Reactivity of a low-valent chromium dinitrogen complex

Article abstract of DOI:10.1016/j.ica.2010.11.024

(Nn^iPrCr)₂(μ₂-κ²: κ²-N₂) (1, Nn^iPr = bis(2,6- diisopropylphenyl)pentane-2,4-ketiminato), formally a chromium(I) complex, was exposed to a variety of small molecules possessing hetero- or homo-atomic single, double, or triple bonds. Reaction of 1 with adamantyl azide yielded complexes in various higher oxidation states, such as (Nn^iPrCr ^II)₂(μ₂-NAd) (2), Nn^iPrCr ^III(κ²-N₄Ad₂) (3), or Nn ^iPrCr^V(NAd)₂ (4). Compound 1 was found to reductively couple 3-pentanone to form Nn^iPrCr(κ²- O₂C₂Et₄) (5) and reductively couple benzylidene aniline to form both Nn^iPrCr^III(cis-κ²- C₂₈H₂₂N₂) (6a) an Nn^iPrCr ^III(trans-κ²-C₂₈H₂₂N ₂) (6b). Reaction with a stochiometric amount of benzylidene aniline yielded the imine complex Nn^iPrCr(η²-NPhCHPh) (7). Exposure of 1 to a bulky isocyanide formed the octahedral Nn ^iPrCr^I[CN(C₆H₄(Me)₂] ₄ (9). Complex 1 was also found to break the O-O, NO, and S-S bonds in various small molecules to form Nn^iPrCr^II(OCMe ₃) (11), Nn^iPrCr^V(O)(NPh) (8), and [Nn ^iPrCr^II(μ-SPh)]₂ (10).

Full text of DOI:10.1016/j.ica.2010.11.024

Inorganica Chimica Acta 369 (2011) 103–119
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Reactivity of a low-valent chromium dinitrogen complex
⇑
Wesley H. Monillas, Glenn P.A. Yap, Klaus H. Theopold
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
a r t i c l e i n f o
a b s t r a c t
j2 2-N2) (1, NniPr = bis(2,6-diisopropylphenyl)pentane-2,4-ketiminato), formally a chro-
:j
(NniPrCr)2(l2
-
Article history:
Available online 23 November 2010
mium(I) complex, was exposed to a variety of small molecules possessing hetero- or homo-atomic single,
double, or triple bonds. Reaction of 1 with adamantyl azide yielded complexes in various higher oxidation
Dedicated to Prof. Robert G. Bergman,
premier physical organometallic chemist
of his generation, mentor of scores of
scientists, and friend.
states, such as (NniPrCrII)2( 2-NAd) (2), NniPrCrIII 2-N4Ad2) (3), or NniPrCrV(NAd)2 (4). Compound 1 was
l (j
found to reductively couple 3-pentanone to form NniPrCr(
j
2-O2C2Et4) (5) and reductively couple benzyl-
2-C28H22N2) (6b). Reaction
2-NPhCHPh) (7).
idene aniline to form both NniPrCrIII(cis- 2-C28H22N2) (6a) an NniPrCrIII(trans-
j
j
with a stochiometric amount of benzylidene aniline yielded the imine complex NniPrCr(
g
Exposure of 1 to a bulky isocyanide formed the octahedral NniPrCrI[CN(C6H4(Me)2]4 (9). Complex 1 was
also found to break the O–O, N@O, and S–S bonds in various small molecules to form NniPrCrII(OCMe3)
Keywords:
Chromium
b-Diketiminates
Nitrogen complex
Bond cleavage
Crystal structures
(11), NniPrCrV(O)(NPh) (8), and [NniPrCrII(
l-SPh)]2 (10).
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
with other molecules featuring X–Y bonds (X, Y = C, N, O, S) of
varying bond orders. Herein we describe the results of some of
these reactions, which result in both bond cleavage and bond
formations.
Before we begin, it may be prudent to clarify our view of the
oxidation state of chromium in 1. The common practice of
considering the closed-shell molecule N2 as a neutral, albeit
Low-valent transition metal complexes featuring labile ligands,
such as dinitrogen or arenes, have proven to be excellent precur-
sors for the activation of small molecules. Facile substitution of
the weakly bonded ligand with a wide range of substrates
commonly yields an assortment of novel molecules [1]. This has
certainly been true for metal complexes supported by b-diketimi-
nate (‘nacnac’ or ‘Nn’) ligands [2]. The research groups of Warren
[3–5], Tolman [6,7], Sadighi [8], Holland [9,10], Stephan [11,12],
Tsai [13,14], Chirik [15], and others have exploited this paradigm
to prepare a variety of intriguing compounds ranging across the
transition metal block.
p-back-bonding ligand, combined with the reluctance of the anio-
nic b-diketiminate ligand to accept electrons, naturally results in
the assignment of a formal oxidation state of +I to chromium.
While not unprecedented, this is certainly an unusually low oxida-
tion state for coordination compounds of this metal [17]. Indeed,
the N–N distance of 1.25 Å in 1 suggests considerable electron
transfer to the coordinated N2, being consistent with a formulation
as N22À dianion and thus a Cr(II) complex. We subscribe to this no-
tion; however, in all of the reactions described below, the N2 ligand
leaves as neutral nitrogen gas. Thus the chromium atom of 1
wields all the electrons attributable to a NnCr(I) fragment. For this
reason we consider 1 a Cr(I) synthon; its reactivity is best rational-
ized in those terms.
Our contributions to this endeavor has been the preparation of
the dinuclear side-on bonded dinitrogen complex (NniPrCr)2-
(
l2- :j
j2 2-N2) (1, NniPr = bis(2,6-diisopropylphenyl)-2,4-ketimina-
to) and the screening of its reactivity with small molecules [16].
For example, the reactions of 1 with the -acids CO and C2H4
yielded the structurally intriguing complexes (NniPrCr)2-
1-CO)2(CO) and (NniPrCr)2(l2 2-C2H4), whereas
p
(l2
-
g1
:g
- :g
g2
‘oxidants’ such as dioxygen and azobenzene resulted in products
of oxidative addition, i.e., NniPrCr(O)2 – the apparent product of a
2. Results and discussion
4-electron oxidative addition – and (NniPrCr)2(
l2-NPh)2. The large
disparity in the formal oxidation states of chromium in these prod-
ucts motivated us to extend the exploration of the reactivity of 1
Alkyl azides are common precursors for metal imido complexes.
Coordination to the metal, followed by extrusion of N2, effects
binding of an RN fragment to the metal and concomitantly
increases its oxidation state. Accordingly, addition of one equiva-
lent of 1-adamantyl azide to a THF solution of 1 at room tempera-
ture resulted in a rapid evolution of N2; removal of THF and
⇑
Corresponding author.
E-mail address: theopold@udel.edu (K.H. Theopold).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.11.024

