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• 363-72-4 Pentafluorobenzene 
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Relevant academic research and scientific papers

Comparisons of photoinduced oxidative addition of B-H, B-B, and Si-H bonds at rhodium(η5-cyclopentadienyl)phosphine centers

Ultraviolet irradiation of [Rh(η5-C5H 5(PMe3)(C2H4] (1a), [Rh(η5-C5H5)(PPh3)(C 2H4)] (1b), and [Rh(η5-C5H 4CF3)(PMe3)(C2H4)] (1c) (collectively abbreviated as [Rh(Cp′)(PR3)(C2H 4)]) in the presence of HBpin (pinacolate = pin = l,2-O 2C2Me4) results in elimination of C 2H4 and B-H oxidative addition, leading to the formation of boryl hydride complexes [Rh(Cp′)(Bpin)(H)(PR3)]. Complete conversion is achieved in liquid HBpin or by photolysis in hexane at -10 °C. Similarly, photolysis of la-c in the presence of B2pin2 in hexane at -10 °C leads to B-B oxidative addition products, [Rh(Cp′)(Bpin)2(PR3)]. Irradiation at room temperature leads to formation of [Rh(Cp′)(PRs)2] in addition to the desired products. The rhodium boryl products were characterized by multinuclear NMR spectroscopy and, in the case of [Rh(η5-C 5H5)(Bpin)(H)(PPh3)], by X-ray crystallography. The structure reveals a Rh-B distance of 2.0196(15) A. The H...B separation of 2.09(2) Atogether with the bond angles at the metal suggest some residual H...B interaction. Photolysis of 1a-c in the presence of tertiary and secondary silanes (HSiEt3, HSiiPr 3, HSi(OMe)3, HSiMe2Et, HSiMeEt2, and H2SiEt2) results in rhodium silyl hydride complexes [Rh(Cp′)(SiR′2R″)(H)(PR3)]. The structure of [Rh(η5-C5H5)(Si iPr3)(H)(PMe3)] was determined by single-crystal X-ray diffraction, yielding a Rh-Si bond length of 2.3617(3) A and a Rh-H bond length of 1.508(17) A. The H...Si distance of 2.278(17) A and the very unequal H-Rh-P and H-Rh-Si angles suggest some residual H...Si interaction. Competition reactions were performed with Ib dissolved in hexane in the presence of HBpin and B2pin2 simultaneously. 31P NMR measurements, made after brief irradiation, showed a slight preference for B-B oxidative addition over B-H oxidative addition. Similar experiments with three-way competition among HBpin, HSiMe 2Et, and HC6F5, analyzed by 1H NMR spectroscopy, showed negligible selectivity among H-B, H-C, and H-Si oxidative addition. Molecular structures were also determined by single-crystal X-ray diffraction for 1b, 1c, [Rh(η5-C5H5) (PPh3)2], and [Rh(η5-C5H 5)Cl2(PPh3)].

Photochemical displacement of co-ordinated ethene from [Rh(η5-C5H5)(PPh3)(C 2H4)]

The rhodium (triphenylphosphine)(ethene) complex [Rh(η5-C5H5)(PPh3)(C 2H4)], was synthesized by reaction of [{Rh(C2H4)2Cl}2] with triphenylphosphine and thallium cyclopentadienide. Like in [Rh(η5-C5H5)(PMe3)(C 2H4)], the co-ordinated ethene ligand may be displaced photochemically. Photoreaction of [Rh(η5-C5H5)(PPh3)(C 2H4)] with SiR3H (R = Pri or Et) and hexafluorobenzene yielded [Rh(η5-C5H5)(PPh3)(SiR 3)H] and [Rh(η5-C5H5)(PPh3)-(η 2-C6F6)], respectively. Oxidative addition of the C-H bonds of partially fluorinated arenes, C6F5H and 1,3-C6F2H4, was demonstrated by NMR spectroscopy to result in formation of [Rh(η5-C5H5)(PPh3)(R)H] (R = C6F5 or 2,6-C6F2H3). Oxidative addition of benzene may be detected following photolysis in benzene-thf mixtures at 233 K, but the product decomposes on warming. The molecular structure of [Rh(η5-C5H5)(PPh3)(SiPr i3)H] has been determined crystallographically. The disorder of the isopropyl groups was modelled with two orientations of the SiPri3 with equal occupancies. The Rh-Si bond length is 2.386(2) A, the first example of measurement of such a distance at cyclopentadienyl rhodium(III).