Hydrazinolysis of Fischer-type oxacarbenes made efficient: A new and easy entry to alkyl and aryl hydrazinocarbene complexes

Article abstract of DOI:10.1039/a900166b

Hydrazinolysis of the pentacarbonyl[alkyl- or aryl-(methoxy)carbene] complexes of W⁰ and Cr⁰ with both 1,1- and 1,2-disubstituted hydrazines affords the corresponding new hydrazinocarbenes 15-18, 21 and 22, and the presence of LiCl in the reaction medium greatly increases their yields.

Full text of DOI:10.1039/a900166b

Hydrazinolysis of Fischer-type oxacarbenes made efficient: a new and easy
entry to alkyl and aryl hydrazinocarbene complexes
Emanuela Licandro,* Stefano Maiorana,* Antonio Papagni, Dario Perdicchia and Raffaella Manzotti
Dipartimento di Chimica Organica e Industriale, Università degli Studi di Milano, via C.Golgi, 19, I-20133 Milano,
Italy. E-mail: maior@icil64.cilea.it
Received (in Liverpool, UK) 14th January 1999, Accepted 16th April 1999
Hydrazinolysis of the pentacarbonyl[alkyl- or aryl-(meth-
oxy)carbene] complexes of W0 and Cr0 with both 1,1- and
1,2-disubstituted hydrazines affords the corresponding new
hydrazinocarbenes 15–18, 21 and 22, and the presence of
LiCl in the reaction medium greatly increases their yields.
All of the attempts to prevent this proton shift, i.e. (i) by
increasing steric hindrance around the b-nitrogen, (ii) by
running the reactions in the presence of an excess of Et3N as an
external competing base and, (iii) by reducing the b-nitrogen
lone pair availability by means of acylation, failed, and there
was no improvement in the yields of the complexes 15–18.
Looking for an alternative way to minimize the undesirable b-
nitrogen protonation, we considered a Lewis acid as a possible
coordinating species capable of engaging the b-nitrogen lone
pair without transforming this nitrogen into a good leaving
group: Li+ (as LiCl) appeared to be a suitable reagent for
achieving this goal.
The results of the hydrazinolysis of complex 11 with the N-
aminomorpholine 8 and N-amino-trans-2,6-dimethylmorpho-
line 9 in the presence of 2.2 equiv. of LiCl were surprisingly
good, with the yields of complexes 16 and 17 being respectively
double and eight times of those obtained in the absence of LiCl
(Scheme 1).
We have recently achieved the first synthesis of a number of
new pentacarbonyl and chelate hydrazino(alkyl)carbene com-
plexes 1–3.1
CH3
CH3
(CO)5Cr
R
CH3
N
(CO)5Cr
N
CH3
R
N
CH2Ph
CH2Ph
3 R = Et, but-3-enyl, Pri
1 R = Me
2 R = Et, but-3-enyl
The synthesis of 1–3 is of general applicability only when
applied to 1-substituted hydrazides.2 The hydrazinolysis of
oxacarbenes was a highly appealing procedure, even if Fischer3
reported that, for the reaction between the 1,1-dimethylhy-
drazine and the pentacarbonyl[methoxy(methyl)carbene]chro-
mium(0), it was unsuccessful. However, the hydrazinolysis of
oxacarbenes has more recently been shown to be possible in a
few specific cases.4,5
We here report on the reactions between the 1,1-disubstituted
hydrazines 5 and 7–10 and the methoxy(methyl)carbene
tungsten(0) complex 11, as well as those between the 1,2-dime-
thylhydrazine 12 and the methoxy(methyl)- and methoxy-
(phenyl)-carbene chromium(0) complexes 4 and 13. The results
of this study eventually revealed a new and efficient entry to
alkyl- and aryl-(hydrazino)carbenes.
The presence of LiCl also had a dramatic effect on the
reaction times, which increased from 30 min to 5 h. We believe
that this effect can be rationalized in terms of the formation of
an aggregate in THF between LiCl and the hydrazines 8 and 9,‡
in which the nucleophilic character of the hydrazines would be
Table 1 Reaction of 11 with various hydrazinesa
R
R
N
OCH3
CH3
NH
R
R
i
N
(CO)5W.NCCH3
+
(CO)5W
(CO)5W
+
NH2
CH3
5, 7–10
11
15–18
14
We initially reacted under nitrogen the 1,1-dimethylhy-
drazine 5 (1.1 mmol) with the tungsten complex 11 (1 mmol) in
dry THF solution at 278 °C for 30 min, but even the use of
tungsten only afforded the (CO)5W/N·C–Me complex 14
(Table 1). However, when we reacted the hydrazines 7–10 with
11 under the same conditions, we isolated a reaction mixture
containing the (Z)-hydrazinocarbenes 15–18† and variable
amounts of the acetonitrile complex 14; the yields are shown in
Table 1.
(Z)-Hydrazinocarbene
15–18 (% yield)
Hydrazine
Yield of 14 (%)
H3C
CH3
—
52
5
N
NH2
7
15 (34)
42
N
NH2
Although the yields of hydrazinocarbenes 15–18 were not
very high, this first set of results showed us that it was possible
to use the simple procedure described above to prepare stable
and isolable alkyl hydrazinocarbene complexes of tungsten. We
therefore decided to look carefully at the possible mechanism of
the hydrazinolysis reaction. The aim was to identify the factors
potentially capable of differentiating the pathway leading to the
acetonitrile complex 14 from that affording the target hydrazi-
nocarbenes 15–18.
O
8
9
16 ( 34)
17 (6)
50
74
N
NH2
O
N
NH2
According to Aumann,4 during the hydrazinolysis of alkoxy-
(alkynyl)carbenes, the hydrazinocarbenes 15–18 are formed
through the elimination of MeOH from the tetrahedral inter-
mediate of the reaction, whereas product 14 arises from the
breaking of the N–N bond with amine elimination. This latter
process is a consequence of the proton shift from the a- to the
b-nitrogen.
CH3
N
10
18 (28)
41
N
NH2
a Reagents and conditions: i, THF, 278 °C, 30 min.
Chem. Commun., 1999, 925–926
925

