Late-metal nitrosyl cations: Synthesis and reactivity of [Ni(NO)(MeNO 2)3][PF6]

Article abstract of DOI:10.1021/ic201821t

The reaction of [NO][PF₆] with excess Ni powder in CH ₃NO₂, in the presence of 2 mol % NiI₂, results in the formation of [Ni(NO)(CH₃NO₂)₃][PF ₆] (1), which can be isolated in modest yield as a blue crystalline solid. Also formed in the reaction is [Ni(CH₃NO₂) ₆][PF₆]₂ (2), which can be isolated in comparable yield as a pale-green solid. In the solid state, 1 exhibits tetrahedral geometry about the Ni center with a linear nitrosyl ligand [Ni1-N1-O1 = 174.1(8)°] and a short Ni-N bond distance [1.626(6) A]. As anticipated, the weakly coordinating nitromethane ligands in 1 are easily displaced by a variety of donors, including Et₂O, MeCN, and piperidine (NC₅H₁₁). More surprisingly, the addition of mesitylene to 1 results in the formation of an η⁶-coordinated nickel arene complex, [Ni(η⁶-1,3,5-Me₃C ₆H₃)(NO)][PF₆] (6). In the solid state, complex 6 exhibits a long Ni-C_cent distance [1.682(2) A], suggesting a relatively weak Ni-arene interaction, a consequence of the strong π-back-donation to the nitrosyl ligand. The addition of anisole to 1 also results in the formation of a η⁶ nickel arene complex, [Ni(η⁶-MeOC₆H₅)(NO)][PF₆] (7). This complex also exhibits a long Ni-C_cent distance [1.684(1) A].

Full text of DOI:10.1021/ic201821t

Article
pubs.acs.org/IC
Late-Metal Nitrosyl Cations: Synthesis and Reactivity of
[Ni(NO)(MeNO2)3][PF6]
Ashley M. Wright, Guang Wu, and Trevor W. Hayton*
Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United States
S
* Supporting Information
ABSTRACT: The reaction of [NO][PF6] with excess Ni powder in
CH3NO2, in the presence of 2 mol % NiI2, results in the formation of
[Ni(NO)(CH3NO2)3][PF6] (1), which can be isolated in modest yield as
a blue crystalline solid. Also formed in the reaction is [Ni(CH3NO2)6]-
[PF6]2 (2), which can be isolated in comparable yield as a pale-green
solid. In the solid state, 1 exhibits tetrahedral geometry about the Ni center with a linear nitrosyl ligand [Ni1−N1−O1 =
174.1(8)°] and a short Ni−N bond distance [1.626(6) Å]. As anticipated, the weakly coordinating nitromethane ligands in 1 are
easily displaced by a variety of donors, including Et2O, MeCN, and piperidine (NC5H11). More surprisingly, the addition of
mesitylene to 1 results in the formation of an η6-coordinated nickel arene complex, [Ni(η 6-1,3,5-Me3C6H3)(NO)][PF6] (6). In
the solid state, complex 6 exhibits a long Ni−Ccent distance [1.682(2) Å], suggesting a relatively weak Ni−arene interaction, a
consequence of the strong π-back-donation to the nitrosyl ligand. The addition of anisole to 1 also results in the formation of a
η6 nickel arene complex, [Ni(η 6-MeOC6H5)(NO)][PF6] (7). This complex also exhibits a long Ni−Ccent distance [1.684(1) Å].
Me2C6H3) to [Ar2nacnac]NiNO (Ar2nacnac = ArNC(Me)-
CHC(Me)NAr; Ar = 2,6-iPr2C6H3) gives [Ar2nacnac]Ni(κ2-
ONN(Ar)O) as the isolated product.18
INTRODUCTION
■
The reaction of an electrophilic late-metal nitrosyl with a
carbon nucleophile holds considerable promise as an efficient
means for C−N bond formation.1−4 Metal nitrosyls of groups 8
and 9 have been the most extensively studied as sources of
electrophilic nitrosyl ligands.1,4,5 For example, Meyer and co-
workers observed the selective nitrosation at the para position
of N,N′-dimethylaniline (DMA) using the ruthenium nitrosyl
[Ru(bipy)2Cl(NO)]2+.6,7 Additionally, Onishi et al. showed
that TpRuCl2(NO) activates a vinyl C−H bond of vinyl-
pyridine to form the nitrosoalkene complex TpRuCl{κ 2-N(
O)CHCH(NC5H3R)} (R = H, Me, Et).8 Other carbon
nucleophiles will also react with group 8 nitrosyls,1,6,9,10
including enols and allylidenearylhydrazones, to give oximes6,10
and arylazooximes, respectively.11 Dinitrosyls of groups 8 and 9
have also proven to be reactive starting materials. For example,
strained alkenes react with [CpCo(NO)]2 or RuCl2(NO)2(L)
(L = tetramethylethylenediamine or 2,2′-bipyridine) to form
the corresponding dinitrosoalkane complexes.12−14
In contrast to the chemistry reported for groups 8 and 9, the
reactivity of group 10 metal nitrosyls with nucleophiles has not
been well explored, in part because of the relative rarity of these
complexes.3,15 However, there are a handful of reports that
detail the reactivity of nickel nitrosyls with nucleophiles.16−19
For instance, CpNiNO reacts with RLi (R = Ph, tBu) to form a
trinuclear bridging imido complex, [Cp3Ni3(μ3-NR)], as the
isolated product.16 This reaction is thought to proceed via
nucleophilic attack at the N atom of the NO ligand. Moreover,
the addition of NO to [NiBr(C3H5)2]2 results in the formation
of 3-oximinopropene.17 While the mechanism of this trans-
formation was not fully elucidated, it was proposed to proceed
through a Ni−NO intermediate. Finally, Warren and co-
workers reported that the addition of ArNO (Ar = 3,5-
Recently, we synthesized a copper nitrosyl complex with a
rare {CuNO}10 configuration, namely, [Cu(CH3NO2)5(NO)]-
[PF6]2, by the addition of [NO][PF6] to Cu powder.20 This
complex readily reacts with mesitylene to produce the donor−
acceptor complex [1,3,5-Me3C6H3,NO][PF6] and a copper(I)
arene π complex, [Cu(η2-1,3,5-Me3C6H3)2][PF6]. While this
transformation is consistent with the presence of an electro-
philic nitrosyl ligand in [Cu(CH3NO2)5(NO)][PF6]2, we
observe no evidence for C−N bond formation during the
reaction. Therefore, we sought to expand our investigation of
late-metal nitrosyl cations to group 10 by targeting the
synthesis of a nickel nitrosyl cation. Herein, we detail the
synthesis of [Ni(NO)(CH3NO2)3][PF6] and explore its
reactivity with a variety of Lewis bases and arenes.
