Electrochemical oxidation of phenylsilatrane (1) in CHCN/0.1 M BuNPF has been studied by voltammetry, UV-Vis and EPR-coupled spectroelectrochemistry supported by DFT calculations. One-electron withdrawal from the HOMO of 1, formed with a predominant contribution of the atrane N atom to the 3c-4e system, results in a short lived radical cation, in which the atrane nitrogen atom is almost planar and carries most of the spin density showing strong coupling with the protons of the axially directed C-H bonds of the three adjacent α-methylene groups (g = 2.0037, aH = 37.93 G, aH = 0.23 G and aH = 1.8 G). EPR spectroscopy and DFT calculations attest that the unpaired electron in the radical cation does not reside at the Si atom.

New highly cytotoxic 3-aminopropyl derivatives of 2-dimethylsilyl-5-trialkylgermylfuran (IC 50 1−3 µg⋅ml −1 ) have been prepared by hydrosilylation of heterocyclic N-allylamines with the corresponding hydrosilane in the presence of Speier's catalyst. The influence of the amine structure and alkyl substituent at the germanium atom on the cytotoxicity has been investigated.The heterocyclic amines are important building blocks for the creation of anticancer drugs [1, 2]. In some cases the benzene ring has been substituted for thiophene or furan to enhance the activity and increase the therapeutic index. Examples are the thiophene-containing folate analogue Raltitrexed [3], the antimetastatic agent Batimastat [4], and the furan-containing anticancer agent Lapatinib [5].Our previous investigations have demonstrated that hetarylaminoalkyl(siloxy)silanes, containing an alkyl(or siloxy) group attached to the silicon atom, have anticancer, neurotropic, and bacteriostatic activity [6−8]. On the other hand, toxicological studies have demonstrated that most tested organogermanium compounds were less toxic than the corresponding organosilicon analogs [9].Taking into consideration the information gained from the fragment analysis of known anticancer drugs as well as the fact that silylation and germylation increase the lypophilicity of the compounds and can change their metabolism [10−12] we decided to combine in one molecule the fragments of germylated furan and silylated heterocyclic amine and to test their cytotoxicity.The starting 2-dimethylsilyl-5-trimethyl(ethyl)germylfurans 1 and 12 have been prepared from the furan by two consecutive organolithium syntheses. These compounds were used for the hydrosilylation of heterocyclic allylamines in the presence of Speier's catalyst (Scheme 1). Hydrosilylation of all studied

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New furan and thiophene derivatives of aldimines o-HO-C 6 H 4 N]CHC 4 H 4 X(R) (X ¼ O, S; R ¼ H, SiMe 3 , SiEt 3 , GeMe 3 , GeEt 3 ) were synthesized by condensation of o-aminophenol with the substituted aldehyde precursor. Their structure, electrochemical reduction/oxidation (in CH 3 CN/0.1 M Bu 4 NPF 6 ), frontier orbital energies, and cytotoxicity have been studied. Their electrochemical redox potentials E p show good correlation with the corresponding orbital energies and the difference E p ox e E p red corresponds well to their orbital hardness.These new compounds have a pronounced cytotoxicity toward cancer cells of human fibrosarcoma HT-1080 and mouse hepatoma MG-22A (IC 50 y 1e8 mg ml À1 ) that can be modulated by introducing a Me 3 M substituent into the fifth position of the heterocycle (e.g., IC 50 (Me 3 Si)/IC 50 (H) ! 50). R 3 M-substitution reduces the orbital hardness of the aldimines studied and facilitates oxidation, promoting their oxidative metabolism. The neighboring group effect in the a-Me 3 Si-substituted thiophene derivative favors S-oxidation, which supposedly makes its metabolic mechanism different compared to R 3 Msubstituted furan series (or for M ¼ Ge in the thiophene series). Interestingly, SiMe 3 and GeMe 3 groups in both heterocyclic series (furan and thiophene) cause opposite trends in cytotoxicity, while the silyl group increases it, the germyl group decreases it.