Synthesis of N,C bound sulfur, selenium, and tellurium heterocycles via the reaction of chalcogen halides with -CH3 substituted diazabutadiene ligands

Article abstract of DOI:10.1021/ic802320s

A series of N,C bound chalcogen heterocycles from the reaction of chalcogen halides (ChX_n; Ch ) S, Se Te; X ) Cl, Br; n ) 2, 4) with N-alkyl or N-aryl 1,4-diazabutadiene (DAB) ligands featuring methyl substituents on the backbone C-C linkage ar

Full text of DOI:10.1021/ic802320s

Inorg. Chem. 2009, 48, 3239-3247
Synthesis of N,C Bound Sulfur, Selenium, and Tellurium Heterocycles
via the Reaction of Chalcogen Halides with -CH3 Substituted
Diazabutadiene Ligands
Jason L. Dutton, Caleb D. Martin, Michael J. Sgro, Nathan D. Jones, and Paul J. Ragogna*
Department of Chemistry, The UniVersity of Western Ontario, 1151 Richmond St.,
London, Ontario, N6A 5B7, Canada
Received December 3, 2008
A series of N,C bound chalcogen heterocycles from the reaction of chalcogen halides (ChXn; Ch ) S, Se Te; X
) Cl, Br; n ) 2, 4) with N-alkyl or N-aryl 1,4-diazabutadiene (DAB) ligands featuring methyl substituents on the
backbone C-C linkage are reported. In contrast to what is observed for other p-block elements with the same
ligand systems, which typically bind in an N,N′ fashion, the chalcogens react with the ligand in an unusual manner,
forming N1C3Ch1 five-membered rings by incorporating a “backbone” methyl group. Solid state structures of the
feature compounds have been confirmed by X-ray crystallographic studies. The reaction mechanism was probed
by deuterium isotope labeling of the DAB ligand and analyzed using stopped-flow kinetics experiments, which
supported attack by the olefin in the enamine form of the DAB ligand with concomitant loss of HX.
Introduction
an R-diimine (1a), their reaction with selenium halides
resulted in cationic SeN2C2 heterocycles. For selenium, this
involved the reduction from Se(IV) to Se(II) with concomi-
tant elimination of Cl2 or Br2 and the loss of an alkyl
substituent from the ligand, generating a 1,2,5-selenadiazo-
lium cation (2).4 In the case of tellurium and tert-butyl
N-substituted DAB ligands, no reduction was observed,
where the reactions instead resulted in the formation of
simple DAB-TeX4 adducts (3; X ) Cl, Br).2 Analogous
chemistry involving the Dipp2-BIAN ligand and TeI4 or the
Dipp2NacNac ligand and SeX4 (X ) Cl, Br) also involved
redox processes resulting in a Dipp2BIANTeI2 (4) complex
or Se(II)Dipp2NacNac compounds (5), where the NacNac
ligand was halogenated as a result of X2 elimination.3,6 The
dependence of the reaction outcome on the specific nature
of the ligand is in contrast to what has been reported for
analogous group 15 R-diimine chemistry, where an internal
charge transfer dominates giving phosphenium or arsenium
cations, regardless of the substituents at nitrogen.8,9
The discovery of new bonding motifs using common
ligands (e.g., amines, imines, phosphines) and the heavier
chalcogen halides (ChX4; Ch ) S, Se, Te; X ) Cl, Br or
ChX2; Ch ) S, Se; X ) Cl, Br) can be restricted by the
propensity for redox processes between the Lewis base and
the metal halide.1 These reactions can result in the undesir-
able production of Ch0 or release of reactive X2 (X ) Cl,
Br, I), leading to halogenation of any susceptible sites within
the system, giving low yields, and causing great difficulty
in controlling the outcome of the transformations.2-4 Despite
these issues, a number of recent reports have demonstrated
high yielding syntheses of a variety of novel bonding
arrangements for selenium and tellurium by employing
bifunctional N,N′ or N,S ligands with corresponding chal-
cogen halides.2,5-7 In cases where the ligand was based on
* To whom correspondence should be addressed. E-mail: pragogna@
uwo.ca.
(1) Dutton, J. L.; Tabeshi, R.; Jennings, M. C.; Lough, A.; Ragogna, P. J.
Inorg. Chem. 2007, 46, 8594–8602.
(2) Dutton, J. L.; Sutrisno, A.; Schurko, R. W.; Ragogna, P. J. Dalton
Trans. 2008, 3470–3477.
(3) Gushwa, A. F.; Richards, A. F. Eur. J. Inorg. Chem. 2008, 728–736.
(4) Dutton, J. L.; Tindale, J. J.; Jennings, M. C.; Ragogna, P. J. Chem.
Commun. 2006, 2474–2476.
Nevertheless, there are three separate reports of N,C
chelation of group 16 centers (Se, 5 and Te, 6) via the
activation of a proximal methyl group on the ligand
framework. These represent the first examples of this type
of reactivity for the chalcogens; however, analogous chem-
istry for sulfur has not been reported.3,6,10
(5) Risto, M.; Assoud, A.; Winter, S. M.; Oilunkaniemi, R.; Laitinen, R.;
Oakley, R. T. Inorg. Chem. 2008, 47, 10100–10109.
(6) Reeske, G.; Cowley, A. H. Chem. Commun. 2006, 4856–4858.
10.1021/ic802320s CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 7, 2009 3239
Published on Web 03/02/2009

Dutton et al.
In this context, we have discovered that utilization of
N-alkyl or N-aryl substituted DAB ligands, which feature
methyl substituents in the “backbone” (1b; 1Dipp, R ) 2,6-
diisopropylphenyl; 1Cy, R ) cyclohexyl), consistently give
N,C bound group 16 element centers (7-9) from a variety
of chalcogen halide starting materials in moderate to excellent
yields. These represent a novel reactivity and coordination
mode for R-diimine ligands of this type within the heavier
p-block elements. Typically ligands of the form 1b are the
preferred choice as the backbone protons on 1a are consider-
ably acidic; thus, the ligand is readily deprotonated, where
subsequent deleterious reactivity is observed.11,12 The mech-
anism for the formation of compounds 7-9 has been probed
using the reaction of 1Dipp and TeCl4 as a model, in
conjunction with deuterium isotope labeling. Although a
definitive mechanism could not be determined, there was a
distinct increase in the time required for the reaction to run
to completion when 1Dipp-d6 was used in place of 1Dipp,
which indicates a primary kinetic isotope effect. Given this
observation, we hypothesize that the dominant factor in
determining the outcome of these reactions relies on a proton
transfer; thus, the presence of the enamine form of the
R-diimine ligand (1c) is critical. Such a mechanism was
postulated for the formation of 5 by Richards et al., albeit
using the NacNac class of ligand, rather than a formal C-H
bond activation.3,13,14
Experimental Section
General Procedures. Manipulations were performed in an N2
filled MBraun Labmaster 130 glovebox in 4 dr. vials affixed with
Teflon lined screw caps, or using standard Schlenk techniques.
