Cyclopentadienyl methoxycarbonyl nitrosyl triphenylphosphine rhenium

The product, decomposition point (gradual darkening) 203-205 C, is air-stable and thermally stable for an indefinite period under ambient conditions. 

Optically active Re(f/ -C5H5)(N0)(PPh3)(C02CH3) can be prepared by reaction of NaOCHj with optically active [Re(f/ -C5H5)(NO)(PPh3)(CO)] [BF4] (below), but for best optical purity the reaction should be conducted at — 24°C or lower. 

This procedure has been scaled up by a factor of 27 without any diminution in yield. 

I Crystallization may commence during rotary evaporation, but this does not affect the de. The de is assayed by integration of the cyclopentadienyl H NMR resonances of the two diastereomers.  

Recrystallization is recommended when a product de of 99% is sought. The amide (0.804 g, 1.084 mmol) is dissolved in CH2CI2 ( 10 mL), and toluene is added ( 11 mL). Then the CH2CI2 is removed as above.j The mixture is kept for 2 days at room temperature, after which time the amide is isolated at bright yellow needles analogously to the first crop obtained above (0.707 g, 0.953 mmol, 88%), 99.6% de. 

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