Carboalumination Reaction Research Articles

Uncatalyzed Carbometallation Involving Group 13 Elements: Carboboration and Carboalumination of Alkenes and Alkynes.

Carbometallation of alkenes and alkynes are powerful carbon-carbon bond-forming reactions. The use of compounds containing bonds between carbon and group 13 elements, particularly boron and aluminum, are particularly attractive because of the versatility of subsequent transformations. Uncatalyzed carboboration and carboalumination represent less common classes of reactions. This Short Review discusses uncatalyzed carboboration and carboalumination reactions of alkenes and alkynes, including the reaction design and mechanism.

Carboalumination of Seven-Membered-Ring trans-Alkenes.

Seven-membered-ring trans-alkenes undergo rapid hydro- and carboalumination reactions in the absence of a catalyst with complete regio- and diastereoselectivity. Control experiments, including deuterium labeling, adding radical inhibitors, and using a radical clock, suggest that these reactions proceed by a concerted mechanism. The products of the reaction possess a new carbon-aluminum bond that can then undergo subsequent transformations, particularly oxidation, providing functionalized products as single stereoisomers.

Group 13-derived radicals from α-diimines via hydro- and carboalumination reactions.

The mechanochemical synthesis of tertiary and secondary alanes AlR3 (R = Np 1 or Mes 2; HAlR2 R = Np 3 or Mes 4) is described. These species are reacted with several α-diimines to give a series of aluminium-derived radicals of the form [(diimine)AlR2]˙ (6-11). EPR and several crystallographic studies are reported. These species are thought to form via hydro- or carboalumination and subsequent elimination reactions. This view is supported by the structural data for minor products C12H7(NHDipp)(NDipp)AliBu25 and C13H8(C(iBu)[double bond, length as m-dash]N(m-Xy)(NH(m-Xy)))AliBu212. In addition, the characterization of (C6F5)2B(OC(C6F5)OC12H8) indicates that such a carboboration pathway also provides access to related boron-derived radicals.

Synthesis of a sumanenyl hafnocene complex

A convex-bound sumanenyl hafnocene complex was selectively synthesized, and the catalytic activity of sumanenyl metallocenes was demonstrated in the carboalumination reaction.

ChemInform Abstract: Unusual Pathway of the Tantalum‐Catalyzed Carboalumination Reaction of Alkenes with Triethylaluminum.

Abstract Carboalumination of 1-alkenes (1-hexene, 1-octene, 1-decene) with Et 3 Al in the presence of catalytic amounts of TaCl 5 results in a mixture of 2-( R -substituted)- and 3-( R -substituted)- n -butylaluminums (1:1 ratio) in total yields of 75–85%. The TaCl 5 -catalyzed reaction of bicyclo[2.2.1]hept-2-ene, endo -tricyclo[5.2.1.0 2,6 ]deca-3,8-diene, and ( exo / endo )-5-methylbicyclo[2.1.1]hept-2-ene with Et 3 Al leads to the formation of diethyl[2- exo -(2′-norbornylethyl)]aluminums in high yields. DFT calculations confirm the thermodynamic preference of the final exo product. The multistep reaction mechanisms for the formation of the resultant organoaluminums through tantalacyclopentanes as key intermediates are also discussed.

Unusual pathway of the tantalum-catalyzed carboalumination reaction of alkenes with triethylaluminum

Carboalumination of 1-alkenes (1-hexene, 1-octene, 1-decene) with Et3Al in the presence of catalytic amounts of TaCl5 results in a mixture of 2-(R-substituted)- and 3-(R-substituted)-n-butylaluminums (1:1 ratio) in total yields of 75–85%. The TaCl5-catalyzed reaction of bicyclo[2.2.1]hept-2-ene, endo-tricyclo[5.2.1.02,6]deca-3,8-diene, and (exo/endo)-5-methylbicyclo[2.1.1]hept-2-ene with Et3Al leads to the formation of diethyl[2-exo-(2′-norbornylethyl)]aluminums in high yields. DFT calculations confirm the thermodynamic preference of the final exo product. The multistep reaction mechanisms for the formation of the resultant organoaluminums through tantalacyclopentanes as key intermediates are also discussed.

