Synthesis and Characterization of a Series of Mononuclear Tantalum(V) Hydride Compounds Containing Aryloxide Ligation
作者:Bernardeta C. Parkin、Janet R. Clark、Valerie M. Visciglio、Phillip E. Fanwick、Ian P. Rothwell
DOI:10.1021/om00006a051
日期:1995.6
A series of seven-coordinate, mononuclear tantalum-hydride compounds [Ta(OC6H3Pr2i-2,6)(2)-(Cl)(3-n)(H)(n)](1, n = 1; 2, n = 2; 3, n = 3; OC6H3Pr2i-2,6 = 2,6-diisopropylphenoxide; L = tertiary phosphines) can be obtained either by hydrogenolysis of the corresponding tantalum alkyl substrate, producing 2 and 3, or by reacting the trichloride [Ta(OC6H3Pr2i-2,6)(2)Cl-3] with one (for 1) or two (for 2) equiv of Bu(3)(n)SnH in the presence of ligand. The hydrogenolysis of the substrate [Ta(OC6H3Pr2i-2,6)(2)(CH2C6H4-4Me)(3)] in the presence of PMe(2)Ph or PMePh(2) produces the complexes [Ta(OC6H3Pr2i-2,6)(2)(H)(3)(L)(2)] (3a, L = PMe(2)Ph; 3b, L = PMePh(2)), while the compounds [Ta(OC(6)H(3)Ph(2)-2,6)(2)(R)(3)] (R = CH2C6H4-4Me, CH(2)SiMe(3)) produce [Ta(OC(6)H(3)Cy(2)-2,6)(2)(H)(3)(L)(2)] (3c, L = PMe(2)Ph; 3d, L = PMePh(2)) with the 2,6-dicyclohexylphenoxide ligand being generated by intramolecular hydrogenation of the ortho phenyl rings in the 2,6-diphenylphenoxide substrate. The hydrogenolysis of the bisalkyl [Ta(OC6H3Pri(2)-2,6)(3)(CH2C6H4-4Me)(2)] in the presence of PMe(2)-Ph produces the six-coordinate [Ta(OC6H3Pr2i-2,6)(3)(PMe(2)Ph)(H)(2)], 4b, which will exchange the phosphine ligand to produce a series of substituted derivatives. A related series of six-coordinate dihydride compounds [Ta(OC(6)H(3)Bu(2)(t)-2,6)(2)(L)(Cl)(H)(2)], 5, are produced by addition of Bu(n)SnH (2 Sn per Ta) to [Ta(OC(6)H(3)Bu(t)(2)-2,6)(2)Cl-3] in the presence of added L. Single-crystal X-ray diffraction analyses of seven-coordinate 1, 2b, and 3c (all cases L = PMe(2)Ph) show them to adopt pentagonal bipyramidal geometries with traits axial aryloxide ligands. In monohydride 1 the unique hydride ligand is cis to both phosphine ligand, while in dihydride 2b the hydride ligands are mutually cis but trans to the chloride group within the pentagonal plane. A crystallographic 2-fold axis in trihydride 3c passes through the unique Ta-H bond and bisects the remaining cis hydride ligands within the pentagonal plane. The solution H-1 NMR spectra of 1, 2, and 3 are consistent with the solid state structure being maintained in solution. Furthermore, analysis and simulation of the downfield hydride resonances in 2 and 3 show these seven-coordinate molecules to be stereochemically rigid on the NMR time scale. The coupling constants obtained from simulations conclusively rule out the formulation of 2 or 3 as containing eta(2)-H-2 ligands. The solid state structures of six-coordinate [Ta(OC6H3Pri(2)-2,6)(3)(PMe(2)Ph)(H)(2)], 4b, and [Ta(OC(6)H(3)Bu(2)(t)-2,6)(2)- (PMePh(2))(Cl)(H)(2)], 5c, show a geometry severely distorted from octahedral.In both compounds the mutually trans hydride ligands are bent toward the phosphine ligand with H-Ta-P angles of 66(2)degrees and 69(1)degrees for 4a and 56(2)degrees and 62(2)degrees for 5b. A steric origin to this distortion is ruled out by the structure of 5b in which the hydride ligands are bent toward the bulky phosphine ligand and away from the Ta-Cl bond. Strong support for the distorted structures of 4 and 5 comes from solution and solid state infrared spectra where two sharp <(nu)over bar>(Ta-H) vibrations are observed. Analysis ofthe intensity ratio for the symmetric and asymmetric bands yields predicted H-Ta-H angles very close to these observed in the solid state structure. The summary of the crystal data is as follows for [Ta(OC6H3Pr2i-2,6)(2)(PMe(2)Ph)(2)(Cl)(2)(H)], 1, at 20 degrees C: a = 26.025(4) Angstrom, b = 10.7954(5) Angstrom, c = 18.509(3) Angstrom, beta = 128.31(1)degrees, Z = 4, d(calcd) = 1.438 g cm(-3) in space group C2/c. For [Ta(OC6H3Pr2i-2,6)(2)(PMe(2)Ph)(2)(Cl)(H)(2)], 2b, at 20 degrees C: a = 9.735(1) Angstrom, b = 24.310(3) Angstrom, c = 17.735(2) Angstrom, beta = 90.76(1)degrees, Z = 4, d(calcd) = 1.344 g cm(-3) in space group P2(1)/n. For [Ta(OC(6)H(3)Cy(2)-2,6)(2)(PMe(2)Ph)(2)(H)(3)], 3c, at 20 degrees C: a = 24.065(3) Angstrom, b = 13.530(2) Angstrom, c = 20.263(3) Angstrom , beta = 131.633(9)degrees, Z = 4, d(calcd) = 1.313 g cm(-3) in space group C2/c. For [Ta(OC6H3Pr2i-2,6)(3)(PMe(2)Ph)(H)(2)], 4b, at 20 degrees C: a = 10.637(1) Angstrom, b = 12.820(2) Angstrom, c = 31.799(4) Angstrom, beta = 98.76(1)degrees, Z = 4, d(calcd) = 1.322 g cm(-3) in space group P2(1)/n. For [Ta(OC(6)H(3)But(2)-2,6)(2)(PMePh(2))(Cl)(H)(2)], 5c, at -100 degrees C, a = 10.851(5) Angstrom, b = 18.110(7) Angstrom, c = 20.09(1) Angstrom, beta = 96.67(5)degrees, Z = 4, d(calcd) = 1.404 g cm(-3) in space group P2(1)/n.