The
previously elusive diphosphadibenzo[a,e]pentalene core skeleton was assembled via a surprisingly
straightforward cyclization pathway starting from R2P-substituted
2,2′-diphosphinotolanes
(R = Ph,
i
Pr). The resulting P-protected
diylidic compounds 4 (R = Ph,
i
Pr) were converted to the corresponding P-bridged ladder stilbenes
via two consecutive oxidation steps: upon selective one-electron oxidation,
the persistent radical monocations 5 (R = Ph,
i
Pr) were obtained and further oxidized to afford
the respective fluorescent and air-stable dications 6 (R = Ph,
i
Pr).
A frustrated Lewis pair composed of an acidic aluminum function (AlR 2 ) and a basic phosphine entity, linked by a xanthene spacer, is capable of cleaving THF. The rate of the ringopening reaction is higher by a factor of 10 for R = C 6 F 5 than that for R = Mes. Structural and theoretical investigations revealed for the case of C 6 F 5 aromatic interactions in the secondary coordination sphere whichin case they also exist in the transition statecould aid ring-opening through a preorientation of the reacting functions. However, in detailed computational studies these were found to occur without contributing significantly to the lowering of the activation barrier.
FLPs featuring aluminum-phosphane interactions, spring-loaded by a rigid biphenylene linker, have been accessed through a route where trimethyltin units at phosphane-functionalized organic backbones are exchanged by an AlCl2 moiety. Upon...
The R2P-functionalized
tolanes 1a (R =
Ph) and 1b (R =
i
Pr) were
employed for the synthesis of [PCCP]-coordinated group 5 complexes.
In the case of vanadium, the d
1-configured
dialkyl species [PCCP]V(CH2SiMe3)2 (3a and 3b) were prepared and found to
be resistant toward oxidation, i.e., the corresponding alkylidene
complexes were not observed upon treatment with various oxidants.
For niobium and tantalum, however, the high-valent d
0-configured alkyl–alkylidene complexes [PCCP]M(=CHSiMe3)(CH2SiMe3) (M = Nb: 6b, M = Ta: 7b) were obtained for the
i
Pr2P-substituted ligand. Both these alkylidenes,
i.e., 6b and 7b, were employed for ring-opening
metathesis polymerizations (ROMP) of strained olefins. Although the
η2-alkyne motifs in 6b and 7b are best described as metallacyclopropenes, the unsaturated ligand
backbone was neither degraded nor copolymerized over the course of
these polymerizations. Upon hydrogenolysis of 7b, however,
the metallacyclopropene backbone was partially hydrogenated, and the
dinuclear (μ-H)3-bridged tantalum(V) complex 8 featuring a metallacyclopropane substructure was formed.
An intermediate in this reaction was shown to catalytically hydrogenate
one or both arenes in naphthalene, while the isolated dimeric species 8 was found to be inactive under identical reaction conditions.
Frustrated Lewis pairs (FLPs) composed of acidic alane and basic phosphane functions, separated by a xanthene linker, can be prepared through the corresponding Me3Sn derivative and methyl aluminum compounds with elimination of Me4Sn. This way MeClAl‐, Cl2Al‐ and (C6F5)2Al‐ moieties could be introduced and the resulting FLPs are stabilized by a further equivalent of the alane precursors. In contact with the FLPs CO2 is bound via the C atom at the phosphane functions and the two O atoms at the Al centers. The residues at the latter determine the binding strength. Hence, in case of MeClAl CO2 capture occurs at higher pressure and under ambient conditions CO2 is released again, while for Cl2Al and (C6F5)2Al CO2 binding becomes irreversible. The results of DFT calculations rationalize these findings by the high thermodynamic stabilization in case of more electronegative residues, which concomitantly lead to higher barriers, and in case of (C6F5)2Al further stabilization is achieved through a low reorganization energy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.