Reactions of α-Diimine Ligands with the in situ generated s(OTf)2 synthon

Article abstract of DOI:10.1021/ic100320u

A series of reactions of α-diimine ligands with a 2:1 mixture of SCl₂ and trimethylsilyltrifluormethanesulfonate(TMS-OTf), which behaves as an S(OTf)₂ synthon, were performed. The reactivity was shown to differ based on the substitution at the nitrogen atoms of the ligand as aromatic groups yielded dicationic sulfur nitrogen heterocycles whereas alkyl groups resulted in the loss of one of the organic substituents at nitrogen giving monocationic 1,2,5-thiadiazolium rings. The substitution on the backbone carbon being a hydrogen atom, phenyl group (diazabutadiene; DAB) or acenaphthene (bisiminoacenaphthene, BIAN) proved not to be influential on the outcome of the reaction as both systems resulted in N,N′-chelated dications. These are rare examples of sulfur structural mimics of the N-heterocyclic silylene, and the BIAN species represent the first complexes of sulfur with this ubiquitous ligand.

Full text of DOI:10.1021/ic100320u

4324 Inorg. Chem. 2010, 49, 4324–4330
DOI: 10.1021/ic100320u
Reactions of r-Diimine Ligands with the in Situ Generated “S(OTf)2” Synthon
Caleb D. Martin and Paul J. Ragogna*
Department of Chemistry, The University of Western Ontario, The Chemistry Building, 1151 Richmond Street,
London, Ontario N6A 5B7, Canada
Received February 17, 2010
A series of reactions of R-diimine ligands with a 2:1 mixture of SCl2 and trimethylsilyltrifluormethanesulfonate(TMS-
OTf), which behaves as an S(OTf)2 synthon, were performed. The reactivity was shown to differ based on the
substitution at the nitrogen atoms of the ligand as aromatic groups yielded dicationic sulfur nitrogen heterocycles
whereas alkyl groups resulted in the loss of one of the organic substituents at nitrogen giving monocationic 1,2,
5-thiadiazolium rings. The substitution on the backbone carbon being a hydrogen atom, phenyl group (diazabutadiene;
DAB) or acenaphthene (bisiminoacenaphthene, BIAN) proved not to be influential on the outcome of the reaction
as both systems resulted in N,N0-chelated dications. These are rare examples of sulfur structural mimics of the
N-heterocyclic silylene, and the BIAN species represent the first complexes of sulfur with this ubiquitous ligand.
Introduction
BCl3 in a 1:1 stoichiometry in hexanes gives rise to covalent
N-B bonds with a loss of the diimine framework giving
a neutral diazaborolidine with double-halogenation of the
backbone carbon atoms (3).6,7 Switching the solvent to
CH2Cl2 produces a different outcome as the elimination of
HCl occurs generating a carbon-carbon double bond in the
ligand framework (4).7
Reactions of DAB or BIAN ligands with PBr3 proceed
cleanly in the presence of a halide trap (e.g., cyclohexene) and
undergo a charge-transfer giving the corresponding bromo-
phosphines (5, 6).8 The reaction proceeds by generating a P(I)
intermediatewhich is then oxidizedto P(III) by the ligand in a
subsequent step; hence, a charge-transfer from the phos-
phorus center to the ligand occurs. These halophosphorus
compounds are precursors to N-heterocyclic phosphenium
cations (7, 8) via halide abstraction. The phosphenium
cations can also be made directly with a 1:1 mixture of SnCl2
and PCl3 or PI3 alone with either DAB or BIAN ligands.9-11
The reactivity proved consistent in all cases regardless of the
substitution on the R-carbon.
The reactivity of R-diimine ligands (e.g., R2DAB,
R2BIAN; Figure 1) with the majority of the elements on
the periodic table has been widely explored. The bulk of these
studies have been conducted on metals, whereas non-metallic
elements have, for the most part, been ignored.1 One ex-
planation for the lack of experimentation on the non-metals
is that they generally have higher electronegativities, are
electron rich (lone pair bearing), and consequently have a
lower affinity for nitrogen based ligand systems. This is
reflected in the number of reports for such chemistry in the
open literature; however, boron and phosphorus have been
extensively studied with Schiff-base ligand systems, and have
revealed highly novel outcomes.2
For example, boron trichloride reacts in a 1:1 stoichio-
metry with aryl BIAN derivatives with the displacement of a
halide resulting in the diimine sequestered boron cation with
a chloride anion (1). If the same reaction is conducted with a
second equivalent of BCl3 or 2 equiv of BBr3, the halide binds
to the second BX3 molecule resulting in a BX4 anion.3,4
-
Over the past several years, there has been a surge in
interest in the chemistry between diimine ligands and the
p-block elements. Our research group has been interested in
the interactions of these ligands with the chalcogens and have
Similarly, an alkyl DAB ligand reacts stoichiometrically with
BBr3 producing an analogous cationic diimine BBr2 complex
with a Br- counterion (2).5 The reaction of an aryl DAB with
*To whom correspondence should be addressed. E-mail: pragogna@
uwo.ca. Phone: 1-519-661-2111, ext: 87048. Fax: 1-519-661-3022.
(1) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151–239.
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253.
