Russian Journal of General Chemistry, Vol. 73, No. 8, 2003, pp. 1198 1200. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 8, 2003,
pp. 1269 1271.
Original Russian Text Copyright
2003 by Kolesova, Polovnyak.
Complexes of Platinum(II) Chloride with Cyanophosphines
M. V. Kolesova and V. K. Polovnyak
Kazan State Technological University, Kazan, Tatarstan, Russia
Received July 23, 2001
Abstract Platinum(II) cyanophosphine complexes PtL2Cl2, where L = P(CN)3, PhP(CN)2, or Ph2PCN,
were synthesized. Their properties and mode of coordination were examined.
Platinum(II) complexes have a square-planar struc-
ture. In particular, quite stable are acido complexes
PtX24 , where X is an acid residue. Complexes like
PtL2X2, where is X is an organoelement ligand, ex-
hibit cis trans isomerism and are quite active in
ligand substitution reactions in which the role of
leaving invariably belongs to the acido ligand as a
result of the trans-effect of the organoelement ligand.
The PtL2X2 complexes, where L is an organic P(III)
ligand and X is an acido ligand (Hlg or SCN ), have
been thoroughly studied in terms of synthesis, com-
position, and structure. Much less work has been on
complexes with bidentate ligands, ambidentate in
particular.
The following modes of coordination of substituted
phosphines are possible: via lone electron pairs (LEP)
of N and P and polydentate coordination via N N and
N P. Here we present the results of an experimental
study of the mode of coordination of cyanophosphines
in square-planar platinum(II) complexes.
It terms of organophosphorus chemistry, the cyano
group in P(III) cyanides plays the role of a pseudo-
halide, and, therefore, these compounds tend to react
similarly to substituted phosphorus halides [1].
With the aim to predict the metal-coordinating
center in the P C N ambidentate system, we per-
formed quantum-chemical calculations of the popula-
tions and energies of the corresponding molecular
orbitals of the free ligands (Table 2) [2].
In the latter case, an important problem is intra-
spherical competition of ambidentate ligands when
coordination via different donor atoms is possible. For
instance, such a typical ambidentate ligand as thio-
cyanate can coordinate both via the nitrogen and
sulfur atoms. Therewith, the thiocyanate ligand co-
ordinated via the nitrogen and sulfur atoms have much
different geometries: linear and angular, respectively.
The different modes of coordination of the thiocyanate
ligand makes possible stabilization of different geo-
metric isomers of Pt(II): Coordination via the nitrogen
atom stabilizes the trans isomer, whereas coordination
via the sulfur atom, the cis isomer. Such a definite
picture is observed when the organoelement ligand is
monodentate (substituted phosphines, phosphites,
amines, etc.). When the organoelement ligand is also
ambidentate, the situation becomes unpredictable. We
synthesized ambidendate ligands of a new type,
substituted cyanophosphines, whose P(III) and N(III)
atoms can act as donor centers (Table 1).
Taking account of the calculation results and
relying on Pearson’s principle of hard and soft acids
and bases [4], one should expect that the mode of
platinum ligand coordination will vary with cyanide
structure.
Thus, P(CN)3 should preferentially coordinate with
Pt by its phosphorus atom (I 12.55 eV). The energy
of HOMO in Ph2PCN (phenyl system) is 9.75 eV,
and, therefore, a considerable contribution of phenyl
electrons would be expected.
Evidence for the above reasoning comes from the
calculated populations of atomic orbitals in HOMO.
Table 3 lists the contributions of atomic orbirals of
Table 1. Properties of ligands
1
Ligand
P(CN)3
PhP(CN)2
Ph2P(CN)
Ph3P
bp,
C
P, ppm
CN, cm
Substituted cyanophosphines would be expected to
act both as monodentate ligands coordinating via the
above donor centers and as bidentate. In the latter case,
cis coordination of acido ligands would be pre-
determined.
50 60
68 70
110
138.3
76.0
36.4
2180
2190
2190
80
1070-3632/03/7308-1198$25.00 2003 MAIK Nauka/Interperiodica
Kolesova
