173601-99-5Relevant academic research and scientific papers
Formation and reactivity of 1,3-cyclohexadiene complexes of niobium and tantalum containing aryloxide ligation: Selectivity differences in the hydrogenation of 1,3-cyclohexadiene
Visciglio, Valerie M.,Nguyen, Mindy T.,Clark, Janet R.,Fanwick, Phillip E.,Rothwell, Ian P.
, p. 551 - 554 (1996)
The sodium amalgam reduction (2 Na per M) of hydrocarbon solutions of [M(OAr)3Cl2] (M = Nb, Ta) or [Nb(OAr)2Cl3]2 (OAr = 2,6-di-isopropylphenoxide) in the presence of either 1,3-or 1,4-cyclohexadiene yielded the complexes [M(OAr)3(β4-C6H8)] (1a: M = Nb; 1b: M = Ta) and [Nb(OAr)2Cl(η4-C6H8)], 2, respectively. The solid state structures of 1a, isomorphous 1b and 2 showed the 1,3-cyclohexadiene strongly bound to the metal. The ligand is not symmetrically bound to the metal in 1 but in 2 there is a crystallographic mirror plane. The solution NMR spectra of 1a and 1b show only one set of aryloxide ligand signals and only four proton and three carbon resonances for the C6H8 group. The hydrolysis of 1 or 2 yielded 2,6-di-isopropylphenol and one equivalent of cyclohexane (1H NMR). The niobium compounds 1a and 2 will catalyse the disproportionation and hydrogenation of 1,3-cyclohexadiene with differing selectivity.
Coordination and hydrogenation of 1,3-cyclohexadiene by niobium and tantalum aryl oxide compounds: Relevance to catalytic arene hydrogenation
Visciglio, Valerie M.,Clark, Janet R.,Nguyen, Mindy T.,Mulford, Douglas R.,Fanwick, Phillip E.,Rothwell, Ian P.
, p. 3490 - 3499 (2007/10/03)
The sodium amalgam (2 Na per M) reduction of hydrocarbon solutions of the chloro, aryl oxide compounds [M(OC6H3Pr(i)2-2,6)2Cl3]2 (1) and [M(OC6H3Pr(i)2-2,6)3C12] (2) (a, M = Nb; b, M = Ta) in the presence of 1,3-cyclohexadiene leads to formation of the η4-cyclohexadiene derivatives [M(OC6H3Pr(i)2-2,6)2Cl(η4-C6H8)] (3) and [M(OC6H3Pr(i)2-2,6)3(η4-C6H8)] (4). Spectroscopic studies of compounds 3 and 4 show in all cases a strongly bound cyclohexadiene ligand which does not readily undergo displacement (NMR) with added reagents such as PMe2Ph and cyclohexene. Single crystal X-ray diffraction analyses of 3a and the isomorphous pair 4a and 4b show in all three cases a geometry about the metal center best described as three-legged piano stool. Compound 4a will catalyze the disproportionation of 1,3-cyclohexadiene into cyclohexene and benzene as well as the hydrogenation of 1,3-cyclohexadiene and cyclohexene into cyclohexane. Mechanistic studies clearly show that cyclohexene is not released during the conversion of 1,3-cyclohexadiene to cyclohexane catalyzed by 4a. In contrast, solutions of 3a will convert 1,3-cyclohexadiene slowly to cyclohexene prior to conversion to cyclohexane. The addition of 1,3-cyclohexadiene to the trihydride compounds [Ta(OC6H3Cy2-2,6)2(H)3(PMe2Ph)2] and [Ta(OC6HPh2-3,5-Cy2-2,6)2(H)3(PMe2Ph)2] leads to the interesting products [Ta(OC6H3Cy2-2,6)2(η1-C6H10-η4-C6H7)] (5) and [Ta(OC6HPh2-3,5-Cy2-2,6)2(η1 C6H10-η4-C6H7)] (6) which, based upon structural studies of 5 contain a partially hydrogenated non-Diels-Alder dimer of 1,3-cyclohexadiene. The addition of 1,3-cyclohexadiene to the dihydride compounds [Ta(OC6H3Pr(i)22,6)2(Cl)(H)2(PMe2Ph)2] and [Ta(OC6H3Bu(t)2-2,6)2(Cl)(H)2(PMe2Ph)] leads to the dehydrogenation product [Ta(OC6H3Pr(i)-η2-CMe=CH2)(OC6H3Pr(i)2-2,6)(Cl)(PMe2Ph)2] (7) and the cyclohexyl compound [Ta(O6H3Bu(t)-CMe2CH2)(OC6H3Bu(t)2-2,6)(Cl)(C6H11)] (8), respectively. The mechanistic implications of these stoichiometric and catalytic reactions are discussed. Crystal data for 3a at 20°C: NbClO2C30H42. M = 563.03, space group P(nma) (no. 62), a = 12.237(1), b = 21.633(1), c = 10.883(2) A?, V = 2881.0(9) A?3, D(c) = 1.298 g cm-3, Z = 4; for 4a at 20 °C: NbO3C42H59. M = 704.84, space group P21/c (no. 14), a = 11.562(1), b = 16.117(2), e = 21.914(3) A?, β = 103.69(1)°, V = 3967(2) A?3, D(c)= 1.180 g cm-3, Z = 4; for 4b at -57 °C: TaO3C42H59. M = 792.88, space group R21/c (no. 14), a = 11.452(2), b = 16.175(3), c = 21.765(3) A?, β = 103.52(1)°, V = 3919(2) A?3, D(c) = 1.343 g cm-3, Z = 4; for 5 at 20 °C: TaO2C48H67. M = 857.02, space group P21 (no. 4), a = 10.559(9), b = 15.828(10), c = 13.266(12) A?, V = 2095(6) A?3, D(c) = 1.358 g cm-3, Z = 2.
