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T.F. Gallatti et al. / Journal of Organometallic Chemistry 692 (2007) 5447–5452
rigid character of such diimines in contrast with the flexible
character of diamines.
2.2. Synthesis of complexes
This fact was quite surprising for us, since we had syn-
thesized previously to the publication of James [18] the
trans-isomer using the same one-pot synthesis, but the
reaction was carried out in the dark and short period of
time.
Our group have been working with complexes trans/
cis-[RuCl2(P–P)(N–X)], where P–P is mono- or diphos-
phines and N–X is diimines, acetyl and benzoyl-pyri-
dines, with the interest in structural and isomerization,
transfer-hydrogenation and epoxidation [1,2,19–23]. In
these works we showed that the reaction condi-
tions are a key role for the isolation of desired isomer
[1,23].
In this work we present the syntheses, characterization,
and electrochemical studies of four complexes trans/cis-
[RuCl2(dppf)(diimines)]. In addition, we show that the
trans-isomer can be synthesized and isolated in disagree-
ment with the recently published work [18], and the iso-
merization trans ! cis was followed by cyclic voltammetry
and UV–vis spectroscopy. The catalytic activity of cis-
[RuCl2(dppf)(diimines)] complexes (N–N = 2,20-bipyridine
and 4,40-dimethyl-2,20-bipyridine) for reduction of aceto-
phenone was tested and the results are compared with anal-
ogous complexes. X-ray structure cis-[RuCl2(dppf)(phen)]
is presented and discussed.
2.2.1. trans-[RuCl2(dppf)(bipy)] trans-(1) and
trans-[RuCl2(dppf)(Me-bipy)] trans-(2)
A Schlenk flask containing a degassed dichloromethane
(10.0 mL) solution of [RuCl2(PPh3)3] (100 mg; 0.104 mmol)
and dppf (57.6 mg; 0.104 mmol) was stirred for 5 min, the
reaction was protected from exposure to light and the 2,20-
bipyridine (16.2 mg; 0.104 mmol) was added. The reaction
was stirred for additional 2 min and n-hexane was added
to yield a dark red solid. After filtration the solid was
washed with n-hexane and diethyl ether and dried under
vacuum. The resulting red solution was concentrated and
addition of diethyl ether afforded a red solid, which was col-
lected, washed with diethyl ether and dried under vacuum.
1
Yield: 87.4 mg (95%). H NMR: 3.87 (s, 4H, C5H4), 4.12
(s, 4H, C5H4), 6.50 (t, 2H, J 6.3, bipy), 6.78 (t, 8H, J 7.5,
Ph), 6.96 (t, 4H, J 7.2, Ph), 7.40 (t, 2H, J 7.4, bipy), 7.56
(br m, 8H, Ph), 7.76 (d, 2H, J 4.4, bipy), 8.38 (br d, 2H, J
4.4, bipy). IR (KBr pellet): 1602 m; 1481 m; 1471 m; 1433
s; 1384 w; 1309 w; 1188 w; 1155 m; 1086 m; 1035 m; 827
w; 745 s; 696 s; 640 m; 545 s; 516 s; 495 s; 476 m; 428 m;
330 w; 303 w; 281 w. Anal. Calc. for C44H36N2Cl2P2Fe-
Ru Æ H2O: C, 58.68; H, 4.25; N, 3.11. Found: C, 58.82; H,
4.05; N, 3.40%. UV–vis (CH2Cl2, 10ꢀ3 M): k/nm (e/
M
ꢀ1 cmꢀ1) 302 (14900), 351 (3600), 498 (2600).
Complex trans-(2) was synthesized following the same
procedure for the synthesis of trans-(1), but the reaction
was carried out in a NMR tube for direct analysis by 31P
NMR.
2. Experimental section
2.1. Material and instrumentation
2.2.2. cis-[RuCl2(dppf)(bipy)]cis-(1)
The cis-isomer can be isolated by two methods: Method
A: isomerization of trans-isomer in dichloromethane at
room temperature and exposure to light (fluorescent).
Method B: (A representative method for direct synthesis
of the cis-isomer is as follow), cis-[RuCl2(dppf)(bipy)]
cis-(1): A Schlenk flask containing degassed dichlorometh-
ane (20.0 mL) solution of cis-[RuCl2(PPh3)2(bipy)]
(100 mg; 0.117 mmol) and dppf (71.5 mg; 0.129 mmol)
was refluxed for 3 h. The resulting red solution was concen-
trated and addition of diethyl ether afforded a red solid,
which was collected, washed with diethyl ether and dried
All manipulations were carried out under purified argon
using standard Schlenk techniques. Reagent grade solvents
were appropriately distilled and dried before use. The
RuCl3 Æ 3H2O was supplied by Johnson Matthey Ltd. or pur-
chased from Aldrich. Triphenylphosphine (PPh3) (Aldrich),
1,4-bis(diphenylphosphino)butane (dppb) (Aldrich), 1,10-
bis(diphenylphosphino)ferrocene (Strem), 2,20-bipyridine
(bipy) (Aldrich), 1,10-phenanthroline (phen) (Aldrich) and
4,40-dimethyl-2,20-bipyridine (Me-bipy) (Aldrich) were used
as received. The [RuCl2(PPh3)3] [24] and [RuCl2(PPh3)2(dii-
mines)] [21] complexes were synthesized following published
procedures.
Cyclic voltammetry (CV) experiments were carried out
at room temperature in CH2Cl2 using a BAS-100B/W Bio-
analytical Systems Instruments; the working and auxiliary
electrodes were stationary Pt foils, and tꢀhe reference elec-
trode was Ag/AgCl, 0.10 M Bu4NþClO4 (TBAP) (Fluka
Purum), a medium in which ferrocene is oxidized at
0.43 V (Fc+/Fc). Elemental analyses were performed in
the Chemistry Department at Universidade Federal de
1
under vacuum. Yield: 82.8 mg (80%). H NMR: 3.41 (s,
1H, C5H4), 4.15 (s, 1H, C5H4), 4.24 (s, 1H, C5H4), 4.34
(s, 1H, C5H4), 4.47 (s, 2H, C5H4), 4.97 (s, 1H, C5H4),
5.98 (s, 1H, C5H4), 6.43 (t, 1H, J 6.5, bipy), 6.92 (t, 2H,
J 7.1, Ph), 6.99 (m, 2H, Ph), 7.11 (m, 8H, Ph), 7.38 (m,
4H, Ph), 7.48 (s, 1H, bipy), 7.61 (d, 1H, J 7.9, bipy), 7.64
(d, 1H, J 6.1, bipy), 7.68 (d, 1H, J 7.5, bipy), 7.74 (d,
1H, J 7.9, bipy), 7.83 (d, 1H, J 7.9, bipy), 8.12 (m, 2H,
Ph), 8.38 (t, 2H, J 8.1, Ph), 9.32 (d, 1H, J 5.0, bipy). IR
(KBr pellet): 1603 m; 1482 m; 1468 m; 1432 s; 1383 w;
1308 w; 1190 w; 1158 m; 1089 m; 1035 m; 816 w; 747 s;
696 s; 636 m; 546 s; 518 s; 499 s; 474 m; 427 m; 348 w;
319 w; 294 w. Anal. Calc. for C44H36N2Cl2P2FeRu: C,
59.88; H, 4.11; N, 3.17. Found: C, 60.13; H, 4.35; N,
Sao Carlos. All NMR experiments were recorded at
˜
298 K on a Bruker AVANCE 400 equipment operating
at 9.4 T, observing 1H at 400.13 MHz and 31P at
161.98 MHz.