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

Reactions of HOC 6 H 4 I-2 with [Pd 2 (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(C 6 H 4 OH-2)I(L 2 )] (L 2 = dtbbpy ( 1a ‘), tmeda ( 1a ‘ ‘), phen ( 1a ‘ ‘‘)). Complexes 1a ‘ and 1a ‘ ‘ react with CO to give the aroyl derivatives [Pd{C(O)C 6 H 4 OH-2}I(dtbbpy)] ( 2a ‘) and [Pd{C(O)C 6 H 4 OH-2}I(tmeda)] ( 2a ‘ ‘), respectively. The compound 1a ‘ reacts with isocyanides RNC (R = 2,6-dimethylphenyl (Xy), t Bu) to give [Pd{C( NR)C 6 H 4 OH-2}I(dtbbpy)] (R = Xy ( 3a ‘ Xy ), t Bu ( 3a ‘ t Bu )). The reactions of complexes [Pd(C 6 H 4 OX-2)I(bpy)] (X = H ( 1a ), C(O)Me ( 1b )) and 1a ‘ with alkynes RC⋮CR give the alkenyl complexes [Pd{CR CR(C 6 H 4 OX-2)}I(L 2 )] (X = H, R = CO 2 Me, L 2 = bpy ( 4a ), dtbbpy ( 4a ‘); X = C(O)Me, L 2 = bpy, R = CO 2 Me ( 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(C 6 H 4 OC(O)Me-2)}(OTf)(bpy)] ( 5 ) is formed. Complexes 1a and 1a ‘ insert 1,5-cyclooctadiene (C 8 H 12 ) in the presence of TlOTf to give [Pd(η 1 ( C ): η 2 ( C,C ) - C 8 H 12 C 6 H 4 OH-2)(L 2 )]TfO (L 2 = bpy ( 6a ), dtbbpy ( 6a ‘)). When similar reactions were carried out with 1a and 2,5-norbornadiene (C 7 H 8 ), dicyclopentadiene (C 10 H 12 ), or norbornene (C 7 H 10 ), polyinserted species were obtained. The FAB + mass spectra of these species give peaks for (M − OTf) +, where M = Pd{(C 7 H 8 ) n C 6 H 4 OH-2}(bpy) ( n = 1−10 or 1−18, depending on the amounts of diolefin used), Pd{(C 10 H 12 ) n C 6 H 4 OH-2}(bpy) ( n = 1−5), and [Pd{(C 7 H 10 ) n C 6 H 4 OH-2}(OTf)(bpy)] ( n = 1−11). The aroyl compound 2a reacts similarly with 2,5-norbornadiene or norbornene to give [Pd{(C 7 H 8 ) n C(O)C 6 H 4 OH-2}(OTf)(bpy)] ( n = 1−10) or [Pd{(C 7 H 10 ) n C(O)(C 6 H 4 OH-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(CO 2 Me) C(CO 2 Me)(C 6 H 4 OH-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-2 H -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(C 6 H 4 OC(O)Me-2)}(CNXy)(bpy)]TfO ( 9b * Xy ) is obtained. The compounds 3a t Bu, [Pd{C( NXy)(C 6 H 4 OC(O)Me-2)}I(bpy)] ( 3bXy ), and [Pd{C( NXy)(C 6 H 4 CN-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- (C 7 H 8 )C( NR)(C 6 H 4 X-2)}(bpy)]TfO (R = t Bu, X = OH ( 10a t Bu ); R = Xy, X = MeCO 2 ( 10bXy ), CN ( 10cXy )) or [Pd{κ 2 -C,N- (C 10 H 12 )C( NXy)(C 6 H 4 O 2 CMe-2)}(bpy)]TfO ( 10b * Xy ), respectively. Other isocyanide/alkene sequentially inserted complexes can be obtained by reaction of trans -[Pd{C( NXy)(C 6 H 4 X-2)}I(CNXy) 2 ] (X = OH ( 11aXy ), CN ( 11cXy )) with 2,5-norbornadiene or norbornene and TlOTf, which renders cis -[Pd{κ 2 C,N- (C 7 H 8 )C( NXy)(C 6 H 4 X-2)}(CNXy) 2 ]TfO (X = OH ( 12aXy ), CN ( 12c ‘ Xy )) or cis -[Pd{κ 2 C,N- (C 7 H 10 )C( NXy)(C 6 H 4 OH-2)}(CNXy) 2 ]TfO ( 12a * Xy ), respectively. The crystal and molecular structures of 2a ‘ ‘, 4a ‘, 4b, 6a, 6a ‘, 10a t Bu, 12aXy, and 12c ‘ Xy have been determined.