Formyl C-H activation in N,N-Dimethylformamide by a dirhenium carbonyl complex

Article abstract of DOI:10.1016/j.jorganchem.2017.03.009

The reaction of Re₂(CO)₈[μ-η²-C(H)=C(H)Buⁿ](μ-H), 1 with N,N-dimethylformamide (DMF) at 70 C for 6 h has yielded three new compounds: Re₂(CO)₈(μ-η²-O=CNMe₂)(μ-H), 2, (16% yield), Re₂(CO)₇(NHMe₂)(μ-η²-O=CNMe₂)(μ-H), 3, (30% yield), Re₂(CO)₉(NHMe₂), 4 (14% yield). Compounds 2 and 3 contain a C,O-η²-bridging formamido (O=CNMe₂) ligand and a bridging hydrido ligand that were formed by the elimination of hexene from 1 and the oxidative addition of the formyl C-H bond of the DMF to the dirhenium group of 1. Compound 3 also contains an NHMe₂ ligand that was apparently formed by the decarbonylation of DMF and the transfer of the formyl hydrogen atom to the NMe₂ group. Compound 4 contains a similarly formed NHMe₂ ligand. Compound 2 was also obtained by the reaction of 3 with CO and compound 3 was obtained by the reaction of 2 with DMF. Compound 4 was obtained independently in a high yield by the reaction of Re₂(CO)₉(NCMe) with NHMe₂. Compounds 2, 3 and 4 were characterized structurally by single-crystal X-ray diffraction analyses.

Full text of DOI:10.1016/j.jorganchem.2017.03.009

Journal of Organometallic Chemistry xxx (2017) 1e5
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Formyl C-H activation in N,N-Dimethylformamide by a dirhenium
carbonyl complex
Richard D. Adams*, Poonam Dhull
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States
a r t i c l e i n f o
a b s t r a c t
2-C(H)¼C(H)Bun](
m-H), 1 with N,N-dimethylformamide (DMF) at 70 C for 6 h
Article history:
The reaction of Re2(CO)8[
has yielded three new compounds: Re2(CO)8(
m
-
h
m
-
h
2-O¼CNMe2)(
m-H), 2, (16% yield), Re2(CO)7(NHMe2)(m-
Received 17 January 2017
Received in revised form
1 March 2017
Accepted 4 March 2017
Available online xxx
h
h
2-O¼CNMe2)(
m-H), 3, (30% yield), Re2(CO)9(NHMe2), 4 (14% yield). Compounds 2 and 3 contain a C,O-
2-bridging formamido (O¼CNMe2) ligand and a bridging hydrido ligand that were formed by the
elimination of hexene from 1 and the oxidative addition of the formyl C-H bond of the DMF to the
dirhenium group of 1. Compound 3 also contains an NHMe2 ligand that was apparently formed by the
decarbonylation of DMF and the transfer of the formyl hydrogen atom to the NMe2 group. Compound 4
contains a similarly formed NHMe2 ligand. Compound 2 was also obtained by the reaction of 3 with CO
and compound 3 was obtained by the reaction of 2 with DMF. Compound 4 was obtained independently
in a high yield by the reaction of Re2(CO)9(NCMe) with NHMe2. Compounds 2, 3 and 4 were characterized
structurally by single-crystal X-ray diffraction analyses.
Keywords:
Rhenium
N,N-dimethylformamide
CH activation
Bridging ligand
Crystal structure
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
reactions under mild conditions by processes involving aromatic C-
H activation [10]. To extend our studies of C-H bond activation re-
The activation of C-H bonds by metal atoms has received much
attention over the last few decades. Most studies have been focused
on the activation of aliphatic [1] and aromatic [2] CH bonds. Today,
there are a variety of metal complexes that can functionalize aro-
matic compounds catalytically by CH activation processes [3].