104
W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
recrystallization of the product from pentane afforded the dinuclear,
bridging imido complex 2 (see Scheme 1), which features chro-
mium in the +II oxidation state. A structure determination by X-
ray diffraction (see Fig. 1 and Table 1) showed 2 to be reminiscent
of a dinuclear nickel complex reported by Warren et al. [18]. A
number of bridging imido complexes containing chromium have
been reported, and while most possess two bridging imido groups
and contain chromium in intermediate or high oxidation states
(P+III), the structural parameters of 2 are not out of the ordinary
[19–23]. Two crystallographically independent molecules of 2 oc-
cupy the asymmetric unit, but they are chemically indistinguish-
able and will be discussed together. The Cr–NAd bond distances
average 1.925 Å, and the average Cr–Cr distance is 2.936 Å. The
imido nitrogens are rigorously planar (sums of the angles: 359.9°
and 359.8°, respectively), with the Cr–NAd–Cr angles being the
smallest (at 98.4° and 100.4°). The latter observation suggests that
there exists some measure of metal–metal bonding in 2. To be sure,
the intermetallic distance is large, but Cr–Cr single bonds up to
ꢀ3.4 Å in length are known [24]. The effective magnetic moment
of 2 ( eff (293 K) = 5.3(1) B) is lower than what would be expected
of two non-interacting Cr(II) ions (S = 2) – i.e., 6.8 lB – and sup-
ports Cr–Cr bonding or antiferromagnetic exchange coupling med-
iated by the imido bridge.
l
l
The reaction with adamantyl azide takes a different course in
the presence of an excess of azide. Thus, addition of three equiva-
lents of 1-adamantylazide to a THF solution of 2 at room temper-
ature (or of four equivalents of 1-adamantanylazide to 1)
resulted in a rapid evolution of copious amounts of N2 gas.
Removal of THF and recrystallization of the product from pentane
yielded NniPrCr( 2-N4Ad2) (3, see Scheme 1, Fig. 2 and Table 2).
j
Compound 3 is a mononuclear complex featuring the tetrahedral
coordination environment of chromium characteristic for Cr(III).
It contains a 5-membered, tetraazametallacycle – the result of cou-
pling of a chromium imido group with a whole molecule of alkyl
azide. Several analogous complexes have been formed this way, the
most similar being a b-diketiminato aluminum tetraazabutadiene
Scheme 1. Synthesis of (NniPrCr)2( 2-NAd) (2), NniPrCr( 2-N4Ad2) (3), and NniPrCr(NAd)2 (4).
l j

W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
105
Fig. 1. Molecular structure of the first molecule of (NniPrCr)2(
l2-NAd) (2) at 30% probability density. Hydrogen atoms and co-crystallized pentane molecule have been
omitted for clarity.
Table 1
high intensity light for 3 weeks yielded bis(imido)complex
NniPrCrV(NAd)2 (4) in 47% yield (see Fig. 3 and Table 3 for structural
details). Compound 4 features tetrahedral chromium, much like its
previously described isoelectronic oxo analog NniPrCr(O)2 [16]. The
Cr@NAd bonds are short (Cr–Navg = 1.66 Å), befitting their double
bond character, the high formal oxidation state (+V), and the low
coordination number of the metal [32]. The imido fragments devi-
ate just slightly from linearity, presumably to avoid steric interac-
tion with the nacnac substituents. The same steric interactions are
also thought to be responsible for the nonplanarity of the nacnac
ligand in 4, and in 3 as well. The N1–Cr–N2 angle between the
imido ligands was found to be large, at 120.55(19)°, while the
N3–Cr–C4 angle subtended by the nacnac ligand is close to 90°,
as expected; all other N–Cr–N angles around the Cr core are all
similar with an average value of 110.4(5)°. Compound 4 contains
Cr(V) and in accord with expectations (S = ½) it has an effective
Selected interatomic distances (Å) and angles (°) for both crystallographically
independent molecules of (NniPrCr)2(
l2-NAd) (2).
Distances (Å)
Cr1–Cr2
Cr1–N1
Cr1–N2
Cr1–N3
Cr2–N1
Cr2–N4
Cr2–N5
2.9150(17)
1.926(3)
2.042(3)
2.081(3)
1.923(3)
2.040(3)
2.067(3)
Cr3–Cr4
2.9564(16)
1.919(3)
2.061(3)
2.066(3)
1.928(3)
2.045(3)
2.071(3)
Cr3–N6
Cr3–N7
Cr3–N8
Cr4–N6
Cr4–N9
Cr4–N10
Angles (°)
N1–Cr1–N2
N1–Cr1–N3
N2–Cr1–N3
Cr1–N1–Cr2
N1–Cr2–N4
N1–Cr2–N5
N4–Cr2–N5
125.50(12)
145.66(12)
88.59(13)
98.44(15)
124.19(13)
145.97(13)
89.03(13)
N6–Cr3–N7
N6–Cr3–N8
N7–Cr3–N8
Cr3–N6–Cr4
N6–Cr4–N9
N6–Cr4–N10
N9–Cr4–N10
127.62(12)
142.71(12)
89.17(12)
100.43(14)
124.57(12)
146.27(12)
88.83(12)
magnetic moment of 2.0(1) lB
.
As 1 cleaves the X@Y double bonds of dioxygen and azoben-
zene, one might be tempted to expect similar bond cleavage reac-
tions for the C@O bond of ketones or the C@N bond of imines. On
the other hand, the strongly reducing nature of the Cr(I) synthon
opens alternative pathways, as shown in Scheme 2. Addition of ex-
complex also formed from adamantyl azide [25–28]. Although
tetraazabutadiene complexes with similar N–N bond distances
throughout the RN4R fragment exist, 3 shows clear bond length
alternation [27,29–31]. The N1–N2 and N3–N4 distances were
found to be 1.361(4) Å and 1.368(4) Å, respectively, while the
N2–N3 distance is significantly shorter at 1.277(4) Å. These dis-
tances are perfectly consistent with a formulation as a ‘diimine
diamide’, i.e., the dianionic form of the ligand as shown in Scheme
1. The relatively short Cr–N bonds to this ligand also support that
notion. Magnetic data support this assignment, as 3 was found to
cess 3-pentanone to a THF solution of (NniPrCr)2(l2 j2 2-N2)
- :j
yielded a rose colored solution after 2 h. Subsequent extraction
and workup in pentane yielded chromium diolate NniPrCr
(j
2-O2C2Et4) (5). As is shown in Fig. 4 (see also Table 4), two 3-
pentanone molecules have undergone a pinacol coupling to yield
a 3,4-diethylhexane-3,4-diolate fragment bound to the metal
center [33–37]. The structure determination of 5 shows the chro-
mium center in a tetrahedral coordination by the diolate ligand
augmented by the two nitrogen atoms of the b-diketiminate at dis-
tances of ca. 1.97 Å, with a N1–Cr–N2 angle of 89°. The Cr–O dis-
tances average a shorter 1.83 Å with an O1–Cr–O2 angle of 85°.
The erstwhile carbon–oxygen double bond of the ketone has been
have an effective magnetic moment of 3.7(1)
a Cr(III) metal center.
lB, consistent with
Finally, the short N2–N3 bond of 3 inspired hopes of an
extrusion – either thermal or photochemical – of another N2 mol-
ecule. Indeed, exposure of a THF solution of 3 in a Pyrex vessel to

