Chemical oxidation of the title compound [W2Cp2(CO)4(μ-dppm)] (Cp = η 5-C5H5; dppm = Ph2PCH2PPh2) with 1 equiv of [FeCp2](BAr‘4) (Ar‘ = 3,5-C6H3(CF3)2) leads to the tetracarbonyl radical [W2Cp2(CO)4(μ-dppm)](BAr‘4), which experiences spontaneous decarbonylation to give the 31-electron radical [W2Cp2(μ-CO)(CO)2(μ-dppm)](BAr‘4). Oxidation of [W2Cp2(CO)4(μ-dppm)] with 2 equiv of [FeCp2](BAr‘4) gives the tricarbonyl derivative [W2Cp2(μ-CO)(CO)2(μ-dppm)](BAr‘4)2. The same result is obtained when oxidizing the radical [W2Cp2(μ-CO)(CO)2(μ-dppm)](BAr‘4) with [FeCp2](BAr‘4). The triply bonded complex [W2Cp2(μ-CO)(CO)2(μ-dppm)](BAr‘4)2, which displays fluxional behavior in solution, reacts with P(OMe)3 to give [W2Cp2(μ-CO)(CO){P(OMe)3}(μ-dppm)](BAr‘4)2, the structure of which has been solved through a single-crystal X-ray diffraction study. Reaction of [W2Cp2(μ-CO)(CO)2(μ-dppm)](BAr‘4)2 with salts of halide ions X- (X = Cl, Br, I) gives the corresponding halo derivatives [W2Cp2(μ-X)(μ-CO)(CO)2(μ-dppm)](BAr‘4). When X = I, a mixture of two isomers differing in the relative positions of the bridging halide and carbonyl is obtained. The same halide compounds were obtained in the reactions of paramagnetic [W2Cp2(μ-CO)(CO)2(μ-dppm)](BAr‘4) with halogens X2. The tricarbonyl radical was found to react slowly with water to give the known hydroxycarbyne derivative [W2Cp2(μ-COH)(CO)2(μ-dppm)](BAr‘4).

Reaction of the unsaturated tricarbonyl complex [W 2 Cp 2 (µ-CO)(CO) 2 (µ-dppm)](BAr′ 4 ) 2 with HSPh leads to the thiolate-bridged complex [W 2 Cp 2 (µ-SPh)(µ-CO)(CO) 2 (µ-dppm)](BAr′ 4 ), which is obtained as a mixture of two isomers. This reaction proceeds faster in the presence of a base (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU), as expected. The title compound also reacts at room temperature with stoichiometric amounts of phosphines HPRwhich display a trans relative geometry of their phosphide and diphosphine ligands. Deprotonation of these hydride complexes with DBU gives the cis phosphide compounds [W 2 Cp 2 (µ-PR 1 R 2 )(CO) 2 (µ-dppm)](BAr′ 4 ), through an unexpected reduction and dehydrogenation/isomerization pathway. This overall deprotonation process is not reversible, and treatment of the latter compound with HBF 4 ‚OEt 2 gives the hydride isomer cis-[W 2 Cp 2 (µ-H)(µ-PR 1 R 2 )(CO) 2 (µ-dppm)](BAr′ 4 )(BF 4 ), which displays a strong hydrogen bond interaction between the bridging hydride ligand and the external BF 4anion. Treatment of the title compound with N 2 CHSiMe 3 or HCtC(p-tol) leads to dicarbonyls [W 2 -Cp 2 {µ-κ 1 -N 2 CH(SiMe 3 )}(CO) 2 (µ-dppm)](BAr′ 4 ) 2 or [W 2 Cp 2 {µ-η 2 :η 2 -HCC(p-tol)}(CO) 2 (µ-dppm)]-(BAr′ 4 ) 2 (two isomers), displaying four-electron-donor diazoalkane or alkyne bridging ligands.

