Isocyanide migration from an axial to an equatorial position in the synthesis of octahedral cationic carbonyl complexes of manganese(I) containing nitrogen donor chelate ligands

Article abstract of DOI:10.1016/0022-328X(90)85513-X

Several manganese carbonyl complexes of the type tBu)n(L)p(L-L)>ClO4 ( m + n + p = 4; m = 1-3; n = 1-3; p = 0, 1; L = P(OMe)3, CNPh; L-L = 2,2'-bipiridine (bipy), 1,10-phenantroline (phen), bis(t-butyl)-1,4-diazabuta-2,3-diene (

Full text of DOI:10.1016/0022-328X(90)85513-X

275
Journal of
Sequoia S.A.,
Chemistry 398 (1990) 275-284
JOM 21176
Isocyanide migration from an axial to an equatorial position
in the synthesis of octahedral carbonyl complexes
of manganese(I) containing nitrogen donor ligands
F.J . Garcia
V. Riera
Departamento de Quimica
Universidnd de Oviedo, 33071 Oviedo (Spain)
and M. Vivanco
Departamento de Quimica
Universidad de
4700.5
(Spain)
(Received May
1990)
Several manganese carbonyl complexes of the type
(m + = 4; m = l-3; = l-3; p =
(bipy), @hen),
ene ( Bu-DAB), N, N, N N ‘-tetramethylethylendiamine (tmed)) have been pre-
L =
L-L =
pared starting either from
and using
or
as decarbonylating agent. The stereochem-
istry of the substitution reactions products is discussed in terms of the nature of the
possible intermediates.
Introduction
The reaction of the tricarbonyl complex
with
and
at room temperature leads to the dicarbonyl
a), which had been reported previously
However, under the same conditions the isocyanide derivatives
(N-N = bipy, phen) were found to react with CNR
in presence of
Moreover, the complex
with and subsequently with
or
ligands occupy equatorial positions (Eq. b)
to give the dicarbonyl
is known to react
in which the
or CO to give

276
N
’
N
’
c o
.
21 L:
N ’
‘ C
c o
O
c o
In order to investigate the stereochemical aspects of these reactions further we
have carried out some aditional experiments, the results of which are presented here.
A preliminary account has appeared
and discussion
The reaction of
(lb)) with an excess of
(N-N = bipy (la) and phen
at room temperature led to
reaction i in Scheme 1) (the possibil-
in
ity of a partial substiution of the
ligand in 2 by
could not be
completely excluded Although compounds 2 could not be isolated in a pure
state, their stereochemistry is suggested to be as shown in Scheme 1, in accordance
N...
Mn’
c o
N-N = bipy
(i)
(ii) CO, (iii) CNR; (iv)
and
in
refluxing

Table 1
Melting points, eonductivities, and analytical data for the new compounds
Analysis [Found
Compound
C
H
N
41.3
(41.8) (4.6)
4.6
7.2
137
141
180
179
148
150
165
115
146
140
136
138
144
143
140
140
141
138
142
138
144
134
142
144
140
(7.3)
6.9
(7.0)
7.1
41.4
(41.8) (4.6)
44.1 4.4
(44.2) (4.4)
54.6
(54.8)
56.4
4.6
(7.3)
7.1
5.0
(4.9)
4.9
(4.9) (11.1)
6.1
11.5
(11.0)
11.4
(7a)
(57.0)
43.6
(6.0)
5.8
(44.1)
38.1
(38.4) (5.8)
43.7
(44.1) (6.0)
48.2
(48.5)
43.2
(43.9)
48.6
(48.5)
43.2
(43.8)
51.2
(52.0)
47.8
(48.2)
52.3
9.5
(9.6)
8.5
6.1
(8.6)
10.2
7.2
(lla)
160
173
204
169
(7.0) (10.3)
7.0 11.6
(6.9) (11.4)
7.4
(7.0)
6.9
(llb)
10.2
(10.3)
11.3
(12b)
(6.9) (11.4)
7.4
(7.9)
8.0
(7.9)
1.8
11.2
(11.7)
12.7
(12.8)
11.7
134
d
(13b)
(14b)
158
133
(52.0)
48.1
(7.9)
8.1
(11.7)
12.9
(48.2)
(7.9)
(12.8)
With decomposition. Measured in 5 x
aeetone solution at 25 C. It isomerixes to
It
isomerixes to
with the spectroscopic data for
(2a) shown
in Table 2. Thus, the
indicates that the
NMR spectrum of
ligand occupies an equatorial position. The assignment is
exhibits a peak at 1.65 ppm which
consistent with the data in Table 3, which show a correlation between the
It should be pointed out that the spectrum of the mixture obtained by adding
to
probably
or
shows a very
such as
which are always detected by infrared
possible to avoid these impurities
peal’ at 1.22 ppm. This
to more substituted
It has not been
of the instability of the diearbonyl complexes 2.

