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. 2017 Apr 1;8(4):3178-3186.
doi: 10.1039/c6sc05391b. Epub 2017 Feb 16.

Fluorocarbene, fluoroolefin, and fluorocarbyne complexes of Rh

Christopher J Pell  1 , Yanjun Zhu  1 , Rafael Huacuja  1 , David E Herbert  1 , Russell P Hughes  2 , Oleg V Ozerov  1
Affiliations

Fluorocarbene, fluoroolefin, and fluorocarbyne complexes of Rh

Christopher J Pell et al. Chem Sci. .

Abstract

The manuscript reports the synthesis, characterization, and analysis of electronic structure in a series of complexes of small perfluorocarbon ligands with the (PNP)Rh fragment (where PNP is a diarylamido/bis(phosphine) pincer ligand). Reactions of (PNP)Rh(TBE) as the source of (PNP)Rh with CHF3 and C2HF5 produced perfluoroalkylidene complexes (PNP)Rh[double bond, length as m-dash]CF2 and (PNP)Rh[double bond, length as m-dash]C(F)(CF3). (PNP)Rh[double bond, length as m-dash]CF2 could also be obtained via the reaction of (PNP)Rh(TBE) with Me3SiCF3/CsF, with an admixture of (PNP)Rh(C2F4), where TBE = tert-butylethylene. Abstraction of fluoride from these neutral (PNP)RhC x F y complexes was successful, although only abstraction from (PNP)Rh[double bond, length as m-dash]CF2 allowed unambiguous identification of the Rh product, [(PNP)Rh[triple bond, length as m-dash]CF]+. DFT computational studies allowed comparison of relative energies of (PNP)Rh(C2F4) and [(PNP)Rh(C2F3)]+ isomers as well as comparisons between the electronic structure of the [double bond, length as m-dash]CF2, C2F4, and [triple bond, length as m-dash]CF+ complexes and their hydrocarbon analogues.

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Figures

Fig. 1
Fig. 1. Perfluoroalkylidenes from Hughes and Baker. Isolated fluorocarbynes by Hughes, the Ir carbyne by Bergman, and matrix-trapped fluorocarbynes by Andrews.
Scheme 1
Scheme 1. Initial observation of (PNP)RhCF2.
Scheme 2
Scheme 2. Synthesis of rhodium fluorocarbenes and tetrafluoroethylene complexes.
Fig. 2
Fig. 2. ORTEPs of (PNP)RhCF2 (left) and (PNP)Rh(C2F4) (right). The ellipsoids are set at the 50% probability level, and hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°) for (PNP)RhCF2: Rh1–C1, 1.821(4); Rh1–N1, 2.043(3); C1–F1, 1.335(4); C1–F2, 1.348(5); N1–Rh–C1, 171.39(15); F2–C1–F1, 100.8(3); Rh1–C1–F2, 130.1(3); Rh1–C1–F1, 128.6. (PNP)Rh(C2F4): Rh1–C14, 2.006(3); Rh1–N1, 2.054(3); C14–F1, 1.378(3); C14–F2, 1.361(3); C14–C14′, 1.354(7); C14–Rh–C14′, 39.4(2); C14–Rh–N1, 160.28(10).
Scheme 3
Scheme 3. Synthesis of [(PNP)RhCF][CHB11Cl11] via fluoride abstraction from (PNP)RhCF2.
Fig. 3
Fig. 3. ORTEP of [(PNP)RhCF][HCB11Cl11]. The ellipsoids are set at the 50% probability level, and hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): Rh1–C1, 1.702(7); Rh1–N1, 2.019(4); C1–F1, 1.257(8); C1–Rh1–N1, 174.1(3); F1–C1–Rh1, 173.4(7).
Fig. 4
Fig. 4. NLMOs for the bonding interactions between C2H4 (column 1) and C2F4 (column 2) and the (PNP)Rh fragment. For clarity the PiPr2 groups have been replaced by PMe2 groups and the aryl part of the pincer truncated to P–CHCH–N linkers.
Fig. 5
Fig. 5. NLMOs for the bonding interactions between the CF2 ligand and the (PNP)Rh fragment. For clarity the PiPr2 groups have been replaced by PMe2 groups and the aryl part of the pincer truncated to P–CHCH–N linkers.
Fig. 6
Fig. 6. NLMOs for the bonding interactions between the CF+ ligand and the (PNP)Rh fragment. For clarity the PiPr2 groups have been replaced by PMe2 groups and the aryl part of the pincer truncated to P–CHCH–N linkers.
Fig. 7
Fig. 7. Resonance forms for the π-system in a linear Rh–X–Y ligand array, with WBI values for the bonds in Rh–C–O, Rh–N–O, and Rh–C–F complexes. All three complexes are isoelectronic and no formal charges are shown.
Fig. 8
Fig. 8. (Top) Calculated structures and relative energies for (PNP)Rh C2F4 isomers. (Bottom) Calculated structures and relative energies for proposed structures resulting from fluoride abstraction from (PNP)RhC(F)(CF3).
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