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 been 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 [TaOCl3]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 [Tp*W(O)2Cl] (4) have been obtained from the oxo chlorides [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 excellent yield. Imido complexes [Tp*V(NtBu)Cl2] (7), [Tp* Nb(NtBu)Cl2] (8), and [Tp*Ta(NtBu)Cl2] (9) are formed by the reaction of KTp* with the precursers [V(NtBu)Cl3]x or 5 and 6, respectively. The corresponding imido complexes of group 6, namely [Tp*Cr(NtBu)2Cl] (10), [Tp*Mo(NtBu)2Cl] (11), and [Tp*W(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 ligand to yield cationic amido species [Tp*M(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 molecular structure of 11 has been determined by X-ray diffraction. Despite of a maximum electron count of 20 valence electrons, all three pyrazolyl groups of the tripodal ligand are facially coordinated. In a way similar to the well-known ring slippage of analogous cyclopentadienyl complexes, the weakest bound pyrazolyl ligand is asymmetrically attached to molybdenum deviating from the positions expected for local C3v symmetry.