Relativistic DFT calculations of structure and 119Sn NMR chemical shifts for bent M[sbnd]Sn[sbnd]C bonding in Power’s metallostannylenes of chromium, molybdenum, tungsten and iron and diaryl stannylenes

Abstract

Dispersion corrected density functional theory calculations of the metallostannylene complexes [(η5-C5H5)(CO)3M(SnC6H3-2,6-Ar2)] (1–6; M = Cr, Mo, W; Ar = Mes, Trip), [(η5-C5H5)(CO)2Fe(SnC6H3-2,6-Dip2)] (7) and [(η5-C5H5)(CO)2Fe(SnC6H3-2,6-Trip2)] (8) and monomeric diaryl stannylenes [Sn(C6H2-2,6-Mes2-4-Cl)2] (9), [Sn(C6H2-2,6-Mes2-4-SiMe3)2] (10), [Sn(C6H-2,6-Mes2-3,5-iPr2)2] (11), [Sn(C6H3-2,6-Mes2)2] (12) and [Sn(C6H3-2,6-Dip2)2] (13) (Mes = C6H2-2,4,6-Me3; Trip = C6H2-2,4,6-iPr3; Dip = C6H2-2,6-iPr2) have been carried out at the BP86-D3(BJ)/TZ2P/ZORA level of theory. The calculated geometrical parameters of the studied metallostannyles (Power et al., Organometallics 21 (2002) 5622; 30 (2011) 6316) and diaryl stannylenes (Power et al., Organometallics 34 (2015) 2222) are in good agreement with the available experimental values. The bent geometries at tin are consistent with the presence of a divalent Sn(II) center. The M-Sn-C bond angles in metallostannylenes are smaller than CSnC bond angles in diaryl stannylenes. The lengthening of M − Sn bonds and decrease in MSnC bond angles are found in the solvent (benzene) phase geometries optimized. The 119Sn NMR chemical shifts (ppm) have been calculated with the direct implementation of the gauge including atomic orbitals (GIAO) method. The calculated 119Sn chemical shifts with ZORA spin orbit level in gas phase yield reliable results. While switching from ZORA spin orbit level to ZORA scalar level results 119Sn upfield shift of ca. 300–400 ppm. Due to greater percentage s character of Sn lone pair in the chromium complexes [(η5-C5H5)(CO)3M(SnC6H3-2,6-Mes2)] (1) and [(η5-C5H5)(CO)3M(SnC6H3-2,6-Trip2)] (4), the upfield 119Sn NMR chemical shifts are observed. The relationship between computed (δcalcd) 119Sn NMR chemical shifts and 1/ΔE(LUMO-HOMO)) clearly exhibit a linear trend. The difference between 119Sn NMR chemical shifts of metallostannylenes (1–8) and diaryl stannylenes (9–13) has been analyzed. The SnC bonds in diaryl stannylenes are weaker than the SnC bonds in metallostannylenes. The Sn nuclei are more shielded in diaryl stannylenes than in metallostannylenes. As a consequence, the upfield values of 119Sn NMR chemical shifts are observed for diaryl stannylenes both experimentally and theoretically. Upfield 119Sn chemical shifts, which deviate much from the experimental values, are observed for optimized geometries of metallostannylenes in solvent (benzene) phase. The decrease in asymmetric parameter (η) causes a downfield 119Sn NMR chemical shift accompanied by an increase in 119Sn chemical shift anisotropy.