(3) Jenkins, H. A.; Dumaresque, C. L.; Vidovic, D.; Clyburne, J. A. C.
Can. J. Chem. 2002, 80, 1398–1403.
(4) Hill, N. J.; Vasudevan, K.; Cowley, A. H. Jordan J. Chem. 2006, 1, 47–
54.
(5) Weber, L.; Rausch, A.; Wartig, H. B.; Stammler, H.-G.; Neumann, B.
Eur. J. Inorg. Chem. 2002, 2438–2446.
(6) Mair, F. S.; Manning, R.; Pritchard, R. G.; Warren, J. E. Chem.
Commun. 2001, 1136–1137.
(7) Hinchliffe, A.; Mair, F. S.; McInnes, E. J. L.; Pritchard, R. G.;
Warren, J. E. Dalton Trans. 2008, 222–233.
(8) Dube, J. W.; Farrar, G. J.; Norton, E. L.; Szekely, K. L. S.; Cooper,
B. F. T.; Macdonald, C. L. B. Organometallics 2009, 28, 4377–4384.
(9) Reeske, G.; Hoberg, C. R.; Hill, N. J.; Cowley, A. H. J. Am. Chem.
Soc. 2006, 128, 2800–2801.
(10) Ellis, B. D.; Macdonald, C. L. B. Inorg. Chim. Acta 2007, 360, 329–
344.
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r
pubs.acs.org/IC
Published on Web 04/09/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4325
Figure 1. R-Diimine complexes of non-metals.
mainly focused on Se and Te.12-21 Initial reports featuring
sulfur identified reactivity differing from boron and phos-
phorus. In reactions of SCl2 with an aryl or alkyl-substitued
diazabutadiene ligand featuring methyl groups on the back-
bone carbon, an unexpected N,C-bound hetercycle is ob-
tained (9, 10).15 The mechanism is believed to occur by attack
of the eneamine tautomer of the ligand to the chalcogen
center, which is supported by analogy to the selenium con-
gener. The reaction of SCl2 with an aryl-DAB ligand posses-
sing hydrogen atoms on the backbone carbon, in the presence
of TMS-OTf (triflouromethanesulfonate, OTf = triflate),
results in the formation of an N,N0-chelated dicationic
sulfur center (11, 12a), where the anion could be exchanged
-
with the weakly coordinating B(C6F5)4 counterion
(12b).18
Aside from these preliminary examples, the chemistry of
sulfur with R-diimine ligands remains virtually undeveloped.
In this context, we have conducted a more comprehensive
study to include varied ligand sets to better understand the
effect of varying the substitution at nitrogen and on the
backbone carbon atoms.
Through these experiments it has been determined that the
BIAN framework, or phenyl groups on the backbone carbon
atoms, have little effect, giving rise to N,N0-chelated hetero-
cycles, analogous to the DAB chemistry. Interestingly the
substitution at nitrogen on the DAB ligands plays a critical
role in the outcome of the reaction. In alkyl derivatives, an
alkyl group is lost in the course of the reaction yielding 1,2,5-
thiadiazolium ring systems in stark contrast to the aryl
substituted derivatives.
(12) Dutton, J. L.; Tindale, J. J.; Jennings, M. C.; Ragogna, P. J. Chem.
Commun. 2006, 2474–2476.
(13) Dutton, J. L.; Tuononen, H. M.; Jennings, M. C.; Ragogna, P. J.
J. Am. Chem. Soc. 2006, 128, 12624–12625.
(14) Dutton, J. L.; Sutrisno, A.; Schurko, R. W.; Ragogna, P. J. Dalton
Trans. 2008, 3470–3477.
(15) Dutton, J. L.; Martin, C. D.; Sgro, M. J.; Jones, N. D.; Ragogna, P. J.
Inorg. Chem. 2009, 48, 3239–3247.
(16) Dutton, J. L.; Farrar, G. J.; Sgro, M. J.; Battista, T. L.; Ragogna, P.
J. Chem.;Eur. J. 2009, 15, 10263–10271.
(17) Dutton, J. L.; Tuononen, H. M.; Ragogna, P. J. Angew. Chem., Int.
Ed. 2009, 48, 4409–4413.
Experimental Section
(18) Martin, C. D.; Jennings, M. C.; Ferguson, M. J.; Ragogna, P. J.
Angew. Chem., Int. Ed. 2009, 48, 2210–2213.
(19) Reeske, G.; Cowley, A. H. Chem. Commun. 2006, 4856–4858.
(20) Dutton, J. L.; Ragogna, P. J. Inorg. Chem. 2009, 48, 1722–1730.
(21) Martin, C. D.; Le, C. M.; Ragogna, P. J. J. Am. Chem. Soc. 2009, 131,
15126–15127.
General Procedures. All manipulations were performed under
an inert atmosphere in a nitrogen filled MBraun Labmaster 130
glovebox or using standard Schlenk techniques. Sulfur dichlor-
ide and the R-diimine ligands pMeOPh2DAB, pMeOPh2BIAN,
Dipp2BIAN, tBu2DAB, and Cy2DAB were synthesized using

4326 Inorganic Chemistry, Vol. 49, No. 9, 2010
Martin and Ragogna
literature procedures.22-26 The Ph2DABPh2 ligand was made by
the procedure described by Gibson substituting aniline as the
amine.27 Dichloromethane, CH3CN, Et2O, and n-pentane were
obtained from Caledon Laboratories and dried using an
MBraun Controlled Atmospheres Solvent Purification System.
