Synthesis, derivatization, and structural characterization of [Mn(CNC6H3Me2-2,6)5]-, a five-coordinate isonitrilate complex containing Mn-I

Article abstract of DOI:10.1039/a700089h

Naphthalenide reduction of [Mn(CNC₆H₃Me₂-2,6)₅Cl] forms solutions of trigonal-bipyramidal [Mn(CNC₆H₃Me₂-2,6)₅]^-, as established by an X-ray diffraction study of a [K(18-C-6)(dme)]⁺ salt and derivatization with SnClPh₃ to give [Mn(CNC₆H₃Me₂-2,6)₅(SnPh ₃)].

Full text of DOI:10.1039/a700089h

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Synthesis, derivatization, and structural characterization of
[Mn(CNC6H3Me2-2,6)5]2, a five-coordinate isonitrilate complex containing
Mn2I
Tracy L. Utz, Patricia A. Leach, Steven J. Geib and N. John Cooper*
Department of Chemistry and Materials Research Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
Naphthalenide reduction of [Mn(CNC6H3Me2-2,6)5Cl]
forms solutions of trigonal-bipyramidal [Mn(CNC6H3Me2-
2,6)5]2, as established by an X-ray diffraction study of a
[K(18-C-6)(dme)]+ salt and derivatization with SnClPh3 to
give [Mn(CNC6H3Me2-2,6)5(SnPh3)].
We recently reported that cobalt(2i) isonitrilates can be
prepared by naphthalenide reduction of any of a range of
cobalt(0), cobalt(i) and cobalt(ii) precursors which contain an
adequate number of isonitrile ligands,1 and this led us to
approach the synthesis of [Mn(CNC6H3Me2-2,6)5]2 by reduc-
tion of [Mn(CNC6H3Me-2,6)5Cl] 2.11 Dropwise addition of 2
equiv. of a 0.4 m potassium naphthalenide [K(Naph)] solution12
to an orange thf solution of 2 at 278 °C gave a blood-red
solution. The sharp nCN bands of 2 at 2062s and 2008(sh) cm21
were replaced by two broad nCN absorptions at 1920s and
1710m cm21 indicating complete consumption of 2 and
formation of a more reduced isonitrile complex. These solutions
are extremely air sensitive, changing from blood red to cherry
red in seconds, and are also thermally unstable, undergoing a
similar colour change in a few days at room temperature.
Initial attempts to isolate the reduction product were
unsuccessful, but it was readily established that this solution is
an effective source of [Mn(CNC6H3Me2-2,6)5]2 by addition of
SnClPh3 (1 equiv. in thf) at 278 °C. The solution became clear
and yellow in colour, and IR spectra indicated complete
consumption of the anion and formation of a new species with
Our recent syntheses of the first isonitrilates (homoleptic
isonitrile complexes of metals in negative oxidation states)
generated complexes of Co2I {[Co(CNC6H3Me2-2,6)4]2}1 and
of Ru2II {[Ru(CNC6H3Me2-2,6)4]22 and [Ru(CNBut)4]22}.2
The existence of these complexes established that isonitrilates
could be prepared with several different metals, with metals in
oxidation states as low as 2ii, and with both alkyl and aryl
substituents on the ligands. It remained unclear, however,
whether isonitrilates could be prepared in geometries other than
tetrahedral; the cobalt(2i) and ruthenium(2ii) complexes are
all four coordinate, and a tetrahedral geometry has been
established crystallographically1 for [Co(CNC6H3Me2-2,6)4]2
and is consistent with IR data in the ruthenium(2ii) case,2 as
would be anticipated on the basis of the d10 configurations of the
metals and by analogy with the isoelectronic carbonylmetalates
[Co(CO)4]23 and [Fe(CO)4]22 4
.
Structurally characterized
higher energy nCN bands at 2135m, 2064(sh) and 1998s cm21
.
homoleptic carbonylmetalates are known in five5,6 and six
coordinate7,8 geometries, but the established propensity of
isonitrile ligands to couple in higher coordinate environments9
left open whether isonitrilates would be accessible in similar
geometries despite the close analogies between isonitriles and
CO.10 We have now examined the synthesis of five coordinate
manganese(2i) isonitrilates, and we wish to report the synthesis
of the trigonal-bipyramidal isonitrilate [Mn(CNC6H3Me2-
2,6)5]2 12 and its structural characterization as a [K(18-crown-
The solvent was removed under reduced pressure and the
product was purified by slow diffusive mixing of a pentane
layer into a concentrated toluene solution to give crystals of
[Mn(CNC6H3Me2-2,6)5(SnPh3)] 3† in 88% yield.
Isolation of a crystalline salt of [Mn(CNC6H3Me2-2,6)5]2
from the reduction of [Mn(CNC6H3Me2-2,6)5Cl] required that
samples be maintained at or below 230 °C, and began with
filtration of a freshly prepared solution through a bed of Celite
545 into a flask containing 1 equiv. of neat 18-crown-6
(18-C-6). After 1 h the solvent was removed under reduced
pressure and the mixture was washed with pentane to give a
red–brown solid from which red–black crystals of [K(18-C-
6]1† could be obtained in 53% yield by crystallization from a
saturated dme solution following addition of a layer of pentane.
This material does not entirely redissolve in dme; this behaviour
is reminiscent of that of alkali-metal salts of [M(CO)5]22
(M = Cr, Mo, W) in the solid state at room temperature.6
Crystals suitable for X-ray diffraction studies were grown
from a freshly prepared sample of [K(18-C-6)]1 by dissolving it
in a minimal volume of dme and cooling the unfiltered solution
to 230 °C overnight. A low-temperature diffraction study‡
established that these crystals contain [K(18-C-6)(dme)]1, a
dme solvate of [K(18-C-6)]1, but this material is not stable in
the solid state at room temperature and crystals do not diffract
well if stored for more than few days.
6)(dme)]+ salt (dme
= dimethoxyethane), together with
evidence that 12 can react as a metal centred nucleophile with
simple electrophiles (Scheme 1).
[Mn(CO)5Cl]
i
[Mn(CNC6H3Me2-2,6)5Cl]
ii
K[Mn(CNC6H3Me2-2,6)5]
iii
iv
–
Ar
N
C
Ar
N
C
In this salt of 12 the bis-chelate dme and the 18-C-6 ligand
are both coordinated to the K+ counter ion, effectively blocking
K+– Mn2 contact ion pairing in the solid state, and allowing the
[Mn(CNC6H3Me2-2,6)5]2 anion (Fig. 1) to adopt a geometry
close to the trigonal bipyramid anticipated by analogy with the
established structures of five coordinate carbonylmetalates5,6
and of the isoelectronic d8 homoleptic isonitrile complex
[Fe(CNBut)5].13 The C(1) and C(5) isonitriles are in the axial
positions, but there are some irregularities in the coordination
CNAr
ArNC Mn SnPh3
ArNC
CNAr
CNAr
ArNC Mn
C
C
N
N
Ar
Ar
[K(18-C-6)(dme)] +
Scheme 1 Reagents and conditions: i, CNC6H3Me2-2,6; ii, 2 K(Naph); iii,
18-C-6, dme; iv, SnClPh3
Chem. Commun., 1997
847

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NMR spectra. These spectra also establish that there is negligible dme in
crystals prepared in this manner.
‡ Crystal data: [K(18-C-6)(dme)]1: triclinic, space group P1, Z = 2,
–
a
= 11.825(5), b = 12.623(6), c = 22.663(2) Å, a = 99.12(4),
b = 101.17(4), g = 112.47(4)°, U = 2964(2) Å3, T = 213(2) K. Of the
9842 reflections measured in the range 3.62 < 2q < 50.56° range, 9376
unique reflections were used in the structure solution by direct methods.
Refinement on F2 converged at R = 0.0705 Rw = 0.1958 (all data), with
GOF = 1.037.
C(16)
N(1)
C(1)
C(46)
N(4)
C(4)
Atomic coordinates, bond lengths and angles, and thermal parameters
have been deposited at the Cambridge Crystallographic Data Centre
(CCDC). See Information for Authors, Issue No. 1. Any request to the
CCDC for this material should quote the full literature citation and the
reference number 182/392.
C(3)
N(3)
C(26)
N(2)
Mn
C(2)
C(36)
C(5)
N(5)
C(56)
K
References
1 P. A. Leach, S. J. Geib, J. A. Corella, G. F. Warnock and N. J. Cooper,
J. Am. Chem. Soc., 1994, 116, 8566.
2 J. A. Corella, R. L. Thompson and N. J. Cooper, Angew. Chem., Int. Ed.
Engl., 1992, 31, 83.
