Diverse reactions of sterically-protected 1,3-diphosphacyclobutane-2,4-diyls with hydride

Abstract

Hydride-induced elimination of resonance stabilized substituents from a phosphorus center of 1,3-diphosphacyclobutane-2,4-diyls leads to the formation of versatile cyclic phosphaallyl anions that are useful for the construction of various electrophile-modified biradical species.

Spectroscopic and stability studies on unsymmetrical 1,3‐dialkyl‐1,3‐diphosphacyclobutane‐2,4‐diyls

“…A DFT‐optimized structure of 5a [Gaussian 09 program, Becke, three‐parameter, Lee–Yang–Parr (B3LYP)/6‐31G(d)] is comparable to the X‐ray structure of 4d and complete active space self consistent field CASSCF(2,2)/6‐31G(d) calculations indicate an occupation in the highest occupied molecular orbital (HOMO) (#139) orbital with 1.88 electrons. In the 31 P NMR spectrum, 4a shows the typical AB pattern signals that are similar to the unsymmetrical P‐heterocyclic biradicals known to us so far . Chemical shifts of the PEt and PMe groups are similar to symmetric 4c (see Experimental Section) and 4d , respectively, and a similar 2 J PP constant for 4a to 4b is observed.…”

Study of the Air‐Tolerant 1,3‐Diphosphacyclobutane‐2,4‐diyl through the Direct Arylation

“…The smaller pyramidalization of the t BuP phosphorus atom and shorter P( t Bu)–C1/C2 bonds would correlate with the electron‐donating character of the t ‐butyl group. The 31 P NMR spectroscopic data show the larger‐field chemical shift of the t BuP group,,,, which might be due to the canonical formula. The molecular structure of 8 indicated that the isopropylamino group increases the electron‐donating property of the P‐heterocyclic chromophore .…”

“…Preparation of CBA via the reductive P–C cleavage of 1,3‐diphosphacyclobutane‐2,4‐diyl was also developed. Reaction with lithium aluminum hydride (LiAlH 4 ) induced removal of the XCH 2 unit (X=aryl, alkenyl, alkynyl, carbonyl) to generate the t Bu‐substituted diphosphacyclobutenyl anion CBA‐1 ( vide infra ) . On the contrary, the predominant reductive cleave of the t Bu–P bond in the 1,3‐diphosphacyclobutane‐2,4‐diyl was induced by t ‐butyllithium to generate the corresponding CBA that are not easy to prepare from 2 together with the hydride‐loaded byproduct (Scheme ) …”

“…Positioning the sterically encumbered Mes* substituents is quite effective to stabilize the cyclic biradical (biradicaloid) skeleton, and handling of 1 in air at ambient temperatures is possible. The synthetic procedures of 1 including nucleophilic alkylation, acylation, and sulfanylation of the P‐heterocyclic anionic intermediates ( CBA ) was advantageous to afford a number of 1,3‐diphosphacyclobutane‐2,4‐diyls . Furthermore, the alkylation process was applicable to catenate the open‐shell singlet P‐heterocyclic units to construct the tetraradical and hexaradical derivatives showing the through‐space static interaction .…”

Exploration of 1-Arylmethyl-1,3-diphosphacyclobutane-2,4-diyls as Hole Transfer Materials

“…In this paper we investigated the effects of the arylmethyl substituent on the solid-state properties of open-shell singlet P-heterocycles. First, we screened several arylmethyl substituents and found that in addition to the previously synthesized 3 and 4, [13] 2-anthrylmethyl-and 2-thieno[3,2,-b]thiophenylmethyl-substituted 1,3-diphosphacyclobutane-2,4-diyls were suitable for use in p-type FET devices. To understand the semiconductor characteristics of the most promising diyls in detail, we evaluated their hole transfer integrals (V) and reorganization energies (l) based on density functional theory (DFT) calculations and X-ray crystallographic analyses, then estimated their hole hopping rates (W) and diffusion coefficients (D).…”