The iridium(I) complex [IrCl(BPEP-H)]
(1), coordinated
with 2,6-bis[2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine
(BPEP-H) as a PNP-pincer-type phosphaalkene ligand, has been synthesized
and fully characterized by elemental analysis, NMR spectroscopy, and
X-ray diffraction analysis. Complex 1 (1 mol %) catalyzes N-alkylation of primary and secondary amines with alcohols,
leading to the selective formation of secondary and tertiary amines,
respectively. Primary amines are smoothly alkylated with a variety
of benzylic and aliphatic alcohols (1 or 3 equiv) at 100 °C under
basic conditions (CsOH, 10 mol %) to give the corresponding secondary
amines in good to high yields. On the other hand, N-alkylation of secondary amines with benzyl alcohol (3 equiv) proceeds
in the presence of KH2PO4 (5 mol %) at 140 °C
to afford tertiary amines in high yields.
A series of Ir I complexes [Ir(L)(PPEP*)] [L = Cl -(3), CO (4), tBuNC (5), PMe 3 (6), PPh 3 (7)], coordinated with a PNP-pincer-type phosphaalkene ligand bearing a dearomatized pyridine ring (PPEP*), have been prepared and their catalytic properties for the dehydration/condensation of amines with alcohols has been examined. The catalytic reactions successfully proceed under base-free conditions to give N-alkylated amines and their dehydrogenation derivatives (imines). The product selectivity is [a]
2,6-Bis[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine
(BPEP-Ph) reacts with [Ru3(CO)12] or [RuCl(η3-allyl)(CO)3] in toluene at elevated temperatures
to afford the three types of PNP-pincer complexes 1–3. The reaction of BPEP-Ph with [Ru3(CO)12] under vacuum forms a mixture of [Ru(CO)2(BPEP-Ph)] (1) and a dicarbonylruthenium(0) complex (2);
the latter complex has an unsymmetrical PNP-pincer ligand with 1-phenyl-2-phosphaethenyl
and phenyl(benzo[b]phospholan-1-yl)methyl groups
at the 2,6-positions of the pyridine core, which is formed by intramolecular
C–H addition of a t-Bu group to the PC
bond. On the other hand, the reaction of BPEP-Ph with [RuCl(η3-allyl)(CO)3] affords a dicarbonylruthenium(II)
chloride (3) with an unsymmetrical PNP-pincer ligand
bearing a dearomatized pyridyl group with 1-phenyl-2-phosphaethenyl
and α-(benzo[b]phospholan-1-yl)benzylidene
substituents at the 2,6-positions. Treatment of 3 with i-PrOK in THF results in selective formation of 2. Complexes 1–3 have been isolated
as crystalline compounds and examined in detail by IR and NMR spectroscopy,
X-ray diffraction studies, and DFT calculations. Complex 1 exhibits catalytic activity toward N-alkylation
of amines (RNH2) with alcohols (R′CH2OH) to give imines (RNCHR′) as major products.
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