We report the first isolable nickel difluorocarbene complexes (NiP 2 [P(OMe) 3 ](CF 2 ); P 2 = Ph 2 P-(CH 2 ) 2 PPh 2 , 2 P(OMe) 3 ), which are also the only examples of formally d 10 metal fluorocarbenes. These [Ni 0 ]CF 2 complexes react with tetrafluoroethylene (TFE) to yield the rare perfluorometallacyclobutanes [NiP 2 (κ 2 -CF 2 CF 2 CF 2 −)], with potential relevance to fluoroalkene metathesis and polymerization. Preliminary kinetic experiments establish that the reactions of the new [Ni]CF 2 compounds with TFE are considerably faster than the analogous reactions of their previously reported [Co]CF 2 counterparts. Further, we show that TFE addition to 2 is a dissociative process, in contrast to [Co]CF 2 , which reacts with TFE in an associative fashion. Finally, the preliminary reactivity of NiP 2 (κ 2 -CF 2 CF 2 CF 2 −) (P 2 = Ph 2 P(CH 2 ) 2 PPh 2 ) is described. M etal alkylidenes ([M]CRR′; R, R′ = H, alkyl, aryl) participate in a variety of catalytic transformations, most notably alkene metathesis. 1 Fluorocarbenes ([M]CFR F , R F = F, perfluoroalkyl), on the other hand, are quite rare 2,3 and have only recently been utilized in catalysis. Takahira and Morizawa reported in 2015 cross metathesis between fluoroalkenes and electron-rich alkenes (CH 2 CHOR), with [Ru]CF 2 and [Ru]CHOR intermediates, in the first examples of metalcatalyzed CF 2 transfer. 4 Catalysis involving fluorinated alkenes/ metal fluorocarbenes is inherently challenging 1,4,9,13 but has tremendous potential in the technologically important area of fluoro-organic synthesis. 5−7We are examining the viability of f irst-row (non-precious) metal fluorocarbenes as initiators for catalytic perfluoroalkene metathesis or polymerization, as outlined in Scheme 1. The metathesis mechanism is identical with that established for nonfluorinated olefins (i.e., the Chauvin mechanism), 1b and our approach to fluoroalkene polymerization is inspired by the Green−Rooney mechanism, originally proposed to describe the polymerization of nonfluorinated alkenes. 8 The fluoro-Green− Rooney mechanism avoids migratory alkene insertion into unreactive metal−perfluoroalkyl bonds, 9 in contrast to the more familiar Cossee−Arlman pathway, 10 and the metal− perfluoroalkyl bonds of the metallacyclobutane intermediates are expected to be destabilized by ring strain.We recently reported the reactions of tetrafluoroethylene (CF 2 CF 2 , TFE) with cobalt(I) fluorocarbenes ([Co] CFR F , R F = F, CF 3 ) to yield metallacyclobutanes (Scheme 2): the first examples of formal [2 + 2] cycloadditition between perfluorinated alkene and metal carbene reactants. 11 However, the perfluorocobaltacyclobutanes (i.e., cobalt(III) bis-(perfluoroalkyl) complexes) are decidedly more stable than the free cobalt perfluorocarbenes and tetrafluoroethylene (ΔG cycl = −25.3 kcal mol −1 for R F = F, from DFT/M06/ def2-TZVP/THF calculations 12 ), despite the destabilizing ring strain in the four-membered metallacycle. The strong M−R F bonds 2,9 of the metallacyclobutanes and the weak sing...

