani, J. Chem. Soc. Dalton Trans., 1991, 263-268.
J.M. Mayer, Inorg. Chem., 1988, 27, 3899-3903.
To illustrate this inequivalence, one phosphorus is attached to
the ring that is raised towards the oxo, while the other
phosphorus is attached to the ring that is pivoted away
from the oxo.
1
5
IR spectra and would like to extend our gratitude to Dr.
Nattamai Bhuvanesh for helpful discussions regarding X-ray
crystallography.
1
6
1
7
Notes and references
The 80
-symmetric isomer (oxo trans to
“flipping”, but that seems less likely. However, isomers
with oxo trans and cis to the Namido for (PNP)ReOCl have
°
C spectrum could also arise from isomerization to a
C
2
amido
N )
with slow
1
(
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