Synthesis and characterization of platinum and palladium pyrrolidinedithiocarbamate complexes

Treatment of (PPh₃)₂MCl₂ (M = Pd or Pt) with ammonium pyrrolidinedithiocarbamate (NH₄S₂CNC₄H₈) in a 1:1 molar ratio gave (PPh₃)M(Cl)(κ ² S,S-S₂CNC₄H₈) [M = Pt (1), Pd (2)]. On the other hand, the interaction of these compounds in a 1:2 [M:L] molar ratio gave (PPh₃)Pt(κS-S₂CNC₄H₈)(κ ² S,S-S₂CNC₄H₈) (3), which contains both terminal and chelated dithiocarbamato ligands, or a yellow insoluble solid for M = Pd. The bis(diphenylphosphino)ethane platinum or palladium dichlorides [(dppe)MCl₂] reacted with the same ligand to give the salts [(dppe)M(κ ² S,S-S₂CNC₄H₈)]Cl (M = Pt (4), Pd (5) which have only one chelating dithiocarbamato ligand. The new compounds were characterized by ¹H-, ¹³C{¹H}- and ³¹P-n.m.r. spectroscopy, mass spectrometry, elemental analysis and X-ray single crystal structure analysis.     

Synthesis and analytical characterization of novel pyridyl‐substituted 1,1′‐ethenedithiolato complexes

Some 1,1′‐ethenedithiolato complexes of nickel(II), palladium(II), and platinum(II) with different phosphine ligands, such as PPh₃, PEt₃, and dppe were prepared. Starting from 2‐, 3‐ as well as 4‐pyridyl methyl ketone, the complexes 1–15 were obtained in an one‐pot synthesis through reaction with carbon disulfide, using potassium‐tert‐butylate as a base. They were characterized by ¹H, ¹³C, and ³¹P NMR, mass spectra, infrared spectra, and UV–VIS spectra. The molecular structures of the (Ph₃P)₂Pd^II complex 9 containing the 3‐pyridyl‐ethenedithiolato ligand and of the (Et₃P)₂Pt^II complex 12 containing the 4‐pyridyl‐ethenedithiolato ligand were determined. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:369–378, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20103     

1,7,9,10-Tetrasubstituted PMIs Accessible through Decarboxylative Bromination: Synthesis,Characterization, Photophysical Studies,and Hydrogen Evolution Catalysis

In this work, we present a new synthetic strategy for fourfold-substituted perylene monoimides via tetrabrominated perylene monoanhydrides. X-ray diffraction analysis unveiled the intramolecular stacking orientation between the substituents and semicircular packing behavior. We observed the remarkable influence of the substituent on the longevity and nature of the excited state upon visible light excitation. In the presence of poly(dehydroalanine)-graft-poly(ethylene glycol) graft copolymers as solubilizing template, the chromophores are capable of sensitizing [Mo₃S₁₃]²⁻ clusters in aqueous solution for stable visible light driven hydrogen evolution over three days.     

A theoretical study on the complete catalytic cycle of the hetero-Pauson-Khand-type [2+2+1] cycloaddition reaction of ketimines,carbon monoxide and ethylene catalyzed by iron carbonyl complexes

The [2+2+1] cycloaddition reaction of 1,4-diazabutadienes, carbon monoxide and ethylene catalyzed by iron carbonyl complexes produces pyrrolidin-2-one derivatives. Only one of the two imine moieties is activated during the catalysis. The mechanism of this cycloaddition reaction is studied by density functional theory at the B3LYP/6-311++G(d,p) level of theory. In accordance with experimental results, a [(diazabutadiene)Fe(CO)(3)] complex of square-pyramidal geometry is used as the starting compound S of the catalytic cycle. Based on experimental experience, the reaction with ethylene is considered to take place before any interaction with carbon monoxide. According to the computational results, the reaction does not proceed by ligand dissociation followed by addition of ethylene and subsequent intramolecular activation steps but by the approach of an ethylene molecule from the base of the square-pyramidal complex. This reaction yields an intermediate I(4) in which ethylene is coordinated to the iron centre and a new C-C bond between ethylene and one of the imine groups is formed. The insertion of a terminal carbon monoxide ligand into the metal-carbon bond between ethylene and iron produces the key intermediate I(7). The reaction proceeds by metal-assisted formation of a lactam P. The catalytic cycle is closed by a ligand-exchange reaction in which the diazabutadiene ligand substitutes P with reformation of S. This reaction pathway is found to be energetically favored over a reductive elimination. It leads to the experimentally observed heterocyclic product P and a reactive [Fe(CO)(3)] fragment.     

