A multinuclear ( 1H, 13C, 15N) NMR study of cis-halonitrosylbis(dithiocarbamato)iron(II) complexes: effect of replacement of S by Se

Abstract

The 1H and proton-decoupled 13C NMR spectra of several cis-Fe(NO)(E 2CNR 2) 2X complexes (where R is an organic substituent, E=S and/or Se, and X=Cl −, Br − or I −) have been measured at room temperature in CDCl 3, as well as the 15N NMR spectrum (natural abundance) of cis-Fe(NO)(S 2CN(C 2H 5) 2) 2I. The two CE 2 signals observed between 190 and 206 ppm in the { 1H} 13C NMR spectra of these cis-Fe(NO)(E 2CNR 2) 2X complexes provide an indication of the structural rigidity of these compounds in solution. The multiple 13C NMR peaks observed for the four E 2CN( CH 2R) 2 α-carbons further support this rigidity. The 13C NMR signal of the α-C atoms of the ligand is dependent on the proximate chalcogen, the second chalcogen of the ligand and the ligand atoms to which each of these is trans. The 13C NMR spectra of the cis-Fe(NO)(E 2CNR 2) 2X complexes are comparable to the spectra of the structurally similar cis-Fe(S 2CNRR ′) 2(CO) 2 complexes and give insight into the interpretation of the 13C NMR spectra of the Co(SSeCNR 2) 3 series. The { 1H} 13C NMR spectrum of cis-Fe(SSeCN(C 2H 5) 2) 2(CO) 2 is included for comparison. The 1H NMR spectra are complex; the diethyl derivative exhibits a complex multiplet which is interpreted as four overlapping ABX 3 systems for the NC H 2(C H 3) protons. The 15N NMR spectrum of cis-Fe(NO)(S 2CN(C 2H 5) 2) 2I exhibits three peaks: 210.92, 209.09 and 29.28 ppm. This is interpreted as each dithiocarbamate ligand experiencing a different magnetic environment and the NO ligand. The 15N NMR spectrum is compared to tetraethylthiuram disulfide, Co(S 2CN(C 2H 5) 2) 3 and cis-Fe(S 2CN(C 2H 5) 2) 2(CO) 2 and is interpreted as indicating similar S 2C-NRR ′ rotational barriers.