Synthesis and Reactivity of Fluorenyl-Based Germanium(II) Compounds.

We present the synthesis of alkyl-substituted germylenes GeFlu2, Ge(FluTMS)2, and FluTMSGeCl (Flu = 9H-fluorenyl, FluTMS = 9-trimethylsilyl-9H-fluorenyl) using bulky fluorenyl ring systems and modifications of that. GeFlu2 can only be crystallized as its three-membered ring trimer, whereby the reaction is accompanied by the formation of several byproducts, such as [Li(THF)4][Ge(Ge3Flu7H)]. These results led to the modification of the fluorenyl framework by substitution the one H atom in the 9-position by a TMS group. With the synthesis of the corresponding Li salt LiFluTMS, Ge(FluTMS)2 could be isolated in good yields in a further reaction. The homoleptic Ge(FluTMS)2 is found in its crystalline form as a monomer and thus belongs to the series of monomeric alkyl-substituted germylenes. Also, the corresponding monoalkyl-substituted halogenido germylene was isolated as a four-membered ring tetramer [FluTMSGeCl]4 during an unselective reaction. However, FluTMSGeCl undergoes significant stabilization through the formation of the monomeric phosphane adduct FluTMSGeCl·PEt3, which greatly increases the selectivity of the reaction. During further reactions of Ge(FluTMS)2 with a GeBr solution (toluol/nPr3P), more impressions of the reactivity of Ge(I)X solutions with germylenes were achieved, showing that those germylenes take part in the disproportionation reaction of metastable Ge(I) solutions to give oxidized Ge(IV) compounds like (FluTMS)2GeBr2.

Synthesis of Chiral Donor-Acceptor Dyes to Study Electron Transfer Across a Chiral Bridge.

Chiral organic dyes comprising a donor (D), spacer (S), primary acceptor (A1), chiral bridge (B(S)), and final acceptor/radical (A2)/(R) have been synthesized and fully characterized. The goal behind this synthetic pursuit is to study whether the chiral dyes can impart a chiral-induced spin selectivity (CISS) spin-filtering effect during an intramolecular charge-transfer (CT) process. Additionally, appending a stable free radical (SFR) allows the study of how an unpaired spin influences the CT state. The dyes are reported to vary in the position of (A1) with respect to (B(S)). Two series of dyes have been synthesized: one series incorporates (A1) before (B(S)) and the second series places (A1) after (B(S)). In the case where (A1) is before (B(S)), CT is observed between (D) and (A1), but the CT state does not transverse over the chiral bridge to the final (A2)/(R) termini. However, when (A1) is placed after (B(S)), CT over or through the bridge occurs. Computations support the experimental data, which indicate that it is necessary to have (A1) located after (B(S)) to achieve CT over the chiral bridge. Hence, the second set of dyes are optimal candidates to explore intramolecular CISS.

Selective metalation of phenol-type proligands for preparative organometallic chemistry.

The selective C-metalation of phenol ester derived proligands is a readily applicable addition to state-of-the-art protocols toward cyclometalated structures, in particular of the base metals. The approach is demonstrated by the ortho-nickelation of a 1,10-phenanthroline based strong-field ligand platform that is a sought-after motif in the field of base-metal photochemistry.