The synthesis of stable heavier analogues of nitriles as monomeric tetrylene−phosphinidenes Mes TerEP(IDipp) (E = Ge, Sn; Mes Ter = 2,6-Mes 2 C 6 H 3 , IDipp = C([N-(2,6-iPr 2 C 6 H 4 )CH] 2 ) was achieved by taking advantage of NHC (N-heterocyclic carbene, here IDipp) coordination to the low-valent phosphorus center. Multiple bonding character of the E−P bonds was examined experimentally and computationally. Both germanium and tin compounds undergo [2+2] cycloaddition with diphenylketene, whereas reaction of the tin derivative with tris(pentafluorophenyl)borane provided unique "push−pull" phosphastannene ( Mes Ter)(Ar)Sn = P(IDipp) (Ar = C 6 F 4 [B(F)(C 6 F 5 ) 2 ]). Going further, we demonstrated the potential of tetrylene−phosphinidene complexes in catalytic hydroboration of carbonyl compounds.

Accurate ring strain energy (RSE) data for parent (CH2)2X rings are reported, where X are group 13–16 elements (El) in their lowest oxidation state, from the second to the sixth row, with their covalence completed by bonds to H. They are obtained from appropriate homodesmotic and hyper-homodesmotic reactions at different levels up to the CCSD­(T) level, thus providing a benchmark of high-quality reference RSE values, as well as acceptably accurate faster lower-level options. Derivatives of indium, thallium, and lead cannot be properly described by a three-member ring connectivity, because they display a unique donor–acceptor structure from an ethylene π­(CC) orbital to an empty p orbital of a metallylene subunit. The RSE of groups 13 and 14 heterocycles increases on descending in the group (except for Ga and Ge), while it decreases for groups 15 and 16. The latter is presumably due to a strain-releasing mechanism favored by the increase of p-character at the sp3-type atomic orbital used by El in the endocyclic El–C bonds, %p­(El)El‑C, originated by the tendency of the El lone pairs in groups 15–16 to increase their s-character. This strain-releasing mechanism does not exist in heavier tetrels, which keep almost unchanged the p-character in the endocyclic bonds at El, whereas for triels the p-character is still lower owing to their sp2-like hybridization. Remarkable linear correlations were found between the RSE and either the above-mentioned %p­(El)El‑C, the distal C–C bond distance or the relaxed force constants for the endocyclic bond angles.

Reactions between acetylenes and a stable digermyne bearing 4-t-Bu-2,6-[CH(SiMe 3 ) 2 ] 2 -C 6 H 2 (Tbb) groups afforded the corresponding stable 1,2-digermabenzenes together with the respective 1,4-digermabarrelenes. The properties of the obtained products and the reaction mechanism are discussed on the basis of experimental and theoretical results. Especially, the aromaticity of the newly obtained 1,2-digermabenzene has been discussed on the detailed calculations, revealing its aromatic character to some degree.

The rational design of a rigid π-extended ligand, suitable for the formation of four-coordinate boron complexes, has led to the synthesis of the fused hexacyclic structure of carbazolo­[2,1-c]­phenanthridine. The photophysical characterization of the novel fluorophore revealed a significant Stokes shift whose intramolecular charge transfer origin has been corroborated by computational calculations. The usefulness of the reported N,N-difluoroboryl complex as fluorescent probe with large Stokes shift has been demonstrated for cancer cells imaging.

The application of organoboron compounds as light-absorbing or light-emitting species in areas as relevant as organic electronics or biomedicine has motivated the search for new materials which contribute to the progress of those applications. This article reports the synthesis of four-coordinate boron complexes based on the unexplored 7-(azaheteroaryl)indole ligands. An easy synthetic approach has enabled the fine-tuning of the electronic structure of the organoboron species by modifying a heteroaromatic component in the conjugated system. Furthermore, a comprehensive characterization by X-ray diffraction, absorption and emission spectroscopy, both in solution and in the solid state, cyclic voltammetry, and computational methods has evidenced the utility of this simple strategy. Large Stokes shifts have been achieved in solid thin-films which show a range of emitted light from blue to orange. The synthesized compounds have been used as biocompatible fluorophores in cell bioimaging.

Abstract:The reaction of Li/Cl phosphinidenoid tungsten(0) complex 2 [R = CH(SiMe 3 ) 2 ] with 1,3,4,5-tetramethylimidazol-2-ylidene (3) yielded the zwitterionic phosphaalkene complex 4. A comparative study on chloro-(5) or dichloro(organo)phosphane complexes 1 [R = CH(SiMe 3 ) 2 ] and NHC 3 revealed the formation of 4 at ambient temperature. First evidence for the forma-

High-quality ring strain energy (RSE) data for 1H-unsaturated (CH)2X parent rings, where X is a group 13–16 element, are reported in addition to the 2H-isomers of the pnictogenirene rings. RSE data are obtained from appropriate homosdesmotic reactions and calculated at the DLPNO-CCSD­(T)/def2-TZVPP//B3LYP-D3/def2-TZVP­(ecp) level. 1H-Tallirene and 1H-plumbirene have unique donor–acceptor structures between an acetylene π­(CC) orbital and an empty p orbital of a metallylene subunit (a Dewar–Chatt–Duncanson description) and therefore cannot be described as proper rings but as pseudocyclic structures. Also, 1H-indirene and 1H-oxirene lack ring critical points and constitute borderline cases of pseudorings. 1H-Unsaturated rings exhibit enhanced RSE compared to their saturated homologues. The mechanism of ring strain relaxation by increasing the s character in the lone pair (LP) of group 15–16 elements is remarkable and increases on descending the groups. Furthermore, RSE is affected by the aromatic character of group 13 rings and certain aromatic or antiaromatic character in group 14 or 15–16 rings, respectively, which tend to vanish on descending the group as shown by NICS(1) values. 2H-Unsaturated rings were found only for group 15 elements (although only 2H-azirine shows a proper cyclic structure) and displayed lower RSE (higher stability) than the corresponding 1H-isomers.

The multi-faceted bonding of CO in molecular phosphorus compounds is described using calculated P-C bond strengths as a criterion. Full compliance matrices at coupled cluster level of HPCO (1a), singlet oxaphosphirane-3-ylidene HP(h 2 -CO)), the dimer (HPC]O) 2 as well as P^CH, HP]CH 2 and H 2 P-CH 3 were calculated to obtain quantifiable data and enable comparison. The quest for CO coordination and activation was examined for phosphaketenes 1a-f: the P-C compliance constants (inÅ mdyn À1 ) reveal a clear trend that shows a weakening of the P-CO bond strength from 1a to mono-ligation as in [(OC) 5 W {P(CO)Me}] (1c) (0.301), in H 3 BP(CO)Me (1b) (0.322), to bis-ligation as in [{(OC) 5 W} 2 P(CO)R] (1f) (0.488)to (H 3 BP) 2 (CO)Me (1d) (0.649). Availability of p-type electron density at phosphorus drastically strengthens the P-CO bond and weakens the C-O bond via p-back-donation, bis complexes are better described as weak CO (C/P) adducts to phosphorus. In complexes [(OC) 5 W{P(CO)R}] the CO activation by phosphorus equals that of CO activation through tungsten in pentacarbonyltungsten complexes. A comparative study of various CO bonding motifs in molecular compounds indicates that acyclic (2) or cyclic diphospha-urea derivatives (2-5) or isomers (6) display P-CO bond strengths (compliance constants range 0.502-0.640) well below that of the P-C bond of H 2 P-CH 3 (0.364), thus providing insight into the bonding and the ease of CO extrusion, experimentally known for some cases. A highly unusual adduct of CO was obtained in silico through two-fold P-ligation in diphosphiren-3-ones 2a-d, the parent compound of which was found to be properly described as a side-on (P]P)/(C]O) complex, in contrast to its aza-analogue 2a N . A drastic weakening of the P-CO bond strength is observed from P 2 CO (2a) (0.502) to the C 2 -symmetrical (H 3 BP) 2 CO (2b) (0.913); the latter represents an extreme case of a weakly bound CO. Furthermore, calculated 31 P NMR shifts and scalar 1 J(P,E) couplings were correlated with P-CO and PC-O compliance constants as a tool for experimentalists.In the area of dinuclear electrophilic phosphinidene complexes and their higher homologues [{L n M} 2 PnR] (L n M ¼ 16e transition-metal complex, pnictogen (Pn), Pn ¼ P, As, Sb, Bi, R ¼ e.g. alkyl, aryl etc.) it has long been known that the central Pn atom can add Lewis bases (e.g. thf, acetone, NH 3 , NEt 3 , TMEDA, pyridine) 13,14thus representing an early landmark in the coordination-to-phosphorus chemistry. 15 In this case the mostly reversible and strongly temperature dependent adduct formation is accompanied by drastic changes in colour caused by the disturbance of the M-P-M p-system. In a recent study, the P-acetonitrile adduct [{W(CO) 5 } 2 P(N^CMe)Cp*] was deduced based on 31 P NMR spectroscopy. 16 In a broader context and although dissociation has not been reported as yet, "adducts" of N-heterocyclic carbenes to pnictinidenes, formally described by the formula NHC/PnR (Pn ¼ P, As), should be mentioned. 17 Upon borane complexation of the phospho...