Table 2 Hydrazinolysis in the presence of LiCl
OCH3
R
(CO)5Cr
H
H3C
CH3
NH
4
R = CH3
N
R
CH3
13 R = Ph
N
THF
(CO)5Cr
+
(CO)5Cr
+
R
H
N
CH3
23 R = CH3
24 R = Ph
21 R = CH3
22 R = Ph
N
H3C
H
12
Hydrazinocarbene
(% yield, E:Z)
Aminocarbene
(% yield)
Complex
LiCl (equiv.)
T/°C
278
Time
4
4
13
13
—
2
—
2
5 min
15 h
5 min
15 h
21 (18, 7:3)
21 (73, 4:6)
22 (30, 1:1)
22 (80, 1.3:1)
23 (40)
23 (7)
24 (35)
23 (13)
278 ? 220
278
278 ? 220
O
R
R
good yields by means of the hydrazinolysis reaction carried out
in the presence of 2 equiv. of LiCl. It is likely that hydrazine/
LiCl aggregates are involved as the reactive species. To the best
of our knowledge, nothing has yet been reported in the literature
concerning the use of stable aggregates between hydrazines and
LiCl for synthetic purposes.6
We gratefully acknowledge joint financial support from
M.U.R.S.T., Rome, and the University of Milan (National
Project ‘Stereoselezione in Sintesi Organica, Metodologie ed
Applicazioni’). We also acknowledge the C.N.R. of Rome.
OCH3
+
(CO)5W
N
CH3
NH2
11
8 R = H
9 R = CH3
R
i
R
O
O
R
R
N
N
(CO)5W
N
C
CH3 + (CO)5W
+
NH
CH3
Notes and references
(CO)5W
† Only the (Z)-rotamers were observed. The lack of isolation of any of the
(E)-rotamers of 15–18 means that they are not formed at all or, if formed,
they are unstable and immediately give the W(CO)5·NCCH3 as postulated
by Fischer (ref. 3).
‡ To a THF solution of LiCl (2 equiv.), the hydrazine 8 (1 equiv.) was added
at room temperature. The resulting white solid was isolated and used for the
hydrazinolysis of complex 11, affording the hydrazino complex 16 in the
same yield as that shown in Scheme 1 (72%). The structure of the above
lithium aggregate is under investigation.
§ Selected data for (Z)-16: yellow solid, mp 112 °C (from CH2Cl2–
pentane); nmax(Nujol)/cm21 3161 (NH), 2060 (COtrans) 1960–1880 (COcis);
dH(300 MHz, CDCl3) 2.92–3.03 (m, 7 H, CrNCCH3 + NCH2), 3.87–3.92
(m, 4 H, OCH2), 8.50 (br s, 1 H, NH); dC(75 MHz, CDCl3) 42 (q, CH3), 55
(t, NCH2), 56.2 (t, CH2 ), 65 (t, OCH2) 198 (s, COcis), 204 (s, COtrans), 253
(s, CNW); m/z (EI) 452 [M+] (Calc. for C11H12N2O6W: C, 29.2, H, 2.7; N,
6.2%. Found, C, 29.50; H, 2.88; N, 6.07%). For (E)-21: light yellow solid,
mp 79–80 °C (from CH2Cl2–pentane); nmax(Nujol)/cm21 3334 (NH), 2054
(COtrans), 1917–1803 (COcis); dH(300 MHz, CDCl3) 2.71 (d, 3 H, J 6.2,
NHCH3) 2.78 (s, 3H, CrNCCH3), 3.96 (s, 3 H, CrNCNCH3), 4.36 (q, 1 H, J
6.2, NHCH3); dC(75 MHz, CDCl3) 36.2 (NHCH3) 37.2 (CrNCCH3), 48.4
(NCH3), 217.8 (s, 2COcis), 223.4 (s, COtrans), 265.2 (s, CNCr) (Calc. for
C9H10CrN2O5: C, 38.86, H, 3.62, N, 10.07. Found: C, 38.93; H, 3.39; N,
9.95%). For (Z)-21: yellow solid, mp 95–96 °C (from EtOAc–pentane);
nmax(Nujol)/cm21 3321 (NH), 2054 (COtrans), 1917–1803 (COcis), dH(300
MHz, CDCl3) 2.61 (s, 3H, CrNCCH3), 2.82 (d, 3 H, J 6.3, NHCH3), 3.41 (s,