RESULTS AND DISCUSSION
■
Following the methodology used to synthesize [Cu-
(CH3NO2)5(NO)][PF6]2,20 [NO][PF6] was treated with
excess Ni powder in CH3NO2. Surprisingly, no reaction was
observed under these conditions. However, a reaction could be
induced by the addition of 2 mol % of NiI2 to the mixture.
Immediately upon the addition of NiI2, gas evolution is
observed concomitant with the formation of a red solution.
This solution transforms to a bright-green color within a few
minutes, and after 10 min, the solution becomes blue. Workup
of the reaction mixture after 1 h of stirring results in the
isolation of blue crystals of [Ni(NO)(CH3NO2)3][PF6] (1) in
Received: August 21, 2011
Published: October 27, 2011
© 2011 American Chemical Society
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18% yield (eq 1). Interestingly, the addition of 2 mol % I2 to
the reaction mixture also results in the formation of complex 1,
(CH3NO2)5(NO)][PF6]2, which contains a much longer M−
N bond and a bent nitrosyl ligand.20 Under the electron-
counting rules normally used for linear nitrosyl ligands,2
complex 1 should be described with a Ni0−(NO+) electronic
structure. This leads to the curious observation that the
reaction of Ni powder with [NO][PF6] does not result in the
formal oxidation of the metal. That said, assigning oxidation
states in nitrosyl complexes is a challenging endeavor, an
observation that resulted in the development of the Enemark−
Feltham notation.45 Accordingly, the Ni0 oxidation state
assignment for 1 is likely an oversimplification.28 Finally, the
Ni−O bond lengths in 1 range from 2.031(5) to 2.053(4) Å
and are comparable to the Cu−O bond distances in
[Cu(CH3NO2)5(NO)][PF6]2.20 Structurally characterized ni-
tromethane complexes are uncommon. Previously reported
examples are limited to [TiCl3(CH3NO2)]2(μ-Cl)2,46
AlCl3(CH3NO2),47 Cu(NO3)2·CH3NO2,48 K(η2-CH3NO2)-
(H2O)4Br·H2O,49 [Cu(CH3NO2)5(NO)][PF6]2, and [Cu-
(CH3NO2)5][PF6]2.20
with isolated yields comparable to the NiI2-mediated trans-
formation. In contrast, the addition of 4 mol % NiCl2 does not
lead to any observable reaction after 1 h.
Complex 1 is extremely air- and moisture-sensitive in both
solution and the solid state. It is also temperature-sensitive,
decomposing to an intractable oil after 24 h at ambient
temperature. However, it is indefinitely stable at −25 °C in the
solid state. In contrast to the related copper analogue,20
complex 1 is stable under a dynamic vacuum. In solution, 1
exhibits a high νNO absorption feature in its IR spectrum (1877
cm−1, CH2Cl2). This νNO value is higher than those observed
for previously reported nickel nitrosyls (1568−1867
cm−1)18,21−40 and can be attributed to the weak Lewis basicity
of CH3NO2 and its overall cationic charge.41 In contrast, this
value is lower than that of [Cu(CH3NO2)5(NO)][PF6]2 (1933
In addition to complex 1, a second product is also formed
during the reaction of Ni powder with [NO][PF6], in the
presence of NiI2. This material is insoluble in CH2Cl2 but
soluble in CH3NO2, permitting its separation from complex 1.
Recrystallization from CH3NO2/CH2Cl2 affords the homo-
leptic nitromethane complex [Ni(CH3NO2)6][PF6]2 (2),
isolated as a light-green crystalline material in 22% yield.
Interestingly, if a dynamic vacuum is applied to the reaction
mixture immediately after the addition of [NO][PF6] to Ni
powder, complex 2 is isolated in higher yields (39%) than if the
reaction is performed in a closed system. Complex 1 is not
observed under these conditions. The connectivity of complex
2 has been definitively established by X-ray diffraction.
However, a complete structure refinement was hampered by
poor data quality. The formulation of complex 2 was also
confirmed by near-IR−UV−vis spectroscopy. Three transitions
at 398 nm (ε = 14 L·mol−1·cm−1), 664 nm (ε = 6
L·mol−1·cm−1), and 1200 nm (ε = 4 L·mol−1·cm−1) are
20
1
cm−1, CH3NO2). The H NMR spectrum of complex 1 in
CD2Cl2 exhibits a singlet at 4.57 ppm, assignable to coordinated
CH3NO2. Additionally, a broad doublet in its 19F NMR
−
spectrum at −76.7 ppm reveals the presence of PF6 .
Blue needles of 1 suitable for X-ray diffraction analysis were
grown from CH2Cl2/hexane at −25 °C. Complex 1 crystallizes
in the hexagonal space group P65 as a hexane solvate,
1·0.16C6H14. Its solid state molecular structure reveals a
discrete cation−anion pair (Figure 1). The cationic Ni center is
consistent with those previously reported for [Ni(CH3NO2)6]-
50,51
[SbCl6]2
and closely match those of the homoleptic aquo
complex [Ni(H2O)6]2+.52
The synthesis of 1 may be mechanistically related to the
synthesis of [Ni(NO)I]n, which is formed by the reaction of
NiI2 with Ni powder, in the presence of NO gas.53,54 This
hypothesis is supported by the reaction of 2 with NO and Ni
powder, in the presence of NiI2 (1 mol %), which results in the
formation of complex 1 in 10% yield (Scheme 1). While the
yield of 1 is low under these conditions, the 1 mol % NiI2
loading indicates that NiI2 is acting in a catalytic fashion.
Notably, the reaction does not proceed without the addition of
NiI2. Further evidence of the proposed mechanism comes from
the observation that complex 1 is not formed when the reaction
of Ni powder with [NO][PF6] is performed under a vacuum.
Presumably, under these conditions, all of the NO gas is
removed as it is formed, prohibiting the nitrosylation reaction.
