We describe the use of the phosphinic amide moiety as an effective directed ortho metallation group for the incorporation of various phosphino groups onto a benzene ring to generate phosphine ligands. These ligands were used to generate active palladium catalysts for the Suzuki-Miyaura reaction in which deactivated aryl bromides and some aryl chlorides were used as substrates. Surprisingly and interestingly, the (2-alkylphenyl)phosphine derivatives were found to be especially active. The stereoelectronic and electronic features of the ligands were probed by use of selenium oxidation products and Vaska's rhodium complexes, respectively. Some unusual features were observed, specifically relating to the inductive effects of the alkyl side chains in relation to the electronwithdrawing phosphinic amide functions. The two probes were also compared, and the results were related to the catalytic data obtained from the Suzuki reactions. Quite unexpectedly, the ligands generate catalysts with good activity despite their being relatively electronpoor. This low electron density, resulting from the phosphinic amide functionality, renders them stable to oxidation and hydrolysis for over six months while exposed to air. Additionally, the use of the phosphinic amide directing group is unusual and rare, and has not, to our knowledge, been noted before in the preparation of phosphine ligands.Ligands are key features of transition-metal catalysts, modifying their activity and selectivity. In C-C bond-formation reactions, the Suzuki-Miyaura reaction, 1 a central reaction type in organic chemistry, has become one of the most important tools. Recent ligand developments allow the use of aryl chloride substrates and low catalyst loadings at temperatures between ambient and 110 °C. 1 Hindered electron-rich ligands are thought to enhance the rate of oxidative addition, 1d-f although preference for the coordinatively unsaturated highly reactive L 1 Pd species may be causative. 1f While electron-rich ligands are susceptible to oxidation, protection and in situ deprotection approaches are known (but involve additional steps or reagents). 2 Ligandless methods for effecting Suzuki-Miyaura reactions with aryl bromides are known, 3a and secondary phosphine oxides 3b have been used as preligands in attempts to circumvent some of the problems associated with more electron-rich systems. The use of N-heterocyclic carbenes as ligands eliminates the oxidation problems associated with electron-rich phosphines, but typically requires higher catalyst loadings and reaction temperatures than with phosphines, 4 although very recent work has improved on those shortcomings. 4b Phosphites are also useful in this context, 5 but tend to be hydrolytically sensitive.Directed ortho metallation (DoM) 6 has been used in a great many syntheses and has been shown to be one of the most powerful methods with which to selectively functionalise aromatic systems.We herein report an expedient rapid synthesis of ligands derived from phosphinic amide that have been found to be...

INTRODUCTIONThe carbonylation of alkynes allows for the synthesis of R,βunsaturated carboxylic esters or acids in an easy one-step synthesis (Scheme 1). The reaction occurs much in the same manner as for alkenes, a reaction that has been quite extensively studied. 1 The reaction requires the presence of a catalyst (usually Pd), carbon monoxide under pressure, methanol or water, and an acidic co-promoter. This reaction is of interest since methyl atropate (methyl 2-phenylacrylate) and its derivatives are potential precursors of nonsteroidal anti-inflammatories such as ibuprofen and naproxen. 2 While several ligands have been applied to the catalytic conversion of phenylacetylene into its unsaturated ester derivatives, N-containing phosphine ligands have been shown to provide good catalysts in terms of stability and activity. Specifically, 2-pyridyldiphenylphosphine has earned a reputation for being particularly suited to this transformation. 3 Alternative systems have included iminophosphine-type analogues 4 and a PPh 3 /pyridine carboxylic acid system. 5 Supported catalysts have also been applied with a fair degree of success. 6 When ligands do not possess the pyridyl moiety, poor results are generally noted. 7 As with other alkoxycarbonylation-type chemistry with alkenes, the application of alkynes as substrates also calls for an acidic co-catalyst, typically a Brønsted acid. Recent work in our laboratories has involved the use of Al(OTf) 3 as a co-catalyst in the methoxycarbonylation of styrene and 1-pentene. 8 We hoped that this robust, recyclable co-catalyst would be useful in the methoxycarbonylation and hydrocarboxylation reactions of phenylacetylene and investigated its application in this reaction, discovering along the way that PÀP bidentate ligands produce excellent catalysts in the presence of this co-promoter. We also demonstrate that the Pd-based catalyst derived from BINAP is stable and capable of being recycled a number of times.' RESULTS AND DISCUSSION Initial reactions using phenylacetylene were carried out under the conditions we earlier reported, 8 making use of Al(OTf) 3 as the co-catalyst in Pd-catalyzed reactions supported by PPh 3 as ligand. The system showed a complete lack of conversion of the phenylacetylene, a result also noted by others when using monodentate phosphine ligands. 9 Several changes to the reaction conditions, while retaining the monodentate ligand, were met with failure. Previous studies have shown 1,4-bis(diphenylphosphino)butane (dppb) to be active as a ligand in the methoxycarbonylation reaction of phenylacetylene. 10 We accordingly investigated a few bidentatetype ligands with varying bite angles (Table 1), including 1,2bis(diphenylphosphino)benzene, 2,2 0 -bis(diphenylphosphino)-1,1 0binaphthyl (BINAP), and SiXantphos, in quite long-duration reactions (24 h).While 1,2-bis(diphenylphosphino)benzene provided no conversion to the desired product, BINAP-and SiXantphos-based catalysts afforded 100% conversion of the starting material, but in reactions in which less than...

In the crystal structure of the title compound, C21H22NOP, the amine H atom is involved in N—H⋯O hydrogen-bonding inter­actions, resulting in chains along the c axis. The crystal lattice is consolidated by weak inter­molecular C—H⋯π inter­actions.

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