Synthesis of a Library of Iridium-Containing Dinuclear Complexes with Bridging PNNN and PNNP Ligands (BL), [LM(μ-BL)M‘L‘]BF₄. 1. Specific Synthesis of Isomeric Heterodinuclear Complexes with Switched Metal Arrangements

Specific synthesis of a series of Ir-containing homo- and heterodinuclear complexes with the PNNP (3,5-bis((diphenylphosphino)methyl)pyrazolato) and PNNN ligands (3-(diphenylphosphino)methyl-5-pyridylpyrazolato) is reported. Reaction of the PNNX-H precursors (X = P, N) with [Ir(cod)2]BF4 gives pale yellow precipitates, which are characterized as the cyclic dimers of the 1:1 adduct, [(μ-κ1(P): κ2(N,X)-PNNX-H)Ir(cod)]2(BF4)2 (X = P, N). In the case of the PNNN system, subsequent sequential treatment of the 1:1 adduct with NEt3 and a second metal reagent ([M(L)(cod)]BF4: M(L) = Rh(cod), Pd(allyl)) (reaction 1) gives [(cod)Ir(PNNN)M(L)]BF4, whereas the reversed addition of the reagents (reaction 2) furnishes [(L)M(PNNN)Ir(cod)]BF4, the regioisomer with the switched metal arrangement. Selective preparation of the heterodinuclear PNNP complexes [(cod)Ir(PNNP)M(L)]BF4 requires the addition according to reaction 1. In reaction 1 of the 1:1 dinuclear adduct of the PNNN system, deprotonation of the N−H part triggers interligand migration of the Ir(cod) fragment from the N,N site of one ligand to the P,N site of the other ligand to give [(cod)Ir(PNNN)]BF4, which reacts with the second metal fragment at the N,N site to furnish [(cod)Ir(PNNN)M(L)]BF4. On the other hand, reaction 2 involves dissociation of the dinuclear species into the mononuclear N,N-coordinated one, [(PNNN-H)Ir(cod)]BF4, and subsequent interaction at the free P moiety followed by deprotonation and coordination gives the other regioisomer. These intriguing transformations result from the unique coordination properties of Ir (cationic vs neutral, hard vs soft, 5- vs 4-coordination, N,N vs P,N chelation), which are controlled by the deprotonation−protonation procedure. As a result of the present study, a library for Ir-containing homo- and heterodinuclear Ir(I) complexes with the PNNP and PNNN ligands has been constructed.