Terphenyl ligands Group 17 derivatives

In spite of the attention focused on these bulky aryl substituents, especially in main-group chemistry, aryl ligands in which crowding is caused by the presence of ortho-aryl substituents formerly received little attention. In contrast, related terphenyl-substituted phenolate derivatives (e.g., -OC6H3-2,6-Ph2) of the early transition metals have been studied for many years, and zinc terphenolate derivatives have attracted attention (vide infra). A small number of similar aryl thiolate derivatives of transition metals (e.g., Mo, Fe, and Rh) have been characterized and published (vide infra). In addition, the related ligand -C6H2-2,4,6-Ph3 (Triph) had been employed as a ring substituent in bulky porphyrins.24... 

Tetra-substitution at the same meso positions of the porphyrin core by bulky ort/ru-terphenyl groups conferred to the macrocycle an overall macro-disk-like shape ((26) M = 2H, Cu). " In this case, both the free-base and the copper complex exhibited an enantiotropic Colt phase from room temperature up to 59 °C for the ligand and 57 °C for the copper complex. The comparison between these macrocycles with the related phthalocyanine derivatives confirmed the perturbing role of the side groups on the stability of the Colh phase, consequent to a disturbed molecular stacking. X-Ray diffraction suggested that the columns would be constituted by the stacking of dimer units, with a periodicity of about 9.5 A. 

Br > OTf Cl. Thus, sequential cross-coupling of halotriflates provides unsymmetrical terphenyls when two leaving groups with different reactivity are selected. An alternative method is a stepwise, double crosscoupling of halophenol derivatives (Eq. 40). However, care must be taken because the phosphine ligand changes the order of reactivity... 

The exploration of the chemistry of terphenyl derivatives of the group 3 metals is due mainly to Rabe and coworkers [13-18]. The ligands used were of the formula C6H3-2,6-Ar2 (Ar = CeHs, C6H2-2,4,6-Mc3, 1-naphthyl, or 3-MeO-C6H4). The halide complexes 1-3 could readily be obtained by simple salt metathesis from the reaction of the terphenyl lithium with anhydrous metal trichlorides MCI3 (M = Sc or Y) in THF at room temperature [13,14], The yttilum complexes 2 and 3 were isolated in moderate yield (ca. 50%) however, only a low yield of the scandium complex 1 could be obtained, most likely because of C-H bond activation as indicated by NMR spectroscopy. These metatheses reactions did not proceed in aromatic solvents or hexanes probably as a result of the low solubility of the reactants in these media. Complex 1 decomposes slowly in THF solution, while 2 and 3 are considerably more stable. 

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