Dichloromethane, THF, MeCN, Et2O, n-pentane, and n-hexane were
obtained from Caledon Laboratories and dried using an MBraun
Solvent Purification system (MB-SPS). The dried solvents were
stored in Strauss flasks under an N2 atmosphere, or over 4 Å
molecular sieves in the glovebox. Solvents for NMR spectroscopy
(CDCl3, CD3CN, C5D5N), D2O, CH3CH2OD, and DCl (35% in
D2O) were purchased from Cambridge Isotope Laboratories; the
solvents used for NMR spectroscopy were dried by stirring for 3
days over CaH2, distilled prior to use, and stored in the glovebox
over 4 Å molecular sieves. Selenium tetrachloride, SeBr4, TeCl4,
TeBr4, and 2,3-butanedione were purchased from Alfa Aeasar and
used as received. Sulfur monochloride, 2,6-diisopropylaniline, SbPh3
and cyclohexylamine were obtained from the Aldrich Chemical Co.
Selenium dichloride, SeBr2, SCl2, 1Dipp, 1Cy, and 2,3-butanedione-
d6 (≈ 95% enrichment) were prepared via literature proce-
dures.15-19 The -CD3 labeled 1Dipp was prepared in an identical
manner
to
the unlabeled version, except CH3CH2OD was used as the solvent.
The SCl2 was stored under an inert atmosphere at -78 °C, the purity
was confirmed by FT-Raman spectroscopy prior to each use. In
the formation of SeCl2 from SeCl4 and SbPh3, the resultant (highly
soluble) SbPh3Cl2 is completely removed during workup in all cases.
NMR spectra were recorded on an INOVA 400 MHz spectrom-
eter. (77Se ) 76.26 MHz; 125Te ) 126.12 MHz; 13C ) 100.52 MHz).
77Se{1H}, and 125Te{1H} were externally referenced to Me2Se (δ
) 0.00 ppm using SeO2 δ ) -1302 ppm) and Me2Te (δ ) 0.00
ppm using H6TeO6 δ ) 712 ppm), respectively. Proton and 13C{1H}
NMR spectra were referenced relative to Me4Si using the residual
proton signals from the NMR solvent (1H: CHCl3, δ ) 7.26 ppm;
(7) Bacon, C. E.; Eisler, D. J.; Melen, R. L.; Rawson, J. M. Chem.
Commun. 2008, 4924–4926.
(8) Reeske, G.; Hoberg, C. R.; Cowley, A. H. Inorg. Chem. 2007, 46,
1426–1430.
(9) Norton, E. L.; Szekely, K. L. S.; Dube, J. W.; Bomben, P. G.;
Macdonald, C. L. B. Inorg. Chem. 2008, 47, 1196–1203.
(10) Gushwa, A. F.; Karlin, J. G.; Fleischer, R. A.; Richards, A. F. J.
Organomet. Chem. 2006, 691, 5069–5073.
(11) Gudat, D.; Haghverdi, A.; Hupfer, H.; Nieger, M. Chem.sEur. J. 2000,
6, 3414–3425.
(15) Del Bel Belluz, P.; Cordes, A. W.; Kristof, E. M.; Kristof, P. V.;
Liblong, S. W.; Oakley, R. T. J. Am. Chem. Soc. 1989, 111, 9276–
9278.
(12) Martin, C. D.; Jennings, M. C.; Ferguson, M. J.; Ragogna, P. J. Angew.
Chem., Int. Ed. [Online early access]. DOI: 10.1002/anie200805198.
Published Online: 2009.
(13) Kim, Y. H.; Kim, T. H.; Lee, B. Y. Organometallics 2002, 21, 3082–
3084.
(16) Coventry, D. N.; Batsanov, A. S.; Goeta, A. E.; Howard, J. A. K.;
Marder, T. B. Polyhedron 2004, 23, 2789–2795.
(17) Milne, J. Polyhedron 1985, 4, 65–68.
(18) Plouzennec-houe, I.; Lemberton, J.; Perot, G.; Guisnet, M. Synthesis
1983, 659–661.
(14) Wik, B. J.; Romming, C.; Tilset, M. J. Mol. Catal. A: Chem. 2002,
189, 23–32.
(19) Steudel, R.; Jensen, D.; Plinke, B. Z. Naturforsch. 1987, 42b, 163–
168.
3240 Inorganic Chemistry, Vol. 48, No. 7, 2009

N,C Bound Sulfur, Selenium, and Tellurium Heterocycles
CHD2CN, δ ) 1.96 ppm; C5D4HN, δ ) 8.71 ppm; 13C{1H} CDCl3
δ ) 77.2 ppm; C5D4HN, δ ) 149.9 ppm).
decanted, and the solids dried in vacuo giving 7CyCl as a colorless
powder. Yield 0.082 g, 84%; single crystals for X-ray diffraction
studies were grown from a saturated Et2O solution of the powder
Samples for FT-Raman spectroscopy were packed in capillary
tubes, flame-sealed, and data were collected using a Bruker RFS
100/S spectrometer, with a resolution of 4 cm-1. FT-IR spectra
were collected on samples as CsI pellets using a Bruker Tensor 27
spectrometer, with a resolution of 4 cm-1. Decomposition/melting
points were recorded in flame sealed capillary tubes using a
Gallenkamp Variable Heater. Suitable single crystals for X-ray
diffraction studies were individually selected under oil (Paratone-
N), mounted on nylon loops, and immediately placed in a cold
stream of N2 (150 K; 193 for 8DippCl and 9DippCl). Data were
collected on a Bruker Nonius Kappa CCD X-ray diffractometer
using graphite monochromated Mo-KR radiation (λ ) 0.71073 Å).
The solution and subsequent refinement of the data were performed
using the SHELXTL suite of programs.
Combustion analysis (CHN) were performed by Columbia
Analytical Services (Tucson, Arizona, U.S.A.). Compounds 7,
8CyCl, and 8CyBr decompose appreciably at room temperature
within 24 h and therefore we have been unable to collect the
necessary analytical data. As an indication of the level of purity
obtained for these compounds, 1H NMR spectra have been included
in the Supporting Information.
1
stored at -30 °C for 2 days; d.p. 110 °C; H NMR (CDCl3; δ
ppm) 4.31 (s, 2H), 3.87 (m, 1H), 3.54 (m, 1H), 2.46 (s, 3H),
2.15-1.31 (CH2); 13C{1H} NMR (CDCl3; δ ppm) 175.1, 156.8,
64.0, 62.4, 56.2, 33.3, 32.7, 25.4, 25.0, 24.8, 23.9, 15.6; 125Te{1H}
NMR (CH2Cl2; δ ppm) 1190.
