Identification of the metal-containing products of reactions of the neutral transition metal atom Zr(4d25s2, 3F) with ethylene and propylene is accomplished using one-photon ionization at 157 nm and time-of-flight mass spectrometry. The reactions proceed in a fast flow reactor at 298 K with He/N2 buffer gas at 0.6 Torr. Mass spectra of the products of both Zr + C2H4 and Zr + C3H6 indicate that H2 elimination occurs as the primary reaction step. The efficiency of the Zr + C2H4 reaction shows that there is no barrier larger than about 2 kcal/mol above reactants along the entire reaction path. This corroborates an earlier theoretical prediction by Blomberg and Siegbahn of facile H2 elimination by ground-state Zr. For the secondary reactions ZrC2H2 + C2H4 and ZrC3H4 + C3H6 and for the reactions ZrO + C2H4 and ZrO + C3H6, mass spectra again indicate that H2 elimination occurs. Rate constant measurements using photoionization detection show that the presence of the C2H2 and C3H4 ligands enhances the reaction efficiency over that of the bare Zr atom, while ZrO reacts at essentially the same rate as Zr.

CN(1) the "nonreducible" nature of the ligand (deprotonated) and(2) relatively unstable precursor complex formation at the nitrile nitrogen.An intramolecular rate of electron transfer with the 4cyanobenzoic acid complex can be estimated. A value of approximately 10 Lmol'1 is available for the complexing of Cr(II) with carboxylates,21 but in this case a somewhat lower value would be appropriate. If we use this value, an intramolecular rate constant for electron transfer <0.028 s'1 is obtained for 4-cyanobenzoic acid coordinated to cobalt(III).One other possibility should be mentioned-a bridged outer-sphere mechanism where the bridging ligand serves only to hold the reductant in close proximity to the oxidant and thus facilitate outer-sphere electron transfer. Examples of this pathway involve oxidants with flexible saturated groups in the bridging ligands.16•22 In the present case, the separation between Cr(II) and Co(III) is large with a rigid bridging ligand maintaining this separation, and this pathway does not appear likely.

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