Also consistent with the proposed mechanism, analysis of the
reaction headspace by gas-phase IR spectroscopy reveals the
presence of NO gas. Surprisingly, however, N2O is also
observed, which may arise via an Ni-mediated NO coupling
reaction.54 The role of NiI2 in the transformation is not entirely
clear, but because it is required for both oxidation of the Ni
powder and nitrosylation of complex 2, we postulate that it is
necessary for the generation of a soluble NiI intermediate that
can be either nitrosylated with NO or oxidized with NO+. The
Figure 1. ORTEP drawing of 1·0.16C6H14 shown with 50%
probability ellipsoids. Hexane solvate, H atoms, and [PF6]− anion
have been excluded for clarity.
coordinated by one nitrosyl ligand and three CH3NO2 ligands,
in a highly distorted tetrahedral geometry. This is evidenced by
large N−Ni−L angles (av. 127.9°), a feature common to many
[Ni(NO)L3]+ and Ni(NO)L2X complexes.2,3 The metrical
parameters of the Ni−N−O moiety [Ni1−N1 = 1.626(6) Å;
N1−O1 = 1.139(9) Å; Ni1−N1−O1 = 174.1(8)°; Table 1] are
within the range observed for other four-coordinate cationic
{NiNO}10 complexes.22,23,32−34,42−44 Notably, the metrical
parameters of the linear NO moiety in 1 are much different
from those observed for the copper analogue [Cu-
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Table 1. Selected Metrical Parameters for Complexes 1·0.16C6H14, 3, and 4·0.33CH2Cl2
bond lengths (Å) and angles (deg)
1·0.16C6H14
1.626(6)
3
4·0.33CH2Cl2
1.633(3)
Ni1−N1
N1−O1
Ni1−N1−O1
Ni−L
1.619(4)
1.160(5)
169.6(4)
1.139(9)
1.158(4)
176.0(3)
174.1(8)
Ni1−O2 = 2.053(4)
Ni1−O3 = 2.031(5)
Ni1−O4 = 2.050(4)
av. 2.045(5)
Ni1−O2 = 2.042(3)
Ni1−O3 = 2.067(3)
Ni1−O4 = 2.018(3)
Ni1−N2 = 1.981(3)
Ni1−N3 = 1.976(4)
Ni1−N4 = 1.987(3)
av. 1.981(4)
a
N1−Ni1−L
N1−Ni1−O2 = 133.2(3)
N1−Ni1−O3 = 126.2(3)
N1−Ni1−O4 = 124.2(3)
N1−Ni1−O2 = 118.8(2)
N1−Ni1−O3 = 130.3(2)
N1−Ni1−O4 = 130.4(2)
N1−Ni1−N2 = 118.5(2)
N1−Ni1−N3 = 122.4(2)
N1−Ni1−N4 = 122.9(2)
a
a
Diethyl ether ligand.
MeCN or piperidine results in the complete displacement of
the CH3NO2 ligands, providing [Ni(NO)(MeCN)3][PF6] (4)
and [Ni(NO)(NC5H11)3][PF6] (5), respectively (Scheme 2).
Complexes 4 and 5 exhibit νNO values of 1845 and 1772 cm−1
in a CH2Cl2 solution, respectively. Both values are substantially
lower than those exhibited by complexes 1 and 3, consistent
with the stronger donating abilities of MeCN and piperidine.
Moreover, the thermal stabilities of 4 and 5 are much greater
than that of 1, and they can be stored as solids at room
temperature for weeks without noticeable decomposition.
Crystals of 3 and 4 were grown by the slow diffusion of
hexane into concentrated CH2Cl2 solutions. Complex 3
crystallizes in the monoclinic space group P21/c, while complex
4 crystallizes as a CH2Cl2 solvate, 4·0.33CH2Cl2, in the
orthorhombic space group Pnma. Their solid-state molecular
structures are shown in Figure 2, while a selection of metrical
Scheme 1
use of a weakly coordinating solvent also appears to be critical
for the generation of a nitrosyl complex. When similar
oxidations are performed in strongly donating solvents, such
as MeCN (Gutmann donor number: MeCN = 14.1; CH3NO2
= 2.7),41 they typically result in the formation of simple
coordination complexes.55 For instance, the reaction of Pd
metal with 2 equiv of [NO][BF4] in MeCN results solely in the
formation of [Pd(MeCN)4][BF4]2,56 while oxidation of Ni0
with [NO][PF6] in MeCN leads exclusively to the formation of
[Ni(MeCN)6][PF6]2.55 Also of note, oxidation of Ni powder
under these conditions does not require the addition of a
catalyst to proceed.55 Finally, the reaction of complex 1 with
[NO][PF6] in MeNO2 results in NO gas evolution and the
formation of complex 2 in modest yield (Scheme 1). This
reaction may partially explain the low yields of 1 because any
[NO][PF6] remaining in the reaction mixture would result in
the reformation of 2.
Not surprisingly, given its low donor number, the nitro-
methane ligands in 1 can easily be displaced with stronger
Lewis bases. For example, the addition of 4 equiv of Et2O to 1
in CH2Cl2 results in an immediate color change from blue to
green and the appearance of a new νNO stretch at 1860 cm−1.
This value is 17 cm−1 lower than that observed for 1. From
these solutions, [Ni(NO)(OEt2)(CH3NO2)2][PF6] (3) can be
isolated in 50% yield (Scheme 2). In contrast, the addition of
Figure 2. ORTEP drawings of 3 (left) and one of two crystallo-
graphically independent molecules of 4·0.33CH2Cl2 (right) shown
with 50% probability ellipsoids. Hydrogen atoms and [PF6]− anions
have been excluded for clarity.
parameters are collated in Table 1. The Ni1−N1 [1.619(4) Å]
and N1−O1 [1.160(5) Å] bond lengths in 3 are identical with
those found in 1, while the Ni−N−O bond angle [169.6(4)°]
deviates slightly from that seen in the parent complex. The
substitution of a CH3NO2 ligand with Et2O lowers the
symmetry of the complex from C3v to Cs, which results in the
splitting of degenerate dπ orbitals and accounts for deviations
in the Ni−N−O angle away from 180°.57 In the solid state,
complex 4 contains two independent molecules in the
asymmetric unit, one of which lies on a special position. Both
exhibit similar metrical parameters, and only one will be
discussed in detail. The monocationic Ni center in 4 is
coordinated by one NO ligand and three MeCN ligands in a
distorted tetrahedron (av. N−Ni−NMeCN = 121.3°). The Ni−
NNO [1.633(3) Å] and N−O [1.158(4) Å] bond lengths in 4
Scheme 2
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are comparable to those observed in 1 and 3, while the Ni−
NMeCN bond lengths range from 1.976(4) to 1.987(3) Å.
