Diverse C–C Bond-Forming Reactions of Bis(carbene)platinum(II) Complexes

• Autores: Rachel C. Klet, Jay A. Labinger, John E. Bercaw
• Localización: Organometallics, ISSN 0276-7333, Vol. 31, Nº. 18, 2012, págs. 6652-6657
• Idioma: inglés
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• Resumen

  • The platinum(0) complex Pt(PPh3)4 catalyzes coupling of the carbene ligands of (CO)5Cr{C(OMe)(p-MeOC6H4)} (1). The stable bis(carbene)platinum(II) complexes Cl2Pt{C(OMe)(Me)}2 (3), Br2Pt{C(OMe)(Me)}2 (4), and Cl2Pt{C(OiPr)(Me)}2 (5) can be induced to undergo C–C coupling reactions by several means. Reduction of 3–5 to platinum(0) with cobaltocene results in formation of internal olefins, (E/Z)-2,3-dimethoxybut-2-ene (6) or (E/Z)-2,3-diisopropoxybut-2-ene (7). Reaction of 3–5 with PPh3 yields terminal olefins, 2,3-dimethoxybut-1-ene (13) or 2,3-diisopropoxybut-1-ene (15), along with Cl2Pt(PPh3)2 (12) or Br2Pt(PPh3)2 (14). In contrast, addition of pyridine to 3–5 does not effect C–C coupling; instead, the acyl complexes cis-Cl(py)Pt(COMe){C(OMe)(Me)} (8), cis-Br(py)Pt(COMe){C(OMe)(Me)} (9), and cis-Cl(py)Pt(COMe){C(OiPr)(Me)} (10) are obtained, with concomitant formation of alkyl halide. Possible mechanistic pathways for C–C bond formation are discussed, as well as explanations for the different reactivities observed for pyridine and PPh3.