Attempts To Prepare Palladium(II) Complexes with the O,C,O Pincer Aryl Ligand C₆(NO₂)₂-2,6-(OMe)₃-3,4,5

Abstract

The complex [HgR2] (R = C6(NO2)2-2,6-(OMe)3-3,4,5-C1 (2)), obtained by thermal decomposition of [Hg(O2CR)2] (1), reacts with Q2[Pd2Cl4(μ-Cl)2] to give [Hg(R)Cl] (3) and Q2[Pd(R)Cl(μ-Cl)]2 (Q = (PhCH2)Ph3P (4a), Me4N (4b)), which react (i) with Tl(acac) (1:2, acac = acetylacetonate) to give Q[Pd(R)Cl(O,O-acac)] (Q = (PhCH2)Ph3P (5a), Me4N (5b)) or (ii) with AgClO4 (1:2) to give [Pd(κ3-R)Cl] (κ3-R = κ3-C6(NO2)2-2,6-(OMe)3-3,4,5-C1,O,O‘ (6)), which can also be obtained by reacting 5a with HBF4. Complex 6 reacts with p-toluidine (1:1, L) to give [Pd(R)(μ-Cl)L]2 (7). Complex 5b decomposes in a mixture of acetone/water to give [Pd(κ2-R)(O,O-acac)] (κ2-R = κ2-C6(NO2)2-2,6-(OMe)3-3,4,5-C1,O (8)), which reacts (i) with neutral monodentate ligands to give [Pd(R)(O,O-acac)L] (L = PPh3 (9), pyridine (py) (10), tetrahydrothiophene (11)), (ii) with bis(diphenylphosphino)methane (dppm) to give a complex that readily oxidizes to give [Pd(R)(O,O-acac)(dppmO)] (dppmO = monoxide of bis(diphenylphosphino)methane (12)), (iii) with 1,10-phenanthroline (phen) to give [Pd(R)(C-acac)(phen)] (13), and (iv) with protonated ligands (HL)ClO4 to give 10 (L = py) or cis-[Pd(R)(H2O)2(PPh3)]·H2O (L = PPh3 (14)). Trifluoromethanesulfonic acid (HOSO2CF3) reacts with 9 and PPh3 or with 13 to give trans-[Pd(R)(OSO2CF3)(PPh3)2] (15) or [Pd(R)(OSO2CF3)(phen)] (16), respectively. The X-ray crystal structures of 7·2CH 2 Cl 2 , 8, 10, and 14·H 2 O have been determined.

Study of the Reactivity of 2-Acetyl-, 2-Cyano-, 2-Formyl-, and 2-Vinylphenyl Palladium(II) Complexes. Mono- and Triinsertion of an Isocyanide into the Pd−C Bond. A 2-Cyanophenyl Palladium Complex as a Ligand

“…We have named this destabilizing effect transphobia (T), a term that has already been accepted by many authors. [19][20][21][49][50][51][52][53][54] When the product of a reaction contains a pair of ligands with high T in trans positions, one of which is generally a C-donor, a further reaction such as an X-Y coupling process (X ) C, Y ) C, N, O, P), 2,20,49,55,56 an insertion of atmospheric O 2 into the C-Pd bond, 19,20 or an intramolecular redox reaction usually takes place. 57,58 In contrast, if the two pairs of trans ligands have low T, the reaction product tends to be stable.…”

The Mechanisms of the Stille Reaction

“…The destabilizing interaction between pairs of ligands (in this case a phosphane ligand and a trans C-donor ligand) in Pd II complexes has been named transphobia, [55] an effect that results in the enhanced kinetic reactivity of such complexes in ligand substitution reactions. [56] A recent study on the oxidative addition of a series of aryl iodides with different Hammet parameters to [Pd(PPh 3 ) 4 ] confirmed that in all cases the oxidative addition step initially gives cis-[PdArI(PPh 3 ) 2 ]. [57] These cis complexes undergo isomerization to trans-[PdArI(PPh 3 ) 2 ] at very different rates, and sometimes extremely fast.…”

“…[143] The resulting species are cis complexes with an apparently open coordination site trans to the aryl group. [55,56] Two of these apparently three-coordinate complexes, [PdPhBr{P(1-Ad)tBu 2 }] (19) and [Pd(2,4-Me 2 C 6 H 3 )I(PtBu 3 )] (20), were structurally characterized. In both complexes there are agostic interactions between the Pd center and the CÀH bonds of the phosphane.…”

Untitled

“…Organometal compounds containing monoanionic L,C,Lcoordinating ligands such as [C 6 H 3 (CH 2 L) 2 -2,6] Ϫ (L ϭ NR 2 , PR 2 , SR) [1] and [C 6 (NL 2 ) 2 -2,6-(OMe) 3 -3,4,5] Ϫ (L ϭ O) [2] are well-studied, and most of these compounds show hypercoordination at the metal site as a result of intramolecular donor acceptor contacts. In recent papers we reported the application of the novel organolithium compound {2,6-[P(O)(OEt) 2 ] 2 -4-tert-Bu-C 6 H 2 }Li (1-Li) to the synthesis of intramolecularly coordinated organosilicon [3,4] and organotin [5Ϫ8] derivatives.…”