Half-sandwich rhenium(III) acyl complexes: synthesis, structure and conversion to rhenium(I) and rhenium(III) isonitrile complexes

Abstract

The synthesis, structure and reactions of rhenium(III)η 1-acyl complexes bearing a cyclopentadienyl (Cp) or a pentamethylcyclopentadienyl (Cp *) ligand are described. Oxidation of the rhenium(I) acyl complexLi[CpRe(CO) 2(η 1-PhCO)] ( 1) with one equivalent of PhICl 2 affords the rhenium(III) acyl complex trans-CpRe(CO) 2(η 1-PhCO)Cl ( trans- 2a). The diphenylcarbene complex Cp(CO) 2Re CPh 2 ( 3) is also formed in this reaction. Similarly, oxidation of 1 with Br 2 givescis/trans-CpRe(CO) 2(η 1-PhCO)Br(cis/trans- 2b), which can also be obtained from the alkoxycarbene complex Cp(CO) 2Re C(OEt)Ph ( 4) with one equivalent of Br 2. Oxidation ofLi[Cp *Re(CO) 2(η 1-PhCO)] ( 5) with one equivalent of PhlCl 2, Br 2 or I 2 affords selectively the rhenium(III) acyl complexescis/trans-Cp *Re(CO) 2(η 1-PhCO)X(X Cl I) [ cis/trans-( 6a–6c)]. Cleavage of the Re C acyl bond of trans- 2a with PhICl 2 and of cis/trans- 2b with Br 2 offers a convenient way to the rhenium(III) dihalo complexes cis/trans-CpRe(CO) 2Cl 2 ( cis/trans- 7a) and cis/trans-CpRe(CO) 2Br 2 ( cis/trans- 7b) respectively. Reduction of cis/trans- 7a with sodium/amalgam gives in the presence of RNC, the rhenium(I) isonitrile complexes CpRe(CO) 2(CNR) ( 8:R Et; 9:R 10:R 1Bu). Oxidation of 8–10 with one equivalent of bromine leads selectively to the rhenium(III) isonitrile complexes [ trans-CpRe(CO) 2(CNR)Br]Br ( 11:R = Et; 12:R - iPr; 13:R = tBu). The crystal structure of the acyl complex trans- 2b and the carbonyl complex [Cp 2 *Re 2(CO) 4(μ-Br)][Re 2(μ-Br) 3(CO) 6] ( 14) are described, complex 14 being formed by the thermal decomposition of cis/trans- 6b.