Alkali metal salts can affect both
the activities and regioselectivities
of alkene hydroformylation catalysts containing polyether-functionalized
phosphorus-donor ligands; however, it is unclear whether these effects
arise from direct alkali metal cation binding to the active catalysts.
To gain more insight into these effects, a series of phosphite-lariat
ether ligands derived from the alkali metal cation binding agents
2-hydroxymethyl-12-crown-4 and 2-hydroxymethyl-15-crown-5 have been
prepared. Rhodium(I) complexes of these ligands have been evaluated
as styrene hydroformylation catalysts in the absence and presence
of a variety of alkali metal salts. The activities of catalysts containing
phosphites derived from 2,2′-biphenol or 1,1′-binaphthol
increased significantly (up to 92%) in the presence of alkali metal
cations that are “moderately oversized” for archetypal
binding to the crown cavity. When this criterion are not met, a decrease
in the catalytic activity is observed upon addition of an alkali metal
salt. NMR titrations (31P{1H} and 1H) of two model cis-Mo(CO)4(phosphite-lariat)2 complexes in which the phosphite was derived from 2,2′-biphenol
were carried out to gain insight into the manner in which the alkali
metal cations interact with the ligands. Both model complexes bind
Li+ through a 2:1 two-site binding mechanism, and the model
complex with the larger crown ether also binds Na+ in this
fashion. In contrast, 1:1 complexes are formed upon Na+ and K+ binding to the model complex containing the smaller
crown ether and upon K+ binding to the model complex containing
the larger crown ether. Correlation between increases in catalyst
activity and binding mode in complexes containing cations “moderately
oversized” for archetypal binding to the crown cavity strongly
suggests that the increases are due to a specific type of alkali metal
cation binding by the lariat ether groups in these catalysts.
Three novel ligands have been prepared by the reactions of 1,1′-(chlorophosphinediyl)bis(1H-pyrrole) with either 2pyridinemethanol or 2,6-pyridinedimethanol or the reaction of 1,1′-biphenyl-2,2′-diyl phosphorochloridite with 2-pyridinemethanol. Measurement of | 1 J P-Se | values demonstrate that the phosphite donor is less basic than the phosphoramidite donors. Coordination preferences of the ligands in octahedral cis-tetracarbonylmolybdenum(0) and square planar cis-dichloropalladium(II) complexes have been evaluated using multinuclear NMR and X-ray crystallography. Rhodium(I) complexes of the Scheme 2. Synthesis of chelating molybdenum complexes 1-3.Scheme 3. Synthesis of palladium chelating complexes 4, 5 and 6.
Capstone teaching laboratory activities
can serve as a crucial
part of the undergraduate learning experience. With this in mind,
a laboratory activity that combines synthesis and multiple characterization
techniques has been developed for an upper-division, laboratory-based
inorganic course. Complexes of Cu(II) and Ni(II) of the amino acid
glycine are first synthesized. These complexes are then characterized
using a variety of spectroscopic (IR, UV–vis, 1H
NMR) techniques to determine the coordination geometries of the metal
centers and thermal (differential scanning calorimetry, thermal gravimetric
analysis) techniques to determine the relative stabilities of geometrical
isomers. Details of the activity, including procedure, experimental
data, and pre/post-test, are provided.
Herein,
we report the 1
J
CH analyses,
natural bond orbital analyses, and X-ray crystal structures
of a number of C, O, and N constrained tricyclic cycles. These experiments
provide access into the nature of the apparent Perlin effect previously
reported in constrained tricyclic cycles, as well as evidence suggesting
both steric contraction and long-range hyperconjugation account for
the observed 1
J
CH perturbations.
We report a true Perlin effect of 10.9 Hz in an azocane and large
steric effect resulting in Δ1
J
C–H = 10.9 Hz in a cyclooctane.
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