Solid-State Chlorine NMR of Group IV Transition Metal Organometallic Complexes

摘要

Static solid-state ~(35)Cl (I = 3/2) NMR spectra of the organometallic compounds Cp_2TiCl_2, CpTiCl_3, Cpv2ZrCl_2, Cp_2HfClv2, Cp~*_2ZrCl_2, CpZrCl_3, Cp~*ZrCl_3, Cp_2ZrMeCl, (Cp_2ZrCl)_2μ-O, and Cp_2ZrHCl (Schwartz's reagent) have been acquired at 9.4 T with the quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) sequence in a piecewise manner. Spectra of several samples have also been acquired at 21.1 T. The electric field gradient (EFG) tensor parameters, the quadrupolar coupling constant (C_Q) and quadrupolar asymmetry parameter (η_Q), are readily extracted from analytical simulations of the spectra. The ~(35)Cl EFG and chemical-shift tensor parameters are demonstrated to be sensitive probes of metallocene structure and allow for differentiation of monomeric and oligomeric structures. First-principles calculations of the ~(35)Cl EFG parameters successfully reproduce the experimental values and trends. The origin of the observed values of C_Q(~(35)CI) are further examined with natural localized molecular orbital (NLMO) analyses. The combination of experimental and theoretical methods applied to the model compounds are employed to structurally characterize Schwartz's reagent (Cp_2ZrHCl), for which a crystal structure is unavailable. Aside from a few select examples of single-crystal NMR spectra, this is the first reported application of solid-state ~(35)Cl NMR spectroscopy to molecules with covalently bound chlorine atoms. It is anticipated that the methodology outlined herein will find application in the structural characterization of a wide variety of chlorine-containing transition-metal and main-group systems.