200
A. Pasini et al. / Inorganica Chimica Acta 315 (2001) 196–204
Table 5
assigned to the P atom trans to the carboxylato moi-
eties, by comparison with literature data of other mixed
phosphine carboxylato or alcolato Pt(II) complexes
[23–25]. In the carboxylato derivatives, 1, 2, 4 and 5,
these resonances display the larger PtꢀP coupling con-
stants. In Pt(II) complexes, where back donation is
negligible, the magnitude of the PtꢀP coupling constant
is related to the strength of the PPt donor bond [26],
which is higher for P trans to the carboxylato group,
because of the low trans influence expected for oxygen
donor ligands [27]. Interestingly in the sph derivatives,
3 and 6, the resonances at higher fields, assigned to the
phosphorus atom trans to O, show a low JPtꢀP, the
phenolato ligand must therefore have a trans influence
stronger than that of other oxygen donor atoms. This
fact can be related with the high stability and/or inert-
ness of the PtꢀO(phenolato) bond in [Pt(en)(sph)]+
reported in our previous studies [2,3].
,
Selected bond distances (A) and angles (°) in compound 1
Pt(1)ꢀO(1)
Pt(1)ꢀP(11)
Pt(1)ꢀP(1)
2.058(11)
2.244(4)
2.310(4)
2.334(4)
1.81(2)
1.814(17)
1.52(2)
1.205(17)
1.274(18)
O(1)ꢀPt(1)ꢀP(1)
P(11)ꢀPt(1)ꢀP(1)
O(1)ꢀPt(1)ꢀS(1)
P(11)ꢀPt(1)ꢀS(1)
C(1S)ꢀS(1)ꢀPt(1)
C(11)ꢀS(1)ꢀPt(1)
O(1)ꢀC(12)ꢀC(11)
C(12)ꢀO(1)ꢀPt(1)
C(12)ꢀC(11)ꢀS(1)
84.8(3)
97.17(15)
84.0(3)
94.08(15)
101.1(7)
96.5(6)
116.9(14)
122.8(10)
113.8(11)
Pt(1)ꢀS(1)
S(1)ꢀC(1S)
S(1)ꢀC(11)
C(11)ꢀC(12)
C(12)ꢀO(12A)
C(12)ꢀO(1)
Pt(2)ꢀO(2)
Pt(2)ꢀP(22)
Pt(2)ꢀP(2)
2.069(12)
2.237(4)
2.308(4)
2.335(4)
1.780(17)
1.785(17)
1.48(2)
O(2)ꢀPt(2)ꢀP(2)
P(22)ꢀPt(2)ꢀP(2)
O(2)ꢀPt(2)ꢀS(2)
P(22)ꢀPt(2)ꢀS(2)
C(2S)ꢀS(2)ꢀPt(2)
C(21)ꢀS(2)ꢀPt(2)
O(2)ꢀC(22)ꢀC(21)
C(22)ꢀO(2)ꢀPt(2)
C(22)ꢀC(21)ꢀS(2)
84.2(4)
99.25(15)
83.4(4)
93.17(15)
103.0(6)
95.4(6)
119.8(16)
117.7(11)
112.6(12)
Pt(2)ꢀS(2)
S(2)ꢀC(2S)
S(2)ꢀC(21)
C(21)ꢀC(22)
C(22)ꢀO(22A)
C(22)ꢀO(2)
1.24(2)
1.321(19)
The non-equivalence of the phoshine ligands is con-
firmed by the 195Pt NMR spectra, which are doublets of
doublets. The chemical shift values in Table 6 are the
mean values of the four lines, of equal intensities, of
these spectra. The PPh3 derivatives display −l values
only slightly lower than those of the dppe complexes, in
accordance with the fact that the donor atoms set is the
predominant influence on l(Pt), with only minor influ-
ence of the ligands backbones [28,29]. These spectra
also confirm the values of the PtꢀP coupling constants
(with discrepancies B8 Hz, see Table 6).
Table 6
195Pt NMR of compounds [Pt(PPh3)2L]+ and [Pt(dppe)L]+ a
L
Pt(PPh3)2
Pt(dppe)
sa
sb
sph
−4446 (3554, 3324)
−4312 (3576, 3335)
−4451 (3317, 3309)
−4556 (3305, 3275)
−4548 (3374, 3294)
−4569 (3309, 3090)
a CHCl3-d solutions; l values from Na2PtCl6; all spectra are dou-
blets of doublets, see text; JPtꢀP in Hz, are given in parentheses.
1
There are certain features of the H NMR spectra
The PtꢀO bond is longer than that of the analogous
cationic complex [Pt(en)(soa)]+ [1], an effect of the
trans influence of the PPh3 group, higher than that of
ethylenediamine. Interestingly also the PtꢀS bond in 1 is
longer than that of the en–soa derivative [1], again this
must be a reflection of the trans influence of phosphine
since our previous reactivity studies on the amine com-
plexes with these ligands [2–4] and the instability of the
mixed phosphine sulfoxide derivatives reported above,
suggest that the Ptꢀsulfoxide bonds are weaker than
those between Pt and thioethers. Finally the PtꢀP bond
trans to S is longer than that trans to O.
(Table 4) that are worthy of discussion:
1. The methyl groups of the sa and sph derivatives
resonate at fields similar or slightly higher than
those of the free ligands, in contrast to what usually
observed upon coordination of these moiety to
Pt(II) [1–4,30]. At least in the case of 1, it could be
that the low field shift, expected upon coordination,
is almost cancelled by the fact that the SCH3 group
is placed in the shielding region of one phenyl ring
of the phosphine (see C(1S) in Fig. 1), a behaviour
reported for a similar case [15]. Incidentally this fact
supports the hypothesis that the conformation of
the sa chelate ring of 1 in solution is the same as
that found in the solid state as discussed below.
Only for the sb complexes we observed the expected
low field shift, we have no explanation for this in the
absence of structural data.
The chelate ring of sa is twisted and the methyl group
is axial, a feature not uncommon in five-member
chelate rings with a methyl group bound to an S [1,15]
or a N (of N-methyl amino acids [19,20]) donor atom.
3.3. NMR studies
2. The resonances of the CH3S groups of all com-
pounds are doublets with satellites due to the cou-
pling with 195Pt (3J between 29 and 36 Hz, see an
example in Fig. 2). The doublets are due to 4J
coupling with 31P, as the resonances become singlets
in the {31P} spectra. The PꢀH coupling was confi-
rmed by HMQC experiments which showed cross
peaks between the 31P resonances at lower fields and
those of the CH3 protons. Incidentally these experi-
31P NMR data are collected in Table 3. The different
chemical shift values shown by the PPh3 and the dppe
complexes are related to the presence of the five-mem-
bered chelate ring of dppe [21,22]. The spectra of
compounds 1–6 show, as expected, two doublets (due
to PꢀP coupling) of the two inequivalent P atoms, both
with PtꢀP satellites. The resonances at higher field are