Oxidative decarbonylation of m-terphenyl isocyanide complexes of molybdenum and tungsten: Precursors to low-coordinate isocyanide complexes

Article abstract of DOI:10.1021/ic2015868

Synthetic studies are presented addressing the oxidative decarbonylation of molybdenum and tungsten complexes supported by the encumbering m-terphenyl isocyanide ligand CNAr^Dipp2 (Ar^Dipp2 = 2,6-(2,6-(i-Pr)₂C₆H₃)₂C ₆H₃). These studies represent an effort to access halide or pseudohalide M/CNAr^Dipp2 species (M = Mo, W) for use as precursors to low-coordinate, low-valent group 6 isocyanide complexes. The synthesis and structural chemistry of the tetra- and tricarbonyl tungsten complexes trans-W(CO)₄(CNAr^Dipp2)₂ and trans-W(NCMe)(CO)₃(CNAr^Dipp2)₂ are reported. The acetonitrile adducts trans-M(NCMe)(CO)₃(CNAr^Dipp2) ₂ (M = Mo, W) react with I₂ to form divalent, diiodide complexes in which the extent of decarbonylation differs between Mo and W. In the molybdenum example, the diiodide, dicarbonyl complex MoI₂(CO) ₂(CNAr^Dipp2)₂ is generated, which has an S = 1 ground state in solution. Paramagnetic group 6 MX₂L₄ complexes are rare, and the structure of MoI₂(CO) ₂(CNAr^Dipp2)₂ is discussed in relation to other diamagnetic and C_2v-distorted MX₂L₄ complexes. Diiodide MoI₂(CO)₂(CNAr^Dipp2)₂ reacts further with I₂ to effect complete decarbonylation, producing the paramagnetic tetraiodide complex trans-MoI₄(CNAr ^Dipp2)₂. The reactivity of the trans-M(NCMe)(CO) ₃(CNAr^Dipp2)₂ (M = Mo, W) complexes toward benzoyl peroxide is also surveyed, and it is shown that dicarboxylate complexes can be obtained by oxidative or salt-elimination routes. The reduction behavior of the tetraiodide complex trans-MoI₄(CNAr^Dipp2) ₂ toward Mg metal and sodium amalgam is studied. In benzene solution under N₂, trans-MoI₄(CNAr^Dipp2)₂ is reduced by Na/Hg to the η⁶-arene-dinitrogen complex, (η⁶-C₆H₆)Mo(N₂)(CNAr ^Dipp2)₂. The diiodide-η⁶-benzene complex (η⁶-C₆H₆)MoI₂(CNAr ^Dipp2)₂ is an isolable intermediate in this reduction reaction, and its formation and structure are discussed in context of putative low-coordinate, low-valent molybdenum isocyanide complexes.

Full text of DOI:10.1021/ic2015868

ARTICLE
pubs.acs.org/IC
Oxidative Decarbonylation of m-Terphenyl Isocyanide Complexes of
Molybdenum and Tungsten: Precursors to Low-Coordinate Isocyanide
Complexes
Treffly B. Ditri, Curtis E. Moore, Arnold L. Rheingold, and Joshua S. Figueroa*
Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Mail Code 0358, La Jolla,
California 92093-0358, United States
S Supporting Information
b
ABSTRACT: Synthetic studies are presented addressing the
oxidative decarbonylation of molybdenum and tungsten com-
plexes supported by the encumbering m-terphenyl isocyanide
ligand CNArDipp2 (ArDipp2 = 2,6-(2,6-(i-Pr)2C6H3)2C6H3).
These studies represent an effort to access halide or pseudoha-
lide M/CNArDipp2 species (M = Mo, W) for use as precursors to
low-coordinate, low-valent group 6 isocyanide complexes. The
synthesis and structural chemistry of the tetra- and tricarbonyl
tungsten complexes trans-W(CO)4(CNArDipp2)2 and trans-W-
(NCMe)(CO)3(CNArDipp2)2 are reported. The acetonitrile
adducts trans-M(NCMe)(CO)3(CNArDipp2)2 (M = Mo, W)
react with I2 to form divalent, diiodide complexes in which the
extent of decarbonylation differs between Mo and W. In the molybdenum example, the diiodide, dicarbonyl complex MoI2(CO)2-
(CNArDipp2)2 is generated, which has an S = 1 ground state in solution. Paramagnetic group 6 MX2L4 complexes are rare, and the
structure of MoI2(CO)2(CNArDipp2)2 is discussed in relation to other diamagnetic and C2v-distorted MX2L4 complexes. Diiodide
MoI2(CO)2(CNArDipp2)2 reacts further with I2 to effect complete decarbonylation, producing the paramagnetic tetraiodide
complex trans-MoI4(CNArDipp2)2. The reactivity of the trans-M(NCMe)(CO)3(CNArDipp2)2 (M = Mo, W) complexes toward
benzoyl peroxide is also surveyed, and it is shown that dicarboxylate complexes can be obtained by oxidative or salt-elimination
routes. The reduction behavior of the tetraiodide complex trans-MoI4(CNArDipp2)2 toward Mg metal and sodium amalgam is
studied. In benzene solution under N2, trans-MoI4(CNArDipp2)2 is reduced by Na/Hg to the η6-arene-dinitrogen complex,
(η6-C6H6)Mo(N2)(CNArDipp2)2. The diiodide-η6-benzene complex (η6-C6H6)MoI2(CNArDipp2)2 is an isolable intermediate in
this reduction reaction, and its formation and structure are discussed in context of putative low-coordinate, low-valent molybdenum
isocyanide complexes.
’ INTRODUCTION
relationship between organoisocyanides and CO8 and (ii) the
established ability of the m-terphenyl framework9 to stabilize
low-coordinate transition-metal and main-group complexes.10
Indeed, when studied in conjunction with zerovalent group 10 metals,
CNArMes2 and CNArDipp2 have been shown to effectively stabilize
isocyanide analogues of the binary carbonyls, [Ni(CO)3]11,12 and
[Pd(CO)2].13 In addition, the CNArMes2 ligand has been used to
provide a stable, homoleptic isocyanide analogue of Co(CO)4,14
which has been proposed as a reactive intermediate15 in cobalt
carbonyl-catalyzed hydroformylation (oxo catalysis).16 Accordingly,
we reasoned that these encumbering isocyanides could simi-
larly provide a protective shield for group 6 species of the type
[M(CNR)4], [M(CNR)3], or [M(CNR)2], without signifi-
cantly affecting their preferred coordination geometries (i.e.,
cis-divacant octahedral-C2v, trigonal pyramidal-C3v, and bent-
C2v, respectively).3ꢀ5
The unsaturated group 6 metal carbonyls, as exemplified by
[Mo(CO)4], [Mo(CO)3], and [Mo(CO)2],1,2 serve as the con-
ceptual hallmark for metal-defined coordination geometry.3ꢀ5
Paradoxically, the properties that render these species so intriguing
have also prevented systematic surveys of their reactivity patterns.
Thus, the high inherent reactivity of the unsaturated group 6
carbonyls, as derived from the juxtaposition of unencumbering
ligands, low-coordination numbers, electron-rich metal centers,
and a strongly π-acidic ligand field, has required that they be
generated and observed by gas phase or matrix isolation techni-
ques. Accordingly, definitive atomic-level detail of their structures
and information regarding their reactivity toward substrates is
limited.
In an effort to construct isolable analogues of the unsaturated
transition-metal carbonyls, we have recently introduced the m-terphe-
nyl isocyanide ligands CNArMes2 and CNArDipp2 (ArMes2 =2,6-(2,4,6-
Me3C6H2)2C6H3; ArDipp2 = 2,6-(2,6-(i-Pr)2C6H3)2C6H3).6,7
These ancillaries were targeted because of (i) the isolobal
Received: July 24, 2011
Published: September 16, 2011
r
2011 American Chemical Society
10448
dx.doi.org/10.1021/ic2015868 Inorg. Chem. 2011, 50, 10448–10459
|

Inorganic Chemistry
ARTICLE
Scheme 1
Figure 2. Molecular structure of trans-W(CO)4(CNArDipp2)2 (2-W) at
the 35% probability level. Selected bond distances (Å) and angles (deg):
W1ꢀC1 = 2.081(10); W1ꢀC2 = 2.084(9); W1ꢀC3 = 2.049(7);
W1ꢀC4 = 2.041(7); C1ꢀW1ꢀC2 = 180.000(2); C1ꢀW1ꢀC3 =
91.82(17); C1ꢀW1ꢀC4 = 90.43(18); C2ꢀW1ꢀC3 = 91.82(17);
C2ꢀW1ꢀC4 = 89.57(18); C3ꢀW1ꢀC4 = 93.1(2).
We initially hoped that chemical reduction of commercially
available group 6 metal halides in the presence of CNArDipp2
would provide a straightforward route to low-valent, low-coor-
dinate [M(CNArDipp2)n] complexes. Such methods have been
successful for the synthesis of homoleptic M(CNR)6 complexes
of the low-valent group 6 metals,17,18 in addition to low-valent
isocyanides of other metals such as Fe19 and Co.14 In our hands,
however, such reduction experiments using CNArDipp2 have led
to intractable mixtures. We have also found that addition of
CNArDipp2 to common molybdenum starting materials20 such as
MoCl3(THF)3 or MoCl4(NCMe)2 does not result in productive
isocyanide binding. Presumably, the presence of chloride ligands
renders these Mo centers insufficiently Lewis acidic to tightly
bind the encumbering CNArDipp2 isocyanide.21 Accordingly, we
have pursued an alternate synthetic strategy to access precursor
compounds. On the basis of our previous findings that CNArDipp2
readily binds to the zerovalent [Mo(CO)3(sol)] (sol = solvento)
fragment,7 we focused on an approach involving oxida-
tive decarbonylation of preformed group 6 M(sol)(CO)3-
(CNArDipp2)2 complexes in a manner that preserves metal-
isocyanide ligation. This approach was inspired in part from
Colton’s classic oxidative-decarbonylation studies of the homo-
leptic group 6 carbonyls with elemental halogens.22ꢀ28
Figure 1. Molecular structure of trans-W(NCMe)(CO)3(CNArDipp2
)
2
(1-W) at the 35% probability level. Selected bond distances (Å) and
angles (deg): W1ꢀC1 = 2.067(4); W1ꢀC2 = 2.029(6); W1ꢀN2 =
2.262(10); C1ꢀW1ꢀC10 = 180.0(3); C2ꢀW1ꢀC20 = 179.998(1);
C5ꢀW1ꢀN2 = 176.5(13); C1ꢀW1ꢀC5 = 90.9(7); C1ꢀW1ꢀN2 =
91.5(4); C1ꢀW1ꢀC2 = 90.5(2).
’ RESULTS AND DISCUSSION
A. Synthesis of W(sol)n(CO)4-n(CNArDipp2
) Complexes.
