Stepwise Reactions of Acetylenes with Iridium Thiocarbonyl Complexes To Produce Isolable Iridacyclobutadienes and Conversion of These to either Cyclopentadienyliridium or Tethered Iridabenzene Complexes

Abstract

Treatment of IrCl(CS)(PPh 3 ) 2 with an excess of KI gives orange IrI(CS)(PPh 3 ) 2 ( 1 ). IrI(CS)(PPh 3 ) 2 ( 1 ) reacts reversibly with dioxygen to form the brown dioxygen complex Ir(O 2 )I(CS)(PPh 3 ) 2 ( 2 ). Reaction between IrI(CS)(PPh 3 ) 2 ( 1 ) and 2 equiv of ethyne produces the green-brown tethered iridacyclobutadiene complex Ir[C 3 H 2 (CH CHS-1)]I(PPh 3 ) 2 ( 3 ), one ethyne combining in a cycloaddition reaction with the IrC multiple bond to the CS ligand to form the four-membered IrC 3 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)(PPh 3 ) 2 to give as the major product the tethered iridacyclobutadiene Ir[C 3 H(CH C{Ph}S-1)(Ph-3)]Cl(PPh 3 ) 2 ( 4 ), with the phenyl substituent adjacent to the iridium, and as the minor product the isomeric tethered iridacyclobutadiene Ir[C 3 H(CH C{Ph}S-1)(Ph-2)]Cl(PPh 3 ) 2 ( 5 ). A thermal reaction of Ir[C 3 H(CH C{Ph}S-1)(Ph-3)]Cl(PPh 3 ) 2 ( 4 ) with further phenylacetylene produces the tethered, substituted cyclopentadienyliridium complex Ir[η 5 -C 5 H 2 (SCPh CH-1)(Ph-3)(Ph-5)]Cl(PPh 3 ) ( 6 ), which retains the iridium−carbon bond to the vinylthio substituent. Methyl propiolate reacts with IrI(CS)(PPh 3 ) 2 ( 1 ) to form exclusively the tethered iridacyclobutadiene Ir[C 3 H(CH C{CO 2 Me}S-1)(CO 2 Me-2)]I(PPh 3 ) 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[C 5 H 2 (CH C{CO 2 Me}S-1)(CO 2 Me-2)(CO 2 Me-4)]Cl(PPh 3 ) 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.