75522-28-0Relevant academic research and scientific papers
Synthesis and Characterisation of Half-sandwich Tantalum Compounds in Oxidation States (I)-(V): Tertiary Phosphine, Acetylene, Butadiene, Carbonyl, and Oxo Derivatives. X-ray Crystal Structures of and
Gibson, Vernon C.,Kee, Terence P.,Clegg, William
, p. 3199 - 3210 (1990)
The half-sandwich tertiary phosphine tantalum compounds (3), (6), (7) and (5) (dmpe = Me2PCH2CH2PMe2) have been prepared by treatment of (R = H or Me) with magnesium in tetrahydrofuran (thf) in the presence of the phosphine.Compounds (3), (6), and (7) decompose in chlorocarbons to give the tetrachlorides .Compound (7) also decomposes in hydrocarbon solvents to give a mixture of products from which (4) may be crystallized selectively.The X-ray crystal structure of (4) has been determined in the orthorhombic space group P212121 and reveals a four-legged piano-stool geometry.Compound (7) reacts with RC2Ph (R = H or Ph) to give the known acetylene complexes 2-RC2Ph)> and with butadiene to give 2-C4H6)> (11).By contrast, (6) reacts with butadiene to give the η2-butadiene complex 2-C4H6)> (12) which is unstable in the absence of an excess of butadiene but does not eliminate PMe3 upon prolonged heating at elevated temperatures to form the known compound 2-C4H6)>.Carbon monoxide reacts with compounds (6) and (7) to give (13) and (14), respectively.The X-ray structure of (14) reveals a pseudo octahedral geometry with mutually trans ring and phosphine ligands and a cis-dichloro/cis-dicarbonyl ligand arrangement.There is also a considerable ring-slip distortion present in the C5Me5 ring.Reduction of (14) with sodium amalgam in thf in the presence of PMe3 affords cis- (15) in 61 percent yield.Although stable indefinitely at room temperature, (15) converts upon warming at 100 deg C to the trans isomer.The reaction has been monitored by 1H n.m.r. spectroscopy giving a pseudo first-order rate constant of 9.9(1)*10-5 s-1.Reduction of (14) with sodium amalgam in the presence of CO (1.5 atm) gives (17) in 65 percent yield.Complex (17) can also be obtained in 47 percent yield in a one-pot reaction by treatment of with 4 equivalents of sodium amalgam in the presence of 1 equivalent of PMe3.The oxide (18) has been obtained by treatment of (7) with CO2.A dimeric structure with bridging oxo ligands is suggested on the basis of i.r. spectroscopy and mass spectrometry.
Carbonyl displacement reactions of (C5Me5)TaCl2(CO)2(THF). Structures of (C5Me5)TaCl2(CO)2(THF), (C5Me5)TaCl2(CO)(dmpe), and (C5Me5)TaCl2(methyl acrylate)
Kwon, Daekeun,Curtis, M. David
, p. 1 - 5 (2008/10/08)
The synthesis and X-ray crystal structure of (C5Me5)TaCl2(CO)2(THF) (1) have been studied. Complex 1 is prepared from the reduction of (C5Me5)TaCl4 by Al/HgCl2 under CO atmosphere and crystallizes in the orthorhombic space group Pbn21 with a = 9.152 (4) ?, b = 14.480 (7) ?, c = 13.738 (6) ?, V = 1821 (1) ?3, and Z = 4. Least-squares refinement converged at R = 0.039 and Rw = 0.036 based on 1777 reflections with I > 3σ(I). Compound 1 reacts with dmpe to yield the complex (C5Me5)TaCl2(CO)(dmpe) (3) in 80% yield. Compound 3 was characterized by a single-crystal X-ray diffraction analysis: space group P21/n; Z = 4; a = 9.463 (6) ?, b = 15.453 (7) ?, c = 14.713 (10) ?; V = 2121 (2) ?3; R = 0.055 and Rw = 0.053 based on 2425 reflections with I > 3σ(I). When allowed to react with methyl acrylate, compound 1 loses two COs to form (C5Me5)TaCl2(methyl acrylate) (6) in 85% yield. Compound 6 was structurally chracterized: space group Pbca; Z = 8; a = 14.704 (4) ?, b = 15.694 (2) ?, c = 14.289 (4) ?; V = 3298 (1) ?3; R = 0.035 and Rw = 0.032 based on 1412 reflections with I > 3σ(I).
