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The palladium(II) β-ketoenaminate complexes cis- and trans-bis(5-imino-2,2-dimethyl-3-hexanonato-N,O)palladium(II), Pd(admh)2, have been prepared by reaction of PdCl2 and 5-amino-2,2-dimethylhex-4-en-3-one, Hadmh, in aqueous NaOH and have been separated by column chromatography on Florisil. The square-planar complexes were characterized in solution by 1H NMR chemical shifts, the nuclear Overhauser effect, and electric dipole moments, which showed that the first-eluted isomer from Florisil is trans and the second-eluted isomer is cis. X-ray crystal structures of the solid complexes confirm the isomer assignments and reveal close NH ⋯ HN contacts between the two ligands in the cis isomer and close NH ⋯ O contacts in the trans isomer. Isomerization equilibria favor the trans isomer in chlorobenzene and favor the cis isomer in pyridine. The kinetics of trans-to-cis isomerization in pyridine was studied in the range 55.8–100.6 °C: ΔH‡ = 100 ± 2 kJ/mol and ΔS‡ = −50 ± 6 J/(K mol). 1H NMR spectra of Ni(admh)2 in CHClF2 down to −170 °C suggests that only one isomer (probably trans) exists in solution.

Six-coordinate titanium(IV) N,N-dialkylmonothiocarbamate complexes Ti(R2mtc)2Cl2 (R = Me, Et, i-Pr, or i-Bu) have been prepared in excellent yield by reaction of titanium(IV) chloride with stoichiometric amounts of sodium N,N-dialkylmonothiocarbamates in dichloromethane or benzene. The complexes were characterized by conductance measurements and by infrared and 1H NMR spectroscopy. The x-ray crystal structure of Ti(Me2mtc)2Cl2 was determined in order to establish the location of the sulfur atoms, which are generally cis in monothiocarbamate and monothio-β-diketonate complexes. Ti(Me2mtc)2Cl2 has a distorted octahedral structure in which the Ti(IV) atom is bonded to two cis Cl atoms and two planar, bidentate monothiocarbamate ligands. The complex exists (unexpectedly) as the C2 stereoisomer that has S atoms in trans positions.

This article is a review of the stereochemistry and molecular rearrangements of selected six-, seven-, and eight-coordinate chelates of early transition metals: primarily, metal β-diketonates, dithiocarbamates, and monothiocarbamates. Dihalobis(β-diketonato)metal complexes M(dik) 2 X 2 (M = Ti, Zr, or Hf) generally have an octahedral cis configuration, but Ti(acac) 2 I 2 and V(dik) 2 X 2 exist in solution as an equilibrium mixture of cis and trans isomers. Nuclear magnetic resonance (NMR) line-shape studies show that the dialkoxy complexes cis -Ti(dik) 2 (OR) 2 rearrange by an intramolecular twisting mechanism whereas the closely related O , O −dimethyl dithiophosphates cis -Ti(Me 2 dtp) 2 (OR) 2 undergo metal-ligand bond rupture. The seven-coordinate complexes Zr(acac) 3 Cl, Ti(S 2 CNMe 2 ) 3 Cl, Ti(SOCNEt 2 )Cl, and CpM(S 2 CNMe 2 ) 3 (M = Ti, Zr, or Hf) have a pentagonal bipyramidal structure with the Cl or Cp ligand in an axial position. Eight-coordinate structures and stereoisomers are described

This article is a review of the stereochemistry and molecular rearrangements of selected six-, seven-, and eight-coordinate chelates of early transition metals: primarily, metal β-diketonates, dithiocarbamates, and monothiocarbamates. Dihalobis(β-diketonato)metal complexes M(dik) 2 X 2 (M = Ti, Zr, or Hf) generally have an octahedral cis configuration, but Ti(acac) 2 I 2 and V(dik) 2 X 2 exist in solution as an equilibrium mixture of cis and trans isomers. Nuclear magnetic resonance (NMR) line-shape studies show that the dialkoxy complexes cis -Ti(dik) 2 (OR) 2 rearrange by an intramolecular twisting mechanism whereas the closely related O , O −dimethyl dithiophosphates cis -Ti(Me 2 dtp) 2 (OR) 2 undergo metal-ligand bond rupture. The seven-coordinate complexes Zr(acac) 3 Cl, Ti(S 2 CNMe 2 ) 3 Cl, Ti(SOCNEt 2 )Cl, and CpM(S 2 CNMe 2 ) 3 (M = Ti, Zr, or Hf) have a pentagonal bipyramidal structure with the Cl or Cp ligand in an axial position. Eight-coordinate structures and stereoisomers are described

Dialkoxybis (O,O'-dimethyl dithiophosphato)titanium(IV) complexe, Ti(Me 2 dtp) 2 (OR) 2 (Me 2 dtp=S 2 P(OMe) 2 ; R=CH 2 Ph, i Pr, CMe 2 Et), have been prepared and characterized by chemical analysis and IR and 1 H NMR spectroscopy. Rates and activation parameters for inversion and dithiophosphate methyl group exchange in these cis-octahedral complexes have been determined by 1 H NMR spectroscopy

