Cycloaddition reaction of tert-butyl isocyanate and a tellurium diimide dimer: Extended helical structure of the ureato telluroxide {[OC(μ-NBu(t))2TeO]2(thf)}∞

Article abstract of DOI:10.1039/b004137h

The reaction of Bu(t)NTe(μ-NBu(t))₂TeNBu(t) with Bu(t)NCO in a 1:4 molar ratio in thf produces N,N'-bis(tert-butyl)ureato telluroxide dimers [OC(μ-NBu(t))₂TeO]₂, which form an extended helical network via weak >C=O···Te interactions.

Full text of DOI:10.1039/b004137h

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Cycloaddition reaction of tert-butyl isocyanate and a tellurium diimide dimer:
extended helical structure of the ureato telluroxide {[OC(m-NBut)2TeO]2(thf)}∞
Gabriele Schatte, Tristram Chivers,* Cory Jaska and Nicole Sandblom
Department of Chemistry, University of Calgary, Calgary, Alberta, Canada T2N 1N4. E-mail: chivers@ucalgary.ca
Received (in Irvine, CA, USA) 22nd May 2000, Accepted 20th July 2000
Published on the Web 11th August 2000
The reaction of ButNTe(m-NBut)2TeNBut with ButNCO in a
1+4 molar ratio in thf produces N,NA-bis(tert-butyl)ureato
telluroxide dimers [OC(m-NBut)2TeO]2, which form an
extended helical network via weak 0CNO…Te inter-
actions.
cyclic tellurium(II) imide [Te(NBut)]3 (95% yield) and no
cycloaddition intermediate could be isolated.
9a
When a solution of 1 in n-hexane is added to a solution of
ButNCO in thf (1+4 molar ratio) a white solid identified by X-
ray crystallography‡ as {[OC(m-NBut)2TeO]2(thf)}∞ (3·thf)∞
is obtained in essentially quantitative yield.† The carbodiimide
ButNNCNNBut was detected as a by-product of this reaction by
1H NMR (dH 1.17). This observation implies that an unstable
tellurium(IV) complex involving both N,NA and N,O-bound
ureato ligands is an intermediate in the formation of 3. As
indicated in Fig. 1 the asymmetric unit in 3 is N,NA-bis(tert-
butyl)ureato telluroxide [d(TeNO) = 1.9040(17) Å] which, in
common with other telluroxides, dimerizes via O?Te
Reactions of transition-metal imido compounds with hetero-
allenes have been investigated extensively.1 The MNNR linkage
reacts with isocyanates RNCO via cycloaddition of the NNC
double bond to give N,NA-ureato complexes which, in some
cases, can be isolated.2 The N,NA-ureato ligand may also be
generated by interaction of oxo complexes of Ru or Os with
ButNCO, presumably through the formation of an MNNR
intermediate.3 N,O-ureato complexes have been implicated in
reactions of isocyanates with some transition-metal complexes,
but none of the products of CNO cycloaddition to the M = NR
bond have been isolated.4–6 Iminophosphoranes Ph3PNNR
normally react with isocyanates by an Aza-Wittig process to
generate carbodiimides and Ph3PO.7 By contrast, sulfur di-
imides, e.g. ButNNSNNBut undergo exchange reactions with
certain isocyanates RNCO (R = RASO2, RACO or Ar) to form
ButNCO and ButNSNR.8 In the context of this divergent
behaviour, we have investigated the reactions of the tellurium-
[2.0723(18) Å] interactions, cf. d(TeO)
= 1.885(7) and
2.170(7) Å in metal complexes of the related dimer [ButNTe(m-
NBut)2(m-O)]2.10 The ureato ligands in 3 adopt a cis arrange-
ment with respect to the Te2O2 ring which is essentially planar
(torsion angle 22.6°). The CNTeN rings are slightly puckered
(torsion angle 27.2°). In the parent urea OC(NHBut)211 and in
ureato complexes of Ru and Os3 the NCN unit is symmetrical
[|d(CN)| = 1.352 and 1.380 Å, respectively]. By contrast, the
CN bonds in 3 are unsymmetrical [d(CN) = 1.345(4) and
1.420(3) Å] as are the TeN bonds [d(TeN) = 2.034(2) and
2.087(2) Å]. The CNO bond length is 1.227(3) Å, cf. 1.252(3) Å
in OC(NHBut)211 and 1.22–1.26 Å in ureato complexes of Ru3,
Os3 and W.12 Complex 3 is readily hydrolyzed by traces of
moisture to give the urea OC[N(H)But]2 and TeO2.
