A stable dianionic 14-electron Pd(0) complex supported by monoanionic carboranyl phosphines is reported. This complex rapidly undergoes the oxidative addition of Cl-C 6 H 5 at room temperature and is a competent catalyst for Kumada cross-coupling. The isosteric PdL 2 complex, supported by neutral o-carboranyl phosphines, does not display the same reactivity. The high reactivity of the dianionic Pd(0) complex toward chloroarenes can be explained by electrostatic effects that promote both formation of monophosphine-ligated LPd 0 and stabilization of the transition state during oxidative addition. This mode of stabilization is distinct from the wellknown π-arene interactions of biaryl phosphines, in that it occurs both on and off cycle. Communication pubs.acs.org/Organometallics

Discovered by Hawthorne in 1965, dicarbollide ions are an intriguing class of nido-carboranes that mimic the behavior of the cyclopentadienyl anion. Herein, we show that it is possible to directly link the dicarbollide ion to an N-heterocyclic carbene (NHC) to form an isolable N-dicarbollide-substituted NHC dianion. This molecule can be accessed by the sequential double deprotonation of a mono-nido-carboranyl imidazolium zwitterion. As revealed by a single-crystal X-ray diffraction study, the first deprotonation leads to a monoanionic dicarbollide ion that adopts a bis(dicarbollide) structure in the solid state. Subsequent deprotonation of this monoanion leads to the first N-dicarbollide NHC, which was fully characterized by multinuclear NMR spectroscopy as well as single-crystal X-ray diffraction.

A phosphine containing a 10-vertex carborane anion substituent and its subsequent ligation to a Rh(I) carbonyl complex is reported. The complex is characterized by NMR spectroscopy and a single crystal X-ray diffraction study. In addition, the inductive effects of both 10 and 12 vertex C-functionalized closo-carborane anions are elucidated via I.R. analysis of the CO stretching frequencies of two Rh carbonyl complexes. Unlike C-functionalized neutral o-carborane the 10 and 12-vertex carborane anions are both strong electron donor substituents.

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.

Outside the cage: A change in the redox properties of a triazole fused to a carborane anion through methylation to form a zwitterion enabled facile chemical reduction of the compound to an isolable triazole radical anion (see structure: C gray, H white, N blue, B brown, Cl green). The radical anion is stabilized by kinetic protection by the chlorinated carborane and the delocalization of spin density throughout the exo-cluster π system.

A zwitterionic palladium complex of a phosphine bearing a perchlorinated carba-closo-dodecaborate anion as a ligand substituent is reported. A single-crystal X-ray diffraction study reveals that, in the solid state, one of the chlorides of the carborane cage occupies a coordination site of the square-planar complex. However, in solution, the P-carborane bond of the ligand is rapidly rotating at temperatures as low as -90 °C, which demonstrates the carborane substituent's weak coordinative ability even though this anion is covalently linked to the phosphine ligand. The complex is thermally stable and catalyzes the vinyl addition polymerization of norbornene.

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Außerhalb des Käfigs: Die Redoxeigenschaften eines Triazol‐anellierten Carboran‐Anions werden durch Methylierung und Zwitterionenbildung so verändert, dass die Verbindung eine einfache chemische Reduktion zu einem isolierbaren Triazol‐Radikalanion eingeht (siehe Struktur: C grau, H weiß, N blau, B braun, Cl grün). Das Radikalanion ist durch kinetischen Schutz und die Delokalisierung der Spindichte über das π‐System außerhalb des Clusters stabilisiert.