Synthesis, structural characterization, and reactivity of (thiolato)bismuth complexes as potential water-tolerant Lewis acid catalysts

Article abstract of DOI:10.1139/cjc-2017-0640

We have synthesized bismuth complexes incorporating polydentate mono-and di-thiolate ligands and examined their utility as water-tolerant Lewis acid catalysts. The reaction of Bi(OAc)₃ or Bi(NO₃)₃·5H₂O and the corresponding mono-or di-thiol(ate) yielded the compounds [(SNNS)Bi(OAc)] (4), [(SNNSPr)Bi(OAc)] (5), [(NNS₂)Bi(OAc)] (6), [(ONS₂)Bi(OAc)] (7), [(ONS₂)Bi(NO₃)] (8), and [(NNS)₂Bi][NO₃] (9) [H₂(SNNS) = N,N′-dimethyl-N,N′-bis(2-mercaptoethyl)ethylenediamine; H₂(SNNSPr) = N,N′-diethyl-N,N′-bis(2-mercaptoethyl)propanediamine; H₂(NNS₂) = N,N-diethyl-N′,N′-bis(2-mercaptoethyl)ethanediamine; H₂(ONS₂) = 2-methoxyethyl-bis(2-mercaptoethyl)amine; H(NNS) = N,N-diethyl-N′-(2-mercaptoethyl)ethanediamine]. The solid-state structures of 4-8 show similar distorted pentagonal pyramidal geometries at the bismuth centre with a thiolate sulfur atom in the axial site, whereas 8 shows second structural arrangement with a distorted trigonal bipyramidal geometry at bismuth. The cation of 9 shows two NNS-bonded ligands and a distorted octahedral geometry at bismuth. Two-dimensional NMR studies of 4-8 show geminal ¹H coupling in-SCH₂CH₂N-groups and suggests strong dative Bi-N intramolecular interactions. Bi(NO₃)₃·5H₂O and BiCl₃ show high activity toward the esterification of stearic acid, Bi(NO₃)₃·5H₂O, and 4-7 and 9 show high activity toward the transesterification of methyl stearate in butanol, and 7 shows moderate activity as a catalyst for the transesterification of glyceryl trioctanoate in methanol.

Full text of DOI:10.1139/cjc-2017-0640

Page 1 of 42
Synthesis, Structural Characterization and Reactivity of (Thiolato)bismuth
Complexes as Potential Water-Tolerant Lewis Acid Catalysts
a
b
a
a
Glen G. Briand *, Andreas Decken , Whitney E.M.M. Shannon and Eric E. Trevors
a
Department of Chemistry and Biochemistry, Mount Allison University,
Sackville, New Brunswick, Canada E4L 1G8
b
Department of Chemistry, University of New Brunswick,
Fredericton, New Brunswick, Canada E3B 6E2
*
To whom correspondence should be addressed. Tel: (506) 364ꢀ2346.
Fax: (506) 364ꢀ2313. Eꢀmail: gbriand@mta.ca

Page 2 of 42
Abstract: We have synthesized bismuth complexes incorporating polydentate monoꢀ and
dithiolate ligands and examined their utility as waterꢀtolerant Lewis acid catalysts. The reaction
of Bi(OAc) or Bi(NO ) ·5H O and the corresponding monoꢀ or dithiol(ate) yielded the
3
3 3
2
compounds [(SNNS)Bi(OAc)] (4), [(SNNSPr)Bi(OAc)] (5), [(NNS )Bi(OAc)] (6) and
2
[
(ONS )Bi(OAc)] (7), [(ONS )Bi(NO )] (8) and [(NNS) Bi][NO ] (9) [H (SNNS) = N,N’ꢀ
2 2 3 2 3 2
dimethylꢀN,N‘ꢀbis(2ꢀmercaptoethyl)ethylenediamine; H (SNNSPr) = N,N’ꢀdiethylꢀN,N‘ꢀbis(2ꢀ
2
mercaptoethyl)propanediamine;
H (NNS )
=
N,NꢀdiethylꢀN’,N‘ꢀbis(2ꢀ
2
2
mercaptoethyl)ethanediamine; H (ONS ) = 2ꢀmethoxyethylꢀbis(2ꢀmercaptoethyl)amine; H(NNS)
2
2
=
N,NꢀdiethylꢀN’ꢀ(2ꢀmercaptoethyl)ethanediamine]. The solidꢀstate structures of 4-8 show
similar distorted pentagonal pyramidal geometries at the bismuth centre with a thiolate sulfur
atom in the axial site, while 8 shows second structural arrangement with a distorted trigonal
bipyramidal geometry at bismuth. The cation of 9 shows two NNSꢀbonded ligands and a
distorted octahedral geometry at bismuth. Twoꢀdimensional NMR studies of 4-8 show geminal
1
H coupling in ꢀSCH CH Nꢀ groups and suggests strong dative BiꢀN intramolecular interactions.
2
2
Bi(NO ) ·5H O and BiCl show high activity toward the esterification of stearic acid,
3
3
2
3
Bi(NO ) ·5H O and 4-7 and 9 show high activity toward the transesterification of methyl stearate
3
3
2
in butanol, and 7 shows moderate activity as a catalyst for the transesterification of glyceryl
trioctanoate in methanol.
Keywords: bismuth; thiolates; Lewis acid catalysts, transesterification, biofuels.

Page 3 of 42
Introduction
A major focus in green chemistry over the past two decades has been the development of
synthetic methods that involve ambient atmosphere conditions and environmentally benign
1
solvents, such as water. Central to this is the identification of catalysts that are stable under
2
,3,4,5
these conditions.
Compounds of low toxicity main group metals, such as bismuth salts (e.g.
chloride, bromide, acetate, triflate), have been successfully employed as useful Lewis acid
catalysts for a wide variety of organic reactions, such as oxidation, reduction, CꢀC bond
formation, protection and deprotection of functional groups, CꢀX (X = C, O, S, I) bond
6
,7,8,9
formation, rearrangements, cyclizations and ring opening reactions.
However, these
compounds are susceptible to hydrolysis and react preferentially with water rather than the
1
0,11
substrates.
Despite this, Bi(OH) has been found to facilitate allenylation reactions in
3
water:THF solvent mixtures, while Bi(NO ) is a useful heterogeneous catalyst for the cycloꢀ
3
3
1
2,13
condensation reaction of 2ꢀaminothiophenol and aldehydes in ethanol.
Very little work has
been carried out with waterꢀtolerant organometallic bismuth complexes, which provide possible
tunability of catalytic activity through modification of organic ligands. Rare examples are the
successful use of in situ generated Bi(OTf) complexes of chiral ligand 1 as catalysts for aldol,
3
1
4,15,16
asymmetric hydroxymethylation and epoxide ringꢀopening reactions,
and the cationic
organobismuth complexes 2 and 3 for allylation, epoxide ringꢀopening and Mannich
1
7,18
reactions.
Structural Drawings of 1-3 near here

Page 4 of 42
Waste greases and oils are cheap and renewable sources of triglycerides that can be
1
9
converted into fatty acid methyl esters (FAME), otherwise known as biodiesel. Conventional
transesterification processes usually involve strongly acidic or basic solutions as homogeneous
2
0
catalysts. However, free fatty acid (FFA) impurities react with basic solutions to form soaps,
2
1
which makes separation of glycerol problematic.
Further, the presence of water leads to
2
2
hydrolysis of oils and FAME in the presence of strong acids and bases. Therefore, ideal
homogeneous catalysts for biodiesel production from waste oils must catalyze esterification
reactions of carboxylic acids (fatty acids) with alcohol, as well as transesterification reactions of
2
3
triglycerides. Lewis acidic tin, lead, mercury and zinc complexes of have been studied for their
2
0,24,25
ability to facilitate these reactions, with tin compounds showing the most promising results.
We have previously reported that indium thiolate compounds incorporating (SOOS) ,
2
ꢀ
2
ꢀ
2ꢀ
2ꢀ
(
SNNS) , (SNNSPr) and (NNS2) ligands [H (SOOS) = 2,2ꢀ(ethylenedioxy)diethanethiol,
2
H (SNNS) = N,N’ꢀdimethylꢀN,N‘ꢀbis(2ꢀmercaptoethyl)ethylenediamine; H (SNNSPr) = N,N’ꢀ
2
2
diethylꢀN,N‘ꢀbis(2ꢀmercaptoethyl)propanediamine; H (NNS )
=
N,NꢀdiethylꢀN’,N‘ꢀbis(2ꢀ
2
2
mercaptoethyl)ethanediamine] are moderately efficient Lewis acid catalysts toward
2
6
esterification/transesterification reactions in the presence of water. Polydentate thiolate ligands
afford metalꢀsulfur bonds that are stable to hydrolysis for soft main group metals, while
secondary donor atoms affect the coordination environment, Lewis acidity and reactivity of the
2
7,28
metal centre.
We now report the synthesis and characterization of a series of
(thiolato)bismuth compounds (4-9), and their ability to perform as waterꢀtolerant Lewis acid
catalysts for esterification and transesterification reactions of fatty acids and fatty acid esters,
respectively.

Page 5 of 42
Structural Drawings of proligands and 4-9 near here
Experimental
General
1
13
1
Solution H and C{ H} NMR spectra were recorded at 23°C on either a JEOL 400 SS
spectrometer (400 and 100 MHz, respectively), or a Varian Mercury 200 MHz + spectrometer
(200 and 50 MHz, respectively), and chemical shifts are calibrated to the residual solvent signal.
ATR FTꢀIR spectra were recorded on a Thermo Nicolet iS5 FTꢀIR spectrometer in the range of
ꢀ1
4
000ꢀ400 cm . FTꢀRaman spectra were recorded on a Thermo Nicolet NXR 9600 Series FTꢀ
ꢀ1
Raman spectrometer in the range 3900ꢀ70 cm . Melting points were recorded on an
Electrothermal MELꢀTEMP melting point apparatus and are uncorrected. Elemental analyses
were performed by Laboratoire d'analyse élémentaire, Université de Montréal, Montreal, Canada.
N,N’ꢀdimethylethylenediamine (85%), N,N’ꢀdiethylꢀ1,3ꢀpropanediamine (97%), N,Nꢀ
diethylethylenediamine (99%), 2ꢀmethoxyethylamine (95%), ethylene sulfide (98%), stearic acid
(98.5%), methyl stearate (99%) and glyceryl trioctanoate (≥99%) were used as received from
SigmaꢀAldrich. Potassium hydroxide pellets (97.0%) were used as received from Caledon.
Bismuth(III) acetate (≥99.99%) was used as received from Alfa Aesar. Bismuth(III) nitrate
2
9
pentahydrate (98.0%) was use as received from Fisher Scientific. H (SNNS), H (SNNSPr),
2
2
3
0
31
H (NNS ), H(NNS), and H (ONS ) were prepared according to literature methods.
2
2
2
2
Synthesis

