Siloxymethylamines as Aminomethylation Reagents for Amines Leading to Labile Diaminomethanes That can be Trapped as Their [Mo(CO)4] Complexes

Article abstract of DOI:10.1002/chem.201600810

Compound Et₃SiOCH₂NMe₂ transfers Me₂NCH₂ to R₂NH (R₂=Et₂, PhMe, [Cr(η⁶-C₆H₅)(CO)₃]Me, PhH) to form previously unknown diaminomethanes, Me₂NCH₂NR₂ and, in the case of R₂=PhH, the triamine Me₂NCH₂N(Ph)CH₂NMe₂. The diaminomethanes exhibit an unreported disproportionation to a mixture of (R₂N)₂CH₂, (Me₂N)₂CH₂, and Me₂NCH₂NR₂, which can be trapped as their [Mo(CO)₄(diamine)] complexes. Whereas PhMeNCH₂NMe₂ is a labile material, the metal-substituted ([(η⁶-C₆H₅)Cr(CO)₃]MeNCH₂NMe₂ is a stable material. The triamine Me₂NCH₂N(Ph)CH₂NMe₂ is unstable with respect to transformation to 1,3,5-triphenyltriazine, but is readily trapped as the bidentate-triamineMo(CO)₄. All metal complexes were characterized by single-crystal X-ray diffraction.

Full text of DOI:10.1002/chem.201600810

DOI: 10.1002/chem.201600810
Communication
&
Organometallic Chemistry
Siloxymethylamines as Aminomethylation Reagents for Amines
Leading to Labile Diaminomethanes That can be Trapped as Their
[
Mo(CO) ] Complexes
4
Hemant K. Sharma, Paulina E. Gonzalez, Alexander L. Craig, Sanchita Chakrabarty,
[
a]
Alejandro Metta-MagaÇa, and Keith H. Pannell*
intermediacy of readily isolated siloxymethyl dimethylamines
obtained in high yield, for example, R SiOCH NMe (1, R =Et
(1a); PhMe (1b); Ph Me (1c); Eq. (2) for 1a, M=catalyst).
Abstract: Compound Et SiOCH NMe transfers Me NCH2
3
2
2
3
3
[4]
3
2
2
2
6
to R NH (R =Et , PhMe, [Cr(h -C H )(CO) ]Me, PhH) to form
2
2
2
2
2
6
5
3
previously unknown diaminomethanes, Me NCH NR
2
The second step B, that is, the reduction of 1 by the silane, led
us to propose that 1 can be used as a masked analogue of Es-
chenmoser’s salt, and thereby act as a dimethylamino trans-
fer agent (Mannich reagent) in the appropriate environment.
2
2
and, in the case of R2 =PhH, the triamine
[
5]
Me NCH N(Ph)CH NMe . The diaminomethanes exhibit an
2
2
2
2
unreported disproportionation to a mixture of (R N) CH ,
2
2
2
(
Me N) CH ,
and
Me NCH NR ,
which
can
be
2
2
2
2
2
2
trapped as their [Mo(CO) (diamine)] complexes. Whereas
4
PhMeNCH NMe is a labile material, the metal-substituted
2
2
6
(
[(h -C H )Cr(CO) ]MeNCH NMe is a stable material. The
6 5 3 2 2
triamine Me NCH N(Ph)CH NMe is unstable with respect
2
2
2
2
to transformation to 1,3,5-triphenyltriazine, but is readily
[
6]
[7]
trapped as the bidentate-triamineMo(CO) . All metal com-
Indeed, we and earlier the Mironov group demonstrated
4
plexes were characterized by single-crystal X-ray diffrac-
tion.
that 1d (Me
Me SiNMe and formaldehyde) reacted with R
E=Si
3
SiOCH
2
NMe
2
,
formed from the reaction of
d+
dÀ
ECl (R
3
E
3
ÀCl ,
3
2
4,6,7
4
4
,
Ge and Sn ) behaving appropriately to form
R SiOER and ClCH NMe . Furthermore, the Mironov group il-
3
3
2
2
lustrated the reaction of 1d with trimethylsilylamines,
Me SiAm, led to the formation of hexamethyldisiloxane and
The organometallic-catalyzed organosilane (R4 SiH ) reduction
Àn
n
3
[
7b]
of organic functional groups has developed into a major area
AmCH NMe . We now report an initial study concerning the
2 2
[1]
of academic and industrial chemistry. In a largely ignored
985 article, the Voronkov group first described the metal-cata-
lyzed reaction between a silane and N,N-dimethylformamide
reactions of 1 with a series of NÀH bonds, more readily avail-
able and more general than silylamines, which illustrates that
1 is a reliable [CH NMe ] transfer reagent to amines, and more
1
2
2
(
DMF) leading to the formation of Me N and the correspond-
fundamentally, illustrate previously unreported chemistry of
the newly formed diaminomethanes.
3
[2]
ing disiloxane [Eq. (1)].
The reactions of 1a with secondary amines, Et NH, PhMeNH
2
6
and [Cr(h -C H )(CO) ]MeNH rapidly resulted in the formation
6
5
3
of the corresponding, unreported, (dimethylaminomethyl)
amines, Me NCH NR [Eq. (3)].
2
2
2
Since this seminal report, the generalized reduction of
amides to form amines has become a popular “green” proce-
dure due to the low energy requirement of the reaction and
[
3]
its regioselectivity. We proposed and proved that by using
Mo and Pt catalysts, the initial step A in the process involved
a hydrosilylation of the amide carbonyl group to produce the
Although tetraethyl and tetramethyl diaminomethane, 2b
and c, respectively, are commercially available materials, 2a is
unreported and simple unsymmetrical aryl/alkyl, alkyl/alkyl dia-
minomethanes are very rare in the literature. A few stable
mixed 1,3-diaryl diamines have been reported, for example,
[
a] H. K. Sharma, P. E. Gonzalez, A. L. Craig, S. Chakrabarty, A. Metta-MagaÇa,
Prof. K. H. Pannell
Department of Chemistry, University of Texas at El Paso
El Paso, TX 79968-0513 (USA)
E-mail: kpannell@utep.edu
[
8a]
[8b]
[8c]
ArNHÀCH ÀNHAr’, and several indole- and imidazole- di-
2
alkylamino-methanes are also known. Symmetrical methylene-
bridged diamines are more common and are useful re-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201600810.
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Communication
[
8d]
agents. The new reagents 1 could be particularly useful in
unsymmetrical diamine synthesis; however, our attempts to
purify the diaminomethane materials by distillation and/or
column chromatography showed their significant lability. In all
such attempts, the unsymmetrical diamines 2 and 3 exhibited
unexpected lability. In the case of 2a, an equilibrium mixture
of all three isomeric diaminomethanes has been discovered
[
Eq. (4)]:
Figure 2. Structure of 4a. Selected bond lengths [Š] and angles [8]: Mo1ÀC1
2
2
.024(4), Mo1ÀC2 2.028(5), Mo1ÀC3 1.935(5), Mo1ÀC4 1.939(5), Mo1ÀN1
.318(3), Mo1ÀN2 2.329(3); N1-Mo-N2 62.3(1), C1-Mo1-C2 (ax) 167.3(2), C3-
This previously unreported chemistry is outside the immedi-
Mo1-C4 (eq) 88.4(2), C7-N1-Mo1 93.1(2), C7-N2-Mo1 92.3(2).
ate scope of the present article; however, we are actively
studying the scope and details of this chemistry and our re-
sults will be the subject of future publications involving
À
+
R NCH NR $[R N] [CH =NR ] dissociations. At this stage, we
2
2
2
2
2
2
1
simply illustrate this simple equilibrium process studied by H
13
and C NMR spectroscopy, in which a 1:1 mixture of 2b and
c eventually transform to an approximately 2:1:1 mixture of
2
a, b, and c, at 308C (Figure 1).
Figure 3. Structure of 4b. Selected bond lengths [Š] and angles [8]: Mo1À
C10 2.027(5), Mo1ÀC11 2.025(5), Mo1ÀC12 1.954(5), Mo1ÀC13 1.939(5),
Mo1ÀN1 2.339(3), Mo1ÀN2 2.349(3); N1-Mo1-N2 62.1(1), C10-Mo1-C11 (ax)
170.6(2), C12-Mo1-C13 (eq) 84.7(2), C5-N1-Mo1 93.3(2), C5-N2-Mo1 93.0(2).
