Synthesis of Neutral (Pd^II, Pt^II), Cationic (Pd^II), and Water-Induced Anionic (Pd^II) Complexes Containing New Mesocyclic Thioether−Aminophosphonite Ligands and Their Application in the Suzuki Cross-Coupling Reaction

Abstract

Mesocyclic thioether-aminophosphonite ligands, {-OC10H6(mu-S)C10H6O-}PNC4H8O (2a, 4-(dinaphtho[2,1-d:1',2'-g][1,3,6,2]dioxathiaphosphocin-4-yl)morpholine) and {-OC10H6(mu-S)C10H6O-}PNC4H8NCH3 (2b, 1-(dinaphtho[2,1-d:1',2'-g][1,3,6,2]dioxathiaphosphocin-4-yl)-4-methylpiperazine) are obtained by reacting {-OC10H6(mu-S)C10H6O-}PCl (1) with corresponding nucleophiles. The ligands 2a and 2b react with (PhCN)2PdCl2 or M(COD)Cl2 (M = Pd(II) or Pt(II)) to afford P-coordinated cis-complexes, [{(-OC10H6(mu-S)C10H6O-)PNC4H8X-kappaP}2MCl2] (3a, M = Pd(II), X = O; 3b, M = Pd(II), X = NMe; 4a, M = Pt(II), X = O; 4b, M = Pt(II), X = NMe). Compounds 2a and 2b, upon treatment with [Pd(eta3-C3H5)Cl]2 in the presence of AgOTf, produce the P,S-chelated cationic complexes, [{(-OC10H6(mu-S)C10H6O-)PNC4H8X-kappaP,kappaS}Pd(eta3-C3H5)](CF3SO3) (5a, X = O and 5b, X = NMe). Treatment of 2a and 2b with (PhCN)2PdCl2 in the presence of trace amount of H2O affords P,S-chelated anionic complexes, [{(-OC10H6(mu-S)C10H6O-)P(O)-kappaP,kappaS}PdCl2](H2NC4H8X) (6a, X = O and 6b, X = NMe), via P-N bond cleavage. The crystal structures of compounds 1, 2a, 2b, 4a, and 6a are reported. Compound 6a is a rare example of crystallographically characterized anionic transition metal complex containing a thioether-phosphonate ligand. Most of these palladium complexes proved to be very active catalysts for the Suzuki-Miyaura reaction with excellent turnover number ((TON), up to 9.2 x 10(4) using complex 6a as a catalyst).

Group 11 Metal Complexes of the Mesocyclic Thioether Aminophosphonites [‐OC10H6(μ‐S)C10H6O‐]PNC4H8E (E = O, NMe)

“…[15] Interestingly, the sulfur atom also appears to show a weak coordinative interaction with phosphorus, as indi- cated by the P···S distance [3.098(2) Å]. This P···S distance is comparable to that observed in our previous report [7] and that of others [16] (see Table 3). While considerably greater than the sum of the covalent radii for sulfur and phosphorus (2.12 Å), [17] this distance is less than the sum of van der Waals radii (3.65 Å) [13] for these two elements.…”

“…The thioether aminophosphonites (2a and 2b) were prepared as reported previously. [7] The metal precursors CuX (X = Cl and Br), [22] [Cu(MeCN) 4 ]BF 4 , [23] [AuCl-(SMe 2 )] [24] and [Ag(OTf)PPh 3 ] [25] were prepared according to the published procedures. The 1 H and 31 P{ 1 H} NMR spectra (δ in ppm) were obtained with a Varian VXR 300 or VRX 400 spectrometer operating at frequencies of 300 or 400 ( 1 H) and 121 or 162 MHz ( 31 P), respectively.…”

“…[7] However, the P,S-chelated cationic complexes [{[-OC 10 [6d,10] have shown the existence of ligand dissociation and/or exchange processes at or below room temperature that lead to broad resonances due to the loss of the expected 1 J Ag,P couplings. Typically, the low-temperature limiting spectra consist of two doublets for each group of chemically equivalent phosphorus nuclei due to coupling with both 109 Ag and 107 Ag.…”

“…[6] We recently reported the synthesis of the mesocyclic mixed P,S ligands 2a and 2b, which exhibit an interesting coordination behavior towards palladium and platinum derivatives that results in cationic, anionic (3a, 3b), and neutral complexes (Scheme 1). [7] In all compounds, the sulfur atom present as part of an eight-membered thioether aminophosphonite ring system shows a coordinative interaction with phosphorus, which creates a pseudo trigonal bipyramidal (TBP) geometry at the phosphorus center. All the palladium complexes synthesized are promising catalysts for Suzuki cross-coupling reactions, with the anionic complexes 3a and 3b being particularly active (TONs of up to 92000).…”

“…Since group 11 metal complexes of P,S ligands are few in number, we sought to examine the reactivity of these thioether aminophosphonites with the group 11 metals. As part of our interest in organometallic chemistry [8] and catalytic investigations, [7,9] we report here on the reactivity of the mesocyclic thioether aminophosphonites 2a and 2b with group 11 metal centers as well as halide-exchange reactions of gold(I) complexes. X-ray structures of copper(I) (5a, 7a, 8a) and gold(I) (13a, 13b, 14a) complexes are also described.…”