The high νNO value observed for complex 1 suggests that its
nitrosyl ligand may be susceptible to reactions with
nucleophiles.1,4,5,58,59 With this in mind, we investigated its
reactivity with a variety of activated arenes.7 Thus, the addition
of 7 equiv of mesitylene to 1 in CH2Cl2 results in a dramatic
color change from blue to red. The in situ IR spectrum of this
solution features a new NO absorption feature at 1910 cm−1,
assignable to [Ni(η6-1,3,5-Me3C6H3)(NO)][PF6] (6). Nota-
bly, this is a higher νNO stretch than that observed for complex
1. No evidence for NO activation, including the formation of
the electron donor−acceptor complex [1,3,5-Me3C6H3,NO]-
[PF6], is observed in these solutions.20 Complex 6 can be
isolated in 71% yield by crystallization from CH2Cl2/hexane
(eq 2). Its 1H NMR spectrum (CD2Cl2) exhibits two singlets at
Figure 3. ORTEP diagrams of 6 (left) and 7 (right) shown with 50%
probability ellipsoids. Hydrogen atoms and [PF6]− anions have been
excluded for clarity.
Table 2. Selected Metrical Parameters for Complexes 6 and
7
bond lengths (Å) and angles (deg)
6
7
CAr−CAr (av.)
Ni−N
N−O
Ni−N−O
Ni−Ccent
1.400(7)
1.610(4)
1.157(4)
177.4(4)
1.682(2)
1.405(3)
1.627(2)
1.144(3)
173.1(2)
1.684(1)
2.172(4) to 2.212(4) Å, while the Ni−Ccent distance is 1.682(2)
Å. Only a few examples of η6 nickel arene complexes are
known, as the η2-coordination mode is more common.60−64
Notably, the Ni−Ccent distance in 6 is significantly longer than
previously reported Ni−Ccent distances (1.592−1.621 Å).60−64
The elongated Ni−C distance results from the strong π-
acceptor ability of NO, which reduces the Ni−arene back-
bonding interaction. Further evidence for this weak interaction
is revealed upon dissolution of 6 in CH3NO2, which results in
the reformation of 1 via displacement of the mesitylene ring.
Complex 7 crystallizes in the monoclinic space group P21/n
(Figure 3). Its Ni−N [1.627(2) Å], N−O [1.144(3) Å], and
Ni−Ccent [1.684(1) Å] distances are similar to those exhibited
by 6. However, the Ni−Caryl bond lengths vary [from 2.152(3)
to 2.253(2) Å], revealing an uncentered coordination of the
ring to the Ni center. For example, the ipso carbon is 0.1 Å
further from the Ni ion than the para carbon. Complexes 6 and
7 are similar to the classic “pogo-stick” complexes Cp′Ni-
(NO).60,65−67 In fact, the metrical parameters of the [Ni-
(NO)]+ moiety in 6 and 7 are comparable to those observed in
Cp*Ni(NO) [Ni−N = 1.620(3) Å; N−O = 1.177(3) Å; Ni−
N−O = 179.2(3)°].67 However, the νNO values between these
two classes of molecules differ by over 100 cm−1 [e.g., 1910
cm−1 for 6 vs 1787 cm−1 for Cp*Ni(NO)], no doubt a
consequence of the positive charge on complexes 6 and 7.
Clearly, the addition of the activated arenes to the
[Ni(NO)]+ fragment does not result in the desired C−N
bond formation with the NO ligand. Instead, the arene ring
only coordinates to the Ni ion via an η6 interaction. Attempts
to promote NO activation by heating to 60−80 °C only result
2.76 and 7.11 ppm, in a 3:1 ratio, respectively, assignable to the
methyl and aryl protons of coordinated mesitylene.
Other arenes are also capable of binding to the [Ni(NO)]+
fragment in a η6 fashion. For example, the addition of 3 equiv
of anisole to 1 in CH2Cl2 results in the formation of [Ni(η6-
MeOC6H5)(NO)][PF6] (7), which can be isolated in 48%
yield by crystallization from CH2Cl2/hexane (eq 2). Similarly,
the addition of 1 equiv of DMA to complex 6 in CH2Cl2 results
in the displacement of mesitylene and the formation of [Ni(η 6-
C6H5NMe2)(NO)][PF6] (8), which can be isolated as a red
solid in 57% yield. The solution IR spectrum of 7 exhibits a
higher νNO value (1915 cm−1, CH2Cl2) than either 1 or 6,
while the solution IR spectrum of 8 features a νNO value of
1894 cm−1 (CH2Cl2). As determined by IR spectroscopy, there
is no evidence for NO activation upon the addition of either
anisole or DMA to the [Ni(NO)]+ fragment. Interestingly, the
addition of excess DMA to 6 in CH2Cl2 results in the formation
of a green solution. The IR spectrum of this solution features a
new NO vibration at 1840 cm−1, in addition to the peak
attributable to 8. Furthermore, the feature at 1840 cm−1
increases in intensity with increasing concentration of DMA
(see the Supporting Information). We have tentatively assigned
this feature to [Ni(NO)(C6H5NMe2)3][PF6] (9), the product
formed by coordination of DMA to the Ni ion via the N atom.
Attempts to crystallize this green material from CH2Cl2/hexane
results in isolation of a green oil, which converts slowly to the
red crystalline material of 8 upon standing, suggesting that the
η6-coordination mode is favored.
Crystals of 6 suitable for X-ray diffraction analysis were
grown from a concentrated CH2Cl2 solution at −25 °C.
Complex 6 crystallizes in the monoclinic space group C2/c and
exhibits a pseudotetrahedral geometry about the Ni metal
center (Figure 3). The metrical parameters of the Ni−NO
moiety [Ni−N = 1.610(4) Å; N−O = 1.157(4) Å; Ni−N−O =
177.4(4)°; Table 2] are comparable to those observed for 1, 3,
and 4 and are within the expected range for a nickel nitrosyl.
Most surprisingly, the [Ni(NO)]+ moiety is supported by
mesitylene coordinated in a η6 fashion to the Ni center. The
Ni−C bond distances are nearly equidistant, ranging from
1
in decomposition, as determined by H NMR spectroscopy.
