Iridium(I) 1,3,4,4‐Tetraamino‐1,2‐cyclobutadiene Complexes

Abstract

AbstractThe dimer of dipiperidinoacetylene, 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne, reacts with [IrCl(COD)]2 (COD=1,5‐cyclooctadiene) to give the corresponding 1,3,4,4‐tetrapiperidino‐1,2‐cyclobutadiene‐iridium complex [(CBA)IrCl(COD)] with a four‐membered cyclic bent allene (CBA) ligand. Reaction with carbon monoxide affords the dicarbonyl complex cis‐[(CBA)IrCl(CO)2], which exhibits low CO stretching frequencies and an associated Tolman electronic parameter (TEP) value of 2030 cm−1, which is lower than any other TEP value reported for cyclic carbene and carbenoid ligand systems. Treatment of [(CBA)IrCl(COD)] with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (NaBARF) followed by addition of phosphines or pyridine (py) yields the cationic complexes [(CBA)IrL(COD)][BARF] (L=PPh3, PPh2Me, PPhMe2, PCy3, py) as potential hydrogen isotope exchange (HIE) catalysts. DFT calculations provide evidence for a suitable pathway for the cyclization of 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne at transition metal complex fragments, here AuCl, IrCl(COD), and IrCl(CO)2, as a general route to four‐membered CBA metal complexes.