Synthesis and reactivity of an N-triphos Mo(0) dinitrogen complex

The preparation and reactivity of a novel molybdenum dinitrogen complex supported by a nitrogen-centred tripodal phosphine ligand (N-triphos, N(CH 2 PPh 2 ) 3 , NP 3 Ph ) are reported. Reaction of N-triphos with [MoX 3 (THF) 3 ] (X = Cl, Br, I) gave the Mo( iii ) complex [MoX 3 (κ 2 -NP 3 Ph )(THF)] ( 1 ), where bidentate N-triphos coordination was observed. Reduction of this complex in the presence of dppm (bis(diphenylphosphino)methane) gave the dinitrogen complex [Mo(N 2 )(dppm)(κ 3 -NP 3 Ph )] ( 2 ), which exhibits moderate dinitrogen activation. An additional hydride complex, [Mo(H) 2 (dppm)(κ 3 -NP 3 Ph )] ( 4 ), was produced either as a minor side product during the reduction step, or as a major product by direct hydrogenation of the dinitrogen complex 2 . The reactivity of the dinitrogen complex 2 with a range of Lewis acids was also investigated. At low temperatures, protic or borane Lewis acids (H + , BBr 3 and tris(pentafluorophenyl)borane (BCF)) were found to coordinate to the apical nitrogen atom of the N-triphos ligand, with no conclusive evidence of any functionalisation of the dinitrogen ligand. Alkali metal Lewis acid addition to 2 resulted in the unexpected rearrangement of the N-triphos ligand to form [Mo(dppm)(PMePh 2 )(PCP)][B(C 6 F 5 ) 4 ] ( 7 ), where PCP, [Ph 2 PCNHCH 2 PPh 2 ] is the carbenic ligand formed upon rearrangement from the reaction of 2 with M[B(C 6 F 5 ) 4 ] (M = Li, Na or K). Single crystal X-ray diffraction of complexes 1 , 2 , 4 and 7 provided structural confirmation of the N-triphos molybdenum complexes described. N-Triphos/Mo(0)-dinitrogen reactivity: hydrogenation; Lewis acid addition; and alkali metal mediated ligand rearrangement.