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), tBu) to give [Pd{C(NR)C6H4OH-2}I(dtbbpy)] (R = Xy (3a‘Xy), tBu (3a‘tBu)). 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{CRCR(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{CPhCPh-CPhCPh(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)nC6H4OH-2}(bpy) (n = 1−10 or 1−18, depending on the amounts of diolefin used), Pd{(C10H12)nC6H4OH-2}(bpy) (n = 1−5), and [Pd{(C7H10)nC6H4OH-2}(OTf)(bpy)] (n = 1−11). The aroyl compound 2a reacts similarly with 2,5-norbornadiene or norbornene to give [Pd{(C7H8)nC(O)C6H4OH-2}(OTf)(bpy)] (n = 1−10) or [Pd{(C7H10)nC(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{CPhCPh(C6H4OC(O)Me-2)}(CNXy)(bpy)]TfO (9b*Xy) is obtained. The compounds 3atBu, [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{κ2C,N-(C7H8)C(NR)(C6H4X-2)}(bpy)]TfO (R = tBu, X = OH (10atBu); R = Xy, X = MeCO2 (10bXy), CN (10cXy)) or [Pd{κ2-C,N-(C10H12)C(NXy)(C6H4O2CMe-2)}(bpy)]TfO (10b*Xy), respectively. Other isocyanide/alkene sequentially inserted complexes can be obtained by reaction of trans-[Pd{C(NXy)(C6H4X-2)}I(CNXy)2] (X = OH (11aXy), CN (11cXy)) with 2,5-norbornadiene or norbornene and TlOTf, which renders cis-[Pd{κ2C,N-(C7H8)C(NXy)(C6H4X-2)}(CNXy)2]TfO (X = OH (12aXy), CN (12c‘Xy)) or cis-[Pd{κ2C,N-(C7H10)C(NXy)(C6H4OH-2)}(CNXy)2]TfO (12a*Xy), respectively. The crystal and molecular structures of 2a‘ ‘, 4a‘, 4b, 6a, 6a‘, 10atBu, 12aXy, and 12c‘Xy have been determined.