Alkene and Carbon Monoxide Insertion Reactions of Nitrogen-Coordinated Monoorganopalladium(II) Complexes: The Stepwise Construction of Alternating Copolymers of CO and Alkenes on a Palladium(II) Center

Abstract

The stepwise synthesis of a palladium(II) bo&d altemating oligomer of CO and strained alkenes is described together with the factors that allow full control of each successive step. The sequence starts with acetylpalladium-(11) complexes PdX(COMe)(N-N) (2,4), (X = Cl(a), Br(b), or I(c); N-N = N,N,","-tetramethylethylenediamine (tmeda) or 2,2'-bipyridyl (bpy)). The bpy-coordinated acetyl complexes (4a-c) show an unexpected isomerization reaction of the groups around the metal center for which thermodynamic parameters have been determined. A mechanism for the isomerization is proposed. The ionic complexes [Pd(COMe)(MeCN)(N-N)]OTf (5, 6; OTf = trifluoromethanesulfonate), obtained in situ from reaction of 2a-c and 4a-c with AgOTf, react with a number of alkenes. Nonstrained alkenes do insert, but decomposition (probably involving B-elimination) is fast. Alkenes containing potential donor groups do not insert at all. Only in the case of strained alkenes like norbomene and its derivatives were the insertion products isolated and fully characterized by I3C NMR, IR, and X-ray analysis. Crystals of the dicyclopentadiene insertion product [Pd(C1$I12COMe)(bpy)]OTf (8c) are monoclinic, space group P21/n, a = 8.3086(4) A, b = 15.3894(6) A, c = 18.1479(9) A, B = 99.98(1)', V = 2285.36(19) A3, Z = 4, R = 0.042 (wR = 0.034). Here, the alkene insertion has occurred in cis,exo fashion on the norbomene-type alkene moiety, indicating this reaction to be both stereo-and chemoselective. The molecular structure shows that the acyl group is coordinated to the metal. Products resulting from a second CO insertion into the Pd-C bond of 8a, i.e. PdX(COC7HloCOMe)-(bpy) (X = C1 (12a) or I (12b)), were formed in the presence of a large excess of a sodium halide salt. Reaction of 12a,b with AgOTf and norbomene gave the alkyl complex [ P~( C~H I~C O C~H I~C O M~) (~~~) ] O T~ (Ua). Norbomadiene was inserted similarly. Attempted recrystallization of the insertion product of 5-norbomene-endu-2,3-dicarboxylic anhydride (13c) gave the alkyl complex 8a. This is the first example of a reversible alkene insertion reaction on an isolated palladium complex. Addition of CO and excess NaI (20 equiv) to 13a gave the neutral acyl complex P~I ( C O C~H~~C O C~H I~C O M~) (~~~) (14), the first isolated and fully characterized CO/alkene oligomer still connected to the palladium(I1) catalytic site. Crystals are triclinic, space group P i with a = 10.128(2) A, b = 11.655(2) A, c = 13.633(2) A, a = 109.89(1)', / 3 = 100.58(1)0, y = 92.92(2)', V = 1476.3(4) A3, Z = 2 and R = 0.044 (wR = 0.057). Norbomadiene also reacts with 2 equiv. of 5 or 6 to give the homoligated dinuclear complexes [(N-N)P~((C~H~)(COM~)~-~,~}P~(N-N)](OT~)Z with N-N = tmeda (9) or bpy (10). Crystals of 9 are orthorhombic, space group P212121, a = 11.176(3) A, b = 11.362(1) A, c = 30.394(3) A, V = 3859(1) A3, Z = 4, wR2 = 0.124, R = 0.049.In this complex a double alkene insertion reaction has taken place involving both alkene functionalities of a dialkene: 9 is symmetrically substituted with the ...

η1- and η3-Allylpalladium(II) Complexes Bearing Potentially Tridentate Ligands: Synthesis, Solution Dynamics, and Crystal Structures

“…[22] The palladiumϪcarbon bond lengths (2.036Ϫ2.075 Å ) agree with the moderate trans influence of pyridine. [23] We also note that the angle between the plane defined by the three allylic carbons and the coordination plane (mean plane defined by the four coordinating atoms) is roughly the same for both complexes [3a: 109.6(6)°; 5a: 111.9(2)°and 109.1(3)°]. Finally, a distinct medium-intensity ν CϭC band can be detected at approximately 1630 cm Ϫ1 in the IR spectra of both dimethylallyl complexes (3: 1629 cm Ϫ1 ; 6: 1634 cm Ϫ1 ), which is characteristic of an η 1 -allyl complex.…”

Coordination chemistry of 1,1′-bis(2-pyridyl)ferrocene in palladium(II) and platinum(II) complexes and reaction of (BPF)Pd(Me)Cl with CO. X-ray structure of (1,1′-bis(2-pyridyl)ferrocene)Pd(Me)Cl and (1,1′-bis(2-pyridyl)ferrocene)[PtCl2(CH2  CH2)]2

“…Nevertheless, many palladium complexes containing nitrogen-based ligancls have been synthesized and CO insertions into palladium--carbon bonds of these complexes have been carried out [10,[13][14][15]. Unexpectedly, a faster reaction rate is observed when, instead of bidentate phosphine ligands, bidentate nitrogen ligands are used [13].…”

Insertion of CO and Strained Olefins into Organometallic (Ferrocenylmethyl)phosphane Palladium Complexes

“…pounds, which could have been generated from double insertion of both NBD C=C bonds into Pd-Ac bonds, [21] was ever observed, even when an equimolar amount of NBD was added to 6. Moreover, complex 7 was completely inert with respect to the insertion of a second CO molecule.…”