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

Abstract

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)Å, 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)Å. 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.