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C. Lopez et al. / Inorganic Chemistry Communications 8 (2005) 631–634
632
followed by a SiO2 column chromatography. However,
when 1b was used, no evidences of the formation of
the platinacycle were detected by NMR spectroscopy
and only FcCHO and cis-[Pt{(g5-C5H5)Fe[(g5-C5H4)–
CH@N–(CH2)2–NMe2]}Cl2] (3b) (previously described
[3]) were isolated. Similar disappointing results were ob-
tained for longer refluxing periods (up to 15 days), and
in these cases the relative amount of FcCHO increased.
These findings suggested that 1b is less prone to undergo
the cycloplatination than 1a.
Fig. 1. Ligands under study.
More interesting were the results obtained when 1b,
cis-[PtCl2(dmso)2] and NaOAc (in a 1:1:2 molar ratio)
were refluxed in a toluene/methanol mixture (20:5) for
3 days. After work up, this method gave [Pt{[(g5-
an envelope-like conformation where the C(13) is
˚
0.571 A out from the main plane.
These results presented here have an additional inter-
est, since the extrapolation of this methodology to 1a
also allowed the preparation of 3a, in a nearly similar
yield as described before [2] but in shorter reaction peri-
ods (3 days).3
C5H3)–CH@N–(CH2)2–NMe2]Fe(g5-C5H5)}Cl]
(2b)
and small amounts of FcCHO and 3b.1 Characterisation
data of 2b were consistent with the proposed formula.
The crystal structure of 2b (Fig. 1)2 consists of discrete
molecules of [Pt{[(g5-C5H3)–CH@N–(CH2)2–NMe2]
Fe(g5-C5H5)}Cl] separated by van der Waals distances.
In each molecule, the platinum(II) is bound to the N(1),
N(2) and C(6) atom of the ferrocenyl Schiff base and a
chloride, in a slightly distorted square-planar environ-
ment. The Pt-ligandsÕ bond lengths agree with the values
reported for other platinacycles holding ‘‘Pt(C,N,N0)Cl’’
cores [5] (see Scheme 1 and Fig. 2).
Complex 2b reacted with the equimolar amount of
PPh3 in CH2Cl2, giving [Pt{[(g5-C5H3)–CH@N–
(CH2)2–NMe2]Fe(g5-C5H5)}Cl(PPh3)] (4b),4 where the
ligand acts as a [C(sp2, ferrocene), N]ꢀ group.
In order to elucidate the effects produced by: (a) the
mode of binding of tꢀhe Schiff base 1b to the platinum(II)
{½C
; N; N0ꢁ (in 2b), ½C
; Nꢁꢀ (in 4b)
ðsp2;ferroceneÞ
ðsp2;ferroceneÞ
or (N,N0) in (3b)} and (b) the size of the chelate ring
upon the electronic environment of the iron(II), electro-
chemical studies based on cyclic voltammetry were car-
ried out. The cyclic voltammograms exhibited an anodic
peak with a directly associated reduction in the reverse
scan. The ratio Ipa/Ipc was close to 1 and a linear rela-
tionship between the Ipa and t1/2 was obtained. These
findings are consistent with those expected for a simple
reversible one-electron transfer process [6] (see Fig. 3).
For 2b and 4b, the waves were shifted to the more
cathodic region than for the free ligand, 1b [7] and the
magnitude of the shift was greater for 2b than for 4b
The complex has a [5,5,5] tricyclic system formed by
the 1,2-disubstituted pentagonal ring of the ferrocenyl
moiety, the platinacycle (which is twisted on the Pt–
N(1) bond) and a five-membered chelate ring that has
1
Preparation and characterisation data for 2b. cis-[PtCl2(dmso)2]
(0.225 g, 5.3 · 10ꢀ4 mol) and 1b (0.151 g, 5.3 · 10ꢀ4 mol) were sus-
pended in toluene (20 mL). Then, a solution formed by 0.087 g
(1.06 · 10ꢀ4 mol) of NaOAc and 5 mL of methanol (HPLC-grade) was
added and the mixture was refluxed for 3 days. Then, the solution was
filtered out and the filtrate was concentrated to dryness on a rotary
evaporator. The residue was dissolved in CH2Cl2 (ca. 10 mL) and
passed though a SiO2-column chromatography (2.5 cm · 3.0 cm).
