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We are establishing the coordinated ligand reactions depicted for reducing CO2 to formaldehyde and methanol; our objective in future studies includes optimizing and combining these ligand reactions into a reaction cycle or a catalytic system. Our approach exploits bimetallic complexation of carbon dioxide and uses a third metal system as the reductant (e.g., catalytic hydrosilation). These bimetallic CO2 adducts feature synergistic CO2 binding in which an electron-rich metal system LxM contributes metallocarboxylate binding and an oxophilic LyM system sequesters one or both metallocarboxylate oxygens (2a and 2b, respectively). In addition ot stabilizing the CO2 adduct, the resulting electronic 'push-pull' also activates the CO2 ligand as a hydride acceptor.

Taphonomy is the study of the fate of information in the fossil record. Information can be lost through the partial or complete destruction of fossils, or through the disruption of their original spatial relationships. Information can be "gained" if the alteration of fossils allows environmental information to be retrieved. In Bahia la Choya, northern Gulf of California, bioerosion, dissolution/maceration, and abrasion produce distinctive textures on the surfaces of shells in intertidal and shallow subtidal environments. Shells from different environments possess different surface textures, suggesting that textures on fossil shells could serve as paleoenvironmental indicators. Algal bioerosion is the chief mode of shell alteration and destruction in Bahia la Choya, though dissolution/maceration and abrasion are locally important. Algal bioerosion of shell surfaces is accelerated by the grazing activity of snails, and is most intense where snails are abundant. Microstratigraphic resolution is limited by vertical mixing of fossils and by the reworking of older fossils into younger deposits. Stratigraphic disorder is the departure from perfect chronological order of fossils in a stratigraphic sequence. I simulated mixing and reworking of fossils by simple computer models, and measured stratigraphic disorder using rank correlation statistics. As modeled, mixing produces disorder slowly, and its effects can be minimized by increasing sample size at each horizon and by increasing the vertical spacing between sampled horizons (though this reduces vertical resolution). Reworking generates disorder more efficiently, and its effects are not reduced by increasing sample size or spacing. The generation of stratigraphic disorder in fossiliferous sediments can also be modeled using M (depth of vertical mixing), I (thickness of sedimentary increments), and L (taphonomic loss rate) as parameters. Increasing M increases the disorder generated, and increasing I and L decreases disord

The rhenium and tungsten (eta 1-O) formates Cp(NO)(CO)Re-OC(O)H and Cp(CO)3W-OC(O)H are available through protonolysis (HBF4-HCO2H) of their methyl complexes. These formates, in turn, afford homobimetallic (ReRe) and (WW) mu(eta1-O,O') formates M-OCHO-M+ upon reacting with requisite organometallic Lewis acid (M-H/Ph3C+). Analogous heterobimetallic mu-formates (FpRe) and (FpW) (Fp=Cp(CO)2Fe) also are prepared using similar reaction chemistry. The (ReRe)mu- formate salt is labile in solution; its dissociative equilibrium can be intercepted with FpOC(O)H to give the mixed (FpRe)mu-formate. Tungsten- containing bimetallic mu-formate salts, in contrast, do not reversibly dissociate in solution. Reactions of hydride donors, including Et3BDLi, with Cp(CO)3W-OCHO-W(CO)3Cp+ give only the W formate and Cp(CO)3W-H(D); no evidence was found for hydride (deuteride) adding to the carboxylate carbon of the formate bridge.

Availability of analogous pairs of carbon dioxide 1. and carbon disulfide 2. transition-metal complexes permits comparing structure-bonding and chemical reactivity of these ligated heterocumulenes 3. Such comparisons permit us to address the prevalent but questionable attitude that studying the generally more accessible CS2 adducts affords insight into their less stable (or more labile) CO2 congeners 4. We are interested in one pair of bonded heterocumulene complexes, the Fe(CO)2Cp metallodithiocarboxylates Fp-CS2-(NA+, K+) and metallocarboxylates Fp-CO2(Li+,Na+).