Iridium Diphosphine Complexes Featuring Pendant Lewis Acids: Efforts toward Selective Heteroarene Borylation

Abstract

The selective forging of carbon‐boron bonds via C−H borylation stands as a central means to access fine chemical precursors. Notwithstanding, achieving selectivity in this reaction is difficult, calling for the design of molecular catalysts that offer a vector for mechanistic control. This report aims to achieve such through the strategic placement of Lewis acids in the ligand periphery, permitting engagement with a substrate through non‐covalent Lewis acid/base interactions. Various diphosphine iridium(I/III) complexes having 1,2‐bis(di‐n‐propylphosphino)ethane) (dnppe), tetrakisallylphosphinoethane (tape) and 1,2‐bis(di(3‐dicyclohexylboranyl)propylphosphino)ethane (P2BCy4) ligands were prepared. The P2BCy4 ligand scaffold boasts four Lewis acidic boron groups in its secondary coordination sphere, which are shown to engage with N‐heterocycles, tape is the precursor to P2BCy4, and dnppe is a saturated n‐propyl analogue devoid of boron functionality. Select combinations of such iridium salts/diphosphine ligands were assayed in the catalytic borylation of 2‐methylpyridine using B2Pin2 (Pin=pinacol).

An Investigation of Allyl‐Substituted Bis(Diphosphine) Iron Complexes: Towards Precursors for Cooperative CO2 Activation

“…[21,22] Notwithstanding, like [2] + , reactions of [3] + with the bases outlined above produced a complicated mixture of products, many of which possessed BÀ Nu (Nu = nucleophile) interactions, as judged by 11 B{ 1 H} NMR spectroscopy, and as reported by us previously for related boron-based SCSs. [23][24][25] Because of these reaction outcomes, chemical reduction of [Fe(tape) 2 (Cl) 2 ] [19] was next explored as a means to access an Fe(0) complex with an unsaturated diphosphine ligand.…”