Back to Unique Hemilabile Phosphorous Ligands for Catalysis

Applications of Bis-phosphine Monoxides (BPMOs)

“Bis-phosphine monoxides (BPMOs) of the general formula R¹R²P-Y-P(O)R³R⁴, where Y is a divalent spacer, constitute an important class of hemilabile ligands.  Due to the presence of both the soft (P) and hard (O) Lewis base centers on one molecule, BPMOs can stabilize various transition metals in low and high oxidation states.  Also, BPMOs often form labile metal chelates which can easily generate reactive, coordinatively unsaturated species.  Consequently, the weak BPMO chelation provides low activation energy paths to various transformations at the metal center, such as ligand exchange, isomerisation, oxidative addition, migratory insertion, reductive elimination, and so forth.  As a result, transition metal BPMO complexes are often capable of catalyzing various reactions under uncommonly mild conditions with very high selectivities.”

-- Chem. Rev. 2004, 104, 1629-1662.

Selected Applications of BPMOs in Synthesis and Catalysis

Asymmetric Diels-Alder reactions, catalyzed by (S)-BINAP(O) Ru and Os Lewis acids, occur with up to 99% ee and 99% de.  The use of BINAP instead of the BINAP(O) in this reaction leads to a significant drop in ee (below 50%).

-- J. Am. Chem. Soc. 2001, 123, 2525 and Organometallics 2001, 20, 697.

The chiral poisoning strategy has been employed for these Diels-Alder reactions, catalyzed by the Ru Lewis acid derived from racemic BINAP(O).  Excellent diastereoselectivity and ee of up to 60% were obtained with L-proline and L-prolinamide as chiral poisons.

-- Organometallics 2002, 21, 1662.

Rh-catalyzed carbonylation of methanol (the Monsanto Acetic Acid Process) accounts for >55% of all acetic acid produced world-wide.  With the standard industrial Rh catalyst the process is run at 200 ^oC and 500 psig of CO at turnover frequency (TOF) of 200–600 h^-1.  If the catalyst is promoted with dppeO (1 equiv per Rh) the reaction occurs under exceedingly mild conditions (80 ^oC and 50 psig of CO) at industrial production rates (TOF = 400 h^-1).  This dppeO-Rh catalyst can also be used for ethanol carbonylation.

-- J. Chem. Soc., Chem. Commun. 1987, 1891.  U.S. 4,670,570.

Asymmetric hydrosilylation with Pd- BINAP(O) catalysts.

-- Tetrahedron: Asymmetry 1998, 9, 391.

Synthesis of chiral ligands from BINAP(O).

-- J. Org. Chem. 2001, 66, 8854.

Asymmetric allylic alkylation in the presence of cinchonidinium salts as chiral phase-transfer catalysts and a Pd-dppeO catalyst occurs with excellent yields and very high ee.

-- J. Org. Chem. 2002, 67, 7418.

Rh-dppeO-catalyzed hydroformylation of olefins in the presence of dppeO occurs with uncommonly high selectivity toward the desired linear product.

-- U.S. 4,522,933, U.S. 4,491,675, and U.S. 4,593,011.

Pd-dppeO-catalyzed hydrocarboxylation of olefins occurs with uncommonly high selectivity toward the desired linear acids.

-- Izv. Akad. Nauk SSSR, Ser. Khim. 1992, 2003.

Highly efficient and selective Pd-dpppO-catalyzed hydrocarboxylation of styrenes.  The use of dpppO rather than dppeO (see Example 6 above) results in the exclusive or almost exclusive formation of the branched product.

-- U.S. 5,482,596 and U.S. 5,902,898.

Cobalt-dppmO-catalyzed hydroformylation of epoxides to b-hydroxyaldehydes which can be then hydrogenated to 1,3-diols without isolation.

-- Chem. Commun. 2000, 1419.

Synthesis of materials, e.g. Eu-Pd-dppeO-based heterobimetallic polymer.

-- Chem. Commun. 2002, 520.

Synthesis of vinylphosphines via the Wittig-Horner reaction of dppmO.

-- J. Prakt. Chem. 1984, 326, 360.

Synthesis of Z-allylphosphine oxides and boranes as precursors to conjugated polyenes via the Wittig-Horner reaction of dppeO.

-- Tetrahedron 2003, 59, 7177.

Ni-Catalyzed Ethylene oligomerization. Nickel catalysts of the type [(h³-methallyl)Ni(h²-BPMO)]⁺ SbF₆^- have been shown to exhibit excellent activity in ethylene oligomerization with high selectivities toward linear products (87-96%) with the terminal C=C bond (up to 89%).  The nature of BPMO strongly influences the reaction outcome.  Thus, the dppmO -based catalyst produces heavier oligomers, up to C₁₆, whereas the dpppO analogue catalyzes the formation of only short-chained alkenes.  The highest molecular weight oligomers (up to C₃₄) is obtained when the dppbzO catalyst is used.  Analogous palladium BPMO complexes also catalyze ethylene oligomerization but mostly to butanes (65-86%).

-- J. Mol. Catal. A 2000, 157, 41.

Carbonylation of MeOH to methyl acetate in the presence of dppeO-Rh catalysts smoothly and selectively occurs under mild conditions.

-- Eur. Pat. Appl. EP 171804.

Rh-dppeO-catalyzed carbonylation of esters to carboxylic acid anhydrides.

-- U.S. 4,563.309.

Isomerisation of methyl formate to acetic acid.

-- PCT Int. Appl. 8600889.