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

Abstract

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.

Metal–Pyrazole Bifunction in Half‐Sandwich CN Chelate Iridium Complexes: Pyrazole–Pyrazolato Interconversion and Application to Catalytic Intramolecular Hydroamination of Aminoalkene

“…Although the NH proton linking the two chelate ligands with a hydrogen bond18 could not be found in the difference Fourier map, its presence is supported by the short N1N3 distance of 2.736(10) Å as well as the 1 H NMR spectrum of 4 at −90 °C, showing a broad singlet at δ =16.04 ppm 19. A dinuclear complex topologically related to 4 ,12a and a mononuclear Cp*Ir complex12b bearing hydrogen‐bonded pyrazolato and pyrazole ligands has been reported.…”

Mononuclear Organometallic Platinum(II) Complexes and Platinum(II)−Copper(I) Mixed Complexes from Symmetrical 3,5-Bis(iminoacetyl)pyrazolate Ligands

“…62 Ligands incorporating pyrazolate as a bridging unit have been used to produce a wide range of bi-and polymetallic structures. [63][64][65][66][67][68][69] Symmetrical dinucleating ligands have the advantage of being synthetically easily accessible, but often require well-controlled successive introduction of both metals, as the binding sites are identical. 64,70 The readily available, symmetrical bis(iminoacetyl)pyrazolate ligands have been recently used to prepare homobimetallic palladium and nickel complexes for olefin polymerization.…”

β‐Protic Pyrazole and N‐Heterocyclic Carbene Complexes: Synthesis, Properties, and Metal–Ligand Cooperative Bifunctional Catalysis

“…[ 40] The intermediary pyrazolato-pyrazole complex 26 has been characterized by a sharp singlet at d = 13.38 ppm with an intensity of 1 H in the 1 H NMR spectrum. The reactions of the pyridylpyrazole complex 28 and pyrazoles lead to the formation of the pyrazolato-pyrazole complexes 29, in which the chelate pyrazole ligand cooperates in binding the substrate pyrazole as shown in Scheme 11.…”