Synthesis of 7CyBr. A solution of 1Cy (0.100 g, 0.403 mmol;
THF 5 mL) was added to a stirred slurry of TeBr4 (0.180 g, 0.403
mmol; THF 5 mL) immediately giving an orange slurry, which
was allowed to stir for 10 min. The volatiles were then stripped in
vacuo resulting in an orange solid. The powder was washed with
Et2O (2 × 5 mL), and dried yielding 7CyBr as an orange powder.
Yield 0.186 g, 75%; single crystals for X-ray diffraction studies
were grown from a concentrated CHCl3 solution of the powder via
vapor diffusion of Et2O; d.p. gradually turns black 135-160 °C;
1H NMR (CDCl3; δ ppm); 4.58 (s, 2H), 3.80 (m, 1H), 3.56 (m,
1H), 2.44 (s, 3H), 2.20-1.20 (CH2) 125Te{1H} NMR (CH2Cl2; δ
ppm) 1195.
Synthesis of 8DippCl. A freshly prepared solution of SeCl2
(0.452 mmol; THF 10 mL) was added to a stirred solution of 1Dipp
(0.182 g, 0.452 mmol; THF 10 mL), giving a yellow solution. The
mixture was stirred for 1 h, and n-pentane (10 mL) was added.
The solution stored at -30 °C overnight, resulting in the formation
of a bright yellow precipitate. The supernatant was decanted, the
solids washed with Et2O (2 × 5 mL), and the volatiles were
removed in vacuo giving 8DippCl as a yellow powder. Yield 0.201
g, 86%; single crystals for X-ray diffraction studies were grown
from a concentrated CH2Cl2 solution of the powder via vapor
Kinetic studies were performed using a Bio-Logic SFM-300 with
a TIDAS diode array. Data acquisition was triggered by the hard
stop signal of the SFM-300 with an approximate dead time of 2
ms. Three thousand spectra were recorded over 30 s with an
integration time of 12 ms and spanning a wavelength range of 302.2
to 1147.5 nm.
Synthesis of 7DippCl. A solution of 1Dipp (0.136 g, 0.337
mmol; THF 5 mL) was added to a stirred slurry of TeCl4 (0.100 g,
0.337 mmol; THF 5 mL) immediately giving an orange solution,
which was allowed to stir for 10 min. The volatiles were then
stripped in vacuo giving 7DippCl as an orange powder. Yield 0.210
g, 98%; single crystals for X-ray diffraction studies were grown
from a concentrated CH2Cl2 solution of the powder via vapor
1
diffusion of Et2O; d.p. 204 °C; H NMR (CDCl3; δ ppm) 8.30 (s,
2
3
1H, JSe-H ) 24.0 Hz), 7.43 (t, 1H, JH-H ) 8 Hz), 7.26 (t, 3H,
3JH-H ) 8 Hz), 7.20 (m), 4.83 (s, 1H), 3.05 (sept, 2H, 3JH-H ) 6.8
Hz), 2.36 (sept, 2H, 3JH-H ) 6.8 Hz), 2.12 (s, 3H), 1.20 (overlapping
doublets, 18H), 1.14 (d, 6H, JH-H ) 6.8 Hz); 77Se{1H} NMR
3
(CH2Cl2; δ ppm) 1013; 13C{1H} NMR (CH2Cl2, δ ppm) 162.8,
145.2, 144.4, 141.64, 139.9, 135.5, 134.3, 133.5, 131.9, 130.7,
129.8, 127.8, 124.7, 124.6, 28.9, 28.6, 25.2, 24.2, 23.9, 17.0;
Elemental analysis (%), Found (Calcd): C 64.83(64.90), H 7.55(7.59),
N 5.39(5.41).
1
diffusion into n-hexane; d.p. 197 °C; H NMR (CDCl3; δ ppm)
7.39 (m), 7.30 (m), 7.21 (m), 4.21 (s, 2H), 3.02 (sept, 2H, 3JH-H
)
3
6.8 Hz), 2.64 (sept, 2H, JH-H ) 6.8 Hz), 2.32 (s, 3H), 1.23
(overlapping doublets, 12H), 1.09 (overlapping doublets, 12H);
125Te{1H} NMR (CH2Cl2; δ ppm) 1274; 13C{1H} NMR (CH2Cl2,
δ ppm) 178.6, 162.1, 144.2, 140.5, 138.0, 134.3, 128.6, 125.9,
124.8, 124.3, 123.7, 59.1, 28.6, 24.6, 23.8, 23.2, 22.1, 18.5; ESI-
MS (m/z): 603 [M - Cl]+.
Synthesis of 8DippBr. A freshly prepared solution of SeBr2
(0.633 mmol; THF 5 mL) was added to a stirred THF solution of
1Dipp (0.255 g, 0.633 mmol; THF 10 mL) at room temperature,
giving a yellow slurry. After 10 min the mixture was centrifuged
and the supernatant decanted. The solvent was removed under
vacuum, giving a yellow powder, which was washed with Et2O (3
× 5 mL). Residual solvent was stripped in vacuo giving 8DippBr
as a yellow powder. Yield 0.275 g, 77%; single crystals for X-ray
diffraction studies were grown from a concentrated CH2Cl2 solution
Synthesis of 7DippBr. A solution of 1Dipp (0.090 g, 0.223
mmol; THF 5 mL) was added to a slurry of TeBr4 (0.100 g, 0.223
mmol; THF 5 mL), which was allowed to stir for 4 h, giving an
orange solution. The volatiles were then stripped in vacuo giving
7DippBr as an orange powder. Yield 0.165 g, 96%; Single crystals
for X-ray diffraction studies were grown from a concentrated
CH2Cl2 solution of the powder via vapor diffusion of Et2O; d.p.
1
of the powder via vapor diffusion of Et2O; d.p. 190 °C; H NMR
(CDCl3; δ ppm)); 8.39 (s, 1H, 2JSe-H ) 24.0 Hz), 7.51 (t, 1H, 3JH-H
) 7.6 Hz), 7.31 (t, 3H, 3JH-H ) 7.6 Hz), 7.22 (d, 2H, 3JH-H ) 7.6
Hz), 4.83 (s, 1H), 3.08 (sept, 2H, 3JH-H ) 6.8 Hz), 2.40 (sept, 2H,
3JH-H ) 6.8 Hz), 2.13 (s, 3H), 1.23 (overlapping doublets, 18H),
1
208 °C; H NMR (CDCl3; δ ppm) 7.36 (m), 7.28 (m), 7.21 (m),
4.55 (s, 2H), 3.14 (sept, 2H, 3JH-H ) 6.8 Hz), 2.74 (sept, 2H, 3JH-H
) 6.8 Hz), 2.36 (s, 3H), 1.29 (overlapping doublets, 12H), 1.15
(overlapping doublets, 12H); 125Te{1H} NMR (CH2Cl2; δ ppm)
1283.
