The reactivity of
cis-bis(alkynyl)bis((diphenylphosphino)alkyne)platinum(II)
complexes cis-[Pt(C⋮CR)2L2] (R = Ph,
But; L = PPh2C⋮CPh (L1),
PPh2C⋮CBut (L2);
1−4), formed by
displacement of the COD ligand from
[Pt(C⋮CR)2(COD)], toward
cis-[M(C6F5)2(thf)2]
(M =
Pt, Pd, thf = tetrahydrofuran; in both a 1:1 and 1:2 molar ratio) has
been investigated.
Treatment of 1−4 with 1 equiv of
cis-[M(C6F5)2(thf)2]
affords dinuclear derivatives
[{L2Pt(μ-η1:η2-C⋮CR)2}M(C6F5)2]
(5−12) with exclusive formation of doubly
alkynyl-bridged
systems. The molecular structure of
[{(ButC⋮CPh2P)2Pt(μ-η1:η2-C⋮CPh)2}Pd(C6F5)2],
10,
is presented. In contrast, it was found that the course of the
reactions with 2 equiv of cis-[M(C6F5)2(thf)2]
strongly depend on the alkynyl substituents and metal centers.
Thus,
treatment of tert-butylalkynyl derivatives
cis-[Pt(C⋮CBut)2L2]
(2, 4) with 2 equiv of
cis-[M(C6F5)2(thf)2]
(M = Pt, Pd) only gives the expected trinuclear complexes
15A and 18A, in
the case of the reactions with
cis-[Pt(C6F5)2(thf)2].
The molecular structure of the complex
[{Pt(μ-κ(P):η2-PPh2C⋮CPh)2(μ-η1:η2-C⋮CBut)2}{Pt(C6F5)2}2],
15A, reveals that both the
complexed
cis-Pt(C6F5)2
moieties are symmetrically linked to the precursor
“cis-[Pt(C⋮CBut)2(PPh2C⋮CPh)2]”, with the platinum atoms
connected by two unusual mixed alkynyl/phosphinoalkyne bridging systems. On the other hand, similar
reactions of phenylethynyl
derivatives (1, 3) with 2 equiv of
cis-[Pd(C6F5)2(thf)2]
and 3 (L = PPh2C⋮CBut) with
cis-[Pt(C6F5)2(thf)2]
lead, instead, to the unexpected trinuclear PtPd2
(14B, 17B) and Pt3
(16B)
derivatives which display terminal phosphinoalkyne ligands and, hence,
contain the alkynyl
groups acting as μ3-η2 (σ-Pt edge Pd or
Pt) bridging ligands. However, a mixture of both
types of isomers 13A and 13B (50:32) is observed
in the reaction system
cis-[Pt(C⋮CPh)2(PPh2C⋮CPh)2]
(1)/cis-[Pt(C6F5)2(thf)2].
The following order of bonding capability is deduced
from this study: alkynyl > P-bonded phosphinoalkyne and
XC⋮CPh fragments > XC⋮CBut
(X = Pt, P).