Reactivity studies of a pseudo three-coordinate vanadium(II) complex: Synthesis of terminal oxo and sulfido complexes of vanadium(IV) and S-S and Se-Se reductive bond cleavage reactions

Article abstract of DOI:10.1016/j.ica.2010.11.040

Terminal oxo and sulfido complexes in the form of (nacnac)VE(Ntol ₂) (nacnac = [ArNC(CH₃)]₂CH^-, Ar = 2,6-(CHMe₂)₂C₆H₃, Ntol₂ = ^-N(C₆H₄-4-Me), E = O (1), S (2)) were isolated from treatment of the masked three-coordinate vanadium(II) complex, (nacnac)V(Ntol₂), with C₅H₅NO and S ₈, respectively. Both vanadium(IV) species, 1 and 2, have been characterized by room temperature X-band EPR spectroscopic studies, and in the case of complex 1, a single crystal molecular structure confirmed the presence of a terminal oxo moiety. Moreover, reaction of (nacnac)V(Ntol₂) with diphenyl-disulfide and diphenyl-diselenide results in the reductive cleavage of these compounds to produce the vanadium(III) complexes (nacnac)V(XPh)(Ntol ₂) (X = S, (3), Se (4)). A molecular structure of the phenylsulfide complex, 3, confirmed formation of the d² complex resulting from reductive cleavage of the S-S bond.

Full text of DOI:10.1016/j.ica.2010.11.040

Inorganica Chimica Acta 369 (2011) 215–222
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Inorganica Chimica Acta
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Reactivity studies of a pseudo three-coordinate vanadium(II) complex: Synthesis
of terminal oxo and sulfido complexes of vanadium(IV) and S–S and Se–Se
reductive bond cleavage reactions
⇑
Ba L. Tran, Chun-Hsing Chen, Daniel J. Mindiola
Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, IN 47405, United States
a r t i c l e i n f o
a b s t r a c t
Terminal oxo and sulfido complexes in the form of (nacnac)V@E(Ntol2) (nacnac = [ArNC(CH3)]2CHꢀ,
Ar = 2,6-(CHMe2)2C6H3, Ntol2
Article history:
Available online 10 December 2010
=
ꢀN(C6H4-4-Me), E = O (1), S (2)) were isolated from treatment of the
masked three-coordinate vanadium(II) complex, (nacnac)V(Ntol2), with C5H5NO and S8, respectively.
Both vanadium(IV) species, 1 and 2, have been characterized by room temperature X-band EPR spectro-
scopic studies, and in the case of complex 1, a single crystal molecular structure confirmed the presence
of a terminal oxo moiety. Moreover, reaction of (nacnac)V(Ntol2) with diphenyl–disulfide and diphenyl–
diselenide results in the reductive cleavage of these compounds to produce the vanadium(III) complexes
(nacnac)V(XPh)(Ntol2) (X = S, (3), Se (4)). A molecular structure of the phenylsulfide complex, 3, con-
firmed formation of the d2 complex resulting from reductive cleavage of the S–S bond.
Ó 2010 Elsevier B.V. All rights reserved.
Dedicated to Professor Robert G. Bergman
on the occasion of his 70th birthday. You are
an excellent scientist and an inspiration to
many for truly blending together physical
organic, organometallic as well as classical
coordination chemistry.
Keywords:
Vanadium
Oxo
Sulfide
Redox chemistry
1. Introduction
multiple bonds, but recent findings revealed that the nacnac ancil-
lary support is also a robust enough ligand to stabilize low-valent
Metal complexes capable of multi-electron redox processes are
of interest for their versatile roles in important transformations for
both organic and inorganic chemistry [1]. The ability of metals to
mediate multi-electron chemistry is generally confined to the
heavier 4d and 5d congeners, given their propensity to populate
mid- to high-valent states. However, in recent years, access to
low-valent and low-coordinate precursors having 3d metals
anchored by the nacnac system (nacnac = [ArNC(CH3)]2CHꢀ,
Ar = 2,6-(CHMe2)2C6H3) has led to the isolation of reactive moieties
such as imido [2], oxo [3], carbene [4], alkylidyne [5], nitride [6],
and inverted sandwiches [7]. Moreover, reaction chemistry involv-
ing low-valent or masked forms of early 3d metals remain
relatively unexplored with the exception of the classical cyclopen-
tadienyl [8] and sterically encumbering aryloxide [9] based sys-
tems. Part of the challenge in preparing low-valent early metal
complexes is the dearth of an ancillary ligand capable of stabilizing
these high energy species, especially in low-coordinate environ-
ments. Our interest in vanadium chemistry anchored by the nacnac
scaffold has been the pursuit of Schrock-type vanadium(V)–carbon
vanadium(I) [7b,d] and vanadium(II) [10] complexes having rich
multi-electron chemistry. Furthermore, the nacnac ligand has been
recently employed to stabilize niobium complexes that exhibit
interesting reactivity by taking advantage of the Nb(III/V) redox
couple [11].
