[754-25-6] · C4H9F3Sn · Trimethyl(trifluoromethyl)stannane · (MW 232.84)
(a low-temperature difluorocarbene source1)
Alternate Name: (trifluoromethyl)trimethyltin.
Physical Data: mp -57 to -53.2 °C;2 bp 100-101 °C;3 1H NMR (90 MHz) d 0.42; 19F NMR (84.6 MHz) d -28;4,5 IR (KBr) (cm-1) 3080, 3010, 2940, 1330, 1220, 1210, 1205, 1160, 1075, 810, 785, 730, 541, 520.2,3
Solubility: sol benzene, carbon tetrachloride, DME, petroleum ether, pyridine, methylene chloride.
Preparative Methods: prepared in 81% yield by reaction of Hexamethyldistannane with Trifluoroiodomethane in a sealed tube at 80 °C for 20 h (eq 1).3 Without compromising the yield, this reaction may also be performed at rt by irradiating for 6 h with a 250 W UV lamp.6,7 Reaction of Me3SnX (X = OCOCF3 or Br) with an alkylating agent, such as (CF3)2Cd, may also be used to synthesize trimethyl(trifluoromethyl)tin in high yields.8-10
Handling, Storage, and Precautions: prolonged contact or heating with water causes decomposition to produce fluoroform. Temperatures above 150 °C cause decomposition to trimethyltin fluoride.3
Heating trimethyl(trifluoromethyl)tin in a sealed tube at 150 °C for 15 h is believed to produce difluorocarbene as evidenced by the formation of gem-difluorocyclopropanes in the presence of alkenes (eq 2).3 Additionally, difluorocarbene insertion into an acid fluoride bond also occurs under these conditions.11
The addition of Sodium Iodide to trimethyl(trifluoromethyl)tin allows the generation of difluorocarbene at significantly lower temperatures (eq 3),12,13 thereby making reactions with thermally unstable alkenes accessible. The reaction is believed to occur via a pentacoordinated trimethyl(trifluoromethyl)tin iodide intermediate. The trifluoromethyl anion, which is unstable even at -100 °C, then decomposes to produce the difluorocarbene.
Fluoride14 and chloride15 anions are also effective as nucleophiles and generate difluorocarbene in good yields. The Tris(dimethylamino)sulfonium Difluorotrimethylsilicate (TASF) catalyzed conversion of sulfonyl fluorides to aryl trifluoromethyl sulfones is an illustration of the use of the former anion (eq 4).14 Interestingly, the corresponding silicon reagent, Trifluoromethyltrimethylsilane, is as effective as the tin reagent in these reactions.14
Reaction of trimethyl(trifluoromethyl)tin with Lewis acids such as BX3 (X = F, Cl) appears to produce difluorocarbene, as indicated by its insertion into the boron-halogen bond.16,17 This too presumably occurs via the aforementioned decomposition of the trifluoromethyl anion.
Theresa A. Devlin & David J. Jebaratnam
Northeastern University, Boston, MA, USA