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

Abstract

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) IsHPCH 2 PHIs (1, Is = 2,4,6-(i-Pr) 3 C 6 H 2 ) gave the cations [Rh(diphos*)(IsHPCH 2 PHIs)][X] (diphos* = (R,R)-Me-DuPhos (2), (R,R)-i-Pr-DuPhos (3), or (R,R)-Me-BPE (4); X = BF 4 or OTf) with high diastereoselectivity as single C 2 -symmetric diastereomers. Deprotonation of 2−4 with NaN(SiMe 3 ) 2 yielded phosphine-phosphido chelates Rh(diphos*)(IsHPCH 2 PIs) 5−7 with high diastereoselectivity. Thermolysis of 5−7 in toluene at 90 °C caused isomerization to give Rh(diphos*)(IsMeP-PIs) (8−10) 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.

N‐Heterocyclic Phosphido Complexes of Rhodium Supported by a Rigid Pincer Ligand

“…A similar decrease of the coupling constant between the P NHP and the metal was observed for the platinum(II) NHPcomplex [(PPP)Pt(PMe3)] + . [15] Further, the structurally characterized rhodium(I) phosphido complexes synthesized by Riley [32] and Glueck [33] both have small 1 JP-Rh values (< 90 Hz). The only reported rhodium(I) planar NHP + complexes both exhibit large (>230 Hz) 1 JPNHP-Rh values, [26,27] so the dramatically diminished rhodium-phosphorus coupling constant in 3 suggests that the central P NHP has adopted a pyramidal geometry.…”

I2/TBHP Mediated Divergent C(sp2)‐P Cleavage of Allenylphosphine Oxides: Substituent‐Controlled Regioselectivity

“…The privileged strategy in this area mainly concerns the cleavage of C−P(III) bond of arylphosphines, which has been recognized as a possible deactivation pathway in some catalytic processes (Scheme a) . Most of the examples involve the oxidative addition of low‐valent Pd‐complex to the C−P bond, and only a handful of other transition metal complexes, such as nickel and rhodium, has been reported. For an elegant work, in 2017, Morandi reported a palladium‐catalyzed carbon‐phosphorus bond metathesis by reversible arylation, which intrinsically involved in sequential cleaving aryl C−P bond.…”

Synthetic Applications of Transition‐Metal‐Catalyzed C−P Bond Cleavage

“…In 2017, Glueck and co‐workers reported another strain‐release process for C−P bond cleavage with a rhodium‐catalyzed transformation of bis(secondary phosphine) 76 into unsymmetrical diphosphine 81 (Scheme ) . They suggested P−H oxidative addition to give rhodium phosphine–phosphido complex 77 , followed by P−P reductive elimination to yield diphosphirane hydride intermediate 78 .…”

“…[43] In 2017, Glueck andc o-workersr eporteda nother strain-release process for CÀPb ond cleavage with ar hodium-catalyzed transformation of bis(secondaryphosphine) 76 into unsymmetrical diphosphine 81 (Scheme 26). [44] They suggested PÀHo xidative addition to give rhodium phosphine-phosphido complex 77,f ollowed by PÀPr eductive elimination to yield diphosphiraneh ydride intermediate 78.O xidativea ddition of the strained diphosphiraneC ÀPb ond in 78 and proton migration of 79 yield 80.H ydrolysiso f80 with bis(secondary phosphine) 76 provided product 81 and rhodium phosphine-phosphido complex 77,w hich reentered the catalytic cycle.…”