Solution dynamics of tin and lead iron carbonyl compounds and the solid state structure of [Et 4N] 2[Sn{Fe 2(CO) 8}{Fe(CO) 4} 2

Abstract

The dynamic rearrangement processes of CO ligands on the Main Group-iron carbonyl compounds, E[Fe 2(CO) 8] 2 ( Ia, E  Pb), [Et 4N] 2[E{Fe 2(CO) 8}{Fe(CO) 4} 2]([Et 4N] 2[ IIa], E  Pb; [Et 4N] 2[ IIb], E  Sn) and [Et 4N] 2[Pb{Fe(CO) 4} 3] ([Et 4N] 2[ IIIa], E  Pb; [Et 4N] 2[ IIIb], E  Sn) were investigated by variable temperature 13C NMR spectroscopy. In Ia, all of the carbonyl ligands exhibit fast exchange over the entire temperature range studied. Limiting spectra were obtained for [Et 4N] 2[ II] while the fluxional processes for [Et 4 N] 2[ IIIa] were slowed but not completely resolved. Variable temperature spectra for [Et 4N] 2[ II] provide evidence for the occurrence of two simultaneous independent carbonyl rearrangement processes, one centered on the Fe(CO) 4 groups and one on the Fe 2(μ-CO) 2(CO) 4 moiety. The dynamics of [Et 4N] 2[ IIIa] suggest that the trigonal planar geometery is preserved in solution. Calculated activation energies for CO scrambling in [Et 4N] 2[ II] and [Et 4N] 2[ IIIa] range from 5.8 to 9.2 kcal/mol. The single crystal structure of [Et 4N] 2[ IIb] was determined: monoclinic space group, Cc (No. 9) with a = 11.572(6) Å, b = 22.46(1) Å, c = 17.049(4) Å, β = 103.00(3)°, V = 4318(3) Å 3 and Z = 4. The structure was refined to R = 4.8% and R w = 5.5% for 2665 observed reflections. The anion exhibits a distorted tetrahedral configuration around Sn, with the Main Group element coordinated to two Fe (CO) 4 groups and one Fe 2(CO) 8 unit.