Page 6 of 42
Synthesis of [(SNNS)Bi(OAc)] (4)
Under a stream of dinitrogen, Bi(OAc) (0.463 g, 1.12 mmol) was added to a solution of
3
H (SNNS) (0.250 g, 1.12 mmol) in 95% ethanol (10 mL) to yield a yellow solution immediately.
2
After stirring for 3 h, the colourless precipitate was filtered. The yellow filtrate was then
concentrated to 1 mL and allowed to sit at 4 °C for 5 d to afford crystals of 4 (0.313 g, 0.660
mmol 55%). Anal. Calc. for C H BiN O S : C, 25.32; H, 4.46; N, 5.91; S, 13.52. Found: C,
1
0
21
2
2 2
ꢀ
1
2
8
1
2
4
1
5.31; H, 4.44; N, 5.94; S, 14.07. M.p. 227ꢀ229°C (d). FTꢀIR(cm ): 619 m, 658 vs, 740 s, 756 s,
79 m, 917 m, 951 s, 1005 m, 1020 m, 1038 m, 1050 m, 1087 m, 1130 m, 1168 m, 1198 m,
215 m, 1259 m, 1280 s, 1308 m, 1334 s, 1378 vs, 1397s, 1421 m, 1446 m, 1557 vs, 2832 m,
ꢀ1
862 m, 2951 w. FTꢀRaman (cm ): 115 m, 142 m, 159 m, 181 m, 277 vs, 295 vs, 316 m, 343 m,
35 w, 472 w, 669 w, 760 vw, 923 w, 1005 vw, 1131 w, 1276 vw, 1300 vw, 1366 vw, 1426 w,
1
561 vw, 2831 w, 2863 w, 2908 w, 2943 w. H NMR (CDCl , ppm): 1.97 (s, O CCH , 3H), 2.44
3
2
3
(
s, NCH , 6H), 2.77ꢀ2.84 (m, N(CH ) NCH , 4H), 2.88ꢀ2.95 (m, NCH CH S, 2H), 3.43ꢀ3.50 (m,
3 2 2 3 a 2
1
3
1
NCH CH S, 2H), 3.54ꢀ3.57 (m, NCH CH S, 2H), 4.63ꢀ4.68 (m, NCH CH S, 2H). C{ H}
2
a
b
2
2
b
NMR (CDCl , ppm): 23.8 (O CCH ), 26.7 (SCH ), 41.35 (NCH ), 56.4 (N(CH ) N), 64.7
3
2
3
2
3
2 2
(
NCH CH S), 180.9 (O CCH ).
2
2
2
3
Synthesis of [(SNNSPr)Bi(OAc)] (5)
Under a stream of dinitrogen, Bi(OAc) (0.385 g, 0.998 mmol) was added to a solution
3
of H (SNNSPr) (0.250 g, 0.998 mmol) in 95% ethanol (10 mL) to yield a yellow solution
2
immediately. After stirring for 3 hours, the reaction was filtered. The yellow filtrate was then
concentrated to 1.5 mL, layered with diethyl ether (4.5 mL) and allowed to sit at 4 °C for 10 d to

Page 7 of 42
afford crystals of 5 (0.258 g, 0.500 mmol, 50%). Anal. Calc. for C H BiN O S : C, 30.23; H,
1
3
27
2
2 2
5
.27; N, 5.42; S, 12.42. Found: C, 30.13; H, 5.25; N, 5.46; S, 12.90. M.p. 173ꢀ175°C (d). FTꢀ
ꢀ1
IR(cm ): 559, w, 615 m, 654 vs, 705 m,740 s, 786 w, 838 w, 872 w, 921 m, 972 s, 993 m, 1019
m, 1045 m, 1059 m, 1091 m, 1110 m, 1123 m, 1154 m, 1175 w, 1199 m, 1213 m, 1230 m, 1254
ꢀ
w, 1281 m, 1313 m, 1328 s, 1376 vs, 1443 m, 1473 m, 1563 s, 2914 w, 2980 s. FTꢀRaman (cm
1
): 118 m, 139 m, 157 m, 175 m, 203 m, 247 m, 282 s, 305 vs, 369 w, 470 w, 534 w, 506 w, 654
w, 891 vw, 922 w, 976 vw, 1022 vw, 1061 w, 1093 w, 1112 w, 1232 vw, 1290 vw, 1333 vw,
1
1
0
379 vw, 1448 w, 1471 w, 1567 vw, 2848 w, 2916 m, 2935 m, 2968 w. H NMR (CDCl , ppm):
3
.99 (t, NCH CH 6H), 1.77 (br, NCH CH CH N, 2H), 1.98 (s, O CCH , 3H), 2.78ꢀ3.37 (m,
2
3,
2
2
2
2
3
1
3
1
NCH , 12H), 3.67 (br, SCH , 2H), 4.40 (br, SCH , 2H). C { H} NMR (CDCl , ppm): 7.61
2
a
b
3
(NCH CH ), 21.9 (NCH CH CH N), 23.5 (O CCH ), 26.2 (SCH ), 44.8 (NCH CH ), 52.3
2 3 2 2 2 2 3 2 2 3
(
NCH CH2CH N), 59.5 (NCH CH S), 179.9 (O CCH ).
2
2
2
2
2
3
Synthesis of [(NNS )Bi(OAc)] (6)
2
Under a stream of dinitrogen, Bi(OAc) (0.408 g, 1.06 mmol) was added to a solution of
3
H (NNS ) (0.250 g, 1.06 mmol) in 95% ethanol (10 mL) to yield a yellow solution immediately.
2
2
After stirring for 3 hours, the reaction was filtered. The yellow filtrate was then concentrated to 2
mL, layered with diethyl ether (4.5 mL) and allowed to sit at 4 °C for 3 d to afford crystals 6
(
0.269 g, 0.535 mmol, 51%). Anal. Calc. for C H BiN O S : C, 28.70; H, 5.02; N, 5.58; S,
12 25 2 2 2
ꢀ1
1
2.80. Found: C, 28.75; H, 5.05; N, 5.52; S, 12.93. M.p. 184ꢀ186°C. FTꢀIR(cm ): 618 m, 658
vs, 720 m, 736 m, 778 m, 841 m, 883 m, 925 m, 941 m, 992 m, 1013 m, 1054 m, 1089 m, 1139
m, 1163 m, 1193 m, 1209 w, 1246 m, 1279 m, 1315 s, 1332 s, 1374 vs, 1393 s, 1436 m, 1457 m,
ꢀ1
1
558 m, 2905 m, 2980 m. FTꢀRaman (cm ): 137 s, 184 m, 259 s, 291 vs, 328 s, 419 vw, 464 vw,

