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

Abstract

The preparation and reactivity of a novel molybdenum dinitrogen complex supported by a nitrogen-centred tripodal phosphine ligand (N-triphos, N(CH2PPh2)3, NP3Ph) are reported. Reaction of N-triphos with [MoX3(THF)3] (X = Cl, Br, I) gave the Mo(iii) complex [MoX3(κ2-NP3Ph)(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(N2)(dppm)(κ3-NP3Ph)] (2), which exhibits moderate dinitrogen activation. An additional hydride complex, [Mo(H)2(dppm)(κ3-NP3Ph)] (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+, BBr3 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)(PMePh2)(PCP)][B(C6F5)4] (7), where PCP, [Ph2PCNHCH2PPh2] is the carbenic ligand formed upon rearrangement from the reaction of 2 with M[B(C6F5)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-Centered Tripodal Phosphine Re(V) and Tc(V) Oxo Complexes: Revisiting a [3 + 2] Mixed-Ligand Approach

“… 37 This ligand was selected due to its ease of synthesis and its known propensity toward forming facial κ 3 -coordination geometries with transition metals in a number of different oxidation states. 38 , 40 , 41 …”

“… 34 − 36 Previous work in our group has utilized the facial coordination of these ligands in the synthesis of hydrogenation catalysts for biomass-derived levulinic acid with ruthenium and other transition metals; 37 − 39 investigation of the electronic and steric properties of several NP 3 R ligands with tungsten; 40 and dinitrogen coordination and activation using molybdenum and cobalt complexes. 41 , 42 …”

Cobalt(-i) triphos dinitrogen complexes: activation and silyl-functionalisation of N2

“…Our group has been investigating the N-triphos ligand motif ({N(CH2PR2)3}), [9][10][11][12][13] and recently, we reported a Mo/N-triphos N2 complex. This complex showed moderate N2 activation that was comparable to the C-triphos analogue, but with a varied reactivity profile.…”

“…This complex showed moderate N2 activation that was comparable to the C-triphos analogue, but with a varied reactivity profile. 13 Of the many triphos derivatives, N-triphos is advantageous (particularly over the similar C-triphos system), due to the ease of synthetic tunability of the steric and electronic ligand parameters, and the accessible lone pair on the apical nitrogen provides an additional reactive site. 11,12 We sought to investigate the relatively unexplored potential of cobalt for N2 activation using the neutral N-triphos (N(CH2PPh2)3 or NP3 Ph ) and C-triphos ({MeC(CH2PPh2)3} or MeCP3 Ph ) scaffolds.…”

HCOOH disproportionation to MeOH promoted by molybdenum PNP complexes

“…Their hydride peaks all show a single well-defined triplet, the intensity of which cannot be compared to any other signal in the spectrum to establish whether it corresponds to one or two hydrogens. 43 Low temperature spectra recorded down to −76 °C did not help clarify this point (Fig. SI-30 † ).…”