As may be expected on progressing in the order tetrameth-
13
Figure 1. C NMR spectrum of the methylene region (N-CH
tion of 2b and c (1:1) in C at 308C: 2c 74.18 ppm; 2b 83.77 ppm; and
a 79.16 ppm.
2
-N) for the reac-
yl/dimethyldiethyl/tetraethyl, there is an increase in the cell
3
6
D
6
volume (1285.0(2)!1460(2)!1674.5(9) Š ). The angle N-Mo-N
2
is not affected by the substituent changes on the nitrogen
(
average 62.4(1)8), but the angle between the axial CO groups
for the tetraethyl is expanded compared to the corresponding
angles for the dimethyldiethyl and tetramethyl derivatives,
170.6(2)8, see also, 167.3(2) and 166.4(2)8, respectively. All the
other parameters are statistically the same. Related Re, Mo,
and W complexes, with a range of differing N substituents ex-
hibit N-W-N bond angle comparable to ours showing that the
bite angle in this class of complex is independent of the sub-
To unambiguously prove the formation of the unsymmetri-
cal diamine, Me NÀCH ÀNEt (2a), the immediately formed
2
2
2
crude reaction product from the reaction outlined in Equa-
[
9]
tion (3) was reacted with [Mo(CO) (norbornadiene)]. Such
4
treatment led to replacement of norbornadiene with diamine
and the formation of [Mo(CO) (Me NCH NEt )] (4a) in reasona-
4
2
2
2
[
10]
ble yield, a rare example of a small-bite angle diaminomethane
stituent on the nitrogen and the metal atom.
[
10]
metal complex. The structure of this complex is illustrated in
Figure 2, and selected bond lengths and angles are presented
in the caption. We also report the related structures of the tet-
The reaction of the 1a with PhMeNH led to the formation of
PhMeNCH NMe , (3a), as was showed by NMR spectroscopy.
2
2
However, this material was also too labile to be isolated, and
raethyl- and tetramethyl diaminomethane [Mo(CO) ] complexes
attempts to form the [Mo(CO) ] complex were unsuccessful,
4
4
4
b and c (Figures 3 and 4).
possibly due to the steric bulk of the phenyl group, and/or re-
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ylanilino)(bromo)boryl)-ferrocene)-bis(tricarbonyl-chromium),
[
14]
the C ÀN distance is 1.431 Š.
ar
The out-of-the plane feature of the amino group in 3b
could be due to the presence of an intramolecular hydrogen
bond N···HÀC of 2.603 Š. It is also possible that in solution,
ar
the amino group is co-planar with the aromatic ring, therefore,
influencing in the increased stability we have found. Further-
more, the [Cr(CO) ] substituent is strongly electron withdraw-
3
ing, and thus the reduced basicity of the amine is also a poten-
tial factor. Together with our studies on the disproportionation
of the other diamines noted above, this is the subject of fur-
ther experimental and theoretical studies.
The reaction of an excess of 1a with the primary amine
1
13
PhNH , as was monitored by H and C NMR spectroscopy, re-
2
sulted in the formation of the “expected”, but previously unre-
Figure 4. Structure of 4c. Selected bond lengths [Š] and angles [8]: Mo1ÀC3
ported, triamine Me NCH ÀNPhÀCH NMe (5). However, as
2
2
2
2
2
2
.040(5), Mo1ÀC4 2.041(5), Mo1ÀC1 1.945(5), Mo1ÀC2 1.955(6), Mo1ÀN1
.330(4), Mo1ÀN2 2.313(4); N1-Mo1-N2 62.8(1), C3-Mo1-C4 (ax) 166.4(2), C1-
with the attempted work-up of Me NÀCH ÀNEt , we have been
2
2
2
unable to obtain the new triamine in a purified form due to
secondary chemistry. In this case, there appears to be an elimi-
nation of 2c, and the transient formation of an imine, C H N=
Mo1-C2 (eq) 89.0(2), C5-N1-Mo1 93.8(3), C5-N2-Mo1 94.1(3).
6
5
duced basicity of the ligand. However, the reaction of 1a with
CH , which rapidly trimerizes to form 1,3,5-triphenyltriazine.
