Cyclic Trinuclear Gold(I) Clusters with N,N and Unusual C,C Mixed-Ligand Bridges

Three crystalline trinuclear gold­(I)
clusters, [Au3f2y] (1), [Au3fy2] (2), and [Au3y3] (3), where f = N,N′-bis­(2,6-dimethylphenyl)­methanimidamidate and y = dimethylendiphenylphosphinate,
exhibit bridges from the N,N-formamidinate
and/or from the ylide anion ligand whose P-methylene groups chelate
in an unusual fashion, where the chelate CPC unit is perpendicular
to the trigonal plane of the metal atoms. Assemblies 1 and 2 are the first gold­(I) trinuclear clusters featuring
mixed-ligand bridges from different N,N and C,C donors; 3 is a previously unknown homoleptic ylide anion cyclic trinuclear
assembly. Formamidinate bridges in 1 and 2 connect gold­(I) atoms at aurophilic distances of 3.084(2) and 3.0543(4)
Å, whereas an out-of-plane (perpendicular) P-ylide anion bite
produces AuI–AuI distances of as large
as 3.900(2) Å in 3. The crystal space groups for 1 and 2 are triclinic P1̅
and that for 3 is monoclinic P21/c, with Z = 2 for 1 and 2 and Z = 4 for 3. Compounds are synthesized under Schlenk conditions at −20
°C in toluene by reacting the proper ratios of the gold­(I) formamidinate
[Au2f2] with the phosphorus ylide [Hy] under
basic conditions (KOH), followed by extraction with ether. This synthesis
also produces a dinuclear cation, [Au2f­(Hy)2]+, previously reported by our group. A neutral mixed-ligand
dinuclear complex, [Au2fy], was not observed. Under UV
light, 1 and 2 display a bright-green luminescence
at room temperature and in frozen methyltetrahydrofuran solutions
under liquid nitrogen, with microsecond lifetimes. All three complexes 1–3 are characterized by their X-ray crystal
structures, 1H NMR, IR, UV–visible, and luminescence
spectroscopies, and elemental analysis.