Terminal oxovanadium or sulfido complexes are known and
isolated as vanadium(V) species by exploiting the more common
V(III/V) redox couple [12]. However, access to vanadyl type oxos
from the V(II/IV) redox couple is not common, given the propensity
of the transient vanadyl radical to dimerize or oligomerize [13].
Although oxidation with S-atom transfer reagents is the more com-
mon route to the known terminal vanadium-sulfidos, N- for S-
atom exchange has been observed in a anionic vanadium nitride
by treatment of CS2 to form the corresponding vanadium(V) sulfide
and NaNCS byproduct [14]. Terminal metal oxos can be also readily
converted to their sulfido analog via exchange reactions with B2S3,
P4S10 and TMS2S, respectively, by taking advantage of the thermo-
dynamically strong X–O bonds strength (X = B, P, Si) [15]. Although
terminal vanadium(IV)-oxyl complexes are known, these are pre-
pared via one-electron reduction of the corresponding vana-
dium(V)-oxo precursor or generated directly from suitalble
starting materials like O@V(acac)2 [16]. However formation of a
vanadium-oxyl via an oxidation (O-atom transfer reaction)
⇑
Corresponding author.
E-mail address: mindiola@indiana.edu (D.J. Mindiola).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.11.040

216
B.L. Tran et al. / Inorganica Chimica Acta 369 (2011) 215–222
involving the vanadium(II/IV) couple, to our knowledge, has not
been reported [16]. For us, this strategy is possible given the recent
isolation of a reactive pseudo three-coordinate vanadium(II) syn-
thon, (nacnac)V(Ntol2) [10], in multigram quantities, which allow
for the exploration of the rich redox chemistry of a low-valent
and low-coordinate vanadium center. Hitherto, we report two
and one-electron chemical reactions of (nacnac)V(Ntol2) to form
oxo or sulfide complexes of the type (nacnac)V@E(Ntol2) (E = O
(1), S (2)), and phenylsulfide and phenylselenide complexes such
as (nacnac)V(XPh)(Ntol2) (X = S (3), Se (4)), respectively. Com-
plexes 1–4 have been characterized using solution EPR spectros-
copy, magnetic measurements by Evans, FT-IR spectroscopy,
combustion analysis, high resolution mass spectrometry, and crys-
tallography when possible.
for optimal steric protection. It has been well documented that
the nacnac scaffold is quite versatile in alternating between differ-
ent hapticities [19]; however, in vanadium chemistry we have only
observed
g
2-coordination in all our complexes prepared thus far.
Despite conserving the g2 ligation, the nacnac orients itself by
placing the vanadium center far below the plane defined by the
NCCCN ring in order to avoid steric clashing of the –Ntol2 groups
with the aryl substituents on the nacnac nitrogens. The facile syn-
thesis and bulk preparation of (nacnac)VCl(Ntol2) on a multi-gram
scale provides a convenient entry to vanadium(II) since one-elec-
tron reduction of (nacnac)VCl(Ntol2) with 0.5% Na/Hg or KC8 read-
ily affords the masked three-coordinate complex (nacnac)V(Ntol2)
(Scheme 1) [10]. Using Na/Hg as opposed to the stronger reductant
KC8, results in cleaner conversion to compound (nacnac)V(Ntol2),
which is isolated as a dark red crystalline material from a saturated
solution of n-pentane cooled to ꢀ37 °C over 24 h (50% yield). How-
ever, formation of (nacnac)V(Ntol2) is much slower (8 h in ben-
zene), and attempts to use a more polar solvent such as THF
result in formation of multiple degradation products. The geomet-
rical and electronic structure of (nacnac)V(Ntol2) has been
reported in detail elsewhere, and data is consistent with a high-
spin (S = 3/2) complex, where the ipso and ortho positions of one
2. Results and discussions
2.1. Synthesis of (nacnac)V(Ntol2) from (nacnac)VCl(Ntol2) and
molecular structure of (nacnac)VCl(Ntol2)
Stoichiometric salt elimination reaction of [Li(Ntol2)]n and
(nacnac)VCl2 [17] in benzene and extraction of the product from
hexanes or n-pentane allowed for isolation of a high spin S = 1
(nacnac)VCl(Ntol2) [6] complex, in 70% yield as a crystalline brown
solid. The molecular structure of (nacnac)VCl(Ntol2) is shown in
Fig. 1. The vanadium center adopts a distorted tetrahedral environ-
ment having angles N(1)–V(1)–N(2) = 118.03(12)° and N(1)–V(1)–
N(3) = 112.31(12)°. The vanadium–nitrogen bond distances are
typical for single bonds ranging from 1.912(3) to 2.005(3) Å
[6,10] and the V(1)–Cl(1) distance is also at a typical distance of
2.2305(13) Å [12]. (nacnac)VCl(Ntol2) is reminiscent of the nitro-
gen rich and isoelectronic complex ClMo(N[tBu]Ar) (Ar = 3,
5-Me2C6H3) [18]. In the molecular structure of complex (nac-
nac)VCl(Ntol2), the two 2,6-diisopropyl-aryl groups on the nacnac
ligand are aligned vertically with respect to the vanadium center
of the tolyl residues interacts in a
g
2-fashion with the electron rich
vanadium(II) center when judged from the solid state structure
(Scheme 1) [10].
