Condensation reactions of monomeric hydroxo palladium complexes with active methyl and methylene compounds

Abstract

Heating a suspension of the monomeric hydroxo palladium complex of the type [Pd(N-N)(C(6)F(5))(OH)](N-N = bipy, Me(2)bipy, phen or tmeda) in methylketone (acetone or methylisobutylketone) under reflux affords the corresponding ketonyl palladium complex [Pd(N-N)(C(6)F(5))(CH(2)COR)]. On the other hand, the reaction of the hydroxo palladium complexes [Pd(N-N)(C(6)F(5))(OH)](N-N = bipy, phen or tmeda) with diethylmalonate or malononitrile yields the C-bound enolate palladium complexes [Pd(N-N)(CHX(2))(C(6)F(5))](X = CO(2)Et or CN), and the reaction of [Pd(N-N)(C(6)F(5))(OH)](N-N = bipy or phen) with nitromethane gives the nitromethyl palladium complexes [Pd(N-N)(CH(2)NO(2))(C(6)F(5))]. [Pd(tmeda)(C(6)F(5))(OH)] catalyses the cyclotrimerization of malononitrile. The crystal structures of [Pd(bipy)(C(6)F(5))(CH(2)COMe)].1/2Me(2)CO, [Pd(tmeda)(C(6)F(5))[CH(CO(2)Et)(2)]], [Pd(tmeda)(C(6)F(5))[CH(CN)(2)]] and [Pd(tmeda)(C(6)F(5))(CH(2)NO(2))].1/2CH(2)Cl(2) have been established by X-ray diffraction.

C–H Bond Activation by a Palladium(II) Thioether Complex: Formation of the Bis(nitromethanate) Complex [Pd(9S3)(CH2NO2)2]

“…Also, we note that the red solid of complex 2 is only stable in solution in the presence of excess nitromethane (the color changes from red to green upon attempting to isolate). In methanol- d 4 , the nitromethanate resonances are observed at 4.83 and 4.78 ppm (two protons for each resonance) in the 1 H NMR spectrum, which match chemical shifts in other reported Pd(II) nitromethanates. , We observe no coalescence of these two peaks at temperatures up to 55 °C and believe that the appearance of two different proton resonances arises from each of the nitromethanate ligands being in a different structural environment (see discussion below). There is only one prior report of bis(nitromethanate) complexes with any transition metal (by Milani and co-workers), but all of those complexes showed equivalent CH 2 NO 2 ligands at room temperature .…”

“…We have identified 14 examples in the CSD which contain one nitromethanate ligand coordinated to a transition-metal ion (see the Supporting Information for a listing of these 14 structures; as noted, there are no CSD examples with two ligands) . These cases include Ir organometallic complexes, , Pt terpy complexes, , Co cobalamins, − A-frame Au and Pd complexes, , Cd and Co polynuclear complexes, , and mononuclear Pd(II) complexes. , Approximately half of these structures contain nitromethanates with resonance in their N–O bonds. In contrast to the resonance observed in the up ligand, the out nitromethanates display slightly differing N–-O bond lengths at 1.238(8) and 1.218(9) Å, with the shorter N–O bond (N2–O4) directed toward the axial sulfur and away from the square plane.…”

“…27 These cases include Ir organometallic complexes, 10,29 Pt terpy complexes, 13,30 Co cobalamins, 31−33 A-frame Au and Pd complexes, 15,34 Cd and Co polynuclear complexes, 35,36 and mononuclear Pd(II) complexes. 12,14 Approximately half of these structures contain nitromethanates with resonance in their N−O bonds. In contrast to the resonance observed in the up ligand, the out nitromethanates display slightly differing N−-O bond lengths at 1.238 (8) donor effects, with the up being the better trans donor of the two.…”

“…11 Most germane to the work presented here, there have been a few reports of Pd compounds that react with nitromethane to form Pd complexes that bear a single nitromethanate ligand. However, each of these examples requires vigorous reaction conditionsthe addition of an external strong base such as NaOH, 12 an inner coordination sphere hydroxide ligand, 13,14 or a Pd(I)−Pd(I) metal−metal σ-bond. 15 The complexation properties of the tridentate ligand 1,4,7trithiacyclononane (9S3) and related thia crowns have been extensively explored during the past 30 years.…”

Pentafluorophenyl imidato palladium(ii) complexes: catalysts for Suzuki cross-coupling reactions

“…We have recently described 34, 35 the synthesis of monomeric hydroxo palladium(II) complexes of the type [Pd(N-N)(C 6 F 5 )(OH)] (N-N = bipy, Me 2 bipy, phen or tmeda) and their reactions with CO or SO 2 in methanol at room temperature to yield the corresponding methoxy carbonyl or alkylsulfito complexes [Pd(N-N)(C 6 F 5 )(X)] (X = CO 2 Me or SO 3 Me)]. We have also shown 36 the reactions of the monomeric hydroxo complexes [Pd(N-N)(C 6 F 5 )(OH)] with some active methyl (CH 3 COR or CH 3 NO 2 ) and methylene (CH 2 X 2 ) (X = CO 2 Et or CN) to yield the corresponding C-bound enolate palladium complexes.…”