The dried solvents were stored in Strauss flasks under an N2
mixture yielding pure material; 0.140 g, 51%; d.p. 160-161 °C.
1H NMR (CD3CN, δ) 8.73 (d, 2H, 3J = 8.4 Hz, aryl-H), 8.12 (d,
2H, 3J = 7.2 Hz, aryl-H), 8.08-8.02 (m, 6H, aryl-H), 7.42 (d, 2H,
3J = 8.8 Hz, aryl-H), 4.03 (s, 6H, PhOCH3); 13C{1H} NMR
(CH3CN, δ) 165.7, 162.1, 148.5, 139.3, 131.6, 131.4, 128.6, 125.4,
120.2, 117.6, 57.3; 19F{1H} NMR (CH3CN, δ) -78.6; UV-vis
(CH3CN) λmax, nm (ε, M-1, cm-1) 276 (700), 312 (450), 459 (200),
535 (sh); FT-IR(cm-1(rankedintensity)) 472(10), 521(7), 571(12),
637(2), 778(9), 837(4), 1030(3), 1154(8), 1218(13), 1276(1),
˚
atmosphere, or over 4 A molecular sieves in the glovebox.
Solvents for 1H NMR spectroscopy (CDCl3, CD3CN) were
purchased from Cambridge Isotope Laboratories, and dried
by stirring for 3 days over CaH2, distilled prior to use and stored
1374(15), 1419(14), 1445(11), 1507(5), 1601(6); FT-Raman (cm-1
-
˚
in the glovebox over 4 A molecular sieves. Trimethylsilyltri-
(ranked intensity)) 358(13), 432(5), 472(11), 792(14), 977(15),
1158(3), 1184(7), 1210(4), 1261(8), 1334(6), 1372(10), 1441(9),
1508(1), 1569(12), 1598(2).
flouromethanesulfonate (TMS-OTf) was purchased from Alfa
Aesar and used as received. Multinuclear NMR data are listed in
parts per million (ppm), relative to Me4Si (13C and 1H) and
CFCl3 (19F), coupling constants are in hertz, and all NMR
spectra were recorded on an INOVA 400 MHz spectrometer
(1H = 399.76 MHz, 13C = 100.52 MHz, 19F = 376.15 MHz).
X-ray diffraction data were collected on a Nonius Kappa-CCD
Compound 15. TMS-OTf (0.167 g, 0.600 mmol), SCl2 (0.031 g,
0.300 mmol), Dipp2BIAN (0.150 g, 0.300 mmol). The volatiles
were removed in vacuo, the powder was redissolved in CH2Cl2
(4 mL), and n-pentane was added (6 mL); the solution was stored
at -30 °C overnight giving a red crystalline material. The
crystals were collected, and n-pentane (2 mL) was added to the
mother liquor yielding a second crop of crystals; 0.171 g, 73%;
d.p. 154-156 °C; 1H NMR (CD3CN, δ) 8.56 (d, 2H, 3J=8.0 Hz,
aryl-H), 7.91 (t, 2H, 3J = 8.0 Hz, aryl-H), 7.84 (t, 2H, 3J = 8.0
Hz, aryl-H), 7.60 (d, 4H, 3J = 8.0 Hz, aryl-H), 7.47 (d, 2H, 3J =
7.2 Hz, aryl-H), 2.94 (sept, 4H, 3J = 6.8 Hz, CH(CH3)2), 1.40 (d,
˚
area detector using Mo-KR radiation (λ = 0.71073 A). Crystals
were selected under oil, mounted on glass fibers then immedi-
ately placed in a cold stream of N2. Structures were solved by
direct methods and refined using full matrix, least-squares on F2.
Samples for FT-Raman spectroscopy were packed in capillary
tubes and flame-sealed. 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 KBr pellets using a Bruker Tensor 27
spectrometer, with a resolution of 4 cm-1. Decomposition points
were recorded in flame-sealed capillary tubes using a Gallenkamp
Variable Heater. UV-visible absorption spectra were acquired
using a Varian Cary 300 spectrophotometer in CH3CN, at 25 °C
in 1 cm quartz cells. Elemental analyses were performed by Guelph
Chemical Laboratories Ltd., Guelph, Ontario, Canada.
3
3
12 H, J = 6.8 Hz, CH(CH3)2), 1.15 (d, 12H, J = 6.4 Hz,
CH(CH3)2); 13C{1H} NMR (CH3CN, δ) 165.5, 146.0, 140.5,
136.0, 132.2, 132.1, 131.9, 130.6, 129.8, 127.6, 120.7, 30.2, 24.4, 24.3;
19F{1H} NMR (CHCl3, δ) -78.3; UV-vis (CH3CN) λmax, nm (ε,
M-1, cm-1) 281 (2250), 439 (450); FT-IR (cm-1(ranked intensity))
353(15), 474(9), 524(6), 577(10), 637(2), 771(5), 810(12), 832(13),
1031(3), 1165(10), 1230(11), 1275(1), 1511(14), 1611(8), 2968(7);
FT-Raman (cm-1(ranked intensity)) 85(5), 136(12), 352(6), 474(3),
562(4), 977(7), 1020(10), 1030(8), 1102(15), 1217(9), 1249(8),
1368(14), 1506(1), 1586(13), 1603(2).