Comparatively, little attention has been paid to the activation of
formyl, HC¼O, C-H bonds as found in aldehydes, HC(¼O)R [4],
formates, HC(¼O)OR and formamides, HC(¼O)NR2 [5] although
such activations are implicit in the catalytic reactions known as
hydroacylation, e.g. (1) [6], hydroesterification e. g. (2) [7] and
hydrocarbamoylation e. g. (3) [8]. The formation of metal com-
plexes containing formamido ligands by the activation of the
formyl C-H bonds of formamide compounds are very rare [5].
Interestingly, Bercaw and Labinger reported that DMF reacts with
actions at dirhenium centers, we have now investigated the re-
actions of the hexenyl ligand-bridged compound Re2(CO)8[
m
-
h2
m-H), 1 with N,N-dimethylformamide (DMF). The
-
C(H) ¼ C(H)Bun](
reaction of 1 with DMF at 70 ꢀC for 6 h yielded three new com-
pounds:
Re2(CO)7(NHMe2)(
Re2(CO)8(
m
-
h
2-O¼CNMe2)(
m
-H),
-H),
2,
(16%
(30%
yield),
yield),
m
-h
2-O¼CNMe2)(
m
3,
Re2(CO)9(NHMe2), 4 (14% yield). Compounds 2 and 3 contain a C,O-
h
2-bridging formamido (O¼CNMe2) ligand and a bridging hydrido
ligand that were formed by the elimination of hexene from 1 and
the oxidative addition of the formyl C-H bond of the DMF to the
dirhenium group of 1. Compound 3 contains an NHMe2 ligand that
was apparently formed by the decarbonylation of DMF and the
transfer of the formyl hydrogen atom to the NMe2 residue. Com-
pound 4 contains a similarly formed NHMe2 ligand. All new com-
pounds were characterized by single-crystal X-ray diffraction
analyses. Details of our studies of these reactions are reported
herein.
[AsPh4][Ir(CO)2I2] to yield the compound [AsPh4][Ir(CO)(k2
-
CH2N(CH3)CHO)Cl2I] by CH activation at one of the N-methyl
groups [9].
In recent studies, we have shown that dirhenium complex
Re2(CO)8)(m-H)(m-Ph) is capable of engaging aromatic substitution
1.1. Experimental details
General Data. Reagent grade solvents were dried by the stan-
dard procedures and were freshly distilled prior to use. Infrared
* Corresponding author.
E-mail address: adamsrd@mailbox.sc.edu (R.D. Adams).
spectra were recorded on a Nicolet IS10 Midinfrared FT-IR
http://dx.doi.org/10.1016/j.jorganchem.2017.03.009
0022-328X/© 2017 Elsevier B.V. All rights reserved.
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R.D. Adams, P. Dhull / Journal of Organometallic Chemistry xxx (2017) 1e5
spectrophotometer. 1H NMR was recorded on a Varian Mercury 300
spectrometer operating at 300 MHz respectively. Mass spectro-
metric (MS) measurements performed by a direct-exposure probe
using electron impact ionization (EI) were made on a VG 70S in-
strument. Re2(CO)10 obtained from STREM and was used without
further purification. Anhydrous N,N-dimethylformamide (DMF)
was purchased from Sigma Aldrich and was used without further
purification. Dimethylamine in a 2 M tetrahydrofuran solution was
1911(s), 1896(sh). 1H NMR (CD2Cl2,
d in ppm) 3.14 (s, 3H, N-CH3),
3.01 (d, CH3, 3J ¼ 6.3 Hz), 2.92 (s, 3H, N-CH3), 2.85 (d, CH3,
3J ¼ 6.3 Hz), ꢁ11.44 (s, 1H, hydride). Mass Spec. EI/MS m/z.
Mþ ¼ 686, Mþ-1CO ¼ 658. The isotope distribution pattern is
consistent with the presence of two rhenium atoms. Spectral data
for 4: IR nCO (cmꢁ1 in CH2Cl2): 2101(w), 2039 (s), 2009(w),1981 (vs),
1954(w), 1916(m). 1H NMR (CD2Cl2,
d in ppm) 2.96 (d, 6H, 2NCH3,
3J ¼ 5.7 Hz). Mass Spec. EI/MS m/z. Mþ ¼ 669 with an isotope dis-
tribution pattern consistent with the presence of two rhenium
atoms.
purchased from Sigma Aldrich. Re2(CO)8[
m-
h
2-C(H) ¼ C(H)Bun](
m-
H), 1 [11] and Re(CO)9(NCMe) [12] was prepared according to
previously reported procedures. Product separations were per-
formed by TLC in air on Analtech 0.25 and 0.5 mm silica gel 60 Å
F254 glass plates.
1.3. Reaction of 1 with excess DMF
150.0 mg (0.22 mmol) of 1 dissolved in a mixture of DMF (5 mL)
and heptane (45 mL). The solution was then heated to reflux for
20 min. The solution was cooled and the solvent was then removed
in vacuo. The residue was extracted in CH2Cl2 and separated by TLC
by using a 4:1 hexane/CH2Cl2 (v/v) solvent mixture to give a 3,
1.2. Reaction of Re2(CO)8[
m
-
h
2-C(H)¼C(H)Bun](
m-H), 1 with DMF
50.0 mg (0.0735 mmol) of 1 was dissolved in 0.80 mL benzene-
d6 in a 5 mm NMR tube. 30 L (0.384 mmol) of DMF were added
and the NMR tube was briefly evacuated and then filled with ni-
trogen. The NMR tube was then heated to 70 ꢀC for 6 h. A 1H NMR
spectrum obtained after this period showed several new hydride
m
78.0 mg (51% yield), 4, 10.0 mg (7% yield) along with Re2(CO)10
,
35.0 mg (24% yield) and 5, 30.0 mg (12% yield).
1.4. Addition of CO to 3
resonances, see below, including a resonance at
d
¼ ꢁ5.66 which is
attributed to HRe(CO)5 [13]. The contents were then put into a flask
and the solvent was removed in vacuo. The residue was dissolved in
CH2Cl2 and separated by TLC by using a 70:30 hexane/CH2Cl2 (v/v)
solvent mixture to yield in the order of elution: 8.0 mg of
75.0 mg (0.109 mmol) of 3 was dissolved in 35 mL of benzene.
The solution was then heated to reflux for 1 h in the presence of a
slow purge of CO gas. After this period, a light yellow solution
formed and the solvent was then removed in vacuo. The residue
was extracted in CH2Cl2 and separated by TLC by using a 70:30
hexane/CH2Cl2 (v/v) solvent mixture to give 60.0 mg of 2 (82%
yield).
Re2(CO)8(
Re2(CO)7(NHMe2)(
m
-
h
2-O¼CNMe2)(
m-H), 2, (16% yield); 15.0 mg of
m-h
2-O¼CNMe2)(
m-H), 3, (30% yield); 7.0 mg of
Re2(CO)9(NHMe2), 4, (14% yield); 9.0 mg of Re2(CO)10 (19% yield),
and 8.0 mg (9% yield) of the known compound [Re(CO)3(m3-OH)]4,
5, [14]. Spectral data for 2: IR nCO (cmꢁ1 in CH2Cl2): 2112(w),
2089(s), 2013(vs), 1992(sh), 1948(s). 1H NMR (CD2Cl2,
d
in ppm) 3.11
1.5. Reaction of 2 with DMF
(s, 3H, N-CH3), 2.88 (s, 3H, N-CH3), ꢁ14.03 (s, 1H, hydride). Mass
Spec. EI/MS m/z. 669, Mþ, plus ions for the loss of each of the 8 CO
ligands. The isotope distribution patterns of the ions are consistent
with the presence of two rhenium atoms. Spectral data for 3: IR nCO
(cmꢁ1 in CH2Cl2): 2094(m), 2020(vs), 2004(m), 1978(s), 1949(m),
25.0 mg (0.037 mmol) of 2 and 28.0 mL (0.37 mmol) of DMF were
dissolved in 0.8 mL toluene-d8 in a 5 mm NMR tube. The NMR tube
was evacuated and then filled with nitrogen. The NMR tube was
then allowed to stand for 3 days at 60 ꢀC. Solvent was then removed
Table 1
Crystallographic data for crystals 2e4.
Compound
2
3
4
Empirical formula
Formula weight
Crystal system
Lattice parameters
a (Å)
Re2O9NC11H7
669.58
Triclinic
Re2O8N2C12H14
686.65
Monoclinic
Re2O9NC11H7
669.58
Triclinic
7.6054(3)
9.7440(4)
11.7187(5)
82.801(1)
81.739(1)
73.812(1)
822.02(6)
P-1, No. 2
2
2.705
14.755
294(2)
56.62
7.6374(5)
18.5391(12)
13.4848(9)
90.00
103.230(1)
90.00
1858.6(2)
P21/n, No. 14
4
2.454
13.052
294(2)
50.06
9.4293(2)
12.9216(3)
14.8114(4)
70.199(1)
87.488(1)
80.331(1)
1673.66(7)
P-1, No. 2
4
2.657
14.493
294(2)
50.06
b (Å)
c (Å)
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Space group
Z value
rcalc (g/cm3)
m
(Mo K
Temperature (K)
qmax(ꢀ)
No. Obs. (I > 2
No. Parameters
a
) (mmꢁ1
)
2
s(I))
4070
214
3280
229
5922
427
Goodness of fit (GOF)
Max. shift in cycle
1.081
0.020
0.0248; 0.0519
Multi-Scan
1.000/0.432
1.143
1.047
0.093
0.0344; 0.0854
Multi-Scan
1.000/0.374
2.387
1.011
0.001
0.0265; 0.0457
Multi-Scan
1.000/0.507
0.819
Residuals:a R1; WR2
Absorption Correction, Max/min
Largest peak Final Diff. Map (eꢁ/Å3)
P
P
P
P
P
R1 ¼ hklðjjFobsj ꢁ jFcalcjjÞ= hkljFobsj; WR2 ¼ ½ hklwðjFobsj ꢁ jFcalcjÞ2= hklwFo2bs
ꢂ
1=2; w ¼ 1=s2ðFobsÞ; GOF ¼ ½ hklwðjFobsj ꢁ jFcalcjÞ2=ðndata ꢁ nvariÞꢂ1=2
.
a
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R.D. Adams, P. Dhull / Journal of Organometallic Chemistry xxx (2017) 1e5
3
in vacuo. The residue was extracted in CH2Cl2 and separated by TLC
by using a 70:30 hexane/CH2Cl2 (v/v) solvent mixture to give
compounds: 3, 8.0 mg (32% yield); 4, 3.0 mg (12% yield); Re2(CO)10
7.0 mg (28% yield) and 5, 5.00 mg (11% yield).
,
1.6. Pyrolysis of 2
To study the effect of presence of DMF on 2, this comparative
experiment was performed. 20.0 mg (0.030 mmol) of 2 was dis-
solved in 0.8 mL toluene-d8 in a 5 mm NMR tube. The NMR tube
was evacuated and filled with N2 gas. The NMR tube was then
heated to 60 ꢀC for 3 days. A 1H NMR spectrum taken after this
period showed only half of 2 was transformed. The solvent was
then removed in vacuo. The residue was extracted in CH2Cl2 and
separated by TLC by using a 70:30 hexane/CH2Cl2 (v/v) solvent
mixture to give compounds: 3, 3.00 mg (15% yield); Re2(CO)10
,
4.00 mg (21% yield) and 5, 2.00 mg (6% yield). 9.00 mg of 2 was also
recovered.
