Zwitterionic stabilization of a reactive cobalt tris-isocyanide monoanion by cation coordination

Article abstract of DOI:10.1002/anie.201205058

A break with tradition: The cation, [Ph₃P=N=PPh ₃]⁺ ([PPN]⁺), was found to provide a stabilizing η²-arene interaction to the coordinatively unsaturated, tris-isocyanide monoanion, [Co(CNAr^Mes2) ₃]^-(Ar^Mes2=2,6-(2,4,6-Me₃C ₆H₂)C₆H₃); Co=purple, N=light purple, and P=orange). The resulting zwitterion is a source of [Co(CNAr ^Mes2)₃]^- anions, performing nucleophilic additions, carbon-element bond activations, and multistep decarbonylations.

Full text of DOI:10.1002/anie.201205058

Angewandte
Chemie
DOI: 10.1002/anie.201205058
Metallates
Zwitterionic Stabiliztion of a Reactive Cobalt Tris-Isocyanide
Monoanion by Cation Coordination**
Alex E. Carpenter, Grant W. Margulieux, Matthew D. Millard, Curtis E. Moore,
Nils Weidemann, Arnold L. Rheingold, and Joshua S. Figueroa*
As a result of their metal-based nucleophilicity and ability to
mediate a wide range of transformations involving main-
group and carbon-based electrophiles, organometallic metal-
lates have received considerable attention.[1] The homoleptic
carbonyl metallates [Fe(CO)4]2ꢀ and [Co(CO)4]ꢀ serve as the
prototypical examples of this molecular class and are
stabilized in part by strong p-back-bonding interactions
between the highly reduced metal centers and the CO
ligands.[2] In addition, several metallates containing other p-
acidic ligands, including olefins, arenes, isocyanides, and PF3,
have been reported.[1 h] However, in the vast majority of these
cases the reduced metal centers possess coordinative and/or
electronic saturation (i.e. 18eꢀ configurations), which adds to
their stability. Accordingly, the chemistry of metallates
featuring coordinatively unsaturated metal centers is signifi-
cantly underdeveloped,[3] despite the promise of coupling
metal-based nucleophilic character with enhanced reactivity
toward Lewis basic substrates.
Previously we reported the [PPN] salt, [PPN][Co-
(CNArMes2)4],[7] as a unique example of a discrete cobalt
tetra-isocyanometallate unperturbed by anion–cation inter-
actions.[8]Prolonged stirring (30 h) of this salt in n-hexane
solution results in CNArMes2 ligand dissociation and the
precipitation of the black, zwitterionic tris-isocyanide com-
plex [(h2-PPN)Co(CNArMes2)3, 1; Figures 1 and 2]. Crystallo-
graphic characterization of (h2-PPN)Co(CNArMes2
)
(1)
3
In an effort to stabilize organometallic complexes featur-
ing both highly reduced metal centers and coordinative
unsaturation, we have surveyed the ligation properties of the
encumbering and p-acidic m-terphenyl isocyanide ligands
CNArMes2 and CNArDipp2 (ArMes2 = 2,6-(2,4,6-Me3C6H2)C6H3);
ArDipp2 = 2,6-(2,6-(iPr)2C6H3)C6H3).[4] Herein, we report the
use of CNArMes2 for the isolation of a zwitterionic complex
that functions as a highly reactive source of the coordinatively
unsaturated, tris-isocyanide cobalt monoanion [Co-
(CNArMes2)3]ꢀ toward electrophilic reagents. In this respect,
[Co(CNArMes2)3]ꢀ serves as an isocyano mimic of the unstable
tricarbonyl monoanion, [Co(CO)3]ꢀ, which has been
observed exclusively in the gas phase.[5] Furthermore, we
detail a unique method for the stabilization of the [Co-
(CNArMes2)3]ꢀ anion that relies on h2-arene coordination of
the well-known and traditionally non-interacting bis-(triphe-
Figure 1. Molecular structure of (h2-PPN)Co(CNArMes2)3. Important
bond lengths [ꢀ]: Co1-C4=2.139(4), Co1-C5=2.166(4), C4-
C5=1.434(6), C4-C9=1.419(6), C5-C6=1.411(6), C6-C7=1.359(6),
C7-C8=1.437(6), and C8-C9=1.375(6).
