Push–Pull Activation of N ₂ : Coordination of Lewis Acids to Dinitrogen Complexes

Abstract

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Synthesis, Characterization, and Comparative Theoretical Investigation of Dinitrogen-Bridged Group 6-Gold Heterobimetallic Complexes

“…To the best of our knowledge, there is only one example of a group 6 N 2 complex reacting with a Lewis acidic, d-block metal compound in the literature, to lead to the Mo(0)/Fe­(II) heterobimetallic complex [(toluene)­(PPh 3 ) 2 Mo­(μ-N 2 )­Fe­(Cp)­(dmpe)]­[BF 4 ] (dmpe = 1,2-bis­(dimethylphosphino)­ethane) Its structure is however very similar to the numerous LA–TMs adducts reported with the d 6 trans -[ReCl­(N 2 )­(PMe 2 Ph) 4 ] complex, and they contrast strikingly with the [Au­(NHC)] + adducts of 2 W and 3 W . In typical adducts with a Lewis acidic metal M′, the M–(μ-N 2 )–M′ core is essentially linear owing to the implication of empty or partially filled d orbitals of M′ in a four-center π molecular orbital .…”

“…Generally, the synthesis of μ-η 1 :η 1 -N 2 -bridged heterobimetallic complexes has been aimed at devising original reactivities for the N 2 ligand since in such a coordination environment, dinitrogen may be polarized to an extent that is not reached with other coordination modes as a result of “push–pull” activation. 6 Starting from a mononuclear end-on dinitrogen complex, two synthetic approaches can be envisioned to prepare a N 2 -bridged heterobimetallic compound, and both take advantage of the basicity imparted to the terminal nitrogen atom of the N 2 ligand upon coordination: (i) formation of a Lewis acid–base adduct with a Lewis acidic TM complex and (ii) halide substitution at a high valent TM complex ( Scheme 1 ). The team of Chatt has systematically investigated the coordination of various early d-block Lewis acids through dative bonding with the terminal N of the N 2 ligand of trans -[ReCl(N 2 )(PMe 2 Ph) 4 ] and recorded more or less important bathochromic shifts of the ν(N 2 ) elongation frequency in IR spectroscopy.…”

“…N 2 -bridged heterobimetallic complexes of the transition elements are more scarcely encountered among the literature and only a handful have been completely characterized. Generally, the synthesis of μ-η 1 :η 1 -N 2 -bridged heterobimetallic complexes has been aimed at devising original reactivities for the N 2 ligand since in such a coordination environment, dinitrogen may be polarized to an extent that is not reached with other coordination modes as a result of “push–pull” activation . Starting from a mononuclear end-on dinitrogen complex, two synthetic approaches can be envisioned to prepare a N 2 -bridged heterobimetallic compound, and both take advantage of the basicity imparted to the terminal nitrogen atom of the N 2 ligand upon coordination: (i) formation of a Lewis acid–base adduct with a Lewis acidic TM complex and (ii) halide substitution at a high valent TM complex (Scheme ).…”

Heterobimetallic-Mediated Dinitrogen Functionalization: N–C Bond Formation at Rhenium-Group 9 Diazenido Complexes

“… ,, Bimetallic complexes are also capable of a “dissociative” activation strategy in which cleavage of N 2 to form two terminal nitrides occurs prior to N functionalization. ,, Recently, models have been developed to predict the tendency of metal complexes to form terminal monometallic versus bridging bimetallic dinitrogen complexes, which in turn should aid the design of species with desired reactivity patterns. Finally, transition metal-mediated N 2 functionalization can also be facilitated through the use of noncovalent or hydrogen bonds, coordination of Lewis acids (LAs), or other secondary sphere interactions (similar to those in nitrogenase active sites) to enhance dinitrogen activation and reactivity. − For example, Szymczak and co-workers found that coordination of LAs to the distal nitrogen of iron dinitrogen complexes causes a “push–pull”-type activation of the dinitrogen fragment that primes these complexes for protonation at the distal N atom and disfavors undesired protonation at the Fe center …”

Dinitrogen-derived (diarylboryl)diazenido complexes with differing coordination to the thallium cation

“…8 We have shown these electrophilic molecules can interact with an end-on bound dinitrogen ligand, 8 a ,9 affording hetero-dinuclear, N 2 -bridged edifices that can also be viewed as frustrated Lewis pair 10 templates for N 2 activation 11 (Scheme 1). Willing to exacerbate the “push–pull” effect 12 in these FLP templates to disclose new reactivity for the N 2 ligand, we have looked for a way to prepare N 2 -derived cationic boryldiazenido tungsten complexes as the equivalent of a “M(0)–N 2 –borinium” dinuclear system. 13 Since, to the best of our knowledge, only a handful of borinium cations have been reported and they are not easily prepared, 14 we have first elected a route starting with the 1,3-addition of the B–Cl bond of a diarylchloroborane over the M–N 2 unit of Hidai-Chatt tungsten complexes.…”