Mixed Chloride Phosphine Complexes of Dirhenium Cores. 1. New Reactions and Unprecedented Structures Involving Trimethylphosphine

Abstract

The unusual 1,2,7-isomer of Re2Cl5(PMe3)3 (1) has been used as a starting material to prepare previously unknown dirhenium complexes. One-electron reduction of 1 by cobaltocene followed by nonredox substitution of the resulting anionic species with PMe3 led to the formation of a triply bonded 1,2,7,8-Re2Cl4(PMe3)4 (2). In the crystal structure of 2, phosphine ligands on both metal centers exhibit a cis arrangement with a P−Re−P angle of 93.3° in contrast to the well-known type of 1,3,6,8-isomers with a trans arrangement of the monodentate phosphines connected to each metal atom. Complex 2 represents the first example of an isomer of this type in the large M2X4(PR3)4 class of compounds (M = Re, Tc, W, Mo; X = Cl, Br, I; PR3 = monodentate phosphine). The one-electron oxidation product of 1 cocrystallized with one molecule of tetrabutylammonium chloride afforded Re2Cl6(PMe3)2 (3), for which all previous synthetic attempts had failed. This quadruply bonded complex exhibits an unusual 3-fold disorder of the Re2 unit with equal populations for all three orientations. We also report that when the “classic” reaction of octachlorodirhenate anion, Re2Cl8 2-, with trimethylphosphine is carried out in benzene at room temperature the reduction processes do not occur and the product is a novel paramagnetic complex, Re2Cl6(PMe3)4 (4), which does not have a metal−metal bond (the Re−Re separation is 3.8476(4) Å). Another interesting feature of compound 4 is that the PMe3 ligands have a cis disposition at each rhenium center and are located in the same plane as the metal atoms and bridging chlorine ligands. For such a ligand arrangement the molecule of 4 is the only example of a nonmetal−metal-bonded dinuclear compound with monodentate phosphine ligands.

Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 5. Reduction or Disproportionation at the Re26+Unit in Reactions with Tertiary Phosphines in Different Solvents

“…It is clear now that face-and edge-sharing complexes having 9 and 10 ligands, respectively, attached to the dirhenium unit play an important role in all processes involving mixed chloride/phosphine species. Thus, recently we found 23 a face-sharing dirhenium(II,III) compound Re 2 (µ-Cl) 3 Cl 2 (PMe 3 ) 4 which is likely to be an intermediate for the cis-trans isomerization that occurs in going from 1,2,7-Re 2 Cl 5 (PMe 3 ) 3 to [1,3,6,8…”

“…This raises the question as to what are the initial products of interaction between the octachlorodirhenate and phosphines, which then undergo disproportionation. We found earlier 6 that, when trimethylphosphine reacts with the [Re 2 Cl 8 ] 2in benzene, the intermediate product could be isolated as an edge-sharing bioctahedral complex Re 2 (µ-Cl) 2 Cl 4 (PMe 3 ) 4 which has no metal-metal bond. An analogous paramagnetic compound has been suggested 7 for the reaction of the [Re 2 Cl 8 ] 2with diethylphosphine.…”

“…[1][2][3] It has more recently been reported that a one-electron reduction of [Re 2 Cl 8 ] 2occurs in alcohols instantly at room temperature when it reacts with the most basic phosphines such as PMe 3 4 and PMe 2 Ph 5 producing the 1,2,7isomers of Re 2 Cl 5 (PR 3 ) 3 . The reduced rhenium species have also been found in other media, such as acetone, 1,2 benzene, 5,6 and acetonitrile. 5 However, the process has been shown [5][6][7] to be very dependent on the solvent used in terms of rates, intermediates, and the final products.…”

“…Alcohols have long been used as reaction media for one- and two-electron reduction of octachlorodirhenate anions with phosphines under reflux conditions giving the products Re 2 Cl 5 (PR 3 ) 3 (PR 3 = PMePh 2 , PEtPh 2 ) 1 and Re 2 Cl 4 (PR 3 ) 4 (PR 3 = PMe 3 , PEt 3 , PPr n 3 , PMe 2 Ph, PEt 2 Ph). − It has more recently been reported that a one-electron reduction of [Re 2 Cl 8 ] 2- occurs in alcohols instantly at room temperature when it reacts with the most basic phosphines such as PMe 3 and PMe 2 Ph producing the 1,2,7-isomers of Re 2 Cl 5 (PR 3 ) 3 . The reduced rhenium species have also been found in other media, such as acetone, , benzene, , and acetonitrile . However, the process has been shown − to be very dependent on the solvent used in terms of rates, intermediates, and the final products.…”

“…The reduced rhenium species have also been found in other media, such as acetone, , benzene, , and acetonitrile . However, the process has been shown − to be very dependent on the solvent used in terms of rates, intermediates, and the final products. At this point we are almost sure that phosphines themselves cannot serve as reducing agents (at least, at moderate temperatures) for the reduction of the dirhenium(III) complexes.…”