Similarly, the addition of a base, such as Cs2CO3 or NEt3, does
not yield any tractable products. While the high νNO value for
complex 1 is indicative of the presence of an electrophilic NO
moiety, the Ni center is still the preferred site of reactivity in all
cases, likely because of the lability of the coligands. Accordingly,
future attempts to engage the NO ligand in reactivity will focus
on using chelating coligands to limit access to the Ni ion.
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MHz): δ 61.65 (CH3NO2). IR (Nujol mull, cm−1): 1880 (s, νNO),
1565 (s), 1404 (s), 1101 (m), 849 (s), 741 (m), 657 (s), 563 (m). IR
(CH2Cl2, cm−1): 1877 (s, νNO). IR (CH3NO2, cm−1): 1857 (s, νNO).
UV−vis (CH2Cl2, 25 °C, 0.75 mM): 399 nm (ε = 112 L·mol−1·cm−1),
662 nm (ε = 266 L·mol−1·cm−1).
SUMMARY
■
Reaction of Ni powder with [NO][PF6] in CH3NO2, in the
presence of 2 mol % NiI2, results in nitrosylation of the metal
and formation of a cationic nickel nitrosyl, [Ni(NO)-
(CH3NO2)3][PF6]. The reaction does not proceed without
the addition of a catalyst, such as NiI2, which we believe is
required for the formation of a NiI intermediate. While the
isolated yield is modest, [Ni(NO)(CH3NO2)3][PF6] is a good
synthon for nickel nitrosyl chemistry because the weakly
coordinating CH3NO2 ligands allow for facile displacement
with a variety of donor ligands. This is manifested most
dramatically by the addition of arenes to 1, which leads to
isolation of a series of η6 nickel arene complexes, [(η6-
arene)Ni(NO)][PF6]. These complexes are rare examples of η6
coordination of an arene ring to a Ni center. Most importantly,
the addition of these activated arenes to 1 does not result in the
desired C−N bond formation with the NO ligand. This
contrasts sharply with the reaction between the cationic copper
nitrosyl, [Cu(CH3NO2)5(NO)][PF6]2, and mesitylene, which
results in facile NO+ transfer from Cu to the arene ring. The
differing reactivity of 1 and [Cu(CH3NO2)5(NO)][PF6]2
possibly relates to a stronger Ni−N interaction due to better
π back-donation from Ni to NO.
[Ni(CH3NO2)6][PF6]2 (2). The green insoluble material generated
during the synthesis of 1 was dissolved in CH3NO2 (2 mL) and
filtered through a Celite column (0.5 cm × 2 cm) supported on glass
wool. The resulting light-green solution was layered onto CH2Cl2 (5
mL). Storage at −25 °C resulted in the deposition of pale-green
needles. These were isolated by decanting off the supernatant, washing
with CH2Cl2 (2 × 2 mL), and drying in vacuo. Yield: 22%, 148 mg.
Anal. Calcd for C6H18F12N6NiO12P2: C, 10.08; H, 2.54; N, 11.76.
1
Found: C, 10.67; H, 2.70; N, 11.36. H NMR (CD3NO2, 22 °C, 500
MHz): δ 4.34 (3H, s, CH3NO2). 19F NMR (CD3NO2, 22 °C, 470
MHz): δ −69.0 (br d). 31P NMR (CD3NO2, 22 °C, 202 MHz): δ
−142.2 (sept, JPF = 699 Hz). IR (Nujol mull, cm−1): 1568 (s), 1385
(m), 1277 (w), 1263 (w), 1110 (m), 1044 (w), 918 (m), 837 (s), 741
(m), 671 (s), 607 (m), 558 (m). UV−vis (CH3NO2, 25 °C, 25.9
mM): 398 nm (ε = 14 L·mol−1·cm−1), 664 nm (ε = 6 L·mol−1·cm−1),
730 nm (ε = 5 L·mol−1·cm−1), 1200 nm (ε = 4 L·mol−1·cm−1, Δoct
=
8300 cm−1).
[Ni(Et2O)(CH3NO2)2(NO)][PF6] (3). A solution of Et2O (54 mg,
0.73 mmol) in CH2Cl2 (1 mL) was added to a stirring solution of 1
(85 mg, 0.20 mmol) in CH2Cl2 (1 mL). This resulted in a color
change to dark turquoise. The reaction mixture was stirred for 5 min
and then filtered through a Celite column (0.5 cm × 2 cm) supported
on glass wool. The supernatant was layered with hexanes (2 mL), and
subsequent storage at −25 °C resulted in the deposition of turquoise-
blue blocks. The crystals were dried in vacuo for <1 min. Yield: 50%,
43 mg. Note: Exposure to a dynamic vacuum results in the partial loss
of diethyl ether. Anal. Calcd for C6H16F6N3NiO6P: C, 16.76; H, 3.75;
N, 9.77. Found: (run A) C, 15.80; H, 3.47; N, 8.87; (run B) C, 15.72;
H, 3.56; N, 9.35. 1H NMR (CD2Cl2, 22 °C, 400 MHz): δ 1.63 (6H, t,
OCH2CH3), 3.71 (4H, q, OCH2CH3), 4.56 (6H, s, CH3NO2). 19F
EXPERIMENTAL SECTION
■
General Procedures. All reactions and subsequent manipulations
were performed under anaerobic and anhydrous conditions under
either high vacuum or an atmosphere of nitrogen or argon.
Nitromethane was recrystallized from Et2O three times and then
distilled over MgSO4 or CaH2. Hexanes and diethyl ether were dried
using a Vacuum Atmospheres DRI-SOLV solvent purification system.
CD2Cl2 and CD3NO2 were dried over activated 3 Å molecular sieves
for 24 h before use. All other reagents were purchased from
commercial suppliers and used as received. NMR spectra were
recorded on a Varian UNITY INOVA 400 or a Varian UNITY
INOVA 500 spectrometer. 1H and 13C{1H} NMR spectra were
referenced to external SiMe4 using the residual protio solvent peaks as
internal standards (1H NMR experiments) or the characteristic
resonances of the solvent nuclei (13C NMR experiments). 19F{1H}
NMR spectra were referenced to external CCl3F. 31P{1H} NMR
spectra were referenced to external 85% H3PO4. IR spectra were
recorded on a Mattson Genesis FTIR or a Thermo Scientific Nicolet
6700 FTIR spectrometer, while UV−vis experiments were performed
on a UV-3600 Shimadzu spectrophotometer. Elemental analyses were
performed by the Microanalytical Laboratory at University of
California, Berkeley (Berkeley, CA).
[Ni(NO)(CH3NO2)3][PF6] (1). NiI2 (14 mg, 0.045 mmol, 2 mol %)
was added to excess Ni metal powder (559 mg, 9.52 mmol) in
CH3NO2 (2 mL) in a 20 mL scintillation vial. To this suspension was
added [NO][PF6] (331 mg, 1.89 mmol). The cap was immediately
fastened, and the solution was vigorously stirred. Gas evolution was
observed, and a red solution quickly formed. This solution became
bright green and then dark blue over the course of 10 min. After 1 h,
the solvent was removed in vacuo and the residue was extracted with
CH2Cl2 (6 mL). The solution was filtered through a Celite column
(0.5 cm × 2 cm) supported on glass wool, leaving a green solid (vide
infra) and excess Ni powder on the Celite plug. The solution was then
concentrated and layered with hexane (5 mL). Storage at −25 °C
resulted in the precipitation of blue fibrous needles that were isolated
by decanting the supernatant and drying under vacuum. Yield: 18%,
144 mg. Anal. Calcd for C3H9F6N4NiO7P: C, 8.65; H, 2.18; N, 13.44.
NMR (CD2Cl2, 22 °C, 470 MHz): δ −76.52 (JPF = 724 Hz, br d). 13
NMR (CD2Cl2, 22 °C, 125 MHz): δ 68.94 (OCH2CH3), 13.04
C
(OCH2CH3). 31P NMR (CD2Cl2, 22 °C, 202 MHz): δ −140.96 (JPF
=
709 Hz, br sept). IR (CH2Cl2, cm−1): 1860 (s, νNO). IR (Nujol mull,
cm−1): 1857 (s, νNO), 1567 (s), 1379 (s), 1192 (w), 1157 (w), 1092
(m), 1046 (m), 837 (s), 741 (w), 671 (m), 605 (w), 561 (m). UV−vis
(CH2Cl2, 25 °C, 2.33 mM): 400 nm (ε = 69 L·mol−1·cm−1), 682 nm
(ε = 274 L·mol−1·cm−1).
[Ni(MeCN)3(NO)][PF6] (4). To a stirring solution of 1 (105 mg,
0.252 mmol) in CH2Cl2 (1 mL) was added MeCN (77 mg, 1.9 mmol)
dissolved in CH2Cl2 (1 mL). This resulted in a color change to dark
purple-blue. The reaction mixture was stirred for 15 min and then
filtered through a Celite column (0.5 cm × 2 cm) supported on glass
wool. The supernatant was layered with hexanes (3 mL), and
subsequent storage at −25 °C resulted in the deposition of blue
needles. The supernatant was decanted, and the crystals were washed
with hexanes (1 mL) and dried in vacuo for 10 min. Yield: 64%, 58
mg. Anal. Calcd for C6H9F6N4NiOP: C, 20.20; H, 2.54; N, 15.70.
1
Found: C, 20.33; H, 2.45; N, 15.36. H NMR (CD2Cl2, 22 °C, 500
MHz): δ 2.40 (3H, s, CH3CN). 19F NMR (CD2Cl2, 22 °C, 470 MHz):
δ −74.66 (JPF = 709 Hz, d). 13C{1H} NMR (CD2Cl2, 22 °C, 125
MHz): δ 129.24 (MeCN) 5.08 (CH3CN). 31P NMR (CD2Cl2, 22 °C,
202 MHz): δ −144.04 (JPF = 710 Hz, sept). IR (Nujol mull, cm−1):
2322 (m, νCN), 2293 (m, νCN), 1842 (s, νNO), 1828 (sh), 1304 (w),
1036 (m), 943 (w), 838 (s), 723 (m), 558 (m). IR (CH2Cl2, cm−1):
1845 (s, νNO). IR (CH3NO2, cm−1): 1842 (s, νNO). IR (CH3CN,
cm−1): 1841 (s, νNO). UV−vis (CH2Cl2, 25 °C, 6.34 mmol): 381 nm
(ε = 21 L·mol−1·cm−1), 617 nm (ε = 99 L·mol−1·cm−1).
[Ni(NO)(NC5H11)3][PF6] (5). To a stirring CH2Cl2 solution (1 mL)
of 1 (114 mg, 0.274 mmol) was added piperidine (77 mg, 0.90 mmol).
After stirring for 5 min, the solution was filtered through a Celite
column (0.5 cm × 2 cm) supported on glass wool. The supernatant
was layered with hexanes (4 mL), and subsequent storage at −25 °C
resulted in the deposition of dark-blue blocks. These were washed with
pentane (5 mL) and dried in vacuo. Yield: 72%, 96 mg. Anal. Calcd for
1
Found: C, 8.74; H, 1.97; N, 12.30. H NMR (CD2Cl2, 22 °C, 500
MHz): δ 4.57 (3H, s, CH3NO2). 19F NMR (CD2Cl2, 22 °C, 470
MHz): δ −76.7 (br d, JPF = 714 Hz). 19F NMR (CD3NO2, 22 °C, 376
Hz): δ −76.7 (d, JPF = 707 Hz). 31P NMR (CD2Cl2, 22 °C, 202 MHz):
δ −141.7 (sept, JPF = 715 Hz). 31P NMR (CD3NO2, 22 °C, 162 Hz): δ
−144.8 (sept, JPF = 706 Hz). 13C{1H} NMR (CD2Cl2, 22 °C, 125
11750
dx.doi.org/10.1021/ic201821t|Inorg. Chem. 2011, 50, 11746−11753

Inorganic Chemistry
Article
Table 3. X-ray Crystallographic Data for Complexes 1·0.16C6H14−7
1·0.16C6H14
3
4·0.33CH2Cl2
6
7
empirical formula
cryst habit, color
cryst size (mm)
cryst syst
C4H11.33F6N4NiO7P
needle, blue
0.60 × 0.20 × 0.20
hexagonal
P6(5)
C6H16F6N3NiO6P
block, dark turquoise
0.50 × 0.30 × 020
