Resisting B–H oxidative addition: The divergent reactivity of the o-carborane and carba-closo-dodecaborate ligand substituents

Abstract

Here, we report a study of two isoelectronic Ir(I) complexes supported by different carboranyl phosphines, bearing either o-carborane or carba-closo-dodecaborate ligand substituents. The neutral Ir(I) complex containing the o-carboranyl phosphine ligand is not isolable and undergoes spontaneous B-H cyclometalation to afford an Ir(III) hydride. In contrast, the anionic Ir(I) complex supported by a phosphine with a carba-closo-dodecaborate ligand R-group is stable towards B-H activation. This divergent reactivity has important implications for the design of carborane containing ligands for catalysis. Both compounds are fully characterized by multinuclear NMR spectroscopy, HRMS spectrometry, and single crystal x-ray diffraction studies.

Activation of B H bonds in Ir(I) complexes supported by phosphine with carba-closo-dodecaborate and o-carborane ligand substituents: A DFT investigation

“…As seen from position of the o-carboranyl is more favorable to be activated than other positions, which are consistent with the experimentally observed results [44]. Selected bond lengths of D5, E5 and F5 were illustrated in Fig.…”

“…-C 8 H 12 )(PR 2 (C 2 B 10 H 11 )) complexes can be activated to give Ir(III) complex, while the oxidative addition of B-H bond in ClIr(η 2 -C 8 H 12 )(PR 2 (CB 11 H 11 -)) cannot occur[44]. In order to understand -C 8 H 12 )(PR 2 (C 2 B 10 H 11 )) complexes, we have adopted two kind of methods to The dispersion corrections of the complexes were computed using DFT-D3 with BJ damping.…”

Chelating N-heterocyclic carbene–carboranes offer flexible ligand coordination to IrIII, RhIII and RuII: effect of ligand cyclometallation in catalytic transfer hydrogenation

“…The 1 H NMR spectrum of 4a exhibits two sets of resonances in a 7:3 ratio due to diasteroisomers, as a result of the sterogenic metal centre and a mixture of B3 and B6 metallation. 31,32 Crystals of complex 4a suitable for X-ray diffraction analysis were obtained from slow evaporation of a MeCN solution, and provide unambiguous confirmation that intramolecular C-H activation of the t Bu group had occurred to give a fivemembered metallacycle, with a C-Ir-C bite angle of 76.27(12) ° ( Figure 2). In addition, coordination through a boron atom of the closo-carborane results in a seven-membered metallacycle, with a C-Ir-B bite angle of 85.65(14) °, forming an interesting and structurally distinct (7,5)-bicyclo-metallated system.…”

“…30,33,38 The carboranyl carbon atoms were determined using the VCD method, and revealed a particularly elongated B3 vertex to centroid distance of 1.89 Å, which are typically in the range 1.72-1.78 Å. 31,39 It can be proposed that the metallated carborane B vertex elongates to relieve steric encumbrance close to the metal centre. Complexes 3a and 4a were isolated in relatively low (but useable) yields, with attempts to improve them unsuccessful.…”

Dehydrogenation of icosahedral carborane anions via gas‐phase collisional activation

“…[7] These characteristics have led to the utilization of 1 and its polyhalogenated derivatives as spectator anions to stabilize highly reactive cations. More recently, such carboranes have found utility as ligand substituents [10][11][12][13][14][15][16] for catalysis and electrolytes [17] for advanced batteries. Another potential application of icosahedral carborane anions could be as hydrogen storage materials; however, due to their stability these species have not previously been observed to extrude hydrogen.…”