Synthesis, reactivity and structural characterization of dinuclear tantalum complexes
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1982
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Abstract
The compounds, Ta(,2)Cl(,6)(THT)(,3), 1, and Ta(,2)Cl(,6)(SMe(,2))(,3), 2 were structurally characterized for use as sources of dinuclear Ta(III). The reactions of 2 and TaCl(,5) with phosphines and phosphinoacetylenes were studied. The addition of PMe(,2)Ph to the TaCl(,5) under reducing conditions followed by the addition of oxygen yielded {PMe(,3)Ph}{Cl(,5)TaOTaCl(,5)}. The structure was determined by X-ray crystallography. The Ta-O-Ta unit is linear by symmetry. Terminal ligand substitution of 2 by P(NMe(,2))(,3) was observed in the structure of Ta(,2)Cl(,6)((mu)-SMe(,2)){P(NMe(,2))(,3)}(,2). Reduction routes from TaCl(,5) could not produce similar complexes. A minor product of this reaction was structurally determined to be {(Me(,2)N)(,3)PPP(NMe(,2))(,3)}{TaCl(,5)(NMe(,2))} where the central atom in the cation, {(Me(,2)N)(,3)PPP(NMe(,2))(,3)}, resulted from the decomposition of P(NMe(,2))(,3). The Ta('V) anion had no ESR signal. The reactions of bis(diphenylphosphino)acetylene (DPPA) with 2 in stoichiometries of 1:2 and 1:1 gave Cl(,4)Ta-CH(PPh(,2))C(PPh(,2))=C(PPh(,2))CH(PPh(,2))-TaCl(,4) and(' )(, ) (Me(,2)S)Cl(,3)Ta=C(PPh(,2))C(PPh(,2))=C(PPh(,2))C(PPh(,2))=TaCl(,3)(SMe(,2)),(, )(' ) Respectively. The products arise from the reductive coupling of two DPPA molecules forming Ta-C and Ta=C bonds. These structures support the existence of Ta-carbene reactive intermediates in the mechanism of acetylene polymerization by Ta('III). The structure of previously reported TaCl(,4)(DMPE)(,2) was determined for comparison to the minor product obtained from 2 combining with bis(dimethylphosphino)ethane, DMPE. The structure of the product was {PMe(,4)}{TaCl(,4)(DMPE)(,2)}(,3)Cl(,4)(.)4SMe(,2). The {PMe(,4)}('+1) is presumed to arise from decomposition of DMPE, while the Cl('-) is from the decomposition of 2. The major product obtained from the combination of DMPE with 2 was found to be Ta(,2)Cl(,6)(DMPE)(,2), 3. The crystal structure of 3 is the first known dinuclear Ta('III) complex containing chelating phosphine ligands.
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Chemsitry