Synthesis and crystal structure of mixed-ligand Tc(I) complexes, with dimethylphenylphosphine and t-butylisonitrile

Abstract

The reaction of mer-Tc(PMe2Ph)3Cl3 with t-butylisonitrile (TBI) in ethanol solution produced, depending on the experimental conditions, two compounds which were identified as trans-[Tc(PMe2Ph)2(TBI)4]+ and [Tc(PMe2Ph)(TBI)5]+. The proton NMR spectra of the two compounds showed that the complexes are quite pure. The two compounds were studied by X-ray diffraction methods. Trans-[Tc(PMe2Ph)2(TBI)4]PF6 (I) is monoclinic, space group C2/c with a = 17.933(9), b = 9.878(6), c = 25.675(18) Å and β = 105.29(5)°. The Tc atom is located on a center of inversion, while P (of PF6−) is located on a two-fold axis. [Tc(PMe2Ph)(TBI)5]PF6 (II) belongs to the tetragonal P4/n space group with a = 29.561(11), c = 10.614(5) Å. The geometry around the Tc atom is octahedral with TcC bonds from 2.036(15) to 2.045(13) Å for I and from 1.996(19) to 2.064(18) Å for II. The TcP bond distances are quite short for I (2.389(3) Å) and slightly longer in crystal II (2.403(6) Å). The short TcP bonds are caused by the presence of multiple bonding which increases as the oxidation state of Tc decreases, while the slightly longer TcP bond distance observed for crystal II is ascribed to a large trans influence of the isonitrile ligands, greater than the one of phosphines.