revealed a pyramidalized cobalt tris-isocyanide core accom-
panied by an h2-arene interaction between the Co center and
the para and meta carbon atoms of one PPN cation phenyl
ring (Figure 1). Dearomatization of the bound phenyl ring in
(h2-PPN)Co(CNArMes2)3 (1) is revealed from the crystallo-
graphic data, thus indicating that the [Co(CNArMes2)3]ꢀ
fragment functions as a strong p-base.[9] Notably, coordina-
tively induced dearomatization is well-known for mononu-
clear h2-arene complexes of the 4d and 5d metals,[9,10] but is
rare for complexes of the first transition series.[10,11] Despite
significant p-back donation into the bound phenyl ring, the
Co center in (h2-PPN)Co(CNArMes2)3 (1) remains consider-
ably reduced in the solid state (KBr) as indicated by the low
+
+
[6]
= =
nylphosphine)iminium cation, [PhP3 N PPh3] ([PPN] ).
[*] A. E. Carpenter,[+] G. W. Margulieux,[+] M. D. Millard, Dr. C. E. Moore,
Dr. N. Weidemann, Prof. Dr. A. L. Rheingold, Prof. Dr. J. S. Figueroa
Department of Chemistry and Biochemistry
University of California, San Diego
9500 Gilman Drive, MC 0358, La Jolla, CA 92093 (USA)
E-mail: jsfig@ucsd.edu
[+] These authors contributed equally to this work.
[**] We are grateful to the U. S. National Science Foundation for
finanical support (grant number CHE-0954710). J.S.F. is a Cottrell
Scholar of Research Corporation and an Alfred P. Sloan Research
Fellow (2011–2012). Professors John D. Protasiewicz and Charles L.
Perrin are acknowledged for helpful discussions.
nCN bands of the CNArMes2 ligands (1952, 1860, and 1824 cmꢀ1
free CNArMes2 = 2118 cmꢀ1).
;
While the solid-state structure of (h2-PPN)Co(CNArMes2
)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201205058.
3
1
(1) is suggestive of a strong h2-arene interaction, H NMR
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Figure 2. A) Synthesis and reaction pinwheel of (h2-PPN)Co(CNArMes2)3 (1); a) n-C6H14, 30 h, ꢀCNArMes2; b) CIP(NEt2)2 (1.05 equivalents), Et2O,
ꢀ100 to 25 8C, ꢀ[PPN]Cl; c) D, RT, 24 h, C6D6, ꢀCNArMes2; d) ClSiMe3 (1.05 equivalents), N2, Et2O, ꢀ100 to 25 8C, ꢀ[PPN]Cl, e) tetrahydrofuran
(THF), ꢀ100 to 25 8C, ꢀ[PPN]Cl, and f) maleic anhydride (MA), ꢀTHF, ꢀ100 to 25 8C. B) Molecular structures of (N2)Co(SiMe3)(CNArMes2)3 (4,
left) and the anionic component of [PPN][(h2-C,C-(IMArMes2)Co(CO)(CNArMes2)2] (5, right).
spectroscopy revealed that [PPN]+ ligation to the [Co-
(CNArMes2)3]ꢀ is both fluxional and labile in solution. At
208C in C6D6, the bound phenyl ring exhibits a Cs-symmetric
within (h2-PPN)Co(CNArMes2)3 (1) is indeed labile and that
the [Co(CNArMes2)3]ꢀ anion slowly migrates between all six
phenyl rings of the [PPN]+ cation.
