Half-sandwich rhenium(III) acyl complexes: Synthesis, structure and conversion to rhenium(I) and rhenium(III) isonitrile complexes 1

Article abstract of DOI:10.1016/S0022-328X(96)06401-7

The synthesis, structure and reactions of rhenium(III) η¹-acyl complexes bearing a cyclopentadienyl (Cp) or a pentamethylcyclopentadienyl (Cp *) ligand are described. Oxidation of the rhenium(I) acyl complex Li[CpRe(CO)₂(η¹-PhCO)] (1) with one equivalent of PhICl₂ affords the rhenium(III) acyl complex trans-CpRe(CO)₂(η¹-PhCO)Cl (trans-2a). The diphenylcarbene complex Cp(CO)₂Re=CPh₂ (3) is also formed in this reaction. Similarly, oxidation of 1 with Br₂ gives cis / trans-CpRe(CO)₂(η¹-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 Br₂. Oxidation of Li[Cp*Re(CO)₂(η¹-PhCO)] (5) with one equivalent of PhICl₂, Br₂ or I₂ affords selectively the rhenium(III) acyl complexes cis / trans-Cp*'e(CO)₂(η¹-PhCO)X (X = Cl-I) [cis / trans-(6a-6c)]. Cleavage of the Re-C_acyl bond of trans-2a with PhICl₂ and of cis / trans-2b with Br₂ offers a convenient way to the rhenium(III) dihalo complexes cis / trans-CpRe(CO)₂Cl₂ (cis / trans-7a) and cis / trans-CpRe(CO)₂Br₂ (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 = ⁱPr; 10: R = ^tBu). 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 Re₂(CO)₄(μ-Br)][Re₂(μ-Br)₃(CO)₆] (14) are described, complex 14 being formed by the thermal decomposition of cis / trans-6b.