Carboalumination of a chromium–chromium quintuple bond

Bonds are at the very heart of chemistry. Although the order of carbon–carbon bonds only extends to triple bonds, metal–metal bond orders of up to five are known for stable compounds, particularly between chromium atoms. Carbometallation and especially carboalumination reactions of carbon–carbon double and triple bonds are a well established synthetic protocol in organometallic chemistry and organic synthesis. We now extend these reactions to compounds containing chromium–chromium quintuple bonds. Analogous reactivity patterns indicate that such quintuple bonds are not as exotic as previously assumed. Yet the particularities of these reactions reflect the specific nature of the high metal–metal bond orders.

Organochromium complexes as catalysts for the carboalumination of unactivated terminal olefins

The addition of aluminium alkyls to terminal olefins leads to branched organoaluminium compounds which can be converted into functionalised alkanes. This carboalumination reaction is efficiently catalysed by a donor functionalised Cp-chromium(III) complex. The active catalyst is obtained by activation of the chromium(III) dichloride precursor with MAO or with a mixture of trialkylaluminium and N,N-dimethylanilinium tetrakispentaflourphenylborate. Primary aminoalkenes deactivate the catalyst whereas secondary and tertiary aminoalkenes can also be carboaluminated.

Diastereoselective, Enantioselective, and Regioselective Carboalumination Reactions Catalyzed by Zirconocene Derivatives

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chiral Indenes and Group‐4 Metallocene Dichlorides Containing α‐ and β‐Pinenyl‐Derived Ligand Substituents: Synthesis and Catalytic Applications in Polymerization and Carboalumination Reactions

AbstractThe synthesis and characterization of chiral bis(indenyl)zirconium dichlorides containing β‐pinenyl‐derived ligand substituents is reported. Unbridged metallocene complexeshaving the {[(1S,2S,5S)‐6,6‐dimethylbicyclo[3.1.1]hept‐2‐yl]methyl}dimethylsilyl substituent in both 1‐ and 2‐positions of the indenyl moiety were prepared and isolated in moderate to low yields by reaction of the corresponding indenyllithium salts with ZrCl4 followed by work‐up and crystallization procedures. The corresponding tetrahydroindenyl complexes were obtained in excellent yields by catalytic hydrogenation of the indenyl six‐membered rings. In a complementary approach, a synthetic route to α‐pinenyl‐substituted indenyl ligand analogues was briefly evaluated, which however, suffered from low yields. Selected β‐pinenyl‐substituted indenyl complexes were scanned as catalysts for the dehydropolymerization of phenylsilane upon activation with nBuLi, for polymerization of ethylene and propylene upon activation with methylaluminoxane (MAO) as well as for enantioselective carboalumination of 1‐octene with triethyl‐ and trimethylaluminum. The bis(indenyl) complexes catalyzed the carboalumination reaction, albeit only low yields (8–16 %) and low enantioselectivities (ee = 0.5–10 %) were obtained. The 2‐substituted bis(indenyl)zirconocene/MAO catalyst system produced atactic low‐molecular weight polypropylene with low polymerization activity whereas both 1‐ and 2‐substituted complexes showed high activities in ethylene polymerization producing polyethylenes with high molecular weights (Mw > 440000). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis of (+)‐Manoalide via a Copper(I)‐Mediated 1,2‐Metalate Rearrangement.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of (+)-manoalide via a copper(I)-mediated 1,2-metalate rearrangement.

An enantiospecific synthesis of the phospholipase A(2) inhibitor (+)-(4R)-manoalide is reported in which all 25 carbons of the sesterterpenoid skeleton are constructed from 3-furaldehyde, trimethylalane, oxirane, CO, beta-ionone, and propargyl bromide. The overall yield for the longest linear sequence (12 steps) is 12%. Key steps include (a) a zirconium-catalyzed carboalumination reaction to construct the C10-C11 trisubstituted alkene, (b) a Cu(I)-mediated 1,2-metalate rearrangement to construct the C6-C7 trisubstituted alkene, (c) a Sharpless kinetic resolution to secure the (4R)-stereochemistry, (d) generation of a 5-stannyl-2,3-dihydrofuran by Mo-catalyzed cycloisomerization of a homopropargylic alcohol, and (e) construction of the hydroxyfuranone ring by photooxidation of a silylfuran.

