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

Abstract

The tin(II) hydride [ArSn(μ-H)](Ar = CH-2,6(CH-2,4,6-Pr)) (1a) reacts with 2 equiv of ethylene or t-butylethylene at ca. 25 °C to yield Sn(Ar)R(R = ethyl or t-butylethyl), which exist either as a symmetric distannene Ar(R)SnSn(R)Ar (2a or 5a) or an unsymmetric stannylstannylene ArSnSnRAr (3a). In contrast, the less crowded Sn(II) hydride [ArSn(μ-H)] (Ar = CH-2,6(CH-2,6-Pr)) (1b) reacts with excess ethylene to give Ar(CHCH)Sn(CHCH)Sn(CHCH)(CHCH)Ar (4) featuring five ethylene equivalents, one of which is dehydrogenated to an vinyl, -CH═CH, group. The Ar isomers of 2a and 3a, i.e., [ArSn(CH)] (2b) and ArSnSn(CH)Ar (3b) are obtained by reaction of [ArSn(μ-Cl)] with EtLi or EtMgBr. The isomeric pairs 2a and 3a are separated by crystallization at different temperatures. Variable-temperature H NMR spectroscopy indicates fast ethyl group exchange between Ar(CH)SnSn(CH)Ar (Ar = Ar (2a) or Ar (2b)) and ArSnSn(CH)Ar (Ar = Ar (3a) or Ar (3b)) with ΔG = 14.2 ± 0.65 kcal mol for 2a/3a and 14.8 ± 0.36 kcal mol for 2b/3b. The bulkier distannenes [ArSn(CHCHBu)] (Ar = Ar (5a) or Ar (5b)), obtained from 1a or 1b and t-butylethylene, dissociate to ArSnCHCHBu monomers in solution. At lower temperature, they interconvert with their stannylstannylene isomers with parameters K = 4.09 ± 0.16 for 5a and 6.38 ± 0.41 for 5b and ΔG = -1.81 ± 0.19 kcal mol for 5a and -1.0 ± 0.03 kcal mol for 5b at 298 K. The 1:1 reaction of 1a or 1b with 5a or 5b yields the unknown monohydrido species SnRHAr which has the structure ArSn-Sn(H)(CHCHBu)Ar (6a) or the monohydrido bridged ArS n(μ-H)S n(CHCHBu)Ar (6b). The latter represents the first structural characterization of a monohydrido bridged isomer of a ditetrelene.

Reactivity of a N→Sn Coordinated Distannyne: Reduction and Hydrogen Abstraction

“…The Sn H group resonates as a broad signal at δ 7.62 ppm. This is very close to values of the Sn H fragment found in the asymmetric tin hydrides Ar i Pr6 SnSn(H)(CH 2 CH 2 t Bu)Ar i Pr6 [Ar i Pr6 = C 6 H 3 ‐2,6‐(C 6 H 3 ‐2,4,6‐ i Pr 2 ) 3 ] ( δ 7.56 ppm) and Ar i Pr8 SnSn(H) 2 Ar i Pr8 [Ar i Pr8 = C 6 H‐2,6‐(C 6 H 2 ‐2,4,6‐ i Pr 3 ) 2 ‐3,5‐ i Pr 2 ] ( δ 7.92 ppm), where the Sn H fragment is coordinated by another ArSn group. In contrast, the value Sn H in 2 is shifted downfield, in comparison with IPr · SnH 2 · W(CO) 5 ( δ 5.56 ppm), but upfield when compared with terphenyltin(II) hydrides (the range of δ SnH is 9.28–9.11 Hz) …”

Structural and electronic studies of substituted m-terphenyl lithium complexes

“…[1][2][3][4][5][6] Although a plethora of m-terphenyl frameworks have been designed, most studies have been structurally focused, aimed at investigating the effects of steric bulk on the geometries, bonding modes, and reactivities of the resulting compounds. [7][8][9][10][11][12][13][14][15][16][17][18] For instance, the solid state structures observed for a series of m-terphenyl lithium complexes vary depending on the steric demands of the flanking ortho-aryl substituents. 19,20 Increasing the steric bulk of 2,6-Ar 2 C 6 H 3 Li alters its aggregation state from a dimer, 19 to a more crowded dimer featuring η 6 -arene coordination of the flanking aryl groups, 20 to a monomer stabilised by a coordinated molecule of benzene, 20 for Ar = Mes (2,4,6-Me 3 C 6 H 2 ), Dipp (2,6-i-Pr 2 C 6 H 3 ) and Tripp (2,4,6-i-Pr 3 C 6 H 2 ) respectively.…”

Facile C–H Bond Metathesis Mediated by a Stannylene

“…31−33 These absorption wavelengths are also consistent with those of the stannylenes mentioned above. These include Ar i P r 4 SnCH 2 CH 2 Bu t (486 nm), 3 1 Ar iPr6 SnCH 2 CH 2 Bu t (484 nm), 31 and Ar iPr4 SnR (R = norbornyl, 494 nm; norbornenyl, 502 nm) 33 and Ar iPr4 Sn-(norbornyl)SnAr iPr4 (496 nm). 33 The reaction depicted in Scheme 2 shows direct cleavage of Sn−C and C−H bonds for which a radical mechanism is a possibility.…”

“…These include Ar i P r 4 SnCH 2 CH 2 Bu t (486 nm), 3 1 Ar iPr6 SnCH 2 CH 2 Bu t (484 nm), 31 and Ar iPr4 SnR (R = norbornyl, 494 nm; norbornenyl, 502 nm) 33 and Ar iPr4 Sn-(norbornyl)SnAr iPr4 (496 nm). 33 The reaction depicted in Scheme 2 shows direct cleavage of Sn−C and C−H bonds for which a radical mechanism is a possibility. 34 The observed ready cleavage of the Sn−C bond, apparently under steric pressure, receives support from the decomposition, under similar reaction conditions, 35,36 of the distannyne Ar iPr4 SnSnAr iPr4 to form the cluster Sn 7 (Ar iPr4 ) 2 in which five of the seven tins no longer carry an Ar iPr4 substituent.…”

“…The similarly substituted distannene Ar i Pr4 SnCH 2 C 6 H 4 -4-Bu t was reported to have a 119 Sn NMR resonance further upfield at 1205.7 ppm and was initially assigned a dimeric structure in solution. However, since that publication in 2004, several other related alkyl/aryl monomeric stannylenes have been characterized and their 119 Sn NMR chemical shifts determined. − These include Ar i Pr4 SnCH 2 CH 2 Bu t and Ar i Pr6 SnCH 2 CH 2 Bu t , which have 119 Sn NMR chemical shifts of 1875 and 1832 ppm and Ar i Pr4 SnR (R = norbornyl, 1530 ppm; norbornenyl, 1709 ppm) and Ar i Pr4 Sn­(norbornyl)­SnAr i Pr4 (1484 ppm). Thus, the majority of reported chemical shifts for stannylenes support monomeric structures for 1a – c in solution.…”