Reactivity of Ortho-Palladated Phenol Derivatives with Unsaturated Molecules. 1. Insertion of CO, Isocyanides, Alkenes, and Alkynes. CO/Alkene, Alkyne/Isocyanide, and Isocyanide/Alkene Sequential Insertion Reactions

Abstract

Reactions of HOC6H4I-2 with [Pd2(dba)3]·dba (“Pd(dba)2”; dba = dibenzylideneacetone) and N-donor ligands (4,4‘-di-tert-butyl-2,2‘-bipyridine (dtbbpy), N,N,N ‘ ,N ‘-tetramethylethylenediamine (tmeda), 1,10-phenanthroline (phen)) lead to the arylpalladium complexes [Pd(C6H4OH-2)I(L2)] (L2 = dtbbpy (1a‘), tmeda (1a‘ ‘), phen (1a‘ ‘‘)). Complexes 1a‘ and 1a‘ ‘ react with CO to give the aroyl derivatives [Pd{C(O)C6H4OH-2}I(dtbbpy)] (2a‘) and [Pd{C(O)C6H4OH-2}I(tmeda)] (2a‘ ‘), respectively. The compound 1a‘ reacts with isocyanides RNC (R = 2,6-dimethylphenyl (Xy), t Bu) to give [Pd{C(NR)C6H4OH-2}I(dtbbpy)] (R = Xy (3a‘Xy), t Bu (3a‘ t Bu)). The reactions of complexes [Pd(C6H4OX-2)I(bpy)] (X = H (1a), C(O)Me (1b)) and 1a‘ with alkynes RC⋮CR give the alkenyl complexes [Pd{CRCR(C6H4OX-2)}I(L2)] (X = H, R = CO2Me, L2 = bpy (4a), dtbbpy (4a‘); X = C(O)Me, L2 = bpy, R = CO2Me (4b), Ph (4b*)) through the insertion of the alkyne molecule into the palladium−carbon bond. When complex 1b reacts with PhC⋮CPh and TlOTf (1:3:1 molar ratio), the diinserted species [Pd{CPhCPh-CPhCPh(C6H4OC(O)Me-2)}(OTf)(bpy)] (5) is formed. Complexes 1a and 1a‘ insert 1,5-cyclooctadiene (C8H12) in the presence of TlOTf to give [Pd(η1(C):η2(C,C)-C8H12C6H4OH-2)(L2)]TfO (L2 = bpy (6a), dtbbpy (6a‘)). When similar reactions were carried out with 1a and 2,5-norbornadiene (C7H8), dicyclopentadiene (C10H12), or norbornene (C7H10), polyinserted species were obtained. The FAB+ mass spectra of these species give peaks for (M − OTf)+, where M = Pd{(C7H8) n C6H4OH-2}(bpy) (n = 1−10 or 1−18, depending on the amounts of diolefin used), Pd{(C10H12) n C6H4OH-2}(bpy) (n = 1−5), and [Pd{(C7H10) n C6H4OH-2}(OTf)(bpy)] (n = 1−11). The aroyl compound 2a reacts similarly with 2,5-norbornadiene or norbornene to give [Pd{(C7H8) n C(O)C6H4OH-2}(OTf)(bpy)] (n = 1−10) or [Pd{(C7H10) n C(O)(C6H4OH-2)}(OTf)(bpy)] (n = 1−10), respectively. The reaction of 4a with XyNC and TlOTf (1:1:1 molar ratio) gives [Pd{C(NXy)C(CO2Me)C(CO2Me)(C6H4OH-2)}(bpy)]TfO (7aXy), which is the result of the successive insertion of an alkyne and an isocyanide into a palladium−carbon bond. The reaction of 4a with a 4-fold excess of isocyanide gives dimethyl 2-(2,6-dimethylphenyl)imino-2H-chromene-3,4-dicarboxylate iminecoumarin (8), a result of the sequential insertion of alkyne and isonitrile into the Pd−C bond, followed by a depalladation process, as the only characterizable product. When 4b* reacts with XyNC and TlOTf [Pd{CPhCPh(C6H4OC(O)Me-2)}(CNXy)(bpy)]TfO (9b*Xy) is obtained. The compounds 3a t Bu, [Pd{C(NXy)(C6H4OC(O)Me-2)}I(bpy)] (3bXy), and [Pd{C(NXy)(C6H4CN-2)}I(bpy)] (3cXy) react with 2,5-norbornadiene or dicyclopentadiene in the presence of TlOTf to give the isocyanide/alkene inserted complexes [Pd{κ 2 C,N-(C7H8)C(NR)(C6H4X-2)}(bpy)]TfO (R = t Bu, X = OH (10a t Bu); R = Xy, X = MeCO2 (10bXy), CN (10cXy)) or [Pd{κ 2 -C,N-(C10H12)C(NXy)(C6H4O2CMe-2)}(bpy)]TfO (10b*Xy), respectively. Other isocyanide/alkene sequentially ...

