In Situ Preparation of Palladium Diphosphane Catalysts

Marson, Angelica; Oort, A. Bart van; Mul, Wilhelmus P.

doi:10.1002/1099-0682(200211)2002:11<3028::aid-ejic3028>3.0.co;2-8

Cited by 33 publications

(41 citation statements)

References 5 publications

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“…Finally, we did not observe any spectroscopic evidence for the formation of cationicbis (dicarbene) palladium(II) species as a consequence of autoionization or ligandd is proportionation, which has previously been observed for diphosphine analogues [12,13] and dicarbene-nickel(II) complexes [14].…”

Section: Synthesis and Characterizationsupporting

confidence: 50%

Co-ligand effects in the catalytic activity of Pd(II)–NHC complexes

Yeung

Huynh

2011

Journal of Organometallic Chemistry

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Section: Synthesis and Characterizationsupporting

confidence: 50%

Co-ligand effects in the catalytic activity of Pd(II)–NHC complexes

Yeung

Huynh

2011

Journal of Organometallic Chemistry

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“…This can be understood by the steric hindrance that the o-MeO-substituents impose on the axial positions of the Pd centre in the catalyst, effectively shielding the d z 2 orbitals of palladium. [42,72,73] Thus, after formation of C5b/c (see Schemes 5 and 6), coordination of CO at the axial position is sterically hampered, as is also (temporarily) associative displacement of a nitroso ligand required for formation of C6 b (Scheme 10, left), and thus also the "2CO/2CH 3 OH" de-oxygenating pathway. Instead, the CH 3 O À anion present outside the first coordination sphere of the P 2 Pd II centre in C5b/c will deprotonate the coordinated CH 3 O À to form methanol and palladiumbound formaldehyde (Scheme 10, right), eventually leading to full dehydrogenation of methanol (Scheme 6).…”

Section: Pd(c(o)och 3 )A C H T U N G T R E N N U N G (Och 3 ) (I)mentioning

confidence: 99%

“…As this species is sterically more crowded in the equatorial positions, a second CH 3 OH molecule will first associate with the Pd centre through its axial positions, with formation of aniline and a P 2 Pd II A C H T U N G T R E N N U N G (OCH 3 ) 2 complex. As the o-MeO-substituents on the ligands shield the axial positions of Pd, [42,72,73] these o-MeO groups will hamper this second protonation step, and thus also DMC formation. Instead, MPC is then formed by the sequence: associative displacement of CH 3 O À by the smaller and neu-tral CO molecule, followed by nucleophilic attack by CH 3 O À at the coordinated CO molecule and reductive elimination of MPC (Scheme 11, upper pathway).…”

Section: Pd(c(o)och 3 )A C H T U N G T R E N N U N G (Och 3 ) (I)mentioning

confidence: 99%

Carbonylation of Nitrobenzene in Methanol with Palladium Bidentate Phosphane Complexes: An Unexpectedly Complex Network of Catalytic Reactions, Centred around a Pd–imido Intermediate

Mooibroek

Schoon

Bouwman

et al. 2011

Chemistry A European J

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The reactivity of palladium complexes of bidentate diaryl phosphane ligands (P(2)) was studied in the reaction of nitrobenzene with CO in methanol. Careful analysis of the reaction mixtures revealed that, besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MPC), N,N'-diphenylurea (DPU), aniline, azobenzene (Azo) and azoxybenzene (Azoxy)], large quantities of oxidation products of methanol were co-produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H(2)O, and CO). From these observations, it is concluded that several catalytic processes operate simultaneously, and are coupled via common catalytic intermediates. Starting from a P(2)Pd(0) compound formed in situ, oxidation to a palladium imido compound P(2)Pd(II)=NPh, can be achieved by de-oxygenation of nitrobenzene 1) with two molecules of CO, 2) with two molecules of CO and the acidic protons of two methanol molecules, or 3) with all four hydrogen atoms of one methanol molecule. Reduction of P(2)Pd(II)=NPh to P(2)Pd(0) makes the overall process catalytic, while at the same time forming Azo(xy), MPC, DPU and aniline. It is proposed that the Pd-imido species is the central key intermediate that can link together all reduction products of nitrobenzene and all oxidation products of methanol in one unified mechanistic scheme. The relative occurrence of the various catalytic processes is shown to be dependent on the characteristics of the catalysts, as imposed by the ligand structure.

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“…Starting from a 1:1 mixture of a Pd II salt and a ligand L with excess of HOMs essentially the same catalyst complex is formed in situ. Catalyst formation supposedly proceeds under the reaction conditions via stoichiometric carbonylative reduction of L Pd II by the alkene and a nucleophilic reagent, such as water, alcohol (or in our case the amide) . We have experimentally verified that both protocols gave similar catalytic results (see Table , entries 1 and 2).…”

Section: Discussionmentioning

confidence: 59%

Palladium‐Catalyzed Isomerization/(Cyclo)carbonylation of Pentenamides: a Mechanistic Study of the Chemo‐ and Regioselectivity

et al. 2017

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A new isomerizing ring‐closing amidocarbonylation reaction is reported using Pd catalysis with bulky diphosphane ligands. From terminal as well as internal pentenamide isomers (PAs), cyclic imides were obtained in good yield (92 %) with cationic Pd catalysts supported by bis‐PCg ligands (PCg=6‐phospha‐2,4,8‐trioxa‐1,3,5,7‐tetramethyladamant‐6‐yl). An excess of strong acid is required to obtain high selectivity for imide products. From a low‐temperature NMR study it was deduced that N coordination of the amide moiety is responsible for a high selectivity to cyclic imide products. In weakly acidic conditions, O coordination of the amide functionality leads to the formation of cyanoacids (i.e., 5‐cyanovaleric acid, 2‐methyl‐4‐cyanobutyric acid and 2‐ethyl‐3‐cyanopropionic acid). It is proposed that the formation of these cyanoacids occurs through a novel intramolecular tandem dehydrating hydroxycarbonylation reaction of PAs. This reaction also occurs in intermolecular versions of amidocarbonylation with mixtures of alkene and amide substrates. Experiments with N‐alkylated amides have been instrumental in developing mechanistic models. The strong acid co‐catalyst ensures double‐bond isomerization to occur faster than product formation, resulting in the same product mixture, irrespective of the use of terminal or internal pentenamides. The remaining challenge is to arrive at the desired adipimide by overcoming the undesirable regioselectivity caused by chelation of the amide.

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In Situ Preparation of Palladium Diphosphane Catalysts

Cited by 33 publications

References 5 publications

Co-ligand effects in the catalytic activity of Pd(II)–NHC complexes

Co-ligand effects in the catalytic activity of Pd(II)–NHC complexes

Carbonylation of Nitrobenzene in Methanol with Palladium Bidentate Phosphane Complexes: An Unexpectedly Complex Network of Catalytic Reactions, Centred around a Pd–imido Intermediate

Palladium‐Catalyzed Isomerization/(Cyclo)carbonylation of Pentenamides: a Mechanistic Study of the Chemo‐ and Regioselectivity

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