The unusual inhibition of a dirhodium tetraphosphine-based bimetallic hydroformylation catalyst by PPh3 |
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| Institution: | Department of Chemistry, Louisiana State University, Baton Rouge, LA, 70803-1804, USA |
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| Abstract: | The addition of even small amounts of PPh3 to the dirhodium tetraphosphine hydroformylation catalyst generated from ?rac-Rh2(nbd)2(et,ph-P4)?(BF4)2 (nbd = norbornadiene; et,ph-P4 = Et2CH2CH2(Ph)PCH2P(Ph)CH2CH2PEt2) causes a dramatic drop in the aldehyde linear-to-branched regioselectivity (25:1 to 3:1) in acetone solvent (90 °C, 6.1 bar, 1-hexene). Catalytic results are presented for differing amounts of added PPh3 along with comparisons to the monometallic Rh catalyst family, HRh(CO)x(PPh3)y (x = 1–3; y = 3 – x), generated from PPh3 and Rh(acac)(CO)2 (acac = acetylacetonate). The results point to the extremely effective inhibition of the regioselective bimetallic hydroformylation mechanism and the formation of an inefficient monometallic catalyst cycle, but not fragmentation to generate free HRh(CO)(PPh3)2 catalysts. |
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