Nitric oxide oxidatively nitrosylates Ni(I) and Cu(I) C-organonitroso adducts

Article abstract of DOI:10.1021/ja903550n

Monovalent nickel and copper β-diketiminato complexes react with ArN=O (Ar = 3,5-Me₂C₆H₃, Ph) to give C-nitroso adducts that exhibit three different modes of bonding with varying degrees of N-O bond activation. The additio

Full text of DOI:10.1021/ja903550n

Published on Web 11/19/2009
Nitric Oxide Oxidatively Nitrosylates Ni(I) and Cu(I)
C-Organonitroso Adducts
Stefan Wiese, Pooja Kapoor, Kamille D. Williams, and Timothy H. Warren*
Department of Chemistry, Georgetown UniVersity, Box 571227, Washington, D.C. 20057-1227
Received May 1, 2009; Revised Manuscript Received September 23, 2009; E-mail: thw@georgetown.edu
Abstract: Monovalent nickel and copper ꢀ-diketiminato complexes react with ArNdO (Ar ) 3,5-Me2C6H3,
Ph) to give C-nitroso adducts that exhibit three different modes of bonding with varying degrees of N-O
bond activation. The addition of ArNO to 2 equiv of [Me2NN]Ni(2,4-lutidine) {[Me2NN]- ) 2,4-bis(2,6-
dimethylphenylimido)pentyl} gives {[Me2NN]Ni}2(µ-η2:η2-ONAr) (1a and 1b), which exhibit symmetrical
bonding of the ArNdO moiety between two [Me2NN]Ni fragments, with a N-O bond distance of 1.440(4)
Å in 1a that is significantly longer than those in free C-organonitroso compounds (1.13-1.29 Å).
[Me2NN]Cu(NCMe) reacts with 0.5 equiv of ArNO in ether to give the dinuclear adducts {[Me2NN]Cu}2(µ-
η2:η1-ONAr) (2a and 2b), which exhibit η2 and η1 bonding of the ArNdO moiety with separate [Me2NN]Cu
fragments possessing N-O distances of 1.375(6) Å (2a) and 1.368(2) Å (2b). In arene solvents, one
ꢀ-diketiminatocopper(I) fragment dissociates from 2 to give [Me2NN]Cu(η2-ONAr) (3a and 3b), which may
be isolated by the addition of 1 equiv of ArNO to [Me2NN]Cu(NCMe). The X-ray structures of 3a and 3b
are similar to those of related Cu(I) alkene adducts, with N-O distances in the narrow range
1.333(4)-1.338(5) Å. IR spectra of the nitrosobenzene adducts 1b, 2b, and 3b exhibit νNO stretching
frequencies at 915, 1040, and 1113 cm-1, respectively, following the decreasing degree of NdO activation
observed in the X-ray structures of species 1, 2, and 3. Both 1a and 3a react with anaerobic NO(g) to give
the corresponding N-aryl-N-nitrosohydroxylaminato complexes [Me2NN]M(κ2-O2N2Ar) [M ) Ni (4), Cu (5)].
In the reaction of dinuclear 1a with NO, one [Me2NN]Ni fragment is trapped as the nickel nitrosyl
[Me2NN]Ni(NO). Reaction of the monovalent complex [Me2NN]Cu(η2-ONAr) with NO(g) to give divalent
[Me2NN]Cu(κ2-O2N2Ar) represents an example of oxidative nitrosylation.
Introduction
In such reductive nitrosylation reactions, nitric oxide is formally
oxidized to NO+ by the metal ion, which is reduced by one
electron.
There are relatively few well-defined examples in which nitric
Nitric oxide (NO) has a rich biochemistry with metalloen-
zymes, though targets for NO incorporation are not limited to
the metal centers themselves.1 For instance, copper ions are
required to induce the S-nitrosylation of the two Cysꢀ93 residues
of oxyhemoglobin with NO;2 oxyhemoglobin exhibits a higher
affinity for NO than its deoxy form.3 Redox-active metal ions
may assist in the nitrosylation of organic substrates such as
alcohols, amines, and thiols (eq 1):4
oxide functionalizes a ligand within the coordination sphere of
a metal. For instance, Ford demonstrated an intramolecular
reductive nitrosylation at Cu2+ that results in N-NO bond
formation at a bound tetraamine cyclam.5 Bergman mechanisti-
cally studied C-NO bond formation in the ligand-induced
migratory insertion of Cp*Co(NO)(R) into Cp*Co(N(O)R)PR′3
(R ) Me, Et).6 This behavior may be contrasted with double
NO insertion into metal alkyls M-R to give N-alkyl-N-
nitrosohydroxylaminato species M(κ2-O2N2R).7 On the other
hand, addition of nitrosonium (NO+) to C-organonitroso adducts
[Pt(ArNO)(PPh3)2] (Ar ) Ph, o-MeC6H4) gave the diazenium-
diolate cations {[Pt(κ2-O2N2Ar)(PPh3)2}+.8
NO + Mn+ + E-H E ) RO, R2N, RS8 E-NO + M(n-1)+ + H+
(1)
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9
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J. AM. CHEM. SOC. 2009, 131, 18105–18111 18105

A R T I C L E S
Wiese et al.
Figure 1. [M](ONAr) bonding modes in representative mononuclear
C-nitroso complexes.
Figure 2. Structures of monovalent ꢀ-diketiminatonickel and -copper
the reduction of the corresponding nitro compounds RNO2.9,10
Motivated by the appreciably greater affinity of hemoglobin for
nitrosobenzene (PhNO) over dioxygen (O2),11 a number of heme
model complexes have been prepared.10 Typically, κ1-N bonding
of the nitrosoarene is observed in ferrous complexes,10 though
κ1-O bonding was observed in the ferric p-amino-substituted
nitrosoarene adduct [(TPP)Fe(ONAr)2]+ (TPP ) meso-tetraphe-
nylporphyrinato; Figure 1).12 In the presence of both NADH
and Cu(II) ions, nitrosobenzene elicits oxidative DNA damage
through the intermediacy of the phenylhydronitroxide radical
PhNHO·.13 This nitroxide has also been identified as a
metabolic product of PhNO14 (as well as PhNH2, PhNHOH,
and PhNO2)15 that also participates in the oxidation of thiol
residues within red blood cells.15
complexes employed in the synthesis of nitrosoarene adducts.
Scheme 1. Synthesis of Dinickel(I) Nitrosoarene Adducts 1
sents an extreme case of RNdO bond activation.19 To system-
atically explore the effect of the metal ion on ArNdO activation,
we report herein the synthesis and structure of ꢀ-diketiminato
Ni(I) and Cu(I) nitrosoarene adducts as well as their reactivity
with NO to give divalent NONOates20 [Me2NN]M(η2-O2N2Ar).
Additionally, organonitroso compounds ArNO serve as
precursors for copper-catalyzed C-N bond-forming reactions16,17
as well as nickel-catalyzed nitrene-group transfer reactions.18
Srivastava showed that allylic C-H bonds undergo amination
in moderate yield by ArNO or ArNHOH under catalysis by
CuI.16 As a part of those mechanistic studies, the trigonal
tris(nitrosoarene)copper(I) adduct [Cu(κ1-N(O)Ar′)3]+ (Ar′ )
p-NEt2C6H4) was structurally characterized.16 Catalyzed by
Ni(CNtBu)4, nitrene-group transfer reactions from PhNO take
Results and Discussion
Nickel Complexes. Addition of the nitrosoarene ArNdO (Ar
) 3,5-Me2C6H3) to 2 equiv of [Me2NN]Ni(2,4-lutidine)21
(Figure 2) in ether allowed for the isolation of green crystals of
{[Me2NN]Ni}2(µ-η2:η2-ONAr) (1a) in 42% yield (Scheme 1).
Single-crystal X-ray analysis revealed a symmetric, butterfly-
shaped [Ni]2(ONAr) core with a pseudo mirror plane containing
the ArNO ligand linking the two Ni fragments (Figure 3). The
Ni-Ni separation is 3.171(2) Å, and the Ni-O bond distances
are 1.881(3) and 1.932(3) Å with Ni-N bond distances of
1.921(3) and 1.879(3) Å. The N-O distance of 1.440(4) Å is
similar to that in [(Cp*Rh)2(µ-Cl)(µ-η2:η2-ONPh)](BF4) [dN-O
) 1.422(4) Å],22 indicating a significant reduction in N-O bond
order relative to that in free C-nitroso compounds, which possess
N-O distances in the range 1.13-1.29 Å.10
t
place with CNtBu, leading to BuNCO and PhNdCdNtBu
among other products.18 Ni(η2-ONPh)(CNtBu)2, whose bonding
mode (Figure 1) was assigned by IR spectroscopy (νNO ) 1032
cm-1) was suggested as an active intermediate on the basis of
its stoichiometric decomposition to PhNHC(O)NHtBu in the
presence of trace water.18
A wide variety of [M](RNO), [M]2(RNO), and [M]4(RNO)
bonding modes in transition-metal C-nitroso complexes that
involve varying degrees of RNdO bond activation are known.10
The four-electron reductive cleavage of ArNdO by the electron-
rich, Co(I) ꢀ-diketiminate complex [Me2NN]Co(η6-toluene) to
give {[Me2NN]Co}2(µ-O)(µ-NAr) (Ar ) 3,5-Me2C6H3) repre-
Because of the commercial availability of Ph15NH2, which
allows for the ready preparation of Ph15NO, characteristic νNO
IR stretching frequencies were measured for the analogous
nitrosobenzene adducts. The addition of PhNO or Ph15NO to 2
equiv of [Me2NN]Ni(2-picoline) {Figure 2; prepared analo-
gously to [Me2NN]Ni(2,4-lutidine) by substituting NiCl2(2-pic)2
for NiCl2(2,4-lut)2 in the synthesis procedure} allowed for the
isolation of {[Me2NN]Ni}2(µ-η2:η2-ONPh) (1b and 1b-15N)
(9) Zuman, P.; Shah, B. Chem. ReV. 1994, 94, 1621–1641.
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1
(Scheme 1), which possess H NMR spectra closely related to
that of 1a. Coordination to two [Me2NN]NiI fragments markedly
reduced the PhNO νNO stretching frequency to 915 cm-1 (901
cm-1 for 1b-15N) (Table 1) relative to that of free, monomeric
PhNO (1506 cm-1).10,23
(11) Eyer, P.; Ascherl, M. Biol. Chem. Hoppe-Seyler 1987, 368, 285–294.
(12) Wang, L.-S.; Chen, L.; Khan, M. A.; Richter-Addo, G. B. Chem.
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H. Arch. Exp. Pathol. Pharmacol. 1950, 210, 393–398.
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311–318.
Low-temperature 1H NMR spectra of 1a at -70 °C in toluene-
d8 revealed four separate ꢀ-diketiminate Ar-Me resonances,
(19) Dai, X.; Kapoor, P.; Warren, T. H. J. Am. Chem. Soc. 2004, 126,
4798–4799.
(16) (a) Srivastava, R. S.; Khan, M. A.; Nicholas, K. M. J. Am. Chem.
Soc. 2005, 127, 7278–7279. (b) Srivastava, R. S.; Tarver, N. R.;
Nicholas, K. M. J. Am. Chem. Soc. 2007, 129, 15250–15258.
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15, 656–660.
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Ni and Cu C-Organonitroso Adducts
A R T I C L E S
Figure 3. ORTEP diagram of the solid-state structure of {[Me2NN]Ni}2(µ-
η2:η2-ONAr) (1a) (with all H atoms omitted). Selected bond distances (Å)
and angles (deg): N5-O, 1.440(4); Ni1-N5, 1.879(3); Ni2-N5, 1.921(3);
Ni1-O, 1.932(3); Ni2-O, 1.881(3); Ni1-N1, 1.859(3); Ni1-N2, 1.868(3);
Ni2-N3,1.869(3);Ni2-N4,1.868(3);N1-Ni1-N2,94.88(14);N3-Ni2-N4,
96.36(15); N5-Ni1-O, 44.37(12); N5-N2-O, 44.48(12); Ni1-N5-Ni2,
113.09(16); Ni1-O-Ni2, 112.52(14); O-N5-C43, 112.8(3).
Figure 4. Spin density plot for 1a (S ) 1). Blue indicates excess spin-R;
red indicates excess spin-ꢀ (isospin value ) 0.001).