106
W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
Fig. 2. Molecular structure of NniPrCr(
j
2-N4Ad2) (3) at 20% probability density. Hydrogen atoms and co-crystallized solvent molecule have been omitted for clarity.
effective magnetic moment of 6 is 3.7(1) lB, which is consistent with
a Cr(III) metal center.
Table 2
Selected interatomic distances (Å) and angles (°) for NniPrCr( 2-N4Ad2) (3).
j
Interestingly, there is no evidence of positional disorder in the
crystal structures of cis- and trans-6 and each form was isolated
as single crystals; it appears that they spontaneously separate dur-
ing crystallization. The space group for both the cis and trans cou-
pling products are centrosymmetric, indicating that both
enantiomers are present in the crystal. Due to the paramagnetism
of the compound, the two isomeric forms could not be reliably as-
signed in the 1H NMR spectrum of the mixture, although the num-
ber of resonances suggested that both forms were present. Heating
a sample of 6a/b in THF-d8 (80 °C, 2 days) did not show any dis-
cernable change of the 1H NMR spectrum; either the initial mixture
is the thermodynamic product or – more likely – isomerization is
not accessible under these conditions. Increasing the temperature
to 120 °C for 3 days resulted in decomposition of the complex.
We note that analogous coupling reactions of benzylidene ani-
line have been observed with zirconocene or titanium aryloxide
complexes [38–40]. In zirconium chemistry the trans coupling
product was observed exclusively, with no evidence (and little
mention) of the possible cis product. The reaction involving tita-
nium was found to yield both cis and trans products based on 1H
NMR and 13C NMR spectroscopy. The reaction mechanism is be-
lieved to involve initial binding of one molecule of benzylidenean-
iline followed by binding of another imine molecule, which can
approach the chromium either way to yield either the cis or trans
product. Indeed, we shall provide evidence for the formation of
the intermediate imine complex (see below).
Distances (Å)
Cr–N1
N1–N2
N2–N3
N3–N4
1.915(3)
1.361(4)
1.277(4)
1.368(4)
Cr–N4
Cr–N5
Cr–N6
1.898(3)
2.014(3)
2.016(3)
Angles (°)
Cr–N1–C1
Cr–N4–C11
130.9(2)
128.6(2)
Cr–N1–N2
Cr–N4–N3
118.2(2)
119.0(2)
elongated to 1.45 Å for O1–C1 and the newly formed C–C bond
measures 1.565(3) Å. The room temperature effective magnetic
moment of 5 was found to be 3.9(1)
Cr(III) complex. Heating 5 (80 °C, 8 days) in THF-d8 showed no
change of the 1H NMR spectrum. Thus, elimination of an alkene
and concomitant formation of known NniPrCr(O)2 is not a facile
transformation. We note, in passing, that the reverse reaction has
also not been observed; thus the bond making or bond breaking
between this chromyl fragment and alkenes seems to face a large
activation barrier.
lB, wholly appropriate for a
A similar reductive coupling was also observed upon exposure
of 1 to 4 equivalents of the imine trans-benzylideneaniline. The
reaction was found to form both the cis and the trans diamido com-
plexes NniPrCr( 2-N2Ph2C2H2Ph2) (6) in an undetermined ratio
j
(compounds 6a and 6b, see Figs. 5 and 6); crystals of both isomers
were picked from the same reaction mixture. Both molecules adopt
the familiar tetrahedral geometry of 4-coordinate Cr(III). The Cr–N
distances to the 1,2-diphenylethane-1,2-bis(phenylamido) moiety
are somewhat shorter (ranging from 1.92 to 1.95 Å) than those
involving the nacnac ligand (P2.00 Å). The newly formed C–C bonds
(1.54 and 1.55 Å) are normal single bonds. Detailed structural
parameters are listed in Tables 5 and 6. The room temperature
Reaction of 1 with only two equivalents of trans-benzylidenean-
iline results in a different product, namely the imine complex
NniPrCr( 2-NPhCHPh) (7). Structural characterization of the prod-
g
uct shows a monomeric species with the benzylideneaniline frag-
ment side-on bound to the chromium with Cr–N and Cr–C
distances 1.85 and 2.10 Å, respectively (see Fig. 7 and Table 7). Sin-
gle crystal X-ray diffraction showed some positional disorder of the

W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
107
Fig. 3. Molecular structure of NniPrCr(NAd)2 (4) at 20% probability density. Hydrogen atoms and co-crystallized pentane molecule have been omitted for clarity.
Table 3
upon the addition of four equivalents of p-nitrotoluene to the
nitrogen complex. Cleavage of the N@O bond apparently occurs,
but the nitrosotoluene fragment is not retained in the complex.
However, addition of two equivalents of nitrosobenzene to a solu-
tion of 1 in THF yielded NniPrCr(O)(NPh) (8, see Fig. 8 and Table 8).
This complex is a mixed imido/oxo complex and can be thought of
as a hybrid of sorts between NniPrCr(O)2 and NniPrCr(NAd)2 (4).
Akin to these complexes, 8 displays approximately tetrahedral
geometry about the chromium center. The nitrogen atoms of the
b-diketiminate ligand are located 1.94 Å from the chromium cen-
ter, similar to those distances for NniPrCr(O)2 but slightly shorter
than the corresponding distances in 4. The chromium-oxo
(1.59 Å) and chromium-imido (1.68 Å) distances of 8 were similar
to the corresponding bond lengths of NniPrCr(O)2 (Cr@O, 1.59 Å)
and 4 (Cr@N, 1.66 Å). On the other hand, the phenylimido ligand
is much more bent at the nitrogen (Cr–N–C, 141°); closer inspec-
tion of the structure suggests that this is a consequence of severe
steric interaction with the isopropyl substituents of the nacnac li-
gand. Interestingly, 8 showed no apparent tendency to dispropor-
tionate to NniPrCr(O)2 and the as yet unknown NniPrCr(NPh)2; the
mixed oxo/imido species may represent be more favored side of
the relevant equilibrium. The room temperature effective magnetic
Selected interatomic distances (Å) and angles (°) for NniPrCr(NAd)2 (4).
Distances (Å)
Cr–N1
Cr–N2
1.669(4)
1.653(4)
Cr–N3
Cr–N4
2.017(3)
2.008(3)
Angles (°)
N1–Cr–N2
N1–Cr–N3
N1–Cr–N4
C1–N1–Cr
120.55(19)
108.83(16)
109.58(16)
173.6(3)
N2–Cr–N3
N2–Cr–N4
N3–Cr–N4
C11–N2–Cr
112.25(16)
110.98(16)
90.59(14)
165.7(3)
phenyl groups of the benzylideneaniline moiety. The C–N bond of
imine has been elongated to 1.39 Å, and the fragment is no longer
planar, indicating extensive rehybridization (sp2 ? sp3) of these
two atoms. Compound 7 is then best understood as a Cr(III) metal-
laaziridine, and the perpendicular orientation of the nacnac and
imine ligands allows the description of the coordination geometry
as approximately tetrahedral about chromium. The nitrogen atom
of the benzylidene aniline moiety is only barely pyramidal (sum of
angles: 353.7°) and the Cr–N distance is very short (1.85 Å) com-
pared to the Cr–C distance of 2.10 Å. Both observations suggest
appreciable
p-donation by the amide nitrogen lone pair to Cr(III).
moment for 8 is 1.7(1) l
B, consistent with the d1 configuration of a
g
2-Bound benzylidene aniline complexes are known to exist for
Cr(V) complex.
molybdenum, nickel, tungsten, zirconium and niobium complexes
[41–46]. However, to the best of our knowledge this is the first
structurally characterized chromium complex possessing this
structural motif.
Although we have not pursued this line of investigation, we
suggest that 7 would likely react with additional benzylidene ani-
line to give 6. Furthermore, it might be subject to heterocoupling
with other imines or even carbonyl compounds. Such reactions
might be useful from a synthetic organic perspective.
As the reaction of 1 with CO yielded the asymmetrical dinuclear
isocarbonyl complex (NniPrCr)2(CO)( -:g1 1-CO)2 [16], an isoelec-
l
:g
tronic replacement for CO was sought in order to prevent formation
of a dinuclear complex. As expected, the reaction between 1 and ex-
cess 2,6-dimethylphenylisocyanide yielded the octahedral, mono-
nuclear complex NniPrCr[CN(C6H4(Me)2]4 (9, see Fig. 9 and Table
9). The symmetry related nitrogen atoms of the b-diketiminate
ligand are located 2.134(2) Å from the chromium center, this being
the longest Cr–N bond distance yet reported for a b-diketiminate
chromium complex and surpassing the previous record by 0.020 Å
[47]. The low formal oxidation state (Cr(I)) and the large
As previously reported, exposure of 1 to O2 rapidly yielded
NniPrCr(O)2, see Scheme 3. The same complex was also formed

