The relationship between molybdaziridine hydride Mo(H)(Me 2C=NAr)(N[i-Pr]Ar) 2 (1, Ar = 3,5-C 6H 3Me 2) and its three-coordinate isomer Mo(N[i-Pr]Ar) 3 (2) has been probed via an investigation of the coordination chemistry of 1 and Mo(N[t-Bu]Ar) 3 (3) with 1-adamantyl-isocyanide (AdNC). One or two equivalents of AdNC react with 1 to form the adducts 2-AdNC and 2-(AdNC) 2, respectively. One equivalent of AdNC coordinates to 3, forming 3-AdNC. Similarly, tert-butylisocyanide (t-BuNC) reacts with 1 to form 2-t-BuNC and 2-(t-BuNC) 2 and with 3 to form 3-t-BuNC. An X-ray crystal structure of 2-(AdNC) 2 reveals a trigonal bipyramidal core with a trans disposition of the isocyanide ligands (C-Mo-C, 172.8(4)°; Mo-C, 2.135(11) and 2.083(11) Å). The structure of 3-t-BuNC features a bent isocyanide ligand with a C-N-C angle of 137.8(7)°, and the compound has a solution IR stretch of 1759 cm -1, revealing Mo-C multiple-bond character. The fast reactions of AdNC with 1, 1-d 3, and 3 were studied by stopped-flow spectrophotometry in a wide temperature range (-80 to 25°C). A comparison of the reaction rates and activation parameters indicates that 2 is not an intermediate on the pathway from 1 to 2-AdNC, but rather that the molybdaziridine hydride opens upon AdNC binding in an associative process. The enthalpies of reaction to generate the compounds of interest were measured using solution calorimetry: 2-AdNC, -24.6 kcal·mol -1. 3-AdNC, -29.1 kcal-mol -1. The enthalpy of binding of the second equivalent of AdNC to generate 2-(AdNC)2 is -10.2 kcal·mol -1.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry