Binuclear Macrocyclic Silver(I) Complex of a Bis(carbone) Pincer Ligand: Synthesis and Application as a Carbone-Transfer Agent.

A facile synthesis of a binuclear AgI complex 2 of a bis(carbone) ligand L and its application as a carbone-transfer agent for the generation of other transition-metal complexes of AuI (3), NiII (4), and PdII (5) is presented. Complex 2 was synthesized through multiple synthetic routes under mild reaction conditions using the tetracationic [LH4][OTf·Cl]2 precursor salt, the dicationic [LH2][OTf]2 ylide salt, and the free ligand L. The first two synthesis routes require no prior isolation of the air-, moisture-, and temperature-sensitive free ligand L, thus affording complex 2 with high yield and purity. Multinuclear NMR techniques, high-resolution mass spectrometry, and single-crystal X-ray diffraction analysis confirmed the identity of complex 2 as a binuclear AgI complex of L with a molecular formula of [L2Ag2][OTf]2 and a 16-membered-ring metallomacrocyclic structure. During the transmetalation reaction with AuI, the binuclear nature of complex 2 remains intact to give analogous complex 3 ([L2Au2][OTf]2). However, the dimeric structure was disrupted upon the carbone-transfer reaction with NiII and PdII, yielding mononuclear C-N-C pincer-type complexes 4 ([LNiCl][OTf]) and 5 ([LPdCl][OTf]), respectively. These results demonstrated the versatile use of complex 2 as a carbone-transfer agent to other transition metals regardless of the type or size of the metals or the geometry they prefer.

A Bis-(carbone) Pincer Ligand and Its Coordinative Behavior toward Multi-Metallic Configurations.

Carbones are divalent carbon(0) species that contain two lone pairs of electrons. Herein, we have prepared the first known stable and isolable free bis-(carbone) pincer framework with a well-defined solid-state structure. This bis-(carbone) ligand is an effective scaffold for forming monometallic (Ni and Pd) and trinuclear heterometallic complexes with Au-Pd-Au, Au-Ni-Au, and Cu-Ni-Cu configurations. Sophisticated quantum-theoretical analyses found that the metal-metal interactions are too weak to play a significant role in upholding these multi-metallic configurations; rather, the four lone pairs of electrons within the bis-(carbone) framework are the main contributors to the stability of the complexes.