Electron‐Rich, Bicyclic Biaryl‐Like KITPHOS Monophosphines via [4+2] Cycloaddition between 1‐Alkynylphosphine Oxides and Anthracene: Highly Efficient Ligands for Palladium‐Catalysed CN and CC Bond Formation

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Advanced Synthesis & Catalysis (Impact Factor: 5.54). 07/2008; 350(11‐12):1801 - 1806. DOI: 10.1002/adsc.200800307

ABSTRACT Electron-rich, bicyclic biaryl-like KITPHOS monophosphines have been prepared via Diels–Alder cycloaddition between 1-alkynylphosphine oxides and anthracene in an operationally straightforward and highly modular synthetic protocol that will allow access to an architecturally and electronically diverse family of ligands. Palladium complexes of these ligands are highly efficient catalysts for the Buchwald–Hartwig amination and Suzuki–Miyaura coupling of a wide range of aryl chlorides, which for the vast majority of substrate combinations outperform their o-(dicyclohexylphosphino)biphenyl-based counterparts.

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    ABSTRACT: The Diels–Alder cycloaddition between dicyclohexylvinylphosphine oxide and anthracene or 9-methylanthracene affords the bulky electron-rich trialkyl-type dihydro-KITPHOS monophosphines 11-(dicyclohexylphosphinoyl)-12-phenyl-9,10-dihydro-9,10-ethenoanthracene and 11-(dicyclohexylphosphinoyl)-9-methyl-12-phenyl-9,10-dihydro-9,10-ethenoanthracene, respectively, after reduction of the corresponding oxide. Both phosphines are highly air-sensitive and rapidly oxidize on silica gel during purification but have been isolated as air-stable cyclometalated palladium precatalysts of the type [Pd{κ2N2′,C1-2-(2′-NH2C6H4)C6H4}Cl(L)]. Both palladium precatalysts form highly active systems for the Suzuki–Miyaura cross-coupling of a range of aryl chlorides with aryl boronic acids, giving the desired products in good to excellent yield under mild conditions and a catalyst loading of 0.25 mol %. A comparison of the performance of catalysts based on dihydro-KITPHOS monophosphines against their first-generation biaryl-like KITPHOS counterparts revealed that the latter are consistently more efficient for the vast majority of substrate combinations examined, albeit by only a relatively small margin in some cases. This, together with the greater air stability and ease of handling of biaryl-like KITPHOS monophosphines, renders them more practical ligands for palladium-based cross-coupling. The steric parameters of both classes of KITPHOS monophosphine and a selection of electron-rich biaryl monophosphines have been quantified using a combination of Solid-G to determine the percentage of the metal coordination sphere shielded by the phosphine (the G parameter), and Salerno molecular buried volume calculations (SambVca) to determine the percent buried volume (%Vbur); the corresponding Tolman cone angles have also been determined from correlations and the relative merits of the two approaches discussed. The electronic properties of these phosphines have also been investigated using DFT to calculate the A1 ν(CO) frequency in LNi(CO)3 (B3LYP/6-31G(2d,p)[LanL2DZ on Ni]), and the resulting computed electronic parameters (CEP) were used to estimate the corresponding experimental Tolman electronic parameters (TEP).
    Organometallics 02/2013; 32(6):1773–1788. DOI:10.1021/om3011992 · 4.25 Impact Factor
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    ABSTRACT: Thermolysis of the P-coordinated KITPHOS monophosphine complex [(p-cymene)RuCl2(KITPHOS)] in chlorobenzene at 120 °C resulted in displacement of the p-cymene to afford [{κ(P)-η6-KITPHOS}RuCl2], the first example of a constrained-geometry complex in which the κ(P)-bonded diphenylphosphino group and the η6-coordinated proximal phenyl ring are connected by an unsaturated two-carbon tether; both complexes form efficient catalysts for the direct ortho arylation of 2-phenylpyridine and N-phenylpyrazole with a range of aryl chlorides.
    Organometallics 10/2011; 30(21):6010–6016. DOI:10.1021/om200843f · 4.25 Impact Factor
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    ABSTRACT: This paper reports the first examples of SuzukiMiyaura cross-couplings involving aryl- and naphthylphosphonate-based boronate esters as the nucleophilic partner. A systematic comparison of the performance of biaryl-like KITPHOS- and XPHOS-based systems revealed that, between them, an electronically and sterically diverse range of substrates can be coupled with remarkable efficiency to afford high yields of the corresponding biaryl and heterobiaryl monophosphonates. The use of an aryl- and naphthylphosphonate-based boronate ester as the coupling partner presents an alternative and potentially complementary pathway to existing couplings in which the aryl- or naphthylphosphonate unit is typically introduced as the electrophile. The potential advantages associated with the use of this new class of coupling partner were clearly demonstrated by the palladium-catalyzed reaction between diethyl [2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]phosphonate and 1-bromo-2-methoxynaphthalene that gave the corresponding biaryl monophosphonate in 56% yield, a marked improvement on the 6% yield obtained from the reaction between 2-methoxy-1-naphthylboronic acid and diethyl (2-bromophenyl)phosphonate with the same catalyst under the same conditions. The potential utility of this new coupling combination was demonstrated by reducing one of the products, 2-methoxy-1-(2'-diethoxyphosphorylphenyl)naphthylene, to the corresponding primary phosphine, which was subsequently converted into a diastereoisomeric mixture of the R,R-hexane-2,5-diol-derived phospholane in reasonable yield.
    Organometallics 10/2014; 33(19):5209-5219. DOI:10.1021/om500520z · 4.25 Impact Factor