Reduction of (OC)gCo3CCO+PF6~with Triethylsilane. (a) In the Absence of Aluminum Chloride. The acylium hexafiuorophosphate prepared from 2.0 mmol of (OC)9Co3CC02Et was slurried in 20 ml of dichloromethane under nitrogen, and 0.80 g (6.6 mmol) of triethylsilane (PCR Inc.) was added. The mixture was stirred at room temperature for 1 hr; a homogeneous solution resulted.The reaction mixture was evaporated under reduced pressure and the residue was extracted with hexane. The red extracts were filtered through a layer of silicic acid and evaporated. The red solid residue was sublimed in vacuo at 50°to give 0.65 g of red solid, melting in the range 95-115°with decomposition. Its ir spectrum suggested that a mixture of CH3CCo3(CO)9 and HCCo3(CO)9 was present (bands at 2960 w, 2920 m, 2880 m, 2820 m, 1160 m, 1000 s, and 855 m cm-1). The entire sample was dissolved in deuteriochloroform and the nmr spectrum which was taken showed that these two products were present in 1 to 1.44 ratio (30 and 43% yields, based on the 0.65 g isolated), respectively, by integration of the resonances at 6 3.76 and 12.10 ppm.(b) In the Presence of Aluminum Chloride. The acylium hexafluorophosphate was prepared from 2.0 mmol of (OC)9Co3CC02-Et and slurried in 15 ml of dichloromethane under nitrogen. To this mixture was added 0.75 g (6.0 mmol) of aluminum chloride. A brief evolution of gas commenced but subsided quickly. Addition of 0.70 g (6.0 mmol) of triethylsilane followed. A brief evolution of gas again was observed and the solution turned from brown to red-brown. Tic (benzene) showed the presence of a single brown material in the solution. After it had been stirred for 10 min at room temperature, the mixture was treated with 150 ml of 15% aqueous HC1 and extracted with 100 ml of dichloromethane.The organic layer was dried and evaporated. The brown solid which remained was taken up in benzene. This solution was passed through a layer of silicic acid and evaporated. The residue was recrystallized from hexane to give 0.68 g (74%) of black needles which decomposed without melting around 115°and whose ir spectrum was identical with that of an authentic sample11 of the aldehyde, (OC)9Co3CCHO.An experiment in which only 2 mmol of aluminum chloride was added to the acylium hexafiuorophosphate prepared from 2 mmol of the cluster-ester and in which this mixture was treated with 6 mmol of triethylsilane gave only CH3CCo3(CO)9 (25%) and HCCo3(CO)9 (45 %) and none of the aldehyde.Reaction of (OC)gCo3CC02CH2C==CCH202CCCo3(CO)g with Dicobalt Octacarbonyl. A 100-ml three-necked flask equipped with a magnetic stirring unit, a nitrogen inlet tube, and a no-air stopper was charged with a solution of the cluster-substituted acetylene (0.42 g, 0.47 mmol) in 20 ml of anhydrous diethyl ether. Subsequently, a solution of 2.3 g (6.7 mmol) of dicobalt octacarbonyl in 50 ml of diethyl ether was added. The mixture was stirred under nitrogen at room temperature for 90 min, during which time a very slow gas evolution and the separation of a solid were observed. The so...