Comparative Study of Phosphine and N‐Heterocyclic Carbene Stabilized Group 13 Adducts [L(EH3)] and [L2(E2Hn)]1. Issue 20 (19th March 2013)

• Record Type: Journal Article
• Authors: Holzmann, Nicole; Stasch, Andreas; Jones, Cameron; Frenking, Gernot
• Is Part Of: Chemistry. Volume 19:Issue 20(2013)
• Page Start: 6467
• Page End: 6479
• Publication Date: 2013-03-19
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201203679
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Quantum chemical calculations using density functional theory at the BP86/TZ2P level have been carried out to determine the geometries and stabilities of Group 13 adducts [(PMe<sub>3</sub>)(EH<sub>3</sub>)] and [(PMe<sub>3</sub>)<sub>2</sub>(E<sub>2</sub>H<sub><italic>n</italic></sub>)] (E=B–In; <italic>n</italic>=4, 2, 0). The optimized geometries exhibit, in most cases, similar features to those of related adducts [(NHC<sup>Me</sup>)(EH<sub>3</sub>)] and [(NHC<sup>Me</sup>)<sub>2</sub>(E<sub>2</sub>H<sub><italic>n</italic></sub>)] with a few exceptions that can be explained by the different donor strengths of the ligands. The calculations show that the carbene ligand L=NHC<sup>Me</sup> (:C(NMeCH)<sub>2</sub>) is a significantly stronger donor than L=PMe<sub>3</sub>. The equilibrium geometries of [L(EH<sub>3</sub>)] possess, in all cases, a pyramidal structure, whereas the complexes [L<sub>2</sub>(E<sub>2</sub>H<sub>4</sub>)] always have an antiperiplanar arrangement of the ligands L. The phosphine ligands in [(PMe<sub>3</sub>)<sub>2</sub>(B<sub>2</sub>H<sub>2</sub>)], which has <italic>C<sub>s</sub></italic> symmetry, are in the same plane as the B<sub>2</sub>H<sub>2</sub> moiety, whereas the heavier homologues [(PMe<sub>3</sub>)<sub>2</sub>(E<sub>2</sub>H<sub>2</sub>)] (E=Al, Ga, In) have <italic>C<sub>i</sub></italic> symmetry in which the ligands bind side‐on to the E<sub>2</sub>H<sub>2</sub> acceptor. This is in contrast to the [(NHC<sup>Me</sup>)<sub>2</sub>(E<sub>2</sub>H<sub>2</sub>)] adducts for which the NHC<sup>Me</sup> donor always binds in the same plane as E<sub>2</sub>H<sub>2</sub> except for the indium complex [(NHC<sup>Me</sup>)<sub>2</sub>(In<sub>2</sub>H<sub>2</sub>)], which exhibits side‐on bonding. The boron complexes [L<sub>2</sub>(B<sub>2</sub>)] (L=PMe<sub>3</sub> and NHC<sup>Me</sup>) possess a linear arrangement of the LBBL moiety, which has a BB triple bond. The heavier homologues [L<sub>2</sub>(E<sub>2</sub>)] have antiperiplanar arrangements of the LEEL moieties, except for [(PMe<sub>3</sub>)<sub>2</sub>(In<sub>2</sub>)], which has a twisted structure in which the PInInP torsion angle is 123.0°. The structural features of the complexes [L(EH<sub>3</sub>)] and [L<sub>2</sub>(E<sub>2</sub>H<sub><italic>n</italic></sub>)] can be explained in terms of donor–acceptor interactions between the donors L and the acceptors EH<sub>3</sub> and E<sub>2</sub>H<sub><italic>n</italic></sub>, which have been analyzed quantitatively by using the energy decomposition analysis (EDA) method. The calculations predict that the hydrogenation reaction of the dimeric magnesium(I) compound L′MgMgL′ with the complexes [L(EH<sub>3</sub>)] is energetically more favorable for L=PMe<sub>3</sub> than for NHC<sup>Me</sup>.</p> </abstract>