Scheme 2. Synthesis of Cu(I) Nitrosoarene Adducts 2 and 3
Table 1. ArNdO Distances and νNO Stretching Frequencies in
Organonitroso Adducts 1-3
(cm-1
)
14 15
NO/ν
compound
dN-O (Å)
ν
NO
1a
1b
2a
2b
3a
3b
1.440(4)
n/a
1.375(6)
1.368(2)
1.333(4)
1.336(6)a
915/901
1040/1029
1113/1093
Copper Complexes. Reaction of the Cu(I) ꢀ-diketiminate
complex [Me2NN]Cu(NCMe)25 (Figure 2) with 0.5 equiv of
ArNO resulted in the formation of a very dark solution from
which crystals of {[Me2NN]Cu}2(µ-η2:η1-ONAr) (2a) could be
isolated in modest yield from ether (Scheme 2). Unlike the one
in 1a, the nitrosoarene ligand in 2a is η2-bound to one Cu center
with Cu1-O and Cu1-N5 distances of 1.843(4) and 2.040(5)
Å and bound only through the N atom to the other Cu center
with a Cu2-N5 distance of 1.879(5) Å (Figure 5). The N-O
bond is less activated than in 1a, with a N-O distance of
1.375(6) Å. The related complex {[Me2NN]Cu}2(µ-η2:η1-ONPh)
(2b) possesses similar metrical parameters (N5-O, 1.368(2) Å;
Cu1-O, 1.840(2) Å; Cu1-N5, 2.013(2) Å; Cu2-N5, 1.900(2)
Å; Figure S19 in the SI) and shows a νNO stretch at 1040 cm-1
(1029 cm-1 for 2b-15N) (Table 1).
This asymmetry suggested that one [Me2NN]Cu fragment of
2a may be labile in solution. Dissolution of crystals of 2a in
benzene-d6 resulted in the quantitative formation of mononuclear
[Me2NN]Cu(η2-ONAr) (3a) with formation of the solvento
species [Me2NN]Cu(benzene)26 (Scheme 2).
Reaction of [Me2NN]Cu(NCMe) with 1 equiv of ArNO
allowed for the isolation of mononuclear 3a (Scheme 2)
possessing nearly symmetric η2-NO bonding with Cu-N3 and
a Average of two independent distances.
consistent with the approximate Cs molecular symmetry ob-
served in the solid state. Warming resulted in coalescence of
two pairs of these Ar-Me resonances, suggesting rotation of one
[Ni] fragment about the remaining [Ni](ONAr) unit in 1a with
an activation barrier (∆Gq) of 10.2(3) kcal/mol at -50(3) °C.
1
While the diamagnetic H NMR chemical shifts of 1a were
otherwise unremarkable, the backbone-CH and backbone-Me
signals were mildly temperature-dependent in toluene-d8. Over
the temperature range -70 to +25 °C, these two signals shifted
upfield from 4.66 to 3.48 ppm and 1.01 to 0.49 ppm,
respectively. These observations suggest contact shifts from a
minute contribution of a higher spin state in solution.24 DFT
studies on 1a (gas phase) identified an S ) 1 excited state ∼12
kcal/mol higher in electronic energy bearing metrical parameters
similar to those of the S ) 0 ground state [Figure S7 in the
Supporting Information (SI)]. In the S ) 1 state, there is
significant unpaired electron density (spin-R) on the central C
atom of the ꢀ-diketiminato ligand (Figure 4). Variable-temper-
ature solid-state magnetic susceptibility measurements on 1a
gave a steadily increasing magnetic moment that reached 2.6µB
at 300 K, which is close to the spin-only value of 2.8µB expected
for an S ) 1 system (Figure S10 in the SI).
(25) Spencer, D. J. E.; Reynolds, A. M.; Holland, P. L.; Jazdzewski, B. A.;
Duboc-Toia, C.; Le Pape, L.; Yokota, S.; Tachi, Y.; Itoh, S.; Tolman,
W. B. Inorg. Chem. 2002, 41, 6307–6321.
(26) (a) Dai, X.; Warren, T. H. J. Am. Chem. Soc. 2004, 126, 10085–
10094. (b) Amisial, L. D.; Dai, X.; Kinney, R. A.; Krishnaswamy,
A.; Warren, T. H. Inorg. Chem. 2004, 43, 6537–6539.
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Chem. 2008, 47, 10187–10189.
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A R T I C L E S
Wiese et al.
Scheme 3. Reactivity of Nitrosoarene Adducts with Nitric Oxide
adduct exhibits the highest νNO at 1113 cm-1 (1093 cm-1 for
3b-15N) among 1b, 2b, and 3b (Table 1).
Despite the larger size of N compared with O, the N-O
distance in 3a is significantly shorter than the O-O distances
of 1.392(12) and 1.392(3) Å found in Tolman’s side-on copper
dioxygen complexes [Cu](η2-O2) supported by ꢀ-diketiminato
and anilidoimine ligands.27 Both of these considerations suggest
modest backbonding from the [Me2NN]Cu fragment to the
nitrosoarene. Indeed, the η2-ArNdO binding mode in 3 is
reminiscent of η2-coordination of an alkene to Cu(I).28 Variable-
temperature NMR spectra of 3b revealed a modest activation
barrier for rotation about the Cu-ArNO moiety {∆Gq ) 11.4(2)
kcal/mol at -44(2) °C, which is similar to the value of 10.7(3)
kcal/mol observed for [Me2NN]Cu(η2-styrene)29}.
Arylnitroso coordination to the [Me2NN]CuI fragment, how-
ever, has a significant effect on the oxidation potential of the
copper(I) center. Cyclic voltammetry of 3a in MeCN revealed
an essentially irreversible oxidation at ca. +1.1 V versus NHE
referenced against an internal ferrocene standard (+0.48 V vs
ferrocene/ferrocenium) (Figure S11 in the SI). This may be
compared with the value of +0.45 V versus NHE reported for
the simple [Me2NN]Cu(NCMe) adduct.25
Figure 5. ORTEP diagram of {[Me2NN]Cu}2(µ-η2:η1-ONAr) (2a)·1/2Et2O
(with all H atoms and ether of solvation omitted; the major occupancy (55%)
of the disordered ꢀ-diketiminato N-aryl ring at N2 is shown). Selected bond
distances (Å) and angles (deg): N5-O, 1.375(6); Cu1-N5, 2.040(5);
Cu2-N5, 1.879(5); Cu1-O, 1.843(4); Cu2 · · ·O, 2.786; Cu1-N1, 1.891(5);
Cu1-N2, 1.891(5); Cu2-N3, 1.984(5); Cu2-N4, 1.907(5); N1-Cu1-N2,
99.9(2); N3-Cu2-N4, 100.16(19); N5-Cu1-O, 41.10(18); Cu1-N5-Cu2,
140.2(3); O-N5-C43, 110.3(5).
