Complexes obtained by electrophilic attack on a dinitrogen-derived terminal molybdenum nitride: electronic structure analysis by solid state CP/MAS 15N NMR in combination with DFT calculations

N Solid state CP/MAS NMR spectroscopy has been used to study a dinitrogen-derived terminal nitride of molybdenum, 15 NMo(N( t Bu)Ar)3 (Ar = 3,5-(CH3)2C6H3). A number of Lewis acid adducts, including X3E-NMo(N( t Bu)Ar)3 (X =F , E =B ; X = Cl, E = B, Al, Ga, In; X = Br, E = Al; X = I, E = Al) and Cl2E-NMo(N( t Bu)Ar)3 (E = Ge, Sn), were prepared by the combi- nation of 15 NMo(N( t Bu)Ar)3 with 1 equiv. of Lewis acid. A series of cationic imido complexes, (RNMo(N( t Bu)Ar)3)X was prepared by the reaction of electrophiles, RX (R = CH3, X = I; R = PhC(O) or Me3Si, X = OTf (OTf = SO3CF3)), with NMo(N( t Bu)Ar)3. Deprotonation of (CH3NMo(N( t Bu)Ar)3)I by LiN(SiMe3)2 afforded the ketimide complex H2CNMo(N( t Bu)Ar)3, which has been shown to undergo a reaction with neat CH3I to form (CH3CH2NMo(N( t Bu)Ar)3)I. 15 N solid state CP/MAS NMR spectroscopy was employed in the characterization of each complex. Complementary density functional theory (DFT) studies of 15 NMo(N( t- Bu)Ar)3 and derivatives enabled a detailed examination of the experimental solid state NMR parameters in terms of electronic struc- ture at the labeled N-atom. Computational analysis demonstrated that significant paramagnetic contributions to the perpendicular components of the chemical shielding tensor (d11 and d22) were responsible for the huge span of the tensor measured for 15 NMo(N( t- Bu)Ar)3 (X = 1187 ppm). Perturbation of the electronic structure in 15 NMo(N( t Bu)Ar)3 upon coordination of a Lewis acid or for- mation of a cationic imido complex was attributed to stabilization of a r-symmetric orbital. An upfield shift in the perpendicular components of the chemical shift tensor results from the reduced paramagnetic contribution to these tensor components upon increasing the energy gap between the magnetically coupled occupied and virtual orbitals (eoccevir). � 2004 Elsevier Ltd. All rights reserved.