Rhenium trichlorotris

The reduction of mer-trichlorotris(dimethylphenylphosphine)rhenium-(III)1 3 with sodium tetrahydroborate(l —), as described below, provides a clean synthesis of tris(dimethylphenylphosphine)pentahydridorhenium(V),... 

A suspension of 3.83 g (5.4 mmol) of mer-trichlorotris(dimethylphenyl-phosphine)rhenium(HI) (or its benzene solvate)1 and 2.48 g (65 mmol) of sodium tetrahydroborate(l —) in 100 mL of absolute ethanol is heated under nitrogen on a steam bath until the orange complex dissolves to give a colorless suspension. The solvent is evaporated under reduced pressure, and the residue is extracted with three 75-mL portions of benzene. The benzene extract is evaporated, and the residue is crystallized from 60 mL of absolute ethanol to give prisms of tris(dimethylphenylphosphine)pentahydrido-rhenium(V) the yield is 2.2 g (67%). Anal. Calcd. for C24H38P3Re C, 47.59 H, 6.32 P, 15.34. Found (checkers values) C, 47.60 H, 6.24 P, 15.51. 

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 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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