Cyclopalladation of 1,1′‐Azonaphthalene (= Di(naphthalen‐1‐yl)diazene): Isolation and characterization of two isomeric complexes

Abstract

The cyclopalladation of 1 ,l'-azonaphthalene (= di(naphtha1en-I -yl)diazene; 2) with bis(hexafluoroacety1-acetonato)palladium(II) (3; [Pd(hfa),]) yields the ortho-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-fc20,0')[i -(naphthalen-l-ylaro-~~2)naphthalen-2-yl-~Cz]palladium(II) (4) as well as the peri-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-d~onato-~~0,O)[8-(naphthalen-l-ylazo-~~~)naphthalen-l-yl-~C']-palladium(I1) (5); their structures were corroborated by X-ray analyses. The formation of the novel peri-metallated product 5 containing a six-membered palladacycle strongly depends upon the reaction conditions.Introduction. -The cyclometallation reaction -albeit described for the first time some 25 years ago [l] [2] -still has an enormous potential as a synthetic tool when employed for the ortho-functionalization of suitable arenes [3 -81. Only recently, cyclopalladated complexes were described that catalyze the Heck olefination [9] or aryl-coupling reactions [lo] in homogeneous solution with high turnover numbers. Other cyclopalladated complexes exhibit some promising liquid-crystalline [ l l -131 or photochemical and electrochemical [14-161 properties. The cyclometallation principle can also be applied effectively to the laboratory-scale syntheses of dyestuff molecules and dyestuff precursors [17].Whereas the papers on investigations of the C-H activation at phenylic ortho-positions 'are copious, far less has been reported on the cyclometallation of naphthalene moieties so far [6][18-281, despite the fact that the naphthalene ring is more reactive towards electrophilic cyclometallating agents. Furthermore, naphthalenes with donorbearing substituents at C( 1) offer both the ortho-and the peri-position for the cyclometallation.To make 1-substituted naphthalenes like naphthalen-1-amine (1) amenable to cyclopalladation, they have to be converted into suitable donor-bearing cyclometallands, as, e.g., the corresponding 1 ,If-azonaphthalene (= di(naphtha1en-1-y1)diazene ; 2). Transforming the original naphthalen-1-amine (1) into the symmetrical 1 ,l'-azonaphthalene (2) has several advantages: this cyclometalland is providing a donor atom for each of the two naphthalene moieties, and the desired functional groups can be introduced into both rings by two separate metallation/cleavage sequences. Finally, the bis-ortho-substituted azonaphthalene would yield two identical ortho-functionalized naphthalen-1-amines upon complete reduction of the azo bridge.The cyclopalladation of the unsubstituted 1 ,l'-azonaphthalene (2) is expected to occur at the C(2) center ortho to the azo bridge, as was shown earlier for various 1 -(phenylazo)naphthalenes [26] [27]. There, the naphthalene peri-position (C(8)) was only

Reactions of Cyclopalladated Complexes with Lithium Diphenylphosphide

“…The observed intramolecular trans-cyclopalladation is especially interesting considering that cyclopalladation of ( S C )-2,4-dibenzyl-2-oxazoline under different conditions results exclusively in the formation of CPC ( S C , S C )- 15 with the endo-palladacycle . However, this case of intramolecular trans-cyclopalladation is not unique; this type of transformation has been previously reported for other CPCs under different conditions. − …”

A Theoretical Assessment of the Thermodynamic Preferences in the Cyclopalladation of Amines

“…[8] However, there are some recent examples of six-membered rings with primary benzyl- [10,30] and ferrocenylamines, [27e] and also with heterocycles. [31] Five-or six-membered rings can be obtained in the cyclopalladation of imines depending on the reaction conditions; [15,32] however, examples with six-membered metallacycles are less common than their five-membered counterparts. [1] In order to test the importance of the ring size we performed calculations with four-, five-, and six-membered rings, both for primary and for tertiary amines (Table 3).…”

Regioselective functionalization of iminophosphoranes through Pd-mediated C–H bond activation: C–C and C–X bond formation

“…While similar isomerizations reported the use of acidic medium as acetic acid, 32 very few have been reported in aprotic media. 33 The transformation of 13exo into 13endo in non protic solvents seems to suggest an intramolecular transfer of the proton, assisted by the basic acetate ligand, although the participation of the solvent in the proton transfer (mainly in the case of toluene) could not be discarded. 34 The X-ray determination of the molecular structure of complex 13exo confirms the structure proposed here.…”