Octahedral Molybdenum(0) Monodinitrogen Complexes Facially Coordinated by the Tripodal Ligand 1,1,1‐Tris(diphenylphosphanylmethyl)ethane – Influence of Diphosphane Coligands on the Activation of N₂

Abstract

The synthesis and physicochemical properties of the new molybdenum dinitrogen complexes [Mo(N 2 )(tdppme)-(dmpm)] (2) and [Mo(N 2 )(tdppme)(dppm)] (3) are reported. Complexes 2 and 3 are facially coordinated by the tripodal ligand 1,1,1-tris(diphenylphosphanylmethyl)ethane (tdppme) and contain the bidentate coligands bis(dimethylphosphanyl)methane (dmpm) and bis(diphenylphosphanyl)-methane (dppm), respectively. They are accessible by amalgam reduction of the Mo III precursor [MoBr 3 (tdppme)] (1) under nitrogen in the presence of dppm and dmpm, respectively. Protonation of 2 with trifluoromethanesulfonic acid

Molybdenum(0)‐N2 Complexes Supported by the Tripod Ligand 1,1,1‐Tris(Diphenyl‐Phosphinomethyl)Ethane: Steric Influence on the Coordination of Mono‐ and Diphosphine Coligands

“…[Mo(N 2 )(tdppme)(dppm)] and [Mo(N 2 )(dpepp)(dppm)] (dpepp = bis(diphenylphosphinoethyl)phenylphosphine). [10,16] [20] Overall, the IR data of the complex supported by the tdppme ligand indicate a slightly lower activation of the N 2 ligand resulting from the electron-withdrawing effect of the diphenylphosphine groups. The IR data is listed in Table 1 for comparison.…”

“…The complexes [Mo(N 2 )-(tdppme)(dppm)] and [Mo(N 2 )(tdppme)(dmpm)] thus are obtained without difficulty. [16] Instead of one diphosphine, two PMe 3 ligands can be accommodated as well; however, we were not able to obtain the corresponding complex 4 ], [18,19] cis-[Mo(N 2 ) 2 -(PMe 2 Ph) 4 ], [20] and cis-α-[Mo(N 2 ) 2 (rac-prP 4 )]. [13] Since tdppme occupies the trans-position of one N 2 ligand only the cis-form is observed in bis(dinitrogen)complexes supported by this ligand.…”

“…The space-filling structure derived by DFT calculations showed the large steric crowding around the molybdenum-N 2 moiety. [16] Unfortunately, the dinitrogen ligand of this complex turned out to be not sufficiently activated for protonation.…”

“…Importantly, protonation of [Mo(N 2 ) (tdppme)(dmpm)] with triflic acid led to the NNH 2 complex [Mo(NNH 2 )(tdppme)(dmpm)](OTf) 2 with retention of the pentaphosphine coordination, thus principally demonstrating the capability of such systems to serve as catalysts in a nitrogen-fixing cycle. [16] Eventually, we were able to tune the activation of the N 2 ligand by consecutively interchanging aryland alkylphosphines in the tripod ligand. [14][15][16][17] In order to de-spectroscopy.…”

“…[19] [Mo(N 2 )(PMe3) 5 ] 1950 [18] cis-α-[Mo(N 2 ) 2 (rac-prP 4 )] 2022, 1972 [13] cis-[Mo(N 2 ) 2 (PMe 2 Ph) 4 ] 2025, 1940 [20] [Mo(N 2 )(tdppme)(dppm)] 2035 [16] [Mo(N 2 )(tdppme)(dppm)] 1980 [16] [Mo(N 2 )(dpepp)(dppm)] 1979 [10] Even though IR data suggests that the N 2 ligand in [Mo(N 2 )-(tdppme)(PMe 3 ) 2 ] (3) and [Mo(N 2 ) 2 (tdppme)(PMe 2 Ph)] (4) is activated, protonation with trifluoromethanesulfonic acid did not lead to any defined derivatives like [Mo(NNH 2 )(tdppme)-(dppm)]. [16] This can be explained by the absence of a stabilizing chelate co-ligand in these complexes. We also investigated the use of the bulkier monophosphines PMePh 2 2 ], as inferred from the respective IR and 31 P NMR spectra.…”