Synthesis and characterization of tantalum(V) complexes containing bis-sulfamide ligands: X-ray crystal structure of Ta[N(Me)2]3[SO2 (NCME3)2]

Article abstract of DOI:10.1016/S0277-5387(02)00933-6

The bis-sulfamide compounds, SO₂[NHCMe₃]₂ and SO₂{NH[CH(Me)Ph]} were successfully employed as chelating diamide ligands in the synthesis of the tantalum complexes Ta[N(Me)₂]₃[SO₂ (NCMe₃)₂] (1) and Ta(NMe₂)₃[SO₂(NCH(Me)Ph)₂] (2). Compound 1 assumes a distorted trigonal pyramidal geometry in the solid state as determined by an X-ray crystallograpic study. Compounds 1 and 2 are fluxional at room temperature. Variable temperature ¹H NMR was used to investigate the nature of these fluxional processes. In addition, preliminary attempts to generate halide and alkyl derivative of 1 and 2 are presented. Specifically, the reaction of 1 with excess A1R₃ (R = Me or Et), in order to generate alkyl derivatives of 1 led to the isolation of A1R₃ adducts.

Full text of DOI:10.1016/S0277-5387(02)00933-6

Polyhedron 21 (2002) 1051ꢁ1055
/
www.elsevier.com/locate/poly
Synthesis and characterization of tantalum(V) complexes containing
bis-sulfamide ligands: X-ray crystal structure of
Ta[N(Me)2]3[SO2(NCMe3)2]
R.C. Mills, P. Doufou, K.A. Abboud, James M. Boncella *
Department of Chemistry and Center of Catalysis, University of Florida, Gainesville, FL 32611, USA
Received 22 May 2001; accepted 28 February 2002
Abstract
The bis-sulfamide compounds, SO2[NHCMe3]2 and SO2{NH[CH(Me)Ph]} were successfully employed as chelating diamide
ligands in the synthesis of the tantalum complexes Ta[N(Me)2]3[SO2(NCMe3)2] (1) and Ta(NMe2)3[SO2(NCH(Me)Ph)2] (2).
Compound 1 assumes a distorted trigonal pyramidal geometry in the solid state as determined by an X-ray crystallograpic study.
Compounds 1 and 2 are fluxional at room temperature. Variable temperature 1H NMR was used to investigate the nature of these
fluxional processes. In addition, preliminary attempts to generate halide and alkyl derivative of 1 and 2 are presented. Specifically,
the reaction of 1 with excess AlR3 (RꢀMe or Et), in order to generate alkyl derivatives of 1 led to the isolation of AlR3 adducts.
/
# 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Bis-sulfamide; Tantalum(V); Diamide; Crystal structures
1. Introduction
interested in examining the chemistry of a relatively
unexplored class of bis-sulfamide ligands [28ꢁ31]. The
/
The organometallic chemistry of early-transition me-
tal compounds has received increased attention in recent
years as applications in a-olefin polymerization have
grown. A significant portion of this research has focused
on metal complexes supported by cyclopentadienyl
relative ease with which the steric and electronic proper-
ties of bis-sulfamides can be varied is evident in their
synthesis (Scheme 1). Typically, the synthesis of these
ligands is a high yield, one-step process involving the
reaction between SO2Cl2 and an amine [32,33]. There-
fore, many derivatives are readily available by varying
the nature of the amine. In addition, upon coordination
the inherent electron withdrawing character of the SO2
backbone should increase the electronic unsaturation at
the metal center. In this paper we describe the reactions
of the bis-sulfamide ligands SO2[NHCMe3]2 and
SO2{NH[CH(Me)Ph]} with Ta(NMe2)5. The molecular
based ligand sets [1ꢁ
the use of complexes with non-cyclopentadienyl ancil-
lary ligands such as dialkoxide [4ꢁ6] or diamide ligands
[7ꢁ17]. Interest in studying chelating-diamide supported
/3], but there is growing interest in
/
/
Group 4 complexes as polymerization catalysts is in part
due to the ease with which the steric and electronic
properties of the catalysts can be altered by varying the
nitrogen substituants. Several research groups have
shown that d0 Group 4 metal complexes (Ti, Zr, Hf),
supported by diamide ligands are active catalysts for the
1
structure and variable temperature H NMR studies of
Ta[N(Me)2]3[SO2(NCMe3)2] (1) are also reported.
polymerization of a-olefins [8ꢁ
/27].
In response to the growing interest in alternatives to
classical metallocene based catalysts, we have become
2. Experimental
2.1. Materials and methods
* Corresponding author. Tel.: ꢂ
3255.
E-mail address: boncella@chem.ufl.edu (J.M. Boncella).
/
1-352-392-9512; fax: ꢂ1-352-392-
/
All experimental procedures were conducted under an
inert atmosphere, either in a N2 filled dry box or by
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 0 9 3 3 - 6

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R.C. Mills et al. / Polyhedron 21 (2002) 1051ꢁ1055
/
3
(d, 6H, JHÃH
ꢀ6.9 Hz, SO2(NCHMe(C6H5))2), 2.75
/
3
(s,18H, N(CH3)2), 5.56 (q, 2H, JHÃH
SO2(NCHMe(C6H5))2), 7.01 (t, 2H, JHÃH
C6H5), 7.09 (t, 4H, JHÃH
4H, 3JHÃH
ꢀ
/
6.9 Hz,
6.9 Hz, p-
7.2 Hz, m-C6H5), 7.27 (d,
7.2 Hz, o-C6H5). 13C NMR (25 8C, C6D6):
3
ꢀ
/
3
ꢀ
/
ꢀ
/
d 24.43 (SO2(NCHMe(C6H5))2), 43.92 (SO2(NCH-
Me(C6H5))2), 55.85 (N(CH3)2), 126.60, 128.13, 146.50
(aromatic).
Scheme 1.
using standard Schlenk techniques. Diethyl ether was
distilled from sodium benzophenone ketyl; toluene,
hexanes, and pentane were distilled from sodium;
dichloromethane was distilled from CaH2. The distilled
solvents were stored under an argon atmosphere and
˚
over 4 A molecular sieves. All NMR solvents were
˚
degassed and stored over 4 A molecular sieves in a N2
filled drybox. Ta(NMe2)5 was synthesized according to
the improved procedure for the preparation of homo-
leptic metal amide complexes reported by Jordan et al.
[34]. The bis-sulfamide compounds SO2[NHCMe3]2 and
SO2{NH[CH(Me)Ph]}2 were synthesized according to
2.4. X-ray data collection and structure refinement for 1
Single crystals for X-ray crystallography of
Ta[N(CH3)2]3[SO2(NC(CH3)3)2] (1) were grown by
slow diffusion of pentane in a saturated toluene solution
of 1. Selected bond lengths and angles are given in Table
1. C14H36N5O2STa; M 519.49; triclinic; space group P1;
˚
aꢀ
1044.15(2) A ; Zꢀ
mmꢃ1; F(000)ꢀ
520; reflections collected 6924; inde-
pendent reflections 4634 (Rint 0.0309).
/
8.9208(1), bꢀ
/
10.0987(1), cꢀ
/
13.7290(1) A; Uꢀ
/
3
˚
/2; Dcalc
ꢀ
/
1.652 Mg mꢃ3; mꢀ
5.378
/
/
ꢀ
/
previously published procedures [28ꢁ31].
/
1H and 13C NMR spectra were measured at 300 MHz
on a Varian VXR-300 spectrometer. The chemical shifts
are reported in parts per million (ppm) downfield from
tetramethylsilane and referenced to residual proton
peaks of the NMR solvents. Mass spectrometry was
performed by the UF Department of Chemistry Analy-
tical Services.
Data were collected at 173 K on a Siemens SMART
PLATFORM equipped with a CCD area detector and a
graphite monochromator utilizing Mo Ka radiation
˚
0.71073 A). Cell parameters were refined using up
(lꢀ
/
to 6753 reflections. A hemisphere of data (1381 frames)
was collected using the v-scan method (0.3 v frame
width). The first 50 frames were remeasured at the end
of data collection to monitor instrument and crystal
stability (maximum correction on I was B1%). C scan
absorption corrections were applied based on the entire
data set.
/
2.2. Ta[NMe2]3[SO2(NCMe3)2] (1)
To a toluene solution of Ta(NMe2)5 (3.31 g, 8.24
mmol) at room temperature (r.t.) was added a toluene
solution of SO2(NHCMe3)2 (1.74 g, 8.24 mmol). No
immediate color change was observed. The mixture was
allowed to stir for 12 h at r.t. (connected to an oil
bubbler to release the HNMe2 produced during the
reaction). Removal of the reaction solvent under
reduced pressure gave a brown oily solid, which was
washed with several portions of hexane to yield 3.86 g
(74%) of 1 as a light beige solid. Mass Spec. Calc. For
The structure was solved by Direct Methods
SHELXTL-5 [35], and refined using full-matrix least-
squares. The non-H atoms were treated anisotropically
where the hydrogen atoms were calculated in ideal
positions and were riding on their respective carbon
atoms. Two hundred and nine parameters were refined
Table 1
˚
Selected bond distances (A) and angles (8) for 1
C14H37O2N5TaS [Mꢂ
H]ꢂ: 520.2143 m/e. Found:
/
Bond distances
1
TaÃN(1)
TaÃN(2)
TaÃN(3)
TaÃN(4)
TaÃN(5)
2.074(3)
2.145(3)
1.961(4)
1.965(3)
1.996(4)
(FAB) 520.2143 m/e. H NMR (25 8C, C6D6): d 1.51
(s, 18H, SO2(NC(CH3)3)2), 3.09 (s, 18H, N(CH3)2). 13C
NMR (25 8C, C6D6): d 32.83, (SO2(NC(CH3)3)2), 45.16
(N(CH3)2).
Bond angles
N(1)ÃTaÃN(5)
N(2)ÃTaÃN(3)
N(2)ÃTaÃN(4)
N(2)ÃTaÃN(5)
N(3)ÃTaÃN(4)
N(3)ÃTaÃN(5)
N(4)ÃTaÃN(5)
N(1)ÃTaÃN(2)
N(1)ÃTaÃN(3)
N(1)ÃTaÃN(4)
98.78(14)
94.94(14)
94.65(14)
166.32(14)
115.70(2)
92.40(2)
2.3. Ta(NMe2)3[SO2(NCH(Me)Ph)2] (2)
Compound 2 was synthesized from Ta(NMe2)5 (2.50
g, 6.23 mmol) and SO2(NCH(Me)Ph)2 (1.90 g, 6.23
mmol) following the same procedure as was used for the
synthesis of compound 1. The reaction yielded 3.41 g
(75%) of 2 as a light brown solid. Mass Spec. Calc. For
92.50(2)
67.54(12)
120.90(14)
121.45(14)
C22H36O2N5TaS [Mꢂ
H]ꢂ: 616.5726 m/e. Found:
/
1
(FAB) 616.5725 m/e. H NMR (25 8C, C6D6): d 1.76

