Chapter FiveTERPHENYL LIGANDS AND COMPLEXES

1. INTRODUCTION

The syntheses described in this chapter concern a range of ligands that feature sterically encumbering terphenyl substituents. The terphenyl groups that are of interest here are of the type ─C6H3‐2,6‐Aryl2, in which two aryl rings are attached to a central phenyl ring in positions that are meta with respect to each other. The attached rings also have alkyl substituents at their ortho positions (and often at their para positions as well), with the result that they are constrained to maintain an almost perpendicular orientation with respect to the central phenyl ring, as shown in Scheme 1.

Skeletal formulas of 3 bulky terphenyl substituents: –C6H3-2,6(C6H3-2,4,6-Me3) {–C6H3-2,6-Mes6}, –C6H3-2,6(C6H3-2,6-Pri2) {–C6H3-2,6-Dipp2}, and –C6H3-2,6(C6H3-2,4,6-Pri3) {–C6H3-2,6-Trip2}.

Scheme 1. Drawings of the three bulky terphenyl substituents employed in compounds that are in this chapter, illustrating the wedge‐shaped space between the flanking aryl rings.

In effect, a wedge‐shaped space is generated that is shielded by the substituted flanking aryl rings. Attachment of such a ligand to a reactive center via the ring carbon atom between the flanking rings (i.e. the ipso carbon of the central ring) often provides sufficient protection from further attack, such that the compound becomes stable enough to isolate. The bulky terphenyl ligands and their derivatives have been the subjects of a number of reviews dealing with aspects of their applications in general,1 main group,2 and transition metal3, 4 chemistry. ...

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