Technetium diazenido complexes. Part 1. Syntheses and structures of [TcCl(NNC6H4Cl-4)2(PPh3)2] and [TcCl(NNPh)(Ph2PCH2CH2PPh2)2][PF6]·H2O

Reaction of [NBu4][TcOCl4] with monosubstituted organohydrazines RNHNH2(R = aryl) in methanol leads to red solutions of technetium diazenido species. These species may be derivatised with the monotertiary phosphine PPh3 to give the khaki to orange bis(diazenido) complexes [TcCl(NNR)2(PPh3)2](R = Ph 1, C6H4Cl-4 2 or C6H4Me-4 3) and the lime-green monodiazenido complex [TcCl2(NNC6H4NO2-4)(PPh3)2]4. These triphenylphosphine derivatives are also easily prepared directly from [NH4][TcO4]. An X-ray crystal structure of one of the bis(diazenido) complexes [TcCl(NNC6H4Cl-4)2(PPh3)2] shows the Tc to be trigonal bipyramidal with axial PPh3 ligands. Derivatisation of the red technetium diazenido containing solutions with the bidentate ditertiary phosphine ligand Ph2PCH2CH2PPh2(dppe) gives the orange cationic complexes [TcCl(NNR)(dppe)2]+(R = Ph 5, C6H4Cl-4 6 or C6H4NO2-4 7) isolated as hexafluorophosphate or tetraphenylborate salts in good yield. These cationic monodiazenido complexes may also be prepared by substitution reactions of complexes 1–4 with dppe, or directly from [NH4][TcO4]. X-Ray structure details for 5: monoclinic, space group C2/c with Z= 4 in a unit cell of dimensions a= 23.808(5), b= 13.830(3), c= 17.452(4)A, β= 92.53(2)°. Complex 5 has slightly distorted trans octahedral geometry with two co-ordinated dppe ligands surrounding both axial phenyldiazenido and chloride ligands. The angle at the α nitrogen Tc–N(1)–N(2) is 163(2)° with Tc–N(1) 1.917(19) and N(1)–N(2) 1.25(4)A. The phenyldiazenido(1–) ligand therefore bonds formally as a singly bent three-electron donor giving complex 5 an overall valence electron count of eighteen. A most important development of this work is that these technetium complexes are directly accessible from ammonium pertechnetate [NH4][TcO4], the chemical form of technetium used in preparation of radiopharmaceuticals.