Page 8 of 42
4
1
95 w, 665 w, 735 vw, 897 vw, 925 w, 992 vw, 1054 vw, 1106 vw, 1136 vw, 1244 vw, 1278 vw,
1
318 vw, 1374 vw, 1459 w, 1564 vw, 2857 m, 2908 m, 2927 m. H NMR (CDCl , ppm): 1.06
3
(
t,NCH CH , 6H), 1.96 (s, O CCH , 3H), 2.70ꢀ2.83 (m, NCH CH N(CH CH ) , 8H), 2.94ꢀ3.00
2 3 2 3 2 2 2 3 2
(
m, NCH CH S, 2H), 3.36ꢀ3.41 (m, NCH CH S, 2H), 3.91ꢀ3.98 (m, NCH CH S, 2H) , 4.46ꢀ4.52
a 2 b 2 2 a
1
3
1
(
m, NCH CH S, 2H). C{ H} NMR (CDCl , ppm): 9.7 (NCH CH ), 23.5 (O CCH ), 28.0
2 b 3 2 3 2 3
(
SCH ), 45.5 (NCH CH ), 49.5 (NCH CH NEt ), 57.1 (NCH CH NEt ), 65.9 (NCH CH S),
2
2
3
2
2
2
2
2
2
2
2
1
80.38 (O CCH ).
2
3
Synthesis of [(ONS )Bi(OAc)] (7)
2
Under a stream of dinitrogen, Bi(OAc) (0.494 g, 1.28 mmol) was added to a clear
3
colorless solution of H (ONS ) (0.250 g, 1.28 mmol) in 95% ethanol (10 mL) to yield a yellow
2
2
solution immediately. After stirring for 3 hours, the reaction was filtered. The yellow filtrate was
allowed to sit at 4 °C for 2 d to afford crystals of 7 (0.247 g, 0.535 mmol, 42%). Anal. Calc. for
C H BiNO S : C, 23.43; H, 3.93; N, 3.04; S, 13.90. Found: C, 23.33; H, 3.90; N, 3.07; S, 13.80.
9
18
3 2
ꢀ1
M.p. 183ꢀ185°C. FTꢀIR(cm ): 619 m, 662 vs, 721 m, 834 s, 891 m, 923 m, 964 m, 983 m, 1006
s, 1018 s, 1082 s, 1103 s, 1126 m, 1181 w, 1194 w, 1238 w, 1261 m, 1333 s, 1375 s, 1398 m,
ꢀ1
1
445 m, 1557 m, 2839 m, 2917 m. FTꢀRaman (cm ): 131 m, 169 m, 210 w, 271 m, 297 s, 340
m, 377 w, 426 vw, 471 vw, 486 vw, 665 w, 722 vw, 836 vw, 887 vw, 927 w, 1019 vw, 1079 vw,
1
1
129 vw, 1201 vw, 1244 vw, 1286 vw, 1379 vw, 1451 w, 1564 vw, 2848 w, 2917 m. H NMR
(
CDCl , ppm):1.96 (s, O CCH , 3H), 2.91 (t, OCH , 2H), 3.00ꢀ3.07 (m, NCH CH S, 2H), 3.23ꢀ
3 2 3 2 a 2
3
2
.31 (m, NCH CH S, 2H), 3.44 (s, OCH , 3H), 3.55 (t, NCH CH O, 2H), 3.99ꢀ4.05 (m, SCH ,
b 2 3 2 2 a
1
3
1
H), 4.30ꢀ4.36 (m, SCH , 2H). C{ H} NMR (CDCl , ppm): 23.3 (O CCH ), 27.5 (SCH ), 58.7
b
3
2
3
2
(
OCH ), 59.0 (OCH ), 64.9 (NCH CH S), 67.2 (NCH CH O), 180.0 (O CCH ).
3 2 2 2 2 2 2 3

Page 9 of 42
Synthesis of [(ONS )Bi(NO )] (8)
2
3
Under a stream of dinitrogen, H (ONS ) (0.250 g, 1.28 mmol) was added to a solution of
2
2
potassium hydroxide (0.144 g, 2.56 mmol) in acetone (10 mL), followed by addition of
Bi(NO ) ·5H O (0.621 g, 1.28 mmol). After stirring for 3 h, the reaction mixture was filtered to
3
3
2
afford a pale yellow solution. The filtrate was concentrated to 1 mL and allowed to sit at 23 °C
for 2 days to afford crystals of 8 (0.087g, 0.19 mmol 15%). Anal. Calc. for C H BiN O S : C,
7
15
2
4 2
1
8.11; H, 3.26; N, 6.03; S, 13.81. Found: C, 18.21; H, 2.99; N, 6.13; S, 13.62. M.p. 138°C. FTꢀ
ꢀ1
IR (cm ): 668 w, 718 m, 808 m, 838 w, 885 vw, 915 vw, 942 vw, 967 vw, 1014 m, 1066 w,
ꢀ
1
1
3
3
105 m, 1266 s, 1417 m, 2359 vw, 2927 vw. FTꢀRaman (cm ): 131 m, 174 m, 298 s, 348 m,
1
93 vw, 505 vw, 669 w, 1028 w, 1446 w, 2928 m. H NMR (dmsoꢀd , ppm): 3.13 (t, OCH , 2H),
6
2
.19ꢀ3.27 (m, NCH CH S, 2H), 3.36 (s, OCH , 3H), 3.51 (t, NCH CH O, 2H), 3.90ꢀ3.98 (m,
a
2
3
2
2
1
3
1
NCH CH S, 4H), 4.69ꢀ4.71 (m, SCH , 2H). C{ H} NMR (dmsoꢀd , ppm): 29.2 (SCH ), 58.6
b
a
b
6
2
(
OCH ), 58.8 (OCH ), 66.3 (NCH CH S), 66.9 (NCH CH O).
3 2 2 2 2 2
Synthesis of [(NNS) Bi][NO ] (9)
2
3
Under a stream of dinitrogen, H(NNS) (0.250 g, 1.42 mmol) was added to a solution of
potassium hydroxide (0.080 g, 1.4 mmol) in acetone (10 mL), followed by addition of
Bi(NO ) ·5H O (0.344 g, 0.709 mmol). After stirring for 3 h, the reaction mixture was filtered to
3
3
2
afford a pale yellow solution. The filtrate was then allowed to sit at ꢀ15 °C for 2 days to afford
crystals of 9 (0.239 g, 0.367 mmol, 52%). Anal. Calc. for C H Bi N O S : C, 32.30; H, 6.35;
3
5
82
2
10
7 4
ꢀ1
N, 10.76; S, 9.86. Found: C, 31.49; H, 6.30; N, 10.76; S, 10.49. M.p. 106°C. FTꢀIR (cm ): 571
m, 663 m, 707 w, 733 s, 787 vw, 812 m, 910 w, 957 w, 985 vw, 1006 m, 1030 s, 1050 vw, 1062
vw, 1099 w, 1148 m, 1191 m, 1220 m, 1264 m, 1329 vs, 1361 s, 1442 m, 1466 w, 1495 w, 2816

