The mechanism of CF2-transfer from TMSCF3 (1), mediated by TBAT (2-12 mol%) or by NaI (5-20 mol%), has been investigated by in situ / stopped-flow 19 F NMR spectroscopic analysis of the kinetics of alkene difluorocyclopropanation, and competing TFE / c-C3F6 / homologous perfluoroanion generation, 13 C/ 2 H KIEs, LFERs, CF2-transfer efficiency and selectivity, the effect of inhibitors, and density functional theory (DFT) calculations. The reactions evolve with profoundly different kinetics, undergoing auto-inhibition (TBAT) or stochastic auto-acceleration (NaI), and co-generating perfluoroalkene side products. An overarching mechanism involving direct and indirect fluoride transfer from a CF3-anionoid to TMSCF3 (1) has been elucidated. It allows rationalization of why the NaI-mediated process is more effective for less-reactive alkenes and alkynes, why a large excess of TMSCF3 ( 1) is required in all cases, and why slow-addition protocols can be of benefit. Issues relating to exothermicity, toxicity, and scale-up are also noted.a Relative rates (krel) are for competitive first-order CF2 capture by the alkene/yne, not to overall rates of reaction. b Values in parenthesis by DFT. 26 See sections S3.7, S3.8 and S6.2 in the SI. Singlet CF2 as the ReactiveIntermediate. We began by studying the reaction of TMSCF3 (1) with alkenes 3i, and E/Z-4 and alkyne 5, Table 1. All underwent difluorocyclopropanation, to varying degrees of conversion, in the presence of TMSCF3 (1, 1.5 M) and 1-5 mol % TBAT, or NaI. Reactions of E/Z-4 proceeded stereospecifically, and with >98 % retention. The difluorocyclopropene 8, generated in low yield (12%) from alkyne 5, under the TBATmediated conditions, underwent partial decomposition to unidentified products. In contrast, 8 was quantitatively-generated, and stable, under NaI-mediated conditions, see section S3.3 in the SI. The same difluorocyclopropane products (6, 7) were obtained from 3i and E/Z-4 on thermalization with the zwitterionic CF2-source Ph3PCF2CO2. 22 The relative reactivities (krel) of alkenes 3i, E-4, and Z-4, and the LFER correlation for a-methylstyrenes (3i-vii, r + = -0.6), 23 were independent of the reagent (1 / Ph3PCF2CO2), and initiator (TBAT / NaI), Table 1, 24 within experimental error. Scheme 3. Experimental a and calculated b KIEs for rapid addition of transient singlet CF2 to 3i, at 300 K. 25 a Experimental (exp.) values in THF; and in PhCl, as solvent. 25 b Calculated (calc.) values by DFT, at the M06/6-31+G* level in Gauss-ian09 employing IEF-PCM single points to account for solvation, and goodvibes, kinisot and PyQuiver to compute free energy corrections and KIEs, see sections S1.6 and S6.2 in the SI. 26Kinetic isotope effects for the reaction of p-F-a-methylstyrene 3i with TMSCF3 (1) initiated by TBAT were obtained by a series of competitions of 13 C-and 2 H-labelled a-methylstyrenes 3i against aryl-D4-3i, monitored by 19 F NMR spectroscopy (aryl-DdF = 0.5 ppm). 25 The resulting primary and secondary kinetic isotope effects, Scheme 3, were consistent with thos...

An intermolecular, three-component reductive dicarbofunctionalization of alkenes is presented here. The combination of Ni catalysis with TDAE as final reductant enables the direct formation of Csp-Csp and Csp-Csp bonds across a variety of π-systems using two different electrophiles that are sequentially activated with exquisite selectivity under mild reaction conditions.

Olefins devoid of directing or activating groups have been dicarbofunctionalized here with two electrophilic carbon sources under reductive conditions. Simultaneous formation of one C(sp 3 )−C(sp 3 ) and one C(sp 3 )−C(sp 2 ) bond across a variety of unbiased π-systems proceeds with exquisite selectivity by the combination of a Ni catalyst with TDAE as sacrificial reductant. Control experiments and computational studies revealed the feasibility of a radical-based mechanism involving, formally, two interconnected Ni(I)/Ni(III) processes and demonstrated the different ability of Ni(I) species (Ni(I)I vs PhNi(I)) to reduce the C(sp 3 )−I bond. The role of the reductant was also investigated in depth, suggesting that a oneelectron reduction of Ni(II) species to Ni(I) is thermodynamically favored. Further, the preferential activation of alkyl vs aryl halides by ArNi(I) complexes as well as the high affinity of ArNi(II) for secondary over tertiary C-centered radicals explains the lack of undesired homo-and direct coupling products (Ar−Ar, Ar−Alk) in these transformations.

A Pd-catalyzed three component reaction involving terminal alkynes, boronic acids, and perfluoroalkyl iodides is presented here. Trisubstituted perfluoroalkenes can be obtained in a highly regio- and stereocontrolled manner by the simultaneous addition of both aryl and CnFm groups across the triple bond in a radical-mediated process. The reaction is operationally simple offering a broad scope and functional group tolerance.

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