(Aminoferrocenyl)phosphine ligands
2-(1-(dimethylamino)ethyl)-1-(diphenylphosphino)ferrocene (PPFA) and
[η5-cyclopentadienyl][η5-4-(endo-dimethylamino)-3-(diphenylphosphino)-4,5,6,7-tetrahydro-1H-indenyl]iron(II) (PTFA),
were used as ligands in palladium(0) and -(II)
complexes. The reaction of
Pd2(dba)3·CHCl3 with
PPFA or PTFA in the presence of the
electron-withdrawing olefins maleic anhydride (MA) and dimethyl
fumarate (DMFU) gave
the complexes Pd(PTFA)(DMFU) (2),
Pd(PPFA)(MA) (3), and Pd(PPFA)(DMFU)
(4). Allylic
complexes
[Pd(η3-2-Me-C3H4)(PTFA)]Tf
(5) and
[Pd(η3-2-Me-C3H4)(PPFA)]Tf
(6) (Tf = triflate)
were obtained by reaction of PTFA or PPFA with
[Pd(η3-2-Me-C3H4)Cl]2
in the presence of
AgTf. In solution all these compounds exist as mixtures of two
diastereomers, with either
the alkene or the allyl group differently oriented with respect to the
aminophosphine ligand.
1H NMR variable-temperature studies have been carried
out for 2−6 and for
Pd(PTFA)(MA) (1). Rotation of the alkene was observed for
complexes 1−4 on the NMR time
scale.
ΔG
⧧
c has been calculated
and values between 57.6 kJ mol -1 (298 K) and
76.6 kJ mol -1 (373
K) have been obtained. A Pd−N bond rupture which interchanges
the two amino methyl
groups is observed (ΔG
⧧
328 =
63.9 kJ mol-1 to
ΔG
⧧
368 = 74.9 kJ
mol-1) for derivatives of
PPFA, but not for complexes containing PTFA. An EXSY experiment
carried out on complex
5 has evidenced a selective
η3−η1−η3 (carbon
cis to phosphorus) allyl isomerization.
Molecular structures of 4 and 6 were
determined by X-ray structure analysis.
A 9-borabicyclo[3.3.1]nonane dimer is used as the first example of metal-free catalysts for the monohydroboration of carbodiimides with pinacol borane.
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