Libor Dostál

Monomeric Organoantimony(I) and Organobismuth(I) Compounds Stabilized by an NCN Chelating Ligand: Syntheses and Structures

The synthesis and structure of compounds containing multiple bonds between heavier Group 15 (Sb, Bi) elements, or analogous low-valent compounds with the central atom in the formal oxidation state + 1, have been among the most exciting targets in the chemistry of main-group elements. However, these compounds are often very unstable under normal conditions. The introduction of sufficiently large substituents is necessary for kinetic stabilization of such reactive species. Utilizing very effective and bulky ligands, such as 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl, or various m-terphenyl ligands, allowed isolation of stable heavier-element dipnictenes RMMR (M = Sb, Bi). Related ligands are able to stabilize unsymmetric compounds, where two different heavier Group 15 elements are connected. Using less stericaly crowded ligands, such as bis(trimethylsilyl)methyl resulted in formation of various cluster compounds, and coordination of a transition metal was necessary for stabilization of the RMMR fragment. Nevertheless, monomeric compounds of the type RM (stibinidenes or bismuthinidenes) have not been isolated in the condensed phase to date, although the existence of such compounds with two lone pairs for bismuth has been predicted based on relativistic effects. We and others have recently demonstrated that using of so-called NCN pincer-type ligand, [2,6bis(dimethylamino)methyl]phenyl (denoted as Ar hereafter), is an alternative to sterically overcrowded ligands for stabilization of low-valent antimony and bismuth compounds and the terminal ArSb=E (E = S, Se, Te) bonds. In view of this fact, it was believed that using of even more rigid and more sterically demanding NCN pincer ligand may lead to a stabilization of monomeric RM species (stibinidenes or bismuthinidenes) by combination of thermodynamical and kinetic influence of the ligand. Herein, we present the syntheses and structures of unprecedented monomeric stibinidene and bismuthinidene by taking advantage of using of 2,6-bis[N-(2’,6’-dimethylphenyl)ketimino]phenyl (denoted as L hereafter; Scheme 1).

Intramolecularly Coordinated Organotin Tellurides: Stable or Unstable?

The step-wise oxidation of an organotin(I) compound with elemental tellurium gave a variety of unprecedented organotin tellurides containing tin atoms in the oxidation states +II and +IV.

Intramolecularly Coordinated Tin(II) Selenide and Triseleneoxostannonic Acid Anhydride