Reactions with Nitric Oxide. The Ni(I) and Cu(I) nitrosoarene
adducts 1a and 3a react with NO(g) under anaerobic conditions
(Scheme 3). Addition of 2.1 equiv of NO to a benzene-d6
solution of 1a resulted in the quantitative formation of the
diamagnetic [Me2NN]Ni(κ2-O2N2Ar)30 (4) and [Me2NN]Ni-
(NO),30 which were identified by H NMR spectroscopy. It
1
should be noted that 4 forms quickly upon addition of ArNO
to the nickel nitrosyl [Me2NN]Ni(NO).30 Perhaps more surpris-
ing was the uptake of NO by [Me2NN]Cu(η2-ONAr) (3a) to
give red crystals of [Me2NN]Cu(κ2-O2N2Ar) (5) in 80% yield
when 3a was exposed to a slight excess of NO (2 equiv). The
X-ray structure of 5 (Figure 7) shows square-planar coordination
at Cu, as found in the structures of Cu(κ2-O2N2R)2 (R ) Ph,31
Cy32). The EPR spectrum of 5 in toluene at room temperature
is consistent with a Cu(II) ion in a square-planar environment
with two N donors (giso ) 2.10, ACu ) 79 G, AN ) 13 G).
In contrast to typical reductive nitrosylation reactions, in
which the metal center is reduced with concomitant oxidation
of the organic fragment,4 the reaction between [Me2NN]Cu(η2-
ONAr) and NO may formally proceed through oxidation of the
copper complex to {[Me2NN]Cu(η2-ONAr)}+ and reduction of
NOtoNO-.However,thehighoxidationpotentialfor[Me2NN]Cu(η2-
ONAr) (E1/2 ≈ +1.1 V vs NHE) as well as the high reduction
Figure 6. ORTEP diagram of the solid-state structure of [Me2NN]Cu(η2-
ONAr) (3a) (with all H atoms omitted). Selected bond distances (Å) and
angles (deg): N3-O, 1.333(4); Cu-N3, 1.936(4); Cu-O, 1.851(3); Cu-N1,
1.886(3); Cu-N2, 1.884(3); N3-C22, 1.441(6); N3-Cu-O, 41.14(14);
N1-Cu-N2, 99.96(15); N1-Cu-O, 106.69(14); N2-Cu-N3, 112.92(15).
Cu-O bond distances of 1.936(4) and 1.851(3) Å, respectively
(Figure 6). [Me2NN]Cu(η2-ONAr) (3a) possesses the least-
activated ArNdO bond, with a N-O bond distance of 1.333(4)
Å, which is shorter than the range of 1.386(3)-1.432(6) Å
established for other mononuclear η2-ONR compounds.10 The
X-ray structure of the corresponding nitrosobenzene adduct
[Me2NN]Cu(η2-ONPh) (3b) possesses two independent mol-
ecules of 3b with similar metrical parameters (N3-O, 1.338(5)
and 1.334(5) Å; Cu-N3, 1.932(4) and 1.935(3) Å; Cu-O,
1.853(3) and 1.855(3) Å; Figures S22 and S23 in the SI).
Consistent with the lowest degree of N-O bond activation
inferred by N-O bond lengths, this mononuclear nitrosobenzene
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W. W.; Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124,
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Brennessel, W. W.; Young, V. G., Jr.; Sarangi, R.; Rybak-Akimova,
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Reynolds, A. M.; Gherman, B. F.; Cramer, C. J.; Tolman, W. B. Inorg.
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(28) Rasika Dias, H. V.; Wu, J. Eur. J. Inorg. Chem. 2008, 509–522.
(29) Dai, X.; Warren, T. H. Chem. Commun. 2001, 1998–1999.
(30) Puiu, S. C.; Warren, T. H. Organometallics 2003, 22, 3974–3976.
(31) Shkol’nikov, L. M.; Shugam, E. A. Zh. Strukt. Khim. 1963, 4, 380–
386.
(32) Klebe, G.; Ha¨dicke, E.; Boehm, K. H.; Reuther, W.; Hickmann, E. Z.
Kristallogr. 1996, 211, 798–803.
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18108 J. AM. CHEM. SOC. VOL. 131, NO. 50, 2009

Ni and Cu C-Organonitroso Adducts
A R T I C L E S
form diazeniumdiolates [M](κ2-O2N2Ar), which represents oxi-
datiVe nitrosylation of the formally monovalent [Me2NN]Cu(η2-
ONAr). This serves as a well-defined example that illustrates
the possibility of oxidizing a metal center via functionalization
of a bound ligand with NO.
The η2-ONAr binding modes and reactivity observed in the
organonitroso complexes {[Me2NN]Ni}2(µ-η2:η2-ONAr) (1),
{[Me2NN]Cu}2(µ-η2:η1-ONAr) (2), and [Me2NN]Cu(η2-ONAr)
(3) may foreshadow possibilities in related “parent” HNO37
adducts. For instance, aromatic nitroso compounds ArNO have
been considered as N-substituted nitroxyls,38 and PhNO rapidly
reacts with HNO (but not NO) to give Cupferron
[HON(Ph)NdO],39 the conjugate acid of the diazeniumdiolate
anion [O2N2Ph]-. Nonetheless, one must bear in mind HNO’s
distinct acid/base behavior (pKa ) 11.4),33,40 facile oxidation
(HNO/NO,H+ ) +0.5 to +0.6 V at pH 7),33,40 H atom transfer
(H-NO bond dissociation energy ≈ 50 kcal/mol),41 and rapid,
irreversible dimerization (k ) 8 × 106 M-1 s-1 in aqueous
solution)40 chemistry. To date, synthetic examples of [M](HNO)
complexes exhibit κ1-N bonding and have been limited to low-
spin, d6 octahedral complexes.42
Figure 7. ORTEP diagram of the solid-state structure of [Me2NN]Cu(κ2-
O2N2Ar) (5) (with all H atoms omitted). Selected bond distances (Å) and
angles (deg): Cu-O1, 1.957(2); Cu-O2, 1.949(2); Cu-N1, 1.931(3);
Cu-N2, 1.929(3); O1-N3, 1.323(3); O2-N4, 1.306(3); N3-N4, 1.282(4);
N1-Cu-N2, 95.59(12); O1-Cu-O2, 79.23(10); N1-Cu-O1, 93.19(11);
N2-Cu-O2, 92.33(10).
