Ligand driven σ,π-η3 structural rearrangements of organopalladium complexes: their relevance to the CO/styrene copolymerisation reaction

Alternating and Non‐Alternating Pd‐Catalysed Co‐ and Terpolymerisation of Carbon Monoxide and Alkenes

“…[6a,16c,16f,17] It is commonly agreed that termination by β-H elimination is favoured over propagation of the polymer due to the higher electron density on the palladium centre in phosphane-modified catalysts, [6,[16][17][18] and it has also been suggested that the (diphosphane)Pd-styryl intermediates formed in the initial steps of the CO/styrene copolymerisation are so strongly stabilised by π-benzylic coordination that this inhibits CO insertion. Termination by β-H elimination thus becomes favoured and oligoketones are formed instead of polyketones.…”

Ligand-Dependent Diastereoselectivity in the Palladium-Catalyzed Copolymerization of Styrene with Carbon Monoxide

“…After 5 min, 24 ml of pentane was added, and the mixture was stirred for 2 h. Evaporation of the solvent and trituration of the residue with Et 2 O gave the desired complex as a pale yellow powder (402 mg, 1.07 mmol, 54.3%). 1 H-NMR: 1.17 (s, PdMe); 1.25 (s, PdMe); 2.79 (dd, 2 J 13.8, 3 J 7.7, 1 H, PhCH 2 ); 2.96 (dd, 2 J 13.8, 3 J 3.8, 1 H, PhCH 2 ); 3.61 (dd, 2 J 8.8, 3 J 9.5, 1 HÀC(5)); 3.85 (dd, 2 J 8.8, 3 J 6.2, 1 HÀC(5)); 4.19 ± 4.28 (m, 1 HÀC(4)); 6.38 (t, 3 J 5.1, HÀC(5) of Py); 6.64 (t, 3 J 7.7, HÀC(4) of Py)); 6.89 (d, 3 …”

“…± The synthesis of alternating copolymers between CO and alk-1-enes (Scheme 1) is achieved through a variety of cationic Pd complexes modified by N or P ligands, in which the ligand is mostly chelate, e.g., [(L L')Pd(S) 2 ]X 2 (L or = L', S solvent) [1]. When styrene is the substrate, catalysis to the corresponding polyketone 1 (R Ph) does not take place with catalytic systems modified by bidentate phosphorus ligands [2] [3] and is efficient essentially only with chelate nitrogen (N N) or hybrid nitrogen-phosphorus (P N) ligands. Notable exceptions are represented by the phosphaneÀphosphite chelate system (R)-2-(diphenylphosphino)-1,1'-binaphthalen-2'-yl-(S)-1,1'-binaphthalen-2'-ylphosphite that shows, however, low productivity [4], and by a bidentate chiral diphosphine ligand, 1,4 : 3,6-dianhydro-2,5-dideoxy-2,5-bis(diphenylphosphino)-l-iditol, which cannot chelate [5].…”

Catalyst activity or stability: the dilemma in Pd-catalyzed polyketone synthesis

“…63,64 In the latter case it was demonstrated that the CO insertion into the Pd-allyl bond is much less efficient than into the Pd-alkyl bond. 65 The observation in the NMR-2D-NOESY spectrum of 1e of a strong cross-peak between H a of styrene unit and H ortho of the CH 3 -substituted aryl ring, together with the lack of such interaction with the H ortho of the CF 3 -substituted aryl ring, probes evidence that only the isomer featured by the Pd-C bond trans to the Pd-N bond of the CF 3 -substituted aryl ring is formed.…”