Page 2 - 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

FIGURE 1. Trans-bending second order JahnTeller effects in HEtEH(E = SiPb) species.
involved reduction of a precursor (monomeric or dimeric or GeMe 3 para-substituents on the central aryl ring of the
organo or silyl substituted element halides) by alkali metals or terphenyl) have tintin distances near 3.06 Å and a bending
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organoaluminum hydrides. Their synthesis had been foresha- angle near 98°. The structures of the latter resemble that of the
dowed by their singly and doubly reduced salts M n REER (M = Li, lead species Ar*PbPbAr* (PbPbC=94.26(4)°;PbPb =
3
5
Naor K;n=1 or 2) in1997 and by the germylyne complex(η - 3.1881(1) Å) and have single bonds. Two isomeric forms are
4
C 5 H 5 )(CO) 2 MoGeC 6 H 3 -2,6-mesityl 2 in 1996. The alkyne ana- possible because there is a very small energy difference (ca. 5
logues have planar, trans-bent core structures with substantial kcal mol ) between them that allows the structures to be
1
deviation from linearity. The bending increases and the bond affected by packing forces. 6,9 In solution, by electronic spec-
order decreases with increasing atomic number so that at lead troscopy, all distannynes are multiple bonded. Only multiple
the PbPb bonding is essentially single. The bending in these bonded isomers have been observed for the digermynes both
5
compounds has been viewed as a second order JahnTeller in solution and the solid state consistent with calculations that
effect involving certain valence orbitals which are vibronically showed that they were the more stable by ca. 15 kcal mol .
1 21
coupledthroughadegeneratesymmetricbendingmodewhich Thisistoolargetoallowsignificantstructuralchangesasaresult
permits orbital mixing as shown in Figure 1. The bending can
of packing forces.
also be interpreted in terms of singlet diradical character The chemistry of stable compounds with multiple bonds
especially in the case of the germanium and tin compounds between the heavier group 13 metals is less developed than
wherethebondorderhasbeendiminishedtoabouttwo.These that of their group 14 neighbors. 1,10,11 Group 13 M(I) metal
compounds are thus “missing” a bond and can be classified as metal bonded clusters have been known for over 20 years. 12
6
non-Kekule singlet diradical species. Currently, about 20stable The metals have a coordination number g 4 which saturates
examples have been isolated or structurally characterized. 1,7,8 the metal valence orbitals. Even in the dimers [M{η -C 5 -
5
5
The tin alkyne analogues can exist as two isomers in the solid (CH 2 Ph) 5 }] 2 (M = In or Tl) 13 the ligands are η -bound which
state and five of the seven structurally characterized distan- leaves no valence orbitals available for further interactions.
nynes feature structures with short tintinbondsnear2.65Å TheMMbondsareweakasevidencedbylong(>3.6Å) MM
distances. Our interest stemmed from attempts to synthesize
and a bending angle near 124°,whereas two(having SiMe 3

628 ’ ACCOUNTS OF CHEMICAL RESEARCH ’ 627–637 ’ 2011 ’ Vol. 44, No. 8