| Abstract
| - A double-oxidation deprotonation sequence transforms the title hydride complexes into the corresponding unsaturated cations [M2Cp2(μ-PPh2)(CO)4]+, which can also be obtained through a two-step oxidation of the title carbonylates. These reactions involve respectively the 33-electron binuclear radicals [M2Cp2(μ-H)(μ-PPh2)(CO)4]+ and [M2Cp2(μ-PPh2)(CO)4] as intermediates, as shown in the scheme.
- Reaction of the hydride complexes [M2Cp2(μ-H)(μ-PPh2)(CO)4] (M = Mo, W; Cp = η5-C5H5)with [FeCp2]BF4 proceeds in a 1:2 ratio to give the unsaturated tetracarbonyl salts [M2Cp2(μ-PPh2)(CO)4]BF4, which spontaneously (M = Mo) or in the presence of CO (M = W)transform into the corresponding electron-precise pentacarbonyls [M2Cp2(μ-PPh2)(μ-CO)(CO)4]BF4. In contrast, reaction of the above hydride complexes with [FeCp2](BAr‘4) (Ar‘ =3,5-C6H3(CF3)2) proceeds in a 1:1 ratio to give the paramagnetic salts [M2Cp2(μ-H)(μ-PPh2)(CO)4](BAr‘4). No further reaction takes place with [FeCp2](BAr‘4) unless a proton acceptorsuch as water or tetrahydrofuran is present, in which case the corresponding salts [M2Cp2(μ-PPh2)(CO)4](BAr‘4) or [M2Cp2(μ-PPh2)(μ-CO)(CO)4](BAr‘4) are rapidly formed. Reactionsof the anions [M2Cp2(μ-PPh2)(CO)4]- (as (H-DBU)+ salts, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene) with [FeCp2]BF4 proceed stepwise to give first the 33-electron radicals [M2Cp2(μ-PPh2)(CO)4], which can be isolated as very air-sensitive green solids, and then theunsaturated salts [M2Cp2(μ-PPh2)(CO)4]BF4, which are identical to those formed from theneutral hydrides. The structure and dynamic behavior of the new compounds are analyzedon the basis of solution IR, 1H, 31P, and 13C NMR or ESR spectroscopic data. In addition,the redox and other chemical transformations connecting all the new compounds arediscussed on the basis of the synthetic and structural data, as well as cyclic voltammetrymeasurements carried out in dichloromethane on the neutral hydrides [M2Cp2(μ-H)(μ-PPh2)(CO)4] and the anions [M2Cp2(μ-PPh2)(CO)4]- (as [N(PPh3)2]+ salts).
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