108
W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
Et
Et
Et
Ar
Cr
Ar
Cr
O
O
N
N
N
N
HC
N
5
7
Ar
Ar
Et
O
HC
Et
Et
2 eqs.
N
Ar
Ar
N
N
N
N
N
N
Cr
Cr
Ar
Ar
HC
4 eqs.
N
Ar
N
N
N
Cr
Ar
6
N
Scheme 2. Syntheses of NniPrCr( 2-O2C2Et4) (5), NniPrCr( 2-N2Ph2C2H2Ph2) (6), and NniprCr(
j j g2-C13H11N) (7).
coordination number (6) are the probable cause of this effect. The
Finally, single bonds between chalcogens (e.g. O–O and S–S) are
room temperature effective magnetic moment of 9 was found to
expected to be readily cleaved by 1; the only question is what oxi-
dation state the products will reach. The following examples ad-
dress that query, see Scheme 4. The room temperature reaction
of diphenyldisulfide with 1 in THF resulted in formation of the
be 2.2(1)
lB, slightly higher than those of other octahedral chro-
mium(I) isocyanide complexes, which possess moments from 1.71
to 2.07 lB [48,49]. As expected due to the strong p-acceptor nature
of the isocyanide ligands 9 adopts a low-spin d5 electronic configu-
dinuclear complex [NniPrCr(
l-SPh)]2 (10, see Fig. 10 and Table
ration (S = ½).
10). Compound 10 is a dinuclear complex joined by two bridging

W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
109
Fig. 4. Molecular structure of NniPrCr(
j
2-O2C2Et4) (5) at 30% probability density. Hydrogen atoms have been omitted for clarity.
Table 4
Selected interatomic distances (Å) and angles (°) for NniPrCr(
j
2-O2C2Et4) (5).
Distances (Å)
Cr–N1
Cr–N2
Cr–O1
Cr–O2
1.9739(19)
1.9608(19)
1.8353(17)
1.8229(16)
O1–C1
C1–C2
C2–O2
1.451(3)
1.565(3)
1.457(3)
Angles (°)
N1–Cr–N2
O1–Cr–O2
88.95(8)
84.64(7)
Cr–O1–C1
Cr–O2–C2
116.13(13)
114.92(13)
Table 5
Selected interatomic distances (Å) and angles (°) for NniPrCr(
(6a).
j
2-cis-N2Ph2C2H2Ph2)
Distances (Å)
Cr–N1
Cr–N2
Cr–N3
Cr–N4
1.954(2)
1.930(2)
2.026(2)
2.000(2)
N1–C1
C1–C2
N2–C2
1.472(4)
1.550(4)
1.475(4)
Angles (°)
N1–Cr–N2
Cr–N1–C1
83.03(10)
113.56(18)
C1–C2–N2
C2–N2–Cr
105.8(2)
115.10(18)
Fig. 5. Molecular structure of NniPrCr(
j
2-cis-N2Ph2C2H2Ph2) (6a) at 30% probability
density. Hydrogen atoms except for H1 and H2, depicted as spheres with arbitrary
radius, have been omitted for clarity.
phenylthio groups located an average of 2.45 Å from the chromium
centers and 3.3 Å apart from each other. The Cr–Cr distance in 10
measures 3.627(4) Å, which effectively precludes any direct me-
tal–metal bonding, and the chromium centers adopt a notably dis-
torted square planar geometry. The geometry around each sulfur
atom is trigonal pyramidal. The room temperature effective
magnetic moment for 10 was found to be 5.4(1) lB and suggests

110
W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
Table 6
Interatomic distances (Å) and angles (°) for NniPrCr(trans- 2-C28H22N2) (6b).
j
Distances (Å)
Cr–N1
Cr–N2
Cr–N3
Cr–N4
1.9410(18)
1.9155(19)
2.0190(19)
2.0131(19)
N1–C1
C1–C2
N2–C2
1.473(3)
1.542(3)
1.471(3)
Angles (°)
N1–Cr–N2
Cr–N1–C1
82.39(8)
114.66(13)
C1–C2–N2
C2–N2–Cr
104.76(17)
114.62(14)
Table 7
Selected interatomic distances (Å) and angles (°) for NniPrCr( 2-NPhCHPh) (7).
g
Distances (Å)
Cr–C1
Cr–N1
C1–N1
2.097(4)
1.846(3)
1.391(5)
Cr–N2
Cr–N3
1.976(3)
1.973(3)
Angles (°)
Cr–N1–C1
N1–C1–Cr
Fig. 6. Molecular structure of NniPrCr( 2-trans-N2Ph2C2H2Ph2) (6b) at 30% proba-
j
bility ellipsoids. Co-crystallized pentane solvent molecule and hydrogen atoms,
except for H1A and H2A, depicted as spheres with arbitrary radius, have been
omitted for clarity.
79.4(2)
59.92(18)
C1–Cr–N1
N2–Cr–N3
40.69(15)
90.11(13)
to form either a mononuclear or a dinuclear complex, an alterna-
tive method to synthesize this complex was sought. Addition of
some degree of antiferromagnetic coupling between the Cr(II)
centers.
potassium tert-butoxide to a THF solution of [NniPrCr(
l-I)]2 and
subsequent workup in pentane cleanly yielded the alkoxide NniPr-
Cr(OCMe3) (11). Comparison of the 1H NMR spectra of the isolated
complex and that of the NMR tube reaction showed them to be
identical. A crystal structure determination of 11 (see Fig. 11 and
Table 11) showed that it is a mononuclear complex wherein the
chromium adopts a distorted trigonal planar geometry. As in the
Addition of excess di-tert-butylperoxide to a room temperature
solution of 1 in THF-d8 cleanly yielded a new compound after
4 days, as monitored by 1H NMR spectroscopy. Unfortunately,
technical difficulties were encountered in scaling this transforma-
tion up to synthetically useful quantities. Acting on the hypothesis
that the new compound was formed via cleavage of the O–O bond
Fig. 7. Molecular structure of NniPrCr( 2-NPhCHPh) (7) with 30% probability ellipsoids. Hydrogen atoms (except for H1A) have been omitted for clarity.
g

W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
111
Ar
N
N
O
O
Cr
Ar
O
O2
N
O
Ar
Ar
N
N
N
N
N
Cr
Cr
N
Ar
Ar
2 eqs.
8 eqs.
C
N
N
O
Ar
Ar
O
N
N
Cr
Ar
N
Cr
C
N
N
N
Ar
4
8
9
Scheme 3. Syntheses of NniPrCr(O)2, NniPrCr(O)(NPh) (8), and NniPrCr[CN(C6H4(Me)2]4 (9).
case of 10, the bond cleavage reaction of the peroxide yielded a
Cr(II) complex. The monomeric nature of 11 is likely due to the ste-
ric bulk of the tert-butyl group and the comparatively short Cr–O
bond (1.84 Å).
4. Experimental
4.1. General
All manipulations were carried out via standard Schlenk, high
vacuum line, and/or glovebox techniques. Pentane, diethyl ether,
tetrahydrofuran, and toluene were dried by passage through acti-
vated alumina. THF-d8 and C6D6 were predried over potassium or
sodium metal and stored under vacuum over Na/K. Synthesis of
3. Conclusions
We have further explored the wide range of reactivity of labile,
low-valent [NniPrCr]2(l2 j2 2-N2) (1). Compound 1 reacts with a
- :j
[NniPrCr( -I)]2 and [NniPrCr]2(l2 j2 2-N2) (1) has been described
l - :j
variety of organic substrates to yield an assortment of mononu-
clear and binuclear chromium complexes in oxidation states rang-
ing from +I to +V. Adamantyl azide produces imido fragments,
whereas ketones and imines suffer reductive coupling. Simple
ligand substitutions can also be observed, as is the case with 2,6-
dimethylphenylisocyanide. Compound 1 reacts with nitro and ni-
troso compounds to form Cr(V) compounds by cleavage of N@O
bonds. Lastly, 1 can cleave S–S and O–O bonds to form binuclear
or mononuclear Cr(II) complexes. These examples demonstrate
the broad utility of 1 as a synthon for the activation of small mol-
ecules by low-valent chromium. Other uses of this versatile re-
agent, including catalytic ones, will be the focus of separate
reports.
previously [16]. All other compounds were purchased from Acros
or Aldrich and dried on the high vacuum line prior to use. 3-Penta-
none was distilled from and stored over molecular sieves. Di(tert-
butyl)peroxide was dried over sieves.
NMR spectra were recorded on a Bruker DRX-400 spectrometer
and were referenced to the residual protons of the solvent. FT-IR
spectra were taken on a Mattson Alpha Centauri, Mattson Genesis
Series, or a Nicolet Magna-IR 560 spectrometers. UV–Vis spectra
were taken on a Hewlett Packard 8453 or a Thermo Electron
Corporation UV1 spectrophotometer. Mass spectral data were
collected by the University of Delaware Mass Spectrometry Facility
in electron ionization mode (+15 eV). Elemental Analyses were

