Oleg L. Tok

Reactivity of some poly-1-alkynylsilicon and -tin compounds towards triallylborane—routes to novel heterocycles

Abstract Triallylborane reacts with most poly-1-alkynylsilanes ( 1 – 5 ), containing up to four CC units, or di(1-alkynyl)tin compounds ( 6 ) to give either siloles ( 8 , 11 , 14 , 16 ), as the result of an intermolecular 1,1-allylboration followed by an intramolecular 1,1-vinylboration, or the novel 2-alkylidene-1,3-silaborolene ( 9 ) or 2-alkylidene1,3-stannaborolene derivatives ( 17 ), as the result of intermolecular 1,1-allylboration followed by an intramolecular 1,2-allylboration. In the case of the borolene derivatives, a second intramolecular 1,2-allylboration takes place to give 1,7-borasila- or 1,7-borastannabicyclo[4.3.0]nona-5,8-diene derivatives ( 10 , 12 , 13 , 15 , 18 ). If the starting materials are di(1-alkynyl)methylsilicon hydrides ( 2 ), the latter reaction affords selectively only one diastereomer ( 10 ( H )). All products were characterised by extensive multinuclear magnetic resonance spectra ( 1 H-, 11 B-, 13 C-, 29 Si-, and 119 Sn-NMR).

Reactivity of mono-1-alkynyltin and -germanium compounds towards triallylborane

Abstract Triallylborane, All3B (4), reacts with trialkyl(1-alkynyl)tin compounds 1 R3SnCCR1 [R=Me, R1=Me (a), tBu (b), Ph (c), SiMe3 (d), SnMe3 (e)] and 2 (R=Bu, R1=ferrocenyl) and also with 1-phenylethynyl(trimethyl)germanium (3c) preferably by 1,1-allylboration to give the organometallic-substituted alkenes 6, 8 and 10. In the cases of 1b and 1d, allyl/alkynyl exchange takes place instead. However, the formation of the alkene 6e was observed at −30°C. In the case of 1c, 1,2-allylboration, leading to the alkene 7c, competes with 1,1-allylboration, the ratio 6c/7c being dependent on the polarity of the respective solvent (more of 6c in a more polar solvent). All3B proved to be much more reactive than triethylborane, Et3B (5). All products were characterised by 1H, 11B, 13C and 119Sn NMR.

Reactivity of 1,6-bis(trimethylsilyl)-hexa-3-ene-1,5-diynes towards triethylborane, triallylborane, and 1-boraadamantane: first molecular structure of a 4-methylene-3-borahomoadamantane derivative, and the first 6,8-diborabicyclo[2.2.2]oct-2-ene derivative.

Compounds (E)- (1) and (Z)-1,6-bis(trimethylsilyl)-hexa-3-ene-1,5-diyne (2) react with triethylborane (3) by 1,1-ethylboration in a 1:1 or 1:2 molar ratio (in the case of 1), whereas in the case of 2 only the 1:1 product is formed. The analogous reactions of 1 or 2 with triallylborane (4) are more complex because of competition between 1,1-allyl- and 1,2-allylboration. Again, compound 2 reacts only with one equivalent of 4. In the case of 1-boraadamantane (5), 1,1-organoboration of 1 and 2 takes place either at one or at both C[triple bond]C bonds leading to compounds containing the 4-methylene-3-borahomoadamantane unit(s). The product of the reaction of 1 with two equivalents of 5 was characterized by X-ray structure analysis. The primary products of the reaction of 2 with 5 rearrange upon heating by deorganoboration and organoboration to give finally a tetracyclic compound 24 that contains an exocyclic allenylidene group. The product of the 1:2 reaction of 2 with 5 rearranges to give the 6,8-dibora-bicyclo[2.2.2]oct-2-ene derivative 25. All reactions were monitored by (1)H, (11)B, (13)C, and (29)Si NMR spectroscopy.

Molecular Lanthanoid–Transition-Metal Cluster through CH Bond Activation by Polar Metal–Metal Bonds