3 P. Z. Klu¨fers, Z. Kristallogr., 1984, 167, 253; D. P. Schussler,
W. R. Robinson and W. F. Edgell, Inorg. Chem., 1974, 13, 153.
4 H. B. Chin and R. Bau, J. Am. Chem. Soc., 1976, 98, 2434; R. G. Teller,
R. G. Finke, J. P. Collman, H. B. Chin and R. Bau, J. Am. Chem. Soc.,
1977, 99, 1104.
Fig. 1 Molecular structure of [K(18-C-6)(dme)][Mn(CNC6H3Me2-2,6)5]
([K(18-C-6)(dme)]1; 35% probability ellipsoids; hydrogen atoms omitted
for clarity). Selected bond lengths (Å) and angles (°): Mn–C(1) 1.847(6),
Mn–C(2) 1.724(6), Mn–C(3) 1.837(6), Mn–C(4) 1.806(6), Mn–C(5)
1.869(6), C(1)–N(1) 1.195(7), C(2)–N(2) 1.185(7), C(3)–N(3) 1.225(7),
C(4)–N(4) 1.219(7), C(5)–N(5) 1.184(6) Å; C(1)–Mn–C(5) 174.4(3),
C(2)–Mn–C(4) 123.7(3), C(2)–Mn–C(3) 111.9(3), C(3)–Mn–C(4)
124.3(2), C(1)–Mn–C(2) 82.9(3), C(1)–Mn–C(3) 98.1(3), C(1)–Mn–C(4)
85.3(2), C(2)–Mn–C(5) 94.2(2), C(3)–Mn–C(5) 87.4(2), C(4)–Mn–C(5)
92.4(2), C(1)–N(1)–C(16) 163.2(7), C(2)–N(2)–C(26) 143.3(6),
C(3)–N(3)–C(36) 149.2(6), C(4)–N(4)–C(46) 149.2(5), C(5)–N(5)–C(56)
163.4(6)°.
5 [Mn(CO)5]2: B. A. Frenz and J. A. Ibers, Inorg. Chem., 1972, 11, 1109;
M. Heberhold, F. Wehrmann, D. Neugebauer and G. Huttner,
J. Organomet. Chem., 1978, 152, 329; B. Balbach, S. Baral, H.
Biersack, W. A. Herrmann, J. A. Labinger, W. R. Scheidt, F. J. Timmers
and M. L. Ziegler, Organometallics, 1992, 11, 35; H. Ben Laarab,
B. Chaudret, F. Dahan, J. Devillers, R. Poilblanc and S. Sabo-Etienne,
New J. Chem., 1990, 14, 321; W. Petz and F. Weller, Z. Naturforsch.,
Teil B, 1991, 46, 297.
6 [W(CO)5]22: J. M. Maher, R. P. Beatty and N. J. Cooper, Organome-
tallics, 1985, 4, 1354.
sphere. The C(2) isonitrile in particular has Mn–C and C·N
bonds which are 0.097 Å ( > 15s) and 0.04 Å ( > 5s) shorter,
respectively, than the average C·N bonds in the other two
equatorial isonitriles; we ascribe this shortening to distortions
induced by van der Waals interactions between neighbouring
[Mn(CNC6H3Me2-2,6)5]2 ions, consistent with the 2.95 and
2.72 Å distances between the hydrogen atoms on the para
carbon and one meta carbon of the C(2) isonitrile and the aryl
plane of the C(3) isonitrile ligand. It is interesting that the axial
isonitriles are less bent at nitrogen (both 163°) than the
equatorial isonitriles (av. 147°, range 143–149°); a similar
pattern in metric parameters for [Fe(CNBut)5] was ascribed to
more effective back bonding from the low-valent Fe(0) metal
centre to the equatorial isonitrile ligands.13
Our results establish that isonitrilates can be prepared in five
coordinate environments, and that a d8 example adopts a
trigonal bipyramidal geometry. The successful synthesis of
[Mn(CNC6H3Me2-2,6)5]2 represents a significant addition to
the small number of complexes accepted to contain manganese
in the 2i oxidation state,14 and its derivatization with SnClPh3
also suggests that 12 may prove a valuable intermediate which
will allow access to an isonitrile chemistry of Mn comparable to
the carbonyl chemistry of Mn accessible from the isoelectronic
carbonylmetalate [Mn(CO)5]2.15
7 [M(CO)6]2 (M = V, Nb or Ta): R. D. Wilson and R. Bau, J. Am. Chem.
