Photoswitching Behavior of a Cyclohexene‐Bridged versus a Cyclopentene‐Bridged Dithienylethene System

Photoswitching is an intriguing way of incorporating functionality into molecules or their subunits. Dithienylethene switches are particularly promising, but have so far mostly been studied with five‐membered ring (cyclopentenyl) backbones. We aim at comparing the switching properties of backbones with five and six carbon atoms in the ring. A major advantage is that cyclohexenyl rings offer new options for chiral functionalization. A slight change in the reaction conditions of a McMurry ring closure reaction leads to the formation of dithienyl derivatives with a cyclohexene backbone in reasonable yield. Density functional theory calculations were carried out, demonstrating the similarity of both compounds. Experimental results confirm the theoretical outcomes.     

Upon the intrinsic optical properties of oligo(p-phenyleneethynylene)s (OPEs). Synthesis of OPE3 for experimental gas-phase absorption studies

A new oligo(p-phenyleneethynylene) (OPE3) was synthesized by step-wise Pd-catalyzed cross-coupling reactions. The molecule incorporates an amine functionality, which allows for transfer of the protonated molecule to the gas phase by electrospray ionization leaving the OPE entity neutral. This method has allowed for the first experimental gas-phase absorption spectrum of an OPE3 by action spectroscopy, employing an electrostatic ion storage ring in combination with a laser system. The studies reveal the effect of having a positive charge in proximity to the conjugated backbone of OPE3 in the absence of any interfering solvent molecules. In addition, ionization energies and electron affinities of OPE2-OPE17 were calculated at the density functional theory (DFT) level.     

State preparation and dynamics of ultracold atoms in higher lattice orbitals

We report on the realization of a multiorbital system with ultracold atoms in the excited bands of a 3D optical lattice by selectively controlling the band population along a given lattice direction. The lifetime of the atoms in the excited band is found to be considerably longer (10-100 times) than the characteristic time scale for intersite tunneling, thus opening the path for orbital selective many-body physics with ultracold atoms. Upon exciting the atoms from an initial lowest band Mott-insulating state to higher lying bands, we observe the dynamical emergence of coherence in 1D (and 2D), compatible with Bose-Einstein condensation to a nonzero momentum state.     

Ruthenium complexes with the stanna-closo-dodecaborate ligand: coexistence of eta1(Sn) and eta3(B-H) coordination

Four stanna-closo-dodecaborate complexes of ruthenium have been prepared and characterized by multinuclear NMR studies in solution and in the solid state. The solid-state structures of the dimeric zwitterions [[Ru(dppb)(SnB11H11)]2] (2) (dppb = bis(diphenylphosphino)butane), [[Ru(PPh3)2(SnB11H11)]2] (3), and the dianionic ruthenium complex [Bu3MeN]2[Ru(dppb)[2,7,8-(mu-H)3-exo-SnB11H11](SnB11H11)] (4) were determined by X-ray crystal structure analysis; they establish an unprecedented structural motif in the chemistry of heteroboranes and transition-metal fragments with the stanna-closo-dodecaborate moiety as a two-faced ligand that exhibits eta1(Sn) as well as eta3(B-H) coordination. The eta3-coordinated stannaborate in 4 and in the isostructural compound [Bu3MeN]2[Ru(PPh3)2[2,7,8-(mu-H)3-exo-SnB11H11](SnB11H11)] (5) shows fluxional behavior, which was studied in detail by using 31P[1H] EXSY and DNMR experiments. The activation parameters for the dynamic process of 5 are given.     

Synthesis and characterization of quasi-two-coordinate transition metal dithiolates M(SAr*)2 (M = Cr, Mn, Fe, Co, Ni, Zn; Ar* = C6H3-2,6(C6H2-2,4,6-Pri3)2

A sequence of first row transition metal(II) dithiolates M(SAr)(2) (M = Cr(1), Mn(2), Fe(3), Co(4), Ni(5) and Zn(6); Ar = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Pr(i)(3))(2)) has been synthesized and characterized. Compounds 1-5 were obtained by the reaction of two equiv of LiSAr with a metal dihalide, whereas 6 was obtained by treatment of ZnMe(2) with 2 equiv of HSAr. They were characterized by spectroscopy, magnetic measurements, and X-ray crystallography. The dithiolates 1, 2, and 4-6 possess linear or nearly linear SMS units with further interactions between M and two ipso carbons from C(6)H(2)-2,4,6-Pr(i)(3) rings. The iron species 3, however, has a bent geometry, two different Fe-S distances, and an interaction between iron and one ipso carbon of a flanking ring. The secondary M-C interactions vary in strength in the sequence Cr(2+) approximately Fe(2+) > Co(2+) approximately Ni(2+) > Mn(2+) approximately Zn(2+) such that the manganese and zinc compounds have essentially two coordination but the chromium and iron complexes are quasi four and three coordinate, respectively. The geometric distortions in the iron species 3 suggested that the structure represents the initial stage of a rearrangement into a sandwich structure involving metal-aryl ring coordination. The bent structure of 3 probably also precludes the observation of free ion magnetism of Fe(2+) recently reported for Fe{C(SiMe(3))(3)}(2). DFT calculations on the model compounds M(SPh)(2) (M = Cr-Ni) support the higher tendency of the iron species to distort its geometry.     

Distal Weak Coordination of Acetamides in Ruthenium(II)‐Catalyzed C−H Activation Processes

C?H activations with challenging arylacetamides were accomplished by versatile ruthenium(II) biscarboxylate catalysis. The distal C?H functionalization offers ample scope—including twofold oxidative C?H functionalizations and alkyne hydroarylations—through facile base‐assisted internal electrophilic‐type substitution (BIES) C?H ruthenation by weak O‐coordination.