General Synthesis of 13-18. Trimethylsilyltrifluoromethane
sulfonate in CH2Cl2 (1.5 mL) was added dropwise to a solution
of SCl2 in CH2Cl2 (10 mL) at -78 °C and stirred for 15 min. A
solution of DAB or BIAN in CH2Cl2 (8 mL) was added dropwise to
the mixture yielding orange/red (15, 18), purple (13, 14), colorless
with a white precipitate (16) or light brown (17) solutions.
Compound 16. TMS-OTf (0.264 g, 1.19 mmol), SCl2 (0.058 g,
0.595 mmol), tBu2DAB (0.100 g, 0.595 mmol). Normal pentane
was added to the reaction mixture, resulting in the formation of
more white precipitate. The supernatant was decanted, and the
solid dried in vacuo giving a white powder. The material was
found to be unstable in solution for periods greater than 15 min
and as a solid for periods greater than 30 min; therefore, 13C
NMR data and elemental analysis could not be obtained.
Compound 13. TMS-OTf (0.372 g, 1.68 mmol), SCl2 (0.086 g,
0.84 mmol), pMeOPh2DAB (0.150 g, 0.558 mmol). Despite
numerous efforts 13 could only be isolated in small quantities
(less than 10 mg) by vapor diffusion of Et2O into CH3CN.; d.p.
185-187 °C; 1H NMR (CD3CN, δ) 9.69 (d, 2H, SN2C2H2), 7.86
(d, 4H, 3J = 6.0 Hz, ortho-PhOCH3), 7.32 (d, 4H, 3J = 4.8 Hz,
meta-PhOCH3), 3.99 (s, 6H, PhOCH3); 19F{1H} NMR
(CH3CN, δ) -78.7; FT-IR (cm-1(ranked intensity)) 518(11),
575(14), 639(8), 760(12), 833(7), 977(15), 1033(3), 1161(2),
1272(1), 1438(9), 1465(6), 1509(5), 1577(13), 1591(4), 3076(10);
FT-Raman (cm-1(ranked intensity)) 415(14), 702(11), 795(13),
1005(9), 1091(5), 1146(7), 1171(8), 1300(1), 1341(2), 1434(3),
1451(4), 1505(10), 1563(12), 1596(6), 1650(15). Elemental Ana-
lysis (%) calcd for S3O6F6C18H16N2: C 36.12, H 2.69, N 4.65;
found C 36.12, H 3.12, N 4.65.
1
0.136 g, 88%; d.p. 95-101 °C; H NMR (CDCl3, δ 10.13 (s,
1H, backbone H), 9.03 (s, 1H, backbone H), 2.01 (s, 9H, tBu);
19F{1H} NMR (CH3CN, δ -78.4; FT-IR (cm-1(ranked in-
tensity)); 518(6), 553(14), 574(11), 638(4), 846(7), 1001(13),
1027(3), 1169(5), 1248(1), 1278(2), 1382(10), 1418(9), 1480(15),
3073(8), 3089(12); FT-Raman (cm-1(ranked intensity)) 314(5),
349(3), 575(12), 706(2), 758(8), 783(11), 846(6), 1030(1), 1151(14),
1226(13), 1448(15), 2920(10), 2997(4), 3088(9).
Compound 17. TMS-OTf (0.202 g, 0.907 mmol), SCl2 (0.047 g,
0.454 mmol), Cy2DAB (0.100 g, 0.454 mmol). Normal pentane
was added to the reaction mixture, resulting in the formation of
a beige precipitate. The supernatant was decanted, and the solid
dried in vacuo giving a beige powder. The material was found to
be unstable in solution for periods longer than 10 min and as a
solid for periods greater than 20 min; therefore, 13C NMR data
and elemental analysis could not be obtained. 0.099 g, 69%; d.p.
48 °C; 1H NMR (CDCl3, δ 10.09 (s, 1H, backbone H), 8.93 (s,
1H, backbone H), 5.33 (m, 1H, ispo-H-Cy), 2.39-1.28 (m, 10H,
Cy); 19F{1H} NMR (CH3CN, δ) -78.4; FT-IR (cm-1(ranked
intensity)) 517(12), 556(4), 575(9), 731(6), 760(5), 812(1), 841(3),
897(2), 1029(15), 1168(13), 1251(14), 1459(11), 2866(8),
2943(10), 3064(7); FT-Raman (cm-1(ranked intensity)) 121(8),
316(7), 349(6), 575(12), 626(15), 760(3), 805(11), 1034(1),
1147(9), 1247(13), 1273(10), 1354(14) 1451(3), 2866(4), 2949(2).
