Page 8 - Interaction of Multiple Bonded and Unsaturated Heavier Main Group Compounds with Hydrogen, Ammonia, Olefins, and Related Molecules

Reactivity of Multiple Bonded and Main Group Compounds Power

1
0
0
hindrance. DFT calculations on the Ar SnSnAr /ethylene illustrated in Scheme 8. VT H NMR studies yielded an
showed that the initial interactioninvolved one ofthe tinatoms activation enthalpy near 15 kcal mol 1 .Uponheating this
as illustrated in Scheme 6 which shows a synergic interaction above 120 °C, the inverted sandwich structure was re-
between the n þ (LUMO) and π(HOMO) orbitals of ethylene. The generated. For the tin system, the inverse sandwich
calculations also showed that the subsequent steps (which bear structure alone is observed under analogous conditions.
a similarity to those reported by Sekiguchi et al. for the stereo- The mechanism of this reversible rearrangement remains
specific interaction of his disilylyne with 1 equiv of a cis or trans under computational study (in collaboration with G. Merino),
but-2-ene) 25 in the formation of the adducts involved essen- but it is a possibility that the reaction initially involves
interaction in a [2 þ 2] fashion of the dimetallyne with a
tiallyzeroactivationbarriers.Investigationofthecorresponding
double bond from the COT ring as shown in Scheme 9. The
reactions of ethylene and norbornadiene with Ar GeGeAr 0
0
heavier ditetrelene double bond of the [2 þ 2] product may
resulted in the isolation of products analogous to those ob-
then dissociate to give a digermylene species and generate
0
served for Ar SnSnAr butnodissociation ofthe olefin was
0
the inverse sandwich product in which each EAr fragment is
0
apparent at temperatures below their decomposition points.
complexed on opposite sides of the COT ring as observed in
More recent investigations have uncovered further reac-
both the tin and germanium (kinetic) products.
tions with olefins. Treatment of Ar MMAr (M = Ge or Sn) with
0
0
Current work involves the reactions of a wider variety of
COT (1,3,5,7-cyclooctatetraene) results in complete cleavage
olefins with unsaturated heavier main group molecules. The
of the MM multiple bonds to give sandwich complexes as
latter include the group 13 element dimetallenes such as the
40
shown in Scheme 7.
earlier mentioned digallene Ar GaGaAr ,and this species has
0
0
In this reaction, the COT rings have been reduced to
already been shown to display a higher reactivity with a wider
2
afford an almost planar C 8 H 8 10-π aromatic ring for
0
variety of olefins than its group 14 counterpart Ar EEAr (E = Ge
0
which the spectroscopic and structural properties are
or Sn). Currently, the only reactions with unsaturated hydro-
consistent with π-electron delocalization. However, the
carbons that have been reported involve 2,3-dimethyl-1-3-
germanium inverse sandwich compound isomerized in
butadiene which affords an unusual 1,6-digalla-2,3,8,9-tetra-
40b
solution to afford a digermanium substituted analo- 41
methylcyclodeca-3,8-diene ring (Scheme 10). In addition, it
gue of the hydrocarbon molecule hypostrophene as
was shown that Ar GaGaAr reacts with phenyacetylene to
0
0
afford the unsaturated digallacyclohexadiene which can be
SCHEME 7. Multiple Bond Cleavage of a Distannyne or Digermyne by readily reduced by potassium to give a delocalized quasi-
Cyclooctatetraene 42
aromatic digallatabenzene ring.
However, Ar GaGaAr reacts with ethylene, propene, as
0
0
well as a variety of other olefins both cyclic and noncyclic.
Details of these reactions will be reported in the near future.
5. Reactions with Other Unsaturated
Molecules
Both the digermyne Ar GeGeAr and distannyne Ar SnSnAr 0
0
0
0
reacted with isocyanides ButNC or MesNC to afford the
products as shown in Scheme 11. 20,43
2
2
SCHEME 8. Reversible Isomerization of (Ar Ge) 2 (μ 2 -η :η -cot) Occurs with CC and GeGe Multiple Bond Cleavage a
0
a ‡ 1 ‡ 1 1
Isomerization occurs in solution to give thermodynamic product with first order kinetics: activation parameters ΔH = 14.9 kcal mol and ΔS = 6.2 cal mol K .
634 ’ ACCOUNTS OF CHEMICAL RESEARCH ’ 627–637 ’ 2011 ’ Vol. 44, No. 8