3 years ago

Rhodium-Catalyzed Isomerization of a Bis(secondary phosphine) to an Unsymmetrical Diphosphine via P–C Cleavage and P–P and C–H Bond Formation

Rhodium-Catalyzed Isomerization of a Bis(secondary phosphine) to an Unsymmetrical Diphosphine via P–C Cleavage and P–P and C–H Bond Formation
Arnold L. Rheingold, Perry M. Scheetz, David S. Glueck
To develop Rh-catalyzed dehydrocoupling for stereocontrolled synthesis of P–P bonds, we prepared potential intermediates, chiral rhodium phosphine-phosphido complexes, and investigated their stoichiometric and catalytic transformations. Treatment of [Rh(diphos*)(COD)][X] with the bis(secondary phosphine) IsHPCH2PHIs (1, Is = 2,4,6-(i-Pr)3C6H2) gave the cations [Rh(diphos*)(IsHPCH2PHIs)][X] (diphos* = (R,R)-Me-DuPhos (2), (R,R)-i-Pr-DuPhos (3), or (R,R)-Me-BPE (4); X = BF4 or OTf) with high diastereoselectivity as single C2-symmetric diastereomers. Deprotonation of 24 with NaN(SiMe3)2 yielded phosphine-phosphido chelates Rh(diphos*)(IsHPCH2PIs) 57 with high diastereoselectivity. Thermolysis of 57 in toluene at 90 °C caused isomerization to give Rh(diphos*)(IsMeP-PIs) (810) as mixtures of diastereomers. Under catalytic conditions, Rh-DuPhos precursors slowly converted 1 to a mixture of diastereomers of its isomer, the unsymmetrical diphosphine IsHP-PMeIs (12). We propose a possible mechanism for the isomerization and discuss its relationship to dehydrocoupling catalysis.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00515

DOI: 10.1021/acs.organomet.7b00515

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