1.7. Alternative synthesis of 4. reaction of Re2(CO)9(NCMe) with
Me2NH
70.0 mg (0.105 mmol) of Re2(CO)9(NCMe) was dissolved in
25 mL of hexane. To this solution, 40 mL (0.755 mmol) of dime-
Fig. 1. An ORTEP diagram of the molecular structure of Re2(CO)8[
m
-
h
2-O¼C(NMe2)](
m-
H), 2 showing 25% thermal ellipsoid probability. Selected bond distances (Å) and an-
gles (ꢀ) are Re1eRe2
¼
3.2215(3), Re2
-
C1
¼
2.191(5), Re1
-
O1
¼
2.133(3),
thylamine from a 2 M solution in tetrahydrofuran was added. The
solution was then heated to reflux for 2 h to form a light yellow
solution. The solvent was removed in vacuo and the residue was
extracted in CH2Cl2 and separated by TLC by using a 70:30 hexane/
CH2Cl2 (v/v) solvent mixture to yield 60.00 mg of Re2(CO)9(NHMe2),
4 (85% yield).
Crystallographic Analyses: Single crystals of compounds 2e4
suitable for X-ray diffraction analyses were obtained by slow
evaporation of solvent from solutions of the pure compounds in
hexane solvent at room temperature. Each data crystal was glued
onto the end of a thin glass fiber. X-ray intensity data were
measured by using a Bruker SMART APEX CCD-based diffractom-
C1eO1 ¼ 1.298(5), C1 - N1 ¼ 1.334(5), Re1 - H1 ¼ 1.88(5), Re2 - H1 ¼ 1.78(5); Re2 -
C1eO1 ¼ 116.5(3), Re2 - C1eN1 ¼ 130.8(3), Re1 - O1eC1 ¼ 116.2(3).
dirhenium compounds: Re2(CO)8(
m-h
2-O¼CNMe2)(
m-H), 2, (16%
yield), Re2(CO)7(NHMe2)(
m-h
2-O¼CNMe2)(
m-H), 3, (30% yield),
Re2(CO)9(NHMe2), 4, (14% yield). Re2(CO)10 (19% yield) and
[Re(CO)3(OH)]4, 5 (9% yield) were also found in the reaction mix-
tures. Compound 5 was most likely derived from the reaction of 1
with traces of H2O present in the DMF reagent [11]. The yield of 3
was increased at the expense of 2 and 4 when the ratio of DMF/1 in
the reaction was increased. In the presence of a large excess of DMF,
no 2 was obtained at all. It was subsequently shown that compound
eter by using Mo K
a
radiation (
l
¼ 0.71073 Å). The raw data frames
were integrated with the SAINT þ program by using a narrow-
frame integration algorithm [15]. Correction for Lorentz and po-
larization effects were also applied with SAINTþ. An empirical ab-
sorption correction based on the multiple measurements of
equivalent reflections was applied by using the program SADABS
were applied in each analysis [15]. All structures were solved by a
combination of direct methods and difference Fourier syntheses,
and refined by full-matrix least squares refinement on F2 by using
the SHELXTL software package [16]. All non-hydrogen atoms were
refined with anisotropic thermal parameters. All hydrogen atoms
were placed in geometrically idealized positions and were included
as standard riding atoms during the final least-squares refinements
with C-H distances fixed at 0.96 Å. The hydride ligands bonded to
the metal atoms in 2 and 3 were located and refined in each
analysis. Compounds 2 and 4 crystallized in the triclinic crystal
system. The space group P-1 was assumed and confirmed by the
successful solution and refinement of each structure. Compound 4
contains two independent formula equivalents of the complex in
the asymmetric crystal unit. Both molecules have similar molecular
structures. Compound 3 crystallized in the monoclinic crystal sys-
tem. The space group P21/n was identified on the basis of system-
atic absences observed in the intensity data. Crystal data, data
collection parameters, and results for the analyses are listed in
Table 1.
Fig. 2. An ORTEP diagram of the molecular structure of Re2(CO)7(NHMe2)[
m
-
h2
m-H), 3 showing 15% thermal ellipsoid probability. Selected bond dis-
-
O¼C(NMe2)](
2. Results and discussion
tances (Å) and angles (ꢀ) are Re1eRe2 ¼ 3.2330(5), Re2 - C1 ¼ 2.209(8), Re1 -
O1 ¼ 2.123(6), Re1eN2 ¼ 2.238(10), C1eO1 ¼ 1.267(9), C1eN1 ¼ 1.326(10), Re2 -
C1eO1 ¼ 115.9(5), Re1 - O1eC1 ¼ 117.7(5).
