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

Abstract

We have prepared and characterized a series of unprecedented group 6–group 11, N 2 -bridged, heterobimetallic [ML 4 (η 1 -N 2 )(μ-η 1 :η 1 -N 2 )Au(NHC)] + complexes (M = Mo, W, L 2 = diphosphine) by treatment of trans -[ML 4 (N 2 ) 2 ] with a cationic gold(I) complex [Au(NHC)] + . The adducts are very labile in solution and in the solid, especially in the case of molybdenum, and decomposition pathways are likely initiated by electron transfers from the zerovalent group 6 atom to gold. Spectroscopic and structural parameters point to the fact that the gold adducts are very similar to Lewis pairs formed out of strong main-group Lewis acids (LA) and low-valent, end-on dinitrogen complexes, with a bent M–N–N–Au motif. To verify how far the analogy goes, we computed the electronic structures of [W(depe) 2 (η 1 -N 2 )(μ-η 1 :η 1 -N 2 )AuNHC] + ( 10 W + ) and [W(depe) 2 (η 1 -N 2 )(μ-η 1 :η 1 -N 2 )B(C 6 F 5 ) 3 ] ( 11 W ). A careful analysis of the frontier orbitals of both compounds shows that a filled orbital resulting from the combination of the π* orbital of the bridging N 2 with a d orbital of the group 6 metal overlaps in 10 W + with an empty sd hybrid orbital at gold, whereas in 11 W with an sp 3 hybrid orbital at boron. The bent N–N–LA arrangement maximizes these interactions, providing a similar level of N 2 “push–pull” activation in the two compounds. In the gold case, the HOMO–2 orbital is further delocalized to the empty carbenic p orbital, and an NBO analysis suggests an important electrostatic component in the μ-N 2 –[Au(NHC)] + bond.

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

“…Despite the array of design strategies for both mono- and bimetallic N 2 fixation, there are relatively few structurally characterized, molecular, heterobimetallic dinitrogen complexes in which both transition metal centers interact with an activated dinitrogen fragment. − Furthermore, to our knowledge, to date, there are no reported examples of N–C bond formation at a heterobimetallic dinitrogen complex. As such, we reasoned that the exploration of heterobimetallic dinitrogen complexes that either display nontraditional dinitrogen coordination geometries or enforce a “push–pull” activation effect between metal centers might increase the likelihood of N–C bond formation.…”

Divergent CO2 Activation by Tuning the Lewis Acid in Iron‐Based Bimetallic Systems

“…It is important to remark that substitution of CO 2 by the very weakly coordinating N 2 ligand is rare [7] and, for this system, it has only been observed in the presence of gold, further certifying the crucial influence exerted by coordination of Lewis acids to transition metals. Formation of 6 from either [(depe) 2 Fe(CO 2 )] or [(depe) 2 Fe(N 2 )] contrasts with prior studies from Simonneau where Au I compounds are prone to participate in push‐pull interactions to activate dinitrogen, [32] while herein the formation of the Fe 0 →Au I dative bond prevails. Changing the atmosphere to an approximate equimolar N 2 /CO 2 mixture led to the presence of both precursor 1 and bimetallic adduct 6 , along with other decomposition products.…”

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

“…We have attempted the synthesis of cationic boryldiazenido-tungsten complexes to judge the impact of N 2 “push–pull” activation in “W(0)–borinium” FLP templates, benchmarking against the already reported B(C 6 F 5 ) 3 adducts. 8 a ,19 We could prepare and fully characterize boryldiazenido(chloro)-tungsten complexes by formal 1,3 addition of the B–Cl bond of diaryl chloroboranes, a reaction that complements the one reported by Braunschweig and employing aryl dichloroboranes. 15 b However, chloride scavenging with Na or Ag BAr F 4 seemed to be accompanied with undesired redox processes.…”