3
1.18 (d, 6H, JH-H ) 6.8 Hz); 77Se{1H} NMR (CH2Cl2; δ ppm)
1023; 13C{1H} NMR (CH2Cl2, δ ppm) 163.24, 145.20, 144.42,
141.27, 139.52, 135.42, 133.89, 133.61, 131.88, 130.85, 129.83,
127.88, 124.78, 124.65, 28.94, 28.68, 25.20, 24.21, 23.97, 17.21;
Elemental analysis (%), Found (Calcd): C 59.46(59.77), H 7.06(6.99),
N 4.87(4.98).
Synthesis of 7CyCl. A solution of 1Cy (0.050 g, 0.202 mmol;
THF 5 mL) was added to a slurry of TeCl4 (0.054 g, 0.202 mmol;
THF 5 mL) immediately giving a yellow solution, which was
allowed to stir for 10 min. The volatiles were then stripped in vacuo
giving a yellow solid. The solids were redissolved in CH2Cl2 (2
mL), Et2O (5 mL) was added, and the mixture stored at -30 °C
overnight, giving a colorless precipitate. The supernatant was
Synthesis of 8CyCl ·HCl. A freshly prepared solution of SeCl2
(0.452 mmol; THF 5 mL) was added to a THF solution of 1Cy
(0.112 g, 0.454 mmol, THF 5 mL), giving a yellow solution. Normal
Inorganic Chemistry, Vol. 48, No. 7, 2009 3241

Dutton et al.
Scheme 1
pentane (10 mL) was added, and the reaction mixture was cooled
to -30 °C overnight, resulting in the formation of a brown
precipitate. The supernatant was decanted, the precipitate washed
with Et2O (2 × 5 mL), and the volatiles were dried in vacuo giving
8CyCl·HCl as a beige powder. Yield 0.133 g, 74%; d.p. 165-168
°C; 1H NMR (C5D5N; δ ppm); 18.00 (bs, 1H), 8.75 (s, 1H, 2JSe-H
) 28.0 Hz), 5.17 (bs, 1H), 3.96 (m, 1H), 3.03 (m, 1H), 2.23 (s,
3H), 2.05-1.00 (CH2); 77Se{1H} NMR (C5D5N; δ ppm) 688;
13C{1H} NMR (C5D5N, δ ppm): 161.6, 138.7, 127.2, 60.1, 52.5,
34.1, 31.6, 25.0, 24.1, 23.8, 14.6; Elemental analysis (%), Found
(Calcd): C 47.52(48.23), H 6.68(7.09), N 6.81(7.04); ESI-MS (m/
z): 327 [M - HCl2]+
Synthesis of 9DippCl. A solution of 1Dipp (0.100 g, 0.248
mmol; THF 5 mL) was added to a solution of SCl2 (0.0255 g, 0.248
mmol; THF 5 mL) immediately giving an orange slurry, which
was allowed to stir for 10 min. The product was precipitated by
the addition of Et2O (5 mL). The precipitate was washed with Et2O
(2 × 5 mL) and dried in vacuo giving 9DippCl as a pale yellow
powder. Yield 0.080 g, 69%; Crystals for X-ray diffraction studies
were grown from a concentrated CH2Cl2 solution of the powder
via vapor diffusion of Et2O; d.p. 230-233 °C.1H NMR (CDCl3; δ
3
ppm); 8.32 (s, 1H), 7.57 (t, 1H, JH-H ) 8.0 Hz), 7.33 (d, 2H,
3JH-H ) 8.0 Hz), 7.29 (m, 1H), 7.21 (d, 2H), 6.10 (s, 1H), 3.14
3
3
(sept, 2H, JH-H ) 7.2 Hz), 2.32 (s, 3H), 2.20 (sept, 2H, JH-H
)
6.8 Hz), 1.15 (m, 24H); 13C{1H} NMR (CDCl3, δ ppm): 158.2,
146.5, 145.9, 142.4, 135.0, 132.1, 131.0, 130.4, 127.8, 124.1, 28.5,
24.9, 24.0, 23.6, 15.7; Elemental analysis (%), Found (Calcd):
71.08(71.38), 8.58(8.35), 5.88(5.95); ESI-MS (m/z): 435 [M - Cl]+
Synthesis of 9CyCl ·HCl. A solution of 1Cy (0.100 g, 0.406
mmol; 5 mL THF) was added to a solution of SCl2 (0.0414 g, 0.406
mmol; THF 5 mL) immediately giving a pale beige precipitate,
and the reaction mixture was allowed to stir for 10 min. The
supernatant was decanted, and the precipitate was washed with THF
(5 × 8 mL) and dried in vacuo giving 9CyCl·HCl. Yield 0.069 g,
49%; d.p. 195-197 °C.1H NMR (CD3CN; δ ppm); 7.86 (s, 1H),
4.61 (m, 1H), 3.21 (m, 1H), 2.55 (s, 3H), 2.19-1.12 (m, 22H);
13C{1H} NMR (C5D5N, δ ppm); 157.4, 142.2, 134.5, 68.2, 62.0,
34.2, 32.9, 26.3, 25.7, 25.6, 25.0, 14.8; Elemental analysis for
SCl2C16H28, Found (Calcd): C 53.98(54.68), H 7.39(8.04), N
7.66(7.98); ESI-MS (m/z): 279 [M - HCl2]+
Synthesis of 8CyBr ·HBr. A freshly prepared solution of SeBr2
(0.633 mmol; THF 5 mL) was added to a THF solution of 1Cy
(0.157 g, 0.633 mmol; THF 5 mL) at room temperature, resulting
in the immediate precipitation of a white solid. The mixture was
allowed to stir for 10 min; then the supernatant was decanted. The
white solids were washed with Et2O (2 × 5 mL) and dried in vacuo
giving 8CyBr·HBr as a white powder. Yield 0.240 g, 77%; d.p.