Metal–metal bonds have been fascinating scientists for long time and nowadays a lot of enthusiasm is devoted to unsupported metal–metal bonds. Until now unsupported Ln–TM bonds (Ln = lanthanoid, TM = transition metal) could only be found in a few compounds. These bonds are rather polar 11] and are important for the fundamental understanding of bonding phenomena between these metals. An improved understanding of a Ln–TM bond is important because intermetallic compounds of these metals play an important role in everyday life. The high bond polarity should allow a systematic approach towards highly aggregated systems. 15] To date there has been little exploration of the reactivity of such Ln–TM bonds. Herein we show how metal clusters can be prepared by multiple C H bond activations at Ln–TM bonds, which leads to the formation of doubly deprotonated Cp ligands. (Cp = cyclopentadienyl). The starting point of this reaction sequence is the fourcoordinate rare-earth-metal compound 2 which has a chiral lanthanoid atom. We recently explored the reaction of tris(alkyl) Ln compounds with [Cp2ReH] and ascertained that in addition to triply Re-bonded Ln complexes, polymeric insoluble byproducts are formed in bulk (66–99 %). Since the reaction of [Cp2Y(thf)(CH2SiMe3)] (Me = methyl) with the above-mentioned rhenium hydride proceeds in very good yields, it was suspected, that the presence of one Ln–carbon bond brings about side reactions of the Ln–TM bond leading to those polymeric materials. Now, if one wants to understand and to use such (side) reactions purposefully, a bis(alkyl) Ln compound which allows the substitution of one of the two alkyl ligands by Cp2Re-ligands should be exploited. The reaction of [Lu(thf)2(CH2SiMe3)3] [16] with one equivalent of 2,6-di-tertbutylphenol affords bis(alkyl) 1 in high yields (Scheme 1). The new complex reacts selectively with one equivalent of [Cp2ReH] to yield compound 2 (Scheme 1). The molecular structure of 2 as determined by X-ray structural analysis is shown in Figure 1. The lutetium ion in 2 is four-coordinated, in a tetrahedral environment, and is chiral owing to the different substituents. The selective introduction of four different substituents appears to be complicated for rare earth ions, which have a tendency for very high coordination numbers. The Lu–Re distance is 2.8498(6) and is significantly shorter than the Lu–Ru distance of 2.955(2) in [Cp2(thf)Lu-Ru(CO)2Cp] [6] and almost identical with the average value of the Lu–Re bonding distances in [Lu(ReCp2)3] [9] [2.886(1)]. The Lu C bond in 2 is 2.359(10) and complies with the expected value for such a bond (2.3781 ). The H NMR spectrum of 2 shows strong temperature dependence (at 188–295 K; see the Supporting Information). By virtue of the chirality, the signal belonging to the protons of the CH2-group of the alkyl ligand appears as AB spin system. By analogy the protons of the coordinated THF ligand should display more than two groups of signals. At room temperature, however, only two broad signals are observed for the H atoms of THF ligand and for the CH2 group merely one broad signal. Upon cooling to 253 K signal separation occurs and for the CH2 group (typical) geminal Scheme 1. Synthesis of 2.

Phosphacarborane Chemistry: The Synthesis of the Parent Phosphadicarbaboranesnido-7,8,9-PC2B8H11 and [nido-7,8,9-PC2B8H10]−, and Their 10-Cl Derivatives − Analogs of the Cyclopentadienide Anion

The reaction of the carborane nido-5,6-C2B8H12 (1) with PCl3 in dichloromethane in the presence of a “proton sponge” [PS = 1,8-bis(dimethylamino)naphthalene], followed by hydrolysis of the reaction mixture, resulted in the isolation of the eleven-vertex nido-phosphadicarbaboranes 7,8,9-PC2B8H11 (2) and 10-Cl-7,8,9-PC2B8H10 (10-Cl-2), depending on the ratio of the reactants. Both of these compounds can be deprotonated by PS to give the nido anions [7,8,9-PC2B8H10]− (2−) and [10-Cl-7,8,9-PC2B8H9]− (10-Cl-2−). The molecular geometries of all compounds were optimized by ab initio methods at a correlated level of theory [RMP2(fc)] using the 6-31G* basis set and their correctness was assessed by a comparison of the experimental 11B NMR chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/6-31G* method. Moreover, the structure of 10-Cl-2− was determined by an X-ray diffraction analysis. The anionic compounds 2− and 10-Cl-2− are analogs of the Cp (Cp = η5-C5H5−) anion. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Die erste Si‐H‐B‐Brücke: Kombination von 1,1‐Organoborierung und Hydrosilylierung

Eindeutig aktiviert ist die Si-H-Bindung von 1, das durch Umsetzen von Triallylboran mit Bis(dimethylsilyl)ethin erhaltlich ist, wegen der Nachbarschaft eines dreifach koordinierten Boratoms [Gl. (1)]. So reagiert 1 ohne Katalysator (!) in einer intramolekularen Hydrosilylierung zu 2.

From bis(silylamino)tin dichlorides via di(1-alkynyl)-bis(silylamino)tin to new heterocycles by 1,1-organoboration

