One-step synthesis of Mo(0) and W(0) bis(dinitrogen) complexes with the linear tetraphosphine ligand prP4: stereoselective formation of cis-[M(N2)2(rac-prP4)] and trans-[M(N2)2(meso-prP4)]; M = Mo, W

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.