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Mono-N-protected amino acid ligands stabilize dimeric palladium(ii) complexes of importance to C-H functionalization.

ABSTRACT: Mono-protected amino acid (MPAA) ligands are used in a number of Pd-catalyzed C-H functionalization reactions. MPAAs have been proposed to bind to Pd(ii) via ?2-(N,O) coordination, but such binding has not yet been experimentally validated. Herein, we report the synthesis and detailed characterization of a series of MPAA complexes prepared via cyclopalladation of dimethylbenzylamine in the presence of MPAAs. The isolated complexes exist as ?-carboxylato (MPAA) bridged dimers and feature potential M-M cooperativity and secondary sphere hydrogen bonding. Selective MPAA coordination and relay of stereochemistry, previously suggested to uniquely result from ?2-(N,O) MPAA coordination, are both observed. The isolated MPAA complexes undergo C-C and C-X (X = Cl, Br, I) bond formation when treated with electrophiles used for catalytic C-H functionalization. Stoichiometric iodination of MPAA palladacycles was found to proceed via a dinuclear palladium species with one equivalent of iodine in the rate limiting transition structure, and the isolated complexes also served as viable precatalysts for catalytic C-H functionalization. Together, these results provide a number of insights into the reactivity of Pd-MPAA complexes relevant to C-H bond functionalization.

SUBMITTER: Gair JJ

PROVIDER: S-EPMC5859881 | biostudies-other | 2017 Aug

REPOSITORIES: biostudies-other

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Mono-N-protected amino acid ligands stabilize dimeric palladium(ii) complexes of importance to C-H functionalization.

Gair Joseph J JJ Haines Brandon E BE Filatov Alexander S AS Musaev Djamaladdin G DG Lewis Jared C JC

Chemical science 20170616 8

Mono-protected amino acid (MPAA) ligands are used in a number of Pd-catalyzed C-H functionalization reactions. MPAAs have been proposed to bind to Pd(ii) via κ2-(N,O) coordination, but such binding has not yet been experimentally validated. Herein, we report the synthesis and detailed characterization of a series of MPAA complexes prepared via cyclopalladation of dimethylbenzylamine in the presence of MPAAs. The isolated complexes exist as μ-carboxylato (MP ...[more]

PMID: 29619194

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Project description:The series of complexes [XRu(CO)(L-L)(L')2][PF6] (X = H, TFA, Cl; L-L = 2,2'-bipyridyl, 1,10-phenanthroline, 5-amino-1,10-phenanthroline and 4,4'-dicarboxylic-2,2'-bipyridyl; L'2 = 2PPh3, Ph2 PC2H4PPh2, Ph2PCH?CHPPh2) have been synthesized from the starting complex K[Ru(CO)3(TFA)3] (TFA = CF3CO2) by first reacting with the phosphine ligand, followed by reaction with the L-L and anion exchange with NaPF6. In the case of L-L = phenanthroline and L'2 = 2PPh3, the neutral complex Ru(Ph3P)(CO)(1,10-phenanthroline)( TFA)2 is also obtained and its solid state structure is reported. Solid state structures are also reported for the cationic complexes where L-L = phenanthroline, L2 = 2PPh3 and X = Cl and for L-L = 2,2'-bipyridyl, L2 = 2PPh3 and X = H. All the complexes were characterized in solution by a combination of 1H and 31P NMR, IR, mass spectrometry and elemental analyses. The purpose of the project was to synthesize a series of complexes that exhibit a range of excited-state lifetimes and that have large Stokes shifts, high quantum yields and high intrinsic polarizations associated with their metal-to-ligand charge-transfer (MLCT) emissions. To a large degree these goals have been realized in that excited-state lifetimes in the range of 100 ns to over 1 ?s are observed. The lifetimes are sensitive to both solvent and the presence of oxygen. The measured quantum yields and intrinsic anisotropies are higher than for previously reported Ru(II) complexes. Interestingly, the neutral complex with one phosphine ligand shows no MLCT emission. Under the conditions of synthesis some of the initially formed complexes with X = TFA are converted to the corresponding hydrides or in the presence of chlorinated solvents to the corresponding chlorides, testifying to the lability of the TFA Ligand. The compounds show multiple reduction potentials which are chemically and electrochemically reversible in a few cases as examined by cyclic voltammetry. The relationships between the observed photophysical properties of the complexes and the nature of the ligands on the Ru(II) is discussed.

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Mono-N-protected amino acid ligands stabilize dimeric palladium(ii) complexes of importance to C-H functionalization.

Publications

Mono-<i>N</i>-protected amino acid ligands stabilize dimeric palladium(ii) complexes of importance to C-H functionalization.

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