Trichlorooxobis triphenylphosphine rhenium V

Rhenium displays an unusual array of oxidation states and coordination numbers that make it the subject of much current research. The following preparation, adapted from one developed by Chatt and coworkers, provides a convenient synthesis of trichlorooxobis(triphenylphosphine)rhenium(V)1 based on either rhenium(VII) oxide or perrhenate salts. The trichlorooxo compound is a versatile intermediate for the synthesis of other rhenium complexes such as wer-trichlorotris(dimethylphenylphosphine)rhenium-(III),2 as described below. The rhenium(III) complex, in turn, provides a starting point for synthesis of other compounds such as frans-tetrachloro-bis(dimethylphenylphosphine)rhenium(IV)3 and tris(dimethylphenylphos-phinepentahydrido)rhenium(V).4 An alternative synthesis of the trichloro-complex is described in the accompanying preparation by Douglas and Shaw.4 

A 1-L two-necked flask, equipped with magnetic stirrer, addition funnel, and condenser surmounted by a nitrogen-flushed tee tube, is charged with 7.30 g (15 mmol) of rhenium(VII) oxide (or 8.68 g of potassium perrhenate), 50 mL of concentrated hydrochloric acid, and 250 mL of absolute ethanol. The solution is stirred and heated to boiling, and a solution of 45 g (170 mmol) of triphenylphosphine in 250 mL of hot ethanol is added. The mixture becomes green immediately, and a precipitate forms even before the addition is complete. The mixture is boiled for 30 min. It is allowed to cool to 55° and is filtered. The lime-green solid product is extracted with 100 mL 

Trichlorooxobis(triphenylphosphine)rhenium(V) is a yellow, diamagnetic, air-stable solid which crystallizes from benzene-heptane as monoclinic prisms, mp 211-214° with decomposition. It is slightly soluble in benzene to give nonconducting solutions. The infrared spectrum shows a strong band at 969 cm 1 assignable to Re=0 stretching. 

A mixture of 9.0 g (10.8 mmol) of trichlorooxobis(triphenylphosphine)-rhenium(V), 7.2 g (52 mmol) of dimethylphenylphosphine,5 and 350 mL of benzene is stirred and boiled for 2 hr under nitrogen in a 1-L flask equipped with magnetic stirrer and condenser. The solution is evaporated to dryness in vacuo and the residue is dried under high vacuum at room temperature. The residue is dissolved in 300 mL of ethanol under nitrogen. On cooling the solution, one obtains 5.6-6.5 g of orange platelets of a benzene solvate of trichlorotris(dimethylphenylphosphine)rhenium(III), mp 153-160°. Partial evaporation of the filtrate gives 3.7 g of triphenylphosphine, mp 76-78°. 

The benzene solvate, which by elemental and nmr analyses contains about one benzene per rhenium, may be used for most preparative purposes. Recrystallization from ethanol gives pure orange crystals of mer-trichlorotris-(dimethylphenylphosphine)rhenium(III). Anal. Calcd. for C24H33Cl3P3Re C, 40.77 H, 4.70 Cl, 15.04. Found C, 40.96 H, 4.84 Cl, 15.14. 

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