Coinage Metal Complexes of a Sterically Encumbered Anionic Pyridylborate.

Sterically loaded, anionic pyridine has been synthesized and utilized successfully in the stabilization of a homoleptic series of coinage metal complexes.  The treatment of [4-(Ph3B)-2,6-Trip2Py]K (Trip =2,4,6-iPr3C6H2) with CuBr(PPh3), AgCl(PPh3) or AuCl(PPh3) (Py = pyridine) afforded the corresponding [4-(Ph3B)-2,6-Trip2Py]M(PPh3) (M = Au, Ag, Cu) complexes, via salt metathesis, as isolable, crystalline solids.  Notably, these reactions avoid the facile single electron transfer chemistry reported with the less bulky ligand systems.  The X-ray structures revealed that they are two-coordinate metal adducts.  The M-N and M-P bond distances are longest in the silver and shortest in the copper adduct among the three group 11 family members.  Computational analysis revealed an interesting stability dependence on steric bulk of the anionic pyridine (i.e., pyridyl borate) ligand.  A comparison of structures and bonding of [4-(Ph3B)-2,6-Trip2Py]Au(PPh3) to pyridine and m-terphenyl complexes, {[2,6-Trip2Py]Au(PPh3)}[SbF6] and [2,6-Trip2Ph]Au(PPh3) are also provided.  The Au(I) isocyanide complex, [4-(Ph3B)-2,6-Trip2Py]Au(CNBut) has been stabilized using the same anionic pyridylborate illustrating that it can support other gold-ligand moieties as well.