74. Gibbons,
S. K.; Xu, Z.; Hughes, R. P.; Glueck, D. S.;
Rheingold, A. L. Chiral Bis(Phospholane) PCP
Pincer Complexes: Synthesis, Structure, and
Nickel-Catalyzed Asymmetric Phosphine
Alkylation. Organometallics2018,
37, 2159–2166.
Abstract
A known ligand precursor, prepared by an improved
method from 1,3-bis(bromomethylbenzene), a base, and (R,R)-2,5-dimethylphospholane-borane,
was deprotected with DABCO and used to prepare chiral m-xylene-based
PCP pincer complexes. Reaction with Ni(DME)Br2 and NEt3
gave square planar Ni(DuPinPhos)(Br) (9), which was
crystallographically characterized. Heating with [Ir(COE)2Cl]2
yielded the dinuclear hydride complex [Ir(DuPinPhos)(H)(Cl)]2(μ-C6H4(CH2-dimethylphospholanyl)2]
(10), which contained both pincer chelates and a bridging
bis(phospholane). Nickel complex 9 was a catalyst
precursor for enantioselective alkylation of secondary phosphines
with 2-bromomethylnaphthalene using the base NaOSiMe3.
The dynamic behavior of a catalytic intermediate, the
P-stereogenic terminal phosphido complex Ni(DuPinPhos)(PPhIs) (Is
= 2,4,6-(i-Pr)3C6H2), was
characterized by variable temperature NMR spectroscopy.
