A bulky three-hindered
quadrant bisphosphine ligand, di-1-adamantylphosphino(tert-butylmethylphosphino)methane, named BulkyP*, has been
synthesized via a convergent short pathway with chromatography-free
procedures. The ligand is a crystalline solid and can be readily handled
in air. Its rhodium(I) complex exhibits very high enantioselectivities
and catalytic activities in the asymmetric hydrogenation of functionalized
alkenes.
The novel rhodium (Rh) catalysts [{nbd-(CH2)4-X}RhR] (1, X = PPh2, R = Cl; 2, X = NPh2, R = Cl; 3, X = PPh2, R = triphenylvinyl; nbd = 2,5-norbornadiene) were synthesized,
and their catalytic activities were examined for the polymerization
of phenylacetylene (PA) and its derivatives. Rh-103 NMR spectroscopy
together with DFT calculations (B3LYP/6-31G*-LANL2DZ) indicated that
catalyst 1 exists in a mononuclear 16-electron state,
while 2 exists in dinuclear states. Catalyst 1 converted PA less than 1% in the absence of triethylamine (Et3N). Addition of Et3N and extension of the polymerization
time enhanced the monomer conversion. On the other hand, catalysts 2 and 3 quantitatively converted PA in the absence
of Et3N to afford the polymer in good yields. Catalyst 3 achieved two-stage polymerization of PA.
Control of the conformation
of polymers can be achieved by the ligand exchange reaction of optically active poly(phenyleneethynylene) 1′ containing −Pt(PPh3)2– moieties
in the main chain. Polymer 1′ was reacted with
1,2-bis(diphenylphosphino)ethane (dppe),
1,3-bis(diphenylphosphino)propane (dppp), and 1,4-bis(diphenylphosphino)butane
(dppb) to give the corresponding polymers 2′, 3′, and 4′ containing −Pt(dppe)–,
−Pt(dppp)– , and −Pt(dppb)– moieties in
the main chain, respectively. Polymers 1′ and 2′ exhibited negligibly small circular dichroism (CD)
signals in THF, indicating the absence of regulated chiral structures,
while polymers 3′ and 4′ exhibited
strong CD signals in THF. The dynamic light scattering (DLS) analysis
of the polymer solutions indicated that polymer 3′ formed a chirally regulated one-handed helix intramolecularly bridged
with dppp, and polymer 4′ formed aggregates intramolecularly
and/or intermolecularly bridged with dppb.
Bulky monophosphine-ligated Pd complexes
served as unprecedented
admirable catalysts for the polymerization of a disubstituted acetylene.
The moderately high polymer yields and cis content of the formed polyacetylene
contrasted with those observed for traditional Mo catalyst-based polymer.
These Pd catalysts are strong tools to promote the understanding of
the structure–property relationships of disubstituted acetylenes.
Platinum
(Pt)-containing conjugated polymers were synthesized by
the dehydrochlorination coupling polymerization of cis- and trans-dichlorobis(N-(p-(diphenylphosphino)benzoyl)-l-valine methyl ester)platinum(II)
{cis-PtL
2Cl2 and trans-PtL
2Cl2, L = P(Ph)2-p-C6H4CONHCH[CH(CH3)2]CO2CH3} with 1,4-diethynylbenzene, aiming at obtaining polymers
with controlled geometry at the Pt centers. In the polymerization
of cis-PtL
2Cl2, the geometry at the Pt centers was controlled by the amine used
in the polymerization and the reaction temperature. The formed polymer
with trans-Pt centers exhibited a circular dichroism
signal at the main chain chromophore region in CH2Cl2/MeOH mixed solvent. Based on the crystal packing state and
non-covalent interaction analysis of a model compound, the chiroptical
activity is attributed to aggregation stabilized by intermolecular
π–π, CH−π, and hydrogen-bonding interactions
between the phosphine ligands.
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