The reaction of 1 with DMF at 70 ꢀC for 6 h yielded three new
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R.D. Adams, P. Dhull / Journal of Organometallic Chemistry xxx (2017) 1e5
single bond distance in Re2(CO)10, 3.041(1) Å [17]. The lengthening
of the Re e Re bond can be attributed to the presence of the
bridging hydrido ligand [18]. Kreiter reported a similar compound
Re2(CO)8(
m
-
h
2-O¼CMe)(
m-H) obtained in a low yield from the
photolysis of Re2(CO)10 in the presence of acetaldehyde which has a
Re e Re bond distance, 3.208(1) Å [4q] similar to that of 2.
An ORTEP diagram of the molecular structure of 3 is shown in
Fig. 2. Compound 3 is an NHMe2 derivative of 2. Compound 3 also
contains a Re e Re bond that is C,O-bridged by a dimethylforma-
mido ligand, O¼CNMe2, and a bridging hydrido ligand,
d
¼ ꢁ11.44.
A NHMe2 ligand coordinated to rhenium atom Re(1) in a site cis to
the O atom of the dimethylformamido ligand, Re1eN2 ¼ 2.238(10)
Å. The ReeRe bond distance in
3 is similar to that in 2,
Re1eRe2 ¼ 3.2330(5) Å. The NHMe2 ligand was presumably formed
by decarbonylation of the dimethylformamido ligand in 2. When
compound 2 was pyrolyzed in solution at 60 ꢀC, small amounts of 3
(15% yield) were obtained together with Re2(CO)10 and some 5.
An ORTEP diagram of the molecular structure of 4 is shown in
Fig. 3. There are two independent molecules in the asymmetric
crystal unit of 4. Compound 4 is a NHMe2 derivative of Re2(CO)10
.
Fig. 3. An ORTEP diagram showing 15% thermal ellipsoid probability of the molecular
structure of one of the two similar independent molecules of Re2(CO)9(NHMe2) in the
crystal of 4. Selected bond distances (Å) and angles (ꢀ) for 4 are: for molecule 1,
Re1eRe2 ¼ 3.0482(4), Re1eN1 ¼ 2.282(7), N1 - Re1 - Re2 ¼ 92.47(19); for molecule 2,
Re3 - Re4 ¼ 3.0488(4), Re3 - N2 ¼ 2.271(6), N2 - Re3 - Re4 ¼ 92.57(17).
The NHMe2 ligand occupies a coordination site cis to the Re e Re
bond, Re1eN1 ¼ 2.282(7) Å [Re3 - N2 ¼ 2.271(6) Å]; N1 - Re1 -
Re2 ¼ 92.47(19)ꢀ[N2 - Re3 - Re4 ¼ 92.57(17)ꢀ]. The ReeRe bond
distance in 4, Re1eRe2 ¼ 3.0482(4) Å [Re3 - Re4 ¼ 3.0488(4) Å], is
very similar to that in Re2(CO)10, 3.041(1) Å [17]. Compound 4 was
also obtained independently in 85% yield from the reaction of
Re2(CO)9(NCMe) with Me2NH by heating a solution of the two
compounds in hexane solvent to reflux for 2 h.
3 can be obtained in 32% yield directly by reaction of 2 with DMF for
3 d at 60 ꢀC. Conversely, compound 2 was obtained from 3 in a good
yield (82%) by reaction with CO (1 atm) in a benzene solution at
reflux for 1 h.
