10.1002/chem.201903379
Chemistry - A European Journal
FULL PAPER
BH3-protected resin-bound potassium phosphides were used in the next
step.
Acknowledgements
Financial support for this work was provided by the University of
St Andrews, the Engineering and Physical Sciences Research
Council (Award Reference 1658187). We thank Dr. D. M.
Dawson for solid-state NMR measurements and Anja Simmula
for the ICP-OES measurements.
Step 2: A previously synthesized BH3-protected resin-bound potassium
phosphide (K·2a, 1.57 mmol, 1.0 equiv.), (K·2b, 0.24 mmol, 1.0 equiv.),
(K·2c, 0.28 mmol, 1.0 equiv.) or (K·2d, 0.22 mmol, 1.0 equiv.) was
swollen in THF (10 mL) and cooled to -78 °C. A 2-(chloromethyl)-6-
(phosphinomethyl)pyridine-borane (1a-h,1.1 equiv.) was azeotropically
dried with toluene (3x5 mL), dissolved in 10 mL THF and added to the
resin at -78 °C under gentle stirring to avoid mechanical abrasion. The
mixture was left with occasional stirring and allowed to warm up to room
temperature overnight. The reaction was monitored using gel-phase 31P
NMR and was allowed to react until full conversion was observed. Next,
the supernatant was removed and the resin was washed three times with
THF (10 mL) followed by three times with Et2O (10 mL) and dried in
vacuo yielding a pale yellow resin-bound PNP borane adduct (3a-n).
Keywords: catalyst immobilization• hydrogenation• N,P ligands•
pincer ligands• solid-phase synthesis
[1]
a) C. J. Moulton, B. L. Shaw, J. Chem. Soc., Dalton Trans. 1976, 1020;
b) G. van Koten, K. Timmer, J. G. Noltes, A. L. Spek, J. Chem. Soc.,
Chem. Commun. 1978, 250; c) J. I. van der Vlugt, J. N. Reek, Angew.
Chem. Int. Ed. 2009, 48, 8832; Angew. Chem. 2009, 121, 8990; d) C.
Gunanathan, D. Milstein, Chem. Rev. 2014, 114, 12024; e) G. A.
Filonenko, R. van Putten, E. J. M. Hensen, E. A. Pidko, Chem. Soc.
Rev. 2018, 47, 1459; f) H. Valdés, M. A. García-Eleno, D. Canseco-
Gonzalez, D. Morales-Morales, ChemCatChem 2018, 10, 3136; g) L.
Alig, M. Fritz, S. Schneider, Chem. Rev. 2019, 119, 2681; h) K. Junge,
V. Papa, M. Beller, Chem. Eur. J. 2019, 25, 122.
Step 3: A resin-bound PNP borane adduct 3a-n synthesized in the last
step was swollen in 10 mL of diethyl amine and heated to 50 °C
overnight with occasional stirring to avoid mechanical abrasion of the
resin. The reaction was monitored using gel-phase 31P NMR and was
allowed to react until full conversion was observed. Next, the mixture was
cooled to room temperature and the supernatant was removed. The resin
was washed with three portions of THF (10 mL) followed by three
portions of Et2O (10 mL) and dried in vacuo yielding a pale yellow resin-
bound PNP pincer ligand (L1-L14).
[2]
[3]
[4]
E. Peris, R. H. Crabtree, Chem. Soc. Rev. 2018, 47, 1959.
M. Asay, D. Morales-Morales, Dalton Trans. 2015, 44, 17432.
a) S. A. M. Smith, P. O. Lagaditis, A. Lupke, A. J. Lough, R. H. Morris,
Chem. Eur. J. 2017, 23, 7212; b) A. Zirakzadeh, K. Kirchner, A. Roller,
B. Stöger, M. Widhalm, R. H. Morris, Organometallics 2016, 35, 3781.
E. Kinoshita, K. Arashiba, S. Kuriyama, Y. Miyake, R. Shimazaki, H.
Nakanishi, Y. Nishibayashi, Organometallics 2012, 31, 8437.
P. E. Goudriaan, P. W. N. M. van Leeuwen, M.-N. Birkholz, J. N. H.
Reek, Eur. J. Inorg. Chem. 2008, 2939.
General Procedure for the Synthesis of Resin-Bound complexes C1-
C14
[5]
[6]
[7]
[8]
A previously synthesized resin-bound PNP pincer ligand (L1-L14, ~80-
170 mg, 1.0 equiv.) and [Ru(HCl(PPh3)3CO] (1.1 equiv.) were weighed
into a Schlenk tube. The mixture was suspended in THF (10 mL) and
heated to 60 °C under gentle stirring. The reaction mixture was left at
60 °C with occasional stirring to avoid mechanical abrasion of the resin
and the progress of the reaction was monitored by gel-phase 31P NMR.