278
Table 2
Spectroscopic data for the new compounds
(cm -‘)
NMR (6 in ppm, J in Hz)
Compound
Other signals
9.03, m; 8.63,
( b i p y )
8.20,
.
8.00, m: 7.57. m
2130, m
1.65,
1.60,
1.65,
1.23,
1.12,
1.58,
1880,
1986,
1914,
1982,
1910,
1971,
1904,
1967,
1900,
1934,
9.00, m; 8.35, m; 8.10, m; 7.70, m; 7.47, m.
(bipy). 3.41 (d, J (HP) = 10)
9.34, m; 8.66, m; 8.20, m; 8.11, 7.88, m.
(phen). 3.31 (d, 10)
9.0, m; 8.74, m; 8.22, m; 7.54, m. (bipy)
3.41 (d,
9.41, m; 8.77, m; 8.21
3.32 (d,
2134,
2130,
2168, m
2157, m
s
=
8.00, m. (phen)
J (HP) = 10)
8.93, m; 8.37, m; 8.08, m; 7.45, m. (bipy)
7.29 (m,
7a
2152,
2105,
2062,
2145,
2097,
s
s
1929, s
1.62,
1.54,
1.69,
1.57,
9.31, m; 8.55, m; 8.04, s; 7.93, m. (phen)
7.30 (m,
2052,
2198, m
2051,
1975, s
1942,
2050,
1960,
1948,
2080,
1999,
1950,
1982, s
1918, s
1965,
1907,
1970,
1905, s
1971,
1904,
1927, vs
162,
8.57, s,
8b
2188, m
2152, m
s
s
2.88, s, br; 2.96, s, br, (tmed)
1.60, 1.61,
8.61, s; 8.54, s,
l l a
l l b
2183, m
2135, s
2172, m
2132, m
2150,
1.52,
1.49,
1.66,
1.48,
1.42,
1.57, br,
8.52, s; 8.46, s,
2.80, m, (tmed)
1.59, s,
8.56, s,
2.72, m, (tmed)
1.54,
2128,
1.56,
8.43,
2170,
2118,
1.49, (18 H)
1.46, (9 H)
13a
13b
14a
2060, s
2155,
2105,
2.64, s, br; 2.74, br, (tmed)
1900,
1891,
1885, s
1.63,
1.43, (18 H)
2040,
1.48, (9 H)
1.40, (18 H)
1.58, s,
8.50, s; 8.46, s,
2155, sh
2120, vs
2062, sh
2150, w
2092,
1.54, (18 H)
1.44, (9 H)
2.76, br; 2.68, s, br, (tmed)
2065, sh
The
NMR spectra were recorded in
The IR spectra were recorded in
solution.
solution.
tion positions of the
ligands and the chemical shifts of their protons. In
terms of the two-step mechanism proposed for the decarbonylating reactions
promoted by the stereochemistry of 2 suggests that the isocyanide

