Reactivity of ortho‐Substituted Aryl–Palladium Complexes towards Carbodiimides, Isothiocyanates, Nitriles, and Cyanamides

Abstract

Complexes [Pd(C(6)H(3)XH-2-R'-5)Y(N;N)] (X=O, NH; Y=Br, I; R'=H, NO(2); N;N=N,N,N',N'-tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), 4,4'-di-tert-butyl-2,2'-bipyridine (dtbbpy)) react with RN=C=E (E=NR, S) or RC identical withN (R=alkyl, aryl, NR''(2)) and TlOTf (OTf=CF(3)SO(3)) to give, respectively, 1) products of the insertion of the C=E group into the C--Pd bond, protonation of the N atom, and coordination of X to Pd, [Pd{kappa(2)-X,E-(XC(6)H(3){EC(NHR)}-2-R'-4)}(N;N)]OTf or [Pd(kappa(2)-X,N-{ZC(6)H(3)(NH=CR)-2-R'-4})(N;N)]OTf, or products of the coordination of carbodiimides and OH addition, [Pd{kappa(2)-C,N-(C(6)H(4){OC(NR)}NHR-2)}(bpy)]OTf; or 2) products of the insertion of the C identical withN group to Pd and N-protonation, [Pd(kappa(2)-X,N-{XC(6)H(3)(NH=CR)-2-R'-4})(N;N)]OTf.

Reactivity towards nitriles, cyanamides, and carbodiimides of palladium complexes derived from benzyl alcohol. Synthesis of a mixed Pd2Ag complex

“…This negative result contrasts with the successful insertion reactions that we observed with the related complexes [PdI-(C 6 H 4 Y-2)(tmeda)] (Y = OH, NH 2 , N^N = tmeda, bpy, tbbpy), and a wide variety of nitriles 10,12 and cyanamides. 12 In those reactions we proposed that the electron-donating OH or NH 2 group in ortho position would play a key role in the mechanism, via delocalization of a negative charge on the aryl ipso carbon. 10,12 That mechanistic proposal would be now supported by the failure of these insertion reactions with the complexes I and II, for which the CH 2 link between the OH function and the aryl ring prevents the delocalization of electron density.…”

“…12 In those reactions we proposed that the electron-donating OH or NH 2 group in ortho position would play a key role in the mechanism, via delocalization of a negative charge on the aryl ipso carbon. 10,12 That mechanistic proposal would be now supported by the failure of these insertion reactions with the complexes I and II, for which the CH 2 link between the OH function and the aryl ring prevents the delocalization of electron density.…”

“…2 A valuable synthetic tool that we have extensively explored is the incorporation of a substituent at the ortho position of the aryl group, [3][4][5][6][7] as this substituent can become involved in the reactivity with the Pd centre and the organic substrate in many interesting ways. [3][4][5][6][8][9][10][11][12] Very often, the ortho-substitution also results in the formation of cyclopalladated complexes. 3,4,7,9,[10][11][12] Following this line of research, our group has previously investigated the reactivity of ortho-palladated phenol derivatives.…”

“…[3][4][5][6][8][9][10][11][12] Very often, the ortho-substitution also results in the formation of cyclopalladated complexes. 3,4,7,9,[10][11][12] Following this line of research, our group has previously investigated the reactivity of ortho-palladated phenol derivatives. 6,[10][11][12][13] Their reactions with CO, isocyanides, alkenes, alkynes, and allenes did not involve the OH group in the ortho position.…”

“…3,4,7,9,[10][11][12] Following this line of research, our group has previously investigated the reactivity of ortho-palladated phenol derivatives. 6,[10][11][12][13] Their reactions with CO, isocyanides, alkenes, alkynes, and allenes did not involve the OH group in the ortho position. 6,13 In contrast, the electron-donating ability of this group played a crucial role in the reactivity towards nitriles, 10,12 carbodiimides, 11,12 cyanamides, 12 and isothiocyanates, 12 which afforded the first examples of the insertion [10][11][12] of these molecules into a C-M bond of a late transition metal.…”