Telluronium salt chemistry: Some fluorides and carboxylates

Ph₃TeF is ionic and no evidence is obtained for a covalent form in solvents of relatively low polarity. By contrast significant covalent interaction is seen for Ph₂(CH₃)Te(OOCR)(R=Ph, o-CH₃O·C₆H₄-, m-NO₂·C₆H₄). Factors influencing the formation and stability of covalent forms of telluronium “salts” are discussed. Phenyl(methyl)telluronium-ortho-phthalate is shown to be a monomer in chloroform solution. The structure of the compound is discussed in relation to NMR and IR data and against the background of previous literature reports of both dimeric and monomeric diorganotellurium-ortho-phthalates.     

New versatile organyltellurium(IV) halides: Synthesis and X-ray structural features of the telluronium tellurolate salts [PhTe(CH3)2]2[TeX6] (X = Cl, Br) and [Ph3Te][PhTeX4] (X = Cl, Br, I)

TeX₄ (X = Cl, Br) react in HCl/HBr with [Ph(CH₃)₂Te]X (X = Cl, Br) to give [PhTe(CH₃)₂]₂[TeCl₆] (1) and [PhTe(CH₃)₂]₂[TeBr₆] (2). The reaction of PhTeX₃ (X = Cl, Br, I) in cooled methanol with [(Ph)₃Te]X (X = Cl, Br, I) leads to [Ph₃Te][PhTeCl₄] (3), [Ph₃Te][PhTeBr₄] (4) and [Ph₃Te][PhTeI₄] (5). In the lattices of the telluronium tellurolate salts 1 and 2, octahedral TeCl₆ and TeBr₆ dianions are linked by telluronium cations through Te?Cl and Te?Br secondary bonds, attaining bidimensional (1) and three-dimensional (2) assemblies. The complexes 3, 4 and 5 show two kinds of Te?halogen secondary interactions: the anion-anion interactions, which form centrosymmetric dimers, and two identical sets of three telluronium-tellurolate interactions, which accomplish the centrosymmetric fundamental moiety of the supramolecular arrays of the three compounds, with the tellurium atoms attaining distorted octahedral geometries. Also phenyl C-H?halogen secondary interactions are structure forming forces in the crystalline structures of compounds 3, 4 and 5.     

Studies of diorganotellurium diisothiocyanates and of a triorganotellurium isothiocyanate in the solid state and in solution

The synthesis of the first diorganotellurium dithiocyanates is reported. It is argued that the tellurium interacts more strongly with the nitrogen than with the sulphur atom of the NCS group. Two structural classes are noted: (a) R₂Te(NCS)₂ (R  Ph, p-CH₃O · C₆H₄) in which interaction of tellurium with the two NCS groups is equal and in which intermolecular association via long TeS bonds probably occurs; (b) [R₂Te(NCS)](NCS) (R  p-C₂H₅O · C₆H₄) in which the tellurium interacts unequally with the two NCS groups to give a structure with some “telluronium salt” character.The chemistry of MePh₂Te(NCS) is studied. In solvents of reasonable polarity (e.g. DMSO), and probably in the solid state, it behaves as an essentially ionic telluronium salt [MePh₂Te](NCS). However, in CDCl₃ solution it exists in a covalent form, MePh₂Te(NCS), from which reductive elimination of, exclusively, methyl thiocyanate occurs. The mechanism of the decomposition is not simple: initially it is probable that a free radical pathway dominates, but after approximately 100 min the rate of decomposition increases. There is evidence that the second rate process is catalysed by diphenyltelluride. Other salts, [MePh₂Te]X (X  BF₄, PF₆) are reported for comparison.     

Synthesis,characterization, and solution properties of some new organotellurium compounds based on di(cyclohexylmethyl)telluride

A new series of organotellurium(IV) compounds based on di(cyclohexylmethyl)telluride ( 1 ) (i.e., (C₆H₁₁CH₂)₂TeX₂ and (C₆H₁₁CH₂)₂Te(R)X) was prepared by the reaction of compound 1 with halogens, N‐bromosuccinimide, and alkyl halides. Phenylation of (C₆H₁₁CH₂)₂TeX₂ with sodium tetraphenylborate gave di(cyclohexylmethyl)phenyltelluronium tetraphenylborate in good yield. Conductivity measurements in dimethylsulfoxide (DMSO) showed a considerable ionic character of these compounds and they behave as 1:1 electrolytes. ¹H NMR studies in CDCl₃ solution indicated that telluronium salts employed in this study are unstable toward reductive elimination. Reaction of di(cyclohexylmethyl)telluride, (C₆H₁₁CH₂)₂Te(CH₃)I, and (C₆H₁₁CH₂)₂Te(PhCH₂)Br with HgX₂ (X = Cl or Br) afforded 1:1 complexes. All compounds were characterized by elemental analyses and spectroscopic data. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:93–99, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20240     

Paramagnetic triangular rhenium sulfide cluster [Re3S4(Dppe)3(NCS)3]Br

A new cluster [Re₃S₄(Dppe)₃(NCS)₃]Br (Dppe = Ph₂PCH₂CH₂PPh₂) is synthesized. The molecular and crystal structures of the cluster are determined by X-ray diffraction analysis. The magnetochemical data indicate the high-spin ground state (S = 3/2) of the cluster at room temperature.     

