A modular total synthesis of the potent V-ATPase inhibitors archazolid A and B is reported. The convergent preparation was accomplished by late-stage diversification of joint intermediates. Key synthetic steps involve asymmetric boron-mediated aldol reactions, two consecutive Still-Gennari olefinations to set the characteristic (Z,Z)-diene system, a Brown crotyboration, and a diastereoselective aldol condensation of highly elaborate intermediates. For macrocyclization, both an HWE reaction and a Heck coupling were successfully employed to close the 24-membered macrolactone. During the synthetic campaign, a generally useful protocol for an E-selective Heck reaction of nonactivated alkenes and a method for the direct nucleophilic displacement of the Abiko-Masamune auxiliary with sterically hindered nucleophiles were developed. The expedient and flexible strategy will enable further SAR studies of the archazolids and more detailed evaluations of target-inhibitor interactions.

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Atom-precise, ligand-stabilized metalloid clusters have emerged as outstanding model systems to study fundamental structure and bonding situations of compositionally related molecules and extended solid phases. However, this fascinating field of research is still largely restricted to homometallic and pseudo-heterometallic systems of closely related d-block metals. In this review, we will highlight our own and others' efforts to project the structural and compositional diversity of intermetallics with dissimilar d- and p-block metal combinations, particularly the Zintl and Hume-Rothery phases, onto the molecular level in order to bridge the still gaping chasm between heterometallic molecular coordination chemistry and solid-state intermetallics. Herein, fundamental synthetic approaches, as well as structural and electronic properties of thus accessible "molecular alloys" will be addressed, and placed against their exceptional position as intermediates on the way to nanomaterials.

The ultrafast ring-opening reaction of photochromic fulgides proceeds via conical intersections to the ground state isomers involving activation barriers in the excited state. The coherent oscillations observed in the femtosecond transient absorption signal of a methyl-substituted indolylfulgide were analysed in the framework of vibrational wavepackets to expose a dominant low-frequency mode at ∼80 cm(-1). The quantum chemical calculations in the relaxed excited state geometry of this fulgide revealed that the experimentally observed vibrational normal mode has a dominant contribution to the relevant ring-opening reactive coordinate.

We report on the synthesis of new derivatives of silylated clusters of the type [Ge (SiR ) ] (R = SiMe , Me = CH ; R = Ph, Ph = C H ) as well as on their reactivity towards copper and zinc compounds. The silylated cluster compounds were synthesized by heterogeneous reactions starting from the Zintl phase K Ge . Reaction of K[Ge {Si(SiMe ) } ] with ZnCl leads to the already known dimeric compound [Zn(Ge {Si(SiMe ) } ) ] (1), whereas upon the reaction with [ZnCp* ] the coordination of [ZnCp*] to the cluster takes place (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) under the formation of [ZnCp*(Ge {Si(SiMe ) } )] (2). A similar reaction leads to [CuPiPr (Ge {Si(SiMe ) } )] (3) from [CuPiPr Cl] (iPr=isopropyl). Further we investigated the novel silylated cluster units [Ge (SiPh ) ] (4) and [Ge (SiPh ) ] (5), which could be identified by mass spectroscopy. Bis- and tris-silylated species can be synthesized by the respective stoichiometric reactions, and the products were characterized by ESI-MS and NMR experiments. These clusters show rather different reactivity. The reaction of the tris-silylated anion 4 with [CuPiPr Cl] leads to [(CuPiPr ) Ge (SiPh ) ] as shown from NMR experiments and to [(CuPiPr ) {Ge (SiPh ) } ] (6), which was characterized by single-crystal X-ray diffraction. Compound 6 shows a new type of coordination of the Cu atoms to the silylated Zintl clusters.

The addition of Sn and Zn ions to [Ge ] clusters by reaction of [Ge ] with SnPh Cl , ZnCp* (Cp*=pentamethylcyclopentadienyl), or Zn [HC(Ph P=NPh) ] is reported. The resulting Sn- and Zn-bridged clusters [(Ge )M(Ge )] (M=Sn, q=4; M=Zn, q=6) display various coordination modes. The M atoms that coordinate to the open square of a C -symmetric [Ge ] cluster form strong covalent multicenter M-Ge bonds, in contrast to the M atoms coordinating to triangular cluster faces. Molecular orbital analyses show that the M atoms of the Ge M fragments coordinate to a second [Ge ] cluster with similar orbitals but in different ways. The [Ge Sn] unit donates two electrons to the triangular face of a second [Ge ] cluster with D symmetry, whereas [Ge Zn] acts as an electron acceptor when interacting with the triangular face of a D -symmetric [Ge ] unit.

Reactions of Zn L (where L=[HC(PPh NPh)] ) with solutions of the Zintl phase K Ge in liquid ammonia lead to retention of the Zn-Zn bond and formation of the anion [(η -Ge )Zn-Zn(η -Ge )] , representing the first complex with a Zn-Zn unit carrying two cluster entities. The trimeric anion [(η -Ge )Zn{μ (η :η Ge )}Zn(η -Ge )] forms as a side product, indicating that oxidation reactions also take place. The reaction of Zn Cp* (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) with K Ge in ethylenediamine yielded the linear polymeric unit 1∞ {[Zn[μ (η :η Ge )]} with the first head-to-tail arrangement of ten-atom closo-clusters. All anions were obtained and structurally characterized as [A(2.2.2-crypt)] salts (A=K, Rb). Copious computational analyses at a DFT-PBE0/def2-TZVPP/PCM level of theory confirm the experimental structures and support the stability of the two hypothetical ten vertex cluster fragments closo-[Ge Zn] and (paramagnetic) [Ge Zn] .

Molecules with low-valent Ge atoms are generally synthesized from organohalogen germanes as precursors. The Zintl phase KGe provides reactive building blocks for a targeted synthesis of germanium-rich molecules. The silylation of Ge9 clusters with chlorosilanes ClSiRR', that carry unsaturated olefin groups R' leads to the introduction of olefinic side chains of variable lengths allowing for further reactions. The compounds K[Ge{Si(SiMe)}(SiPhR')] (R' = -CH[double bond, length as m-dash]CH (1); -(CH)CH[double bond, length as m-dash]CH (2)) carry one such functionality, whereas K[Ge(SiPhR')] (3 and 4) offer the possibility for an interconnection of clusters due to three functional groups on the Ge core. XPS measurements show that the silylated clusters are much more air-stable than the unsubstituted, bare cluster units.