monoclinic
P2(1)/c
1605.3(2)
8.4116(7)
12.0802(9)
15.826(2)
90
C6.33H9.66Cl0.66F6N4NiOP
C9H12F6NNiOP
rod, red-orange
0.20 × 0.20 × 0.10
monoclinic
C2/c
C7H8F6NNiO2P
needle, red-orange
0.60 × 0.40 × 0.20
monoclinic
P2(1)/n
1139.6(2)
10.1766(6)
9.5538(6)
12.4940(7)
90
block, blue
0.50 × 0.30 × 0.20
orthorhombic
Pnma
space group
vol (Å3)
2272.4(2)
17.4863(5)
17.4863(5)
8.5815(5)
90
4432.7(6)
21.2921(15)
19.4726(14)
10.6911(8)
90
2606.3(10)
23.003(5)
7.983(2)
16.518(4)
90
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
90
93.449(2)
90
90
120.773(3)
90
110.257(1)
90
γ (deg)
120
90
Z
6
4
4
8
4
fw (g/mol)
density (calcd, Mg/m3)
431.16
429.90
387.68
353.88
341.82
1.880
1.779
1.728
1.804
1.992
abs coeff (mm−1
)
1.491
1.401
1.605
1.674
1.916
F000
1248
872
2296
1424
680
total no. reflns
unique reflns
Rint
19 641
12 843
35 152
10 337
9297
3093
3220
4647
2622
2352
0.0585
0.0754
0.1083
0.1779
0.0715
final R indices [I > 2σ(I)]
R1 = 0.0541, wR2 =
0.1361
R1 = 0.0563, wR2 =
0.1565
R1 = 0.0486, wR2 = 0.1069 R1 = 0.0518, wR2 =
0.1040
R1 = 0.0336, wR2 =
0.0789
largest diff peak and hole
0.911 and −0.362
1.061 and −0.762
0.681 and −0.623
0.550 and −0.497
0.327 and −0.532
(e·Å−3
)
GOF
1.087
0.983
0.973
0.937
1.061
C15H33F6N4NiOP: C, 36.83; H, 6.80; N, 11.45. Found: C, 36.33; H,
6.50; N, 11.05. 1H NMR (CD2Cl2, 22 °C, 500 MHz): δ 1.83 (br s, β/
γ-CH, 18H), 3.47 (br s, α-CH, 12H). NH resonances not observed.
13C NMR (CD2Cl2, 22 °C, 125 MHz): δ 25.90 (γ-CH2), 29.21 (β-
CH2), 53.55 (α-CH2). 19F NMR (CD2Cl2, 22 °C, 470 MHz): δ
−72.79 (d, JPF = 712 Hz). 31P NMR (CD2Cl2, 22 °C, 202 MHz): δ
−144.22 (JPF = 711 Hz, sept). IR (CH2Cl2, cm−1): 1772 (s, νNO). IR
(CH3NO2, cm−1): 1769 (s, νNO). IR (Nujol mull, cm−1): 3278 (m),
2727 (w), 1757 (s, νNO), 1452 (m), 1314 (w), 1271 (m), 1191 (m),
1174 (w), 1116 (w), 1077 (m), 1040 (w), 1024 (w), 1002 (m), 946
(m), 842 (s), 740 (m), 723 (m), 557 (m). UV−vis (0.71 mM, CH2Cl2,
25 °C): 358 nm (ε = 265 L·mol−1·cm−1), 633 nm (ε = 487
L·mol−1·cm−1).
48%, 23 mg. Anal. Calcd for C7H8F6NNiO2P: C, 24.60; H, 2.36; N,
4.10. Found: C, 24.47; H, 2.47; N, 4.06. H NMR (CD2Cl2, 22 °C,
1
500 MHz): δ 4.17 (3H, s, OCH3), 7.10 (1H, t, J = 7 Hz, p-H), 7.17
(2H, d, J = 8 Hz, o-H), 7.46 (2H, t, J = 7 Hz, m-H). 19F NMR
(CD2Cl2, 22 °C, 470 MHz): δ −72.28 (JPF = 711 Hz, d). 13C NMR
(CD2Cl2, 22 °C, 125 MHz): δ 114.23 (m-C), 105.14 (p-C), 100.66 (o-
C), 59.85 (OCH3). The resonance for the ipso-C was not observed.
31P NMR (CD2Cl2, 22 °C, 202 MHz): δ −143.94 (JPF = 710 Hz, sept).
IR (Nujol mull, cm−1): 1918 (vs, νNO), 1629 (w), 1560 (m), 1538
(w), 1485 (w), 1326 (w), 1311 (w), 1274 (m), 1184 (w), 1174(w),
1159 (w), 1151 (w), 1070 (w), 1022 (m), 988 (w), 933 (w), 879 (sh),
834 (s), 789 (m), 740 (w), 723 (w), 558 (m). IR (CH2Cl2, cm−1):
1915 (vs, νNO). UV−vis (3.13 mM, CH2Cl2, 25 °C): 414 nm (ε = 164
L·mol−1·cm−1), 487 nm (ε = 155 L·mol−1·cm−1), 690 nm (ε = 33
L·mol−1·cm−1).
[Ni(η6-1,3,5-Me3C6H3)(NO)][PF6] (6). To a stirring CH2Cl2 (2
mL) solution of 1 (105 mg, 0.251 mmol) was added mesitylene (222
mg, 1.85 mmol). This resulted in a color change to orange-red. After
stirring for 2 min, the solution was filtered through a Celite column
(0.5 cm × 2 cm) supported on glass wool. The filtrate was layered with
hexane (2 mL), and subsequent storage at −25 °C over 24 h resulted
in the deposition of orange-red needles. The crystals were washed with
hexanes (1 mL) and dried in vacuo. Yield: 71%, 63 mg. Anal. Calcd for
C9H12F6NNiOP: C, 30.55; H, 3.42; N, 3.96. Found: C, 30.28; H, 3.43;
N, 3.89. 1H NMR (CD2Cl2, 25 °C, 500 MHz): δ 2.76 (s, ArCH3, 9H),
7.11 (s, ArH, 3H). 13C NMR (CD2Cl2, 25 °C, 125 MHz): δ 22.26
(ArCH3), 112.16 (ArCH), 128.52 (ArCMe). 19F NMR (CD2Cl2, 25 °C,
470 MHz): δ −73.69 (d, JPF = 710 Hz). 31P NMR (CD2Cl2, 22 °C,
212 MHz): δ −142.52 (sept, JPF = 711 Hz). IR (Nujol mull, cm−1):
3067 (w), 1921 (s, νNO), 1557 (m), 1307 (w), 1035 (w), 835 (s), 740
(w), 723 (w), 678 (w), 558 (m). IR (CH2Cl2, cm−1): 1910 (s, νNO).