Understanding the nature of chemical bonding remains a central focus of fundamental research, and one of the valuable methods for the increasing of the understanding of intramolecular binding forces is the investigation of compounds containing multiple bonds between heavier Group 14 elements of the type RE ER (where E= group elements Si, Ge, Sn, and Pb). Recent studies of these heavier Group 14 element analogues of alkynes revealed essential structural differences between alkynes, RC CR, and their heavier Group 14 analogues, RE ER (E=Si, Ge, Sn, Pb) and opened debate as to whether the Group 14 analogue compounds exhibit a true triple bond (A), a double bond (B), or a single bond whose geometry is strongly trans-bent (C) (see Scheme 1). The presence of rather bulky substituents such as a variety of substituted aryl and silyl groups afforded the synthesis of RE ER that possess multiple bonds. The presence of a multiple bond was proposed by the UV/Vis absorptions, molecular orbital (MO) calculations, and also by the reactivity studies on these molecules. All these experiments afforded insights into the nature of the E E triple bonds. Scission of the Si Si or Ge Ge triple bond was observed by the addition of an olefin 9, 22–27] and most recently, Power and coworkers nicely outlined the cleavage of the Sn Sn multiple bond in the distannyne [ArSnSnAr] (Ar=C6H3-2,6-(C6H32,6-iPr2)2) by complexation with two molecules of either ethylene or norbornadiene or by cyclic polyolefinic molecules. 29] Moreover, the latest study dealing with the reactivity of [ArSnSnAr] with cyclooctatetraene (cot) showed the powerful reducing character of the tin(I) compound towards neutral cot. Recently, we have shown that the use of intramolecularly coordinating built-in N,C,N-coordinating pincer-type ligands is an alternative concept for the synthesis and stabilization of the reactive distannyne [({2,6-(Me2NCH2)2C6H3}Sn)2] (1). This compound showed, however, Sn Sn single bond character with a central tin atom in the oxidation state + I. We have, therefore, concentrated on the redox-type reaction of compound 1 instead of cycloadditions of the olefins. In the course of a systematic studies on the metal-type redox reactivity of 1 we present here the reaction of 1 with Se as the oxidizing agent and show that the reaction results in the two-step oxidation of the tin(I) atom along with complete cleavage of the Sn Sn bond to give a new organotin(II) selenide [({2,6-(Me2NCH2)2C6H3}Sn)2Se] (2) in the first step of the oxidation (Scheme 2). This compound is unprecedented and there is no report on well-defined selenides of low-valent Group 14 elements. Preparation of organotin(IV) selenide [({2,6-(Me2NCH2)2C6H3}Sn(Se))2Se] (3), the first example of an intramolecularly coordinated triseleneoxostannonic acid anhydride, as the final product of the oxidation of 1 by Se is reported as well (Scheme 2). Compound 3 contains two terminal Sn Se bonds and represents a new [a] M. Bouška, Dr. L. Dost l, Dr. A. Růžička, Dr. R. Jambor Department of General and Inorganic Chemistry Faculty of Chemical Technology University of Pardubice Čs legi 565, 53210, Pardubice (Czech Republic) E-mail : roman.jambor@upce.cz [b] Dr. F. de Proft Eenheid Algemene Chemie (ALGC) Vrije Universiteit Brussel (VUB) Pleinlaan 2, 1050 Brussels, (Belgium) [c] Prof. A. Lyčka Research Institute for Organic Chemistry VUOS a.s. 532 10, Pardubice, (Czech Republic) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201002641. Scheme 1. Canonical formulas for compounds of the type REER.

Oxidation of intramolecularly coordinated distannyne by S8: from tin(I) to tin(IV) polysulfide via tin(II) sulfide.

The investigation of heavier Group 14 element analogues of alkynes of the type (RE)2 (where E=Si, Ge, Sn, or Pb) is of current interest. These studies showed that the presence of rather bulky substituents such as a variety of substituted aryl and silyl groups allowed the synthesis of RE ER, which possess multiple bonds. The studies dealing with the reactivity of the RE ER multiple bonds showed scission of the Si Si or Ge Ge triple bond by the addition of an olefin, and most recently, Power and coworkers nicely outlined the cleavage of the Sn Sn multiple bond in the distannyne [ArSnSnAr] (Ar=C6H3-2,6-(C6H32,6-iPr2)2) by complexation with two molecules of either ethylene or norbornadiene. Moreover, the latest study dealing with the reactivity of [ArSnSnAr] with cyclooctatetraene (cot) showed the powerful reducing character of the tin(I) compound towards neutral cot. The reactivity studies of [ArSnSnAr] towards N2O also showed the reducing character of the Sn species, yielding the organotin(II) oxide [ArSnOSnAr] as the final product. Recently, the single-bonded dimeric species [{SiACHTUNGTRENNUNG(NtBu)2CPh}2] and [({2,6-(Me2NCH2)2C6H3}Sn)2] (1), as the first example of an Sn N intramolecularly coordinated distannyne containing a built-in N,C,N-pincer-type ligand, were reported as well. The redox reaction of [{Si ACHTUNGTRENNUNG(NtBu)2CPh}2] with N2O showed the reducing character of the Si I species, and led to the production of the well-defined [R4Si4O6] compound (R= (NtBu)2CPh) with a double-decker structure. [8]

