New synthesis of Fischer-type hydrazino(alkyl) complexes. First X-ray characterisation of a chelate hydrazino derivative

Article abstract of DOI:10.1039/a708018b

The first Fischer-type hydrazino(methyl)carbene complex has been synthesized from the appropriate acetylhydrazine and Na₂Cr(CO)₅; the new complex has some peculiar features in comparison with aminocarbene complexes: (i) the E rotamer can be completely transformed into the Z rotamer through the formation of its anion, and (ii) as a result of a thermal reaction, the Z isomer affords a new unusual chelate hydrazino(methyl)carbene complex that can be mono- or dialkylated.

Full text of DOI:10.1039/a708018b

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New synthesis of Fischer-type hydrazino(alkyl) complexes. First X-ray
characterisation of a chelate hydrazino derivative
Emanuela Licandro,*a Stefano Maiorana,a† Raffaella Manzotti,a Antonio Papagni,a Dario Perdicchia,a Mary
Pryce,b Antonio Tiripicchio*c and Maurizio Lanfranchic
a Dipartimento di Chimica Organica e Industriale, Universita` degli Studi di Milano, via C. Golgi, 19, I-20133 Milan, Italy
b School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
c Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universita` di Parma, Centro di Studio per
la Strutturistica Diffrattometrica del CNR, viale delle Science, I-43100 Parma, Italy
The first Fischer-type hydrazino(methyl)carbene complex
has been synthesized from the appropriate acetylhydrazine
and Na2Cr(CO)5; the new complex has some peculiar
features in comparison with aminocarbene complexes: (i) the
E rotamer can be completely transformed into the Z rotamer
through the formation of its anion, and (ii) as a result of a
thermal reaction, the Z isomer affords a new unusual chelate
hydrazino(methyl)carbene complex that can be mono- or di-
alkylated.
remaining unchanged after heating in hexane at 50 °C for 2 h
whereas, after heating at 39 °C in CH2Cl2 for 3.5 h, (Z)-1 was
transformed into a new, red–orange solid complex, 3‡ with the
Bn
Me
N
Me
N
(CO)4Cr
Me
3
Only a few hydrazinocarbene complexes have so far been
reported in the literature.1 This is certainly due to the very
limited applicability of the hydrazinolysis reaction of alkoxy-
carbenes,2 which seems to be partially successful only in the
case of alkynyl carbene complexes.1b
displacement of a CO ligand. As far as we know, only one
example of an N-chelate complex with a four-membered ring
has been previously reported.4 The structure of 3 was supported
by the X-ray analysis of the structure of the homologue 5a§
whose formation is described below (Scheme 2). The pure
rotamers (E)-1 and (Z)-1 were treated with BunLi at 270 °C and
quenched with a saturated aq. NH4Cl; rotamer (E)-1 was
completely transformed into rotamer (Z)-1, whereas the latter
proved to be configurationally stable. The complete conversion
of (E)-1 into (Z)-1 is rather surprising since this transformation
is usually incomplete in aminocarbene complexes and generally
leads to a mixture of the two rotamers. The treatment of the
anion generated from the pure (E)-1 or (Z)-1 rotamers with
alkylating reagents such as iodomethane and allyl bromide gave
the expected ethyl(hydrazino)carbene complexes (Z)-4a and
(Z)-4b, together with the tetracarbonyl N-chelate derivatives 5a
and 5b (Scheme 2).‡ It can be seen that the formation of the
coordinated derivatives 3, 5a and 5b is easier as the bulk of the
a- substituent increases (Me < Et < allyl). Column chromato-
graphy over silica gel gave pure samples of the complexes 5a
and 5b, whereas complexes 4a and 4b were always recovered in
the form of mixtures with 5a and 5b respectively.‡ Unlike an
amino(ethyl)carbene complex, the ethyl(hydrazino)carbene 5a
can easily be further alkylated with MeI to give complex 6
(Scheme 3).‡ Compound 5a is the first structurally charac-
terized chelate hydrazinocarbene complex (see Fig. 1). The
coordination around Cr is distorted octahedrally, with the
organic moiety acting as a chelating ligand through N(1) and
C(5). The four-membered ring is planar, and the chelation
N(1)–Cr–C(5) angle is very narrow at 62.9(2)°. Although the
Cr–N bond length of 2.211(4) Å is comparable with the average
Alkyl(hydrazino)carbene complexes are unknown and could
in principle have some unique features due to the potential of the
b-nitrogen of the hydrazine moiety as a coordinating group to
the metal, and the influence of this coordination on the
stereodynamic properties of the complex and the reactivity of
the a-carbanions.
We here report the synthesis of the first hydrazino-
(methyl)carbene complex 1, its thermally promoted trans-
formation, and the reaction of its anion with electrophiles. The
Bn
N
NMe2
(OC)5Cr
Me
1
apparently simple but long-standing problem associated with
the controlled synthesis of alkyl (hydrazino)carbene complexes
has been solved by extending the known Hegedus method3 for
preparing amino carbene complexes from amides to hydrazide
derivatives. The hydrazide 2 was reacted with disodium
pentacarbonylchromate,3 affording complex 1 as a 1:1.3 E:Z
rotameric mixture (Scheme 1).‡ The (E)-1 and (Z)-1 rotamers
were fully characterized after chromatographic separation over
silica gel. Rotamer (E)-1 proved to be thermally stable,
Me
Me
Bn
N
Bn
N
N
N
Me
Me
R
Bn
N
R
Me
Me
Me
Bn
N
Bn
N
i
N
N
Bn
+
Me
Me
Me
N
i
O
Me
N
(CO)5Cr
Me
(CO)5Cr
(E)-1
N
+
Me
Me
2
(Z)-1
(CO)5Cr
Me
(CO)4Cr
(CO)5Cr
Me
(E)-1 or (Z)-1
(Z)-4a,b
5a,b
Scheme 1 Reagents and conditions: i, Na2Cr(CO)5 (2 equiv.), anhydrous
THF, N2, 278 °C, 40 min, allowed to warm to 0 °C, 4 h, then cooled to
278 °C, Me3SiCl (3 equiv.), 278 °C, 30 min, then Al2O3 (45 g on a base
of 0.61 g of 2), 45 min, then chromatographic separation on silica gel to give
(E)-1 (0.32 g) and (Z)-1 (0.36 g), eluent light petroleum–CH2Cl2 8:2
(overall yield 59%)
a R = Me 3.4 : 1
b R = allyl 1.3 : 1
Scheme 2 Reagents and conditions: BunLi (1 equiv.), THF, N2, 278 °C, 30
min, then RX, 278 °C, 10 min, 0 °C, 30 min
Chem. Commun., 1998
383

