HIGHER-VALENT DERIVATIVES OF THE D-METAL ACIDS .13. HOMOSCORPIONATES AS TRIPODAL ANCHORING LIGANDS OF CHLORO FUNCTIONALIZED OXO AND IMIDO COMPLEXES OF ELEMENTS OF GROUP 5-7

Hydridotris(pyrazolyl)borate complexes of elements of group 5-7 have b een prepared by reaction of d0-metalloyl chlorides [M(Y)nClm)x (Y = O, NR) with KTp (Tp* = kappa3-HB(3,5Me2pz) 3). Thus [NbOCl3]x and [TaOC l3]x are converted into monomeric and well-characterized oxo complexes [Tp Nb(O)Cl2] (1) and [Tp*Ta(O)Cl2] (2). In a similar way [Tp* Mo(O) 2Cl] (3) and [TpW(O)2Cl] (4) have been obtained from the oxo chloride s [MoO2Cl2]x and [WO2Cl2]x, respectively. tert-Butylamine reacts with NbCl5 and TaCl5 in the presence of pyridine to give the imido pyridine complexes [Nb(NtBu)Cl3(py)2] (5) and [Ta(NtBu)Cl3(py)2] (6) in excell ent yield. Imido complexes [TpV(NtBu)Cl2] (7), [Tp* Nb(NtBu)Cl2] (8), and [TpTa(NtBu)Cl2] (9) are formed by the reaction of KTp* with the precursers [V(NtBu)Cl3]x or 5 and 6, respectively. The corresponding i mido complexes of group 6, namely [TpCr(NtBu)2Cl] (10), [Tp*Mo(NtBu)2 Cl] (11), and [TpW(NR)2Cl] (R = tBu 12a, 2,4,6-Mesityl 12b, SO2Ph 12c ) are obtained directly from the imidoyl chlorides or their complexes with Lewis bases. 11 and 12 are prone to protonation at the imido liga nd to yield cationic amido species [TpM(NtBu)(NHtBu)Cl]BF4 (M = Mo 13 , W 14). Finally the preparation of cationic imido rhenium complex [Tp Re(NtBu)2Cl]PF6 (15), isoelectronic with 10-12, is described. The mo lecular structure of 11 has been determined by X-ray diffraction. Desp ite of a maximum electron count of 20 valence electrons, all three pyr azolyl groups of the tripodal ligand are facially coordinated. In a wa y similar to the well-known ring slippage of analogous cyclopentadieny l complexes, the weakest bound pyrazolyl ligand is asymmetrically atta ched to molybdenum deviating from the positions expected for local C3v symmetry.