Lewis Adducts of the Side‐On End‐On Dinitrogen‐Bridged Complex [{(NPN)Ta}₂(μ‐H)₂(μ‐η¹:η²‐N₂)] with AlMe₃, GaMe₃, and B(C₆F₅)₃: Synthesis, Structure, and Spectroscopic Properties

Abstract

Reaction of the side-on end-on dinitrogen complex [{(NPN)Ta}(2)(mu-H)(2)(mu-eta(1):eta(2)-N(2))] (1; in which NPN=(PhNSiMe(2)CH(2))(2)PPh), with the Lewis acids XR(3) results in the adducts [{(NPN)Ta}(2)(mu-H)(2)(mu-eta(1):eta(2)-NNXR(3))], XR(3)=GaMe(3) (2), AlMe(3) (3), and B(C(6)F(5))(3) (4). The solid-state molecular structures of 2, 3, and 4 demonstrate that the N-N bond length increases relative to those found in 1 by 0.036, 0.043, and 0.073 A, respectively. In solution complexes 2-4 are fluxional as evidenced by variable-temperature (1)H NMR spectroscopy. The (15)N{(1)H} NMR spectra of 2-4 are reported; furthermore, their vibrational properties and electronic structures are evaluated. The vibrational structures are found to be closely related to that of the parent complex 1. Detailed spectroscopic analysis on 2-4 leads to the identification of the theoretically expected six normal modes of the Ta(2)N(2) core. On the basis of experimental frequencies and the QCB-NCA procedure, the force constants are determined. Importantly, the N-N force constant decreases from 2.430 mdyn A(-1) in 1 to 1.876 (2), 1.729 (3), and 1.515 mdyn A(-1) (4), in line with the sequence of N-N bond lengths determined crystallographically. DFT calculations on a generic model of the Lewis acid adducts 2-4 reveal that the major donor interaction between the terminal nitrogen atom and the Lewis acid is mediated by a sigma/pi hybrid molecular orbital of N(2), corresponding to a sigma bond. Charge analysis performed for the adducts indicates that the negative charge on the terminal nitrogen atom of the dinitrogen ligand increases with respect to 1. The lengthening of the N-N bond observed for the Lewis adducts is therefore explained by the fact that charge donation from the complex fragment into the pi* orbitals of dinitrogen is increased, while electron density from the N-N bonding orbitals p(sigma) and pi(h) is withdrawn due to the sigma interaction with the Lewis acid.

Remarkable Dinitrogen Activation and Cleavage by the Gd Dimer: From Dinitrogen Complexes to Ring and Cage Nitrides

“…[10] The NÀN stretching frequencies of these dinuclear complexes were determined to be around 1150 cm À1 , [11] similar to that reported here. The [GdGdNN] and [Gd 2 (m-NN)] isomers with terminal and bridging N 2 ligands were also calculated, but they are 55.6 and 34.9 kcal mol À1 higher in energy than (2.0 km mol À1 ), respectively.…”

Bimetallic Activation of White Phosphorus

“…11 Theoretical studies are in progress to clarify the nature of 6 and the general mechanism accounting for the intriguing single and double P-P coupling between dppm and activated P 4 . 12 In summary, we have shown that bimetallic cooperativity is relevant to promote P 4 activation and to govern the activation products as for the recent reports in N 13 2 and P 10 4 chemistry. Complexes 4 and 5 represent a new bonding mode for a metal-activated P 4 ligand featuring an unprecedented pentaphosphorus moiety resulting from the intramolecular coupling of the metal-activated P 4 -tetrahedron with a Downloaded by [Simon Fraser University] at 13:30 18 November 2014 neighbouring nucleophilic dppm ligand.…”

Dinitrogen activation by group 4 and group 5 metal complexes supported by phosphine-amido containing ligand manifolds

“…As shown in Scheme 17, the exposed nitrogen of the side-on end-on N 2 unit forms adducts with a variety of simple Lewis acids [77]. Specifically, trimethylaluminum (17.…”