Unmodified Homogeneous Rhodium-Catalyzed Hydroformylation of Styrene. The Detailed Kinetics of the Regioselective Synthesis

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• 作者：Jinhai Feng and Marc Garland
• 刊名：Organometallics
• 出版年：1999
• 出版时间：February 1, 1999
• 年：1999
• 卷：18
• 期：3
• 页码：417 - 427
• 全文大小：271K
• 年卷期：v.18,no.3(February 1, 1999)
• ISSN：1520-6041

文摘

The homogeneous regioselective catalytic hydroformylation of styrene to (±)-2-phenylpropanal and 3-phenylpropanal was studied starting with Rh₄(CO)₁₂ as catalyst precursor inn-hexane as solvent. The reaction conditions were T = 298-313 K, P_H2 = 0.27-1.01 MPa(0.002-0.0074 mol fraction), P_CO = 3.0-6.0 MPa (0.042-0.075 mol fraction), [Rh₄(CO)₁₂]_o =3.5 × 10^-5 to 1.7 × 10^-4 mol fraction, and [C₈H₈]_o = 0.118-0.349 mol fraction. Quantitativehigh-pressure in-situ infrared spectroscopic measurements were made under isobaric andisothermal conditions during the 5-h kinetic experiments. In all experiments, the disappearance of the precursor Rh₄(CO)₁₂ resulted in the formation of two observable acylintermediates, namely the major isomer (±)-PhCH(CH₃)CORh(CO)₄ and the minor isomerPhCH₂CH₂CORh(CO)₄. Clean, high-signal-to-noise spectra of the two intermediates (±)-PhCH(CH₃)CORh(CO)₄ and PhCH₂CH₂CORh(CO)₄ were obtained. The disappearance of Rh₄(CO)₁₂ was found to followed the rate expression rate = k_o^{mages/gifchars/alpha.gif" BORDER=0>} [Rh₄(CO)₁₂]^1.0[CO]^1.3[H₂]^0.9[C₈H₈]^0.15where k_o^{mages/gifchars/alpha.gif" BORDER=0>} = (mages/gifchars/kappa.gif" BORDER=0 >T/h)exp(-62.6 kJ/(mol RT)) + 37.2 J/(mol R)). This rate expression suggeststhat cluster fragmentation of Rh₄(CO)₁₂ proceeds via CO addition and polyhedron openingas the first step. The hydrogenolysis of (±)-PhCH(CH₃)CORh(CO)₄ to yield the major product(±)-PhCH(CH₃)CHO was found to follow the rate expression rate = k_o^{mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">}[PhCH(CH₃)CORh(CO)₄]^1.0[CO]^-1.0[H₂]^1.0[C₈H₈]^0.0 with k_o^{mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">} = (mages/gifchars/kappa.gif" BORDER=0 >T/h)exp(-78.8 kJ/(mole RT) + 15.2 J/(mol R),and the hydrogenolysis of PhCH₂CH₂CORh(CO)₄ to yield the minor product PhCH₂CH₂CHO was found to follow the rate expression rate = k_o^{mages/gifchars/gamma.gif" BORDER=0 >} [PhCH₂CH₂CORh(CO)₄]^1.0[CO]^-1.0[H₂]^1.0[C₈H₈]^0.0 with k_o^{mages/gifchars/gamma.gif" BORDER=0 >} = (mages/gifchars/kappa.gif" BORDER=0 >T/h)exp(-113 kJ/(mol RT)) - 102 J/(mol R). The two rateexpressions for hydrogenolysis are consistent with (1) equilibrium controlled dissociation ofa CO ligand from the acyl intermediates to form coordinatively unsaturated species, (2) arate-limiting step involving hydrogen activation on the 4-coordinate species, and (3) productformation accompanied by the formation of a transient species {HRh(CO)₃}.