Homoleptic alkyl- and aryl-complexes of transition metals (Ti, Zr, Hf, Nb, and Cr) and tetra-organyloxyvanadium-(V) and -(IV) complexes (2010)

In order to explore the geometry of six and five d0 complexes of the transition metals, new aryl complexes [Li(THF)4][Ti(C6H5)5], [Li(Et2O)4][Ti(p-C6H4-CH3)5], [Li4Cl(THF)8][Ti(C6H5)6], [Li4Cl(Et2O)8][Ti(p-C6H4-CH3)6], [Bu4N][Zr(C6H5)5] [Li2(THF)4][Zr(C6H5)6], [Li2(Et2O)4][Zr(p-C6H4-CH3)6], and [Li2(THF)4][Hf(C6H5)6], have been synthesized and their crystal structure determined by X-ray diffraction measurements. The Arylation of TiCl4•xEt2O with C6H5Li gives five-coordinate, homoleptic organotitanium(IV) derivatives with the formula [Li(THF)4][Ti(C6H5)5]. The anion Ti(C6H5)5− has an almost square pyramidal SP-5 geometry, as observed in the solid-state structure of [Li(THF)4][Ti(C6H5)5], similarly the [Li(Et2O)4][Ti(p-C6H4-CH3)5] was prepared and the titanium center is located in square pyramidal environment. When the same reaction performed at different conditions of temperature and mole ratio, the new complexes with hexa aryl derivative of titanium(III) were isolated and structurally determined. From the X-ray measurement, the titanium atom in the two anions Ti(C6H5)63− and Ti(p-C6H4-CH3)63− located in an octahedral arrangement with some additional interaction between two Li+ cations and the metal center. The preparation of the unusual five-coordionate zirconium aryl:[Bu4N][Zr(C6H5)5] is achieved by the low temperature arylation of ZrCl4 with C6H5Li in presence of BrNBu4. The structure of the anion is best described as a square pyramidal arrangement. The arylation of ZrCl4 with C6H5Li and Li(p-C6H4-CH3) under different arylation conditions also give a homoleptic hexa-arylzirconium(IV) compounds, [Li2(THF)4][Zr(C6H5)6] and [Li2(Et2O)4][Zr(p-C6H4-CH3)6]. From x-ray diffractions result, the six C6H5, or p-C6H4-CH3 groups define an approximately trigonal prismatic environment for the zirconium atom in both anions. On the other hand the reaction of HfCl4 with C6H5Li under the same conditions also affords the hexaphenylhafnmoium(IV) complex, and the structure of the anion is surprisingly octahedral. Attempts to prepare related [Nb(C6H5)6]− complexes lead instead to the isolation of the new heax-arylniobiate(IV) complexes, [Nb(C6H5)6]2− and [Nb(p-C6H4-CH3)6]2−, which both adopt an approximate trigonal prismatic structures, and the anion is affected by interaction with two Li+ cations. Attempts to prepare a related vanadium complexes such as V(C6H5)62− lead instead to the isolation of the reduced, well-known product V(C6H5)64−. The high unusual class of tetra- organyl complexes containing oxovanadium(V) and oxovanadium(IV) anions have been prepared and structurally characterized: VO(CH3)4−, VO(CH3)42− and VO(C6H5)42− where the vanadium atom in these anions is located in square pyramidal environment with the oxygen atom in the apical position. Several attempts to syntheses hexamethyl or hexaphenylchromium(IV) compounds starting from the reaction of CrCl3 or Cr(O-t-Bu)4 with different alkyling agent (RLi, Me2Zn, AlMe3, RMgX) were performed. Unfortunately these attempts were unsuccessful, and usually the reaction proceeds with metal reduction or without specific products. The synthesis and crystal structure determination of Cr(i-C3H7)4 is described. All four isopropyl groups are -bonded to the Cr(IV) center, which is located in a tetrahedral environment.