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Starting from the mononuclearprecursor trans-Fe(depe)2I2(depe = 1,2-bis(diethylphosphino)ethane), four dinuclear complexesIFe(depe)2–R–Fe(depe)2I, withR = 1,4-(−CC–C6H4–CC−) 1, 1,3-(−CC–C6H4–CC−) 2, 4,4′-(−CC–C6H4–C6H4–CC−) 3, and 2,5-(−CC–thiophene–CC−) 4, as well as a trinuclear complex, {I–Fe(depe)2(CC−)}3(1,3,5-C6H3)} 5, were prepared in a facile way by transmetalationfrom stannylated precursors. Substitution of the terminal iodidesapplying an excess of NaSCN yielded the corresponding isothiocyanatecomplexes 6–10in very good yields.All complexes 1–10are intrinsicallyfunctional due to the redox-active Fe centers embedded in a structurallyrigid and covalent sp/sp2framework. 1–10were characterized by NMR, IR, and Raman spectroscopy,as well as elemental analyses. X-ray diffraction studies were carriedout for 1, 2, 4, 5, 6, 8, and 9. Cyclic voltammetrywas employed to explore the redox behavior of 1–10. The 1,4-(−CC–C6H4–CC−) and the 2,5-(−CC–thiophene–CC−)bridged compounds 1, 4, 6,and 9exhibit two fully reversible oxidation waves, whilethe 1,3-(−CC–C6H4–CC−)and 4,4′-(−CC–C6H4–C6H4–CC−) bridgeddinuclear complexes and the trinuclear complexes show only one reversibleoxidation wave corresponding to 2 e–and 3 e–processes, respectively. Calculations were carriedout for truncated model complexes to determine the HOMO/LUMO energies.The DFT results confirmed that by changing the sp/sp2bridgingligand, tuning of the energies of the molecular orbitals and modifyingof the HOMO–LUMO gap ΔE(H-L)and the chemical hardness are possible. [ABSTRACT FROM AUTHOR]

The borohydride complex [Re(η2-BH4)(NO)(PPh3)2] (1ph) reactswith ethylene to yield [Re⁽(η2-C2H4)(NO)(PPh3)2] (2ph) and triethylborane formed by ethylene hydroboration.Subsequent ethylene insertion into the Re–H bond of 2phand uptake of another 1 equiv of ethylene led to the kineticallystable cis-hydrido–ethyl complex [Re(Et)(η2-C2H4)(NO)(PPh3)2] (3ph). 3phwas foundto slowly reductively eliminate ethane. The rate of this process wasdetermined by quantitative NMR spectroscopy in the temperature rangefrom 293 to 338 K, enabling calculation of the activation parameters(ΔH⧧= 68.7 kJmol–1, ΔS⧧= −94 J mol–1K–1; half-life time 1.8 h at 303 K). The reaction was found to followfirst-order kinetics in c(3ph) and iszeroth order in c(C2H4) and c(PPh3), ruling out preceding ligand dissociation.The presumptive intermediate [Re–I(η2-C2H4)(NO)(PPh3)2] couldnot be traced, since it rapidly reacted further with ethylene, furnishingthe stable butadiene complex [Re–I(η2-C2H4)(η4-C4H6)(NO)(PPh3)] (4ph) in 88% yield. Thistransformation of dehydrogenative ethylene coupling is suggested toinvolve the elementarysteps of rhenacyclopentane formation from two coordinated ethyleneligands and then double C–H activation via β-hydrideshifts to generate the butadiene unit and formal H2eliminationfrom the rhenium dihydride with concomitant triphenylphosphine elimination.An X-ray crystallographic study confirmed the spectroscopically derivedpentacoordinate structure of 4ph. [ABSTRACT FROM AUTHOR]