Table 3
Chemical shift of the t-butykcyanide protons
Reference
Compound
to a N atom
to both N atoms
1.28
3
3
1.66
1.72
3
9
9
3
3
3
3
9
9
1.24
1.12
1.58 (9H)
1.65 (9H)
1.54 (18H)
1.62 (18H)
1.58 (9H)
1.63 (9H)
1.26 (9H)
1.16 (9H)
1.26 (9H)
1.20 (9H)
1.22 (18H)
1.18 (18H)
The reference 3 only includes the preparation
All the NMR spectra were recorded in
solution.
of the compounds, the NMR data, however, have been obtained recently in order to make out this Table.
ligand migrates from an axial to an equatorial position in the square pyramid
intermediate. This is in accord with the “site preference model”
which predicts
that an isocyanide ligand (a weaker a-acceptor than CO) should prefer a basal
position in the square pyramid intermediate. Moreover, assuming a dissociative
pathway in the substitution of
complexes 3 (ii in Scheme 1) and the
in 2, the formation of
compounds 4 (iii in Scheme
1)
further supports the suggestion that there is a stable intermediate containing a
basal isocyanide.
The
ligand in 2 can also be readily replaced by
in
at
room temperature to give
(iv in
Scheme 1). Their analytical and spectroscopic data are collected in Tables 1 and 2.
The peaks at 1.60 and 1.65 ppm in the NMR spectra show that the
are in equatorial positions, as in the starting complexes.
CN Bu
On the other hand, the dicarbonyls
(isomers of 5) were obtained by adding
in
and CN’Bu to a
Their analytical and
solution of
spectroscopic data are collected in Tables 1 and 2. In this case, the
show four groups of signals in the aromatic region, corresponding to equivalent
chelated N atoms; the chemical shifts of the protons (1.23 and 1.12
ppm (6b)) are in the range expected for axial CN’Bu ligands. The stereochemistry of
6a and indicates that, unlike isocyanides, the phosphites do not migrate in these
NMR spectra
substitution reactions.
The
dicarbonyl complexes
(N-N = bipy or phen, (4)) were found to react with
and
in refluxing
to yield
(7) (v in Scheme 1).
The stereochemistry of the monocarbonyl complexes 7 is suggested on the basis of
their
NMR spectra. Thus, the appearance of singlets at 1.58 (7a) and 1.62 ppm
indicate the presence of two equivalent equatorial terbutylisocyanides. On the
other hand, the four groups of signals in the aromatic region indicate the

280
co
c o
10 I
N
”
c o
I
c o
c o
N’
Scheme 2. N’-N’
at room temperature for lob, (ix) CN’Bu; (x)
or
(vi)
(vii) CO; (viii) refluxing hexane for
and (xi) refluxing
or
only for
of the two N atoms in the chelates. The stereochemistry of 7a and
confirms that the isocyanide migration also takes place during the formation of the
monocarbonyl compounds
At this point, it seemed of interest to extend our study to other related carbonyl
complexes, containing
(‘Bu-DAB), and N, N,
N’, N’-tetramethylethylendiamine (tmed) as nitrogen donor chelates.
The tricarbonyl complexes
(N’-N’ =
DAB
and tmed
reacted in
with
in the absence of other
ligands to give mainly the dicarbonyl derivatives of formula
(N’-N’ = ‘Bu-DAB
Because of the presence of an excess of
and tmed (vi in Scheme 2)
and partial decomposition of the
products, they could not be isolated and so have not been fully characterized.
However, from their IR spectra
1876 s, = 2133
contain an isocyanide ligand and a
Irrespective of the stereochemistry of 9, bubbling CO through a
tions of this product gave the tricarbonyl complexes
cm-‘;
= 1955 1866
= 2130
= 1945 s,
it is clear that they
arrangement.
solu-
(10) (vii in Scheme 2). The complex
characterized (see Tables 1 and but complex
= ‘Bu-DAB), was fully
(N’-N’ = tmed) could not be
isolated in a pure state because of its rapid isomerization to the corresponding
(viii in Scheme 2) and it was identified only by IR spectroscopy on the
product of a reaction carried out at 0°C
1939 1868 s). The mer to isomerization also occurs in the case of the
but only at the higher temperature of refluxing hexane.
cm-‘;
= 2117
=
compound
It is possible that small amounts of
were also formed, since
the reaction was carried out in presence of an excess of

