Evaluating 1,1′-Bis(phosphino)ferrocene Ancillary Ligand Variants in the Nickel-Catalyzed C–N Cross-Coupling of (Hetero)aryl Chlorides

详细信息    查看全文

• 作者：Jillian S. K. Clark ; Christopher N. Voth ; Michael J. FergusonMark Stradiotto
• 刊名：Organometallics
• 出版年：2017
• 出版时间：February 13, 2017
• 年：2017
• 卷：36
• 期：3
• 页码：679-686
• 全文大小：565K
• ISSN：1520-6041

文摘

Previous reports in the literature have established the utility of 1,1′-bis(diphenylphosphino)ferrocene (DPPF, L^Ph) in the nickel-catalyzed cross-coupling of (hetero)aryl electrophiles with primary or secondary amines. In an effort to evaluate the effect of varying the PR₂-donor groups on catalytic performance in such transformations, a series of 10 structurally varied 1,1′-bis(bis(alkyl/aryl)phosphino)ferrocene ancillary ligands (L^X) were systematically examined in selected competitive test cross-couplings of (hetero)aryl halides with furfurylamine, morpholine, and indole employing Ni(COD)₂/L^X catalyst mixtures. In addition to the excellent performance observed for the parent ligand L^Ph in a number of the test transformations explored, selected dialkylphosphino (e.g., DiPPF, L^iPr) and meta-disubstituted diarylphosphino variants of L^Ph also proved highly effective. In particular, the electron-deficient ligand variant L^CF3 featuring 3,5-bis(trifluoromethyl)phenyl groups on phosphorus was found to exhibit superior catalytic performance relative to L^Ph in most of the test transformations involving the N-arylation of indole. Our efforts to prepare Ni(II) precatalysts of the type (L^X)Ni(o-tolyl)Cl, in analogy with known (L^Ph)Ni(o-tolyl)Cl, by employing several literature methods met with mixed results. Whereas (L^iPr)Ni(o-tolyl)Cl was prepared straightforwardly and was crystallographically characterized, the use of L^CF3 or ligands featuring tert-butyl (L^tBu), o-tolyl (L^o-tol), or 4-methoxy-3,5-dimethylphenyl (L^OMe) groups on phosphorus under similar conditions resulted in poor conversion to product and/or the formation of poorly soluble materials, highlighting the limitations of this commonly used precatalyst design.