Compound 18. TMS-OTf (0.195 g, 0.878 mmol), SCl2 (0.045 g,
0.439 mmol), Ph2DABPh2 (0.160 g, 0.439 mmol). The volatiles
were removed in vacuo, and the powder was redissolved in
Compound 14. TMS-OTf (0.169 g, 0.76 mmol), SCl2 (0.039 g,
0.38 mmol), p-MeOPh2BIAN (0.150 g, 0.38 mmol). The vola-
tiles were removed in vacuo, the powder was redissolved in
CH3CN (4 mL) and Et2O was added (4 mL), and the solution
was stored at -30 °C for 2 h giving a deep red microcrystalline
material. This was recrystallized from a 1:1 CH3CN:Et2O
(22) Steudel, R.; Jensen, D.; Plinke, B. Z. Naturforsch. 1987, 42b, 163–168.
(23) Abrams, M. B.; Scott, B. L.; Baker, R. T. Organometallics 2000, 19,
4944–4956.
(24) Kliegman, J. M.; Barnes, R. K. Tetrahedron 1970, 26, 2555–2560.
(25) Coventry, D. N.; Batsanov, A. S.; Goeta, A. E.; Howard, J. A. K.;
Marder, T. B. Polyhedron 2004, 23, 2789–2795.
(26) El-Ayaan, U.; Paulovicova, A.; Fukuda, Y. J. Mol. Struct. 2003, 645,
205–212.
(27) Shaver, M. P.; Allan, L. E. N.; Rzepa, H. S.; Gibson, V. C. Angew.
Chem., Int. Ed. 2006, 45, 1241–1244.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4327
Scheme 1. Reactions of R-Diimines with “S(OTf)2”
CH2Cl2 (4 mL), and n-pentane was added (4 mL), the solution
was then stored at -30 °C overnight giving an orange powder.
The supernatant was decanted, and the solids were washed with
n-pentane (3 ꢀ 5 mL). 0.184 g, 60%; d.p. 111-113 °C; 1H NMR
(CDCl3, δ) 8.08 (d, 4 H, 3J = 8.4 Hz, aryl-H), 7.73 (t, 2H, 3J =
7.6 Hz, aryl-H), 7.67-7.55 (m, 10H, aryl-H) 7. 37 (t, 4H, 3J =
8.0 Hz, aryl-H); 13C{1H} NMR (CH3CN, δ) 165.9, 135.5, 132.8,
132.1, 131.6, 130.4, 128.1, 124.0; 19F{1H} NMR (CH3CN, δ)
-78.4; UV-vis (CH3CN) λmax, nm (ε, M-1, cm-1) 278 (1450),
316 (sh); FT-IR (cm-1(ranked intensity)) 1596(9), 1485(10),
1457(14), 1433(8), 1296(13), 1250(1), 1162(5), 1025(2), 788(15),
758(4), 729(11), 694(6), 637(3), 574(12), 519(7) ; FT-Raman
(cm-1(ranked intensity)) 3074(11), 1596(2), 1505(8), 1484(15),
1433(6), 1365(1), 1318(13), 1117(4), 1026(7), 1002(3), 627(14),
464(9), 404(10), 356(12), 102(5).
integrated to two, with respect the six methoxy protons.
A single resonance at -78.7 ppm was observed in the
19F{1H} NMR spectrum consistent with ionic triflate in
solution ([NOct4][OTf] δ = -78.5 ppm). On the basis of
these data, the bonding was assigned as the N,N0-chelated
dicationic chalcogen complex (13).
Upon increasing the stoichiometry of “S(OTf)2” to 1.5
stoichiometric equivalents, the yield in the crude mixture
increased to approximately 85%. We postulate that the
imine nitrogen atoms are sufficiently basic to deprotona-
tate the backbone protons on the dicationic heterocycle
which are acidic upon the coordination of the ligand to
the highly charged sulfur center. This ultimately results in
decomposition of the desired product, as protonated
1
ligand became more prevalent in the crude H NMR
Results and Discussion
sprectrum. Decreasing the amount of free ligand in solu-
tion hinders this process and allows the reaction to
proceed more cleanly. Increasing the stoichiometry of
“S(OTf)2” did not result in a greater yield in the R2BIAN
(14 and 15) or the Ph2DABPh2 (18) complexes, which do
not possess the acidic backbone protons. A related ob-
servation has been made with the heterocyclic nitrenium
cation (nitrogen analogue of 7) as the proton on these
systems can also be abstracted.29 Despite extensive efforts
to develop a high yielding purification procedure, the
highest isolated yield of a pure product for the para-
methoxy derivative was on the order of 5%, despite the
reaction going to 85% as indicated by 1H NMR spectros-
copy. The difficulties in purifying this material can be
attributed to the high insolubility of 13 in organic solvents
and adding to this problem, 13 also has the same solubi-
lity as the impurities. Single crystals were grown from the
small amount of purified material by vapor diffusion of
Et2O into acetonitrile, which were suitable for X-ray
diffraction experiments, confirming the structural assign-
ment of 13.
To examine an analogous ligand framework lacking
these reactive backbone protons, the chemistry was ex-
tended to the BIAN ligand system and the DAB ligand
featuring phenyl groups on the backbone carbon atoms.
Crude powders from the reactions of “S(OTf)2” with
Dipp2BIAN, pMeOPh2BIAN, and Ph2DABPh2 dis-
played enhanced solubilities in organic solvents making
the isolation of larger quantities of pure material possible.