2 8 1
While the reaction of
afforded
Scheme
mixture of two isomers
(2) with CN’Bu
(4) as a single product
(iii in
the reaction of 9 with CN’Bu in
at room temperature gave a
(11) and
(12) (ix in Scheme 2). These. were isolated by
careful fractional crystallization from
bles 1 and 2). The NMR and IR spectra of the crude reaction mixture reveal that
there is a preponderance of the In addition, we observed that the
and fully characterized (Ta-
isomers 11 and 12 cannot be interconverted under the conditions in which they are
generated. This could be an indication that the product 9 is itself a mixture of two
isomers.
The results can be explained by assuming that two square-pyramidal inter-
mediates exist in equilibrium in all substitution reactions involving complexes
containing N’-N’ chelates, in contrast to the single pentacoordinate intermediate
proposed for the analogous reactions involving bipy and phen complexes. The
intermediate present in higher proportion (A) would have the isocyanide ligand in
the base of the square-pyramid, while the other one (B) would have it in the apical
position. Thus, in the reaction of 9 with CN’Bu, the species A would give 11 (the
main product), whereas the intermediate B would give 12. In the reaction of 9 with
CO, however, only the mer-tricarbonyl isomer 10 is formed indicating that the low
concentration of CO forces the reaction to proceed only through the intermediate A.
Consistently, when 9 was reacted with a very dilute solution of CN’Bu the
proportion of the isomer 11 was higher than that obtained when a concentrated
solution of the isocyanide was used.
The existence of two intermediates in equilibrium is also supported by the fact
that the separate reactions of 8 and 10 with
and CN’Bu gave the same
mixture of isomers (11 and 12). Furthermore, the proportion of the isomer 11 in the
final mixture could be increased by raising the temperature in the reaction of 8 with
and CN’Bu, suggesting that the ratio of the intermediates A and B is
temperature dependent.
Again there is a marked contrast between the reactions of
(4) and
(11) with
(14)
and CNR. Thus while the former gave
(7) as single product
(v in Scheme
(13) and
the latter gave a mixture of
(x in Scheme which could be separated by fractional crystallization. Although the
complex
with
(14b) always
by heating the corresponding
contaminated
it could be
13b in
refluxing
(xi in Scheme 2). In the substitution reactions involving complexes
containing N’-N’chelates, the formation of the mixture of 13 and 14 further
support s the existence of two intermediates differing in the coordination position of
the isocyanide ligand.
Experimental
All reactions were carried out under nitrogen, and except for those involving
complexes containing tmed, in the dark. The IR spectra were recorded with
599 and Perk&Elmer 883 spectrometers, and calibrated by reference

to the 1602 cm-’ band of the polystyrene. The NMR spectra were recorded on
Varian FT-80 and Bruker AC 80 instruments, with TMS as internal reference. The
compounds
(N-N = bipy and phen)
CN’Bu
and
DAB
were prepared by published methods.
Preparation of
(N-N = bipy
phen
A mixture of
g, 0.63 mmol) and
(1) (0.63 mmol),
0.69 mmol) in (40
(0.047
was stirred
(0.082
at room temperature for 1.5 h. The solution was evaporated to dryness, the residue
washed with light petroleum, and the product crystallized from
at 20°C to give orange crystals. Yields 60%
and 62%
Preparation of
(N-N = bipy
phen
To a solution of
(0.58 mmol) in
(0.044 g, 0.58 mmol) and CN’Bu (0.050 g, 0.60 mmol),
(40
were added
and the mixture was stirred for 1 h. After evaporation of the solvent, the residue was
washed with light petroleum to give a solid, which was recrystallized from
to afford yellow orange crystals. Yields 65%
and 63%
Preparation of
(N-N = bipy
phen (76))
A mixture of
g, 0.47 mmol) and
(0.47
(0.035
(0.052 g, 0.50 mmol) was refluxed in
(40
for
5 h. The liquid was evaporated off under vacuum and the residue washed with light
petroleum. Recrystallization from
gave dark red crystals. Yields
55% (7a) and 53% (7b).
Preparation of
A solution of
hexane (60
Yield 95%.
(1 g, 3.64 mmol) and tmed (0.6
3.97 mmol) in
was refluxed for 30 min. The product separated out yellow solid.
140°C. Anal. Found: C, 32.3; H, 4.9; N, 8.4. Calcd: C, 32.3; H,
4.8; N, 8.4%. IR spectra
NMR spectra
in cm-‘),
in ppm): 2.61 (s,
= 2039 s, 1935 s, 1898 s.
2.90 (s,
2.96 (s,
Preparation of
= ‘Bu-DAB
tmed
A mixture of
mmol) in
the
(0.77 mmol) and Ag
was stirred for 1 h in the dark, then filtered to remove
To the filtrate was added CN’Bu (0.071 g, 0.85 mmol), and the mixture
(0.177 g, 0.85
(60
was refluxed for 30 min. After removal of the solvent, the residue was washed with
light petroleum to give a yellow solid. Yields 85%
and 87%
Preparation of
To a solution of
(0.25 g, 0.51 mmol)
(0.096 g, 1.28 mmol), and the resulting
in
(40
was added