Preparation and reaction chemistry of trimethylsilyl derivatives of tantalum. X-ray structures of d0 (η5-C5Me5)Ta(SiMe3)Cl 3 and d1 (η5-C5Me5)Ta(SiMe3)(PMe 3)Cl2
Arnold, John,Shina, David N.,Tilley, T. Don,Arif, Atta M.
, p. 2037 - 2044 (2008/10/08)
The preparation of Cp*Ta(SiMe3)Cl3 (1, Cp* = η5-C5Me5) from Cp*TaCl4 and Al(SiMe3)3·OEt2 is reported. Compound 1 is converted to the derivatives Cp*Ta(SiMe3)(OR)Cl2 (2, R = SiMe3; 3, R = CMe3) upon treatment with KOSiMe3 or LiOCMe3, respectively. Reaction of 1 with MeMgBr (3 equiv) produces Cp*Ta(SiMe3)Me3 (4). Donor ligands induce reductive elimination of Me3SiCl from 1. In the case of alkyne addition, the resulting tantalum (III) products are Cp*Ta(RC≡CR′)Cl2 (R = R′ = Me3Si, Ph, Me; R = Ph, R′ = H). When the incoming ligand is PMe3, it appears that an initially formed tantalum(III) product reacts with starting material to afford the tantalum(IV) silyl Cp*Ta(SiMe3)(PMe3)Cl2 (8) and Cp*TaCl4(PMe3) via a series of redox transformations. Complexes 1 and 8 have been structurally characterized. Dark green crystals of 1 belong to space group P21/c with unit cell dimensions a = 15.133 (2) A?, b = 8.522 (2) A?, c = 14.157 (1) A?, β = 91.923 (1)°, V = 1824.7 (5) A?3, and Z = 4. The final R value refined against 1959 data was 3.84%. The paramagnetic d1 silyl 8 also crystallizes in the monoclinic space group P21/c with a = 13.3309 (14) A?, b = 10.3770 (10) A?, c = 16.1017 (25) A?, β = 94.061 (10)°, V = 2221.8 (8) A?3, and Z = 4. The final R value for 2494 data was 1.54%. Both structures exhibit a four-legged piano-stool geometry with noncrystallographic Cs symmetry. The Ta(IV)-Si bond in 8, 2.642 (1) A?, is slightly shorter than the Ta(V)-Si bond in 1, 2.669 (4) A?. These distances are discussed with respect to electron density at the transition-metal center and Ta-Si π-bonding.
Synthesis of alkyne complexes of the type Ta(η5-C5Me5) (alkyne)Cl2 and crystal structure of Ta(η5-C5Me5)(PhC≡CPh)Cl2
Smith, Gary,Schrock, Richard R.,Churchill, Melvyn Rowen,Youngs, Wiley J.
, p. 387 - 393 (2008/10/08)
Ta(η5-C5Me5)(olefin)Cl2 complexes (olefin = styrene or cyclooctene) react with alkynes (PhC≡CPh, PhC≡CH, 2-butyne, 3-hexyne, HC≡CH) to give analogous Ta(η5-C5Me5)(alkyne)Cl2 complexes which do not react with additional alkyne, CO, HCl, or ethylene with one exception; Ta(η5-C5Me5)(HC≡CH)Cl2 reacts with ethylene at 80°C to give (η5-C5Me5)Cl2TaCH=CHCH 2CH2 irreversibly. The diphenylacetylene ligand in Ta(η5-C5Me5)(PhC≡CPh)Cl2 is bonded parallel to the η5-C5Me5 ring with a long acetylenic linkage (1.337 (8) A?) and short Ta-C(alkyne) bonds (2.067 (6) A and 2.075 (6) A?), consistent with it being a 4-electron donor. The lack of reactivity of these alkyne complexes is postulated to be due to this strong metal-alkyne bond.
