Hypervalent Bond Formation in Halogeno(2-acylphenyl)bismuthanes

Reactivity of a carbonyl moiety in organotin(iv) compounds: novel Pd(ii) and Cu(ii) complexes supported by organotin(iv) ligands

Converting the carbonyl moiety of an (aryl)organotin(iv) compound gives other functional groups that can act as metalloligands.

One-Pot Synthesis of Hypervalent Diaryl(iodo)bismuthanes from o-Carbonyl Iodoarenes by Zincation

Diaryl(iodo)bismuthanes possessing a hypervalent C=O•••Bi–I bond were conveniently synthesized in a one-pot reaction by using arylzinc reagents generated from o-carbonyl iodobenzenes and zinc powder under ultrasonication. This method is superior to the conventional organolithium and Grignard methods because it has a wide functional group tolerance, requires no protecting group manipulations, and proceeds under mild reaction conditions that do not need low temperature control. Furthermore, no intermediate triarylbismuthane precursor for the hypervalent iodobismuthane is necessary.

Mixed triorganobismuthines RAr2Bi [Ar = C6F5, 2,4,6-(C6F5)3C6H2] and hypervalent racemic Bi-chiral diorganobismuth(iii) bromides RArBiBr (Ar = C6F5, Mes, Ph) with the ligand R = 2-(Me2NCH2)C6H4. Influences of the organic substituent

RAr₂Bi and chiral RArBiBr were structurally characterized; N–Bi bond distances in RArBiBr appear to be similar regardless of the electronic properties of the Ar ligand.

Activity of antifungal organobismuth(III) compounds derived from alkyl aryl ketones against S. cerevisiae: comparison with a heterocyclic bismuth scaffold consisting of a diphenyl sulfone

A series of hypervalent organobismuth(III) compounds derived from alkyl aryl ketones [XBi(5-R'C₆H₃-2-COR)(Ar)] was synthesized to investigate the effect of the compounds’ structural features on their antifungal activity against the yeast Saccharomyces cerevisiae. In contrast to bismuth heterocycles [XBi(5-RC₆H₃-2-SO₂C₆H₄-1'-)] derived from diphenyl sulfones, a systematic quantitative structure-activity relationship study was possible. The activity depended on the Ar group and increased for heavier X atoms, whereas lengthening the alkyl chain (R) or introducing a substituent (R') reduced the activity. IBi(C₆H₄-2-COCH₃)(4-FC₆H₄) was the most active. Its activity was superior to that of the related acyclic analogues ClBi[C₆H₄-2-CH₂N(CH₃)₂](Ar) and ClBi(C₆H₄-2-SO₂tert-Bu)(Ar) and also comparable to that of heterocyclic ClBi(C₆H₄-2-SO₂C₆H₄-1'-), which was the most active compound in our previous studies. Density function theory calculations suggested that hypervalent bismuthanes undergo nucleophilic addition with a biomolecule at the bismuth atom to give an intermediate ate complex. For higher antifungal activity, adjusting the lipophilicity-hydrophilicity balance, modeling the three-dimensional molecular structure around the bismuth atom, and stabilizing the ate complex appear to be more important than tuning the Lewis acidity at the bismuth atom.

Syntheses, structures, and dynamic behavior of chiral racemic organoantimony and -bismuth compounds RR'SbCl, RR'BiCl, and RR'SbM [R = 2-(Me2NCH2)C6H4, R' = CH(Me3Si)2, M = H, Li, Na]

RR'SbCl (1) and RR'BiCl (2) [R = 2-(Me(2)NCH(2))C(6)H(4), R' = CH(Me(3)Si)(2)] form by the reaction of R'ECl(2) (E = Sb, Bi) with RLi. The reaction of 1 with LiAlH(4) and metalation with n-BuLi gives RR'SbH (3) and RR'SbLi.2THF (4) (THF = tetrahydrofuran). Transmetalation of 4 with sodium tert-butoxide in the presence of TMEDA (TMEDA = tetramethylethylenediamine) leads to RR'SbNa.TMEDA (5). Structural analyses by (1)H NMR in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO with a variation of the temperature (1, 2, 4, and 5) and by single-crystal X-ray diffraction (1, 2, 4, and 5) revealed the intramolecular coordination of the pendant Me(2)N group on the pnicogen centers in 1 and 2 and on Li or Na in 4 or 5. The variable-temperature (1)H NMR spectra of the hydride 3 in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO show that the pyramidal configuration on antimony is stable up to 100 degrees C, whereas inversion at the nitrogen is not prevented by internal coordination even at -80 degrees C. The crystals of 1, 2, 4, and 5 consist of discrete molecules with the Sb and Bi atoms in an approximately Psi-trigonal-bipyramidal environment in the cases of 1 and 2 and in a pyramidal environment in the cases of 4 and 5. Crystal data for 1: triclinic, space group Ponemacr;, a = 7.243(4) A, b = 10.373(3) A, c = 15.396(5) A, alpha = 79.88 degrees, beta = 78.27 degrees, gamma = 71.480(10) degrees, V = 1066.2(7) A(3), Z = 2, R = 0.0614. 2: monoclinic, space group P2(1)/n, a = 10.665(2) A, b = 14.241(2) A, c = 14.058(2) A, beta = 90.100(10) degrees, V = 2135.1(6) A(3), Z = 4, R = 0.049. 4: monoclinic, space group P2(1)/n, a = 11.552(2) A, b = 16.518(3) A, c = 15.971(5) A, beta = 96.11(2) degrees, V = 3030.2(12) A(3), Z = 4, R = 0.0595. 5: monoclinic, space group P2(1)/n, a = 9.797(2) A, b = 24.991(5) A, c = 14.348(3) A, beta = 94.98(3) degrees, V = 3499.66(12) A(3), Z = 4, R = 0.0571. The dissociation of the intramolecular N-pnicogen bond and inversion at the nitrogen occurs when solutions of 1 or 2 in C(6)D(6) or C(6)D(5)CD(3) are heated above 25 or 30 degrees C. 1 and 3-5 are stable with respect to inversion of the configuration at the antimony in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO up to 160 degrees C. Bismuth inversion, probably via the edge mechanism, is observed in solutions of 2 in (CD(3))(2)SO at 45 degrees C but not in C(6)D(5)CD(3) below 125 degrees C.

