Rational Design of Rhodium Complexes Featuring κ 4 ‐ N , N , N , N ‐ and κ 5 ‐ N , N , N , P , P ‐Bis(imino)pyridine Ligands

The addition of aminoalkyl‐substituted 2,6‐bis(imino)pyridine (or pyridine diimine, PDI) ligands to [(COD)RhCl] 2 (COD = 1,5‐cyclooctadiene) resulted in the formation of rhodium monochloride complexes with the general formula ( N PDI)RhCl ( N PDI = i Pr 2 NEt PDI or Me 2 NPr PDI). The investigation of ( i Pr 2 NEt PDI)RhCl and ( Me 2 NPr PDI)RhCl by single‐crystal X‐ray diffraction verified the absence of amine arm coordination and a pseudo square‐planar geometry about rhodium. Replacement of the chloride ligand with an outer‐sphere anion was achieved by adding AgBF 4 directly to ( i Pr 2 NEt PDI)RhCl to form [( i Pr 2 NEt PDI)Rh][BF 4 ]. Alternatively, this complex was prepared by chelate addition following the salt metathesis reaction between AgBF 4 and [(COD)RhCl] 2 . Using the latter method, both [( N PDI)Rh][BF 4 ] complexes were isolated and found to exhibit κ 4 ‐ N , N , N , N ‐PDI coordination regardless of arm length or steric bulk. In contrast, the metallation of P PDI chelates featuring alkylphosphane imine substituents ( P PDI = Ph 2 PEt PDI or Ph 2 PPr PDI) resulted in the formation of cationic complexes featuring κ 5 ‐ N , N , N , P , P ‐PDI coordination in all instances, [( P PDI)Rh][X] (X = Cl, BF 4 ). Adjusting the metallation stoichiometry allowed the preparation of [( Ph 2 PPr PDI)Rh][(COD)RhCl 2 ], as validated by multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction.