Arylation ligand

The field of alkyl and aryl Co complexes in low formal oxidation states has been extensively studied, and is frequently associated with cluster chemistry.92 Alkyl and aryl ligands, with or without additional functionality, are often co-ligands with tt acceptors such as carbonyls and/or phosphines, e.g., (MeOCOCH2)Co(CO)3(PPh3).93 A simple example of a cluster is (RC)Co3(CO)9, where the triangular Co(CO)3 3 moiety is capped by the 73-alkyl fragment, which occupies the apex of a distorted Co3C tetrahedron. 

III. Complexes with R2Sb-SbR2 and R2Sb (R = alkyl, aryl) Ligands. 99... 

As a ligand class, the aryls have usually been treated in the same context as the alkyls. In 1991, however, a review,8 which dealt exclusively with aryl transition metal complexes, drew attention to their often unique structures and reactivity. It was also apparent that the influence of steric properties of aryl ligands had not been extensively investigated for transition-metal complexes. The bulkiest aryl ligand to be widely employed with these metals... 

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... 

Terphenyl derivatives of boron were originally synthesized with the object of preparing compounds with B-B triple bonds. It was thought that these aryl ligands would be effective in the stabilization of triple bonds in a similar manner to their success in the stabilization of double bonds. For example, a B-B triple-bonded boron analogue of a substituted acetylene might be accessible by reduction of an ArBX2 or l,2-dimethoxydiborane(4) species as shown by Eq. (3). 

The complexes discussed in the review generally comprise five- or six-coordinate complexes containing tr-alkyl or aryl ligands. This contrast with transition metal organometallic porphyrin complexes which provide, in addition to cr-bonded... 

The ylides and imides are present as monomers, and the bismuth center adopts a distorted tetrahedral geometry. In contrast, the structural properties of the bismuth oxides vary widely depending on the aryl ligands attached to the bismuth center the oxides exist as hydrates, dimers, or polymers in solution and in the solid state. X-ray structural analysis of an oxide dimer revealed that the bismuth center has a distorted, trigonal bipyramidal geometry with the two oxygen atoms at the apical and equatorial positions [47, 48]. 

Aryl ligands bearing a methyl group at the ortho position and/or an electron-withdrawing group at the para position dramatically enhance the overall rate of oxidation. 

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