Mendeleev Commun., 2017, 27, 618–620 – 618 – Mendeleev Communications © 2017 Mendeleev Communications. Published by ELSEVIER B.V. on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences. Organic light emitting diode (OLED) technology, first intro- duced in 1987, 1 has undergone significant development in recent years. 2 In multilayered structures of small-molecule OLEDs, emitting layers are positioned between electron- and hole-trans- porting layers, and the electrode materials. Hole-transporting materials usually consist of polyaromatic amines bearing triaryl- amine moieties. 3,4 Thus, efficient methods for the synthesis of such triarylamines are constantly sought. Convenient precursors of triarylamines are obviously diaryl- amines. 5 Palladium mediated Buchwald–Hartwig amination of aryl halides is arguably the most versatile and efficient synthetic entry to them. 6–9 However, arylation of anilines with bulky aryl bromides proceeds rather sluggishly even with state-of-the-art catalysts. 10–12 Usually, high loadings of catalysts exceeding 1 mol% are required. Moreover, significant quantities of hard- to-separate diarylation products are also obtained, which demands for specific isolation procedures to purify diarylamines. Most of these hardens can be overcome using a new catalytic system based on expanded-ring N-heterocyclic carbene palladium complex (THP-Dipp)Pd(cinn)Cl [THP-Dipp is 1,3-bis(2,6-diisopropyl- phenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene; cinn is cinnamyl] and a solvent-free protocol for the Buchwald–Hartwig amination recently developed in our group. 5 In this contribution, we aimed at developing a highly selective and easily scalable monoarylation procedure operative at high substrate concentrations (solvent-free conditions), low catalyst loadings (0.1 mol%), and equimolar (no excess of aryl halide or aniline) amounts of the coupling partners. It was previously reported that carbene and phosphine palladium complexes bearing indenyl ligands (L)Pd(3-Bu t Ind)Cl (3-Bu t Ind is 3-tert-butyl- 1-indenyl) exhibited higher catalytic activities than their cinnamyl counterparts. 13 Presumably, this was due to easier activation of the precatalyst in case of indenyl derivatives. Therefore, we performed comparative catalytic studies of cinnamyl and indenyl palladium complexes in the Buchwald–Hartwig amination. Cinnamyl-containing complex 1 was prepared as outlined in Scheme 1. † The reaction between cyclic amidinium salt (THP-Dipp)HBF 4 and palladium source [Pd(3-Bu t Ind)Cl] 2 afforded new complex (THP-Dipp)Pd(3-Bu t Ind)Cl 2 (Scheme 2). 13 Catalytic tests of the Buchwald–Hartwig amination were per- formed using equimolar amounts of arylamine and aryl bromide, 0.1 mol% of palladium complexes, 1.2 equiv. of NaOBu t as a Solvent-free Buchwald–Hartwig amination with low palladium loadings Gleb A. Chesnokov, a Pavel S. Gribanov, b Maxim A. Topchiy, b Lidiya I. Minaeva, c Andrey F. Asachenko, b,c Mikhail S. Nechaev,* a,b Evgeniya V. Bermesheva b,d and Maxim V. Bermeshev* b a Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation. E-mail: m.s.nechaev@org.chem.msu.ru b A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 119991 Moscow, Russian Federation. E-mail: bmv@ips.ac.ru c Peoples Friendship University of Russia (RUDN University), 117198 Moscow, Russian Federation d I. M. Sechenov First Moscow State Medical University, 119991 Moscow, Russian Federation DOI: 10.1016/j.mencom.2017.11.027 Ar 1 –Br Ar 2 –NH 2 + (0.1 mol%, Dipp = 2,6-Pr 2 C 6 H 3 ) NaOBu t , 110 °C Ar 1 H N Ar 2 Ph N N Dipp Pd Dipp Cl 11 examples i A highly efficient ‘green’ solvent-free monoarylation of primary anilines with aryl bromides mediated by the expanded-ring N-heterocyclic carbene palladium complex (THP-Dipp)- Pd(cinn)Cl [THP-Dipp is 1,3-bis(2,6-diisopropylphenyl)- 3,4,5,6-tetrahydropyrimidin-2-ylidene; cinn is cinnamyl] can be performed at low catalyst loadings (0.1 mol%) to provide excellent yields and remarkable selectivities for various substrates. NH 2 Pr i Pr i HC(OEt) 3 AcOH, 180 °C 85% DIPEA, 100 °C 86% i, NaHMDS, Et 2 O ii, [Pd(cinn)Cl] 2 34% Ph N N Dipp Pd Dipp Cl N Pr i Pr i N H Pr i Pr i Br(CH 2 ) 3 Br N N Dipp Dipp Br H 2 O–acetone 98% NaBF 4 N N Dipp Dipp BF 4 (THP-Dipp)Pd(cinn)Cl (THP-Dipp)HBF 4 Dipp = 2,6-Pr 2 C 6 H 3 1 i Scheme 1 † Complex (THP-Dipp)Pd(cinn)Cl 1. A 10 ml Schlenk flask equipped with a magnetic stirring bar and rubber septum was charged with (THP-Dipp)- HBF 4 14 (492 mg, 1 equiv.) and dry diethyl ether (5 ml). Then, a solution of NaHMDS in THF (2.0 M, 0.5 ml) was added. The mixture was stirred at room temperature for 1 h, then it was transferred to another 10 ml Schlenk flask containing a suspension of [Pd(cinn)Cl] 2 (258 mg, 0.5 equiv.) in dry diethyl ether (2 ml) and stirred overnight. The mixture was filtered through Celite ® pad and the filtrate was discarded. The pad was washed with dichloromethane to give dark yellow solution, which was evaporated to dryness and purified by column chromatography (CH 2 Cl 2 and CH 2 Cl 2 – MeOH, 10 : 1) to give 226 mg (34%) of complex 1 as a bright yellow powder. Analytical data were consistent with those previously reported. 14