Page 10 of 42
ꢀ1
m, 2966 m, 3162 m. FTꢀRaman (cm ): 130 s, 188 m, 263 s, 333 vs, 666 vw, 734 vw, 908 vw,
1
1
043 m, 1125 vw, 1220 vw, 1284 vw, 1374 vw, 1446 w, 2858 w, 2922 m. H NMR (CDCl ,
3
1
3
1
ppm): 0.95ꢀ1.00 (m, NCH CH , 12H), 1.69ꢀ5.79 (m, 26H). C{ H} NMR (CDCl , ppm): 10.0
2
3
3
(NCH CH ), 27.9 (SCH 6), 45.7 (NCH CH ), 48.6 (NCH CH NEt ), 51.8 (NCH CH NEt ), 58.5
2 3 2 2 3 2 2 2 2 2 2
(
NCH CH S).
2
2
Catalysis experiments
Esterification of stearic acid
To a solution of stearic acid (0.100 g, 0.352 mmol) in MeOH (1 mL, 0.792 g, 24.7 mmol)
was added 10 mol% of the bismuth precatalyst (0.035 mmol). The resulting solution was heated
to reflux for 4 h, after which the excess methanol was removed under reduced pressure. The
residue was extracted with diethyl ether and the solvent was removed under vacuum to yield the
1
crude product. Samples were analyzed by H NMR spectroscopy in CDCl to determine
3
conversion of stearic acid to methyl stearate.
Transesterification of methyl stearate
Methyl stearate (0.100 g, 0.335 mmol) was dissolved in 1ꢀbutanol (1 mL, 0.810 g, 10.9
mmol) with subsequent addition of 10 mol% of the bismuth precatalyst (0.035 mmol). The
resulting solution was heated at reflux for 19 h, after which the solvent was removed under
vacuum. The residue was extracted with diethyl ether (5 mL) and the solution washed with
distilled water (5 mL). The organic layer was then dried over anhydrous sodium sulfate and the

Page 11 of 42
1
solvent removed under vacuum to yield the crude product. Samples were analyzed by H NMR
spectroscopy in CDCl to determine conversion of methyl stearate to 1ꢀbutyl stearate.
3
Transesterification of glyceryl trioctanoate
Glyceryl trioctanoate (0.150 g, 0.319 mmol) was dissolved in MeOH (1 mL, 0.792 g, 24.7
mmol) with subsequent addition of 10 mol% of the bismuth precatalyst (0.032 mmol). The
resulting solution was refluxed for 19 h, after which excess alcohol was removed under vacuum.
The residue was extracted with diethyl ether (5 mL), washed with distilled water (5 mL), dried
over anhydrous sodium sulfate, and the solvent removed under vacuum to yield the crude
1
product. Samples were analyzed by H NMR spectroscopy in CDCl to determine conversion of
3
glyceryl trioctanoate to methyl stearate.
X-ray crystallography
Crystals of 4-9 were isolated from the reaction mixtures as indicated above. Single
crystals were coated with ParatoneꢀN oil, mounted using a polyimide MicroMount and frozen in
the cold nitrogen stream of the goniometer. A hemisphere of data was collected on a Bruker
AXS P4/SMART 1000 diffractometer using ω and θ scans with a scan width of 0.3° and 10 s
3
2
exposure times. The detector distance was 5 cm. The data were reduced (SAINT) and
3
3
corrected for absorption (SADABS). The structures were solved by direct methods and refined
2
34
by fullꢀmatrix least squares on F (SHELXTL). All nonꢀhydrogen atoms were refined using
anisotropic displacement parameters. Hydrogen atoms were included in calculated positions and
refined using a riding model. Crystallographic data are given in Table 1.

Page 12 of 42
For 7, the thiol ligand was disordered and the site occupancies determined using an
isotropic model as 0.6 [S(1), N(1), C(1)ꢀC(2)] and 0.4 [S(1a), N(1a), C(1a)ꢀC(2a)] and fixed in
subsequent refinement cycles. Bond distances within the disordered moiety were restrained to
similar values and thermal parameters of atoms in close proximity were constrained to equal
values. Data were collected at room temperature. All attempts at collecting data at low
temperatures failed and led to poor data quality. For 9, one of C units of one of the ligands was
2
disordered over two positions and the site occupancy determined using an isotropic model as
0
.56 (C(9)ꢀC(10)) and 0.44 (C(9A)ꢀC(10A)) and fixed in subsequent refinement cycles. Atoms
in close proximity had thermal parameters constraint to identical values. The acetone molecule
was disordered and could not be modelled properly. The solvent molecule was modelled using
3
5
disordered electron densities (SQUEEZE).
Computational methods
DFT calculations were performed using Gaussian 09 at the B3LYP 6ꢀ31G* level of
theory for all atoms except Bi, for which Stuttgart electron core pseudoꢀpotentials (sdd) were
3
6
employed. All structures were geometry optimized and structural parameters for input files
were derived from crystal structure data where possible. Frequency calculations were performed
on all structures and gave no imaginary frequencies. Structural parameters are given in the
Supplementary material.
Results and discussion
Synthesis

Page 13 of 42
Compounds 4-7 were prepared via the metathesis reaction of bismuth acetate and one
equivalent of the corresponding dithiol in 95% ethanol. Compound 8 was prepared via the
deprotonation of H (ONS ) with two equivalents of KOH in acetone, followed by addition of one
2
2
equivalent of Bi(NO ) ·5H O. Compound 9 was prepared in a similar manner, but required two
3
3
2
equivalents of the monothiol H(NNS). Reactions were stirred at 23°C for 3 h, filtered, and the
product crystallized from the reaction filtrate in moderate yield (42ꢀ55 %), with the exception of
8
which was isolated in low yield (15%). The latter may be the result of an undesirable KOH
catalyzed aldol condensation reaction of the acetone solvent.
X-ray crystal structures
Crystals suitable for Xꢀray crystallographic analysis were isolated from the corresponding
reaction mixtures at 4°C (4-7), 23°C (8) or ꢀ15°C (9). Selected bond distances and angles are
given in Tables 2 and 3.
The structure of [(SNNS)Bi(OAc)] (4) (Figure 1) shows bismuth bonded to a tetradentate
2
(
SNNS) ligand and a chelating acetateꢀκ O,O’ group. The geometry at the metal centre is
distorted pentagonal pyramidal, with a thiolate sulfur atom (S2) in the axial position and a
thiolate sulfur atom, two amine nitrogen atoms and two acetate oxygen atoms in equatorial
positions. The open coordination site is occupied by a stereochemically active valence lone pair
of electrons (vide infra). The BiꢀS bond distance [Bi1ꢀS1 = 2.577(2) Å] is much larger than the
eq
BiꢀS bond distance [Bi1ꢀS2 = 2.529(2) Å], as a result of the trans influence of the amine
ax
nitrogen atom N2 [S1ꢀBi1ꢀN2 = 140.9(1)°]. Also, the Bi1ꢀN2 bond distance [2.786(5) Å] is
much larger than Bi1ꢀN1 [2.564(6) Å], as a result of stronger trans influence of the thiolate

