Platinum-Catalyzed Acrylonitrile Hydrophosphination. P−C Bond Formation via Olefin Insertion into a Pt−P Bond

Abstract

The acrylonitrile complexes Pt(diphos)(CH 2 CHCN) (diphos ) dppe (1), dcpe (2); dppe ) Ph 2 PCH 2 CH 2 PPh 2 , dcpe ) Cy 2 PCH 2 CH 2 PCy 2 , Cy ) cyclo-C 6 H 11 ) are catalyst precursors and, for some substrates, resting states, during addition of P-H bonds in primary and secondary phosphines across the CdC double bond of acrylonitrile (hydrophosphination). Oxidative addition of P-H bonds to related catalyst precursors gives the phosphido hydride complexes Pt(diphosAcrylonitrile does not insert into the Pt-H bond of these hydrides to give cyanoethyl ligands; the putative products, the phosphido complexes Pt(diphos 11)) were prepared independently and found to be stable to P-C reductive elimination. Instead, catalysis appears to occur by selective insertion of acrylonitrile into the Pt-P bond to yield the alkyl hydrides Pt(diphos)[CH(CN)CH 2 PRR′](H), followed by C-H reductive elimination and regeneration of 1 or 2. This insertion was observed directly in model methyl phosphido complexes M(dppe)-(Me)(PRR′) (M ) Pt, R ) H, R′ ) Mes* (12), R ) R′ ) Mes (13); M ) Pd, R ) H, R′ ) Mes* (17)), yielding M(dppe)[CH(CN)CH 2 PRR′](Me), (14, 15, 18). Similarly, treatment of Pt(dcpe)-(PHMes*)(H) (22) with acrylonitrile gives Pt(dcpe)[CH(CN)CH 2 PHMes*](H) (24) as a mixture of diastereomers; the isomeric Pt(dcpe)[PMes*(CH 2 CH 2 CN)](H) (25), which was prepared independently, was also observed during this reaction. Both 24 and 25 decompose in the presence of acrylonitrile to form Pt(dcpe)(CH 2 CHCN) (2) and PHMes*(CH 2 CH 2 CN) (3a). The C-H reductive elimination step was modeled by studies of Pt(dcpe)[CH(Me)(CN)](H) (26). Another isomer, Pt(dcpe)[CH(Me)(CN)](PHMes*) (29), which formally results from insertion of acrylonitrile into the Pt-H bond of 22, was formed by decomposition of complex 2 during catalysis. Complex 29 is inactive in catalysis but decomposes to partially regenerate the active catalyst 2. The cyanoethyl compounds Pt(dcpe)(CH 2 CH 2 CN)(PHMes*) (11), trans-Pt-(PPh 3 ) 2 (CH 2 CH 2 CN)(Br), and PMes 2 (CH 2 CH 2 CN) (23) were structurally characterized by X-ray crystallography.

Synthesis, structure, and reactivity of platinum compounds featuring terminal amido and phosphido ligands

“…The methyl ligand possess a Pt-C(3) = 2.129(4) Å, which is longer than Pt-C(3) = 2.083(3) Å of 6, but not atypical of platinum methyl species [42]. The highly analogous platinum phosphide Pt(dcpe)(CH 2 CH 2 CN)(PHMes ⁄ ) (dcpe = 1,2 bis(dicyclohexylphosphino)ethane) reported by Glueck and coworkers has a Pt-P = 2.390(2) Å which is quite similar to Pt-P(3) = 2.386(1) Å observed for 11 [50]. Chloride-substituted platinum phosphides 9 and 10 have nearly the same platinumphosphorus bond lengths Pt-P(3) = 2.3910(9) Å and Pt-P(3) = 2.396 (2) [12][B(C 6 F 5 ) 4 ]) as translucent crystals in 87% and 85% isolated yield, respectively (Scheme 2).…”

Electrophilic Activation of Alkenes by Platinum(II): So Much More Than a Slow Version of Palladium(II)

“…(26)]. [97,98] Phosphines were shown to Originally, a mechanism analogous to Scheme 3 was proposed, in which the initial PÀH oxidative addition to Pt 0 is followed by a regioselective alkene insertion into the PtÀP bond, and subsequent CÀH reductive elimination releases the product to complete the catalytic cycle.…”

Synthesis and Coordination Chemistry of Cyano-Substituted Phosphines

“…On the other examples, the mechanism of the hydrophosphination was extensively investigated by Glueck et al [59][60][61][62]. To exclude the alternative possibility of catalysis by binuclear complexes [57,5] complexes of 2 -coordinated acrylonitrile and bidentate phosphine ligands (diphos) were used as precatalysts [59].…”

“…Assuming that the insertion of acrylonitrile into the Pt-P bond in phosphido-hydride complexes proceeds regioselectively, the authors suggested that using of a chiral precatalyst could give rise to a enantiomerically enriched tertiary phosphine [60]. To examine this possibility the investigation of the stereochemical aspect of the acrylonitrile insertion into phosphido-hydride complexes was performed followed by 31 P NMR.…”