Enantio- and Diastereoselective Catalytic Carboalumination of 1-Alkenes and α,ω-Dienes with Cationic Zirconocenes: Scope and Mechanism

Bis(pentamethylcyclopentadienyl) dimethylzirconium (Cp*2ZrMe2) and bis(1-(−)-neomenthylindenyl) dimethylzirconium ((NMIn)2ZrMe2) upon activation by tris(pentafluorophenyl)borane are efficient catalysts for the carboalumination of a variety of 1-alkenes and nonconjugated dienes. The organoalane products can be oxidized to alcohol products, which are isolated in 50−90% yield. (NMIn)2ZrMe2 carboaluminates 1-alkenes and dienes with moderate (55−65%) enantioselectivities. In contrast, ethylenebis(tetrahydroindenyl) dimethylzirconium ((EBTHI)ZrMe2) and related zirconocenes give low activities and selectivities in the carboalumination reaction. Study of the interaction of zirconocene methyl cations with trimethylaluminum by 1H NMR shows that [(EBTHI)ZrMe][MeB(C6F5)3] forms a stable bis(μ-methyl) aluminum adduct. Zirconocene methyl cations derived from Cp*2ZrMe2 and (NMIn)2ZrMe2 react slowly with large excesses of trimethylaluminum to form weakly bound trimethylaluminum adducts. The difference in trimethylaluminu...

Pheromone synthesis, CLXX. A new synthesis of faranal [(3S,4R,6E,10Z)‐3,4,7,11‐tetramethyl‐6,10‐tridecadienal], the trail pheromone of the pharaoh's ant, Monomorium pharaonis

AbstractFaranal (1), the trail‐following pheromone of the worker of Pharaoh's ant (Monomorium pharaonis), was synthesized by the coupling reaction of the iododiene 3 with the chiral building block 8 as the key step. The geometrically pure iododiene 3 was prepared by the zirconocene‐mediated carboalumination reaction of 2 followed by treatment with iodine.

The Organometallic Chemistry of Carbon Suboxide

Abstract Carbon suboxide, C3, O2, reacts with a great variety of organometallic compounds. With organo-silicon and aluminium compounds it reacts with the C˭O moiety, giving sililation and carboalumination reactions. Insertion reactions of C˭C are performed with compounds having M-H, M-OR, M-NR2, M-PR2 bonds (M ≠ Si, Al), giving mono-metal derivatives (ketenyl) or di-metal derivatives of acil groups (amides, esthers, phospides). The coordination of C˭O or C˭C to transition metal complexes, the formation of allenic compounds and the decarbonylation reactions allow the synthesis of a series of particular metal derivatives (ketenyl, ketenylidene and carbonyl complexes) which, in some cases, present a peculiar reactivity.

ChemInform Abstract: π‐Bonding to Main Group Elements

Publisher Summary This chapter discusses the π complexes of all main-group elements, including their synthesis, structure, and bonding and the literature up to 1985. Compounds described have been characterized by X-ray or electron diffraction or at least by conclusive infrared (IR) or nuclear magnetic resonance (NMR) data. The term “π complex” is connected with compounds in which π ligands are polyhapto bonded to a transition metal. Many examples of the interaction between lithium and diverse π systems are documented in the literature. There are many examples known of π bonding between the heavier alkali metals and carbanionic fragments. There is no example in the literature of a stable alkene (or alkyne) complex with magnesium as central atom. Many compounds of the heavier alkaline–earth metals with organic ligands are described in the literature, for which from spectroscopic data π-interactions can be anticipated. π complexation is believed to be involved in the first step of the hydroboration of alkenes and alkynes; rearrangement reactions of organoboranes most likely involve the intermediates of a π-complex type. Alkene or alkyne complexes are mechanistically important intermediates in hydroalumination and carboalumination reactions. Using the isolobal relationship between CH or CH 2 units and corresponding transition metal or main-group element fragments, the majority of the nonclassical carbocations can be theoretically treated as π complexes.