2
Previously, we reported that treatment of 2.0 equiv of CNArDipp2
with Mo(CO)3(NCR)3 (R = Me or Et) produced a mixture of
the tricarbonyl and tetracarbonyl molybdenum complexes trans-
Mo(NCMe)(CO)3(CNArDipp2)2 (1-Mo) and trans-Mo(CO)4-
(CNArDipp2)2 (2-Mo).7 As shown in Scheme 1, a similar mixture
of tungsten complexes is available by combination of CNArDipp2
and W(CO)3(CNEt)3 in a 2:1 ratio. Extended photolysis of this
mixture in 1:1 Et2O/MeCN solution with a low-pressure Hg
Our approach toward the synthesis of these low-coordinate,
group 6 species has focused on the reduction of suitable mid- to
high-valent isocyanide precursor complexes. Herein we present
synthetic studies leading to such iodo- and carboxylate-contain-
ing precursors supported by the isocyanide CNArDipp2 specifi-
cally. Furthermore, we provide evidence that chemical reduction
of molybdenum-iodo species, in particular, lead to low-coordi-
nate Mo-CNArDipp2 complexes that can be trapped by arene-
solvent molecules.
lamp (254 nm) provides trans-W(NCMe)(CO)3(CNArDipp2
(1-W) as the exclusive product. Correspondingly, addition of an
excess of CO to the mixture is sufficient to fully generate trans-
W(CO)4(CNArDipp2)2 (2-W). As expected, single-crystal X-ray
)
2
10449
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
Table 1. νCN and νCO Stretching Frequencies
complex
νCN (cm-1) νCO (cm-1)
trans-W(NCMe)(CO)3(CNArDipp2)2 (1-W)a
2026(s)
1996(s)
1886(s)
1873(s)
1863(m)
1895(s)
1873(s)
1864(m)
1926(vs)
trans-Mo(NCMe)(CO)3(CNArDipp2)2 (1-Mo)a,b 2027(s)
1998(s)
trans-W(CO)4(CNArDipp2)2 (2-W)a
trans-Mo(CO)4(CNArDipp2)2 (2-Mo)a,b
WI2(CO)3(CNArDipp2)2 (3-W)c
2061(s)
2009(w)
2061(s)
2005(w)
2150(s)
2099(m)
1932(vs)
2037(s)
1982(vs)
1944(s)
2004(s)
1994(s)
1982(s)
1940(w)
2006(s)
1997(s)
1969(s)
1947(w)
Figure 3. Molecular structure of WI2(CO)3(CNArDipp2)2 (3-W) at the
35% probability level. Selected bond distances (Å) and angles (deg):
W1ꢀC1 = 2.113(6); W1ꢀC2 = 2.134(6); W1ꢀC3 = 2.032(7);
W1ꢀC4 = 1.980(7); W1ꢀC5 = 2.039(6); W1ꢀI1 = 2.8401(5);
W1ꢀI2 = 2.8174(5); C1ꢀW1ꢀC2 = 168.7(2); I1ꢀW1ꢀC5 =
trans,trans,trans-MoI2(CO)2(CNArDipp2)2 (4)c
cis,cis,trans-MoI2(CO)2(CNArDipp2)2 (4)a,d
trans,trans,trans-MoI2(CO)2(CNArDipp2)2 (4)a,d
MoI2(THF)(CO)2(CNArDipp2)2 (5)e
trans-MoI4(CNArDipp2)2 (6)c
2109(vs)
2110(vs)
2110(vs)
2079(vs)
159.5(2); I2ꢀW1ꢀC3
=
159.3(2); C1ꢀW1ꢀI1
= 80.20(15);
C1ꢀW1ꢀI2 = 82.08(15); C1ꢀW1ꢀC3 = 108.2(2); C1ꢀW1ꢀC4 =
76.2(3); C1ꢀW1ꢀC5 107.2(3); C2ꢀW1ꢀI1 90.97(15);
C2ꢀW1ꢀI2 = 90.79(15); C2ꢀW1ꢀC3 = 76.0(3); C2ꢀW1ꢀC4 =
90.97(15);
=
=
115.1(3); C2ꢀW1ꢀC5
=
78.9(3); C2ꢀW1ꢀI1
=
C2ꢀW1ꢀI2 = 90.79(15); I1ꢀW1ꢀI2 = 89.452(18); I1ꢀW1ꢀC3 =;
C3ꢀW1ꢀC4 = 75.1(2); C4ꢀW1ꢀC5 = 71.7(3); C5ꢀW1ꢀI2 = 73.1(2).
2163(s)
2135(w)
2135(w)
2071(vs)
2131(w)
2068(vs)
2107(w)
2032(vs)
2142(vs)
1979(m)
1927(vs)
2086(m)
2040(vs)
2007(w)
W(O2CPh)2(CO)2(CNArDipp2)2 (7)c
W(O2CMe)2(CO)2(CNArDipp2)2 (8-W)c
Mo(O2CMe)2(CO)(CNArDipp2)2 (9)c
2002(w)
1949(vs)
2002(w)
1943(vs)
2007(s)
Scheme 2
1921(m)
trans-MoI3(THF)(CNArDipp2)2 (10)c
(η6-C6H6)Mo(N2)(CNArDipp2)2 (11)c
(η6-C6H6)MoI2(CNArDipp2)2 (12)c
a KBr pellet. b Spectrum taken in C6D6 solution in ref 7 and KBr pellet
for this work. c C6D6 solution. d Crystalline mixture of trans,trans,trans-
MoI2(CO)2(CNArDipp2
e THF solution.
)
and cis,cis,trans-MoI2(CO)2(CNArDipp2)2.
2
diffraction revealed that both trans-W(NCMe)(CO)3(CNArDipp2
)
2
(1-W) and trans-W(CO)4(CNArDipp2)2 (2-W) are isostructural with
their Mo counterparts (Figures 1 and 2).7 In addition, the IR spectra
of trans-W(NCMe)(CO)3(CNArDipp2)2 (1-W) and trans-W(CO)4-
(CNArDipp2)2 (2-W) are identical in pattern to their Mo congeners
and feature the expected slight shift of the νCO bands to lower energy
(Table 1).29 This shift is consistent with the increased π-basicity of W
relative to Mo. Despite the presence of a labile NCMe ligand, trans-
W(NCMe)(CO)3(CNArDipp2)2 (1-W), like its Mo counterpart,
resists ligation of another equivalent of CNArDipp2 and does not eng-
age in isocyanide exchange as assayed by 1H NMR and IR spectros-
copy (C6D6, 20 °C).
isolation of stable m-terphenyl-isocyanide-ligated Cu and Co
iodo complexes in a range of formal oxidation states.6,30 Notably,
direct treatment of CNArDipp2 with the trivalent molybdenum
complex, MoI3(THF)3,31 resulted in an array of products and
insoluble materials. We believe that aggregation and dispropor-
tionation processes of incipiently formed [MoI3(CNArDipp2
)
(sol)n] complexes may kinetically compete with the binding of a
second isocyanide, ultimately leading to undesired products.32
We reasoned that preligation of two CNArDipp2 units to the metal
center may succeed in controlling reaction outcomes by (i)
sterically inhibiting multinuclear aggregation and (ii) disfavoring
electron transfer reactions by furnishing strong π-back-bonding
interactions. Importantly, a cursory survey showed that the tetra-
carbonyl complexes trans-M(CO)4(CNArDipp2)2 (M=Mo(2-Mo),
W (2-W)) did not react with elemental iodine under ambient
B. Chemical Oxidation of M(NCMe)(CO)3(CNArDipp2
Complexes with I2. To promote isocyanide retention in higher
valent complexes, we targeted group 6 metal centers featuring
multiple iodide ligands. This choice stemmed from the successful
)
2
10450
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
Figure 5. Molecular structure of MoI2(THF)(CO)2(CNArDipp2)2 (5)
at the 35% probability level. Selected bond distances (Å) and angles
(deg): Mo1ꢀC1 = 2.121(6); Mo1ꢀC2 = 2.114(6); Mo1ꢀC3 =
1.977(7); Mo1ꢀC4 = 1.960(8); Mo1ꢀI1 = 2.8531(6); Mo1ꢀI2 =
2.8523(6); Mo1ꢀO3
=
2.199(4); C1ꢀMo1ꢀC2
= 178.0(2);
C3ꢀMo1ꢀI1 = 72.0(2); C3ꢀMo1ꢀC4 = 68.2(3); C4ꢀMo1ꢀI2 =
70.8(2); I1ꢀMo1ꢀI2 = 154.32(2); I1ꢀMo1ꢀO3 = 77.34(10);
I2ꢀMo1ꢀO3 = 77.09(10).
Scheme 3
Figure 4. Disorder models for the molecular structure of MoI2(CO)2-
(CNArDipp2)2 (4). Top: disorder model for trans,trans,trans -MoI2(CO)2-
(CNArDipp2)2. Bottom: disorder model for cis,cis,trans- MoI2-
(CO)2(CNArDipp2)2. Both isomers are present in crystals of MoI2-
(CO)2(CNArDipp2)2 (4) grown from toluene at ꢀ35 °C.
solution at 20 °C indicates the presence of a single species with
resonances ranging from +16.18 to ꢀ6.33 ppm (Figure S1). This
species is persistent at room temperature for at least 24 h as
conditions (THF, 20 °C). We therefore focused on the reactivity
of the acetonitrile adducts trans-M(NCMe)(CO)3(CNArDipp2
)
2
1
(M = Mo, W;1-M) toward I2, in anticipation that dissociation of the
labile NCMe ligand would promote inner-sphere oxidation events.
Importantly, this isocyanide retention strategy was successful,
but the extent of decarbonylation between the Mo and W con-
geners differed. Accordingly, treatment of the tungsten derivative
trans-W(NCMe)(CO)3(CNArDipp2)2 (1-W) with 1.0 equiv of I2
in Et2O readily afforded the seven-coordinate complex, WI2-
(CO)3(CNArDipp2)2 (3-W), as determined by X-ray diffraction
(Scheme 1, Figure 3). The solid-state geometry of WI2(CO)3-
(CNArDipp2)2 (3-W) is readily described as capped-octahedral33
and is similar to other structurally characterized MX2(CO)n(L)m
(m = 5 ꢀ n) group 6 complexes.34 In the solid state, WI2(CO)3-
(CNArDipp2)2 (3-W) possesses mirror symmetry and two in-
equivalent CO sites. However, its 13C{1H} NMR spectrum in
C6D6 at 20 °C shows only one carbonyl resonance, thus
indicating that the encumbering CNArDipp2 ligands do not
impede CO-ligand site exchange in solution at this temperature.
In contrast to its W counterpart, treatment of trans-Mo-
(NCMe)(CO)3(CNArDipp2)2 (1-Mo) with 1.0 equiv of I2 in
Et2O solution leads to CO loss and formation of the paramag-
netic dicarbonyl complex, MoI2(CO)2(CNArDipp2)2 (4, Scheme 2).
Evans method magnetic moment determination (C6D6/
(Me3Si)2O, 20 °C) resulted in a μeff value of 2.71(3) μB,
consistent with an S = 1 ground state in solution for the d4
Mo center in MoI2(CO)2(CNArDipp2)2 (4). Importantly, the
1H NMR spectrum of MoI2(CO)2(CNArDipp2)2 (4) in C6D6
assayed by H NMR spectroscopy, and no additional reso-
nances appear in spectra recorded over this time. However,
while structural determination on red crystals grown from
toluene at ꢀ35 °C revealed a six-coordinate complex with
trans-disposed isocyanides, refinement indicated a 50/50
mixture of the cis- and trans-carbonyl orientations in the solid
state (Figure 4). In C6D6 solution and before crystallization
from toluene, MoI2(CO)2(CNArDipp2)2 (4) features a single
νCN band (2109 cmꢀ1) and two strong, closely separated νCO
bands (2004 and 1994 cmꢀ1) in its IR spectrum (Table 1). We
attribute the close separation of the νCO bands to splitting of a
single band from coupling with other vibronic modes and
therefore assign this species as the trans-dicarbonyl isomer of
MoI2(CO)2(CNArDipp2
) (4). A solid-state IR spectrum
2
(KBr) on the toluene-grown crystals, however, features an
additional set of well-separated νCO bands of unequal inten-
sity (1982 and 1940 cmꢀ1), which we believe indicates the
presence of the cis-dicarbonyl complex in the solid state
(Table 1). Dissolution of these crystals in C6D6 followed by
1
analysis with both H NMR and IR spectroscopy within 20
min revealed near-complete regeneration of the spectroscopic
signatures for the trans-dicarbonyl isomer.35 Although we have not
performed further investigations, these results suggest that a rapid
isomerization process is available to MoI2(CO)2(CNArDipp2)2 (4)
that favors the trans-dicarbonyl configuration in solution at room
temperature.
10451
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
Scheme 4
Figure 6. Molecular structure of trans-MoI4(CNArDipp2)2 (6) at the
35% probability level. Selected bond distances (Å) and angles (deg):
Mo1ꢀC1 = 2.148(5); Mo1ꢀI1 = 2.6508(8); Mo1ꢀI2 = 2.7380(7);
C1ꢀMoꢀI10 = 89.26(13); C10ꢀMoꢀI10 = 90.74(13); I1ꢀMo1ꢀ
I2 = 90.0.
Most interestingly, the room-temperature dominant isomer of
MoI2(CO)2(CNArDipp2)2 (4) represents a very rare paramag-
netic group 6 complex with the general formula MX2(CO)2L2
(cis- or trans-(CO)2).25,36 Indeed, the stability of 16eꢀ, d4
MX2(CO)2L2 complexes (M = Mo, W) is well-known to arise
from a pronounced Oh f C2v electronic distortion that promotes
a large HOMOꢀLUMO gap and, consequently, spin-pairing.37
However, it has been proposed that strong π-acceptor L ligands,
trans-oriented as found in trans-MoI2(CO)2(CNArDipp2)2, can
stabilize an octahedral S = 1 MX2(CO)2L2 complex.37 In this
context MoI2(CO)2(CNArDipp2)2 (4) is notable, as the com-
plexes [MX2(CO)4] (M = Mo, W; X = Cl, Br, I), which are the
prototypical MX2(CO)2L2 examples containing only π-acidic
ligands, have been well established as bridging-halide dimers
featuring seven-coordinate, diamagnetic metal centers.22,27,38ꢀ40
As shown in Figure 4, the isomers of MoI2(CO)2(CNArDipp2
)
2
(4) possess fairly regular octahedral coordination geometries,
with CꢀMoꢀC angles of 178.0(3)° and 180.0(3)° between the
two trans-CNArDipp2 ligands in the crystallographically indepen-
dent molecules.
Figure 7. Molecular structure of W(O2CPh)2(CO)2(CNArDipp2)2 (7)
at the 35% probability level. Selected bond distances (Å) and angles
(deg): W1ꢀC1 = 2.038(6); W1ꢀC2 = 2.065(6); W1ꢀC3 = 2.018(7);
WꢀC4 = 2.012(7); W1ꢀO3 = 2.204(4); W1ꢀO4 = 2.222(4); W1ꢀ
O5 = 2.058(4); C1ꢀW1ꢀC2 = 120.1(2); C1ꢀW1ꢀC3 = 72.4(2);
C1ꢀW1ꢀC4 = 73.9(2); C2ꢀW1ꢀC3 = 74.2(2); C2ꢀW1ꢀC4 =
74.2(2); C1ꢀW1ꢀO3 = 117.00(19); C1ꢀW1ꢀO4 = 76.7(2);
C2ꢀW1ꢀO5 = 95.9(2); O3ꢀW1ꢀO4 = 58.90(15); O3ꢀW1ꢀO5 =
78.46(17); O4ꢀW1ꢀO5 = 74.19(17).
As expected from its electronically unsaturated nature, MoI2-
(CO)2(CNArDipp2)2 (4) can bind additional Lewis basic ligands.
Thus, dissolution in THF, followed by crystallization, provides the
seven-coordinate, pentagonal bipyramidal complex MoI2(THF)-
(CO)2(CNArDipp2
) (5) as determined by X-ray diffraction
2
(Scheme 2, Figure 5). The THF ligand in MoI2(THF)(CO)2-
(CNArDipp2)2 (5) is labile, and readily dissociates when the
complex is dissolved in C6D6 solution. Furthermore, placement
of MoI2(CO)2(CNArDipp2)2 (4) under a CO atmosphere (1 atm)
results in an equilibrium mixture between it and a diamagnetic
species (Scheme 2). Wepresumethat this speciesisthe tricarbonyl
complex, MoI2(CO)3(CNArDipp2)2 (3-Mo), on the basis of its
Thus, treatment of WI2(CO)3(CNArDipp2)2 (3-W) with another
equivalent of I2 results in no reaction, whereas MoI2(CO)2-
(CNArDipp2)2 (4) reacts readily in fluorobenzene (C6H5F) to
form the tetraiodo-complex trans-MoI4(CNArDipp2)2 (6, Scheme 3,
Figure 6). As expected, trans-MoI4(CNArDipp2)2 (6) is para-
1H NMR spectroscopic similarities to WI2(CO)3(CNArDipp2
)
2
(3-W). However, removal of the CO atmosphere from the reac-
tion mixture readily regenerates MoI2(CO)2(CNArDipp2)2 (4). This
behavior is similar to that reported for other d4 MoX2(CO)2L2
complexes.27,41 Notably, the tungsten complex WI2(CO)3-
(CNArDipp2)2 (3-W) shows no tendency to release CO at
temperatures up to 80 °C (C6D6).
magnetic and gives rise to solution magnetic moment of μeff =
2.90(3) μB, consistent with an S = 1, d2 metal center. The IR
spectrum of trans-MoI4(CNArDipp2)2 (6) in C6D6 solution is
also consistent with its formulation and exhibits νCN bands ca.
30ꢀ60 cmꢀ1 higher in energy than the corresponding band in d4,
MoI2(CO)2(CNArDipp2)2 (4). Thus, complete oxidative decarbonyla-
tion of Mo(NCMe)(CO)3(CNArDipp2)2 (1-Mo) with isocyanide
retention can be achieved for molybdenum in two synthetic steps.
Another contrast between these d4 Mo- and W-CNArDipp2
systems is that only the Mo complex is reactive toward additional I2.
10452
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
Scheme 5
Figure 8. Molecular structure of W(O2CMe)2(CO)2(CNArDipp2
)
2
(8-W) at the 35% probability level. Selected bond distances (Å) and angles
(deg): W1ꢀC1 = 2.077(4); W1ꢀC2 = 2.037(4); W1ꢀC3 = 1.999(4);
W1ꢀC4 = 2.022(4); W1ꢀO3 = 2.213(2); W1ꢀO4 = 2.191(3);
W1ꢀO5 = 2.083(2); C1ꢀW1ꢀC2 = 121.23(14); C1ꢀW1ꢀC3 =
75.43(14); C1ꢀW1ꢀC4 = 75.04(14); C2ꢀW1ꢀC3 = 70.98(13);
C2ꢀW1ꢀC4 = 74.40(14); C1ꢀW1ꢀO3 = 108.77(12); C1ꢀW1ꢀ
O5 = 85.69(12); C2ꢀW1ꢀO4 = 77.90(12); O3ꢀW1ꢀO4 = 59.01(9);
O3ꢀW1ꢀO5 = 75.60(10); O4ꢀW1ꢀO5 = 77.14(10).
Unfortunately, we have found that much lower yields of trans-
MoI4(CNArDipp2)2 (6) result from treatment of Mo(NCMe)-
(CO)3(CNArDipp2)2 (1-Mo) with 2.0 equiv of I2 (ca. 20%), than
are obtained when MoI2(CO)2(CNArDipp2)2 (4) is isolated and
treated with I2 in a subsequent step (ca. 40ꢀ45% overall). Notably,
trans-MoI4(CNArDipp2)2 (6) represents, to our knowledge, the first
example of a structurally characterized, neutral d2 MoI4L2
complex.42,43
C. Acyl Peroxide Oxidation and Coordinatively Induced
Decarbonylation. In addition to iodine, it was of interest to
survey if other chemical oxidants could similarly decarbonylate
these M(sol)(CO)3(CNArDipp2)2 (1-M) complexes while re-
taining isocyanide ligation. Particularly appealing were reagents
that could deliver oxidizing equivalents while promoting addi-
tional decarbonylation events via secondary coordination. In this
respect acyl peroxides were intriguing prospects. It was
anticipated that the ability of acyl peroxides to effect 2eꢀ
oxidations, coupled with the propensity for k2-coordination of
the resultant carboxylate ligands, could potentially induce the
dissociation of several monodentate CO ligands. Further-
more, carboxylate complexes of medium- and high-valent
Mo and W are known,44ꢀ47 and could serve as useful pre-
cursors for subsequent reduction reactions.
Addition of benzoyl peroxide to trans-W(NCMe)(CO)3-
(CNArDipp2)2 (1-W) in THF solution cleanly provided the
orange, bis-benzoate dicarbonyl complex, W(O2CPh)2(CO)2-
(CNArDipp2)2 (7, Scheme 4). Crystallographic structure deter-
mination revealed both k2- and k1-coordinated benzoate groups
and an overall seven-coordinate geometry best described as a 4:3
piano stool (Figure 7).48 The 1H NMR spectrum of W(O2CPh)2-
(CO)2(CNArDipp2)2 (7) at room temperature (C6D6) exhibits
onlyonebenzoate environment, thus indicating interconversion of
the k2- and k1-coodinated ligands. Such coordination behavior has
been observed previously for group 6 dicarboxylate complexes47,49
and, in this system, undoubtedly aids the loss of CO from the
Figure 9. Molecular structure of Mo(O2CMe)2(CO)(CNArDipp2
)
2
(9) at the 35% probability level. Selected bond distances (Å) and angles
(deg): Mo1ꢀC1 = 2.017(3); Mo1ꢀC2 = 2.051(2); Mo1ꢀC7 =
1.967(3); Mo1ꢀO1 = 2.2175(16); Mo1ꢀO2 = 2.1435(17); Mo1ꢀO3
= 2.2085(18); Mo1ꢀO4 = 2.2285(17); C1ꢀMo1ꢀC2 = 118.69(9);
C1ꢀMo1ꢀC7
=
73.20(10); C1ꢀMo1ꢀO3
=
81.11(8);
C1ꢀMo1ꢀO1 = 79.12(8); C2ꢀMo1ꢀC7 = 76.58(9); C2ꢀMo1ꢀO3
= 80.44(8); C2ꢀMo1ꢀO2 = 107.77(8); C2ꢀMo1ꢀO4 = 86.96(8);
O1ꢀMo1ꢀO2 = 59.77(6); O1ꢀMo1ꢀO4 = 80.21(6); O2ꢀMo1ꢀO4
= 88.02(7).
W center relative to the diiodide complex WI2(CO)3(CNArDipp2
)
2
(3-W). To this end, CO loss from WI2(CO)3(CNArDipp2)2 (3-W)
can be induced by addition of external carboxylate ligands. As shown
in Scheme 4, treatment of WI2(CO)3(CNArDipp2)2 (3-W) with 2
equiv of silver acetate (AgOAc) results in the diacetate com-
plex W(O2CMe)2(CO)2(CNArDipp2)2 (8-W). Crystallographic
characterization of W(O2CMe)2(CO)2(CNArDipp2
)
(8-W)
2
revealed overall structural features similar to the bis-benzoate
derivative W(O2CPh)2(CO)2(CNArDipp2)2 (7) including both
k2- and k1-coordinated carboxylate groups (Figure 8).
The molybdenum complex trans-Mo(NCMe)(CO)3(CN-
ArDipp2)2 (1-Mo) did not react cleanly with benzoyl peroxide
under a variety of conditions. However, carboxylate ligands can
be readily introduced by treatment of the diiodide complex
MoI2(CO)2(CNArDipp2)2 (4) with silver acetate (Scheme 5).
Interestingly, 1H NMR analysis of the reaction mixture after 24 h
indicated complete consumption of the starting material and the
10453
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
Scheme 6
Figure 10. Molecular structure of trans-MoI3(THF)(CNArDipp2
)
2
(10) at the 35% probability level. Selected bond distances (Å) and
angles (deg): Mo1ꢀC1 = 2.170(8); Mo1ꢀC2 = 2.173(8); Mo1ꢀI1 =
2.6925(14); Mo1ꢀI2 = 2.7507(12); Mo1ꢀI3 = 2.7497(12); Mo1ꢀ
O1 = 2.188(5); C1ꢀMo1ꢀC2 = 175.4(3); C1ꢀMo1ꢀI1 = 88.77(18);
C1ꢀMo1ꢀI2 = 93.5(2); C1ꢀMo1ꢀI3 = 88.3(2); C2ꢀMo1ꢀI1 =
presence of two new acetate-containingspecies. Afteranadditional
24 h of stirring only a single product was present, which was identified
as the monocarbonyl, diacetate complex Mo(k2-O2CMe)2(CO)-
(CNArDipp2)2 (9) by X-ray diffraction (Figure 9). While not isolated,
we strongly believe that the intermediate in this reaction is the
dicarbonyl complex Mo(O2CMe)2(CO)2(CNArDipp2)2 (8-Mo), as
87.09(19); C2ꢀMo1ꢀI2
=
88.8(2); C2ꢀMo1ꢀI3
= 90.0(2);
I2ꢀMo1ꢀI1 = 95.34(4); I2ꢀMo1ꢀI3 = 171.27(3).
1
it possesses near-identical H NMR signatures to the tungsten
congener W(O2CMe)2(CO)2(CNArDipp2)2 (8-W). Notably, de-
spite the presence of two acetate ligands, W(O2CMe)2(CO)2-
(CNArDipp2)2 (8-W) does not release an additional CO ligand in
solution at temperatures up to 80 °C. Thus, like the Mo and W
diiodide complexes discussed above, CO appears to be significantly
more labile in the Mo dicarboxylate species relative to its W congener.
Monocarbonyl Mo(k2-O2CMe)2(CO)(CNArDipp2)2 (9) also
potentially offers access to unique low-coordinate complexes upon
reduction or further elaboration. In this regard it is notable that
attempts to convert Mo(k2-O2CMe)2(CO)(CNArDipp2)2 (9) to
the five-coordinate diodide complex [MoI2(CO)(CNArDipp2)2]
via carboxylate esterification50 with Me3SiI were unsuccessful.
Instead, these reactions resulted in mixtures of the dicarbonyl
complex MoI2(CO)2(CNArDipp2)2 (4) along with several other
unidentified products (1H NMR), thereby further punctuating the
lability of the Mo-CO unit in this isocyanide-supported system.
Additional reactivity and reduction studies of these group 6
isocyanide-carboxylate complexes are ongoing.
(2-Mo) was generated in various quantities in these experiments,
which we believe again reflects the lability of the Mo-CO linkage in
these isocyanide systems. Accordingly, zerovalent, four-coordinate,
isocyanide or mixed carbonyl/isocyanide MoL4 complexes remain
desired targets.
Despite our difficulties controlling the reduction chemistry of
MoI2(CO)2(CNArDipp2)2 (4), fully decarbonylated trans-MoI4-
(CNArDipp2)2 (6) displayed much cleaner reactivity toward
chemical reductants and allowed for a more systematic survey
of its reduction behavior. As shown in Scheme 6, treatment of
trans-MoI4(CNArDipp2)2 (6) with an excess of Mg metal in THF
solution afforded the triiodide complex trans-MoI3(THF)-
(CNArDipp2)2 (10) as determined by X-ray diffraction (Figure 10).
Evans method magnetic moment determination resulted in a μeff
value of 3.95(1) μB, which is consistent with an S = 3/2 ground
state for trans-MoI3(THF)(CNArDipp2
) (10). In addition,
2
trans-MoI3(THF)(CNArDipp2)2 gives rise to a sharp νCN band
at 2142 cmꢀ1, which is lower in energy than the corresponding
band in the tetra-iodide complex trans-MoI4(CNArDipp2)2 (6) and
reflects additional electron density on the Mo center (Table 1). Most
D. Chemical Reduction of Iodo-Molybdenum Complexes
and Arene-Trapping of Low-Coordinate, Low-Valent Inter-
mediates. Synthetic access to the di- and tetravalent iodo-
molybdenum complexes, MoI2(CO)2(CNArDipp2)2 (4) and trans-
MoI4(CNArDipp2)2 (6), allowed us to probe their utility as
precursors to low-valent, low-coordinate molybdenum isocyanides.
It was hoped that reduction of MoI2(CO)2(CNArDipp2)2 (4) by
2eꢀ with concomitant iodide loss would generate the four-
coordinate complex [Mo(CO)2(CNArDipp2)2]. The latter repre-
sents a mixed isocyanide/carbonyl analogue of [Mo(CO)4] and
should similarly adopt a C2v, cis-divacant octahedral coordina-
tion geometry.1ꢀ5 Correspondingly, full reduction of tetraiodide
trans-MoI4(CNArDipp2)2 (6) to the zerovalent state could po-
tentially provide a two-coordinate molybdenum isocyanide
complex sharing the bent-C2v geometry of [Mo(CO)2].1,2,4 Dis-
appointingly, however, treatment of MoI2(CO)2(CNArDipp2)2 (4)
with a range of reducing agents resulted in complex and intractable
notably, however, the isolation of trans-MoI3(THF)(CNArDipp2
)
2
(10) via 1eꢀ reduction of trans-MoI4(CNArDipp2)2 (6) highlights
the success of isocyanide preligation as a synthetic strategy for this
system, whereas direct treatment of MoI3(THF)3 with CNArDipp2
failed to cleanly generate the desired bisisocyanide complex.
Tetraiodide MoI4(CNArDipp2)2 (6) can also be reduced past
the trivalent state when stronger reductants are employed. For
example, treatment of trans-MoI4(CNArDipp2)2 (6) with 1% Na/
Hg in C6H6 solution under an N2 atmosphere generates the
zerovalent, η6-benzene complex, (η6-C6H6)Mo(N2)(CNArDipp2
)
2
(11), which contains dinitrogen bound in an end-on fashion
(Scheme 6, Figure 11). The molecular structure of (η6-C6H6)Mo-
(N2)(CNArDipp2)2 (11) exhibits the three-legged piano stool motif
of classical group 6, (η6-arene)MoL3 complexes (L = monodentate,
2eꢀ donor ligand). However, it is noteworthy that dinitrogen-
containing variants of this class are relatively rare.51ꢀ54
mixtures. The tetracarbonyl complex trans-Mo(CO)4(CNArDipp2
)
2
10454
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
Figure 11. Molecular structure of (η6-C6H6)Mo(N2)(CNArDipp2
)
2
Figure 12. Molecular structure of (η6-C6H6)MoI2(CNArDipp2)2 (12)
at the 35% probability level. Selected bond distances (Å) and angles
(deg): Mo1ꢀC1 = 2.067(3); Mo1ꢀC2 = 2.068(3); Mo1ꢀI1 =
2.8492(12); Mo1ꢀI2 = 2.8481(19); Mo1ꢀC3 = 2.255(4); Mo1ꢀ
C4 = 2.361(4); Mo1ꢀC5 = 2.329(4); Mo1ꢀC6 = 2.275(4); Mo1ꢀ
C7 = 2.385(3); Mo1ꢀC8 = 2.330(4); C3ꢀC4 = 1.404(5); C4ꢀC5 =
1.380(5); C5ꢀC6 = 1.425(5); C6ꢀC7 = 1.402(6); C7ꢀC8 =
1.382(5); C1ꢀMo1ꢀC2 = 113.98(13); C1ꢀMo1ꢀI1 = 78.60(9);
C1ꢀMo1ꢀI2 = 75.92(9); C2ꢀMo1ꢀI1 = 76.88(9); C2ꢀMo1ꢀ
I2 = 80.93(9).
(11) at the 35% probability level. Selected bond distances (Å) and
angles (deg): Mo1ꢀC1 = 2.020(3); Mo1ꢀC2 = 2.038(3); Mo1ꢀN3 =
2.075(4); N3ꢀN4 = 1.041(6); Mo1ꢀC3 = 2.264(5); Mo1ꢀC4 =
2.291(5); Mo1ꢀC5 = 2.312(5); Mo1ꢀC6 = 2.265(5); Mo1ꢀC7 =
2.309(5); Mo1ꢀC8
=
2.322(5); C1ꢀMo1ꢀC2
= 92.63(13);
C1ꢀMo1ꢀN3 = 90.50(15); C2ꢀMo1ꢀN3 = 91.74(14).
The most intriguing aspect of (η6-C6H6)Mo(N2)(CNArDipp2
)
2
(11) concerns its formation upon reduction of trans-MoI4-
(CNArDipp2)2 (6). While it is interesting to speculate that a
zerovalent molybdenum complex of the formulation [Mo(N2)n-
(CNArDipp2)2] (n e 4) is present fleetingly in solution, aliquots
of the reaction mixture taken before complete formation of
(η6-C6H6)Mo(N2)(CNArDipp2)2 (11) revealed the presence of a
diamagnetic intermediate (1H NMR spectroscopy). This inter-
mediate was amenable to isolation by quenching the reduction
reaction after 3 h, and X-ray diffraction revealed it to be the η6-
can in fact be isolated and that it possesses a pseudotetrahedral C2v
geometry owing to the combined effects of minimizing MoꢀO
σ* interactions and maximizing MofPMe3 π-backbonding inter-
actions within the d-orbital manifold.62 While the coordination
spheres of Mo(silox)2(PMe3)2 and putative [MoI2(CNArDipp2)2]
are clearly different, they are related in that both possess a
(π-donor)2(π-acceptor)2 ligand set. However, the π-donor ability
of iodide is clearly marginal relative to silox, and the π-acceptor of
an isocyanide is much greater than that of PMe3. How these
differences will ultimately affect the chemistry available to the
[MoI2(CNArDipp2)2] fragment is intriguing. To this end, isolation
of Mo(silox)2(PMe3)2 also reveals that such low-coordinate
divalent Mo complexes can be stabilized when the proper steric
protection is employed. Accordingly, we speculate that the two-
atom linker between the metal center and the m-terphenyl unit in
[MoI2(CNArDipp2)2] is insufficient in this regard and evidently
does not preclude arene binding. Nevertheless, studies aimed at
uncovering the chemistry available to [MoI2(CNArDipp2)2] by
generation and trapping in the presence of other small molecule
substrates are continuing.
benzene, diiodide complex, (η6-C6H6)MoI2(CNArDipp2
) (12,
2
Scheme 6, Figure 12).55 In contrast to zerovalent (η6-C6H6)Mo-
(N2)(CNArDipp2)2 (11), (η6-C6H6)MoI2(CNArDipp2)2 (12) pos-
sesses an asymmetrically bound benzene ring as indicated by short
MoꢀC3 and MoꢀC6 bond distances (2.255(4) and 2.275(4) Å,
respectively) relative to the remaining MoꢀCring contacts
(2.35(3)av). This “folded” or “boat” conformation of the bound
benzene is accompanied by a fair degree of dearomatization and is
consistent with a 1,4-dienediyl formulation as observed in other
η6-arene complexes (Figure 12).56ꢀ61 Most importantly, however,
addition of 1% Na/Hg to isolated (η6-C6H6)MoI2(CNArDipp2
)
2
(12) in benzene solution under N2 generates (η6-C6H6)Mo(N2)-
(CNArDipp2)2 (11), thereby showing that the former is indeed a
plausible intermediate en route to the zerovalent state.
Several elements of this reduction scheme are noteworthy in
the context of generating low-coordinate group 6 isocyanide
complexes. At present, we hypothesize that 2eꢀ reduction of
trans-MoI4(CNArDipp2)2 (6) in benzene generates the four-
coordinate, divalent complex [MoI2(CNArDipp2)2], which is
then rapidly intercepted by solvent. Unfortunately, efforts to
selectively generate [MoI2(CNArDipp2)2] in nonaromatic sol-
vents have been unsuccessful thus far, with attempted reductions
of trans-MoI4(CNArDipp2)2 (6) in Et2O, THF, or n-pentane in
particular leading to intractable mixtures. Importantly, four-
coordinate molybdenum ML2X2 complexes are extremely un-
common, as is expected for a heavier group 6 complex with a formal
12eꢀ configuration. However, Wolczanski has recently shown
that the Mo complex, Mo(silox)2(PMe3)2 (silox = OSi(t-Bu)3),
’ EXPERIMENTAL SECTION
General Considerations. All manipulations were carried out
under an atmosphere of dry dinitrogen using standard Schlenk and glovebox
techniques. Solvents were dried and deoxygenated according to standard
procedures. Unless otherwise stated, reagent-grade starting materials
were purchased from commercial sources and were used as received or
purified by standard procedures. The isocyanide ligand CNArDipp2 7
,
W(CO)3(NCEt)3,63 Mo(CO)3(MeCN)3,63 and trans-Mo(NCMe)-
(CO)3(CNArDipp2 7 were prepared as previously reported. Benzene-
)
2
d6 (Cambridge Isotope Laboratories) was degassed and stored over 4 Å
molecular sieves under N2 for 2 days prior to use. THF-d8 was vacuum
distilled from Na metal and then stored over 4 Å molecular sieves under
N2 for 2 days prior to use. Celite 405 (Fisher Scientific) was dried under
10455
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
vacuum (24 h) at a temperature above 250 °C and stored in the glovebox
prior to use.
(0.230 g, 0.908 mmol, 1.05 equiv, 20 mL). The resulting mixture was
stirred for 1 h resulting in the precipitation of a yellow solid. The reaction
mixture was then filtered, and the resulting yellow precipitate was
washed with 10 mL of Et2O, collected, and dried in vacuo to afford
trans-WI2(CO)3(CNArDipp2)2 (3-W). Yield: 0.564 g, 0.412 mmol, 48%.
1H NMR (300.1 MHz, C6D6, 20 °C): δ = 7.34 (t, 4H, J = 8 Hz, p-Dipp),
7.20 (d, 8H, J = 8 Hz, m-Dipp), 6.89 (d, 4H, J = 8 Hz, m-Ph), 6.78 (t, 2H,
J = 7 Hz, p-Ph), 2.61 (sept, 8H, J = 7 Hz, CH(CH3)2), 1.39 (d, 24H, J = 7
Hz, CH(CH3)2), 1.00 (d, 24H, J = 7 Hz, CH(CH3)2) ppm. 13C{1H}
NMR (100.6 MHz, C6D6, 20 °C): δ = 192.5 (CꢁO), 188.5 (CꢁN),
146.4, 140.4, 134.0, 130.7, 130.1, 129.3, 128.6, 126.9, 123.9, 31.4 (CH-
(CH3)2), 24.8 (CH(CH3)2), 24.4 (CH(CH3)2) ppm. FTIR (C6D6, KBr
windows): (νCN) 2150(s) and 2099(m) cmꢀ1, (νCO) 2037(s), 1982(vs)
and 1944(s) cmꢀ1 also 2961, 2927, 2868, 1459, 1411, 1384, 1362, 1057,
794, 754 cmꢀ1. Anal. Calcd for C65H74N2O3I2W: C, 57.03; H, 5.45; N,
2.05. Found: C, 57.12; H, 5.41; N, 1.93.
Solution 1H and 13C{1H} spectra were recorded on Varian Mercury
300 and 400 spectrometers, a Varian X-Sens500 spectrometer, or a
JEOL ECA-500 spectrometer. 1H and 13C{1H} chemical shifts are
reported in ppm relative to SiMe4 (1H and 13C δ = 0.0 ppm) with
reference to residual solvent resonances of 7.16 ppm (1H) and 128.06
ppm (13C) for benzene-d6 and 1.72 ppm (1H) for THF-d8.64 FTIR
spectra were recorded on a Thermo-Nicolet iS10 FTIR spectrometer.
Samples were prepared as C6D6 solutions injected into a ThermoFisher
solution cell equipped with KBr windows or as KBr pellets. For solution
FTIR spectra, solvent peaks were digitally subtracted from all spectra by
comparison with an authentic spectrum obtained immediately prior to
that of the sample. The following abbreviations were used for the
intensities and characteristics of important IR absorption bands: vs =
very strong, s = strong, m = medium, w = weak, vw = very weak; b =
broad, vb = very broad, sh = shoulder. Combustion analyses were
performed by Robertson Microlit Laboratories of Madison, NJ.
Synthesis of trans-W(NCMe)(CO)3(CNArDipp2)2 (1-W). To an
Et2O slurry of W(CO)3(NCEt)3 (1.000 g, 2.257 mmol, 1 equiv, 30 mL)
was added a Et2O solution of CNArDipp2 (1.912 g, 4.12 mmol, 2 equiv,
100 mL). The mixture was stirred for 2 h, after which 70 mL of
acetonitrile was added. The reaction mixture was then irradiated with
a 254 nm Hg lamp while under an Ar purge for 24 h. The reaction
Synthesis of MoI2(CO)2(CNArDipp2)2 (4). To a thawing Et2O
solution of trans-Mo(NCMe)(CO)3(CNArDipp2
) (1-Mo, 0.100 g,
2
0.0936 mmol, 1.00 equiv, 40 mL) was added a thawing Et2O solution
of I2 (0.024 g, 0.0955 mmol, 1.02 equiv, 20 mL). The reaction mixture
was allowed to stir for 6 h, after which the solution was filtered and all
volatile materials were removed under reduced pressure. Dissolution of
the resulting red residue in a 5:1 toluene/n-pentane mixture (6 mL total)
followed by filtration and storage at ꢀ35 °C for 24 h resulted in red
crystals which were collected and dried in vacuo. Yield: 0.085 g, 0.0678
mmol, 77%. 1H NMR (400.1 MHz, C6D6, 20 °C): δ = 16.18 (d, 4H, J = 7
Hz, m-Ph), 9.25 (d, 8H, J = 8 Hz, m-Dipp), 8.48 (t, 4H, J = 8 Hz, p-Dipp),
6.04 (s, 8H, CH(CH3)2), 3.38 (d, 24H, J = 6 Hz, CH(CH3)2), 2.32 (d,
24H, J = 7 Hz, CH(CH3)2), ꢀ6.33 (t, 2H, J = 8 Hz, p-Ph) ppm. μeff
(Evans method, C6D6 with O(SiMe3)2, 400.1 MHz, 20 °C) = 2.71-
((0.03) μB (average of 5 independent measurements). FTIR (C6D6, KBr
windows; trans,trans,trans-MoI2(CO)2(CNArDipp2)2): (νCN) 2109-
(vs) cmꢀ1, (νCO) 2004(s) and 1994(s) cmꢀ1 also 3061, 3020, 2925,
2868, 1577, 1462, 1415, 1386, 1357, 1333, 1252, 1180, 1060, 809,
755 cmꢀ1. FTIR (C6D6, KBr pellet; trans,trans,trans-MoI2(CO)2-
(CNArDipp2)2 and cis,cis,trans-MoI2(CO)2(CNArDipp2)2): (νCN) 2110-
1
mixture was then concentrated to ca. /2 its original volume under
reduced pressure, resulting in the precipitation of an orange solid. This
solid was collected via filtration, slurried in cold acetonitrile (20 mL,
ꢀ35 °C), and then filtered again. Thorough drying of the resulting solid
in vacuo then afforded trans-W(NCMe)(CO)3(CNArDipp2
) (1-W).
2
Yield: 1.853 g, 0.160 mmol, 71%. 1H NMR (400.1 MHz, C6D6, 20 °C):
δ = 7.33 (t, 4H, J = 8 Hz, p-Dipp), 7.19 (d, 8H, J = 8 Hz, m-Dipp), 6.95
(d, 4H, J = 7 Hz, m-Ph), 6.86 (t, 2H, J = 7 Hz, p-Ph), 2.78 (sept, 8H, J = 7
Hz, CH(CH3)2), 1.34 (d, 24H, J = 7 Hz, CH(CH3)2), 1.18 (s, 3H,
NCCH3), 1.11 (d, 24H, J = 7 Hz, CH(CH3)2) ppm. 13C{1H} NMR
(100.6 MHz, C6D6, 20 °C): δ = 205.0 (CꢁO), 199.8 (CꢁO), 170.9
(CꢁN), 146.7, 138.8, 135.6, 129.9, 129.5, 129.2, 128.6, 125.9, 123.2,
119.0 (NCCH3), 31.4 (CH(CH3)2), 24.5 (CH(CH3)2), 24.4
(CH(CH3)2), 2.8 (NCCH3) ppm. FTIR (KBr pellet): (νCN) 2026(s)
and 1996(s) cmꢀ1, (νCO) 1886(s), 1873(s) and 1863(m) cmꢀ1 also
2960, 2925, 2866, 1459, 1415, 1382, 1362, 1046, 803, 755, 584,
521 cmꢀ1. Anal. Calcd for C67H77N3O3W: C, 69.60; H, 6.71; N, 3.63.
Found: C, 69.05; H, 6.75; N, 3.51.
(vs) cmꢀ1, (νCO) 2006(s) and 1997(s) cmꢀ1 (trans-Mo(CO)2), (νCO
)
1982(s) and 1940(w) cmꢀ1 (cis-Mo(CO)2). Anal. Calcd for C64H74N2-
O2I2Mo: C, 61.35; H, 5.95; N, 2.24. Found: C, 61.16; H, 5.95; N, 2.23.
Alternative Synthesis of MoI2(CO)2(CNArDipp2)2 (4). To a
thawing acetonitrile solution of Mo(CO)3(NCMe)3 (0.773 g, 2.552
mmol, 1 equiv, 25 mL) was added I2 (0.648 g, 2.552 mmol, 1 equiv). The
reaction mixture was stirred for 1 h, after which all volatile materials were
removed under reduced pressure to afford MoI2(CO)3(NCMe)2 as a
burgundy solid. A 10:1 Et2O/THF (75 mL/7.5 mL) solution was added
to MoI2(CO)3(NCMe)2, and the reaction mixture was frozen. To the
thawing Et2O/THF solution of MoI2(CO)3(NCMe)2 was added a
thawing Et2O solution of CNArDipp2 (2.000 g, 4.721 mmol, 1.85 equiv,
75 mL). The reaction mixture was allowed to stir for 2 h, after which all
volatile materials were removed under reduced pressure. Dissolution of the
resulting red residue in a 5:1 toluene/n-pentane mixture (100 mL total)
followed by filtration and storage at ꢀ35 °C for 24 h resulted in red crystals,
which were collected and dried in vacuo. Yield: 2.253 g, 1.798 mmol, 76%.
Synthesis of trans-W(CO)4(CNArDipp2
) (2-W). CO gas
2
(0.043 mL, 1.730 mmol, 10 equiv) was added to a THF solution
of trans-W(NCMe)(CO)3(CNArDipp2
)
(1-W, 0.200 g, 0.173 mmol,
2
20 mL), and the mixture was stirred for 24 h, resulting in the
precipitation of a red solid. The reaction mixture was then filtered
through a medium porosity frit, and the resulting red powder was
washed with THF (2 ꢂ 5 mL), collected, and dried in vacuo to afford
trans-W(CO)4(CNArDipp2
) (2-W). Yield: 0.137 g, 0.119 mmol,
2
68%. 1H NMR (400.1 MHz, C6D6, 20 °C): δ = 7.36 (t, 4H, J = 8 Hz,
p-Dipp), 7.18 (d, 8H, J = 8 Hz, m-Dipp), 6.92 (d, 4H, J = 8 Hz, m-Ph), 6.85
(t, 2H, J = 7 Hz, p-Ph), 2.68 (sept, 8H, J = 7 Hz, CH(CH3)2), 1.32 (d,
24H, J = 7 Hz, CH(CH3)2), 1.06 (d, 24H, J = 7 Hz, CH(CH3)2) ppm.
13C{1H} NMR (100.6 MHz, C6D6, 20 °C): δ = 195.5 (CꢁO), 160.8
(CꢁN), 146.5, 139.2, 134.9, 129.6, 129.5, 129.2, 127.2, 123.4, 31.4
(CH(CH3)2), 24.5 (CH(CH3)2), 24.3 (CH(CH3)2) ppm. FTIR
(KBr pellet): (νCN) 2061(s) and 2009(w) cmꢀ1, (νCO) 1926(vs) cmꢀ1
Synthesis of MoI2(THF)(CO)2(CNArDipp2
) (5). Solid MoI2-
2
(CO)2(CNArDipp2)2 (4, 0.100 g, 0.0798 mmol) was dissolved in 1 mL of
THF and stirred for 10 min, gradually changing in color from red to
brown. Addition of 0.5 mL of n-pentane to the resulting solution
followed by filtration and storage at ꢀ35 °C for 24 h resulted in brown
crystals, which were collected and dried in vacuo. Yield: 0.080 g, 0.0604
mmol, 80%. 1H NMR (400.1 MHz, THF-d8, 20 °C): δ = 7.45 (t, 4H, J =
7 Hz, p-Ph), 7.27 (t, 4H, J = 8 Hz, p-Dipp), 7.24 (t, 4H, J = 8 Hz, p-Dipp),
7.16 (d, 8H, J= 8 Hz, p-Ph), 2.54 (sept, 8H, J= 7 Hz, CH(CH3)2), 1.26 (d,
24H, J = 7 Hz, CH(CH3)2), 1.02 (d, 24H, J = 7 Hz, CH(CH3)2) ppm.
FTIR (THF, KBr windows): (νCN) 2079(vs) cmꢀ1, (νCO) 1969(s) and
also 2961, 2927, 2868, 1459, 1415, 1363, 1055, 803, 755, 596, 570 cmꢀ1
.
Anal. Calcd for C66H74N2O4W: C, 69.34; H, 6.53; N, 2.45. Found:
C, 67.95; H, 6.64; N, 2.46.
Synthesis of WI2(CO)3(CNArDipp2)2 (3-W). To a thawing Et2O
solution of trans-W(NCMe)(CO)3(CNArDipp2)2 (1-W, 1.000 g, 0.864
mmol, 1.00 equiv, 50 mL) was added a thawing Et2O solution of I2
10456
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
1947(s) cmꢀ1 also 1594, 1559, 1472, 1465, 1414, 1386, 1364, 872, 823,
809, 793, 158 cmꢀ1. Satisfactory combustion analysis was not obtained
due to repeated and substoichiometric loss of THF. Dissolution of trans-
Synthesis of Mo(CO)(MeCO2)2(CNArDipp2)2 (9). To a THF
solution of MoI2(CO)2(CNArDipp2)2 (4, 1.000 g, 0.779 mmol, 1 equiv,
30 mL) was added a THF slurry of AgOAc (0.280 g, 1.677 mmol, 2.05
equiv, 30 mL). The reaction mixture was allowed to stir for 6 h, filtered,
and then stirred for another 48 h. All volatile materials were removed
under reduced pressure, and dissolution of the resulting red residue in a
4:1 Et2O/acetonitrile mixture (20 mL total) followed by filtration and
storage at ꢀ35 °C for 24 h resulted in orange crystals which were
collected and dried in vacuo. Yield: 0.350 g, 0.321 mmol, 41%. 1H NMR
(400.1 MHz, C6D6, 20 °C): δ = 7.38 (t, 4H, J = 8 Hz, p-Dipp), 7.25 (d,
8H, J = 8 Hz, m-Dipp), 6.97 (d, 4H, J = 8 Hz, m-Ph), 6.85 (t, 2H, J = 7 Hz,
p-Ph), 2.72 (sept, 7H, J = 7 Hz, CH(CH3)2), 1.53 (s, 6H, CH3CO2),
1.24 (d, 24H, J = 6 Hz, CH(CH3)2), 1.14 (d, 24H, J = 7 Hz, CH(CH3)2)
ppm. 13C{1H} NMR (100.6 MHz, C6D6, 20 °C): δ = 265.2 (CꢁO),
204.2 (CꢁN), 186.3 (CdO) 146.5, 137.2, 135.0, 130.1, 129.4, 128.7,
127.4, 123.4, 31.5 (CH(CH3)2), 24.7 (CO2CH3), 24.3 (CH(CH3)2),
24.0 (CH(CH3)2) ppm. FTIR (C6D6, KBr windows): (νCN) 2107(w)
and 2032(vs) cmꢀ1, (νCO) 2007(s) and1921(m) cmꢀ1 also 2965, 2925,
2867, 1580, 1466, 1416, 1363, 755 cmꢀ1 (acetate νCdO not conclusively
identified). Anal. Calcd for C67H80N2O5Mo: C, 73.87; H, 7.40; N, 2.57.
Found: C, 73.75; H, 7.59; N, 2.61.
1
MoI2(THF)(CO)2(CNArDipp2)2 (5) in C6D6 returned H NMR reso-
nances for MoI2(CO)2(CNArDipp2)2 (4) and free THF.
Synthesis of trans-MoI4(CNArDipp2)2 (6). To a thawing fluor-
obenzene (C6H5F) solution of MoI2(CO)2(CNArDipp2)2 (4, 0.200 g,
0.160 mmol, 1.00 equiv, 20 mL) was added a thawing fluorobenzene
solution of I2 (0.043 g, 0.168 mmol, 1.05 equiv, 10 mL). The reaction
mixture was allowed to stir for 4 h, after which all volatile materials were
removed under reduced pressure. Dissolution of the resulting royal-blue
residue in a 2:1 toluene/n-pentane mixture (6 mL, total) followed by
filtration and storage at ꢀ35 °C for 48 h resulted in royal-blue crystals
which were collected and dried in vacuo. Yield: 0.125 g, 0.086 mmol,
53%. 1H NMR (400.1 MHz, C6D6, 20 °C): δ = 14.79 (d, 4H, J = 8 Hz,
m-Ph), 8.26 (d, 8H, J=8Hz,m-Dipp), 6.95 (t, 4H, J=8Hz,p-Dipp), 3.38 (d,
24H, J = 7 Hz, (CH(CH3)2), 1.24 (sept, 8H, J = 7 Hz), 1.01 (d, 24H, J =
7 Hz, CH(CH3)2), ꢀ10.69 (t, 2H, J = 8 Hz, p-Ph) ppm. μeff (Evans
method, C6D6 with O(SiMe3)2, 400.1 MHz, 20 °C) = 2.86((0.03) μB
(average of 3 independent measurements). FTIR (C6D6, KBr windows):
(νCN) 2163(s) and 2135(w) cmꢀ1 also 2956, 2926, 2867, 1615, 1587, 1579,
1460, 1407, 1385, 1363, 808, 758, 677 cmꢀ1. Anal. Calcd for C62H74N2I4Mo:
C, 51.33; H, 5.14; N, 1.93. Found: C, 52.17; H, 5.38; N, 1.82.
Synthesis of trans-MoI3(THF)(CNArDipp2)2 (10). To a THF
solution of trans-MoI4(CNArDipp2)2 (6, 0.200 g, 0.137 mmol, 50 mL
total) was added I2-activated magnesium turnings (0.083 g, 3.446 mmol,
25 equiv). The reaction mixture was allowed to stir for 12 h and gradually
changed in color from pale-brown to pale-orange. The resulting solution
was decanted off the residual magnesium turnings and then dried under
reduced pressure. The residue was then slurried in Et2O (15 mL), stirred
for 20 min, and then dried in vacuo. The resulting tan solid was then
slurried in Et2O (20 mL) and filtered through Celite. The solid remaining
on the Celite pad was then extracted with THF (5 mL), filtered, layered
with n-pentane (5 mL), and stored at ꢀ35 °C for 1 day, whereupon tan
crystals were obtained. Yield: 0.070 g, 0.050 mmol, 36%. 1H NMR (400.1
MHz, C6D6, 20°C): δ= 69.65 (s, 2H, p-Ph), 27.72 (s, 4H, p-Dipp), 8.35 (s,
8H, m-Dipp), 6.26 (s, 4H, THF), 6.04 (s, 4H, THF), 3.55 (s, 24H,
CH(CH3)2), 2.48 (s, 24H, CH(CH3)2), 1.37 (s, 8H, CH(CH3)2), ꢀ17.71
(s, 4H, m-Ph) ppm. μeff (Evans method, C6D6 with O(SiMe3)2, 400.1
MHz, 20 °C) = 3.95((0.10) μB (average of 3 independent measurements).
FTIR (C6D6, KBr windows): (νCN) 2142(vs) cmꢀ1 also 2962, 2927, 2869,
1461, 1412, 1387, 1364, 1328 cmꢀ1. Anal. Calcd for C66H82N2OI3Mo: C,
56.14; H, 5.85; N, 1.89. Found: C, 56.21; H, 6.13; N, 1.94.
Synthesis of W(O2CPh)2(CO)2(CNArDipp2
) (7). To a THF
2
solution of trans-W(NCMe)(CO)3(CNArDipp2)2 (1-W, 0.200 g, 0.173
mmol, 1 equiv, 5 mL) was added a THF solution of benzoyl peroxide
(0.084 g, 0.346 mmol, 2 equiv, 5 mL). The reaction mixture was allowed
to stir for 24 h, after which all volatile materials were removed under
reduced pressure. Dissolution of the resulting orange residue in Et2O
(3 mL) followed by filtration and storage at ꢀ35 °C for 5 days resulted in
orange crystals, which were collected and dried in vacuo. Yield: 0.050 g,
0.038 mmol, 22%. 1H NMR (400.1 MHz, C6D6, 20 °C): δ = 8.04 (m,
4H), 7.34 (t, 4H, J =8 Hz, p-Dipp), 7.21 (d, 8H, J =8 Hz, m-Dipp), 7.06 (t,
4H), 7.04 (d, 2H), 6.99 (d, 4H, J = 8 Hz, m-Ph), 6.86 (t, 2H, J = 8 Hz,
p-Ph), 2.71 (sept, 8H, J = 7 Hz, CH(CH3)2), 1.27 (d, 24H, J = 7 Hz,
CH(CH3)2), 1.08 (d, 24H, J = 7 Hz, CH(CH3)2) ppm. 13C{1H} NMR
(100.6 MHz, C6D6, 20 °C): δ = 223.1 (CꢁO), 177.3 (CꢁN), 175.1
(CdO), 146.3, 139.1, 135.6, 134.2, 131.4, 130.3, 129.9, 128.6, 127.7,
123.63, 31.4 (CH(CH3)2), 24.9 (CH(CH3)2), 24.1 (CH(CH3)2) ppm.
FTIR (C6D6, KBr windows): (νCN) 2135(w) and 2071(vs) cmꢀ1, (νCO
)
2002(w) and 1949(vs) cmꢀ1 also 2962, 2926, 2868, 1619 (νCdO), 1505,
1449, 1161, 869, 755, 714 cmꢀ1. Anal. Calcd for C78H84N2O6W: C,
70.47; H, 6.37; N, 2.11. Found: C, 70.27; H, 6.40; N, 2.05.
Synthesis of Mo(N2)(η6-C6H6)(CNArDipp2)2 (11). To a stirred
mixture of 1.0% Na/Hg (Na: 0.633 g, 27.57 mmol; Hg: 63.4 g; 100 equiv
Na per Mo) and C6H6 (50 mL) was added a C6H6 solution of trans-
MoI4(CNArDipp2)2 (6, 0.400 g, 0.276 mmol, 75 mL). The resulting
mixture was allowed to stir for 36 h and then filtered through Celite. All
volatile materials were then removed under reduced pressure. The
resulting red residue was then suspended in Et2O (10 mL) and filtered
through Celite. The filtrate was evaporated to dryness in vacuo, and the
remaining solid was dissolved in Et2O (2 mL), filtered, and layered with
O(SiMe3)2 (3 mL) and stored at ꢀ35 °C for 2 days, whereupon red
Synthesis of W(CO)2(O2CMe)2(CNArDipp2)2 (8-W). To a THF
solution of WI2(CO)3(CNArDipp2
) (3-W, 0.100 g, 0.073 mmol, 1
2
equiv, 3 mL) was added a THF slurry of AgOAc (0.037 g, 0.183 mmol, 3
equiv, 5 mL). The reaction mixture was allowed to stir for 12 h, after
which the solution was filtered and all volatile materials were removed
under reduced pressure. Dissolution of the resulting red residue in a 4:1
Et2O/acetonitrile mixture (5 mL total) followed by filtration and storage
at ꢀ35 °C for 24 h resulted in orange crystals, which were collected and
dried in vacuo. Yield: 0.083 g, 0.069 mmol, 38%. 1H NMR (400.1 MHz,
C6D6, 20 °C): δ = 7.36 (t, 4H, J = 8 Hz, p-Dipp), 7.24 (d, 8H, J = 8 Hz,
m-Dipp), 6.99 (d, 4H, J = 7 Hz, m-Ph), 6.86 (t, 2H, J = 8 Hz, p-Ph), 2.69
(sept, 8H, J = 6 Hz, CH(CH3)2), 1.72 (s, 6H, CH3CO2), 1.28 (d, 24H,
J = 6 Hz, CH(CH3)2), 1.09 (d, 24H, J = 6 Hz, CH(CH3)2) ppm.
