SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF A DIIRIDIUM MU-ACYL COMPLEX

The metallacyclopentadiene chloride complex Ir(CR=CRCR=CR)(AsPh(3))(2) Cl (3, R = CO2CH3) undergoes reaction with 3-butyn-1-ol at room temper ature to give the metallacycle-carbene complex Ir((CR=CRCR=CR)[=C(CH2) (3)O](AsPh(3))(2)Cl (1-AsPh(3), R = CO2CH3). Thermolysis of 1-AsPh(3) at 75 degrees C leads to a 73% isolated yield of the diiridium mu-eta( 2)-(C,O) acyl complex =CR)(AsPh(3)](mu-Cl)(2)[mu-C(=O)(CH2)(3)(AsPh(3) )] [Ir(CR=CRCR=CR)(=C(CH2)(3)O)]} (4, R = CO2CH3). We previously repor ted the quantitative conversion of the iridacyclopentadiene-carbene co mplex Ir(CR=CRCR=CR)[=C(CH2)(3)O](PPh(3))(2)Cl (1-PPh3, R = CO2CH3) to iridacyclobutene 2 upon thermolysis of 1-PPh(3) at 72 degrees C in ch loroform solution (Scheme 1).2 On the basis of phosphine inhibition st udies, we proposed an initial loss of PPh(3) from 1-PPh(3). Subsequent steps would then include insertion of the carbene ligand into the iri dium-carbon bond of the metallacycle and ring contraction of the metal lacyclohexadiene intermediate (I). In the hope of facilitating this un precedented insertion reaction we prepared the triphenylarsine analogu e of 1-PPh(3) and report herein that thermolysis of the arsine derivat ive leads not to a metallacyclobutene but rather to the first homodinu clear mu-eta(2)-(C,O)-acyl complex of the cobalt triad metals.