(
IV) diimide dimer ButNTe(m-NBut)2TeNBut 1, which contains
two highly reactive terminal TeNNBut groups,9 with iso-
cyanates. We describe here, the facile reaction between 1 and
ButNCO, which yields the N,NA-ureato telluroxide 3 via the
corresponding ureato tellurium imide 2 (Scheme 1). In the solid
state 3 forms an extended helical network via weak 0CNO…Te
interactions.
The presence of a two-fold screw axis (21) at the centre and
corners of the unit cell and a four-fold (41) axis at the mid-points
of the cell axes results in two different channels parallel to the
ab plane involving weak 0CNO…Te contacts [3.020(2) Å, cf.
sum of van der Waals radii for Te and O = 3.58 Å]13 as depicted
in Fig. 2. The first type involves a lantern-shaped arrangement
of four dimers. Two disordered thf molecules located in the
middle of the lantern also engage in weak Te…O interactions
[2.961(6) Å]. The second type of 0CNO…Te interaction
involves only one Te atom of four dimeric units and gives rise
Treatment of the dimer 1 with 2 equiv. of ButNCO in toluene
at 23 °C produces an extremely moisture-sensitive yellow solid,
which was identified as the N,NA-ureato tellurium(IV) imide
ONC(m-NBut)2TeNNBut 2 on the basis of CHN analysis, IR and
NMR spectroscopic data.† The 1H NMR spectrum of 2 in C6D6
exhibits two singlets at d 1.46 and 1.35 in the intensity ratio 1+2.
An IR absorption attributed to the CO stretch is observed at
1653 cm21, and the carbonyl carbon appears in the 13C{1H}
NMR spectrum at d 160.7. Hydrolysis of 2 by atmospheric
moisture produces N,NA-bis(tert-butyl)urea OC[N(H)But]2 (dH
1.24 in d8-thf). Complex 2 can be viewed as the product of the
cycloaddition reaction of the monomeric tellurium(IV) diimide
ButNNTeNNBut and ButNCO. By contrast, the reaction of 1 with
ButNCS (1+2 molar ratio) in n-hexane at 65 °C produces the
Fig. 1 The structure of [OC(m-NBut)2TeO]2 3 with the atomic numbering
scheme. Thermal ellipsoids are drawn at the 50% probability level. Selected
bond angles (°): Te(1)–O(2)–Te(1)* 102.84(8), O(2)–Te(1)–O(2)*
77.10(8), O(2)–Te(1)–N(2) 104.52(9), O(2)*–Te(1)–N(2) 92.08(8), O(2)–
Te(1)–N(1) 88.71(9), O(2)*–Te(1)–N(1) 148.18(9), N(1)–Te(1)–N(2)
63.88(9), Te(1)–N(1)–C(1) 95.79(17), Te(1)–N(2)–C(1) 95.76(17), N(1)–
C(1)–N(2) 104.0(2). Symmetry transformation used to generate equivalent
atoms marked with an asterisk: y, x, 2z.
Scheme 1 Reagents and conditions: i, +2ButNCO; ii, 22ButNCNBut.
