Synthesis of molybdenum complexes that contain hybrid triamidoamine ligands, [(hexaisopropylterphenyl-NCH2CH 2)2NCH2CH2N-aryl]3-, and studies relevant to catalytic reduction of dinitrogen

Article abstract of DOI:10.1021/ic0613457

In the Buchwald-Hartwig reaction between HIPTBr (HIPT = 3,5-(2,4,6-i-Pr₃C₆H₂)₂C ₆H₃ = hexaisopropylterphenyl) and (H₂NCH ₂CH₂)₃N, it is possible to obtain a 65% isolated yield of (HIPTNHCH₂CH₂)₂NCH ₂CH₂NH₂. A second coupling then can be carried out to yield a variety of hybrid ligands, (HIPTNHCH ₂CH₂)₂NCH₂CH₂NHAr, where Ar = 3,5-Me₂C₆H₃, 3,5-(CF₃) ₂C₆H₃, 3,5-(MeO)₂C₆H ₃, 3,5-Me₂NC₅H₃, 3,5-Ph ₂NC₅H₃, 2,4,6-i-Pr₃C ₆H₂, or 2,4,6-Me₃C₆H₂. The hybrid ligands may be attached to Mo to yield [hybrid]MoCl species. From the monochloride species, a variety of other species such as [hybrid]MoN, {[hybrid]MoN₂}Na, and {[hybrid]Mo(NH₃)}⁺ can be prepared. [Hybrid]MoN₂ species were prepared through oxidation of {[hybrid]MoN₂}Na species with ZnCl₂, but they could not be isolated. [Hybrid]Mo=N-NH species could be observed as a consequence of the protonation of {[hybrid]MoN₂}^- species, but they too could not be isolated as a consequence of a facile decomposition to yield dihydrogen and [hybrid]MoN₂ species. Attempts to reduce dinitrogen catalytically led to little or no ammonia being formed from dinitrogen. The fact that no ammonia was formed from dinitrogen in the case of Ar = 3,5-Me₂C ₆H₃, 3,5-(CF₃)₂C₆H ₃, or 3,5-(MeO)₂C₆H₃ could be attributed to a rapid decomposition of intermediate [hybrid]Mo=N-NH species in the catalytic reaction, a decomposition that was shown in separate studies to be accelerated dramatically by 2,6-lutidine, the conjugate base of the acid employed in the attempted catalytic reduction. X-ray structures of [(HIPTNHCH₂CH₂)NCH₂CH₂N{3,5-(CF ₃)₂C₆H₃}]MoCl and [(HIPTNHCH ₂CH₂)₂NCH₂CH₂N(3,5- Me₂C₆H₃)]MoN₂}Na(THF)₂ are reported.

Full text of DOI:10.1021/ic0613457

Inorg. Chem. 2006, 45, 9185−9196
Synthesis of Molybdenum Complexes that Contain “Hybrid”
Triamidoamine Ligands,
-
[(Hexaisopropylterphenyl-NCH2CH2)2NCH2CH2N-aryl]3 , and Studies
Relevant to Catalytic Reduction of Dinitrogen
Walter W. Weare, Richard R. Schrock,* Adam S. Hock, and Peter Mu1ller
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307
Received July 19, 2006
In the Buchwald−Hartwig reaction between HIPTBr (HIPT ) 3,5-(2,4,6-i-Pr3C6H2)2C6H3 ) hexaisopropylterphenyl)
and (H2NCH2CH2)3N, it is possible to obtain a 65% isolated yield of (HIPTNHCH2CH2)2NCH2CH2NH2. A second
coupling then can be carried out to yield a variety of “hybrid” ligands, (HIPTNHCH2CH2)2NCH2CH2NHAr, where Ar
)
3,5-Me2C6H3, 3,5-(CF3)2C6H3, 3,5-(MeO)2C6H3, 3,5-Me2NC5H3, 3,5-Ph2NC5H3, 2,4,6-i-Pr3C6H2, or 2,4,6-Me3C6H2.
The hybrid ligands may be attached to Mo to yield [hybrid]MoCl species. From the monochloride species, a variety
+
of other species such as [hybrid]MoN,
species were prepared through oxidation of
[Hybrid]Mo
{
[hybrid]MoN2
}
Na, and
{
[hybrid]Mo(NH3)
}
can be prepared. [Hybrid]MoN2
{
[hybrid]MoN2
}
Na species with ZnCl2, but they could not be isolated.
NH species could be observed as a consequence of the protonation of
-
dN−
{
[hybrid]MoN2
}
species,
but they too could not be isolated as a consequence of a facile decomposition to yield dihydrogen and [hybrid]-
MoN2 species. Attempts to reduce dinitrogen catalytically led to little or no ammonia being formed from dinitrogen.
The fact that no ammonia was formed from dinitrogen in the case of Ar
(MeO)2C6H3 could be attributed to a rapid decomposition of intermediate [hybrid]Mo
)
3,5-Me2C6H3, 3,5-(CF3)2C6H3, or 3,5-
NH species in the catalytic
dN−
reaction, a decomposition that was shown in separate studies to be accelerated dramatically by 2,6-lutidine, the
conjugate base of the acid employed in the attempted catalytic reduction. X-ray structures of [(HIPTNHCH2CH2)2-
NCH2CH2N{3,5-(CF3)2C6H3}]MoCl and [(HIPTNHCH2CH2)2NCH2CH2N(3,5-Me2C6H3)]MoN2}Na(THF)2 are reported.
Introduction
to yield pseudooctahedral species,2 or even seven-coordinate
species,3 is possible in cases where tungsten is the central
metal and strongly bound substrates such as isocyanides or
acetylenes are involved.
In the last 10 years, we have been exploring early transition
metal complexes that contain a triamidoamine ligand,
[(RNCH2CH2)3N]3- ([RN3N]3-).1 These trianionic ligands
bind to an early transition metal in a relatively high oxidation
state (∼3+ or higher) in a tetradentate fashion, leaving three
orbitals for binding substrates in the trigonally symmetric
“pocket” surrounded by the three amido substituents. Two
of these orbitals have π symmetry (dxz and dyz) and one has
Recently we have been most interested in the chemistry
of Mo complexes that contain the [HIPTN3N]3- ligand,
where HIPT ) 3,5-(2,4,6-i-Pr3C6H2)2C6H3 (hexaisopropyl-
terphenyl, see Figure 1),4 and in particular, in the reduction
of dinitrogen at a single metal center. The HIPT-substituted
ligand was designed to prevent formation of relatively stable
and unreactive [ArN3N]Mo-NdN-Mo[ArN3N] complexes,1b
2
σ symmetry (∼dz ). These orbitals can be employed in three
combinations (2π/1σ, 1π/2σ, or 3σ) to bind substrates in the
trigonal pocket. Distortion of the pseudotrigonal symmetry
(2) Dobbs, D. A.; Schrock, R. R.; Davis, W. M. Inorg. Chim. Acta 1997,
36, 171.
* To whom correspondence should be addressed. E-mail: rrs@mit.edu.
(1) (a) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9. (b) Greco, G. E.;
Schrock, R. R. Inorg. Chem. 2001, 40, 3850. (c) Greco, G. E.; Schrock,
R. R. Inorg. Chem. 2001, 40, 3861. (d) O’Donoghue, M. B.; Davis,
W. M.; Schrock, R. R. Inorg. Chem. 1998, 37, 5149.
(3) Greco, G. E.; O’Donoghue, M. B.; Seidel, S. W.; Davis, W. M.;
Schrock, R. R. Organometallics 2000, 19, 1132.
(4) (a) Yandulov, D. V.; Schrock, R. R. Science 2003, 301, 76. (b)
Yandulov, D. V.; Schrock, R. R. Inorg. Chem. 2005, 44, 1103. (c)
Yandulov, D. V.; Schrock, R. R. Can. J. Chem. 2005, 83, 341.
10.1021/ic0613457 CCC: $33.50
Published on Web 10/12/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 23, 2006 9185

Weare et al.
methylterphenyl ([HMTN3N]3-) ligand, and a variation of
the [HIPTN3N]3- ligand in which a bromide is present in
the para position of the central phenyl ring, [pBrHIPTN3N]3-.6
It became clear from various stoichiometric reactions involv-
ing the [HTBTN3N]3- system that proton and electron
transfer was much slower than in the parent [HIPTN3N]3-
system, perhaps by an order of magnitude or more. (The
rate of conversion of [HTBTN3N]Mo(NH3) into [HTBTN3N]-
Mo(N2) has now been confirmed to be extremely slow, with
a half-life of ∼30 h compared to ∼2 h for the parent system
under a given set of conditions.)7 We believe it is for this
reason that [HTBTN3N]MotN produces no significant
ammonia from dinitrogen (0.06 equiv); the nitride is reduced
to ammonia, but the system does not turn over to any
significant extent. An attempted catalytic reduction with
[HMTN3N]MotN as the catalyst precursor was barely
catalytic (0.49 equiv). The hexamethylterphenyl system was
not explored in detail because of the low yields involved in
synthesis of the ligand. Therefore the reason for poor catalytic
activity has not been established in the hexamethylterphenyl
system. Various [pBrHIPTN3N]Mo compounds were suc-
cessful catalysts for reduction of dinitrogen; 6.4-7.0 equiv
of total ammonia were formed, which is not quite as high as
the amount formed when [HIPTN3N]Mo species are em-
ployed. Since electronic differences (redox potentials and
values for νNN) between the three variations and the parent
system are relatively insignificant,6 steric differences appear
to play a major role in the success or failure of the HTBT-
and HMT-substituted ligand complexes for the catalytic
reduction of dinitrogen.
Figure 1. Drawing of [HIPTN3N]MoN2 ) MoN2.
maximize steric protection of a metal coordination site in a
monometallic species, and provide increased solubility in
nonpolar solvents. We showed that several [HIPTN3N]Mo
complexes could be prepared that contain dinitrogen or some
dinitrogen reduction product.5 Examples include paramag-
netic MoN2 (where Mo ) [HIPTN3N]Mo), diamagnetic
[MoN2]-, diamagnetic Mo-NdN-H, diamagnetic [Mod
N-NH2]BAr′4 (Ar′ ) 3,5-(CF3)2C6H3), diamagnetic Mot
N, diamagnetic [ModNH]BAr′, paramagnetic [Mo(NH3)]-
BAr′4, and paramagnetic Mo(NH3). Several of these species
were successful for the catalytic reduction of dinitrogen to
ammonia with protons and electrons.4a,b Dinitrogen is reduced
through a combination of reduction and protonation at a
single molybdenum in a trigonally symmetric coordination
pocket that is sterically protected by three hexaisopropyl
terphenyl substituents. Some combination of the frontier (two
π and one σ) orbitals is sufficient to bind all of the
intermediates in a proposed Chatt-like reduction cycle.
“Symmetric” variations of the [HIPTN3N]3- ligand that
have been prepared and attached to molybdenum include the
hexa-tert-butylterphenyl ([HTBTN3N]3-) ligand, the hexa-
During studies concerning the [HTBTN3N]3- system, we
discovered that in the arylation reaction between 3 equiv of
Figure 2. Labeling scheme for ligands and metal complexes described in this paper.
9186 Inorganic Chemistry, Vol. 45, No. 23, 2006

Mo Complexes Containing “Hybrid” Triamidoamine Ligands
HTBTBr and (H2NCH2CH2)3N the third equivalent of
HTBTBr reacts significantly more slowly than the second
equivalent. Therefore, (HTBTNHCH2CH2)2NCH2CH2NH2
could be isolated in good yield6 by adjusting the stoichiom-
etry. It then became possible to add a different aryl group to
the third “arm” of the ligand to yield what we call a hybrid
(HTBTNHCH2CH2)2NCH2CH2NHAr species. We found that
the same is true for the (HIPTNHCH2CH2)2NCH2CH2NHAr
species (Figure 2). An advantage of the [(HIPTNCH2CH2)2-
NCH2CH2NAr]3- species is that steric protection in the
coordination pocket can be tuned more finely. In this paper,
we report the synthesis of hybrid ligands and a selection of
molybdenum compounds that contain some of them. We also
report attempts to reduce dinitrogen catalytically with
compounds that contain hybrid ligands. No Mo compound
that contains one of the hybrid ligands is as successful as a
catalyst as a compound that contains the parent [HIPTN3N]3-
ligand, and some fail completely to produce ammonia from
gaseous dinitrogen. Although the hybrid catalysts are poor
catalysts, or not catalysts at all, these studies have helped us
to understand what may be some of the key problems in the
catalytic cycle.
H32g (eq 2, Figure 2). The final arylation can be complicated
by overarylation of one or more secondary amines. However,
careful optimization of the conditions allowed the pure
ligands to be isolated and purified through column chroma-
tography. These ligands all exhibit features in their NMR
spectra that are entirely consistent with their Cs symmetry.
NaO-t-Bu, 0.5% Pd2(dba)3,
1.5% rac-BINAP
H41 toluene, 80-100 °C, 24 h 8
(2)
(HIPTNHCH2CH2)2NCH2CH2NHAr
H32a-H32g
The hybrid ligands were attached to Mo in the same way
as the [HIPTN3N]3- ligands (i.e., the parent ligands were
added to a solution of MoCl4(THF)2 and the mixture was
then treated with three equivalents of LiN(TMS)2 (Figure
3)). The resulting bright orange paramagnetic [hybrid]MoCl
compounds 3a-3g (Figure 2) could be isolated in good
yields, even though they tend to be significantly more soluble
than the already highly soluble [HIPTN3N]MoCl species.4
The proton NMR spectra of the [hybrid]MoCl compounds
reveal paramagnetically shifted methylene resonances similar
to those observed for [HIPTN3N]MoCl, with separate me-
thylene resonances for the HIPT and Ar-substituted arms.
In some cases separate “inner” and “outer” (diastereotopic)
methylene proton resonances can be observed in the HIPT-
substituted arms of the ligands, consistent with the overall
Cs symmetry of the hybrid complex. It should be noted that
symmetric (ArNHCH2CH2)3N ligands cannot be placed onto
Mo using the method described above when Ar is 2,4,6-
trimethylphenyl,1b presumably for steric reasons. One mesityl
or TRIP group is tolerated in 3f or 3g as a consequence of
the two HIPT groups having no substituents in the ring’s
ortho positions.
Results and Discussion
If 2.1 equiv of HIPTBr are employed in the Buchwald-
Hartwig reaction8 between HIPTBr and (H2NCH2CH2)3N,
then a mixture results that consists largely of (HIPTN-
HCH2CH2)2NCH2CH2NH2 mixed with a small amount of
(HIPTNHCH2CH2)3N. These two products can be separated
readily using a silica gel column pretreated with triethyl-
amine, from which (HIPTNHCH2CH2)3N (11% yield) elutes
readily with toluene. The flushing of the column with a
1:1 mixture of toluene and tetrahydrofuran then yields
(HIPTNHCH2CH2)2NCH2CH2NH2 (H41, 65% yield on a ∼50
g scale; eq 1). The (HIPTNHCH2CH2)3N ligand can be
accumulated and employed in other studies.
An X-ray structure of 3c was carried out (Figure 4, Tables
1 and 2). The main difference between 3c and the
[HIPTN3N]3- compounds is a disruption of the trigonally
symmetric pattern of steric protection around the apical
position on the Mo (i.e., an opening up of one face of the
ligand binding pocket). Bond distances and angles around
the metal are similar to those found in symmetric [HIPTN3N]-
Mo, [HTBTN3N]Mo, and [pBrHIPTN3N]Mo systems.
One of the least air-sensitive [HIPTN3N]Mo compounds
that can be employed as a catalyst precursor in dinitrogen
reduction is the nitride, [HIPTN3N]MoN. The bright yellow,
diamagnetic [hybrid]MoN compounds 4a-4g (Figure 3)
were prepared in reactions between [hybrid]MoCl and
trimethylsilyl azide in benzene at elevated temperatures.
NMR spectra of the diamagnetic [hybrid]MoN species are
fully consistent with their Cs symmetry. The [hybrid]MoN
species also are relatively crystalline and readily isolated.
All have been analyzed and fully characterized.
A second Buchwald-Hartwig coupling can be carried out
on the terminal amine in (HIPTNHCH2CH2)2NCH2CH2NH2
to yield (HIPTNHCH2CH2)2NCH2CH2NHAr species H32a-
(7) Weare, W. W.; Dai, C.; Byrnes, M. J.; Chin, J.; Schrock, R. R. Proc.
Nat. Acad. Sci. in press.
(5) Schrock, R. R. Acc. Chem. Res. 2005, 38, 955.
(6) Ritleng, V.; Yandulov, D. V.; Weare, W. W.; Schrock, R. R.; Hock,
A. R.; Davis, W. M. J. Am. Chem. Soc. 2004, 126, 6150.
(8) (a) Wolfe, J. P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc.
Chem. Res. 1998, 31, 805. (b) Hartwig, J. Acc. Chem. Res. 1998, 31,
852.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9187

Weare et al.
Figure 3. Synthesis of molybdenum complexes that contain hybrid ligands.
Figure 4. X-ray crystal structure of 3c. Hydrogen atoms have been
removed for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) of 3c versus
HTBTMoCl6
Figure 5. X-ray crystal structure of 5d. Hydrogen atoms and isopropyl
groups have been removed for clarity.
bond
Mo-Cl
Mo-N1 (amide)
Mo-N4 (amine)
3c
HTBTMoCl
2.331(2)
1.978(7)
2.199(6)
2.33
1.99
2.34
all {[hybrid]MoN2}Na(THF)2 complexes could be identified
in solution, we attempted to isolate only 5c and 5d.
Unfortunately, neither 5c nor 5d could be isolated in a
sufficiently pure state to pass elemental analyses. Fortunately,
however, an X-ray crystal structure was completed on a
suitable crystal of 5d (Figure 5). As in 3c, the presence of
an unsymmetric arm does not alter the metrical parameters
around molybdenum to any significant degree (Table 2). The
most obvious and significant feature is the off-axis coordina-
tion of the sodium atom (Na-N6-N6 ) 110°) to the 3,5-
dimethylphenyl group. Coordination of the sodium ion to
the two nitrogens in the diazenido ligand decreases the Mo-
NdN angle slightly to 174°.
N4-Mo-N1
N4-Mo-Cl
100.20(18)
176.10(17)
99
179
Table 2. Selected Bond Lengths (Å) and Angles (deg) of 5d versus
[HIPTMoN2][MgBr(THF)3]17
bond
5d
[HIPTMoN2][MgBr(THF)3]
N5-N6 (nitrogen)
Mo-N5 (dinitrogen)
Mo-N4 (amine)
Mo-N3 (amide)
1.171(6)
1.882(4)
2.209(4)
2.022(4)
1.15
1.86
2.24
2.02
N4-Mo-N5
N4-Mo-N1
Mo-N5-N6
N5-N6-Na
174.09(17)
81.25(16)
174.2(4)
178
80
178
The {[hybrid]MoN2}Na(THF)2 compounds 5a-5g can be
oxidized with ZnCl2 to yield [hybrid]MoN2 species, 6a-
6g. The extreme solubility of 6a-6g and the presence of
5-10% of free ligand, (HIPTNHCH2CH2)2NCH2CH2NHAr,
so far have thwarted attempts to isolate these species.
Therefore, 6a-6g could be characterized only through IR
110.7(4)
Reduction of [hybrid]MoCl compounds with sodium sand
or 0.5% sodium/mercury amalgam yields diamagnetic an-
ionic complexes that can be described as either Mo(II)
dinitrogen complexes or, alternatively, as deprotonated Mo-
(IV) diazenido species, {[hybrid]MoN2}Na(THF)2. Although
1
and NMR techniques. In H NMR spectra of these species,
9188 Inorganic Chemistry, Vol. 45, No. 23, 2006

Mo Complexes Containing “Hybrid” Triamidoamine Ligands
Table 3. Dinitrogen Stretching Modes for LMoN2 Compounds
Table 4. Equivalents of Ammonia Obtained When LMoN Is the
Precatalyst
compound
ν
N-N (cm-1
)
compound
NH3 from N2 (equiv)
[HIPTN3N]MoN2
[pBrHIPTN3N]MoN2
[HTBTN3N]MoN2
6a
6b
6c
6d
6e
6f
1990
1992
1990
1991
1988
1992
1987
1984
1986
2007
4a
4b
4c
4d
4e
4f
0.6
0.3
0
0
0
0.2
2.0
4g
6g
None of the compounds that contain one of the new hybrid
ligands is as efficient a catalyst for the reduction of dinitrogen
as the [HIPTN3N]Mo analogue. However, 4a, 4b, 4f, and
4g are catalytic to a small degree (0.6, 0.3, 0.2, and 2 equiv
of ammonia from dinitrogen, respectively; Table 4). At least
one equivalent of ammonia is formed in all runs (i.e., the
nitride is reduced to ammonia under the conditions em-
ployed). Compounds 4a and 4b are not directly comparable
to the others as a consequence of the presence of the pyridyl
ring, which could be protonated in several intermediates. In
fact all that we can say at this point is that the [HIPTN3N]-
Mo system is not unique, although successful catalytic
reduction appears to be extraordinarily sensitive to steric
effects. It is important to know that one run in which 6c
was employed yielded 0.7 equiv of ammonia. This is an
important result that we will revisit later.
A crucial step in dinitrogen reduction is conversion of a
Mo(III) ammonia complex into a Mo(III) dinitrogen complex.
Two of the LMoNH3 complexes were prepared in situ
through reduction of 7c and 7e with CrCp*2. The resulting
LMoNH3 complexes (8c and 8e) could not be isolated as a
consequence of their high solubility and their ready conver-
sion under dinitrogen into LMoN2 complexes, as observed
through growth of LMoN2 in IR studies in aliquots of the
solution of LMoNH3 over a period of several hours. The
rate of formation of LMoN2 was shown to be approximately
a first-order process in Mo through at least two half-lives,
as found in the parent system.7 For 8c, t1/2 ) 180 min, while
for 8e, t1/2 < 45 min. It should be stressed that these results
are only semiquantitative, since the ammonia that is released
is in equilibrium with the newly formed LMoN2 is not
immediately released into the gas phase. In the parent system,
conversion of the ammonia complex into the dinitrogen
complex was shown to be first order in dinitrogen with t1/2
≈ 120 min. Exchange was estimated to actually be ap-
proximately 10 times faster than that observed in “bulk”
exchange reactions.7 However, data for this first-order
reaction of hybrid complexes are useful when compared with
analogous data obtained for the parent system.7 In short, the
rate of exchange appears to be slightly slower when CF3
groups are present (t1/2 ) 180 min) and faster when methoxy
groups are present (t1/2 < 45 min). Although we have not
shown that the exchange rates in the hybrid systems depend
on dinitrogen pressure, as in the parent system,7 we believe
that this is likely to be the case. The exchange rate is faster
when the metal is slightly more electron-rich, consistent with
more efficient back-bonding into dinitrogen when it displaces
ammonia in a bimolecular reaction. The position of the
equilibria in the hybrid ligand systems are not known. In
which are characteristic of a single Mo compound (plus free
ligand), multiple resonances are observed for backbone
methylene protons, as in many of the paramagnetic [hybrid]-
MoCl compounds. IR spectra reveal a strong νNN absorption
near 1990 cm-1, as previously observed for MoN2 com-
pounds that contain “symmetric” ligands such as [HIPTN3N]-
MoN2.4 These νNN stretches are listed in Table 3. The νNN
stretches in 6a-6g respond to the slightly different electronic
characteristics of the hybrid ligands. In the 3,5-substituted
compounds, the energy of the νNN stretch moves to lower
energies as the hybrid ligand’s substituents become more
electron-donating (i.e., νNN ) 1992 cm-1 for 6c vs νNN
)
1984 cm-1 for 6e). The exception to this trend is 6g, where
νNN is found at 2007 cm-1. We propose that this relatively
high value results from steric crowding at the metal by the
ortho isopropyl substituents, which lengthens the Mo-N2
bond slightly and therefore reduces the amount of back-
bonding to dinitrogen. As we shall see, however, the νNN
stretches, which in any case vary relatively little, do not
correlate with the success or failure of a catalytic reduction
of dinitrogen, at least in the series of complexes prepared
here.
Two cationic ammonia complexes, {[hybrid]MoNH3}-
BAr4′ species (7c and 7e) were prepared in reactions between
3c and 3e, respectively, and ammonia in dichloromethane
in the presence of NaBAr4′ (Ar′ ) 3,5-(CF3)2C6H3). Com-
pound 7e could be crystallized cleanly and was analyzed
successfully. Compound 7c could not be freed completely
from NaBAr4′ and so could be characterized only via NMR.
Both 7c and 7e were used in studies involving the exchange
of ammonia for dinitrogen discussed below.
Attempts to reduce dinitrogen catalytically were carried
out in the manner described for the parent system, which
produced 7-8 equiv of ammonia/1 equiv of Mo.4 Briefly, a
heptane slurry containing 48 equiv of [2,6-lutidinium][BAr4′]
and 4a-4g was placed in the reaction vessel, and 36 equiv
of decamethylchromocene in 10 mL of heptane was added
with a syringe pump.4a (See the Experimental Section for a
representative experiment.) The reducing agent was added
over a period of 6 h, and the mixture was stirred for an
additional hour. The volatiles were then vacuum transferred
onto 1 M HCl in ether. The remaining solids were treated
with NaO-t-Bu in a 2:1 mixture of methanol and tetrahy-
drofuran, and the volatiles again were transferred onto 1 M
HCl in ether. The ether and HCl were removed in vacuo,
and the resulting solid was analyzed for ammonia using the
indophenol method. The results are summarized in Table 4.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9189

Weare et al.
Figure 6. Synthesis and decomposition of hybrid diazenide 9c.
Figure 7. 14N2 exchange into the 15N2-labeled diazenide 9c.
any case, the main point is that slow exchange cannot be
the reason these catalysts fail, since the exchange rates for
the CF3- and OMe-substituted hybrid ligands bracket that
observed in the successful HIPT system. We also were able
to observe free NH3 in runs where two NH3 collections
(initial volatiles and post base workup) were separated and
quantified. When 4c is used as the precatalyst 0.3 out of the
0.97 equiv of the ammonia observed was found in the initial
volatiles, indicating that NH3 is indeed released during
catalysis and that approximately 1/3 of the ammonia is
order in Mo to form 6c quantitatively (and H2) with a t1/2 of
17 ( 2 h. In contrast, pure [HIPTN3N]Mo-NdNH decom-
poses only very slowly to [HIPTN3N]MoH (at 60 °C, t1/2
)
90 h).4b Interestingly, during some of these experiments, we
also were able to observe conversion of Mo-15Nd15NH to
Mo-14Nd14NH (t1/2 of 4.5 h; Figure 7). The mechanism of
this exchange (which also can be observed in [HIPTN3N]-
Mo-15Nd15NH, albeit with a much slower t1/2 of ap-
proximately 150 h) is under further study. We suspect that
nitrogen exchange is dependent upon nitrogen pressure (i.e.,
it does not involve â-hydride elimination to yield [HIPTN3N]-
MoH, followed by “insertion” of dinitrogen into the Mo-H
bond). It should be noted that 9c is prepared in situ.
Therefore, we do not know if the pure compound (if it
somehow could be purified) would decompose at the same
rate as that prepared in situ.
+
present as NH3 rather than NH4 .
If exchange of ammonia for dinitrogen in the hybrid
systems is not the problem with 8c and 8e as catalyst
precursors, then what is the problem? We focused on the
next step in the catalytic reaction, formation of the neutral
diazenide (M-NdNH) species. As opposed to the M-Nd
NR species (e.g., R ) alkyl), M-NdNH species are rare in
the literature, although some have been claimed.9 However,
to our knowledge only the molybdenum and tungsten
compounds in the symmetric HIPT system have been
confirmed to have a proton on the â nitrogen in 15N-labeled
compounds. Fortunately, the [ArN3N]Mo-NdNH species
are diamagnetic, so the presence of a proton on Nâ can be
established through 15N labeling studies. Because of its
relative ease of synthesis and the availability of an 19F NMR
handle, we focused on the [ArN3N]Mo-NdNH compound
containing the 3,5-trifluoromethylphenyl-substituted arm (9c).
Although the results for this compound have been reported
recently,7 a summary is reported below.
Treatment of 5c (both 15N and 14N) with a proton source
(initially H(OEt2)2BAr4′) resulted in the formation of 9c. This
species was identified through observation of Mo-NdNH
at 8.6 ppm, with JNâH ) 54.5 Hz and JNRH ) 8 Hz (absolute
values) in the 15N-labeled compound (Figure 6). These values
are nearly identical to those obtained for [HIPTN3N]Mo-
NdNH.4b Compound 9c decomposes in a manner that is first
When [2,6-lutidinium]BAr4′ was used to form 9c, the
decomposition rate was enhanced by an order of magnitude,
resulting in a t1/2 of 1.1 h. When 9c was prepared with
H(OEt2)2BAr4′ and 4 equiv of 2,6-lutidine, 2,4,6-trimeth-
ylpyridine (collidine), or Et3N were added subsequently, 9c
could not be observed 5 min after addition of the base: only
6c and H2 were observed as the major products. The ability
of Et3N to decompose 9c catalytically suggests that this
reaction is unlikely to be involved in redox chemistry, as it
might when some lutidine is the base. These results suggest
that a lutidine-catalyzed shunt that produces hydrogen is
operative in the less sterically shielded compounds (Figure
8). This finding could explain the inability of 4c to catalyze
dinitrogen reduction. Clearly much more work needs to be
done to understand this base-catalyzed chemistry. It is
especially important to understand if dihydrogen formation
is bimolecular or unimolecular in Mo. Regardless of the
precise mechanism, it is nevertheless ironic that one method
of forming dihydrogen takes place in a cycle that involves
the dinitrogen complex as the catalyst! Of course there are
9190 Inorganic Chemistry, Vol. 45, No. 23, 2006

Mo Complexes Containing “Hybrid” Triamidoamine Ligands
being the metal that will reduce dinitrogen most easily and
the site of reduction in the FeMo nitrogenase. It is possible
that in “alternative” FeV and all Fe nitrogenases13 dinitrogen
is reduced at V or Fe instead of Mo in a similar core
structure, with V and Fe being progressively less selective
toward forming ammonia instead of dihydrogen. The dra-
matic sensitivity of catalytic dinitrogen reduction toward
small changes in the nature of the triamidoamine ligand, as
we have demonstrated here, further emphasizes that dini-
trogen reduction is an extremely complex and sensitive
catalytic reaction, with many points where it can fail. We
hope to continue to improve our understanding of the
complex process of catalytic reduction of dinitrogen at Mo
and believe that an abiological vanadium-based catalytic
reduction of dinitrogen is a goal that can be reached with
the right ligand system. Catalytic reduction by V catalysts
remains to be achieved, as does the catalytic reduction of
dinitrogen with Fe-based systems.14
Figure 8. Hydrogenase shunt that limits catalysis in less sterically
demanding systems.
other ways of forming dihydrogen, the most direct consisting
of reduction of the acid by the chromocene reducing agent.
It is interesting and important to note that, when 6c is
employed in a catalytic run, 0.7 equiv of NH3 were found.
The fact that some ammonia is formed suggests that the
reaction can proceed through the diazenido stage early in
the reaction, but no additional ammonia is then formed from
free dinitrogen. Apparently any diazenido species that is
formed upon the addition of one electron and one proton to
MoN2 is not completely decomposed by 2,6-lutidine, since
only 1 equiv is present at this stage. Later in the cycle,
however, more 2,6-lutidine is present, and the reaction then
does not proceed beyond the diazenido stage.
Experimental Section
General. Air- and moisture-sensitive compounds were manipu-
lated using standard Schlenk and drybox techniques under an
atmosphere of dinitrogen. All glassware used was oven or flame
dried immediately prior to use. Pentane, diethyl ether, toluene, and
benzene were purged with dinitrogen and passed through activated
alumina columns. Benzene additionally was passed through a Q5
column.15 THF and benzene-d6 were dried over sodium/benzophe-
none ketyl and vacuum transferred prior to use. All other solvents
mentioned were freeze-pump-thaw degassed three times prior to
use. All dried and deoxygenated solvents were stored in a
dinitrogen-filled glovebox over molecular sieves or in Teflon-sealed
glass solvent bombs. 1,3,5-Triisopropylbenzene (Aldrich), 2,4,6-
tribromoaniline (Lancaster), N-bromo-succinimide (Aldrich), NaO-
t-Bu (Aldrich), Pd2(dba)3 (Strem), rac-BINAP (Strem), and tris(2-
Conclusions and Comments
A number of compounds that contain unsymmetric “hy-
brid” ligands have been synthesized that help expand our
knowledge of molybdenum-centered catalytic dinitrogen
reduction. While none of the compounds catalyzes the
dinitrogen reaction as successfully as compounds that contain
the parent [HIPTN3N]3- ligand, and several fail completely,
the study of several observable intermediates in dinitrogen
reduction have helped us understand what is necessary for
successful catalytic reduction. The primary requirement is
that the binding pocket be sterically protected to a dramatic
degree, not only to prevent bimetallic reactions but also, we
have discovered, to prevent decomposition of unstable
dinitrogen reduction intermediates, especially the diazenido
complex, through an, as yet, unknown mechanism. We also
have shown that electron-donating ligands may speed the
rate of ammonia for dinitrogen exchange. However, an
increase of the rate of exchange of ammonia for dinitrogen
was not sufficient to avoid the shunt that prevents catalytic
turnover. Clearly many other studies are required to under-
stand important details of the shunt that produces dihydrogen.
The larger question remains whether abiological studies
of the type described here suggest that dinitrogen is reduced
to ammonia at Mo in the FeMo nitrogenase.10,11 Since we
have (I believe) proven that dinitrogen can be reduced with
protons and electrons catalytically to a mixture of ammonia
and hydrogen at a single Mo center in systems of the type
described here and since no other abiological system will
accomplish this feat,12 we are biased toward molybdenum
(10) (a) Burgess, B. K.; Lowe, D. J. Chem. ReV. 1996, 96, 2983. (b) Hardy,
R. W. F.; Bottomley, F.; Burns, R. C. A Treatise on Dinitrogen
Fixation; Wiley-Interscience: New York, 1979. (c) Veeger, C.;
Newton, W. E., AdVances in Nitrogen Fixation Research; Dr. W. Junk/
Martinus Nijhoff: Boston, 1984. (d) Coughlan, M. P. Molybdenum
and Molybdenum-Containing Enzymes; Pergamon: New York, 1980.
(11) (a) Rees, D. C.; Howard, J. B. Curr. Opin. Chem. Biol. 2000, 4, 559.
(b) Bolin, J. T.; Ronco, A. E.; Morgan, T. V.; Mortenson, L. E.; Xuong,
L. E. Proc. Natl. Acad. Sci. 1993, 90, 1078. (c) Kim, J.; Rees, D. C.
Science 1992, 257, 1677. (d) Einsle, O.; Tezcan, F. A.; Andrade, S.
L. A.; Schmid, B.; Yoshida, M.; Howard, J. B.; Rees, D. C. Science
2002, 297, 1696.
(12) The only other known systems that will catalytically reduce dinitrogen
are those discovered by Shilov (Shilov, A. E. Russ. Chem. Bull. Int.
Ed. 2003, 52, 2555). These systems require Mo and are catalytic with
respect to Mo, but they reduce dinitrogen to a mixture of hydrazine
and ammonia (∼10:1). The reaction is run in methanol in the presence
of magnesium hydroxide and a strong reducing agent such as sodium
amalgam. Few mechanistic details are known.
(13) (a) Eady, R. R. Chem. ReV. 1996, 96, 3013. (b) Smith, B. E. AdV.
Inorg. Chem. 1999, 47, 159. (c) Rehder, D. Coord. Chem. ReV. 1999,
182, 297.
(14) (a) Brown, S. D.; Peters, J. C. J. Am. Chem. Soc. 2005, 127, 1913.
(b) Brown, S. D.; Peters, J. C. J. Am. Chem. Soc. 2004, 126, 4538.
(c) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2004, 126, 6252. (d)
Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2003, 125, 10782. (e)
Smith, J. M.; Sadique, A. R.; Cundari, T. R.; Rodgers, K. R.; Lukat-
Rodgers, G.; Lachicotte, R. J.; Flaschenriem, C. J.; Vela, J.; Holland,
P. L. J. Am. Chem. Soc. 2006, 128, 756. (f) Holland, P. L. Can. J.
Chem. 2005, 83, 296. (g) Smith, J. M.; Lachicotte, R. J.; Holland, P.
L. J. Am. Chem. Soc. 2003, 125, 15752. (h) Smith, J. M.; Lachicotte,
R. J.; Holland, P. L. J. Am. Chem. Soc. 2003, 125, 15752.
(15) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(9) (a) Lehnert, N.; Tuczek, F. Inorg. Chem. 1999, 38, 1659. (b) Lehnert,
N.; Tuczek, F. Inorg. Chem. 1999, 38, 1671 and references therein.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9191

Weare et al.
aminoethyl)amine (Aldrich) were used as received, unless indicated
otherwise. Hexaisopropylterphenyl bromide (HIPTBr),16,17 2,4,6-
trimethoxy-1-iodobenzene, and 4-bromo-2,6-dimethylpyridine18
were prepared according to published procedures or with slight
modifications. Proton and carbon NMR spectra were recorded on
a Varian Mercury 300. NMR spectra are referenced to internal
residual solvent peaks (1H and 13C NMR) or to external C6H5F (δ
) -113.15 ppm in the 19F NMR spectrum). All stated coupling
constants should be considered as absolute values.
was then filtered through Celite into a 300 mL toluene solution
containing 1 (4.41 g, 3.98 mmol), 4-bromo-2,6-dimethyl-pyridine
(0.80 g, 4.30 mmol), and NaO-t-Bu (0.76 g, 7.91 mmol). This
solution was then heated at 95 °C for 2 days, after which time it
was filtered through Celite and concentrated in vacuo to dryness.
The resulting solid was dissolved in pentane and loaded onto a
silica column which had been pretreated with triethylamine. The
side products were eluted with toluene, while the product was eluted
with a 1:1 mixture of toluene and THF. Yield: 3.66 g of a foamy,
tan solid (76%). 1H NMR (C6D6, 20 °C): δ 7.22 (s, 8H, 3,5,3′′,5′′-
H), 6.53 (br t, JHH ) 1.4 Hz, 2H, 4′-H), 6.48 (d, JHH ) 1.3 Hz, 4H,
2′,6′-H), 6.02 (s, 2H, Lut-3,5-H), 3.93 (t, JHH ) 4.9 Hz, 1H, Lut-
(HIPTNHCH2CH2)2NCH2CH2NH2. The procedure is similar
to that of the previous syntheses of symmetric ligands4 but uses
2.1 equiv of HIPTBr instead of 3.1 equiv. A 100 mL toluene
solution of Pd2(dba)3 (0.91 g, 0.9 mmol) and rac-BINAP (1.85 g,
2.9 mmol) was stirred with mild heating to preform the active
catalyst. The catalyst solution was then filtered through Celite into
a 500 mL toluene solution containing HIPTBr (78.21 g, 139 mmol),
tris(2-aminoethyl)amine (10.09 g, 67 mmol), and NaO-t-Bu (20.4
g, 212 mmol). This mixture was then heated at ∼100 °C for 2 days.
After 2 days, the organic layer was combined with 500 mL of water,
and the mixture was extracted with ether. The organic layers were
combined and dried over magnesium sulfate. This ether solution
was then filtered, and the ether was removed in vacuo. Column
chromatography was then carried out on a silica gel column.
Byproducts were eluted with toluene (including 11 g (10%) of the
symmetric ligand), and the product was eluted with a 1:1 mixture
of toluene and THF. (Note that it is important to pretreat the silica
gel with triethylamine to obtain acceptable separations.) Upon
removal of solvent from the column fractions in vacuo, 47.3 g of
NH), 3.71 (t, JHH ) 4.8 Hz, 2H, HIPT-NH), 3.16 (septet, JHH
)
6.9 Hz, 8H, 2,6,2′′,6′′-CHMe2), 2.92 (septet, JHH ) 6.9 Hz, 4H,
4,4′′-CHMe2), 2.80 (br q, JHH ) 5.4 Hz, 4H, HIPT-NHCH2CH2),
2.63 (br q, JHH ) 5.9 Hz, 2H, Lut-NHCH2CH2), 2.39 (s, 6H, Lut-
CH3), 2.16 (br t, JHH ) 5.7 Hz, 4H, HIPT-NHCH2CH2), 2.11 (br
t, JHH ) 6.8 Hz, 2H, Lut-NHCH2CH2), 1.32 (d, JHH ) 6.9 Hz,
24H, 4,4′′-CH(CH3)2), 1.28 (d, JHH ) 6.9 Hz, 24H, 2,6,2′′,6′′-CH-
(CH3)2), 1.25 (d, JHH ) 6.9 Hz, 24H, 2,6,2′′,6′′-CH(CH3)2). 13C
NMR (C6D6, 20 °C): δ 158.72, 154.58, 148.55, 148.4, 147.15,
142.68, 138.44, 121.96, 121.09, 112.84, 104.75, 52.78, 52.15, 41.48,
40.51, 35.26, 31.21, 30.94, 25.30, 25.10, 24.93, 24.87. MS (ESI):
1212.9662 ([M + H]+, calcd 1212.9695).
H3[PhLutHIPT2N3N] (2b). A solution of Pd2(dba)3 (0.045 g,
0.049 mmol) and rac-BINAP (0.094 g, 0.15 mmol) in 25 mL of
toluene was stirred with mild heating until the orange catalyst was
formed. The orange solution was then filtered through Celite into
a 300 mL toluene solution containing 1 (3.75 g, 3.39 mmol),
4-bromo-2,6-diphenylpyridine (1.55 g, 5.02 mmol), and NaO-t-Bu
(0.64 g, 6.66 mmol). This mixture was then heated at 95 °C for 2
days, at which time it was filtered through Celite and concentrated
in vacuo to dryness. The resulting solid was dissolved in pentane,
and the product was isolated through column chromatography on
silica column as described in earlier preparations. Yield: 2.07 g of
1
a pale yellow solid was isolated (64%). H NMR (C6D6, 20 °C):
δ 7.22 (s, 8H, 3,5,3′′,5′′-H), 6.50 (s, 6H, 2′,4′,6′-H), 4.92 (t, JHH
)
4.9 Hz, 2H, NH), 3.17 (septet, JHH ) 6.9 Hz, 8H, 2,6,2′′,6′′-
CHMe2), 2.94 (overlapped septet, JHH ) 6.6 Hz, 4H, 4,4′′
-CHMe2), 2.85 (overlapped multiplet, 4H, NH2CH2CH2 and
NH2CH2CH2), 2.74 (br q, JHH ) 5.2 Hz, 4H, NHCH2CH2), 2.03
(br t, JHH ) 5.2 Hz, 4H, NHCH2CH2), 1.32 (d, JHH ) 7.1 Hz, 24H,
4,4′′-CH(CH3)2), 1.26 (br d, JHH ) 6.9 Hz, 48H, 2,6,2′′,6′′-CH-
(CH3)2). 0.44 (br s, 2H, NH2). 13C NMR (C6D6, 20 °C): δ 148.77,
148.40, 147.19, 142.48, 138.69, 121.38, 121.03, 112.84, 55.91,
52.97, 41.64, 40.19, 31.18, 25.36, 25.05, 24.91. MS (ESI):
1107.9119 ([M + H]+, calcd 1107.9116).
4-Bromo-2,6-diphenyl-pyridene. This compound was synthe-
sized via a method similar to that of Talik et al.18 Briefly, 2,6-
diphenyl-pyridin-4-ylamine (3.75 g, 15.4 mmol) and copper bromide
(11.5 g, 80.3 mmol) were added to 150 mL of 48% hydrobromic
acid and cooled to <5 °C in an ice bath. Sodium nitrite (22.5 g,
326 mmol) in 100 mL water was slowly added, ensuring that the
temperature did not rise above 5 °C. After the addition, the mixture
was allowed to stir overnight, at which time it was basified with
150 g of sodium hydroxide in 300 mL water. The product was
extracted with ether, which was dried over magnesium sulfate,
filtered, and dried in vacuo, yielding a bright orange oil. This was
triturated with methanol to yield 1.55 g of a bright orange powder,
(34%) which is sparingly soluble in most solvents. 1H NMR (C6D6,
20 °C): δ 7.95 (dd, 4H, 2,6,2′′,6′′-H), 7.42 (s, 2H, 3′,5′-H) 7.22
(m, 6H, 3,4,5,3′′,4′′,5′′-H). MS (ESI): 309.0146 ([M + H]+, calcd
309.0148).
1
the product as a light yellow foamy solid (46%). H NMR (C6D6,
20 °C): δ 8.32 (m, 4H, PhLut-2,6,2′′,6′′-H), 7.33 (m, 6H, PhLut-
3,4,5,3′′,4′′,5′′-H), 7.22 (s, 8H, 3,5,3′′,5′′-H), 6.75 (s, 2H, PhLut-
3′,5′-H), 6.57 (br t, JHH ) 1.3 Hz, 2H, 4′-H), 6.51 (d, JHH ) 1.4
Hz, 4H, 2′,6′-H), 3.98 (t, JHH ) 5.2 Hz, 1H, PhLut-NH), 3.60 (br
s, 2H, HIPT-NH), 3.17 (septet, JHH ) 6.9 Hz, 8H, 2,6,2′′,6′′-
CHMe2), 2.89 (m, 8H, 4,4′′-CHMe2 and HIPTNHCH2CH2 overlap-
ping), 2.75 (br q, JHH ) 5.8 Hz, 2H, PhLutNHCH2CH2), 2.24 (m,
6H, HIPTNHCH2CH2 and PhLutNHCH2CH2 overlapping), 1.31 (d,
JHH ) 6.9 Hz, 24H, 4,4′′-CH(CH3)2), 1.29 (d, JHH ) 6.9 Hz, 12H,
2,6,2′′,6′′-CH(CH3)2), 1.28 (br d, JHH ) 6.9 Hz, 36H, 2,6,2′′,6′′-
CH(CH3)2). 13C NMR (C6D6, 20 °C): δ 158.41, 155.34, 148.61,
148.28, 147.16, 142.75, 141.27, 138.38, 129.14, 127.88, 122.10,
121.12, 112.82, 103.64, 52.87, 41.42, 35.24, 31.22, 25.31, 25.03,
24.83. MS (ESI): 1337.0025 ([M + H]+, calcd 1337.0008).
H3[3,5-Bis(CF3)HIPT2N3N] (2c). This compound was prepared
in a manner similar to other hybrid ligand systems. Briefly, a toluene
solution of 0.050 g (55 mmol) of Pd2(dba)3 and 0.101 g (162 mmol)
of rac-BINAP was heated until orange. This solution was filtered
through Celite into 100 mL of toluene containing 4 g (3.6 mmol)
of 1, 1.05 g (3.6 mmol) of 1-bromo-3,5-(bis)trifluoromethylbenzene,
and 0.69 g (7.2 mmol) of NaO-t-Bu. This solution was then heated
at 105 °C for 2 days and filtered. The volatiles were removed in
vacuo, and the residue was then extracted into pentane. The pentane
insoluble material was removed via filtration, and the resulting
solution was subject to column chromatography on silica gel. The
product was eluted with toluene to yield 0.91 g (20%) of the final
product as a light yellow solid. 1H NMR (C6D6, 20 °C): δ 7.25 (s,
H3[LutHIPT2N3N] (2a). Pd2(dba)3 (0.054 g, 0.058 mmol) and
rac-BINAP (0.11 g, 0.18 mmol) were stirred with mild heating in
25 mL of toluene to preform the bright orange catalyst. This solution
(16) Yandulov, D. V.; Schrock, R. R. J. Am Chem. Soc. 2002, 124, 6252.
(17) Yandulov, D. V.; Schrock, R. R.; Rheingold, A. L.; Ceccarelli, C.;
Davis, W. M. Inorg. Chem. 2003, 42, 796.
(18) Talik, T.; Talik, Z.; Ban-Oganowska, H. Synthesis 1974, 293.
9192 Inorganic Chemistry, Vol. 45, No. 23, 2006

Mo Complexes Containing “Hybrid” Triamidoamine Ligands
1H, CF3 arm 4-H), 7.22 (s, 8H, HIPT 3,5,3′′,5′′-H), 6.64 (s, 2H,
CF3 arm 2,6-H), 6.57 (s, 2H, HIPT 4′-H), 6.48 (s, 4H, HIPT-2′,6′-
H), 3.88 (t, JHH ) 5.2 Hz, 1H, CF3 arm NH), 3.51 (br s, 2H, HIPT-
NH), 3.15 (septet, 8H, JHH ) 6.9 Hz, 8H, 2,6,2′′,6′′-CHMe2), 2.90
(septet, JHH ) 6.9 Hz, 4H, 4,4′′-CHMe2), 2.82 (br t, JHH ) 5.8 Hz,
4H, HIPT-NCH2CH2), 2.40 (br q, JHH ) 5.2 Hz, 2H, CF3 arm-
NCH2CH2), 2.17 (br t, JHH ) 5.8 Hz, 4H, HIPT-NHCH2CH2), 2.10
(br t, JHH ) 5.8 Hz, 2H, CF3 arm-NCH2CH2) 1.32 (d, JHH ) 6.9
Hz, 24H, 4,4′′-CH(CH3)2), 1.28 (d, JHH ) 6.9 Hz, 24H, 2,6,2′′,6′′-
NCH2CH2), 1.26 (d, JHH ) 6.8 Hz, 24H HIPT-4,4′′-CH(CH3)2),
1.22 (d, JHH ) 6.8 Hz, 24H HIPT-2,6,2′′,6′′-CH(CH3)2), 1.19 (d,
JHH ) 6.8 Hz, 24H HIPT-2,6,2′′,6′′-CH(CH3)2). 13C NMR (C6D6,
20 °C): δ 162.9, 162.5, 150.8, 148.4, 147.2, 142.6, 138.6, 138.2,
129.7, 126.0, 121.0, 112.8, 92.9, 54.9, 52.8, 41.5, 35.3, 31.2, 25.3,
25.0, 24.9. MS (ESI): 1243.9694 ([M + H]+, calcd 1243.9641).
H3[MesHIPT2N3N] (2f). This compound was prepared in a
manner similar to other hybrid ligand systems. Briefly, 0.037 g
(40 mmol) of Pd2(dba)3 and 0.075 g (12 mmol) of rac-BINAP were
heated in toluene, and the orange solution was then filtered through
Celite into a toluene mixture containing 3 g (2.7 mmol) of 1, 0.59
g (29.8 mmol) of 1-bromo-2,4,6-trimethylbenzene, and 0.52 g (5.4
mmol) of NaO-t-Bu. The vessel was then sealed and heated at 110
°C for 2 days. The product mixture was worked up in a manner
similar to that described for previous ligands, and the product was
isolated via column chromatography with an 8:1 mixture of toluene
and THF as the eluent. Yield: 2 g (60%) of a pale yellow solid.
1H NMR (C6D6, 20 °C): δ 7.22 (s, 8H, HIPT 3,5,3′′,5′′-H), 6.77
(s, 2H, Mes-3,5-H), 6.54 (s, 2H, HIPT 4′-H), 6.48 (s, 4H, HIPT-
2′,6′-H), 3.79 (br s, 2H, HIPT-NH), 3.18 (septet, JHH ) 6.9 Hz,
8H, 2,6,2′′,6′′-CHMe2), 2.88 (m, 8H, containing 4,4′′-CHMe2 and
HIPT-NCH2CH2), 2.78 (br t, JHH ) 5.8 Hz, 2H, Mes-NCH2CH2),
2.2 (m, 15H, containing Mes-CH3, Mes-NCH2CH2, and HIPT-
NCH2CH2), 1.32 (d, JHH ) 6.9 Hz, 24H, 4,4′′-CH(CH3)2), 1.28 (d,
JHH ) 6.9 Hz, 24H, 2,6,2′′,6′′-CH(CH3)2), 1.26 (d, JHH ) 6.9 Hz,
24H, 2,6,2′′,6′′-CH(CH3)2). 13C NMR (C6D6, 20 °C): δ 162.80,
148.48, 147318, 144.65, 142.59, 138.54, 131.03, 130.23, 129.14,
121.83, 121.07, 112.77, 55.29, 53.30, 46.83, 41.56, 35.26, 31.19,
25.32, 25.12, 24.86, 21.06, 19.22. HRMS (ESI): 1225.9906 ([M
+ H]+, calcd 1225.9899).
H3[TripHIPT2N3N] (2g). This compound was prepared in a
manner similar to other hybrid ligand systems. Briefly, 0.037 g
(40 mmol) of Pd2(dba)3 and 0.077 g (162 mmol) of X-Phos were
heated mildly in toluene to preform the active orange catalyst
species. This was then filtered into a toluene mixture containing 3
g (2.7 mmol) of 1, 0.92 g (3.2 mmol) of 1-bromo,2,4,6-triisopro-
pylbenzene, and 0.39 g (40.5 mmol) of NaO-t-Bu. This mixture
was then heated at 120 °C for 2 days. The solvent was removed in
vacuo; the resulting solid was taken up in pentane, and the mixture
was filtered in preparation for column chromatography on silica
gel. Elution with an 8:1 mixture of toluene and THF yielded a
mixture of (HIPTNHCH2CH2)2NCH2CH2NH2 and the desired
product from which the solvent was removed in vacuo. The resulting
solid was taken up in toluene and passed through a silica plug,
yielding 0.35 g (10%) of the desired product as a light yellow solid.
1H NMR (C6D6, 20 °C): δ 7.21 (s, 8H, HIPT 3,5,3′′,5′′-H), 7.06
(s, 2H, Trip-3,5-H), 6.54 (br t, JHH ) 1.1 Hz, 2H, HIPT 4′-H),
6.51 (d, JHH ) 1.1 Hz, 4H, HIPT-2′,6′-H), 3.88 (br s, 2H, HIPT-
NH), 3.38 (septet, JHH ) 6.9 Hz, 2H, Trip-2,6-CHMe2), 3.17 (septet,
JHH ) 6.9 Hz, 8H, HIPT-2,6,2′′,6′′-CHMe2), 2.89 (m, 12H,
containing HIPT-NCH2CH2, Trip-NCH2CH2, HIPT-4,4′′-CH(CH3)2,
and Trip-4-CH(CH3)2), 2.44 (br t, JHH ) 5.5 Hz, 2H, Trip-
NCH2CH2), 2.33 (br t, JHH ) 5.5 Hz, 4H, HIPT-NCH2CH2), 1.32
(d, JHH ) 6.9 Hz, 24H, 4,4′′-CH(CH3)2), 1.25 (m, 60H, 2,6,2′′,6′′-
CH(CH3)2). 13C NMR (C6D6, 20 °C): δ 148.58, 148.47, 147.17,
144.52, 142.77, 142.10, 138.51, 121.98, 121.91, 121.05, 113.00,
55.60, 53.70, 50.16, 42.13, 35.26, 31.17, 30.84, 28.56, 25.35, 25.01,
24.92, 24.96, 24.87. HRMS (ESI): 1310.0833 ([M + H]+; calcd
1310.0838).
CH(CH3)2), 1.25 (d, JHH ) 6.9 Hz, 24H, 2,6,2′′,6′′-CH(CH3)2). 13
C
NMR (C6D6, 20 °C): δ 149.41, 148.66, 148.25, 147.13, 142.79,
138.31, 133.33, 132.91, 122.28, 121.12, 122.89, 112.30, 110.36,
52.95, 52.21, 41.55, 40.91, 35.25, 31.21, 25.28, 24.99, 24.83. 19F
NMR (C6D6, 20 °C): δ -62.74. HRMS (ESI): 1319.9156 ([M +
H]+, calcd 1319.9177).
H3[3,5-DimethylHIPT2N3N] (2d). This compound was prepared
in a manner similar to other hybrid ligand systems. Briefly, 0.037
g (4 mmol) of Pd2(dba)3 and 0.075 g (12 mmol) of rac-BINAP
were stirred in toluene to form the orange catalyst. This solution
was then filtered through Celite into a toluene mixture containing
3 g (2.8 mmol) of 1, 0.5 g (2,7 mmol) of 1-bromo-3,5-dimethyl-
benzene, and 0.52 g (5.4 mmol) of NaO-t-Bu. This solution was
then heated at 85 °C overnight, with the temperature then being
raised to 95 °C for 1 day. The mixture was then filtered through
Celite, and the solvent was removed in vacuo. The solid was taken
up in pentane, and the solution was filtered again through Celite.
The product was isolated from a silica gel column. The compound
was eluted with a 9:1 mixture of toluene and THF to yield 0.78 g
1
(24%) of the product as a light yellow solid. H NMR (C6D6, 20
°C): δ 7.22 (s, 8H, HIPT 3,5,3′′,5′′-H), 6.52 (br t, JHH ) 1.1 Hz,
2H, HIPT 4′-H), 6.46 (d, JHH ) 1.1 Hz, 4H, HIPT-2′,6′-H), 6.37
(s, 1H, dimethyl-4-H), 6.26 (s, 2H, dimethyl-2,6-H), 3.94 (br s,
2H, HIPT-NH), 3.75 (br s, 1H, dimethyl-NH), 3.16 (septet, JHH
)
6.9 Hz, 8H, HIPT-2,6,2′′,6′′-CHMe2), 2.95 (septet JHH ) 6.9 Hz,
4H, HIPT-4,4′′-CHMe2), 2.79 (m, 8H, contains HIPT-NCH2CH2
and dimethyl-NCH2CH2), 2.17 (m, 8H, contains HIPT-NCH2CH2
and dimethyl-NCH2CH2), 2.08 (s, 6H, dimethyl-CH3), 1.46 (d, JHH
) 6.9 Hz, 24H, 4,4′′-CH(CH3)2), 1.38 (d, JHH ) 6.9 Hz, 24H,
2,6,2′′,6′′-CH(CH3)2), 1.27 (d, JHH ) 6.9 Hz, 24H, 2,6,2′′,6′′-CH-
(CH3)2). 13C NMR (C6D6, 20 °C): δ 148.79, 148.49, 148.44, 147.17,
142.58, 139.28, 138.58, 121.66, 121.03, 120.74, 112.71, 111.71,
52.59, 52.29, 41.73, 41.41, 35.27, 31.19, 30.84, 25.32, 25.06, 24.89,
21.93. HRMS (ESI): 1211.9734 ([M + H]+, calcd 1211.9742).
H3[3,5-dimethoxyHIPT2N3N] (2e). This compound was pre-
pared in a manner similar to other hybrid ligand systems. Briefly,
0.037 g (0.04 mmol) of Pd2(dba)3 and 0.075 g (0.12 mmol) of rac-
BINAP were heated in toluene. This solution was filtered through
Celite into a solution containing 3 g (2.7 mmol) of 1, 0.56 g (2.5
mmol) of 3,5-dimethoxy bromobenzene, and 0.52 g (5.4 mmol) of
NaO-t-Bu in 75 mL of toluene. This container was then sealed and
heated at 90 °C for 2 days. The resulting brown solution was
filtered, and the solvent was removed in vacuo. A column was
employed to isolate the product, with pentane and toluene as the
eluents. Yield: 2.2 g (65%) of product as a light yellow powder.
1H NMR (C6D6, 20 °C): δ 6.46 (s, 4H, 3,5,3′′,5′′ HIPT-H), 6.42
(s, 4H, 3,5,3′′,5′′ HIPT-H), 6.40 (d, JHH ) 2 Hz, 2H, dimethoxy
2,6-H), 6.13 (t, JHH ) 2 Hz, 1H, dimethoxy 4-H), 5.94 (t, JHH
)
1.9 Hz, 2H HIPT 4′-H), 5.88 (d, JHH ) 1.9 Hz, 4H HIPT 2′6′-H),
3.94 (br s, 1H, dimethoxy N-H), 3.77 (br s, 2H, HIPT N-H), 3.27
(s, 6H, dimethoxy-OCH3), 3.11 (septet, JHH ) 6.8 Hz, 8H HIPT-
2,6,2′′,6′′-CHMe2), 2.85 (septet, JHH ) 6.8 Hz, 4H HIPT-4,4′′-
CHMe2), 2.75 (m, 10H, contains HIPT-NCH2CH2 and dimethoxy-
NCH2CH2 and dimethoxy NCH2CH2), 2.14 (br t, 4H, HIPT-
[LutHIPT2N3N]MoCl (3a). The procedure followed was nearly
identical to published procedures.4,6 Briefly, H32a (0.6 g, 0.50
mmol) and MoCl4(THF)2 (0.19 g, 0.50 mmol) were dissolved in
THF (40 mL). This solution was stirred for 1 h and (Me3Si)2NLi
Inorganic Chemistry, Vol. 45, No. 23, 2006 9193

Weare et al.
(0.258 g, 0.1.54 mmol) was then added slowly. The solution was
stirred for 2 h, and the solvent was removed in vacuo with mild
heating. The solid residue was extracted with pentane (2 × 10 mL),
followed by benzene (3 × 20 mL), and all extracts were passed
through Celite. The filtrate was then evaporated to dryness in vacuo.
The residue was recrystallized from pentane to yield 0.42 g of an
The solvent was removed in vacuo, and the solid was extracted
into pentane; the extract was filtered through Celite. The solvent
was removed in vacuo, and the residue was recrystallized from
pentane yielding 0.32 g (70%) of the compound as a deep orange
powder. 1H NMR (C6D6, 20 °C): δ 11.6 (br s), 10 (br s), 7.27 (s),
3.96 (s), 3.18 (s), 2.95 (s), 2.63 (s), 1.34 (s), -14.5 (br s), -20.4
1
orange solid in multiple crops (63%). H NMR (C6D6, 20 °C): δ
(br s), -69.6 (br s), -79.6 (br s). Anal. Calcd for C86H119-
11.8 (br s), 7.3 (m), 3.1 (br s), 3.0 (m), 2.7 (br s), 1.6 (br s), 1.4 (br
s), -16.7 (br s), -23.8 (br s), -65.0 (br s), -69.4 (br s). Anal.
Calcd for C85H118ClMoN5: C, 76.11; H, 8.87; N, 5.22. Found: C,
76.01; H, 9.06, N, 5.16.
ClMoN4O2: C, 75.27; H, 8.74; N, 4.08. Found: C, 75.06; H, 8.65;
N, 4.08.
[MesHIPT2N3N]MoCl (3f). This compound was synthesized
similarly to other compounds of this type described above. Briefly,
1.0 g (0.81 mmol) H32f was added to 70 mL of THF. MoCl4(THF)2
(0.32 g, 1.0 mmol) was added slowly with stirring. After 2 h, 0.42
g (2.6 mmol) of (Me3Si)2NLi was added. After 1 h, the solvent
was evaporated in vacuo; the resulting solid was dissolved into
pentane, and the extract was filtered through Celite. The solvent
was removed in vacuo, and the residue was recrystallized from
pentane to yield 0.74 g (67%) of a deep orange crystalline solid.
1H NMR (C6D6, 20 °C): δ 17.73 (br s), 7.28 (s), 7.22 (s), 6.42 (br
s), 3.83 (s), 3.5 (br s), 3.17 (br s), 2.97 (m), 1.52 (br s), 1.41 (br s),
-20 (br s), -23.5 (br s), -74.68 (br s), -97.50 (br s). Anal. Calcd
for C87H121ClMoN4: C, 77.16; H, 9.01; N, 4.14. Found: C, 77.04;
H, 9.04; N 4.11.
[TripHIPT2N3N]MoCl (3g). This compound was synthesized
similarly to other compounds of this type described above. Briefly,
0.35 g (0.25 mmol) of H32g was dissolved in 50 mL of THF. MoCl4-
(THF)2 (0.112 g (0.29 mmol) was added, and the solution was
stirred for 2 h. The color changed from orange to bright red; 0.138
g (0.83 mmol) of (Me3Si)2NLi was slowly added to this solution,
and the solution was stirred for an additional hour. The solvent
was removed in vacuo; the resulting solid was extracted into
pentane, and the mixture was filtered through Celite. The solvent
was removed in vacuo, and the residue was recrystallized to yield
0.22 g (56%) of a bright orange powder in multiple crops. 1H NMR
(C6D6, 20 °C): δ 18.14 (br s), 9.66 (br s), 7.30 (s), 7.20 (s), 4.09
(br s), 3.53 (br s), 3.20 (br s), 2.99 (m), 1.40 (br s), 1.26 (s), -11.52
(br s), -16.97 (br s), -23.75 (br s), -61.65 (br s), -83.70 (br s),
-96.15 (br s). Anal. Calcd for C93H133ClMoN4: C, 77.65; H, 9.32;
N, 3.89. Found: C, 77.42; H, 9.38; N, 3.77.
[PhLutHIPT2N3N]MoCl (3b). The procedure followed was
nearly identical to published procedures.4,6 Briefly, H32b (1 g, 0.75
mmol) and MoCl4(THF)2 (0.286 g, 0.75 mmol) were dissolved in
THF (75 mL). This solution was stirred for 1 h, and (Me3Si)2NLi
(0.388 g, 2.3 mmol) was then added slowly. After 2 h, the solvent
was removed in vacuo. The solid residue was extracted with pentane
(2 × 10 mL) and benzene (3 × 20 mL), and all filtrates were passed
through Celite. The filtrates were then reduced to dryness in vacuo.
The product was crystallized from pentane to yield 0.9 g of an
1
orange-brown solid in multiple crops (82%). H NMR (C6D6, 20
°C): δ 14.4 (br s), 8.3 (br s), 7.50 (br m), 7.2 (s), 3.1 (br s), 2.9 (br
s), 2.5 (br s), 1.3 (br s), -21.5 (br s), -62.2 (br s), -81.1 (br s),
-86.7 (br s). Anal. Calcd for C95H122ClMoN5: C, 77.86; H, 8.39;
N, 4.78. Found: C, 77.73; H, 8.46; N, 4.83.
[3,5-Bis(CF3)HIPT2N3N]MoCl (3c). This compound was syn-
thesized similarly to other compounds of this type described above.
Briefly, 0.75 g (0.57 mmol) of H32c as added to 50 mL of THF.
MoCl4(THF)2 (0.24 g, 0.62 mmol) was then added slowly, and the
mixture was stirred for 1 h, during which time the solution darkened
to a deep red. To this red solution, 0.30 g (1.8 mmol) of (Me3-
Si)2NLi was added, and the reaction mixture was stirred for 2 h.
The solvent was removed in vacuo, and the resulting solid was
extracted into pentane. The mixture was filtered through Celite,
and the solvent was removed in vacuo. Recrystallization of the
residue from pentane yielded 0.45 g (55%) of a deep orange powder.
1H NMR (C6D6, 20 °C): δ 11.1 (br s), 7.27 (s), 7.19 (s), 3.18 (br
s), 2.95 (m), 1.62 (br s), 1.49 (br s), 1.34 (br s), -10.3 (br s), -13.8
(br s), -29.7 (br s), -69.5 (br s), -82.7 (br s), -86.9 (br s). 19F
NMR (C6D6, 20 °C): δ -57.9. Anal. Calcd for C86H113ClF6-
MoN4: C, 71.32; H, 7.86; N, 3.87. Found: C, 71.25; H, 7.76; N,
3.94.
[3,5-DimethylHIPT2N3N]MoCl (3d). This compound was syn-
thesized similarly to other compounds of this type described above.
Briefly, 0.76 g (0.63 mmol) of H32d was added to 0.26 g (0.68
mmol) of MoCl4(THF)2 in 50 mL of THF. This mixture was stirred
for 1 h, and 0.33 g (1.9 mmol) of (Me3Si)2NLi was added. After 2
h, the solvent was removed in vacuo; the resulting solid was
extracted into pentane, and the extract was filtered through Celite.
The solvent was removed in vacuo, and the residue was recrystal-
lized from pentane to yield 0.47 g (56%) of a deep orange solid.
1H NMR (C6D6, 20 °C): δ 9.68 (br s), 7.26 (s), 7.24 (s), 3.18 (br
s), 2.97 (m), 2.05 (s), 1.54 (br s), 1.44 (s), 1.36 (br s), -11.25 (br
s), -13.80 (br s), -23.5 (br s), -66.5 (br s), -77.5 (br s), -84.0
(br s). Anal. Calcd for C86H119ClMoN4: C, 77.07; H, 8.95; N, 4.18.
Found: C, 76.87; H, 9.06; N, 4.11.
[LutHIPT2N3N]MoN (4a). This compound could not be isolated
in pure form because the reaction between (3a) and Me3SiN3 is
low yielding, and the final product consequently was contaminated
with H32a, even after multiple recrystallizations. A sample contain-
ing ∼10% H32a (according to 1H NMR) was used in test catalytic
runs.
[PhLutHIPT2N3N]MoN (4b). Me3SiN3 (0.044 g, 0.38 mmol)
and 3b (0.138 g, 0.092 mmol) were added to 25 mL of benzene,
and the mixture was heated overnight at 90 °C. The resulting yellow
solution was stripped to dryness in vacuo. The residue was taken
up in pentane; the mixture was filtered through Celite, and the
filtrate volume was reduced to 0.5 mL in vacuo. When it was
cooled, 50 mg of a bright, canary yellow solid was obtained (37%).
1H NMR (C6D6, 20 °C): δ 8.35 (d, 4H, JHH ) 1.3 Hz, PhLut,
2,6,2′′,6′′-H), 8.14 (s, 2H, PhLut 3′,5′-H), 7.79 (d, 4H, JHH ) 1.1
Hz, HIPT 3′,5′-H), 7.40 (m, 6H, PhLut 3,4,5,3′′,4′′,5′′-H), 7.17 (m,
8H, HIPT 3,5,3′′,5′′-H), 6.73 (br t, 2H, JHH ) 1.1 Hz, HIPT 4′-H),
3.59 (br t, 4H, JHH ) 5.1 Hz, HIPT-NHCH2CH2), 3.20 (br t, 2H,
JHH ) 4.2 Hz, PhLut-NCH2CH2), 3.11 (septet, 8H, JHH ) 6.9 Hz,
8H, 2,6,2′′,6′′- CHMe2), 2.89 (septet, JHH ) 6.9 Hz, 4H, 4,4′′-
CHMe2), 2.08 (br t, 2H, JHH ) 3.4 Hz, PhLut-NCH2CH2), 2.02 (br
t, 4H, JHH ) 5.1 Hz, HIPT-NCH2CH2), 1.33 (dd, 24H, 4,4′′-CH-
(CH3)2), 1.22 (d, JHH ) 6.9 Hz, 12H, 2,6,2′′,6′′-CH(CH3)2), 1.19
(d, JHH ) 6.9 Hz, 12H, 2,6,2′′,6′′-CH(CH3)2), 1.16 (d, JHH ) 6.9
[3,5-DimethoxyHIPT2N3N]MoCl (3e). This compound was
synthesized similarly to other compounds of this type described
above. Briefly, 0.41 g (0.3 mmol) of H32e was added to 0.13 g
(0.3 mmol) of MoCl4(THF)2 in 30 mL of THF. Upon addition of
the molybdenum, the solution’s color immediately darkened to deep
red. The solution was stirred for 1 h, and 0.17 g (1 mmol) of (Me3-
Si)2NLi was then added. The solution slowly turned orange-red.
9194 Inorganic Chemistry, Vol. 45, No. 23, 2006

Mo Complexes Containing “Hybrid” Triamidoamine Ligands
Hz, 12H, 2,6,2′′,6′′-CH(CH3)2), 1.11 (d, JHH ) 6.9 Hz, 12H,
2,6,2′′,6′′-CH(CH3)2). Anal. Calcd for C95H122MoN6: C, 79.02; H,
8.52; N, 5.82. Found: C, 78.88; H, 8.45; N, 5.88.
2,6,2′′,6′′-CH(CH3)2), 1.14 (d, JHH ) 6.9 Hz, 12H, 2,6,2′′,6′′-CH-
(CH3)2). Anal. Calcd for C86H119MoN5O2: C, 76.47; H, 8.88; N,
5.18. Found: C, 76.38; H, 8.85; N, 5.06.
[3,5-Bis(CF3)HIPT2N3N]MoN (4c). This compound was made
in a manner similar to other compounds of its type. Briefly, 0.17
g (117 mmol) of 3c and 0.07 g (608 mmol) of Me3SiN3 was added
to 50 mL of benzene in a Teflon-sealed glass bomb. This was heated
to 90 °C for 12 h and then brought to dryness in vacuo. The
resulting yellow solid was taken into pentane and filtered through
Celite. The solvent was removed in vacuo, and the residue was
[MesHIPT2N3N]MoN (4f). This compound was synthesized
similarly to compounds of this type. Briefly, 0.19 g (0.14 mmol)
of 3f was combined with 0.1 g (0.86 mmol) of Me3SiN3 in 25 mL
of benzene, and the mixture was heated in a Teflon-sealed glass
bomb at 90 °C for 1 day. The solvent was removed in vacuo, and
the solid was extracted into pentane; the extract was filtered through
Celite. The solvent was removed in vacuo, and the residue was
recrystallized from pentane to yield 0.11 g (59%) of a bright yellow
1
recrystallized to yield 0.12 g (72%) of a bright yellow solid. H
1
NMR (C6D6, 20 °C): δ 7.93 (s, 2H, CF3 arm 2,6-H), 7.70 (d, JHH
) 1.4 Hz, 4H, HIPT-2′,6′-H), 7.39 (s, 1H, CF3 arm 4-H), 7.19 (s,
8H, HIPT 3,5,3′′,5′′-H), 6.81 (br t, JHH ) 1.1 Hz, 2H, HIPT 4′-H),
3.53 (br t, JHH ) 4.7 Hz, 4H, HIPT-NCH2CH2), 3.15 (overlapping
powder. H NMR (C6D6, 20 °C): δ 7.76 (d, JHH ) 1.1 Hz, 4H,
HIPT-2′,6′-H), 7.20 (s, 8H, HIPT 3,5,3′′,5′′-H), 6.70 (br t, JHH
)
1.1 Hz, 2H, HIPT 4′-H), 6.65 (s, 2H, Mes-3,5-H), 3.47 (m, 4H,
HIPT-NCH2CH2), 3.20 (m, 10H, containing 2,6,2′′,6′′-CHMe2 and
Mes-NCH2CH2), 2.90 (septet, JHH ) 6.9 Hz, 4H, 4,4′′-CHMe2),
2.25 (s, 9H, Mes-CH3) 2.1 (m, 6H, containing Mes-NCH2CH2, and
HIPT-NCH2CH2), 1.34 (d, JHH ) 6.9 Hz, 24H, 4,4′′-CH(CH3)2),
septets, JHH ) 6.9 Hz, 8H, 2,6,2′′,6′′- CHMe2), 2.90 (septet, JHH
)
6.9 Hz, 4H, 4,4′′ -CHMe2), 2.83 (br t, JHH ) 4.8 Hz, 2H, CF3
arm-NCH2CH2), 1.97 (br t, JHH ) 5.1 Hz, 4H, HIPT-NHCH2CH2),
1.92 (br t, JHH ) 5.0 Hz, 2H, CF3 arm-NCH2CH2), 1.34 (d, JHH
)
1.30 (d, JHH ) 6.9 Hz, 24H, 2,6,2′′,6′′-CH(CH3)2), 1.20 (d, JHH )
6.9 Hz, 24H, 4,4′′-CH(CH3)2), 1.26 (d, JHH ) 6.9 Hz, 12H,
2,6,2′′,6′′-CH(CH3)2), 1.22 (d, JHH ) 6.9 Hz, 12H, 2,6,2′′,6′′-CH-
(CH3)2), 1.20 (d, JHH ) 6.9 Hz, 12H, 2,6,2′′,6′′-CH(CH3)2), 1.11
(d, JHH ) 6.9 Hz, 12H, 2,6,2′′,6′′-CH(CH3)2). 19F NMR (C6D6, 20
°C): δ -62.4. Anal. Calcd for C86H113F6MoN5: C, 72.40; H, 7.98;
N, 4.91. Found: C, 72.56; H, 7.98; N, 4.81.
6.9 Hz, 12H, 2,6,2′′,6′′-CH(CH3)2), 1.17 (d, JHH ) 6.9 Hz, 12H,
2,6,2′′,6′′-CH(CH3)2). Anal. Calcd for C87H121MoN5: C, 78.40; H,
9.15; N, 5.25. Found: C, 77.26; H, 9.17; N, 5.19.
[TripHIPT2N3N]MoN (4g). This compound was synthesized in
a manner similar to that of previously characterized compounds of
this type. Briefly, 0.05 g (0.035 mmol) of 3g was combined with
0.028 g (0.24 mmol) in 10 mL of benzene and heated 100 °C for
1 day. The solvent was removed in vacuo; the resulting solid was
extracted into pentane, and the extract was filtered through Celite.
The solvent was removed in vacuo, and the residue was recrystal-
lized from pentane to yield 0.04 g (80%) of a bright yellow powder.
1H NMR (C6D6, 20 °C): δ 7.77 (d, JHH ) 1.1 Hz, 4H, HIPT-2′,6′-
H), 7.19 (m, 8H, HIPT 3,5,3′′,5′′-H), 7.08 (s, 2H, Trip-3,5-H), 6.73
(br t, JHH ) 1.1 Hz, 2H, HIPT 4′-H), 3.52 (m, 6H, HIPT-NCH2-
CH2), 3.34 (br t, JHH ) 5.5 Hz, 2H, Trip-NCH2CH2), 3.17 (m, 10H,
containing HIPT-2,6,2′′,6′′-CHMe2, and Trip-2,6- CHMe2), 2.95
(septet, JHH ) 6.9 Hz, 2H, HIPT-4,4′′-CHMe2), 2.81 (septet, JHH
) 6.9 Hz, 1H, Trip-4-CHMe2), 2.21 (m, 8H, containing Trip-
NCH2CH2 and HIPT-NCH2CH2), 1.38 (d, JHH ) 6.9 Hz, 24H, HIPT
4,4′′-CH(CH3)2), 1.24 (m, 36H, contains Trip-4- CH(CH3)2 and
HIPT-2,6,2′′,6′′-CH(CH3)2), 1.13 (m, 24H, contains Trip-2,6,2′′,6′′-
[3,5-DimethylHIPT2N3N]MoN (4d). This compound was made
in a manner similar to other compounds of this type. Briefly, 0.15
g (0.11 mmol) of 2d and 0.064 g (0.56 mmol) of Me3SiN3 was
added to 40 mL of benzene, and the mixture was heated in a Teflon-
sealed bomb at 100 °C for 1 day. The volatiles were removed in
vacuo; the resulting solid was taken up in pentane, and the mixture
was filtered through Celite. The solvent was removed in vacuo,
and the residue was recrystallized to yield 0.073 g (50%) of a bright
yellow powder. 1H NMR (C6D6, 20 °C): δ 7.86 (d, JHH ) 1.1 Hz,
4H, HIPT-2′,6′-H), 7.21 (dd, JHH ) 1.4 and 3.3 Hz, 8H, HIPT
3,5,3′′,5′′-H), 7.05 (s, 2H, dimethyl-2,6-H), 7.76 (br t, JHH ) 1.1
Hz, 2H, HIPT 4′-H), 6.51 (s, 1H, dimethyl-4-H), 3.54 (br t, JHH
)
5.2 Hz, 4H, HIPT-NCH2CH2), 3.64 (br t, JHH ) 5.2 Hz, 2H,
dimethyl-NCH2CH2), 3.19 (septet, JHH ) 6.9 Hz, 8H, HIPT-
2,6,2′′,6′′ -CHMe2), 2.93 (septet, JHH ) 6.9 Hz, 4H, HIPT-4,4′′
-CHMe2), 2.18 (s, 6H, dimethyl-CH3), 2.03 (m, 8H, contains HIPT-
NCH2CH2 and dimethyl-NCH2CH2), 1.34 (d, JHH ) 6.9 Hz, 24H,
4,4′′-CH(CH3)2), 1.26 (d, JHH ) 6.9 Hz, 24H, 2,2′′,6,6′′-CH(CH3)2),
CH(CH3)2 and HIPT-2,6,2′′,6′′-CH(CH3)2). Anal. Calcd for C93H133
-
MoN5: C, 78.83; H, 9.46; N, 4.94. Found: C, 78.91; H, 9.48; N,
4.86.
1.21 (d, JHH ) 6.9 Hz, 12H, 2,6,2′′,6′′-CH(CH3)2), 1.16 (d, JHH
)
{[3,5-Bis(CF3)HIPT2N3N]MoN2}Na(THF)2 (5c). Compound 3c
(0.56 g) was dissolved in 20 mL of THF and 4.8 g of 0.5% Na/Hg
amalgam was added. The mixture was stirred with a glass stir bar
for 2 h until the solution turned a deep green. The solution was
decanted from the mercury, and the volatiles were removed in
vacuo. The resulting solids were dissolved in pentane, and the
mixture was filtered through Celite to yielding a deep purple
solution. The product was recrystallized from pentane to yield 0.45
g (70%) of a purple powder in multiple crops. A similar method
6.9 Hz, 24H, 2,6,2′′,6′′-CH(CH3)2). Anal. Calcd for C86H119MoN5:
C, 78.32; H, 9.09; N, 5.31. Found: C, 78.19; H, 8.96; N, 5.23.
[3,5-DimethoxyHIPT2N3N]MoN (4e). This was synthesized
similarly to other compounds of its type. Briefly, 0.12 g (0.08 mmol)
of 3e was added to 0.05 g (0.4 mmol) of Me3SiN3 in 25 mL of
benzene. This mixture was heated at ∼100 °C overnight. The
solvent was removed in vacuo; the resulting solid was taken up in
pentane, and the solution was filtered through Celite. The solvent
was removed in vacuo, and the residue was recrystallized from
pentane to yield 0.07 g (55%) of a bright yellow powder in multiple
crops. 1H NMR (C6D6, 20 °C): δ 7.91 (d, JHH ) 0.8 Hz, 4H, HIPT-
2′,6′-H), 7.23 (d, JHH ) 1.8 Hz, 2H, dimethoxy-2,6-H), 7.21 (s,
8H, HIPT 3,5,3′′,5′′-H), 6.76 (s, 2H, HIPT 4′-H), 6.30 (t, JHH
1.8 Hz, 1H, dimethoxy-4-H), 3.55 (br t, 4H, HIPT-NCH2CH2), 3.43
(s, 6H, -OCH3), 3.31 (br t, 2H, dimethoxy-NCH2CH2), 3.20
(septet, JHH ) 6.9 Hz, 8H, 2,6,2′′,6′′-CHMe2), 2.92 (septet, JHH
6.9 Hz, 4H, 4,4′′′′-CHMe2), 1.94 (br t, 6H, overlapped HIPTNCH2-
CH2 and dimethoxyNCH2CH2), 1.32 (d, JHH ) 6.9 Hz, 24H, 4,4′′-
CH(CH3)2), 1.22 (overlapping doublets, JHH ) 6.9 Hz, 24H,
1
was used to synthesize the 15N2-labeled species. H NMR (C6D6,
20 °C): δ 7.68 (s, 1H, CF3 arm 4-H), 7.59 (s, 2H, HIPT 4′-H),
7.45 (d, JHH ) 1.2 Hz, 2H, CF3 arm 2,6-H), 7.35 (d, JHH ) 1.3 Hz,
4H, HIPT- 2′,6′-H), 7.18 (s, 4H, HIPT 3,5,3′′,5′′-H), 7.13 (s, 4H,
HIPT 3,5,3′′,5′′-H), 3.76 (m, 6H, containing both HIPT-NCH2CH2
and CF3-NCH2CH2), 3.38 (overlapping septets, JHH ) 6.9 Hz, 8H,
2,6,2′′,6′′-CHMe2), 3.22 (br m, 8H, THF O-CH2), 2.84 (overlapping
septets, JHH ) 6.9 Hz, 4H, 4,4′′-CHMe2), 1.94 (br m, containing
both HIPT-NCH2CH2 and CF3-NCH2CH2), 1.23 (overlapping
)
)
doublets, 52H containing 2,4,6,2′′,4′′,6′′-CH(CH3)2), 1.1 (d, JHH
)
6.9 Hz, 12H, 4,4′′-CH(CH3)2). 19F NMR (C6D6, 20 °C): δ -61.76.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9195

