Reaction of
[Pt2(RNC)6](PF6)2
(R = 2,6-xylyl (Xyl) (a) and 2,4,6-mesityl (Mes)
(b)) with 2
equiv of bis((diphenylphosphino)methyl)phenylphosphine
(dpmp) afforded a mixture of
isomeric diplatinum complexes,
syn-[Pt2(μ-dpmp)2(RNC)2](PF6)2
(1) and
anti-[Pt2(μ-dpmp)2(RNC)2](PF6)2 (2),
which were purified by cycles of recrystallization and were
characterized
by X-ray crystallography. Complexes 1 and 2
consist of a diplatinum core (Pt−Pt = 2.7094(8)
Å (1a) and 2.683(2) Å (2a)) asymmetrically
bridged by two dpmp ligands. The central
phosphorus atoms of the dpmp ligands coordinate to the same metal
center in the syn-dimer
(1) and to different metal centers in the
anti-dimer (2). Complexes 1 and
2 were fluxional
in solution through symmetrical structures of
syn-1‘ and anti-2‘,
respectively, in which two
terminal phosphine units are uncoordinated. At reflux in
CH3CN or by treatment with [Cu(CH3CN)4](PF6), complexes
1a and 2a lost one isocyanide molecule to be
transformed into
syn-[Pt2(μ-dpmp)2(XylNC)](PF6)2
(3, Pt−Pt = 2.6834(8) Å) and
anti-[Pt2(μ-dpmp)2(XylNC)](PF6)2 (4, Pt−Pt = 2.7150(7)
Å), respectively. Reactions of the syn-dimer
(1) with
[M3(XylNC)6] readily afforded the
linearly ordered trinuclear clusters,
linear-[Pt2M(μ-dpmp)2(XylNC)2](PF6)2 (M = Pt
(5), Pd (6)). The additional zerovalent
metal atom is incorporated
into the terminal position of the trinuclear aggregation, resulting in
a d9−d10−d9
configuration
via one electron transfer from the additional metal to the
diplatinum core. The three metal
atoms are joined by two metal−metal σ-bonds (average Pt−Pt =
2.724(2) Å (5), Pt−Pt/Pd =
2.690(1) Å) and are symmetrically bridged by two dpmp ligands, to
form a linearly ordered
trinuclear structure (Pt−Pt−M = 178.66(8)° (5),
180.0° (6)). The similar reactions of
the
anti-dimer (2) with
[M3(RNC)6] led to a formation of the
A-frame trinuclear clusters, A-frame-[Pt2M(μ-dpmp)2(RNC)2](PF6)2
(7, M = Pt, R = Xyl; 8, M = Pd, R = Mes).
The three metal
atoms are joined by two metal−metal bonds (Pt−M = 2.6039(7)
Å (7), 2.599(3) Å (8)) and
asymmetrically bridged by two dpmp ligands, resulting in a so-called
trimetallic A-frame
structure (Pt−M−Pt = 76.76(3)° (7),
78.5(1)° (8)). The additional metal is trapped
into the
middle position of the trinuclear core, through the insertion of
d10 ML2 fragment into the
Pt−Pt σ-bond, which is interestingly contrasted with the terminal
position observed in the
reactions of the syn-dimer.