2
6
[11]
[
Cr(h -C H )(CO) ]MeNH formed the corresponding diamino-
Such trimerization reactions of imines are reported in the liter-
6
5
3
[
15]
methane (3b) in good yield as a stable material [Eq. (3)]. Com-
plex 3b was readily purified, and we managed to obtain crys-
tals of this complex, and its structure is illustrated in Figure 5.
The geometry around Cr exhibits the usual piano-stool ar-
ature (Scheme 1).
6
rangement, with an h interaction with the aromatic ring. The
arylamino group is not coplanar with the aromatic ring by 168
although it is planar (sum of the angles at N is 358.38); howev-
Scheme 1. Formation of 1,3,5-triphenyl-1,3,5-triazine.
er, the C ÀN distance of 1.368(3) Š shows that there is a conju-
ar
gation of the nitrogen with the aryl p system. The related com-
However, the [Mo(CO) (norbornadiene)] complex was used
4
6
plex, (h -N,N-dimethylaniline)-tricarbonyl-chromium, in which
for isolation of the triamine 5 as the Mo complex 6. The tria-
mine acts as a bidentate ligand by coordination of the two ter-
minal dimethylamino groups, as illustrated in Figure 6, with se-
lected parameters noted in the caption.
the N is coplanar with the aromatic ring, has a C ÀN distance
ar
[
12]
6
of 1.361 Š,
whereas (h -N-tert-utyldimethylsilyl-N-methylani-
6
line)-tricarbonylchromium and bis-(h -N,N,-dimethylaniline)
chromium with similar non-planar N-aryl arrangements exhibit
The heteronuclear six-membered ring adopts a chair confor-
mation, and the distances MoÀN, 2.376(3) and 2.389(3) Š, are
longer than those for the diaminomethane complexes report-
ed above. The 3D lattice structure is held together by hydro-
gen bonds of the type CH···OC ranging from 2.593(5) to
[13]
C ÀN distances of 1.387 and 1.390 Š, respectively. When all
ar
6
conjugation is lost, as in the case of (bis(m -1,1’-bis(h -N-meth-
2
2
.827(5) Š. This structure is similar to three triamine complexes
[
10c]
described in the literature, that is, CoCl [(Me NCH ) NMe],
2
2
2 2
[
16a]
and [Co(CO) CuNMe ) NR (R=H and propyl),
together with
4
2 2
a similar biuret iridium complex, Ir(NHÀCOÀNHÀCOÀNH), both
involving bidentate structural motif.
[
16b]
Overall, siloxymethylamines reagents are produced in high
yield, are stable indefinitely in dry O -free environments, and
2
perform facile (low-energy) transfer of the dimethylamino
group to NH-containing compounds. Previously unreported re-
arrangements of the simple new diaminomethanes have been
noted, and their isomers were trapped by metal coordina-
[
17]
tion.
6
Figure 5. Structure of [Cr(h -C
6
H
5
)(CO)
3
]MeNCH
2
NMe
2
(3b). Selected bond
Experimental Section
lengths [Š] and angles [8]: Cr1ÀPhcenter 1.751(2); Cr1-C11 1.840(2), Cr1-C12
1
.832(2), Cr1-C13 1.840(2), C7-N1-C1-C2 4.8(2), C8-N1-C1-C2 159.7(2), C1-N1-
All reactions were performed under N or Ar atmospheres by using
2
C8-N2 86.4(2). C7-N1-C8-N2 À109.0(2).
Schlenk techniques. A typical reaction of 1a is outlined below, and
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Communication
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Mo1ÀC16 1.927(4), Mo1ÀN1 2.376(3), Mo1ÀN3 2.389(3), N1-Mo1-N2 87.8(9),
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Acknowledgements
[
[
We thank the Welch Foundation for support of this research
by grant AH-0546, and J.C. acknowledges a Student Finance,
England loan to cover the academic year 2014–2015 study
abroad from Newcastle University.
[
[
Keywords: diaminomethane
molybdenum · silanes · siloxymethylamine
·
disproportionation
·
Received: February 20, 2016
Published online on April 25, 2016
Chem. Eur. J. 2016, 22, 7363 – 7366
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim