Synthesis and X-ray characterization of a monomeric Cp-free dMmido-vanadiumOrv complex

Article abstract of DOI:10.1039/b008761k

Straightforward synthesis of the new imido complexes ArN=V(NMe2)2(HNMe2)2 1 and ArN=VCl₂(HNMe₂)₂ 2 (Ar = 2,6-i-Pr₂C₆H₃) is described along with the molecular structure of 2 and preliminary ethylene polymerization catalytic studies. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b008761k

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis and X-ray characterization of a monomeric Cp-free
d1-imido–vanadium(IV) complex
Christian Lorber,* Bruno Donnadieu and Robert Choukroun*
Equipe Précurseurs Moléculaires et Matériaux, Laboratoire de Chimie de Coordination,
CNRS UPR 8241, 205 route de Narbonne, 31077 Toulouse Cedex 04, France.
E-mail: lorber@lcc-toulouse.fr
Received 31st October 2000, Accepted 6th November 2000
First published as an Advance Article on the web 27th November 2000
Straightforward synthesis of the new imido complexes
ArN᎐V(NMe ) (HNMe ) 1 and ArN᎐VCl (HNMe ) 2
᎐
᎐
2
2
2
2
2
2 2
(Ar ؍ 2,6-i-Pr2C6H3) is described along with the molecular
structure of 2 and preliminary ethylene polymerization
catalytic studies.
Few areas of inorganic chemistry have experienced such
remarkable growth in recent years as that of transition metal
imido chemistry.1 In the case of imides of the Group 5 transi-
tion metals, the majority contain the d0-(V᎐NR) functional
᎐
group. However, paramagnetic d1-vanadium monoimides have
been known for some time with stabilizing cyclopentadienyl
ligands.2 Nevertheless, there are only a few examples of isolated
d1-(V᎐NR) complexes that do not contain one or two cyclo-
᎐
pentadienyl ligands, and, to our knowledge none of them have
been structurally characterized,1,3–5 except the heptamer com-
plex [t-BuNH3]2[(t-BuN)7V7(µ-Cl)14Cl2].6 Within this context,
and in relation to our recent studies on bis-amido–vanadium()
complexes as catalysts for olefin polymerization,7,8 we wish to
report the unprecedented synthesis and single crystal X-ray
structure of a monomeric vanadium() imido complex without
Cp co-ligands.
Fig. 1 Molecular structure of 2 with selected bond distances (Å) and
angles (Њ); V1–N1 1.654(3), V1–N2 2.018(5), V1–N3 2.171(4), V1–Cl1
2.3202(14), V1–Cl2 2.3257(12), N1–C1 1.388(5), C1–N1–V1 178.4(3),
Cl1–V1–Cl2 136.48(5), N2–V1–N3 165.23(16).
atoms, and have V–Namine bonds of 2.018(5) and 2.171(4) Å and
a Namine–V–Namine angle of 165.23(16)Њ.
Reaction of 2,6-isopropylaniline, ArNH2 (Ar = 2,6-i-Pr2-
C6H3), with V(NMe2)4 in toluene at 100 ЊC for 1 day affords the
Both 1 and 2 are paramagnetic; EPR spectra of toluene
solutions at room temperature show typical eight band patterns
for d1-vanadium() species, with g = 1.985, a(51V) = 65.3 G
and g = 1.989, a(51V) = 92.5 G, respectively. Additionally,
magnetic susceptibility measurements have been carried out
on 2. The effective moment µeff is 1.744µB at 300 K, which is
consistent with a VIV unit.
arylimido complex ArN᎐V(NMe ) (NHMe ) 1 (see Scheme 1)
᎐
2
2
2 2
Compound 2 may be the key starting material in a whole
new coordination chemistry of vanadium. Preliminary studies
show that HNMe2 ligands in 2 can be displaced by amines,
phosphines, and 2,2Ј-bipyridine. For example, after dissolution
of 2 in pyridine, the complex ArN᎐VCl (Py) has been quanti-
᎐
2
3
tatively synthesized and characterized by single crystal X-ray
crystallography.8
The complexes 1 and 2 will provide interesting comparisons
with their titanium/zirconium analogues9 and with very recent
amido-,10 bis-amido-7,8 or linked Cp–amido-11 vanadium()
complexes that are active olefin polymerization catalysts.
Indeed, preliminary studies demonstrate that 1 is an active
catalyst for ethylene polymerization when 10 equivalents of
EtAlCl2 are used as co-catalyst (activity = 2.2 × 104 (g of PE)
(mol catalyst)Ϫ1 hϪ1 atmϪ1. Similarly, a combination of 2/MAO
(ratio 1/500, MAO = methylaluminoxane) or 2/EtAlCl2 (ratio
1/10) catalyzes ethylene polymerization at room temperature
and under 1 atm of ethylene (with activities of 5.9 × 104 and
1.2 × 105 (g of PE) (mol catalyst)Ϫ1 hϪ1 atmϪ1, respectively).
Solid polyethylene is obtained in all cases, and in the tests run
with EtAlCl2 as activator high molecular weight polyethylene
was formed (see Table 1).
Scheme 1 Synthesis of complexes 1 and 2.
as a dark red solid, after recrystallization from cold pentane.
The bis-chloro analogue, namely ArN᎐VCl (HNMe ) 2, is
᎐
obtained by treatment of 1 with an excess of2chlorotr2imethyl-
silane at room temperature in toluene (Scheme 1, yield = 82%
with respect to V(NMe2)4).†‡
2
The crystal structure of 2 is presented in Fig. 1 and confirms
the presence of a bis-dimethylamine adduct.§ The molecular
structure is best described as distorted square-pyramid with an
axial arylimido that exhibits a V–N distance of 1.654(3) Å,
the imido linkage being almost linear (V1–N1–C1 angle =
178.4(3)Њ). The two chlorine atoms are mutually trans with
a Cl1–V1–Cl2 angle of 136.48(5)Њ and V1–Cl bonds of
2.3202(14) and 2.3257(12) Å. The two trans dimethylamino
ligands form the base of the square-pyramid with the chlorine
In summary, we have described a convenient synthesis of
imido–vanadium() complexes 1 and 2, and, to our knowledge,
DOI: 10.1039/b008761k
J. Chem. Soc., Dalton Trans., 2000, 4497–4498
This journal is © The Royal Society of Chemistry 2000
4497

View Article Online
Table 1 Results of ethylene polymerisation runs using pre-catalysts 1 and 2a
Polymer
yield/mg
Productivity/(g of PE)
(mol catalyst)Ϫ1 hϪ1 atmϪ1 Mn
d
d
Run
Precatalyst
Activator
Time/min
Mw
Mw/Mn
1
2
3
1b
2c
2b
EtAlCl2
MAO
EtAlCl2
3
10
2
35
254
98
2.2 × 104
5.9 × 104
1.2 × 105
6.285 × 105
6.490 × 103
6.505 × 105
1.795 × 106
2.146 × 104
1.933 × 106
2.875
3.306
2.972
a General conditions: 0.025 mmol of pre-catalyst dissolved in 5 g of toluene, 20 ЊC, 1 atm of ethylene. b EtAlCl2 10 equiv. c MAO 500 equiv.
d Determined by SEC analysis.
the first structurally characterized monomeric d1-(V᎐NR)
GOF = 1.067. Data collection were performed at ca. 160 K on a
᎐
STOE Imaging Plate Diffraction System (I.P.D.S) diffractometer using
graphite monochromatized Mo-Kα radiation. The structure was solved
by direct methods and subsequent difference Fourier maps. CCDC
reference number 186/2265. See http://www.rsc.org/suppdata/dt/b0/
complex that does not possess Cp ligands. We have also
demonstrated the activity of such imido complexes as catalysts
for ethylene polymerization. Full details of the coordination
chemistry, reactivity, and olefin polymerization activity of 1
b008761k/ for crystallographic files in .cif format.
and 2 and other analogues will be published shortly.
We are grateful to the CNRS for financial support, and to
1 D. E. Wigley, Progress in Inorganic Chemistry, ed. K. D. Karlin,
Dr G. Langstein (Bayer, Germany) for polymer analyses.
Interscience, New York, vol. 42, 1994, pp. 239–482.
2 (a) N. Wiberg, H.-W. Häring and U. Schubert, Z. Naturforsch.,
Teil B, 1980, 35, 599; (b) F. Preuss, H. Becker and T. Wieland,
Z. Naturforsch., Teil B, 1988, 43, 1195; (c) S. Gambarotta, A. Chiesi-
Villa and C. Guastini, J. Organomet. Chem., 1984, 270, C49.
3 (a) J. W. Buchler and S. Pfeifer, Z. Naturforsch., Teil B, 1985,
40, 1362; (b) U. Piarulli, E. Solari, C. Floriani, A. Chiesi-Villa and
C. Rizzoli, J. Am. Chem. Soc., 1996, 118, 3634.
4 W.-H. Leung, A. A. Danopoulos, G. Wilkinson, B. Hussain-Bates
and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1991, 2051.
5 M. Mazzanti, M. Kadkhodayan and W. H. Armstrong, Abstract of
the 203rd National Meeting, ACS, INOR No. 461, San Francisco,
CA, 1992.
6 F. Preuss, J. Perner, W. Frank and G. Reiss, Z. Anorg. Allg. Chem.,
1999, 625, 901.
7 C. Lorber, B. Donnadieu and R. Choukroun, Organometallics,
2000, 19, 1963.
8 C. Lorber, unpublished work.
9 (a) R. Duchateau, A. J. Williams, S. Gambarotta and M. Y. Chiang,
Inorg. Chem., 1991, 30, 4863; (b) R. D. Profilet, C. H. Zambrano,
P. E. Fanwick, J. J. Nash and I. P. Rothwell, Inorg. Chem., 1990, 29,
4362; (c) D. J. Arney, M. A. Bruck, S. R. Huber and D. E. Wigley,
Inorg. Chem., 1992, 31, 3749.
Notes and references
† Direct synthesis of 2: A toluene solution (4 g) of 1.00 g of V(NMe2)4
(4.40 mmol) and 780 mg of 2,6-i-Pr2C6H3NH2 (4.40 mmol) was heated
at 100 ЊC for 1 day giving a dark red solution. After removal of
the volatiles, toluene (4 g) and Me3SiCl (4.00 g) were added and the
solution was stirred for 2 days. Removal of the volatiles and recrystal-
lization in cold pentane afforded 1.40 g of dark red-purple crystals of 2
(82%). These compounds release NHMe2 during standard combustion
analysis and therefore satisfactory (C,H,N) elemental analyses have not
been obtained (and correspond to partial (for 2) or total (for 1) loss
of the NHMe2 ligands). When 2 is reacted with pyridine however,
an exchange reaction occurs leading to red microcrystals of ArN᎐
᎐
VCl2(Py)3. The pyridine ligands of this material are more strongly
bound to the metal, permitting a satisfactory elemental analysis to
be obtained.
‡ Selected data for 1 and 2: 1 EPR (PhCH3, 20 ЊC) g = 1.985,
a(51V) = 65.3 G, IR (KBr) νV᎐N = 952 cmϪ1. 2 EPR (PhCH3, 20 ЊC)
g = 1.989, a(51V) = 92.5 G. µef᎐f = 1.744µB (300 K), IR (KBr) νV᎐N
=
᎐
934 cmϪ1
.
§ Crystallographic data for 2: C16H31Cl2N3V, M = 387.28, monoclinic,
space group P21/n, a = 10.6595(13), b = 9.7366(10), c = 20.783(2) Å,
β = 103.099(14)Њ, U = 2100.9(4) Å3, Z = 4, Dc = 1.224 Mg mϪ3, R
(Rw) = 0.0905 (0.1374) for 2726 unique data and 213 parameters,
10 N. D. Desmangles, S. Gambarotta, C. Bensimon and S. Davis,
J. Organomet. Chem., 1998, 562, 53.
11 P. T. Witte, A. Meetsma and B. Hessen, Organometallics, 1999, 18,
2944.
4498
J. Chem. Soc., Dalton Trans., 2000, 4497–4498