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.