NH₃-Promoted Ligand Lability in Eleven-Vertex Rhodathiaboranes

Abstract

The reaction of the 11-vertex rhodathiaborane, [8,8-(PPh3)2-nido-8,7-RhSB9H10] (1), with NH3 affords inmediately the adduct, [8,8,8-(NH3)(PPh3)2-nido-8,7-RhSB9H10] (4). The NH3-Rh interaction induces the labilization of the PPh3 ligands leading to the dissociation product, [8,8-(NH3)(PPh3)-nido-8,7-RhSB9H10] (5), which can then react with another molecule of NH3 to give [8,8,8-(NH3)2(PPh3)-nido-8,7-RhSB9H10] (6). These clusters have been characterized in situ by multielement NMR spectroscopy at different temeperatures. The variable temperature behavior of the system demonstrates that the intermediates 4-6 are in equilibrium, involving ligand exchange processes. On the basis of low intensity signals present in the (1)H NMR spectra of the reaction mixture, some species are tentatively proposed to be the bis- and tris-NH3 ligated clusters, [8,8-(NH3)2-nido-8,7-RhSB9H10] (7) and [8,8,8-(NH3)3-nido-8,7-RhSB9H10] (8). After evaporation of the solvent and the excess of NH3, the system containing species 4-8 regenerates the starting reactant, 1, thus closing a stoichiometric cycle of ammonia addition and loss. After 40 h at room temperature, the reaction of 1 with NH3 gives the hydridorhodathiaborane, [8,8,8-(H)(PPh3)2-nido-8,7-RhSB9H9] (2), as a single product. The reported rhodathiaboranes show reversible H3N-promoted ligand lability, which implies weak Rh-N interactions, leading to a rare case of metal complexes that circumvent "classical" Werner chemistry.

[1,1-(η2-dppe)-3-(NC5H5)-closo-1,2-RhSB9H8]: conformational lability and reactivity with H2 upon protonation

“…1). This structural attribute is manifest by the Rh(8)⋯B (10) and Rh(8)⋯B (11) non-bonding distances of 3.333(11) and 3.463(12) Å, respectively, which in compound 2 correspond to the Rh(1)-B(6) and Rh(1)-B(5) bonding lengths of 2.380(2) and 2.498(2) Å. A common feature of this type of 11-vertex nido-cages is that the Scheme 1 Reaction of 1 with dppe to give 2, and its protonation with triflic acid to form 3.…”

“…By simple protonation, it is possible to labilize the metal-thiaborane linkage leading to an increase of the structural non-rigidity of the deltahedral clusters and of their Lewis acidity, promoting consequently new reactivity that allows the optimization of H 2 splitting on cationic 11-vertex rhodathiaboranes. 10,[11][12][13][14] In this manuscript, the possibility of influencing the reactivity of metallaheteroboranes by modifying the exo-polyhedral ligands and by the protonation of the clusters is further demonstrated with the synthesis of new 11-vertex rhodathiaboranes that contain the bis-(diphenylphosphino)ethane (dppe) ligand. In comparison with monodentate phosphines previously studied, 11,13,14 the use of a chelating ligand such as dppe has shown to have a large influence on the structural and electronic properties of the 11-vertex cluster, which allows (i) the characterization of a new tautomeric process that reflects the non-rigidity of the dppe-ligated cationic species and (ii) the reversible addition of H 2 to the cage.…”

Oxidation of germa- and stanna-closo-dodecaborate

“…Heteroborane cluster chemistry is an active field of research and many interesting studies have been published in recent years. [1][2][3][4][5][6][7][8][9][10] In heteroborane clusters a BH vertex of a borane cluster skeleton is replaced by a main group element or a transition metal. Following the isolobal principle a BH unit can for example be substituted by a Ge atom or an anionic BH − unit by an N atom.…”

Molybdatricarbaboranes as examples of isocloso metallaborane deltahedra with three carbon vertices

“…The lowest energy structures were then reoptimized at a higher level, that is, M06L/6‐311G(d,p)/SDD and these are the structures presented in the manuscript . This computational approach has proven to be reliable and gives results correlating well with available experimental data …”

“…[39] This computational approach has proven to be reliable and gives results correlating well with available experimental data. [40][41][42][43][44] The natures of the stationary points after optimization were checked by calculations of the harmonic vibrational frequencies. If significant imaginary frequencies were found, the optimization was continued by following the normal mode corresponding to imaginary frequencies to insure that genuine minima were obtained.…”