²⁹Si DFT/NMR Observation of Spin–Orbit Effect in Metallasilatrane Sheds Some Light on the Strength of the Metal→Silicon Interaction

Abstract

Der richtige Dreh: Nicht oft wird nach experimentellen Belegen für relativistische Effekte auf den Tensor der chemischen Verschiebung in der Festkörper‐NMR‐Spektroskopie gesucht. 29Si‐MAS‐NMR‐spektroskopische Messungen mit langsamer Rotation (MAS=Rotation im magischen Winkel) an der Triade [ClTM(μ‐mt)4SiCl] (TM=Pt, Pd, Ni; mt=2‐Mercapto‐1‐methylimidazolid) zeigten, dass die Schweratom‐Spin‐Bahn‐Kopplung die Form des 29Si‐NMR‐Signals stark beeinflusst.

Atomic Contributions from Spin‐Orbit Coupling to 29Si NMR Chemical Shifts in Metallasilatrane Complexes

“…This is an important sanity test of the procedure. A corresponding set of data is collected in Table 4 for the 29 Si shielding tensor span W. As shown in reference [13], the MAS solid-state NMR spectra are strongly affected by the tensor span, and only the simulated spectra based on the SO calculations agree with the experimental spectra obtained for slow spinning rates. For the isotropic shielding, Figure 6 provides a visual summary of the results along with separate contributions from the different chlorine ligands.…”

“…(mt = 2mercapto-1-methylimidazolide), as shown in Figure 1, with M = Pt, Pd, Ni, and X = Y = Cl. [13,14] The dative metal-Si bond is indicated by an arrow in the chemical formula in Figure 1. There are interesting structural analogies to a recently reported Pd-Sb complex (also with a linear arrangement of the type X-E-M-Y), which acts as an optical fluoride sensor.…”

“…Structural variations among the metal triad do not cause the observed 29 Si shift variations. In reference [13], we speculated that SO coupling originating at other heavy atoms present in the system, such as the Cl and S ligands, might be causing or contributing to an apparent Ni anomaly. This hypothesis was motivated by analyses of the electronic structure of the X = Y = Cl complexes, showing a significant degree of electron delocalization within the Cl-M-Si-Cl moiety and its first coordination sphere.…”

“…Keywords: density functional calculations · metallasilatranes · NMR spectroscopy · silicon · structure elucidation [ 29 Si shifts). not only modifies the isotropic carbon shifts (the aforementioned NHD), but also have a strong impact on the 13 Cshielding tensor anisotropies. [12] The impact on the tensor properties of nuclear magnetic shielding evidently has important implications regarding the interpretation of solidstate NMR spectra.…”

Disilicon Complexes with Two Hexacoordinate Si Atoms: Paddlewheel‐Shaped Isomers with (ClN4)SiSi(S4Cl) and (ClN2S2)SiSi(S2N2Cl) Skeletons

“…Even more recently, electron-rich transition-metal atoms have acted as donors of lone pairs of electrons toward higher-coordinate silicon atoms. [5] Phenomena such as the relatively high stability of Si À X bonds to the above mentioned donor atoms, [6] the tendency of Si À Si bonds to undergo bond cleavage upon Si hexacoordination, [7] or ionic dissociation of, for example, SiÀBr bonds, [8] have rendered the synthesis of hypercoordinate Si complexes with heavier donor atoms a challenging task.…”