Direct Detection, Dimerization, and Chemical Trapping of Dimethyl- and Diphenylstannylene from Photolysis of Stannacyclopent-3-enes in Solution

Abstract

Dimethyl- and diphenylstannylene (SnMe2 and SnPh2, respectively) have been successfully detected and characterized in solution. The stannylenes were generated by photolysis of 1,1,3-trimethyl-4-phenyl- (2) and 3,4-dimethyl-1,1-diphenylstannacyclopent-3-ene (3), respectively, which have been shown to extrude the species cleanly and in high (0.6 < Φ < 0.8) quantum yields through trapping studies using dichlorodimethylstannane (Me2SnCl2) as the stannylene substrate. Laser flash photolysis of 2 and 3 in deoxygenated hexanes affords promptly formed transient absorptions assigned to SnMe2 (λmax = 500 nm; ε500 = 1800 ± 600 M–1 cm–1) and SnPh2 (λmax = 290, 505 nm; ε500 = 2500 ± 600 M–1 cm–1), respectively, which decay with absolute second-order rate constants within a factor of 2 of the diffusional limit in both cases. The decay of the stannylenes is accompanied by the growth of new transient absorptions ascribable to the corresponding dimers, the structures of which are assigned with the aid of DFT and time-dependent (TD) DFT calculations at the (TD)­ωB97XD/6-31+G­(d,p)C,H,O-LANL2DZdpSn level of theory. Dimerization of SnMe2 affords a species exhibiting λmax = 465 nm, which is assigned to the expected SnSn doubly bonded dimer, tetramethyldistannene (Me2SnSnMe2, 16a), in agreement with earlier work. In contrast, the spectrum of the dimer formed from SnPh2 exhibits strong absorptions in the 280–380 nm range and a very weak absorption at 650 nm, on the basis of which it is assigned to phenyl­(triphenylstannyl)­stannylene (17b). The calculations suggest that 17b is formed via ultrafast rearrangement of a novel phenyl-bridged stannylidenestannylene intermediate (20), which can be formed either directly by “endo” dimerization of SnPh2 or by isomerization of the “exo” dimer, tetraphenyldistannene (16b); the predicted barriers for these rearrangements are consistent with the experimental finding that the observed product is formed at close to the diffusion-controlled rate. Absolute rate and equilibrium constants are reported for the reactions of SnMe2 and SnPh2 with Me2SnCl2 and methanol (MeOH), respectively, in hexanes at 25 °C.

Dynamic Behavior and Isomerization Equilibria of Distannenes Synthesized by Tin Hydride/Olefin Insertions: Characterization of the Elusive Monohydrido Bridged Isomer

“…In addition, the relatively large C(6)–Sn(2)–Sn(1)–C(3) angle indicates that a (C(3)) methyl or ethyl substituent is aligned with the empty p-orbital on the Sn(2) atom which lies perpendicular to the coordination plane at Sn(2), suggesting incipient methyl or ethyl bridging. This is consistent with the calculated transition state for the conversion of the related distannene­(SnPh 2 ) 2 to its asymmetric isomer PhSnSnPh 3 …”

“…This is consistent with the calculated transition state for the conversion of the related distannene(SnPh 2 ) 2 to its asymmetric isomer PhSnSnPh 3 . 43 The structural data for Ar 4, left) reveal it to have an asymmetric monohydrido stannylstannylene structure. The Sn(1) atom has a distorted tetrahedral coordination and is bound to its partner tin atom Sn(2), a t-butylethyl group, a terphenyl ligand, and a hydride with a Sn−H distance of 1.575(7) Å.…”

Molecular Zinc Species with Ge–Zn and Sn–Zn Bonds: A Reversible Insertion of a Stannylene into a Zinc–Carbon Bond

“…The tetrylenes of the heavier group 14 elements (:ER 2 , E = Si, Ge, Sn, or Pb; R = bulky substituent) have an extensive chemistry that has been investigated for over four decades. − They are characterized by a singlet ground state in which a nonbonded electron pair occupies one of the two valence orbitals and which may function as an electron pair donor. The existence of an adjacent unoccupied p-orbital allows the tetrylenes to behave as donor–acceptor molecules in a synergistic manner, and this has enabled their facile reactions with small molecules such as H 2 , − NH 3 , − CO, and C 2 H 4 . , The insertion chemistry of group 14 metalylenes has also been especially well documented through reactions with the aforementioned small molecules as well as with organohalides, − transition metal halides, H 2 O, − MeOH, , N 2 H 4 , the group 13 alkyls AlMe 3 and GaR 3 (R = Me, Et), and white phosphorus P 4 . These insertions have proven useful for the synthesis of uncommon bond types in molecular species, such as Ge–Al, Sn–Al, and Sn–Ga bonds.…”

Reactions of m-Terphenyl-Stabilized Germylene and Stannylene with Water and Methanol: Oxidative Addition versus Arene Elimination and Different Reaction Pathways for Alkyl- and Aryl-Substituted Species

“…A logical extension of this chemistry is the investigation of the reactions of E­(Ar Me 6 ) 2 with hydroxyl compounds and of water and methanol in particular. Although the insertion of transient tetrylenes such as EH 2 , EMe 2 , or EPh 2 (E = Si, Ge, or Sn) into O–H bonds has been studied both experimentally and theoretically, there are only a few examples of similar reactions involving stable acyclic tetrylenes that yield structurally characterized products. Most notably, Lappert et al have reported the crystallographic characterization of {(Me 3 Si) 2 CH} 2 Ge­(H)­OEt from the reaction of Ge­{CH­(SiMe 3 ) 2 } 2 with ethanol, while Pörschke et al obtained {(Me 3 Si) 2 CH} 2 Sn­(H)­OH by reacting Sn­{CH­(SiMe 3 ) 2 } 2 with excess water .…”