Once full complexation of the resin-bound PNP ligand was observed, the
mixture was cooled to room temperature and the supernatant was
removed. The resin-bound complex was washed with three portions of
THF (10 mL), three portions of CH2Cl2 (10 mL) followed by three portions
of Et2O (10 mL). After drying in vacuo a yellow to brown resin-bound Ru-
PNP complex (C1-C14) was obtained.
D. Benito-Garagorri, E. Becker, J. Wiedermann, W. Lackner, M. Pollak,
K. Mereiter, J. Kisala, K. Kirchner, Organometallics 2006, 25, 1900.
a) R. B. Merrifield, J. Am. Chem. Soc. 1963, 85, 2149; b) D. Obrecht, J.
M. Villalgordo, Introduction, Basic Concepts and Strategies, in Solid-
Supported Combinatorial and Parallel Synthesis of Small-Molecular-
Weight Compound Libraries, Elsevier Science ltd., Oxford, 1998, pp. 1-
184; c) S. E. Booth, C. M. Dreef-Tromp, P. H. H. Hermkens, J. A. P. A.
de Man, H. C. J. Ottenheijm, Survey of Solid-Phase Organic Reactions,
in Combinatorial Chemistry (Ed.: G. Jung), Wiley-VCH Verlag GmbH,
Weinheim, 1999, pp. 35-76.
[9]
a) K. Burgess, Solid-Phase Organic Synthesis, John Wiley & Sons, Inc.,
New York, 2002; b) M. C. Samuels, B. H. G. Swennenhuis, P. C. J.
Kamer, Solid‐phase Synthesis of Ligands, in Phosphorus(III) Ligands in
Homogeneous Catalysis: Design and Synthesis (Eds.: P. C. J. Kamer,
P. W. N. M. v. Leeuwen), John Wiley & Sons, Ltd, Chichester, 2012, pp.
463-479.
General Procedure for Ru-catalyzed Ester Hydrogenation
The hydrogenation experiments were performed in a stainless steel
autoclave charged with an insert suitable for up to 12 reaction vessels
(2 mL) including Teflon mini stirring bars. Inside a glove box, a reaction
vessel was charged with a resin-bound Ru-PNP complex C1-C14 (~7 mg,
5.0 μmol, 1.0 mol%). To the reaction vessel 0.5 mL of a stock solution of
KOtBu (10 mol%) in THF was added and the mixture was stirred for 5
minutes. Next, 0.5 mL of the substrates S1-S12 (0.5 mmol) and the
internal standard dodecane (50 mol%) dissolved in THF were added.
Subsequently, the autoclave was purged three times with 10 bar of argon
gas and the insert loaded with reaction vessels was transferred into the
autoclave. Next, the autoclave was purged three times with 10 bar of H2
and then pressurized (30-50 bar) and heated to the desired temperature
(40-100 °C). The reaction mixtures were gently stirred at 450 rpm for 16-
24 hours. The autoclave was cooled to room temperature, depressurized
and the conversion was determined by GC-FID.
[10] a) D. J. Cole-Hamilton, R. P. Tooze, Homogeneous Catalysis
-
Advantages and Problems, in Catalyst Separation, Recovery and
Recycling: Chemistry and Process Design (Eds.: D. J. Cole-Hamilton, R.
P. Tooze), Springer Netherlands, Dordrecht, 2006, pp. 1-8; b) A. E. C.
Collis, I. T. Horváth, Cat. Sci. Technol. 2011, 1, 912-919; c) R. Konrath,
F. J. L. Heutz, P. C. J. Kamer, D. Vogt, Catalyst Separation, in
Contemporary Catalysis (Eds.: P. C. J. Kamer, D. Vogt, J. W. Thybaut),
The Royal Society of Chemistry, 2017, pp. 711-747.
[11] M. A. Goni, E. Rosenberg, S. Meregude, G. Abbott, J. Organomet.
Chem. 2016, 807, 1.
[12] H. K. Lo, I. Thiel, C. Coperet, Chem. Eur. J. 2019, 25, 9443.
[13] X. Wang, E. A. P. Ling, C. Guan, Q. Zhang, W. Wu, P. Liu, N. Zheng, D.
Zhang, S. Lopatin, Z. Lai, K.-W. Huang, ChemSusChem 2018, 11,
3591.
[14] J. Brünig, Z. Csendes, S. Weber, N. Gorgas, R. W. Bittner, A. Limbeck,
K. Bica, H. Hoffmann, K. Kirchner, ACS Catal. 2018, 8, 1048.
This article is protected by copyright. All rights reserved.