Metal-metal multiply-bonded complexes of technetium .3. 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 Tc2Cl4(PMe(2)Ph)(4) with ferrocenium hexafluorophosphate in acetonitrile produces [Tc2Cl4(PMe(2)Ph)(4)][PF6] (1) in 82% yield. One-electron oxidation of Tc2Cl4(PMe(2)Ph)(4) by ferrocenium hexafluorophosphate in the presence of ppnCl (ppn = bis(triphenylphosphine)iminium) yielded the neutral compound Tc2Cl5(PMe(2)Ph)(3) (2) in 89% yield. Both species are paramagnetic, as evidenced by EPR spectroscopy, and possess a sigma(2) pi(4) delta(2) delta* 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: [Tc2Cl4(PMe(2)Ph)(4)][PF6] (1a, orthorhombic form), C222(1) with a = 9.448(1) Angstrom, b = 24.299(1) Angstrom, c = 18.231(1) Angstrom, V = 4185.4(6) Angstrom(3), and Z = 4; [Tc2Cl4(PMe(2)Ph)(4)][PF6] (1b, monoclinic form), P2(1)/n with a = 12.799(4) Angstrom, b = 18.254(2) Angstrom, c = 17.945(5) Angstrom, beta = 96.39(1)degrees, V = 4166(2) Angstrom(3), and Z = 4; [Tc2Cl4(PMe(2)Ph)(4)][PF6]. 1/2THF (1 . 1/2THF), P2(1)/c with a = 10.580(3) Angstrom, b = 33.327(3) Angstrom, c = 13.861(5) Angstrom, beta = 111.04(2)degrees, V = 4562(1) Angstrom(3), and Z = 4; Tc2Cl5(PMe(2)Ph)(3) (2), P2(1)/c with a = 11.134(1) Angstrom, b = 14.406(1) Angstrom, c = 19.501(5) Angstrom, beta = 98.144(6)degrees, V = 3096.3(7) Angstrom(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 . 1/2THF, and 2 (2.1092(9), 2.106(1), 2.1073(8), and 2.1092(4) Angstrom, respectively) are slightly shorter than those of the corresponding Tc2Cl4(PR(3))(4) complexes, consistent with the removal of one electron from a delta* 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. LR, EPR, and UV-vis spectroscopic data are presented for compounds 1 and 2.