Mixed Organotin(IV) Chalcogenides: From Molecules to Sn‐S‐Se Semiconducting Thin Films Deposited by Spin‐Coating

Put the right spin on it: Mixed monomeric organotin(IV) chalcogenides of the general formula L(2)Sn(2)EX(2) containing two terminal Sn-X (X = Se, Te) bonds were prepared and were tested as potential single-source precursors for the deposition of semiconducting thin films. Spin-coating deposition of [{2,6-(Me(2)NCH(2))(2)C(6)H(3)}SnSe](2)(μ-S), as the useful single-source precursor, provided amorphous Sn-S-Se semiconducting thin films.

Hydrosilylation Induced by N→Si Intramolecular Coordination: Spontaneous Transformation of Organosilanes into 1‐Aza‐Silole‐Type Molecules in the Absence of a Catalyst

Our attempts to synthesize the N→Si intramolecularly coordinated organosilanes Ph2 L(1) SiH (1 a), PhL(1) SiH2 (2 a), Ph2 L(2) SiH (3 a), and PhL(2) SiH2 (4 a) containing a CH=N imine group (in which L(1) is the C,N-chelating ligand {2-[CH=N(C6 H3 -2,6-iPr2)]C6 H4}(-) and L(2) is {2-[CH=N(tBu)]C6 H4}(-)) yielded 1-[2,6-bis(diisopropyl)phenyl]-2,2-diphenyl-1-aza-silole (1), 1-[2,6-bis(diisopropyl)phenyl]-2-phenyl-2-hydrido-1-aza-silole (2), 1-tert-butyl-2,2-diphenyl-1-aza-silole (3), and 1-tert-butyl-2-phenyl-2-hydrido-1-aza-silole (4), respectively. Isolated organosilicon amides 1-4 are an outcome of the spontaneous hydrosilylation of the CH=N imine moiety induced by N→Si intramolecular coordination. Compounds 1-4 were characterized by NMR spectroscopy and X-ray diffraction analysis. The geometries of organosilanes 1 a-4 a and their corresponding hydrosilylated products 1-4 were optimized and fully characterized at the B3LYP/6-31++G(d,p) level of theory. The molecular structure determination of 1-3 suggested the presence of a Si-N double bond. Natural bond orbital (NBO) analysis, however, shows a very strong donor-acceptor interaction between the lone pair of the nitrogen atom and the formal empty p orbital on the silicon and therefore, the calculations show that the Si-N bond is highly polarized pointing to a predominantly zwitterionic Si(+) N(-) bond in 1-4. Since compounds 1-4 are hydrosilylated products of 1 a-4 a, the free energies (ΔG298), enthalpies (ΔH298), and entropies (ΔH298) were computed for the hydrosilylation reaction of 1 a-4 a with both B3LYP and B3LYP-D methods. On the basis of the very negative ΔG298 values, the hydrosilylation reaction is highly exergonic and compounds 1 a-4 a are spontaneously transformed into 1-4 in the absence of a catalyst.

NCN-chelated organoantimony(III) and organobismuth(III) phosphates: synthesis and solid-state and solution structures.

.Organoantimony(III) and organobismuth(III) phosphates (LM)(3)(PO(4))(2) [M = Sb (3) and Bi (4)], containing the NCN-chelating ligand L [L = 2,6-(CH(2)NMe(2))(2)C(6)H(3)], were prepared by the simple treatment of parent oxides 1 and 2 with H(3)PO(4). Both compounds were characterized by elemental analysis, electrospray ionization mass spectrometry, and IR and NMR spectroscopy and in the case of 3 by X-ray diffraction techniques. Compound 3 has an interesting behavior in solution, i.e., the formation of two possible conformational isomers, which was studied by (1)H, (13)C, and (31)P NMR spectroscopy.

Stibinidene and Bismuthinidene as Two‐electron Donors for Transition Metals (Co and Mn).