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5 H, arom); dC (300 MHz, CDCl3) 39.6 (q, CH3), 44.3 [q, N(CH3)2], 56.2
(t, CH2 ), 126.6, 128.0, 128.8 (arom), 135.6 (s, arom), 217.6 (s, CO cis),
223.4 (s, CO trans), 277.5 (s, CNCr); m/z (EI) 368 [M+]. For (Z)-1: mp
85 °C; dH (300 MHz, CDCl3) 2.65 [s, 6 H, N(CH3)2], 2.70 (s, 3 H, CH3),
4.95 (s, 2 H, CH2Ph), 7.40–7.20 (m, 5 H, arom); dC (300 MHz, CDCl3) 39.1
(q, CH3), 44.2 [q, N(CH3)2], 48.9 (t, CH2), 125.2, 127.8, 129.3 (arom),
133.5 (s, arom), 218.4 (s, CO cis), 225.2 (s, CO trans), 280.6 (s, CNCr); m/z
(EI) 368 [M+]. For 3: mp 123–6 °C; n (Nujol)/cm21 1997, 1888–1830 (CO);
dH (80 MHz, CDCl3) 2.73 (s, 3 H, CH3), 2.78 [s, 6 H, N(CH3)2], 4.65 (s, 2
H, CH2Ph), 7.05–7.55 (m, 5 H, arom); m/z (FAB+) 340 [M+]. For 5a: mp
120 °C (decomp.); n (Nujol)/cm21 1998 (CO trans), 1917–1803 (CO cis);
dH (80 MHz, CDCl3) 1.50 (t, 3 H, CH2CH3), 2.65 (q, 2 H, CH2CH3), 2.80
[s, 6 H, N(CH3)2], 4.65 (s, 2 H, CH2Ph), 7.10–7.45 (m, 5 H, arom); dC (300
MHz, CDCl3) 13.0 (q, CH3), 34.7 (q, CH3), 49.1 (t, CH2 ), 52.3 [q,
N(CH3)2], 126.1, 128.5, 129.5 (arom), 133.5 (s, arom), 218.5 (s, 2CO cis),
230.1 (s, CO cis), 232.2 (s, CO trans), 294.7 (s, CNCr); m/z (FAB+) 354
[M+]. Spectroscopic and analytical data for complexes 4a, 4b, 5b and 6 are
in line with the reported structure.
Bn
Me
N
i
Me
5a
Me
N
(CO)4Cr
Me
6
Scheme 3 Reagents and conditions: BunLi (1 equiv.), THF, N2, 278 °C, 30
min, then MeI, 278 °C, 10 min then 0 °C, 20 min, then room temp., 10
min
C(14)
C(15)
C(7)
C(16)
C(13)
C(6)
C(12)
C(11)
§ Crystal data for 5a: C16H18CrN2O4, Mr = 354.32, monoclinic, space
C(5)
N(2)
O(4)
C(4)
group C2/c,
a
=
21.346(6),
=
b
=
12.782(4),
8, rcalc
c
=
14.136(4) Å,
C(10)
b
=
113.70(2)°, V
3532(2) Å3, Z
=
=
1.333 Mg m23
,
F(000) = 1472, l = 1.54184 Å, m(Cu-Ka) = 5.507 mm21. Crystal
dimensions: 0.15 3 0.21 3 0.33 mm. The intensity data were collected by
means of a Siemens AED diffractometer using the q–2q scan technique at
room temperature. 3494 reflections were measured (with q in the range
3–70°) of which 3357 were independent and included in the structural
refinement. Correction for absorption was applied (maximum and minimum
values for the transmission coefficient were 1.000 and 0.637). The structure
was solved by means of direct and Fourier methods, and refined using full-
matrix least-squares procedures (based on Fo2), with anisotropic thermal
parameters in the last cycles of refinement for all of the non-hydrogen
atoms. The hydrogen atoms were introduced into the geometrically
