Metal−Metal Multiply-Bonded Complexes of Technetium. 3.1 Preparation and Characterization of Phosphine Complexes of Technetium Possessing a Metal−Metal Bond Order of 3.5

Two new ditechnetium complexes possessing Tc−Tc bonds with a formal bond order of 3.5 have been prepared in high yield. Mild chemical oxidation of Tc 2 Cl 4 (PMe 2 Ph) 4 with ferrocenium hexafluorophosphate in acetonitrile produces [Tc 2 Cl 4 (PMe 2 Ph) 4 ][PF 6 ] ( 1 ) in 82% yield. One-electron oxidation of Tc 2 Cl 4 (PMe 2 Ph) 4 by ferrocenium hexafluorophosphate in the presence of ppnCl (ppn = bis(triphenylphosphine)iminium) yielded the neutral compound Tc 2 Cl 5 (PMe 2 Ph) 3 ( 2 ) in 89% yield. Both species are paramagnetic, as evidenced by EPR spectroscopy, and possess a σ 2 π 4 δ 2 δ* ground state electronic configuration on the basis of structural and spectroscopic data. The solid state structures of three forms of 1 have been investigated by X-ray crystallography together with the structure of 2 . The crystallographic parameters for these structures are as follows: [Tc 2 Cl 4 (PMe 2 Ph) 4 ][PF 6 ] ( 1a, orthorhombic form), C 222 1 with a = 9.448(1) Å, b = 24.299(1) Å, c = 18.231(1) Å, V = 4185.4(6) Å 3, and Z = 4; [Tc 2 Cl 4 (PMe 2 Ph) 4 ][PF 6 ] ( 1b, monoclinic form), P 2 1 / n with a = 12.799(4) Å, b = 18.254(2) Å, c = 17.945(5) Å, β = 96.39(1)°, V = 4166(2) Å 3, and Z = 4; [Tc 2 Cl 4 (PMe 2 Ph) 4 ][PF 6 ]· 1 / 2 THF ( 1 · 1 / 2 THF), P 2 1 / c with a = 10.580(3) Å, b = 33.327(3) Å, c = 13.861(5) Å, β = 111.04(2)°, V = 4562(1) Å 3, and Z = 4; Tc 2 Cl 5 (PMe 2 Ph) 3 ( 2 ), P 2 1 / c with a = 11.134(1) Å, b = 14.406(1) Å, c = 19.501(5) Å, β = 98.144(6)°, V = 3096.3(7) Å 3, and Z = 4. The cation in 1 is the 1,3,6,8-isomer, and the molecule in 2 is the 1,3,6-isomer. The Tc−Tc bond lengths for 1a, 1b, 1 · 1 / 2 THF, and 2 (2.1092(9), 2.106(1), 2.1073(8), and 2.1092(4) Å, respectively) are slightly shorter than those of the corresponding Tc 2 Cl 4 (PR 3 ) 4 complexes, consistent with the removal of one electron from a δ* orbital. Electrochemical studies reveal that both compounds are capable of undergoing a one-electron oxidation and a one-electron reduction to yield the respective Tc 2 6+ and Tc 2 4+ dinuclear cores. IR, EPR, and UV−vis spectroscopic data are presented for compounds 1 and 2.