Zirkonadihydrofuran-komplexe: Darstellung, struktur und reaktivitäts-betrachtungen

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.

Addition and metathesis reactions of zirconium and hafnium imido complexes

The zirconium and hafnium imido metalloporphyrin complexes (TTP)M = NArtPr (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion; M = Zr (1), Hf; AriPr = 2,6-diisopropylphenyl) were used to mediate addition reactions of carbonyl species and metathesis of nitroso compounds. The imido complexes react in a stepwise manner in the presence of 2 equiv of pinacolone to form the enediolate products (TTP)M[OC(tBu)CHC(tBu)(Me)O] (M = Zr (2), Hf (3)), with elimination of H2NAriPr. The bis(mu-oxo) complex [(TTP)ZrO]2 (4) is formed upon reaction of (TTP)Zr = NAriPr with PhNO. Treatment of compound 4 with water or treatment of compound 2 with acetone produced the (mu-oxo)bis(mu-hydroxo)-bridged dimer [(TTP)Zr]2(mu-O)(mu-OH)2 (5). Compounds 2, 4, and 5 were structurally characterized by single-crystal X-ray diffraction.