1
179-181 °C; H NMR (C5D5N; δ ppm); 12.85 (bs, 1H), 8.65 (s,
2
1H, JSe-H ) 28.7 Hz), 5.2 (bs, 1H), 4.10(m, 1H), 3.08 (m, 1H),
2.46(s, 3H), 2.08-1.00 (CH2); 77Se{1H} NMR (C5D5N; δ ppm)
704; 13C{1H} NMR (CH2Cl2, δ ppm); 161.7, 139.0, 126.3, 60.3,
52.5, 34.1, 31.4, 24.9, 24.2, 24.0, 23.7, 15.0; Elemental analysis
(%), Found (Calcd): C 38.65(39.43), H 5.39(5.80), N 5.64(5.75);
ESI-MS (m/z): 327 [M - HBr2]+
Synthesis of 8CyCl. Triethylamine (22.3 µL, 0.160 mmol) was
added to a THF (5 mL) slurry of 8CyCl·HCl (0.064 g, 0.160 mmol)
resulting in a colorless precipitate within a yellow solution. After
10 min the reaction mixture was centrifuged and the supernatant
decanted. The THF was removed in vacuo giving 8CyCl as a light
yellow powder. Yield 0.048 g, 83%; d.p. 150-160 °C (solid
Results and Discussion
The 1:1 stoichiometric reaction of 1Dipp or 1Cy with
TeX4 (X ) Cl, Br) resulted in the formation of a yellow
solution, either immediately, or over 4 h (for 1Dipp; X )
Br). Upon no further color change, the volatiles were
removed in vacuo affording yellow powders in all cases
(Scheme 1). Samples of the material redissolved for 1H NMR
spectroscopy revealed signals consistent with a single
product; however, it was clear that the symmetry of the ligand
framework had been broken. The two methine protons from
1Dipp were distinct (δ ) 3.08 and 2.70 ppm), and the
backbone methyl groups were also differentiable, integrating
in a 2:3 fashion, rather than the expected 1:1 ratio (7DippCl:
δ ) 4.26 ppm, 2.37 ppm; 7DippBr: δ ) 4.55 ppm, 2.36
ppm; cf. 2.07 ppm in free 1Dipp). Analogous NMR spectra
were obtained when using 1Cy with an obvious doubling of
the cyclohexyl signals and an identical distinction of the
backbone methyl groups that was observed when using
1Dipp. Tellurium-125 NMR spectra of all four samples
1
2
blackens); H NMR (CDCl3; δ ppm); 8.37 (s, 1H, JSe-H ) 29.6
Hz), 4.07 (m, 1H), 3.20 (N-H overlaps Cy-ipso, 2H), 2.28 (s, 3H),
2.07-1.15 (CH2); 77Se{1H} NMR (CH2Cl2; δ ppm) 713; 13C{1H}
NMR (CH2Cl2, δ ppm): 158.1, 137.0, 127.3, 59.3, 50.9, 33.0, 30.4,
23.1, 23.0, 22.5, 22.4, 13.0; ESI-MS (m/z): 327 [M - Cl]+
Synthesis of 8CyBr. Triethylamine (57 µL, 0.410 mmol) was
added to a THF (10 mL) slurry of 8CyBr·HBr (0.200 g, 0.410
mmol) resulting in a colorless precipitate within a yellow solution.
After 10 min the reaction mixture was centrifuged and the
supernatant decanted. The solids were washed with THF (2 × 5
mL), and the washings added to the initial supernatant. The THF
was removed in vacuo giving 8CyBr as a light yellow powder.
Yield 0.070 g, 42%; d.p. 195-197; 1H NMR (CDCl3; δ ppm); 8.40
2
(s, 1H, JSe-H ) 29.4 Hz), 4.08 (m, 1H), 3.29 (s, 1H), 3.12 (m,
1H), 2.29 (s, 3H), 2.10-1.18 (CH2); 77Se{1H} NMR (C5D5N; δ
ppm) 720; 13C{1H} NMR (CH2Cl2, δ ppm): 158.3, 136.5, 127.5,
59.4, 50.9, 43.5, 32.9, 30.4, 23.3, 22.9, 22.4, 22.3, 13.1; ESI-MS
(m/z): 327 [M - Br]+
3242 Inorganic Chemistry, Vol. 48, No. 7, 2009

N,C Bound Sulfur, Selenium, and Tellurium Heterocycles
Figure 3. Solid-state structure of 7CyBr. Thermal ellipsoids are drawn to
the 50% probability level, CHCl3 solvate and hydrogen atoms are omitted
for clarity.
Figure 1. Solid-state structure of 7DippCl. Thermal ellipsoids are drawn
to the 50% probability level and hydrogen atoms are omitted for clarity.
Figure 4. Solid-state structure of 7CyCl. Thermal ellipsoids are drawn to
the 50% probability level and hydrogen atoms are omitted for clarity.
mixture of products. However after work up, the redissolved
solids analyzed by 1H NMR spectroscopy, revealed a single
compound that appeared to have a framework related to
7Dipp. Again, the symmetry of the ligand was broken: the
methine protons displayed two resonances at δ ) 3.08 and
2.39 ppm. A singlet was observed at δ ) 2.12 ppm
integrating to three protons consistent with a methyl group
on the ligand, as well as two signals integrating to one proton
each (δ ) 8.31 and 4.83 ppm). The resonance at δ ) 4.83
ppm was significantly broadened, whereas the signal at δ )
8.31 ppm clearly displayed coupling to 77Se (2JSe-H ) 24
Hz). To identify the material conclusively, single crystals
were grown for X-ray diffraction, and subsequent solid state
studies revealed the compound to feature an N,C bound five-
membered selenium heterocycle (8DippCl), analogous to 7.
However, based on the geometry and coordination environ-
ment about the central element, it was apparent that a
reduction had taken place, leaving selenium in the +2
oxidation state. The low isolated yield (<20%), combined
with the reduction at Se, prompted us to investigate the same
chemistry using sources of Se(II) rather than Se(IV).
Figure 2. Solid-state structure of 7DippBr. Thermal ellipsoids are drawn
to the 50% probability level and hydrogen atoms are omitted for clarity.
revealed one resonance in all cases, indicating the production
of a single tellurium-containing product. Determining the
connectivity of these molecules was not possible from an
examination of the multinuclear NMR spectra, so single
crystals suitable for X-ray diffraction were grown. These
experiments revealed parallel products in all cases, where a
novel and unexpected Te1N1C3 5-membered ring system was
generated by the incorporation of a carbon atom from a
methyl group from the ligand backbone (7), with three
halogen atoms remaining on the Te center, indicating
retention of the +4 oxidation state, pointing to the formal
loss of HX (Figures 1-4). By repeating these reactions in
the presence of Et3N, it was ascertained that there was indeed
a stoichiometric release of the hydrohalide, which was
sequestered quantitatively as the [Et3NH][X] salt, with all
products being recovered in yields between 75-98%.
To investigate if this reactivity would be observed with
selenium, the reaction of SeCl4 with 1Dipp in THF was
carried out. This immediately resulted a bright yellow
solution, which after removal of the THF in vacuo, gave a
In this context, the reaction of 1Dipp with SeX2 (X ) Cl,
Br) in THF resulted in the immediate generation of yellow
solutions and after workup, bright yellow powders (Scheme
1). For X ) Cl, the redissolved (CDCl3) powder showed
1
yellow powder. Unlike the tellurium systems, the H NMR
spectra of the crude material revealed an apparently complex
Inorganic Chemistry, Vol. 48, No. 7, 2009 3243

Dutton et al.
for the N-substituents (Cy-ispo; X ) Cl, δ ) 3.96, 3.03 ppm;
X ) Br, δ ) 4.10, 3.08 ppm) and the backbone methyl group
integrated only for 3 protons, as was observed for 8Dipp.