The pMeOPh2BIAN derivative (14) was purified as deep
Synthesis. To explore the chemistry of sulfur with
R-diimine ligands, an in situ “S(OTf)2” synthon was
prepared by reaction of TMS-OTf and SCl2 in a 2:1
stoichiometry in CH2Cl2 at -78 °C yielding a light orange
solution.18,28 To the solution of “S(OTf)2”, 1 equiv of a
DAB or BIAN ligand in CH2Cl2 was added dropwise
generating crimson (Dipp2BIAN, 15; Ph2DABPh2, 18) or
purple (pMeOPh2DAB, 13; pMeOPh2BIAN, 14) solu-
tions, or beige precipitates (tBu2DAB, 16; Cy2DAB, 17)
(Scheme 1). Removal of the volatiles in vacuo for Dipp2-
BIAN, Ph2DABPh2, pMeOPh2DAB, and pMeOPh2-
BIAN gave rise to red or purple powders. Normal
pentane was added to the solutions of the alkyl derivatives
resulting in the further precipitation of material; the
supernatant was then decanted, and the powder dried in
vacuo.
Proton NMR spectroscopy of the redissolved crude
powder from the pMeOPh2DAB reaction in CD3CN
revealed a major product (∼70% purity) with a diagnos-
tic downfield shift of the backbone protons on the DAB
ligand (δ = 9.77 ppm cf. free ligand δ = 8.42 ppm)
reminiscent of 11 and 12a (δ = 10.23-10.21 ppm cf. free
ligand δ = 8.13 ppm).18,23 The major product in the
spectrum consisted of one set of resonances indicative of a
symmetric bonding environment. The backbone protons
(28) In an attempt to characterize this “S(OTf)2” species, the mixture was
probed by 19F NMR spectroscopy. The 19F NMR spectrum at room
temperature gave a singlet shifted to lower field, indicating a more ionic
triflate. However, despite extensive attempts to identify a single, pure product,
nothing definitive could be ascertained. Furthermore, if the chemistry
(reported in this manuscript) is carried out in the absence of OTf-, only
starting material and decomposition products are observed in the 1H NMR
spectrum. Therefore, we assign the S(OTf)2 as an in situ preparation.
(29) Mathew, P.; Neels, A.; Albrecht, M. J. Am. Chem. Soc. 2008, 130,
13534–13535.

4328 Inorganic Chemistry, Vol. 49, No. 9, 2010
Martin and Ragogna
Figure 2. Stacked plot of 1H NMR spectra of 16 bottom in CDCl3 and the selenium congener top in CD3CN.
red crystals in 51% yield by two subsequent recrystalliza-
tions of a 1:1 mixture of CH3CN and Et2O of the bulk
powder at -30 °C as confirmed by 1H NMR spectroscopy.
Crystals suitable for X-ray crystallographic studies were
grown by vapor diffusion of Et2O into acetonitrile con-
firming the structure of 14. The Dipp2BIAN analogue
(15) and Ph2DABPh2 (18) derivative were purified by
recrystallization of the bulk powder from a saturated
solution of CH2Cl2 and pentane stored at -30 °C over-
night, which generated orange X-ray quality crystals of 15
and 18 in good yield (15, 73%; 16, 60%). In all cases 1H
NMR spectroscopy revealed a symmetric bonding environ-
To examine the effect of alkyl substitution on the
nitrogen atom, the reactions of “S(OTf)2” with tBu2DAB
1
and Cy2DAB ligands were carried out. The H NMR
spectrum of the solids revealed pure products (tBu2DAB,
16; Cy2DAB, 17). A break in symmetry of the backbone
protons, contrary to that in 13-15 and 18 (tBu, 16, δ =
10.13, 9.03 ppm; Cy, 17, δ = 10.09, 8.93 ppm), was
observed in both cases, indicative of a different reaction.
Also noteworthy, was a reduction of the integration
values of the tert-butyl or cyclohexyl protons by half
suggesting the loss of an alkyl group contrary to what
occurs in the aryl DAB and BIAN species. An in situ 1H
NMR spectroscopy experiment in CDCl3 of the reaction
of tBu2DAB with “S(OTf)2” clearly indicated the forma-
tion of tert-butyl chloride (δ = 1.62 ppm) as a reaction
byproduct. The 1H NMR spectra were reminiscent of the
related selenium system with tBu2DAB (δ = 9.49, 9.40
ppm) showing a break in symmetry of the ligand framework
(Figure 2).14 The 19F{1H} spectra displayed one signal
diagnostic of ionic triflate (δ = -78.4 ppm). On the basis
of these data the compounds were assigned the same
connectivity as the selenium derivative, as the thiadiazolium
triflate salts 16 and 17. This 1,2,5-chalcadiazolium ring
system is not unusual for the heavy chalcogens (S, Se,
Te).12,14,20,31-33 Unfortunately these compounds were
highly unstable in solution with 17 decomposing within 10
min of being synthesized. Even as a powder at room
temperature, decomposition was observed within 20 min.
Given this instability, crystallization attempts were unsuc-
cessful. However, on the basis of the similarity of the data
with those obtained for selenium and tellurium, the struc-
tures were assigned as 16 and 17.14,20
1
ment regarding the ligand framework. The H NMR
spectra displayed downfield shifts of the BIAN (14 and
15) and phenyl protons (18) on the backbone carbon
atoms in the products consistent with the coordination of
the ligand to a highly charged center. Single resonances in the
19F{1H} NMR spectra were indicative of ionic triflate (14
δ = -78.6 ppm; 15 δ = -78.3 ppm, 18 δ = -78.4 ppm).
