Nickel promoted C–H, C–C and C–O bond activation in solution

• Published in: Inorganica Chimica Acta 2004-11, Vol.357 (13), p.4015-4023
• Main Authors: van der Boom, Milko E., Liou, Shyh-Yeon, Shimon, Linda J.W., Ben-David, Yehoshoa, Milstein, David
• Format: Article
• Language: English
• Subjects: Bond activation; Nickel; Pincer complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2004.06.002

Reaction of ethanolic NiI2with one equiv. of the phosphine {1-Et-2,6-(CH2PiPr2)2-C6H3} results in a selective metal insertion into the strong Ar–Et bond. This reaction proceeds with no intermediacy of activation of the adjacent sp3–sp3 ArCH2–CH3 bond. In contrast to this nickel promoted dealkylation process, reaction of {1,3,5-(CH3)3-2,6-(CH2PiPr2)2-C6H} with a stoichiometric amount of ethanolic NiI2 leads to selective C–H bond activation. Reaction of ethanolic NiI2 with one equiv. of the aryl–methoxy bisphosphine {1-OMe-2,6-(CH2PiPr2)2-C6H3 resulted in selective sp3–sp3 C–O bond activation. No products indicative of sp2–sp3 C–O bond activation were observed. Reaction of NiI2 with the PCP-ligand {1-Et-2,6-(CH2PiPr2)2-C6H3} (1) results in selective activation of the strong sp2–sp3 aryl–ethyl bond to afford the aryl–nickel complex [Ni{2,6-(CH2PiPr2)2-C6H3}I] (2), whereas reaction of NiI2 with {1,3,5-(CH3)3-2,6-(CH2PiPr2)2-C6H} (4) leads to the formation of the benzylic complex [Ni{1-CH2-2,6-(CH2PiPr2)2-3,5-(CH3)2-C6H}I] (5) by selective C–H bond activation. Thermolysis of 5 results in formation of [Ni{2,6-(CH2PiPr2)2-3,5-(CH3)2-C6H}I] (6) by activation of the sp2–sp3 C–C bond. The identity of the new 16-electron complexes 2 and 6 was confirmed by reaction of NiI2 with {1,3-(CH2PiPr2)2-C6H4} (3) and {1,3-(CH3)2-4,6-(CH2PiPr2)2-C6H2} (7), respectively, lacking the aryl–alkyl groups between the “phosphines arms” (alkyl=ethyl, methyl). Complexes 2 and 5 have been fully characterized by X-ray analysis. Nickel-based activation of an unstrained C–O single bond was observed as well. Reaction of the aryl–methoxy bisphosphine {1-OMe-2,6-(CH2PiPr2)2-C6H3} (8) with NiI2 results in the formation of the phenoxy complex [Ni{1-O-2,6-(CH2PiPr2)2-C6H3}I] (9) by selective sp3–sp3 C–O bond activation.