112
W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
Fig. 8. Molecular diagram of NniPrCr(O)(NPh) (8) with 30% probability ellipsoids. Hydrogen atoms have been omitted for clarity.
Table 8
10. Solution in the centrosymmetric space group options yielded
chemically reasonable and computationally stable results of refine-
ment. One molecule of cocrystallized pentane solvent was found in
the asymmetric unit of 6a. The data for 2, 3, and 4 were treated
with Squeeze [51] to model as diffused contributions the severely
disordered, cocrystallized solvent molecules. The compound mole-
cule in several structures was each located at special positions: for
9 a two-fold axis; for 10, an inversion point; and for 8 and 11, a
mirror plane. Two symmetry unique yet chemically identical com-
pound molecules were found in the asymmetric unit of 2 with one
of the molecules displaying a disordered adamantyl group with an
80/20 refined site disorder. The major disordered component in 2
was treated as a rigid group modeled from the non-disordered sec-
ond molecule while the minor disordered group was treated with
non-crystallographic symmetry restraints keeping equal atomic
displacement parameters between corresponding equivalent
atoms. Compound 7 displayed disorder in two phenyl groups and
an isopropyl group, respectively, with refined site occupancy ratios
of 51/49, 52/48 and 58/42, respectively. A second isopropyl group
in 7 displayed unresolvable disorder causing large apparent Ueq of
the affected atoms. Rigid bond restraints were applied in 8 to com-
pensate for slight unresolvable disorder at the mirror plane occurs
for 8 and 11: for 8 rigid bond restraints were applied; for 11 unre-
solvable disorder at the t-butoxy group on the mirror led to large
apparent Ueq. The pentane solvent molecule of crystallization in
10 was found disordered at an inversion point. Nonhydrogen
atoms were refined with anisotropic displacement parameters.
Hydrogen atoms H1 and H2 in 6a were located from the difference
map and positionally refined with 1.2 Ueq of the bonded carbon
atom. All other hydrogen atoms were treated as idealized contribu-
tions. Atomic scattering factors are contained in the SHELXTL 6.12
program library (Sheldrick, G.M., op. cit.). The crystal structures
have been deposited at the Cambridge Crystallographic Data
Centre and allocated the deposition numbers CCDC 789832–789842.
Selected interatomic distances (Å) and angles (°) for NniPrCr(O)(NPh) (8).
Distances (Å)
Cr–N1
Cr–O1
1.681(6)
1.592(5)
Cr–N2
1.938(4)
Angles (°)
N1–Cr–O1
N2–Cr–N2A
Cr–N1–C1
119.7(3)
93.4(2)
N1–Cr–N2
N2–Cr–O1
109.47(17)
110.85(17)
141.1(5)
performed by Desert Analytics (now Columbia Analytical Services).
Room temperature magnetic susceptibility measurements were
carried out using a Johnson Matthey magnetic susceptibility bal-
ance. Measurements were corrected for diamagnetism using Pascal
constants and converted into effective magnetic moments.
4.2. X-ray diffraction studies
Crystals were selected, sectioned as required, and mounted on
glass fibers or MiTeGen™ plastic mesh with viscous oil and flash-
cooled to the data collection temperature. Diffraction data were
collected on a Brüker-AXS APEX CCD diffractometer with graph-
ite-monochromated Mo Ka radiation (k = 0.71073 Å). The data-sets
were treated with SADABS absorption corrections based on redun-
dant multiscan data [50]. The structures were solved using direct
methods and refined with full-matrix, least-squares procedures
on F2. Unit cell parameters were determined by sampling three dif-
ferent sections of the Ewald sphere. The systematic absences and
equivalent reflections in the diffraction data were consistent with
space groups Cc and C2/c for 9; with Pn21a (Pna21) and Pnma for
8 and 11; uniquely with Pbca for 3; and, uniquely with P21/c
(P21/n) for 4, 5, 6a and 7. Despite two unit cell angles being close
(but not equal) to 90° for 2, inspection of the symmetry equivalent
reflections showed no symmetry higher than triclinic for 2, 6b and

W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
113
2
3
4
CCDC deposit number
789832
789833
789834
Formula
Formula weight (Da)
T (K)
C73H109N5Cr2
1160.65
120(2)
C54H81N6OCr
882.25
120(2)
C54H83N4Cr
840.24
120(2)
k (Å)
0.71073
triclinic
P1
brown
14.994(8)
18.316(10)
24.534(14)
92.799(11)
90.388(12)
90.375(11)
6729(6)
0.71073
orthorhombic
Pbca
dark red
17.780(5)
21.091(6)
26.550(7)
90
90
90
9956(5)
8
1.177
0.273
3832
0.71073
monoclinic
P21/c
dark red
19.574(3)
10.8025(15)
23.654(3)
90
104.519(3)
90
4841.8(12)
4
1.153
0.275
1836
0.20 Â 0.19 Â 0.11
2.08–25.00
100.0%
Crystal system
Space group
Color
a (Å)
b (Å)
ꢀ
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
4
Dcalc (g cmÀ3
)
1.146
0.366
2520
0.25 Â 0.23 Â 0.21
1.36–26.37
99.7%
l
(Mo K
F(0 0 0)
Crystal size (mm)
a
) (mmÀ1
)
0.25 Â 0.12 Â 0.10
h Range for data collection (°)
Completeness to hmax = 25°
1.68–25.00
99.5%
Maximum and minimum transmission
0.9270 and 0.9140
27 355/30/1395
1.001
0.9732 and 0.9348
8719/0/515
1.019
0.9717 and 0.9475
8522/0/497
1.062
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0702, wR2 = 0.1668
R1 = 0.1141, wR2 = 0.1879
0.536 and À0.387
R1 = 0.0663, wR2 = 0.1241
R1 = 0.1196, wR2 = 0.1396
0.347 and À0.346
R1 = 0.0854, wR2 = 0.3254
R1 = 0.1019, wR2 = 0.3439
0.555 and À0.955
R indices (all data)
Largest difference in peak and hole (e ÅÀ3
)
5
6a
6b
CCDC deposit number
789835
789836
789837
Formula
Formula weight (Da)
T (K)
C39H61N2O2Cr
641.90
120(2)
C55H63N4Cr
832.09
120(2)
C60H75N4Cr
904.24
120(2)
k (Å)
0.71073
monoclinic
P21/n
0.71073
monoclinic
P21/n
0.71073
monoclinic
P1
Crystal system
Space group
Color
ꢀ
red
black
black
a (Å)
b (Å)
c (Å)
10.674(3)
20.166(5)
17.218(4)
90
15.144(5)
15.842(5)
20.415(7)
90
11.1858(14)
15.087(2)
15.986(2)
a
(°)
84.117(2)
b (°)
93.844(4)
90
3697.7(15)
4
1.153
0.343
109.999(7)
90
4602(3)
76.733(2)
74.750(2)
2530.8(6)
2
1.187
0.268
1974
0.37 Â 0.30 Â 0.28
1.66–25.00
100.0%
c
(°)
V (Å3)
Z
4
Dcalc (g cmÀ3
)
1.201
0.289
1780
0.08 Â 0.06 Â 0.05
1.67–25.00
100.0%
l
(Mo K
F(0 0 0)
Crystal size (mm)
a
) (mmÀ1
)
1396
0.46 Â 0.31 Â 0.25
2.02–25.00
100.0%
h Range for data collection (°)
Completeness to hmax = 25°
Maximum and minimum transmission
0.9185 and 0.8576
6516/0/411
1.088
0.9871 and 0.9767
8101/0/557
1.028
0.9274 and 0.9063
8902/0/598
1.020
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0461, wR2 = 11.06
R1 = 0.0696, wR2 = 0.1246
0.414 and À0.344
R1 = 0.0546, wR2 = 0.1033
R1 = 0.0934, wR2 = 0.1220
0.367 and À0.323
R1 = 0.0460, wR2 = 0.1046
R1 = 0.0688, wR2 = 0.1182
0.387 and À0.378
R indices (all data)
Largest difference in peak and hole (e ÅÀ3
)
(continued on next page)