These data supported the synthesis of a dicationic SC2N2
heterocycle (14, 15, and 18).
The connectivity of 14, 15, and 18 was analogous to the
R2DAB complexes confirming that the acenaphthene or
the phenyl groups on the backbone does not change the
outcome of the reaction but improves the solubility of the
products allowing for the isolation of the para-methoxy
derivative. The dicationic salts (13-15) all were unstable
in solution at room temperature (periods greater than 2
h), but solid samples could be stored for weeks in an inert
atmosphere at room temperature. Compounds 13-15
and 18 represent dicationic structural mimics of the N-
Heterocyclic silylene, and 14 and 15 are the first sulfur
BIAN complexes reported.30
(31) Bacon, C. E.; Eisler, D. J.; Melen, R. L.; Rawson, J. M. Chem.
Commun. 2008, 4924–4926.
(32) Risto, M.; Reed, R. W.; Robertson, C. M.; Oilunkaniemi, R.;
Laitinen, R. S.; Oakley, R. T. Chem. Commun. 2008, 3278–3280.
(33) Berionni, G.; Pegot, B.; Marrot, J.; Goumont, R. CrystEngComm.
2009, 11, 986.
(30) Denk, M.; Lennon, R.; Hayashi, R.; West, R.; Belyakov, A. V.;
Verne, H. P.; Haaland, A.; Wagner, M.; Metzler, N. J. Am. Chem. Soc. 1994,
116, 2691–2692.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4329
Table 1. X-ray Details of 13-15, 18
13 CH3CN
3
14
15 0.5CH2Cl2
3
18
empirical formula
FW (g/mol)
C20H19F6N3O8S3
639.56
orthorhombic
Pna2(1)
7.2453(9)
16.174(2)
22.279(3)
90
90
90
2610.8(6)
4
1.627
C28H20F6N2 O8S3
722.64
orthorhombic
Pbca
18.324(4)
13.677(3)
23.463(5)
90
90
90
5880(2)
8
1.633
C38.5H40Cl0.70F6N2O6S3
872.36
C28H20F6N2O6S3
690.64
triclinic
P1
10.446(2)
11.972(2)
13.970(3)
113.30(3)
94.40(3)
108.73(3)
1477.4(5)
2
crystal system
space group
monoclinic
P2(1)/c
20.459(4)
12.219(2)
17.293(4)
90
110.96(3)
90
4036.8(14)
4
1.435
0.71073
150(2)
0.0717
0.1982
1.0200
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
Dc (mg m-3
)
1.553
˚
radiation, λ (A)
temp (K)
0.71073
193(2)
0.0597
0.1476
1.055
0.71073
150(2)
0.0601
0.1749
1.017
0.71073
150(2)
0.0481
0.1377
1.089
R1[I > 2σ(I)]a
wR2(F2)a
GOF (S)a
P
P
a R1(F[I > 2σ(I)]) = ||Fo| - |Fc||/ |Fo|; wR2(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 para-
meters varied; w = 1/[2(Fo2) þ (aP)2 þ bP] where P = (Fo þ 2Fc2)/3 and a and b are constants suggested by the refinement program.
2
Table 2. Selected Metrical Parameters for Compounds 11, 12a, 13, 14, 15, and 18a
1118
12a18
13
14
15
18
ccalculated35
bS-N
bN-C
bC-C
1.695(3)
1.305(5)
1.390(8)
2.615(3)
2.309
1.696(6) 1.699(6)
1.293(9) 1.324(9)
1.407(10)
2.313(5)
2.265
1.658(5) 1.682(4)
1.323(7) 1.339(6)
1.379(8)
2.997(6)
2.290
1.697(3) 1.708(3)
1.312(5) 1.316(5)
1.439(5)
1.705(3) 1.704(3)
1.323(4) 1.325(4)
1.412(4)
1.676(2) 1.679(2)
1.325(3) 1.329(3)
1.421(4)
1.705
1.331
1.389
O
O
S
2.654(4)
2.454(2)
2.638(2)
3 3 3
3 3 3
H
N-S-N
88.0(2)
0.005(8)
87.8(3)
0.011(10)
90.3(2)
0.020(9)
90.38(15)
0.019(5)
90.15(12)
0.005(4)
88.80(11)
0.0039(5)
90.3
bSN2C2 deviation
from planarity
Aryl/SC2N2 angle
76.1
80.7, 97.2
˚
26.8, 37.9
76.2, 81.3
46.3, 80.5
86.2, 90.5
a
b
Bond lengths are in angstroms (A) and angles in degrees (deg). All metrical parameters refer to endocyclic E-E bonds. c Calculated optimized
geometries are for the N-Ph substituted derivatives featuring protons on the backbone carbon atoms.
Figure 3. Solid-state structure of 13. Ellipsoids are drawn to 50%
probability, all hydrogen atoms excluding hydrogen atoms interacting
with the anion and solvates are omitted for clarity.
Figure 4. Solid-state structure of 14. Ellipsoids are drawn to 50%
probability and all hydrogen atoms are omitted for clarity.