1
2:2:1 pattern of up-field H NMR resonances for the ortho,
Although opposite in charge, h2-arene coordination of
[PPN]+ to [Co(CNArMes2)3]ꢀ is reminiscent of h2-C,C-coordi-
nation of tetraphenylborate ([BPh4]ꢀ) to highly Lewis acidic
early transition-metal and lanthanide monocations that are
active in a-olefin polymerization and small-molecule activa-
tion chemistry.[12,13] In these formally zwitterionic complexes,
h2-C,C-binding of the “weakly coordinating” [BPh4]ꢀ anion
serves to stabilize an otherwise highly reactive cationic d0-
metal fragment from both intra- and intermolecular decom-
position pathways. Similarly, we believe that h2-arene binding
meta and para protons, respectively. At this temperature,
broadening is observed only for the meta position resonances,
thus indicating rapid migration of the [Co(CNArMes2)3]ꢀ
fragment between equivalent Cmeta/Cpara sites of the bound
phenyl ring. Variable-temperature 1H NMR studies in
[D8]toluene were consistent with this notion and revealed
that intraring migration remains fast on the NMR time scale
down to ꢀ408C. In addition, 1H EXSY NMR experiments at
208C in C6D6 solution revealed that the h2-arene interaction
2
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of the traditionally non-coordinating [PPN]+ cation is critical
to the kinetic stabilization of the coordinatively unsaturated,
electron-rich [Co(CNArMes2)3]ꢀ anion. Accordingly, attempts
to prepare alkali metal, alkaline-earth metal, tetra-alkylam-
monium or tetra-alkylphosphonium derivatives of [Co-
(CNArMes2)3]ꢀ by chemical reduction, cation-exchange or
cation-sequestration reactions have been unsuccessful to
date, leading instead to intractable mixtures.[14] Furthermore,
given the lability of the h2-arene/Co interaction within (h2-
PPN)Co(CNArMes2)3 (1), it is important to note that neutral
arenes do not displace the [h2-PPN]+ cation from the
coordination sphere of cobalt. Thus, dissolution of (h2-
PPN)Co(CNArMes2)3 (1) in benzene, toluene, or fluoroben-
zene (C6H5F) does not result in intermolecular arene
displacement (1H NMR spectroscopy), irrespective of the
electronic properties of the arene solvents. However, treat-
ment of (h2-PPN)Co(CNArMes2)3 (1) with 2.0 equivalents of
tris-isocyanide complex Ni(CNArDipp2)3.[17] Notably, Ni(C-
NArDipp2 and [Co(CNArMes2)3]ꢀ are isoelectronic with
respect to their [M(CNAr)3] cores, which highlights the
ability of electron-rich 3d-metal tris-isocyanides to activate
strong carbon–element bonds.
)
3
Consistent with the presence of a labile [h2-PPN]+ cation,
(h2-PPN)Co(CNArMes2)3 (1) functions readily as a source of
three-coordinate [Co(CNArMes2)3]ꢀ upon reaction with elec-
trophilic substrates. For example, treatment of (h2-PPN)Co-
(CNArMes2)3 (1) with bis(diethylamino)chlorophosphine (ClP-
(NEt2)2) affords the pseudo-tetrahedral phosphide/phosphe-
nium[18] complex (Et2N)2PCo(CNArMes2
) (3) concomitant
3
with the release of [PPN]Cl (Figure 2). Complex 3 is an
isocyanide variant of Lappertꢀs tricarbonyl complex
(RR’P)Co(CO)3 (R = N(iPr)2; R’ = N(SiMe3)2),[19] and simi-
larly possesses significant Co–P p-bonding as determined by
X-ray
31P{1H} NMR spectroscopy (d =+ 277 ppm) and DFT calcu-
lations. Zwitterionic (h2-PPN)Co(CNArMes2
also reacts
diffraction
(Co–P
distance = 2.0198(10) ꢁ),
the soluble salt [PPN][BArF ] (ArF = 3,5-(CF3)2C6H3) in C6D6
4
solution does result in exchange of free and h2-bound [PPN]+
as assayed by 31P EXSY NMR spectroscopy. We contend that
this intermolecular cation-exchange reaction emphasizes the
unique and favorable combination of electrostatic stabiliza-
tion and coordinative protection afforded by the phenyl-
containing [PPN]+ cation to the coordinatively unsaturated
[Co(CNArMes2)3]ꢀ anion.
)
3
smoothly with trimethylsilyl chloride (ClSiMe3) in the pres-
ence of N2 to form the trimethylsilyl-dinitrogen complex,
(N2)Co(SiMe3)(CNArMes2
) (4, Figure 2). In this reaction,
3
electrophilic silylation of the Co center presumably generates
the coordinatively unsaturated complex [Co(SiMe3)-
(CNArMes2)3], which then binds dinitrogen in an end-on
fashion.[20] Importantly, the formation of complex 4 demon-
Despite its kinetic persistence at room temperature,
zwitterionic (h2-PPN)Co(CNArMes2
)
(1) is observed to
strates that (h2-PPN)Co(CNArMes2
)
3
(1) can function as
3
decompose slowly in C6H6 solution over 30 h to the h6-
a nucleophilic metallate, but remain active for small-molecule
binding after electrophilic functionalization of the Co center.