Experimental Section
potential for NO to NO- [estimated at -0.8 V vs NHE for 1 M
NO(aq)33] strongly suggest inner-sphere attack of NO on
[Me2NN]Cu(η2-ONAr).
General Considerations. All of the experiments were carried
out under a dry nitrogen atmosphere using an MBraun glovebox
and/or standard Schlenk techniques. Activation of 4 Å molecular
sieves was carried out in vacuo at 180 °C for 24 h. Diethyl ether
and tetrahydrofuran (THF) were first sparged with nitrogen and
then dried by passage through activated alumina columns.43 Pentane
was first washed with concentrated HNO3/H2SO4 to remove olefins,
stored over CaCl2, and then distilled from sodium/benzophenone
before use. All of the deuterated solvents were sparged with
nitrogen, dried over activated 4 Å molecular sieves, and stored under
nitrogen. 1H and 13C NMR spectra were recorded on a Varian 300
or 400 MHz spectrometer (300 or 400 and 75.4 or 100.4 MHz,
respectively). All of the NMR spectra were recorded at room
temperature (RT) unless otherwise noted and were indirectly
referenced to tetramethylsilane using residual solvent signals as
internal standards. X-band EPR spectra were recorded in toluene
at RT in a quartz tube using a Bruker EMX-A spectrometer control
system equipped with a Bruker B-E2549 10 in. magnet and a built-
in microwave frequency meter. Elemental analyses were performed
on a PerkinElmer PE2400 microanalyzer in our laboratories.
Cyclic voltammetry on 3a (Figure S11 in the SI) was performed
in 0.1 M [NBu4]BF4/MeCN using a Schlenk flask as the standard
cell. The auxiliary and working electrodes were 500 and 250 µm
platinum wires, respectively. A nonaqueous reference electrode was
Conclusions
The two-coordinate, monovalent fragments [Me2NN]M (M
) Ni, Cu) favor π interactions with the ArNdO bond of
C-nitroso compounds, thereby providing what are to the best
of our knowledge the first X-ray structures of Ni and Cu
C-nitroso adducts in which the NO functionality is not
κ1-N-bound.10,16 We note that a recent theoretical study sug-
gested that η2-ONPh coordination in copper(I) ꢀ-diketiminates
may be slightly favored over κ1-N bonding34 and that IR data
suggest side-on nitrosobenzene coordination in the zero-valent
complex Ni(ONPh)(CNtBu)2 (Figure 1).18
The dinuclear complexes {[Me2NN]Ni}2(µ-η2:η2-ONAr) (1)
are conceptually related to the dinuclear toluene adduct {[Nac-
nac]Ni}2(µ-η3:η3-toluene) of a related [ꢀ-diketiminato]NiI frag-
ment that possesses o-iPr N-aryl substituents.35 The mono-
valent, mononuclear [Me2NN]Ni(η2-ONAr) fragment likely
possesses a significant amount of unpaired electron density on
the η2-ON moiety, as found on the η2-O2 ligand in the square-
planar superoxide complex [Nacnac]Ni(η2-O2).36 Thus, the
mononuclear species [Me2NN]Ni(η2-ONAr) would be a ready
target for the less sterically hindered [Me2NN]Ni metalloradical
to give 1. Perhaps more unusual is the unsymmetrical
metal-organonitroso interaction in {[Me2NN]Cu}2(µ-η2:η1-
ONAr) (2), in which the κ1-N interaction is readily displaced
by benzene to give [Me2NN]Cu(η2-ONAr) (3) and
[Me2NN]Cu(benzene).
(37) (a) Fukuto, J. M.; Bartberger, M. D.; Dutton, A. S.; Paolocci, N.; Wink,
D. A.; Houk, K. N. Chem. Res. Toxicol. 2005, 18, 790–801. (b)
Miranda, K. M.; Ridnour, L. A.; Espey, M. G.; Citrin, D.; Thomas,
D. D.; Mancardi, D.; Donzelli, S.; Wink, D. A.; Katori, T.; Tocchetti,
C. G.; Ferlito, M.; Paolocci, N.; Fukuto, J. M. Prog. Inorg. Chem.
2005, 54, 349–384. (c) Paolocci, N.; Jackson, M. I.; Lopez, B. E.;
Miranda, K.; Tocchetti, C. G.; Wink, D. A.; Hobbs, A. J.; Fukuto,
J. M. Pharmacol. Ther. 2007, 113, 442–458. (d) Irvine, H. C.; Ritchie,
R. H.; Favaloro, J. L.; Andrews, K. L.; Widdop, R. E.; Kemp-Harper,
B. K. Trends Pharmacol. Sci. 2008, 29, 601–608.
The C-nitroso adducts reported herein are capable of incor-
porating 1 equiv of NO into the coordinated ONAr ligand to
(38) Nagasawa, H. T.; Yost, Y.; Eberling, J. A.; Shirota, F. N.; DeMaster,
E. G. Biochem. Pharmacol. 1993, 45, 2129–2134.
(39) Shoeman, D. W.; Nagasawa, H. T. Nitric Oxide 1998, 2, 66–72.
(40) Shafirovich, V.; Lymar, S. V. Proc. Natl. Acad. Sci. U.S.A. 2002, 99,
7340–7345.
(33) Bartberger, M. D.; Liu, W.; Ford, E.; Miranda, K. M.; Switzer, C.;
Fukuto, J. M.; Farmer, P. J.; Wink, D. A.; Houk, K. N. Proc. Natl.
Acad. Sci. U.S.A. 2002, 99, 10958–10963.
(41) (a) Bartberger, M. D.; Fukuto, J. M.; Houk, K. N. Proc. Natl. Acad.
Sci. U.S.A. 2001, 98, 2194–2198. (b) Gomes, J. R. B.; Ribeiro da Silva,
M. D. M. C.; Ribeiro da Silva, M. A. V. J. Phys. Chem. A 2004, 108,
2119–2130.
(34) Kazi, A. B.; Cundari, T. R.; Baba, E.; DeYonker, N. J.; Dinescu, A.;
Spaine, L. Organometallics 2007, 26, 910–914.
(35) Bai, G.; Wei, P.; Stephan, D. W. Organometallics 2005, 24, 5901–
5908.
(42) Farmer, P. J.; Sulc, F. J. Inorg. Biochem. 2005, 99, 166–184.
(43) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.
(36) Yao, S.; Bill, E.; Milsmann, C.; Wieghardt, K.; Driess, M. Angew.
