1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

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Chemical Redox Agents for Organometallic Chemistry

The homologous series M(TCNQ)2 (M = Mn(II), Fe(II), Co(II), and Ni(II); TCNQ = 7,7,8,8-tetracyanoquinodimethane) prepared from reactions of [M(CH3CN)6][BF4]2 and [n-Bu4N][BF4] in CH3CN has been carefully analyzed from the perspective of synthetic issues and physical characterization, including complete magnetic analyses by the tools of dc and ac magnetometry. The preparative method was optimized to definitively establish the reproducibility of the chemistry as judged by infrared spectroscopy, thermal gravimetric analysis, powder X-ray crystallography, and elemental analysis. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) studies results are also in accord with the conclusion that these materials are pure, isostructural phases. The dc magnetic measurements reveal a spontaneous magnetization for the four materials at low temperatures with a weak field coercivity of 20, 750, 190, and 270 G at 2 K for Mn(TCNQ)2, Fe(TCNQ)2, Co(TCNQ)2, and Ni(TCNQ)2, respectively. At low tempera...

Glassy Magnets Composed of Metals Coordinated to 7,7,8,8-tetracyanoquinodimethane: M(TCNQ)2 (M = Mn, Fe, Co, Ni)†

The title compound was prepared by treating a mixture of UCI4 and K with C7H8 or by reacting UCl4 with KC7H9; the crystal structure shows that the two C7H7 ligands are planar, parallel and perpendicular to the linear axis defined by the uranium atom and the ring centroids.

Synthesis and crystal structure of [K(C12H24O6)][U(η-C7H7)2], the first cycloheptatrienyl sandwich compound

Just over 20 years have elapsed since the first recognition of the existence of compounds that contain metal-metal multiple bonds. The present article surveys many of the important developments that have occurred in this field since the publication in 1982 of the text “Multiple Bonds Between Metal Atoms” by the present authors. Detailed updates are provided of the chemistry surrounding ditungsten, ditechnetium, and dirhenium complexes that possess quadruple bonds (σ2Π4δ2 electronic configuration) and electron-rich triple bonds (σ2Π4δ2δ*2 electronic configuration). The rapidly developing chemistry of multiply bonded diruthenium and diosmium complexes that possess the M 2 +4 , M 2 5+ , and M 2 6+ cores, especially those containing ligand bridges, is also surveyed. Additional topics that have been covered are the following: the reactivity of dimolybdenum(III) and ditungsten(III) hexaalkoxides; the chemistry of singly bonded diplatinum(III) complexes; experimental and theoretical aspects of the bonding in 
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complexes; the diatomics Mo2, Cr2, V2 and Ru2; and the photoelectron spectroscopy, optical activity, and M-M bond length/bond order and charge correlations that characterize compounds that contain metal-metal multiple bonds.

Metal-metal multiple bonds in dinuclear clusters

The anions [X3U(µ-η7,η7-C7H7)UX3]–(X = NEt2 or BH4) have been obtained by treatment of UX4 with K[C7H9]; the cation [U(BH4)2(thf)5]+ was formed by protonation of [U(BH4)3(thf)3] with [NHEt3][BPh4] in tetrahydrofuran (thf).

Inverse cycloheptatrienyl sandwich complexes. Crystal structure of [U(BH4)2(OC4H8)5][(BH4)3U(µ-η7,η7-C7H7)U(BH4)3]

An improved route to [Mo(η-C7H7)(η-C7H9)]2 has been found which involves the reduction of MoCl5 with sodium amalgam in the presence of cycloheptatriene followed by thermolysis. Compound 2 can be oxidised with a half equivalent of iodine or tetrafluoroboric acid forming the corresponding cation [Mo(η-C7H7)(η-C7H9)]+3, which reacts with ethanol or an excess of iodine to yield the binuclear cations [(η-C7H7)Mo(µ-X)3Mo(η-C7H7+](X = OEt 4 or I 5 respectively). Treatment of 2 with 1 equivalent of iodine, bromine or an excess of PhlCl2 in the presence of a weak co-ordinating solvent or σ-donor affords the 17-electron compounds [Mo(η-C7H7)LX2][L = tetrahydrofuran (thf), MeCN, PPh3, PMe3 or Et2S; X = Cl, Br or I). Treatment of [Mo(η-C7H7)(MeCN)I2]11 with [NBu4]I gives [NBu4][Mo(η-C7H7)I3]18 and reduction of 11 with sodium amalgam in the presence of 1,2-bis(dimethylphosphino)ethane (dmpe), 1,2-bis(diphenylphosphino)ethane (dppe) or PMe3 gives [Mo(η-C7H7)(dmpe)I]19, [Mo(η-C7H7)(dppe)I]20 or [Mo(η-C7H7)(PMe3)2I]13, respectively. Compound 11 also reacts with Na(C5H4R)(R = H or Me) or lithium indenide to yield the mixed-sandwich compounds [Mo(η-C7H7)(η-C5H4R)](R = H 21 or Me 22) or [Mo(η-C7H7)(η-C9H7)]23. The crystal structures of [NBu4][Mo(η-C7H7)I3]18 and [Mo(η-C7H7)(η-C5H4Me)]22 have been determined. Compound 22 reacts with 1 equivalent of tetracyanoethene (tcne) to give the electron-transfer complex [Mo(η-C7H7)(η-C5H4Me)][tcne]24 while compound 21 reacts with 1 equivalent of 7,7,8,8-tetracyanoquinodimethane (tcnq) to yield [Mo(η-C7H7)(η-C5H5)]2[tcnq]25.

Synthesis and reactions of η-cycloheptatrienyl derivatives of molybdenum

The synthesis of [Mo(η-C7H7)(η-C7H9)] from MoCl5 provides a convenient route to η-cycloheptatrienylmolybdenum compounds such as [Mo(η-C7H7)LX2] and [Mo(η-C7H7)L2X], where L = tertiary phosphines or acetonitrile and X = halogen, and [Mo(η-C7H7)(η-C5H4R)], R = H, Me.

New synthetic pathways in η-cycloheptatrienyl molybdenum chemistry

Reactive halocarbons such as 1,2-dibromo-(or dichloro-) ethane or allyl chloride will halogenate atoms of molybdenum and rhenium under co-condensation conditions giving solvated transition metal halides in lower valency states, e.g.[Re3Cl9(THF)3](THF = tetrahydrofuran), which are useful synthetic precursors; co-condensation of rhenium with oxalyl chloride gives [Re(CO)4Cl]2, ruthenium atoms when co-condensed with oxalyl chloride give a carbonyl halide compound which adds trimethylphosphine forming [Ru(Me3)P3(CO)Cl2], and similarly, iridium atoms with oxalyl chloride and then triphenylphosphine give [Ir(CO)2(PPh3)Cl3].

Synthesis of binuclear and trinuclear cluster halides of molybdenum and rhenium, and of carbonyl halides of rhenium, iridium, ruthenium, and platinum using metal atoms

Robert C. Tovey

Papers

Synthesis and reactions of η-cycloheptatrienyl derivatives of molybdenum

New synthetic pathways in η-cycloheptatrienyl molybdenum chemistry

Synthesis of binuclear and trinuclear cluster halides of molybdenum and rhenium, and of carbonyl halides of rhenium, iridium, ruthenium, and platinum using metal atoms