Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 2. New Reactions Involving Dimethylphenylphosphine

Dinuclear and Mononuclear Rhenium Coordination Compounds upon Employment of a Schiff-Base Triol Ligand: Structural, Magnetic, and Computational Studies

The 1:1 reaction of trans-[Re^IIICl₃(PPh₃)₂(MeCN)] with 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol, H₃L, in toluene gave the dinuclear complex [Re^III₂Cl₄(HL)(PPh₃)]·2C₇H₈ (1·2C₇H₈), while the 1:2 reaction led to the formation of complex [Re^IVCl₂(HL)(PPh₃)] (2). In both species, the Schiff-base ligand exists in its doubly deprotonated form, HL^2-, forming chelate rings around the metallic centers. In addition, 1·2C₇H₈ displays a unique triple metal-to-metal bond between the two trivalent rhenium ions separated at a 2.229(1) Å bond distance, while in complex [Re^IVCl₂(HL)(PPh₃)] (2) the two aromatic ligands, HL^2- and PPh₃, occupy axial positions, with the terminal Cl^- ions in the trans position. Investigation of the magnetic properties revealed a Curie paramagnetic behavior ( S = 1/2) with a pronounced temperature independent paramagnetism (TIP) for 1·2C₇H₈ and 2. Both the geometry and the electronic structure of both compounds have been studied by means of density functional theory (DFT) calculations, confirming the triplet and doublet spin ground state of the complexes and furthermore establishing an electron-rich σ²π⁴δ¹δ^*1 bond order of 3 for 1·2C₇H₈. In addition, the absorption spectrum of 1·2C₇H₈ in CH₂Cl₂ was simulated by means of DFT calculations and is in excellent agreement with both the crystallographic and theoretical studies. Complex 1·2C₇H₈ is the first dinuclear rhenium complex with a triple metal-metal bond between trivalent rhenium centers.

New dirhenium(III) compounds bridged by carboxylate ligands: N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] and Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2)

The solvothermal reaction of (N(C(4)H(9))(4))(2)[Re(2)Cl(8)] with trifluoroacetic acid and acetic anhydride leads to the new rhenium trifluoroacetate dimer N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] (1) and to the rhenium carbonyl dimer Re(2)(mu(2)-Cl)(2)(CO)(8) as the rhenium-reduced byproduct. The reaction of the precursor complex, N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] (1), with the organometallic carboxylic acid (CO)(6)Co(2)HCCCOOH leads to the cluster of clusters compound Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2), which has the dimer structure of Re(2)(OOCR)(4)Cl(2). Cyclic voltammetric measurements show that Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2) has one reduction centered on the dirhenium core and a reduction centered on the cobalt atoms. DFT calculations have been used to rationalize the observed displacements of the voltammetric signals in Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2) compared to the parent ligand (CO)(6)Co(2)HCCCOOH and rhenium pivalate.

Mixed chloride/phosphine complexes of the dirhenium core. 10. Redox reactions of an edge-sharing dirhenium(III) non-metal-metal-bonded complex, Re(2)(mu-Cl)(2)Cl(4)(PMe(3))(4)

Reduction and oxidation reactions of the dirhenium(III) non-metal-metal-bonded edge-sharing complex, Re(2)(mu-Cl)(2)Cl(4)(PMe(3))(4) (1), have been studied. Several new mono- and dinuclear rhenium compounds have been isolated and structurally characterized in the course of this study. Reductions of 1 with 1 and 2 equiv of KC(8) result in an unusual face-sharing complex having an Re(2)(5+) core, Re(2)(mu-Cl)(3)Cl(2)(PMe(3))(4) (2), and a triply bonded Re(II) compound, 1,2,7,8-Re(2)Cl(4)(PMe(3))(4) (3), respectively. Two-electron reduction of 1 in the presence of tetrabutylammonium chloride affords a new triply bonded complex of the Re(2)(4+) core, [Bu(n)()(4)N][1,2,7-Re(2)Cl(5)(PMe(3))(3)] (4). Oxidation of 1 with NOBF(4) yields a Re(IV) mononuclear compound, trans-ReCl(4)(PMe(3))(2) (5). Two isomers of the monomeric Re(III) anion, [ReCl(4)(PMe(3))(2)](-) (6, 7), have been isolated as side products. The crystal structures of compounds 2 and 4-7 have been determined by X-ray crystallography. The Re-Re distance in the face-sharing complex 2 of 2.686(1) A is relatively short. The metal-metal bond length in anion 4 of 2.2354(7) A is consistent with the usual values for the triply bonded Re(2)(4+) core compounds. In addition, a cis arrangement of trimethylphosphine ligands in the starting material 1 is retained upon reduction in the dinuclear products 2-4.

Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 5. Reduction or Disproportionation at the Re(2)(6+) Unit in Reactions with Tertiary Phosphines in Different Solvents

For reactions of the octachlorodirhenium anion, [Re(2)Cl(8)](2)(-), with tertiary phosphines PEt(3) and PPr(n)(3), the influence of solvent on the reaction pathway has been studied. It has been shown that in 1-propanol at room temperature the reaction leads to a one-electron reduction of the Re(2)(6+) core. The novel dirhenium(II,III) paramagnetic products of stoichiometries [Bu(n)(4)N][Re(2)Cl(6)(PEt(3))(2)] (1a) and Re(2)Cl(5)(PPr(n)(3))(3) (2a) have been isolated and characterized. In benzene a disproportionation process occurs resulting in mononuclear rhenium(IV) complexes ReCl(4)(PR(3))(2) (PR(3) = PEt(3) (1b) and PPr(n)(3) (2b)) in addition to 1a and 2a, respectively. The solid state structures of compounds 1a, 1b, 2a.0.25C(6)H(14), and 2b have been investigated by X-ray crystallography. The crystallographic parameters are as follows: for 1a, tetragonal space group P4(2)/m with a = 11.821(2) Å, c = 14.770(3) Å, and Z = 2; for 1b, monoclinic space group P2(1)/n with a = 8.0555(4) Å, b = 12.536(2) Å, c = 10.2041(6) Å, beta = 99.167(9) degrees, and Z = 2; for 2a.0.25C(6)H(14), monoclinic space group P2(1)/n with a = 11.7679(9) Å, b = 18.574(5) Å, c = 19.688(4) Å, beta = 93.37(2) degrees, and Z = 4; for 2b, monoclinic space group P2(1)/c with a = 8.219(2) Å, b = 11.210(1) Å, c = 14.331(3) Å, beta = 93.171(9) degrees, and Z = 2. It has also been found that the disproportionation process in benzene goes by way of an intermediate complex which is an initial product of interaction between the [Re(2)Cl(8)](2)(-) and the phosphine. In the case of the triethylphosphine ligand we formulate this complex as [Bu(n)(4)N][Re(2)Cl(7)(PEt(3))(3)] (1c).

Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 3. Novel Structures with Diethylphosphido-bridges and Terminal Diethylphosphines

The interaction between octachlorodirhenium anions and diethylphosphine has been shown to strongly depend on reaction conditions, mainly the nature of the solvent and the amount of phosphine. As a result, novel dirhenium products with oxidation states ranging from Re(II) to Re(IV) have been obtained. The reaction of [Re(2)Cl(8)](2)(-) with an excess of PEt(2)H in dichloromethane or acetonitrile led to the first example of a face-sharing complex of rhenium(IV) with three phosphido-bridges, namely [Bu(n)(4)N][Re(2)(&mgr;-PEt(2))(3)Cl(6)] (1). The unusual edge-sharing Re(2)(&mgr;-PEt(2))(2)Cl(4)(PEt(2)H)(4) (2) complex of rhenium(III) with C(i)() core symmetry, containing both terminal phosphines and phosphido-bridges, has been obtained by carrying out the reaction with an excess of PEt(2)H in a benzene (or propanol) - HCl mixture at room temperature. A new example of the 1,2,7,8-type of dirhenium(II) complex, Re(2)Cl(4)(PEt(2)H)(4) (3), having diethylphosphine ligands located cis on each Re atom, has been isolated from the reaction of [Re(2)Cl(8)](2)(-) with PEt(2)H in an ethanol-HCl medium. The solid-state structures of complexes 1-3 have been investigated by X-ray crystallography. Complexes 1 and 2 both crystallized in two forms: [Bu(n)(4)N][Re(2)(&mgr;-PEt(2))(3)Cl(6)] 1a, P2(1)/n with a = 10.482(1) Å, b = 16.512(2) Å, c = 23.986(2) Å, beta = 93.637(8) degrees, and Z = 4; [Bu(n)(4)N][Re(2)(&mgr;-PEt(2))(3)Cl(6)].1.5 C(7)H(8) 1b, C2/c with a = 38.746(9) Å, b = 10.322(2) Å, c = 27.277(3) Å, beta = 110.35(1) degrees, and Z = 8; Re(2)(&mgr;-PEt(2))(2)Cl(4)(PEt(2)H)(4) 2a, P2(1)/n with a = 11.081(3) Å, b = 11.029(3) Å, c = 15.627(2) Å, beta = 90.05(1) degrees, and Z = 2; 2b, P2(1)/c with a = 16.094(3) Å, b = 15.193(3) Å, c = 15.548(3) Å, beta = 100.98(3) degrees, and Z = 4. X-ray data for complex Re(2)Cl(4)(PEt(2)H)(4) 3 are as follows: P2(1)/n with a = 10.445(2) Å, b = 10.113(3) Å, c = 13.473(2) Å, beta = 102.17(2) degrees, and Z = 2. Three bridging &mgr;-PEt(2) groups in the face-sharing complex 1 span a short metal-metal distance of 2.4060(6) Å, averaged over 1a and 1b, with a small Re-PEt(2)-Re angle of 61.34(7) degrees. The rhenium-rhenium bond length in the edge-sharing complex 2 is 2.7545(7) Å, averaged over 2a and 2b, while the bridging Re-PEt(2)-Re angle is 72.16(6) degrees, and the P-Re-P angle for the terminal phosphine ligands is 87.11(7) degrees. The Re-Re bond distance in 3, 2.2533(8) Å, is typical for triply bonded dirhenium complexes, and the P-Re-P angle for the cis phosphine groups is 93.12(6) degrees.