Etude des profils des raies RMN de 1 H, des complexes cites. On en deduit 3 processus cinetiques d'echange des groupes methyle. La cinetique et le mecanisme de ces processus sont interpretes en fonction de la structure et des liaisons

Etude a partir de spectres RMN de 1 H a differentes temperatures, sur des complexes dodecahedres [M(N,N-dimethylmonothiocarbamate) 4 ] avec M=Ti ou Zr, du processus de rearrangement du metal et de la rotation de la liaison double partielle C→N du coordinat; les parametres cinetiques de ces deux processus sont donnes

The kinetics of N-methyl group exchange in zirconocene N,N-dimethyldithiocarbamates, CP 2 ZrX(Me 2 dtc)(X=Cl, Br, I, Me, CH 2 SiMe 3 , CH 2 CMe 2 Ph, CH 2 Ph, OPh, Opy(4-hydroxypyridinate), OXyl(2,6-dimethylphenoxide)), and N,N,-dimethylthiocarbamates, Cp 2 ZrX(Me 2 mtc) (X=Cl, Opy), have been studied by variable-temperature 1 H NMR spectroscopy

The crystal and molecular structure of the benzene solvate of ~5-cyclopentadienyltris(~,~-dimethyldithiocarbamato)titanium(IV), (q5-C5H5)Ti[S2CN(CH3)Zlj, has been determined by X-ray diffraction. The compound crystallizes in the monoclinic space group P21/c with four formula units in a cell having dimensions a = 10.154 (1) A, b = 11.444 (2) A, c = 22.411 (2) A, and /3 = 97.11 (6)' (pabsd = 1.44, pcalcd = 1.418 g ~ m ~ ) . Least-squares refinement, which employed 5072 independent diffractometer-recorded reflections having 2BZIoKai 5 54.83' and lFol > 1.580,, afforded residuals Rl = 0.077 and R2 = 0.079. Anisotropic thermal parameters were used for Ti, S, and the five C atoms of the cyclopentadienyl ligand; isotropic thermal parameters were employed for the remaining nonhydrogen atoms. The crystal contains discrete seven-coordinate molecules which have pentagonal-bipyramidal geometry and approximate symmetry C,-m. The v5cyclopentadienyl ligand occupies one axial position (Ti-C = 2.420-2.425 A), one bidentate dithiocarbamate ligand spans the other axial position and one equatorial position, and the other two bidentate dithiocarbamate ligands take the remaining equatorial positions. As expected, the TiS6C5 coordination group is extremely crowded, with all of the S-S and C-8 nonbonded contacts being less than the sum of the van der Waals radii. Because of the crowding, the Ti-§ bond distances are unusually long; the average Ti-S bond length of 2.611 A is 0.10 A longer than that in the closely related compound Ti[SzCN(CH3)2]3CI. Nonbonded repulsions are reduced, primarily, by expansion of the Ti-S bonds to the two equatorial ligands; these bonds average -0.07 8, longer than the Ti-S bonds to the spanning ligand.

The metal N,N-diisopropyldithiocarbamate complexes NaL, NiL/sub 2/, CoL/sub 3/, AlL/sub 3/, InL/sub 3/, and ZrL/sub 4/ (L = S/sub 2/CN(i-Pr)/sub 2/) have been prepared and characterized by IR and /sup 1/H NMR spectroscopy. Low-temperature /sup 1/H NMR spectra of these compounds exhibit two equally intense isopropyl methyl doublets and two equally intense methine septets, attributed to a ligand conformation in which the methine protons of the inequivalent isopropyl groups are located in the plane of the liqand in environments that may be labeled ''inner'' or ''outer'' with respect to the quasi-twofold axis of the ligand. Between -50 and +15/sup 0/C the methyl doublets and methine septets coalesce to a single doublet and a single septet, respectively, owing to hindered rotation about the C-N single bonds. Rate constants (s/sup -1/) at -10/sup 0/C in CH/sub 2/Cl/sub 2/ solution vary from 1400 for CoL/sub 3/ to 8.3 for NaL; E/sub a/ = 10-12 kcal/mol and ..delta..S/sup + +/ = -7 to -13 eu. The rates increase with decreasing size, increasing charge, and increasing class by character of the metal ion and with decreasing SCS angle and increasing CNC angle in the analogous N,N-diethyldithiocarbamates. These trends can be understood in terms of amore » metal-induced variation in the amount of steric congestion in the N(i-Pr)/sub 2/ group. The methyl ester MeSC(S)N(i-Pr)/sub 2/ exists in CH/sub 2/Cl/sub 2/ solution as a 0.58:0.42 equilibrium mixture of two conformers that have the ''outer'' methine proton cis and trans, respectively, to the SMe group. Exchange of isopropyl methyl groups among the four inequivalent sites of the two conformers has been analyzed in terms of hindered rotation about (i) the C-N single bonds and (ii) the C-N partial double bond. Kinetic data are also reported for rotation about the C-N bond in the diisobutyl derivative MeSC(S)N(i-Bu)/sub 2/.« less