One-step synthesis of Mo(0) and W(0) bis(dinitrogen) complexes with the linear tetraphosphine ligand prP_4: Stereoselective formation of cis-[M(N_2)_2(rac-prP_4)] and trans-[M(N _2)_2(meso-prP_4)]; M = Mo, W

摘要

A new synthetic pathway to Chatt-type Mo(0) and W(0) bis(dinitrogen) complexes with the ligand prP_4 is presented (prP_4 is a linear tetraphos ligand with two ethylene bridges and a central propylene bridge). The synthesis starts from MoCl_5 and WCl_6, respectively, employing Mg as reductant. Whereas the electrochemical reduction of the oxido-iodido-molybdenum(iv) complex [Mo(O)I(meso-prP_4] ~+ (1) only gave trans-[Mo(N_2)_2(meso-prP _4)] (2a; R?mer et al., Eur. J. Inorg. Chem.2008, 3258), the direct synthesis under normal conditions affords both trans and cis complexes 2a and 2b. The reaction products are characterised by vibrational and NMR spectroscopy. Moreover, a single-crystal X-ray structure determination of cis-α-[Mo(N_2)_2(rac-prP_4)] (2b) is performed. In contrast to the trans bis(dinitrogen)molybdenum(0) complex 2a supported by the meso prP_4 ligand the corresponding cis-complex is exclusively coordinated by the rac isomer of prP_4. The reactivity of 2 with acids is investigated as well, leading to the NNH_2 complex [MoF(NNH_2)(meso-prP_4)]BF_4 (15). Analogous results are obtained with the tungsten complexes.