Cyclic aromatic systems with hypervalent centers

Strong attractive intramolecular X<--Y(S, NR') interactions of 1,5-type occurring between terminal electron-rich main-group 15-17 centers (X = pnictogen, chalcogen, or halogen) and carbonyl, thione, or imine groups (Y = O, S, NR') incorporated into the conjugated -X-CH=CH-CH=Y fragments result in significant stabilization of cis-s-cis structure of these molecules, which may be viewed as the five-membered pseudo-heterocycles with the hypervalent arrangements across the pnictogen, chalcogen, or halogen centers. In derivatives of beta-chalcovinylaldehydes and isoelectronic chloronium cations, one of two lone electron pairs at X = S, Se, Te, Cl+ possesses pure p character and is involved in conjugation with the pi-system of the rest of the molecule, which leads to an appreciable contribution of the aromatic stabilization of the 6 pi-electron ring closed by the X<--Y bond. The aromaticity of these structures evaluated through calculation of the homodesmotic stabilization energies (HSE) increases in parallel with an increase in the strength of the intramolecular coordination bonds, i.e., in the order X = S, Se, Te and with an increase in electronegativity of a substituent attached to the chalcogen atom. Clear manifestation of the aromatic character of the cis-s-cis isomers of beta-chalcovinylaldehydes, their imines, as well as congeneric thiones and chloronium cations comes from the theoretical and experimental evidence for the pronounced equalization (as compared with the open trans-s-trans isomers) of the CC bond lengths. The cooperative effects of the hypervalent bonding and aromaticity are most distinct in the bicyclic structures of 1,6,6a lambda 4-trichalcapentalenes, their 1,6-dioxa(aza) analogues, and 1,6-dioxa-3a-aza-6a lambda 4-pnictapentalenes, in which two conjugated -X-CH=CH-CH=Y fragments are fused together via the symmetric -Y-X-Y- triad. The assessments based on the HSE values indicate that the aromaticity of these 10 pi-electron compounds is estimated as about 30-50% of the aromatic character of the most aromatic bicyclic structure of naphthalene. As shown by extensive ab initio calculations, substantial hypervalent bonding effects also operate in the case of beta-pnictovinylaldehydes formed by second and lower row pnictogen atoms (X = P, As, Sb, Bi), providing for the enhanced stability of their cis-s-cis configuration with respect to the free-of-strain trans-s-trans structures. The bicyclic 1,6,6a lambda 5-dioxapnictapentalene structure is also the most energy favorable form of these compounds. However, by contrast with the chalcogen and halonium analogues, the pseudo-cyclic structure of beta-pnictovinylaldehydes and the bicyclic structure of 1,6,6a lambda 5-dioxapnictapentalenes are maintained through primarily the occurrence of the hypervalent bonding across the pnictogen centers, whereas pi-delocalization is not (or weakly) operative in these compounds. A possible explanation for this finding is the low p character of the single lone electron pair at the pnictogen and orientation of the axis of its orbital, which is unfavorable for the optimal overlap with the pi-system of the rest of a molecule. As first proposed by Arduengo and Dixon, configurational isomerizations at the second and lower row tricoordinate pnictogen centers may proceed through the T-shaped hypervalent structures. Such a structure is strongly stabilized in the aromatic 1,6-dioxa-3a-aza-6a lambda 4-pnictapentalenes. It was found by calculations that the aromatic stabilization of the T-shaped hypervalent arrangement at the tricoordinate pnictogen center in 2H-1,3,2-dioxaphosphole and arsole arising due to withdrawal of two electrons from the pi-system of the ring onto the hypervalent electron-excessive center facilitates the rearrangement and directs it along the reaction path with the aromatic transition-state structure. Investigation of the influence of cooperative effects of hypervalent bonding and aromaticity on stability and mechanisms of reactions of main-group 14-17 compounds not considered in this review is the subject of our continuing research.