The ability to deliver a coordinatively unsaturated, metal-
based nucleophile also enables (h2-PPN)Co(CNArMes2)3 (1) to
induce multi-step transformations of electrophilic organic
carbonyl compounds. As shown in Figure 3, treatment of (h2-
PPN)Co(CNArMes2)3 (1) with maleic anhydride affords the
arene,
phenyl-substituted
iminoacyl
complex,
(h6-
MesArMesN C(Ph))Co(CNArMes2) (2, Figure 2). Decomposi-
=
tion of deuterium-labeled (h2-[D30]-PPN)Co(CNArMes2
)
3
([D30]-1) under identical conditions results exclusively in
(h6-MesArMesN C(C6D5))Co(CNArMes2) ([D5]-2), thereby sig-
=
nifying that the iminoacyl Ph group originates from the
[PPN]+ cation. Analysis of the reaction mixture by mass
spectrometry, 1H NMR, 31P{1H} NMR and FTIR spectroscopy
revealed that the byproducts of this decomposition are free
isomaleimide-containing
salt,
[PPN][(h2-
C,C-(IMArMes2)Co(CO)(CNArMes2)2]
(5;
IMArMes2 = 5-
CNArMes2 and the known phosphinophos-
[15]
=
phazene, Ph2P-N PPh3. The formation
=
ꢀ
of Ph2P-N PPh3 is indicative of P C bond
cleavage of [PPN]+ and formal transfer of
a [C6H5]+ cation unit to the Co-containing
fragment. This process requires a two-
unit, formal oxidation state increase at the
Co center and is therefore distinct from
the well-established and non-oxidative
phenyl-anion transfer from [BPh4]ꢀ to
electrophilic transition-metal cations.[16]
Most plausibly, the CoI-phenyl tris-isocy-
anide complex, [PhCo(CNArMes2)3], is an
intermediate in the decomposition of (h2-
PPN)Co(CNArMes2
) (1) and transforms
3
further through a-phenyl migration,
CNArMes2 ejection and h6-mesityl ring
(h6-MesArMes
N
=
ligation
to
form
C(Ph))Co(CNArMes2) (2). A similar a-
aryl migration/CNAr-ejection sequence
has been observed upon oxidative addi-
tion of aryl chlorides to the neutral Ni0
Figure 3. Proposed mechanism of formation for [PPN][(h2-C,C-(IMArMes2)Co(CO)(CNArMes2)2]
(5); a) MA, ꢀTHF, ꢀ100 to 25 8C.
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(ArMes2-imino)furanone), as determined by X-ray diffraction
(Figure 2).[21]
Weber, Angew. Chem. 1998, 110, 1597; Angew. Chem. Int. Ed.
1998, 37, 1515; h) J. E. Ellis, Inorg. Chem. 2006, 45, 3167.
[2] J. E. Ellis, Organometallics 2003, 22, 3322.
Under current unoptimized conditions (Figure 3), com-
plex 5 is isolated in low yield (about 20%), but is remarkable
in that it represents a formally isovalent O for NArMes2
exchange within the maleic anhydride ring concomitant with
the formation of a carbonyl ligand. Selective 13C labeling of
the CNArMes2 isocyanide carbon atom, followed by treatment
of (h2-PPN)Co(13CNArMes2)3 ([C1]-1) with maleic anhydride,
revealed that the cobalt-bound carbonyl ligand in the labeled
[3] Only three reports featuring stable, electronically unsaturated
17eꢀ metallates have appeared. See, a) [Ti(h6-C6H6)2]ꢀ: J. A.
Bandy, A. Berry, M. L. H. Green, R. N. Perutz, K. Prout, J. N.
Verpeaux, J. Chem. Soc. Chem. Commun. 1984, 729; b) [Mn(1,5-
COD)2]2ꢀ (COD = 1,5-cyclooctadiene): K. Jonas, C. C. Hꢂsel-
hoff, R. Goddard, C. Krꢃger, Inorg. Chim. Acta 1992, 198 – 200,
533; c) [Ti(h6-arene)2]ꢀ (arene = biphenyl, 4,4’-tBu2-biphenyl):
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1520; Angew. Chem. Int. Ed. Engl. 1992, 31, 1495.
[4] a) B. J. Fox, Q. Y. Sun, A. G. DiPasquale, A. R. Fox, A. L.
Rheingold, J. S. Figueroa, Inorg. Chem. 2008, 47, 9010; b) T. B.
