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AYDEMIR et al./Turk J Chem
are in agreement with the anticipated structures and the compositions of the two complexes were supported by
microanalysis.
Reaction of [Pt(cod)Cl2 ] (cod = 1,5-cyclooctadiene) with one equivalent of 1 or 2 in thf solution yields the
respective {N ,N ’-bis(dicyclohexylphosphino)-2-(aminomethyl)aniline} dichloroplatinum(II) (5) and {N ,N ’-
bis(diisopropylphosphino)-2-(aminomethyl)aniline} dichloroplatinum(II) (6), respectively, by replacement of cod
1
with 1 or 2. 31 P-{ H} -NMR spectra of complexes 5 and 6 contained two singlets for each at δ 66.04 and
55.63 ppm and 72.82 and 61.71 ppm, respectively.24−26 The large 1J(195 Pt-31 P) coupling constants of 4093
and 3905 Hz for 5 and 4092 and 3907 Hz for 6 are indicative of a cis arrangement of aminophosphine around
the platinum(II) centers.27−29 Typical spectra of these two platinum complexes are illustrated in the ESI,
Figure 2 (Spectra 1.2.). Their 1 H NMR and 13 C NMR spectra are consistent with the literature values.30−32
The complexes were able to be isolated as solid materials and characterized by IR as well as microanalysis.
Furthermore, we extensively tried to obtain crystals suitable for X-ray analysis, but unfortunately were not
successful.
2.2. Suzuki–Miyaura and Mizoroki–Heck coupling reactions
In a pilot study to examine the catalytic activity of palladium complexes, we initially tested the Suzuki cross-
coupling reaction between aryl bromides with boronic acid.33−35 The reaction parameters for the Suzuki cross-
coupling reaction were optimized through a series of experiments. The effects of several parameters such as
temperature, base, solvent, and ambient atmosphere were systematically studied by using the coupling of p-
bromoacetophenone and phenylboronic acid as a probe reaction. As can be seen in Table 1, the best catalytic
activities were only obtained when the Suzuki reaction was performed at 100 ◦ C in dioxane with Cs2 CO3 .
On the other hand, one can easily observe in Table 1 that the efficiency of complexes is not the same for each
complex. For instance, the Suzuki reaction with catalyst 3 always afforded higher catalytic activity than that
with catalyst 4. It can also be seen in Table 1 that a typical reaction of p-bromoacetophenone and phenylboronic
acid indicated that the reaction rate depended on the alkyl substituents on the phosphorus atom, i.e. results of
the optimization studies clearly show that complex 3 having cyclohexyl (Cy) moiety on the phosphorus atom
is a more active and efficient catalyst leading to nearly quantitative conversions.
With the best conditions in hand, next we conducted further experiments to investigate the scope of the
Suzuki cross-coupling of catalysts 3 and 4 with various substrates, including aryl bromides and chlorides having
electron-withdrawing or electron-donating substituents (Table 1, entries 3–12). Encouraged by these results, we
attempted to study the reactivity between substituted aryl bromides and phenylboronic acid. In this case, the
reaction was slower compared to aryl iodides; therefore, we can easily conclude that the electronic nature of the
aryl bromides has an obvious influence on the coupling reactions (Table 1, entries 3–10). We also investigated
catalytic activity of the complexes in Suzuki coupling reactions of arylchlorides with phenylboronic acid (Table
1, entries 11 and 12). However, the highest conversion was up to 57% in the presence of Cs2 CO3 within 24 h in
dioxane at 100 ◦ C for catalyst 3 and elongation of the reaction time did not afford any further conversion. This
can be expected since it is well known that chlorides are often less reactive towards the Suzuki coupling reaction
under the same conditions used for the coupling of bromides and iodides.36 Encouraged by the good catalytic
activities obtained in the Suzuki–Miyaura cross-coupling reaction, we next extended our investigations to the
Mizoroki–Heck reaction, and the results are given in Tables 2 and 3. It is well known that among the different
methods used to form carbon–carbon bonds palladium-catalyzed carbon–carbon bond formation between aryl
halides and olefins has become an excellent tool for the synthesis of a variety of styrene derivatives.37−39
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Aydemir, Murat
