Synthesis, structure and fluxional behaviour of isomeric bis(trimethylstannyl)dihydropentalenes

The hexamethylpentalene dianion and other reagents for organometallic pentalene chemistry

“…The C 5 rings deviate slightly from planarity and are slightly bent away from the SnMe 3 substituents such that the angle between their best planes is 7.9u. The Sn-Me bond lengths are slightly less than the sum of the covalent radii of Sn and C (2.17 A ˚), yet the Sn-Pn* bonds are longer; the latter value is comparable to that found in trans-(SnMe 3 ) 2 Pn [2.209(7) A ˚], 20 SnMe 3 (g 1 -Flu*) [2.221(3) A ˚]21 and SnMe 3 (g 1 -Ind*) [2.232(6) A ˚]. 22 The RT 1 H and 13 C NMR spectra of cis/trans-3 show that these isomers are fluxional (presumably proceeding via 1,2-metallotropic rearrangements) and the results are comparable to those found by Ustynyuk on the unsubstituted system.…”

C,N-chelated hexaorganodistannanes, and triorganotin(IV) hydrides and cyclopentadienides

“…The sum of the equatorial C-Sn-C angles is 349.69°, which demonstrates a deviation towards the tetrahedral geometry. There is a notable elongation of Sn1-C10 (2.2922 (19) [19], likely related to the trans effect of the weakly tin coordinating Me 2 N moiety. Also the Sn1-C10-Cg (as centroid of Cp ring) angle (108.95°) is smaller than expected for a non-distorted structure (ideally 125°) [19], for example for (1-(CH 3 ) 3 Sn)(3-(C 6 H 5 ) 3 C)C 5 H 4 (118.0(1)°) [20].…”

“…At 180 K, the onset to a decoalescence, evidenced by a saddle point in the resonance, was observed at 6.81 ppm for 2a. An estimation of the Gibbs free energy for this sigmatropic migration in 2a, based on these data, provides 37 ± 1 kJ/mol, which is higher than for Me 3 Sn(g 1 -C 5 H 5 ), 29.7 ± 2.9 kJ/mol [19]. One might expect that the coordination of Me 2 N-group to tin would increase the ionic character of Sn-Cp bond (trans effect), thus leading to the decrease in energy barrier.…”

Synthesis of organometallic pentalenide complexes

“…Ustynyuk et al reported the synthesis of mono-and bis-Me 3 Sn derivatives of H 2 Pn using tin amides. 55 The reaction of H 2 Pn with one equivalent of Me 3 Sn(NEt 2 ) in boiling hexane produced, after distillation, a mixture of 1-and 2-η 1 -(Me 3 Sn)PnH (Fig. 32).…”