vague similarity of the MALDI mass spectra of 2a–d and 3a–d
we suggested that the formation of pincer complexes from their
precursors might proceed in the gas phase as well.
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Therefore, in this communication we report for the first
time the solid-state reactivity of the coordinated benzothiazole-
substituted SCN-pincer ligands, namely, the formation of 5,5-
or 5,6-membered Pd(II) pincer complexes via elimination of HCl
upon heating of their solid metal precursors. To conclude the
results presented, benzothiazole-substituted SCN pincer ligands
1a–d were shown to form in the reaction with (PhCN)2PdCl2 in
solutions under kinetic control (20 ◦C) the complexes 2a–d which
were tentatively assigned to the dimeric m-chlorine bridged species
or monomeric complexes with bidentate structure depending on
the ligand nature. Similar reaction at elevated temperature and
over prolonged time in solution (thermodynamic control of the
reaction) resulted in the direct cyclometallation of the benzene
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3
core and formation of the corresponding k -SCN pincer products
3a–d. The intermediate complexes 2a–d or a homogeneous mixture
of the initial reactants could be easily transformed into the
pincer products using solid-phase synthesis which efficacy is
comparable with synthesis in solution in terms of the yields and is
advantageous from simplicity, short reaction times and even green
chemistry point of view dictating the development of solvent-free
processes or application of the alternative ones such as ionic liquids
water, and supercritical liquids.
To the best of our knowledge, till now the solid phase synthetic
approach has never been applied for the preparation of pincer
complexes. Taking into account the above data, this approach
obviously is not restricted to the above SCN-thiophosphoryl-
benzothiazole ligands and may be applied for the synthesis of a
range of pincer complexes known to possess high thermal and
chemical stability. Quite high reaction temperatures that were
needed to complete reactions affording pincer complexes in the
solid state apparently may be lowered using an inert support
similar to that for monocyclometallations.20–23 Furthermore, mi-
crowave assistance might be useful in optimization the process.
The investigations in this area are now in progress.
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24 (a) V. A. Kozlov, D. V. Aleksanyan, Yu. V. Nelyubina, K. A. Lyssenko,
E. I. Gutsul, L. N. Puntus, A. A. Vasil’ev, P. V. Petrovskii and I.
L. Odinets, Organometallics, 2008, 27, 4062; (b) V. A. Kozlov, D. V.
Aleksanyan, Yu. V. Nelyubina, K. A. Lyssenko, E. I. Gutsul, A. A.
Vasil’ev, P. V. Petrovskii and I. L. Odinets, Dalton Trans., 2009, 8657;
(c) V. A. Kozlov, D. V. Aleksanyan, Yu. V. Nelyubina, K. A. Lyssenko,
A. A. Vasil’ev, P. V. Petrovskii and I. L. Odinets, Organometallics, 2010,
29, 2054; (d) D. V. Aleksanyan, V. A. Kozlov, Yu. V. Nelyubina, K. A.
Lyssenko, L. N. Puntus, E. I. Gutsul, N. E. Shepel, A. A. Vasil’ev, P. V.
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25 To the best of our knowledge, formation of Pd(II) complex III (X =
NH) over 5 min in 93% isolated yield is the fastest procedure for the
pincer complex preparation known in the literature.
Acknowledgements
26 V. A. Kozlov, D. V. Aleksanyan, Yu. V. Nelyubina, K. A. Lyssenko, P.
V. Petrovskii, A. A. Vasil’ev and I. L. Odinets, Organometallics, 2011,
DOI: 10.1021/om101012r, ASAP paper.
The authors are grateful to the Russian Basic Research Foundation
(grant 08-03-00508) for financial support.
27 Synthesis of complexes 2a–d (general procedure): A solution of
(PhCN)2PdCl2 (65.7 mg, 0.171 mmol) in 4 mL of dichloromethane
was slowly dropwise added to a solution of the corresponding ligand
1a–d (0.171 mmol) in 4 mL of CH2Cl2. In 15 min, the resulting
precipitate of complex 2a–c was filtered off, washed with CH2Cl2 (10
mL) and Et2O (15 mL), and dried in vacuo. In the case of ligand 1d,
the homogeneous reaction mixture was evaporated to dryness and the
resulting residue was washed with ether (15 mL) and dried in vacuo
to give 2d as a dark-beige solid. 2a. Yield: 115.6 mg (98%). Anal.
Calc. for C25H18Cl2NPPdS2·CH2Cl2: C, 45.27; H, 2.92; N, 2.03. Found:
C, 45.51; H, 2.94; N, 2.07%. 2b. Yield: 101.0 mg (95%). Anal. Calc.
for C25H18Cl2NOPPdS2: C, 48.37; H, 2.92; N, 2.26. Found: C, 48.07;
H, 2.74; N, 2.18%. 2c. Yield: 92.0 mg (86%). Performing of the same
reaction in acetonitrile instead of dichloromethane provided complex
2c in a slightly lower yield of 77%. Anal. Calc. for C25H18Cl2NOPPdS2:
C, 48.37; H, 2.92; N, 2.26. Found: C, 48.04; H, 2.78; N, 2.13%. 2d.
Yield: 103.0 mg (97%). Anal. Calc. for C25H19Cl2N2PPdS2: C, 48.44; H,
3.09; N, 4.52. Found: C, 48.64; H, 3.20; N, 4.51%.
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