Nitrosyl and Thionitrosyl Complexes of Technetium and Rhenium and Their Reactions with Hydrotris(pyrazolyl)borates

The very limited number of structurally known thionitrosyl complexes of technetium was increased by the synthesis of [Tc^II(NS)Cl₃(PPh₃)₂] (<b>3</b>) and [Tc^II(NS)Cl₃(PPh₃)(OPPh₃)] (<b>4</b>) and their reaction products with hydrotris(pyrazolyl)borates, {HB(pz^R)₃}^-. Similar reactions were conducted with [Tc^I(NO)Cl₂(PPh₃)₂(CH₃CN)] and related rhenium thionitrosyls. Remarkably, most such reactions result in a rapid cleavage of the boron-nitrogen bonds of the ligands and the formation of pyrazole complexes of the two group 7 metals. Only one compound with an intact {HB(pz^R)₃}^- ligand could be isolated: the technetium(I) complex [Tc^I(NO)Cl(PPh₃){HB(pz)₃}] (<b>2</b>). Other products show the coordination of one or four neutral pyrazole ligand(s) in the coordination spheres of technetium generated by thermal decomposition of the pyrazolylborates [Tc^I(NO)Cl₂(PPh₃)₂(pz^H)] (<b>1</b>) and [Tc^I(NS)Cl(pz^HMe2)₄]⁺ (<b>5</b>). Reactions with the corresponding thionitrosylrhenium complex [Re^II(NS)Cl₃(PPh₃)₂] require higher temperatures and only compounds with one pyrazole ligand, [Re^I(NS)Cl₂(PPh₃)(pz^HR)] (<b>6a</b>-<b>6c</b>), were isolated. The products were studied spectroscopically and by X-ray diffraction.