Molybdenum dinitrogen complexes facially coordinated by linear tridentate PEP ligands (E = N or P): impact of the central E donor in trans-position to N₂

Abstract

The syntheses of molybdenum dinitrogen complexes supported by the tridentate PEP ligands (E = N, P) prPP(Ph)P = (Ph2PCH2CH2CH2)2P(Ph), prPPHP = (Ph2PCH2CH2CH2)2PH, PN(Ph)P = (Ph2PCH2CH2)2N(Ph) and prPN(Ph)P = (Ph2PCH2CH2CH2)2N(Ph) are reported. Together with the coligand dmpm = (CH3)2PCH2P(CH3)2 dinitrogen complexes of the type [Mo(N2)(PEP)(dmpm)] are formed. The new systems are characterized by IR and NMR spectroscopy and compared with the literature-known complex [Mo(N2)(dpepp)(dmpm)] (1) (dpepp = PhP(CH2CH2PPh2)2). The consequences of the substitution of the central P-donor of dpepp by N and the replacement of its C2 by C3 linkages as well as the exchange of the EPh by an EH function are investigated with respect to the stability of the corresponding N2-complexes. Importantly, the activation of the N2 ligand drastically increases upon replacing the trans-phosphine with a trans-amine donor.

Coordination of 3‐Methylindole‐Based Tripodal Tetraphosphine Ligands to Iron(+II), Cobalt(+II), and Nickel(+II) and Investigations of their Subsequent Two‐Electron Reduction

“…The weakest activation of the N 2 ligand is observed in the case of the connectivity isomer L2 , which features a more π‐acidic pivotal phosphine ( trans to the N 2 ). This is in line with the studies of the influence of π‐acidity of the donors trans to molybdenum‐coordinated N 2 by Tuczek et al who reported that when going from purely σ‐donating N‐donor to a slightly π‐acidic P‐donor the N 2 stretch frequency shifts to higher wavenumbers . The effect of the trans ‐effect of nitrogen vs. phosphorus in terms of N 2 activation is also apparent when comparing the IR data for Fe 0 (N 2 )[N(CH 2 CH 2 PPh 2 ) 3 ] ν N2 = 1967 cm –1 vs. Fe 0 (N 2 )[P(CH 2 CH 2 P i Pr 2 ) 3 ] (ν N2 = 1985 cm –1 ) as reported by the groups of George and Zubieta and Field, respectively.…”

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

“…Tuczek and co-workers also reported the formation of Me3Al-N2 adduct complexes by the addition of trimethylaluminium to various molybdenum dinitrogen complexes with pentaphosphine ligand environments. 14,32 With regards to borane Lewis acid functionalisation, recent promising work by both Szymczak and Etienne has shown that the addition of boranes to iron or molybdenum/tungsten dinitrogen complexes results in adduct formation of the borane to the dinitrogen ligand, enhancing dinitrogen activation and allowing for further dinitrogen functionalisation by protonation, borylation or silylation. 33,34 We surmised that a similar addition of a strongly Lewis acidic borane could also result in adduct formation at the dinitrogen ligand of 2.…”

A Chatt‐Type Catalyst with One Coordination Site for Dinitrogen Reduction to Ammonia

“…In view of the above-mentioned problemso ft he classic Chatt complexes,w ehad in the past developedaseries of molybdenum dinitrogen complexes in which the trans position is occupied by ad onor atom of am ultidentate ligand.T hese systems were intended to provide only one site for the coordination and reduction of N 2 and avoid all other ligand exchange reactions occurring at the single Mo center. Initially, we had employed ac ombination of at ripodal( 1) [21] or al inear tridentate ligand (2) [22] with ab identate co-ligand (Scheme 4) for this purpose. Compounds 2 and 1,h owever,s uffered from isomerization and, respectively,i nstability of the tridentate phosphine ligand coordinationu pon protonation of the N 2 -complex, which was ascribed to the fact that the trans-donor is not fixed strongly enough to the center Mo atom.…”

“…In comparison, n NN of 1 and 2 are by 45 and 50 cm À1 higher, re- Scheme3.Formation of ad inuclear Mo I complex from [Mo(N 2 ) 2 (depe) 2 ]v ia one-electron oxidation, leadingt oaMo IV nitrido complex by dinitrogen cleavage; adapted from Masuda et al [17] Scheme4. [Mo(N 2 )(tdppme)(dmpm)] (1) [21] [Mo(N 2 )(prPPHP)(dmpm)] [22] (2), and [Mo(N 2 )(P 2 Me PP 2 Ph )] (3). [23] spectively.T he activation of N 2 is af unctiono ft he electron density on the Mo 0 center,w hich in turn sensitively depends on the type of phosphine donors.…”