Transition Met Chem
Pt(1)–Cl(2) and Pt(1)–Cl(2) bond lengths are in the normal
pre-catalysts in the Suzuki coupling and Heck reactions of
aryl halides. The Pt(II) iminophosphine 1b and 2b system
exhibited no catalytic activity. Only the palladium com-
plexes were found to show catalytic activity in both the
Suzuki and Heck coupling reactions of aryl bromides. In
both cases, the catalytic activities of complexes 1a and 2a
were found to be higher in the reactions of aryl bromides
with electron-withdrawing substituents than those with
electron-releasing substituents (Table 5).
ranges. The Pt–Cl bond length trans to the P atom
˚
(2.3639(14) A) is longer than that trans to the N atom
˚
(2.2901(15) A) owing to the stronger trans influence of a
tertiary phosphine with respect to an imine. The bond angle
at the Pt(1) atom exhibits only minor deviations from a
right angle. The torsion angle Pt(1)–P(1)–C(9)–C(8) =
44.8(5)° indicates that the =CHC6H4– unit lies above the
PtCl2(P,N) plane. These deviations have been observed in
similar complexes with iminophosphine ligands [34–36].
Suzuki reaction catalysis
Supplementary materials
The palladium complexes 1a and 2a were tested as catalysts
in the Suzuki reaction of aryl bromides with boronic acid.
Following optimization experiments, we found that the use
of 0.01 mmoL the palladium complexes (1a, 2a) with
Cs2CO3 as the base at 60 and 80 °C in dioxane appeared to be
best, respectively. We initially tested the catalytic activity of
the complexes (1a, 2a) for the coupling of p-bromobenzal-
dehyde with phenylboronic acid and the control experiments
showed that the coupling reaction does not occur in the
absence of the catalyst. Under these conditions, p-bromo-
benzaldehyde, p-bromobenzene, p-bromoanisole and
p-bromotoluene react cleanly with phenylboronic acid in
high yields (Table 4).
Supplementary data and figures for complexes 1b and 2b
are available from the IUCR electronic archives (Refer-
ences: GO2028 and NR2014). Crystallographic data for the
structural analysis have been deposited with the Cambridge
Crystallographic Data Centre, CCDC Nos. 851988 and
919298 for complexes 1a and 2b, respectively. Copies of
this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK, fax: ?44-1223-336033, e-mail: deposit@ccdc.cam.ac.
Acknowledgments Financial support from the University of Cape
Town, the National Research Foundation of South Africa, and a
donation of metal salts from the Anglo Platinum Corporation is
gratefully acknowledged.
Heck reaction catalysis
The rate of coupling is dependent on a variety of param-
eters such as temperature, solvent, base and catalyst load-
ing. We found that the use of 0.01 mmoL catalyst, 2
equivalents K2CO3 in DMF at 80 °C for both 1a and 2a,
led to the best conversions. We initially tested the catalytic
activities of 1a and 2a for the coupling of p-bromobenz-
aldehyde with styrene. A control experiment indicated that
the coupling reaction did not occur in the absence of 1a and
2a. Under the determined reaction conditions, a wide range
of aryl bromides bearing electron-donating and electron-
withdrawing groups reacted with styrene, affording the
coupled products in excellent yields. Electron-deficient
bromides gave higher conversions.
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The coordination behavior of ligands 1 and 2 toward Pd(II)
and Pt(II) is described. Single crystal X-ray diffraction
revealed that in complexes 1b and 2b, there is a slightly
distorted square-planar geometry around the platinum
metal center and the Pt–P distances are within the expected
ranges. We have also demonstrated the application of
palladium complexes of these iminophosphine ligands as
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