Time-resolved studies of germylene, GeH2, generated by laser flash photolysis of 3,4-dimethylgermacyclopentene-3, have been carried out to obtain rate constants for its bimolecular reaction with monogermane, GeH4. The reaction was studied in the gas phase over the pressure range 1−100 Torr, with SF6 as bath gas, at five temperatures in the range 292−520 K. The reaction of GeH2 with GeH4 to form digermane, Ge2H6, is pressure dependent, consistent with a third-body assisted association reaction. The high-pressure rate constants, obtained by extrapolation, gave the following Arrhenius equation:  log(k ∞ /cm3 molecule-1 s-1) = (−11.17 ± 0.10) + (5.2 ± 0.7 kJ mol-1)/RT ln 10. These Arrhenius parameters are consistent with a moderately fast reaction occurring at approximately one-fifth of the collision rate. RRKM modeling, based on a variational transition state, used in combination with a weak collisional deactivation model, gave good fits to the pressure dependent curves, for a suitable choice of the critical energy, E o , for reverse decomposition of Ge2H6. The step size (energy removed in a down collision) was chosen by analogy with the corresponding system for Si2H6 (collisional efficiency (βc) of ca. 0.7 for SF6). The value obtained for E o was 155 kJ mol-1. Corrected for thermal energy and combined with the insertion activation energy this gives Δ H° = 166 kJ mol-1 for the decomposition of Ge2H6. There is no previous experimental determination of this quantity. From it we derive = 237 ± 12 kJ mol-1, in reasonable agreement with earlier estimates. From bond dissociation energy values the Divalent State Stabilization Energy (DSSE) of germylene (119 kJ mol-1) is larger than that of silylene (94 k J mol-1). Ab initio calculations at the correlated level reveal the presence of two weak complexes (local energy minima) on the potential energy surface corresponding to either direct or inverted geometry of the inserting germylene fragment. Surprisingly, the latter is the lower in energy, lying 25 kJ mol-1 below the unassociated reactants. These complexes rearrange to digermane with very low barriers. The implications of these findings and the nature of the insertion process are discussed.

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Time resolved studies of germylene, GeH 2 , generated by laser flash photolysis of 3,4dimethylgermacyclopentene-3, have been carried out to obtain rate constants for its bimolecular reaction with acetylene, C 2 H 2 . The reaction was studied in the gas-phase over the pressure range 1-100 Torr, with SF 6 as bath gas, at 5 temperatures in the range 297-553 K. The reaction showed a very slight pressure dependence at higher temperatures. The high pressure rate constants (obtained by extrapolation at the three higher temperatures) gave the Arrhenius equation:These Arrhenius parameters are consistent with a fast reaction occurring at approximately 30% of the collision rate at 298 K. Quantum chemical calculations (both DFT and ab initio G2//B3LYP and G2//QCISD) of the GeC 2 H 4 potential energy surface (PES), show that GeH 2 þ C 2 H 2 react initially to form germirene which can isomerise to vinylgermylene with a relatively low barrier. RRKM modelling, based on a loose association transition state, but assuming vinylgermylene is the end product (used in combination with a weak collisional deactivation model) predicts a strong pressure dependence using the calculated energies, in conflict with the experimental evidence. The detailed GeC 2 H 4 PES shows considerable complexity with ten other accessible stable minima (B3LYP level), the three most stable of which are all germylenes. Routes through this complex surface were examined in detail. The only product combination which appears capable of satisfying the observed lack of a strong pressure dependence is Ge( 3 P) þ C 2 H 4 . C 2 H 4 was confirmed as a product by GC analysis. Although the formation of these products are shown to be possible by singlet-triplet curve crossing during dissociation of 1-germiranylidene (1-germacyclopropylidene), it seems more likely (on thermochemical grounds) that the triplet biradical, GeCH 2 CH 2 , is the immediate product precursor. Comparisons are made with the reaction of SiH 2 with C 2 H 2 .

The results of time resolved gas phase studies of labile germylenes (GeH 2 and GeMe 2 ) and dimethylstannylene (SnMe 2 ) reactions reported to date are considered together with data of quantum chemical investigations of the potential energy surfaces of these systems. Reaction mechanisms are discussed. A comparison of reactivity in the series of carbene analogs, ER 2 (E = Si, Ge, Sn, R = H, Me), is made.

Electrons and photons are essential chemical "currencies" commonly traded in chemical transformations. The many applications of photon upconversion, i.e., conversion of low energy photons into high energy photons, raises the question about the possibility of "electron upconversion". In this review, we illustrate how reduction potential can be increased by using the free energy of exergonic chemical reactions. The electron (reductant) upconversion can produce up to ~20-25 kcal/mol of additional redox potential, creating powerful reductants under mild conditions. We will present the two common types of electron-upconverting systems - dissociative (based on unimolecular fragmentations) and associative (based on bimolecular formation of three-electron bonds). The possible utility of reductant upconversion encompasses redox chain reactions in electrocatalytic processes, photoredox cascades, design of peroxide-based medicines, firefly luminescence, and reductive repair of DNA photodamage.

H 3 SiGeH 3 process are discussed.

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