mixture was stirred for 5 mm. The solution was washed
remove the excess of dried over and filtered. CO was bubbled
through the filtrate for 1 h. After removal of the solvent, the residual oil was washed
with water to
with light petroleum to give a solid. Recrystallization from
20 C affords yellow orange crystals. Yield 38%.
at
Preparation of
tmed and
tmed (12b))
To a solution of
(40 were added
(N
(N
= ‘ B u - D A B
(8) (0.82 mmol) in
(0.061 g, 0.82 mmol) and CN’Bu (0.136 g, 1.63 mmol),
and the mixture was stirred at room temperature for 2 h (‘Bu-DAB) or 5 h (tmed).
After removal of the solvent, the residue was washed with light petroleum. Recrys-
tallization of the crude product from
12, orange crystals of
afforded the
gave first the ci.s,trans-isomers
(yield 15%) or yellow crystals of 1 2 b (yield 19%).
1 1 , red crystals of lla (yield 32%) and
yellow crystals of
(yield 53%).
Preparation of
(‘Bu-DAB)]
and
(14a)
Although the complexes 13 and 14 could be obtained starting from the
it was more convenient to prepare them
from
since in this way the isolation of the
dicarbonyl complexes 1 1 and 12 was avoided.
( A ) F r o m
(8a). A mixture of
(0.25 g, 0.51 mmol),
(0.096 g, 1.28
mmol) and CN’Bu (0.127 g, 1.53 mmol)in
(30
was stirred at room
temperature for 3 days. The liquid was evaporated to dryness and the residue was
washed with light petroleum. Crystallization from
first
Et
at 20 C gave
and then,
(lla) (yield
after addition of light petroleum, deep-red crystals of
(13a) (yield
and finally deep-red crystals of
(14a) (yield 6%).
(B) From
A mixture of
(lla) (0.20 g, 0.37 mmol),
0.48 mmol), and and CN’Bu (0.063 g, 0.76 mmol) in (30
(0.036 g,
was stirred
for 3 days at room temperature. After removal of the solvent, the residue was
washed with light petroleum and the crude product recrystallized from
petroleum to give first 13a (42%) and then 14a (9%).
Preparation of
( A ) F r o m
(13b)
(8b). To a solution of
(0.20 g, 0.46 mmol) in (30
(0.086 g, 1.15 mmol) and CN’Bu (0.136 g, 1.63 mmol), and the
were
added
mixture was stirred at room temperature for 15 days. The solution was then filtered
to remove the insoluble decomposition products, and the solvent then evaporated
off and the residue washed with light petroleum. Recrystallization of the crude

284
product from
then mixtures of 13b and 14b
gave first yellow-orange crystals of the 13b (35%) and
(llb). A mixture of
(B) From
(0.20 g, 0.41 mmol), and
was stirred for 10 days at room temperature. The
solution was evaporated to dryness and the residue was washed with light petro-
(0.063 g,
0.76 mmol) in
(30
leum. The crude product was recrystallized from
mainly 13b (37%).
petroleum to give
It should be noted that in this reaction the presence of
is unnecessary.
Acknowledgements
We thank D.G. I.C.Y.T. for financial support and Prof. G.A.
valuable discussions.
for
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