Synthesis of triamidoamine ligands of the type (arylNHCH2CH2)3N and molybdenum and tungsten complexes that contain an [(arylNCH2CH2)3N]3-ligand

Article abstract of DOI:10.1021/ic001122v

Aryl bromides react with (H₂NCH₂CH₂)₃N in a reaction catalyzed by Pd₂(dba)₃ in the presence of BINAP and NaO-t-Bu to give the arylated derivatives (ArylNHCH₂CH₂)₃N [Aryl = C₆H₅ (1a), 4-FC₆H₄ (1b), 4-t-BuC₆H₄ (1c), 3,5-Me₂C₆H₃ (1d), 3,5-Ph₂C₆H₃ (1e), 3,5-(4-t-BuC₆H₄)₂C₆H₃ (1f), 2-MeC₆H₄ (1g), 2,4,6-Me₃C₆H₂ (1h)]. Reactions between (ArNHCH₂CH₂)₃N (Ar = C₆H₅, 4-FC₆H₄, 3,5-Me₂C₆H₃, and 3,5-Ph₂C₆H₃) and Mo(NMe₂)₄ in toluene at 70 °C lead to [(ArNHCH₂CH₂)₃N]Mo(NMe₂) complexes in yields ranging from 64 to 96%. Dimethylamido species (Ar = 4-FC₆H₄, 3,5-Me₂C₆H₃) could be converted into paramagnetic [(ArNHCH₂CH₂)₃N]-MoCl species by treating them with 2,6-lutidinium chloride in tetrahydrofuran (THF). The direct reaction between 1a-f and MoCl₄(THF)₂ in THF followed by 3 equiv of MeMgCl yielded [(ArNHCH₂CH₂)₃N]MoCl species (3a-f) in high yield. If 4 equiv of LiMe instead of MeMgCl are employed in the direct reaction, then [(ArNHCH₂CH₂)₃N]MoMe species are formed. Tungsten species, [(ArNHCH₂CH₂)₃N]WCl, could be prepared by analogous direct methods. Cyclic voltammetric studies reveal that MoCl complexes become more difficult to reduce as the electron donating ability of the [(ArNHCH₂CH₂)₃N]^3- ligand increases, and the reductions become less reversible, consistent with ready loss of chloride from {[(ArNHCH₂CH₂)₃N]MoCl}^-. Tungsten complexes are more difficult to reduce, and reductions are irreversible on the CV time scale.

Full text of DOI:10.1021/ic001122v

3850
Inorg. Chem. 2001, 40, 3850-3860
Synthesis of Triamidoamine Ligands of the Type (ArylNHCH2CH2)3N and Molybdenum
and Tungsten Complexes That Contain an [(ArylNCH2CH2)3N]3- Ligand
George E. Greco and Richard R. Schrock*
Department of Chemistry 6-331, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
ReceiVed October 11, 2000
Aryl bromides react with (H2NCH2CH2)3N in a reaction catalyzed by Pd2(dba)3 in the presence of BINAP and
NaO-t-Bu to give the arylated derivatives (ArylNHCH2CH2)3N [Aryl ) C6H5 (1a), 4-FC6H4 (1b), 4-t-BuC6H4
(1c), 3,5-Me2C6H3 (1d), 3,5-Ph2C6H3 (1e), 3,5-(4-t-BuC6H4)2C6H3 (1f), 2-MeC6H4 (1g), 2,4,6-Me3C6H2 (1h)].
Reactions between (ArNHCH2CH2)3N (Ar ) C6H5, 4-FC6H4, 3,5-Me2C6H3, and 3,5-Ph2C6H3) and Mo(NMe2)4
in toluene at 70 °C lead to [(ArNHCH2CH2)3N]Mo(NMe2) complexes in yields ranging from 64 to 96%.
Dimethylamido species (Ar ) 4-FC6H4, 3,5-Me2C6H3) could be converted into paramagnetic [(ArNHCH2CH2)3N]-
MoCl species by treating them with 2,6-lutidinium chloride in tetrahydrofuran (THF). The “direct reaction” between
1a-f and MoCl4(THF)2 in THF followed by 3 equiv of MeMgCl yielded [(ArNHCH2CH2)3N]MoCl species
(3a-f) in high yield. If 4 equiv of LiMe instead of MeMgCl are employed in the direct reaction, then [(ArNHCH2-
CH2)3N]MoMe species are formed. Tungsten species, [(ArNHCH2CH2)3N]WCl, could be prepared by analogous
“direct” methods. Cyclic voltammetric studies reveal that MoCl complexes become more difficult to reduce as
the electron donating ability of the [(ArNHCH2CH2)3N]3- ligand increases, and the reductions become less
reversible, consistent with ready loss of chloride from {[(ArNHCH2CH2)3N]MoCl}-. Tungsten complexes are
more difficult to reduce, and reductions are irreversible on the CV time scale.
Introduction
as have transition metal complexes that contain three sterically
bulky monodentate amido ligands.42-51 Triamidoamine ligands
bind to transition metals in oxidation state +3 or higher in a
tetradentate manner, leaving three metal orbitals (one of σ
symmetry and two of π symmetry) to bind additional ligands
Transition metal and actinide complexes that contain a
triamidoamine ligand of the general formula [(RNCH2CH2)3N]3-
have been explored extensively over the past several years,1-41
(1) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9.
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O’Donoghue, M. B.; Davis, W. M.; Reiff, W. M. J. Am. Chem. Soc.
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10.1021/ic001122v CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/19/2001

Synthesis of Triamidoamine Ligands
Inorganic Chemistry, Vol. 40, No. 16, 2001 3851
in the apical pocket, an arrangement that favors the formation
of metal-ligand multiple bonds. This feature of the triami-
doamine ligand has led to some unusual results, e.g., the
synthesis of terminal phosphido and arsenido complexes9,35 and
the discovery that some Mo alkyl complexes and many W
complexes decompose by R,R-dehydrogenation to give alkyli-
dyne complexes.4,10 In the process of elucidating the chemistry
of Mo and W alkyl complexes it was discovered that in the
absence of two R hydrogens molybdenum and tungsten alkyl
complexes undergo R hydride elimination as much as 6 orders
of magnitude faster than â hydride elimination.4,10,11,36 In
complexes that contain a [(RNCH2CH2)3N]3- ligand only two
M-Neq π-bonds can form. Therefore, the [(RNCH2CH2)3N]3-
ligand can donate a maximum of 12 electrons to the metal
center. However, orbital overlap is more favorable for one of
the two π-bonds, so in most cases essentially only one M-Neq
π-bond is present and the [(RNCH2CH2)3N]3- ligand can be
said to contribute only 10 electrons to the total electron count.
Before the work to be described here was begun, all transition
metal chemistry involving [(RNCH2CH2)3N]3- ligands had been
carried out on complexes in which the R group was a
methyl,37-39 a trialkylsilyl,16,40 or a pentafluorophenyl group.41
However, during the course of our experiments on complexes
in which R ) SiMe3 or C6F5, several drawbacks were revealed.
The silicon-nitrogen bond is inherently weak, and several
complexes were found to decompose by loss of a trimethylsilyl
(TMS) group or by CH activation within a TMS group.10,11,13,33,40
Also, low yields of Mo and W chloride complexes containing
TMS substituted triamidoamine ligands were attributed to
cleavage of N-Si bonds during preparation of complexes of
the type [((TMS)NCH2CH2)3N]MCl.10,11 The primary drawback
of the C6F5 ligand is its instability toward strong nucleophiles.12
The C6F5 groups also lead to a relatively electron deficient metal
center, which can be undesirable if strong π back-donation into
a ligand in the coordination pocket is desired.
Figure 1. Arylated TREN precursors to triamidoamine ligands.
of anilines is commercially available. However, we found
construction of aromatic carbon-nitrogen bonds by methods
pioneered by the Buchwald52-59 and Hartwig60-63 groups to be
more convenient. Eight ligands have been synthesized by this
method and are reported here along with the syntheses of several
Mo and W starting materials. In view of the greater convenience
of the catalytic C-N coupling method, syntheses of several of
the (ArylNHCH2CH2)3N species reported here by the nitrilo-
acetic acid route are provided only as Supporting Information.
A portion of this work has been reported in the form of a
communication.64
We believed that the chemistry of a complex containing a
triamidoamine ligand substituted with ordinary aryl groups
would be richer for cases that required a significant amount of
π back-donation, e.g., metal dinitrogen complexes, that such
complexes would not suffer the drawbacks of analogous
complexes that contain C6F5 and TMS substituted ligands, and
that some steric variation should be possible that would slow
intermolecular reactions or the formation of bimolecular com-
plexes. We first developed a route to such ligands that was based
upon formation of the appropriate triamide of nitrilotriacetic
acid followed by reduction with lithium aluminum hydride. This
method initially was attractive to us because nitrilotriacetic acid
is an inexpensive starting material, and because a wide variety
Results and Discussion
Ligand Syntheses. The aryl bromides that are required for
the synthesis of 1a-d, 1g, and 1h (Figure 1) are commercially
available. Those required to prepare ligands 1e and 1f are not
commercially available, but they can be prepared in two steps
from inexpensive 2,4,6-tribromoaniline, as shown in eq 1. The
literature procedure was followed in the first step,65 except that
2,4,6-tribromoiodobenzene was recrystallized from dichlo-
romethane instead of benzene/ethanol. 2,4,6-Tribromoiodoben-
zene was then coupled with 2 equiv of aryl Grignard reagent in
a reaction that proceeds through two benzyne intermediates.65
(52) Wolfe, J. P.; Wagaw, S.; Marcoux, J. F.; Buchwald, S. L. Acc. Chem.
Res. 1998, 31, 805.
(42) Laplaza, C. E.; Johnson, M. J. A.; Peters, J. C.; Odom, A. L.; Kim,
E.; Cummins, C. C.; George, G. N.; Pickering, I. J. J. Am. Chem.
Soc. 1996, 118, 8623.
(43) Cummins, C. C. Chem. Commun. 1998, 1777.
(44) Cummins, C. C. Prog. Inorg. Chem. 1998, 47, 685.
(45) Odom, A. L.; Arnold, P. L.; Cummins, C. C. J. Am. Chem. Soc. 1998,
120, 5836.
(46) Brock, J. R.; Odom, A. L.; Klei, S. R.; Cummins, C. C. Organome-
tallics 1999, 18, 1360.
(47) Odom, A. L.; Mindiola, D. J.; Cummins, C. C. Inorg. Chem. 1999,
38, 3290.
(53) Yang, B. H.; Buchwald, S. L. J. Organomet. Chem. 1999, 576, 125.
(54) Harris, M. C.; Geis, O.; Buchwald, S. L. J. Org. Chem. 1999, 64,
6019.
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2413.
(56) Wolfe, J. P.; Buchwald, S. L. J. Org. Chem. 2000, 65, 1144.
(57) Wolfe, J. P.; Tomori, H.; Sadighi, J. P.; Yin, J.; Buchwald, S. L. J.
Org. Chem. 2000, 65, 1158.
(58) Yin, J.; Buchwald, S. L. Org. Lett. 2000, 2, 1101.
(59) Old, D. W.; Harris, M. C.; Buchwald, S. L. Org. Lett. 2000, 2, 1403.
(60) Hartwig, J. F. Angew. Chem., Int. Ed. Eng. 1998, 37, 2046.
(61) Hartwig, J. F.; Kawatsura, M.; Hauck, S.; Shaughnessy, K. H.; Alcazar-
Roman, L. M. J. Org. Chem. 1999, 64, 5575.
(48) Peters, J. C.; Baraldo, L. M.; Baker, T. A.; Johnson, A. R.; Cummins,
C. C. J. Organomet. Chem. 1999, 591, 24.
(49) Peters, J. C.; Cherry, J. P. F.; Thomas, J. C.; Baraldo, L.; Mindiola,
D. J.; Davis, W. M.; Cummins, C. C. J. Am. Chem. Soc. 1999, 121,
10053.
(50) Tsai, Y. C.; Johnson, M. J. A.; Mindiola, D. J.; Cummins, C. C.;
Klooster, W. T.; Koetzle, T. F. J. Am. Chem. Soc. 1999, 121, 10426.
(51) Mindiola, D. J.; Meyer, K.; Cherry, J. P. F.; Baker, T. A.; Cummins,
C. C. Organometallics 2000, 19, 1622.
(62) Alcazar-Roman, L. M.; Hartwig, J. F.; Rheingold, A. L.; Liable-Sands,
L. M.; Guzei, I. A. J. Am. Chem. Soc. 2000, 122, 4618.
(63) Stauffer, S. R.; Lee, S.; Stambuli, J. P.; Hauck, S. I.; Hartwig, J. F.
Org. Lett. 2000, 2, 1423.
(64) Greco, G. E.; Popa, A. I.; Schrock, R. R. Organometallics 1998, 17,
5591.
(65) Du, C. J. F.; Hart, H.; Ng, K. K. D. J. Org. Chem. 1986, 51, 3162.

3852 Inorganic Chemistry, Vol. 40, No. 16, 2001
Greco and Schrock
3,5-Diphenylbromobenzene is a known compound.65 3,5-Bis-
(4-tert-butylphenyl)bromobenzene is a new compound, but it
was prepared by virtually the same method as 3,5-diphenyl-
bromobenzene.
“overarylated” material equals the yield of material in which
one of the three arms has not been arylated at all, thereby
decreasing the yield of 1a even further.
Compounds 1a-d must be purified by column chromatog-
raphy on silica gel using a 3:1 mixture of hexane and ethyl
acetate to which 3% (by volume) of a saturated solution of
ammonia in methanol has been added. The overarylated
compounds elute from these columns immediately before
compounds of type 1. The products of type 1 are often initially
obtained as pale yellow oils, but colorless crystals can be grown
from mixtures of ether and hexane (1a, 1b, and 1d), or pure
hexane (1c). We speculate that the low yield of 1b can be
ascribed to the sensitivity of the fluorine atom to sodium tert-
butoxide, but we did not attempt to optimize the reaction by
using different bases. Compounds 1a-d are slightly sensitive
to the combination of air and light. If a vial of powder is stored
on the laboratory shelf, the material on the outside of the vial
will turn pale yellow over the course of several weeks, while
material not exposed to the light remains white. No discoloration
is observed if the compounds are stored in a glovebox under
dinitrogen or in a vial covered with aluminum foil.
Arylated triethylenetetramines were synthesized via the
coupling of 3 equiv of the aryl bromide in the presence of 3
equiv of sodium tert-butoxide per (H2NCH2CH2)3N using
Pd2(dba)3 (1 mol % versus ArBr) and BINAP as the catalyst
(eq 2).56,66 Yields ranged from a low of 27% for 1b (aryl )
Yields of 1g (Ar ) o-tolyl) and 1h (Ar ) mesityl) are
relatively high (90 and 79%, respectively) because little or no
overarylated material is formed. Also 1g and 1h need not be
purified by column chromatography. Analytically pure material
can be obtained simply by recrystallization of the product from
a mixture of ether and hexane. Chromatography also is
unnecessary in order to purify 1e or 1f, even though overarylated
material is formed, because the solubility of overarylated
material in these cases in common organic solvents is much
higher than that of 1e and 1f. Purification of 1f poses a challenge
as a consequence of its low solubility in organic solvents.
Chloroform is the only common solvent in which it exhibits
some significant solubility. Compound 1f can be separated easily
from other organic products by simple filtration, but separation
of it from the NaBr produced during the coupling reaction must
be accomplished by means of a chloroform/water extraction.
Evidently this process is not efficient, as the low values for
elemental analyses (C, H, and N) suggest that some inorganic
salts are still present.
4-FC6H4) to 90% for 1g (aryl ) 2-MeC6H4). (The yield for 1a
(aryl ) C6H5) was 57%, for 1c (aryl ) 4-t-BuC6H4) 47%, for
1d (aryl ) 3,5-Me2C6H3) 58%, for 1h (aryl ) 2,4,6-Me3C6H2)
79%, for 1e (aryl ) 3,5-Ph2C6H3) 51%, and for 1f (aryl ) 3,5-
(4-t-BuC6H4)2C6H3) 64%.) Reactions typically were run at 80
°C in toluene for 18 h. However, 100 °C was necessary for the
preparation of 1g and 1h due to the increased steric demand of
the aryl bromide. We found that if all components of the reaction
were combined before heating the reaction, the yield of the
desired product was highly irreproducible. We speculate that
TREN competes with BINAP as a ligand for Pd based on the
observation that when TREN is added to the reaction mixture,
the color changes from the purple of Pd2(dba)3 to dark yellow,
but no color change is observed when only Pd2(dba)3, solid
racemic BINAP, aryl bromide, and toluene are present in the
reaction flask. Upon heating, the reactions turn dark brown, and
a large amount of gray solid, which appears to be Pd metal, is
formed. The problem appears to be that racemic BINAP is not
very soluble in toluene at room temperature and many equiva-
lents of TREN are present for each Pd. Irreproducible yields
are avoided if BINAP is heated in toluene (150 mL/g of BINAP)
until it dissolves, and then Pd2(dba)3 is added as a solid in order
to form the catalyst. This strategy has also been employed in
certain circumstances by the Buchwald group.56 A small amount
of black solid forms, but after it is filtered off, the orange color
persists upon addition of the catalyst to the other reaction
components and throughout the course of the coupling reaction.
When the catalyst is “pre-formed” in this manner, the yields of
the coupling reactions are reproducible.
It is possible that (ArNHCH2CH2)2NCH2CH2NAr2 com-
pounds could be employed as diamidodiamine ligands for early
transition metals. Therefore the C-N coupling reactions were
run until all of the aryl bromide was consumed in order to
maximize the yield of tetraarylamine. Compounds in which Ar
) 4-fluorophenyl, 4-tert-butylphenyl, and 3,5-bis(4-tert-bu-
tylphenyl)phenyl were isolated and fully characterized. When
Ar ) 4-tert-butylphenyl, the compound can be crystallized from
hexane, while that in which Ar ) 3,5-bis(4-tert-butylphenyl)-
phenyl can be crystallized from ether. That in which Ar )
4-fluorophenyl has been obtained only as an oil.
There is a second complication that limits the yields in some
circumstances. Reactions that employ BINAP as a ligand are
inherently selective for primary amines over secondary amines,56
but a second arylation of one “arm” of the desired product
cannot be completely avoided if the aryl group is small. Products
in which one of the three arms of the ligand has been doubly
arylated (e.g., (PhNHCH2CH2)2NCH2CH2NPh2) can be isolated
during column chromatography, typically in ∼15% yield.
Performing the reactions at lower temperatures for longer times
did not increase the isolated yield of 1a significantly. Since
exactly 3 equiv of aryl bromide are employed, the amount of
Synthesis of Molybdenum Chloride Complexes from Mo-
(NMe2)4. The most desirable starting material in order to explore
the chemistry of molybdenum(IV) triamidoamine complexes
would be a monochloride species, but we would expect such a
species to be paramagnetic. Therefore we found it attractive
initially to prepare a diamagnetic dimethylamido complex, the
synthesis of which is easily followed by NMR, and subsequently
to convert the dimethylamido complex to the chloride by
protonolysis. Dimethylamido complexes of Mo(IV) that contain
a triamidoamine ligand are diamagnetic as a consequence of
strong M-N π bonding involving one of the two π orbitals on
the metal available for bonding to a ligand in the trigonal pocket,
leaving the two d electrons paired up in the other π orbital.
(66) Wolfe, J. P.; Wagaw, S.; Buchwald, S. L. J. Am. Chem. Soc 1996,
118, 7215.

Synthesis of Triamidoamine Ligands
Inorganic Chemistry, Vol. 40, No. 16, 2001 3853
Reactions between (ArNHCH2CH2)3N (Ar ) C6H5, 4-FC6H4,
19F NMR spectroscopy is an especially useful probe for
reactions involving paramagnetic complexes, which was the
primary motivation for the preparation of complexes containing
the 4-fluorophenyl ligand. Resonances in the 19F NMR spectrum
also are often sharper for paramagnetic complexes than those
67
3,5-Me2C6H3, and 3,5-Ph2C6H3) and Mo(NMe2)4 in toluene
at 70 °C lead to [(ArNHCH2CH2)3N]Mo(NMe2) complexes (eq
3) in yields ranging from 64 to 96%. In the case of ligands
containing highly electron deficient aryl groups such as C6F5,
dimethylamide complexes can be prepared in pentane at room
temperature over the course of several hours.41 However, more
forcing conditions are required for complete reaction when the
aryl group is more electron rich, but the temperature must be
controlled carefully. No reaction occurs below ∼65 °C, while
complexes of type 2 decompose above 80 °C.
1
in the H NMR spectrum, especially in the case of 3b, where
the fluorine is relatively far removed from the metal. Therefore,
it is relatively easy to determine how many compounds are
present in a crude reaction mixture. Furthermore, reactions can
be followed by recording spectra of aliquots from the reaction
mixture. The 19F resonance for 3b occurs at -110.5 ppm,
slightly downfield from the normal diamagnetic position.
Direct Synthesis of Molybdenum Chloride and Methyl
Complexes. Although the syntheses shown in eqs 3 and 4 are
relatively foolproof, synthesis of more than a gram or two of a
chloride complex by this method is not practical by virtue of
the limited quantities of Mo(NMe2)4 that can be prepared and
isolated at one time, at least in our hands. Monochloride
complexes that contain the more sterically protective ligands
derived from 1e and 1f also are not preparable by this route.
Therefore, with our knowledge of the NMR spectra of com-
pounds 3b and 3d we began a search for a more “direct”
synthesis of a monochloride complex. We chose the readily
Compounds 2a, 2b, 2d, and 2e are diamagnetic, dark purple
crystalline solids, which are insoluble in pentane. They are
extremely air, moisture, and thermally sensitive and decompose
rapidly upon exposure to dichloromethane. Their 1H NMR
spectra are typical of trigonally symmetric diamagnetic com-
plexes in that two triplets are observed for the methylene
backbone protons and the aryl rings rotate freely about the
N-Cipso bond. Rotation of the dimethylamide ligand with respect
to the TREN ligand is also rapid (one singlet is observed for
the dimethylamide protons), which is a common feature of
dimethylamido complexes of earlier transition metals. The
resonance in the 19F NMR spectrum for 2b occurs at -124.4
ppm, which is in the normal range for a fluorine in the para
position of an arylamine.
68
available MoCl4(THF)2 as the starting material.
The strategy that proved to be successful was inspired by
the synthesis of [(C6F5NCH2CH2)3N]MoCl, where a red Mo-
(IV) complex of unknown type is prepared in situ by adding
the free amine to MoCl4(THF)2, followed by addition of
triethylamine in order to remove 3 equiv of HCl.41 Since the
amine proton in the arylamines employed here is not as acidic
as that in (C6F5NHCH2CH2)3N, we found that triethylamine is
not a strong enough base. A number of stronger bases such as
DBU, KH, proton sponge, and n-butyllithium were tried, but
none yielded appreciable amounts of chloride. However, when
3 equiv of neopentyllithium or methyllithium were added to a
mixture of the tetraamine and MoCl4(THF)2 and the mixture
was allowed to stand for 24 h, chlorides 3a (Ar ) C6H5), 3b
(Ar ) 4-FC6H4), 3c (Ar ) 4-t-BuC6H4), and 3d (Ar ) 3,5-
Me2C6H3) were produced in good yield.
Reaction of 2b or 2d with 2,6-lutidinium chloride in THF
produced 3b or 3d (eq 4). Compound 3d is less soluble than
the other chlorides (it will crystallize out of concentrated THF
solutions), while 3b is soluble in aromatic hydrocarbons. No
reaction was observed when 2e was treated with 2,6-lutidinium
chloride, presumably for steric reasons. Compounds 3b and 3d
are red, paramagnetic solids. (The π-bonding from the chloride
ligand is not strong enough to break the degeneracy of the two
π-type orbitals on the metal.) The practical consequence of the
paramagnetism is that resonances in the 1H NMR spectrum are
broadened and shifted to a significant degree compared to the
parent compounds 1. Nevertheless, 1H NMR spectroscopy is a
useful diagnostic tool, since all of the compounds’ resonances
occur at characteristic chemical shifts and can be assigned. The
resonances for the protons on the backbone of the TREN ligand
always occur upfield, with one resonance around -20 ppm and
the other around -75 ppm. The resonances for the ortho and
meta protons on the aryl ring always occur downfield, with the
meta resonance always being further downfield and sharper (16
ppm) than the ortho resonance (9 ppm).
The formation of chloride 3b using 3 equiv of methyllithium
as a base was monitored by 19F NMR. After 24 h, the only
peak present in the 19F NMR spectrum other than free amine
was at -110 ppm (in THF), matching that of 3b prepared by
protonolysis of 2b (eq 4). Surprisingly, after 1 h, the major
product present in the mixture had a 19F NMR signal at -104
ppm. Over the course of 16 h, the signal for this product
decreased in intensity as the signal for 3b increased in intensity.
When 4 equiv of methyllithium was added to a mixture of 1b
and MoCl4(THF)2, this product was the only metal containing
product formed after 30 min, and it was not converted to 3b
after leaving it in the reaction mixture for 24 h.
Isolation and characterization of the product formed upon
addition of 4 equiv of LiMe (eq 5) confirmed that it is a methyl
complex, [(4-FC6H4NCH2CH2)3N]MoMe (4b). In addition to
elemental analysis, evidence to support this formulation includes
the fact that adding 1 equiv of methyllithium or methylmag-
nesium chloride to 3b in THF yields 4b quantitatively. Methyl
complexes 4a (Ar ) C6H5), 4c (Ar ) 4-t-BuC6H4), and 4d (Ar
) 3,5-Me2C6H3) also were prepared by adding 4 equiv of
(67) Bradley, D. C.; Chisholm, M. H. J. Chem. Soc. A 1971, 2741.
(68) Dilworth, J. R.; L., R. R.; Chen, G. J.; McDonald, J. W. Inorg. Synth.
1980, 20, 119.

3854 Inorganic Chemistry, Vol. 40, No. 16, 2001
Greco and Schrock
methyllithium to the initial amine adduct, as shown in eq 5.
and 3d are sparingly soluble in THF, and they crystallize out
of reaction mixtures as they are formed. Material that is collected
by filtration of the reaction mixture is analytically pure, since
the magnesium salts remain in solution. The other chlorides are
highly soluble in THF, so the magnesium salts have to be
removed by complexation with 1,4-dioxane. Compound 3b
crystallizes upon concentration of the THF solution. Compounds
3c and 3f can be isolated by removing all of the THF, washing
the crude residue with ether, and collecting the ether insoluble
material. Complexes 3a-d and 3f are soluble and stable in
dichloromethane and chloroform, and they can be recrystallized
from mixtures of dichloromethane and pentane.
All of the methyl complexes shown in eq 5 are soluble in
benzene or toluene, while 4c is highly soluble in ether and
somewhat soluble in pentane. All can be crystallized from
mixtures of toluene and pentane. Proton NMR spectra of 4a-d
are similar to spectra of 3a-d, but there are enough differences
to allow for easy identification. Specifically, the high-field
methylene resonances in compounds 4 are about 8 ppm
downfield of the corresponding resonances in compounds 3,
and the resonance for the ortho hydrogens is about 5 ppm
upfield. A proton or carbon resonance cannot be observed for
the methyl group in 4a-d using routine NMR methods. This
has been true for all methyl and alkyl complexes of this general
type.11
Methyl complexes that contain the ligands derived from 1a-d
could be converted to chloride complexes cleanly by treating
them with 1 equiv of 2,6-lutidinium chloride (eq 6). This proved
to be a more convenient and reliable synthesis of the chlorides
than allowing a mixture of the Mo-ligand adduct and 3 equiv
of methyllithium to stir for 24 h.
The most difficult compound to isolate is 3e; it does not
crystallize readily, and once it crystallizes, it does not dissolve
again readily. Storage of a crude reaction mixture at -40 °C
overnight does not result in the crystallization of any product.
If dioxane is added to remove magnesium salts, and the MgCl2-
(dioxane) is filtered off within 30 min, pure product can be
obtained by concentrating the THF solution of the filtrate until
crystallization begins. However, if the MgCl2(dioxane) is not
filtered off quickly, 3e starts to crystallize out; at this stage the
crystals can no longer be separated from magnesium salts.
However, from a point of view of preparing dinitrogen
complexes by reduction under dinitrogen, as will be described
in a subsequent paper, contamination of 3e with MgCl2(dioxane)
is not a serious problem.
It was not possible to prepare compounds 3 or 4 in which
the aryl group contains ortho substituents (Ar ) mesityl or
o-tolyl) using methods analogous to those described above.
When 1g or 1h is added to MoCl4(THF)2 in THF, a red “adduct”
is not formed readily at room temperature. We propose that
steric inaccessibility of the ortho-substituted arylamines prevents
formation of the intermediate that reacts smoothly with meth-
yllithium, and therefore addition of methyllithium or methyl-
magnesium chloride to what amounts to a mixture of free ligand
and MoCl4(THF)2 simply leads to decomposition. The initial
red adduct that we presume to be an intermediate in all
successful reactions has never been isolated or identified.
We felt that compounds 4 were formed first in a reaction
involving methyllithium because of the relatively high reactivity
of methyllithium and further speculated that a less aggressive
alkylating agent (MeMgCl) might result in formation of
compounds 3 directly. This proved to be the case, as shown in
eq 7.
It also proved impractical to prepare compounds 3 by treating
MoCl4(THF)2 with the trilithium salt of several of the ligands.
A typical yield (e.g., of 3c) by this method is only ∼10%. We
suspect that reduction of Mo(IV) to Mo(III) by the trilithium
salt leads to low yields of the desired Mo(IV) monochloride
species. No further effort was made to prepare compounds 3
using this approach.
Direct Synthesis of Tungsten Chloride and Methyl Com-
plexes. Since W(NMe2)4 is not known, the most convenient
starting material for preparing a tungsten monochloride complex
is WCl4(DME).70 One complication associated with the use of
WCl4(DME) in THF is that WCl4(DME) reacts with THF to
form WCl4(THF)2, and the THF ligands are much more difficult
to displace than is DME.70 Therefore, although methods
analogous to the most successful described above for molyb-
denum can be employed for tungsten, it is imperative that WCl4-
(DME) be added slowly as a solid to a warm (50 °C) THF
solution of the ligand. The TREN ligand apparently is a better
ligand for W than is THF, so a soluble adduct is formed readily.
If WCl4(DME) is added too quickly, or the mixture is kept at
room temperature, white WCl4(THF)2 begins to precipitate out,
and it does not react further. The initial W adduct is yellow.
No attempt was made to isolate this adduct.
Compounds 3a-f can be prepared directly in high yield in
less than 3 h, without significant contamination by the mono-
methyl complexes. It is important that methylmagnesium
chloride is employed; reactions employing methylmagnesium
iodide yielded a mixture of chloride and the analogous iodide
complexes.69
The solubility of compounds 3 in various solvents differs
dramatically, so several different methods had to be developed
for their isolation in the reactions shown in eq 7. Chlorides 3a
(69) George E. Greco, Ph.D. Thesis, Massachusetts Institute of Technology,
2000.
(70) Persson, C.; Andersson, C. Inorg. Chim. Acta 1993, 203, 235.

Synthesis of Triamidoamine Ligands
Inorganic Chemistry, Vol. 40, No. 16, 2001 3855
Deprotonation of the adducts with 3 equiv of methylmagne-
sium chloride leads to tungsten monochloride complexes (5) in
yields ranging from 24 to 43% (eq 8). Lower yields for tungsten
complexes versus molybdenum complexes also were observed
in syntheses of [(Me3SiNCH2CH2)3N]3- 10 and [(C6F5NCH2-
CH2)3N]3- 41 complexes, while a yield of only 10% was reported
for the synthesis of [(i-PrNCH2CH2)3N]WCl from Li3[(i-Pr-
NCH2CH2)3N] and WCl4(DME).71 As was the case for Mo
compounds 3, differences in solubility between the various W
complexes necessitated different workup procedures. In general,
the workup procedure developed for the Mo chloride complex
containing a particular ligand also was applicable for the W
chloride complex. Specifically, 5a and 5d crystallized out of
crude reaction mixtures and were collected by filtration, while
5b, 5c, and 5e were isolated by removing the MgCl2 as its
dioxane adduct and then crystallizing the products from either
THF or mixtures of THF and ether. Like 3e, once crystals of
5e have formed, they cannot be redissolved in any solvent,
including boiling THF and boiling toluene, so a 1H NMR
spectrum of 5e could not be obtained.
Figure 2. CV of [(C6F5NCH2CH2)3N]MoCl.
One of the reasons for preparing 6c was to determine whether
it decomposes to a W(VI) methylidyne complex by R,R-
dehydrogenation, which is the observed mode of reactivity for
alkyl complexes containing a [(Me3SiNCH2CH2)3N]3- ligand.4,10
While 6c is an unstable compound, it decomposes in a complex
fashion to unidentified species whose NMR spectra are clearly
not consistent with formation of a methylidyne complex. The
decomposition of 6c appears to be accelerated in the presence
of MeMgCl. The low yield of 6c also could be explained on
this basis. Due to the instability of 6c, satisfactory elemental
analysis could not be obtained. It should also be noted that
attempts to prepare [(C6F5NCH2CH2)3N]WMe by alkylation of
[(C6F5NCH2CH2)3N]WCl in a variety of solvents resulted in
the formation of unidentified decomposition products.12 It is
certainly possible that [(C6F5NCH2CH2)3N]WtCH and [(4-t-
BuC6F4NCH2CH2)3N]WtCH are both formed at some stage,
but themselves are unstable, perhaps as a consequence of the
methylidyne ligand being a sterically less well protected than
in the [(Me3SiNCH2CH2)3N]3- complexes. Synthesis of other
alkyl complexes and resolution of stability issues will be the
subject of future investigations.
Cyclic Voltammetry Studies on Molybdenum and Tung-
sten Chloride Complexes. The primary motivation behind the
synthesis of [(ArNCH2CH2)3N]MoCl complexes was our desire
to reduce them under N2 and prepare dinitrogen complexes. The
successful preparation of dinitrogen complexes is detailed in
the following paper in this issue, but we report electrochemical
studies of compounds 3 and 5 here. All potentials are referenced
to the ferrocene/ferrocenium couple.72 Measurements were
performed in THF using Bu4NPF6 as the supporting electrolyte.
All data were recorded at a scan rate of 500 mV/s.
Like their Mo analogues, compounds 5a-e are all paramag-
1
netic, and resonances in H NMR spectra are broadened and
shifted accordingly. However, resonances in the spectra of W
complexes are sharper than in the spectra of the corresponding
Mo complexes, presumably as a consequence of greater spin-
orbit coupling in the W systems. A graphic demonstration of
this fact is that coupling can be observed between the meta and
para protons on the aryl ring in the spectrum of 5a. Two notable
differences in chemical shifts exist between the Mo and W
complexes. The resonance for the ortho protons on the aryl rings
occurs about 9 ppm further downfield in the W complexes, so
that it is actually downfield of the meta resonance. More
significant is the downfield shift of the upfield backbone
resonance, which shifts from -75 ppm in Mo complexes to
-50 ppm in W complexes.
Treatment of the adduct formed from 1c and WCl4(DME)
with 4 equiv of MeMgCl resulted in the formation of [(4-t-Bu-
C6H4NCH2CH2)3N]WMe (6c) in 22% yield (eq 9). Unlike 5c,
6c is soluble in ether, so it was isolated by recrystallization from
ether. Like 5c, 6c is paramagnetic, and the difference in 1H NMR
chemical shifts between 6c and 5c mirrors the difference
between compounds 4 and compounds 3. Specifically, the
resonance for the ortho protons on the aryl ring is shifted upfield
by 5 ppm (from 17.3 to 12.8 ppm), and the resonance for the
low-field backbone protons is shifted downfield by 4 ppm (from
-25.6 to -21.6 ppm). We did not attempt to prepare other
examples of methyl complexes, although we would not expect
those syntheses to be significantly different from that of 6c.
For reference the CV of [(C6F5NCH2CH2)3N]MoCl 41 is
shown in Figure 2. The key features are a reversible reduction
at -1.878 V and a reversible oxidation at +0.397 V. The
oxidation wave is also observed upon first scanning to positive
potentials, so it corresponds to a reversible oxidation of [(C6F5-
NCH2CH2)3N]MoCl to [[(C6F5NCH2CH2)3N]MoCl]+. The re-
versibility of the reduction suggests that {[(C6F5NCH2CH2)3N]-
MoCl}- does not lose chloride readily on the time scale
employed. [(C6F5NCH2CH2)3N]MoCl is not a suitable starting
material for preparing complexes that contain dinitrogen,
possibly for this reason.41 [(C6F5NCH2CH2)3N]Mo(triflate) is
a suitable starting material, but this compound is too insoluble
for CV studies under the conditions reported here.
The CV’s of 3b (Figure 1S; see Supporting Information) and
3a (Figure 3) are similar to that of [(C6F5NCH2CH2)3N]MoCl,
(71) Scheer, M.; Muller, J.; Schiffer, M.; Baum, G.; Winter, R. Chem. Eur.
J. 2000, 6, 1252.
(72) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877.

3856 Inorganic Chemistry, Vol. 40, No. 16, 2001
Greco and Schrock
smaller than that of the anodic wave, indicating partial
decomposition of the oxidation product on the time scale of
the experiment.
Cyclic voltammograms of [(ArNCH2CH2)3N]WCl com-
pounds in which Ar is C6H5, 4-FC6H4, 3,5-Me2C6H3, or 4-t-
BuC6H4 are similar to the CV shown in Figure 4. The peak
potentials for the irreversible reductions for these compounds
are listed in Table 1. Irreversible oxidations are also observed,
but no attempt was made to understand them in any detail. Two
trends can be observed from the data in Table 1. First, W
complexes are reduced at a potential ∼0.5 V more negative
than the analogous Mo complexes. Second, compounds contain-
ing the 4-F ligand are reduced at potentials ∼0.1 V more positive
than those containing the phenyl ligand, and compounds that
contain the C6F5 ligand are reduced at potentials ∼0.3 V more
positive than those containing the phenyl ligand. These trends
are consistent with what one might have predicted qualitatively.
Figure 3. CV of [(C6H5NCH2CH2)3N]MoCl (3a).
Table 1. Reduction Potentials of [(ArNCH2CH2)3N]]MCl (M ) Mo
or W) Compoundsa
Ar
molybdenum
tungsten
Conclusions
b
C6F5
-1.878 (rev)
-2.39 (peak)
-2.58 (peak)
-2.65 (peak)
-2.69 (peak)
-2.62 (peak)
4FC6H4 (3b)c
C6H5 (3a)
3,5-Me2C6H3 (3d)
4-t-BuC6H4 (3c)
-2.085 (quasi-rev)
-2.18 (peak)
-2.24 (peak)
-2.26 (peak)
We have shown that it is possible to substitute (H2NCH2-
CH2)3N readily with a variety of aryl groups using palladium
catalyzed addition of aryl bromides, a method that is more
convenient than the synthesis and reduction of a triamide of
nitrilotriacetic acid. Paramagnetic molybdenum and tungsten
complexes of the type [(ArNCH2CH2)3N]MCl and [(ArNCH2-
CH2)3N]MMe could be prepared directly from MCl4 starting
materials in good yields if the aryl group does not contain an
ortho methyl group. Diamagnetic complexes of the type
[(ArNCH2CH2)3N]Mo(NMe2) also could be prepared from the
free ligand and Mo(NMe2)4. Cyclovoltammetric studies revealed
both oxidation and reduction waves for the monochloride
complexes at positions that reflect the expected trends.
a See Experimental Section for conditions. All potentials are relative
to the ferrocene/ferrocenium couple. “Peak” refers to the peak potential
of the irreversible wave. b Reversible oxidation potential ) +0.397 V.
c Reversible oxidation potential ) -0.370 V.
Experimental Procedures
General Details. All reactions were conducted under a nitrogen
atmosphere in a Vacuum Atmospheres drybox or using Schlenk
techniques. Ether, toluene, and pentane were sparged with nitrogen for
45 min followed by passage through a 1 gallon column of activated
alumina as described in the literature.73 Tetrahydrofuran, dimethoxy-
ethane, and 1,4-dioxane were distilled from sodium benzophenone ketyl,
and dichloromethane was distilled from CaH2. C6D6 was sparged with
nitrogen and stored over 4 Å molecular sieves. CDCl3 was dried over
CaH2, vacuum transferred to a solvent storage flask, stored at -35 °C,
and passed through a plug of alumina before use. 2,4,6-Tribromoiodo-
benzene,65 3,5-diphenylbromobenzene,65 MoCl4(THF)2,68 Mo(NMe2)4,67
WCl4(DME),70 [(C6F5NCH2CH2)3N]MoCl, and [(C6F5NCH2CH2)3N]-
WCl 41 were prepared by published methods. 2,6-Lutidinium chloride
was prepared by treating an ethereal solution of 2,6-lutidine with HCl
in ether. All other starting materials are commercially available and
were used as received.
1H NMR spectra were recorded at an operating frequency of 300 or
500 MHz, and 13C NMR spectra were recorded at an operating
frequency of 75.5 or 125.8 MHz. The residual protons or carbon-13
atoms of the deuterated solvents were used as internal references. 19F
NMR spectra were recorded at an operating frequency of 282.2 MHz
and were referenced externally using CFCl3 (0 ppm). Chemical shifts
are reported in parts per million, and coupling constants are in hertz.
All spectra were acquired at ca. 22 °C. Elemental analyses (C, H, N)
were performed in our laboratory using a Perkin-Elmer 2400 CHN
analyzer, or by H. Kolbe Mikroanalytisches Laboratorium, Mu¨lheim
an der Ruhr, Germany.
Figure 4. CV of [(C6F5NCH2CH2)3N]WCl.
but only the oxidations are reversible on the 500 mV/s time
scale. Compound 3b is harder to reduce than [(C6F5NCH2-
CH2)3N]MoCl (by 207 mV; Table 1), while 3a is the most
difficult to reduce of the three. In short, the most difficult
complex to reduce leads to a monoanion that loses chloride most
readily. This is the trend that one might expect on the basis of
the progressively greater electron donating ability of the three
ligands involved. The CV’s for 3d and 3c (see Supporting
Information, Figures 2S and 3S, respectively) are similar to that
of 3a. The reductions are irreversible on the time scale
employed, and no well-behaved oxidation is observed. Com-
pounds 3d and 3c are slightly more difficult to reduce than 3a
(Table 1).
The CV of [(C6F5NCH2CH2)3N]WCl 41 is shown in Figure
4. Compared to [(C6F5NCH2CH2)3N]MoCl, the reduction po-
tential is more negative by 459 mV, and the oxidation potential
is more negative by 377 mV, consistent with the expected
greater difficulty of reducing W(IV) relative to Mo(IV) and
greater ease of oxidizing W(IV) relative to Mo(IV). The
reduction is clearly irreversible. A return wave is observed for
the oxidation, but the intensity of the cathodic wave is much
3,5-Bis(4-tert-butylphenyl)bromobenzene. In the glovebox, a 1 L
round-bottom flask was charged with Mg powder (12.12 g, 507 mmol)
and 300 mL of THF. 4-Bromo-tert-butylbenzene (97.5 g, 457 mmol)
(73) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

Synthesis of Triamidoamine Ligands
Inorganic Chemistry, Vol. 40, No. 16, 2001 3857
was dissolved in 250 mL of THF in an addition funnel. A small amount
of the bromide was added to the reaction flask, and the Grignard
reaction was initiated by heating. After initiation, the remainder of the
bromide was added over a period of 2 h. The flask was heated with
the heat gun until the THF boiled and then allowed to cool to room
temperature. The solution of the Grignard reagent was decanted from
the excess Mg into a 2 L flask. 2,4,6-Tribromoiodobenzene (63.9 g,
145 mmol) was dissolved in 250 mL of THF in an addition funnel and
then added dropwise to the aryl Grignard solution. The reaction mixture
was stirred at room temperature for 3 h and then heated under reflux
(on the Schlenk line) for 2 h. The reaction was quenched by pouring
it into a mixture of ice and 2 M HCl. THF was removed on the rotary
evaporator, and a large amount of solid formed in the flask. The aqueous
phase was extracted three times with dichloromethane, and the
dichloromethane layers were dried over MgSO4 and concentrated to a
thick oil. tert-Butylbenzene and 4-tert-butyliodobenzene were removed
by vacuum distillation. The residue was dissolved in a minimal amount
of hexane, and the product was collected as colorless crystals in three
crops; yield 35.12 g (83.3 mmol, 57%): 1H NMR (CDCl3): δ 7.71 (t,
1, para), 7.68 (t, 6, ortho), 7.55 (d, 4, aryl), 7.49 (d, 4, aryl), 1.39 (s,
18, t-Bu). 13C NMR (CDCl3): δ 151.24, 143.63, 137.11, 128.72, 127.05,
126.07, 124.73, 123.36, 34.81, 31.56. HRMS. Calcd for C26H29Br:
420.1453. Found (EI): 420.1445.
2, 2′, 2′′-Tris(phenylamino)triethylamine (1a). The Pd catalyst was
pre-formed by dissolving racemic BINAP (1.49 g, 2.40 mmol) in 150
mL of toluene with vigorous heating and stirring, adding Pd2(dba)3
(0.82 g, 0.90 mmol) as a solid, and removing unreacted Pd by filtration
through Celite to yield a light orange solution. A 1 L Schlenk flask
was charged with TREN (8.77 g, 60.0 mmol), bromobenzene (28.3 g,
180 mmol), sodium tert-butoxide (20.0 g, 208 mmol), and toluene (500
mL). The Pd catalyst solution was added last, and the reaction mixture
remained light orange. The reaction mixture was heated to 80 °C under
nitrogen (on the Schlenk line) for 20 h. It was then cooled to room
temperature, and NaBr was removed by filtration. Toluene was removed
on a rotary evaporator, and the resulting brown oil was purified by
column chromatography on silica gel. The column was eluted with a
3:1 mixture of hexane and ethyl acetate to which was added 3% (by
volume) of a saturated solution of NH3(g) in methanol. A yellow oil
was isolated from the column, which solidified when exposed to high
vacuum. White crystals (12.82 g, 34.2 mmol, 57%) were obtained upon
recrystallization from ether/pentane at -40 °C: 1H NMR (CDCl3): δ
7.12 (t, 6, meta), 6.70 (t, 3, para), 6.50 (d, 6, ortho), 4.09 (br s, 3, NH),
3.19 (t, 6, CH2), 2.81 (t, 6, CH2); 13C NMR (CDCl3) δ 148.72(Cipso),
129.82 (Cm), 118.10 (Cp), 113.59 (Co), 53.80 (CH2), 42.41(CH2); IR
(Nujol; cm-1): 3359, 1601, 1506, 1322, 1264, 1178, 1116, 1059, 991,
912, 866, 748, 693, 508. Anal. Calcd for C24H30N4: C, 76.97; H, 8.07;
N, 14.96. Found: C, 76.74; H, 8.20; N, 14.96.
(CH2), 42.70 (CH2), 34.56, 32.30 (t-Bu). IR (Nujol; cm-1): 3372, 1616,
1521, 1407, 1324, 1305, 1259, 1192, 1165, 1128, 1060, 920, 821, 550.
HRMS. Calcd for C36H54N4: 542.4348. Found (EI): 542.4348.
2, 2′, 2′′-Tris(3,5-dimethylphenylamino)triethylamine (1d). This
compound was synthesized in a manner similar to that used to prepare
1a starting from TREN (3.66 g, 25.0 mmol), 5-bromo-m-xylene (13.6
g, 75 mmol), Pd2(dba)3 (0.34 g, 0.37 mmol), rac-BINAP (0.70 g, 1.1
mmol), sodium tert-butoxide (8.4 g, 88 mmol), and toluene (250 mL).
Column chromatography and recrystallization from ether/hexane gave
6.64 g (14.6 mmol, 58%) of white crystals: 1H NMR (CDCl3): δ 6.38
(s, 3, Hp), 6.13 (s, 6, Ho) 4.03 (br s, 3, NH), 3.17 (t, 6, CH2), 2.80 (t,
6, CH2), 2.21 (s, 18, Ar-CH3). 13C NMR (CDCl3): δ 148.49 (Cipso),
138.94(Cm), 119.70 (Cp), 111.26 (Co), 53.22 (CH2), 41.97 (CH2), 21.67
(ArCH3). IR (Nujol; cm-1): 3384, 1603, 1509, 1339, 1303, 1263, 1193,
1114, 1059, 988, 857, 819, 689. Anal. Calcd for C30H42N4: C, 78.56;
H, 9.23; N, 12.21. Found C, 78.62; H, 9.45; N, 11.97.
2, 2′, 2′′-Tris[(3,5-diphenyl)phenyl]triaminotriethylamine (1e). A
100 mL Schlenk flask was charged with TREN (439 mg, 3.0 mmol),
3,5-diphenylbromobenzene (2.78 g, 9.00 mmol), Pd2(dba)3 (41 mg,
0.045 mmol), rac-BINAP (65 mg, 0.11 mmol), sodium tert-butoxide
(1.01 g, 10.5 mmol), and toluene (45 mL). The reaction mixture was
heated to 80 °C overnight. The reaction mixture was then cooled to
room temperature and filtered to remove NaBr. The toluene was
removed on the rotary evaporator, and the residue was dissolved in
dichloromethane. The solution was filtered once again and concentrated
to 20 mL. Hexane was added until the solution turned slightly cloudy.
Colorless crystals were grown at 0 °C, collected, washed with hexane,
and dried in vacuo; yield 1.28 g (1.54 mmol, 51%): 1H NMR
(CDCl3): δ 7.41 (m, 12), 7.25 (m, 18), 7.07 (t, 3), 6.71 (d, 6), 4.5 (br
s, 3), 3.38 (br s, 6, CH2), 2.98 (br s, 6, CH2). 13C NMR (CDCl3): δ
148.80 (Cipso), 142.84 (Cm), 141.40 (3,5-Cipso), 128.48 (3,5-Cm), 127.10
(3,5-Co and 3,5-Cp), 116.30 (Cp), 110.67 (Co), 53.29 (CH2), 42.12 (CH2).
IR (Nujol; cm-1): 3370, 1595, 1577, 1523, 1489, 1422, 1295, 1256,
1222, 1174, 1157, 1115, 1076, 1057, 1029, 989, 949, 913, 858, 848,
757, 701, 612, 566. Anal. Calcd for C60H54N4: C, 86.71; H, 6.55; N,
6.74. Found: C, 86.56; H, 6.48; N, 6.70.
2, 2′, 2′′-Tris[(3,5-bis(4-tert-butylphenyl)phenyl]triaminotri-
ethylamine (1f). The Pd catalyst was preformed by dissolving rac-
BINAP (109 mg, 0.175 mmol) in toluene (20 mL) with vigorous heating
and stirring, adding Pd2(dba)3 (69 mg, 0.075 mmol) as a solid, and
removing unreacted Pd by filtration through Celite to yield a light
orange solution. A 250 mL Schlenk flask was charged with TREN
(731 mg, 5.00 mmol), 5b (6.32 g, 15.0 mmol), sodium tert-butoxide
(1.68 g, 17.5 mmol), and toluene (75 mL). The Pd catalyst solution
was added last; the reaction mixture remained light orange. The reaction
was heated to 80 °C overnight and then cooled to room temperature.
Most of the product precipitated from toluene and was collected by
filtration; it was contaminated with NaBr. The toluene mother liquor
was concentrated to dryness, and the residue was extracted with ether.
Another crop of ether-insoluble product (757 mg) was collected in this
manner. All of the crude white solid was partitioned between 100 mL
of chloroform and 100 mL of water. It required vigorous heating for
all of the product to dissolve in chloroform. The aqueous phase was
extracted two more times with chloroform, and these extracts were
combined, dried over MgSO4, and concentrated to 70 mL. Hexane was
added to precipitate out the product as a white solid; yield 3.75 g (3.21
mmol, 64%): 1H NMR (CDCl3): δ 7.34 (d, 12, 3,5-aryl), 7.25 (d 12,
3,5-aryl), 7.07 (t, 3, para), 6.69 (d, 6, ortho), 4.56 (br s, 3, NH), 3.35
(br s, 6, CH2), 2.98 (br s, 6, CH2), 1.28 (s, 54, t-Bu). 13C NMR
(CDCl3): δ 149.68 (3,5-Cp), 148.63 (Cipso), 142.44 (Cm), 138.50 (3,5-
2, 2′, 2′′-Tris(4-fluorophenylamino)triethylamine (1b). This com-
pound was synthesized in a manner similar to that used to prepare 1a
starting from TREN (7.31 g, 50.0 mmol), p-bromofluorobenzene (26.3
g, 150 mmol), Pd2(dba)3 (0.69 g, 0.75 mmol), rac-BINAP (1.25 g, 2.00
mmol), sodium tert-butoxide (16.8 g, 175 mmol), and toluene (400
mL). Column chromatography and recrystallization from ether/hexane
gave 5.84 g (13.6 mmol, 27%) of white crystals: 1H NMR (CDCl3):
δ 6.65 (t, 6, Hm), 6.39 (dd, 6, Ho) 4.03 (br s, 3, NH), 3.22 (t, 6, CH2),
2.60 (t, 6, CH2). 13C NMR (CDCl3): δ 156.44 (d, Cp, JCF ) 235), 145.05
(d, Cipso, JCF ) 1.8), 116.20 (d, Cm, JCF ) 22.1), 114.27 (d, Co, JCF
)
7.2), 53.78 (CH2), 43.08 (CH2). 19F NMR (CDCl3): δ -127.695 (7
lines). IR (Nujol; cm-1): 3382, 1613, 1509, 1315, 1292, 1260, 1214,
1156, 1114, 1057, 917, 823, 514. HRMS. Calcd for C24H27F3N4:
428.2188. Found (EI): 428.2188.
C
ipso), 126.65 (3,5-Cm), 125.28 (3,5 Co), 116.04 (Cp), 110.37 (Co), 53.52
(CH2), 42.31 (CH2), 34.44 (t-Bu), 31.39 (t-Bu). IR (Nujol; cm-1): 3384,
1602, 1520, 1497, 1270, 1112, 1055, 1022, 990, 860, 826, 763, 699,
612, 579. HRMS. Calcd for C84H102N4: 1166.8105. Found (FAB):
1166.8076.
2, 2′, 2′′-Tris(4-tert-butylphenylamino)triethylamine (1c). This
compound was synthesized in a manner similar to that used to prepare
1a starting from TREN (8.77 g, 60.0 mmol), 4-bromo-tert-butylbenzene
(38.4 g, 180 mmol), Pd2(dba)3 (0.82 g, 0.90 mmol), rac-BINAP (1.49
g, 2.40 mmol), sodium tert-butoxide (20.2 g, 210 mmol), and toluene
(500 mL). Column chromatography and recrystallization from hexane
at -80 °C afforded 15.91 g (29.3 mmol, 49%) of white crystals: 1H
NMR (C6D6): δ 7.26 (d, 6, Hm), 6.53 (d, 6, Ho), 3.85 (br s, 3 NH),
2.84 (t, 6, CH2), 2.26 (t, 6, CH2), 1.30 (s, 27, t-Bu). 13C NMR
(CDCl3): δ 146.55 (Cipso), 140.85 (Cp), 126.70 (Cm), 113.48 (Co), 53.93
2, 2′, 2′′-Tris(2-methylphenylamino)triethylamine (1g). This
compound was synthesized in a manner similar to that used to prepare
1a starting from TREN (3.66 g, 25.0 mmol), 2-bromotoluene (12.8 g,
75.0 mmol), Pd2(dba)3 (0.34 g, 0.37 mmol), rac-BINAP (0.70 g, 1.1
mmol), sodium tert-butoxide (8.41 g, 175 mmol), and toluene (300
mL). However, after removing most of the toluene on the rotary

3858 Inorganic Chemistry, Vol. 40, No. 16, 2001
Greco and Schrock
evaporator, cold hexane was added to the concentrated oily orange
solution to yield pale orange crystals. No chromatography was necessary
for the purification of this compound. Further recrystallization from
ether/hexane gave 9.41 g (22.6 mmol, 90%) of white crystals: 1H NMR
(CDCl3): δ 7.09 (t, 3, Hm), 7.02 (d, 3, Hm), 6.66 (t, 3, Hp), 6.57 (d, 3,
Ho), 3.91 (br s, 3, NH), 3.28 (t, 6, CH2), 2.90 (t, 6, CH2), 2.00 (s, 9,
CH3); 13C NMR (CDCl3) δ 145.91 (Cipso), 129.99 (Cm), 127.05 (Cm),
121.95 (Co), 117.02 (Cp), 109.64 (Co), 53.80 (CH2), 41.76 (CH2), 17.16
(Ar-CH3). IR (Nujol; cm-1): 3380, 1606, 1583, 1508, 1319, 1302,
1262, 1190, 1160, 1140, 1089, 1057, 1049, 1025, 981, 923, 748, 717.
HRMS. Calcd for C27H36N4: 416.2940. Found (EI): 416.2940.
2, 2′, 2′′-Tris(mesitylamino)triethylamine (1h). This compound was
synthesized in a manner similar to that used to prepare 1g starting from
TREN (3.66 g, 25.0 mmol), 2-bromomesitylene (14.9 g, 75.0 mmol),
Pd2(dba)3 (0.343 g, 0.375 mmol), rac-BINAP (0.701 g, 1.13 mmol),
sodium tert-butoxide (8.4 g, 88 mmol), and toluene (200 mL).
Recrystallization from ether/hexane gave 9.92 g (19.96 mmol, 79%)
of white crystals: 1H NMR (C6D6) δ 6.79 (s, 6, aryl), 3.37 (br s, 3,
NH), 2.94 (t, 6, CH2), 2.51 (t, 6, CH2), 2.24 (s, 18, Meo), 2.18 (s, 9,
Mep). 13C NMR (CDCl3): δ 144.28 (Cipso), 131.83 (Cp), 130.20 (Co),
130.15 (Cm), 55.67 (CH2), 46.81 (CH2), 21.30, 19.19 (ArCH3). Anal.
Calcd for C33H48N4: C, 79.15; H, 9.66; N, 11.19. Found C, 78.71; H,
9.47; N, 10.95.
(4-FC6H4NHCH2CH2)2NCH2CH2N(4-FC6H4)2. This compound was
obtained as a byproduct in the preparation of 1b on a 44 mmol scale.
It is the product immediately above 1b on a TLC plate and was isolated
as an oil by column chromatography; yield 2.80 g (5.36 mmol, 12%):
1H NMR (C6D6): δ 6.82 (t, 4, meta), 6.73 (t, 4, meta), 6.63 (dd, 4,
ortho), 6.18 (d, 6, ortho), 3.63 (br s, 2, NH), 3.34 (t, 2, tertiary CH2),
2.60 (t, 4, secondary CH2), 2.32 (t, 2, tertiary CH2), 2.18 (t, 4, secondary
CH2). 13C NMR (CDCl3): δ 157.76 (d, Cp, JCF ) 241), 155.65 (d, Cp,
JCF ) 235), 144.32 (d, Cipso, JCF ) 2), 144.07 (d, Cipso, JCF ) 5), 122.10
(d, Co, JCF ) 8), 115.93 (d, Cm, JCF ) 22), 115.56 (d, Cm, JCF ) 22),
113.57 (d, Co, JCF ) 7), 53.56 (secondary CH2), 51.96 (tertiary CH2),
51.44 (tertiary CH2), 42.26 (secondary CH2). 19F NMR (C6D6): δ
-121.76 (7 lines, 2, tertiary), -128.01 (7 lines, 2, secondary). HRMS.
Calcd for C30H30F4N4: 522.2407. Found (FAB): 522.2424.
(4-t-BuC6H4NHCH2CH2)2NCH2CH2N(4-t-BuC6H4)2. This com-
pound was obtained as a byproduct in the preparation of 1c in a reaction
run on a 25 mmol scale. It is the product immediately above 1c on a
TLC plate. It was isolated by column chromatography and then
recrystallized from cold hexane; yield 2.65 g (3.93 mmol, 16%): 1H
NMR (C6D6): δ 7.28 (d, 4, secondary meta), 7.22 (d, 4, tertiary meta),
7.08 (d, 4, tertiary ortho), 6.53 (d, 4, secondary ortho), 3.97 (br s, 2,
NH), 3.71 (t, 2, tertiary CH2), 2.86 (t, 4, secondary CH2), 2.57 (t, 2,
tertiary CH2), 2.34 (t, 4, secondary CH2), 1.33 (s, 18, t-Bu), 1.27 (s,
18, t-Bu). 13C NMR (CDCl3): δ 145.68 (Cipso), 145.12 (Cipso), 143.70
(Cp), 139.89 (Cp), 126.00 (Cm), 125.81 (Cm), 120.05 (Co), 112.64 (Co),
53.93 (secondary CH2), 52.02 (tertiary CH2), 50.85 (tertiary CH2), 42.70
(secondary CH2), 34.16, 33.85, 31.60, 31.48 (t-Bu). Anal. Calcd for
C46H66N4: C, 81.85; H, 9.85; N, 8.30. Found: C, 81.80; H, 9.93; N,
8.24.
[3,5-(4-t-BuC6H4)2C6H3)NHCH2CH2]2NCH2CH2N(3,5-(4-t-
BuC6H4)2C6H3)2. This compound was obtained as a byproduct in the
preparation of 1f. It remains in toluene solution and dissolves in ether
when the ether extraction is performed. It crystallizes out of ether in
pure form; yield 292 mg (0.194 mmol, 4%): 1H NMR (CDCl3): δ
7.47 (d, 8, 3,5-aryl), 7.41 (s, 2, tertiary para), 7.38 (m, 12, 3,5-aryl and
tertiary ortho), 7.34 (d, 8, 3,5-aryl), 7.31 (d, 8, 3,5-aryl), 7.03 (s, 2,
secondary para), 6.65 (s, 4, secondary ortho), 4.48 (br s, 2 NH), 4.13
(t, 2, tertiary CH2), 3.28 (br s, 4, secondary CH2), 3.05 (t, 2, tertiary
CH2), 2.94 (t, 4, secondary CH2), 1.31 (s, 36, t-Bu), 1.28 (s, 36, t-Bu).
13C NMR (CDCl3): δ 150.20 (3,5-Cp), 149.72 (3,5-Cp), 148.74 (Cipso),
148.62 (Cipso), 142.65 (Cm), 142.32 (Cm), 138.70 (3,5-Cipso), 138.05 (3,5-
(1.87 g, 5.00 mmol), and toluene (80 mL). The reaction mixture was
heated under argon at 60 °C for 2 days then filtered through Celite to
remove any insoluble decomposition products. The solvent was
removed, and the residue was washed with pentane. The pentane-
insoluble black material was collected, dried in vacuo, and found to
be pure by 1H NMR; yield 2.08 g (4.06 mmol, 81%): 1H NMR
(C6D6): δ 7.15 (t, 6, meta), 6.85 (t, 3, para), 6.75 (d, 6, ortho), 3.43 (t,
6, CH2), 3.37 (s, 6, NMe2), 2.67 (t, 6, CH2).
[(4-FC6H4NCH2CH2)3N]MoNMe2 (2b). A 250 mL Schlenk flask
was charged with Mo(NMe2)4 (2.84 g, 10.5 mmol), (4-FC6H4NHCH2-
CH2)3N (3.90 g, 9.10 mmol), and toluene (100 mL). The reaction was
heated to 70 °C for 2 days on the Schlenk line. Solids which formed
during the reaction were filtered off, and the solution was concentrated
to dryness. The residue was washed with pentane, and dried in vacuo
to yield 4.80 g (8.48 mmol, 93%) of nearly black crystals. Analytically
pure material was obtained by recrystallization from mixtures of DME
and pentane at -40 °C: 1H NMR (C6D6): δ 6.76 (t, 6, Hm), 6.45 (dd,
6, Ho), 3.25 (s, 6, NCH3), 3.23 (t, 6, CH2), 2.60 (t, 6, CH2). 13C NMR
(C6D6): δ 159.04 (d, Cp, JCF ) 239), 158.91 (Cipso), 125.07 (d, Co, JCF
) 7), 115.14 (d, Cm, JCF ) 21), 63.91 (br, NCH3 and CH2), 57.04 (CH2).
19F NMR (C6D6): δ -123.40. Anal. Calcd for C26H30F3N5Mo: C,
55.22; H, 5.35; N, 12.38. Found: C, 55.08; H, 5.35; N, 12.43.
[(3,5-Me2C6H3NCH2CH2)3N]MoNMe2 (2d). A 250 mL Schlenk
flask was charged with Mo(NMe2)4 (1.77 g, 6.50 mmol), (3,5-Me2C6H3-
NHCH2CH2)3N (2.29 g, 5.00 mmol), and toluene (125 mL). The
reaction was heated to 70 °C for 2 days on the Schlenk line. Toluene
was removed, and the residue was washed with pentane until the
pentane washings were colorless. The resulting solid was collected and
recrystallized from ether/pentane to yield 1.90 g (3.18 mmol, 64%) of
dark purple crystals: 1H NMR (C6D6): δ 6.51 (s, 3, Hp), 6.44 (s, 6,
Ho), 3.49 (t, 6, CH2), 3.37 (s, 6, NCH3), 2.69 (t, 6, CH2). 2.21 (s, 18,
ArCH3). 13C NMR (C6D6): δ 137.18, 128.80, 122.91, 121.91 (all aryl
C), 63.70 (NCH3), 62.68, 57.14 (backbone methylenes), 21.74, (ArCH3).
Anal. Calcd for C32H45N5Mo: C, 64.52; H, 7.61; N, 11.76. Found: C
64.26; H, 7.64; N, 11.52.
[(3,5-Ph2C6H3NCH2CH2)3N]MoNMe2 (2e). A 100 mL Schlenk flask
was charged with (3,5-Ph2C6H3NHCH2CH2)3N (1.45 g, 1.75 mmol),
Mo(NMe2)4 (673 mg, 2.47 mmol), and toluene (50 mL). The flask was
transferred to the Schlenk line and heated to 70 °C for 2 days. Toluene
was removed, and the residue was dissolved in THF. Insoluble
impurities were filtered off, and the solution was concentrated to give
1.87 g. (96%) of crude material. Spectroscopically pure material can
be obtained by recrystallization from a mixture of THF and pentane
followed by three washings of the crystals with pentane: 1H NMR
indicates 2 molecules of THF in the crystals: 1H NMR (C6D6): δ 7.57-
7.53 (m, 12), 7.47 (t, 3), 7.13 (m, 18), 7.09 (d, 6), 3.55 (t, 6, CH2),
3.44 (s, 6, NMe2), 2.76 (t, 6, CH2). 13C NMR (C6D6): δ 142.49, 142.45,
127.82, 127.69, 121.95, 120.02, 63.46, 57.15.
[(C6H5NCH2CH2)3N]MoCl (3a). Solid MoCl4(THF)2 (2.41 g, 6.30
mmol) was added to a solution of (C6H5NHCH2CH2)3N (2.25 g, 6.0
mmol) in THF (120 mL) resulting in an immediate color change to
dark red followed by the precipitation of a red oil. The reaction mixture
was cooled to -35 °C. A solution of methylmagnesium chloride (6
mL, 3.0 M in THF, 18 mmol) was diluted to 20 mL, cooled to -35
°C, and then added dropwise to the reaction mixture. The reaction
mixture was allowed to warm to room temperature with stirring
overnight. The red product precipitated out in analytically pure form.
It was collected, washed once with THF, twice with ether, and dried
in vacuo; yield 1.71 g (3.40 mmol, 57%): 1H NMR (CDCl3): δ 16.36
(Hm), 9.06 (Ho), 1.47 (Hp), -19.30 (CH2), -77.78 (CH2). Anal. Calcd
for C24H27ClN4Mo: C, 57.32; H, 5.41; N, 11.14; Cl, 7.05. Found: C
57.08; H, 5.37; N, 11.19; Cl, 7.11.
[(4-FC6H4NCH2CH2)3N]MoCl (3b). A 250 mL flask was charged
with MoCl4(THF)2 (1.91 g, 5.00 mmol), THF (60 mL), and (4-FC6H4-
NHCH2CH2)3N (2.14 g, 2.10 mmol). The reaction mixture turned deep
red immediately. It was stirred for 10 min and then cooled to -35 °C.
MeMgCl (5.0 mL, 3.0 M in THF, 15 mmol) was diluted to 20 mL,
cooled to -35 °C, and added dropwise to the reaction mixture. The
reaction was stirred at room temperature for 2 h and then allowed to
sit overnight without further stirring. 1,4-Dioxane (8 mL) was added,
followed by another hour of stirring. The reaction mixture was then
Cipso), 126.74 (3,5-Cm), 126.68 (3,5-Cm), 125.60 (3,5-Co), 125.30 (3,5-
Co), 119.65 (Cp), 118.61 (Cp), 115.78 (Co), 110.44 (Co), 53.94
(secondary CH2), 52.59 (tertiary CH2), 51.33 (tertiary CH2), 41.91
(secondary CH2), 34.52 (t-Bu), 34.49 (t-Bu), 31.44 (t-Bu), 31.37 (t-
Bu). HRMS. Calcd for C110H130N4: 1507.0296. Found (FAB): 1507.0255.
[(C6H5NCH2CH2)3N]MoNMe2 (2a). A 250 mL Schlenk flask was
charged with Mo(NMe2)4 (1.95 g, 7.15 mmol), (C6H5NHCH2CH2)3N

Synthesis of Triamidoamine Ligands
Inorganic Chemistry, Vol. 40, No. 16, 2001 3859
filtered through Celite and concentrated to 15 mL. Red crystals formed
during the process. The crystals were collected, washed with ether,
and dried in vacuo; yield 1.77 g (3.17 mmol, 63%): 1H NMR
(CDCl3): δ 15.64 (Hm), 9.41 (Ho), -17.71 (CH2), -80.07 (CH2). 19F
NMR (THF): δ -110.5. Anal. Calcd for C24H24F3ClN4Mo: C, 51.77;
H, 4.34; N, 10.06; Cl, 6.37. Found: C, 51.86; H, 4.37; N, 9.95; Cl,
6.31.
to room temperature with stirring, 1,4-dioxane (2 mL) was added,
resulting in the precipitation of a white powder. THF was removed on
the rotary evaporator, and the residue was redissolved in toluene. MgCl2-
(dioxane) was filtered off, and the toluene was removed. The product
was suspended in ether and collected on a frit, although the finely
divided nature of the product rendered this a slow process; yield 1.47
g (1.13 mmol, 44%). 1H NMR (C6D6): δ 7.82, 7.43, 2.57, 1.22(t-Bu),
-16.51(CH2), -70.90(CH2). Anal. Calcd for C84H99ClN4Mo: C, 77.84;
H, 7.70; N, 4.32; Cl, 2.74. Found: C, 77.91; H, 7.62; N, 4.19; Cl,
2.82.
Synthesis of 3b from 2b. A solution of 2b (4.80 g, 8.48 mmol) in
THF (50 mL) was cooled to -40 °C. 2,6-Lutidinium chloride (1.22 g,
8.48 mmol) was added as a solid, and the stirred reaction was allowed
to warm to room temperature over a period of 2 h, during which time
the color turned dark red. THF was removed in vacuo, and the crude
residue was washed with ether, toluene, and pentane. The red product
(4.08 g, 7.33 mmol, 86%) was collected on a frit and dried in vacuo.
[(4-t-BuC6H4NCH2CH2)3N]MoCl (3c). A 500 mL round-bottom
flask was charged with (4-t-BuC6H4NCH2CH2)3N (7.06 g, 13.0 mmol)
and MoCl4(THF)2 (4.97 g, 13.0 mmol). THF (150 mL) was added,
and the reaction mixture was stirred at room temperature for 30 min to
yield a dark red solution and then cooled to -40 °C for 2 h. MeMgCl
(13 mL, 3.0 M in THF, 39 mmol) was diluted to 50 mL, cooled to
-40 °C, transferred to a precooled addition funnel, and added dropwise
to the reaction mixture over a period of 30 min. After the reaction
mixture was stirred overnight at room temperature, THF was removed
on the rotary evaporator. The residue was dissolved in toluene,then 4
mL of 1,4-dioxane (4.5 g, 47 mmol) was added, and the mixture was
stirred for 1 h. Filtration through Celite removed MgCl2(dioxane).
Toluene was removed in vacuo, and the residue was extracted with
ether. The ether-insoluble red product was collected on a frit and dried
in vacuo; yield 5.51 g (8.21 mmol, 63%): 1H NMR (C6D6): δ 15.66
(Hm), 9.50 (Ho), 1.48 (t-Bu), -17.74 (CH2), -75.96 (CH2). Anal. Calcd
for C36H51ClN4Mo: C, 64.42; H, 7.66; N, 8.35; Cl, 5.28. Found: C,
64.13; H, 7.48; N, 8.28; Cl, 5.34.
[(3,5-Me2C6H3NCH2CH2)3N]MoCl (3d). This material was prepared
in a manner similar to that used to prepare 3a starting from (3,5-
Me2C6H3NHCH2CH2)3N (3.67 g, 8.00 mmol), MoCl4(THF)2 (3.06 g,
8.00 mmol), and MeMgCl (8.0 mL, 3.0 M in THF, 24 mmol). Pure
product crystallized out of the reaction mixture; yield 2.89 g (4.92
mmol, 62%): 1H NMR (CDCl3): δ 8.99 (Ho), 1.76 (Hp), 1.66 (CH3),
-16.15 (CH2), -73.89 (CH2). Anal. Calcd for C30H39ClN4Mo: C,
61.38; H, 6.70; N, 9.54; Cl, 6.04. Found: C, 61.04; H, 6.62; N, 9.33;
Cl, 6.17.
Synthesis of 3d from 2d. This material was prepared in a manner
similar to that described for the synthesis of 3b from 2b, starting from
2d (595 mg, 1.00 mmol) and 2,6-lutidinium chloride (144 mg, 1.00
mmol). The product precipitated out of THF as it formed; yield 374
mg (0.64 mmol, 64%).
[(3,5-Ph2C6H3NCH2CH2)3N]MoCl (3e). MoCl4(THF)2 (573 mg,
1.50 mmol) was added as a solid to a solution of (3,5-Ph2C6H3NHCH2-
CH2)3N (1.25 g, 1.50 mmol) in THF (50 mL). All initially dissolved
to give a red solution, but after stirring for 5 min a large amount of red
precipitate formed. After cooling to -35 °C, the precipitate dissolved.
MeMgCl (1.5 mL, 3.0 M in THF, 4.5 mmol) was diluted to 15 mL,
and cooled to -35 °C. The solution of MeMgCl was then added
dropwise to the reaction mixture, resulting in a color change from red
to orange. After allowing the reaction to warm to room temperature
with stirring, 1,4-dioxane (2 mL) was added, resulting in the precipita-
tion of a white powder, which was filtered off. Removal of THF on
the rotary evaporator yielded an orange solid, which could not be
redissolved in any solvent, including THF. The product was collected,
washed with THF, and dried in vacuo; yield 546 mg (0.57 mmol,
38%): 1H NMR (C6D6): δ 9.31, 7.56, 7.19, 7.04, 2.52, 0.18, -15.26,
-76.08 (all br s). Anal. Calcd for C60H51ClN4Mo: C, 75.11; H, 5.36;
N, 5.84; Cl, 3.70. Found: C, 75.13; H, 5.44; N, 5.69; Cl, 3.62.
[{3,5-(4-t-BuC6H4)2C6H3NCH2CH2}3N]MoCl (3f). A sample of
{3,5-(4-t-BuC6H4)2C6H3NHCH2CH2}3N (3.04 g, 2.60 mmol) was
dissolved in 150 mL THF with vigorous heating. MoCl4(THF)2 (0.993
g, 2.6 mmol) was added as a solid to give a dark red solution, which
was cooled to -35 °C. MeMgCl (2.6 mL, 3.0 M in THF, 7.8 mmol)
was diluted to 10 mL, and also cooled to -35 °C. The solution of
MeMgCl was added dropwise to the reaction mixture, resulting in a
color change from red to orange. After allowing the reaction to warm
[(C6H5NCH2CH2)3N]MoMe (4a). A 100 mL round-bottom flask
was charged with MoCl4(THF)2 (1.07 g, 2.8 mmol), (C6H5NHCH2-
CH2)3N (1.05 g, 2.8 mmol) and THF (30 mL). The mixture was stirred
at room temperature for 15 min, during which time it turned dark red.
The mixture was cooled to -40 °C, methyllithium (8 mL, 1.4 M in
ether, 11.2 mmol) was added dropwise, and the reaction was allowed
to warm to room temperature over a period of 1 h while being stirred.
The THF was removed, and the residue was extracted with 50 mL
toluene. Gentle heating was required to dissolve all of the complex.
LiCl and some purple insoluble material were removed by filtration.
Toluene was removed, and the residue was extracted with ether. The
insoluble product was collected, washed with ether and pentane, and
dried in vacuo to yield 689 mg (1.43 mmol, 51%) of dark orange
powder. Analytically pure material could be obtained by recrystallization
1
from cold toluene. H NMR (C6D6): δ 16.00 (Hm), 3.94 (Ho), -1.06
(Hp), -11.02 (CH2), -66.48 (CH2). Anal. Calcd for C25H30N4Mo: C,
62.24; H, 6.27; N, 11.61. Found: C 62.39; H, 6.14; N, 11.42.
Conversion of 4a to 3a. A solution of 4a (724 mg, 1.50 mmol) in
THF (50 mL) was cooled to -40 °C. 2,6-Lutidinium chloride (215
mg, 1.50 mmol) was added as a solid, and the reaction was allowed to
warm to room temperature while being stirred over a period of 1 h,
during which time some red product began to precipitate out of solution.
The solvent was removed in vacuo, and the residue was extracted with
ether. The insoluble product was collected, washed with ether and
pentane, and dried in vacuo to give 609 mg (1.21 mmol, 81%) of orange
solid. The product could be recrystallized from a mixture of dichlo-
romethane and pentane at -40 °C.
[(4-FC6H4NCH2CH2)3N]MoMe (4b). This complex was synthesized
in a manner similar to that used to prepare 4a starting from MoCl4-
(THF)2 (802 mg, 2.10 mmol), (4-FC6H4NHCH2CH2)3N (900 mg, 2.10
mmol) and MeLi (6 mL). The red solid was recrystallized from toluene
1
to yield 709 mg (1.32 mmol, 63%) of red crystals in two crops. H
NMR (C6D6): δ 16.28 (Hm), 4.15 (Ho), -10.50 (CH2), -72.60 (CH2).
19F NMR (THF): δ -104.8. Anal. Calcd for C25H27F3N4Mo: C, 55.97;
H, 5.07; N, 10.44. Found: C, 55.74; H, 5.08; N, 10.39.