3 H, CrNCNCH3), 6.10 (q, 1 H, J 6.3, NHCH3); dC(75 MHz, CDCl3) 36.7
(NHCH3) 37.6 (CrNCCH3), 39.1 (NCH3 ), 217.1 (s, 2COcis), 222.7 (s,
COtrans), 258.9 (s, CNCr) (Calc. for C9H10CrN2O5: C, 38.86, H, 3.62; N,
10.07. Found: C, 38.79; H, 3.60; N, 10.26%).
CH3
16 R = H, 72%
14 4%
19 R = H, 3%
9%
17 R = CH3, 48%
20 R = CH3, 11%
Scheme 1 Reagents and conditions: i, LiCl (2 equiv.), THF, 240 °C, 3 h.
reduced. As a result of the decrease in reaction rates, the amines
produced in the N–N bond breaking step can compete with the
hydrazine in the reaction with 11 affording the aminocarbenes
19 and 20 (Scheme 1).
Even in the presence of LiCl, only the (Z)-isomer of the
hydrazinocarbenes 16 and 17 was formed. In a typical
procedure, LiCl (0.0999 g, 2.47 mmol) was dissolved in
anhydrous THF (3 ml) and hydrazine 8 (0.115 ml, 1.19 mmol.)
was added under N2 at the same temperature, thus generating a
white slurry to which a 3 ml THF solution of 11 (0.412 g, 1.08
mmol.) was added dropwise over 5 min at 278 °C. After 2 h at
278 °C, the temperature was raised and kept at 240 °C for a
further 3 h. Standard work-up followed by purification by flash
chromatography [eluent: Et2O–light petroleum (6:4) then
Et2O] gave the hydrazinocarbene 16.§
The hydrazinolysis reaction was then extended to the
1,2-dimethylhydrazine 12 which was reacted with the chro-
mium(0) carbenes 4 and 13 (Table 2). When the free hydrazine
was used, the expected hydrazinocarbenes 21 (E/Z = 7:3) and
22 (E/Z = 1:1) were obtained in 18 and 30% yield respectively,
as well as the methyl(amino)carbene complexes 23 and 24
(yields of 40 and 35%, respectively). Also in this case, the
presence of 2 equiv. of LiCl in the reaction mixture greatly
increased the yields of hydrazinocarbenes 21 and 22 (see Table
2), thus demonstrating a general and important effect of the
presence of this salt in the reaction medium. The reaction was
carried out starting from a commercially available dihy-
drochloride salt of the 1,2-dimethylhydrazine (0.328 g, 2.46
mmol) suspended in anhydrous THF (20 ml), and treated under
nitrogen at 0 °C with a stoichiometric amount of BunLi (1.4 M
n-hexane solution, 3.5 ml, 4.92 mmol) (Table 2).
1 E. Licandro, S. Maiorana, R. Manzotti, A. Papagni, D. Perdicchia, M.
Pryce, A. Tiripicchio and M. Lanfranchi, Chem. Commun., 1998, 383.
2 Results to be published.
3 E. O. Fischer and R. Aumann, Chem. Ber., 1968, 101, 963.
4 R. Aumann, B. Jasper and R. Fröhlich, Organometallics, 1995, 14,
2447.
5 M. Iyota, L. Zhao and M. Matsuyama, Chem. Lett. , 1994, 777
6 M. A. Klochko and M. P. Mikhailova, Zh. Neorgan. Khim., 1960, 5,
2319.
In conclusion, carbene complexes of tungsten(0) and chro-
mium(0) 16, 17, 21 and 22 were synthesized in satisfactory to
Communication 9/00166B
926
Chem. Commun., 1999, 925–926