Mo– and W–N 2 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 (pyNP 2, 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 (pyN 2 P 4, 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 (NCCH 3 )(pyNP 2 )] ( 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(N 2 ) 2 (dppe)(PNP)] ( 9 ) and [Mo(N 2 ) 2 (dppe)(pyNP 2 ) ( 10 ), respectively, are prepared. Both systems are investigated by vibrational and NMR spectroscopy; in addition, complex 10 is structurally characterized.