Chem., Int. Ed. 2008, 47, 7110–7113.
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A R T I C L E S
Wiese et al.
used with 0.01 M AgNO3 in 0.1 M [NBu4]BF4/MeCN as the
electrolyte solution. Potential was applied using an IBM model 225
Radiometer Voltalab 10 potentiostat; current was applied and
monitored throughout cycling between -400 and +1000 mV
relative to the Ag reference electrode.
{[Me2NN]Ni2}(µ-η2:η2-ONPh) (1b). A solution of nitrosoben-
zene (0.024 g, 0.22 mmol) in toluene (3 mL) was slowly added
with stirring to a solution of [Me2NN]Ni(2-picoline) (0.203 g, 0.44
mmol) in ether (10 mL). The solution was stirred for 1 h,
concentrated to dryness, taken up in ether (10 mL), and filtered
through Celite. The filtrate was concentrated and cooled to -35
°C. The green crystals were isolated to afford 0.109 g (30% yield)
of product. 1H NMR (C6D6, RT): δ 7.083 (d, 5H, Ar-H), 6.870 (m,
7H, Ar-H), 6.452 (t, 5H, Ar-H), 5.210 (br, 1H, p-PhNO-H), 3.495
(2H, backbone-CH), 3.010 (s, 12H, o-Ar-Me), 2.264 (s, 12H, o-Ar-
Me), 0.487 (s, 12H, backbone-Me). 13C{1H} NMR (C6D6): δ
164.39, 152.37, 151.06, 150.38, 147.26, 137.68, 137.40, 136.23,
126.85, 126.57, 125.02, 122.73, 106.30, 65.89, 27.37, 26.69, 19.18,
18.22, 17.32, 15.58. IR: νNO ) 915 cm-1 (901 cm-1 for 1b-15N).
UV-vis (Et2O): λmax ) 583 nm (ε ) 2000 M-1 cm-1). The RT 1H
NMR spectra of 1a and 1b were nearly superimposible except for
the ONAr and ONPh signals (Figures S1 and S2).
The nitrosoarene ArNdO (Ar ) 3,5-Me2C6H3),19 [Me2NN]Ni(2,4-
lutidine),21 [Me2NN]Cu(MeCN),25 and Tl[Me2NN]29 were synthe-
sized according to literature procedures. 15N-labeled aniline
(Ph15NH2) was purchased from Cambridge Isotope Laboratories.
Preparation of Compounds. [15N]Nitrosobenzene (Ph15NO).
Ph15NO was prepared by a procedure analogous to that used for
3,5-dimethylnitrosobenzene:19 To a solution of 15N-labeled aniline
(1.00 g, 10.8 mmol) in a 1:1 pentane/dichloromethane mixture (100
mL) was added Na2WO4 ·2H2O (0.171 g, 0.52 mmol), tetrabuty-
lammonium chloride (0.043 g, 0.15 mmol), and 30% aqueous
hydrogen peroxide (5 mL). The mixture was vigorously stirred for
18 h at RT. The organic layer was separated, washed with 0.01 M
HCl (50 mL) followed by water (50 mL), and then dried over
anhydrous MgSO4. The organic layer was concentrated to dryness,
and the resulting oil was crystallized using 1:1 pentane/dichlo-
romethane to afford 0.70 g (60% yield) of the product as brown
{[Me2NN]Cu}2(µ-η2:η1-ONAr) (2a). A solution of ArNO (0.046
g, 0.34 mmol) in ether (5 mL) was slowly added with stirring to a
solution of [Me2NN]Cu(MeCN) (0.290 g, 0.68 mmol) in ether (15
mL). The solution turned dark immediately. The solution was stirred
for 30 min and then filtered through Celite, after which the filtrate
was concentrated and cooled to -35 °C. Black crystals were
separated from the solution, washed with cold pentane, and dried
in vacuo to afford 0.094 g (30% yield) of the product. This dinuclear
species dissociates in benzene-d6 to give [Me2NN]Cu(η2-ONAr)
(3) and [Me2NN]Cu(benzene).26 1H NMR (C6D6): δ 7.11-6.96 (m,
12H, Ar-H), 6.751 (s, 1H, p-ArNO-H (3)), 6.596 (s, 2H, o-ArNO-H
(3)), 4.771 (s, 2H, backbone-CH (both 3 and [Cu](benzene)), 2.174
(br, 12H, o-Ar-Me (3)), 2.046 (s, 6H, m-ArNO-Me (3)), 2.012 (s,
6H, o-Ar-Me ([Cu](benzene)), 1.629 (s, 6H, backbone-Me ([Cu](ben-
zene)), 1.445 (s, 6H, backbone-Me (3)). 13C{1H} NMR (C6D6): δ
163.24, 162.43, 160.88, 150.56, 147.90, 138.61, 132.08, 130.61,
129.77, 128.44, 125.00, 123.13, 118.28, 95.81, 93.07, 23.13, 22.87,
21.01, 18.83, 18.50. UV-vis (Et2O): λmax ) 582 nm (ε ) 1400
M-1 cm-1), 791 nm (ε ) 2000 M-1 cm-1). Anal. Calcd for
C50H59O1N5Cu2: C, 68.78; H, 6.81; N, 8.02. Found: C, 68.50; H,
6.82; N, 7.90.
The UV-vis molar absorptivities are approximate: the higher-
energy band at λ ) 582 nm corresponds to [Me2NN]Cu(η2-ONAr)
(3b) from dissociation of a [Me2NN]Cu fragment in dilute solution.
{[Me2NN]Cu2}(µ-η2:η1-ONPh) (2b). A solution of PhNO (0.036
g, 0.34 mmol) in ether (5 mL) was slowly added with stirring to a
solution of [Me2NN]Cu(MeCN) (0.279 g, 0.68 mmol) in ether (10
mL). The solution turned dark immediately. The solution was stirred
for 1 h and then filtered through Celite, after which the filtrate was
concentrated to dryness. Crystallization from pentane at -35 °C
afforded 0.199 g (67% yield) of dark crystals of the product. This
dinuclear species dissociates in benzene-d6 to give [Me2NN]Cu(η2-
ONPh) and [Me2NN]Cu(benzene).7 1H NMR (C6D6, RT): δ 7.026
(m, 15H, Ar-H), 6.840 (d, 2H, Ar-H), 6.755 (t, 3H, Ar-H), 4.772
(s, 1H, backbone-CH for [Me2NN]Cu(benzene)), 4.762 (s, 1H,
backbone-CH for [Me2NN]Cu(η2-ONPh)), 2.127 (br, 12H, o-Ar-
Me for [Me2NN]Cu(η2-ONPh)), 2.012 (s, 12H, Me), 1.630 (s, 6H,
backbone-Me for [Me2NN]Cu(η2-ONPh)), 1.433 (s, 6H,
[Me2NN]Cu(benzene)). 13C{1H} NMR (C6D6): δ 163.28, 162.44,
160.50, 160.39, 150.62, 147.86, 132.18, 130.63, 129.36, 128.60,
128.24, 125.12, 123.16, 120.13, 95.88, 93.11, 23.15, 22.54, 18.84,
18.52, 14.27. IR: νNO ) 1040 cm-1 (1029 cm-1 for 2b-15N).
