Exploring new lanthanide metallacycles
and finding their unique
chemistry different from the analogues of transition metals are of
great interest and importance. In this work, we reported the synthesis,
characterization, and reactivity toward nitriles of two lanthanide
metallacyclopropenes: lutetacyclopropene 2a and dysprosacyclopropene 2b. The selective coupling of 2a and three molecules
of PhCN was found for the first time to provide the unexpected fused
lutetacycle 3a with one 1,6-dihydropyrimidine ring. Mechanistic
studies by DFT calculations reveal that the triple insertion of PhCN
into 2a proceeds through four key steps: the insertion
of the first PhCN into 2a giving azalutetacyclopentadiene IM1, the insertion of the second PhCN into the Lu–N
bond of IM1, the intramolecular electrocyclization providing
a highly strained η2-pyrimidine metallacycle, and
the insertion of the third PhCN into the Lu–Csp3 bond. Isolation and characterization of two active intermediates,
azalutetacyclopentadiene IM1 and η2-pyrimidine
dysprosacycle, provide critical evidence for the formation of 3a. Furthermore, IM1 was also reported to react
with TMSCN, isocyanides, or W(CO)6 to furnish the fused
[4,5] lutetacycles. The chemistry of two lanthanide metallacyclopropenes
with nitriles is significantly different from these metallacyclopropenes
of scandium and other metals. Most notably, the azalutetacyclopentadienes,
η2-pyrimidine complex, and other metallacycles all
represent the first examples in rare-earth organometallic chemistry;
the formation of these new lutetacycles provides concrete evidence
for understanding the mechanism of transition metal promoted or catalyzed
[2+2+2] cycloaddition between alkynes and nitriles.
Converting
elemental white phosphorus directly into organophosphorus
or polyphosphorus is meaningful, challenging and attractive. The ate-complexes
of aluminacyclopentadienes 1a,b react with
P4 to afford selectively the cyclotetraphosphanes 2a,b featuring four newly formed P–C bonds
and a planar square cyclo-P4 ring. Density
functional theory calculations show that the conversion of tetrahedral
P4 to planar cyclo-P4 moiety
undergoes through an unexpected 1,1-P-insertion/Diels–Alder reaction/isomerization
cascade process. The reaction of 2a with iodomethane
or p-benzoquinone afforded the P-methylation product 3 and the metal-free cyclotetraphosphane 4, respectively. Interestingly, reduction of 4 generated the phospholyl anions 5 and 6 while treatment of 4 with iodomethane afforded the
phospholyl cation 7.
Selective cleavage of C–C bonds within arene rings
is of
great interest but remains elusive, especially for the molecules possessing
the active and inert C–C bonds. Here, we report that the active
and inert C–C bonds of biphenylene could be controllably cleaved
by the reaction of biphenylene, potassium graphite, and rare-earth
complexes with different metal centers. For scandium, the bond activation
occurs at the Caryl–Caryl single bond,
yielding 9-scandafluorene. For Lu, the reaction goes through ring
contraction of the aromatic ring in biphenylene to provide benzopentalene
dianionic lutetium. The origin of the selectivity and the reaction
mechanism were illustrated by the isolation of intermediates and DFT
calculations.
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