Page 9 - 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

SCHEME 9. Possible Route to Group 14 Element Inverse Sandwich Compounds

SCHEME 10. Reaction of Ar GaGaAr with 2,3-Dimethyl-1,3-butadiene SCHEME 11. Reactions of Ar MMAr (M = Ge or Sn) with Isonitriles
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or Phenylacetylene and the Reduction of the Latter Product to Give a
Delocalized Digallatabenzene

complexes were unsuccessful. The 2:1 complexes were
unstable to dissociation in toluene at room temperature
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The reaction of Bu NC with Ar GeGeAr forms the 1:1 adduct although they can be isolated and structurally characterized
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Ar GeGeAr (CNBu ) only. The isocyanidebinds to oneof the at low temperature. The complexes featured relatively long
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germaniums in the Ge 2 {C(ipso)} 2 core plane and not perpendi- SnSn bonds of 2.928(2) Å for Ar SnSnAr (CNBu ) 2 and
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cular to it as would be expected if it bonded to a π*orbital. 3.0412(3) Å for Ar SnSnAr (CNMes) 2 consistent with SnSn
Moreover the GeGe bond distance increases only slightly single bonds. They were isolated as red crystals but when
from 2.2850(6) to2.3432(9) Å. This findingis entirely consistent dissolved in hexane at room temperature they gave a green
with the MO picture shown in Figure 2 where the LUMO to solution that displayed two absorptions at 410 and 597 nm,
which the isocyanide binds is only slightly bonding and lies in characteristic of the π f n þ and n f n þ transitions of
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the Ge 2 {C(ipso)} 2 plane. In contrast, use of the essentially two- Ar SnSnAr . Cooling the solution to ca. 40° restored the red
dimensional MesNC: permitted binding of a second isocyanide color (absorption at 510520 nm) and van't Hoff analysis of
which interacts with lowest energy orbital available, the the VT 1 H NMR spectra afforded ΔH assn = 25(3) and
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LUMOþ1. This produces a large increase (>0.4 Å) in the GeGe 127(4) kJ mol 1 for the Bu NC and MesNC adducts, with
bond length to 2.6626(8) Å consistent with the antibonding the difference being attributable to the higher steric require-
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character of the orbital. ment of the Bu NC which promotes dissociation. Coordina-
The less crowded distannyne complexed two equiv. of tion occurred in the empty 5p orbital perpendicular to the
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both Bu NC: and MesNC:. 43 Attempts to synthesize 1:1 coordination plane. Sekiguchi 44 and co-workers showed
Vol. 44, No. 8 ’ 2011 ’ 627–637 ’ ACCOUNTS OF CHEMICAL RESEARCH ’ 635