Diolefin complexes of transition metals as 'venus fly-trap' templates

[摘要] English: The aim of this study was to gain a further insight into the bonding modes of 1,5-cyclooctadieneto various middle to late transition metal centres. The intension was to design atheoretical model of the influences of the variations of the metal centres and ligands onthe 'Venus fly-trap system. Two principle geometric features were classified in the 1,5-cyclo-octadine when co-ordinated, i.e. the (bite) angle of the olefinic moieties to themetal centre, and the (jaw) angle, i.e. the dihedral angle between the two planes formedbetween the alkane ethylene groups. The latter mimicking the 'jaws of the Venus flytrap.A range of 1,5-cyclo-octadiene metal complexes were successfully synthesized andcharacterized via NMR and IR spectroscopy, the metal centers chosen were that ofrhodium(I), platinum(II) and palladium(II). The ligands selected were divided into threecategories namely· β-diketonato· β-enaminonato· tropolonatoFrom each of these categories ligands were selected to vary the electron withdrawing ordonating ability. Both symmetrical and non-symmetrical ligands were made use of, tosee the influence of the nitrogen trans effect on the 1,5-cyclo-octadiene moiety. Finally,the tropolonato category added the influence of the smaller five membered metal chelatering.A single crystal X-ray crystallographic study of the complexes was undertaken. Thereported X-ray crystallographic structure determinations include the followingcomplexes: [Pd(cod)(acac)]PF6 (1, Monoclinic P21/n, R = 3.59 %), [Pd(cod)(acac)]BF4(2, Orthorhombic Pca21, R = 2.24 %), [Pd(cod)(thtfac)]PF6 (3, Monoclinic P21/n, R =2.43 %), [Pd(cod)(thtfac)]BF4 (4, Monoclinic P21/n, R = 2.83 %), [Pd(cod)(tfacac)]PF6(5, Triclinic P1 , R = 13.41 %), [Pd(cod)(hfacac)]PF6 (6, Monoclinic P21/c, R = 2.60 %), [Pt(cod)(acac)] (7, Orthorhombic Pca21, R = 1.75 %), [Pt(cod)(acac)]PF6 (8, MonoclinicP21/n, R = 3.02 %), [Pt(cod)(dbm)]BF4 (9, Triclinic P1), [Pt(cod)(thtfac)]BF4 (10,Monoclinic P21/n, R =2.80 %), [Pd(cod)(3Br-trop)]PF6 (11, Triclinic P1, R = 5.90 %),[Pd(cod)(3Br-trop)]BF4 (12, Triclinic P1, R = 3.40 %), [Pd(cod)(trop)]PF6 (13,Tetragonal P42bc, R = 4.08 %), [Pt(cod)(trop)]PF6 (14, Tetragonal P42/mbc, R = 3.45 %),[Pt(cod)(trop)]BF4 (14, Tetragonal P42bc, R = 2.91 %), [Pt(cod)(3Br-trop)]PF6 (16,Monoclinic C2/c, R = 4.38 %), [Pt(cod)(3Br-trop)]BF4 (17, Triclinic P1, R = 2.66 %),[Pd(cod)(NH-acac)]BF4 (18, Monoclinic P21/c, R = 2.24 %), [Pt(cod)(NH-acac)]BF4 (19,Monoclinic P21/c, R = 2.09 %), [Pt(cod)(NH-acac)]PF6 (20, Monoclinic C2/m, R = 3.88%), [Pt(cod)(NMe-acac)]BF4 (21, Orthorhombic P212121, R = 1.50 %), [Pt(cod)(NMeacac)]PF6 (22, Monoclinic C2, R = 2.44 %), [Pt(cod)(NPh-acac)]BF4 (23, MonoclinicP21/n, R = 3.25 %), [Pt(cod)(NPh-acac)]PF6 (24, Triclinic P1, R = 3.29 %),[Rh(cod)(acac)] (25, Monoclinic Cc, R = 2.21 %), [Rh(cod)(dbm)] (26, Monoclinic Cc, R= 2.80 %), [Rh(cod)(thtfac)] (27, Monoclinic P21/n, R = 4.75 %) and [Rh(cod)(trop)] (28,Orthorhombic P212121, R = 1.39 %).The co-ordination geometry of the crystal structures was square planar, for palladium(II)and platinum(II) crystal structures resulting in a cationic charged species which wasbalanced with either BF4- or PF6- counter ions. Extensive hydrogen bonding wasobserved for the solid state structures with some interesting metal ring chelateinteractions. The twist angle, the distortion from the square planar co-ordinationgeometry, for the crystal structures was found to be of a similar order.A theoretical DFT study was carried out on the group 7-11 transition metals withacetylacetone (Hacac), trifluoroacetylacetone (Htfacac), hexafluoroacetylacetone(Hhfacac), 4-aminopent-3-en-2-one (HNH-acac), 4-(methylamino)pent-3-en-2-one(HNMe-acac), 4-anilinopent-3-en-2-one (HNPh-acac), tropolone (Htrop) andtribromotropolone (H3Br-trop). The comparison of the calculated structures with the Xraycrystal structures was found to be in good agreement with R-values of greater than 98%. The molecular orbitals showed the influences of the π orbital delocalization and thebonding orbitals of the cyclo-octadiene with the various transition metal centres andprovided an easy graphical method to compare both the variations of ligands and metal centres. Both the molecular orbital energies and band gap energies were presented andreflected the changes in the cyclo-octadiene complexes. A push-pull effect was observedthough the use of the 'core co-ordination geometry, where the metal displays a lateralmovement within the co-ordination area (Atot). The bite and jaw angleswere determined for all the theoretical structures as well as the solid state crystalstructures obtained. A maximum opening of c.a. 15° for the β-diketonato complexeswhile both the β-enaminonato and tropolonato complexes have a c.a. 14° variation in thejaw angle affected by both the metal and trans ligand manipulations.

[发布机构] University of the Free State