Acidification of TczCk(PR3)4 with HBF4.Et20 in a mixture of acetonitrile and methylene chloride results in the formation of the metal-metal triply-bonded solvated complex [Tc2(CH3CN)lo] [BF& (1) in 80% yield. This compound may also be prepared through reduction of [ B u~N ]~[ T c C~~] with either BusSnH or finely divided Zn followed by treatment with HBF40Et20, but in lower yields (approximately 50%). The quadruply bonded species Tc2Cls2-also reacts with HBF4.Et20 in a mixture of acetonitrile and diethyl ether under mild heating to produce small amounts of blue [TC~(CH~CN)I~][BF& (yield 14%). In addition to the formation of 1, yellow crystals that proved to be the mononuclear Tc (II1) species [ T c C~~( C H~C N )~] [ B F~] (2) were isolated in 34% yield from the reaction solution. The dinuclear cation [Tc2(CH3CN)1ol4+ was crystallized as tfie mixed salt [ T c~( C H~C N )~( C F~-S03)2](BF&CH3CN (laCH3CN) by addition of 8 equivs of Tl(CF3S03) to a CH3CN solution of 1 followed by slow diffusion of a mixture of Et20 and hexanes. Compound laCH3CN crystallized in the tetragonal space group P41212 with a = 12.181(2) A, c = 27.385(3) A, V = 4063(1) A3 and 2 = 4. The molecular structure of la entails a staggered M2L8 conformation with approximate D u symmetry. The two axial positions of the dinuclear cation are occupied by CF3SO3-anions. The BF4-anions occupy general positions within the unit cell. The T c q c bond distance is 2.122(1) A, consistent with a Tc-Tc multiple bond. Single crystal X-ray analysis of [ T c C~~( C H~C N )~] [ B F~] revealed a trans disposition of chloride ligands with approximate D4h symmetryo about the Tc atom. Crystal data for 2: orthorhombic space group Zbam, with a = 6.250(1) A, b = 12.189(2) A, c = 20.880(5) A, V = 1590.7(5) A3 and Z = 4. Nitrile complexes 1 and 2 have been fully characterized by a variety of physical and spectroscopic techniques including 'H NMR, UV-vis and IR spectroscopies and cyclic voltammetry.
Samples of Wilkinson's catalyst, RhCl(PPh3)3, prepared from RhCl3'xH20 are inevitably contaminated by a paramagnetic impurity, the exact nature of which has eluded researchers for years.1 Recently, Ogle, Masterman, and Hubbard (OMH) communicated the isolation of a small quantity of a yellow, airstable paramagnetic material formulated as RhCl2(PPh3)2'2CH2-Cl2(l).2•3 The compound was reported asan impurity in samples of (cod)RhCl(PPh3) synthesized from [Rh(cod)Cl]2 and PPh3 in chloroform or dichloromethane. The molecular structure revealed that the rhodium atom resides on an inversion center in the orthorhombic space group Pcab with a square-planar arrangement of trans phosphine and chloride ligands. Characterization of the sample included far-IR, NMR, and EPR spectroscopies and mass spectrometry. Unfortunately, detailed studies were hampered by the authors' inability to reproduce the result either by the original serendipitous route beginning with [Rh2(cod)2Cl2] or by other more rational methods.2 Herein we report our deliberate synthesis and full characterization of the orthorhombic solvated form of RhCl(CO)(PPh3)2, viz., RhCl(CO)(PPh3)r 2CH2C12 (2); these results, when taken together with spectroscopic data, suggest that the orthorhombic crystal structures reported for "RhCl2(PPh3)2" and RhCl(CO)(PPh3)2 are in fact the same.During the course of our work, Chaloner et al. independently reported the orthorhombic form of RhCl(CO)(PPh3)2'2CH2Cl2 as a byproduct isolated from a purification of trans-[Rh2(PPh3)2-Experimental SectionSynthesis of RhCl(CO)(PPh3)2 (2). A quantity of [Rh(cod)Cl]2 (0.100 g, 0.2 mmol) was dissolved in 5 mL of THF under a CO atmosphere and treated with• 4 equiv of PPh3 (0.213 g, 0.8 mmol). The reaction was stirred for 10 min, after which time the resulting yellow precipitate was collected by suction filtration in air. Additional solid was obtained from the filtrate by addition of diethyl ether. The combined solids were recrystallized from a minimal volume of hot THF and Et20; yield 0.242 g (86%). IR (Nujol mull/CsI, cm-1): t-co = 1965 s; other bands, 1480
