636
Can. J. Chem. Vol. 81, 2003
Fig. 1. Crystallographic views of (a) 6a, (b) 6b, (c) 7a, (d) 8,
(e) 9a. Thermal ellipsoids are drawn to 50% probability. Hydro-
gen atoms have been omitted for clarity.
reasonable yield. Some yields are relatively low, however,
conditions to optimize them have not yet been assessed.
Compounds 6–9a have been crystallographically and
spectroscopically characterized. Molecular structures are
shown in Fig. 1 and selected bond lengths are compared
with those of compounds 1–5 in Table 3. The spirocyclic en-
vironments observed for bismuth in 6a, 6b, 7a, and 9a con-
firm auxiliary coordination of the hydroxyl (6b), amino (6a,
7a, and 9a) and alkoxide (9a) functional groups to the bis-
muth centre in each respective example. The structures are
consistent with the homoleptic thiolate series 1–3 (3, 4, 13),
except for compound 8 in that the ester functionality is ter-
minal (Bi-O, 3.55(2) Å; cf. Bi-O 2.56–2.86 Å (8, 11)),
showing no evidence of interaction with bismuth. This is an
unexpected structural feature, when one compares the struc-
ture of tris(thiosalicylato)bismuth 11, which exhibits a defin-
itively hexacoordinate site for bismuth and typical Bi—O
coordinate bond distances (Bi—O 2.72(2)–3.08(2) Å) (14).
Although the cross-ring S2—Bi distance is relatively long
(3.0688 (4) Å) in 8, we speculate that this interaction lowers
the Lewis acidity of the bismuth center to render the car-
bonyl donation ineffective.
The structural features of compounds 6–9a represent a
useful contribution to the developing database for the che-
late–thiolate coordination chemistry of bismuth, as docu-
mented in Table 3. Mono-, bis-, and tris-thiolate complexes
of bismuth exhibit a narrow range of Bi—S bond distances.
The geometry at bismuth varies considerably throughout the
series of complexes including a variety of coordination num-
bers. Nevertheless, most complexes are observed to have
Bi—S bond lengths within a narrow range (2.5 to 2.6 Å), so
that the thiolate interaction is essentially independent of the
number of thiolate ligands, the presence of auxiliary intra-
molecular coordination to bismuth, or the number of inter-
molecular interactions at bismuth. The unusually long Bi—S
bonds in 1c, 2b, and 2c are likely due to strong inter-
molecular interactions in the solid state that provide for a
dimeric arrangement for 1c and a polymeric (ribbon-like)
structure for 2b and 2c (3, 8). The fourth Bi-S contact in 7a
and 8 represent the intramolecular cross-ring thioether dona-
tion, which is predictably weaker than those of the thiolates.
The relatively weak interactions of the amines are likely
made possible by the chelate arrangement. The Bi—N dis-
tances are comparable to those of the thiolates despite the
smaller size of nitrogen. These observations are consistent
with the realization that amine complexes of bismuth are
extremely rare and the most reliable comparative data comes
from complexes of pyridine derivatives (2), which are in the
range of the Bi—N distances listed in Table 3. The relative
Bi—O distances are in agreement with the relative Lewis ba-
sicity of the oxygen donor in that interactions of hydroxyl
(2b, 6b, 9b, 10) and carbonyl (1c, 2c, 3c, 8, 11) ligands are
longer than interactions with alkoxide (9a, 9b, 10)
functionalities.
rather than a series of related compounds and general syn-
thetic procedures have not been established to allow for as-
sessment of physical and chemical properties.
A wide range of bismuth thiolate complexes are known
due to the high thermal and hydrolytic stability of the sulfur–
bismuth bond (2), however, most complexes involve multi-
thiolation. Hetero-bifunctional ligands containing a thiolate
moiety and an auxiliary donor have proven effective for de-
veloping complexes of bismuth with new donors. Moreover,
the chelate interaction of the weaker donor mediates the
thiophilicity of the bismuth centre and it is possible to iso-
late kinetically stable, partially thiolated complexes, so that
all three stoichiometric combinations (1, 2, 3) have been pre-
pared for aminoethanethiolate (4) and esterthiolate (8, 11)
complexes.
We have now exploited the features of bifunctional thio-
late ligands to develop synthetic procedures for heteroleptic
bismuth complexes. The starting materials 4 (12) and 5 (9)
that are readily obtained via precipitation, react slowly at
room temperature with potassium thiolate solutions in a
slurry with little or no change in the visual appearance of the
reaction mixture. Nevertheless, the precipitates are charac-
terized as analytically pure metathesis products formed in
Conclusion
The use of thiolates in bifunctional ligands offers a syn-
thetically versatile approach to bismuth complexes involving
weak Lewis donors and provides for a general systematic
and comprehensive development of bismuth chemistry.
© 2003 NRC Canada