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Photochemical Reactions of Fluorinated Pyridines at Half-Sandwich Rhodium Complexes: Competing Pathways of Reaction.

ABSTRACT: Irradiation of CpRh(PMe₃)(C₂H₄) (1; Cp = ?⁵-C₅H₅) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable ?²-C,C-coordinated pentafluoropyridine complex, CpRh(PMe₃)(?²-C,C-C₅NF₄) (2). The molecular structure of 2 was determined by single-crystal X-ray diffraction, showing coordination by C3-C4, unlike previous structures of pentafluoropyridine complexes that show N-coordination. Corresponding experiments with 2,3,5,6-tetrafluoropyridine yield the C-H oxidative addition product CpRh(PMe₃)(C₅NF₄)H (3). In contrast, UV irradiation of 1 in hexane, in the presence of 4-substituted tetrafluoropyridines C₅NF₄X, where X = NMe₂, OMe, results in elimination of C₂H₄ and HF to form the metallacycles CpRh(PMe₃)(?²-C,C-CH₂N(CH₃)C₅NF₃) (4) and CpRh(PMe₃)(?²-C,C-CH₂OC₅NF₃) (5), respectively. The X-ray structure of 4 shows a planar RhCCNC-five-membered ring. Complexes 2-5 may also be formed by thermal reaction of CpRh(PMe₃)(Ph)H with the respective pyridines at 50 °C.

SUBMITTER: Procacci B

PROVIDER: S-EPMC3929166 | biostudies-literature | 2014 Jan

REPOSITORIES: biostudies-literature

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Photochemical Reactions of Fluorinated Pyridines at Half-Sandwich Rhodium Complexes: Competing Pathways of Reaction.

Procacci Barbara B Blagg Robin J RJ Perutz Robin N RN Rendón Nuria N Whitwood Adrian C AC

Organometallics 20131231 1

Irradiation of CpRh(PMe3)(C2H4) (1; Cp = η5-C5H5) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable η2-C,C-coordinated pentafluoropyridine complex, CpRh(PMe3)(η2-C,C-C5NF4) (2). The molecular structure of 2 was determined by single-crystal X-ray diffraction, showing coordination by C3-C4, u ...[more]

PMID: 24563575

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Project description:Indenyl (Ind) rhodium N-heterocyclic carbene (NHC) complexes [Rh(η5 -Ind)(NHC)(L)] were synthesised for 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) with L=C2 H4 (1), CO (2 a) and cyclooctene (COE; 3), for 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIMes) with L=CO (2 b) and COE (4), and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) with L=CO (2 c) and COE (5). Reaction of SIPr with [Rh(Cp*)(C2 H4 )2 ] did not give the desired SIPr complex, thus demonstrating the "indenyl effect" in the synthesis of 1. Oxidative addition of HSi(OEt)3 to 3 proceeded under mild conditions to give the Rh silyl hydride complex [Rh(Ind){Si(OEt)3 }(H)(SIPr)] (6) with loss of COE. Tethered-fluorenyl NHC rhodium complexes [Rh{(η5 -C13 H8 )C2 H4 N(C)C2 Hx NR}(L)] (x=4, R=Dipp, L=C2 H4 : 11; L=COE: 12; L=CO: 13; R=Mes, L=COE: 14; L=CO: 15; x=2, R=Me, L=COE: 16; L=CO: 17) were synthesised in low yields (5-31 %) in comparison to good yields for the monodentate complexes (49-79 %). Compounds 3 and 1, which contain labile alkene ligands, were successful catalysts for the catalytic borylation of benzene with B2 pin2 (Bpin=pinacolboronate, 97 and 93 % PhBpin respectively with 5 mol % catalyst, 24 h, 80 °C), with SIPr giving a more active catalyst than SIMes or IMes. Fluorenyl-tethered NHC complexes were much less active as borylation catalysts, and the carbonyl complexes were inactive. The borylation of toluene, biphenyl, anisole and diphenyl ether proceeded to give meta substitutions as the major product, with smaller amounts of para substitution and almost no ortho product. The borylation of octane and decane with B2 pin2 at 120 and 140 °C, respectively, was monitored by 11 B NMR spectroscopy, which showed high conversions into octyl and decylBpin over 4-7 days, thus demonstrating catalysed sp3 C-H borylation with new piano stool rhodium indenyl complexes. Irradiation of the monodentate complexes with 400 or 420 nm light confirmed the ready dissociation of C2 H4 and COE ligands, whereas CO complexes were inert. Evidence for C-H bond activation in the alkyl groups of the NHC ligands was obtained.

Dataset Information

Photochemical Reactions of Fluorinated Pyridines at Half-Sandwich Rhodium Complexes: Competing Pathways of Reaction.

Publications

Photochemical Reactions of Fluorinated Pyridines at Half-Sandwich Rhodium Complexes: Competing Pathways of Reaction.

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