Activation of tetrafluoropropenes by rhodium(i) germyl and silyl complexes.

The reaction of the rhodium(i) complexes [Rh(E)(PEt3)3] (E = GePh3 (1), Si(OEt)3 (5)) with HFO-1234yf (2,3,3,3-tetrafluoropropene) afforded [Rh(F)(PEt3)3] (2) and the functionalized olefins Z-CF3CH[double bond, length as m-dash]CH(E) (E = GePh3 (4a), Si(OEt)3 (7)). Conceivable reaction pathways were assessed using DFT calculations. Reactions of [Rh(E)(PEt3)3] with HFO-1234ze (E-1,3,3,3-tetrafluoropropene) yielded the rhodium fluorido complex 2 and [Rh{(E)-CH[double bond, length as m-dash]CH(CF3)}(PEt3)3] (9) via two different reaction pathways. Using complexes 1 and 5 as catalysts, functionalized building blocks were obtained.

C-H and C-F Bond Activation Reactions of Fluorinated Propenes at Rhodium: Distinctive Reactivity of the Refrigerant HFO-1234yf.

The reaction of [Rh(H)(PEt3 )3 ] (1) with the refrigerant HFO-1234yf (2,3,3,3-tetrafluoropropene) affords an efficient route to obtain [Rh(F)(PEt3 )3 ] (3) by C-F bond activation. Catalytic hydrodefluorinations were achieved in the presence of the silane HSiPh3 . In the presence of a fluorosilane, 3 provides a C-H bond activation followed by a 1,2-fluorine shift to produce [Rh{(E)-C(CF3 )=CHF}(PEt3 )3 ] (4). Similar rearrangements of HFO-1234yf were observed at [Rh(E)(PEt3 )3 ] [E=Bpin (6), C7 D7 (8), Me (9)]. The ability to favor C-H bond activation using 3 and fluorosilane is also demonstrated with 3,3,3-trifluoropropene. Studies are supported by DFT calculations.

Reactivity of 3,3,3-Trifluoropropyne at Rhodium Complexes: Development of Hydroboration Reactions.

The rhodium compounds [Rh(C≡CCF3 )(PEt3 )3 ] (2), fac-[RhH(C≡CCF3 )2 (PEt3 )3 ] (3), and fac-[Rh{(E)-CH=CHCF3 }(C≡CCF3 )2 (PEt3 )3 ] (4) were synthesized by reactions of the rhodium(I) complexes [Rh(H)(PEt3 )3 ] (1) and [Rh(Bpin)(PEt3 )3 ] (5, HBpin=pinacolborane) with the alkyne 3,3,3-trifluoropropyne. Reactivity studies of [Rh(C≡CCF3 )(PEt3 )3 ] (2) were performed with CO and 13 CO to form [Rh(C≡CCF3 )(CO)(PEt3 )3 ] (7) and subsequently trans-[Rh(C≡CCF3 )(CO)(PEt3 )2 ] (8) as well as the labeled derivatives. Using 1-4 as catalysts, hydroboration reactions selectively afforded borylated building blocks.

The control of stereochemistry by the pentafluorosulfanyl group.

The influence of pentafluorosulfanylation on biological activity has been revealed in numerous comparative studies of biologically active compounds, but considerably less is known about the influence of pentafluorosulfanylation on reactivity. Among the distinctive properties of the pentafluorosulfanyl group is the profound dipole moment that results from introduction of this substituent. It has been shown that dipolar effects coupled with the steric demand of the SF5 group may be employed to influence the stereochemistry of reactions, especially those processes with significant charge separation in the transition state. The Staudinger ketene-imine cycloaddition reaction is an ideal platform for investigation of dipolar control of diastereoselectivity by the pentafluorosulfanyl group.

Fluorine in fragrances: exploring the difluoromethylene (CF2) group as a conformational constraint in macrocyclic musk lactones.

The CF2 group is incorporated into specific positions within the lactone ring of the natural musk lactone, (12R)-(+)-12-methyl-13-tridecanolide, a constituent of Angelica root oil, Angelica archangelica L. The approach is taken as it was anticipated that CF2 groups would dictate corner locations in the macrocycle and limit the conformational space available to the lactone. Three fluorine containing lactones are prepared by organic synthesis. One (8) has CF2 groups located at the C-6 and C-9 positions, another (9) with CF2 groups at the C-5 and C-9 positions, and a third (10) with a CF2 group at C-8. Two of the fluorine containing lactones (8 and 10) were sufficiently crystalline to obtain X-ray crystal structures which revealed that the CF2 groups do adopt corner locations. All three lactones were subject to computational analysis at the B3LYP-D3/6-311+G** level to assess the relative energies of different conformers. In all cases, the global minima and most of the lowest energy minima have squared/rectangular geometries and located the CF2 groups at the corners. The lowest energy structures for 8 and 10 closely approximated the observed X-ray structures, suggesting good convergence of theory and experiment in determining relevant low energy conformations. All three compounds retained a pleasant odour suggesting the rings retained sufficient conformational flexibility to access relevant olfactory conformations.

Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines.

ß-Lactams were diastereoselectively formed by the reaction of SF5-containing aldimines, or an SF5-containing ketimine, with benzyloxyketene in a conrotatory ring closure process. Imine formation and cyclization were possible in spite of the acidification of protons on the carbon bound to SF5. The reactions of the aldimines demonstrated very good 1,2-lk diastereoselectivity, however lack of stereochemical control of the C-N ketimine geometry was reflected in the stereochemistry of the product ß-lactam. Cyclization of imines with a stereogenic center bearing SF5 was reflected in the 1,2-lk,lk selectivity of the ß-lactam.

Reactivity of rhodium and iridium peroxido complexes towards hydrogen in the presence of B(C6F5)3 or [H(OEt2)2][B{3,5-(CF3)2C6H3}4].

The peroxido complexes trans-[M(4-C5F4N)(O2)(CNtBu)(PR3)2] (1: M = Rh, R = Et; 2a: M = Ir, R = iPr) can be used in the metal-mediated hydrogenation of O2. The reaction of trans-[Rh(4-C5F4N)(O2)(CNtBu)(PEt3)2] (1) with B(C6F5)3 and H2 gave trans-[Rh(4-C5F4N)(CNtBu)(PEt3)2] (3), OPEt3 and (H2O)·B(C6F5)3, whereas treatment of [H(OEt2)2][B{3,5-(CF3)2C6H3}4] with 1 in the presence of H2 yielded trans-[Rh(4-C5F4N)(CNtBu)(PEt3)2] (3) and H2O2. The reactivity of 2a towards B(C6F5)3 and BClCy2 was also studied and an intermediate was detected which is assigned to be trans-[Ir(4-C5F4N)(Cl)(OOBCy2)(CNtBu)(PiPr3)2] (4a).