Synthesis, Structure and Cation-Binding Properties of Some [4 + 4] Metallocyclic MO₂²⁺ (M = Mo or W) Derivatives of 9‑Phenyl-2,3,7-trihydroxyfluor-6-one

The
trianion Z3– obtained from 9-phenyl 2,3,7-trihydroxyfluor-6-one,
ZH3, affords dioxomolybdenum and dioxotungsten derivatives
which contain [4 + 4] metallocycles of composition [(MO2)4Z4]4– (M = Mo, W) in combination
with a variety of counter cations. The syntheses, structures and ESMS
of the following compounds are presented: compound 1,
(MePPh3)3(NBu4)­[(MoO2)4Z4]; compound 2, (MePPh3)3(NBu4)­[(WO2)4Z4]; compound 3, (MePPh3)4[(WO2)4Z4]; compound 4, (PPh4)2(NBu4)2[(MoO2)4Z4]; compound 5, (AsPh4)3(NBu4)­[(MoO2)4Z4]; compound 6, (AsPh4)2(NBu4)2[(WO2)4Z4]; compound 7, (Ph3PNPPh3)­(NBu4)3[(MoO2)4Z4];
compound 8, (Ph3PNPPh3)­(NBu4)3[(WO2)4Z4];
compound 9, (NEt4)­(NBu4)3[(MoO2)4Z4]. The metallocycles in
all of these compounds have similar structures, with the four metal
centers located at the corners of a square slightly distorted, to
varying degrees, toward a rhombus and also toward a tetrahedron. Various
cations are bound inside the anionic metallocycles. ESI mass spectrometry
shows that the metallocycles remain intact in the gas phase, forming
[(MO2)4Z4]4–, {X-[(MO2)4Z4]}3– and in some
cases {X2-[(MO2)4Z4]}2– where X+ is an organic cation.