María-Teresa Chicote

The reactions of iodoanilines IC₆H₄NRR′‐2 with [Pd(PPh₃)₄] gave complexes [Pd(C₆H₄NRR′‐2}I(PPh₃)₂] [R=H, R’=H (1 a), Me (1 b); R=R’=Me (1 c)] while a mixture of 1 a, and the dimeric [Pd{μ‐C,N‐C₆H₄NH₂‐2)I(PPh₃)]₂ (2 a) was obtained when the appropriate iodoaniline was reacted with [Pd(dba)₂] (dba=dibenzylideneacetone) and 1 equiv. of PPh₃. The phosphonium salts [Ph₃PC₆H₄NRMe‐2]OTf [R=H (3 b), Me (3 c)] formed upon reacting complexes 1 b,c with TlOTf (OTf=CF₃SO₃). Complexes of the type [Pd(C₆H₄NRR′‐2}I(N N)] (4) were obtained from the reaction of [Pd(dba)₂] with the appropriate iodoaniline and a N N bidentate ligand (N N=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine or N,N,N′,N′‐tetramethylethylenediamine). Complexes 4 reacted with TlOTf and PPh₃ or XyNC (Xy=C₄H₄Me₂‐2,6) to give [Pd(C₆H₄NRR′‐2)(N N)(PPh₃)]OTf (5) or [Pd{C,N‐C(=NHXy)C₆H₄NRR′‐2)(N N)]OTf (6), respectively. In the absence of any added ligand, the reactions of complexes 4 with TlOTf produced the dimeric complexes [Pd{μ‐C,N‐C₆H₄NHR‐2)(N N)]₂(OTf)₂ (7) or the four‐membered palladacycles [Pd(κ²‐C₆H₄NMe₂‐2)(N N)]OTf (8), depending on the substitution degree of the aniline reagent.

Oxidative addition of N-(2-iodophenyl)formamide to Pd(dba)₂ (dba = dibenzylideneacetone) in the presence of 4,4′-ditertbutyl-2,2′-bipyridine (^tBubpy) produces [Pd(C₆H₄NHCHO-2)I(^tBubpy)] (1) which inserts 2-iodophenyl isocyanide to give [Pd{C(NC₆H₄I-2)C₆H₄NHCHO-2}I(^tBubpy)] (2). Dehydroiodination of 2 with Tl(acac) (acacH = acetylacetone) gives the stable Pd(IV) complex OC-6-35-[Pd{C,N,N–C(NC₆H₄-2)C₆H₄NCHO-2}I(^tBubpy)] (4) likely resulting from the spontaneous oxidative addition of the I–Ar moiety present in the unstable intermediate Pd(II) complex [Pd{C,N–C(NC₆H₄I-2)C₆H₄NCHO-2}(^tBubpy)] (3). The crystal structure of 4 shows various C–H⋯O hydrogen bonds resulting in chains of dimers stacked along the a axis.

Orthopalladation of the phenyl ring in the cyclopalladated complex [Pd{C,N-pyl-SCHC(O)Ph}(μ-X)]₂ (pyl = 2-pyridyl, X = Cl; 1·Cl) occurs upon reacting it with AgOAc (1 : 2) in MeCN to give the pincer complex [Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}(NCMe)] (2). The nature of the base and X plays a key role because palladation neither occurs with other bases nor when AgOAc is the base and X is Br, in which case 1·OAc is obtained. In addition, complex 2 is not obtained upon refluxing 1·OAc in MeCN. Complex 2 affords complexes [Pd{C,C,N,S-pyl-SCHC(O)C₆H₄-2}]_n, [Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}L] (L = PPh₃, ^tBuNC, XyNC) or Me₄N[Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}Cl] upon acetonitrile loss, or its replacement by neutral or anionic ligands, respectively. Some such complexes act as metallaligands towards AgClO₄ or [PdCl₂(NCPh)₂] giving rise to heterodinuclear [{Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}(PPh₃)}{Ag(PPh₃)}]ClO₄ or homodinuclear [{Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}(Cl)}{Pd(μ-Cl)}]₂, [{Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}(Cl)}{Pd(Cl)(PPh₃}] complexes. Some derivatives of complexes 1 were also obtained.

Cyclopalladated benzamidoxime complexes [Pd{C,N-C₆H₄{C(NH₂)NOH}-2}Cl(L)] (L = PTol₃, Tol = C₆H₄Me-4 (2a); XyNC, Xy = C₆H₃Me₂-2,6 (2b); pic, C₅H₄Me-4 (2c)), [Pd{C,N-C₆H₄{C(NH₂)NOH}-2}(L₂)]ClO₄ (L = pic (3a); L₂ = 4,4′-di-tert-butyl-2,2′-bipyridine, tbbpy (3b)) and PPN[Pd{C,N-C₆H₄{C(NH₂)NOH}-2}Cl₂] (4) are prepared by reacting [Pd{C,N-C₆H₄{C(NH₂)NOH}-2}(μ-Cl)]₂ (1) with the appropriate neutral ligand or with [PPN]Cl, respectively. The cationic complexes are obtained in the presence of NaClO₄. The reaction of 2a with K^tBuO affords the dinuclear oximato complex [Pd{μ-C,N,O-C₆H₄{C(NH₂)NO}-2}(PTol₃)]₂ (5) or, in the presence of ClCH₂py·HCl, the pincer derivative [Pd{C,N,N′-C₆H₄{C(NH₂)NOCH₂(C₅H₄N-2)}-2}(PTol₃)]ClO₄ (6). Complex 2b reacts with XyNC to give the iminobenzoyl complex [Pd{C,N-C(NXy)C₆H₄{C(NH₂)NOH}-2}Cl(CNXy)] (7) resulting from the insertion of XyNC into the Pd–C bond. The dinuclear complex [{Pd(tbbpy)}₂{C,N,N′,O-C₆H₄{C(NH)NO}-2}]ClO₄ (8) bearing a bridging tetradentate benzimido(oximate) ligand is obtained by reacting Pd(OAc)₂ with tbbpy and the metal–ligand complex 3b. The crystal structures of complexes 2a, 6, 7 and 8 have been determined.