Stuart L. Bartley

Bis- and tetrakis-(diphenylphosphino) tetrathiafulvalenes as precursors of redox-active organic—inorganic polymeric networks

Abstract Lithiation of the (Z)-, (E)-dimethyltetrathiafulvalene mixture and subsequent reaction with ClPPh2 afford (Z)- and (E)-dimethylbis(diphenylphosphino)tetrathiafulvalene which are separated by fractional recrystallization. The identity of (Z)-P2 has been ascertained by its X-ray crystal structure determination. By similar methods, tetrakis(diphenylphosphino)tetrathiafulvalene (P4) is obtained from the tetrathiafulvalene tetralithium derivative. Cyclic voltammetry experiments reveal that the new compounds oxidize reversibly in two one-electron steps to the radical cation and dication. Reaction of o-P2 with the dinuclear complex [Rh2(NCCH3)10](BF4)4 has been investigated and found to produce the square-planar Rh(I) compound [(o-P2)2Rh][BF4]. The identity of the product has been confirmed by X-ray crystallography, FAB-MS, elemental analysis, and NMR spectroscopy. Several reactions of solvated cations were also performed, all of which appear to lead to products with o-P2 and P4 ligands.

Acetonitrile and cyanide compounds containing metal-metal bonds: syntheses, structures and applications to solid-state chemistry

Abstract Compounds with acetonitrile and cyanide ligands have been prepared from mild substitution reactions of well- known metal-metal bonded precursors. Facile non-redox substitution of the carboxylate ligands in Mo2(O2CCH3)4 occurs in chlorinated solvents treated with excess [R4N][CN] (R=Et, Bun) to produce the salts [R4N]4[Mo2(CN)8] (R=Et (3); Bun (1)) in high yields. These reactions were found to be solvent dependent, with the major product isolated from reactions performed in THF being [Bun4N]3[Mo2(O2CCH3)(CN)6] (2). The chloride ligands in multiply-bonded dirhenium compounds are readily displaced by cyanide as demonstrated by the reaction between Re2Cl4(dppm)2 and [Bun4N]CN to give [Bun4N]2(Re2(CN)6(dppm)2] (4). Compounds 1–4 were characterized by IR and electronic spectroscopies; single crystal X-ray data were collected for 1, 2 and 4. 1·8CHCl3: orthorhombic, Pbca, a=20.526(8), b=28.122(5), c=19.855(7) A, V=11461(4) A3, R=0.082, Rw=0.083; 2: monoclinic, P21, a=12.046(3), b=16.050(10), c=16.854(3) A, β=94.11(2)°, V=3250(2) A3, R=0.067, Rw=0.067; 4·8CH2Cl2: triclinic, P 1 , a=13.835(2), b=18.172(2), c 12.261(1) A, α=106.788(8), β=107.850(9), γ=93.894(9)°, V=2767.5(6) A3, R=0.041, Rw=0.045. The molecular structure of [Bun4N]4[Mo2(CN)8] contains dimolybdenum(II) centers ligated by eight CN− ligands in the familiar unbridged M2L8 arrangement, with the two Mo(CN)4 units being perfectly eclipsed as expected for a molecule with a δ component to the MM bond. The MoMo distance of 2.122(2) A is the shortest reported distance for an unbridged homoleptic Mo2II,IIL8 compound. The related salt, (Bun4N]3[Mo2(O2CCH3)(CN6] (2), contains an anion displaying a structure similar to 1, but with one bridging acetate ligand, the presence of which results in a slight contraction of the MoMo bond to 2.114(2) A. The hexacyanodirhenium compound, 4, is reminiscent of M(III) complexes of the type M2X6(dppm)2 with one important exception, namely it is of the type [M2X6(dppm)2]2− with divalent metal centers. The equatorial plane in 4, bisected by two trans dppm ligands, consists of four unidentate terminal cyanide ligands and two cyanide groups that adopt an unusual η2-(σ,π) bridging arrangement. The ReRe distance of 3.0505(6) A is formally a single bond based on the conventional overlap scheme for a d5d5 M2L10 compound, viz. σ2π2(σ2π*2)π*2 this assignment is supported by the diamagnetism of the compound as revealed by NMR and magnetic susceptibility studies. With the exception of the bridging cyanides in 4, the v(CN) stretches in the new compounds 1–4 occur at higher frequencies than free CN−, indicating that they are acting purely as donors. In related chemistry, the alkylcyanide CH3CN is used as the sole supporting ligand in dinuclear metal cations. The compounds [Bun4N]2[Re2Cl8] and Re2Cl4(PPrn3)4 react with HBF4 etherate solutions to yield the hitherto unknown compound [Re2(MeCN)10][BF4]4 (5), containing a triply-bonded solvated cation. Compound 5 and the previously reported salts [M2(MeCN)10][BF4]4 (M=Mo, Rh) were metathesized with [Bun4N]2[M6O19] (M=Mo, W) and [Bun4N]4[Mo8O26] in MeCN to give [M2(MeCN)10][M′6O19]2 (M=Re, M′=Mo (6); M=Rh, M′=Mo (7); M=Rh, M′=W (9); M=M′=Mo (10); M=Mo, M′=W (12)) and [M2(MeCN)10][M′8O26] (M=Rh (8); M′=Mo (11)). The products were isolated directly from acetonitrile solutions as insoluble salts and characterized primarily by IR and UV-Vis spectroscopies which are diagnostic tools for the presence of the MM bonded chromophore with coordinated nitrile ligands as well as the intact polyoxometallate anions. Layering of the two separate salt solutions led to the isolation of single crystals in two cases. Crystal data for representative salts are: 6·4CH3CN·2H2O: monoclinic C2/c, a=18.36(2), b=22.67(2), c=17.45(2) A, β=90.31(9)°, V=7263(13) A3, R=O.066, Rw=0.083; 7·4CH3CN: monoclinic C2/c, a=18.457(2), b=22.723(2), c=17.190(2) A, β=90.07(1)°, V=7209(2) A3, R=0.079, Rw=0.059. Compounds 6 and 7 were subjected to thermal gravimetric analysis and found to undergo quantitative loss of acetonitrile solvent ligands to give amorphous metal oxide materials of empirical composition MMo6O19 (M=Rh (13); Re (15)). The anaerobic thermal treatment of [Mo2(MeCN)10][Mo6O19]2 (10) leads to a crystalline material of empirical formula Mo′Mo6O19 (14) whose powder X-ray pattern revealed tetragonal symmetry with unit cell dimensions a=b=10.811(1), c=2.819(8) A, V=329.56(6) A3. These results will be discussed along with the cyanide chemistry in light of the design of new ordered materials starting from metal-metal bonded molecules.

