Reactions between
W(η2-Ph2C2)Cl4
and salicylic acid derivatives generate analytically pure
free acids of formula
W(η2-Ph2C2)Cl3(Hsal-R)
(1) in high yields (Hsal = a salicylate
monoanion). The products exist as hydrogen-bonded dimers in the
solid state. The acid
functionality on one molecule hydrogen bonds to one of the
cis-chloride ligands of an adjacent
complex at a 3.03 Å distance. The more electron-rich tungsten
center renders these acetylene
complexes less acidic than their oxo and arylimido analogs. As a
result,
W(η2-Ph2C2)Cl3(Hsal) exhibits partial dimerization in solution and have relatively
weak hydrogen bonds to
nitrogen- and oxygen-containing organic molecules. Among a range
of possible phenol−phenoxide complexes of the
W(η2-Ph2C2)Cl3
subunit, only the ether adduct of the catecholate,
W(η2-Ph2C2)Cl3(Hcat···OEt2)
(2), has been isolated and structurally characterized.
The weaker
hydrogen bond strength of larger chelating bis(phenolates)
evidently destabilize the phenol−phenoxide structures in favor of simple chelating bis(phenoxides).
The salicylate free acids
form various supramolecular complexes in solution and the solid state,
including [W(η2-Ph2C2)Cl3(Hsal)]4(18-crown-6)
(5), one of a family of tetranuclear systems organized
around
hydrogen bonding to an 18-crown-6 template. This structure is
characterized by π-stacking
of the Hsal ligands between confacial free acid complexes and the
steric screening of the
two non-hydrogen-bonded 18-crown-6 oxygens by pairs of antarafacial
W(Ph2C2) units.
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