Saturated versus unsaturated bonds

Bianchini and coworkers [126] found a difference in the chemoselectivity between the metals Fe, Ru, and Os in the complexes [M(H2)H(P(CH2CH2PPh2)3)]-BPh4 in the hydrogenation of benzylideneacetone by transfer from iso-propanol. The Fe and Ru catalysts reduced the 0=0 bond to give the allyl alcohol, with Ru more active than iron (TOF 79 IT1 at 60°C for Ru versus 13 IT1 at 80°C for Fe), while the Os catalyst first reduced the 0=0 bond but then catalyzed isomerization of the allyl alcohol to give the saturated ketone (TOF 55 IT1 at 80°C). The difference in reactivity was attributed to the weak binding of the alkene of the allyl alcohol to Fe and Ru relative to Os in these complexes. A variety of selec-tivities was noted for other unsaturated ketones, whereas unsaturated aldehydes were not hydrogenated. 

Multimetallic sandwiches, including polymetallocenes, bis(fulvalene)-dimetal compounds, multi-decker sandwiches, and compounds in which two metals are bonded to a common unsaturated cyclic hydrocarbon are discussed in Section II. Sections III and IV are subdivided according to the metal group, and describe ligand-bridged bimetallics and metal clusters, respectively. Where appropriate, redox potentials have been included. Unless otherwise stated they are referenced versus the aqueous saturated calomel electrode (see). 

Unsaturated fatty adds have lower melting points than their saturated counterparts. The greater the degree of unsaturation, the lower the melting point (see "Connections to Biological Chemistry The Importance of Cis Double Bonds in Fats versus Oils"in Section 5.4). Compare, for example, the melting points of linoleic acid, a polyunsaturated fatty add, and stearic acid, a saturated fatty acid. 

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