Oxidation of the compounds [M2Cp2(CO)4(μ-L2)] (M = Mo, W; Cp = η5-C5H5; L2 = Ph2PCH2PPh2 (dppm), Me2PCH2PMe2 (dmpm), (EtO)2POP(OEt)2 (tedip)) with [FeCp2](BAr‘4) (Ar‘ = 3,5-C6H3(CF3)2) gives the corresponding tetracarbonyl radicals [M2Cp2(μ-CO)2(CO)2(μ-L2)](BAr‘4). The stability of these paramagnetic complexes depends on the ligand and the metal. Thus, the dmpm complexes are stable in solution for reasonable periods of time, whereas the dppm complexes experience spontaneous decarbonylation at room temperature to give the radicals [Mo2Cp2(μ-CO)2(μ-dppm)](BAr‘4) and [W2Cp2(μ-CO)(CO)2(μ-dppm)](BAr‘4). The tedip-bridged derivatives are the most unstable radicals, with the ditungsten cation experiencing rapid hydrogen atom capture to give the hydride complex [W2Cp2(μ-H)(CO)4(μ-tedip)](BAr‘4). The complexes [M2Cp2(μ-CO)2(CO)2(μ-L2)](BAr‘4) react with NO to give the binuclear nitrosyl derivatives [M2Cp2(CO)4(NO)(μ-L2)](BAr‘4) (M = Mo, W; L2 = dmpm, tedip) and [Mo2Cp2(μ-CO)(CO)2(NO)(μ-dmpm)](BAr‘4). Some mononuclear products such as [MCp(CO)2(OPMe2CH2PMe2)](BAr‘4) were identified in these reaction mixtures. The diphosphine-bridged dimolybdenum radicals are reactive toward small molecules containing H−E bonds (with E = N, P, O, S) under mild conditions. Thus, reaction of [Mo2Cp2(μ-CO)2(CO)2(μ-dppm)](BAr‘4) with water at room temperature yields the hydroxo complexes [Mo2Cp2(μ-OH)(CO)2(μ-dppm)](BAr‘4) and [Mo2Cp2(μ-H)(μ-OH)(CO)2(μ-dppm)](BAr‘4)(OH), while reactions with HSPh give mixtures of cis-[Mo2Cp2(μ-SPh)(μ-CO)(CO)2(μ-L2)](BAr‘4), cis-[Mo2Cp2(μ-SPh)(CO)2(μ-dppm)](BAr‘4), and cis-[Mo2Cp2(μ-H)(μ-SPh)(CO)2(μ-dppm)](BAr‘4)(SPh), with their relative amounts depending on the diphosphine and experimental conditions. The tricarbonyls cis-[Mo2Cp2(μ-SPh)(μ-CO)(CO)2(μ-L2)](BAr‘4) rearrange to the corresponding trans isomers upon exposure to UV−visible light, and the dppm derivative even experiences a reversible decarbonylation to give trans-[Mo2Cp2(μ-SPh)(CO)2(μ-dppm)](BAr‘4). cis- and trans-dicarbonyls [Mo2Cp2(μ-SPh)(CO)2(μ-dppm)](BAr‘4) are protonated by HBF4·OEt2 with retention of geometry to yield the corresponding hydride derivatives cis- and trans-[Mo2Cp2(μ-H)(μ-SPh)(CO)2(μ-dppm)](BAr‘4)(BF4). Deprotonation of the latter with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is not reversible, as it gives in both cases the cis isomer, which suggest the operation of a reduction/dehydrogenation reaction pathway. The structures of the new complexes are analyzed on the basis of the corresponding IR and NMR (1H, 31P, 13C) data, and the reaction pathways operative in the reactions with H2O and HSPh are discussed on the basis of the available data and some additional experiments.

The reactions of radicals [Mo 2 Cp 2 (µ-CO) 2 (CO) 2 (µ-L 2 )](BAr′ 4 ) [Cp ) η 5 -C 5 H 5 ; L 2 ) Ph 2 PCH 2 -PPh 2 (dppm), Me 2 PCH 2 PMe 2 (dmpm)] with an excess of the 1-alkynes HCCR (R ) p-tol, t Bu, CO 2 Me) give two main type of products, the paramagnetic alkyne-bridged complexes [Mo 2 Cp 2 (µ-η 2 :η 2 -HC 2 R)(CO) 2 (µ-L 2 )](BAr′ 4 ) and the diamagnetic dicarbonyls [Mo 2 Cp 2 {µ-η 2 :η 3 -HCC(R)C(OH)}(CO) 2 (µ-L 2 )](BAr′ 4 ), which result from coupling of the incoming alkyne and a hydroxycarbyne ligand. The reaction of [Mo 2 Cp 2 (µ-CO) 2 (CO) 2 (µ-dmpm)](BAr′ 4 ) with HCC(CO 2 Me) gave additionally the compound [Mo 2 Cp 2 {µ-η 2 :η 2 ,κ-C(CO 2 Me)CPMe 2 CH 2 PMe 2 }-(CO) 3 ](BAr′ 4 ), resulting from coupling of the diphosphine and the alkyne. The relative amounts of the products in the above reactions were found to be strongly dependent on the alkyne used. The compounds [Mo 2 Cp 2 {µ-η 2 :η 3 -HCC(R)C(OH)}(CO) 2 (µ-L 2 )](BAr′ 4 ) (R ) t Bu, CO 2 Me) experience overall deprotonation by reaction with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), to give the corresponding neutral species [Mo 2 Cp 2 {µ-η 2 :η 2 -HCC(R)C(O)}(CO) 2 (µ-L 2 )] through an unexpected reduction/dehydrogenation pathway. This overall deprotonation is reversible, and reaction of the neutral complexes with HBF 4 ‚OEt 2 occurs specifically at the oxygen atom of the acyl group to give the starting cations as BF 4salts. Unexpectedly, the reduction of the alkyne-bridged radicals [Mo 2 Cp 2 (µ-η 2 :η 2 -HC 2 R)(CO) 2 (µ-L 2 )](BAr′ 4 ) with Na amalgam gave unstable paramagnetic derivatives that could not be characterized. The complexes [Mo 2 Cp 2 {µ-η 2 :η 3 -HCC( t Bu)C(OH)}(CO) 2 (µ-dmpm)](BAr′ 4 ), [Mo 2 Cp 2 {µ-η 2 :η 2 ,κ-C(CO 2 -Me)CPMe 2 CH 2 PMe 2 }(CO) 3 ](BAr′ 4 ), and [Mo 2 Cp 2 {µ-η 2 :η 2 -HCC(CO 2 Me)C(O)}(CO) 2 (µ-dppm)] were characterized through single-crystal X-ray diffraction studies. The solution structures of all new compounds are analyzed in the light of IR and NMR spectra, and plausible reaction pathways are proposed in order to explain the formation of the products isolated.

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