Direct Detection of Dimethylstannylene and Tetramethyldistannene in Solution and the Gas Phase by Laser Flash Photolysis of 1,1-Dimethylstannacyclopent-3-enes

Abstract

The photochemistry of 1,1-dimethyl- and 1,1,3,4-tetramethylstannacyclopent-3-ene (4a and 4b, respectively) has been studied in the gas phase and in hexane solution by steady-state and 193-nm laser flash photolysis methods. Photolysis of the two compounds results in the formation of 1,3-butadiene (from 4a) and 2,3-dimethyl-1,3-butadiene (from 4b) as the major products, suggesting that cycloreversion to yield dimethylstannylene (SnMe2) is the main photodecomposition pathway of these molecules. Indeed, the stannylene has been trapped as the Sn-H insertion product upon photolysis of 4a in hexane containing trimethylstannane. Flash photolysis of 4a in the gas phase affords a transient absorbing in the 450-520-nm range that is assigned to SnMe2 by comparison of its spectrum and reactivity to those previously reported from other precursors. Flash photolysis of 4b in hexane solution affords results consistent with the initial formation of SnMe2 (lambda(max) approximately 500 nm), which decays over approximately 10 micros to form tetramethyldistannene (5b; lambda(max) approximately 470 nm). The distannene decays over the next ca. 50 micros to form at least two other longer-lived species, which are assigned to higher SnMe2 oligomers. Time-dependent DFT calculations support the spectral assignments for SnMe2 and Sn2Me4, and calculations examining the variation in bond dissociation energy with substituent (H, Me, and Ph) in disilenes, digermenes, and distannenes rule out the possibility that dimerization of SnMe2 proceeds reversibly. Addition of methanol leads to reversible reaction with SnMe2 to form a transient absorbing at lambda(max) approximately 360 nm, which is assigned to the Lewis acid-base complex between SnMe2 and the alcohol.

The photochemistry of a potential diphenylsilylene precursor. Time-resolved spectroscopic studies of the reactivity of a transient vinylsilirane

“…The results of this work indicate that 1-silacyclopent-3-ene derivatives will likely not show the same general suitability as their germanium [23,24,34,40] and tin [41] homologues as photochemical precursors to reactive metallylenes for study by time-resolved UV/vis absorption methods in solution. Nevertheless, they clearly show considerable potential as precursors for more detailed kinetic studies of the chemistry of reactive vinylsiliranes, the key primary intermediates in the reaction of silylenes with conjugated dienes [18,27,28,[42][43][44].…”

Direct detection of methylphenylgermylene and 1,2-dimethyl-1,2-diphenyldigermene — Kinetic studies of their reactivities in solution

“…This behaviour is again consistent with rapid reversible reaction, but with an equilibrium constant of less than ca. 1000 (mol/L) -1 (13). A rate constant of k Q = (4 ± 2) × 10 9 (mol/L) -1 s -1 was estimated from the decay rate constants for the fast initial component of the bimodal decay profiles from several determinations (at shorter timescales) in the presence of 1.0-2.0 mmol/L DMB, analyzed in the same way as the data obtained with DMP, while a value of K SV = 175 ± 25 (mol/L) -1 was obtained from analysis of the digermene peak signal strengths according to eq.…”

Functionalized tetrastannacyclobutanes, Part I

“…Single crystals of the ethyl (3) and propyl (4) substituted molecules could be isolated from THF (3,4) and toluene(3) solution. However due to high disorder of the t butyl groups none of these crystals gave reliable structures.…”

“…Puff et al [2] were the first who fully characterized octa-t butyl-and octa-t amyltetrastannacyclobutane in 1986. Also octa-methyl- [3] and octa-phenyltetrastannacyclobutane [4] were postulated, although their structures have never been proven by X-ray analysis.…”

“…Sn(1)) = 15.0 Hz,3 J( 1 H-119/117 Sn(2,4)) = 30.9 Hz], 1.42-1.55 ppm [m, 63 H] 13 C { 1 H} NMR (75.50 MHz, CDCl 3 ): d = À10.83 ppm [s, 1 C 4 , 1 J( 13 C-119/117 Sn(1)) = 66.8 Hz, 2 J( 13 C-119/117 Sn(2,4)) = 22.4 Hz], 37.18 ppm [s, 1 C q , 1 J( 13 C-119/117 Sn) = n.obs. ], 37.56 ppm [s, 2 C q ], 39.55 ppm [s, 1 C q ], 34.66-35.09 ppm [m, 21 C].…”