X-ray Crystallographic Studies. Upon examination of
the crystal structures of 13-15 and 18 the bonding motif
is congruent to those reported previously (11 and 12;
see Tables 1 and 2 for details, Figures 3, 4, 5, and 6).18
The structures display planar 5-membered C2N2S rings
[largest deviation from planarity 0.020(9)A]. The color
of compound 13 in the solid state and in solution
is deep purple, contrary to 11 and 12, which are orange.
This high coloration is likely a result of the oxygen atoms
para to the DAB ligand donating into the DAB π-system
extending the conjugation. The metrical parameters in-
dicate that the interplanar aryl/C2N2S ring angles are
significantly smaller than those of 13. The angles are on
the order of 30° whereas in 11 and 12, the aryl rings are
much closer to being orthogonal to the sulfur heterocycle
(13: 26.8°, 37.9° cf. 11: 80.7°, 97.2°; 12a 76.1°). This
˚

4330 Inorganic Chemistry, Vol. 49, No. 9, 2010
Martin and Ragogna
˚
˚
single bonds [1.658(5)-1.708(3) A cf. 1.74 A] are ob-
served, which can be rationalized by the binding of the
ligand to the electron deficient sulfur(II) center.34 These
endocyclic bond lengths are in close agreement with
computational results [C-C 1.389, C-N 1.331, S-N
1.705 A].35 The bonding of these compounds can be best
˚
described as a N,N0-chelated sulfur center bearing two
lone pairs with a formal charge of þ2.
Sulfur-oxygen contacts between the cations and an-
ions in all species within the sum of the van der Waals
33
radii (3.25 A) are observed. However, there is no dis-
˚
tortion of the corresponding sulfur-oxygen bond in the
triflate ions, contrary to what is observed in covalently
bound substituents. In these covalent species, the corre-
sponding S-O bond length for the coordinated oxygen
atom is significantly elongated with respect to the other
two S-O bonds within the triflate.17 In compound 13, the
closest cation-anion interactions lie between the oxygen
atom and the acidic backbone proton. The contact is well
within the sum of the van der Waals radii (shortest
Figure 5. Solid-state structure of 15. Ellipsoids are drawn to 50%
probability, all hydrogen atoms, isopropyl groups and solvates are
omitted for clarity.
˚
˚
contact 2.290 A cf. 2.60 A).
In spite of the oxygen contacts with the dicationic sulfur
center, these species are distinct dication-anion pairs.
Spectroscopic solution data and the metrical parameters
are consistent of a dicationic species as they are in
agreement with the computational results.
Conclusion
By reacting SCl2 with TMS-OTf, a “S(OTf)2” synthon was
generated, which was effective in the synthesis of new sulfur
nitrogen heterocycles by reactions with diimine ligands. If
aryl DAB or BIAN ligands were used N,N0-chelated sulfur
dications were obtained. These complexes represent the first
sulfur BIAN complexes reported and are structural mimics of
the N-heterocyclic silylene or phosphenium cation. If an alkyl
DAB ligand is used, the loss of an alkyl group on the nitrogen
atom is observed resulting in thiadiazolium complexes. This
differs from the reactivity of the other non-metals which are
prone to undergo charge transfer with the ligand. This is new
reactivity for sulfur and these BIAN compounds show
promise as S2þ delivery reagents which is currently under
exploration in our laboratory.
Figure 6. Solid-state structure of 18. Ellipsoids are drawn to 50%
probability and all hydrogen atoms are omitted for clarity.
phenomenon also could be present as 13 does not present
bulky substituents on the ortho positions of the aryl ring
permitting the ring to orient itself with the C2N2S plane.
The BIAN and Ph2DABPh2 complexes are essentially
isostructural to the DAB derivatives bearing protons on
the backbone carbons 11-13. The bulkier BIAN and
phenyl substituted backbone orient the aryl rings more
out of the plane than the DAB ligands. With respect to the
BIAN complexes, 14, as it bears para-methoxy groups is
highly colored as with 13 and orients the aryl rings more
in plane than the bulkier Dipp derivative, 15 (interplanar
angles: 14 = 46.3, 80.5 cf. 15 = 76.2°, 81.3°). The
endocyclic bonds in all structures within the C2N2S ring
Acknowledgment. The authors are very grateful to the
Natural Sciences and Engineering Research Council of
Canada (NSERC), the Canada Foundation for Innova-
tion, Ontario Ministry of Research and Innovation, and
UWO for generous financial support. We also thank J. L.
Dutton for assistance with X-ray crystallographic studies
and the synthesis of Ph2DABPh2.
˚
[C-N 1.312(5)-1.339(6); C-C 1.379(8)-1.439(5) A]
support the retention of two CdN double bonds and a
C-C single bond consistent with the free ligand. Sulfur-
nitrogen bonds slightly shorter than typical sulfur-nitrogen
Supporting Information Available: Crystallographic data in
CIF format and Figures S1-S3. This material is available free of
charge via the Internet at http://pubs.acs.org.
(35) Tuononen, H. M.; Roesler, R.; Dutton, J. L.; Ragogna, P. J. Inorg.
Chem. 2007, 46, 10693–10706.
(34) Pauling, L. The Nature of the Chemical Bond; Cornell University Press:
Ithaca, 1960.