Bis(imino)carbazolate: A Master Key for Barium Chemistry

Abstract

Reported here is a readily available bis(imino)carbazole‐based proligand that constitutes a convenient entry point into the challenging synthetic molecular chemistry of barium. It enables the preparation of rare or even, up to now, unknown, solution‐stable heteroleptic barium complexes. The syntheses and structural features for the first molecular barium fluoride and the first barium stannylide, with an unsupported Ba−Sn bond, are described, along with other carbazolate barium species: an amide (both a remarkably stable starting material and an excellent hydrophosphination precatalyst), iodide, and silanylide. DFT analysis of bonding patterns in the barium stannylide and barium silanylide highlights a prevailingly ionic barium–tetrelide bond with a small covalent contribution.

Metal–metal bonded alkaline-earth distannyls

“…They are almost coplanar, and the Ba1 atom rests only 0.031(2) Å away from the best average plane defined by these five O-atoms. The Ba1-Sn interatomic distances (3.6575 (12) and 3.6821(12) Å) are noticeably longer than in the heteroleptic complex [{Carb DiPP }BaSn(SiMe3)3.thf] (3.521(3) Å), 12 the only other referenced complex with an unsupported Ba-Sn bond. 23 The Ba1-Sn bond lengths in 3' are also much longer than in the strontium complex 2' (3.4293(4) Å), with an increase greater than expected from the difference of ionic radii between Sr 2+ and Ba 2+ (1.18 and 1.35 Å, respectively).…”

“…They represent the first families of homologous alkaline-earth stannylenes with the large Ae metals Ca, Sr and Ba, and complement the handful of related complexes that display Ae-Sn unsupported bonds. [10][11][12][13] Beyond Westerhausen's seminal [Ca(SnMe3)2. (thf)4], 10 they also are the sole sets of homoleptic Ae stannylides available to date.…”

“…properties are now being unravelled with these metals, 2,6,[11][12][13][34][35][36][37] and this study of heterobimetallic compounds featuring Ae-Sn bonds constitutes the initial step in a wider research program aimed at exploring and exploiting the specificities of the bonding between s-and p-block metals.…”

“…10 The heteroleptic β-diketiminato-calcium stannyls [{BDI DiPP }CaSn(μ2-H)(SnPh3)Ca{BDI DiPP }] and [{BDI DiPP }CaSnPh3]2, as well as the monomeric Lewis adducts [{BDI DiPP }CaSnPh3•(L)x] (L = thf, 2,2,5,5-Me4-thf and Ph3P=O; x = 1-2), were obtained much later; the adducts were shown to be suitable sources of tin-centred nucleophiles that reacted with Cl2SntBu2 or carbodiimines. 11 On the other hand, strontium stannyls are still unknown, while characterisation of the very first barium stannyl, the heteroleptic [{Carb DiPP }BaSn(SiMe3)3.thf] (Carb DiPP = 2,9-(CH=N-2,6-i Pr2-C6H3)2-4,7-t Bu2-C12H4N) was recently accomplished by our group, 12 along with the preparation of its calcium congener, [{Carb DiPP }CaSn(SiMe3)3.thf]. 13 Bonding analysis by DFT methods in these complexes pointed at a highly ionic Ae-to-Sn bond, with a HOMO essentially located on tin, even if a non-negligible orbital contribution was also found in the barium stannyl.…”

“…While working on [{Carb DiPP }BaSn(SiMe3)3.thf], 12 it came to our attention that the magnesium distannyl [Mg{Sn(SiMe3)3}2] had been made from [MgBr2.Et2O] and [KSn(SiMe3)3. (thf)2]; 17 it was recrystallised from thf as the disolvate [Mg{Sn(SiMe3)3}2.(thf)2].…”