Bis(silylamino)tin dichlorides 1 [X 2 SnCl 2 with X=N(Me 3 Si) 2 ( a ), N(9-BBN)SiMe 3 ( b ), N( t Bu)SiMe 3 ( c ), and N(SiMe 2 CH 2 ) 2 ( d )] were prepared from the reaction of two equivalents of the respective lithium amides ( Li - a – d ) with tin tetrachloride, SnCl 4 , or from the 1:1 reaction of the respective bis(amino)stannylene with SnCl 4 . The compounds 1 react with two equivalents of lithium alkynides LiCCR 1 to give the di(1-alkynyl)-bis(silylamino)tin compounds X 2 Sn(CCR 1 ) 2 , 2 (R 1 =Me), 3 (R 1 = t Bu), and 4 (R 1 =SiMe 3 ). Problems were encountered, mainly with LiCC t Bu as well as with 1b , since side reactions also led to the formation of 1-alkynyl-bis(silylamino)tin chlorides 5 – 7 and tri(1-alkynyl)(silylamino)tin compounds 8 and 9 . 1,1-Ethylboration of compounds 2 – 4 led to stannoles 10 , 11 , and in the case of propynides, also to 1,4-stannabora-2,5-cyclohexadiene derivatives 12 . The molecular structure of the stannole 11b (R 1 =SiMe 3 ) was determined by X-ray analysis. The reaction of 2a and d with triallylborane afforded novel heterocycles, the 1,3-stannabora-2-ethylidene-4-cyclopentenes 14 . These reactions proceed via intermolecular 1,1-allylboration, followed by an intramolecular 1,2-allylboration to give 14 , and a second intramolecular 1,2-allylboration leads to the bicyclic compounds 15 .

First agostic closo-metallacarboranes with η3-cyclooctenyl type ligand: synthesis and structural characterization of closo-3-[η3-(endo-1,5-dimethylcycloocten-1-yl)]-1,2-μ-(1′,2′-xylylene)-3,1,2-IrC2B9H9 and its isomerization to closo-3-[η3-(exo-1-methylene-5-methylcyclooctene-1-yl)]-1,2-μ-[η2-(1′,2′-xylylene)]-3,1,2-IrC2B9H9

Abstract The reaction of a new iridium reagent [Ir(η4-1,5-Me2COD)Cl]2 (1) with [nido-7,8-μ-(1′,2′-CH2C6H4CH2)-7,8-C2B9H10]−K+ (2) in solution of C6H6–MeOH mixture or in C6H6 afforded either an agostic (CH⋯Ir) closo-3-[η3-(endo-1,5-Me2COD)]-1,2-μ-(1′,2′-CH2C6H4CH2)-3,1,2-IrC2B9H9 (3) along with closo-3-[η3-(endo-1,5-Me2COD)]-1,2-μ-(1′,2′-CH2C6H4CH2)-8-(EtO)-3,1,2-IrC2B9H8 (4) or the only complex 3 in high yield. Complex 3 in dichloromethane solution is quantitatively converted to isomeric η3-exo-allylic complex closo-3-[η3-(1-exo-CH2-5-MeC8H12)]-1,2-μ-[η2-(1′,2′-CH2C6H4CH2)]-3,1,2-IrC2B9H9 (5) for a few days. All new complexes 3, 4 and 5 were characterized by single-crystal X-ray diffraction studies, which confirmed the existence of an agostic CH⋯Ir interaction in 3 and revealed a weak η2-coordination of the metal atom with one of the aromatic bonds of ortho-xylylene cage substituent in 5. The normal and low-temperature 1H- and 13C/13C{1H}-NMR spectra as well as 2D COSY/HETCOR NMR data obtained for the studied complexes are discussed in details.

57Fe NMR spectroscopy of ferrocenes derived from aminoferrocene and 1,1′‐diaminoferrocene

Three series of ferrocenes, derived from aminoferrocene Fc‐NH2 and 1,1′‐diaminoferrocene fc(NH2)2, were studied by 57Fe NMR spectroscopy. A marked decrease in 57Fe magnetic nuclear shielding with respect to ferrocene is observed if the nitrogen atom becomes part of a π‐acceptor linked to one or both cyclopentadienyl rings. In contrast, π‐donor properties of the amino group(s) affect δ57Fe to a much smaller extent. In the case of the fairly rigid structures of 1,3‐diaza‐2‐element‐[3]ferrocenophanes, a significant increase of 57Fe nuclear magnetic shielding is observed, in contrast to the corresponding [n]ferrocenophanes with n > 3. Structures of numerous of the ferrocene derivatives have been optimized for the gas phase by calculations (B3LYP/6–311 + G(d,p) level of theory), and 57Fe nuclear magnetic shieldings were calculated using these geometries. There is reasonable agreement in the trends for experimental and calculated data. Copyright

Electrophilic substitution reactions of ferracarborane 3-(η5-Cp)-4-SMe2-3,1,2-FeC2B9H10

Mercuration and bromination reactions of ferracarborane 3-(η5-Cp)-4-SMe2-3,1,2-FeC2B9H10 (1) were investigated. Mercuration of 1 under mild conditions (mercury trifluoroacetate in dichloromethane) results in 8-monosubstituted mercury derivative as the only reaction product. Depending on the reaction conditions, bromination of 1 results in 8-mono- or 7,8-disubstituted bromo derivatives. The structures of the monomercury and dibromo derivatives of 1 were established by X-ray analysis.