Comparative Theoretical Study of 1,3-Dipolar Cycloadditions of Allyl-Anion Type Dipoles to Free and Pt-Bound Nitriles

1,3-Dipolar cycloadditions of a series of 12 allyl-anion type 1,3-dipoles X=Y(+)-Z(-) (X, Z = CH(2), NH, O; Y = N(Me), O) to acetonitrile MeC[triple bond]N, both free and coordinated to Pt(II) and Pt(IV) in the complexes trans-[PtCl(n)(NCMe)(2)] (n = 2, 4), were investigated by theoretical methods. The reactivity increases along the following sequence of dipoles, the first three being inert toward nitriles: ON(Me)O < NHN(Me)O < NHN(Me)NH < CH(2)N(Me)O < OOO approximately NHONH < CH(2)N(Me)NH < NHOO < CH(2)N(Me)CH(2) < CH(2)OCH(2) approximately CH(2)ONH < CH(2)OO. The thermodynamic stability of the cycloaddition products (reaction energies) inversely correlates with the activation energies with exception of dioxadiazoles N=C(Me)OO NH which cannot exist in the uncoordinated state. A complete ortho selectivity of these reactions is predicted. Coordination of MeCN to platinum accelerates the reactions of CH(2)N(Me)CH(2), CH(2)ONH, and particularly CH(2)N(Me)O and CH(2)N(Me)NH and stabilizes the corresponding products. Coordination accelerates the reactions of CH(2)OCH(2), CH(2)OO, and NHONH only slightly and inhibits the reactions of NHOO and OOO. The cycloadditions of nitrones to nitriles are potentially interesting for dynamic combinatorial chemistry. The details of the reaction mechanisms and correlations of activation and reaction energies, synchronicity, and charge transfer vs dipole nature, FMO energies, atomic charges, HSAB properties, distortion energies, and regioisomeric pathways are discussed.