In addition, two signals that integrated to one proton, with
one being broad and the other clearly coupling to Se were
observed (2JSeH ) 24 Hz). Despite the similarities in the
spectroscopic data (1H NMR, FT-IR, and FT-Raman spectra),
the extreme differences in solubilities between the Dipp and
Cy congeners pointed to some marked dissimilarities.
Unfortunately all attempts to grow single crystals of the
cyclohexyl analogues for X-ray diffraction studies resulted
in the precipitation of bulk powders. Combustion mi-
croanalysis (C, H, N) of both derivatives gave results
consistent with a molecular formula of C16H28X2N2Se1, which
indicated that the HX eliminated in the other cases remained
in the final product. Upon reexamination of the solution 1H
NMR spectra, in the far downfield region a second broad
resonance also integrating for one proton was present (δ )
18 ppm, X ) Cl; δ ) 13 ppm, X ) Br). Given that the
NMR spectra were collected in pyridine-d6, we surmised that
the insoluble compounds were the HX salts of the N,C bound
Se(II) heterocycles (8CyCl·HCl; 8CyBr·HBr), which were
subsequently deprotonated by the NMR solvent. The HX was
eliminated in a facile fashion by adding a stoichiometric
equivalent of NEt3 in THF, which resulted in the immediate
precipitation of [HNEt3][X] and the generation of a yellow
solution. Removal of the ammonium salt and volatiles gave
light yellow powders. These had solubilites similar to the
Dipp analogues, and the 1H NMR spectra in CDCl3 revealed
resonances very similar to the hydrogen halide salts, albeit
without the broad resonance shifted to low field. All
characterization data were consistent with the assignment as
the N1Se1C3 heterocycles (8CyCl or 8CyBr), isolated in 84%
and 40% yields, respectively.
Given these results with Te and Se, we wondered if
analogous molecules could be synthesized with sulfur as the
central element. Sulfur tetrachloride has been reported; but
we have not been able to reproduce its synthesis and SBr4
is synthetically inaccessible.20 However, SCl2 can be pre-
pared via the reaction of S2Cl2 with chlorine gas over a
catalytic amount of FeCl2 and stored for extended periods
(>6 months) under an N2 atm at -78 °C. Given the known
thermal instability of SCl4, SCl2 was used as a reagent to
generate the sulfur analogues. The 1:1 stoichiometric reaction
of 1Dipp with SCl2 in THF followed by addition of
n-pentane after 10 min, gave a yellow powder (Scheme 1).
Proton NMR spectroscopy of the isolated solids showed one
set of signals, with similar resonances as observed in
8DippCl. Single crystals suitable for X-ray diffraction studies
were grown from a CH2Cl2 solution of the bulk material,
which revealed the anticipated connectivity of a N1S1C3
heterocycle (9DippCl), isolated from the reaction in 69%
Figure 5. Solid-state structure of 8DippCl. Thermal ellipsoids are drawn
to the 50% probability level and unrefined hydrogen atoms are omitted for
clarity.
Figure 6. Solid-state structure of 8DippBr. Thermal ellipsoids are drawn
to the 50% probability level and unrefined hydrogen atoms are omitted for
clarity.
signals identical to that of 8DippCl in the 1H NMR spectrum,
and X-ray diffraction studies on crystals grown from the bulk
powder showed that the material was identical and obtained
in a much better yield (ca. 85%; Figure 5). For X ) Br, the
1H NMR spectrum was essentially identical to that of
8DippCl, and X-ray analysis of single crystals grown from
the bulk powder confirmed generation of the brominated
derivative (8DippBr; Figure 6). In both cases there was the
formal loss of HX, similar to the tellurium analogues.
However unlike the Te chemistry, a proton transfer took
place to give an exocyclic amine functionality. A further
contrast between the selenium and the tellurium chemistry
occurred when an alkyl substituted ligand was employed
(1Cy) rather than the aryl derivative 1Dipp. When the
reaction was carried out between the selenium(II) halides
and 1Cy under identical reaction conditions, a colorless solid
precipitated immediately. The dried powders were found to
be completely insoluble in a variety of common solvents used
for 1H NMR spectroscopy (CDCl3, C6D6, CD3CN), in stark
contrast to the other derivatives (8DippCl, 8DippBr). The
(20) There have been many reports in the older literature concerning the
isolation (and use of) SCl4 at low temperatures, by reacting liquid Cl2
with SCl2. This species is unstable and reported to decompose at
temperatures above -30°C (See King, R. B. Encyclopedia of Inorganic
Chemistry; Wiley: Hoboken, 2005; pp 5364-5367). Our attempts to
prepare SCl4 in situ as CH2Cl2 and THF solutions did not reveal any
evidence for the formation of SCl4.
1
powders were soluble in C5D5N and the H NMR spectra
for both X ) Cl and Br, revealed a similar break in symmetry
3244 Inorganic Chemistry, Vol. 48, No. 7, 2009

N,C Bound Sulfur, Selenium, and Tellurium Heterocycles
bond (8DippCl, 1.931(1); X ) 8DippBr, 1.942(3) Å) is
slightly elongated, indicative of a dative interaction.1,23 In
contrast to the Te rings, C(1)-C(2) clearly form a double
bond (8DippCl, 1.365(2); 8DippBr, 1.350(5) Å), and the
C(2)-N(2) is elongated (8DippCl, 1.386(2); 8DippBr,
1.388(5) Å). The proton bound to N(2) can be located in
the difference map and refined for both 8DippCl and
8DippBr. The existence of the N-H functionality is also
1
confirmed by way of the H NMR spectra (8DippCl and
8DippBr, δ ) 4.83 ppm); as well a distinct N-H stretch
observed in IR spectra.
In the case of sulfur (9DippCl)), an examination of the
metrical parameters reveals a similar N-C bound AX3E2
sulfur center as detected for selenium (S(1)-N(1) ) 1.709(4)
Å, S(1)-C(1) ) 1.687(5) Å). The result of a proton transfer
is again obviated by the C(1)-C(2) bond length of 1.373(6)
Å and the C(2)-N(2) bond at 1.380(6) Å, which is single.
A significant deviation from the Se version is the elongated
chalcogen-chlorine contact at 2.849(2) Å (S(1)-Cl(1)) as
compared to Se(1)-Cl(1) at 2.5965(5) Å. Considering the
greater distance, combined with the larger size of selenium,
this metrical parameter indicates an ionic character to the
sulfur analogue. However, the distance is well within the
sum of the van der Waals radii (Σv.d.w. (S-N) ) 3.65 Å)24
and despite this elongation, the chlorine atom still defines a
T-shaped geometry about sulfur. This elongation of the S-Cl
bond may be a function of hydrogen bonding in the solid
state to the proton bound to N(2) of an adjacent molecule
(Cl · · · H ) 2.50 Å).
Figure 7. Solid-state structure of 9DippCl Thermal ellipsoids are drawn
to the 50% probability level, CH2Cl2 solvate and hydrogen atoms are omitted
for clarity.
yield (Figure 7). As was the case for Se, reaction of SCl2
with 1Cy in THF resulted in the precipitation of a highly
insoluble powder, though sparingly soluble in MeCN. The
1H NMR spectrum gave resonances reminiscent of 8CyCl,
and elemental analysis of the powder was consistent with
the hydrochloride salt 9CyCl · HCl.
X-ray Crystallography. Compounds 7DippCl, 7DippBr,
7CyCl, 7CyBr, 8DippCl, 8DippBr, and 9DippCl have been
characterized by single crystal X-ray diffraction studies.
Views of the formula units are shown in Figures 1-7, and
key refinement details and a listing of pertinent bond lengths
and angles are found in Tables 1 and 2, respectively. All of
the tellurium compounds have analogous structural features
barring the R substituent on nitrogen and the halide present.
The geometry about Te in all cases is a distorted square-
based pyramid as described by the AX5E electron pair
formula, where the distortion is imposed by the stereochemi-
cally active “lone pair” of electrons. This “lone pair” of
electrons and the endocyclic carbon C(1) occupy the axial
sites, where the N and remaining three halogen atoms all
reside in equatorial positions.
Isotope Labeling. In an effort to garner a greater
understanding of this unusual transformation, we have
undertaken some additional experiments using the TeCl4/
1Dipp system as a model.25 To confirm that the proton
eliminated from the reaction (which can be sequestered using
NEt3) originated from within a backbone methyl group,
-CD3 labeled 1Dipp was synthesized from labeled 2,3-
butanedione, with an isotopic purity for the -CD3 groups
of approximately 95%. The 1:1 stoichiometric reaction of
TeCl4 with the labeled ligand (1Dipp-d6) in THF followed
by the addition of NEt3 results in the precipitation of a
The Te(1)-N(1) (2.298-2.448 Å) and Te(1)-(C1) (av.
2.125 Å) bond lengths are consistent with Te-N or Te-C
single bonds.6,21,22 The endocyclic (N(1)-C(3)) and exo-
cyclic (N(2)-C2)) bonds are relatively short (av. endo: 1.284
Å; av. exo. 1.269 Å), reflective of imine functionalities. Also
apparent is the nonplanarity of the Te1N1C3 heterocycles:
the atoms C(1) are sp3 hybridized methylene groups with a
distorted tetrahedral geometry, which forces a nonplanar five
membered ring. This assignment of the bonding is congruent
1
colorless powder within a yellow solution. A H NMR
spectrum of the isolated solid in C5D5N indicated the
presence of [DNEt3]+, as the ethyl resonances were identical
to that from the analogous -CH3 1Dipp experiment, and
only a small residual peak was visible for the N-H proton,
1
which arises from the 5% undeuterated material. The H
1
with the H NMR data obtained from solution in that there
NMR spectrum of the 7DippCl-d5 recovered revealed the
is a methyl and a methylene fragment requiring an integration
ratio of 3:2 and there is no evidence of a N-H functionality.
The selenium compounds characterized by X-ray crystal-
lography are isostructural with respect to the 5 membered
ring. Given the +2 oxidation state for selenium, a T-shaped
geometry is imposed by a AX3E2 electron pair formula. The
Se(1)-C(1) bonds (8DippCl, 1.849(2); 8DippBr, 1.849(4)
Å) are typical Se-C single bond lengths, and the Se(1)-N(1)
expected spectrum, with approximately 95% disappearance
(23) Risto, M.; Reed, R. W.; Robertson, C. M.; Oilunkaniemi, R.; Laitinen,
R. S.; Oakley, R. T. Chem. Commun. 2008, 3278–3280.
(24) Pauling, L. The Nature of the Chemical Bond; Cornell University Press:
Ithaca, 1960.
(25) The kinetics stopped-flow instrumentation requires that all species
remain in solution throughout the experiment. Additionally, the
stopped-flow system is not compatible with THF. The reaction of TeCl4
and 1Dipp in toluene gives identical products as the THF reaction,
and both the products and the reactants are soluble. In the case of
TeBr4, SeX2 and SCl2, with 1Dipp, and all compounds using 1Cy the
products precipitate from toluene. Therefore, we were limited to the
TeCl4 system; however, the reactivity of the other analogues appears
to be the same.
(21) Furukawa, N.; Sato, S. Heteroat. Chem. 2002, 13, 406–413.
(22) Kuhn, N.; Abu-Rayyan, A.; Piludu, C.; Steimann, M. Heteroat. Chem.
2005, 16, 316–319.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3245

Dutton et al.
Table 1. Crystal Data for Compounds 7-9
7DippCl
7DippBr
7CyCl
7CyBr
8DippCl
8DippBr
9DippCl
empirical formula
formula weight
crystal system
space group
a (Å)
C28H39Cl3N2Te1 C28H39Br3N2Te1 C16H27Cl3N2Te1 C17H28Br3Cl3N2Te1 C28H39Cl1N2Se1 C28H39Br1N2Se1 C29H41Cl3N2S1
637.56
monoclinic
P21/n
770.94
481.35
734.09
monoclinic
P21/n
518.02
monoclinic
P21/n
562.48
monoclinic
P21/n
556.05
monoclinic
P21/c
triclinic
triclinic
j
j
P1
P1
10.236(2)
16.801(3)
17.921(4)
90
94.66(3)
90
9.304(2)
9.630(2)
18.133(4)
84.58(3)
82.27(3)
69.86(3)
1509.5(5)
1.696
9.190(2)
9.967(2)
11.624(2)
84.70(3)
69.45(3)
75.26(3)
964.1(3)
1.658
10.697(2)
10.211(2)
23.173(5)
90
100.44(3)
90
9.2685(5)
22.653(1)
13.6431(7)
90
102.3574(7)
90
9.306(2)
22.436(5)
13.720(3)
90
100.08(3)
90
10.887(2)
19.883(4)
14.898(3)
90
92.75(3)
90
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
3072(1)
1.247
2489.2(8)
1.959
2798.1(2)
1.230
2820(1)
1.325
3221(1)
1.147
Dc (mg m-3
)
radiation, λ (Å)
0.71073
150(2)
0.0507
0.1379
0.71073
150(2)
0.0389
0.1056
1.044
0.71073
150(2)
0.0549
0.1294
1.085
0.71073
150(2)
0.0540
0.1486
1.037
0.71073
193(2)
0.0323
0.0824
1.062
0.71073
150(2)
0.0526
0.1241
1.021
0.71073
193(2)
0.0795
0.2628
1.045
temp. (K)
R[I > 2σI]a
wR2(F2)b
Goodness of fit (S)a 0.965
a R(F [I > 2σ(I)]) ) ∑||Fo| - |Fc||/∑|Fo|; wR(F2 [all data]) ) [∑w(Fo2 - Fc2)2]1/2; S(all data) ) [∑w(Fo2 - Fc2)2/(n - p)]1/2 (n ) no. of data; p ) no. of
b
2
2
parameters varied. w ) 1/[σ2(Fo ) + (aP)2 + bP] where P ) (Fo + 2Fc2)/3 and a and b are constants suggested by the refinement program.
