Selective formation of cis-diacyl, cis-PPh_2R rhodium(III) complexesby the reaction of rhodium(III) cis-diacyl, trans-PPh_2R complexeswith aliphatic diamines

摘要

The cis-diacyl, trans-PPh_2Rcomplex [RhCl(PPh_2(o-C_6H_4CO))_2(Pyridine)] (1) reacts with substitutedaliphatic diamines to afford selectively cationic cis-diacyl, cis-PPh_2R, diamine derivatives[Rh(PPh_2(o-C_6H_4CO))_2(NN')]+ (NN' = 1,2-diphenylethylenediamine, 2; 1,2-propanediamine, 3;N-methylethylenediamine, 4; N,N-dimethylethylenediamine, 5; N,N'-dimethylethylenediamine, 6;N,N,N'-trimethylethylenediamine, 7) with high stereoselectivity depending on the N-donor ligandemployed. Complexes 2 and 3 contain a single isomer, while 4 is a mixture of two isomers, 4a and 4b.Formation of 4a occurs first and is followed by isomerisation to 4b until the equilibrium 4a:4b = 1:4ratio is attained. In contrast, 5 and 6 contain a single isomer. More basic amino groups prefer positionstrans to an acyl group while less basic amino groups are trans to a phosphine group. The preferredintramolecular N—H ? ? ? O hydrogen bond formation between an amino and an acyl coordinatedligands, trans to the phosphorus atoms, appears to be relevant to the selectivity observed. 7 is a mixtureof two isomers 7a and 7b in a 7a:7b = 5.7:1 ratio. N,N,N',N'-tetramethylethylenediamine orN,N'-diphenylethylenediamine led to the elimination of the N-donor ligands and the formation of amixture of isomers of [Rh_2(μ-Cl)(μ-PPh_2(0-C_6H_4CO))_2(PPh_2(0-C_6H_4CO))_2]+ (8), where the Rh atomsare triply bridged by two acyl groups in a head-to-tail arrangement and by a chloride. The reaction of[Rh(PPh_2(0-C_6H_4CO))_2(ndmeen)]ClO_4(5) with acids led to the displacement of the diamine and theformation of a [8a]+:[8b]+:[8c]+ = 1:1:3 mixture. 8c, containing the weakest σ-donor oxygen atoms transto the strongest a-donor acyl groups, represents the most electronically favourable geometry for 8. Allthe complexes were fully characterized spectroscopically. Single crystal X-ray diffraction analysis wasperformed on 5, 6, 8a and 8b.