Mo– and W–N2 and –CO complexes with novel mixed P/N ligands: Structural properties and implications to synthetic nitrogen fixation

Four new ligands containing a pyridine or thiazole group and one or more N-(diphenylphosphinomethyl)amine functions have been prepared and employed for the synthesis of Mo(0) and W(0) carbonyl and dinitrogen complexes. For comparison coordination of the literature-known ligand N,N-bis(diphenylphosphinomethyl)-methylamine (PNP, 1) to such systems has been investigated as well. Two new ligands are N,N-bis(diphenylphosphinomethyl)-2-aminopyridine (pyNP2, 2) and N,N′-bis(diphenylphosphinomethyl)-2,6-diaminopyridine (PpyP, 3). In a third new ligand, N-diphenylphosphinomethyl-2-aminothiazole (thiazNP, 4), the pyridine group is replaced by thiazol. Finally, the pentadentate ligand N,N,N′,N′-tetrakis(diphenylphosphinomethyl)-2,6-diaminopyridine (pyN2P4, 5) has been synthesized. Coordination of ligands 2, 3 and 4 to low-valent metal centers is investigated on the basis of the three molybdenum carbonyl complexes [Mo(CO)3(NCCH3)(pyNP2)] (6), [Mo(CO)4(PpyP)] (7) and [Mo(CO)4(thiazNP)] (8), respectively, all of which are structurally characterized. Moreover, employing ligands 1 and 2 the two dinitrogen complexes [W(N2)2(dppe)(PNP)] (9) and [Mo(N2)2(dppe)(pyNP2) (10), respectively, are prepared. Both systems are investigated by vibrational and NMR spectroscopy; in addition, complex 10 is structurally characterized.