Concurrent Synergism and Inhibition in Bimetallic Catalysis: Catalytic Binuclear Elimination, Solute−Solute Interactions and a Hetero-Bimetallic Hydrogen-Bonded Complex in Rh−Mo Hydroformy

详细信息    查看全文

• 作者：Chuanzhao Li ; Shuying Cheng ; Martin Tjahjono ; Martin Schreyer ; Marc Garland
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：April 7, 2010
• 年：2010
• 卷：132
• 期：13
• 页码：4589-4599
• 全文大小：465K
• 年卷期：v.132,no.13(April 7, 2010)
• ISSN：1520-5126

文摘

Hydroformylations of cyclopentene and 3,3-dimethylbut-1-ene were performed using both Rh₄(CO)₁₂ and (η⁵-C₅H₅)Mo(CO)₃H as precursors in n-hexane at 298 K. Both stoichiometric and catalytic hydroformylations were conducted as well as isotopic labeling experiments. Six organometallic pure component spectra were recovered from the high-pressure FTIR experiments, namely the known species Rh₄(CO)₁₂, (η⁵-C₅H₅)Mo(CO)₃H, RCORh(CO)₄, and the new heterobimetallic complexes RhMo(CO)₇(η⁵-C₅H₅), a weak hydrogen bonded species (η⁵-C₅H₅)Mo(CO)₃H−C₅H₉CORh(CO)₄, and a substituted RhMo(CO)_7-y(η⁵-C₅H₅)L_y, where y = 1 or 2 and L = (π-C₅H₈). The main findings were (1) catalytic binuclear elimination (CBER) occurs between (η⁵-C₅H₅)Mo(CO)₃H and RCORh(CO)₄ resulting in aldehyde and RhMo(CO)₇(η⁵-C₅H₅), and this mechanism is responsible for ca. 10% of the product formation; (2) molecular hydrogen is readily activated by the new heterobimetallic complex(es); (3) FTIR and DFT spectroscopic evidence suggests that the weak hydrogen bonded species (η⁵-C₅H₅)Mo(CO)₃H−C₅H₉CORh(CO)₄ has an interaction of the type η⁵-C₅H₄−H···O═C; and (4) independent physicochemical experiments for volumes of interaction confirm that significant solute−solute interactions are present. With respect to the efficiency of the catalytic cycle, the formation of a weak (η⁵-C₅H₅)Mo(CO)₃H−C₅H₉CORh(CO)₄ complex results in a significant decrease in the measured turnover frequency (TOF) and is the primary reason for the inhibition observed in the bimetallic catalytic hydroformylation. Such hydrogen bonding through the η⁵-C₅H₅ ring might have relevance to inhibition observed in other catalytic metallocene systems. The present catalytic system is an example of concurrent synergism and inhibition in bimetallic homogeneous catalysis.