Formal Co(0),Fe(0),and Mn(0)complexes with NHC and styrene ligation

The limited knowledge on low-coordinate zero-valent transition-metal species has intrigued great synthetic efforts in developing ligand sets for their stabilization.While the combined ligand set of Nheterocyclic carbene(NHC)with vinylsilanes was the only known ligand system amenable to the stabilization of three-coordinate formal zero-valent cobalt,iron,and manganese complexes,the exploration on other ligands has proved that the ligand set of NHCs with styrene is equally effective in stabilizing three-coo rdinate formal zero-valent metal complexes in the form of(NHC)M(η2-CH2CHPh)2(NHC=IPr,IMes;M=Co,Fe,Mn).These styrene complexes can be prepared by the one-pot reactions of MCl2 with styrene,NHC and KC8,and have been characterized by various spectroscopic methods.Preliminary reactivity study indicated that the interaction of[(IMes)Fe(η2-CH2 CHPh)2]with DippN3 produces the iron(IV)bisimido complex[(IMes)Fe(NDipp)2]and styrene,which hints at the utility of these zero-valent metal styene complexes as synthons of the mono-coordinate species(NHC)M(O).

Trichlorozirconium η~2-Hydrazonides： Synthesis, Characterization and Their Catalytic Behavior toward Ethylene Polymerization

The trichlorozirconium η~2-hydrazonides（R=H, A; R=CH_3, B） were synthesized through the finely controlled stoichiometrical reactions of anhydrous zirconium tetrachloride with the lithium salt of either 1-（furan-2-ylmethylene）-2-phenylhydrazonide or 1-（furan-2-ylethylidene）-2-phenyl hydrazonide in the solvent tetrahydrofuran（THF）, respectively. These complexes were highly sensitive to air and moisture due to solely using less bulky ligand of hydrazonides. The molecular structures of the title complexes, determined by means of single crystal X-ray diffraction, were found to be the distorted pentagonal bipyramid geometry around zirconium atom, with three chlorides and the hydrazonato ligand acting as the η~2-coordination mode as well as two incorporated THF molecules. Upon activation with either methylaluminoxane（MAO） or modified methylaluminoxane（MMAO）, both complexes A and B exhibited catalytic activities toward ethylene polymerization, producing polyethylenes with ultra-high molecular weights.