Platinum-catalyzed acrylonitrile hydrophosphination. P-C bond formation via olefin insertion into a Pt-P bond

The acrylonitrile complexes Pt(diphos)(CH2CHCN) (diphos = dppe (1), dcpe (2 ); dppe Ph2PCH2CH2PPh2, dcpe = Cy2PCH2CH2PCy2, Cy = cyclo-C6H11) are cataly st precursors and, for some substrates, resting states, during addition of P-H bonds in primary and secondary phosphines across the C=C double bond or acrylonitrile (hydrophosphination). Oxidative addition of P-H bonds to rel ated catalyst precursors gives the phosphido hydride complexes Pt(diphos)(P RR')(H) (diphos = dppe, R = H, R' = Mes* (20), R = R' = Mes (21); diphos dc pe, R = H, R' = Mes* (22); Mes = 2,4,6-Me3C6H2, Mes* = 2,4,6-(t-Bu)(3)C6H2) . Acrylonitrile does not insert into the Pt-H bond of these hydrides to giv e cyanoethyl ligands; the putative products, the phosphido complexes Pt(dip hos)(CH2CH2CN)(PRR') (diphos = dppe, R = H, R' = Mes* (9), R = R' = Mes (10 ); diphos = dcpe, R = H, R' = Mes* (11)) were prepared independently and fo und to be stable to P-C reductive elimination. instead, catalysis appears t o occur by selective insertion of acrylonitrile into the Pt-P bond to yield the alkyl hydrides Pt(diphos)[CH(CN)CH2PRR'](H), followed by C-H reductive elimination and regeneration of I or 2. This insertion was observed direct ly 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)CH2PRR'](Me), (14, 15, 18). Similarly, treatment of Pt(dcpe)(PH Mes*)(H) (22) with acrylonitrile gives Pt(dcpe)[CH(CN)CH(2)PHMes*](H) (24) as a mixture of diastereomers; the isomeric Pt(dcpe)(PMes*(CH2CH2CN)](H) (2 5), which was prepared independently, was also observed during this reactio n. Both 24 and 25 decompose in the presence of acrylonitrile to form Pt(dcp e)(CH2CHCN) (2) and PHMes*(CH2CH2CN) (3a). The C-H reductive elimination st ep 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 com plex 2 during catalysis. Complex 29 is inactive in catalysis but decomposes to partially regenerate the active catalyst 2. The cyanoethyl compounds Pt (dcpe)(CH2CH2CN)(PHMes*) (11), trans-Pt(PPh3)(2)(CH2CH2CN)(Br), and PMes(2) (CH2CH2CN) (23) were structurally characterized by X-ray crystallography.