Synthesis, structure, and electrochemical studies of molybdenum and tungsten dinitrogen, diazenido, and hydrazido complexes that contain aryl-substituted triamidoamine ligands

Inorg. Chem. 2001, 40, 3861-3878

3861

Synthesis, Structure, and Electrochemical Studies of Molybdenum and Tungsten Dinitrogen,

Diazenido, and Hydrazido Complexes That Contain Aryl-Substituted Triamidoamine

Ligands

George E. Greco and Richard R. Schrock*

Department of Chemistry 6-331, Massachusetts Institute of Technology,

Cambridge, Massachusetts 02139

ReceiVed October 11, 2000

One-electron reduction of [ArN₃N]MoCl complexes (Ar ) C₆H₅, 4-FC₆H₄, 4-t-BuC₆H₄, 3,5-Me₂C₆H₃) yields

complexes of the type [ArN₃N]Mo-NdN-Mo[ArN₃N], while two-electron reduction yields {[ArN₃N]Mo-Nd

N}^-derivatives (Ar ) C₆H₅, 4-FC₆H₄, 4-t-BuC₆H₄, 3,5-Me₂C₆H₃, 3,5-Ph₂C₆H₃, and 3,5-(4-t-BuC₆H₄)₂C₆H₃).

Compounds that were crystallographically characterized include {[t-BuC₆H₄N₃N]Mo}₂(N₂), Na(THF)₆{[PhN₃N]Mo-

NdN}₂Na(THF)₃, [t-BuC₆H₄N₃N]Mo-NdN-Na(15-crown-5), and {[Ph₂C₆H₃N₃N]MoNN}₂Mg(DME)₂. Com-

pounds of the type [ArN₃N]Mo-NdN-Mo[ArN₃N] do not appear to form when Ar ) 3,5-Ph₂C₆H₃or 3,5-(4-

t-BuC₆H₄)₂C₆H₃, presumably for steric reasons. Treatment of diazenido complexes (e.g., [ArN₃N]Mo-NdN-

Na(THF)_x) with electrophiles such as Me₃SiCl or MeOTf yielded [ArN₃N]Mo-NdNR complexes (R ) SiMe₃

or Me). These species react further to yield {[ArN₃N]Mo-NdNMe₂}⁺species in the presence of methylating

agents. Addition of anionic methyl reagents to {[ArN₃N]Mo-NdNMe₂}⁺species yielded [ArN₃N]Mo(NdNMe₂)-

(Me) complexes. Reduction of [4-t-BuC₆H₄N₃N]WCl under dinitrogen leads to a rare {[t-BuC₆H₄N₃N]W}₂(N₂)

species that can be oxidized by two electrons to give a stable dication (as its BPh₄^-salt). Reduction of hydrazido

species leads to formation of MotN in low yields, and only dimethylamine could be identified among the many

products. Electrochemical studies revealed expected trends in oxidation and reduction potentials, but also provided

evidence for stable neutral dinitrogen complexes of the type [ArN₃N]Mo(N₂) when Ar is a relatively bulky terphenyl

substituent.

Introduction

Mo-NdN}₃VCl.⁵During the course of our research on dini-

trogen and other types of complexes that contain a [C₆F₅N₃N]^3-

or [Me₃SiN₃N]^3-ligand, several drawbacks were revealed. For

example, several [Me₃SiN₃N]^3-complexes were found to

decompose by loss of a TMS group or by CH activation within

a TMS group.^4,6-9The primary drawback of the C₆F₅ligand

was proposed to be its instability toward strongly nucleophilic

reagents, although no direct evidence for that statement has yet

come to light.¹⁰The C₆F₅groups also produce a relatively

electron deficient metal center, which can be undesirable if

strong π back-donation into a ligand in the coordination pocket

is desired, as in dinitrogen binding. For this reason we turned

to the synthesis of triamidoamine ligands substituted with

ordinary aryl groups ([(ArNCH₂CH₂)₃N]^3-) [ArN₃N]^3-) and

the preparation of Mo and W complexes that would be useful

for exploring dinitrogen chemistry, namely, monochloride

complexes, [ArN₃N]MCl. In the preceding paper in this issue¹¹

We have been interested in exploring the chemistry of

transition metal complexes containing triamidoamine ([(RNCH₂-

CH₂)₃N]^3-) [RN₃N]^3-) ligands,¹in part with respect to

activation and further reactions of dinitrogen. The first dinitrogen

complex containing a [RN₃N]^3-ligand, {[t-BuMe₂SiN₃N]Mo}₂-

(µ-N₂) was isolated as a byproduct of the synthesis of [t-BuMe₂-

SiN₃N]MoCl from Li₃[t-BuMe₂SiN₃N] and MoCl₃(THF)₃.²

More rational syntheses of dinitrogen complexes were ac-

complished in systems that employed the [C₆F₅N₃N]^3-ligand.³

For example, reduction of [C₆F₅N₃N]Mo(OTf) with 2 equiv of

sodium amalgam yielded diazenido complexes of the type

[C₆F₅N₃N]Mo-NdN-Na(THF)_x(x unknown), which could be

treated with i-Pr₃SiCl to yield [C₆F₅N₃N]Mo-NdNSi(i-Pr)₃in

high yield.⁴More recent work has involved the synthesis of

dinitrogen complexes from [Me₃SiN₃N]MoCl. For example,

reduction of [Me₃SiN₃N]MoCl by magnesium in THF in the

presence of dinitrogen led to {[Me₃SiN₃N]Mo-NdN}₂Mg-

(THF)₂in high yield. A number of heterobimetallic dinitrogen

complexes could be prepared employing the magnesium species

such as {[Me₃SiN₃N]Mo-NdN}₃Fe, {[Me₃SiN₃N]Mo-NdN}₂-

ZrCl₂, {[Me₃SiN₃N]Mo-NdN}₂VCl(THF), and {[Me₃SiN₃N]-

(5) O’Donoghue, M. B.; Davis, W. M.; Schrock, R. R.; Reiff, W. M.

Inorg. Chem. 1999, 38, 243.

(6) Schrock, R. R.; Seidel, S. W.; Mo¨sch-Zanetti, N. C.; Dobbs, D. A.;

Shih, K.-Y.; Davis, W. M. Organometallics 1997, 16, 5195.

(7) Schrock, R. R.; Seidel, S. W.; Mo¨sch-Zanetti, N. C.; Shih, K.-Y.;

O’Donoghue, M. B.; Davis, W. M.; Reiff, W. M. J. Am. Chem. Soc.

1997, 119, 11876.

(8) Schrock, R. R.; Rosenberger, C.; Seidel, S. W.; Shih, K.-Y.; Davis,

W. M.; Odom, A. L. Organometallics 2001, 617-618, 495.

(9) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Organometallics 1992,

11, 1452.

(10) Seidel, S. W.; Schrock, R. R.; Davis, W. M. Organometallics 1998,

17, 1058.

(1) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9.

(2) Shih, K.-Y.; Schrock, R. R.; Kempe, R. J. Am. Chem. Soc. 1994, 116,

8804.

(3) Kol, M.; Schrock, R. R.; Kempe, R.; Davis, W. M. J. Am. Chem.

Soc. 1994, 116, 4382.

(4) O’Donoghue, M. B.; Davis, W. M.; Schrock, R. R. Inorg. Chem. 1998,

37, 5149.

(11) Greco, G. E.; Schrock, R. R. Inorg. Chem., preceding paper in this

issue.

Published on Web 05/19/2001

3862 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

Scheme 1

we report the synthesis of eight such ligands from triethylene-

tetraamine by coupling an aryl bromide to the terminal amine

functionalities, where Ar ) C₆H₅, 4-FC₆H₄, 4-t-BuC₆H₄, 3,5-

Me₂C₆H₃, and 3,5-Ph₂C₆H₃, 3,5-(4-t-BuC₆H₄)₂C₆H₃, 2,4,6-

Me₃C₆H₂, and 2-MeC₆H₄. A “direct” synthesis of complexes

of the type [ArN₃N]MCl from the corresponding tetrachlorides

of Mo or W was possible with the first six of these ligands. In

this paper we report the synthesis of dinitrogen complexes

containing several of these ligands, and in particular how the

chemistry of such species changes with the steric bulk of the

triamidoamine ligands and their electronic characteristics.

much from its normal diamagnetic position as the corresponding

peak in [t-BuC₆H₄N₃N]MoCl.

Stirring a THF solution of [t-BuC₆H₄N₃N]MoCl overnight

over 1 equiv of Na/Hg under dinitrogen results in the formation

of 1c in 27% yield. The remainder of the material consists of

unidentified ether-soluble material. Unlike in the case of

compounds containing the C₆F₅ligand,³the reaction is not rapid.

The purple color begins to appear after several hours, but at

least 12 h are required for complete reaction. If 2.5 equiv of

Na/Hg is employed, a 3:2 mixture of 1c and 2c is obtained,

1

according to H NMR spectra, while 5 equiv of Na/Hg yields

a 1:2 mixture of 1c and 2c. We have not been able to convert

1c to 2c with a large excess of sodium amalgam, in contrast to

complexes containing the [C₆F₅N₃N]^3-ligand.³A Raman

spectrum of 1c in THF solution showed a sharp peak at 1681

cm^-1that can be assigned to the N-N stretch. For comparison,

the N-N stretch is found at 1630 cm^-1in the Raman spectrum

of [Mo(N([R]Ar)₃]₂(µ-N₂).¹²

X-ray quality crystals of 1c were grown from a saturated THF

solution at -35 °C. Crystallographic data, collection parameters,

and refinement parameters are collected in Table 1, while

selected bond lengths and angles can be found in Table 2. One

molecule of THF is present in the unit cell. Side and end views

of the molecule are depicted in Figure 1. The crystallographic

inversion center is located at the midpoint of the N-N bond.

Most of the bond lengths and angles are typical for five-

coordinate Mo complexes containing triamidoamine ligands.¹

The Mo-N-N-Mo axis is linear, and the NdN bond length

is 1.19 Å, both of which are typical of bridging dinitrogen

complexes in this category. In another structurally characterized

bridging N₂dimer of Mo containing [t-BuMe₂SiN₃N]^3-ligands,

the N-N bond length is 1.195 Å.²As can be seen from the top

view in Figure 1, the two halves of the molecule are staggered

Results and Discussion

Dimolybdenum Bridging Dinitrogen Complexes. Reduction

of [ArN₃N]MoCl complexes by one electron under dinitrogen

results in the formation of dimolybdenum bridging dinitrogen

complexes of type 1 (Scheme 1). Magnesium, sodium amalgam,

and sodium naphthalenide are all effective reducing agents,

although we have obtained the cleanest reductions with sodium

naphthalenide. Compounds 1 are purple paramagnetic solids

which are relatively insoluble in common organic solvents (THF,

methylene chloride, DMF, hot toluene, chlorobenzene, aceto-

nitrile, and 1,4-dioxane), except for 1c, which is soluble in

benzene, toluene, and THF. Therefore only 1c can be separated

from the NaCl or MgCl₂salts that are also formed in the

reaction.

The best method of preparing 1c (in 56% yield) is by addition

of 1 equiv of sodium naphthalenide to a solution of [t-BuC₆-

H₄N₃N]MoCl in THF at -40 °C. The anionic diazenido

complex (2c, see below) was not formed, according to ¹H NMR

1

spectra. The H NMR spectrum of 1c is characteristic of a

paramagnetic species. The resonance for the meta hydrogen of

the ligand aryl group is relatively sharp and shifted downfield,

while the resonances for the methylene protons of the ligand

backbone are shifted upfield. The backbone resonance that is

furthest upfield is the broadest. None of the peaks is shifted as

(12) 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.

Mo and W Complexes with Triamidoamine Ligands

Inorganic Chemistry, Vol. 40, No. 16, 2001 3863

Table 1. Crystallographic Data, Collection Parameters, and

Refinement Parameters for

[t-BuC₆H₄N₃N]Mo-NdN-Mo[t-BuC₆H₄N₃N] (1c) and

Na(THF)₆{[PhN₃N]Mo-NdN[Na(THF)₃]NdN-Mo[PhN₃N]} (2a)^a

1c

2a

empirical formula

formula w

space group

a (Å)

b (Å)

c (Å)

C₄₀H₅₉MoN₅O

721.86

P1h

C₉₆H₁₀₂Mo₂N₁₂Na₂O₁₀

1831.52

R3hc

13.3659(15)

93.012(13)

90

120

14390(3)

6

11.1627(2)

13.19800(10)

14.0430(3)

76.8720(10)

86.3670(10)

78.3060(10)

1972.67(6)

2

R (deg)

â (deg)

γ (deg)

V (Å³)

Z

temp (K)

R1 [I > 2σ(I)]

wR2 [I > 2σ(I)]

R1 (all data)

wR2 (all data)

183(2)

0.0615

0.1302

0.0669

183(2)

0.0544

0.1314

0.0856

0.1330

0.1471

^aAll structures were solved on a Bruker SMART/CCD diffractometer

using 0.710 73 Å Mo KR radiation. ^bR1 ) ∑||F_o| - |F_c||/∑|F_o|.

^cwR2 ) [(∑w(|F_o| - |F_c|)²/∑wF_o)]^1/2

.

2

Table 2. Selected Bond Lengths (Å) and Angles (deg) for

[t-BuC₆H₄N₃N]Mo-NdN-Mo[t-BuC₆H₄N₃N] (1c) and

Na(THF)₆{[PhN₃N]Mo-NdN[Na(THF)₃]NdN-Mo[PhN₃N]} (2a)

1c

2a

N(5)-N(5A)

Mo-N(5)

Mo-N(1)

Mo-N(2)

Mo-N(3)

Mo-N(4)

N(5)-Mo-N(4)

N(1)-Mo-N(2)

N(2)-Mo-N(3)

N(1)-Mo-N(3)

C(1)-N(1)-Mo

1.186(7)

1.930(4)

1.996(4)

2.014(4)

2.015(4)

-2.253(4)

178.40(16)

115.98(17)

117.75(17)

116.00(18)

130.2(3)

N(1)-N(2)

Mo-N(1)

Mo-N(3)

Mo-N(4)

Na-N(2)

Na-O(2)

1.195(13)

1.862(13)

2.034(5)

2.209(9)

2.160(14)

2.532(13)

N(1)-Mo-N(4) 180.0

N(3)-Mo-N(4) 80.77(16)

N(2)-Na-O(2)

N(2)-N(1)-Mo 180.0

N(1)-N(2)-Na 180.0

C(1)-N(3)-Mo 130.4(5)

90.000(4)

Figure 1. Two views of the structure of [t-BuC₆H₄N₃N]Mo-NdN-

Mo[t-BuC₆H₄N₃N] (1c).

C(13)-N(2)-Mo 131.0(3)

C(25)-N(3)-Mo 131.5(3)

N(5A)-N(5)-Mo 178.9(5)

state structure is preserved in benzene. Proton NMR spectra of

2c and 2d in C₆D₆revealed the presence of one molecule of

THF per [RN₃N]^3-ligand. Attempts to grow crystals of the pink

solids from mixtures of toluene and pentane resulted only in

the formation of red oils.

with respect to each other, a consequence of the steric demand

of each [t-BuC₆H₄N₃N]Mo unit.

Anionic Molybdenum Diazenido Complexes. Reduction of

[ArN₃N]MoCl complexes with 2 equiv of sodium naphthalenide

under dinitrogen produces diamagnetic anionic diazenido com-

plexes (2a-d) in yields ranging from 42 to 54% (Scheme 1).

The choice of reducing agent is very important for this reaction;

in our hands sodium naphthalenide is the only reducing agent

that leads to yields greater than 20%. Unlike reductions that

employ Na/Hg or Mg (vide infra), there is no evidence of any

1 present in the reaction mixture, and the reaction is very rapid,

even at -40 °C. Exactly 2 equiv of sodium naphthalenide should

be employed in order to obtain the highest yield, since some

decomposition occurs in the presence of any excess.

The IR spectra of 2a-d in THF contain NdN stretching

absorptions in the region 1813-1818 cm^-1(Table 6). Since

these frequencies approximately match those of the structurally

characterized monomeric 15-crown-5 derivative 3c (vide infra),

we believe that 2a-d are monomers of the form [ArN₃N]Mo-

NdN-Na(THF)_xin THF. THF solutions of pure 2a-d are

purple. If THF is removed and the residue is washed with ether

(or toluene for 2b), pink solids can be isolated. The solid-state

IR spectra of these pink solids contain NdN absorptions in the

region from 1741 to 1752 cm^-1. The NdN absorption of 2c is

found at 1745 cm^-1in benzene, which suggests that the solid-

Single crystals of 2a could be grown from THF. Crystal-

lographic data, collection parameters, and refinement parameters

are collected in Table 1, while selected bond lengths and angles

can be found in Table 2. As can be seen from the ORTEP

drawing in Figure 2, 2a is a monoanionic dimolybdenum species

in the solid state, with two {[t-BuC₆H₄N₃N]Mo-NdN}^-units

bound to a central sodium along with three molecules of THF.

The sodium counterion is surrounded by six molecules of THF.

One molecule of unbound THF is contained in the lattice. The

structure is highly symmetric with the crystallographically

imposed 3-fold axis coincident with the Mo-NdN-Na-Nd

N-Mo axis of the molecule. The presence of an inversion center

at sodium means that the two NdN and Mo-N bond lengths

are identical, at 1.195(13) and 1.862(13) Å, respectively. Other

bond distances and angles are similar to what has been seen in

other triamidoamine complexes of this general nature.^4,5,13

We presume that 2b-d, if they have been crystallized from

THF, all have structures in the solid state similar to that found

(13) O’Donoghue, M. B.; Zanetti, N. C.; Schrock, R. R.; Davis, W. M. J.

Am. Chem. Soc. 1997, 119, 2753.

3864 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

Scheme 2

Compound 2c was oxidized with Cp₂FeOTf and ZnCl₂in

the hope of obtaining a terminal dinitrogen complex, “[t-Bu-

C₆H₄N₃N]Mo(N₂)”. However, in both cases, 1c was the only

product, with no sign of [t-BuC₆H₄N₃N]Mo(N₂) by IR or NMR.

We propose that [t-BuC₆H₄N₃N]Mo(N₂) is the initial product

of oxidation and that it begins to lose dinitrogen to yield

[t-BuC₆H₄N₃N]Mo. A reaction between [t-BuC₆H₄N₃N]Mo and

[t-BuC₆H₄N₃N]Mo(N₂) could then lead to 1c directly, even

though each is present in only a low concentration. Alternatively

[t-BuC₆H₄N₃N]Mo could react with some source of {[t-BuC₆-

H₄N₃N]Mo-NdN}^-(e.g., 2c) to yield {[t-BuC₆H₄N₃N]Mo-

NdN-Mo[t-BuC₆H₄N₃N]}^-, which could be oxidized readily

to yield 1c. In a later section we present electrochemical studies

of compounds of types 1 and 2 that (inter alia) include the

formation of {[t-BuC₆H₄N₃N]Mo-NdN-Mo[t-BuC₆H₄N₃N]}^-

and its fate. The main message at this point is that steric factors

do not prevent formation of 1c, so species of this general type

form rapidly, perhaps by multiple pathways and are kinetic

“sinks” that cannot be reduced readily to compounds of type 2.

Addition of 1 equiv of 15-crown-5 to 2c or 2d results in

conversion to compounds of the type [ArN₃N]Mo-NdN-Na-

(15-crown-5) (3c and 3d) (Scheme 2). The ¹H NMR resonance

for the crown ether occurs at δ 3.04 ppm in 2c and at δ 2.91

ppm in 2d, and it integrates to 20 protons. If an excess of crown

ether is present, the crown ether resonance is broadened and

shifted closer to the position of the resonance for free 15-

crown-5 at δ 3.50 ppm, behavior which suggests that crown

ether exchange is facile. The NdN stretching absorptions can

be observed at 1815 cm^-1in the IR spectra of both 3c and 3d,

and they do not change significantly when the spectra are

recorded in THF. Therefore, the solid state and solution

structures are likely to be the same. IR spectra do not change

when crown ether is added, which suggests that a compound in

which the sodium is removed from the â-nitrogen and ligated

by two molecules of the crown ether¹⁷is not formed in this

system, or at least it is not an observable, stable entity.

Figure 2. ORTEP drawing of the anion in Na(THF)₆{[PhN₃N]Mo-

NdN}₂Na(THF)₃(2a).

for 2a, based on similar solubility properties and IR spectra.

1

Since H NMR spectra of vacuum-dried powders indicate that

only one THF is present per Mo, most of the THF in the crystal

must be relatively labile. Indeed, if the single crystals of 2a

that were employed for the X-ray study are exposed to pentane,

they immediately disintegrate to give a powder.

Reduction of [t-BuC₆H₄N₃N]MoCl with 2 equiv of sodium

naphthalenide under ¹⁵N₂produced Na{[t-BuC₆H₄N₃N]Mo-

¹⁵Nd¹⁵N}₂Na(THF)₂(2c-¹⁵N). The N-N stretch in the IR

spectrum of 2c-¹⁵N was found at 1688 cm^-1in the solid state

and 1755 cm^-1in THF solution, which correspond to shifts of

53 and 60 cm^-1, respectively, compared to 2c. The ¹⁵N NMR¹⁴

spectrum of 2c-¹⁵N consists of two doublets at 374.44 and

336.07 ppm, which we assign to the R- and â-nitrogens,

respectively. The one-bond N-N coupling constant is 10 Hz.

The ¹⁵N chemical shifts and coupling constants of all compounds

reported in this paper are consistent with those of the analogous

compounds containing the [(TMS)N₃N]^3-ligand⁴and related

complexes in the literature.^14-16

An X-ray diffraction study of 3c was carried out on crystals

that had been grown from a mixture of THF and pentane at

(14) Mason, J. Chem. ReV. 1981, 81, 205.

(15) Donovan-Mtunzi, S.; Richards, R. L.; Mason, J. J. Chem. Soc., Dalton

Trans. 1984, 1329.

(16) Haymore, B. L.; Hughes, M.; Mason, J.; Richards, R. L. J. Chem.

Soc., Dalton. Trans. 1988, 2935.

(17) 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.

Mo and W Complexes with Triamidoamine Ligands

Inorganic Chemistry, Vol. 40, No. 16, 2001 3865

Table 3. Crystallographic Data, Collection Parameters, and

Refinement Parameters for

for a diazenido complex. For comparison, two related sodium

diazenido complexes prepared by Cummins and co-workers

have N-N bond lengths of 1.17 and 1.15 Å.¹⁷The bent

geometry at the â-nitrogen can be ascribed in part to crystal

packing. Examination of the packing diagram (not shown)

reveals that the crown ether fits between two of the ligand arms

of an adjacent molecule, an arrangement that is best achieved

if the bond angle at N(6) is not 180°.

[t-BuC₆H₄N₃N]Mo-NdN-Na(15-crown-5) (3c) and

{[Ph₂C₆H₃N₃N]Mo-NdN}₂Mg(DME)₂(4f)^a

3c

4f

empirical formula

fw

space group

a (Å)

b (Å)

c (Å)

C₄₆H₇₁MoN₆NaO₅

907.02

P4₃

17.1059(7)

16.8153(10)

90

4920.4(4)

4

C₁₅₀H₁₃₂MgMo₂N₁₂O₆

2414.87

P2₁/c

25.316(4)

16.114(2)

33.761(5)

99.927(3)°

13567(4)

4

Various [ArN₃N]MoCl complexes were reduced with mag-

nesium under dinitrogen in an effort to obtain a Mg diazenido

complex {[ArN₃N]Mo-NdN}₂Mg(L)_x(4) analogous to that

obtained in the [Me₃SiN₃N]^3-system.^4,13In all cases described

thus far (Ar ) C₆H₅, 4-FC₆H₄, 4-t-BuC₆H₄, and 3,5-Me₂C₆H₃)

reduction of the [ArN₃N]MoCl complexes yields a mixture of

1 and 4. Since 1c (Ar ) 4-t-BuC₆H₄) is soluble in C₆D₆, it was

possible to determine the ratio of 1c to 4c by ¹H NMR.

Reduction of [t-BuC₆H₄N₃N]MoCl with 3 equiv of magnesium

powder under dinitrogen yields a mixture of 1c and two

diamagnetic compounds after 16 h, one of which is 4c. Addition

of 2 equiv of 1,4-dioxane resulted in conversion of the unknown

compound to 4c. This result suggests, by analogy with what

was observed for complexes containing the [Me₃SiN₃N]^3-

ligand,^4,13that one of the compounds is {[t-BuC₆H₄N₃N]Mo-

NdN}MgCl(THF)_x, while the other is {[t-BuC₆H₄N₃N]Mo-

NdN}₂Mg(THF)_y. Examination of the crude reaction mixture

â (deg)

V (Å³)

Z

temp (K)

R1 [I > 2σ(I)]

wR2 [I > 2σ(I)]

R1 (all data)

wR2 (all data)

183(2)

0.0398

0.0807

0.0602

183(2)

0.0981

0.2167

0.1602

0.0858

0.2489

^aAll structures were solved on a Bruker SMART/CCD diffractom-

eter using 0.710 73 Å Mo KR radiation. ^bR1 ) ∑||F_o| - |F_c||/∑|F_o|.

^cwR2 ) [(∑w(|F_o| - |F_c|)²/∑wF_o)]^1/2

.

2

Table 4. Selected Bond Lengths (Å) and Angles (deg) for

[t-BuC₆H₄N₃N]Mo-NdN-Na(15-crown-5) (3c)

Bond Lengths (Å)

N(5)-N(6)

Mo-N(5)

Mo-N(1)

Mo-N(2)

1.161(5)

1.898(5)

2.008(4)

2.063(4)

Mo-N(3)

Mo-N(4)

Na-N(6)

2.033(4)

2.219(4)

2.362(5)

1

by H NMR at this point indicated a 2:1 ratio of 4c to 1c. We

found it difficult to separate 4c and 1c, since their solubilities

are similar in common solvents. It was possible to obtain a

mixture enriched in 4c by adding ether to a concentrated toluene

solution of the mixture, which results in the selective precipita-

tion of 1c. However, even after two iterations of this process,

the material obtained was only 90% pure 4c. Therefore it would

appear that sodium is the reducing agent of choice for the

preparation of anionic diazenido complexes containing the

relatively “small” [ArN₃N]^3-ligands.

Bond Angles (deg)

N(5)-Mo-N(4)

N(1)-Mo-N(2)

N(2)-Mo-N(3)

N(1)-Mo-N(3)

C(1)-N(1)-Mo

177.20(18)

120.97(17)

117.77(16)

113.12(18)

129.3(4)

C(13)-N(2)-Mo

C(25)-N(3)-Mo

N(6)-N(5)-Mo

N(5)-N(6)-Na(1)

130.8(3)

126.3(3)

178.2(5)

163.1(4)

Dihedral Angles (deg)

N(4)-Mo-N(1)-C(1) 177.2(5) N(4)-Mo-N(3)-C(25) 156.0(4)

N(4)-Mo-N(2)-C(13) 161.3(4)

When [ArN₃N]MoCl complexes containing the larger

[Ph₂C₆H₃N₃N]^3-([TerN₃N]^3-) or [(4-t-BuC₆H₄)₂C₆H₃N₃N]^3-

([t-BuTerN₃N]^3-) ligands are reduced under dinitrogen, one

compound can be isolated when Mg is used as the reducing

agent (Scheme 3). Stirring a suspension of [TerN₃N]MoCl and

Mg powder in THF overnight yielded a soluble anionic

diazenido complex of the form {[TerN₃N]Mo-NdN}₂Mg-

(THF)_x(4f-THF) in 87% yield. This material is not highly

crystalline, and it is not known how many molecules of THF

are coordinated to magnesium, but on the basis of the structure

of the DME adduct discussed below, we assume that x ) 4.

Complex 4f-THF is soluble in THF and benzene and is red in

1

solution. H and ¹³C NMR spectra differ from those of other

anionic diazenido complexes only by the additional resonances

due to the [TerN₃N]^3-ligand. The N-N stretch in the IR

spectrum is centered at 1775 cm^-1in the solid state, and at

1789 cm^-1in THF solution, but both peaks are broad. Therefore,

we assume that the solid-state and solution values are identical

within experimental error. This observation contrasts with the

large difference in the position of the N-N stretch between

the solid state and solution for compounds of type 2. Apparently

a dimeric complex with Mg²⁺at the center is the only readily

accessible form when the [TerN₃N]^3-ligand is present.

Figure 3. ORTEP drawing of the structure of [t-BuC₆H₄N₃N]Mo-

NdN-Na(15-crown-5) (3c).

-35 °C. Crystallographic data, collection parameters, and

refinement parameters are collected in Table 3, while selected

bond lengths and angles can be found in Table 4. Figure 3

contains an ORTEP drawing of the structure, with thermal

ellipsoids at the 35% probability level. One molecule of crown

ether is bound to the sodium, and the sodium atom is bound to

the â-nitrogen with a Na-N(6) bond length (2.362(5) Å) that

is significantly longer than the Na-N(2) distance found in 2a

(2.160(14) Å). The NdN bond length is 1.16 Å, as expected

When [t-BuTerN₃N]MoCl is stirred with an excess of

magnesium powder under dinitrogen, {[t-BuTerN₃N]Mo-

NdN}₂Mg(THF)_x(4g-THF) is formed in good yield. Complex

4g-THF is highly soluble in most organic solvents and mod-

erately soluble in pentane. The N-N stretch can be found at

1782 cm^-1in the solid-state IR spectrum and at 1805 cm^-1in

3866 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

Scheme 3

THF solution. Once again, both peaks are broad, so differences

between the solid state and solution probably are not significant.

When 4f-THF and 4g-THF are dissolved in DME, the color

of the solutions darken as they are converted into {[ArN₃N]Mo-

NdN}₂Mg(DME)₂(4f-DME, 4g-DME) species. The solubility

of 4f-DME in organic solvents is low; it crystallizes out of DME

as it is formed. It can be dissolved in THF to give a red solution,

but partial reversion to the THF adduct takes place. If the cycle

of dissolving 4f-DME or 4g-DME in THF and removing THF

in vacuo is repeated three times, the THF adduct is the only

species present. Compound 4g-DME was soluble enough in

for 4f-DME is found at 1785 cm^-1in the solid state and at

1789 cm^-1in THF solution, which suggests that major structural

changes are not taking place upon replacement of THF by DME.

A crystal of 4f-DME suitable for an X-ray diffraction study

was grown by allowing a warm, dilute solution of 4f-DME in

dimethoxyethane to cool to room temperature. Crystallographic

data, collection parameters, and refinement parameters are

collected in Table 3, while selected bond lengths and angles

can be found in Table 5. Figure 4 contains an ORTEP drawing

of the structure, with thermal ellipsoids at the 35% probability

level. The Mg atom is six-coordinate, with two diazenido ligands

occupying axial sites and two DME ligands occupying equatorial

sites. The Mo-NdN-Mg-NdN-Mo axis of the molecule is

1

C₆D₆to obtain a H NMR spectrum, which indicated that one

molecule of DME was present per ligand. The N-N stretch

Table 5. Selected Bond Lengths (Å) and Angles (deg) for {[Ph₂C₆H₃N₃N]Mo-NdN}₂Mg(DME)₂(4f-DME)

Bond Lengths (Å)

N(5)-N(6)

Mo-N(5)

Mo-N(1)

Mo-N(2)

Mo-N(3)

Mo-N(4)

Mg-N(6)

1.166(12)

1.884(12)

1.999(9)

2.007(11)

2.011(10)

2.221(9)

N(7)-N(8)

1.173(12)

1.879(12)

2.004(10)

2.006(10)

2.020(10)

2.227(9)

Mo(2)-N(8)

Mo(2)-N(9)

Mo(2)-N(11)

Mo(2)-N(10)

Mo(2)-N(12)

Mg-N(7)

2.120(12)

2.136(12)

Bond Angles (deg)

N(4)-Mo-N(5)

Mo-N(5)-N(6)

N(5)-N(6)-Mg

N(6)-Mg-N(7)

Mg-N(7)-N(8)

N(7)-N(8)-Mo(2)

N(8)-Mo(2)-N(12)

N(5)-Mo-N(1)

N(5)-Mo-N(2)

N(5)-Mo-N(3)

N(1)-Mo-N(2)

N(1)-Mo-N(3)

N(2)-Mo-N(3)

N(1)-Mo-N(4)

N(2)-Mo-N(4)

N(3)-Mo-N(4)

173.0(4)

172.0(10)

160.3(10)

174.8(5)

160.3(10)

172.5(10)

174.4(4)

99.0(4)

N(8)-Mo(2)-N(9)

N(8)-Mo(2)-N(10)

N(8)-Mo(2)-N(11)

N(9)-Mo(2)-N(10)

N(9)-Mo(2)-N(11)

N(10)-Mo(2)-N(11)

N(9)-Mo(2)-N(12)

N(10)-Mo(2)-N(12)

N(11)-Mo(2)-N(12)

C(1)-N(1)-Mo

98.6(4)

96.0(4)

103.8(4)

123.7(4)

117.7(4)

110.7(4)

80.3(4)

81.4(4)

95.1(4)

105.1(4)

122.0(4)

117.8(4)

111.9(4)

79.4(4)

80.2(4)

81.6(4)

129.2(8)

129.1(8)

131.6(8)

130.5(8)

129.8(9)

129.1(8)

C(21)-N(2)-Mo

C(41)-N(3)-Mo

C(61)-N(9)-Mo(2)

C(81)-N(10)-Mo(2)

C(101)-N(11)-Mo(2)

Dihedral Angles (deg)

N(4)-Mo-N(1)-C(1)

N(4)-Mo-N(2)-C(21)

N(4)-Mo-N(3)-C(41)

175.6(12)

155.4(11)

171.6(11)

N(12)-Mo(2)-N(9)-C(61)

N(12)-Mo(2)-N(10)-C(81)

N(12)-Mo(2)-N(11)-C(101)

177.8(13)

156.5(11)

166.2(11)

Mo and W Complexes with Triamidoamine Ligands

Inorganic Chemistry, Vol. 40, No. 16, 2001 3867

spectrum at 1679 cm^-1in the solid state (vs 1738 cm^-1for 5c)

and at 1615 cm^-1in THF (vs 1651 cm^-1for 5c). The ¹⁵N NMR

spectrum of labeled 5c consists of two doublets at 374.39 and

220.72 ppm (with J_NN) 13) for the R- and â-nitrogens,

respectively, consistent with the diazenido ligand being linear

at the R-nitrogen.¹⁶In the ¹³C NMR spectrum of 5c-¹⁵N the

trimethylsilyl carbon resonance is split into a doublet by a two-

bond ¹⁵N-¹³C coupling with a coupling constant of 3.4 Hz.

Addition of exactly 1 equiv of MeOTs to 2 or 4 produces

neutral methyl diazenido complexes [ArN₃N]Mo-NdN-Me

(6) in yields ranging from 37 to 69% (Schemes 2 and 3). Unlike

the reaction with Me₃SiCl, the reaction with MeOTs requires

several hours to go to completion. If too much MeOTs is added,

a mixture of 6 and {[ArN₃N]ModN-NMe₂}OTs (7) results,

and it is difficult to separate the two compounds. When the

proper stoichiometry is maintained, the primary byproduct in

the synthesis of 6 is 1, formed by oxidation of 2. However, 1

is considerably less soluble than 6, so it can be removed by

filtration. Compounds 6a-f represent the first examples of

methyl diazenido complexes that contain triamidoamine ligands,

but a similar Mo complex containing three N(R)Ar ligands has

been reported.¹⁷Like compounds 5, 6a-f are also yellow, C₃-

symmetric, diamagnetic compounds, with unremarkable ¹H

NMR spectra. It is interesting to note that the NdN stretching

frequencies in the IR spectra of compounds 6, which do not

differ greatly between the solid-state and THF solution, are

lower than those of any other compound. However, it is likely

that the observed IR stretch is not a pure NdN stretch; i.e., it

may also contain the Mo-N and N-C modes. For this reason

it would not be appropriate to attempt to correlate the frequency

of the “N-N stretch” with the degree of N-N bond reduction

without additional detailed knowledge.

Figure 4. ORTEP drawing of the structure of {[Ph₂C₆H₃N₃N]MoNN}₂-

Mg(DME)₂(4f-DME).

bent slightly at each nitrogen atom. The deviation from linearity

is most pronounced at N(6) and N(7), where the N(5)-N(6)-

Mg and Mg-N(7)-N(8) bond angles are both 160°. The

geometry at magnesium is essentially linear (174.8(5)°), which

contrasts sharply with the 135° N-Mg-N angle in {[N₃N]-

(TMS)Mo-NdN}₂Mg(THF)₂, in which the Mg atom is four-

coordinate and in which the bond angles at the â-nitrogens are

178 and 166°.^4,13Most of the metrical parameters are similar

in the two halves of 4f-DME. The two N-N bond lengths are

statistically identical at 1.17 Å, which is essentially the same

bond length as found in 3c (1.16 Å) and 2a (1.19 Å) and other

published molybdenum diazenido complexes containing amido

ligands.^2,3,13,17

Attempts to isolate a terminal dinitrogen complex by reducing

[TerN₃N]MoCl with 1 equiv of sodium naphthalenide were

unsuccessful. This observation contrasts with the behavior of

complexes containing the [Me₃SiN₃N]^3-ligand.⁴Later in this

paper we will confirm through electrochemical studies that

terminal dinitrogen complexes are not stable for the majority

of triamidoamine Mo complexes that contain aryl-substituted

ligands.

Neutral Molybdenum Diazenido Complexes. Addition of

Me₃SiCl to 2 or 4 in THF leads to neutral trimethylsilyl

diazenido complexes [ArN₃N]Mo-NdN-SiMe₃(5) in yields

ranging from 73 to 86% (Schemes 2 and 3). Diazenido

complexes 5 also can be formed in one pot from [ArN₃N]MoCl

by reduction under dinitrogen with sodium naphthalenide or

magnesium, depending on the ligand, followed by reaction with

Me₃SiCl (eq 1). However, for most ligands 2 is easier to purify

than 5, the conversion of 2 to 5 is trivial, and 2 is a more

versatile compound since it can be treated with other electro-

philes. Complex 5e was prepared from [C₆F₅N₃N]Mo(OTf)

using the literature procedure for closely related [C₆F₅N₃N]Mo-

NdNSi(i-Pr)₃.

¹⁵N-labeled 6c (Ar ) 4-t-BuC₆H₄) was prepared by treating

2c-¹⁵N with MeOTs. The N-N stretch in the IR spectrum shifts

from 1585 to 1542 cm^-1in the solid state upon labeling. The

¹⁵N NMR spectrum consists of two doublets at 407.02 and

231.94 ppm (J_NN) 16 Hz) for the R- and â-nitrogens,

respectively. The N-methyl resonance in the ¹³C NMR spectrum

of 6c-¹⁵N is a doublet of doublets by virtue of coupling between

¹³C and both labeled nitrogens. The one-bond coupling constant

to the â-nitrogen is 8.8 Hz, while the two-bond coupling constant

to the R-nitrogen is 4.5 Hz. The resonance for the protons on

the methyl group bound to the â-nitrogen is also a doublet of

1

doublets, with a two-bond H-¹⁵N(â) coupling constant of 3

1

Hz, and a three-bond H-¹⁵N(R) coupling constant of 0.6 Hz.

Molybdenum Hydrazido and Nitride Complexes. Alkyla-

tion of neutral diazenido complexes 5 and 6 produces cationic

hydrazido complexes in high yield (Scheme 4). The product

that is obtained depends strongly on the starting material and

the reaction conditions. The simplest case involves complexes

that contain the 4-tert-butylphenyl ligand. Reaction of 5c with

2 equiv of methyl triflate in toluene produces the dimethyl

hydrazido complex {[t-BuC₆H₄N₃N]ModN-NMe₂}⁺OTf^-(8c)

in 62% yield. Complex 8c does not react further with methyl

triflate, so an excess of methyl triflate is employed in order to

ensure complete reaction. Complex 8c is soluble in benzene

and toluene, but insoluble in ether. Therefore, it can be isolated

Compounds 5 are all yellow, C₃-symmetric, diamagnetic

1

solids, with H and ¹³C NMR spectra that are typical of such

species. The peaks in the IR spectra that correspond to N-N

stretches are very broad, and there is sometimes a significant

difference between the position of the peak in the solid state

and in THF solution (e.g., 87 cm^-1for 5c, Table 6). Compound

5c that has been labeled with ¹⁵N has its N-N stretch in the IR

3868 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

Table 6. N-N Stretching Frequency in the IR Spectra of Diazenido Complexes

compd

ν(N-N) (Nujol)

ν(N-N) (THF)

ref

3

[Me₃SiN₃N]MoNtN

1910, 1900

1848

1934 (pentane)

[C₆F₅N₃N]MoNdN-Na(15-crown-5)

[Me₂C₆H₃N₃N]Mo-NdN-Na(15-crown-5) (3d)

[t-BuC₆H₄N₃N]Mo-NdN-Na(15-crown-5) (3b)

[Me₃SiN₃N]MoNdN-Na(15-crown-5)

[(N[R]Ar)₃Mo-NdN][Na(12-crown-4)₂]

{[TerN₃N]MoNN}₂Mg(THF)_x(4f-THF)

{[TerN₃N]MoNN}₂Mg(DME)₂(4f-DME)

{[t-BuTerN₃N]MoNN}₂Mg(THF)_x(4g-THF)

{[t-BuTerN₃N]MoNN}₂Mg(DME)₂(4g-DME)

{[t-BuC₆H₄N₃N]MoNN}₂Mg(THF)_x(4c)

{[Me₃SiN₃N]MoNdN}₂Mg(THF)₂

Na{[FC₆H₄N₃N]MoNN}₂Na(THF)₂(2b)

Na{[PhN₃N]MoNN}₂Na(THF)₂(2a)

Na{[Me₂C₆H₃N₃N]MoNN}₂Na(THF)₂(2d)

Na{[t-BuC₆H₄N₃N]MoNN}₂Na(THF)₂(2c)

Na{[t-BuC₆H₄N₃N]Mo¹⁵N¹⁵N}₂Na(THF)₂(2c-¹⁵N)

[Na][(NdN)Mo(N[R]Ar)₃]

1815

1791

1832

1815

25

17

1761

1789

1805

1775

1785

1782

1787

1758

1719

1813

1818

1816

1815

1755

1761

1651

1657

1714

1615

1657

4

1752

1750

1742

1741

1688

17

4

[t-BuC₆H₄N₃N]Mo-NdN-SiMe₃(5c)

[Me₂C₆H₃N₃N]Mo-NdN-SiMe₃(5d)

[Me₃SiN₃N]Mo-NdN-SiMe₃

1738

1722

1712

1679

1674

1672

1646

1643

1642

[t-BuC₆H₄N₃N]Mo-¹⁵Nd¹⁵N-SiMe₃(5c-¹⁵N)

[FC₆H₄N₃N]MoNdN-SiMe₃(5b)

[C₆F₅N₃N]Mo-NdN-SiMe₃(5e)

[TerN₃N]Mo-NdN-SiMe₃(5f)

1645

1663

1648

1650

1602

1601

1596

1579

1582

[PhN₃N]Mo-NdN-SiMe₃(5a)

[t-BuTerN₃N]Mo-NdN-SiMe₃(5g)

(N[R]Ar)₃Mo-NdN-SiMe₃

17

[Me₂C₆H₃N₃N]Mo-NdN-Me (6d)

[PhN₃N]Mo-NdN-Me (6a)

1603

1598

1596

1585

1581

1542

[TerN₃N]Mo-NdN-Me (6f)

[t-BuC₆H₄N₃N]Mo-NdN-Me (6c)

[FC₆H₄N₃N]Mo-NdN-Me (6b)

[t-BuC₆H₄N₃N]Mo-¹⁵Nd¹⁵N-Me (6c-¹⁵N)

(N[R]Ar)₃Mo-NdNMe

1538

by removing toluene and washing the crude residue with ether,

or by growing crystals from a mixture of THF and pentane.

As was discussed briefly in the context of the synthesis of

compounds 6, treatment of 6c with 1 equiv of methyl tosylate,

which is a milder electrophile than methyl triflate, produces {[t-

BuC₆H₄N₃N]ModN-NMe₂}⁺OTs^-(7c) in 64% yield (Scheme

4). Complex 7c is much more soluble in organic solvents than

complex 8c (triflate counterion), and even though it is cationic,

it is soluble in ether, whereas neutral 6c is not. Complex 7c

was isolated by crystallization from a concentrated ether

solution. The ¹H NMR spectrum of 7c is consistent with it being

a cationic species in that the ligand backbone resonances are

shifted downfield relative to neutral complexes.

Treatment of 6c with 1 equiv of methyl triflate also produces

8c in 95% yield. ¹⁵N labeled 8c was also prepared by this

method from 6c-¹⁵N. The two-step yield of 8c from 2c is

virtually identical whether 5c or 6c is an intermediate. If 5c is

the intermediate, a high-yielding first step is followed by a

moderate yield for the second step. If 6c is employed as the

intermediate, the opposite is true. The clean preparation of 8c

in high yield stands in sharp contrast with syntheses of

[Me₃SiN₃N]^3-complexes, where the yield is only ∼20% after

fractional crystallization, and compounds in which one of the

trimethylsilyl groups on the ligand has been replaced by a methyl

group are also formed.⁴

Reaction of 5e (Ar ) C₆F₅) with 3 equiv of methyl triflate

in toluene produces 8e (Scheme 4). Higher temperatures and

longer reaction times are needed for the synthesis of 8e, in part

because the electron-withdrawing C₆F₅groups on the [RN₃N]^3-

ligand render the â-nitrogen of 5e less nucleophilic than that

of 5c. A 96% yield is obtained after overnight reaction at 50

°C in a pressure tube. Compound 8e precipitates out of toluene,

so it can be isolated simply by filtering the reaction mixture.

Complex 8e is insoluble in ether and sparingly soluble in THF.

As with 8c, no degradation of the ligand occurs, the ligand

All cationic hydrazido complexes reported here are diamag-

netic species that are soluble and stable in CDCl₃. Therefore,

¹H NMR spectra of 8c were recorded both in CDCl₃and in

C₆D₆. The chemical shifts for all aryl protons are accidentally

coincident in C₆D₆, so only a singlet integrating as 12 protons

is observed. However, in CDCl₃the normal pattern of two

doublets is observed for the aryl protons. In both solvents, the

backbone proton resonances of the ligand are shifted downfield

relative to where they are found in related neutral complexes.

The ¹⁵N NMR spectrum of 8c-¹⁵N consists of two doublets at

368.27 and 154.40 ppm (J_NN) 11 Hz) for the R- and

â-nitrogens, respectively. The N-methyl resonance in the ¹³C

1

backbone resonances are shifted downfield in the H NMR

spectrum, and no N-N stretch can be found in the IR spectrum.

No reaction is observed when 5c is treated with an excess of

methyl tosylate under similar conditions.

Treatment of 5b (Ar ) 4-FC₆H₄) with an excess of methyl

triflate in toluene results in the immediate precipitation of an

orange powder. On the basis of the solubility properties of 8e,

it was assumed that the orange powder was 8b. However,

1

NMR spectrum of 8c-¹⁵N is a doublet with J(¹³C,¹⁵N) ) 9.2

Hz. Two-bond coupling to ¹⁵N was not observed in either ¹³C

or ¹H NMR spectra of 8c-¹⁵N. No peak that can be assigned to

an N-N stretch is readily apparent in the IR spectrum of 8c,

since the spectra of 8c and 8c-¹⁵N are essentially identical.

1

examination of the H NMR spectrum (recorded in CDCl₃),

reveals that the orange powder is actually [FC₆H₄N₃N]Mod

Mo and W Complexes with Triamidoamine Ligands

Inorganic Chemistry, Vol. 40, No. 16, 2001 3869

Scheme 4

N-N(Me)(SiMe₃) (9b) (Scheme 4). The isolated yield of 9b is

99%. If a solution of 9b in dichloromethane is allowed to stir

overnight with an excess of methyl triflate, it is converted into

8b. However this reaction is not clean, and 8b is isolated in

only 42% yield after removing CH₂Cl₂and washing away the

more soluble byproducts with THF.

The formation of 9b and its conversion into 8b suggest that

the first step in formation of 8 from 5 in general is electrophilic

attack of methyl triflate on the â-nitrogen of 5 to produce 9.

Since 9b precipitates from solution, alkylation does not proceed

further. However, when 9 remains in solution, a second

equivalent of methyl triflate reacts with 9 to yield 8. The

mechanistic details of this second step are not clear. Compound

8b can be produced cleanly in 81% yield from 6b under the

same reaction conditions used to convert 6c into 8c.

peak in the ¹³C NMR spectrum is at 38.62 ppm, which is the

chemical shift for the methyl carbon in a sample of dimethyl-

amine in THF obtained independently. Our hypothesis is that

the first step in the conversion of 8 to 10 is the reduction of 8

to a neutral Mo(V) dimethyl hydrazido complex. As we will

show later, the Mo(V) dimethylhydrazido species is stable on

the CV time scale (500 mV/s), but we do not know about its

longer term stability. The Mo(V) dimethylhydrazido species also

can be reduced to give an unstable anion. If the Mo(V)

dimethylhydrazido species ultimately decomposes via homolytic

N-N bond cleavage, it would yield 10 and a dimethylamine

radical. In solvents such as THF or toluene, which are good

hydrogen atom donors relative to C₆D₆, the dimethylamine

radical would abstract a hydrogen atom from the solvent to give

dimethylamine. However, the dimethylamine radical is also

likely to react in other more destructive ways, thereby leading

to a large number of byproducts. It is also possible that 10 forms

in a more complex manner after the Mo(V) dimethylhydrazido

species is reduced further.

Chemical reduction of 9b with sodium amalgam in THF

produced 6b in 42% yield (Scheme 5), along with about 10%

unidentified paramagnetic material (by ¹⁹F NMR). As in the

reduction of 8, an unstable Mo(V) intermediate is postulated.

However, in this case, the weakest bond is the Si-N bond, so

the Mo(V) intermediate decomposes by Si-N bond cleavage

to give the methyl diazenido complex. Si-N bond cleavage is

a common, undesired side reaction for compounds containing

the [Me₃SiN₃N]^3-ligand.^4,6,8

Reduction of 8b, 8c, or 8e with 1 equiv of sodium amalgam

in THF produces a mixture of products, but [ArN₃N]MotN

(10) is the major metal-containing product (Scheme 5). How-

ever, the NMR yield of 10b is only 28% (by integration against

the triflate resonance). The large number of peaks in the crude

NMR spectra of these reductions is consistent with extensive

decomposition. Nitride 10e is a known compound.³Nitrides 10b

and 10c also were prepared by treating [ArN₃N]MoCl with NaN₃

(Scheme 5). The yield of 10b is 57%, and 10c is obtained in

58% yield after 2 days. Both compounds are yellow solids which

are soluble in THF and toluene, but insoluble in ether and

pentane. Dark red byproducts can be washed away with ether,

and the nitrides can be recrystallized from a mixture of toluene

and pentane.

Alkylation of 8c or 8e with methylmagnesium bromide (3.0

M in ether) at -40 °C immediately yields the neutral trimeth-

ylhydrazido complexes, [ArN₃N]Mo(Me)(NNMe₂) (11) (Scheme

5). Conversion of 8e to 11e proceeds rapidly in ether even

A ¹³C-labeled version of 8c was prepared by treating 6c with

¹³CH₃OTf. Reduction of 8c-¹³C with Na/Hg was carried out in

an NMR tube in THF and monitored by ¹³C NMR. The major

3870 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

Scheme 5

though 8e is insoluble in ether. Complex 11c is pentane soluble,

and midnight blue in solution, while complex 11e is burgundy

colored. Complex 11c was isolated in 86% yield by crystal-

lization from pentane at -40 °C, while complex 11e was

isolated in 79% yield by washing the crude residue with pentane

after filtering off Mg salts and removing ether in vacuo.

Precedent for the conversion of 8 to 11 exists for complexes

region of the spectrum suggests that one of the decomposition

pathways is abstraction of a hydrogen atom from the ligand

backbone and subsequent cleavage of a C-N bond, as was

observed for certain Ta complexes containing the [Me₃SiN₃N]^3-

ligand.^18,19

Two ¹³C-labeling labeling studies were carried out in an

attempt to gain more insight into the organic products of the

thermolysis of 11. One experiment involved ¹³C labeling the

methyl group bound to the metal. Compounds 11c-¹³C(M) and

11e-¹³C were prepared in the same manner as unlabeled material

using ¹³CH₃MgI. Thermolyses were performed in C₆D₆and

monitored by both ¹H and ¹³C NMR. Both spectra indicate that

nitride is the major product after decomposition is complete,

and the most intense peak in both ¹³C NMR spectra is that of

methane. A second resonance for a labeled methyl group can

be found at 22.7 ppm, but the identity of this product could not

be established. The absence of a peak at 48 ppm indicates that

trimethylamine is not one of the products.

1

containing the [Me₃SiN₃N]^3-ligand.⁴The H NMR spectrum

of 11c is characteristic of a C_s-symmetric complex. The

1

resonances at 0.60 ppm in the H NMR spectrum and 18 ppm

in the ¹³C NMR spectrum are assigned to the methyl group

bound to the metal. The ¹H and ¹⁹F NMR spectra of 11e (Ar )

C₆F₅) at elevated temperatures show evidence for a reversible

fluxional process (broadened resonances) that was not studied

further.

Both 11c and 11e decompose upon heating to give the

corresponding nitride as the major metal-containing product.

Heating 11e to 50 °C overnight is sufficient to promote its

complete decomposition, but 11c must be heated to 90 °C for

2 days before it is all consumed. Three separate decompositions

were carried out on 11e in sealed NMR tubes, two in toluene-

d₈and one in THF. In all three experiments, the color of the

solution changes from blood red to yellow-orange. In the THF

experiment and in one of the toluene experiments, two new

trigonally symmetric, diamagnetic products are formed in about

a 1:1 ratio. One of the products is nitride 10e, but the identity

of the other compound is unknown. The second toluene

decomposition reaction was carried out using analytically pure

11e; in this case nitride 10e was the only metal-containing

product that could be identified. We conclude that the ther-

molysis reaction is sensitive to the purity of the starting material

(inter alia). Nitride 10c is by far the major metal-containing

The other labeling experiment involved ¹³C labeling one of

the methyl groups bound to the â-nitrogen. Compound 11c-

¹³C(N) was prepared from 8c-¹³C by reaction with unlabeled

methylmagnesium bromide; a resonance for the labeled methyl

group could be observed at 43.34 ppm in the ¹³C NMR

spectrum. After decomposition of 11c-¹³C(N) was complete, 14

1

product in the decomposition of 11c in C₆D₆(by H NMR),

(18) Freundlich, J. S.; Schrock, R. R.; Davis, W. M. J. Am. Chem. Soc.

but a close examination of the tert-butyl region of the NMR

spectrum indicates that no fewer than nine other products are

present in small amounts. The presence of peaks in the vinylic

1996, 118, 3643.

(19) Freundlich, J. S.; Schrock, R. R.; Davis, W. M. Organometallics 1996,

15, 2777.

Mo and W Complexes with Triamidoamine Ligands

Inorganic Chemistry, Vol. 40, No. 16, 2001 3871

resonances were observed in the ¹³C NMR spectrum in the

region from 30 to 50 ppm. Dimethylamine is one of the

products, but it is by no means a major product, at least when

C₆D₆is the solvent.

Tungsten Dinitrogen Complexes. Simultaneous addition of

a solution of [t-BuC₆H₄N₃N]WCl and a solution of sodium

naphthalenide to a flask containing vigorously stirred THF

resulted in the formation of pink, paramagnetic [t-BuC₆H₄N₃-

N]W-NdN-W[t-BuC₆H₄N₃N] (12) in 61% yield (eq 2).

Elemental analysis, ¹H NMR spectroscopy, and cyclic voltam-

metry (see later) all support the proposed composition of this

species. Similar ditungsten bridging dinitrogen complexes appear

to be formed upon reduction of [ArN₃N]WCl complexes

containing the phenyl, 4-fluorophenyl, or 3,5-dimethylphenyl

ligands, but since they are insoluble in all organic solvents, they

could not be characterized. As with Mo compounds 1 (Scheme

1), no N-N stretch is expected in the IR spectrum of 12, and

none was observed. Recently Scheer has published the X-ray

structure of {[(Me₃CCH₂NCH₂CH₂)₃N]W}₂(µ-Ν₂), which pre-

sumably is an analogue of 12; it was isolated in low yield as a

byproduct during the synthesis of (Me₃CCH₂NCH₂CH₂)₃]WCl

from W(dme)Cl₄and Li₃[(Me₃CCH₂NCH₂CH₂)₃N].²⁰

Figure 5. CV of [C₆F₅N₃N]Mo-NdN-Mo[C₆F₅N₃N] (1e).

Figure 6. CV of [C₆F₅N₃N]Mo-NdN-Na(15-Crown-5) (2e).

The ¹H NMR spectra of 1c and 12 display many similarities.

Both spectra contain a relatively sharp resonance at 12.22 ppm

corresponding to the meta hydrogens on the aryl rings of the

ligand. However, due to the sharper resonances for paramagnetic

W complexes, it is possible to resolve a doublet with a coupling

constant of 8.4 Hz. Another doublet with the same coupling

constant can be found at 2.63 ppm which is assigned to the

ortho hydrogens on the aryl rings. The ligand backbone

resonances occur in a region of the spectrum similar to those

in 1c, and as with 1c, the upfield resonance is much broader

than the downfield one. A C₆D₆solution of 12 remained

unchanged upon heating to 90 °C for several days.

1

Electrochemical (CV) studies (see below) first established

that compound 12 could be oxidized readily by two electrons.

We found that it can be oxidized cleanly by Cp₂FeBPh₄in

dichloromethane to give {[t-BuC₆H₄N₃N]W-NdN-W[t-

BuC₆H₄N₃N]}(BPh₄)₂(13) in 85% yield (eq 3). Compound 13

is diamagnetic, as expected for a MNNM system that contains

diamagnetic material was observed in crude H NMR spectra.

Addition of Me₃SiCl to crude reaction mixtures did not produce

compounds analogous to 5.

Electrochemical Studies. In Figures 5 and 6 are shown CV

scans of 1e and 2e. During the initial reductive scan for

{[C₆F₅N₃N]Mo(N₂)}^-(2e), no cathodic waves are present out

to -2500 mV. On the anodic scan {[C₆F₅N₃N]Mo(N₂)}^-is

oxidized at -1357 mV. Only a small return wave is observed

for this oxidation because “[C₆F₅N₃N]Mo(N₂)” is unstable, we

propose toward loss of dinitrogen to yield “[C₆F₅N₃N]Mo”.

Apparently “[C₆F₅N₃N]Mo(N₂)” and “[C₆F₅N₃N]Mo” combine

under these conditions to yield 1e, since the anodic wave at

-439 mV and the irreversible cathodic wave at -1993 mV in

Figure 6 can also be found in the CV of 1e, as shown in Figure

5. Compound 1e (Figure 5) is reduced irreversibly at -1988

mV to what we presume is {[C₆F₅N₃N]Mo-NdN-Mo-

[C₆F₅N₃N]}^-. Apparently, however, {[C₆F₅N₃N]Mo-NdN-

Mo[C₆F₅N₃N]}^-decomposes to {[C₆F₅N₃N]Mo(N₂)}^-and

“[C₆F₅N₃N]Mo”, which at this potential and under dinitrogen

is reduced to a second equivalent of {[C₆F₅N₃N]Mo(N₂)}^-. The

anodic wave of low intensity that is observed at -1374 mV in

Figure 5 corresponds to the oxidation of {[C₆F₅N₃N]Mo(N₂)}^-

to “[C₆F₅N₃N]Mo(N₂)”, the same process that can be seen more

1

8 π electrons.^3,12,21The ligand backbone resonances in the H

NMR spectrum are found at 4.18 and 2.84 ppm, similar to other

cationic diamagnetic complexes containing a triamidoamine

ligand reported here. Unfortunately, several attempts to grow

X-ray quality crystals of 12 and 13 were unsuccessful.

Since ditungsten bridging dinitrogen complexes are formed

by the one-electron reduction of [ArN₃N]WCl, we hoped that

anionic diazenido complexes of W could be produced by the

two-electron reduction of [ArN₃N]WCl. [ArN₃N]WCl (Ar )

4-FC₆H₄, 3,5-Me₂C₆H₃, 3,5-Ph₂C₆H₃) was treated with 2 equiv

of sodium naphthalenide, and the reactions were worked up in

the same manner as the analogous Mo reactions, but no

compounds similar to 2 (Scheme 1) could be isolated, and no

(20) Scheer, M.; Muller, J.; Schiffer, M.; Baum, G.; Winter, R. Chem. Eur.

J. 2000, 6, 1252.

(21) Sanner, R. D.; Duggan, D. M.; McKenzie, T. C.; Marsh, R. E.; Bercaw,

J. E. J. Am. Chem. Soc. 1976, 98, 8358.

3872 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

Figure 9. CV of {[Ph₂C₆H₃N₃N]Mo-NdN}₂Mg(THF)_x(4f).

Figure 7. CV of [t-BuC₆H₄N₃N]Mo-NdN-Mo[t-BuC₆H₄N₃N] (1c).

return wave that corresponds to the reduction of “[t-BuC₆H₄N₃N]-

Mo(N₂)” is observed, consistent with the ready loss of dinitrogen

to yield “[t-BuC₆H₄N₃N]Mo”. A reaction between “[t-BuC₆H₄-

N₃N]Mo(N₂)” and “[t-BuC₆H₄N₃N]Mo” then yields 1c and in

subsequent scans the waves that correspond to the oxidation

and reduction of 1c shown in Figure 7 are observed.

The CV of 2d is similar to that of 2c. (See Figure 1S in

Supporting Information.) No reduction is observed in the initial

cathodic scan, while an oxidation wave for 2d is observed at

-1623 mV. Decomposition of “[Me₂C₆H₃N₃N]Mo(N₂)” to

“[Me₂C₆H₃N₃N]Mo” then leads to 1d, which is reduced at

-2.37 V and oxidized at -0.99 and -0.30 V. The second

oxidation (of {[Me₂C₆H₃N₃N]Mo-NdN-Mo[Me₂C₆H₃N₃N]}⁺

to {[Me₂C₆H₃N₃N]Mo-NdN-Mo[Me₂C₆H₃N₃N]}²⁺) is ir-

reversible at low scan rates. (Data not shown in Figure 1S.)

Figure 8. CV of [t-BuC₆H₄N₃N]Mo-NdN-Na(THF)_x(2c).

The CVs of 2a (Figure 2S, Supporting Information) and 2b

show waves for the oxidation of the anion to the neutral

dinitrogen complex clearly at -1572 and -1555 mV, respec-

tively. However, the reduction and oxidation(s) of the bridging

dinitrogen complexes are not readily observed as a consequence

of the insolubility of these bridging dinitrogen complexes. Visual

examination of the working electrode after completion of the

experiment whose CV is shown in Figure 2S reveals a coating

of what we presume to be 1a on the electrode. Electrochemical

studies of 1a and 1b therefore are also not practical for that

reason.

The CV trace for 4f is shown in Figure 9. That for 4g is

similar, although the reduction wave is more pronounced in the

CV of 4g. No wave is observed upon initially scanning to

negative potentials. The main feature in Figure 9 is a relatiVely

reVersible oxidation of {[TerN₃N]Mo(N₂)}^-to “[TerN₃N]Mo-

(N₂)” at -1.49 V (-1.54 V for 4g). The X-ray structure of 4f

suggests that formation of a bridging dimolybdenum dinitrogen

complex analogous to 1c or 1e would be difficult. In short,

[ArN₃N]Mo(N₂) is relatively stable when the Ar group is

sterically relatively bulky because even if [ArN₃N]Mo(N₂) loses

dinitrogen to yield “[ArN₃N]Mo”, which we suspect it does,

[ArN₃N]Mo(N₂) and [ArN₃N]Mo cannot combine (for steric

reasons) to yield a compound of type 1. Therefore, at least under

an atmosphere of dinitrogen, [ArN₃N]Mo(N₂) appears to be

relatively stable.

clearly in Figure 6. The anodic wave at -432 mV in Figure 5

corresponds to the oxidation of [C₆F₅N₃N]Mo-NdN-Mo-

[C₆F₅N₃N] to {[C₆F₅N₃N]Mo-NdN-Mo[C₆F₅N₃N]}⁺, in a

reversible manner on this time scale. Note that in Figure 6 the

cathodic peak that corresponds to an irreversible reduction of

1e at -1993 mV is not present during the initial reductive scan.

These data support the chemical observation that oxidation of

2e generates 1e and reduction of 1e generates 2e and suggest

that “[C₆F₅N₃N]Mo(N₂)” and {[C₆F₅N₃N]Mo-NdN-Mo-

[C₆F₅N₃N]}^-are both unstable on the time scale employed. No

effort was made to isolate {[C₆F₅N₃N]Mo-NdN-Mo[C₆F₅-

N₃N]}⁺, and if the potential is scanned to more positive values

than those shown in Figure 5, irreversible anodic waves

characteristic of decomposition are observed. Therefore hypo-

thetical {[C₆F₅N₃N]Mo-NdN-Mo[C₆F₅N₃N]}²⁺, a variation

of which can be observed in CV studies of tungsten species

(see below) and which can be isolated (see above), is not stable.

The CV of 1c is shown in Figure 7. Compound 1c is reduced

at -2523 mV, compared with -1988 mV for 1e, as one might

expect on the basis of the greater electron withdrawing power

of the pentafluorophenyl group. However, the reduction of 1c

is more reversible than it is for 1e. Apparently {[t-BuC₆H₄N₃N]-

Mo-NdN-Mo[t-BuC₆H₄N₃N]}^-is not transformed readily

into 2 equiv of {[C₆F₅N₃N]Mo(N₂)}^-. An anodic wave that

corresponds to the relatively reversible oxidation of {[t-

BuC₆H₄N₃N]Mo-NdN-Mo[t-BuC₆H₄N₃N]} to {[t-BuC₆H₄-

N₃N]Mo-NdN-Mo[t-BuC₆H₄N₃N]}⁺is observed at -986

mV, again about 500 mV more negative than the oxidation of

1e. The second oxidation (at -44 mV) in Figure 7 is clearly

irreversible, which suggests that {[t-BuC₆H₄N₃N]Mo-NdN-

Mo[t-BuC₆H₄N₃N]}²⁺is unstable on the CV time scale. No peak

is observed during the initial cathodic scan out to -2900 mV

in the CV of {[t-BuC₆H₄N₃N]Mo(N₂)}^-(2c, Figure 8), while

irreversible oxidation is observed at -1659 mV. Only a tiny

An electrochemical study was carried out on 12 in order to

compare the behavior of the tungsten complex with its molyb-

denum analogue, 1c (Figure 7). A CV of 12 is shown in Figure

10. Compound 12 is reduced cleanly at -3.03 V, which is

considerably more negative than the reduction wave for 1c. It

is important to note that {[t-BuC₆H₄N₃N]W-NdN-W[t-

BuC₆H₄N₃N]}^-apparently is stable toward W-N cleavage to

give {[t-BuC₆H₄N₃N]W-NdN}- and “W[t-BuC₆H₄N₃N]”. It

Mo and W Complexes with Triamidoamine Ligands

Inorganic Chemistry, Vol. 40, No. 16, 2001 3873

N₃N]^3-ligand can be prepared, but W-NdN-M diazenido

complexes have not yet been observed. The W-NdN-W

linkage is strong enough to survive both a one-electron reduction

and two one-electron oxidations, and [{[4-t-BuC₆H₄N₃N]W}₂-

(N₂)]²⁺(as its BPh₄salt) can be isolated. Reduction of Mo-

NdN-M and ModN-NE₂hydrazido species leads to forma-

tion of MotN in low yields, but N_âappears to end up in many

products, of which only dimethylamine could be identified.

Electrochemical studies reveal expected trends in oxidation and

reduction potentials, but also provide insight into the stabilities

of various intermediates, in particular, neutral dinitrogen

complexes of the type [ArN₃N]Mo(N₂). Since the chemistry of

complexes that contain the sterically more bulky terphenyl-

substituted ligands appears to be restricted to the mononuclear

species, i.e., bimetallic diazenido complexes are avoided, we

plan to employ sterically more protective ligands of this general

type in future studies.

Figure 10. CV of [t-BuC₆H₄N₃N]W-NdN-W[t-BuC₆H₄N₃N] (12).

should also be noted that two reversible oxidations are observed

at -1.63 and -0.75 V. The CV of isolated {[t-BuC₆H₄N₃N]W-

NdN-W[t-BuC₆H₄N₃N]}²⁺(13, Figure 3S, Supporting Infor-

mation) is identical to the CV shown in Figure 10. The initial

cathodic scan reveals a reduction of {[t-BuC₆H₄N₃N]W-Nd

N-W[t-BuC₆H₄N₃N]}²⁺to {[t-BuC₆H₄N₃N]W-NdN-W[t-

BuC₆H₄N₃N]}⁺, a reduction of {[t-BuC₆H₄N₃N]W-NdN-

W[t-BuC₆H₄N₃N]}⁺to {[t-BuC₆H₄N₃N]W-NdN-W[t-BuC₆-

H₄N₃N]}, and a reduction of {[t-BuC₆H₄N₃N]W-NdN-W[t-

BuC₆H₄N₃N]} to {[t-BuC₆H₄N₃N]W-NdN-W[t-BuC₆H₄N₃-

N]}^-, followed by the expected waves in the return anodic scan.

The greater W-N bond strength (vs Mo-N) results in the

integrity of the W-N-N-W core being maintained through

three one-electron processes.

Experimental Section

General Procedures. 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.²²Tetrahydrofuran, dimethoxy-

ethane, and 1,4-dioxane were distilled from sodium benzophenone ketyl,

and dichloromethane was distilled from CaH₂. C₆D₆was sparged with

nitrogen and stored over 4 Å molecular sieves. CDCl₃was dried over

CaH₂, vacuum transferred to a solvent storage flask, stored at -35 °C,

and passed through a plug of alumina before use. [ArN₃N]MoCl and

[ArN₃N]WCl complexes were prepared as described in the preceding

23

paper in this issue.¹¹[C₆F₅N₃N]Mo(OTf)³and Cp₂FeBPh₄were

prepared as described in the literature. Sodium naphthalenide was

prepared by stirring sodium sand and naphthalene overnight in THF;

it was titrated with n-PrOH before use. ¹³CH₃MgI was prepared in the

usual fashion in diethyl ether from ¹³CH₃I. All other starting materials

are commercially available and were used as received.

CV studies also were carried out on 8b (Ar ) 4-FC₆H₄;

Figure 4S, Supporting Information), 8c (Ar ) 4-t-BuC₆H₄;

Figure 5S, Supporting Information), and 8e (Ar ) C₆F₅; Figure

6S, Supporting Information). All three compounds display a

relatively reversible reduction, which is the most facile for 8e

(E ) -1.22 V) followed by 8b (E ) -1.60 V) and 8c (E )

-1.68 V). Irreversible second reductions, presumably to produce

a Mo(IV) monoanion, are observed at -2.61 V for 8b, -2.76

V for 8c, and -2.49 V for 8e. Apparently the neutral Mo(V)

dimethylhydrazido species, [ArN₃N]ModN-NMe₂, which are

17 electron species counting one triamidoamine π bond and

donation of an electron pair from NR to the metal, are relatively

stable on the electrochemical time scale. They can be reduced

further to 18e {[ArN₃N]ModN-NMe₂}^-species, but not

reversibly. The mode of decomposition of the 18e species is

not known.

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). ¹⁵N NMR spectra

were recorded at an operating frequency of 50.7 MHz and were

referenced externally using nitromethane (380.2 ppm). Chemical shifts

are reported in parts per million, and coupling constants are in hertz.

All spectra were acquired at ca. 22 °C. IR spectra were recorded on a

Perkin-Elmer 1600 FT-IR spectrometer. Elemental analyses (C, H, N)

were performed by H. Kolbe Mikroanalytisches Laboratorium, Mu¨lheim

an der Ruhr, Germany. X-ray data were collected on a Bruker SMART/

CCD diffractometer, and general experimental details are described in

the literature.²⁴

Conclusions

[t-BuC₆H₄N₃N]Mo-NdN-Mo[t-BuC₆H₄N₃N] (1c). A solution of

[t-BuC₆H₄N₃N]MoCl (218 mg, 0.325 mmol) in THF (7 mL) was cooled

to -35 °C. A 0.65 M stock solution of sodium naphthalenide (0.5 mL,

0.325 mmol) in THF was diluted to 3 mL and cooled to -35 °C. The

sodium naphthalenide solution was added dropwise to the solution of

[t-BuC₆H₄N₃N]MoCl, and the reaction mixture was allowed to warm

to room temperature while being stirred over a period of 2 h. The color

changed from red to deep purple. The THF was removed in vacuo, the

residue was dissolved in toluene, and the mixture was filtered through

Celite. Toluene was removed from the extract in vacuo, and the product

We have found that [ArN₃N]MoCl complexes (Ar ) C₆H₅,

4-FC₆H₄, 4-t-BuC₆H₄, 3,5-Me₂C₆H₃, 3,5-Ph₂C₆H₃, and 3,5-(4-

t-BuC₆H₄)₂C₆H₃) can be reduced to give various Mo-NdN-M

(M ) Na, Mg) diazenido complexes. Dimolybdenum diazenido

complexes are readily formed when Ar ) C₆H₅, 4-FC₆H₄, 4-t-

BuC₆H₄, or 3,5-Me₂C₆H₃, but for steric reasons not when

Ar ) 3,5-Ph₂C₆H₃or 3,5-(4-t-BuC₆H₄)₂C₆H₃. Conversely, only

when the terphenyl-substituted ligands are present is there any

indication that [ArN₃N]Mo(N₂) complexes are stable under

dinitrogen; i.e., they are not readily converted into Mo-Nd

N-Mo species. Addition of electrophiles to various Mo-Nd

N-M species proceeds relatively smoothly to give first [ArN₃N]-

Mo-NdN-E species (E ) electrophile) followed by {[ArN₃-

N]ModN-NE₂}⁺species, in contrast to similar reactions in

[Me₃SiN₃N]^3-systems where trimethylsilyl groups are lost. A

ditungsten diazenido complex that contains the [4-t-BuC₆H₄-

(22) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;

Timmers, F. J. Organometallics 1996, 15, 1518.

(23) Jordan, R. F.; LaPointe, R. E.; Bradley, P. K.; Baezinger, N.

Organometallics 1989, 8, 2892.

(24) Rosenberger, C.; Schrock, R. R.; Davis, W. M. Inorg. Chem. 1997,

36, 123.

(25) M. B. O’Donoghue, Ph.D. Thesis, Massachusetts Institute of Technol-

ogy, 1998.

3874 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

was washed with ether and dried in vacuo; yield 119 mg (0.092 mmol,

56% based on Mo). H NMR (C₆D₆): δ 11.02 (s, 12, meta), 4.29 (br

s, 12, ortho), 1.76 (s, 54, t-Bu), -8.46 (br s, 12, CH₂), -36 (br, 12,

CH₂). Anal. Calcd for C₇₂H₁₀₂N₁₀Mo₂: C, 66.55; H, 7.91; N, 10.78.

Found: C, 66.42; H, 7.82; N, 10.66.

mixture was stirred under ¹⁵N₂for 1 h. The vessel was resealed and

returned to the glovebox (under ¹⁴N₂) for the remainder of the workup,

which was performed in an analogous manner as for the unlabeled

material; yield 225 mg (0.148 mmol, 30%). ¹⁵N NMR (C₆D₆/THF): δ

374.44 (d, N_R, J_NN) 10), 336.07 (d, N_â, J_NN) 10). IR (cm^-1): 1688

(Nujol), 1755 (THF).

1

Na({[PhN₃N]Mo-NdN}₂Na)(THF)₂(2a). A 0.33 M stock solution

of sodium naphthalenide (7.25 mL, 2.40 mmol) in THF was diluted to

20 mL and cooled to -35 °C. [PhN₃N]MoCl (604 mg, 1.20 mmol)

was added as a solid, and the reaction was allowed to warm to room

temperature with stirring for 1 h. The color became burgundy. The

reaction mixture was filtered through Celite to remove salts. The filtrate

was concentrated to 4 mL, during which time purple crystals formed.

The crystals were collected, washed with ether, and dried in vacuo;

yield ) 384 mg (0.65 mmol, 54%). ¹H NMR (C₆D₆spiked with THF):

δ 7.28 (t, 12, meta), 7.16 (d, 12, ortho), 6.91 (t, 6, para), 3.67 (t, 12,

CH₂), 3.53 (THF), 2.15 (t, 12, CH₂), 1.43 (THF). ¹³C NMR (THF): δ

160.24 (C_ipso), 126.44 (C_o), 119.59 (C_m), 115.31 (C_p), 67.15 (THF),

54.44 (CH₂), 53.52 (CH₂), 25.37 (THF). IR (cm^-1): 1750 (Nujol), 1818

(THF). Anal. Calcd for C₅₆H₇₀N₁₂O₂Na₂Mo₂: C, 56.95; H, 5.970; N,

14.23. Found: C, 57.11; H, 6.06; N, 14.18.

Na({[Me₂C₆H₃N₃N]Mo-NdN}₂Na)(THF)₂(2d). A 0.42 M stock

solution of sodium naphthalenide (7.50 mL, 3.15 mmol) in THF was

diluted to 20 mL and cooled to -35 °C. [Me₂C₆H₃N₃N]MoCl (925

mg, 1.57 mmol) was added as a solid, and the reaction was allowed to

warm to room temperature with stirring for 1 h, after which time the

solution was plum colored. The reaction mixture was filtered through

Celite and concentrated to dryness to yield a black oily residue. The

residue was washed with pentane to remove naphthalene and red

impurities. The resulting pink solid was pure by NMR, but analytically

pure material was obtained by recrystallization from a mixture of THF

1

and pentane at -40 °C; yield 445 mg (0.66 mmol, 42%). H NMR

(C₆D₆): δ 6.98 (s, 12, ortho), 6.47 (s, 6, para), 3.70 (t, 12, CH₂), 3.46

(m, 8, THF), 2.25 (s, 36, 3,5-Me₂), 2.19 (t, 12, CH₂), 1.36 (m, 8, THF).

¹³C NMR (THF): δ 160.57 (C_ipso), 134.83 (C_p), 118.37 (C_o), 117.39

(C_m), 67.15 (THF), 55.03 (CH₂), 53.33 (CH₂), 25.37 (THF), 21.12 (3,5-

Me₂). IR (cm^-1): 1742 (Nujol), 1816 (THF). Anal. Calcd for

C₆₈H₉₄N₁₂O₂Na₂Mo₂: C, 60.53; H, 7.02; N, 12.46. Found: C, 60.39;

H, 6.88; N, 12.35.

Na({[FC₆H₄N₃N]Mo-NdN}₂Na)(THF)₂(2b). A 0.54 M stock

solution of sodium naphthalenide (6.0 mL, 3.24 mmol) in THF was

diluted to 50 mL and cooled to -35 °C. [FC₆H₄N₃N]MoCl (902 mg,

1.62 mmol) was added as a solid, and the reaction was allowed to warm

to room temperature with stirring for 1 h. The plum colored reaction

mixture was filtered through Celite, and the filtrate was concentrated

in vacuo to give a brown oily residue. The residue was washed with

pentane in order to remove naphthalene. The rust colored solid was

washed with toluene to yield a magenta solid. Analytically pure material

was obtained by recrystallization from a mixture of THF and pentane

[t-BuC₆H₄N₃N]Mo-NdN-Na(15-crown-5) (3c). 15-Crown-5 (66

mg, 0.3 mmol) was dissolved in 2 mL of THF and added dropwise to

a solution of 2c (228 mg, 0.3 mmol) in 6 mL of THF. The reaction

was stirred at room temperature for 2 h, then THF was removed, and

the residue was dissolved in 2 mL of toluene. Pentane was added until

crystals began to form. The reaction was cooled to -35 °C for 2 h to

complete crystallization. The mother liquor was decanted off, and the

purple crystals were washed three times with ether; yield ) 209 mg

1

at -35 °C; yield 490 mg (0.76 mmol, 47%). H NMR (C₆D₆spiked

with THF): δ 7.18 (dd, 12, Ar), 6.97 (t, 12, Ar), 3.64 (t, 12, CH₂),

3.54 (THF), 2.18 (t, 12, CH₂), 1.43 (THF). ¹³C NMR (THF): δ 157.48

(s, C_ipso), 155.82 (d, C_p, J_CF) 232), 120.39 (d, C_o, J_CF) 7), 113.17 (d,

C_m, J_CF) 21), 67.72 (THF), 55.39 (CH₂), 53.99 (CH₂), 25.88 (THF).

¹⁹F NMR (C₆D₆spiked with THF): δ -129.76 (br s). IR (cm^-1): 1752

(Nujol), 1813 (THF). Anal. Calcd for C₅₆H₆₄F₆N₁₂O₂Na₂Mo₂: C, 52.18;

H, 5.00; N, 13.04. Found: C, 52.28; H, 4.87; N, 13.12.

1

(0.23 mmol, 77%). H NMR (C₆D₆): δ 7.67 (d, 6, meta), 7.37 (d, 6,

ortho), 3.83 (t, 6, CH₂), 3.04 (s, 20, crown), 2.16 (t, 6, CH₂), 1.48 (s,

27, t-Bu). ¹³C NMR (C₆D₆/THF): δ 159.86 (C_ipso), 137.42 (C_p), 124.52

(C_m), 120.14 (C_o), 70.10 (crown), 56.07 (CH₂), 53.94 (CH₂), 34.40 (t-

Bu), 32.42 (t-Bu). IR (cm^-1): 1815 (Nujol), 1815 (THF). Anal. Calcd

for C₄₆H₇₁N₆O₅NaMo: C, 60.91; H, 7.89; N, 9.27. Found: C, 61.11;

H, 7.96; N, 9.21.

Na({[t-BuC₆H₄N₃N]Mo-NdN}₂Na)(THF)₂(2c). A 0.65 M stock

solution of sodium naphthalenide (20.0 mL, 13.0 mmol) in THF was

diluted to 80 mL and cooled to -40 °C. A separate solution of

[t-BuC₆H₄N₃N]MoCl (4.36 g, 6.50 mmol) in 40 mL of THF was also

cooled to -40 °C. The Mo solution was added dropwise over a period

of 15 min to the sodium naphthalenide with vigorous stirring. The

reaction mixture was allowed to warm to room temperature and was

stirred for 1 h. The volume was reduced to 10 mL in vacuo, and the

reaction mixture was filtered through Celite to remove NaCl. Pentane

(15 mL) was added, and the solution was stirred at -35 °C for 3 h to

yield pink crystals (1.53 g). The filtrate was concentrated to dryness

in vacuo, and the residue was triturated with pentane to yield another

809 mg of powder which was spectroscopically identical to the

[Me₂C₆H₃N₃N]Mo-NdN-Na(15-crown-5) (3d). 15-Crown-5 (76

mg, 0.34 mmol) was dissolved in 2 mL of THF and added dropwise to

a solution of 2d (216 mg, 0.32 mmol) in 6 mL of THF. The color

changed immediately from purple to black. The reaction was stirred at

room temperature for 30 min, then THF was removed, and the residue

was washed with pentane to give a black solid. This material was

recrystallized from a mixture of ether and toluene to give purple crystals,

which were washed with ether until the washings were colorless and

dried in vacuo; yield 69 mg. (0.084 mmol, 26%). ¹H NMR (C₆D₆): δ

7.43 (s, 6, ortho), 6.47 (s, 3, para), 3.92 (t, 6, CH₂), 2.91 (s, 20, crown),

2.41 (s, 18, 3,5-Me₂), 2.20 (t, 6, CH₂). ¹³C NMR (C₆D₆/THF): δ 161.82

(C_ipso), 136.28 (C_m), 119.17 (C_o), 118.03 (C_p), 69.66 (crown), 56.14

(CH₂), 53.74 (CH₂), 22.46 (Ar CH₃). IR (cm^-1): 1815 (Nujol), 1832

(THF). Anal. Calcd for C₄₀H₅₉N₆O₅NaMo: C, 58.39; H, 7.23; N, 10.21.

Found: C, 58.46; H, 7.18; N, 10.17.

1

crystallized product; total yield 2.34 g. (3.09 mmol, 48%). H NMR

(C₆D₆): δ 7.29 (d, 12, meta), 7.13 (d, 12, ortho), 3.66 (t, 12, CH₂),

3.42 (m, 8, THF), 2.15 (t, 12, CH₂), 1.34 (s, 54, t-Bu), 1.32 (m, 8,

THF). ¹³C NMR (C₆H₆): δ 158.05 (C_ipso), 140.43 (C_p), 124.97 (C_o),

120.11 (C_m), 67.84 (THF), 55.39 (CH₂), 53.16 (CH₂), 34.04 (t-Bu),

31.88 (t-Bu Me), 25.37 (THF). ¹³C NMR (THF): δ 158.33 (C_ipso),

136.72 (C_p), 123.11 (C_o), 119.15 (C_m), 67.16 (THF), 54.74 (CH₂), 53.36

(CH₂), 33.28 (t-Bu), 31.24 (t-Bu Me), 25.37 (THF). IR (cm^-1): 1741

(Nujol), 1815 (THF), 1745 (benzene). Anal. Calcd for C₈₀H₁₁₈N₁₂O₂-

Na₂Mo₂: C, 63.31; H, 7.84; N, 11.07. Found: C, 63.26; H, 7.91; N,

10.89.

Na({[t-BuC₆H₄N₃N]Mo-¹⁵Nd¹⁵N}₂Na)(THF)₂(2c-¹⁵N). One cham-

ber of a two-chamber reaction vessel was charged with a solution of

[t-BuC₆H₄N₃N]MoCl (671 mg, 1.00 mmol) in 10 mL of THF, and the

other chamber was charged with a solution of sodium naphthalenide

(4.0 mL of a 0.50 M stock solution, 2.0 mmol) in 10 mL of THF. The

vessel was sealed and degassed on the Schlenk line by the freeze-

pump-thaw method. When the vessel was evacuated, ¹⁵N₂was

introduced directly from a breakseal flask through a piece of rubber

tubing. The contents of the two chambers were mixed, and the reaction

{[t-BuC₆H₄N₃N]Mo-NdN}₂Mg(THF)₂(4c). A 20 mL reaction vial

was charged with a solution of [t-BuC₆H₄N₃N]MoCl (200 mg, 0.30

mmol) in 5 mL of THF and Mg powder (24 mg, 1.0 mmol). The

reaction was stirred overnight at room temperature, and the color

became pinkish purple. A 1 mL aliquot of 1,4-dioxane was added, and

the reaction was allowed to stir for 1 more hour. THF was removed in

vacuo, and the residue was dissolved in toluene. Filtration of the extract

through Celite removed MgCl₂(dioxane). The toluene was removed in

vacuo, and the residue was washed with ether to yield a peach colored

ether-insoluble solid (∼100 mg?) which was collected and dried in

1

vacuo. This material could not be purified to homogeneity. H NMR

(C₆D₆): δ 7.41 (br s, 6, meta), 7.36 (br s, 6, ortho), 3.79 (br s, 6, CH₂),

3.25 (m, 4, THF), 2.26 (br s, 6, CH₂), 1.28 (s, 27, t-Bu). IR (Nujol;

cm^-1) 1758.

{[TerN₃N]Mo-NdN}₂Mg(THF)₄(4f-THF). A suspension of

[TerN₃N]MoCl (441 mg, 0.46 mmol) in THF (12 mL) was stirred over

Mg powder (100 mg, 4.16 mmol) under dinitrogen overnight. All of

Mo and W Complexes with Triamidoamine Ligands

Inorganic Chemistry, Vol. 40, No. 16, 2001 3875

the Mo starting material dissolved as it reacted to produce a scarlet

red solution. Addition of 1,4-dioxane (1 mL) resulted in the precipitation

of MgCl₂(dioxane), which was filtered off. The solvent was removed

from the filtrate in vacuo and the residue was washed with pentane.

The red insoluble product was collected and dried in vacuo; yield 443

in THF (5 mL). The reaction mixture was allowed to warm to room

temperature with stirring for 30 min; then the THF was removed in

vacuo. The residue was extracted with ether and the extract was filtered.

The dark yellow filtrate was concentrated to dryness in vacuo, and the

resulting residue was washed with pentane and dried in vacuo; yield

1

mg (0.20 mmol, 87%). H NMR (C₆D₆): δ 7.72 (d, 24, 3,5-ortho),

175 mg (0.28 mmol, 56%). H NMR (C₆D₆): δ 6.85-7.00 (m, 12,

7.60 (s, 12, ortho), 7.48 (s, 6, para), 7.21 (t, 24, 3,5-meta), 7.07 (t, 12,

3,5-para), 3.87 (t, 12, CH₂), 3.18 (br s, THF), 2.36 (t, 12, CH₂), 1.04

(br s, THF). ¹³C NMR (THF): δ 161.91 (C_ipso), 141.94 (C_m), 140.73

(3,5-ipso), 128.12 (3,5-meta), 126.78 (3,5-ortho), 126.15 (3,5-para),

120.11(C_o), 116.64 (C_p), 57.11 (CH₂), 53.77 (CH₂). IR (cm^-1):1775

(Nujol), 1789 (THF).

Ar), 3.40 (t, 6, CH₂), 2.11 (t, 6, CH₂), -0.17 (s, 9, SiMe₃). ¹³C NMR

(THF): δ 158.49 (d, C_p, J_CF) 239), 155.46 (d, C_ipso, J_CF) 2), 122.94

(d, C_o, J_CF) 7), 115.08 (d, C_m, J_CF) 21), 57.27 (CH₂), 53.69 (CH₂),

0.93 (SiMe₃). ¹⁹F NMR (C₆D₆): δ -122.72 (7 lines). IR (cm^-1): 1674

(Nujol), 1657 (THF). Anal. Calcd for C₂₇H₃₃F₃N₆SiMo: C, 52.09; H,

5.34; N, 13.50. Found: C, 51.96; H, 5.27; N, 13.38.

{[TerN₃N]Mo-NdN}₂Mg(DME)₂(4f-DME). Compound 4f-THF

(110 mg, 0.050 mmol) was dissolved in DME (8 mL). Purple crystals

formed over the course of several hours. The mother liquor was

decanted off and the crystals were washed with pentane and dried in

[t-BuC₆H₄N₃N]Mo-NdN-SiMe₃(5c). (a) From [t-BuC₆H₄N₃N]-

MoCl. A solution of sodium naphthalenide in THF (5.0 mL of a 0.28

M solution, 1.4 mmol) was diluted to 20 mL and cooled to -35 °C. A

separate solution of [t-BuC₆H₄N₃N]MoCl (376 mg, 0.56 mmol) in THF

(10 mL) was also cooled to -35 °C. This solution was added dropwise

to the sodium naphthalenide solution with vigorous stirring. The reaction

mixture was allowed to warm to room temperature with stirring for 1

h; then it was cooled back down to -35 °C. A solution of Me₃SiCl

(122 mg, 1.12 mmol) in THF (5 mL) was added dropwise. THF was

removed in vacuo, and the residue was dissolved in toluene. NaCl was

removed by filtration of the extract through Celite. Toluene was

removed from the filtrate in vacuo, and the residue was washed with

pentane to yield a yellow solid (185 mg, 45%), which was collected

and dried in vacuo. Analytically pure material was obtained by

recrystallization from a mixture of toluene and pentane. ¹H NMR

(C₆D₆): δ 7.32 (s, 12, aryl), 3.63 (t, 6, CH₂), 2.20 (t, 6, CH₂), 1.29 (s,

27, t-Bu), -0.12 (s, 9, SiMe₃). ¹³C NMR (C₆D₆/THF): δ 156.87 (C_ipso),

143.17 (C_p), 125.52 (C_m), 121.73 (C_o), 57.13 (CH₂), 53.80 (CH₂), 34.67

(t-Bu), 32.07 (t-Bu), 1.23 (SiMe₃). IR (cm^-1): 1738 (Nujol), 1651

(THF). Anal. Calcd for C₃₉H₆₀N₆SiMo: C, 63.56; H, 8.21; N, 11.40.

Found: C 63.38; H, 8.16; N, 11.30.

(b) From 2c. A solution of 2c (380 mg, 0.25 mmol) in THF (10

mL) was cooled to -35 °C. A separate solution of Me₃SiCl (82 mg,

0.75 mmol) in THF (1 mL) was also cooled to -35 °C and added

dropwise to the solution of 2c; the color changed immediately from

purple to yellow. THF was removed in vacuo and the residue was

dissolved in toluene. The solution was filtered through Celite, and the

toluene filtrate was concentrated to 3 mL in vacuo. Pentane (10 mL)

was added in order to complete the formation of yellow crystals. The

red mother liquor was decanted away from the crystals, which were

washed twice with pentane and dried in vacuo; yield 315 mg (0.427

mmol, 85%).

1

vacuo; yield 98 mg (0.046 mmol, 93%). H NMR (C₆D₆/DME): δ

7.42 (d, 24, 3,5-ortho), 7.32 (s, 12, H_o), 7.16 (s, 6, H_p), 7.14 (t, 24,

3,5-meta), 7.06 (t, 12, 3,5-para). IR (cm^-1): 1785 (Nujol), 1789 (THF).

Anal. Calcd for C₁₂₈H₁₂₂N₁₂O₄MgMo₂: C, 72.91; H, 5.83; N, 7.97.

Found: C, 73.08; H, 5.75; N, 8.08.

{[(t-BuC₆H₄)₂C₆H₃N₃N]Mo-NdN}₂Mg(THF)₄(4g-THF). A solu-

tion of [(t-BuC₆H₄)₂C₆H₃N₃N]MoCl (555 mg, 0.43 mmol) in THF (12

mL) was stirred over Mg powder (50 mg, 2.08 mmol) under dinitrogen

overnight. 1,4-Dioxane (0.5 mL) was added, and the mixture was stirred

for 30 more minutes. Insoluble material was filtered off, and THF was

removed to yield a red oil. The oil was dissolved in pentane, and more

salts were filtered off. Storage of the pentane solution at -40 °C

overnight resulted in the formation of orange crystals. The mother liquor

was decanted off and the crystals were washed with pentane and dried

1

in vacuo; yield 499 mg (0.33 mmol, 78%). H NMR (C₆D₆): δ 7.78

(d, 24, 3,5-meta), 7.69 (s, 12, H_o), 7.61 (s, 6, H_p), 7.35 (d, 24, 3,5-

ortho), 3.92 (t, 12, CH₂), 3.32 (br s, THF), 2.35 (t, 12, CH₂), 1.25 (s,

108, t-Bu), 1.14 (br s, THF). ¹³C NMR (C₆D₆): δ 162.25 (C_ipso), 149.86

(3,5-para), 142.01 (C_m), 140.42 (3,5-ipso), 127.76 (3,5-meta), 126.31

(3,5-ortho), 120.26 (C_o), 117.95 (C_p), 69.32 (THF), 56.78 (CH₂), 54.58

(CH₂), 34.83 (t-Bu), 31.89 (t-Bu), 25.80 (THF). IR (cm^-1): 1782

(Nujol), 1805 (THF).

{[(t-BuC₆H₄)₂C₆H₃N₃N]Mo-NdN}₂Mg(DME)₂(4g-DME). Com-

pound 4g-THF (90 mg, 0.031 mmol) was dissolved in DME (4 mL).

The solvent was removed, and the residue was washed with pentane.

The lavender, pentane-insoluble product was collected and dried in

1

vacuo; yield 70 mg (0.025 mmol, 81%). H NMR (C₆D₆): δ 7.65 (d,

24, 3,5-meta), 7.58 (s, 12, H_o), 7.42 (d, 30, 3,5-ortho, and H_p), 3.79 (t,

12, CH₂), 2.34 (s, 8, DME), 2.26 (s, 12, DME). 2.12 (t, 12, CH₂), 1.34

(s, 108, t-Bu). ¹³C NMR (C₆D₆): δ 163.34 (C_ipso), 149.95 (3,5-para),

141.65 (C_m), 140.41 (3,5-ipso), 127.74 (3,5-meta), 126.26 (3,5-ortho),

121.57 (C_o), 117.18 (C_p), 69.84 (DME), 60.24 (DME), 58.04 (CH₂),

54.55 (CH₂), 34.92 (t-Bu), 32.05 (t-Bu). IR (cm^-1): 1787 (Nujol).

[PhN₃N]Mo-NdN-SiMe₃(5a). A solution of 2a (154 mg, 0.13

mmol) in 8 mL of THF was cooled to -40 °C. Me₃SiCl (48 mg, 0.44

mmol) was dissolved in 1 mL of THF, cooled to -40 °C, and added

to the reaction mixture. The color immediately changed from purple

to yellow. THF was removed, and the residue was dissolved in toluene.

NaCl was filtered off, and yellow crystals formed upon concentration

of the toluene solution. The crystals were collected, washed with ether,

and dried in vacuo; yield 124 mg (0.22 mmol, 84%). ¹H NMR (C₆D₆):

δ 7.26 (d, 12, H_oand H_m), 6.90 (septet, 3, H_p), 3.55 (t, 6, CH₂), 2.15

(t, 6, CH₂), -0.08 (s, 9, SiMe₃). ¹³C NMR (C₆D₆): δ 159.05 (C_ipso),

129.19 (C_m), 122.29 (C_o), 121.79 (C_p), 56.61 (CH₂), 53.28 (CH₂), 1.44

(SiMe₃). IR (cm^-1): 1643 (Nujol), 1663 (THF). Anal. Calcd for

C₂₇H₃₆N₆SiMo: C, 57.03; H, 6.38; N, 14.78. Found: C, 57.12; H, 6.31;

N, 14.70.

[FC₆H₄N₃N]Mo-NdN-SiMe₃(5b). A solution of sodium naph-

thalenide (7.5 mL of a 0.17 M solution) was diluted to 20 mL with

THF and cooled to -40 °C. A separate solution of [FC₆H₄N₃N]MoCl

(278 mg, 0.5 mmol) in 10 mL of THF was prepared, cooled to -40

°C, and added dropwise to the naphthalenide solution, causing a color

change from green to red. The reaction mixture was allowed to warm

to room temperature with stirring for 30 min; then it was cooled to

-40 °C and added slowly to a solution of Me₃SiCl (87 mg, 0.8 mmol)

[t-BuC₆H₄N₃N]Mo-¹⁵Nd¹⁵N-SiMe₃(5c-15N). This material was

prepared in a manner identical to that used to prepare unlabeled material

starting from 2c-¹⁵N (68 mg, 0.045 mmol) and Me₃SiCl (13 mg, 0.12

mmol); yield 50 mg (0.068 mmol, 75%). ¹⁵N NMR (C₆D₆/THF): δ

374.39 (d, N_R, J_NN) 13), 220.72 (d, N_â, J_NN) 13). ¹³C NMR (C₆D₆/

2

THF): δ 1.174 (d, ¹⁵N-SiMe₃, J(¹³C,¹⁵N) ) 3.4). IR (cm^-1): 1679

(Nujol), 1615 (THF).

[Me₂C₆H₃N₃N]Mo-NdN-SiMe₃(5d). (a) From [Me₂C₆H₃N₃N]-

MoCl. A 0.42 M stock solution of sodium naphthalenide (4.0 mL, 1.68

mmol) in THF was diluted to 10 mL and cooled to -35 °C.

[Me₂C₆H₃N₃N]MoCl (493 mg, 0.84 mmol) was added as a solid, and

the reaction was allowed to warm to room temperature with stirring

for 2 h. A solution of Me₃SiCl (200 mg, 1.84 mmol) in THF (2 mL)

was then added to the plum colored solution resulting in a color change

to dark yellow. After 15 min, the reaction mixture was filtered through

Celite and the THF was removed in vacuo. The residue was washed

with pentane to yield a yellow solid which was pure by NMR; yield

234 mg (0.36 mmol, 43%). Analytically pure yellow crystals were

obtained by recrystallization from a mixture of toluene and pentane at

1

-35 °C. H NMR (C₆D₆): δ 7.02 (s, 6, ortho), 6.59 (s, 3, para), 3.65

(t, 6, CH₂), 2.29 (s, 18, 3,5-Me₂), 2.25 (t, 6, CH₂), -0.14 (s, 9, SiMe₃).

¹³C NMR (THF): δ 158.67 (C_ipso), 136.57 (C_p), 122.29 (C_m), 120.10

(C_o), 56.61 (CH₂), 52.75 (CH₂), 20.84 (3,5-Me₂), -0.59 (SiMe₃). IR

(cm^-1): 1722 (Nujol); 1657 (THF). Anal. Calcd for C₃₃H₄₈N₆MoSi:

C, 60.72; H, 7.41; N, 12.87. Found: C, 60.59; H, 7.47; N, 12.97.

(b) From 2d. A solution of 2d (81 mg, 0.060 mmol) in THF (6

mL) was cooled to -40 °C. A separate solution of Me₃SiCl (22 mg,

3876 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

0.20 mmol) in THF (1 mL) was also cooled to -40 °C, and added to

the reaction mixture. The color changed immediately from purple to

yellow. THF was removed in vacuo, and the residue was dissolved in

toluene. The extract was filtered, and the filtrate was stored at -40

°C. The crystals were collected, washed with ether, and dried in vacuo;

yield 57 mg (0.087 mmol, 73%).

NMR (THF): δ 159.06 (C_ipso), 127.46 (C_m), 121.07 (C_o), 120.40 (C_p),

55.97 (CH₂), 53.27 (CH₂), 39.53 (NCH₃). IR (cm^-1): 1598 (Nujol),

1601 (THF). Anal. Calcd for C₂₅H₃₀N₆Mo: C, 58.82; H, 5.92; N, 16.46.

Found: C, 58.75; H, 6.08; N, 16.55.

[FC₆H₄N₃N]Mo-NdN-Me (6b). This material was synthesized

in a manner similar to that used to prepare 6a, starting from 2b (338

mg, 0.262 mmol) and methyl tosylate (97 mg, 0.52 mmol). Three hours

were sufficient for complete reaction; yield 180 mg (0.319 mmol, 61%).

¹H NMR (C₆D₆): δ 6.98 (dd, 6, Ar), 6.87 (t, 6, Ar), 3.36 (t, 6, CH₂),

2.89 (s, 3, N-Me), 2.14 (t, 6, CH₂). ¹³C NMR (THF): δ 157.76 (d, C_p,

J_CF) 238), 155.35 (d, C_ipso, J_CF) 2), 121.98 (d, C_o, J_CF) 8), 113.78

(d, C_m, J_CF) 22), 56.35 (CH₂), 53.22 (CH₂), 39.54 (NCH₃). ¹⁹F NMR

(C₆D₆): δ -122.30 (7 lines). ¹⁹F NMR (THF): δ -124.25 (7 lines).

IR (cm^-1): 1581 (Nujol), 1582 (THF). Anal. Calcd for C₂₅H₂₇F₃N₆-

Mo: C, 53.20; H, 4.82; N, 14.89. Found: C, 53.31; H, 4.83; N, 14.96.

[t-BuC₆H₄N₃N]Mo-NdN-Me (6c). A 20 mL reaction vial was

charged with 2c (760 mg, 1.0 mmol), methyl tosylate (186 mg, 1.0

mmol), and THF (25 mL). The reaction was stirred at room temperature

for 3 h during which time the color changed from violet to dark yellow.

THF was removed in vacuo, and the residue was dissolved in toluene.

The solution was filtered through Celite to remove NaOTs, and the

toluene solution was concentrated to 5 mL. Addition of 15 mL of

pentane resulted in the formation of yellow-green crystals. The burgundy

colored mother liquor was decanted off, and the crystals were washed

with pentane and dried in vacuo; yield 417 mg (0.61 mmol, 61%). ¹H

NMR (C₆D₆): δ 7.27 (s, 12, aryl), 3.60 (t, 6, CH₂), 2.91 (s, 3, N-Me),

2.23 (t, 6, CH₂), 1.26 (s, 27, t-Bu). ¹³C NMR (THF): δ 156.56 (C_ipso),

142.69 (C_p), 124.19 (C_m), 120.63 (C_o), 56.10 (CH₂), 53.04 (CH₂), 39.05

(NCH₃), 33.53 (t-Bu), 30.97 (t-Bu Me). IR (cm^-1):1585 (Nujol), 1579

(THF). Anal. Calcd for C₃₇H₅₄N₆Mo: C, 65.47; H, 8.02; N, 12.38.

Found: C 65.59; H, 8.04; N, 12.27.

[C₆F₅N₃N]Mo-NdN-SiMe₃(5e). Sodium amalgam (0.5%, 7 g,

1.5 mmol Na) was covered with THF. [C₆F₅N₃N]MoOTf (443 mg, 0.50

mmol) was added as a solid, and the reaction was stirred at room

temperature for 3 h. The insoluble Mo triflate dissolved, and the color

of the reaction turned red. The solution was decanted from the mercury,

and the solvent was removed in vacuo. The residue was dissolved in

ether, the ether solution was cooled to -40 °C, and a -40 °C solution

of Me₃SiCl (68 mg, 0.625 mmol) in THF was added. The color turned

orange immediately, but the reaction was allowed to warm to room

temperature over a period of 30 min. Addition of a small amount of

pentane led to precipitation of sodium salts as well as some black

material, which was removed by filtration. The ether solution was then

concentrated, and pentane was added. The solution was cooled to -40

1

°C to yield crystals (277 mg, 0.33 mmol, 67%). H NMR (C₆D₆): δ

3.31 (t, 6, CH₂). 2.01 (t, 6, CH₂), -0.37 (s, 9, SiMe₃). ¹³C NMR

(THF): δ 142.67 (d, J_CF) 245.1), 138.44 (d, J_CF) 241.3), 137.52 (d,

J_CF) 246.4), 132.65 (br s, ipso), 56.95 (CH₂), 53.81 (CH₂), -0.09

(SiMe₃). ¹⁹F NMR (THF): δ -151.39 (d, 6, ortho), -166.93 (t, 6,

meta), -167.58 (t, 3, para). IR (Nujol; cm^-1): 1672 (NdN).

[TerN₃N]Mo-NdN-SiMe₃(5f). A solution of 4f-DME (137 mg,

0.065 mmol) in THF (6 mL) was cooled to -40 °C. A separate solution

of Me₃SiCl (26 mg, 0.24 mmol) in THF (1 mL) was cooled to -40 °C

and then added to the reaction mixture; the color changed from red to

yellow. NaCl was filtered off, and crystals formed in the filtrate during

the process. The crystals were collected, washed with ether, and dried

in vacuo; yield 115 mg (0.112 mmol, 86%). H NMR (C₆D₆): δ 7.83

[t-BuC₆H₄N₃N]Mo-¹⁵Nd¹⁵N-Me (6c-¹⁵N). This material was

prepared in amanner identical to that used to prepare unlabeled material

starting from 2c-¹⁵N (103 mg, 0.068 mmol) and MeOTs (26 mg, 0.14

1

(t, 12, 3,5-ortho), 7.71 (s, 6, ortho), 7.61 (s, 3, para), 7.20 (t, 12, 3,5-

meta), 7.13 (t, 6, 3,5-para), 3.68 (t, 6, CH₂), 2.30 (t, 6, CH₂), -0.36 (s,

9, SiMe₃). ¹³C NMR (C₆D₆/THF): δ 159.90 (C_ipso), 142.79 (C_m), 142.70

(3,5-ipso), 129.04 (3,5-meta), 128.05 (3,5-ortho), 127.53 (3,5-para),

121.01(C_o), 119.52(C_p), 57.39 (CH₂), 53.68 (CH₂), 0.11 (SiMe₃). IR

(cm^-1): 1646 (Nujol), 1645 (THF). Anal. Calcd for C₆₃H₆₀N₆MoSi:

C, 73.81; H, 5.90; N, 8.20. Found: C, 73.94; H, 6.03; N, 8.11.

[(t-BuC₆H₄)₂C₆H₃N₃N]Mo-NdN-SiMe₃(5g). A solution of [(t-

BuC₆H₄)₂C₆H₃N₃N]MoCl (259 mg, 0.20 mmol) in THF (6 mL) was

stirred over Mg powder (24 mg, 1.00 mmol) under dinitrogen overnight.

The reaction mixture was cooled to -40 °C, and a solution of Me₃-

SiCl (26 mg, 0.24 mmol) in THF (1 mL) was added. After 30 min

1,4-dioxane (0.5 mL) was added. The reaction mixture was filtered

through Celite and concentrated to dryness in vacuo. The residue was

dissolved in ether and filtered again to remove more insoluble white

powder. The ether was removed from the filtrate in vacuo, and the

residue was washed with pentane. A pentane-insoluble orange solid

was collected, washed with pentane, and dried in vacuo; yield 162 mg

(0.119 mmol, 59%). Analytically pure material was obtained by

recrystallization from a mixture of toluene and pentane. ¹H NMR

(C₆D₆): δ 7.90 (d, 12, 3,5-ortho), 7.80 (s, 6, ortho), 7.75 (s, 3, para),

7.35 (d, 12, 3,5-meta), 3.72 (t, 6, CH₂), 2.30 (t, 6, CH₂), 1.27 (s, 54,

t-Bu), -0.25 (s, 9, SiMe₃). ¹³C NMR (THF): δ 159.79 (C_ipso), 150.27

(3,5-para), 142.54 (C_m), 140.09 (3,5-ipso), 127.87 (3,5-meta), 126.10

(3,5-ortho), 120.62 (C_o), 119.09 (C_p), 57.21 (CH₂), 53.37 (CH₂), 35.07

(t-Bu), 31.86 (t-Bu), 0.24 (SiMe₃). IR (cm^-1): 1642 (Nujol), 1648

(THF). Anal. Calcd for C₈₇H₁₀₈N₆MoSi: C, 76.73; H, 7.99; N, 6.17.

Found: C, 76.48; H, 7.86; N, 6.08.

1

mmol); yield 53 mg (0.078 mmol, 57%). H NMR (C₆D₆): δ 2.908

15

2

3

1

(dd, N-CH₃, J _H,) 3, J _H,) 0.6). ¹⁵N NMR (C₆D₆/THF): δ

1

15

N

407.02 (d, N_R, J_NN) 16), 231.94 (d, N_â, J_NN) 16). ¹³C NMR (C₆D₆/

THF): δ 40.188 (dd, ¹⁵N-CH₃, J

_N) 8.8, J

_N) 4.5). IR (Nujol;

1

2

13 15

C,

cm^-1): 1542.

[Me₂C₆H₃N₃N]Mo-NdN-Me (6d). This material was synthesized

in a manner similar to that used to prepare 6a, starting from 2d (236

mg, 0.175 mmol) and methyl tosylate (65 mg, 0.35 mmol). Three hours

were sufficient for complete reaction; yield 78 mg (0.13 mmol, 37%).

¹H NMR (C₆D₆): δ 7.01 (s, 6, ortho), 6.57 (s, 6, para), 3.64 (t, 6, CH₂),

3.11 (s, 6, N-Me), 2.28 (t, 6, CH₂), 2.23 (s, 18, 3,5-Me₂). ¹³C NMR

(C₆D₆): δ 159.50 (C_ipso), 137.28 (C_p), 123.61 (C_m), 120.13 (C_o), 56.33

(CH₂), 53.36 (CH₂), 40.57 (NCH₃), 21.66 (3,5-Me₂). IR (cm^-1): 1603

(Nujol), 1602 (THF). Anal. Calcd for C₃₁H₄₂N₆Mo: C, 62.61; H, 7.12;

N, 14.13. Found: C, 62.48; H, 7.19; N, 14.02.

[TerN₃N]Mo-NdN-Me (6f). A 20 mL reaction vial was charged

with 4f-DME (316 mg, 0.15 mmol), methyl tosylate (56 mg, 0.30

mmol), and THF (6 mL). The reaction mixture was stirred for 4 h,

during which time the color lightened from dark burgundy to yellow.

1,4-Dioxane (0.5 mL) was added. The white precipitate was filtered

off, and THF was removed from the filtrate in vacuo. The residue was

washed three times with ether, and dried in vacuo; yield 200 mg (0.207

mmol, 69%). Analytically pure material was obtained by recrystalli-

1

zation from toluene. H NMR (C₆D₆): δ 7.77 (d, 12, 3,5-ortho), 7.67

(s, 6, ortho), 7.57 (s, 3, para), 7.20 (t, 12, 3,5-meta), 7.13 (t, 3, 3,5-

para), 3.66 (t, 6, CH₂), 2.83 (s, 3, N-Me), 2.36 (t, 6, CH₂). ¹³C NMR

(THF): δ 159.36 (C_ipso), 141.77 (C_m), 141.61 (3,5-ipso), 128.25 (3,5-

meta), 127.07 (3,5-ortho), 126.59 (3,5-para), 119.35 (C_o), 118.62 (C_p),

56.30 (CH₂), 52.83 (CH₂), 38.79 (NCH₃). IR (cm^-1):1596 (Nujol), 1596

(THF). Anal. Calcd for C₆₁H₅₄N₆Mo: C, 75.76; H, 5.63; N, 8.69.

Found: C, 75.58; H, 5.68; N, 8.59.

{[t-BuC₆H₄N₃N]ModN-NMe₂}OTs (7). Solid methyl tosylate (67

mg, 0.36 mmol) was added to a solution of 6c (204 mg, 0.3 mmol) in

THF (10 mL). No immediate color change was observed. The ¹H NMR

spectrum of an aliquot taken after 2 h indicated 50% conversion to

product. Another 25 mg (0.05 mmol, 17 equiv) of MeOTs were added,

and the reaction was stirred for 36 h. Proton NMR indicated the reaction

[PhN₃N]Mo-NdN-Me (6a). Solid methyl tosylate (56 mg, 0.3

mmol) was added to a solution of 2a (177 mg, 0.15 mmol) in THF (12

mL). The reaction was stirred at room temperature for 6 h. (A solution

IR study of an aliquot after 3 h suggested incomplete reaction). The

THF was removed, and the residue was dissolved in toluene. Insoluble

material was filtered off to yield a clear yellow solution. The solvent

was removed in vacuo, and the residue was washed with ether to give

89 mg (0.174 mmol, 58%) of the product as a yellow powder.

Analytically pure material was obtained by recrystallization from

1

toluene. H NMR (C₆D₆): δ 7.24 (t, 6, meta), 7.17 (d, 6, ortho), 6.88

(t, 3, para), 3.52 (t, 6, CH₂), 2.99 (s, 3, NCH₃), 2.18 (t, 6, CH₂). ¹³C

Mo and W Complexes with Triamidoamine Ligands

Inorganic Chemistry, Vol. 40, No. 16, 2001 3877

to be 93% complete. THF was removed in vacuo, and the residue was

dissolved in ether. The ether solution was filtered through Celite.

Pentane was added to the filtrate, and the mixture was stored at -35

°C for several weeks to yield 167 mg of purple crystals of product

41.44 (NCH₃). ¹⁹F NMR (CH₂Cl₂): δ -79.07 (s, triflate), -148.92 (d,

6, ortho), -157.13 (t, 3, para), -161.59 (t, 6, meta). Anal. Calcd for

C₂₇H₁₈F₁₈N₆O₃SMo: C, 34.34; H, 1.92; N, 8.90. Found: C, 34.48. H,

2.05; N, 8.83.

1

(0.193 mmol, 64%). H NMR (C₆D₆): δ 8.24 (d, 2, Ts), 7.25 (d, 6,

{[FC₆H₄N₃N]ModN-N(Me)(SiMe₃)}OTf(toluene)_0.5(9b). A solu-

tion of 5b (441 mg, 0.71 mmol) in toluene (10 mL) was cooled to

-35 °C. A separate solution of methyl triflate (328 mg, 2.0 mmol) in

toluene was cooled to -35 °C and added slowly to the reaction mixture.

The color changed from yellow to orange and an orange powder

precipitated before addition of the methyl triflate was complete. No

further changes were observed over a period of 1 h. The toluene was

decanted away from the product, which was washed with toluene and

pentane and dried in vacuo; yield 555 mg (0.705 mmol, 99%). ¹H NMR

(CDCl₃): δ 7.11 (dd, 6, Ar), 6.99 (t, 6, Ar), 4.23 (t, 6, CH₂), 3.62 (t,

6, CH₂), 2.04 (s, 3, N-Me), -0.38 (s, 9, SiMe₃). ¹³C NMR (CH₂Cl₂):

δ 160.30 (d, C_p, J_CF) 244), 154.26 (s, C_ipso), 125.20 (d, C_o, J_CF) 8),

115.85 (d, C_m, J_CF) 23), 61.31 (CH₂), 54.15 (CH₂), 36.35 (NCH₃),

-2.72 (SiMe₃). ¹⁹F NMR (CDCl₃): δ -77.97 (OTf), -116.81 (7 lines).

Anal. Calcd for C₃₂H₄₀F₆N₆O₃SSiMo: C, 46.49; H, 4.88; N, 10.16.

Found: C, 46.15; H, 4.71; N, 9.79.

Ar), 7.22 (d, 6, Ar), 6.96 (d, 2, Ts), 3.94 (t, 6, CH₂), 2.90 (t, 6, CH₂),

2.45 (s, 6, NMe₂), 2.02 (s, 3, Ts Me), 1.22 (s, 27, t-Bu). ¹³C NMR

(C₆D₆): δ 156.97 (C_ipso), 145.44 (C_p), 138.54 (Ts), 128.76 (Ts), 128.35

(Ts), 127.25 (Ts), 125.52 (C_o), 121.98 (C_m), 59.02 (CH₂), 55.88 (CH₂),

41.72 (NCH₃), 34.26 (t-Bu), 31.72 (t-Bu Me), 21.24 (Ts Me). Anal.

Calcd for C₄₅H₆₄N₆O₃SMo: C, 62.48; H, 7.46; N, 9.72. Found: C,

62.52; H, 7.40; N, 9.64.

{[FC₆H₄N₃N]ModN-NMe₂}OTf (8b). (a) From 6b. This material

was synthesized in a manner similar to that used to prepare 7, starting

from 6b (153 mg, 0.271 mmol) and methyl triflate (51 mg, 0.31 mmol);

1

yield 160 mg (0.22 mmol, 81%). H NMR (CDCl₃): δ 7.08 (dd, 6,

Ar), 6.98 (t, 6, Ar), 4.22 (t, 6, CH₂), 3.64 (t, 6, CH₂), 2.24 (s, 6, N-Me₂).

¹³C NMR (CH₂Cl₂): δ 160.21 (d, C_p, J_CF) 244), 154.31 (d, C_ipso

,

J_CF) 3), 124.57 (d, C_o, J_CF) 8), 115.68 (d, C_m, J_CF) 22), 60.80

(CH₂), 54.61 (CH₂), 41.17 (NCH₃). ¹⁹F NMR (CDCl₃): δ -77.97 (OTf),

-116.71 (7 lines). Anal. Calcd for C₂₇H₃₀F₆N₆O₃SMo: C, 44.51; H,

4.15; N, 11.54. Found: C, 44.46; H, 4.21; N, 11.46.