Page 14 of 42
versus the acetate group [N1ꢀBi1ꢀC9 = 173.3(2)°]. Finally, the acetate group is bonded
asymmetrically to the bismuth centre [Bi1ꢀO1 = 2.874(6), Bi1ꢀO2 = 2.375(4) Å].
The structure of [(SNNSPr)Bi(OAc)] (5) (Figure 2) is similar to that of 4. The most
significant structural differences in 5 are a larger N1ꢀBi1ꢀN2 ligand bite angle [4: 67.8(2)°, 5:
7
7.9(1)°], due to the propylene (NCH CH CH N) versus ethylene (NCH CH N) linkage, and a
2 2 2 2 2
larger S1ꢀBi1ꢀS2 angle [4: 88.51(6)°, 5: 99.02(5)°]. Further, corresponding BiꢀN bond distances
Bi1ꢀN1 = 2.607(4) and Bi1ꢀN2 = 2.901(5) Å] are larger than in 4, as is the Bi1ꢀO1 bond
[
distance [4: 2.874(6) Å, 5: 2.921(6) Å]. However, no resultant shortening of the BiꢀS bonds is
observed in 5.
The structure of [(NNS )Bi(OAc)] (6) (Figure 3) shows bismuth bonded to a tetradentate
2
2
(
NNS ) ligand and a chelating acetateꢀκ O,O’ group. The geometry at the metal centre is
2
distorted pentagonal pyramidal, with a thiolate sulfur atom (S2) in the axial position and a
thiolate sulfur atom, two amine nitrogen atoms and two acetate atoms in equatorial positions.
The open coordination site is occupied by a stereochemically active valence lone pair of
electrons. Overall, the bonding environment at bismuth resembles that of compounds 4 and 5.
Despite the change in connectivity of the ligand donor atoms in (NNS ) versus (SNNS), the
2
structural parameters for 6 are very similar to that of 4. However, the S2ꢀBi1ꢀN1 angle
[
75.5(1)°] in 6 is more acute as a result of tethering of S2 and N1 by a –CH CH – linkage as
2 2
compared to 4 and 5, while the absence of a –CH CH – linkage between S2 and N2 results in a
2
2
more obtuse S2ꢀBi1ꢀN2 [85.75(9)°] angle. This affects a larger S1ꢀBi1ꢀS2 angle [96.02(5)°],
larger equatorial Bi1ꢀS1 [2.613(2) Å] and Bi1ꢀN2 [2.919(5) Å] bond distances, and a
corresponding decrease in the Bi1ꢀO1 bond distance [4: 2.874(6) Å, 5: 2.725(5) Å].

Page 15 of 42
The structure of [(ONS )Bi(OAc)] (7) (Figure 4) is similar to that of 6, except that the
2
ligand NEt group is replaced with an –OMe group. The most significant structural differences
2
in 7 are shorter BiꢀS, BiꢀN and BiꢀOacetate bond distances. This is presumably a result of the
weaker donor ability of the ether oxygen in (ONS ) versus the amine nitrogen in (NNS ).
2
2
The structure of [(ONS )Bi(NO )] (8) (Figure 5) contains four unique molecules in the
2
3
asymmetric unit, and two different bonding environments at bismuth (see Table S1). The metal
bonding environment at Bi1/3 is similar to that of 7 with the most significant structural
differences being the longer BiꢀOnitrate bond distances in 8 [Bi1ꢀO1 = 2.778(12) and Bi1ꢀO2 =
2
.498(9) Å] versus the BiꢀOacetate bond distances in 7 [Bi1ꢀO1 = 2.709(6) and Bi1ꢀO2 = 2.332(4)
Å]. However, this is not accompanied by a decrease in BiꢀS/N/Oligand bond distances in 8.
Unlike Bi1/3, the metal bonding environments at Bi2/4 show similar BiꢀS bond distances [Bi1ꢀ
S1 = 2.573(3) and Bi1ꢀS2 = 2.528(3) Å; Bi2ꢀS3 = 2.547(3) and Bi2ꢀS4 = 2.547(3) Å]. There is
also a shorter BiꢀOMe bond at Bi2/4 [Bi1ꢀO3 = 2.826(10) Å; Bi2ꢀO8 = 2.770(8) Å] and a longer
secondary BiꢀONO3 interaction [Bi1ꢀO2 = 2.778(12) Å; Bi2ꢀO6 = 3.031(10) Å]. This is
accompanied by a significant increase in the SapicalꢀBiꢀOMe bond angle [S2ꢀBi1ꢀO3 = 87.7(2)°;
S4ꢀBi2ꢀO8 = 134.4(2)°]. The geometry at Bi2/4 may be most accurately described as distorted
trigonal bipyramidal if the nitrate group is considered to occupy a single coordination site [N3ꢀ
Bi2ꢀN4 = 160.9(4)°; S3ꢀBi2ꢀS4 = 101.04(10)°, S3ꢀBi2ꢀO8 = 100.5(3)° and S4ꢀBi2ꢀO8 =
1
34.4(2)°].
The solidꢀstate structures of 4-7 and 8 (Bi1/3) are similar to observed to that of
3
7
tris(aminoethanethiolato)bismuth [(H NCH CH S) Bi], reported previously.
All feature a
2
2
2
3
distorted pentagonal pyramidal structure and an apical thiolate sulfur atom. These are also

