Syntheses of Di- and Trinuclear Platinum Complexes with Multibridged Germanium Centers Derived from Unsymmetrical Digermanes

A trigonal-bipyramidal Pt3Ge2 cluster
was
synthesized by the reaction of the zerovalent platinum complex [Pt­(dppe)­(η2-C2H4)] (dppe = 1,2-bis­(diphenylphosphino)­ethane)
with the unsymmetrical digermane H3GeGeEt3 at
a 3/2 molar ratio. The platinum centers formed a triangular plane
bridged by two germylyne ligands, one of which maintained the Ge–Ge
bond. To investigate the Pt3Ge2 cluster formation
process, the phenyl-substituted digermanes HPh2GeGeMe3 and H2PhGeGeR3 (R = Me, Et), in which
two hydrogen atoms and one hydrogen atoms of the reactive GeH3 moiety were replaced by the bulkier phenyl group(s) together
with the substitution of the GeEt3 group by a GeMe3 group, respectively, were used to simplify the reaction system.
They provided the digermylplatinum hydride [Pt­(dppe)­(H)­(GePh2GeMe3)] (2) and the bis­(μ-germylene)­diplatinum
complexes [Pt2(dppe)2(μ-GeHPh)­(μ-Ge­(Ph)­GeR3)] (3, R = Me; 4, R = Et) in moderate
yields, respectively. For 3 and 4, the first-formed
digermylplatinum hydride I-1 underwent dissociation of
one of the phosphorus donors followed by 1,2-germyl migration to give
the corresponding bis­(germyl)platinum complex I-2, as
observed in the previously reported silicon system. On the one hand,
the germyl migration did not take place in the case of 2, owing the Ge–Ge bond being less reactive than the Si–Si
bond. Intermediates I-1 and I-2 coupled
to each other to afford the germylene-bridged diplatinum complexes 3 and 4 accompanied by extrusion of H2 and R3GeH. In the case of H3GeGeEt3, the corresponding bis­(μ-germylene)­diplatinum complex reacted
with [Pt­(dppe)­(η2-C2H4)], resulting
in the formation of the desired Pt3Ge2 cluster.
The spiro-type Pt4Ge complex was obtained only by changing
mole equivalents of [Pt­(dppe)­(η2-C2H4)], demonstrating the usefulness of the present method using
H3GeGeEt3, which can readily regulate the molar
ratio.