Structure vs 119Sn NMR Chemical Shift in Three-Coordinated Tin(II) Complexes: Experimental Data and Predictive DFT Computations
Résumé
The new amido-/alkoxy-tin complexes [Sn(μ-OSiPh3)(OSiPh3)]2 (4), [Sn(μ-OiPr)(OSiPh3)]2 (5), [Sn(μ-OSiPh3)(Cl)]2 (6), [Sn(μ-OiPr)(Cl)]2 (7), [Sn(OSiPh3)(NMe2)]2 (8), and [Sn(OiPr)(NMe2)]2 (9) have been synthesized. The molecular solid-state structures of 4–7 established by XRD analysis show these complexes to exist as μ-O-bridged dimers with three-coordinated tin(II) atoms. Diffusion-ordered NMR spectroscopy (DOSY) measurements demonstrated that the complexes retain their dimeric structure in solution in aromatic solvents. The 119Sn{1H} NMR data for 4–7 and those of the known dimers [Sn(μ-OiPr)(OiPr)]2 (2), [Sn(μ-NMe2)(NMe2)]2 (3), [Sn(μ-OiPr)(N(SiMe3)2)]2 (10), and Lappert’s [Sn(μ-Cl)(N(SiMe3)2)]2 (11) have been recorded in toluene-d8 (using Sn(N(SiMe3)2)2 (1), δ119Sn = +771 ppm, as a reference compound). The resonances, located in the range +138 to −338 ppm, are increasingly shifted toward high fields with substitution according to NMe2 ∼ N(SiMe3)2 < Cl < OtBu ≤ OiPr < OSiPh3. DFT computations have been performed to model the 119Sn NMR chemical shifts in these tin(II) complexes as well as in 10 other heteroleptic, monometallic phenolate-supported stannylenes featuring three-coordinated metal atoms, taking into account the coordination number of the metal atoms. The applied methodology produces computed data that match those recorded experimentally by 119Sn{1H} NMR spectroscopy, hence providing a convenient tool that complements traditional spectroscopic (119Sn NMR, DOSY NMR) and diffraction methods to predict the structural and spectroscopic features of stannylenes.