Page 16 of 42
reminiscent of distorted square pyramidal structure of [(Me NCH CH S) BiCl], which possesses
2
2
2
2
3
7
a monodentate chloride versus bidentate acetate group.
The structure of 9 (Figure 6) shows a monomeric unit in which two of the NNS ligands
chelate the bismuth center in an NNS manner. The nitrate group is not coordinated to the bismuth
centre [Bi1ꢀO1 = 3.616(5) Å; sum of ionic radii = 2.43 Å; sum of van der Waals radii = 3.80
3
8
Å], and the bismuth complex is therefore cationic. The bismuth centre is sixꢀcoordinate and has
a distorted octahedral geometry [S1ꢀBi1ꢀN2 = 143.77(8)°; S2ꢀBi1ꢀN4 = 141.38(9)°; N1ꢀBi1ꢀN3
=
152.26(12)°]. This deviation from ideal bond angles is due to the constraints imposed by the
ligand backbone and a stereochemically active lone pair. The Bi1ꢀN2 and Bi1ꢀN4 bond distances
2.972(4) and 3.005(4) Å, respectively] are significantly longer than the Bi1ꢀN1 and Bi1ꢀN3
[
bond distances [2.488(4) and 2.527(5) Å, respectively]. Further, the sulfur atoms are in cis
positions [S1ꢀBi1ꢀS2 = 93.71(5)°] and the two central NꢀH ligand nitrogen atoms [N2 and N4]
are in orthogonal trans positions. Therefore, the structure appears to have a core ψꢀtrigonal
bipyramidal structure with the two thiolate sulfur atoms and a stereochemically active lone pair
in the equatorial sites, and the two NꢀH nitrogen atoms occupying axial sites. This arrangement
mimics the structures of the bis(aminoethanethiolato)bismuth nitrate compounds
3
7,39
[
(H NCH CH S) Bi(NO )] and [(H NCH CH S) Bi(NO )(H O)].
The terminal –NEt amine
2
2
2
2
2
3
2
2
2
2
3
2
groups are weakly coordinated to the open face of the structure containing the lone pair of
electrons (vide infra).
DFT computational studies
DFT calculations were performed to rationalize the observed solidꢀstate structures and

Page 17 of 42
probe bonding at bismuth. Structural parameters for geometry optimized [(SNNS)Bi(OAc)] are
similar to those of 4 in the solidꢀstate (Table S2), though BiꢀOacetate bond distances are short [Bi1ꢀ
O1 = 2.31 vs. 2.375(4) Å; Bi1ꢀO2 = 2.66 vs. 2.874(6) Å]. Analysis of molecular orbitals shows
that HOMO, HOMOꢀ1 and HOMOꢀ2 (Figure 7) are primarily thiolate sulfur lone pairs with
electron density in the position trans to the axial Bi1ꢀS2 bond, i.e. in the assumed position of the
stereochemically active lone pair of electrons on bismuth. The geometry optimized structure of
[
(NH ) (MeS) Bi(OAc)], which features untethered amine and thiolate groups, shows a distorted
3 2 2
pentagonal pyramidal bonding environment at bismuth (Table S3) similar to that observed for the
solidꢀstate structures of 4-6. This suggests that this is the most favourable structural arrangement
and tethering of the amine nitrogen atoms, and thiolate sulfur atoms via ꢀCH ꢀ (n = 2, 3) linkages
n
causes minimal distortion of the bismuth bonding environment. Structural parameters for
geometry optimized [(ONS )Bi(NO )] are similar to those of the two unique bonding
2
3
environments of 8 in the solidꢀstate (Table S4), though BiꢀOnitrate bond distances are short [Bi1ꢀ
O1 = 2.32 vs. 2.375(4) Å; Bi1ꢀO2 = 2.62 vs. 2.874(6) Å; Bi2ꢀO5 = 2.29 vs. 2.514(8) Å; Bi2ꢀO6
ꢀ1
=
2.74 vs. 3.031(10) Å]. The structure of the Bi2 molecule was calculated to be 8 kJ mol lower
in energy than that of the Bi1 molecule. The observation of both structural arrangements in the
solidꢀstate is presumably a result of packing forces. Finally, geometry optimization of
+
[
(H NCH CH S) Bi] shows a similar ψꢀtrigonal bipyramidal N S bonding environment and
2
2
2
2
2 2
structural parameters at bismuth as the core structure of 9 (Table S5), suggesting very weak
bonding interactions from the ligand –NEt groups.
2
Solution NMR Characterization

Page 18 of 42
1
H NMR spectra of 4-8 show that the protons of the two ꢀSCH CH Nꢀ units within each
2
2
of the ligands (SNNS), (SNNSPr), (NNS ) and (ONS ) are chemically equivalent, suggesting that
2
2
the observed chiral solidꢀstate pentagonal pyramidal structures are fluxional and not retained in
1
3
1
solution. This is further supported by the C{ H} NMR spectra, which show a single set of
SCH CH N resonances for each compound. Despite this, geminal coupling of the methylene
2
2
1
protons within each SCH CH N unit is observed (see Figures S1ꢀS5). In the H NMR spectrum
2
2
of compound 7, for example, the magnetically inequivalent SCH protons display an overlapping
2
doublet of triplets (H ) and doublet of doublets (H ) splitting pattern (Figure 8a). The coupling
a
b
pattern expected for H from the Newman projection of 7 (Figure 8b) suggests that the coupling
a
of H to H , followed by equal coupling to H /H will give rise to a doublet of triplets pattern.
a
b
c
d
This will occur if the dihedral angle of H to H and H equals approximately 60°, which is the
a
c
d
case for the calculated positions of the corresponding hydrogen atoms in the Xꢀray crystal
structure of 7. Alternatively, the coupling pattern of H arises from the geminal coupling of H to
b
b
H , followed by unequal coupling to H and H . The latter results from the differing dihedral
a
c
d
angles of H to H (180°) and H (60°).
b
c
d
1
These assignments are confirmed by the COSY H NMR spectrum of compound 7
(Figure 9a), which shows coupling among the multiplets at 3.00ꢀ3.07, 3.23ꢀ3.31, 3.99ꢀ4.05 and
4
4
3
.30ꢀ4.36 ppm. The corresponding HSQC spectrum (Figure 9b) confirms that the peaks at 3.99ꢀ
.05 and 4.30ꢀ4.36 ppm are bonded to the same carbon atom (27.5 ppm, SCH ), and those at
2
.00ꢀ3.07, 3.23ꢀ3.31 ppm are bonded to the same carbon atom (64.9 ppm , NCH ). Similar
2
1
coupling patterns are observed for the ꢀSCH CH Nꢀ groups in the H NMR spectra of 4-6 and 8,
2
2
3
1
1
though peak broadening in 5 obscures the J( Hꢀ H) coupling. This is presumably a result of
increased ligand (BiꢀN) lability afforded by the ꢀNCH CH CH Nꢀ backbone. Alternatively, no
2
2
2