Ditri, B. J. Fox, C. E. Moore, A. L. Rheingold, J. S. Figueroa,
Inorg. Chem. 2009, 48, 8362.
product
(that
is,
[PPN][(h2-C,C-(5-13C-
IMArMes2)Co(CO)(13CNArMes2)2])
is
not
isotopically
enriched.[22] This result suggests that decarbonylation of
a maleic anhydride C O unit and full transfer of a CNAr
Mes2
=
group to the resultant isomaleimide ring is operative. Indeed,
in a related reaction, treatment of (h2-PPN)Co(CNArMes2)3 (1)
with pivaloyl chloride (tBuC(O)Cl, Figure 2) results readily in
acyl-group decarbonylation en route to a 4:1 mixture of the
[5] a) L. S. Sunderlin, D. Wang, R. R. Squires, J. Am. Chem. Soc.
1993, 115, 12060-; b) M. Zhou, L. Andrews, J. Phys. Chem. A
1998, 102, 10250; c) M. Zhou, L. Andrews, C. W. Bauschlicher,
Chem. Rev. 2001, 101, 1931.
[6] For the original report and reliable syntheses of [PPN]+ salts,
see: a) R. Appel, A. Hauss, Z. Anorg. Allg. Chem. 1961, 311,
290; b) J. K. Ruff, W. J. Schlientz, Inorg. Synth. 1974, 15, 84. For
monohydride HCo(CO)(CNArMes2
) (6) and the iminoacyl
3
complex Co(CO)(h -C,N-(tBuC NArMes2)(CNArMes2
)
2
(7),
2
=
through b-H elimination and tBu a-migration, respectively.
Notably, this decarbonylation behavior mirrors that of the
reactive and unstable 16eꢀ acyl cobalt tricarbonyl intermedi-
ates (i.e. R(O)CCo(CO)3) proposed in Co-catalyzed hydro-
formylation cycles.[23] Accordingly, with respect to the for-
mation of complex 5, we currently favor the stepwise
mechanism shown in Figure 3, which involves anhydride
ꢀ
an example of irreversible C H activation and arene binding of
[PPN]+ to a low-valent Ta center, see: c) V. J. Sussman, J. E.
Ellis, Chem. Commun. 2008, 5642.
[7] G. W. Margulieux, N. Weidemann, D. C. Lacy, C. E. Moore,
A. L. Rheingold, J. S. Figueroa, J. Am. Chem. Soc. 2010, 132,
5033.
[8] For tetra-isocyanide cobaltate salts containing significant anion–
cation interactions, see: a) G. F. Warnock, N. J. Cooper, Organo-
metallics 1989, 8, 1826; b) P. A. Leach, S. J. Geib, J. A. Corella II,
G. F. Warnock, N. J. Cooper, J. Am. Chem. Soc. 1994, 116, 8566.
[9] a) W. D. Harman, Chem. Rev. 1997, 97, 1953; b) B. C. Brooks,
T. B. Gunnoe, W. D. Harman, Coord. Chem. Rev. 2000, 206 – 207,
3; c) J. M. Keane, W. D. Harman, Organometallics 2005, 24,
1786.
ꢀ
ring opening, metal–acyl decarbonylation and C C bond
reductive elimination to furnish the isomaleimide ring.
However, additional studies detailing the mechanism and
generality of the reactions between (h2-PPN)Co(CNArMes2
(1) and cyclic carbonyl compounds are underway.
)
3
As a point of contrast, it is noteworthy that the long-
known tetra-carbonyl metallate salt, [PPN][Co(CO)4],[24]
does not undergo CO-ligand displacement by the [PPN]+
cation.[2] Given the isolobal relationship between isocyanides
and CO, we believe this behavioral difference further
illustrates the unique aspects of m-terphenyl-isocyanide
ligation in both the synthesis and stabilization of low-valent,
low-coordinate transition-metal fragments. Further investi-
gations into the nature of the [PPN]+/Co interaction within
(h2-PPN)Co(CNArMes2)3 (1), as well as its ability to serve as
a reliable source of the anion [Co(CNArMes2)3]ꢀ toward other
electrophilic substrates, are continuing.
[10] S. M. Hubig, S. V. Lindeman, J. K. Kochi, Coord. Chem. Rev.
2000, 200 – 202, 831.
[11] Structurally characterized mononuclear h2-arene 3d-metal com-
plexes exhibiting dearomatization are limited to the electron-
rich [Ni0(PR3)2] fragment. For the original report, see: D. J.
Brauer, C. Krꢃger, Inorg. Chem. 1977, 16, 884.