R.C. Mills et al. / Polyhedron 21 (2002) 1051ꢁ
/
1055
1053
in the final cycle of refinement using 4356 reflections
with I ꢀ2s(I) to yield R1 3.04% and wR2 7.70%,
/
respectively. Refinement was performed using F2.
3. Results and discussion
The reaction of 2 equiv. of RNH2 (Rꢀt-butyl or a-
/
methylbenzyl) with 2 equiv. of NEt3 and O2SCl2 yields
the bis-sulfamide ligands SO2[NHC(CH3)3]2 and
SO2{NH[CH(Me)Ph]}2 [28ꢁ31]. Unsuccessful attempts
/
to deprotonate either of these ligands using a wide array
of bases and deprotonation techniques led us to examine
the amine elimination reaction as a means to incorpo-
rate them into a metal coordination sphere [8,27,36ꢁ38].
/
Reaction of the bis-sulfamides SO2[NHCMe3]2 and
SO2{NH[CH(Me)Ph]}2 with Ta(NMe2)5 for 12 h at
room temperature produced the complexes Ta[N-
Me2]3[SO2(NCMe3)2]
(1),
Ta[NMe2]3[SO2(NCH-
(Me)Ph]2 (2) in high yield (75%) (Scheme 2). The room
temperature 1H NMR spectrum of 1 displays two
singlets at 1.46 and 3.12 ppm, corresponding to the
CMe3 and NMe2 groups, respectively. In the proton
NMR spectrum of compound 2, the sulfamide methyl
protons appear as a doublet (1.76 ppm) while the NMe2
protons appear as a singlet (2.75 ppm) and the methine
proton resonates as a quartet (5.56 ppm). Since com-
pounds 1 and 2 are pentacoordinate, they can adopt
either a square pyramidal or trigonal bipyramidal
idealized geometry [39]. Both of these structures have
different chemical environments for their NMe2 groups.
The observed equivalency of the NMe2 groups at room
temperature implies the presence of a fluxional process,
which equilibrates the NMe2 groups on the NMR
timescale.
Fig.
1. Variable
Ta[N(CH3)2]3[SO2(NC(CH3)3)2] (1).
temperature
1H
NMR
spectra
of
Assuming a trigonal bipyramidal geometry, resolu-
tion of the NMe2 resonance into three peaks instead of
two, suggests that at very low temperatures, rotation
about the TaÃ
Rapid rotation of the equatorial NMe2 groups at low
temperature would produce two peaks in a 2:1 ratio
/N bonds of the NMe2 ligands is slow.
In order to determine the nature of the fluxional
process, a variable temperature 1H NMR study was
performed on compound 1 (C7D8). The 1H NMR
spectra of 1 at various temperatures are shown in (Fig.
(equatorial:axial). Slow rotation about the TaÃ
/N bonds
renders each methyl on the equatorial NMe2 ligands
inequivalent with respect to the other, but equivalent
with the adjacent NMe2 methyl group by a mirror plane
that includes the (Fig. 2). The value of DG% for the
coalescence of the NMe2 (2.95, 2.98 ppm) and the t-
butyl (1.50, 1.56 ppm) resonances were each estimated
to be 12.3 kcal molꢃ1 using the equally populated two-
site exchange approximation [40]. Using the unequally
populated two-site exchange approximation, the activa-
tion energy DG% for the coalescence of the NMe2 peaks
1). At ꢃ60 8C, the spectrum of 1 has inequivalent
/
CMe3 peaks (1.50, 1.56 ppm, 9H each) of equal intensity
and three NMe2 resonances (2.95, 2.98, 3.19 ppm) each
integrating to six protons. Two of the NMe2 resonances,
2.95 and 2.98 ppm, coalesce at ꢃ
CMe3 resonances coalesce at ꢃ
coalesced NMe2 resonance at 2.97 ppm coalesces with
the resonance at 3.19 ppm at ꢃ9 8C.
/
35 8C (2.97 ppm). The
/
30 8C whereas the
/
Fig. 2. Proposed structure of 1 to explain the low temperatue 1H
NMR spectrum.
Scheme 2.