Structural, electronic and magnetic properties of metal–metal bonded dinuclear rhenium complexes bridged by organocyanide acceptor ligands

The syntheses, spectroscopic properties, redox chemistry, and solid-state structures of products obtained from the reaction of Re2Cl4(dppm)2 (dppm = bis(diphenylphosphino) methane) with the polycyano acceptors TCNQ (7,7,8,8-tetracyanoquinodimethanido) and DM-DCNQI (2,5-dimethyl-N,N′-dicyanoquinonediimine) are described. The compounds [Re2Cl4(dppm)2]2(μ-TCNQ), 1, and [Re2Cl4(dppm)2]2(μ-DM-DCNQI), 2, have been prepared by reaction of two equivalents of Re2Cl4(dppm)2 with TCNQ and DMDCNQI, respectively, in THF or CH2Cl2. A single-crystal X-ray crystallographic study of [Re2Cl4(dppm)2]2(μ-TCNQ)·10THF revealed the presence of a trans-μ2 bidentate mode for the bridging TCNQ ligand that joins two Re2Cl4(dppm)2 molecules through equatorial positions. In a similar fashion, the compound [Re2Cl4(dppm)2]2(μ-DM-DCNQI)·10THF consists of two Re2 units coordinated to the two nitrile positions of the DM-DCNQI ligand. The electronic properties of both compounds are unusual in that they exhibit intense, broad absorptions that span the near-IR region and extend into the mid-IR. The electrochemistry of the compounds consists of numerous oxidation and reduction processes in the range of +2.0 to −2.0 V as determined by cyclic voltammetry. Both 1 and 2 exhibit temperature independent paramagnetism (TIP) with large χTIP values of 7.29 × 10−3 and 6.23 × 10−3 emu mol−1, respectively.

The oxygenation of the electron-rich triple bond in the complexes [Re2X4(µ-dppm)2][X = Cl or Br; dppm = bis(diphenylphosphino)methane]. Multielectron redox behaviour involving retention of the Re2X4P4 unit

The reactions of the triply bonded complexes [Re2X4(µ-dppm)2](X = Cl or Br; dppm = Ph2PCH2PPh2) with O2 proceed to give the products [Re2(µ-O)(µ-X)(O)X3(µ-dppm)2] and [Re2(µ-O)(O)2X4(dppm)2] in high yield in which net four- and six-electron redox reactions have occurred and the integrity of the ligand sets of the precursor complex is preserved.