Alkene metathesis with directly fluorinated alkenes is challenging, limiting its application in the burgeoning field of fluoro-organic chemistry. A new nickel tris(phosphite) fluoro(trifluoromethyl)carbene complex ([P Ni]=CFCF ) reacts with CF =CF (TFE) or CF =CH (VDF) to yield both metallacyclobutane and perfluorocarbene metathesis products, [P Ni]=CF and CR =CFCF (R=F, H). The reaction of [P Ni]=CFCF with trifluoroethylene also yields metathesis products, [P Ni]=CF and cis/trans-CFCF =CFH. However, unlike reactions with TFE and VDF, this reaction forms metallacyclopropanes and fluoronickel alkenyl species, resulting presumably from instability of the expected metallacyclobutanes. DFT calculations and experimental evidence established that the observed metallacyclobutanes are not intermediates in the formation of the observed metathesis products, thus highlighting a novel variant of the Chauvin mechanism enabled by the disparate four-coordinate transition states.

An improved synthesis of the known trifluoromethyl cobalt compound Co(CO) 4 (CF 3 ) (1), which gives significantly higher yields than previously reported methods, allows for an investigation of its carbonyl substitution chemistry. Treatment of 1 with P-donor ligands of varying denticity under thermal conditions afforded Co[P(O-otolyl) 3 ](CO) 3 (CF 3 ) (2), Co(DPPE)(CO) 2 (CF 3 ) (3), and Co(P 3 )(CO)(CF 3 ) (4) in high isolated yields [DPPE = Ph 2 PCH 2 CH 2 PPh 2 ; P 3 = PhP(CH 2 CH 2 PPh 2 ) 2 ]. The new cobalt N-heterocyclic carbene complex Co(SIPr)(CO) 3 (CF 3 ) (5) [SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2ylidene)] was obtained by phosphine substitution from Co(PPh 3 )(CO) 3 (CF 3 ), a known compound efficiently prepared from 1. Additionally, we report the synthesis of two rare cobalt difluorocarbene complexes ([Co] = CF 2 ) produced by fluoride abstraction from 3 or 4. These results are relevant to our efforts to assess the reactivity of first-row metal perfluoroalkyl and fluorocarbene complexes.

The synthesis, characterization and reactivity of several bi- and tridentate, N-ligated manganese carbonyl trifluoromethyl complexes are presented. These complexes exhibit elongated Mn–CCF3 bonds (versus Mn(CF3)(CO)5), suggesting a lability that could be utilized for the transfer or insertion of the CF3 functional group into organic substrates. Unlike their Mn–X congeners (X = Cl, Br), these Mn–CF3 complexes exhibit a preference for hard donor ancillary ligands, thus enabling the synthesis of 4 N-ligated Mn–CF3 complexes including a mixed-donor tridentate complex using an NNS Schiff base ([2-(methylthio)-N-(1-(pyridin-2-yl)ethylidene)aniline]). Although we have not yet identified efficient CF3 transfer reactions, fluoride abstraction from the Mn–CF3 complexes using trimethylsilyl triflate affords the first stable Mn fluorocarbenes as evidenced by 19F NMR spectroscopy.

Alkene metathesis with directly fluorinated alkenes is challenging,limiting its application in the burgeoning field of fluoro-organic chemistry.Anew nickel tris(phosphite) fluoro(trifluoromethyl)carbene complex ([P 3 Ni]=CFCF 3 )r eacts with CF 2 =CF 2 (TFE) or CF 2 =CH 2 (VDF) to yield both metallacyclobutane and perfluorocarbene metathesis products, [P 3 Ni] = CF 2 and CR 2 = CFCF 3 (R = F, H). The reaction of [P 3 Ni] = CFCF 3 with trifluoroethylene also yields metathesis products,[ P 3 Ni] = CF 2 and cis/trans-CFCF 3 = CFH. However, unlike reactions with TFE and VDF,t his reaction forms metallacyclopropanes and fluoronickel alkenyl species,resulting presumably from instability of the expected metallacyclobutanes.D FT calculations and experimental evidence established that the observed metallacyclobutanesa re not intermediates in the formation of the observed metathesis products, thus highlighting an ovel variant of the Chauvin mechanism enabled by the disparate four-coordinate transition states. Scheme 1. Chauvin mechanism.