3. Summary and conclusions
Compounds 2e4 were characterized by a combination of IR, 1H
NMR, mass spectrometry and single crystal X-ray diffraction anal-
ysis. An ORTEP diagram of the molecular structure of 2 is shown in
Fig. 1. Compound 2 contains two Re(CO)4 groups joined by a Re e Re
We have discovered the first example of a binuclear oxidation
addition of a formyl C-H bond of a formamide to yield a h
2-bridging
formamido ligand with the C atom bonded to one metal atom and
the O atom bonded to the other metal atom. The reactions, products
and their interrelationships are shown in Scheme 1. The mecha-
nism of the reactions have not yet been established. Hexene was
eliminated from 1 when it was heated in the presence of DMF and
three new dirhenium products, compounds 2e4, were obtained.
bond that is C,O-bridged by
a dimethylformamido ligand,
O¼CNMe2, and a bridging hydrido ligand,
d
¼ ꢁ14.03; Re1 -
O1 ¼ 2.133(3) Å, Re2 - C1 ¼ 2.191(5) Å, C1eO1 ¼1.298(5) Å and Re1
- H1 ¼ 1.88(5) Å, Re2 - H1 ¼ 1.78(5) Å. Compound 2 formally con-
tains
a ReeRe single bond, but Re e Re bond distance,
Re1eRe2 ¼ 3.2215(3) Å, is significantly longer than the Re e Re
Compound 2 contains a bridging C,O-h
2-formamido ligand formed
Scheme 1. A summary of the products obtained from the reaction of 1 with DMF and their interrelationships. For clarity, the CO ligands are shown only as lines.
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R.D. Adams, P. Dhull / Journal of Organometallic Chemistry xxx (2017) 1e5
1742e1751;
5
by the activation of the CH bond of DMF and the transfer of the
(f) D.L. Thorn, Organometallics 1 (1982) 197;
(g) E.F. Landvatter, T.B. Rauchfuss, Organometallics 1 (1982) 506e513;
(h) D. Milstein, Organometallics 1 (1982) 1549e1551;
(i) J.J. Koh, W.-H. Lee, P.G. Williard, W.M. Risen Jr., J. Organomet. Chem. 284
(1985) 409e419;
(j) D. Milstein, W.C. Fultz, J.C. Calabrese, J. Am. Chem. Soc. 108 (1986)
1336e1338;
(k) C. Bianchini, A. Meli, M. Peruzzini, A. Vacca, F. Zanobini, Organometallics 6
(1987) 2453e2455;
(l) C. Bianchini, A. Meli, M. Peruzzini, A. Vacca, F. Vizza, F. Zanobini, Organo-
metallics 8 (1989) 337e345;
(m) C. Bianchini, A. Meli, M. Peruzzini, F. Vizza, F. Bachechi, Organometallics
10 (1991) 820e823;
formyl hydrogen atom to the rhenium atoms to form a bridging
hydrido ligand. The formamido ligand serves as a three electron
donor to the two rhenium atoms and the hydrido ligand serves as a
one electron donor; thus with 34 valence electrons compound 2 is
expected to contain a Re e Re single bond. This is consistent the
observed Re e Re distance, see above. Compound 3 also contains a
bridging C,O-h
2-formamido ligand and a bridging hydrido ligand,
but it also contains a NHMe2 ligand in the place of one of the CO
ligands in 2.
The NHMe2 ligand was apparently formed by decarbonylation of
(n) K. Wang, T.J. Emge, A. Goldman, C. Li, S.P. Nolan, Organometallics 14 (1995)
4929e4936;
the DMF, presumably via the C-H activated C,O-h
2-formamido
ligand followed by the return of the hydrogen atom to the resultant
NMe2 group. Metal complexes have been shown to decarbonylate
DMF [5,19,20] via pathways that involve initial activation of the
formyl C-H bond [5,19]. To support this, it was found that com-
pound 2 can be converted to 3 and 4 thermally in the absence of
additional DMF, but the reaction proceeds better if DMF is added.
Small amounts of Re2(CO)10, HRe(CO)5 and [Re(CO)3(OH)]4 were
also found in the reaction mixtures. These products are believed to
be a result of reactions of 1 and 2 with traces of water in the DMF
reagent [11].
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Acknowledgement
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This research was supported by grant CHE-1464596 from the
National Science Foundation.
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2017.03.009.
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́
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