Synthesis of ansa-Dimethylsilanediyl−dicyclopentadienyl− zirconacyclopent-3-yne, Me2Si(η5-C5H4)2Zr(η4-H2C4H2), and Its Reactions with Ni(0) and B(C6F5)3

Development and application of redox-active cyclometallating ligands based on W(II) alkyne complexes

The assembly of dinuclear complexes with the ultimate smallest ditopic ligands based on side-on complexes of methyl substituted alkynes is presented. In fact, the coordination of Ru(II) and Ir(III) by a W alkyne complex based cyclometallating metalla-ligand causes close intermetallic electronic cooperation, which substantially changes the electrochemical and photophysical properties of the single isolated moieties.

Reactions of five-membered zirconacycloalkynes and zirconacycloallenes with Cp2Zr(H)Cl; formal hydrogenation by metal hydrides

Reactions of five-membered zirconacycloalkynes and zirconacyloallenes (1-zirconacyclopent-3-ynes and 1-zirconacyclopenta-2,3-dienes) with an excess of Cp₂Zr(H)Cl, known as the Schwartz reagent, were studied. Both reactions gave five-membered zirconacycloalkenes, 1-zirconacyclopent-3-enes without subsequent work-up such as protonolysis and hydrogenolysis. The product was identical to the zirconocene-diene complex that was prepared from Cp₂Zr(n-Bu)₂ (Negishi reagent) and the corresponding 1,4-disubstituted 1,3-dienes. These results indicate that formal hydrogenation by metal hydride took place. The use of diisobutylaluminum hydride or 9-borabicyclo[3.3.1]nonane also gave the same product, albeit in lower yields. The reactions starting from deuterated compounds suggested that double hydrozirconation followed by elimination of a dinuclear zirconium complex resulted in the hydrogenated products.

Acetylenic Carbon-Containing Stable Five-Membered Metallacycles

Due to the linear property around an acetylenic carbon, the introduction of such an atom to a small cycle would result in high ring strain. Currently, the smallest isolated rings are five-membered, including metallacycloalkynes and metallapentalynes. Both types contain at least one unusual small bond angle around the acetylenic carbon, thus exhibiting abnormal reactivities. This feature article gives a comprehensive overview on these two kind complexes. The synthesis and reactivities are extensively described, the source of stability is presented, and the future prospect is discussed. The article aims to provide a better development for the chemical diversity of five-membered metallacycloalkynes and metallapentalynes.

Acetylene dithiolate linking up the [Tp'W(CO)(CN)] moiety with Ru(II) or Pd(II.)

A series of heterodinuclear complexes with acetylene dithiolate (acdt(2-) ) as the bridging moiety were synthesised by a facile one-pot procedure that avoided use of the highly elusive acetylene dithiol. Generation of the W-Ru complex [Tp'W(CN)(CO)(C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )] (Tp'=hydrotris(3,5-dimethylpyrazolyl)borate) and the W-Pd complexes [Tp'W(CN)(CO)(C2 S2 )Pd(dppe)] and [Tp'W(CO)2 (C2 S2 )Pd(dppe)][PF6 ] (dppe=1,2-bis(diphenylphoshino)ethane), which exhibit a [W(η(2) -κ(2) -C2 S2 )M] core (M=Ru, Pd), was accomplished by using a transition-metal-assisted solvolytical removal of the Me3 Si-ethyl thiol protecting groups. All intermediate species of the reaction have been fully characterised. The highly coloured W-Ru complex [Tp'W(CN)(CO)(C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )] shows reversible redox chemistry, as does the prototype complex [Tp'W(CO)2 (C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )][PF6 ]. Single crystal X-ray diffraction and IR, EPR and UV/Vis spectroscopic studies in conjunction with DFT calculations prove the high electronic delocalisation of states over the acdt(2-) linker. Comparative studies revealed a higher donor strength and more pronounced dithiolate character of acdt(2-) in [Tp'W(CN)(CO)(C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )] relative to [Tp'W(CO)2 (C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )](+) . In addition, the influence of the overall complex charge on the metric parameters was investigated by single-crystal X-ray diffraction studies with the W-Pd complexes [Tp'WL2 (C2 S2 )Pd(dppe)] (L=(CN(-) )(CO) or (CO)2 ). The central [W(C2 S2 )Pd] units exhibit high structural similarity, which indicates the extensive delocalisation of charge over both metals.

Combination of spectroscopic methods: in situ NMR and UV/Vis measurements to understand the formation of group 4 metallacyclopentanes from the corresponding metallacyclopropenes

By reaction of the dichloride rac-(ebthi)HfCl(2) [ebthi = 1,2-ethylene-1,1'-bis(eta(5)-tetrahydroindenyl)] with lithium in the presence of bis(trimethylsilyl)acetylene, the hafnacyclopropene rac-(ebthi)Hf(eta(2)-Me(3)SiC(2)SiMe(3)) (1-Hf) was obtained. The reaction of the blue-green complex 1-Hf with an excess of ethylene at room temperature leads by insertion of the olefin to the yellow-green hafnacyclopentene 2-Hf which is only stable in solution and eliminates the alkyne at 100 degrees C under ethylene to form the corresponding yellow hafnacyclopentane 3-Hf, which was characterized by X-ray crystal structure analysis. The reaction of 1-Hf to give stepwise via 2-Hf the complex 3-Hf was investigated in detail and compared to the formation and stability of the corresponding zirconacyclopropene 1-Zr, zirconacyclopentene 2-Zr, and zirconacyclopentane 3-Zr. Moreover, the reaction of the titanocene alkyne complex 1-Ti with ethylene was studied. For investigating the reaction behavior of the alkyne complexes 1-M, NMR spectroscopy was used and the results were compared with UV/vis spectroscopy, suggesting the existence of a bis-pi-complex prior to the formation of the hafnacyclopentene 2-Hf.