Macrocyclic complexes of Pt(ii) and Rh(iii) with iso-tellurazole N-oxides

Abstract

Pt(II) and Rh(III) readily form complexes with 3-methyl-5-aryl-1,2-tellurazole 2-oxides (L = (3-Me-5-Ar-1,2-C₃HTe(NO)). The aryl group is either phenyl or 3,5-di-tert-butylphenyl, the latter case being a new derivative with enhanced solubility. The compound [Pt(3-Me-5-(3,5-^tBu₂C₆H₃)-1,2-C₃HTe(NO))₄](BF₄)₂ crystallizes in the P2₁/C space group featuring a square planar complex in the lattice. The crystal of [RhCl₂(3-Me-5-(C₆H₅)-1,2-C₃HTe(NO))₄](BF₄) belongs to the I space group and contains an octahedral complex. In both instances, the iso-tellurazole N-oxide molecules are linked by Te⋯O chalcogen bonding interactions confirming an annular tetramer that binds the metal ion as a κ⁴Te macrocycle in a boat conformation. Low-frequency shifts of the ¹²⁵Te magnetic resonance upon coordination and the observation of ¹²⁵Te–¹⁹⁵Pt and ¹²⁵Te–¹⁰³Rh ¹J coupling constants indicate that the complexes are stable species in solution. The complex ions were also observed in the electrospray mass spectra.