Michael T. H. Liu

Does Gd@C82 have an anomalous endohedral structure? Synthesis and single crystal X-ray structure of the carbene adduct.

We report here the results on single crystal X-ray crystallographic analysis of the Gd@C82 carbene adduct (Gd@C82(Ad), Ad = adamantylidene). The Gd atom in Gd@C82(Ad) is located at an off-centered position near a hexagonal ring in the C2v-C82 cage, as found for M@C82 (M = Sc and La) and La@C82(Ad). Theoretical calculation also confirms the position of the Gd atom in the X-ray crystal structure.

Isolation and characterization of carbene derivatives of La@C82(Cs).

The photochemical reaction of La@C82(Cs) with 2-adamantane-2,3-[3H]-diazirine (1) affords the adduct 2 of La@C82(Cs) with adamantylidene (Ad:) in a high selectivity. The two isomers of La@C82(Cs)(Ad), 2a and 2b, are isolated by HPLC and characterized by electron spin resonance, mass, and UV-vis-near-infrared spectroscopies. The electronic properties of 2a and 2b are very similar to that of the pristine La@C82(Cs), suggesting that 2a and 2b retain the essential electronic and structural character of La@C82(Cs).

Regioselective bis-functionalization of endohedral dimetallofullerene, La2@C80: extremal La-La distance.

Bis-functionalization of endohedral metallofullerene La(2)@C(80) by carbene addition is reported herein. Adducts were characterized using spectroscopic and single-crystal X-ray structure analyses. Crystallographic data for bisadduct La(2)@C(80)(CClPh)Ad (3, Ad = adamantylidene) revealed that both carbene additions occur at the 6,6-bond junction on the C(80) cage with ring cleavages and that La atoms are positioned collinearly with spiro carbons. It is noteworthy that the La-La distance in 3 is highly elongated by carbene bis-functionalization compared to the distance in pristine La(2)@C(80) and reported functionalized derivatives. The metal positions were confirmed through density functional calculations.

Reactivity and selectivity in intermolecular insertion reactions of chlorophenylcarbene

Abstract Reactivities for intermolecular C-H/Si-H/Sn-H insertion reactions of chlorophenylcarbene follow the order tri-n-butyltin hydride⪢diphenylsilanetriethylsilane⪢ cumenethylbenzene⪢toluene, and these reactions are competitive with addition to the double bond of α,β-unsaturated esters.

Sulfur ylides generated from the reaction of arylchlorocarbenes with trimethylenesulfide: determination of rate parameters by laser flash photolysis

Abstract Reaction of arylchlorodiazirines with trimethylenesulfide gives a mixture of aryldi(3-chloropropyl)thioacetal and aryl(2-propenyl)(3-chloropropyl)thioacetal in a good yield. The reaction goes through a formation of a sulfur ylide as an intermediate. Rate constants have been determined using laser flash photolytic techniques.

Activation parameters for the reaction of phenylchloro carbene with pyridine, tri-n-butyltin hydride, and triethylsilane; evidence against the need to invoke reversibly formed complexes in the reaction of this carbene with olefins

Abstract The activation energies for reaction of phenylchloro carbene with pyridine, tri-n-butyl-tin hydride and triethylsilane are reported. The data argues against reversibly formed complexes in the reaction of this carbene with olefins.

Carbonyl ylide from 3-chloro-3-p-nltrophenylcarbene and acetone

Abstract 3-chloro-3-p-nitrophenylcarbene readily reacts with acetone to from carbonyl ylide which undergoes 1,3 cycloaddition with dipolarophiles.

1,2-H shift in benzylchlorocarbene: isotope effect and influence of the solvent

Abstract Laser Flash photolysis of 3-chloro-3-benyzldiazirine and 3-chloro-3(phenyldideuteriomethyl)diazirine in isooctane over the 60 to −80°C temperature range gives rise to curved Arrhenius plots for both 1,2-H and 1,2-D migration in benzylchlorcarbene. The κ H /κ D values increase smoothly from 0.87 to 2.62 when the temperature increases from −60 to +30 °C. The κ H /κ D value is approximately 4 for most of the temperatures studied if a solvent correction is applied. Quantum mechanical tunnelling or the influence of the solvent may be a possible explanation for these observations.

NEW SYNTHESIS OF 2,2'-HETEROARYLPYRROLES FROM HETEROARYLCHLOROCARBENES

Abstract 2,2′-Pyridyl- and 2,2′-thienylpyrroles containing substitutets at the 1- and 3-positions of the pyrrole ring have been prepared from the reaction of heteroarylchlorocarbenes with 1-azabuta-1,3-dienes. Laser flash photolysis of heteroarylchlorocarbene in isooctane in the presence of 1-azabuta-1,3-diene yields an azomethine ylide (λ=550 nm) as an intermediate. The kinetic parameters for the ylide formation and further 1,5-intramolecular cyclization to the pyrrole ring have been determined.

Insertion of phenylchlorocarbenes in the CH bonds of alkanes: measurement of the rate constants by laser flash photolysis

Abstract Phenylchlorocarbenes, produced by photolysis of the parent diazirines, have a very limited lifetime in alkane solvents. The rate of disappearance of p-methyl- and p-chlorophenylch-lorocarbenes has been measured in iso-octane, cyclohexane and n-hexane as well as in benzene for comparison. The rate constants of several processes (dimerization, addition to the diazirine, reaction with the solvent, etc. ) contributing to the disappearance of the phenylchlorocarbenes have been determined. The rate of reaction with the solvent, which is much lower in benzene than in alkanes and depends strongly on the nature of the alkane, is assumed to be an insertion of the carbene in the CH bonds of the solvent. Consequences of this reaction on the chemistry of carbenes produced by continuous irradiation (or thermolysis) of diazirines in alkanes are briefly discussed.