Table 2. Selected Bond Lengths for Compounds 7-9; Ch ) Te for 7, Se for 8, S for 9
7DippCl
7DippBr
7CyCl
7CyBr
8DippCl
8DippBr
9DippCl
Ch(1)-N(1)
Ch(1)-C(1)
C(1)-C(2)
C(2)-C(3)
C(2)-N(2)
C(3)-N(1)
N(1)-C(5)
N(2)-C(6)
Ch(1)-X(1)
Ch(1)-X(2)
Ch(1)-X(3)
2.416(3)
2.124(4)
1.506(6)
1.493(6)
1.267(5)
1.293(5)
1.457(5)
1.440(5)
2.473(1)
2.404(1)
2.499(1)
2.448(3)
2.130(3)
1.505(5)
1.503(5)
1.274(4)
1.278(5)
1.446(4)
1.431(4)
2.6589(7)
2.669(1)
2.6610(7)
2.309(4)
2.119(5)
1.509(7)
1.494(7)
1.271(6)
1.283(6)
1.474(7)
1.470(7)
2.475(2)
2.447(2)
2.523(2)
2.298(4)
2.127(6)
1.503(8)
1.487(7)
1.265(7)
1.282(7)
1.490(7)
1.454(7)
2.634(1)
2.6260(8)
2.680(1)
1.931(1)
1.849(2)
1.365(2)
1.438(2)
1.387(2)
1.314(2)
1.444(2)
1.435(2)
2.5964(5)
1.942(3)
1.850(4)
1.350(5)
1.441(5)
1.386(5)
1.312(5)
1.443(4)
1.434(5)
2.759(1)
1.710(3)
1.686(4)
1.374(6)
1.422(6)
1.377(5)
1.322(6)
1.465(5)
1.442(5)
2.848(2)
Scheme 2. Proposed Reaction Pathway for the Generation of the N,C Heterocycles, Using 7DippX As a Model
of the signals arising from the methyl and methylene protons.
This experiment confirmed the assertion that the proton is
eliminated from a backbone methyl group, and no other
scrambling or rearrangement occurs during the reaction.
Low temperature experiments carried out in THF and
monitored by 1H NMR spectroscopy, showed that the
reaction initiates at -45 °C, with no species being observed
other than 1Dipp and 7DippCl. Given the low temperature
at which the transformation proceeds and that no intermedi-
ates were detected, we hypothesized that the reaction was
unlikely to rely on the direct deprotonation of a -CH3 group
by a third species in solution.
In an attempt to understand the mechanism of the reaction,
a stopped-flow kinetics study was performed on the TeCl4/
1Dipp system. As suspected from visual observation, the
reaction is indeed very fast, going to completion in 1.2 s at
a concentration of 0.031 mmol for both reactants. Using
-CD3 labeled 1Dipp the reaction goes to completion 6-7
times slower than using the proteo-ligand, likely indicating
a strong primary kinetic isotope effect and that a proton
transfer is part of the rate determining step. Also observed
was an inverse dependence on the rate with respect to the
concentration of TeCl4, likely a result of aggregation of the
TeCl4 at higher concentrations. However, we were unable
to effectively model the kinetic data to establish a defini-
tive rate law. Nevertheless based on the data obtained, the
transformation is proposed to occur via olefin attack on the
chalcogen center from the enamine form of the ligand,
analogous to the related NacNac system outlined by Richards
et al.3 The carbon-chalcogen bond formation is concomitant
with coordination by the imine nitrogen proximal to the
tellurium atom, generating the 5 membered ring, and H-X
elimination (Scheme 2).
The proton-dependent rate determining process is likely
the establishment of the enamine/imine equilibrium for the
ligand, with the enamine form being consumed as the
reaction proceeds. It must be noted that regardless of
the metal starting material used (Se or Te), a distinct increase
in the reaction completion time was observed when using
the labeled ligand. This gives additional credence to the
3246 Inorganic Chemistry, Vol. 48, No. 7, 2009

N,C Bound Sulfur, Selenium, and Tellurium Heterocycles
assertion that the enamine/imine tautomerization process is
the rate limiting step, provided the HX elimination is faster.
The reasoning for the preference of the imine (Te) versus
enamine (Se, S) tautomer in the final product remains an
open question, as it is dependent on either the identity of
the central element or the oxidation state it adopts. Unfor-
tunately, attempts to resolve this issue by either reducing
the tellurium congeners or oxidizing the Se/S heterocycles
were unsuccessful. However, our observations are consistent
with those of Cowley et al. in the report of the reaction
between TeCl4 and the DIMPY ligand, where Te-C con-
nectivity was observed as well as the imine tautomer
remaining resilient.6
delay in the completion of the reaction was observed,
pointing toward a primary kinetic isotope effect. This lends
substantial support to the assertion that the enamine form of
the ligand plays a key role the reaction progress and no C-H
bond activation is apparent.
Acknowledgment. We thank Natural Sciences and En-
gineering Research Council (NSERC of Canada), The
Canada Foundation for Innovation (CFI), The Ontario
Ministry for Research and Innovation (OMRI), and The
University of Western Ontario for generous support, Allison
Brazeau (UWO) for her assistance with the stopped-flow/
kinetic experiments, and Dr. R. McDonald and Dr. M. J.
Ferguson (University of Alberta) for the collection of X-ray
diffraction data for compounds 8DippCl and 9DippCl.
Conclusion
The reactions of CH3 substituted R-diimine ligands with
N-alkyl or N-aryl substituents at nitrogen result in the
formation of N1Ch1C3 ring systems. This is in contrast to
what has been reported for the reactions of other main group
element halides with analogous DAB ligands or for the
chalcogens using non-methylated analogues. By employing
a CD3 substituted version of the ligand, a distinct 6 to 7 fold
Supporting Information Available: Further details are given
in Figures S-1 to S-8 including IR and Raman data for all
compounds. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC802320S
Inorganic Chemistry, Vol. 48, No. 7, 2009 3247