A series of ferriostannylenes with differing terphenyl substituents

Abstract

A series of ferriostannylenes of formula ArMe6SnFeCp(CO)2 (ArMe6 = −C6H3-(C6H2–2,4,6-Me3)2, Cp = η5-C5H5) (1), ArMe6SnFeCp*(CO)2 (Cp* = η5-C5Me5) (2), and ArMe6SnFeCp(CO)(PMe3) (3) with differing iron and/or tin substituents was synthesized. Their structures and spectroscopic properties were examined by X-ray crystallography, NMR, IR, and UV–vis spectroscopy and compared with data for related species. The structural data showed that, as the size of the terphenyl substituent increases, the C-Sn-Fe angle decreases slightly which is contrary to steric expectations. The 1H and 119Sn NMR chemical shifts of the least crowded species 1 is similar to, but slightly upfield of those of its more hindered ferriostannylene analogs. Unexpectedly, 3 displayed a 119Sn NMR chemical shift that is ca. 800 ppm downfield of 1 as a result of the substitution of one of the iron carbonyl groups with a PMe3 ligand. This unusual finding is probably a reflection of a decreased paramagnetic shielding of the 119Sn nucleus by the more electron releasing character of the PMe3 ligand which decreases the n→p energy gap. The infrared spectrum of 1 also displayed slightly higher νCO frequencies, and its electronic spectrum indicated a small hypsochromic shift in the energy of its n→p transition whereas both 2 and 3 displayed much greater hypsochromic shifts than 1 consistent with the more electron donating character of the iron phosphine substituent. The results were interpreted in terms of the electronic/steric properties of the various substituents and their effects on metal electron density.