Soc., 1974, 96, 7601; L. D. Silverman, P. W. R. Corfield and
S. J. Lippard, Inorg. Chem., 1981, 20, 3106; F. Calderazzo, U. Englert,
G. Pampaloni, G. Prelizzi and R. Zamboni, Inorg. Chem., 1983, 22,
1865; F. Calderazzo, G. Pampaloni, D. Vitali and R. Zanazzi, J. Chem.
Soc., Dalton Trans., 1982, 1993.
8 [M(CO)6]22 (M = Ti, Zr or Hf): J. E. Ellis and K.-M. Chi, J. Am. Chem.
Soc., 1990, 112, 6022.
9 E. M. Carnahan, J. D. Protasiewicz and S. J. Lippard, Acc. Chem. Res.,
1993, 26, 90.
10 L. Malatesta, Prog. Inorg. Chem., 1959, 1, 283; L. Malatesta and
F. Bonati, Isocyanide Complexes of Transition Metals, Wiley, New
York, 1969; P. M. Treichel, Adv. Organomet. Chem., 1973, 11, 21;
Y. Yamamoto, Coord. Chem. Rev., 1980, 32, 193; E. Singleton and
M. E. Oosthuizen, Adv. Organomet. Chem., 1983, 22, 209.
11 Prepared by a procedure analogous to that used to prepare the
corresponding CNPh complex: K. K. Joshi, P. L. Pauson and
W. H. Stubbs, J. Organomet. Chem., 1963, 1, 51; P. M. Treichel,
G. E. Dirreen and H. J. Mueh, J. Organomet. Chem., 1972, 44, 339.
12 J. M. Maher, R. P. Beatty, G. R. Lee and N. J. Cooper, Organometallic
Syntheses; ed. R. B. King and J. J. Eisch, Elsevier, Amsterdam, 1986,
vol. 3, p. 35.
13 J. M. Bassett, M. Green, J. A. K. Howard and F. G. A. Stone, J. Chem.
Soc., Chem. Commun., 1977, 853; J. M. Bassett, D. E. Berry,
G. K. Barker, M. Green and J. A. K. Howard, J. Chem. Soc., Dalton
Trans., 1979, 1003.
14 There are few accepted examples other than [Mn(CO)5]2 and
[Mn(NO)2(CN)2]32 (H. von Behrens, E. Linder and H. Schindler,
Z. Anorg. Allg. Chem., 1969, 365, 119): B. Chiswell, E. D. McKenzie
and L. F. Lindoy, in Comprehensive Coordination Chemistry, ed. G.
Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon, Oxford,
1987, vol. 4, ch. 41.
We thank the National Science Foundation for financial
support through grant CHE-9632202.
Footnotes
* E-mail: cooperj+@pitt.edu
† 3: IR nCN; 2135m, 2064(sh). 1998s cm21. 1H NMR (CD2Cl2, 300 MHz):
d 7.60–7.57 (m, 5 H, p-H of C6H3), 6.99–6.87 (m, 25 H, m-H of
CNC6H3Me2 and SnPh3), 2.42 (s, 6 H, CH3 of CNC6H3Me2 trans to SnPh3),
2.16 (s, 24 H, CH3 of CNC6H3Me2 cis to SnPh3).
15 P. M. Treichel, in Comprehensive Organometallic Chemistry II, ed.
E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995,
vol. 6, section 1.3; P. M. Treichel, in Comprehensive Organometallic
Chemistry, ed. G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon,
Oxford, 1982, vol. 4, section 29.2.
[K(18-C-6)]1: IR nCN: 1920s, 1710m cm21 1H NMR (CD3CN, 300
.
MHz): d 6.92 (d, 7.2 Hz, 10 H, m-H of CNC6H3Me2), 6.73 (t, 7.2 Hz, 1 H,
p-H of CNC6H3Me2), 3.53 (s, 24 H, C12H24O6), 2.37 (s, 30 H, CH3 of
CNC6H3Me2). The instability of the compound has precluded satisfactory
combustion analysis, but the 18-C-6:isonitrile ratio is confirmed by 1H
Received in Bloomington, IN, USA, 3rd January 1997; Com.
7/00089H
848
Chem. Commun., 1997