Synthesis and Structure of a Trigonal Monopyramidal Vanadium(III) Complex, [(C6F5NCH2CH2)3N]V, and the Vanadium(IV) Product of Its Oxidation, {[(C6F5NCH2CH2)2N(CH 2CH2NHC6F5)]V(O)}2

Full text of DOI:10.1021/ic960889d

Inorg. Chem. 1997, 36, 123-125
123
Synthesis and Structure of a Trigonal
Monopyramidal Vanadium(III) Complex,
[(C6F5NCH2CH2)3N]V, and the Vanadium(IV)
Product of Its Oxidation,
{[(C6F5NCH2CH2)2N(CH2CH2NHC6F5)]V(O)}2
Celine Rosenberger, Richard R. Schrock,* and
William M. Davis
Department of Chemistry 6-331, Massachusetts Institute of
Technology, Cambridge, Massachusetts 02139
ReceiVed July 25, 1996
Introduction
A vanadium triamidoamine complex such as d2 [(RNCH2-
CH2)3N]V (e.g., R ) trialkylsilyl) would seem likely to form a
bimetallic or a monomeric dinitrogen complex for several
reasons. First, the apical coordination site contains two
orthogonal π orbitals and a σ orbital pointing along the z axis,
a circumstance that is optimal for binding dinitrogen in an “end-
on” fashion.1 Second, two triamidoamine complexes of mo-
lybdenum are known that contain a bridging dinitrogen,
{[N3NF]Mo}2(N2)2 ([N3NF]3- ) [(C6F5NCH2CH2)3N]3-) and
{[(t-BuMe2SiNCH2CH2)3N]Mo}2(N2).3 Third, monometallic
triamidoamine complexes that contain a single dinitrogen are
known, the sodium salt of the d4 “Mo(II)” species, {[N3NF]-
Mo(N2)}-,2 and the isoelectronic Re(III) species, [N3NF]Re-
(N2).4 Fourth, a wide variety of vanadium triamidoamine
complexes have been reported that contain a bulky silyl
group5-10 or the [N3NF]3- ligand.11 Finally, among the variety
of recently prepared vanadium complexes that contain di-
nitrogen12-20 are V(III) complexes that contain a µ dinitrogen
ligand. However, the d3 “trigonal monopyramidal” complex,
[(t-BuMe2SiNCH2CH2)3N]V,7 does not form either a terminal
or a µ dinitrogen complex readily. Here we show that [N3NF]V,
which can be prepared by reduction of [N3NF]VCl in a
Figure 1. Two views of [(C6F5NCH2CH2)3N]V.
noncoordinating solvent, also does not bind dinitrogen, or even
carbon monoxide.
Results and Discussion
Reduction of [N3NF]VCl11 with sodium amalgam in THF is
known to yield [N3NF]V(THF), in which THF occupies the
apical coordination position in an approximate trigonal bipyra-
mid. Other σ-bonding ligands such as nitriles or chloride ion
will form related species. However, reduction of [N3NF]VCl
with sodium amalgam in toluene yields dark green paramagnetic
[N3NF]V (1, eq 1) instead of the sodium salt of known11
(1) Schrock, R. R. Acc. Chem. Res. In press.
(2) Kol, M.; Schrock, R. R.; Kempe, R.; Davis, W. M. J. Am. Chem.
Soc. 1994, 116, 4382.
(3) Shih, K.-Y.; Schrock, R. R.; Kempe, R. J. Am. Chem. Soc. 1994, 116,
8804.
(4) Neuner, B.; Schrock, R. R. Organometallics 1996, 15, 5.
(5) Plass, W.; Verkade, J. G. J. Am. Chem. Soc. 1992, 114, 2275.
(6) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Organometallics 1992,
11, 1452.
(7) Cummins, C. C.; Lee, J.; Schrock, R. R.; Davis, W. M. Angew. Chem.,
Int. Ed. Engl. 1992, 31, 1501.
(8) Plass, W.; Verkade, J. G. Inorg. Chem. 1993, 32, 3762.
(9) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Inorg. Chem. 1994,
33, 1448.
(10) Hill, P. L.; Yap, G. A.; Rheingold, A. L.; Maatta, E. A. J. Chem.
Soc., Chem. Commun. 1995, 737.
(11) Nomura, K.; Schrock, R. R.; Davis, W. M. Inorg. Chem. 1996, 35,
3695.
(12) Hidai, M.; Mizobe, Y. Chem. ReV. 1995, 95, 1115.
(13) Woitha, C.; Rehder, D. Angew. Chem., Int. Ed. Engl. 1990, 29, 1438.
(14) Leigh, G. J.; Prietoalcon, R.; Sanders, J. R. J. Chem. Soc., Chem.
Commun. 1991, 921.
(15) Rehder, D.; Woitha, C.; Priebsch, W.; Gailus, H. J. Chem Soc., Chem.
Commun. 1992, 364.
(16) Ferguson, R.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.
Angew. Chem., Int. Ed. Engl. 1993, 32, 396.
(17) Buijink, J.-K. F.; Meetsma, A.; Teuben, J. H. Organometallics 1993,
12, 2004.
(18) Berno, P.; Hao, S.; Minhas, R.; Gambarotta, S. J. Am. Chem. Soc.
1994, 116, 7417.
(19) Song, J.-I.; Berno, P.; Gambarotta, S. J. Am. Chem. Soc. 1994, 116,
6927.
{[N3NF]VCl}-. The observed magnetic moment of [N3NF]V
at room temperature by the Evans method was 3.7 µB, slightly
higher than µ for [(t-BuMe2SiNCH2CH2)3N]V7 (3.1 µB), but
essentially the same as that for [N3NF]V(THF) (3.7 µB).11 All
data are consistent with these complexes being high-spin V(III)
(d3) species.
The crystal structure of 1 (Figure 1) shows it to be a trigonal
monopyramid with a core structure that is closely similar to
that of [(t-BuMe2SiNCH2CH2)3N]V7 (Table 1). The vanadium
atom is displaced from the amido plane by only 0.21 Å in the
direction of the vacant coordination site, and the V-N(2) bond
length is consequently relatively short. The V-N(1)-C(11)
angle is approximately 125°, a typical value for many triami-
doamine complexes.1 Since Câ,ax is the “flap” in the envelope-
shaped VN2C2 ring, the N(2)-V-N(1)-C(11) dihedral angle
is close to 180°. An important difference between the structure
(20) Gailus, H.; Woitha, C.; Rehder, D. J. Chem. Soc., Dalton Trans. 1994,
3471.
S0020-1669(96)00889-0 CCC: $14.00 © 1997 American Chemical Society

124 Inorganic Chemistry, Vol. 36, No. 1, 1997
Notes
Table 1. Summary of Crystallographic Data for 1 and 2
1
2
empirical formula
fw
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C24H12F15N4V
692.32
14.40(2)
14.40(2)
21.84(4)
90
90
120
3923(9)
R3h
6
C24H13F15N4VO
709.31
24.4401(4)
19.2403(4)
17.0602(2)
90
116.3690(10)
120
7187.6(2)
C2/c
space group
Z
8
F
Calcd (g cm-3
)
1.758
0.0697
1.309
0.0801
R1 (all data)a
a R1 ) ∑||Fo| - |Fc||/∑|Fo|.
Figure 2. A view of the structure of {[(C6F5NCH2CH2)2N(CH2CH2-
NHC6F5)]V(O)}2.
of 1 and an analogous [N3NF]3- complex that contains a ligand
in the apical coordination site (such as [N3NF]V(THF)11 or
[N3NF]MoCl2) is that the three C6F5 rings are not arranged to
produce a bowl-like cavity, but turned so that the ortho fluorines
“fill” the apical cavity. In fact, the V‚‚‚Fortho distance (2.652
Å) could be construed as a weak interaction. The positions of
the fluorines are roughly the same relative to the V(Neq)3
framework as the three hydrides in [(Me3SiNCH2CH2)3N]-
WH3.21 It is still possible that the C6F5 rings are oriented the
way they are only for steric reasons and that the V‚‚‚Fortho
distance is circumstantially short.
Table 2. Selected Interatomic Distances (Å) and Bond Angles
(deg) for [(RNCH2CH2)3N]V (R ) C6F5 or t-BuMe2Sia)
C6F5
t-BuMe2Si
V-N(1)
V(1)-N(2)
1.947(4)
2.079(6)
1.926(13)
2.083(3)
V-N(1)-X
N(1)-V-N(1*)
N(2)-V(1)-N(1)
125.4(3) (X ) C(11))
118.72(4)
83.45(10)
127.6(2) (X ) Si)
119.2(1)
84.9(1)
a See ref 7.
Compound 1 reacts readily with THF to give [N3NF]V(THF),
and like [N3NF]V(THF), it reacts with propylene oxide to afford
[N3NF]VdO.11 However, it does not react with CO at 1 atm
and room temperature over a period of 24 h. Not surprisingly,
therefore, it also does not form stable [N3NF]V(N2). Apparently,
a good σ-donating ligand will bind to [N3NF]V to form an adduct
in which the electronic configuration can remain high spin.
Ligands that would bind largely via π back-bonding do not bind
to [N3NF]V, perhaps largely because the low-spin configuration
in triamidoamine complexes of this sort is required for efficient
binding and the high energy of the low-spin configuration cannot
be compensated by a high metal-ligand bond strength. Some-
what surprisingly, however, there also is no indication that 1
will form a µ dinitrogen complex analogous to several known
V(III) complexes and related to the Mo(IV) “diazenido(2-)”
species, [N3NF]MosNdNsMo[N3NF].2
During attempts to recrystallize 1 from toluene at room
temperature, bright green crystals formed over a period of 2
weeks. The relatively insoluble product (2) is also paramag-
netic, but its 19F NMR spectrum in THF reveals that it is no
longer C3 symmetric; two types of C6F5 groups are observed in
a 2:1 ratio, characteristic of a molecule with a mirror plane.
The IR spectrum revealed absorptions at 3683 and 3453 cm-1
consistent with N-H vibrations. An X-ray study (Figure 2,
Table 2) revealed that 2 is a V(IV) species containing a V2O2
core with one of the (protonated) arms of the [N3NF]3- ligand
not coordinated. We speculate that 1 was oxidized to 2 by traces
of water, as shown schematically in eq 2, even though the
Table 3. Selected Interatomic Distances (Å) and Bond Angles
(deg) for {[(C6F5NHCH2CH2)(C6F5NCH2CH2)2N]VO}2
V-O(1)
V-O(1)*
V-N(2)
2.042(4)
1.953(4)
2.079(5)
V-N(3)
V-N(4)
1.909(5)
2.185(5)
O(1)-V-N(4)
N(2)-V-N(3)
O(1)*-V-N(2)
O(1)*-V-N(3)
175.3(2)
116.1(2)
125.0(2)
118.3(2)
V-N(2)-C(21)
O(1)*-V-O(1)
V-O(1)-V*
130.5(4)
78.2(2)
101.8(2)
ment of traces of oxygen cannot be excluded at this stage. We
did not deliberately add known amounts of water or oxygen to
1. Each vanadium in 2 has approximately a trigonal bipyramidal
coordination geometry in which the two amido nitrogen atoms
(N(2) and N(3)) and one oxygen (O(1)*) make up the trigonal
plane; all V-Neq and V-Oeq distances are in the range 1.91-
1.95 Å. The other oxygen (O(1)) and the amine donor (N(4))
occupy apical coordination positions and have V-Nax and
V-Oax distances that are approximately 0.1 Å longer than the
V-Neq and V-Oeq distances. The vanadium-vanadium dis-
tance (3.100 Å), V-O-V angle (101.8(2)°), O-V-O angle
(78.2(2)°), and paramagnetic nature of 2 suggest that there is
little interaction between the metals. No intermolecular hydro-
gen bonding was found. Compound 2 is similar to the recently
published structure of {V(O)[N(SiMe3)2]2}2 in which the
arrangement about each V is pseudotetrahedral.22 In {V(O)-
[N(SiMe3)2]2}2, the V2O2 core is symmetric with V‚‚‚V ) 2.612-
(2) Å and V-O ) 1.802(4) Å. The shorter bond lengths are
to be expected in {V(O)[N(SiMe3)2]2}2 as a consequence of
four-coordination about V versus five-coordination about V in
2. Other examples of crystallographically characterized com-
plexes that contain V2O2 cores are known,23-25 but apparently
{V(O)[N(SiMe3)2]2}2 is the only other divanadium(IV) species.
(22) Duan, Z.; Schmidt, M.; Young, V. G. J.; Xie, X.; McCarley, R. E.;
Verkade, J. G. J. Am. Chem. Soc. 1996, 118, 5302.
(23) Edwards, A. J.; Slim, D. R.; Guerchais, J. E.; Sala-Pala, J. J. Chem.
Soc., Dalton Trans. 1977, 984.
(24) Bottomley, F.; Paez, D. E.; White, P. S. J. Am. Chem. Soc. 1985,
107, 7226.
sample was kept in a drybox. However, the possible involve-
(21) Schrock, R. R.; Shih, K.-Y.; Dobbs, D.; Davis, W. M. J. Am. Chem.
Soc. 1995, 117, 6609.

Notes
Inorganic Chemistry, Vol. 36, No. 1, 1997 125
s, 2), -165.9 (sharp, 2), -174.6 (sharp, 1), -175.2 ppm (sharp, 2); IR
In a typical divanadium(V) species the V2O2 core is even less
symmetric than found in the divanadium(IV) species, although
the V-O-V and O-V-O angles are similar to what is found
in the divanadium(IV) species. In {VO2F(bipy)}2, for ex-
ample,23 the V-O distances are 1.691 and 2.361 Å and the
V-O-V and O-V-O angles are 101.6 and 78.4°.
(Nujol, cm-1) 3683, 3453.
Reaction of [N3NF]V with Propylene Oxide. Propylene oxide (12
mg, 0.21 mmol) was added to a solution of [N3NF]V (0.1 g, 0.14 mmol)
in 15 mL of toluene. After 15 min the solvent was evaporated in vacuo,
and the known vanadium(V) oxo complex,11 [N3NF]VdO (90 mg, 91%),
was recovered and identified by NMR.
The “arm-off” feature of this molecule is what was found
also in five-coordinate [(C6F5NCH2CH2)2N(CH2CH2NHC6F5)]-
Re(O)Cl,4 although the details could not be elucidated by X-ray
crystallography as a consequence of a ligand disorder problem.
Triamido ligands are prone to protonolysis, and the monopro-
tonated form found in 2 and [(C6F5NCH2CH2)2N(CH2CH2-
NHC6F5)]Re(O)Cl is the first stage of a process that ultimately
would lead to the triamidoamine ligand being removed com-
pletely from the metal.
Description of the X-ray Study of [(C6F5NCH2CH2)3N]V. The
crystal was mounted under Paratone N and transferred to a Siemens
Smart/CCD, three-circle (ø fixed at 54.78°) diffractometer equipped
with a cold stream of N2 gas. An initial unit cell was determined by
harvesting reflections I > 20σI from 45 frames of 0.30 ω scan data
with monochromated Mo KR radiation (λ ) 0.710 73 Å). Crystal
quality was checked by computing 3.0° rocking curves from which
the ω width at half-height was found to be 0.23°. The data were
collected using 0.30 ω scans. The data that were collected (5413 total
reflections, 1261 unique, Rint ) 0.0611) were corrected for Lorentz
and polarization effects, but not for absorption. The structure was
solved (SHELXTL 5.0) by direct methods and standard difference
Fourier techniques. Crystallographic data: formula, C24H12F15N4V; fw,
692.32; space group, R3h; a ) 14.40(2) Å, b ) 14.40(2) Å, c )
21.84(4) Å; R ) 90°, â ) 90°, γ ) 120°; V ) 3923(9) Å3; Z ) 6;
FCalcd ) 1.758 g cm-3; R1 (all data) ) 0.0697.