Weare et al.
IR: νNN ) 1801 cm-1
;
15N2-labeled νNN ) 1741 cm-1. Elemental
X-ray Structural Studies. Low-temperature diffraction data
were collected on a Siemens Platform three-circle diffractometer
coupled to a Bruker-AXS SMART Apex CCD detector with
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å),
performing φ and ω scans. The structures were solved by direct
methods using SHELXS19 and refined against F2 on all data by
full-matrix least squares with SHELXL-97.20 All non-hydrogen
atoms were refined anisotropically. All hydrogen atoms were
included into the model at geometrically calculated positions and
refined using a riding model. The isotropic displacement parameters
of all hydrogen atoms were fixed to 1.2 times the U value of the
atoms they are linked to (1.5 times for methyl groups). Crystal and
structural refinement data for all structures is listed in the Supporting
Information.
The structure of 3c is strongly affected by disorder: both CF3
groups and about half of all carbon atoms are found distributed
over two positions. These disorders were refined with the help of
similarity restraints on 1-2 and 1-3 distances and displacement
parameters as well as rigid bond restraints for anisotropic displace-
ment parameters. The relative occupancies of the disordered
components were refined freely, while constraining the total
occupancy of both components to unity. Probably because of the
massive disorder, the crystal diffracted only to about 1.0 Å
resolution and gave rise to data of only mediocre quality. To
counteract the effects of the resulting low data-to-parameter ratio,
rigid bond and similarity restraints were used for the displacement
parameters of all atoms.
5d crystallizes with one molecule of C86H119MoN6, one sodium
ion, and the following solvent molecules in the asymmetric unit:
two THF molecules (one of which is disordered) coordinated to
the sodium ion, one-sixth of a noncoordinated THF molecule (6-
fold disordered about the crystallographic -3 axis), two-half
occupied heptane molecules, and one-sixth of a pentane molecule
(6-fold disordered about the crystallographic -3 axis). The pentane
molecule is probably a heptane molecule where the two methyl
groups are disordered in addition to the disorder described, however
refinement as heptane was not stable. These disorders were refined
as described above.
analyses are variable as a consequence (it is believed) of a variable
amount of THF being present depending on individual preparation
and isolation procedures. Variable amounts of THF also have been
observed in the parent compound.17
{LMoN2}Na(THF)2. Synthetic procedures for all other LMoN2-
Na(THF)2 compounds were similar to that for 5c. It was found
that both Na/Hg amalgam or finely divided Na sand would reduce
LMoCl similarly, so typically Na sand was used. A crystal structure
was performed on 5d, but elemental analyses were not successful
and reproducible for any compound of this type.
LMoN2 (6a-6g). No neutral dinitrogen complexes could be
isolated as pure compounds. They could be observed only via IR
and NMR spectroscopy. Typically LMoCl was treated with a 0.5%
Na/Hg amalgam or sodium sand in THF. When the solution had
turned from bright orange to either green (6b, 6f, or 6g) or purple
(6a, 6c, 6d, or 6e) it was filtered through a Celite plug onto a mild
oxidant such as ZnCl2. The resulting brown solution was then
filtered through Celite, and the solvent was removed in vacuo. NMR
and IR analysis suggested that 10-20% of the free ligand was
present in the resulting solid, depending on the compound and the
specific experiment. The paramagnetically shifted protons in the
1H NMR were similar to those of the symmetric compounds of
this type (3 peaks at ∼10 to 20 ppm, 2 peaks at ∼-3 to -10 ppm,
and 3 peaks at -20 to -40 ppm).
[(3,5-Bis(CF3)HIPT2N3N)MoNH3][BAr4′] (7c). This compound
has been identified via NMR from the 1:1 reaction of 3c and
NaBAr4′ under 6 equiv of ammonia in dichloromethane. After the
mixture was stirred for 1 day, the solvent was removed in vacuo,
and the resulting solid was filtered through Celite using pentane as
the eluent. The solvent was removed in vacuo, and the residue was
1
recrystallized from pentane to yield the product as a red solid. H
NMR (C6D6, 20 °C): δ 8.23 (s, BAr4′), 7.61 (s, BAr4′), 7.12 (br
s), 2.88 (br s), 2.68 (br s), 1.29 (br s), 1.16 (br s), -12.5 (br s),
-17.5 (br s), -33 (br s). 19F NMR (C6D6, 20 °C): δ -61.3
(MoNH3+), -61.45 (BAr4′). We were unable to remove NaBAr4′
from the solid completely (∼5% via 19F NMR).
[(3,5-DimethoxyHIPT2N3N)Mo(NH3)][BAr4′] (7e). A mixture
of 3e (100 mg) and 65 mg of Na[BAr4′] was dissolved in 10 mL
of CH2Cl2 in a 50 mL Teflon-sealed vessel. Dry ammonia (200
Torr, ∼6 equiv) was vacuum-transferred onto this solution. The
reaction mixture turned bright red after being stirred for 6 h. The
volatiles were removed in vacuo, and the resulting solid was
extracted into pentane. The pentane extract was filtered through
Celite, and the solvents were removed in vacuo. The product was
isolated as a red solid upon crystallization of the residue from
Acknowledgment. R.R.S. is grateful to the National
Institutes of Health (GM 31978) for research support.
Supporting Information Available: Crystal data and structure
refinement, atomic coordinates and equivalent isotropic displace-
ment parameters, bond lengths and angles, and anisotropic displace-
ment parameters for 3c and 5d. This material is available free of
charge via the Internet at http://pubs.acs.org.
1
pentane. Yield: 120 mg (75%). H NMR (C6D6, 20 °C): δ 8.36
IC0613457
(br s, BAr4′), 7.68 (br s, BAr4′), 6.67 (br s), 6.36 (br s), 3.5 (br s),
3.2 (s), 2.7 (br m), 1.85 (br m), 1.2 (br m), -4.0 (br s), -8.5 (br
s). Anal. Calcd for C118H134BF24MoN5O2: C, 63.92; H, 6.09; N,
3.16. Found: C, 64.10; H, 6.13; N, 2.97.
(19) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(20) Sheldrick, G. M. SHELXL 97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
9196 Inorganic Chemistry, Vol. 45, No. 23, 2006