Thio derivatives of β-diketones and their metal chelates. I. Some Monothio-β-diketones and their nickel(II) chelates

Abstract

Monothio-β-diketones of general formula RC(SH)=CHCOR? (R = Me, R* = Me, Ph, OEt; R = Ph, R' = Ph, OEt; R = α-thienyl, R' = CF₃; and 12 = R' = CMe,) have been prepared in order to study their metal complexes. Five of these thio derivatives are new and were prepared by treatment of a dilute solution of the corresponding β-diketone in alcohol with hydrogen sulphide at low temperature. Mass spectrometric examination has established the structures of MeC(SH)=CHCOPh and RC(SH)=CHCOCF, (R = α-thienyl). The red compounds PhC(SH)=CHCOPh (VI) and MeC(SH)=CHCOPh (V) can be oxidized to yellow products. The structure of the yellow compound (XV) obtained from (VI) was established by mass and n.m.r. spectroscopy as the disulphide PhCOCH=C(Ph)SSC(Ph)=CHCOPh. The molecular ion of (XV) undergoes novel rearrangement reactions involving, inter alia, elimination of H₂S to produce a thiophene ion. The nickel chelates Ni(RCS=CHCOR')₂ are brown, diamagnetic, and soluble in organic solvents. Unstable paramagnetic bis-pyridine adducts, derived from two of the nickel chelates, were isolated. The infrared spectra of the monothio-β-diketones and their nickel chelates are reported. The spectra of the monothio-β-diketones show no SH band at c. 2570 cm^-1 ; this indicates strong chelation of the thiol hydrogen between the sulphur and oxygen atoms. The monothio-β-diketones display four characteristic bands which are assigned as follows : 1670-1590 cm^-1, v(C--O) ; 1638-1530 cm^-1, v(C=C) ; 1267-1190 cm^-1, v(C=S) ; 837-805 cm^-1, provisionally assigned as v(C=S) + δ(C-H). The nickel chelates exhibit five characteristic bands: 1590-1535 cm^-1, V(C=C); 1542-1477 cm^-1, v(C-0); 1261-1220 cm^-1, v(C--S); 817-800 cm^-1, provisionally assigned to v(C-S)+ δ(C-H); 499-451 cm^-1, v(Ni-O). No band corresponding to v(Ni-S) was detected above 250 cm^-1. However, the metal-sulphur stretching frequency was observed as a peak of medium intensity within the range 360-308 cm^-1 in the spectra of bis(o-methylthiobenzenethiolo)-nickel(II) and the diethyl dithiophosphate complexes of nicke1(II), palladium(II), chromium(III), and cobalt(III).