Carbopalladation of Maleate and Fumarate Esters and 1,1-Dimethylallene with Ortho-Substituted Aryl Palladium Complexes

Abstract

Dimethyl maleate and dimethyl and diethyl fumarates (RO2CCHCHCO2R) have been reacted with [Pd(C6H4Ro-2)Y(N∧N)] (Ro = OH, CHO, CN, Y = Br, I, N∧N = tmeda, bpy, dtbbpy; 1:1:4.5 molar ratio) and TlOTf to afford complexes resulting from the stereoselective insertion of the olefin and coordnation to Pd of one carbonyl oxygen, giving an enantiomeric mixture of the five-membered metallacyclic complexes [Pd{κ2 C,O-2-[CH(CO2R)CHCO2R]C6H4Ro}(N∧N)]OTf (R = Me, Et). From dimethyl maleate, the isolated complexes were RR/SS mixtures with Ro = OH, N∧N = tmeda (2aOH), dtbbpy (2cOH) and N∧N = bpy, Ro = CHO (2bCHO), CN (2bCN) and from the fumarates RS/SR mixtures with N∧N = bpy, Ro = CHO, R = Me (3bCHO), Et (4bCHO). Complex 2bCHO reacts with RNC in a 1:1 or 1:3 molar ratio to give the complexes [Pd{2-[CH(CO2R)CHCO2R]C6H4CHO}}(CNR′) n (bpy)3−n ]OTf (R = Me, n = 1, R′ = Xy (5bCHO), tBu = (6bCHO); n = 3, R = Xy (7bCHO), tBu = (8bCHO)). Similarly, the fumarate derivative 3bCHO or 4bCHO afforded the corresponding complexes where R = Me, n = 1, R′ = Xy (9bCHO), n = 3, R′ = tBu (10bCHO) or R = Et, n = 3, R′ = Xy (11bCHO), tBu (12bCHO), respectively. 1,1-Dimethylallene reacts with [Pd(C6H4OH-2)I(N∧N)] to give the η3-allyl complexes [Pd{η3-CH2C(C6H4OH-2)CMe2}(N∧N)]OTf (N∧N = tmeda (13aOH), dtbbpy (13cOH)). The crystal structures of 2aOH, 4bCHO, 7bCHO, and 13aOH have been determined.

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

“…Other NOE and correlation data confirm these structures and allow the assignment of the different groups within the molecules (see the ESI †). For 3a,b and 6, the position of the proton at the uncoordinated N is also confirmed by the 1 H-NOESY and 1 H, 13 C-HMBC spectra, and is similar to that observed in the related complexes resulting from the reaction of carbodiimides with ortho-palladated phenol derivatives. 11,12 The CvNH proton in complex 1 resonates at much higher frequency (δ 8.45 ppm) than in 2a,b (δ 4.81 and 4.76 ppm), for which the partial release of the lone pair from the NR 2 group results in a resonance form with a negative charge at the NH group.…”

“…For the complexes 1-5, the insertion of the organic molecules (MeCuN, R 2 NCuN, or RNvCvNR) into the O-Pd bond, and not the C-Pd bond, is confirmed by the three-bond correlation between the inserted iminic CvN carbon and the methylenic CH 2 OH protons, observed in the 1 H, 13 C-HMBC spectra. For complex 6, in contrast, a three-bond correlation between the iminic CvN carbon and the o-H of the aryl ligand is observed.…”

“…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. These insertion reactions occurred together with the deprotonation and coordination of the hydroxyl oxygen to Pd, forming 6-membered chelate rings (Chart 1).…”

“…Thermal ellipsoid plot (50% probability level) of 3a. Selected bond lengths (Å) and angles (°): Pd-C(1) = 1.9716(15), Pd-N(1) = 2.0313(13), Pd-N(21) = 2.0331(13), Pd-N(31) = 2.1157(12), O(1)-C(7) = 1.4567(19), O(1)-C(8) = 1.3350(19), C(8)-N(1) = 1.3054(18), C(8)-N(2) = 1.346(2), C(9)-N(1) = 1.494(2), C(12)-N(2) = 1.4658(19); C(1)-Pd-N(1) = 84.69(6), C(1)-Pd-N(21) = 98.38(6), N(1)-Pd-N(31) = 97.75(5), N(21)-Pd-N(31) = 79.53(5), N(1)-Pd-N(21) = 175.14(5), C(1)-Pd-N(31) = 174.44(6), C(7)-O(1)-C(8) = 123.79(12), O(1)-C(8)-N(1) = 125.21(14), O(1)-C(8)-N(2) = 111.20(13), N(1)-C(8)-N(2) = 123.58(16), C(8)-N(1)-Pd = 125.84(12).…”

Allenes and computational chemistry: from bonding situations to reaction mechanisms

“…Finally, a nucleophilic attack by Nu À leads to the expected adducts 81 and/or 82 depending on the individual substrates and reaction conditions. The isolation of Z 3 -allylpalladium intermediate 120 and its structural characterization by using X-ray analysis support this mechanism.…”