UV-vis (Et2O): λmax ) 580 nm (ε ) 2100 M-1 cm-1), 781 nm (ε
) 3300 M-1 cm-1). Anal. Calcd for C48H55Cu2N5O: C, 68.22; H,
6.56; N, 8.29. Found: C, 67.87; H, 6.78; N, 8.33.
1
crystals. H NMR (C6D6, RT): δ 7.596 (m, 2H, Ar-H), 6.976 (m,
3H, Ar-H). 13C{1H} NMR (C6D6): δ 166.13, 165.97, 135.06, 129.22,
120.69, 120.63. IR: ν
) 1353 cm-1 (from PhNO dimer).10
15NO
{[Me2NN]Ni}2(µ-η2:η2-ONAr) (1a). A solution of 3,5-dimeth-
ylnitrosobenzene (0.015 g, 0.11 mmol) in ether (3 mL) was slowly
added with stirring to a solution of [Me2NN]Ni(2,4-lutidine) (0.108
g, 0.23 mmol) in ether (10 mL). The solution was stirred for 1 h
and then filtered through Celite, and the filtrate was concentrated
and cooled to -35 °C. The green crystals that had formed were
separated from the solution, washed with cold pentane, and dried
in vacuo to afford 0.042 g (42% yield) of the product. Recrystal-
lization from pentane afforded green crystals suitable for X-ray
1
diffraction. H NMR (C6D6, RT): δ 7.095 (d, 4H, m-Ar-H), 6.887
(d, 4H, m-Ar-H), 6.509 (s, 1H, p-ArNO-H), 6.456 (t, 6H, p-Ar-H
+ o-ArNO-H), 3.476 (s, 2H, backbone-CH), 3.029 (s, 12H, o-Ar-
Me), 2.279 (s, 12H, o-Ar-Me), 2.192 (s, 6H, ArNO-Me), 0.485 (s,
12H, backbone-Me). 13C{1H} NMR (C6D6): δ 162.82, 160.46,
159.82, 136.42, 132.00, 122.02, 102.48, 98.21, 24.00, 21.08, 16.86
(two signals obscured). UV-vis (Et2O): λmax ) 615 nm (ε ) 1100
M-1 cm-1). Anal. Calcd for C50H59O1N5Ni2: C, 69.55; H, 6.88; N,
8.11. Found: C, 69.60; H, 6.97; N, 8.34.
1H NMR (-70 °C, toluene-d8): δ 7.514 (s, 1H, p-ArNO),
6.87-6.56 (br, 14H, ArH), 4.662 (s, 2H, backbone-CH), 2.980 (s,
6H, o-Ar-Me), 2.617 (s, 6H, o-Ar-Me), 2.282 (s, 6H, o-Ar-Me),
1.989 (s, 6H, ArNO-Me), 1.549 (s, 6H, o-Ar-Me), 1.006 (s, 12H,
backbone-Me). Coalescence of the two o-Ar-Me peaks at 2.980
and 2.617 ppm (300 MHz) gave ∆Gq ) 10.3(2) kcal/mol at -55(3)
°C; coalescence of the two o-Ar-Me peaks at 2.282 and 1.549 ppm
(300 MHz) gave ∆Gq ) 10.2(2) kcal/mol at -50(3) °C.
[Me2NN]Ni(2-picoline). A solution of Ni(2-picoline)2Cl2 (2.00
g, 6.33 mmol) (prepared analogously to Ni(2,4-lutidine)2Cl244) in
30 mL of THF was added to a solution of [Me2NN]Tl (3.22 g,
6.33 mmol) in 50 mL of THF. The reaction mixture was allowed
to stir for 1 h and then was passed through Celite. Na/Hg [38.7 g,
0.5% (w/w) Na] was added to the reaction mixture, and a color
change to red was observed after vigorous shaking. The solution
was stirred for an additional 3 h, after which it was decanted off
and passed through Celite. All of the volatiles were removed in
vacuo. The remaining solid was recrystallized from Et2O at -35
°C to afford 1.40 g (49% yield) of red crystals, which were dried
in vacuo. UV-vis (Et2O): λmax ) 522 nm (ε ) 1000 M-1 cm-1).
EPR (X-band, toluene glass, 90 K, with a small amount of added
2-picoline): g1 ) 2.41, g2 ) 2.12, g3 ) 2.06. Anal. Calcd for
C27H32N3Ni: C, 70.92; H, 7.05; N, 9.19. Found: C, 70.73; H, 7.46;
N, 9.20.
The UV-vis molar absorptivities are approximate: the higher-
energy band at λ ) 580 nm corresponds to [Me2NN]Cu(η2-ONAr)
(3b) from dissociation of a [Me2NN]Cu fragment in dilute solution.
[Me2NN]Cu(η2-ONAr) (3a). A solution of ArNO (0.067 g, 0.49
mmol) in ether (5 mL) was slowly added to a solution of
[Me2NN]Cu(MeCN) (0.204 g, 0.49 mmol) in ether (15 mL). The
solution turned greenish-black immediately and was allowed to stir
(44) Wiencko, H. L.; Kogut, E.; Warren, T. H. Inorg. Chim. Acta 2003,
345, 199–208.
