Cationic Niobium-Sandwich and Piano-Stool Complexes.

The syntheses of the homoleptic bis(arene) niobium cations [Nb(arene)2 ]+ (arene = C6 H3 Me3 , C6 H5 Me) with 16 valence electrons and heteroleptic arene-carbonyl cations [(CO)Nb(arene)2 ]+ (arene = C6 H3 Me3 , C6 H5 Me) and [(arene)M(CO)4 ]+ (arene = C6 H3 Me3 , C6 H6 ) obeying 18 valence electrons are described. Stabilization of these complexes was achieved by using the weakly coordinating anions [Al(ORF )4 ]- or [F{Al(ORF )3 }2 ]- (RF = C(CF3 )3 ). The limits of two synthesis routes starting from neutral Nb(arene)2 (arene = C6 H3 Me3 , C6 H5 Me) or [NEt4 ][M(CO)6 ] (M = Nb, Ta) were investigated. All compounds were analyzed by single crystal X-ray determination, vibrational and NMR spectroscopy. DFT calculations were executed to support the experimental data.

Oxidative addition, reduction and reductive coupling: the versatile reactivity of subvalent gallium cations.

Inspired by the successful oxidative addition of a P-H bond to univalent Ga[Al(ORF)4] that gives the unprecedented dicationic gallium hydride complex [H-Ga(PPh3)3][Al(ORF)4]2 (ORF = OC(CF3)3), the oxidative addition of E-Cl containing substrates was investigated. The reductive coupling of three PPh2Cl to the catenated phosphorus cation [P3Ph6]+ hinted towards a formal two-electron-three-halide reduction (2e--3X- reduction). Similarly, from SbCl3, a cationic formal SbI compound and from RhCl3, [RhI(HMB)(COD)]+ and [RhI(COD)2]+ (HMB = C6Me6, COD = 1,5-cyclooctadiene) are formed as [Al(ORF)4]- salts when reacted with Ga+. Thus, Ga[Al(ORF)4] allows for a one-pot 2e--3X- reduction with the concomitant introduction of a weakly coordinating anion (WCA).