calculated positions and refined riding on the parent atoms. The refinement
converged at wR2 = 0.1579 for all data, and 209 variables [R1 = 0.0506 for
O(1)
C(1)
O(3)
Cr
C(3)
C(9)
N(1)
C(8)
C(2)
O(2)
Fig. 1 View of the molecular structure of complex 5a together with the
atomic numbering system. Selected bond distances (Å) and angles (°): Cr–
C(5) 2.028(4), Cr–N(1) 2.221(4), C(5)–N(2) 1.308(7), N(1)–N(2) 1.451(5),
N(2)–C(10) 1.481(6), C(5)–C(6) 1.494(7); N(1)–Cr–C(5) 62.9(2), Cr–
C(5)–N(2) 101.3(3), Cr–N(1)–N(2) 88.5(2), N(1)–N(2)–C(5) 107.3(3),
N(1)–N(2)–C(10) 120.8(3), C(5)–N(2)–C(10) 131.8(4).
1603 reflections with I
>
2s(I)]; min/max residual electron density:
20.356/0.408
e
Å23
. The SHELXS-86 and SHELXL-93 computer
programs were used (ref. 6). CCDC 182/726.
value found in complexes of Cr0 with tertiary amines (2.21 Å),
the 2.028(4) Å Cr–C(5) bond length is much shorter than those
found in aminocarbene complexes of Cr0 (in the range of
2.123–2.156 Å).5 This means that the Cr–C(5) bond has a more
noticeably double bond character than the other aminocarbene
complexes. It is also worth noting that the 1.813(6) Å Cr–C(1)
bond involving the carbonyl trans to the aminic N(1) atom is
shorter than other Cr–C(carbonyl) bonds [in the range
1.871(5)–1.882(5) Å].
1 (a) H. Fischer and G. Roth, J. Organomet. Chem., 1995, 490, 229; (b)
R. Aumann, B. Jasper and R. Fro¨hlich, Organometallics, 1995, 14,
2447.
2 E. O. Fischer and R. Aumann, Chem. Ber., 1968, 101, 963.
3 R. Imwinkelried and L. S. Hegedus, Organometallics, 1988, 7, 702.
4 K. H. Do¨tz and C. G. Kreiter, Chem. Ber. , 1976, 109, 2026.
5 J. A. Connor and O. S. Mills, J. Chem. Soc. A, 1969, 334; H. Rudler,
A. Parlier, R. Yefsah, B. Denise, J.-C. Daran, J. Vaissermann and
C. Knobler, J. Organomet. Chem., 1988, 358, 245; R. Aumann,
S. Althaus, C. Kruger and P. Betz, Chem. Ber., 1989, 122, 357; A. Parlier,
N. Rudler, H. Rudler, R. Goumont, J.-C. Daran and J. Vaissermann,
Organometallics, 1995, 134, 2760.
We thank the M.U.R.S.T. and the C.N.R. of Rome, and the
European
community
(HCM
Programme,
contract
ERBCHRXCT940501), for their financial support.
6 G. M. Sheldrick, SHELXS-86 Program for the solution of crystal
structures, University of Go¨ttingen, 1986; SHELXL-93 Program for
crystal structure refinement, University of Go¨ttingen, 1993.
Notes and References
† E-mail: maior@icil64.cilea.it
‡ Selected data for (E)-1: mp 57 °C (decomp.); dH (300 MHz, CDCl3) 2.45
[s, 6 H, N(CH3)2], 3.05 (s, 3 H, CH3), 5.55 (s, 2 H, CH2Ph), 7.40–7.20 (m,
Received in Liverpool, UK, 6th November 1997; 7/08018B
384
Chem. Commun., 1998