Low-Nuclearity Alkynyl d¹⁰ Clusters Supported by Chelating Multidentate Phosphines

The coordination
chemistry of the tri- and tetradentate chelating
phosphines (2-PPh2C6H4)2P­(O)­Ph (P3O) and (2-PPh2C6H4)3P
(P4) with respect
to d10 copper subgroup metal ions has been investigated.
Depolymerization of (MC2R)n (M = Cu, Ag) with P4 affords the series of mono- and trinuclear complexes (P4)­CuC2Ph
(1), (P4)­Cu3(C2Ph)3 (2), (P4)­Ag3(C2Ph) (Hal)2 (Hal = Cl (3), Br (4), I (5)). Reactions of the M+ (M = Cu, Ag) ions with (M′C2R)n (M′ = Cu, Ag, Au) acetylides in the presence
of P4 yield
the family of dinuclear species [(P4)­MM′(C2R)]+ (6–12), which comprise the Cu2/Ag2 (6, 7; R = Ph), AuCu (8–10; R = Ph, C­(OH)­Me2, C­(OH)­Ph2), and AuAg (11, 12; R = Ph, C­(OH)­Ph2) metal cores. A related triphosphine, (2-PPh2C6H4)2PPh (P3), applied in a similar protocol undergoes
partial oxidation and leads to the heterotrimetallic clusters [{(P3O)­M}2Au­(C2R)2]+ (M = Cu, R = C­(OH)­Ph2, 13; M = Ag, R = C­(OH)­Ph2, 14; M = Ag, R = Ph, 15), which can be prepared more efficiently starting from
the oxidized ligand P3O. The structures of the complexes 1–4 and 6–15 were established by single-crystal X-ray crystallography. According
to the variable-temperature 1H and 31P­{1H} NMR experiments, compounds 1–12 demonstrate fluxional behavior in solution. The title complexes
do not show appreciable luminescence in solution at 298 K, and the
photophysical properties of 1–15 were
studied in the solid state. The observed phosphorescence (Φem up to 0.46, λem from 440 to 635 nm) is
assigned to cluster-centered transitions mixed with some MLCT d →
π*­(alkynyl) character.