The reaction of stibinidene and bismuthinidene ArM [where Ar=C6 H3 -2,6-(CH=NtBu)2 ; M=Sb (1), Bi (2)] with transition metal (TM) carbonyls Co2 (CO)8 and Mn2 (CO)10 produced unprecedented ionic complexes [(ArM)2 Co(CO)3 ](+) [Co(CO)4 ](-) and [(ArM)2 Mn(CO)4 ](+) [Mn(CO)5 ](-) [where M=Sb (3, 5), Bi (4, 6)]. The pnictinidenes 1 and 2 behaved as two-electron donors in this set of compounds. Besides the M→TM bonds, the topological analysis also revealed a number of secondary interactions contributing to the stabilization of cationic parts of titled complexes.

Synthesis and structural characterization of heteroboroxines with MB2O3 core (M = Sb, Bi, Sn).

Reaction of organoantimony and organobismuth oxides (LSbO)(2) and (LBiO)(2) (where L is [2,6-bis(dimethylamino)methyl]phenyl) with four equivalents of the organoboronic acids gave new heteroboroxines LM[(OBR)(2)O] 1a-2c (for M = Sb: R = Ph (1a), 4-CF(3)C(6)H(4) (1b), ferrocenyl (1c); for M = Bi: R = Ph (2a), 4-CF(3)C(6)H(4) (2b), and ferrocenyl (2c)). Analogously, reaction between organotin carbonate L(Ph)Sn(CO(3)) and two equivalents of organoboronic acids yielded compounds L(Ph)Sn[(OBR)(2)O] (where R = Ph (3a), 4-CF(3)C(6)H(4) (3b), and ferrocenyl (3c)). All compounds were characterized by elemental analysis and NMR spectroscopy. Their structure was described both in solution (NMR studies) and in the solid state (X-ray diffraction analyses 1a, 1c, 2b, 3b, and 3c). All compounds contain a central MB(2)O(3) core (M = Sb, Bi, Sn), and the bonding situation within these rings and their potential aromaticity was investigated by the help of computational methods.

From Stiba- and Bismaheteroboroxines to N,C,N-Chelated Diorganoantimony(III) and Bismuth(III) Cations—An Unexpected Case of Aryl Group Migration

An unprecedented transfer of an aryl group from boron to Sb and Bi is observed in the reaction of heteroboroxines of general formula ArM[(OBR)2O] [where M = Sb, Bi; Ar = C6H3-2,6-(CH2NMe2)2; R = Ph, 4-CF3C6H4, 4-BrC6H4] with corresponding boronic acid RB(OH)2. Using this procedure, ion pairs [ArMR](+)[R4B5O6](-) were obtained [where M = Sb and R = Ph (4), 4-CF3C6H4 (5), 4-BrC6H4 (6); where M = Bi and R = Ph (7), 4-CF3C6H4 (8), 4-BrC6H4 (9)]. All compounds were characterized using elemental analysis, electrospray ionization mass spectrometry, and multinuclear NMR spectroscopy, and molecular structures of 4 and 7 were determined by single-crystal X-ray diffraction analysis. The central metal atoms in 4-9 were arylated by respective boronic acids, which represents, to the best of our knowledge, unprecedented reaction path in the chemistry of heavier group 15 elements. Investigation of the mechanism of this transformation indicated that Lewis pairs consisting of monomeric oxides ArMO and boroxine rings are probably key intermediates. In this regard, molecular structures of ArSbO[(4-CF3C6H4)3B3O3]·(4-CF3C6H4)B(OH)2 (10) and {ArSbO[(3,5-(CF3)2C6H3)3B3O3]} (13) were established by single-crystal X-ray diffraction analysis, and compound 13 was also fully characterized in solution by multinuclear NMR spectroscopy. The bonding in 13 was analyzed in detail by using density functional theory and natural bond order calculations and compared with known adduct ArSbOB(C6F5)3 (14) and hypothetical ArSbO monomer.