2.2. Monomeric (nacnac)V@E(Ntol2) (E = O, S) via O- and S-atom
transfer to (nacnac)V(Ntol2)
Reaction of (nacnac)V(Ntol2) with pyridine N-oxide results in
rapid transformation to (nacnac)V@O(Ntol2) (1), which was iso-
lated in 58% yield as dark red crystalline material from a concen-
trated n-pentane solution cooled to ꢀ37 °C (Scheme 1). The fact
that pyridine N-oxide can oxidize the V(II) fragment to 1 implies
that the bond dissociation enthalpy for the reverse reaction,
1 ? [O] + (nacnac)V(Ntol2), must exceed ꢁ72 kcal/mol [20,21].
Identification of a terminal V@O moiety was inferred by FT-IR
spectroscopy (stretch at 985 cmꢀ1), which is expected for group
5 terminal metal-oxos (Fig. 2) [12]. Room temperature solution
magnetic susceptibility measurement of 1 by the method of Evans
(leff = 1.92 lB) is consistent with a vanadium(IV) metal center
(S = 1/2). The V(IV) oxidation state of 1 was further corroborated
by X-band EPR spectroscopy (giso = 1.97), recorded at room tem-
perature in toluene solution, and which gave rise to the expected
eight line pattern resulting from hyperfine coupling of the
unpaired electron to the 51V center (I = 7/2; 99.6%, Aiso = 45.5 ꢂ
10ꢀ4 cmꢀ1, Fig. 2). Comparison of this data to the X-band EPR spec-
tral data of the five coordinate L2V@O (L = quin = 2-methyl-8-
quinolinolatoꢀ, or L = acacꢀ, also collected in toluene at 77 K, for
L = quin: gavg = 1.99, Aavg = 88.5 ꢂ 10ꢀ4 cmꢀ1) [23] suggests that
the unpaired electron in complex 1 is significantly less metal-cen-
tric (by being delocalized about the other ligands), despite the low-
er-coordination environment. In fact, even a higher Aavg value was
observed for (acac)V@O (gavg = 1.97, Aavg = 100.2 ꢂ 10ꢀ4 cmꢀ1
)
[23]. Moreover, from comparison of 1 to its related analog (nac-
nac)V@NAd(Ntol)2 (giso = 1.97; Aiso = 24.7 ꢂ 10ꢀ4 cmꢀ1), it is appar-
ent that the unpaired electron in these environments have
unusually low metal-centric character and greater degree of cova-
lency than one would have anticipated (vide infra). The degree of
aggregation and structural connectivity of 1 was unambiguously
confirmed by single crystal X-ray diffraction studies while the for-
mulation has been corroborated by elemental combustion analysis.
Shown in Fig. 3 is the solid state structure 1 which confirmed the
presence of a terminal vanadium(IV)-oxo functionality with a short
V–O bond distance of 1.597(2) Å. The V@O distance is comparable
to that observed for the solid state structure of VO(acac)2 as well as
Fig. 1. The molecular structures of (nacnac)VCl(Ntol2) with thermal ellipsoids at
the 50% probability level. Hydrogen atoms have been excluded for clarity. Selected
bond lengths (Å) and angles (°): V(1)–N(1), 1.982(3); V(1)–N(2), 2.005(3); V(1)–
N(3), 1.912(3); V(1)–Cl(1), 2.2305(13); N(1)–V(1)–N(2), 92.23(11); N(1)–V(1)–N(3),
112.31(12); N(1)–V(1)–N(3), 118.03(12); N(1)–V(1)–Cl(1), 102.61(8); N(2)–V(1)–
Cl(1), 119.76(9); N(3)–V(1)–Cl(1), 110.73(9).

B.L. Tran et al. / Inorganica Chimica Acta 369 (2011) 215–222
217
iPr
Cl
V
N
N
N
iPr
Ar
0.5% Na/Hg
C6H6
-NaCl
O
N
iPr
iPr
O
V
iPr
1/2 Ph2X2
C6H6
X
V
hexanes
N
N
N
N
N
N
N
V
N
iPr
N
-
iPr
N
Ar
1
iPr
Ar
Ar
3
X = S (3), Se (4)
1/8 S8
C6H6
iPr
S
V
N
N
N
iPr
Ar
2
Scheme 1. Synthesis of vanadium complexes 1–4 from precursor (nacnac)V(Ntol2) involving one electron or two electron processes.
other structurally characterized oxo-vanadium complexes [24].