Conversion of 4b to 3b. The procedure was the same as for the
conversion of 4a to 3a, starting from 4b (230 mg, 0.43 mmol) and
2,6-lutidinium chloride (61 mg, 0.43 mmol). The red product (200 mg,
0.36 mmol, 84%) was obtained after removal of THF and washing the
crude residue with ether and pentane.
[(4-t-BuC6H4NCH2CH2)3N]MoMe (4c). This complex was synthe-
sized in a manner similar to that used to prepare 4a starting from MoCl4-
(THF)2 (802 mg, 2.10 mmol), (4-t-BuC6H4NHCH2CH2)3N (1.14 g, 2.10
mmol) and MeLi (6 mL). Red crystals were collected in one crop (943
mg, 1.45 mmol, 69%) upon recrystallization from a mixture of toluene
1
and pentane at -40 °C. H NMR (C6D6): δ 16.16 (Hm), 3.88 (Ho),
1.57 (t-Bu), -11.48 (CH2), -70.10 (CH2). Anal. Calcd for C37H54N4-
Mo: C, 68.29; H, 8.36; N, 8.61. Found: C, 68.11; H, 8.28; N, 8.44.
Conversion of 4c to 3c. The procedure was the same as for the
conversion of 4a to 3a starting from 4c (488 mg, 0.75 mmol) and 2,6-
lutidinium chloride (108 mg, 0.75 mmol). The red solid was recrystal-
lized from a mixture of toluene and pentane at -40 °C to yield 371
mg (0.55 mmol, 74%) of red crystals in one crop.
[(3,5-Me2C6H3NCH2CH2)3N]MoMe (4d). This complex was syn-
thesized in a manner similar to that used to prepare 4a starting from
MoCl4(THF)2 (1.07 g, 2.80 mmol), (3,5-Me2C6H3NHCH2CH2)3N (1.28
g, 2.80 mmol) and MeLi (8 mL). An orange powder was obtained after
removing toluene and washing the residue with ether and pentane (1.01
g, 1.78 mmol, 63%). Analytically pure material could be obtained by
recrystallization from toluene. 1H NMR (C6D6): δ 3.80 (Ho), 1.07

3860 Inorganic Chemistry, Vol. 40, No. 16, 2001
Greco and Schrock
(CH3), -0.82 (Hp), -11.59 (CH2), -68.78 (CH2). Anal. Calcd for
C31H42N4Mo: C, 65.71; H, 7.47; N, 9.89. Found: C, 65.76; H, 7.43;
N, 9.98.
Conversion of 4d to 3d. The procedure was the same as for the
conversion of 4a to 3a starting from 4d (670 mg, 1.20 mmol) and 2,6-
lutidinium chloride (172 mg, 1.20 mmol). The orange product crystal-
lized out of THF, and was isolated by filtering the crude reaction
mixture after cooling the mixture to -40 °C; yield 543 mg,(0.93 mmol,
77%). Analytically pure material was obtained by recrystallization from
a mixture of dichloromethane and pentane at -40 °C.
CH2). Anal. Calcd for C30H39ClN4W: C, 53.38; H, 5.82; N, 8.30; Cl,
5.25. Found: C, 53.22; H, 5.74; N, 8.19; Cl, 5.21.
[(3,5-Ph2C6H3NCH2CH2)3N]WCl (5e). This material was synthe-
sized in a manner similar to that used to prepare 5b, starting from (3,5-
Ph2C6H3NHCH2CH2)3N (416 mg, 0.500 mmol), WCl4(DME) (208 mg,
0.500 mmol), and MeMgCl (0.5 mL, 3.0 M in THF diluted to 2 mL,
1.5 mmol); yield 184 mg (0.175 mmol, 35%). Anal. Calcd for C60H51-
ClN4W: C, 68.81; H, 4.91; N, 5.35; Cl, 3.38. Found: C, 69.11; H,
4.92; N, 5.28; Cl, 3.43.
[(4-t-BuC6H4NCH2CH2)3N]WMe (6c). WCl4(DME) (934 mg, 2.25
mmol) was added to a solution of (4-t-BuC6H4NCH2CH2)3N (1.22 g,
2.25 mmol) in 20 mL of THF. The reaction mixture was stirred at
room temperature for 30 min to yield a pale orange solution and then
cooled to -35 °C for 2 h. MeMgCl (3 mL, 3.0 M in THF, 9 mmol)
was diluted to 15 mL, cooled to -35 °C, and then added dropwise to
the reaction mixture over 10 min. The reaction mixture was stirred 1
h at room temperature, and THF was removed on the rotary evaporator.
The residue was dissolved in 30 mL of toluene, and 1.2 mL 1,4-dioxane
(1.35 g, 14.0 mmol) was added. The mixture was stirred for 30 min
and then filtered through Celite to remove MgCl2(dioxane). Toluene
was removed in vacuo, and the residue was dissolved in ether. The
mixture was cooled to -35 °C to give orange crystals, which were
washed with pentane and dried in vacuo; yield 275 mg (0.370 mmol,
[(C6H5NCH2CH2)3N]WCl (5a). A solution of (C6H5NHCH2CH2)3N
(1.50 g, 4.00 mmol) in 50 mL THF was heated with a heat gun until
the solvent was almost boiling. WCl4(dme) (1.66 g, 4.00 mmol) was
added as a solid in 200 mg portions to the stirring solution such that
all dissolved before another portion was added. A yellow precipitate
formed upon completion of the addition. After stirring at room
temperature for 15 min, the reaction mixture was cooled to -35 °C.
MeMgCl (4.0 mL, 3.0 M in THF, 12.0 mmol) was diluted to 20 mL,
cooled to -35 °C, and added slowly to the reaction mixture. The yellow
precipitate completely dissolved to give an orange solution. The reaction
was stirred overnight at room temperature during which time the product
precipitated out as an orange powder. It was collected, washed with
THF and ether, and dried in vacuo; yield 570 mg (0.96 mmol, 24%).
1H NMR (CD2Cl2): δ 18.13 (s, 6, Ho), 17.34 (d, 6, Hm), 3.12 (t, 3,
Hp), -25.64 (br s, 6, CH2), -50.97 (br s, 6, CH2). Anal. Calcd for
C24H27ClN4W: C, 48.79; H, 4.61; N, 9.48; Cl, 6.00. Found: C, 48.85;
H, 4.71; N, 9.43; Cl, 5.84.
[(4-FC6H4NCH2CH2)3N]WCl (5b). A solution of (4-FC6H4NHCH2-
CH2)3N (1.72 g, 4.00 mmol) in 50 mL THF was heated with a heat
gun until the solvent was almost boiling. WCl4(DME) (1.66 g, 4.0
mmol) was added as a solid in 200 mg portions to the stirring solution
such that all dissolved before another portion was added. No precipitate
was observed. After stirring at room temperature for 15 min, the reaction
mixture was cooled to -35 °C. MeMgCl (4.0 mL, 3.0 M in THF, 12.0
mmol) was diluted to 20 mL, cooled to -35 °C, and added slowly to
the reaction mixture. The reaction was stirred overnight at room
temperature, then 6 mL of 1,4-dioxane were added, and the reaction
was stirred for another 30 min. The reaction mixture was filtered
through Celite and concentrated to 15 mL, which resulted in the
crystallization of the red product. The crystals were collected, washed
once with THF, twice with ether, and dried in vacuo; yield 732 mg
(1.13 mmol, 28%). 1H NMR (CD2Cl2): δ 18.79 (s, 6, Ho), 16.93 (d, 6,
Hm), -24.36 (br s, 6, CH2), -52.77 (br s, 6, CH2). 19F NMR (THF):
δ -108.47. Anal. Calcd for C24H24ClF3N4W: C, 44.71; H, 3.75; N,
8.69; Cl, 5.50. Found: C, 44.59; H, 3.81; N, 8.61; Cl, 5.43.
[(4-t-BuC6H4NCH2CH2)3N]WCl (5c). This material was prepared
by a method similar to that used to prepare 3c starting from (4-t-BuC6H4-
NCH2CH2)3N (2.36 g, 4.35 mmol), WCl4(DME) (1.99 g, 4.80 mmol),
and MeMgCl (4.5 mL, 3.0 M in THF, 13.5 mmol). The only difference
is that WCl4(DME) was added slowly to a solution of the ligand prior
to cooling and addition of MeMgCl; yield 1.41 g. (1.86 mmol, 43%).
1H NMR (C6D6): δ 17.34 (s, 6, ortho), 17.04 (s, 6, meta), 2.03 (s, 27,
t-Bu), -25.65 (br s, 6, CH2), -49.8 (br s, 6, CH2). Anal. Calcd for
C36H51N4ClW: C, 56.96; H, 6.77; N, 7.38; Cl, 4.67. Found: C 57.11;
H, 6.72; N, 7.29; Cl, 4.61.
1
22%). H NMR (C6D6): δ 17.98 (s, 6, Cm), 12.79 (s, 6, Co), 1.97 (s,
27, t-Bu), -21.61 (br s, 6, CH2), -49.6 (br s, 6, CH2).
Cyclic Voltammetry. Electrochemical measurements were per-
formed using a Bioanalytical Systems CV-50W potentiostat interfaced
to a VC-2 voltammetry cell. All measurements were performed in THF
using Bu4NPF6 as the supporting electrolyte.
Platinum disk working and platinum wire auxiliary electrodes were
employed. The nonaqueous reference electrode was assembled from
the kit provided by BAS. A 0.1 M solution of Bu4NPF6 in acetonitrile
was prepared, and 17 mg of AgNO3 were added to 10 mL of this
solution to produce a 0.01 M solution of Ag+ ion. This solution was
stored in the drybox freezer when not in use in order to prevent light-
induced decomposition (brown color), but warmed to room temperature
again before use. The reference electrode was prepared by filling the
electrode body with Ag+ ion solution and replacing the silver wire.
When not in use, the reference electrode body was filled with a 0.1 M
solution of Bu4NPF6 in CH3CN, and the entire electrode was stored in
a stoppered Schlenk tube containing electrolyte solution. The sweep
rate employed was 500 mV/s.
All analyte solutions consisted of 1.00 g of Bu4NPF6 dissolved in 6
mL of THF (0.43 M solution). A typical sample size was 50 mg for
compounds with molecular weights on the order of 1000. A standard
solution of ferrocene was run at the start of each day, and the oxidation
potential was measured. All other measurements were referenced to
the ferrocene/ferrocenium couple as recommended by IUPAC.72 The
rest potential of every analyte solution was measured using the function
of the same name under the Control menu of the BAS software.
Separation between the anodic and cathodic peaks for a well-behaved
process was usually ∼100 mV.
Acknowledgment. R.R.S. is grateful to the National Insti-
tutes of Health (Grant GM 31978) for research support.
[(3,5-Me2C6H3NCH2CH2)3N]WCl (5d). This material was synthe-
sized in a manner similar to that used to prepare 5a starting from (3,5-
Me2NHCH2CH2)3N (2.29 g, 5.00 mmol), WCl4(DME) (2.07 g, 5.00
mmol), and MeMgCl (5.0 mL, 3.0 M in THF, 15 mmol); yield 1.38 g
Supporting Information Available: Text describing further details
of syntheses and Figures 1S, 2S, and 3S showing CV’s of 3b, 3d, and
3c, respectively . This material is available free of charge via the Internet
at http://pubs.acs.org.
1
(2.04 mmol, 41%). H NMR (CD2Cl2): δ 18.92 (s, 6, Ho), 3.62 (s, 3,
Hp), 3.05 (s, 18, 3,5-Me2), -23.93 (br s, 6, CH2), -50.72 (br s, 6,
IC001122V