Insertion of internal acetylenes into orthopalladated α-methylbenzylamine. Crystal structure of [Pd{C(Ph)C(Ph)C(Ph)C(Ph)C₆H₄CH(Me)NH₂}Br]

Abstract

The complex [Pd{C,H,CH (Me)NH,}( Me,CO),]CIO, reacted with diphenylacetylene to give [ Pd2(q5-C,Ph,),(p-q2-PhC=CPh)]. A pathway for this reaction is suggested. Species related with the postulated intermediates can be isolated starting from [{Pd[C,H,CH( Me) NH,] (p-Br)},] which reacts with disubstituted alkynes (RCECR, R = C0,Me or Ph) to afford [Pd{C(R)=C(R)C(R)=C(R)C,H,CH-(Me)NH,}Br) (R = C0,Me l a or Ph 1 b) through a double insertion of the alkyne into the Pd-C bond. Complex l a reacted with 1 equivalent of MeO,CC=CCO,Me to give the tri-insertion reaction product 2. These are the first products of alkyne insertion into a cyclopalladated primary amine. Neutral ligands, s u c h as pyridine (py) or CO, can break the Pd-n-olefinic bond in l a to give the corresponding adducts [Pd{C(R)=C(R)C(R)=C(R)C,H,CH(Me)NH,}Br(L)] ( R = C0,Me; L = py 3 or CO 4). Complexes l a and 1 b reacted with AgCIO, (1 : 1 ) in acetone to afford AgBr and [Pd{C(R)=C(R)C(R)=C(R)C,H,CH(Me)NH2}(solv)]CI0, (R = CO,Me, solv = H,O 5a; R = Ph, solv = Me,CO 5b). The reaction of complex l a with AgCIO, (1 :1) and excess of pyridine gave the cationic complex [Pd{C(R)=C(R)C(R)=C(R)C,H,CH(Me)NH,}(py),]CIO, 6 ( R = C0,Me). The crystal structure of complex l b has been determined by X-ray diffraction. The palladium atom is bonded to Br, N, C ( l ) and to the midpoint of the C(3)-C(4) double bond in a distorted square-planar geometry.The metakarbon bond in orthopalladated tertiary amines undergoes insertion reactions with, for example, carbon monoxide, alkenes, acyl halides and alkynes, 5-7 and, upon decomposition, can afford interesting organic compounds. 5 * 8 , 9 These compounds have therefore attracted great interest in organic synthesis.Recently we have described the orthopalladation of amethylbenzylamine. ' We were interested in the reaction of these cyclometallated primary amines with alkynes, first because such reactions have not been reported yet and, secondly, because a different behaviour from their analogous complexes containing tertiary amines is expected. Thus, more stable insertion products are predicted due to their greater basic character and therefore there exists the possibility of studying the reactivity of such mono-or di-inserted complexes with different ligands to afford new types of organopalladium complexes. This is the main objective of the present work. The only reported reactions of cyclopalladated primary amines are those of CO or isocyanides with cyclopalladated benzylamine affording, after insertion and depalladation, phthalimidine or isoindolinimines, respectively. However, these results were published some time ago as a preliminary comm~nication.~

Reactivity of cyclopalladated compounds derived from biphenyl-2-ylamine towards carbon monoxide, tbutyl isocyanide and alkynes

“…Thus, these compounds adopt the structure found in most organopalladium compounds derived from the insertion of two alkyne molecules into the C-Pd r bonds of five-and six-membered cyclopalladated compounds, in which the resulting butadienyl fragment presents a trans-cis configuration and is g 2 -j 1 coordinated to the palladium(II) centre [16]. Distances and angles around the palladium(II) centre in compounds 5 and 6 were within the normal range for this kind of organopalladium compound [20,24,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. As expected (i) the carbon-carbon distances of the alkene units coordinated g 2 to the palladium(II) centres were larger than the carbon-carbon distances of the alkene units coordinated j 1 to the palladium(II) centres À1.409(3) Å and 1.325(3) Å for compound 5 and 1.387(6) Å and 1.376 (7) Å for compound 6 -and (ii) the alkene units coordinated g 2 to the palladium(II) centre were no longer planar -the dihedral angles C14-C13-C20-C21 for compound 5 and C14-C13-C16-C17 for compound 6 were 152.1(2)°a nd 164.5(4)°, respectively.…”

A comparative study of the reactivity of the σ(Pd–Csp2, ferrocene) and σ(Pd–Csp2, biphenyl) bonds in cyclopalladated complexes derived from [Fe(η5-C5H5)(η5-C5H4CHNC6H4C6H5-2)]

“…separated by van der Waals contacts. The palladium atom is four-co-ordinated, since it is bound to a chlorine, the nitrogen atom, the terminal carbon of the η 3 -butadienyl fragment [C (12)] and the middle point of the segment defined by atoms C(18) and C (21), hereinafter referred to as χ. A slightly distorted square-planar environment is the result.…”

“…[11][12][13][14][15] However, one of the main interests of this sort of compounds is based on their use as precursors for organic or organometallic synthesis. [16][17][18][19][20][21][22][23][24][25][26][27][28][29] For instance, cyclopalladated complexes show high reactivity towards a wide variety of substrates, such as CO, isocyanides, alkenes or alkynes. [16][17][18][19][20][21][22][23][24][25][26][27][28] Reactions of this kind have provided new procedures for the syntheses of novel organic compounds.…”

“…[16][17][18][19][20][21][22][23][24][25][26][27][28][29] For instance, cyclopalladated complexes show high reactivity towards a wide variety of substrates, such as CO, isocyanides, alkenes or alkynes. [16][17][18][19][20][21][22][23][24][25][26][27][28] Reactions of this kind have provided new procedures for the syntheses of novel organic compounds. Several examples of mono-, bis-and even tris-(insertions) of alkynes into the σ(Pd-C sp 2 , aryl ) bond have been reported for cyclopalladated complexes derived from organic N-donor ligands.…”

“…Several examples of mono-, bis-and even tris-(insertions) of alkynes into the σ(Pd-C sp 2 , aryl ) bond have been reported for cyclopalladated complexes derived from organic N-donor ligands. [16][17][18][19][20][21][22][23] However, only a few articles involving insertions of alkynes into the σ(Pd-C sp 2 , ferrocene ) bond have been reported so far, [25][26][27][28][29][30] and most of them focus exclusively on the insertion of diphenylacetylene.…”