Facile two-electron reduction of a closo-rhodathiadecaborane

Abstract

Closo-to-arachno redox flexibility in metallaheteroboranes may be viewed as a metal-to-ligand cooperative action with application in catalysis. The treatment of [PSH][arachno-4-SB(8)H(11)] with [RhCl(PPh(3))(3)] affords, after chromatography, three new 10-vertex rhodathiaboranes, [2,2,2-(H)(PPh(3))(2)-closo-2,1-RhSB(8)H(8)] (3), [6,6,9-(PPh(3))(3)-arachno-6,5-RhSB(8)H(9)] (4) and [2,2,2-(Cl)(H)(PPh(3))-6-(PPh(3))-closo-2,1-RhSB(8)H(7)] (5). 3 reacts quantitatively with PPh(3) to form 4, which, in turn, reacts with chlorinated solvents to give the chloro-ligated cluster 5. Kinetic studies demonstrate that the reaction of 3 with PPh(3) obeys a second-order rate law, with an associative mechanism. The Lewis acidity of 3 is quite remarkable, and, given its closo-to-arachno structural and electronic response, this cluster is expected to exhibit a rich chemistry.

Postsynthetic modifications of [2,2,2-(H)(PPh3)2-closo-2,1-RhSB8H8] with Lewis bases: cluster modular tuning

“…In the arachno-6,5-species, 3 and 4, there is an {Rh(PPh 3 ) 2 } fragment and an {L-B} group, where L = PCy 3 or 2-Mepy, present on opposite sides of the open face and occupying the vertices of connectivity three at positions 9 and 6, respectively. Other structural features of note on the 6,5-isomers, 3 and 4, also found in previously reported 2, 14 are the presence of an endo-hydrogen atom on the ligandsubstituted vertex, L-B(9)-H, and the presence of a bridging hydrogen atom along the B(7)-B(8) edge.…”

“…Thus, in compound 9, the metal hydride, having the choice, avoids lying trans to cage boron vertices. The same tendency has been identified in a significant number of hydridometallathiaboranes 9, 14,15,18 where the exo-polyhedral ligand orientation is mainly controlled by cage S atoms that, in the metal-thiaborane linkage, force the hydride ligands to occupy positions trans to the heteroatom: the strong transinfluence hydride ligand avoids the cage B atoms that exhibit a stronger structural trans effect than the cage sulfur atoms.…”

“…Although in the pyridinic 9,6 isomers, 6b-8b, the 2 J P,H coupling constant cannot be resolved (in contrast to the PPh 3 [6, ) 2 -9-(PCy 3 )-arachno-6,5-RhSB 8 H 9 ] (3), [6, ) 2 -9-(2-Mepy)-arachno-6,5-RhSB 8 H 9 ] (4) and [6, ) 2 -9-(2-Etpy)-arachno-6,5-RhSB 8 H 9 ] (5) in CD 2 Cl 2 compared to the corresponding DFT/GIAO-calculated 11 ligated 9,6 isomer 2, which shows a pseudo-quartet at δ H −8.41, see ref. 14), the proton resonance at the lowest frequency can be assigned with confidence to the Rh(9)-H-B(8) bridging hydrogen atom, being a proof of the presence of the arachno-9,6-species versus their arachno-6,5-isomers.…”

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

“…The chemistry of metallaheteroboranes is traditionally achieved by the reaction of polyhedral heteroborane anions with metal fragments or the incorporation of heteroatoms into metallaborane clusters . 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 .…”

Rhodathiaborane reaction cycles driven by C2H4 and H2: synthesis and characterization of [(H)2(PPh3)RhSB8H7(PPh3)] and [(η2-C2H4)(PPh3)RhSB8H7(PPh3)]

“…4 The reaction of 1 with an excess of ethylene in dichloromethane at room temperature yields [2,2-(η 2 -C 2 H 4 )(PPh 3 )-6-(PPh 3 )-closo-2,1-RhSB 8 H 7 ] (2) (Scheme 1). This ethylene-ligated rhodathiaborane is the result of the substitution at the metal centre of a PPh 3 ligand by ethylene, the loss of two hydrogen atoms from the cage and a consequent arachno-to-closo structural transformation.…”