Elution with CH2Cl2 released orange bands which gave, after work
up, FcCHO (6 mg) and 3b (12 mg). The subsequent use of a
CH2Cl2:MeOH (100:0.05) mixture as eluant gave a deep red band,
which was collected concentrated to ca. 5 mL on a rotary evaporator.
Slow evaporation at ca. 4 ꢁC gave 2b (yield: 49 mg). Anal. Calc. (%) for
3
Optimised method for the preparation of 2a. This complex was
prepared as described for 2b, but using cis-[PtCl2(dmso)2] (0.225 g,
5.3 · 10ꢀ4 mol), 1a (0.158 g, 5.3 · 10ꢀ4 mol) and NaOAc (0.087 g,
1.06 · 10ꢀ4 mol). In this case, three bands were collected by SiO2
column chromatography using CH2Cl2 as eluant. The two orange
bands gave after work up: FcCHO (14 mg) and 3a, and the third lead
2a (75 mg) as a deep-purple solid.
4
C
15H19ClFeN2Pt (Found): C, 35.07(35.1); H, 3.73(3.8) and N,
Preparation and characterisation data for 4b. To a solution formed
5.45(5.6). MS(FAB+): m/z = 514 [M+] and 478 {[M ꢀ Cl]+}. IR:
1579 cmꢀ1{m(C@N–)}. 1H NMR data in CDCl3 d (in ppm): 4.24 [s,
5H, C5H5]; 4.34[s, 1H, H3]; 4.61[s, 1H, H4], 4.78[s, 1H, H5], [br, 2H,
=N–CH2–]; 3.50–2.82[br.m, 2H, –CH2–N]; 2.87[s, 6H, 2 Me] and
8.23[s, 1H, –CH@N–, JPt–H = 118). 195Pt{1H} NMR in CDCl3):
by 2b (35 mg, 6.8 · 10ꢀ5 mol) and 10 mL of CH2Cl2, PPh3 (18 mg,
6.8 · 10ꢀ5 mol) was added. The mixture was stirred at 20 ꢁC for 20 min
and then filtered out. Concentration to dryness of the filtrate produced
a solid which was collected and dried in vacuum for 3 days (yield:
39 mg, 78%). Anal. Calc. (%) for C33H34ClFeN2PtP (Found): C,
51.08(51.3); H, 4.42(4.6) and N, 3.61(3.7). MS(FAB+): m/z = 776 [M+]
and 740 {[M ꢀ Cl]+}. IR: 1593 cmꢀ1{m(C@N–)}. 1H NMR data in
CDCl3 d (in ppm): 3.86[s, 5H, C5H5], 3.71[s, 1H, H3], 4.28[s, 1H, H4],
4.45[s, 1H, H5], 3.30–3.50[br.m, 2H, =N–CH2–], 2.80–3.10[br.m, 2H, –
CH2–N–], 2.53[s, 6H, 2 Me] and 7.19–7.70 [br.m, 16H, –CH@N– and
aromatic protons]. 195Pt{1H} NMR data in CDCl3: d = ꢀ4197 ppm,
1JPt–P = 4135 Hz). 31P{1H} NMR data in CDCl3: d = 16.50 ppm,
1JP–Pt = 4135.
d = ꢀ3348 ppm.
2
Crystal data of 2b. Empirical formula: C15H19ClFeN2Pt; MW=
513.71; crystal system: orthorhombic; a=13.3210(10), b=11.1420(10); c
3
˚
˚
20.6420(10) A; a = b = c = 90.0ꢁ; Space group =Pbca; V=3064.7(4) A ;
Z = 8; Dcalc=2.227 mg · mꢀ3; l = 10.234 mmꢀ1; F(000)=1952; number
of data and parameters 4203 and 181, respectively; Final R indices for
I > 2r(I): wR1=0.0421 and wR2=0.1179; for all data: wR1=0.0493 and
wR2=0.1289.
López, Concepción
