Structural studies on rhenium and tungsten halo trialkylphosphine, M2X4(PR3)4 compounds (M = rhenium, tungsten; X = Cl, Br; R = Me, n-Pr, n-Bu). The first examples of simple three-way disorder of dimetal units within ordered ligand cages

Abstract

The following, previously known, multiply bonded dirhenium and ditungsten compounds have been characterized by X-ray crystallography: Re2C14(PMe3)4 (l), [RezC14(PMe3)4]Re04 (2), RezC14(P-n-Pr3)4 (3), Re2Br4(P-n-Pr3)4 (4), and W,CI,(P-n-B u~)~C~H~ (5). Pertinent crystal data are as follows: for 1, monoclinic space group C2/c, a = 18.058 (3) A, 6 = 9.247 (1) A, c = 18.725 (2) A, 0 = 124.64 (I)', V = 2572 (1) A3, Z = 4; for 2, orthorhombic space group Pmcn, a = 14.166 (2) A, b = 9.799 (2) A, c = 20.836 (4) A, V = 2892 (I) A', 2 = 4; for 3, monoclinic space group 12/a, a = 18.564 (6) A, 6 = 14.766 (6) A, c = 19.283 (5) A, 6 = 106.21 (2)'. V = 5076 (3) A3, Z = 4; for 4, monoclinic space group C2/c, a = 18.513 (5) A, 6 = 14.767 (4) A, c = 19.381 (6) A, p = 104.57 ( 2 ) O , V = 5128 (2) A', 2 = 4; for 5, triclinic space grou Pi, a = 13.947 ( I ) A, b = 20.743 (7) A, c = 13.612 (6) A, a = 96.28 (3)O, 6 = 117.78 ( 2 ) O , y = 74.73 (2)", V = 3361 (2) i3, 2 = 2. Complexes 3-5 exhibitan unprecedented form of crystallographic disorder for this type of compound in which the dimetal unit adopts three orientations within a quasi-cube of halide and phosphine ligands. These complexes have the dimetal unit in three orientations with occupancies of 43%. 29%. 28% for 3, 50%, 32%, 18% for 4, and 88%, 8.5%, 3.5% for 5. Compounds 1 and 2 are not disordered in any way.The role played by the size and shape of the phosphine in promoting this type of disorder is discussed.

Molecular and Electronic Structure of Re2Br4(PMe3)4

“…The average Re–Br (i.e., 2.504(1) Å) and Re–P (i.e., 2.420(2) Å) distances in Re 2 Br 4 (PMe 3 ) 4 are respectively ∼0.08 and 0.05 Å shorter than in Re 2 Br 4 (P- n -Pr 3 ) 4 ; these differences are presumably due to steric effects induced by the bulkier phosphine ligand. The Re–P distance in Re 2 Br 4 (PMe 3 ) 4 is similar to the one found in Re 2 Cl 4 (PMe 3 ) 4 (i.e., 2.417(2) Å) . The Re–Br and Re–P distances are both slightly shorter by ∼0.02 Å than the Tc–Br and Tc–P distances in Tc 2 Br 4 (PMe 3 ) 4 (Table ).…”

“…Steric effects induced by the halogen ligands are presumably the cause of these differences. The Re–Re separation is similar to the one found in Re 2 Br 4 (P- n -Pr 3 ) 4 (i.e., 2.253(4) Å) and indicates that the nature of the phosphine has a minor effect on the metal–metal separation. The Re–Re separation in Re 2 Br 4 (PMe 3 ) 4 is 0.12 Å larger than the one in Tc 2 Br 4 (PMe 3 ) 4 .…”

“…The Re 2 X 4 (PMe 3 ) 4 (X = Cl, Br, I) dinuclear complexes are fundamental compounds. Re 2 Cl 4 (PMe 3 ) 4 and Re 2 I 4 (PMe 3 ) 4 have been extensively studied; , the chemistry of Re 2 Br 4 (PMe 3 ) 4 less so. The latter compound was first reported in 1985 and was characterized by elemental analysis and cyclic voltammetry; , its crystallographic structure and electronic spectrum have not been reported, and no electronic structure calculations have been performed.…”

A Novel Tetranuclear Compound: Crystal Structure and Mass Spectra of [Re4(C6H5NCOCH3)6(Cl)(μ-O)(μ-OH)(MeOH)3][ReO4]2

“…These were later shown , to contain instead Re 2 (O 2 CR) 4 2+ or Re 2 (O 2 CR) 3 Cl 2 + cations together with ReO 4 - anions. Just a few years ago, it was found that, on exposure to air, Re 2 Cl 4 (PMe 3 ) 4 gives rise to [Re 2 Cl 4 (PMe 3 ) 4 ]ReO 4 . Thus, the present observations are, in this respect at least, not unprecedented.…”

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

“…Several years ago, we began to take a systematic approach to elucidating the “rules of the game”, and we present here our latest report, wherein we deal with the simplest case (barring [Re 2 Cl 7 PR 3 ], where only one isomer 5 can exist), namely, [Re 2 Cl 6 (PR 3 ) 2 ]. To summarize briefly the position to date for cases where n = 2−4, we note that the most often characterized species are the 1,3,6,8 isomers ,4d, of the Re 2 X 4 (PR 3 ) 4 ( I ) molecules with a trans arrangement of phosphine ligands on each end of the molecule. The second isomer of that formula, namely, the 1,2,7,8 isomer, having PR 3 groups cis on each rhenium atom, was recently discovered by us 4a and is now known for three different phosphines. 4a-c Replacing one phosphine ligand by the halide in each of the isomers of I gives the isomeric compounds of composition [Re 2 X 5 (PR 3 ) 3 ] ( II ), namely, 1,2,7 and 1,3,6, both of which are now well established. 4b,e, Finally, for the [Re 2 X 6 (PR 3 ) 2 ] stoichiometry ( III ), the only form known so far corresponds to the centrosymmetric 1,7 arrangement. 4a,b, Neither the 1,2, 1,3, nor 1,6 isomers have yet been made.…”