Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 6. Rare or Unprecedented Isomers of [Re₂Cl₆(PR₃)₂] Stoichiometry

Abstract

Several new paramagnetic dirhenium(II,III) anions of the formula [Re2Cl6P2]- (P2 = (PPrn 3)2 (1), (PEt2Ph)2 (2), dppp (3)) have been isolated in the form of their tetrabutylammonium salts as the kinetic products in reactions of [Re2Cl8]2- with an appropriate phosphine ligand. All three complexes have been characterized in solution by cyclic voltammetry, ESR, and mass spectroscopy. Three different isomeric forms of the [Re2Cl6P2] core have been recognized in the solid state by X-ray crystallography. The known 1,7-isomer (C 2 h ) with a centrosymmetric disposition of phosphine groups was found for PPrn 3 (1a) and PEt2Ph (2) ligands. The compound [Bun 4N][Re2Cl6(PPrn 3)2] was also crystallized in the unprecedented form of a 1,6-isomer (C 2) (1b) which can be derived from 1a by a 90° rotation of the ligands around the metal−metal bond. For the diphosphine, a C s isomer of [Re2Cl6(dppp)]- (3) was discovered having the dppp ligand chelating on one rhenium atom. Crystallographic data are as follows: for 1a, monoclinic space group P21/n with a = 12.758(1) Å, b = 15.755(5) Å, c = 24.160(3) Å, β = 104.22(1)°, and Z = 4; for 1b, monoclinic space group P21/c with a = 16.3355(8) Å, b = 12.656(1) Å, c = 22.892(2) Å, β = 94.735(6)°, and Z = 4; for 2, triclinic space group P1̄ with a = 11.868(1) Å, b = 12.125(2) Å, c = 15.375(3) Å, α = 88.01(1)°, β = 82.64(1)°, γ = 88.47(1)°, and Z = 2; for 3, triclinic space group P1̄ with a = 11.8986(4) Å, b = 11.913(1) Å, c = 18.383(2) Å, α = 102.23(2)°, β = 108.003(5)°, γ = 97.38(1)°, and Z = 2.

Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 8. Synthesis and Crystal Structure of the Quadruply Bonded Dirhenium(III) Anion [Re2Cl7(PMe3)]-

“…Here, a monoclinic polymorph of 2 has been found as a side product of the above-mentioned reaction. A crystal structure determination for 2 has confirmed the 1,7-disposition of phosphines in the centrosymmetric dirhenium Re 2 Cl 6 P 2 core . There are two independent dimetal units in the cell, one of which is disordered over two orientations with occupancies of 0.92(1) and 0.08(1).…”

An Intramolecular Disproportionation Reaction Leading to the Formation of the Quadruply Bonded Complex Cl4ReReCl2(dppf) (dppf = 1,1‘-Bis(diphenylphosphino)ferrocene). An Example of the Missing 1,3-Re2Cl6(PR3)2 Isomer

“…The discovery of the electron-rich Re−Re triple bond as present in complexes of the type Re 2 Cl 4 (PR 3 ) 4 (where PR 3 represents a monodentate tertiary phosphine) − was followed by studies of their electronic structure , and the redox chemistry of multiply bonded dirhenium species of the type Re 2 Cl 6 - x (PR 3 ) 2+ x ( x = 0, 1, or 2). ,− By the mid-1990s the structural chemistry of complexes of these types appeared to be well understood − who have been able to demonstrate that such compounds can be isolated in different isomeric forms. On the basis of the numbering scheme shown in Chart , the following isomers have been isolated and structurally characterized in their cationic, neutral, and / or anionic forms: 1,2,7,8- and 1,3,6,8-[Re 2 Cl 4 (PR 3 ) 4 ], 1,2,7- and 1,3,6-[Re 2 Cl 5 (PR 3 ) 3 ], and 1,6- and 1,7-[Re 2 Cl 6 (PR 3 ) 2 ]. ,,− It was noted that while 1,2- and 1,3- isomers of Re 2 Cl 6 (PR 3 ) 2 were improbable when PR 3 is a monodentate phosphine, by resorting to chelating diphosphines the 1,2-isomer should be isolable .…”

Mixed Chloride/Amine Complexes of Dimolybdenum(II,II). 4. Rotational Isomers of Mo2Cl4(R-py)4(R-py = 4-Picoline, 3,5-Lutidine, and 4-tert-Butylpyridine)

“…Instances of rotational isomerism are rare, and this is by far the most spectacular array. The only prior examples of which we are aware are (1) [Mo 2 Br 6 (H 2 O) 2 ] 2- , which forms eclipsed structures with both C 2 h and C 2 conformations, and (2) [Re 2 Cl 6 (PPr n 3 ) 2 ] - , which is known with C 2 h and C 2 symmetries . There is no prior example of such isomerism for any M 2 X 4 L 4 species.…”