Page 19 of 42
geminal coupling is observed for the ꢀOCH CH Nꢀ protons in 7 or 8, as demonstrated by the
2
2
triplets at 2.91 (OCH ) and 3.55 ppm (CH N) in 7, or the ꢀNCH CH Nꢀ/ꢀNCH CH CH Nꢀ
2
2
2
2
2
2
2
protons in 4-6.
1
The H NMR spectrum of 9 in CDCl at 23°C shows very broad peaks, which is
3
presumably a result of weak BiꢀNEt2 bonding interactions, as observed in the Xꢀray crystal
structure, and fluxional behavior in solution. Peaks are better resolved at ꢀ50°C and complex
second order patterns suggest the presence of geminal coupling. However, decreased solubility
of the compound at lower temperatures precludes the collection of HSQC data and peak
assignments are not possible.
Esterification and transesterification reactions
The esterification of stearic acid to methyl stearate was carried out in refluxing methanol
for 4 hours using bismuth salts and compounds 4-9 as catalysts (Table 4). BiCl and
3
Bi(NO ) ·5H O gave near quantitative yields, respectively. Of the bismuth (di)thiolate
3
3
2
compounds, compound 8 gave a low yield (22%), while trace amounts of product were found for
-7 and 9.
The transesterification of methyl stearate to butyl stearate was carried out in refluxing nꢀ
4
butanol for 19 hours using bismuth salts and compounds 4-9 as catalysts (Table 5). Both BiCl3
and Bi(NO ) ·5H O gave high yields, with the latter near quantitative. Bismuth thiolate
3
3
2
compounds 4-9 also gave high yields (79ꢀ100%), with the exception of compound 5 which gave
a yield of 25%.
Finally, the transesterification of glyceryl trioctanoate to methyl stearate was carried out
in refluxing methanol for 19 hours using bismuth salts and compounds 4-9 as catalysts (Table 6).

Page 20 of 42
BiCl was the only salt that afforded any appreciable amount of product (26%). Bismuth
3
thiolate compounds 4-6, 8 and 9 gave very low yields (4ꢀ16%). However, compound 7 gave a
2
6
yield of 75%, outperforming the indium salts and indium thiolates reported previously.
Conclusion
The reaction of bismuth acetate with polydentate dithiols in 95% ethanol or bismuth
nitrate with polydentate (di)thiolates in acetone at room temperature is a facile route to the
synthesis of (dithiolato)ꢀ and bis(thiolato)bismuth complexes. Xꢀray crystallography and DFT
calculations confirm the preference for a distorted pentagonal pyramidal geometry and the
presence of a stereochemically active lone pair in (diamino)(dithiolato)bismuth acetate
complexes 4-6, while both distorted pentagonal pyramidal and distorted trigonal bipyramidal
geometries are observed for (ONS )Bi(NO ) (8). Although solution NMR shows that solidꢀstate
2
3
structures are not retained in solution, geminal coupling in ꢀNCH CH Sꢀ groups suggests some
2
2
restricted motion in the ligand backbones. Bi(NO ) ·5H O and BiCl show high activity toward
3
3
2
3
the esterification of stearic acid, while Bi(NO ) ·5H O, 4-7 and 9 show very high activity (>90%)
3
3
2
toward the transesterification of methyl stearate to butyl stearate.
Compound 7 shows
moderately high catalytic activity for the transesterification of glyceryl trioctanoate and is more
reactive than indium or bismuth salts. Overall, these bismuth compounds show much higher
activity than the corresponding indium compounds for esterification/transesterification reactions.
We are currently preparing bismuth complexes with other thiolate ligand frameworks and
exploring the application of these materials in additional green chemical syntheses.

Page 21 of 42
Acknowledgements
We thank the following: Dan Durant for assistance in collecting solution NMR data; and the
Natural Sciences and Engineering Research Council of Canada (RGPINꢀ2014ꢀ05250), the New
Brunswick Innovation Foundation, the Canadian Foundation for Innovation (Project No. 9211)
and Mount Allison University for financial support.
Supplementary material
1
H NMR spectra of 4-9, selected bond distances and angles for 8, and DFT calculated bond
distances and angles for geometry optimized structures. CCDC 1579431ꢀ1579436 contains the
supplementary crystallographic data for 4-9, respectively. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336
0
33; or eꢀmail: deposit@ccdc.cam.ac.uk.

Page 22 of 42
Structures of 1-3
Structural drawings of (di)thiol proligands.
(
CH2)
n
E
NR
SH
RN
N
N
H
NEt2
SH
HS
HS
SH
H (SNNS), R = Me, n = 2
H (NNS ), E = NEt
2
H(NNS)
2
2
2
H (SNNSPr), R = Et, n = 3
H (ONS ), E = OMe
2 2
2

Page 23 of 42
Structural drawings of 4-9.

Page 24 of 42
Figure 1. Xꢀray crystal structure of 4 (50% probability ellipsoids). Hydrogen atoms are not
shown for clarity.

Page 25 of 42
Figure 2. Xꢀray crystal structure of 5 (50% probability ellipsoids). Hydrogen atoms are not
shown for clarity.

Page 26 of 42
Figure 3. Xꢀray crystal structure of 6 (50% probability ellipsoids). Hydrogen atoms are not
shown for clarity.

Page 27 of 42
Figure 4. Xꢀray crystal structure of 7 (30% probability ellipsoids). Hydrogen atoms are not
shown for clarity.

Page 28 of 42
Figure 5. Xꢀray crystal structure of 8 showing two crystallographically unique molecules (50%
probability ellipsoids). Hydrogen atoms are not shown for clarity.

Page 29 of 42
Figure 6. Xꢀray crystal structure of 9 (30% probability ellipsoids). Hydrogen atoms are not
shown for clarity.

Page 30 of 42
Figure 7. Selected DFTꢀcalculated molecular orbitals of [(SNNS)Bi(OAc)] (4).