Reactivity of ortho‐Palladated Phenol Derivatives with Unsaturated Molecules: Insertion of Nitriles into a Late‐Transition‐Metal–Carbon Bond

“…General procedure: The nitrile (1.15 mmol) and TlOTf (81 mg, 0.23 mmol) was added to a solution of [Pd{2-(OH)C 6 H 4 }I(tmeda)] [11] (100 mg, 0.23 mmol) in CH 2 Cl 2 (15 mL). The resulting mixture was stirred for 4 h at room temperature, the suspension was filtered over celite, the yellow solution was concentrated (3 mL), and Et 2 O (10 mL) was added, which resulted in the precipitation of a solid.…”

“…We have reported that CO and olefins insert into the CÀPd bond of [Pd{2-(OH)C 6 H 4 }I(tmeda)] without intervention of the hydroxy group. [11] The insertion of a nitrile group into an aryl-Pd bond has been postulated as a step in the mechanism of the synthesis of aryl ketones by the Pd-catalyzed reaction of arenes with nitriles at 75-100 8C. [12] The proposed subsequent step is the protonation of the resulting imido complex to give an imine.…”

Mono- and Dipalladated Derivatives of 2,5-Distyrylbenzene. Reactivity toward XyNC and Alkynes. Synthesis of Complexes with Indacenediide Ligands

“…3−5,7−33 Very often new ligands and/or organic compounds are formed, involving both the insertion of the organic molecule into the carbon−palladium bond and its interaction with the group in an ortho position. 3,4,8,10,[13][14][15][16][17][18][20][21][22][23][24][25][26][27]29,31,33 We are now exploring the extension of this chemistry to complexes with two 34−37 or three 35, 37 Pd atoms around a benzene ring, each or them ortho to an organic group. The reactions of such complexes with unsaturated organic molecules could lead to novel polynuclear Pd complexes and/or new organic polycyclic compounds that are otherwise difficult to prepare.…”

“…Some of these results have been reported in a preliminary communication. 36 It is well-known that arylpalladium complexes react with alkynes to give mono-, di-, and tri-inserted derivatives 7,11,19,20,32,41,42 or, after depalladation, organic compounds 43 such as spirocycles, 3,4,21,23,42,44−46 benzofulvenes, 21 indenols, 8,10,23,45,47 indenones, 10,23,47 carbocycles, 42,44,48,49 and oxygen-, 13,50,51 sulfur-, 18,45,52 or nitrogencontaining 4,14,15,31,33,48,50,53 heterocycles. Sometimes these reactions are part of catalytic cycles yielding interesting organic compounds.…”

“…Although the insertion reactions of isocyanides into Ar−Pd bonds have been extensively investigated, 4,9,[11][12][13][14][15][16][17][18][19][20][25][26][27]30,33,78,79 this is the first report of the simultaneous insertion of isocyanide into two aryl−Pd bonds on the same benzene ring of a complex. trans,trans-2,5-distyryl-2,4-dibromobenzene 80 to 2 equiv of [Pd(dba) 2 ] in the presence of tbbpy or tmeda (Scheme 1).…”