The First Complexes with Two Metallacycles Fused Around a Common Aryl Substituent: “Akimbo” Complexes

Abstract

Following the reaction sequence i) oxidative addition of RNHC(O)C6H3I2-2,6 (R = Me, Tol) to [Pd2(dba)3]·dba in the presence of chelating ligands N∧N or XyNC (Xy = C6H3Me2-2,6), ii) treatment of the resulting complexes with TlTfO or Tl(acac) (acac = acetylacetonato), and iii) insertion of unsaturated molecules (CO, XyNC, MeO2CCCCO2Me, MeC(O)CHCH2) into one of the Pd–Caryl bonds of the resulting complexes allowed the synthesis of aryldipalladated complexes containing the ligands L1 = μ-C,C-{C6H3C(O)NHR}-2,6, L2 = μ-C,C-{C6H3C(O)NHMe}(CNXy)2-2,6, L3 = μ-C,O,C-{C6H3C(O)NHMe}-2,6, L4 = μ-C,O,C,N-{C6H3C(O)NR}-2,6, L6 = μ-C,N,C,O-{C6H3C(O)NR}-2-(CO)-6, L7 = μ-C,N,C,O-{C6H3C(O)NR}-2-{C(CO2Me)C(CO2Me)}-6, L8 = μ-C,N,C,O-{C6H3C(O)NR}-2-(CNXy)-6 and two arylmonopalladated complexes with the ligands L5 = C,O-{C6H4C(O)NHMe}-2 and L9 = C,N-{C6H3C(O)NTol}-2-{CHCHC(O)Me}-6. The complex with the ligand L7 inserted CO into the second Pd–Caryl bond to give an L10-Pd2 complex (L10 = μ-C,N,C,O-{C6H3C(O)NTol}(CO)-2-{C(CO2Me)C(CO2Me)}-6. The dipalladated species display a different environment for each palladium atom and represent the first systems containing two 5 + 5, 5 + 6, 5 + 7, or 6 + 7-membered palladacycles condensed over the central benzamide group. The two arms of the ligands L4 and L6-L8 and L10 are “akimbo”, and we coin this name both for the ligands and for the dimetallic complexes bearing them. The crystal structure of a [{Pd(N∧N)}2L6]+ complex has been determined.

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

“…Mononuclear analogues to 9 have been previously prepared by insertion reactions of XyNC into C−Pd bonds of arylpalladium complexes. 9,13,15,17,18,25,26,79 Three dinuclear complexes with a similar pattern around the Pd atoms have also been reported by our group: one of them was obtained by oxidative addition, instead of insertion into an already formed complex, 19 and in the other two compounds the Pd atoms were not on the same aryl ring. 18 The tri-inserted complexes 10 and 10* form as a mixture of isomers (1:0.3 ratio) by oxidative addition of trans,trans-2,5-distyryl-2,4-dibromobenzene to [Pd(dba) 2 ] in the presence of 8 equiv of XyNC.…”

“…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).…”

“…The reactivity toward XyNC of the mixture of trans,trans-2,5distyryl-2,4-dibromobenzene and "[Pd(dba) 2 ]" ([Pd 2 (dba) 3 ]• dba; dba = dibenzylideneacetone) and also of the dipalladated derivatives [C 6 H 2 {PdBr(N ∧ N)} 2 -1,4-((E)-CHCHPh) 2 -2,5] (N ∧ N = tbbpy, tmeda) has also been investigated, resulting in the tri-and monoinsertion of the isocyanide into C−Pd bonds, respectively. 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).…”

Stepwise cyclopalladation of 2-phenacylthiopyridine to give C,C,N-pincer complexes

“…Transmetallation reactions between C and [PdCl 2 (NCPh) 2 ] or deprotonation of B with Na 2 CO 3 allowed the syntheses of dinuclear complexes D. Reactions of complex B or D (R = Ph) with excess Na 2 CO 3 , which we carried out in an attempt to prepare pincer complexes resulting from the additional cyclometalation of the phenyl group, were unsuccessful. This was not surprising because, although double C-H activation processes leading to various types of doubly cyclopalladated compounds are well known, 15 cyclometalation reactions involving two C-H bond activations per metal atom are very rare, not only for palladium 8,9,13 but also for any metal. 16 However, in this paper we report that using AgOAc as a base it is possible to prepare, from complex D (R = Ph), pincer complexes bearing a dianionic C(sp 2 ),C(sp 3 ),Ndonor ligand.…”