UV−vis (CH2Cl2, 25 °C, 7.41 mM): 405 nm (ε = 121 L·mol−1·cm−1),
487 nm (ε = 139 L·mol−1·cm−1), 689 nm (ε = 12 L·mol−1·cm−1).
[Ni(η6-C6H5OMe)(NO)][PF6] (7). To a CH2Cl2 solution (2 mL) of
1 (57 mg, 0.14 mmol) was added anisole (42 mg, 0.39 mmol) as a
CH2Cl2 solution (1 mL). This resulted in a color change to orange.
After stirring for 2 min, the solution was filtered through a Celite
column (0.5 cm × 2 cm) supported on glass wool. The filtrate was
layered with pentane (4 mL), and subsequent storage at −25 °C over
24 h resulted in the deposition of orange crystals. These were isolated
by decanting off the solution and washing with hexane (1 mL). Yield:
[Ni(η6-C6H5NMe2)(NO)][PF6] (8). To a CH2Cl2 solution (2 mL)
of 6 (30 mg, 0.085 mmol) was added DMA (10 μL, 0.079 mmol).
After stirring for 2 min, the solution was filtered through a Celite
column (0.5 cm × 2 cm) supported on glass wool. The filtrate was
layered with hexane (2 mL), and subsequent storage at −25 °C over
12 h resulted in the deposition of orange blocks. These were isolated
by decanting off the solution and washing with hexane (1 mL). Yield:
57%, 16 mg. Anal. Calcd for C8H11F6N2NiOP: C, 27.08; H, 3.12; N,
1
7.89. Found: C, 26.76; H, 3.30; N, 7.52. H NMR (CD2Cl2, 22 °C,
500 MHz): δ 3.30 (6H, s, NCH3), 6.64 (2H, br s, o-H), 6.69 (1H, br s,
p-H), 7.21 (2H, br s, m-H). 19F NMR (CD2Cl2, 22 °C, 470 MHz): δ
−72.60 (JPF = 711 Hz, d). 31P NMR (CD2Cl2, 22 °C, 202 MHz): δ
−143.93 (JPF = 710 Hz, sept). IR (Nujol mull, cm−1): 3107 (w), 1892
(s, νNO), 1581 (m), 1513 (w), 1234 (m), 1194 (m), 1073 (w), 1019
(w), 1004 (w), 992 (w), 982 (w), 911 (sh), 837 (s), 808 (sh), 723
(w), 684 (w), 557 (m). IR (CH2Cl2, cm−1): 1894 (s, νNO). UV−vis
(0.29 mM, 25 °C, CH2Cl2): 445 nm (ε = 847 L·mol−1·cm−1), 700 nm
(ε = 103 L·mol−1·cm−1).
[Ni(NO)(C6H5NMe2)3][PF6] (9). To a CH2Cl2 (4 mL) solution of
6 (35 mg, 0.10 mmol) was added DMA (0.31 mL, 2.45 mmol). This
resulted in the formation of a dark-green solution. The solution IR
spectrum exhibited two νNO features at 1895 and 1840 cm−1,
assignable to complexes 8 and 9, respectively (see Figure S67 in the
Supporting Information). The solution was layered with hexane (4
11751
dx.doi.org/10.1021/ic201821t|Inorg. Chem. 2011, 50, 11746−11753

Inorganic Chemistry
Article
mL), and subsequent storage at −25 °C over 12 h resulted in the
deposition of a dark-green oil. Upon standing at −25 °C for 3 weeks,
this oil converted into an orange crystalline solid, which was identified
as complex 8.
(8) Arikawa, Y.; Asayama, T.; Itatani, K.; Onishi, M. J. Am. Chem. Soc.
2008, 130, 10508−10509.
(9) Lee, J.; Chen, L.; West, A. H.; Richter-Addo, G. B. Chem. Rev.
2002, 102, 1019−1066.
X-ray Crystallography. Data for 1·0.16C6H14, 3, 4·0.33CH2Cl2,
6, and 7 were collected on a Bruker 3-axis platform diffractometer
equipped with a SMART-1000 CCD detector using a graphite
monochromator with a Mo Kα X-ray source (α = 0.710 73 Å). The
crystals were mounted on a glass fiber under Paratone-N oil, and all
data were collected at 150(2) K using an Oxford nitrogen gas
cryostream system. A hemisphere of data was collected using ω scans
with 0.3° frame widths. Frame exposures of 12, 20, 15, 15, and 20 s
were used for complexes 1·0.16C6H14, 3, 4·0.33CH2Cl2, 6, and 7,
respectively. Data collection and cell parameter determination were
conducted using the SMART program.68 Integration of the data frames
and final cell parameter refinement were performed using SAINT
software.69 Absorption correction of the data was carried out
empirically based on reflection ψ scans. Subsequent calculations
were carried out using SHELXTL.70 Structure determination was done
using direct or Patterson methods and difference Fourier techniques.
All H-atom positions were idealized and rode on the atom of
attachment. Structure solution, refinement, graphics, and creation of
publication materials were performed using SHELXTL.
Data collection for 2 was performed on Mo and Cu X-ray sources;
however, the diffraction data were of poor quality in both cases.
Connectivity of the atoms in complex 2 was confirmed, but anomalous
Q peaks in the lattice and significant disorder in the PF6 anions
resulted in unsatisfactory R1 and wR2 values. The unit cell parameters
for complex 2 are a = 7.9665(2) Å, b = 45.7424(10) Å, c = 12.0144(3)
Å, α = 90.00°, β = 105.040(1)°, and γ = 90.00°.
The PF6 anion in complex 3 possessed significant rotational
disorder. It was disordered over two orientations in a 50:50 ratio. The
P−F bond distances were fixed at 1.57(5) Å, while the closest
neighboring F-atom distances were fixed at 1.20(5) Å. The FLAT
command was also performed on P1, F1A, F1B, F2A, F2B, F4A, F4B,
F6A, and F6B. In addition, the PF6 anion in complex 6 possessed
rotational disorder around one axis in a 72:28 ratio. A summary of
relevant crystallographic data is presented in Table 3.
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ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic data in CIF format, additional exper-
imental details, and NMR and IR spectral data. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: hayton@chem.ucsb.edu.
■
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ACKNOWLEDGMENTS
We thank the University of California, Santa Barbara, for
financial support of this work.
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