Cyclopalladation of ferrocene tertiary amines: Experimental, theoretical, and reactive studies toward Suzuki-Miyaura cross- coupling reaction Hengyu Qian a , Tongyan Zhang a , Zhigang Yin a, * , Quanling Wang a , Qi Yuan a , Rui Jiang a , Shihai Yan b, ** , Xile Zhao a a Key Laboratory of Surface & Interface Science of Henan, School of Material & Chemical Engineering, Zhengzhou University of Light Industry, Zhengzhou, 450002, PR China b College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao, 266109, PR China article info Article history: Received 29 May 2016 Received in revised form 19 September 2016 Accepted 3 October 2016 Available online 3 October 2016 Keywords: Tertiary amines Palladacycle Suzuki-Miyaura abstract The ferrocene tertiary amines of general formula [(h 5 eC 5 H 5 )Fe(h 5 eC 5 H 4 )eCH 2 N(CH 3 )eCH 2 eC(R)] CHeC 6 H 5 ,R]H(3a) and R]CH 3 (3b)] were conveniently prepared from the corresponding ferroceny- limines [(h 5 eC 5 H 5 )Fe(h 5 eC 5 H 4 )eCH 2 N]CHeC(R)]CHeC 6 H 5 ,R]H(1a) and R]CH 3 (1b)] in two steps. Metalation of 3a, 3b with Li 2 PdCl 4 and CH 3 COONa, followed by treatment with PPh 3 , gave the ortho palladium (II) complexes Pd{[(h 5 eC 5 H 5 )Fe(h 5 eC 5 H 3 )eCH 2 N(CH 3 )eCH 2 eCH]CHeC 6 H 5 ]}ClPPh 3 (5a) and Pd{[(h 5 eC 5 H 5 )Fe(h 5 eC 5 H 3 )eCH 2 N(CH 3 )eCH 2 eC(CH 3 )]CHeC 6 H 5 ]}ClPPh 3 (5b), respectively. However, Palladation of ferrocenylimines 1a and 1b afforded the heteroannular palladium (II) complexes. This protocol proved that the isomerism around the C]N moiety might indicate that the palladium entered into the lower ferrocene ring, giving the heteroannular palladium (II) complexes. Additionally, theoretical studies indicated that the CeH bond in the substituted ferrocene ring for the ligands 3a and 3b was prior to metalation. As for the catalyst, the palladacycles showed high efficiency in Suzuki-Miyaura cross- coupling reaction using low catalyst loading 0.1 mol%. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The utility of transition metals to catalyze cross-coupling re- actions has been widely recognized as an efficient strategy for the construction of carbon-carbon bonds [1]. Especially palladium catalysis has dominated this field and shown wide applicability in synthesis of natural products [2,3], pharmaceuticals and fine chemicals [4,5], as well as in optoelectronic materials synthesis [6,7]. Following seminal work on the cyclopalladated complexes derived from azobenzene by Cope et al., in 1965 [8,9], the palla- dium(II) complexes continue to be of immense interest in organ- ometallic chemistry. In particular, the ortho-palladated derivatives are always obtained in metalation of ferrocene compounds, where the palladium-carbon bond is stabilized by the intramolecular co- ordination of donor atoms (N, P, As, O, Se, or S) (Scheme 1a). Meanwhile, they can provide more active palladium species than traditional palladium source for performing cross-coupling re- actions [10e13]. In contrast to these complexes, the heteroannular cyclopalladated complexes by using a carbon atom in the unsub- stituted cyclopentadiene ring have not been studied extensively (Scheme 1b). In 2005, Moyano pioneered the cyclopalladation of 4- ferrocenyl-1,3-oxazoline compounds that led to the heteroannular palladated complexes [14]. Meanwhile, we and others have re- ported the unusual heteroannular palladation of Schiff bases derived from a-ferrocenylethylamine [15e17]. We have also dis- closed that ferrocenylimines of general formula [(h 5 eC 5 H 5 ) Fe(h 5 eC 5 H 4 )eCH 2 N]CHeC(R)]CHeC 6 H 5 ,R]H or CH 3 ] can be employed to afford the heteroannular palladated complexes in cyclometalation and their application in Suzuki-Miyaura reaction has been examined [18]. It would therefore be interesting to extend metalation of ferrocenyl ligands to generate the palladated com- plexes in which the CeH bond metalation was preferential with the unsubstituted cyclopentadiene ring and their application in cross- coupling reactions, which unfortunately remains highly desirable. * Corresponding author. ** Corresponding author. E-mail addresses: yinzg2014@126.com (Z. Yin), yansh@qibebt.ac.cn (S. Yan). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2016.10.006 0022-328X/© 2016 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 824 (2016) 124e130