Syntheses and Molecular Structures of [(thf)4Li] [{(thf)Li}M(C4H8)3] (M = Zr,Hf) and Their Solution Behavior

The reaction of MCl₄(thf)₂ (M = Zr, Hf) with 1,4-dilitiobutane in diethyl ether at –25 °C or at 0 °C with a molar ratio of 1 : 3 yields the homoleptic “ate” complexes [(thf)₄Li] [{(thf)Li}M(C₄H₈)₃] 1 - Zr (M = Zr) and 1 - Hf (M = Hf). The crystalline compounds form ion lattices with solvent-separated [(thf)₄Li]⁺ cations and [{(thf)Li}M(C₄H₈)₃]^– anions. The NMR spectra at –20 °C show magnetic equivalence of the M–CH₂ and of the β-CH₂ groups of the butane-1,4-diide ligands on the NMR time scale. Analogous reactions of MCl₄(thf)₂ with 1,4-dilithiobutane with a molar ratio of 1 : 2 proceed unclear. However, single crystals of [Li(thf)₄] [HfCl₅(thf)] ( 2 ) can be isolated with the hafnium atom in a distorted octahedral coordination sphere of five chloro and one thf ligand. NMR spectra allow to elucidate the time-dependent degradation of 1-Hf and 1-Zr in THF and toluene at 25 °C via THF cleavage. Addition of tmeda to a solution of 1-Zr allows the isolation of intermediately formed [{(tmeda)Li}₂Zr(nBu)₂(C₄H₈)₂] ( 3 ).     

Domino reactions of 1,2-diimidoyl-1,2-dichloroethanes. Synthesis of 3-imino-1,2-dithia-3h-cyclopent-4-enes, 3-amino-2-thioxo-2,5H-pyrrol-5-ones, 2,3-diamino-4-thioxo-4H-thiopyrans, and 6-imino-6H-1,3-oxazines

The reaction of mono- and dilithiated ethyl thioglycolate with 1,2-diimidoyl-1,2-dichloroethanes, aza-analogues of oxalyl chloride, afforded (depending on the reaction conditions) 3-imino-1,2-dithia-3H-cyclopent-4-enes, 3-amino-2-thioxo-2,5H-pyrrol-5-ones, and 2,3-diamino-4-thioxo-4H-thiopyrans. The reaction of the dianion of ethyl hippurate with 1,2-diimidoyl-1,2-dichloroethanes afforded 6-imino-6H-1,3-oxazines.     

Self‐Assembly of 3,6‐Bis(4‐triazolyl)pyridazine Ligands with Copper(I) and Silver(I) Ions: Time‐Dependant 2D‐NOESY and Ultracentrifuge Measurements

Two 3,6‐bis(R‐1H‐1,2,3‐triazol‐4‐yl)pyridazines (R=mesityl, monodisperse (CH₂ CH₂O)₁₂CH₃) were synthesized by the copper(I)‐catalyzed azide–alkyne cycloaddition and self‐assembled with tetrakis(acetonitrile)copper(I) hexafluorophosphate and silver(I) hexafluoroantimonate in dichloromethane. The obtained copper(I) complexes were characterized in detail by time‐dependent 1D [¹H, ¹³C] and 2D [¹H‐NOESY] NMR spectroscopy, elemental analysis, high‐resolution ESI‐TOF mass spectrometry, and analytical ultracentrifugation. The latter characterization methods, as well as the comparison to analog 3,6‐di(2‐pyridyl)pyridazine (dppn) systems and their corresponding copper(I) and silver(I) complexes indicated that the herein described 3,6‐bis(1H‐1,2,3‐triazol‐4‐yl)pyridazine ligands form [2×2] supramolecular grids. However, in the case of the 3,6‐bis(1‐mesityl‐1H‐1,2,3‐triazol‐4‐yl)pyridazine ligand, the resultant red‐colored copper(I) complex turned out to be metastable in an acetone solution. This behavior in solution was studied by NMR spectroscopy, and it led to the conclusion that the copper(I) complex transforms irreversibly into at least one different metal complex species.     

Substituted 2,2′‐Bis(2‐oxidobenzylideneamino)‐4,4′‐dimethyl‐1,1′‐biphenyl Complexes of Zinc

The condensation reaction of 2,2′‐diamino‐4,4′‐dimethyl‐6,6'‐dibromo‐1,1′‐biphenyl with 2‐hydroxybenzaldehyde as well as 5‐methoxy‐, 4‐methoxy‐, and 3‐methoxy‐2‐hydroxybenzaldehyde yields 2,2′‐bis(salicylideneamino)‐4,4′‐dimethyl‐6,6′‐dibromo‐1,1′‐biphenyl ( 1a ) as well as the 5‐, 4‐, and 3‐methoxy‐substituted derivatives 1b , 1c , and 1d , respectively. Deprotonation of substituted 2,2′‐bis(salicylideneamino)‐4,4′‐dimethyl‐1,1′‐biphenyls with diethylzinc yields the corresponding substituted zinc 2,2′‐bis(2‐oxidobenzylideneamino)‐4,4′‐dimethyl‐1,1′‐biphenyls ( 2 ) or zinc 2,2′‐bis(2‐oxidobenzylideneamino)‐4,4′‐dimethyl‐6,6′‐dibromo‐1,1′‐biphenyls ( 3 ). Recrystallization from a mixture of CH₂Cl₂ and methanol can lead to the formation of methanol adducts. The methanol ligands can either bind as Lewis base to the central zinc atom or as Lewis acid via a weak O–H ··· O hydrogen bridge to a phenoxide moiety. Methanol‐free complexes precipitate as dimers with central Zn₂O₂ rings.