Description of the X-ray Study of {[(C6F5NHCH2CH2)(C6F5-
NCH2CH2)2N]VO}2. The crystal was mounted under Paratone N and
transferred to a Siemens Smart/CCD, three-circle (ø fixed at 54.78°)
diffractometer equipped with a cold stream of N2 gas. An initial unit
cell was determined by harvesting reflections I > 20σI from 45 frames
of 0.30 ω scan data with monochromated Mo KR radiation (λ )
0.710 73 Å). Crystal quality was checked by computing 3.0° rocking
curves from which the ω width at half-height was found to be 0.23°.
The data were collected using 0.30 ω scans. The data that were
collected (8293 total reflections, 3330 unique, Rint ) 0.0942) were
corrected for Lorentz and polarization effects, but not for absorption.
The structure was solved (SHELXTL 5.0) by direct methods and
standard difference Fourier techniques. Crystallographic data: formula,
C24H13F15N4VO; fw, 709.31, space group, C2/c, a ) 24.4401(4) Å, b
) 19.2403(4) Å, c ) 17.0602(2) Å; R ) 90°, â ) 116.3690(10)°, γ )
120°; V ) 7187.6(2) Å3; Z ) 8; FCalcd ) 1.309 g cm-3; R1 (all data) )
0.0801.
It is clear from this study and earlier study7 that trigonal
monopyramidal complexes of V(III) that contain triamidoamine
ligands, at least the two that have been investigated so far, do
not bind even traditionally strong π acceptors such as CO
readily, let alone dinitrogen. It is also curious that no trigonal
monopyramidal complex of a second- or third-row metal (e.g.,
Ta, Mo, W, or Re) has yet been isolated.1 It is hoped that further
studies of triamidoamine complexes of the heavier, earlier
metals, especially Mo, will provide some answers as to why
this is the case. We suspect that such species can attain the
low-spin configuration, either prior to or during binding of a
ligand in the apical position, and therefore are much more
reactive.
Experimental Section
General experimental procedures and methods were analogous to
those described elsewhere.11
[N3NF]V (1). [N3NF]VCl (0.62 mmol, 0.45 g) was added to a
suspension of sodium amalgam (20 mg of Na in 3 g of Hg) in 15 mL
of toluene at room temperature. The reaction mixture was stirred for
15 h and filtered through a pad of Celite. The solvents were removed
in vacuo, and the resulting dark green solid was washed with pentane
and dried in vacuo: yield 340 mg (80%); 19F NMR (C6D6) δ -145
ppm (br s, 6), -179 ppm (br s, 3); no resonances were observed in 1H
NMR spectra; µ ) 3.7 at 22 °C (Evans method). Anal. Calcd for
C24H12F15N4V: C, 41.64; H, 1.75; N, 8.09. Found: C, 41.37; H, 1.70;
N, 8.21.
[{(C6F5NHCH2CH2)N(CH2CH2NC6F5)2}VO]2 (2). [N3NF]V (0.110
g) was dissolved in minimum toluene (∼5 mL), and the solution was
allowed to stand at room temperature in a closed vial in a nitrogen-
filled drybox for ∼2 weeks. Bright green crystals of 2 (72 mg) were
collected: yield 50%; 19F NMR (C6D6) δ -150.1 (br s, 4), -158.9 (br
Acknowledgment. We thank the National Institutes of
Health (GM 31978) for support and the National Science
Foundation for funds to help purchase a Siemens SMART/CCD
diffractometer.
Supporting Information Available: An ORTEP drawing, crystal
data and structural refinement, atomic coordinates, bond lengths and
angles, and anisotropic displacement parameters for both [(C6F5NCH2-
CH2)3N]V and {[(C6F5NHCH2CH2)(C6F5NCH2CH2)2N]VO}2 (11 pages).
Ordering information is given on any current masthead page.
(25) Colpas, G. J.; Hamstra, B. J.; Kampf, J. W.; Pecoraro, V. L. Inorg.
Chem. 1994, 33, 4669.
IC960889D