DOI: 10.1039/b004137h
Chem. Commun., 2000, 1657–1658
This journal is © The Royal Society of Chemistry 2000
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product was washed with cold n-pentane (3 mL) to give 2 (0.185 g, 0.501
mmol, 45%) as a yellow solid. 1H NMR (400.13 MHz, C6D6, 25 °C) d 1.46
(9 H), 1.35 (18 H). 13C NMR (100.62 MHz, C6D6, 25 °C) d 160.70 (CO),
64.17 [C(CH3)3], 54.83 [C(CH3)3], 34.69 [C(CH3)3], 31.86 [C(CH3)3].
125Te NMR (126.20 MHz, C6D6, 25 °C) d 1225. IR:1653 [n(CO)] cm21
.
3: an orange solution of 1 (0.30 g, 0.556 mmol) in n-hexane (10 mL) was
added to a colourless solution of ButNCO (0.257 mL, 2.223 mmol) in thf (10
mL) at 23 °C. The pale yellow solution was stirred for 1.5 h and then volatile
materials were removed under vacuum and 3·2 thf (0.423 g, 0.549 mmol,
99%) was obtained as a white solid. Colourless crystals of 3·thf suitable for
X-ray diffraction were obtained after two days at 23 °C by layering an
orange–red solution of 3 in n-hexane (3 mL) over a solution of ButNCO in
1
thf (3 mL). H NMR (400.13 MHz, C6D6, 25 °C) d 3.55 (thf), 1.45 (But,
18H), 1.41 (thf). 13C NMR (100.62 MHz, C6D6, 25 °C) d 160.39 (CO),
68.15 (thf), 54.97 [C(CH3)3], 31.27 [C(CH3)3], 26.15 (thf). 125Te NMR
(126.20 MHz, C6D6, 25 °C) d 1090. IR: 1669 [n(CO)], 663 [n(TeO)]
cm21
.
‡ Crystal data for (3·thf)∞ : C22H44N4O5Te2, M = 699.81, tetragonal, space
group P41212 (no. 92), a = b = 15.5941(7), c = 12.4867(8) Å, V =
3036.5(3) Å3, Z = 4, Dc = 1.531 g cm23, m(Mo-Ka) = 19.55 cm21
.
Crystal dimensions 0.26 3 0.23 3 0.15 mm. Data were collected on a
Bruker AXS P4/RA/SMART 1000 CCD diffractometer with graphite-
monochromated Mo-Ka radiation using f and w scans. The structure was
solved using direct methods (SIR-97) and refined by full-matrix least
squares on F2 (SHELXL-97). The thf molecule was disordered around the
two-fold screw axis with partial occupancy factors of 0.5. Of the 2593
unique reflections 2410 had I ! 2.00s (I). The final agreement factors were
R1 = 0.0164 and wR2 = 0.041.
Fig. 2 Unit cell of {[OC(m-NBut)2TeO]2(thf)}∞ viewed down the c-axis.
Disordered thf molecules are omitted.
CCDC 182/1728. See http://www.rsc.org/suppdata/cc/b0/b004137h/ for
crystallographic files in .cif format.
to a square-shaped arrangement. In both of these structural
motifs one of the 0CNO…Te interactions links dimeric units in
adjacent planes of the unit cell to give a helical arrangement,
which is apparent when viewed down the c axis. The Te…Te
distance in both cases is 12.4867(8) Å, i.e. the length of the c
axis. Although weak intermolecular E…Te (E = O, N, S)
interactions are a well known feature of tellurium complexes,14
an extended network involving carbonyl–tellurium contacts is
unique.
1 For reviews, see: D. E. Wigley, Prog. Inorg. Chem., 1994, 42, 239; P.
Mountford, Chem. Commun., 1997, 2127.
2 For some recent examples, see: R. I. Michelman, R. A. Andersen and
R. G. Bergman, J. Am. Chem. Soc., 1991, 113, 5100; M. Jolly, J. P.
Mitchell and V. C. Gibson, J. Chem. Soc., Dalton Trans., 1992, 1329; P.
Legzdins, E. C. Phillips, S. J. Rettig, J. Trotter, J. E. Veltheer and V. C.
Lee, Organometallics, 1992, 11, 3104; A. J. Blake, P. Mountford, G. I.
Nikonov and D. Swallow, Chem. Commun., 1996, 1835.
3 W.-H. Leung, G. Wilkinson, B. Hussain-Bates and M. B. Hursthouse,
J. Chem. Soc., Dalton Trans., 1991, 2791.
4 P. J. Walsh, F. J. Hollander and R. G. Bergman, Organometallics, 1993,
12, 3705.
5 K. R. Birdwhistell, T. Boucher, M. Ensminger, S. Harris, M. Johnson
and S. Toporek, Organometallics, 1993, 12, 1023.
In summary, the presence of two TeNNBut linkages in 1
presents a unique opportunity for the study of double cycloaddi-
tions with heteroallenes. The reaction of 1 with ButNCO
generates a N,NA-ureato ligand and converts a tellurium imide
(TeNBut) to a telluroxide (TeO) linkage, presumably via an
unstable N,O-ureato complex. Thus it combines features of the
reactions of both transition-metal imides and iminophosphor-
anes with isocyanates.
6 J. L. Thorman, I. A. Guzzi, V. G. Young Jr. and L. K. Woo, Inorg.
Chem., 1999, 38, 3814.
7 A. W. Johnson, Ylides and Imides of Phosphorus, John Wiley & Sons
Ltd., N.Y., 1993, pp. 429–430.
8 R. Appel and M. Montenarh, Chem. Ber., 1976, 109, 2437; H. W.
Roesky and G. Sidiropoulos, Chem. Ber., 1978, 111, 3460.
9 (a) T. Chivers, X. Gao and M. Parvez, J. Am. Chem. Soc., 1995, 115,
2359; (b) T. Chivers, X. Gao and M. Parvez, Angew. Chem., Int. Ed.
Engl., 1995, 34, 2549; (c) T. Chivers, G. D. Enright, N. Sandblom, G.
Schatte and M. Parvez, Inorg. Chem, 1999, 38, 5431.
We thank the NSERC (Canada) for financial support, Dr R.
MacDonald (University of Alberta) for assistance with the data
collection, and Dr M. Parvez for helpful discussions of the
disorder problem.
10 T. Chivers, M. Parvez and G. Schatte, Inorg. Chem., 1999, 38, 5171.
11 T. Chivers, A. Downard and G. P. A. Yap, unpublished work.
12 H.-W. Lam, G. Wilkinson, B. Hussain-Bates and M. B. Hursthouse,
J. Chem. Soc., Dalton Trans., 1993, 781.
13 N. W. Alcock, Adv. Inorg. Chem. Radiochem., 1972, 15, 1.
14 For examples, see: E = O: R. O. Day and R. R. Holmes, Inorg. Chem.,
1981, 20, 3071; E = N: R. E. Allan, H. Gornitzka, J. Kärcher, M. A.
Paver, M.-A. Rennie, C. A. Russell, P. R. Raithby, D. Stalke, A. Steiner
and D. S. Wright, J. Chem. Soc., Dalton Trans., 1996, 1727; E = S: A.
Silvestru, I. Haiduc, K. H. Ebert, H. J. Breunig and D. B. Sowerby,
J. Organomet. Chem., 1994, 482, 253.
Notes and references
† Experimental procedure: all manipulations were performed under an inert
atmosphere of dry argon using standard Schlenk techniques. All solvents
were dried prior to use.
2: a colourless solution of ButNCO (0.120 mL, 1.112 mmol) in toluene
(10 mL) was added to an orange solution of 19c (0.30 g, 0.556 mmol) in
toluene (5 mL) at room temperature. The addition of a small amount of
ButNCNBut prevents the formation of 3. A yellow precipitate of 2 was
formed after 3 min. The pale orange solution was stirred for 2 h, cooled to
210 °C and then the supernatant was decanted via cannula. The solid
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Chem. Commun., 2000, 1657–1658