1054
R.C. Mills et al. / Polyhedron 21 (2002) 1051ꢁ1055
/
at 2.97 and 3.19 ppm was estimated to be 12.8 kcal
12 kcal
to replace the NMe2 groups with Clꢃ utilizing SiMe3Cl
gave mixtures of uncharacterizable products. Alkyl
aluminum reagents have also been useful in converting
amido complexes to alkyl derivatives [37,38]. The
reaction of compound 1 with either AlMe3 or AlEt3
led to the formation of new complexes, which contain 1
equiv. of AlR3. It appears that these complexes are
coordination complexes between 1 and the aluminum
reagent. However, due to inconclusive spectroscopic
results and our inability to obtain X-ray quality crystals
of these compounds, we do not know whether the AlR3
groups coordinate to the sulfamide oxygen(s) or the
amido N atoms. Further heating of these materials did
not lead to characterizable products.
molꢃ1. The similar activation energy values (ꢁ
/
molꢃ1) that were calculated for the coalescence of the
axial-equatorial NMe2 groups and the t-butyl groups
suggest the fluxional process which equilibrates these
groups follows a Berry pseudorotation mechanism [39].
A similar variable temperature 1H NMR study of
compound 2 exhibited no significant broadening of the
peaks, even at ꢃ90 8C. The difference between the
/
dynamic behavior of compounds 1 and 2 may be
attributed to the decreased steric bulk of the alkyl
substituents of the bis-sulfamide in complex 2.
The X-ray diffraction study of 1 shows that a trigonal
bipyramidal coordination geometry is found in the solid
1
state, which is consistent with the low temperature H
NMR spectroscopy of 1. A molecular drawing of 1 is
shown in Fig. 3 and selected bond lengths and angles are
presented in Table 1. Compound 1 adopts a distorted
trigonal bipyramidal geometry about the Ta metal
center with the bidentate sulfamide ligand occupying
one axial and one equatorial site. The bite angle of the
ligand (67.58) is smaller than that observed for other
bidentate amido complexes reported in the literature due
4. Summary
Bis-sulfamide compounds were successfully employed
as chelating diamide ligands in the synthesis of the
tantalum amido complexes Ta[NMe2]3[SO2(NCMe3)2]
(1) and Ta(NMe2)3[SO2(NCH(Me)Ph)2] (2) via the
amine elimination method. Attempts to remove the
NMe2 ligands from either 1 or 2 using Et3NHCl,
to the four-membered chelate ring. The TaÃ
/
N(1) and
TaÃN(2) bond lengths of the bis-sulfamide ligand
/
Me2NH×/HCl or SiMe3Cl were unsuccessful. The use
˚
(2.074(3), 2.145(3) A) are longer than the TaÃ
/N bond
of AlR3 reagents to form alkylated derivatives of 1 led to
the formation of AlR3 adduct complexes that have
proved difficult to characterize. The synthesis of other
metal complexes containing bis-sulfamide ligands is
currently being explored.
lengths of the NMe2 ligands (1.961(4), 1.965(3), 1.996(4)
˚
A). The angles around N(3) and N(4) and N(5) sum to
3608 indicating a trigonal planar geometry at the NMe2
nitrogen atoms. This suggests that p-donation from the
NMe2 ligands to the metal center is possible and
probably plays a role in the observed slow rotation of
the NMe2 groups at low temperature in solution.
Acknowledgements
In order to explore the reactivity and further deriva-
tization of complexes 1 and 2, removal of the dimethyl
amido ligands was attempted. Attempts to protonate the
J.M. B. thanks the National Science Foundation
(CHE 9523279) for funding of this work and K.A. A.
thanks the NSF and the University of Florida for
funding X-ray equipment purchases.
NMe2 groups using either Et3NHCl or Me2NH×
/
HCl or
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