The nitrogen-vanadium bond distances are similar to the related
tetrahedral vanadium complex, (nacnac)VCl(Ntol2). For example,
the vanadium-nitrogen bond distance in the anilide ligand in (nac-
nac)VCl(Ntol2) (1.915(3) Å) is nearly identical to the distance of
1.912(3) Å observed in 1. The metal center in complex 1 is confined
to a highly distorted tetrahedral geometry, due to the angles
deviating from the ideal 109.5° (i.e. N(3)–V–O(1) = 115.42(12)°).
recrystallization from cold n-pentane at ꢀ37 °C. Room temperature
X-Band EPR spectroscopic recording of 2, in toluene, reveals the
formation of a d1 vanadium species with a giso = 1.97 and isotropic
hyperfine coupling to vanadium (I = 7/2, 99.76%), Aiso = 59.4 ꢂ
10ꢀ4 cmꢀ1
. The room temperature X-band EPR spectroscopic
parameter compares well with the reported terminal vanadium-
sulfido anion complex [(Ph4P)Na][VS(edt)2] (edt2ꢀ = ethane-1,2,-
dithiolate) with giso = 1.97 and Aiso = 64.5 ꢂ 10ꢀ4 cmꢀ1 recorded
in diluted solution of DMF and acetone [15a]. Based on electroneg-
ativity differences, one would anticipate the isotropic coupling
constant to vanadium to decrease from 1 to 2, because of the antic-
ipated greater covalency of the V@S bond (and polarization) when
compared to the more ionic V@O bond. However, we observe the
opposite trend when judging from the Aiso values obtained from
the isotropic X-band EPR spectra of 1 and 2, therfore tantalizingly
suggesting an opposite trend. As a result, one should expect the
electrostatic character of the V@E (E = O oar S) to increase when
moving down the chalcogenide series. In addition, the room
Complex
1 is isoelectronic to the nitrogen rich species,
(Ar[tBu]N)3Mo@O (Ar = 3,5-Me2C6H3) reported by Cummins et al.,
via O-atom transfer reactions to the three-coordinate fragment
(Ar[tBu]N)3Mo [21,22].
In stark contrast to terminal vanadium(IV)-oxo species, well-
defined terminal sulfido analogs are scarce [15a,b]. Therefore,
utilizing a similar approach for the synthesis of 1, we sought after
a
terminal sulfido moiety. Accordingly, treatment of
(nacnac)V(Ntol2) with elemental S8 (1/8 equiv) produced dark
red (nacnac)V@S(Ntol2) (2), which was isolated in 40% yield after

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B.L. Tran et al. / Inorganica Chimica Acta 369 (2011) 215–222
Fig. 3. The molecular structures of (nacnac)V@O(Ntol2) (1) with thermal ellipsoids
at the 50% probability level. Hydrogen atoms have been excluded for clarity.
Selected bond lengths (Å) and angles (°): V(1)–O(1), 1.597(2); V(1)–N(1), 2.011(3);
V(1)–N(2), 2.010(3); V(1)–N(3), 1.915(3); N(1)–V–O(1), 111.09(12); N(2)–V–O(1),
104.17(12); N(1)–V–N(2), 91.54(11);N(1)–V–N(3), 112.30(12); N(3)–V–O(1),
115.42(12).
diagram in Fig. 4 displays a vanadium center adopting a distorted
tetrahedral geometry with typical average nitrogen–vanadium
bond distances of 1.9 Å and with a V(1)–S(1) bond distance at
2.3087(13) Å, thus consistent with a single metal–sulfur bond.
Not surprisingly, the phenylthiolate ligand is coordinated to the
Fig. 2. Assignment of the terminal V@O stretch by FT-IR, and solution X-band EPR
spectrum of complex 1.
vanadium at
a bent angle of 109.94(14)° (V(1)–S(1)–C(44)).
Analogously, complex (nacnac)V(SePh)(Ntol2) (4) can be also pro-
duced from the reductive cleavage of diphenyl–diselenide, by
(nacnac)V(Ntol2), in 41% isolated yield. As noted before, a similar
reaction has been observed with the isoelectronic complex
(Ar[tBu]N)3Mo and 0.5 equiv of PhSeSePh and to produce
temperature solution magnetic susceptibility measurement of 2 by
the method of Evans (leff = 1.90 lB), indisputably suggests the
presence of a vanadium(IV) center (S = 1/2). However, the identity
of the sulfido moiety remains uncertain since the presence of an
(Ar[tBu]N)3Mo(SePh) [21]. 1H NMR spectroscopic data of
4
g
2-disulfido could also leads to formation of a vanadium(IV) com-
collected at room temperature revealed broad and diagnostic
resonances consistent with paramagnetic vanadium center.
Moreover, room temperature magnetic susceptibility measure-
plex. Although we have been unable to obtain a single crystal suit-
able for X-ray diffraction analysis, subjection of compound 2 for
HRMS-CI revealed the presence of ion having m/z value of
697.9609, which is consistent with the formulation (nacnac)V
@S(Ntol2).
ment by the method of Evans revealed leff = 2.87 lB and thus sup-
porting the presence of a high spin S = 1 vanadium(III) center.