[12] a) A. D. Horton, J. H. G. Frijns, Angew. Chem. 1991, 103, 1181;
Angew. Chem. Int. Ed. Engl. 1991, 30, 1152; b) M. Bochmann,
S. J. Lancaster, J. Organomet. Chem. 1992, 434, C1; c) M.
Bochmann, J. Chem. Soc. Dalton Trans. 1996, 255.
[13] a) W. J. Evans, C. A. Seibel, J. W. Ziller, J. Am. Chem. Soc. 1998,
120, 6745; b) W. J. Evans, B. L. Davis, T. M. Champagne, J. W.
Ziller, Proc. Natl. Acad. Sci. USA 2006, 103, 12678.
[14] See the Supporting Information for
attempted preparations.
a full description of
Received: June 28, 2012
[15] a) M. Taillefer, N. J. Rahier, A. Hameau, J. N. Volle, Chem.
Commun. 2006, 3238; b) N. J. Rahier, J. N. Volle, M. A. Lacour,
M. Taillefer, Tetrahedron 2008, 64, 6645.
[16] S. H. Strauss, Chem. Rev. 1993, 93, 927.
[17] B. M. Emerich, C. E. Moore, B. J. Fox, A. L. Rheingold, J. S.
Figueroa, Organometallics 2011, 30, 2598.
[18] L. Rosenberg, Coord. Chem. Rev. 2012, 256, 606.
[19] J.-P. Bezombes, P. B. Hitchcock, M. F. Lappert, J. E. Nycz,
Dalton Trans. 2004, 499.
Published online: && &&, &&&&
Keywords: cation coordination · cobalt ·
.
coordinative unsaturation · isocyanide ligands · metallates
[1] For reviews and historical accounts detailing the physical
properties and chemistry accessible to metallates, see: a) R. B.
King, Adv. Organomet. Chem. 1965, 2, 157; b) R. B. King, Acc.
Chem. Res. 1970, 3, 417; c) J. P. Collman, Acc. Chem. Res. 1975, 8,
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[20] For structurally related trisphosphine-silyl CoI dinitrogen com-
plexes, see: M. T. Whited, N. P. Mankad, L. Lee, P. F. Oblad, J. C.
Peters, Inorg. Chem. 2009, 48, 2507. Complex 4 gives rise to
a remarkably high energy nNN infrared stretch band in both the
solid state (2231 cmꢀ1) and solution (2224 cmꢀ1, C6D6). This
high-energy stretch band likely arises from inefficient Co!N2 p-
4
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back bonding in the presence of three strongly p-acidic
isocyanide ligands. The infrared stretch band nNN for free N2 is
found at 2330 cmꢀ1, see: T. R. Gilson, I. R. Beattie, J. D. Black,
D. A. Greenhalgh, S. N. Jenny, J. Raman Spectrosc. 1980, 9, 361.
[21] For a discussion of isomaleimides and identification of erroneous
isomalemide syntheses, see: N. R. Conley, R. J. Hung, C. G.
Willson, J. Org. Chem. 2005, 70, 4553.
[22] See the Supporting Information for details. In control experi-
ments, no reaction was observed between free CNArMes2 and
maleic anhydride up to 1008C.
[23] a) V. Galamb, G. Palyi, Coord. Chem. Rev. 1984, 59, 203; b) F.
Hebrard, P. Kalck, Chem. Rev. 2009, 109, 4272.
[24] J. K. Ruff, Inorg. Chem. 1968, 7, 1818.
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Communications
=
A break with tradition: The cation, [Ph3P
Metallates
+
+
=
N PPh3] ([PPN] ), was found to provide
a stabilizing h2-arene interaction to the
coordinatively unsaturated, tris-isocya-
nide monoanion, [Co-
A. E. Carpenter, G. W. Margulieux,
M. D. Millard, C. E. Moore,
N. Weidemann, A. L. Rheingold,
J. S. Figueroa*
&&&& — &&&&
(CNArMes2)3]ꢀ(ArMes2=2,6-(2,4,6-
Me3C6H2)C6H3); Co=purple, N=light
purple, and P=orange). The resulting
zwitterion is a source of [Co(CNArMes2)3]ꢀ
anions, performing nucleophilic addi-
tions, carbon–element bond activations,
and multistep decarbonylations.
Zwitterionic Stabiliztion of a Reactive
Cobalt Tris-Isocyanide Monoanion by
Cation Coordination
6
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!