[FC₆H₄N₃N]MotN (10b). Solid sodium azide (52 mg, 0.8 mmol)

was added to a solution of [FC₆H₄N₃N]MoCl (297 mg, 0.533 mmol)

in THF (8 mL). The reaction was stirred for 2 days, during which time

the color changed from orange to green. The reaction was filtered

through Celite in order to remove NaCl. The THF was removed in

vacuo and the residue was washed with ether. The red ether-soluble

material was washed away to leave a yellow solid; yield 162 mg (0.303

mmol, 57%). Analytically pure material was obtained by recrystalli-

(b) From 9b. An orange solution of 9b (100 mg, 0.131 mmol) in

CH₂Cl₂(6 mL) was cooled to -35 °C. A separate solution of methyl

triflate (43 mg, 0.262 mmol) in 2 mL of CH₂Cl₂was cooled to -35

°C and added slowly to the reaction mixture. No color change was

observed. ¹H and ¹⁹F NMR spectra of an aliquot taken after 1 h indicated

25% conversion to product. An additional 60 mg of methyl triflate

was added, and the reaction was allowed to stir overnight. NMR spectra

taken at this time indicate complete consumption of starting material.

The solvent was removed in vacuo, and the residue was extracted with

a 1:1 mixture of THF and toluene. The insoluble orange powder was

washed with toluene and pentane, and dried in vacuo; yield 40 mg

(0.055 mmol, 42%).

1

zation from toluene. H NMR (C₆D₆): δ 7.38 (dd, 6, Ar), 6.80 (t, 6,

Ar), 3.25 (t, 6, CH₂), 2.07 (t, 6, CH₂). ¹³C NMR (THF): δ 158.76 (d,

C_p, J_CF) 239), 157.08 (s, C_ipso), 121.20 (d, C_o, J_CF) 8), 113.70 (d,

C_m, J_CF) 22), 56.32 (CH₂), 50.49 (CH₂). ¹⁹F NMR (C₆D₆): δ -122.16

(7 lines). Anal. Calcd for C₂₄H₂₄F₃N₅Mo: C, 53.84; H, 4.52; N, 13.08.

Found: C, 53.91; H, 4.40; N, 12.95.

{[t-BuC₆H₄N₃N]ModN-NMe₂}OTf (8c). (a) From 5c. A solution

of 5c (315 mg, 0.426 mmol) in 12 mL of toluene was cooled to -35

°C. A separate solution of methyl triflate (197 mg, 1.2 mmol) in 3 mL

of toluene was cooled to -35 °C and added dropwise to the solution

of 5c, resulting in an immediate color change from yellow to orange.

The reaction was allowed to warm to room temperature over a period

of 10 h. The volume was reduced to 1 mL in vacuo, and pentane was

added. The orange crystals were collected, washed with ether, and dried

[t-BuC₆H₄N₃N]MotN (10c). Solid sodium azide (49 mg, 0.75

mmol) was added to a solution of [t-BuC₆H₄N₃N]MoCl (335 mg, 0.5

mmol) in THF (8 mL). The reaction was stirred for 2 days. The green

reaction mixture was filtered through Celite. The THF was removed

in vacuo, and the residue was washed with ether to give a yellow solid;

yield 188 mg (0.29 mmol, 58%). Analytically pure material was

obtained by recrystallization from a mixture of toluene and pentane.

¹H NMR (C₆D₆): δ 7.63 (d, 6, meta), 7.16 (d, 6, ortho), 3.50 (t, 6,

CH₂), 2.16 (t, 6, CH₂), 1.24 (s, 27, t-Bu). ¹³C NMR (C₆D₆): δ 159.22

(C_ipso), 145.50 (C_p), 125.53 (C_o), 121.02 (C_m), 56.61 (CH₂), 51.33 (CH₂),

34.71 (t-Bu), 32.23 (t-Bu Me). Anal. Calcd for C₃₆H₅₁N₅Mo: C, 66.55;

H, 7.91; N, 10.78. Found: C 66.64; H, 7.85; N, 10.62.

1

in vacuo; yield 222 mg (0.263 mmol, 62%). H NMR (C₆D₆): δ 7.21

(s, 12, aryl), 4.10 (t, 6, CH₂), 3.40 (t, 6, CH₂), 1.85 (s, 6, N-Me), 1.19

(s, 27, t-Bu). ¹H NMR (CDCl₃): δ 7.29 (d, 6, meta), 6.98 (d, 6, ortho),

4.24 (t, 6, CH₂), 3.67 (t, 6, CH₂), 2.10 (s, 3, N-Me), 1.27 (s, 27, t-Bu).

¹³C NMR (THF): δ 156.00 (C_ipso), 147.35 (C_p), 125.27 (C_o), 122.37

(C_m), 60.01 (CH₂), 54.21 (CH₂), 40.12 (NCH₃), 33.95 (t-Bu), 30.82

(t-Bu Me). ¹⁹F NMR (C₆D₆): δ -77.85. Anal. Calcd for C₃₉H₅₇F₃N₆O₃-

SMo: C, 55.57; H, 6.82; N, 9.97. Found: C, 55.41; H, 6.70; N, 9.88.

(b) From 6c. The procedure was identical starting with 6c (271 mg,

0.4 mmol), and MeOTf (72 mg, 0.44 mmol); yield 320 mg (0.38 mmol,

95%).

{[t-BuC₆H₄N₃N]ModN-N(CH₃)(¹³CH₃)}OTf (8c-¹³C). This mate-

rial was synthesized in a manner identical to that used to prepare

unlabeled 8c starting from 6c (82 mg, 0.12 mmol), and ¹³CH₃OTf (23

mg, 0.14 mmol); yield 88 mg (0.104 mmol, 87%).

[t-BuC₆H₄N₃N]Mo(Me)NNMe₂(11c). Solid 8c (146 mg, 0.173

mmol) was suspended in 5 mL of ether, and the solution was cooled

to -35 °C. An aliquot of MeMgBr (55 µL of a 3.0 M solution in ether,

0.165 mmol) was diluted to 1 mL, and the solution was added dropwise

to the stirred reaction mixture to give a midnight blue solution. Addition

of 1,4-dioxane (0.5 mL) resulted in the precipitation of a white powder,

which was removed by filtration through Celite. The ether was removed

in vacuo, and the residue was washed once with pentane. The product

was soluble enough in pentane to turn the pentane dark blue, but the

majority of the material did not dissolve. The pentane solution was

removed by pipet, and the remaining material was dried in vacuo; yield

105 mg (0.148 mmol, 86%). ¹H NMR (C₆D₆): δ 7.27 (d, 4, Ar), 7.18

(d, 2, Ar), 7.10 (d, 4, Ar), 6.96 (d, 2, Ar), 3.84 (dd, 2, backbone), 3.63

(6 lines, 2, backbone), 3.38 (t, 2, backbone), 3.12 (6 lines, 2, backbone),

2.57 (s, 6, NMe₂), 2.54 (t, 2, backbone), 2.33 (dd, 2, backbone), 1.29

(s, 18, t-Bu), 1.22 (s, 9, t-Bu), 0.60 (s, 3, MoMe). ¹³C NMR (THF): δ

156.68 (C_ipso), 155.82 (C_ipso), 140.59 (C_p), 138.27 (C_p), 124.14 (C_m),

124.03 (C_m), 117.98 (C_o), 117.39 (C_o), 62.65 (CH₂), 60.59 (CH₂), 57.83

(CH₂), 54.30 (CH₂), 41.77 (NCH₃), 33.58 (t-Bu), 33.47 (t-Bu), 31.08

(t-Bu Me), 31.01 (t-Bu Me), 16.48 (Mo-CH₃). Anal. Calcd for

C₃₉H₆₀N₆Mo: C, 66.08; H, 8.53; N, 11.86. Found: C, 65.93; H, 8.40;

N, 11.92.

{[t-BuC₆H₄N₃N]Mod¹⁵N-¹⁵NMe₂}OTf (8c-¹⁵N). This material was

synthesized in a manner identical to that used to prepare unlabeled 8c

starting from 6c-¹⁵N (40 mg, 0.058 mmol) and CH₃OTf (16 mg, 0.097

mmol); yield 49 mg (0.058 mmol, 100%):.¹⁵N NMR (C₆D₆/THF): δ

368.27 (d, N_R, J_NN) 11), 154.40 (d, N_â, J_NN) 11). ¹³C NMR (C₆D₆/

15

1

13 15

THF): δ 41.04 (d, N-CH₃, J

) 9.2).

C,

N

{[C₆F₅N₃N]ModN-NMe₂}OTf (8e). Methyl triflate (1.28 g, 7.80

mmol) was added to a solution of 5e (2.18 g, 2.60 mmol) in 40 mL of

toluene. The reaction was heated to 45 °C overnight, during which

time a yellow precipitate formed. The precipitate was collected, washed

with ether to remove unreacted starting material and dried in vacuo;

yield 2.36 g (2.50 mmol, 96%). ¹H NMR (CD₂Cl₂): δ 4.24 (t, 6, CH₂),

3.80 (t, 6, CH₂), 2.68 (s, 6, NCH₃). ¹³C NMR (CH₂Cl₂): δ 143.16,

141.29, 139.57, 137.53 (aryl), 131.69 (ipso), 60.88 (CH₂), 54.74 (CH₂),

[t-BuC₆H₄N₃N]Mo(¹³CH₃)NNMe₂(11c-¹³C(M)). This material was

prepared in a manner analogous to that used to prepare unlabeled

material starting from 8c (72 mg, 0.085 mmol) and ¹³CH₃MgI (0.05

3878 Inorganic Chemistry, Vol. 40, No. 16, 2001

Greco and Schrock

mL, 1.7 M in ether, 0.085 mmol). The crude product was subjected to

residue was washed with pentane (to remove naphthalene), followed

by ether (to remove dark red impurities). The resulting dark pink solid

was collected and dried in vacuo; yield 755 mg (0.51 mmol, 62%).

Analytically pure material was obtained by recrystallization from a

1

thermolysis. H NMR (C₆D₆): δ 0.59 (d, Mo¹³CH₃, J_CH) 121). ¹³C

NMR (C₆D₆): δ 18.03 (Mo¹³CH₃).

[t-BuC₆H₄N₃N]Mo(Me)NN(CH₃)(¹³CH₃) (11c-¹³C(N)). This mate-

rial was prepared in a manner analogous to that used to prepare

unlabeled material starting from 8c-¹³C (50 mg, 0.059 mmol) and CH₃-

MgBr (0.02 mL, 3.0 M in ether, 0.060 mmol). The crude product was

subjected to thermolysis. ¹H NMR (C₆D₆): δ 2.566 (d, N¹³CH₃,

1

mixture of THF and pentane. H NMR (C₆D₆): δ 12.22 (d, 6, meta),

3.05 (s, 27, t-Bu), 2.63 (d, 6, ortho), -11.05 (br s, 6, CH₂), -16 (br,

6, CH₂). Anal. Calcd for C₇₂H₁₀₂N₁₀W₂: C, 58.62; H, 6.97; N, 9.49.

Found: C, 58.54; H, 7.08; N, 9.38.

3

¹J_CH) 139), 2.568 (d, NCH₃, J_CH) 3). ¹³C NMR (C₆D₆): δ 43.35

{[t-BuC₆H₄N₃N]W-NdN-W[t-BuC₆H₄N₃N]}(BPh₄)₂(13). A so-

lution of 12 (148 mg, 0.1 mmol) was dissolved in CH₂Cl₂, and the

solution was cooled to -35 °C. Cp₂FeBPh₄(101 mg, 0.2 mmol) was

added as a solid, and the reaction mixture was allowed to warm to

room temperature while being stirred over a period of 45 min. All of

the ferrocenium salt dissolved, and the color of the reaction turned

black. The reaction mixture was filtered through Celite. The solvent

was removed from the filtrate in vacuo, and the oily residue was washed

with pentane (to produce a solid), toluene (to remove any unreacted

12), and pentane again (to remove toluene). The sample was dried in

vacuo to yield 180 mg (0.085 mmol, 85%) of a black powder.

Analytically pure material was obtained by recrystallization from a

(N¹³CH₃).

Thermolysis of 11c. A 20 mg sample of 11c was dissolved in C₆D₆.

The sample was transferred to an NMR tube which was flame sealed,

and the tube was heated in an oil bath. Decomposition of 11c required

2 days at 90 °C. Resonances in the NMR spectra of the final products

matched those of 10.

[C₆F₅N₃N]Mo(Me)NNMe₂(11e). This material was prepared in a

manner similar to that used to prepare 11c starting from 8e (368 mg,

0.39 mmol), and MeMgBr (0.13 mL of a 3.0 M solution in ether, 0.39

mmol). This compound is burgundy in color and completely insoluble

in pentane, so the final pentane washings were colorless; yield 250 mg

1

(0.308 mmol, 79%). H NMR (toluene-d₈, -20 °C) :δ 3.98 (m, 2),

mixture of dichloromethane and toluene at -35 °C. H NMR (CD₂-

3.56 (m, 4), 2.98 (m, 2), 2.62 (m, 2), 2.17 (m, 2), 2.13 (s, 6, N-CH₃),

0.18 (s, 3, Mo-CH₃). ¹³C NMR (toluene-d₈): δ 143.15 (d, J_CF) 243),

142.80 (d, C_p, J_CF) 244), 138.63 (d, J_CF) 249), 135.09 (br s, C_ipso),

62.97 (CH₂), 61.73 (CH₂), 60.78 (CH₂), 57.88 (CH₂), 39.77 (N-CH₃),

27.42 (Mo-CH₃). Anal. Calcd for C₂₇H₂₁F₁₅N₆Mo: C, 40.02; H, 2.61;

N, 10.37. Found: C, 39.92; H, 2.65; N, 10.28.

Cl₂): δ 7.36 (br s, 16, BPh₄ortho), 7.01 (t, 16, BPh₄meta), 6.96 (d,

12, H_m), 6.85 (t, 8, BPh₄para), 6.15 (d, 12, H_o), 4.18 (t, 12, CH₂), 2.84

(t, 12, CH₂), 1.20 (s, 54, t-Bu). ¹³C NMR (CH₂Cl₂): δ 163.92 (q, BPh₄

ipso, J_BC) 49), 154.30 (C_ipso), 150.09 (C_p), 135.95 (BPh₄meta), 126.44

(C_m), 125.80 (BPh₄ortho), 122.00 (BPh₄para), 121.38 (C_o), 61.68

(CH₂), 53.26 (CH₂), 34.49 (t-Bu), 31.33 (t-Bu). Anal. Calcd for

C₁₂₀H₁₄₂N₁₀B₂W₂: C, 68.19; H, 6.77; N, 6.63. Found: C, 68.26; H,

6.84; N, 6.49.

[C₆F₅N₃N]Mo(¹³CH₃)NNMe₂(11e-¹³C). This material was prepared

in a manner analogous to that used to prepare unlabeled material starting

from 8e (80 mg, 0.085 mmol) and ¹³CH₃MgI (0.05 mL, 1.7 M in ether,

0.085 mmol). The crude material was subjected to thermolysis. ¹H NMR

(C₆D₆): δ 0.29 (d, Mo¹³CH₃, J_CH) 124). ¹³C NMR (C₆D₆): δ 27.35

(Mo¹³CH₃).

Thermolysis of 11e. A 20 mg sample of 11e was dissolved in C₆D₆,

toluene-d₈, or THF. The sample was transferred to an NMR tube which

was flame sealed, and the tube was heated in an oil bath. Decomposition

of 11e was complete after 24 h at 60 °C. Resonances in the NMR

spectra of the final products matched those of 10.

[t-BuC₆H₄N₃N]W-NdN-W[t-BuC₆H₄N₃N] (12). A solution of

[t-BuC₆H₄N₃N]WCl (1.26 g, 1.66 mmol) in THF (10 mL) was cooled

to -40 °C. A 0.33 M stock solution of sodium naphthalenide (6.00

mL, 1.98 mmol) in THF was diluted to 20 mL, and the solution was

cooled to -40 °C. The two solutions were added simultaneously to a

100 mL flask containing THF (10 mL), which was being vigorously

stirred. The reaction mixture was stirred for 2 h as it was allowed to

warm to room temperature. It was filtered through Celite to remove

NaCl. The solvent was removed from the filtrate in vacuo, and the

Acknowledgment. R.R.S. is grateful to the National Insti-

tutes of Health (Grant GM 31978) for research support. We

thank Dr. Ramachandra Dasari and Dr. Gene Hanlon in the

Harrison Spectroscopy Laboratory for Raman spectra and Dr.

Peter J. Bonitatebus, Jr. for assistance with X-ray crystal-

lography.

Supporting Information Available: X-ray crystallographic files

in CIF format for the structure determinations of 1c, 2a, 3c, and 4f.

Figures showing the CV's of [Me₂C₆H₃N₃N]Mo-NdN-Na(THF)_x

(2d), [PhN₃N]Mo-NdN-Na(THF)_x(2a), {[t-BuC₆H₄N₃N]W-NdN-

W[t-BuC₆H₄N₃N]}(BPh₄)₂(13), {[FC₆H₄N₃N]ModN-NMe₂}OTf (8b),

{[t-BuC₆H₄N₃N]ModN-NMe₂}OTf (8c), and {[C₆F₅N₃N]ModN-

NMe₂}OTf (8e). This material is available free of charge via the Internet

at http://pubs.acs.org.

IC001123N

Article Doi

Synthesis, structure, and electrochemical studies of molybdenum and tungsten dinitrogen, diazenido, and hydrazido complexes that contain aryl-substituted triamidoamine ligands

DOI: 10.1021/ic001123n

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Article abstract of DOI:10.1021/ic001123n

Full text of DOI:10.1021/ic001123n

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