Subphthalocyaninato Boron(III) Hydride: Synthesis, Structure and Reactivity

Abstract

Subphthalocyanine (SubPc) chemistry has been limited so far by their high sensitivity toward strong nucleophiles. In particular, the substitution of the axial chlorine atom by a nucleophilic group in the case of less‐reactive SubPcs, such as those bearing electron‐withdrawing peripheral substituents, presents some limitations and requires harsh conditions. By taking advantage of the electrophilic character of DIBAL‐H, it has been possible to prepare for the first time SubPc‐hydride derivatives that exhibit high reactivity as hydroboration reagents of aldehydes. This hydride transfer requires using a typical carbonyl activator (trimethylsilyl triflate) and only one equivalent of aldehyde, affording SubPcs with an axial benzyloxy group in good yield. This transformation has proven to be a useful alternative method for the axial functionalisation of dodecafluoroSubPc, a paradigmatic SubPc derivative, by using electrophiles for the first time. Considering the increasing interest in SubPcs as electron‐acceptor semiconductors with remarkable absorption in the visible range to replace fullerene in organic photovoltaic (OPV) devices, it is of the utmost importance to develop new synthetic methodologies for their axial functionalisation.

Electronic Structure, Bonding, and Stability of Boron Subphthalocyanine Halides and Pseudohalides

“…Reaction of F-BsubPc (X = F) also does not apply, c) end points for the formation mechanism of H-BsubPc. [55] PhO, 2,3,4,5,6F-PhO>Br-BsubPc). Hence, Br-BsubPc is a fitting precursor structure for further synthesis steps, whereas F-BsubPc is the most suitable candidate for long term device performance.…”

“…[23][24][25][39][40][41][42]44] Likewise, for all pseudohalides the B-O bond length is found to be ≈1.43 Å, whereas for H-BsubPc it is found to be 1.21 Å , also in excellent agreement with experimental findings in the solid state (see Section S1, Supporting Information). [15,43,55] We further compute selected bond lengths and "bowl depths" for the various systems. For Cl-BSubPc, as a typical system, the results are compared to experimental ones from numerous crystal structures in Figure 2, with a similar comparison for various BsubPc derivatives given in Section S1, Supporting Information.…”

“…[ 23–25,39–42,44 ] Likewise, for all pseudohalides the B–O bond length is found to be $$\approx$$1.43 Å, whereas for H‐BsubPc it is found to be 1.21 Å , also in excellent agreement with experimental findings in the solid state (see Section S1, Supporting Information). [ 15,43,55 ]…”

“…As formation of I-BsubPc is not possible, I does not apply. Reaction of F-BsubPc (X = F) also does not apply, c) end points for the formation mechanism of H-BsubPc [55].…”

A Theoretical Survey of the UV–Visible Spectra of Axially and Peripherally Substituted Boron Subphthalocyanines

“…SubPcs with ferrocenecarboxylic acid as an axial ligand also combine very interesting redox and photophysical properties, as the first reversible oxidations take place at the axial ligand, while the second oxidation is located in the SubPc ring [12]. Very recently, SubPc hydride derivatives with a high reactivity have been prepared for the first time as hydroboration reagents of aldehydes [13]. Another interesting case is that of the axial-phenoxylated SubPcs, which show spectroscopical properties for the singly reduced and singly oxidized species that can be tuned with changes in axial and peripheral substituents [14], whereas the reversibility of the redox reactions seems to be correlated with some characteristics of the boron-to-axial ligand bond [14].…”