A NEW DONOR ATOM SYSTEM [(SNN)(S)] FOR THE SYNTHESIS OF NEUTRAL OXOTECHNETIUM(V) MIXED-LIGAND COMPLEXES

A new approach to the ''3 + 1'' mixed ligand oxotechnetium complexes o f the general formula TcOL1L2, with ligands (L1H(2)) containing the SN N donor set and various monodentate thiols as coligands (L2H) is repor ted. The ligands L1H(2) (1-3, general formula R(1)CH(2)CH(2)NHCH(2)C(R (2))(2)SH where R(1) = N(CH3)(2) and R(2) = H in 1, R(1) = pyrrolidin- 1-yl and R(2) = H in 2, and R(1) = piperidin-1-yl and R(2) = CH3 in 3) act as tridentate SNN chelates to the TcO3+ core, leaving open one co ordination site cis to the oxo group. In the presence of a monodentate thiol (L2H) and using Tc-99(V)-gluconate as precursor, the vacancy is filled by the thiol which acts as the coligand. With this approach fo ur neutral oxotechnetium complexes (4-7, general formula TcO[R(1)CH(2) CH(2)NCH(2)C(R(2))(2)S][SR] where RSH = p-methoxybenzenethiol, or p-me thylbenzenethiol or benzyl mercaptan) were prepared in high yield by r eacting L1H(2) and L2H with Tc(V)-gluconate in a ratio 1:1:1. The comp lexes were characterized by elemental analysis and spectroscopic metho ds. Complete assignments of H-1 and C-13 NMR resonances were made for all complexes. X-ray crystallographic studies of 5 (R(1) = pyrrolidin- 1-yl, R(2) = H, RSH = p-methylbenzenethiol) and 7 (R(1) = piperidin-1- yl, R(2) = CH3, RSH = benzyl mercaptan) showed that the complexes crys tallize in the monoclinic space group P2(1)/n (a = 10.223(1) Angstrom, b = 9.283(1) Angstrom, c = 18.337(2) Angstrom, beta = 97.262(2)degree s, V = 1726.3(4) Angstrom(3), Z = 4; a = 11.876(2) Angstrom, b = 10.47 0(2) Angstrom, c = 17.098(3) Angstrom, beta = 105.990(4)degrees, V = 2 043.8(6) Angstrom(3), Z = 4, for 5 and 7, respectively). Complexes 5 a nd 7 have distorted square pyramidal coordination geometry with the ox o ligand in the axial position. The steric requirements of the oxo gro up cause the Tc atom to be displaced 0.68 Angstrom out of the mean equ atorial plane of the NNSS donor atoms in both complexes.