The syntheses, spectral properties, redox chemistry, and structures of complexes obtained from the reaction of carbon monoxide with a rare mononuclear Rh(I1) species are described. The ionic compound [Rh(q3-TMPP)2] [BF4I2 (1) {TMPP = tris(2.4,6-trimethoxyphenyl)phosphine, P(C6H2(OMe)3),] has been prepared in high yield by reaction of the unbridged Rh: + complex [Rh2(CH3CN),,][BF4], with 4 equiv of TMPP in CH3CN. The product crystallizes in the orthorhombic space group Pbcn with unit cell dimensions a = 15.938 (5) A, b = 17.916 (7) A, c = 21.015 (8) A, V = 5376 (3) A', and Z = 4. Residualsof R = 0.073 and R, = 0.089 were obtained after least-squares refinement of 369 parameters to convergence and a quality-of-fit of 2.37. The Rh atom, which is situated on a 2-fold axis, is bonded to two ether phosphine groups in a capping, tridentate mode through the phosphorus atom and two o-methoxy substituents. The geometry about the metal is pseudooctahedral, and, surprisingly, the phosphorus atoms lie cis to one another. A Jahn-Teller structural distortion was observed for 1 along the direction of the two trans oxygen atoms, which constitutes the first documentation of this effect in a molecular Rh(I1) d7 complex.[ Rh(q'-TMPP),] [ BF4]? was also characterized by infrared, electronic and EPR spectroscopies, and by elemental analysis. Complex 1 reacts reversibly with carbon monoxide by a series of redox reactions, initiated by a highly unstable Rh(1I) dicarbonyl adduct. Products isolated from the reaction under a CO atmosphere are the Rh (lI1) complex [Rh(q3-TMPP),] [BF413 (2) and the Rh(l) dicarbonyl complex [Rh(TMPP)2(CO)2][BF,] (3). Compound 3 has been crystallized as its CH2C12 solvate in the space group Pi with unit cell dimensions a = 13.318 (4) A, b = 13.404 (2) A, c = 18.104 (4) A, a = 95.908 (3)O, /3 = 97.037 (3)O, y = 90.71 1 (3)O, V = 3200 (2) A', and Z = 2. Least-squares refinement of 779 parameters gave residuals of R = 0.059 and R, = 0.084 and a quality-of-fit = 2.316. The Rh(1) cation occupies a general position and exhibits a trans squawplanar coordination geometry, with the phosphine ligands acting as monodentate groups. In the absence of a CO atmosphere, 3 rcadily loses a molecule of C O to form the monocarbonyl species [Rh(q2-TMPP)(TMPP)CO] [BF,] (4) which has been structurally characterized as the benzene solvate [Rh(q2-TMPP)(TMPP)CO] [BF4]-2C6H6; triclinic space group PI with unit cell dimensions of a = 14.898 (5) A, b = 18.060 (8) A, c = 14.343 (4) A, a = 96.56 (4)O, /3 = 113.84 (2)O, y = 104.80 (4)O, V = 3308 (2) A', and Z = 2. Final refinement of 757 parameters gave residuals of R = 0.067 and R, = 0.069 with a quality-of-fit of 2.59. The immediate coordination sphere of the Rh atom consists of one CO ligand and two trans phosphorus atoms with the fourth site being occupied by a pendant methoxy group. The resulting structure is a highly distorted square-planar arrangement as evidenced by the bond angle O(I)-Rh(I)-C(55) of 150.2 (4)O. Complex 4 reversibly adds CO, both in the solid state and in solution, t...
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