Although we have been unable to confirm the proposed connectiv-
ity of 4 by single crystal X-ray diffraction studies, combustion data
analysis were in accord with the formulation C49H60N3SeV.
2.3. Synthesis of monomeric (nacnac)V(Ntol2)(XPh) (X = S, Se)
complexes via one electron oxidation at vanadium
Treatment of diphenyl–disulfide with (nacnac)V(Ntol2) resulted
in the reductive cleavage of the sulfur–sulfur bond to render for-
mation of the vanadium(III) complex (nacnac)V(SPh)(Ntol2) (3).
Such reactivity is reminiscent of nickel [25] or molybdenum [21]
mediated reductive bond cleavage of disulfide and/or diselenide
substrates. Compound 3 is isolated in 43% yield after recrystalliza-
tion from a concentrated n-pentane solution cooled to ꢀ37 °C. An
3. Conclusions
In this work we have demonstrated that terminal chalcogenides
of the type (nacnac)V@E(Ntol2) (E = O or S) can be readily prepared
from the two-electron oxidation of the pseudo three-coordinate
vanadium(II) complex (nacnac)V(Ntol2). The higher isotropic
hyperfine coupling constant (based from X-band EPR spectros-
copy) observed for (nacnac)V@S(Ntol2) versus (nacnac)V@O(Ntol2)
arguably suggests that the latter could be a better atom-transfer
reagent ([O] source in this case) [26]. We anticipate a hypothetical
(nacnac)V@Se(Ntol2) to follow a similar trend to the sulfide com-
plex given the similarities of electronegativities on the Pauling
scale between S (2.55) and Se (2.55). In addition to preparing
Evans magnetic susceptibility measurement (leff = 2.75 lB) is in
accord with a high-spin vanadium(III) center (S = 1). Single crystal
X-ray diffraction studies of compound 3 (single crystal grown from
a saturated n-pentane solution at ꢀ37 °C), unambiguously con-
firmed the proposed molecular connectivity and formulation has
been corroborated by elemental combustion analysis. The ORTEP

B.L. Tran et al. / Inorganica Chimica Acta 369 (2011) 215–222
219
Fig. 4. The molecular structures of (nacnac)V(SPh)(Ntol2) (3) with thermal ellipsoids at the 50% probability level. Hydrogen atoms have been excluded for clarity. Selected
bond lengths (Å) and angles (°): V(1)–N(1), 1.981(3); V(1)–N(2), 1.998(3); V(1)–N(3), 1.962(3); V(1)–S(1), 2.3087(13); N(1)–V(1)–N(2), 92.78(12); N(1)–V(1)–N(3),
118.80(12); N(1)–V(1)–S(1), 111.29(9); N(2)–V(1)–S(1), 100.19(9); N(3)–V(1)–S(1), 113.92(10).
terminal chalcogenides, one-electron oxidation of (nacnac)V(Ntol2)
with PhXXPh (X = S or Se) results in formation of the vanadium(III)
complexes (nacnac)V(XPh)(Ntol2), as opposed to the oxidative-
addition product (nacnac)V(XPh)2(Ntol2), presumably due to
sterics. Current efforts will be devoted to the redox chemistry of
complexes (nacnac)V@E(Ntol2), especially in the context of
O- and S-atom transfer chemistry.
performed on the Thermo Nicolet 6700 FT-IR equipped with soft-
ware under PC control. The synthesis of (nacnac)VCl(Ntol2) [6]
and (nacnac)V(Ntol2) [10] were prepared according to publish
protocol.
4.2. Synthesis of (nacnac)V@O(Ntol2) (1)
At room temperature, to a 20 mL scintillation vial containing
complex (nacnac)V(Ntol2) (156 mg, 0.23 mmol) dissolved in 5 mL
of hexanes was added a suspension of pyridine-oxide (24.0 mg,
0.25 mmol) in 5 mL of hexanes. The reaction mixture rapidly
turned to a different shade of red. The reaction was allowed to pro-
ceed for an additional 3 h. All volatiles were removed to give red-
dish solids, which were dissolved in n-pentane and the solution
filtered through a medium porosity frit containing Celite. The fil-
trate volume was reduced to 3 mL and storage of the filtrate at
ꢀ37 °C overnight rendered precipitation of a red crystalline product.
Yield = 58% (91 mg, 0.13 mmol). 1H NMR (25 °C, 300 MHz, C6D6):
4. Experimental section
4.1. General considerations
Unless otherwise stated, all operations were performed in an M.
