Well-shuffled: An unexpected substituent distribution reaction via alkyldiarylsilylium ions leads to a distribution of substituents. Starting from alkyldiaryl silanes, this reaction provides a facile synthetic approach to sterically highly hindered triarylsilylium ions. These silylium ions can be applied in dihydrogen activation reactions.

The readily available iron carbonyl complexes, [CpFe(CO)2]2 (1) and CpFe(CO)2I (2) (Cp = η-C5H5), were found to be efficient precatalysts for the dehydrocoupling/dehydrogenation of the amine-borane Me2NH·BH3 (3) to afford the cyclodiborazane [Me2N-BH2]2 (4), upon UV photoirradiation at ambient temperature. In situ analysis of the reaction mixtures by (11)B NMR spectroscopy indicated that different two-step mechanisms operate in each case. Thus, precatalyst 1 dehydrocoupled 3 via the aminoborane Me2N═BH2 (5) which then cyclodimerized to give 4 via an off-metal process. In contrast, the reaction with precatalyst 2 proceeded via Me2NH-BH2-NMe2-BH3 (6) as the key intermediate, affording 4 as the final product after a second metal-mediated step. The related complex Cp2Fe2(CO)3(MeCN) (7), formed by photoirradiation of 1 in MeCN, was found to be a substantially more active dehydrocoupling catalyst and not to require photoactivation, but otherwise operated via a two-step mechanism analogous to that for 1. Significantly, detailed mechanistic studies indicated that the active catalyst generated from precatalyst 7 was heterogeneous in nature and consisted of small iron nanoparticles (≤10 nm). Although more difficult to study, a similar process is highly likely to operate for precatalyst 1 under photoirradiation conditions. In contrast to the cases of 7 and 1, analogous experimental studies for the case of photoactivated Fe precatalyst 2 suggested that the active catalyst formed in this case was homogeneous. Experimental and computational DFT studies were used to explore the catalytic cycle which appears to involve amine-borane ligated [CpFe(CO)](+) as a key intermediate.

The catalyst loading is the key to control the molecular weight of the polymer in the iron-catalyzed dehydropolymerization of phosphine-borane adducts. Studies showed that the reaction proceeds through a chain-growth coordination-insertion mechanism.

The reaction of diarylalkylsilanes and -germanes with trityl cation in the presence of a weakly coordinating anion to give the corresponding triarylsilylium or -germylium ions was investigated. This reaction provides a facile access to a larger range of these sterically highly hindered Lewis acids. The factors that promote the substituent exchange were studied, and significant effects of the substituent, of the solvent, and of the group 14 element were revealed. A combined solid-state XRD and NMR investigation of the tris(pentamethylphenyl) silylium borate [(Me5C6)3Si]2[B12Cl12] disclosed the trigonal planar coordination environment of the silicon atom in this silylium ion. NMR investigations indicate for 2,4,6-triisopropylphenyl-substituted silylium and germylium ions the onset of C–H···E+ three-center interactions (E = Si, Ge) between the distant CH bond of the isopropyl group and the positively charged group 14 element atom.