Synthesis and Characterization of Organopalladium Complexes Containing a Fluoro Ligand

Abstract

The synthesis of organopalladium complexes containing a fluoro ligand, [(Ph3P)2Pd(F)R], is described. Two general synthetic strategies have been developed: (i) neutralization of hydroxo palladium dimers, [(Ph3P)2Pd2(R)2(μ-OH)2] (R = Me or Ph), with TREAT HF ([(HF)3·NEt3]) in the presence of PPh3 and (ii) the ultrasound-promoted exchange between [(Ph3P)2Pd(I)R] and AgF in benzene. It is essential for the synthesis with TREAT HF that no excess of the HF source is used; otherwise, the corresponding bifluorides, [(Ph3P)2Pd(FHF)R], are formed instead. Conducting the I/F exchange in the presence of 5−10% of the corresponding organic iodide, RI, is beneficial for purity of the desired fluoro complexes. All complexes 1 − 10 have been fully characterized by a variety of methods. The fluoro ligand in [(Ph3P)2Pd(F)R] is inert in anhydrous media of low polarity. However, in the presence of trace amounts of water, F ligand exchange is observed. No irreversible hydrolysis of the Pd−F bond takes place as [(Ph3P)2Pd(F)R] remains the only observable (NMR) species in the system. VT NMR studies of various [(Ph3P)2Pd(F)R] in CH2Cl2 saturated with water have been conducted, revealing a push/pull-type, “ambiphilic” mechanism of the H2O-promoted F ligand-exchange process. The Pd−F bond cleavage likely involves nucleophilic attack of water on the metal center, concomitantly occurring with the formation of a hydrogen bond between the fluoro ligand and H2O.

Synthesis and reactivity of rhodium fluoro complexes

“…The 19 F NMR spectrum at 223 K shows two signals at characteristic chemical shifts at d À176.4 ppm for the distal fluorine and at d À278.3 ppm for the proximal fluorine (Fig. 3)[14,15,25,[32][33][34][35][36][37][38]. The latter signal reveals a coupling of %175 Hz to a phosphorus nucleus.…”

“…For these reasons, transition metal-fluorine bonds also often exhibit unusual properties [5][6][7][8][9]. However, the sometimes exceptional chemistry [1][2][3][4][10][11][12][13][14] of coordination compounds bearing fluoro ligands implies, in turn, the requirement of innovative synthetic methods for their preparation [1][2][3][4]8,[13][14][15][16][17][18][19][20][21]. We have, for instance, been developing a route to nickel fluoro complexes by C-F activation of aromatic molecules [10,[22][23][24][25][26].…”

“…Some of these fluoro compounds exhibit a distinctively different reactivity compared with their chloro analogues [22,25,26]. Other typical routes to fluoro complexes involve direct fluorination reactions at hydroxo, chloro or hydrido precursors using appropriate fluorination reagents [1][2][3][4]8,[14][15][16][17][18][19][20][21].…”

Palladium-Mediated Organofluorine Chemistry

“…288 289 These are the two most general methods for the preparation of monofluoro palladium organometallic derivatives. 290,291 Since this first report several monomeric palladium fluoro complexes have been synthesized in the context of the study of C-F activation or C-F formation. Some of them have been already mentioned in this chapter or will be referred to below.…”

Transition Metal-Mediated and Metal-Catalyzed Carbon–Fluorine Bond Formation

“…Early work in this field was primarily led by Grushin, who began exploring the synthesis and reactivity of the first mononuclear arylpalladium (II) fluoride complexes (Fig. 49) [97][98][99]. It was quickly discovered, however, that such complexes did not undergo the desired C-F reductive elimination under any conditions investigated [3,100].…”