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18110 J. AM. CHEM. SOC. VOL. 131, NO. 50, 2009

Ni and Cu C-Organonitroso Adducts
A R T I C L E S
for 30 min at room temperature. The solution was then filtered
through Celite, and the filtrate was concentrated and cooled to -35
°C. The mauve crystals were isolated from the solution, washed
with cold pentane, and dried in vacuo, which afforded 0.150 g (60%
analysis of the reaction mixture indicated a 1:1 molar ratio of
[Me2NN]Ni(κ2-O2N2Ar)30 (4) and [Me2NN]Ni(NO).30 1H NMR
(C6D6): δ 7.192 (d, 4H, m-Ar-H, ([Ni]NO)), 7.04-7.00 (m, 8H,
p-Ar-H ([Ni]NO), all Ar-H [Ni](O2N2Ar)), 6.556 (s, 2H, o-ArNO-
H), 6.410 (s, 1H, p-ArNO-H), 4.883 (s, 1H, backbone-CH
[Ni](O2N2Ar)), 4.351 (s, 1H, backbone-CH ([Ni]NO)), 2.693 (s,
12H, o-Ar-Me [Ni](O2N2Ar)), 2.568 (s, 12H, o-Ar-Me ([Ni]NO)),
1.825 (s, 6H, ArNO-Me [Ni](O2N2Ar)), 1.460 (s, 6H, backbone-
Me ([Ni]NO)) 1.433 (s, 6H, backbone-Me [Ni](O2N2Ar)).
Addition of NO to [Me2NN]Cu(η2-ONAr) (3a) To Form
[Me2NN]Cu(K2-O2N2Ar) (5). With a syringe, NO gas (5.7 mL at
300 K and 1 atm., 0.23 mmol) was slowly bubbled into a solution
of [Me2NN]Cu(η2-ONAr) (0.056 g, 0.11 mmol) in 5 mL of pentane.
The color changed instantaneously from green to red. Volatiles were
removed in vacuo, after which the residue was extracted with
pentane and the extracts were filtered through Celite. The filtrate
was concentrated and cooled to afford 0.046 g (80% yield) of the
product. EPR (toluene, RT) giso ) 2.10 (ACu ) 79 G; AN ) 13 G).
UV-vis (Et2O): λmax ) 573 nm (ε ) 450 M-1 cm-1), 768 nm (ε
) 180 M-1 cm-1); Anal. Calcd. for C25H34N4O2Cu: C, 65.20; H,
6.41; N, 10.49. Found: C, 64.98; H, 6.44; N, 10.54.
1
yield) of the isolated product. H NMR (C6D6): δ 7.058 (d, 4H,
m-Ar-H), 6.974 (t, 2H, p-Ar-H), 6.790 (s, 1H, p-ArNO-H), 6.587
(s, 2H, o-ArNO-H), 4.772 (s, 1H, backbone-CH), 2.161 (br, 12H,
o-Ar-Me), 2.046 (s, 6H, ArNO-Me), 1.447 (s, 6H, backbone-Me).
13C{1H}NMR (C6D6): 163.25, 160.90, 138.63, 132.09, 129.78,
128.45, 125.00, 118.27, 95.82, 22.48, 21.00, 18.49. UV-vis (Et2O):
λmax ) 583 nm (ε ) 550 M-1 cm-1). Anal. Calcd for C29H34N3OCu:
C, 69.09; H, 6.79; N, 8.33. Found: C, 68.90; H, 6.81; N, 8.24.
1H NMR (-60 °C, toluene-d8, upfield Me region): δ 2.449 (s,
3H, o-Ar-Me) 2.398 (s, 6H, two coincident o-Ar-Me groups), 2.054
(s, 6H, ArNO-Me), 1.449 (s, 3H, backbone-Me), 1.357 (s, 3H,
backbone-Me), 1.287 (s, 3H, o-Ar-Me). Coalescence of the two
backbone-Me peaks at 1.449 and 1.357 ppm (300 MHz) gave ∆Gq
) 11.4(2) kcal/mol at -44(2) °C.
[Me2NN]Cu(η2-ONPh) (3b). A solution of nitrosobenzene
(0.049 g, 0.49 mmol) in toluene (5 mL) was slowly added with
stirring to a solution of [Me2NN]Cu(MeCN) (0.205 g, 0.49 mmol)
in toluene (10 mL). The solution was stirred for 30 min,
concentrated to dryness, taken up in pentane (10 mL), and filtered
through Celite. The filtrate was concentrated and cooled to -35
°C. The brown crystals were isolated to afford 0.191 g (82% yield)
of product. 1H NMR (C6D6, RT): δ 7.026 (t, 2H, m-PhNO-H), 6.838
(d, 2H, o-PhNO-H), 6.753 (t, 1H, p-PhNO-H), 4.762 (s, 1H,
backbone-CH), 2.143 (br, 12H, o-Ar-Me), 1.434 (s, 6H, backbone-
Me). 13C{1H} NMR (C6D6): δ 163.26, 160.44, 147.86, 132.16,
129.32, 128.57, 125.08, 120.10, 95.89, 95.82, 22.50, 18.48. IR: νNO
) 1113 cm-1 (1093 cm-1 for 3b-15N). UV-vis (Et2O): λmax ) 588
nm (ε ) 1000 M-1 cm-1). Anal. Calcd for C27H30CuN3O: C, 68.11;
H, 6.35; N, 8.83. Found: C, 68.20; H, 6.61; N, 8.72.
Acknowledgment. T.H.W. thanks Georgetown University for
a Pilot Research Grant, the ACS PRF (G and AC), and the NSF
(CAREER program and CHE-0716304). We also thank Prof. Jeffrey
Petersen for acquiring the EPR spectra of 5, Prof. Karsten Meyer
for SQUID data on 1a, and Prof. Faye Rubinson and Mr. Anthony
Kammerich for assistance with the cyclic voltammetry of 3a.
Supporting Information Available: Synthetic details for the
15N-labeled adducts (1b-3b); additional characterization data
for compounds 1-5, including NMR, EPR, and IR spectra;
cyclic voltammetry of 3a; DFT calculational details for 1a; and
X-ray data (CIF) and fully labeled ORTEP plots for 1a, 2a,
2b, 3a, 3b, and 5. This material is available free of charge via
the Internet at http://pubs.acs.org.
Addition of NO to {[Me2NN]Ni}2(µ-η2:η2-ONAr) (1a) To
Form [Me2NN]Ni(K2-O2N2Ar) (4) and [Me2NN]Ni(NO). With a
syringe, NO gas (2.0 mL @ 300 K and 1 atm, 0.078 mmol) was
slowly bubbled into a solution of {[Me2NN]Ni}2(µ-η2:η2-ONAr)
(0.032 g, 0.037 mmol) in 5 mL of C6D6. The color of the solution
changed instantaneously from dark-green to yellow-green. 1H NMR
JA903550N
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J. AM. CHEM. SOC. VOL. 131, NO. 50, 2009 18111