A Simple and Highly Efficient P,O-Type Ligand for Suzuki?Miyaura Cross-Coupling of Aryl Halides.

Department of Chemistry, The Chinese University of Hong Kong, Hong Kong, 00, Hong Kong
Chemical Communications (Impact Factor: 6.83). 10/2004; 36(17):1922-3. DOI: 10.1039/b407243j
Source: PubMed


A simple and efficient hemilabile-type phosphine ligand, found to be highly effective in Suzuki-Miyaura cross-coupling of aryl chlorides with generally low Pd-catalyst loading (0.05%), was prepared in one step based on an economically attractive approach from commercially available benzamide starting material.

3 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Low-coordinate organometallic complexes are important in structure and catalysis, and hemilability or secondary interactions such as hydrogen bonding enabled by hybrid ligands are receiving increasing attention. To study the factors controlling these phenomena, three new imidazol-2-ylphosphine ligands, L, were made. In these ligands, the bulk around P and the hindrance at the basic and potentially coordinating imidazole N-3 were varied. Remarkably, L(2)Pd(0) complexes 3a-c were shown to be two-coordinate, 12-electron species, despite the availability of imidazole N-3 to enter into eta(2)-P,N chelation. In oxidative additions of C-X bonds to the Pd(0) complexes, reaction rates and products could be controlled by the nature of the C and X groups and the R groups on the phosphine. Most significantly, whereas 4c-PhI and 4c-MeOTf from 3c are normal trans-bis(phosphine)Pd(R)(X) species, 5a-PhI, 5a-PhBr, and 5b-PhI from 3a and 3b were shown by X-ray diffraction to be a monomeric species with a single eta(2)-P,N-chelating phosphine. From 3a and methyl triflate, an ionic complex [6a-Me](+)[OTf](-) with one chelating and one nonchelating phosphine was formed, with temperature-dependent windshield-wiper exchange of the two, showing hemilability. Thus, large phosphine substituents (R = tert-butyl rather than isopropyl) favor chelation. The chelate Pd-imidazole N-3 bond is longer when the heterocyclic nitrogen is hindered by an adjacent tert-butyl group at C-4 (comparing 5a-PhI and 5b-PhI). Finally, whereas in [8b-Ph](+)[OTf](-) from 5b-PhI and isopropylamine, the amine coordinates without chelate opening or hydrogen bonding, in [10c-Me](+)[OTf](-) made from 4c-MeOTf and isopropylamine, the amine is not only coordinated at N but also donates a hydrogen bond to each phosphine imidazol-2-yl substituent.
    No preview · Article · Feb 2006 · Journal of the American Chemical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A series of nickel(II) and palladium(II) complexes containing one or two pentafluorophenyl ligands and the phosphino-amides o-Ph2PC6H4CONHR [R = iPr (a), Ph (b)] displaying different coordination modes have been synthesised. The chelating ability of these ligands and the influence of both coligands and the metal centre in their potential hemilabile behaviour have been explored. The crystal structure of (b) has been determined and reveals N–H� � �O intermolecular hydrogen bonding. Bis-pentafluorophenyl derivatives [M(C6F5)2(o-Ph2PC6H4CO-NHR)] [M = Ni; R = iPr (1a); R = Ph (1b); M = Pd; R = iPr (2a); R = Ph (2b)] in which (a) and (b) act as rigid P, O-chelating ligands were readily prepared from the labile precursors cis-[M(C6F5)2(PhCN)2]. X-ray structures of (1a), (1b) and (2a) have been established, allowing an interesting comparative structural discussion. Dinuclear [{Pd(C6F5)(tht)(l-Cl)}2] reacted with (a) and (b) yielding the monopentafluorophenyl complexes [Pd(C6F5)Cl{PPh2(C6H4–CONH–R)}] (R = iPr (3a), Ph (3b)) that showed a P, O-chelating behaviour of the ligands, confirmed by the crystal structure determination of (3a). New cationic palladium(II) complexes in which (a) and (b) behave as P-monodentate ligands have been synthesised by reacting them with [{Pd(C6F5)(tht)(l-Cl)}2], stoichiometric Ag(O3SCF3) and external chelating reagents such as cod [Pd(C6F5)(cod){PPh2(C6H4-CONH-R)}](O3SCF3)(R = iPr (4a), Ph (4b)) and 2,20-bipy [Pd(C6F5)(bipy){PPh2(C6H4-CONH-R)}](O3SCF3) (R=i Pr (5a), Ph (5b)). When chloride abstraction in [{Pd(C6F5)(tht)(l-Cl)}2] is promoted by means of a dithioanionic salt as dimethyl dithiophospate in the presence of (a) or (b), the corresponding neutral complexes [Pd(C6F5){S(S)P(OMe)2}{PPh2(C6H4-CONH-R)}] (R = iPr (6a), Ph (6b)) were obtained.
    Full-text · Article · Apr 2006 · Inorganica Chimica Acta
  • [Show abstract] [Hide abstract]
    ABSTRACT: New heterofunctional phosphine ligands have been synthesised, incorporating the substitutionally labile sulfone and sulfonamide moieties as chelating groups, which display activity in the palladium-catalysed Suzuki and amination cross-coupling reactions. Single-crystal X-ray diffraction studies of the complexes formed with [Pd(mu-Cl)(dmba)] (dmba-H = N,N-dimethylbenzylamine) highlight the coordinating nature of these ligands; showing the formation of a bis chelate complex through a six-membered Pd-P-C-C-S-O ring with the sulfonamide class of ligands.
    No preview · Article · Jun 2006 · Dalton Transactions
Show more