Tantalum Metal-Metal Bonded Organometallics.

The dimeric tantalum(III) phosphine complex, {TaCl(,2)(PMe(,3))(,2)}(,2)((mu)-Cl)(,2), 1, has been prepared from the reaction of tantalum pentachloride, trimethylphosphine, and sodium amalgam in toluene. The crystal and molecular structure of the latter has been determined at -170(DEGREES)C by X-ray diffraction. 1 is a distorted edge-sharing bioctahedral complex with axial phosphines on one tantalum and equatorial phosphines on the second. The metal-metal bond length in 1 is 2.721(1) (ANGSTROM) and the formal metal-metal bond order in this d('2)-d('2) dimer is two. 1 reacts with molecular hydrogen to form the tantalum(IV) dimer, {TaCl(,2)(PMe(,3))(,2)}(,2)((mu)-Cl)(,2)((mu)-H)(,2), 3. The crystal and molecular structure of the latter has been determined at -170(DEGREES)C by X-ray diffraction. 3 may be described as a quadruply bridged tantalum(IV) dimer with a metal-metal single bond of 2.621(1) (ANGSTROM). The tantalum(III) dimer, {TaCl(,2)(PMe(,3))(,2)}(,2)((mu)-H)(,2), 5, can be isolated from the reaction of 3 with two equivalents of sodium amalgam in ethylene glycol dimethyl ether (glyme). The crystal and molecular structure of 3 was determined from X-ray diffraction data collected at -160(DEGREES)C. The molecular geometry consists of two pyramidal TaCl(,2)(PMe(,3))(,2) end groups, in the eclipsed conformation, bridged by two hydride lig and s which lie on a diagonal plane. The Ta=Ta separation is 2.545(1) (ANGSTROM). 5 reacts with hydrogen, hydrogen chloride, and chlorine under mild conditions to form the quadruply bridged tantalum(IV) dimers {TaCl(,2)(PMe(,3))(,2)}(,2)((mu)-H)(,4), 7, {TaCl(,2)(PMe(,3))(,2)}(,2)((mu)-Cl)((mu)-H)(,3), 6, and 3, respectively. {TaCl(,2)(PMe(,3))(,2)}(,2)((mu)-H)(,2)((mu)-CO), 10, forms when 5 reacts with carbon monoxide.PhDInorganic chemistryUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158935/1/8215106.pd