13C{1H} NMR (100.6 MHz, C6D6, 20 °C): δ = 224.5 (CꢁO), 182.0
(CꢁN), 175.6 (CdO), 146.3, 139.0, 134.0, 130.3, 129.8, 128.2, 123.6,
123.4, 31.4 (CH(CH3)2), 25.0 (CO2CH3), 24.9 (CH(CH3)2), 24.0
(CH(CH3)2) ppm. FTIR (C6D6, KBr windows): (νCN) 2131(w) and
2068(vs) cmꢀ1, (νCO) 2002(w) and 1943(vs) cmꢀ1 also 2963, 2925,
2868, 1476, 1413, 1386, 1360, 1302, 761, 691, 664 cmꢀ1 (acetate νCdO
not conclusively identified). Anal. Calcd for C68H80N2O6W: C, 67.77;
H, 6.69; N, 2.32. Found: C, 67.69; H, 6.81; N, 2.32.
1
crystals were obtained. Yield: 0.150 g, 0.143 mmol, 52%. H NMR
(400.1 MHz, C6D6, 20 °C): δ = 7.35 (t, 4H, J = 8 Hz, p-Dipp), 7.21 (dd,
8H, J = 8 Hz, m-Dipp), 6.96 (d, 4H, J = 8 Hz, m-Ph), 6.87 (t, 2H, J = 6 Hz,
p-Ph), 3.57 (s, 6H, η6-C6H6), 2.88 (m, 8H, J = 7 Hz, CH(CH3)2), 1.30
(d, 12H, J = 7 Hz, CH(CH3)2), 1.18 (d, 12H, J = 7 Hz, CH(CH3)2), 1.16
(d, 12H, J = 7 Hz, CH(CH3)2), 1.13 (d, 12H, J = 7 Hz, CH(CH3)2)
ppm. 13C{1H} NMR (100.6 MHz, C6D6, 20 °C): δ = 196.2 (CꢁN),
147.1, 146.6, 137.3, 137.1, 131.0, 130.5, 128.9, 124.3, 123.4, 123.2, 84.6
(C6H6), 31.2 (CH(CH3)2), 25.0 (CH(CH3)2), 24.6 (CH(CH3)2), 24.1
(CH(CH3)2), 24.0 (CH(CH3)2) ppm. FTIR (C6D6, KBr windows):
(νNN) 2101(s), (νCN) 1979(m) and 1927(vs) cmꢀ1 also 2965, 2923,
2870, 1618, 1455, 1410, 1155, 758 cmꢀ1. Anal. Calcd for C68H80N4Mo:
C, 77.86; H, 7.69; N, 5.34. Found: C, 75.56; H, 7.48; N, 4.27. Repeated
10457
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
attempts failed to give a more satisfactory combustion analysis. We
attribute this to the presence of minor MoI impurities.
instrumentation grants to the UCSD Department of Chemistry
and Biochemistry (CHE-0741968 and CHE-9709183). J.S.F. is a
Cottrell Scholar of Research Corporation and an Alfred P. Sloan
Research Fellow (2011-2013). We also thank a reviewer for very
helpful comments concerning the IR data of MoI2(CO)2-
(CNArDipp2)2 (4).
Synthesis of MoI2(η6-C6H6)(CNArDipp2)2 (12). To a stirred
mixture of 0.5% Na/Hg (Na 0.023 g, 3.43 mmol; Hg 15.8 g; 25 equiv
Na per Mo) and C6H6 (50 mL) was added a C6H6 solution of trans-
MoI4(CNArDipp2)2 (6, 0.200 g, 0.137 mmol, 50 mL). The resulting
mixture was allowed to stir for 3 h, and gradually changed from royal
blue to red. The reaction mixture was then filtered through Celite and all
volatile materials were removed under reduced pressure. The residue was
then slurried in n-pentane (5 mL), filtered, and washed with n-pentane (2 ꢂ
5 mL). The remaining solid was dissolved in Et2O (3 mL), filtered, and
layered with O(SiMe3)2 (3 mL) and stored at ꢀ35 °C for 1 d, whereupon
brown crystals were obtained. Yield: 0.040 g, 0.031 mmol, 23%. 1H NMR
(400.1 MHz, C6D6, 20 °C): δ = 7.36 (t, 4H, J = 8 Hz, p-Dipp), 7.23 (d, 8H,
J=8Hz, m-Dipp), 6.95 (d, 4H, J=7Hz, m-Ph), 6.82 (t, 2H, J=8 Hz, p-Ph),
4.35 (s, 6H, η6-C6H6), 2.85 (sept, 8H, J = 7 Hz, CH(CH3)2), 1.43 (d, 24H,
J = 7 Hz, CH(CH3)2), 1.09 (d, 24H, J = 7 Hz, CH(CH3)2) ppm. 13C{1H}
NMR (100.6 MHz, C6D6, 20 °C): δ = 172.4 (CꢁN), 147.2, 139.1, 136.6,
131.5, 129.5, 129.1, 128.6, 126.9, 123.5, 98.3 (C6H6), 31.3 (CH(CH3)2),
25.1 (CH(CH3)2), 24.9 (CH(CH3)2) ppm. FTIR (C6D6, KBr windows):
(νCN) 2086(m), 2040(vs), 2007(w) cmꢀ1 also 2959, 2927, 2867, 1614,
1461, 1453, 1416, 1384, 1363, 807, 758 cmꢀ1. Anal. Calcd for C68H80N2I2-
Mo: C, 64.05; H, 6.32; N, 2.20. Found: C, 62.87; H, 6.13; N, 2.22.
Crystallographic Structure Determinations. Single crystal
X-ray structure determinations were carried out at low temperature on
a Bruker P4, Platform or Kappa diffractometer equipped with a Bruker
APEX detector. All structures were solved by direct methods with SIR
200465 and refined by full-matrix least-squares procedures utilizing
SHELXL-97.66 Crystallographic data-collection and refinement infor-
mation is listed in Table S1. The crystal structure of 1-W contained
positional disorder between one CO ligand and the coordinated
acetonitrile molecule. The disorder was modeled such that both the
CO and acetonitrile molecules are represented at 50% occupancy in each
site. The crystal structure of 4 revealed co-crystallization of a 50/50
mixture of both the cis- and trans-dicarbonyl isomers. Both cis- and trans-
dicarbonyl isomers contain whole molecule disorder, and consequently,
the heavier Mo and I atoms were modeled and refined over several positions.
Also, the cis-carbonyl isomer contains positional and compositional disorder
between the CO ligands and terminal iodides within the equatorial plane of
the molecule. The disorder was modeled such that the total of all ligand
occupancy equals two CO ligands and two iodide ligands. The crystal
structure of 7 contains isopropyl-group positional disorder, which was
modeled and refined. The crystal structure of 10 contains positional disorder
in one of the bound acetate ligands, which was modeled and refined. The
crystal structures of 6 and 11 contain disordered toluene and O(SiMe3)2
molecules of cocrystallization, respectively. These disordered components
were also modeled and refined.
’ REFERENCES
(1) For experimental detection and characterization, as well as
theoretical consideration of [M(CO)4], [M(CO)3] and [M(CO)2]
(M = Cr, Mo, W), see: (a) Perutz, R. N.; Turner, J. J. J. Am. Chem.
Soc. 1975, 97, 4800–4804. (b) Burdett, J. K.; Graham, M. A.; Perutz,
R. N.; Poliakoff, M.; Rest, A. J.; Turner, J. J.; Turner, R. F. J. Am. Chem.
Soc. 1975, 97, 4085–4808. (c) Fletcher, T. R.; Rosenfeld, R. N. J. Am.
Chem. Soc. 1985, 107, 2203–2212. (d) Seder, T. A.; Church, S. P.; Weitz,
E. J. Am. Chem. Soc. 1986, 108, 4721–4728. (e) Ishikawa, Y.-I.; Hackett,
P. A.; Rayner, D. M. J. Phys. Chem. 1988, 92, 3863–3869. (f) Ganske,
J. A.; Rosenfeld, R. N. J. Phys. Chem. 1989, 93, 1959–1963. (g) Ishikawa,
Y.-I.; Brown, C. E.; Hackett, P. A.; Rayner, D. M. J. Phys. Chem. 1990,
94, 2404–2413. (h) Andrews, L.; Zhou, M.; Gutsev, G. L.; Wang, X.
J. Phys. Chem. A 2003, 107, 561–569. (i) Andrews, L.; Zhou, M.; Gutsev,
G. L. J. Phys. Chem. A 2003, 107, 990–999. (j) Ishikawa, Y.-I.; Kawakami,
K. J. Phys. Chem. A 2007, 111, 9940–9944.
(2) For a review on unsaturated metal binary carbonyls, see: Zhou,
M.; Andrews, L.; Bauschlicher, C. W. Chem. Rev. 2001, 101, 1931–1961.
(3) Burdett, J. K. J. Chem. Soc., Faraday Trans. 2 1974, 70, 1599–1613.
(4) Burdett, J. K. Inorg. Chem. 1975, 14, 375–382.
(5) Elian, M.; Hoffmann, R. Inorg. Chem. 1975, 14, 1058–1076.
(6) Fox, B. J.; Sun, Q. Y.; DiPasquale, A. G.; Fox, A. R.; Rheingold,
A. L.; Figueroa, J. S. Inorg. Chem. 2008, 47, 9010–9020.
(7) Ditri, T. B.; Fox, B. J.; Moore, C. E.; Rheingold, A. L.; Figueroa,
J. S. Inorg. Chem. 2009, 48, 8362–8375.
(8) (a) Malatesta, L.; Bonati, F. Isocyanide Complexes of Transition
Metals; Wiley: New York, 1969. (b) Bonati, F.; Minghetti, G. Inorg.
Chim. Acta 1974, 9, 95–112. (c) Sarapu, A. C.; Fenske, R. F. Inorg. Chem.
1974, 14, 247–253. (d) Yamamoto, Y. Coord. Chem. Rev. 1980,
32, 193–233.
(9) (a) Twamley, B.; Haubrich, S. T.; Power, P. P. Adv. Organomet.
Chem. 1999, 44, 1–65. (b) Clyburne, J. A. C.; McMullen, N. Coord.
Chem. Rev. 2000, 210, 73–99.
(10) For reviews and representative applications of m-terphenyl
ligands to transition-metal and main-group systems, see: (a) Power,
P. P. Chem. Rev. 1999, 99, 3463–3504. (b) Robinson, G. H. Acc. Chem.
Res. 1999, 32, 773–782. (c) Robinson, G. H. Chem. Commun.
2000, 2175–2181. (d) Shah, S.; Simpson, M. C.; Smith, R. C.; Prota-
siewicz, J. D. J. Am. Chem. Soc. 2001, 123, 6925–6926. (e) Gavenonis, J.;
Tilley, T. D. Organometallics 2002, 21, 5549–5563. (f) Power, P. P.
Chem. Commun. 2003, 2091–2101. (g) Waterman, R.; Hillhouse, G. L.
Organometallics 2003, 22, 5182–5184. (h) Smith, R. C.; Shah, S.;
Urnezius, E.; Protasiewicz, J. D. J. Am. Chem. Soc. 2003, 125, 40–41.
(i) Gavenonis, J.; Tilley, T. D. Organometallics 2004, 23, 31–43.
