The synthesis, structural, and theoretical characterization of heterobimetallic complexes [CH3Si{SiMe2N(4-CH3C6H4)}3M−Co(CO)3(L)] (M = Ti, Zr; L = CO, PPh3, PTol3) with unsupported metal−metal bonds between cobalt atoms and titanium or zirconium atoms is being reported. The synthesis of the dinuclear compounds was achieved by salt metathesis of the chlorotitanium and zirconium complexes and the alkalimetal carbonylates. X-ray crystal structure analyses of four of these heterobimetallic complexes established the unsupported metal−metal bonds [M = Ti, L = CO (3):  2.554(1) Å; M = Ti, L = PTol3 (4b):  2.473(4) Å; M = Zr, L = CO (5):  2.705(1) Å; M = Zr, L = PPh3 (6a):  2.617(1) Å] as well as the 3-fold molecular symmetries. Upon axial phosphine substitution, a metal−metal bond contraction of ca. 0.08 Å is observed, which also results in the quantum chemical structure optimizations performed on the model compounds [(H2N)3Ti−Co(CO)4] (3x) and [(H2N)3Ti−Co(CO)3(PH3)] (4x) using gradient-corrected and hybrid density functionals. A theoretical study of the homolytic dissociation of the metal−metal bonds focuses on the relaxation energies of the complex fragments and indicates that the geometrical constraints imposed by the tripod ligand lead to a major thermodynamic contribution to the stability of the experimentally investigated complexes. The central question of the polarity of the metal−metal bond is addressed by detailed analysis of the calculated electron charge distribution using natural population analysis (NPA), charge decomposition analysis (CDA), Bader's atoms in molecules (AIM) theory, and the electron localization function (ELF). Both the orbital-based NPA and CDA schemes and the essentially orbital-independent AIM and ELF analysis suggest a description of the Ti−Co bond as being a highly polar covalent single bond. The combination of AIM and ELF is employed for the first time to analyze metal−metal bond polarity and appears to be a powerful theoretical tool for the description of bond polarity in potentially ambiguous situations.

The novel tridentate diamidoamine ligands [RC(2-C5H4N)(CH2NSiMe,),l2~ (R = H, CH3) have been synthesized and coordinated to TiIV and ZrIV giving the pentacoordi- [~] have been studied in most detail. While they have enabled the stabilization of otherwise elusive molecular stuctures and offered the possiblity to investigate their reactivity, the scope of their use is limited. This warrants continuing efforts in the area of ligand design[9' and, given the results of the approach mentioned above, polyfunctional derivatives of amido systems are attractive candidates when early transition metals are involved.Our research has focussed on the metals of the titanium triad and the trianionic tripodal aniido ligands employed have generated nionofunctional MIv complexes, i.e. compounds in which one anionic ligand (such as a halide) may be substituted to yield derivatives. In order to study the chemistry of d

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A comprehensive investigation into the cooperative reactivity of two chemically complementary metal-complex fragments in early-late heterodinuclear complexes has been carried out. Reaction of the partially fluorinated tripodal amidozirconium complexes [HC-(SiMe2NR)3Zr(mu-Cl)2Li(OEt2)2] (R = 2-FC6H4: 2a, 2,3,4-F3C6H4: 2b) with K[CpM(CO)2] (M=Fe, Ru) afforded the stable metal-metal bonded heterodinuclear complexes [HC[SiMe2NR]3-Zr-MCp(CO)2] (3-6). Reaction of the dinuclear complexes with methyl isonitrile as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Two of these complexes, [HC[SiMe2N(2-FC6-H4)]3Zr(S2C)Fe(CO)2Cp] (9a) and [HC-[SiMe2N(2-FC2H4)]3Zr-(SCNPh)Fe(CO)2-Cp] (12), have been structurally characterized by a single crystal X-ray structure analysis, proving the structural situation of the inserted substrate as a bridging ligand between the early and late transition metal centre. The reactivity towards organic carbonyl derivatives proved to be varied. Reaction of the heterobimetallic complexes with benzyl and ethylbenzoate led to the cleavage of the ester generating the respective alkoxozirconium complexes [HC[SiMe2N(2-FC6H4)]3ZrOR] (R = Ph-CH2: 13a, Et: 13b) along with [CpFe-[C(O)Ph](CO)2], whereas the analogous reaction with ethyl formate gave 13b along with [CpFeH(CO)2]; this latter complex results from the instability of the formyliron species initially formed. Aryl aldehydes were found to react with the Zr-M complexes according to a Cannizzaro disproportionation pattern yielding the aroyliron and ruthenium complexes along with the respective benzoxyzirconium species. The transfer of the aldehyde hydrogen atom in the course of the reaction was established in a deuteriation experiment. [HC[SiMe2-N(2-FC6H4)]3Zr-M(CO)2Cp] reacted with lactones to give the ring-opened species containing an alkoxozirconium and an acyliron or acylruthenium fragment; the latter binds to the early transition metal centre through the acyl oxygen atom, as evidenced from the unusuallly low-field shifted 13C NMR resonances of the RC(O)M units. Ketones containing a-CH units react with the Zr-Fe complexes cooperatively to yield the aldol coupling products coordinated to the zirconium complex fragment along with the hydridoiron compound [CpFeH(CO)2], whereas 1,2-diphenylcyclopropenone underwent an oxygen transfer from the keto group to a CO ligand to give a linking CO2 unit and a cyclopropenylidene ligand coordinated to the iron fragment in [HC-[Si(CH3)2N(2,3,4-F3C6H2)]3Zr(mu-O2C)-Fe(CO)[C3Ph2)Cp] (19). The atom transfer was established by 17O and 13C labelling studies. Similar oxygen-transfer processes were observed in the reactions with pyridine N-oxide, dimethylsulfoxide and methylphenylsulfoxide.

Raman spectroscopy has proven to be a very effective approach for the detection of microorganisms colonising hostile environments on Earth. The ExoMars rover, due for launch in 2018, will carry a Raman laser spectrometer to analyse samples of the martian subsurface collected by the probe's 2-m drill in a search for similar biosignatures. The martian surface is unprotected from the flux of cosmic rays, an ionising radiation field that will degrade organic molecules and so diminish and distort the detectable Raman signature of potential martian microbial life. This study employs Raman spectroscopy to analyse samples of two model organisms, the cyanobacterium Synechocystis sp. PCC 6803 and the extremely radiation resistant polyextremophile Deinococcus radiodurans, that have been exposed to increasing doses of ionising radiation. The three most prominent peaks in the Raman spectra are from cellular carotenoids: deinoxanthin in D. radiodurans and β-carotene in Synechocystis. The degradative effect of ionising radiation is clearly seen, with significant diminishment of carotenoid spectral peak heights after 15 kGy and complete erasure of Raman biosignatures by 150 kGy of ionising radiation. The Raman signal of carotenoid in D. radiodurans diminishes more rapidly than that of Synechocystis, believed to be due to deinoxanthin acting as a superior scavenger of radiolytically produced reactive oxygen species, and so being destroyed more quickly than the less efficient antioxidant β-carotene. This study highlights the necessity for further experimental work on the manner and rate of degradation of Raman biosignatures by ionising radiation, as this is of prime importance for the successful detection of microbial life in the martian near subsurface.