Lewis Base Mediated β-Elimination and Lewis Acid Mediated Insertion Reactions of Disilazido Zirconium Compounds

The reactivity of a series of disilazido zirconocene complexes is dominated by the migration of anionic groups (hydrogen, alkyl, halide, OTf) between the zirconium and silicon centers. The direction of these migrations is controlled by the addition of two-electron donors (Lewis bases) or two-electron acceptors (Lewis acids). The cationic nonclassical [Cp2ZrN(SiHMe2)2]+ ([2]+) is prepared from Cp2Zr{N(SiHMe2)2}H (1) and B(C6F5)3 or [Ph3C][B(C6F5)4], while reactions of B(C6F5)3 and Cp2Zr{N(SiHMe2)2}R (R = Me (3), Et (5), n-C3H7 (7), CH═CHSiMe3 (9)) provide a mixture of [2]+ and [Cp2ZrN(SiHMe2)(SiRMe2)]+. The latter products are formed through B(C6F5)3 abstraction of a β-H and R group migration from Zr to the β-Si center. Related β-hydrogen abstraction and X group migration reactions are observed for Cp2Zr{N(SiHMe2)2}X (X = OTf (11), Cl (13), OMe (15), O-i-C3H7 (16)). Alternatively, addition of DMAP (DMAP = 4-(dimethylamino)pyridine) to [2]+ results in coordination to a Si center and hydrogen migration to zirconium, giving the cationic complex [Cp2Zr{N(SiHMe2)(SiMe2DMAP)}H]+ ([19]+). Related hydrogen migration occurs from [Cp2ZrN(SiHMe2)(SiMe2OCHMe2)]+ ([18]+) to give [Cp2Zr{N(SiMe2DMAP)(SiMe2OCHMe2)}H]+ ([22]+), whereas X group migration is observed upon addition of DMAP to [Cp2ZrN(SiHMe2)(SiMe2X)]+ (X = OTf ([12]+), Cl ([14]+)) to give [Cp2Zr{N(SiHMe2)(SiMe2DMAP)}X]+ (X = OTf ([26]+), Cl ([20]+)). The species involved in these transformations are described by resonance structures that suggest β-elimination. Notably, such pathways are previously unknown in early metal amide chemistry. Finally, these migrations facilitate direct Si–H addition to carbonyls, which is proposed to occur through a pathway that previously had been reserved for later transition metal compounds

The synthesis and characterization of rhenium nitrosyl complexes. The X-ray crystal structures of [ReBr2(NO)(NCMe)3], [Re(NO)(N5)](BPh4)2] and [ReBr2(NO)(NCMe){py-CH2-NH∼CH2CH2-N(CH2-py)2}]

Reactions of low oxidation state rhenium–nitrosyl complexes with polyamine ligands have been examined. Rhenium(II)–nitrosyl complexes gave an array of unstable products that were difficult to isolate cleanly. The rhenium(I)–nitrosyl complex [ReBr2(NO)(NCMe)3] gave multiple products which were more easily isolated. The major product from the reaction of [ReBr2(NO)(NCMe)3] with the potentially pentadentate ligand N1,N1,N2-tris(2-pyridinylmethyl)-1,2 ethanediamine was the dicationic species [Re(NO)(N5)]2+, which was isolated as the bis-tetraphenylborate salt. The other major product [ReBr2(NO)(NCMe){py-CH2NH∼CH2CH2N(CH2-py)2}], was separated from a number of other neutral species via chromatography. This species contains the same potentially pentadentate ligand, only here it is coordinated through only two of its amine functional groups. Left dangling is the secondary amine and both of its pyridyl groups. Both amine complexes are diamagnetic and both display their respective parent ions in the ESI(+) mass spectra. The dication [Re(NO)(N5)]2+ shows its half mass parent peak at 275 m/z while [ReBr2(NO)(NCMe){py-CH2NH∼CH2CH2N(CH2-py)2}] shows its parent peak at 751 m/z. The infrared spectrum of [ReBr2(NO)(NCMe){py-CH2NH∼CH2CH2N(CH2-py)2}] displays its ν(Ndouble bond; length as m-dashO) at 1676 cm−1. And the infrared spectrum of [Re(NO)(N5)](BPh4)2 displays its ν(Ndouble bond; length as m-dashO) at 1714 cm−1

Neutralization of CD95 ligand protects the liver against ischemia-reperfusion injury and prevents acute liver failure

Ischemia-reperfusion injury is a common pathological process in liver surgery and transplantation, and has considerable impact on the patient outcome and survival. Death receptors are important mediators of ischemia-reperfusion injury, notably the signaling pathways of the death receptor CD95 (Apo-1/Fas) and its corresponding ligand CD95L. This study investigates, for the first time, whether the inhibition of CD95L protects the liver against ischemia-reperfusion injury. Warm ischemia was induced in the median and left liver lobes of C57BL/6 mice for 45 min. CD95Fc, a specific inhibitor of CD95L, was applied prior to ischemia. Hepatic injury was assessed via consecutive measurements of liver serum enzymes, histopathological assessment of apoptosis and necrosis and caspase assays at 3, 6, 12, 18 and 24 h after reperfusion. Serum levels of liver enzymes, as well as characteristic histopathological changes and caspase assays indicated pronounced features of apoptotic and necrotic liver damage 12 and 24 h after ischemia-reperfusion injury. Animals treated with the CD95L-blocker CD95Fc, exhibited a significant reduction in the level of serum liver enzymes and showed both decreased histopathological signs of parenchymal damage and decreased caspase activation. This study demonstrates that inhibition of CD95L with the CD95L-blocker CD95Fc, is effective in protecting mice from liver failure due to ischemia-reperfusion injury of the liver. CD95Fc could therefore emerge as a new pharmacological therapy for liver resection, transplantation surgery and acute liver failure