Abstract
The gas-phase chemistry of a number of bare transition metal-nitrene and -imido ion complexes, MNH/sup +/ are reported herein. Group 3, 4, and 5 atomic metal ions react with NH/sub 3/ at thermal energies to generate MNH/sup +/ via dehydrogenation. A reaction mechanism is proposed involving initial oxidative addition to an N-H bond, in analogy to mechanisms proposed for reactions of gaseous atomic metal ions with hydrocarbons. Cr/sup +/ reacts with NH/sub 3/ via slow condensation to form CrNH/sub 3//sup +/, as do all group 6-11 atomic metal ions investigated. However, excited-state Cr/sup +/ reacts with NH/sub 3/ via bond-insertion reactions to form CrNH/sub 2//sup +/ and CrNH/sup +/. An unidentified metastable electronic state of Cr/sup +/, produced by direct laser desorption of chromium foil, reacts with much higher efficiency than does kinetically excited Cr/sup +/. FeO/sup +/ reacts with NH/sub 3/ to generate FeNH/sup +/ with loss of H/sub 2/O. Thermochemical studies of VNH/sup +/ and FeNH/sup +/ involving ion-molecule reactions indicate values of D/degree/(V/sup +/-NH) = 101 /plus minus/ 7 kcal/mol and D/degree/(Fe/sup +/-NH) = 54 /plus minus/ 14 kcal/mol, the latter value in accord with D/degree/(Fe/sup +/-NH) = 61 /plus minus/ 5 kcal/mol obtained from photodissociation. Themore » high bond strength for VNH/sup +/ indicates multiple bonding, analogous to that in the isoelectronic VO/sup +/, while the weaker bond strength for FeNH/sup +/ indicates a single bond, analogous to that in the isoelectronic FeO/sup +/. Proton-transfer experiments indicate PA(VN) = 220 /plus minus/ 4 kcal/mol from which /delta/H/sub f/(VN) = 111 /plus minus/ 9 kcal/mol and D/degree/(V-N) = 125 /plus minus/ 9 kcal/mol are obtained. VNH/sup +/ is unreactive with ethene and benzene, but FeNH/sup +/ transfers NH to ethene and benzene through metathesis and homologation reactions. 41 references, 2 figures, 2 tables.« less
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