Braun Lab Master double-dry box under an atmosphere of purified
nitrogen or using high vacuum standard Schlenk techniques under
a nitrogen atmosphere. Anhydrous n-hexanes, n-pentane, toluene,
and benzene were purchased from Aldrich in sure-sealed reser-
voirs (18L) and dried by passage through two columns of activated
alumina and a Q-5 column. Diethyl ether and CH2Cl2 were dried by
passage through a column of activated alumina. THF was distilled,
under nitrogen, from purple sodium benzophenone ketyl and
stored under sodium metal. Distilled THF was transferred under
vacuum into bombs before being pumped into a dry box. C6D6
was purchased from Cambridge Isotope Laboratory (CIL), degassed
and vacuum transferred to 4 Å molecular sieves. Celite, alumina,
and 4 Å molecular sieves were activated under vacuum overnight
at 200 °C. 1H and 13C NMR spectra were recorded on Varian 300
and 400 MHz NMR spectrometer. 1H and 13C NMR are reported
with reference to solvent resonances of C6D6 at 7.16 ppm and
128.0 ppm, respectively. X-ray diffraction data were collected on
a SMART6000 (Bruker) system under a stream of N2 (g) at 150 K.
Room temperature X-band EPR spectra were recorded in diluted
toluene solution on a Bruker EMX spectrometer under PC control.
EPR data acquisition was performed using an integrated Bruker
WIN-EPR software package. Elemental analysis was performed at
Indiana University, Bloomington. Infrared spectroscopy was
d
11.09
4043 Hz), 4.29,
1/2 = 330 Hz), 0.39
ꢀ1.96 (
1/2 = 3320 Hz). FT-IR (KBr, Nujol, cmꢀ1): 985 (
eff = 1.92 lB (25 °C). Anal. Calc. for C43H55N3OV: C, 75.85; H,
(
D
m
1/2 = 2206 Hz), 7.57
1/2 = 3935 Hz), 1.70
1/2 = 26 Hz), ꢀ0.88
(
D
m
1/2 = 216 Hz), 5.41
1/2 = 443 Hz), 1.22
1/2 = 2457 Hz),
V@O).
(Dm1/2 =
(
D
m
(Dm
(D
m
(
D
m
(Dm
D
m
m
l
8.14; N, 6.17. Found: C, 75.75; H, 8.35; N, 6.30%.
4.3. Synthesis of (nacnac)V@S(Ntol2) (2)
At room temperature, to a 20 mL scintillation vial containing
complex (nacnac)V(Ntol2) (150 mg, 0.22 mmol) dissolved in 5 mL
of benzene was added 1/8 S8 (8 mg, 0.27 mmol) in 3 mL of benzene.
The reaction mixture rapidly turned to a different shade of red. The
reaction was allowed to proceed for an additional 2 h. All volatiles
were removed to give brown solids, which were dissolved in 5 mL
of n-pentane and the solution filtered through a medium porosity
frit containing Celite. The subsequent filtrate was reduced to 3 mL
and stored at ꢀ37 °C overnight rendered red crystalline product.

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B.L. Tran et al. / Inorganica Chimica Acta 369 (2011) 215–222
Yield = 40%. 1H NMR (25 °C, 400 MHz, C6D6): d 10.87 (
5474 Hz), 8.66 1/2 = 4629 Hz), 7.77 1/2 = 536 Hz), 5.44
1/2 = 2235 Hz), 5.02 1/2 = 78 Hz), 3.66 1/2 = 1180 Hz),
3.00 ( 1/2 = 1224 Hz), 1.58 ( 1/2 = 405 Hz), 1.23 ( 1/2 = 41 Hz),
ꢀ0.94 1/2 = 22 Hz), ꢀ1.98
5474 Hz).
D
m1/2
=
tane was added dropwise PhSe–SePh (47.0 mg, 0.15 mmol) in 3 mL
of n-pentane. The reaction mixture rapidly turned brown from the
original deep red. The reaction was allowed to proceed for an addi-
tional 2 h. The n-pentane solution was filtered through a medium
porosity frit containing Celite. Reduction of the volume of the fil-
trate to 3 mL and storing of the solution to ꢀ37 °C overnight pro-
(
D
m
(Dm
(D
m
(
D
m
(Dm
D
m
D
m
Dm
(D
m
l
1/2 = 4774 Hz), ꢀ.45
(D
m
(Dm1/2 =
eff = 1.80 lB (25 °C). MS-CI for C43H55N3SV: Theoretical
[M]+: 697.9245; Experimental [M]+: 697.9609.
duced
(25 °C, 400 MHz, C6D6): d 15.64 (
483 Hz), 8.10 ( 1/2 = 195 Hz), 5.43 (overlap), 4.31 (overlap), 3.64
1/2 = 1128 Hz), 3.25 1/2 = 535 Hz), 2.99 1/2 = 584 Hz),
ꢀ0.15 1/2 = 70 Hz), ꢀ0.93 1/2 = 444 Hz), ꢀ1.98
537 Hz). eff = 2.87 lB (25 °C). Anal. Calc. for C49H60N3SeV: C,
a
brownish crystalline product. Yield = 41%. 1H NMR
Dm1/2 = 189 Hz), 10.42 (Dm1/2 =
D
m
4.4. Synthesis of (nacnac)V(SPh)(Ntol2) (3)
(D
m
(
D
m
(Dm
(D
m
(D
m
(Dm1/2 =
At room temperature, to a 20 mL scintillation vial containing
complex (nacnac)V(Ntol2) (103 mg, 0.15 mmol) in 5 mL of n-pen-
tane was added dropwise PhSSPh (35 mg, 0.15 mmol) in 5 mL of
n-pentane. The reaction mixture rapidly turned yellow–brown
from the original deep red. The reaction was allowed to proceed
for an additional 2 h. The n-pentane solution was filtered through
a medium porosity frit containing Celite. The solvent volume of
the filtrate was reduced to 4 mL and stored at ꢀ37 °C overnight
rendered brown crystalline product. Yield = 43% (50 mg,
l
71.69; H, 7.37; N, 5.12. Found: C, 72.00; H, 7.25; N, 5.32%.
4.6. Crystallographic data
4.6.1. Data collection, structure solution and refinement for (nacnac)
VCl(Ntol2)
Due to the small size of the crystal, the diffraction data were ac-
quired with synchrotron X-ray radiation at ChemMatCARS beam-
line, Advanced Photon Source, Argonne National Laboratory. The
data collection was carried out using synchrotron radiation
(k = 0.41328 Å, diamond 111 monochromator) with a frame time
of 1 s and a detector distance of 6.0 cm. Two major sections of
frames were collected with 0.5° stepsize in / and a detector posi-
tion of ꢀ10° in 2h. Data to a resolution of 0.8 Å were considered in
the reduction. Final cell constants were calculated from the xyz
centroids of 1495 strong reflections from the actual data collection
after integration (SAINT) [27]. The intensity data were corrected for
absorption (SADABS) [28]. Please refer to Table 1 for additional crys-
tal and refinement information.
0.06 mmol). 1H NMR (25 °C, 400 MHz, C6D6): d 16.95 (
151 Hz), 10.20 ( 1/2 = 134 Hz), 9.02 ( 1/2 = 61 Hz), 5.31 (broad
overlapping shoulder), 5.24 1/2 = 117 Hz), 3.64
1116 Hz), 3.25 1/2 = 528 Hz), 2.98
1/2 = 638 Hz), ꢀ0.95
1/2 = 74 Hz). eff = 2.75 lB (25 °C).
D
m1/2
=
D
m
Dm
(
D
m
(
D
m1/2
=
(
D
m
(Dm
(
D
m
1/2 = 2900 Hz), ꢀ2.11 (
D
m
l
Anal. Calc. for C49H60N3SV: C, 76.03; H, 7.81; N, 5.43. Found: C,
76.33; H, 8.00; N, 5.66%.
4.5. Synthesis of (nacnac)V(SePh)(Ntol2) (4)
At room temperature, to a 20 mL scintillation vial containing
dissolved (nacnac)V(Ntol2) (100 mg, 0.15 mmol) in 5 mL of n-pen-
Table 1
Crystallographic data and parameters for (nacnac)VCl(Ntol2), (nacnac)V@O(Ntol2) (1), and (nacnac)V(SPh)(Ntol2) (3).
(nacnac)VCl(Ntol2)
43H55N3ClV
700.29
70(2)
1
3
Molecular formula
Formula weight
Temperature (K)
Crystal dimensions (mm3)
Space group
Cell constants
a (Å)
C
C43H55N3OV
680.87
150(2)
C49H60N3SV
774.04
150(2)
0.10 ꢂ 0.03 ꢂ 0.02
0.44 ꢂ 0.15 ꢂ 0.10
0.46 ꢂ 0.10 ꢂ 0.07
P21/c
P121/c1
P121/n1
10.6917(10)
22.066(2)
16.6730(16)
90
10.7474(19)
22.097(4)
16.621(3)
90
12.061(5)
17.969(7)
21.410(8)
90
b (Å)
c (Å)
a
(°)
b (°)
99.957(2)
90
98.989(3)
90
92.978(7)
90
c
(°)
Z
4
4
4
V (Å3)
3874.3(6)
1.201
0.191
3898.7(13)
1.160
0.289
4402(3)
1.168
0.308
Dcal (Mg/m3)
Absorption coefficient (mmꢀ1
F(0 0 0)
)
1496
1460
1656
Radiation
Synchrotron radiation
(k = 0.41328 Å)
ꢀ12 < h < 14,
ꢀ29 < k < 29,
ꢀ22 < l < 22
0.90–15.99
89 616
Mo K
a
Mo Ka
(k = 0.71073 Å)
ꢀ12 < h < 12,
ꢀ25 < k < 25,
ꢀ19 < l < 18
1.545–24.101
24 230
(k = 0.71073 Å)
ꢀ12 < h < 10,
ꢀ16 < k < 16,
ꢀ21 < l < 21
1.527–20.837
18 244
h,k,l ranges collected
h range (°)
Reflections collected
Independent reflections
9485
6119
4568
[R(int) = 0.0920]
7009
[R(int) = 0.095]
3703
[R(int) = 0.049]
3415
Observed reflections
Data/parameter ratio
Refinement method
R(F)a
21.31
14.13
9.50
full-matrix least-squares of F2
0.1104
full-matrix least-squares of F2
0.0556
full-matrix least-squares of F2
0.0617
Rw(F2)b
0.2287
1.098
2.998 and ꢀ1.847
0.1214
0.9842
0.70 and ꢀ0.63
0.1185
0.9993
0.60 and ꢀ0.49
GOFwc
Largest difference in peak and hole (e Å3)
a
b
c
R ¼ ½
R
j
D
wð
F j =
R
FÞ =
j Fo jꢃ.
