Transition-metal complexes bearing outer-sphere pendent bases have been shown to undergo metal-ligand cooperative alcohol acceptorless dehydrogenation (ADH) catalysis. Our research group has been focused on preparing a series of new BIPHEP-type ligands bearing 2-substituted diarylphosphine groups (-P(2-X-Ph)2) and their corresponding Ru(II) complexes to test the effect of ligand proton affinity and basicity on ADH catalytic rate.This presentation will highlight the synthesis and characterization of a new BIPHEP-type ligand and three new Ru(II) complexes by NMR and IR spectroscopy, HRMS, and single-crystal X-ray analysis. A four-step synthesis of 2,2'-bis(di(2-ethylphenyl)phosphino)biphenyl (2-Et-BIPHEP) is reported. The final step, a C-C cross-coupling from o-bromo(di(2-ethylphenyl)phosphine (P(2-Br-Ph)(2-Et-Ph)2), required significant trouble-shooting as several C-C coupling reactions reported in the literature for BIPHEP were unsuccessful for this more sterically-bulky ligand. Two Ru(II) complexes of type [CpRu(diphosphine)(MeCN)]PF6 were prepared from 2,2'-bis(diphenyl)phosphino)biphenyl (BIPHEP) and new ligand 2-Et-BIPHEP. We also present the XRD structure of a rare Ru(II) complex bearing a bromoarene chelating ligand, synthesized independently from monophosphine P(2-Br-Ph)(2-Et-Ph)2 or by transmetallation from a Cu(II)-(P(2-Br-Ph)(2-Et-Ph)2) complex. Finally, we will discuss our initial performance results of these complexes in ADH catalysis.

Synthesis and characterization of Ru(II) complexes bearing BIPHEP-type ligands and a chelating phosphine-bromoarene ligand

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