114
W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
7
8
9
CCDC deposit number
789838
789839
789840
Formula
Formula weight (Da)
T (K)
C42H52N3Cr
650.87
120(2)
C35H46N3OCr
576.75
120(2)
C65H77N6Cr
994.33
120(2)
k (Å)
0.71073
0.71073
0.71073
Crystal system
Space group
Color
a (Å)
b (Å)
monoclinic
P21/n
red
11.642(7)
20.802(13)
15.323(9)
90
orthorhombic
Pnma
red-brown
16.632(5)
20.874(6)
9.395(3)
monoclinic
C2/c
red
17.1508(16)
16.7867(15)
19.1205(17)
90
c (Å)
a
(°)
90
b (°)
95.265(13)
90
3695(4)
90
90
90.906(2)
90
5504.2(9)
4
1.200
0.254
c
(°)
V (Å3)
3247.5(17)
4
1.180
0.382
1236
0.13 Â 0.11 Â 0.08
1.96–25.00
99.8%
Z
4
Dcalc (g cmÀ3
)
1.170
0.341
1396
0.17 Â 0.11 Â 0.07
1.66–28.43
100.0%
l
(Mo K
F(0 0 0)
Crystal size (mm)
a
) (mmÀ1
)
2132
0.10 Â 0.08 Â 0.06
1.99–28.32
100.0%
h Range for data collection (°)
Completeness to hmax = 25°
Maximum and minimum transmission
0.9772 and 0.9542
9261/135/468
1.020
0.9719 and 0.9513
2943/186/190
1.048
0.9949 and 0.9755
6837/0/335
1.003
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0806, wR2 = 0.1459
R1 = 0.1864, wR2 = 0.1870
0.561 and À0.583
R1 = 0.0700, wR2 = 0.1596
R1 = 0.1074, wR2 = 0.1843
0.654 and À0.498
R1 = 0.0572, wR2 = 0.1151
R1 = 0.1192, wR2 = 0.1393
0.317 and À0.360
R indices (all data)
Largest difference in peak and hole (e ÅÀ3
)
10
11
CCDC deposit number
789841
789842
Formula
Formula weight (Da)
T (K)
C75H104N4S2Cr2
1229.74
120(2)
C33H49N2OCr
541.74
120(2)
k (Å)
0.71073
triclinic
P1
0.71073
orthorhombic
Pnma
Red
Crystal system
Space group
Color
ꢀ
green
a (Å)
b (Å)
c (Å)
12.021(3)
12.821(3)
13.525(4)
91.004(4)
114.494(3)
109.114(4)
1763.5(8)
1
18.645(5)
20.586(4)
8.3968(19)
90
90
90
3222.9(13)
4
1.116
0.380
1172
0.41 Â 0.27 Â 0.10
1.98–25.00
99.3%
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmÀ3
)
1.158
0.410
662
l
(Mo K
F(0 0 0)
Crystal size (mm)
a
) (mmÀ1
)
0.26 Â 0.07 Â 0.05
h Range for data collection (°)
Completeness to hmax = 25°
1.68–28.25
99.7%
Maximum and minimum transmission
0.9782 and 0.9016
7923/9/410
1.063
0.9637 and 0.8613
2904/0/180
1.065
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0766, wR2 = 0.0947
R1 = 0.1540, wR2 = 0.1137
0.470 and À0.349
R1 = 0.0561, wR2 = 0.1736
R1 = 0.0709, wR2 = 0.1943
0.635 and À0.498
R indices (all data)
Largest difference in peak and hole (e ÅÀ3
)

W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
115
Fig. 9. Molecular diagram of NniPrCr[CN(C6H4(Me)2]4 (9) with 30% probability ellipsoids. Hydrogen atoms have been omitted for clarity.
Ar
Ar
Ar
S
S
N
N
N
N
N
N
10
Cr
Cr
Cr
O
11
Ar
Ar
Ar
S
O
O
S
Ar
Ar
N
N
N
N
N
N
Cr
Cr
Ar
Ar
Scheme 4. Synthesis of [NniPrCr( -SPh)]2 (10) and NniPrCr[OC(Me)3] (11).
l

116
W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
Table 9
Table 10
Selected interatomic distances (Å) and angles (°) for NniPrCr[CN(C6H4(Me)2]4 (9).
Selected interatomic distances (Å) and angles (°) for [NniPrCr(
l-SPh)]2 (10).
Distances (Å)
Distances (Å)
Cr–C1
C1–N1
Cr–C10
1.948(2)
1.171(3)
1.950(3)
C10–N2
Cr–N3
1.182(3)
2.1332(19)
Cr–S1
Cr–S1A
Cr–N1
2.4645(12)
2.4414(12)
2.056(3)
Cr–N2
Cr–CrA
2.055(3)
3.627(4)
Angles (°)
N3–Cr–C1
N3–Cr–C10
Angles (°)
N1–Cr–S1
N1–Cr–S1A
C1–S1–Cr
92.41(8)
89.86(9)
C1–Cr–C10
C1–Cr–C1A
86.19(10)
81.47(13)
162.00(8)
96.68(8)
C1–S1–CrA
Cr–S1–CrA
97.19(14)
95.33(4)
108.25(13)
4.2.1. Preparation of (NniPrCr)2(
l
2-NAd) (2)
the solution effervesced. The solution was stirred for 1 h after
which time the solvent was removed and the product was ex-
tracted with pentane. Concentration and cooling of the solution
to À30 °C yielded red crystals of 3 (0.051 g, 70% yield). 1H NMR
(400 MHz, THF-d8): 57.5 (br), 11.83 (br), 9.97 (br), 6.67 (br), 5.71
(br), 2.37 (br), À9.8 (br), À13.1 (br) ppm. IR (KBr): 2962 (m),
2907 (s), 2850 (m), 1653 (w), 1515 (m), 1508 (m), 1457 (m),
1436 (m), 1384 (m), 1372 (m), 1354 (s), 1315 (m), 1261 (m),
1167 (w), 1129 (w), 1101 (m), 1009 (m), 1048 (w), 1016 (m),
Compound (1) (0.050 g, 0.052 mmol) was dissolved in 20 mL
THF. 1-Azidoadamantane (0.006 g, 0.052 mmol) was added, where-
upon the solution effervesced. The solution was stirred for 1 h after
which time the solvent was removed and the product was ex-
tracted with pentane. Concentration and cooling of the solution
to À30 °C yielded red/brown crystals of 2 (0.038 g, 68% yield). 1H
NMR (400 MHz, THF-d8): 39.7 (br), 6.89 (br), 6.39 (br), 5.67 (br),
4.81 (br), 3.05 (br), 2.37 (br), 1.31 (br), À4.72 (br) ppm. IR (KBr):
2964 (vs), 2904 (s), 2847 (s), 1530 (m), 1511 (s), 1469 (s), 1438
(s), 1373 (vs), 1357 (m), 1343 (m), 1315 (s), 1300 (m), 1260 (m),
1225 (w), 1197 (w), 1170 (m), 1107 (m), 1097 (m), 1060 (w),
1047 (m), 1017 (s), 936 (w), 852 (w), 796 (s), 760 (w), 752
934 (w), 795 (m), 759 (w) cmÀ1. UV–Vis (pentane): kmax
(e) = 391
(6323 MÀ1 cmÀ1), 469 (1620 MÀ1 cmÀ1), 659 (322 MÀ1 cmÀ1) nm.
leff (293 K) = 3.7(1) lB. Mp: 222 °C (dec). Mass Spectrum m/z (%):
417.0
(22)
[(M+ÀN2–(C10H15N)2–Cr.
Anal.
Calc.
for
(w) cmÀ1. UV–Vis (pentane): kmax
(e
) = 660 (189 MÀ1 cmÀ1) nm.
C49H71N6CrÃC5H12: C, 74.69; H, 9.64; N, 9.68. Found: C, 74.66; H,
leff (293 K) = 5.3(1)
l
B. Mp: 206 °C (dec). Mass Spectrum m/z (%):
9.10; N, 10.42%.
616.0 (4) [M+ÀCr–C29H41N2], 469.2 (16) [M+ÀCr–C29H41N2–
C
10H15N], 417.3 (24) [M+À(Cr)2–C29H41N2–C10H15N]. Anal. Calc.
4.2.3. Alternative preparation of 3
for C68H98N5Cr2: C, 74.96; H, 9.07; N, 6.43. Found: C, 75.03; H,
9.64; N, 6.00%.
Compound 1 (0.150 g, 0.156 mmol) was dissolved in 20 mL THF.
1-Azidoadamantane (0.111 g, 0.640 mmol) was added, whereupon
the solution effervesced. The solution was stirred for 18 h after
which time the solvent was removed and the product was ex-
tracted with pentane. Concentration and cooling of the solution
to À30 °C yielded red crystals of 3 (0.156 g, 63% yield).
4.2.2. Preparation of NniPrCr( 2-N4Ad2) (3)
j
Compound 2 (0.050 g, 046 mmol) was dissolved in 20 mL THF.
1-Azidoadamantane (0.025 g, 0.143 mmol) was added, whereupon
Fig. 10. Molecular diagram of [NniPrCr(
l-SPh)]2 (10) with 30% probability ellipsoids. Hydrogen atoms and co-crystallized pentane solvent molecule have been removed for
clarity.

W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
117
2 h the solution assumed a rose color after which time the THF
and remaining ketone was removed under vacuum and the residue
extracted with pentane. Concentration and cooling of the pentane
solution to À30 °C yielded rose crystals of 5 (0.083 g, 63% yield). 1H
NMR (400 MHz, C6D6): 156.6 (br), 75.3 (br), 28.0 (br), 6.58 (br),
5.48 (br), 3.53 (br), 1.42 (br), 1.23 (br) À1.31 (br) ppm. IR (KBr):
3058 (w), 2962 (vs) 2928 (s), 2869 (m), 1652 (w), 1539 (s), 1460
(m), 1436 (m), 1384 (s), 1366 (vs), 1320 (s), 1259 (m), 1176 (w),
1108 (m), 1058 (m), 1032 (m), 960 (m), 940 (s), 910 (w), 797 (s),
779 (w), 759 (w), 704 (w), 625 (w) cmÀ1. UV–Vis (pentane): kmax
(e) = 440
(999 MÀ1 cmÀ1),
496
(357 MÀ1 cmÀ1) nm.
leff
(293 K) = 3.9(1)
l
B. Mp: 133 °C (dec). Mass Spectrum m/z (%):
469.6 (100) [M+ÀC10H20O2]. Satisfactory elemental analysis for 5
could not be obtained despite repeated attempts. Best results are
as follows; Anal. Calc. C, 72.97; H, 10.05; N, 4.37. Found: C,
70.92; H, 8.81; N, 4.51%.
4.2.6. Preparation of NniPrCr( 2-N2Ph2C2H2Ph2) (6)
j
Compound 1 (0.100 g, 0.103 mmol) was dissolved in 20 mL THF
and 0.079 mg (0.436 mol) of benzylideneaniline was added, and
the solution was stirred for 30 h during which time the solution
turned dark green. The THF was removed and the residue was
extracted with pentane. Subsequent concentration and cooling to
À30 °C yielded dark green crystals of 6 (0.089 g, 52% yield). 1H
NMR (400 MHz, C6D6): 104.1 (br), 19.64 (br), 14.87 (br), 9.84 (br),
8.43 (br), 8.14 (br), 7.72 (br), 6.60 (br), 5.71 (br), 3.56 (br), 2.73
(br), 1.85 (br), À0.98 (br) ppm. IR (KBr): 3055 (m), 3023 (w),
2961 (s), 2924 (m), 2868 (m), 1588 (s), 1565 (w), 1527 (m), 1487
(s), 1465 (s), 1433 (m), 1370 (s), 1354 (m), 1314 (s), 1251 (s),
1178 (m), 1107 (m), 1090 (m), 1054 (w), 1024 (m), 993 (w), 927
(w), 901 (w), 853 (w), 795 (s), 777 (m), 758 (s), 700 (s), 642 (w),
504 (w) cmÀ1. UV–Vis (pentane): kmax
(e
) = 404 (6418 MÀ1 cmÀ1),
B. Mp: 194 °C
Fig. 11. Molecular diagram NniPrCr(OCMe3) (11) with 30% probability ellipsoids.
Hydrogen atoms have been omitted for clarity.
612 (1693 MÀ1 cmÀ1) nm. leff (293 K) = 3.7(1)
l
(dec). Mass Spectrum m/z (%): 469.3 (55) [M+ÀC26H22N2], 362.1
(27) [C26H22N2]. Anal. Calc. for C55H63N4Cr: C, 79.38; H, 7.63; N,
6.73. Found: C, 79.48; H, 7.36; N, 6.73%.
Table 11
Interatomic distances (Å) and angles (°) for NniPrCr(OCMe3) (11).
4.2.7. Preparation of NniPrCr( 2-NPhCHPh) (7)
g
Distances (Å)
Cr–N1
1.978(2)
Cr–O1
1.838(3)
Compound 1 (0.200 g, 0.206 mmol) was dissolved in 20 mL THF
and 0.079 g (0.436 mol) of benzylideneaniline was added and the
solution was stirred for 6 h. The THF was removed and the product
was extracted with pentane. Concentration and cooling to À30 °C
yielded brown crystals of 7 (0.21 g, 77%yield). 1H NMR (400 MHz,
C6D6): 101.1 (br), 19.6 (br), 14.7 (br), 9.85 (br), 5.73 (br), 4.23
(br), 1.44 (br) ppm. IR (KBr): 3055 (w), 3016 (w), 2962 (s), 2925
(s), 2867 (m), 1600 (m), 1589 (s), 1501 (s), 1465 (s), 1450 (s),
1433 (s), 1383 (s), 1370 (s), 1356 (s), 1315 (s), 1285 (m), 1243
(s), 1178 (m), 1093 (s), 1054 (m), 1025 (m), 993 (m), 966 (m),
927 (w), 900 (w), 874 (w), 854 (w), 795 (s), 777 (m), 758 (s), 700
Angles (°)
Cr–O1–C1
N1–Cr–N1A
149.3(3)
89.69(13)
N1–Cr–O1
134.86(6)
4.2.4. Preparation of NniPrCr(NAd)2 (4)
Compound 3 (0.100 g, 0.125 mmol) was placed in an Pyrex
ampoule with 25 mL THF. The N2 atmosphere was removed via
three freeze-pump-thaw cycles. The ampoule was then irradi-
ated/heated under a Pyrex-filtered 175 W UV light with stirring
for 21 days after which time the ampoule was returned to the
glovebox. The solvent was removed and the product extracted with
pentane. Cooling of the pentane extract to À30 °C yielded dark red
needles of 4 (0.045 g, 47%). 1H NMR (400 MHz, THF-d8): 7.3 (br),
2.49 (br), 1.5 (br), 1.33 (br) ppm. IR (KBr): 3057 (vw), 2964 (m),
2904 (s), 2847 (m), 1656 (vw), 1530 (w), 1510 (m), 1463 (m),
1450 (m), 1438 (m), 1374 (s), 1357 (m), 1343 (w), 1316 (m),
1300 (w), 1260 (m), 1225 (w), 1197 (w), 1170 (w), 1107 (w),
1097 (w), 1060 (w), 1017 (m), 978 (vw), 852 (vw), 796 (m), 760
(s),
691
(s) cmÀ1
.
UV–Vis
(pentane):
kmax
(e) = 364
(6908 MÀ1 cmÀ1), 604 (1165 MÀ1 cmÀ1) nm. Mp: 101 °C (dec).
Mass Spectrum m/z (%): 182.2 (100%) [C13H11N]. Anal. Calc. for
C42H52N3Cr: C, 77.50; H, 8.05; N, 6.46. Found: C, 77.40; H, 7.83;
N, 6.37%.
4.2.8. Preparation of NniPrCr(O)(NPh) (8)
Compound 1 (0.100 g, 0.103 mmol) was dissolved in 20 mL THF
and 0.022 g, (0.211 mmol) of nitrosobenzene was added where-
upon the solution effervesced. After an hour the THF was removed
and the residue extracted with pentane. Concentration and cooling
of the solution to À30 °C yielded brown crystals of 8 (0.083 g, 63%
yield). 1H NMR (400 MHz, C6D6): 82.7 (br), 11.8 (br), 7.91 (br), 3.78
(br), 2.58 (br), 1.34 (br), À3.85 (br) ppm. IR (KBr): 3057 (w), 2963
(s), 2925 (s), 2867 (m), 1653 (w), 1583 (w), 1528 (s), 1468 (s),
1439 (s), 1357 (s), 1372 (s), 1318 (s), 1289 (m), 1260 (m), 1177
(w), 1102 (w), 1057 (w), 966 (s), 932 (m), 869 (w), 799 (s), 758
(w), 752 (w) cmÀ1
(557 MÀ1 cmÀ1), 455 (944 MÀ1 cmÀ1), 659 (322 MÀ1 cmÀ1) nm. leff
(293 K) = 2.0(1) B. Mp: 264 °C (dec). Mass Spectrum m/z (%): Anal.
Calc. for C49H71N4Cr: C, 76.62; H, 9.32; N, 7.30. Found: C, 76.87; H,
8.76; N, 7.34%.
.
UV–Vis (pentane): kmax
(e) = 532
l
4.2.5. Preparation of NniPrCr( 2-O2C2Et4) (5)
j
Compound (1) (0.100 g, 0.103 mmol) was dissolved in 20 mL
THF and 10 drops of 3-pentanone were added. Over the course of

