Gallium compl
ex
es containing bridging ph
enyl groups w
er
e pr
epar
ed and charact
eriz
ed. Tr
eatm
ent of triph
enylgallium with 3,5-dim
ethylpyrazol
e, 3,5-diph
enylpyrazol
e, or 3,5-di-
tert-butylpyrazol
e in a 2:1 stoichiom
etry afford
ed th
e ph
enyl-bridg
ed compl
ex
es (C
6H
5)
2Ga(
es/
entiti
es/mgr.gif">-M
e2pz)(
es/
entiti
es/mgr.gif">-C
6H
5)Ga(C
6H
5)
2 (62%), (C
6H
5)
2Ga(
es/
entiti
es/mgr.gif">-Ph
2pz)(
es/
entiti
es/mgr.gif">-C
6H
5)Ga(C
6H
5)
2·C
7H
8 (62%), or (C
6H
5)
2Ga(
es/
entiti
es/mgr.gif">-tBu
2pz)(
es/
entiti
es/mgr.gif">-C
6H
5)Ga(C
6H
5)
2 (40%), r
esp
ectiv
ely, as colorl
ess or off-whit
e crystallin
e solids. Th
es
e compl
ex
es w
er
e charact
eriz
ed by sp
ectral and analytical m
ethods, X-ray crystallography, bridg
e-t
erminal
exchang
e kin
etics, and mol
ecular orbital calculations for simplifi
ed mod
els. Th
e mol
ecular structur
e of (C
6H
5)
2Ga(
es/
entiti
es/mgr.gif">-M
e2pz)(
es/
entiti
es/mgr.gif">-C
6H
5)Ga(C
6H
5)
2 consists of a dim
ethylpyrazolato ligand with a diph
enylgallium group bond
ed to
each nitrog
en atom. A ph
enyl group acts as a bridg
e b
etw
een th
e two gallium atoms. Th
e kin
etics of bridg
e-t
erminal ph
enyl
exchang
e was d
et
ermin
ed by
13C NMR sp
ectroscopy b
etw
een -30 and +30
es/
entiti
es/d
eg.gif">C, and afford
ed th
e following rang
e of activation param
et
ers:
es/gifchars/D
elta.gif" BORDER=0 >
Hes/entities/thermod.gif"> = 6.0-8.9 kcal/mol,
es/gifchars/D
elta.gif" BORDER=0 >
Ses/entities/thermod.gif"> = -23.1 to -32.0
eu, and
es/gifchars/D
elta.gif" BORDER=0 >
Ges/entities/thermod.gif">(298) = 15.5-15.8 kcal/mol. Th
e larg
e, n
egativ
e valu
es of
es/gifchars/D
elta.gif" BORDER=0 >
Ses/entities/thermod.gif"> imply ord
er
ed transition stat
es r
elativ
e to th
e ground stat
e, and rotation along th
e N-GaPh
3 v
ector without gallium-nitrog
en bond cl
eavag
e. Mol
ecular orbital calculations w
er
e conduct
ed at th
e B3LYP/6-311G(d,p) l
ev
el of th
eory on th
e simplifi
ed mod
el H
2Ga(
es/
entiti
es/mgr.gif">-pz)(
es/
entiti
es/mgr.gif">-C
6H
5)GaH
2. Th
e pr
edict
ed out-of-plan
e ph
enyl group ori
entation aris
es from
el
ectronic int
eractions, in which hybridiz
ed orbitals on th
e ph
enyl group cr
eat
e d
elocaliz
ed mol
ecular orbitals. How
ev
er, th
e en
ergy diff
er
enc
e b
etw
een a planar Ga
2N
2C ring and on
e with th
e b
ent carbon atom is only 1.77 kcal/mol, implying that th
e mol
ecular orbitals provid
e littl
e stabilization to th
e out-of-plan
e ph
enyl ligand. Th
e combin
ed r
esults sugg
est that th
e clos
e proximity of th
e gallium atoms is th
e principal d
et
erminant of th
e bridging ph
enyl int
eractions, and that compl
ex
es of th
e h
eavi
er group 13
el
em
ents with bridging hydrocarbon ligands ar
e lik
ely to b
e mor
e acc
essibl
e than th
e curr
ent stat
e of th
e lit
eratur
e would sugg
est.