(j) Filippou, A. C.; Weidemann, N.; Philippopoulos, A. I.; Schnakenburg,
G. Angew. Chem., Int. Ed. 2006, 45, 5987–5991. (k) Nguyen, T.; Sutton,
A. D.; Brynda, M.; Fettinger, J. C.; Long, G. J.; Power, P. P. Science 2005,
310, 844–847. (l) Carson, E. C.; Lippard, S. J. Inorg. Chem. 2006,
45, 828–836. (m) Klein, D. P.; Young, V. G.; Tolman, W. B.; Que, L.
Inorg. Chem. 2006, 45, 8006–8008. (n) Power, P. P. Organometallics 2007,
26, 4362–4372. (o) Rivard, E.; Power, P. P. Inorg. Chem. 2007,
46, 10047–10064. (p) Wolf, R.; Brynda, M.; Ni, C.; Long, G. J.; Power,
P. P. J. Am. Chem. Soc. 2007, 129, 6076–6077. (q) Wolf, R.; Ni, C.; Nguyen,
T.; Brynda, M.; Long, G. J.; Sutton, A. D.; Fischer, R. C.; Fettinger, J. C.;
Hellman, M.; Pu, L.; Power, P. P. Inorg. Chem. 2007, 46, 11277–11290.
(r) Ni, C.; Power, P. P. Struct. Bonding (Berlin) 2010, 136, 59–111. (s) Kays,
D. L. Dalton Trans. 2011, 769–778.
’ ASSOCIATED CONTENT
1
S
Supporting Information. H NMR and FTIR spectra for
b
MoI2(CO)2(CNArDipp2)2 and crystallographic information files
(PDF and CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: jsfig@ucsd.edu.
’ ACKNOWLEDGMENT
We are grateful to the U.S. National Science Foundation for
support through a CAREER Award (CHE-0954710) and NMR
(11) Fox, B. J.; Millard, M. D.; DiPasquale, A. G.; Rheingold, A. L.;
Figueroa, J. S. Angew. Chem., Int. Ed. 2009, 48, 3473–3477.
10458
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459

Inorganic Chemistry
ARTICLE
(12) Emerich, B. M.; Moore, C. E.; Fox, B. J.; Rheingold, A. L.;
Figueroa, J. S. Organometallics 2011, 30, 2598–2608.
(13) Labios, L. A.; Millard, M. D.; Rheingold, A. L.; Figueroa, J. S.
J. Am. Chem. Soc. 2009, 131, 11318–11319.
(43) Some trivalent, d3 anions of the formulation [MoI4L2]ꢀ have been
structurally characterized. (a) [HPPhEt2][trans-MoI4(PPhEt2]: Cotton,
F. A.; Poli, R. Inorg. Chem. 1986, 25, 3624–3629. (b) [Na(THF)3]-
[cis-MoI4(dppe)]: Mattamana, S. P.; Poli, R. Inorg. Chim. Acta 1995,
229, 55–60. (c) [IPMe3][trans-MoI4(PMe3)2]: Maria, S.; Stoffelbach, F.;
Mata, J.; Daran, J.-C.; Richard, P.; Poli, R. J. Am. Chem. Soc. 2005,
127, 5946–5956.
(44) Lyons, D.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse,
M. B. J. Chem. Soc., Dalton Trans. 1984, 695–700.
(45) Alvarez, R.; Carmona, E.; Galindo, A.; Gutiꢀerrez, E.; Marín,
J. M.; Monge, A.; Poveda, M. L.; Ruiz, C.; Savariault, J. M. Organome-
tallics 1989, 8, 2430–2439.
(14) Margulieux, G. M.; Weidemann, N.; Lacy, D. C.; Moore, C. E.;
Rheingold, A. L.; Figueroa, J. S J. Am. Chem. Soc. 2010, 132, 5033–5035.
(15) For studies suggesting that Co(CO)4 is an intermediate in Co-
carbonyl-catalyzed hydroformylation, see: (a) Wegman, R. W.; Brown,
T. L. J. Am. Chem. Soc. 1980, 102, 2494–2495. (b) Nalesnlk, T. E.;
Orchin, M. Organometallics 1982, 1, 222–223. (c) Klingler, R. J.; Rathke,
J. W. J. Am. Chem. Soc. 1994, 116, 4112–4785.
(16) (a) Heck, R. F.; Breslow, D. S. J. Am. Chem. Soc. 1961,
83, 4023–4027. (b) Muetterties, E. L.; Stein, J. Chem. Rev. 1979, 79,
479–490. (c) Hebrard, F.; Kalck, P. Chem. Rev. 2009, 109, 4272–4282.
(17) Chiu, K. W.; Jones, R. A.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1981, 2088–2097.
(18) Mann, K. R.; Cimolino, M.; Geoffroy, G. L.; Hammond, G. S.;
Orio, A. A.; Albertin, G.; Gray, H. B. Inorg. Chim. Acta 1973, 16, 97–101.
(19) Bassett, J.-M.; Berry, D. E.; Barker, G. K.; Green, M.; Howard,
J. A. K.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1979, 1003–1011.
(20) Stoffelbach, F.; Saurenz, D.; Poli, R. Eur. J. Inorg. Chem. 2001,
2699–2703.
(46) Green, M. L. H.; Parkin, G.; Chen, M.; Prout, K. J. Chem. Soc.,
Dalton Trans. 1986, 2227–2236.
(47) Zhu, G.; Parkin, G. Inorg. Chem. 2005, 44, 9637–9639.
(48) Dreyer, E. B.; Lam, C. T.; Lippard, S. J. Inorg. Chem. 1979,
18, 1904–1908.
(49) For a study concerning the interconversion of k1- and
k2-carboxylate ligands in rhodium complexes, see: Boyer, P. M.; Roy,
C. P.; Bielski, J. M.; Merola, J. S. Inorg. Chim. Acta 1996, 245, 7–15.
(50) Cotton, F. A.; Dunbar, K. R.; Poli, R. Inorg. Chem. 1986,
25, 3700–3703.
(21) For estimates of the relative Lewis acidity of metal halides and
pseudohalides, see: (a) Singh, P. P.; Srivatava, S. K.; Srivatava, A. K.
J. Inorg. Nucl. Chem. 1980, 42, 521–532. (b) Yamamoto, Y. J. Org. Chem.
2007, 72, 7817–7831.
(51) Green, M. L. H.; Silverthorn, W. E. J. Chem. Soc., Dalton Trans.
1973, 301–306.
(52) Luck, R. L.; Morris, R. H.; Sawyer, J. F. Organometallics 1984,
3, 247–255.
(22) Colton, R.; Tomkins, I. B. Aust. J. Chem. 1966, 19, 1143–1146.
(23) Colton, R.; Tomkins, I. B. Aust. J. Chem. 1966, 19, 1519–1521.
(24) Anker, M. W.; Colton, R.; Tomkins, I. B. Aust. J. Chem. 1967,
20, 9–12.
(25) Colton, R.; Rix, C. J. Aust. J. Chem. 1968, 21, 1155–1158.
(26) Bowden, J. A.; Colton, R. Aust. J. Chem. 1968, 21, 2657–2661.
(27) Colton, R.; Rix, C. J. Aust. J. Chem. 1969, 22, 305–310.
(28) Drew, M. G. B.; Tomkins, I. B.; Colton, R. Aust. J. Chem. 1970,
23, 2517–20.
(29) See for example: (a) Albers, M. O.; Coville, N. J.; Ashworth,
T. V.; Singleton, E.; Swanepoel, H. E. J. Organomet. Chem. 1980,
199, 55–62. (b) Coville, N. J.; Albers, M. O. Inorg. Chim. Acta 1982,
65, L7–L8. (c) Filippou, A. C.; Gr€unleitner, W. J. Organomet. Chem.
1990, 398, 99–115.
(30) Weidemann, N.; Margulieux, G. W.; Moore, C. E.; Rheingold,
A. L.; Figueroa, J. S. Inorg. Chim. Acta 2010, 354, 238–245.
(31) Cotton, F. A.; Poli, R. Inorg. Chem. 1987, 26, 1514–1518.
(53) Luck, R. L.; Morris, R. H. Inorg. Chem. 1984, 23, 1489–1491.
(54) Ernst, M. F.; Roddick, D. M. Organometallics 1990,
9, 1586–1584.
(55) A purposeful synthesis of (η6-C6H6)MoI2(CNArDipp2)2 (11)
is provided in the Experimental Section.
(56) Hubig, S. M.; Lindeman, S. V.; Kochi, J. K. Coord. Chem. Rev.
2000, 200ꢀ202, 831–873.
(57) Atwood, J. L.; Hunter, W. E.; Rogers, R. D.; Carmona-Guzman,
E.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1979, 1519–1523.
(58) Radonovich, L. J.; Koch, F. J.; Albright, T. A. Inorg. Chem. 1980,
19, 3373–3383.
(59) Amey, D. J.; Wexler, P. A.; Wigley, D. E. Organometallics 1990,
9, 1282–1289.
(60) Wexler, P. A.; Wigley, D. E.; Koerner, J. B.; Albright, T. A.
Organometallics 1991, 10, 2319–2327.
(61) Jones, N. G.; Green, M. L. H.; Vei, I. C.; Rees, L. H.; Pascu, S. I.;
Watkin, D.; Cowley, A.; Morise, X.; Braunstein, P. J. Chem. Soc., Dalton
Trans. 2002, 2491–2500.
(32) For
a report of aggregation processes in MoX3L3
complexes, see: Poli, R.; Mui, H. D. J. Am. Chem. Soc. 1990, 112, 2446–
2448.
(62) Kuiper, D. S.; Wolczanski, P. T.; Lobkovsky, E. B.; Cundari,
T. R. Inorg. Chem. 2008, 47, 10542–10553.
(33) Hoffmann, R.; Beier, B. F.; Muetterties, E. L.; Rossi, A. R. Inorg.
Chem. 1977, 16, 511–522.
(63) Kubas, G. J.; Van der Sluis, L. S. Inorg. Synth. 1990, 28, 29–33.
(64) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. Organome-
tallics 2010, 29, 2176–2179.
(65) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.;
Cascarano, G. L.; De Caro, L.; Gaicovazzo, C.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 2005, 38, 381–388.
(34) Drew, M. G. B. Prog. Inorg. Chem. 1977, 23, 67–210.
(35) See the Supporting Information for details and relevant spectra. For
an early discussion of the relative intensity features and separation of νCO
bands in cis- and trans-dicarbonyl group 6 complexes featuring isocyanide co-
ligands, see: King, R. B.; Saran, M. S. Inorg. Chem. 1974, 13, 74–48.
(36) For additional examples, see: (a) Shiu, K.-B.; Liou, K.-S.; Wang,
S.-L.; Cheng, C. P.; Wu, F.-J. J. Organomet. Chem. 1989, 359, Cl–C4.
(b) Shiu, K.-B.; Liou, K.-S.; Wang, S.-L.; Wei, S.-C. Organometallics
1990, 9, 669–675.
(66) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(37) (a) Kubꢀacek, P.; Hoffmann, R. J. Am. Chem. Soc. 1981,
103, 4320–4332. (b) Templeton, J. L.; Winston, P. B.; Ward, B. C.
J. Am. Chem. Soc. 1981, 103, 7713–7721.
(38) Colton, R. Coord. Chem. Rev. 1971, 6, 269–284.
(39) Davidson, J. L.; Vasapollo, G. J. Chem. Soc., Dalton Trans.
1985, 2231–2238.
(40) Cotton, F. A.; Poli, R. J. Am. Chem. Soc. 1986, 108, 5628–5629.
(41) Colton, R.; Scollary, G. R.; Tomkins, I. B. Aust. J. Chem. 1968,
21, 15–19.
(42) Cambridge Structural Database, CSD v. 5.32; Nov. 2010; Allen,
F. H. Acta Crystallogr. 2002, B58, 380ꢀ388.
10459
dx.doi.org/10.1021/ic2015868 |Inorg. Chem. 2011, 50, 10448–10459