118
W.H. Monillas et al. / Inorganica Chimica Acta 369 (2011) 103–119
(m),
714
(w) cmÀ1
.
UV–Vis
(Et2O):
kmax
(e) = 364
Appendix A. Supplementary material
(1793 MÀ1 cmÀ1) nm. leff (293 K) = 1.7(1)
l
B. Mp: 209 °C (dec).
Mass Spectrum m/z (%): 469.3 (100%) [M+ÀO–NC6H5]. Anal. Calc.
for C35H46N3CrO: C, 72.88; H, 8.04; N, 7.30. Found: C, 71.84; H,
8.09; N, 7.07%.
CCDC 789832–789842 contain the supplementary crystallo-
graphic data for 2–11. 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 associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.11.024.
4.2.9. Preparation of NniPrCr[CN(C6H4(Me)2]4 (9)
Compound 1 (0.100 g, 0.103 mmol) was dissolved in 20 mL THF
and 0.109 g (0.834 mmol) of 2,6-dimethylphenylisocyanide was
added and the solution was allowed to stir overnight. The THF
was removed and the product extracted with Et2O. Concentration
and cooling of the solution to À30 °C yielded dark red crystals of
9 (0.136 g, 66%yield). 1H NMR (400 MHz, THF-d8): 12.29 (br),
10.48 (br), 8.33 (br), 7.21 (br), 2.63 (br), 1.08 (br), À0.16 (br) ppm.
IR (KBr): 3050 (w), 2961 (s), 1924 (s), 2865 (m), 2011 (m), 1953
(vs), 1459 (s), 1437 (s), 1433 (s), 1413 (s), 1384 (m), 1363 (m),
1316 (w), 1308 (m), 1261 (s), 1192 (w), 1174 (m), 1163 (m), 1098
(s), 1022 (m), 966 (w), 933 (w), 800 (m), 771 (m) cmÀ1. UV–Vis
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4.2.10. Preparation of [NniPrCr(
l-SPh)]2 (10)
Compound 1 (0.100 g, 0.103 mmol) was dissolved in 20 mL THF
and 0.024 mg (0.110 mmol) of diphenyldisulfide was added and the
solution was allowed to stir overnight. The THF was removed and
the product extracted with pentane. Concentration and cooling of
the solution to À30 °C yielded light green crystals of 10 (0.085 g,
71%yield). 1H NMR (400 MHz, THF-d8): 156.2 (br), 134.2 (br), 79.2
(br), 18.70 (br), 15.38 (br), 13.06 (br), 9.95 (br), 7.41 (br), 7.20
(br), 4.77 (br), 1.22 (br) ppm. IR (KBr): 3056 (w), 2961 (s), 2925
(s), 2867 (m), 1652 (m), 1575 (m), 1538 (s), 1476 (s), 1436 (s),
1419 (m), 1399 (s), 1384 (s), 1363 (m), 1314 (m), 1259 (m), 1174
(w), 1099 (w), 1081 (w), 1056 (w), 1024 (s), 934 (w), 794 (m),
736 (s), 760 (w), 669 (s) cmÀ1. UV–Vis (THF): kmax
(e) = 384
(2811 MÀ1 cmÀ1) nm. leff (293 K) = 5.4(1)
lB. Mp: 166 °C (dec).
Mass Spectrum m/z (%): 469.2 (100) [M+À(C9H9N)5. Anal. Calc. for
C
70H92N4Cr2S2ÃC5H12: C, 73.24; H, 8.52; N, 4.56. Found: C, 73.17,
H, 8.60; N, 4.91%.
4.2.11. Preparation of NniPrCrOC(Me)3 (11)
[NniPrCr(
l-I)]2 (0.100 g, 0.084 mmol) was dissolved in 20 mL
THF and 0.019 mg (0.169 mol) of potassium-tert-butoxide was
added. The solution quickly changes to a red color and after
20 min the THF was removed. The product was extracted with pen-
tane; concentration and cooling of the solution to À30 °C yielded
bright red crystals of 11 (0.068 g, 74%yield). 1H NMR (400 MHz,
C6D6):164.8 (br), 10.76 (br), 7.97 (br), 4.87 (br), 3.32 (br), 1.90
(br), 1.66 (br), 1.17 (br), À1.33 (br) ppm. IR (KBr): 3058 (w), 3960
(s), 2926 (m), 2867 (m), 1623 (m), 1550 (m), 1526 (m), 1457 (m),
1437 (s), 1387 (s), 1362 (m), 1349 (m), 1317 (m), 1257 (m), 1203
(m), 1176 (m), 1101 (m), 1054 (m), 1020 (m), 934 (m), 920 (w),
796 (m), 767 (m), 668 (w) cmÀ1. UV–Vis (pentane): kmax
(e
) = 512
(354 MÀ1 cmÀ1) nm.
leff (293 K) = 4.7(1) lB. Mp: 104 °C (dec). Mass
Spectrum m/z (%): 542.4 (47) [M+], 469.4 (70) [M+ÀOC4H9]. Anal.
Calc. for C33H41N2CrO: C, 73.02; H, 5.16; N, 9.29. Found: C, 73.03;
H, 4.99; N, 9.00%.
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We thank the National Science Foundation (Grants CHE-
0616375 and CHE-0911081) and the Department of Energy (Grant
DE-FG02-92ER14273) for financial support.

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