Stepwise reactions of acetylenes with iridium thiocarbonyl complexes to produce isolable iridacyclobutadienes and conversion of these to either cyclopentadieneyl-iridium or tethered iridabenzene complexes

Abstract

Treatment of IrCl(CS)(PPh3)2 with an excess of KI gives orange IrI(CS)(PPh3)2 (1). IrI(CS)(PPh3)2 (1) reacts reversibly with dioxygen to form the brown dioxygen complex Ir(O2)I(CS)(PPh3)2 (2). Reaction between IrI(CS)(PPh3)2 (1) and 2 equiv of ethyne produces the green-brown tethered iridacyclobutadiene complex Ir[C3H2(CHdCHS-1)]I(PPh3)2 (3), one ethyne combining in a cycloaddition reaction with the IrC multiple bond to the CS ligand to form the four-membered IrC3 ring and the second ethyne alkylating the sulfur atom to give the vinylthio substituent at the 1-position of the metallacyclic ring, which is tethered to the iridium through an Ir-C bond. In reactions related to those with ethyne, phenylacetylene reacts with IrCl(CS)(PPh3)2 to give as the major product the tethered iridacyclobutadiene Ir[C3H(CHd C{Ph}S-1)(Ph-3)]Cl(PPh3)2 (4), with the phenyl substituent adjacent to the iridium, and as the minor product the isomeric tethered iridacyclobutadiene Ir[C3H(CHdC{Ph}S-1)(Ph-2)]Cl(PPh3)2 (5). A thermal reaction of Ir[C3H(CHdC{Ph}S-1)(Ph-3)]Cl(PPh3)2 (4) with further phenylacetylene produces the tethered, substituted cyclopentadienyliridium complex Ir[è 5 -C5H2(SCPhdCH-1)(Ph-3)(Ph-5)]Cl(PPh3) (6), which retains the iridium-carbon bond to the vinylthio substituent. Methyl propiolate reacts with IrI(CS)- (PPh3)2 (1) to form exclusively the tethered iridacyclobutadiene Ir[C3H(CHdC{CO2Me}S-1)(CO2Me- 2)]I(PPh3)2 (7). Treatment of this iridacyclobutadiene, 7, with silver triflate allows introduction of a third methyl propiolate, which brings about ring expansion of the iridacyclobutadiene to form the stable tethered iridabenzene Ir[C5H2(CHdC{CO2Me}S-1)(CO2Me-2)(CO2Me-4)]Cl(PPh3)2 (8). Complex 8 retains the same vinylthio tethering group as found in 7. The structures of 2-8 have been confirmed by X-ray crystal structure determinations. Both NMR spectroscopic and structural data for 8 support the formulation of this compound as a tethered metallaaromatic molecule.