Nickel and Platinum PCP Pincer Complexes Incorporating an Acyclic Diaminoalkyl Central Moiety Connecting Imidazole or Pyrazole Rings

Abstract

This work explores avenues toward PCP pincer complexes with acyclic diaminocarbene central moieties that are suitable for ligand-assisted reactivity involving the carbene carbon. For this purpose, diphosphine chelating ligands 1 and 2, with bis(imidazolyl)methyl and bis(pyrazolyl)methyl backbones, respectively, were prepared in two high-yield synthetic steps. Nickel(II) and platinum(II) dihalide complexes 3 and 6, incorporating 1, were prepared and converted into PCP pincer ligands 5 and 7 upon deprotonation with KHMDS. Chelated nickel(I) complex 4 was obtained as a byproduct to 3. Although the solid-state structures of 5 and 7 presented geometric strain at the diaminomethyl carbon, this moiety could not be converted into a diaminocarbene by proton or hydride abstraction. 7 could be converted into platinum(IV) analog 8 by oxidation with PhICl 2 . Ligand 2 proved more versatile than 1, or less dependable in its behavior, generating P,N-chelating cobalt(II) dibromide complex 9. Easily accessible ligands 1 and 2 provide a new and versatile PCP pincer platform.

Platinum Assisted Tandem P–C Bond Cleavage and P–N Bond Formation in Amide Functionalized Bisphosphine o-Ph2PC6H4C(O)N(H)C6H4PPh2-o: Synthesis, Mechanistic, and Catalytic Studies

“…Bidentate ligands, in particular bisphosphines, capable of inducing cyclometalation are of great importance in transition metal pincer chemistry and catalytic applications. − In these systems, the steric and electronic attributes can be readily modulated by varying the phosphorus substituents and bridging units or linkers. As a result, they show remarkable flexibility in their coordination behavior and confer interesting structures to metal complexes thereby influencing their reactivity and catalytic utility in several organic transformations. − In a majority of metal complexes, phosphines act as innocent “spectators” conferring a specific electronic, steric, or even chiral environment at the metal center ,− through σ-donor and π-acceptor modulations.…”

Nickel, Ruthenium, and Rhodium NCN-Pincer Complexes Featuring a Six-Membered N-Heterocyclic Carbene Central Moiety and Pyridyl Pendant Arms

“…The carbene assumed a highly uncommon, noninnocent role in this reaction, with the highly nucleophilic carbene carbon binding the NH proton while the nickel center connected to the amide functionality, through a mechanism that was not yet elucidated. Aiming to improve on the stability of the ligands in B and further expand the chemistry of NHC-based pincer systems, we explored the synthesis and properties of ligands 1 , formally obtained by adorning the ligands in complexes of type C with tert -butyl groups (Scheme ). The replacement of the imine pendant arms with pyridyl functionalities was expected to substantially improve the robustness of the metal systems.…”