(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.
The ruthenium(II) arene dimer [{RuCl(μ-Cl)(η 6 -p-cymene)} 2 ] readily reacted with 4 equiv of guanidines ( i PrHN) 2 CNR (R = i Pr (1a), 4-C 6 H 4 t Bu (1b), 4-C 6 H 4 Br (1c), 2,4,6-C 6 H 2 Me 3 (1d), 2,6-C 6 H 3 i Pr 2 (1e)) in toluene at room temperature to generate the mononuclear complexes [RuCl{κ 2 N,N′-C(NR)(N i Pr)NH i Pr}(η 6 -p-cymene)] (2a−e) and the easily separable guanidinium chloride salts [( i PrHN) 2 C(NHR)][Cl] (3a−e). Compounds 2a−e and 3a−e were fully characterized by elemental analysis and IR and NMR spectroscopy. The structures of [RuCl{κ 2 N,N′-C-(N i Pr) 2 NH i Pr}(η 6 -p-cymene)] (2a) and [RuCl{κ 2 N,N′-C(N-4-C 6 H 4 t Bu)(N i Pr)NH i Pr}(η 6 -p-cymene)] (2b) were also determined by X-ray diffraction analysis. Regardless of the steric requirements of the aromatic substituents, a nonsymmetric coordination of the guanidinate anions in 2b−e was observed, in complete accord with theoretical calculations (DFT) on the corresponding [RuCl{κ 2 N,N′-C(NR)(N i Pr)-NH i Pr}(η 6 -p-cymene)] and [RuCl{κ 2 N,N′-C(N i Pr) 2 NHR}(η 6 -p-cymene)] models. Remarkably, complexes 2a−e were active catalysts for the redox isomerization of allylic alcohols in the absence of base, which represents the first catalytic application known for ruthenium guanidinate species.
N,N′-Phosphinoguanidinate Al compounds rearrange under mild conditions to phosphinimine-amidinato derivatives via an unprecedented carbodiimide de-insertion followed by [3+2] cycloaddition.
Carbodiimides catalyse the reduction of CO2 with H-BBN or BH3·SMe2 to give either mixtures of CH2(OBBN)2 and CH3OBBN or (MeOBO)3 and B(OMe)3 under mild conditions (25-60 °C, 1 atm CO2). Stoichiometric reactions and theoretical calculations were performed to unveil the mechanism of these catalytic processes.
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