Synthetic, Structural, and Spectroscopic Studies of Sterically Crowded Tin–Chalcogen Acenaphthenes

A series of sterically encumbered peri-substituted
acenaphthenes have been prepared containing chalcogen and tin moieties
at the close 5,6-positions (Acenap­[SnPh3]­[ER], Acenap =
acenaphthene-5,6-diyl, ER = SPh (1), SePh (2), TePh (3), SEt (4); Acenap­[SnPh2Cl]­[EPh], E = S (5), Se (6); Acenap­[SnBu2Cl]­[ER], ER = SPh­(7), SePh (8),
SEt (9)). Two geminally bis­(peri-substituted)
derivatives ({Acenap­[SPh2]}2SnX2,
X = Cl (10), Ph (11)) have also been prepared,
along with the bromo–sulfur derivative Acenap­(Br)­(SEt) (15). All 11 chalcogen–tin compounds align a Sn–CPh/Sn–Cl bond along the mean acenaphthene plane and
position a chalcogen lone pair in close proximity to the electropositive
tin center, promoting the formation of a weakly attractive intramolecular
donor–acceptor E···Sn–CPh/E···Sn–Cl
3c-4e type interaction. The extent of E→Sn bonding was investigated
by X-ray crystallography and solution-state NMR and was found to be
more prevalent in triorganotin chlorides 5–9 in comparison with triphenyltin derivatives 1–4. The increased Lewis acidity of the tin center
resulting from coordination of a highly electronegative chlorine atom
was found to greatly enhance the lp­(E)−σ*­(Sn–Y)
donor–acceptor 3c-4e type interaction, with substantially shorter
E–Sn peri distances observed in the solid
state for triorganotin chlorides 5–9 (∼75% ∑rvdW) and significant 1J(119Sn,77Se) spin–spin
coupling constants (SSCCs) observed for 6 (163 Hz) and 8 (143 Hz) in comparison to that for the triphenyltin derivative 2 (68 Hz). Similar observations were observed for geminally
bis­(peri-substituted) derivatives 10 and 11.