Pentacoordinated diolefinic rhodium(I) organocomplexes with α-diimine ligands. Crystal structures of [Rh(Nbd)(LL)(PPh3)]ClO4 (Nbd=norbornadiene; LL=Bdh, biacetylidihydrazone; Pvdh, pyruvaldihydrazone; Bda, biacetyldianil)

Abstract Pentacoordinated [Rh(Nbd)(LL)(PPh 3 )]ClO 4 (Nbd=norbornadiene; LL=biacetyldihydrazone (Bdh) ( 1 ), pyruvaldehydedihydrazone (Pvdh) ( 2 ), glyoxaldihydrazone (Gdh) ( 3 ), biacetyldianyl (Bda) ( 4 )) complexes are studied. The molecular structures of 1 , 2 , and 4 have been determined by X-ray diffraction. The three cations are best described as having distorted trigonal bipyramidal geometry with the olefinic bonds of Nbd spanning axial–equatorial sites; in 1 and 2 the other equatorial positions are occupied by the diimine groups and the PPh 3 is in axial position while in 4 the diimine occupies axial–equatorial sites and the PPh 3 is in equatorial position. Complexes 1 and 2 show intermolecular hydrogen bond NH⋯OClO 3 linkages, strong in 2 . In acetone solution compounds 1 – 4 undergo phosphine dissociation, inhibited at 273 K; 2 , 3 and 4 behave as dimers with bridging diimine ligands. Neutral pentacoordinated [Rh(X)(L 2 )(LL)] (X=Cl, SnCl 3 ; L 2 =Nbd, 1,5-cyclooctadiene (Cod); LL=Pvdh, Gdh) compounds undergo ionic dissociation in solution where at 183 K [Rh(SnCl 3 )(Nbd)(Pvdh)] shows a square pyramidal structure with SnCl 3 in apical position.