Dinuclear palladium–azido complexes containing thiophene derivatives: reactivity toward organic isocyanides and isothiocyanates

Abstract

Cyclopalladated tetranuclear Pd(II) complexes, [Pd2(micro-Cl)2(Y)]2 (Y = L1 or L2; H2L1 = di(2-pyridyl)-2,2'-bithiophene; H2L2 = 5,5''-di(2-pyridyl)-2,2':5',2''-terthiophene), containing two pyridyl-alpha, alpha'-disubstituted derivatives of thiophene were prepared. Treating these products with PR3 and subsequently with NaN3 produced the dinuclear Pd-azido complexes [(PR3)2(N3)Pd-Y-Pd(N3)(PR3)2] (Y = L1 or L2) or a cyclometallated complex [(PR3)(N3)Pd-Y'-Pd(N3)(PR3)] (Y' = C,N-L2). Reactions of these Pd-azido complexes with CN-Ar (Ar = 2,6-Me(2)C(6)H(3), 2,6-i-Pr(2)C(6)H(3)) or R-NCS (R = i-Pr, Et, allyl) led to the complexes containing end-on carbodiimido groups [(PMe3)2(N[double bond]C[double bond]N-Ar)Pd-Y-Pd(N[double bond]C[double bond]N-Ar)(PMe3)2] or S-coordinated tetrazole-thiolato groups {(PMe3)2[CN4(R)]S-Pd-Y-Pd-S[CN4)(R)](PMe3)2}. Interestingly, when treated with elemental sulfur, the carbodiimido complexes transformed into the cyclometallated derivatives, [(PMe3)(N[double bond]C[double bond]N-Ar)Pd-Y'-Pd(N[double bond]C[double bond]N-Ar)(PMe3)] (Y' = C,N-L1, C,N-L2). We also report the preparation of linear, thienylene-bridged dinuclear Pd complexes [L2(N3)Pd-X(or X')-Pd(N3)L2] (L = PMe3 or PMe2Ph; H2X = 2,2'-bithiophene or H2X' = 2,2':5',2''-terthiophene) and their reactivity toward organic isocyanide and isothiocyanates.

Azide Chemistry – An Inorganic Perspective, Part II[‡][3+2]‐Cycloaddition Reactions of Metal Azides and Related Systems

“…[108] In the cases studied by X-ray, metal to sulfur coordination was confirmed almost without exception. [52,53,55,60,61,64,65,391,392,[396][397][398] Still, contrary to different opinions, [108] spectroscopic data (IR, 1 H NMR) alone proved absolutely adequate to draw the right conclusion, as shown, e.g. by Beck's paper on transition metal complexes with anions of 1-substituted tetrazoline-5-thiones.…”

“…Kim and his group on the reactivity of azidopalladium and -platinum complexes toward organic isothiocyanates (as well as iso-cyanides, see chapter 4). [52,53,55,60,61,64,65] Recently Kim et al extended their studies to include chiral organic isothiocyanates whose absolute configurations were retained during the reactions. Moreover, the structural analyses of the resulting tetrazole-thiolato complexes revealed syn and/or anti conformations of the S-bound tetrazole rings.…”

“…Refs. [53,61,64,65] . [391,392] The majority of transition metal and main group element 1-R-5-thiotetrazoles, however, has not been derived from the cycloaddition reaction under discussion, but from direct metathesis (salt elimination) processes between metal salts [393][394][395] or their chloro complexes [396] and thiotetrazolate anions.…”

“…This has been interpreted as initial stage of a reaction pathway ultimately generating an η 5 -CN 4 -Pb interaction. [196] The above-mentioned discrepancy between the calculations of the relative stabilities of the two possible linkage isomers VI and VII (Scheme 15) which clearly favour N 4 coordination, [56] and the recent accumulated experimental evidence of 'S-coordination without exception', [52,53,55,60,61,64,65,[390][391][392][396][397][398] has been resolved by a detailed study of the reaction mechanisms. [56] According to that, a two-step process occurs in which the isothiocyanate Satom first approaches the metal with simultaneous attack by the azide N α -on the isothiocyanate C-atom to give an intermediate S-bonded imidoyl azide, XVI, strongly reminiscent of the imidoyl azide intermediate previously found in the theoretical study on the mechanism of azidometal to nitrile [3+2]-cycloadditions (cf.…”

Synthesis and Reactivity of Dinuclear Ni(II) Azido Complexes Containing Bithienylene or Terthienylene Bridging Ligands

“…14,15 Those complexes exhibited interesting reactivity toward organic isocyanides or isothiocyanates. However, Ni(II) analogues are still unknown, which are believed to be useful precursors or intermediates in Ni-catalyzed syntheses of oligomeric thienylene or polymeric thienylenes.…”