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

Abstract

Metallaheteroboranes are versatile compounds that can be conveniently modified and eventually tailored by ligand modification at either the metal centre or the boron vertices. Recently, we have discovered that protonation of some rhodathiaboranes affords cationic clusters with interesting reaction chemistry. In order to tune the reactivity of some of these polyhedral boron-based compounds, we have prepared air-stable orange [1,1-(η(2)-dppe)-3-(NC5H5)-closo-1,2-RhSB9H8] (2) by the treatment of the known hydridorhodathiaborane [8,8,8-(H)(PPh3)2-9-(NC5H5)-nido-8,7-RhSB9H9] (1) with dppe. The new 11-vertex rhodathiaborane, 2, reacts readily with triflic acid (TfOH) in CH2Cl2 to give orange cationic [8,8-(η(2)-dppe)-9-(NC5H5)-nido-8,7-RhSB9H9](+) (3). VT NMR experiments have allowed the characterization of a structural closo ↔ nido tautomerism, which involves hapticity changes in the ligation of the {SB9H9-(NC5H5)} moiety to the {Rh(dppe)} fragment, with the proton moving between the Rh(1)-B(3) and the B(9)-B(10) edges of the closo- and nido-isomers, respectively. The proton enhances the stereochemical non-rigidity and Lewis acidity of 3 versus the neutral 2. This modification of the chemical and structural basis permits the efficient heterolytic splitting of the H-H bond, leading to the formation of new hydridorhodathiaborane isomers [8,8,8-(H)(η(2)-dppe)-μ-8,9-(H)-9-(NC5H5)-nido-8,7-RhSB9H10](+) ()4 that are in equilibrium with the reactants, H2 and 3.

Chemistry of Triple‐Decker Sandwich Complexes Containing Four‐Membered Open B2E2 Rings (E = S or Se)

“…The developments towards large numbers of metallaheteroboranes have gained a good deal of interest, owing to their utility in the preparation of high‐nuclearity clusters . Among them, group 9 metallaheteroboranes have received significant attention, due to their applications in catalysis , . For example, nido ‐rhodathiaborane [8,8,8‐(PPh 3 ) 2 H‐9‐(NC 5 H 5 )‐ nido ‐8,7‐RhSB 9 H 9 ] acts as a catalyst for the isomerization and hydrogenation of alkenes.…”

“…For example, nido ‐rhodathiaborane [8,8,8‐(PPh 3 ) 2 H‐9‐(NC 5 H 5 )‐ nido ‐8,7‐RhSB 9 H 9 ] acts as a catalyst for the isomerization and hydrogenation of alkenes. [8c] Although metallaheteroboranes comprised of thia, , , and aza[4b] ligands have been explored, compounds that contain heavier heteroatoms, such as selenolato and tellurolato ligands, are relatively limited. As a result, we[5a], [5b], [5c], and others have synthesized interesting metallaheteroborane clusters containing selenium and tellurium that illustrate reactivity and structural patterns different from those containing sulfide …”

Reversible Small‐Molecule Interactions with Coordinatively Unsaturated Metal Centers Held in Metallathiaborane Clusters

“…71, 65 and 71°, respectively (Figure a). This twist of the M{(L) 2 } moiety with respect the {SB 9 H 9 } fragment is a common structural feature in 11‐vertex metallaheteroboranes that incorporate {M(L) 2 } (M = Rh,[8g] Ir, Pt, Pd) groups. A larger ϕ angle of 81° is found in the 9‐vertex nickellathiaborane [7,7‐(dppe)‐ arachno ‐6,8‐NiS 2 B 6 H 8 ], in which the {Ni(dppe)} moiety is bound to the {S 2 B 6 H 9 } unit in a tetrahapto fashion (Figure c).…”

“…This exploratory synthetic work is completed by studies of the reactivities of the new nickellathiaboranes with small molecules such as NH 3 and CO and the comparison of their reactivities with those exhibited by the rhodathiaboranes that we reported in recent years ,. [7e], In this regard, this work also includes new reactivity studies between ammonia and the previously reported iridathiaborane [(PMe 3 ) 2 ‐ isonido ‐IrSB 9 H 10 ][8m] and its PMe 2 Ph‐ligated counterpart, [(PMe 2 Ph) 2 ‐ isonido ‐IrSB 9 H 10 ].…”

“…In recent years, we have demonstrated the benefits of this modular strategy through the synthesis from common precursors of a large family of 10‐ and 11‐vertex rhodathiaboranes that combine different rhodium fragments with boron‐bound Lewis bases in their structures ,. [7e], The systematic alteration of the metal‐ and boron‐bound ligands has permitted the tuning of the reactivities of these polyhedral compounds, for example, to provide the first examples of the heterolytic splitting of H 2 by a polyhedral boron‐containing compound with the full participation of the cage, as illustrated in Scheme ,. [8a], [8h], [8o], [8p]…”