2
Rw ¼ ½R
D
R
wF2o ꢃ.
Goodness of fit on F2.

B.L. Tran et al. / Inorganica Chimica Acta 369 (2011) 215–222
221
The space group P21/c was determined based on intensity sta-
tistics and systematic absences. The structure was solved and re-
fined using SHELXTL [29]. A direct methods solution was calculated,
which provided most atomic positions from the E-map. Full-matrix
least squares/difference Fourier cycles refined with anisotropic dis-
placement parameters. The hydrogen atoms were placed in ideal
positions and refined as riding atoms with relative isotropic dis-
placement parameters. The final full matrix least squares refine-
ment converged to R1 = 0.1104, wR2 = 0.2287 (F2, all data). The
remaining electron density is minuscule and located on bonds.
The poor quality and weakly diffracting nature of the crystal had
resulted in somewhat high values of the R factors.
solution was calculated, which provided most non-hydrogen
atoms from the E-map. Full-matrix least squares/difference Fourier
cycles were performed, which located the remaining non-hydro-
gen atoms. All ordered non-hydrogen atoms were refined with
anisotropic displacement parameters. The hydrogen atoms were
placed at calculated geometric positions and refined as riding
atoms with individual relative isotropic displacement parameters.
The solid state structure exhibits significant disorder located at
the p-tolylamino group, which was modeled successfully. The dis-
order was described with a constraint that the occupancies of the
major and minor components sum to 1.0, and both the manor
and minor disorder components were refined with isotropic dis-
placement parameters. The major component of the disorder for
C(30), C(31), C(32), C(33), C(34), C(35), C(36) showed occupancies
of 0.617(11). The final full matrix least squares refinement con-
4.6.2. Data collection, structure solution and refinement for (nacnac)V
@O(Ntol2) (1)
A preliminary set of cell constants was calculated from reflec-
tions harvested from three sets of 12 frames. These initial sets of
frames were oriented such that orthogonal wedges of reciprocal
space were surveyed. This produced initial orientation matrices
determined from 207 reflections. The data collection was carried
verged to R1 = 0.0433 (I > 2r
(I), 3415 data) and wR2 = 0.1185 (F2,
4568 data, 481 parameters).
Acknowledgments
out using Mo Ka radiation (graphite monochromator) with a frame
We thank the Chemical Sciences, Geosciences and Biosciences
Division, Office of Basic Energy Science, Office of Science, US
Department of Energy (No. DE-FG02-07ER15893). ChemMatCARS
Sector 15 is principally supported by the National Science Founda-
tion/Department of Energy under Grant Number CHE-0535644.
Use of the Advanced Photon Source was supported by the US
Department of Energy, Office of Science, Office of Basic Energy Sci-
ences, under Contract No. DE-AC02-06CH11357.
time of 30 s and a detector distance of 5.0 cm. A randomly oriented
region of reciprocal space was surveyed to achieve complete data
with a redundancy of 4. Sections of frames were collected with
0.50° steps in
x and / scans. Data to a resolution of 0.77 Å were
considered in the reduction. Final cell constants were calculated
from the xyz centroids of 1890 strong reflections from the actual
data collection after integration (SAINT) [27]. The intensity data were
corrected for absorption (SADABS) [28]. Please refer to Table 1 for
additional crystal and refinement information.
Appendix A. Supplementary material
The space group P21/c was determined based on intensity sta-
tistics and systematic absences. The structure was solved using
SIR-92 [30] and refined (full-matrix-least squares) using the Oxford
University Crystals for Windows system [31]. A direct-methods
solution was calculated, which provided most non-hydrogen
atoms from the E-map. Full-matrix least squares/difference Fourier
cycles were performed, which located the remaining non-hydro-
gen atoms. All non-hydrogen atoms were refined with anisotropic
displacement parameters. The hydrogen atoms were placed at cal-
culated geometric positions and refined as riding atoms with indi-
vidual relative isotropic displacement parameters. The final full
matrix least squares refinement converged to R1 = 0.0556
CCDC 790882, 790883, and 790884 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.11.040.
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