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Palladium(ii) complexes supported by PBP and POCOP pincer ligands: a comparison of their structure, properties and catalytic activity†
Yazhou Ding,Qiang-Qiang Ma,Jiaxin Kang,Jie Zhang,Shujun Li
Dalton Transactions Pub Date : 11/08/2019 00:00:00 , DOI:10.1039/C9DT03954F
Abstract

A Pd(II) chloride complex supported by a Yamashita–Nozaki PBP pincer ligand, [C6H4-1,2-(NCH2PtBu2)2B]PdCl (1a), was synthesized. The structure, properties and catalytic activity of complex 1a were compared with those of the corresponding POCOP pincer complex [C6H3-2,6-(OPtBu2)2]PdCl (2a). It was found that the Pd centre in complex 1a is more electron rich and easier to be oxidized than that in complex 2a; complex 1a is a much better catalyst for Suzuki–Miyaura cross-coupling reactions than complex 2a. Starting from complexes 1a and 2a, two series of Pd(II) pincer complexes bearing a SH, BH4, [N with combining low line]CS, [N with combining low line]CSe or N3 covalent ligand, [C6H4-1,2-(NCH2PtBu2)2B]PdY (Y = SH, 1b; BH4; 1c; [N with combining low line]CS, 1d; [N with combining low line]CSe, 1e; and N3, 1f) and [C6H3-2,6-(OPtBu2)2]PdY (Y = SH, 2b; BH4, 2c; [N with combining low line]CS, 2d; [N with combining low line]CSe, 2e; and N3, 2f), were synthesized and fully characterized. Single crystal X-ray diffraction analysis indicated that the Pd centre is less tightly chelated in PBP pincer complexes. The strong σ-donor ability of the PBP pincer ligand has little influence on the structure of the covalent ligand possessing both σ-donor and π-acceptor properties. However, the stretching vibrational frequencies of [N with combining low line]CS, [N with combining low line]CSe and N3 ligands and the coordination mode of the BH4 ligand are significantly different in these two types of palladium pincer complexes.

Graphical abstract: Palladium(ii) complexes supported by PBP and POCOP pincer ligands: a comparison of their structure, properties and catalytic activity
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