16-Electron cycloheptatrienyl zirconium allyl complexes

Replacement of THF in [(eta(7)-C7H7)Zr{C3H3(TMS)(2)}(thf)] (1) by trimethylphosphine (PMe3), 4-(dimethylamino)pyridine (DMAP), 1,3,4,5- tetramethylimidazolin-2-ylidene (IMe) or 1,3,4,5- tetramethyl-2-methyleneimidazoline (H2C-IMe) resulted in the new 16-electron cycloheptatrienyl zirconium allyl complexes [(eta(7)-C7H7)Zr{C3H3(TMS)(2)}(L)] (2: L = PMe3, 3: L = DMAP, 4: L = IMe, 5: L = H2C-IMe), which were all structurally characterized by X-ray diffraction analysis. The two-electron donor ligands are coordinated at the open edge of the 1,3-bis(trimethylsilyl)allyl ligand, which requires the TMS-substituents to point away from the metal (syn-syn orientation). In 5, the ylidic character of the exocyclic sp(2) carbon atom of the ligand led to end-on coordination accompanied by a pronounced elongation of the C-C bond distance. According to DFT calculations on 1, 2 and 4 and a variable temperature NMR study on 2, the Zr-L bonds feature significantly higher stabilities than in the corresponding 18-electron adducts of [(eta(7)-C7H7)Zr(eta(5)-C5H5)]. (C) 2012 Elsevier B.V. All rights reserved.