RESUMEN
The ambi-valent character of the P-I bond in iodophosphonium complexes ensures that it can be electrophilic at either P or I. Herein, we use an ensemble of computational tools and methodologies to probe the nature of this ambi-valent bond. Geometric and atomic electron population analyses yielded strong trends between the electron donating ability of the phosphine and the strength and polarity of the P-I bond. Quasi-atomic orbital analysis demonstrated the near homo-polarity of the P-I bond, and energy decomposition analysis calculations demonstrated the ability to tune the polarization of the bond with only mild changes in secondary structural features. Finally, the ambi-valent nature of the P-I bond was demonstrated to follow hard-soft considerations in reactions with nucleophiles, with harder nucleophiles preferentially forming products of addition to P and softer nucleophiles to I.
RESUMEN
Complexes of copper and 1,10-phenanthroline have been utilized for organic transformations over the last 50 years. In many cases these systems are impacted by reaction conditions and perform best under an inert atmosphere. Here we explore the role the 1,10-phenanthroline ligand plays on the electronic structure and redox properties of copper coordination complexes, and what benefit related ligands may provide to enhance copper-based coupling reactions. Copper(II) triflate complexes bearing 1,10-phenanthroline (phen), ([Cu(phen)2(OTf)]OTf, 1) and oxidized derivatives of phen including [Cu(edhp)2](OTf)2 (2), [Cu(pdo)2](OTf)2 (3), [Cu(dafo)2](OTf)2 (4) were prepared and characterized. X-ray crystallographic data show these related ligands subtly impacted the coordination geometry of the copper(II) ion. Complexes 1-3 had only incremental changes to the redox properties of the copper ions, complex 4 showed a drastically different redox potential affording a remarkably air stable copper(I) complex. These complexes 1-4 were then used to catalyze the C-N bond forming cross coupling between imidazole and various boronic acid substrates, where the increased stability of the copper(I) species in complex 4 appears to better support these CEL cross couplings.