Page 3 - 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 1. Reaction of the Digermyne Ar GeGeAr (Ar =C 6 H 3 -
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2,6(C 6 H 3 -2,6-Pr 2 ) 2 ) with H 2 under Ambient Conditions

low-coordinate species with multiple bonds between heavy
group 13 elements. It was shown that the large Ar* terphenyl
substituent stabilized the highly colored, monomeric :InAr* in
which the metal had a nonbonded pair and two unoccupied
valence p-orbitals. In 2002, it was shown that the slightly less
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crowding Ar ligand (Ar =C 6 H 3 -2,6(C 6 H 3 -2,6-Pr 2 ) 2 ) permitted
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dimerization to afford the InIn bonded Ar InInAr which had a
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trans-bent structure and a nominal double bond with an InIn
15
distance of 2.9786(5) Å. It wasalso shownthat its gallium and
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thallium analogues Ar GaGaAr and Ar TlTlAr had trans-bent, FIGURE 2. Illustration of the KohnSham valence orbitals for the
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planar, core structures with GaGa and TlTl distances of model species MeGeGeMe. 28
2.6268(7) and 3.0936(8) Å. 15 All three dimers were to varying 2e
butadiene to give [2 þ 2] and [2 þ 4] addition products.
degrees dissociated to monomers in hydrocarbons. The use of Also Sekiguchi et al. have reported that his stable disilyne
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extremely large terphenyls such as C 6 H-2,6(C 6 H 2 -2,4,6-Pr 3 ) 2 - RSitSiR (R = SiPr {CH(SiMe 3 ) 2 } 2 ) reacted stereospecifically
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3,5-Pr 2 (abbreviated Ar*-3,5-Pr 2 ) was shown to stabilize mono- with cis and trans but-2-ene. 25
mers featuring one-coordinate gallium in the solid state. 16 A wide-ranging investigation of the chemical properties
Attempts to synthesize the dimer Ar AlAlAr led to a reaction of the digermynes and distannynes showed that they were
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with solvent toluene to give a [2 þ 4] cycloaddition product. 17a highly reactive. This prompted testing of their reactivity with
Apparently, the putative Ar AlAlAr species, which can be saturated molecules of which the simplest example is
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reduced to form Na 2 Ar AlAlAr , has extremely high reac- 26
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hydrogen. Although no reactions had been reported be-
tivity partly as a result of its singlet diradical character. 18 The
tween any main group molecule and hydrogen under
dimetallenes react 14,15c,19 with a large variety of reagents to 27
ambient conditions, Himmel and Schn€ ockel calculated
give transition metal complexes, 20,14 imides, 21 phosphi- θ
that HGetGeH exhibited a heat of hydrogenation (ΔH R =
nidenes, 22 or chalcogenide derivatives. 23 1
ca. 250 kJ mol ) to give H 2 GeGeH 2. This displayed a
θ
ΔH R = 150 kJ mol 1 when reacted with further equivalent
2. Reactions with Saturated Small Molecules of hydrogen to give H 3 GeGeH 3 . We discovered that the
The low coordination numbers (1 or 2) of group 13 and digermyne Ar GeGeAr reacted readily at 25° and one atm
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group 14 dimers, their deep colors, and their singlet diradical to give a mixture of products as shown in Scheme 1. 26
character 6,18 suggested high reactivity. An early investiga- The addition of 1, 2, or 3 equiv of H 2 produced different
tion in 2002 showed that the stable digermyne Ar*GeGeAr* ratios of the products in Scheme 1. With excess H 2 , only
readily underwent a cyclization with 2,3-dimethy1,3-buta- Ar (H) 2 GeGe(H) 2 Ar and Ar GeH 3 , were obtained in an ap-
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diene to give the product depicted in eq 1. 24 proximately 2:1 ratio. The appearance of the mononuclear
germane Ar GeH 3 in the products indicated cleavage of the
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GeGe bond which may occur via partial dissociation of
the digermene Ar (H)GedGe(H)Ar to germylene, :Ge(H)Ar , 0
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monomers in solution. H 2 may then add to :Ge(H)Ar to yield
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the monogermane Ar GeH 3 . The initial step involves the
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interaction of H 2 with the frontier orbitals at one of the
germanium atoms Ar GeGeAr . Some of the calculated va-
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In 2004, Wiberg et al. showed that the quasi-stable disilyne lence orbitals for the model species MeGeGeMe are illu-
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RSitSiR (R = SiMe(SiBu 3 ) 2 ) reacted with ethylene and strated in Figure 2 where it can be seen that the
Vol. 44, No. 8 ’ 2011 ’ 627–637 ’ ACCOUNTS OF CHEMICAL RESEARCH ’ 629