The synthesis and spectroscopic examination of telluronium salts based on the 1-organo-3,4-benzo-1-telluracyclopentane cation

The syntheses of a new range of telluronium salts based on the 1-organo-3,4-benzo-1-telluracyclopentane cation are reported (C₈H₈TeRX: R  CH₃, CH₂CH₃, X  I; R  CH₃, X  PhCOO; R  CH₃, X  ClO₄; R  CH₃, X  BPh₄; R  Ph, X  BPh₄; R  CH₂Ph, CH₂CHCH₂, CH₂COPh, X  Br.) Solution studies using ¹H, ¹³C and ¹²⁵Te NMR spectroscopy in conjunction with conductivity and molecular weight measurements show the salts to be associated via weak “ionic” bonds in solvents of lower polarity such as chloroform but to be more ionic and strongly solvated in DMSO. Solvents such as DMF provide an intermediate and more complex situation.Mass spectra indicate that association can extend to the gas phase and some novel features in the spectra are discussed. Infrared studies indicate polymorphism for 1-methyl-3,4-benzo-1-telluracyclopentane perchlorate with one form containing perchlorate ions interacting with tellurium.     

Spectral and crystallography studies of new palladacycle complexes with P,C‐ and C,C‐donor ligands; Application of (OAL16) to optimizing the yield of Mizoroki‐Heck reaction

The new symmetrical diphosphonium salt [Ph₂P(CH₂)₂PPh₂(CH₂C(O)C₆H₄Br)₂] Br₂ ( S ) was synthesized in the reaction of 1,2‐bis (diphenylphosphino) ethane (dppe) and related ketone. Further treatment with NEt₃ gave the symmetrical α‐keto stabilized diphosphine ylide [Ph₂P(CH₂)₂PPh₂(CHC(O)C₆H₄Br)₂] ( Y ¹ ). The unsymmetrical α‐keto stabilized diphosphine ylide [Ph₂P(CH₂)₂PPh₂(CHC(O)C₆H₄Br)] ( Y ² ) was synthesized in the reaction of diphosphine in 1:1 ratio with 2.3′‐dibromoacetophenone, then treatment with NEt_3. The reaction of dibromo (1,5‐cyclooctadiene)palladium (II), [PdBr₂(COD)] with this ligand ( Y ¹ ) in equimolar ratio gave the new C,C‐chelated [PdBr₂(Ph₂P(CH₂)₂PPh₂(C(H)C(O)C₆H₄Br)₂)] ( 1 ) and with unsymmetrical phosphorus ylide [Ph₂P(CH₂)₂PPh₂C(H)C(O)C₆H₄Br] ( Y ² ) gave the new P, C‐chelated palladacycle complex [PdBr₂(Ph₂P(CH₂)₂PPh₂C(H)C(O)Br)] ( 2 ). These compounds were characterized successfully by FT‐IR, NMR (¹H, ¹³C and ³¹P) spectroscopic methods and the crystal structure of Y ¹ and 2 were elucidated by single crystal X‐ray diffraction. The results indicated that the complex 1 was C, C‐chelated whereas complex 2 was P, C‐chelated. These air/moisture stable complexes were employed as efficient catalysts for the Mizoroki‐Heck cross‐coupling reaction of several aryl chlorides, and the Taguchi method was used to optimize the yield of Mizoroki‐Heck coupling. The optimum condition was found to be as followed: base; K₂CO₃, solvent; DMF and loading of catalyst; 0.005 mmol.     

Preparation & Stereochemistry of some Diphosphorus Heterocycles

Abstract

Cleavage of Ph₂P(CH₂)nPPh₂(n=2?5) with Li in THF provides a convenient source of the corresponding dianions which may be alkylated with X(CH₂)_nX (X=Cl,Br,n=1?3) to give diphosphorus heterocycles with a ring size 5–7. These are separated into their stereoisomers and stereochemical assignments made. An alternative route to an eight-membered ring is described.     

Reactions of (η-allyl)dicarbonylmolybdenum(II) complexes with phosphorus and arsenic donor ligands

Reaction of [MoX(CO)₂(η-C₃H₅)(MeCN)₂] with the arsines Ph₂AsCH₂CH₂AsPh₂ (dae) and Ph₂AsCH₂AsPh₂ (dam) yields complexes of stoichiometry [MoX(CO)₂(η-C₃H₅)dae] (where X = Cl, Br or I) and [MoX(CO)₂(η-C₃H₅)]₂dam (where X = Cl or Br). The former are isomorphous with the known Ph₂PCH₂CH₂PPH₂ complexes, whereas the latter probably contain halogen and dam bridges. Under forcing conditions the corresponding ditertiary phosphines form the molybdenum(0) derivatives $\text{cis}$-Mo(CO)₂(Ph₂P(CH₂)_nPPh₂]₂ (where n = 1 or 2).     

Neue Silber‐Tellurid Cluster stabilisiert mit zweizähnigen Phosphanen: Synthese und Struktur von {[Ag5(TePh)6(Ph2P(CH2)2PPh3)](Ph2P(CH2)2PPh2)}∞, [Ag18Te(TePh)15(Ph2P(CH2)3PPh2)3Cl] und [Ag38Te13(TetBu)12(Ph2P(CH2)2PPh2)3]

Novel Silver‐Telluride Clusters Stabilised with Bidentate Phosphine Ligands: Synthesis and Structure of {[Ag₅(TePh)₆(Ph₂P(CH₂)₂PPh₃)](Ph₂P(CH₂)₂PPh₂)}_∞, [Ag₁₈Te(TePh)₁₅(Ph₂P(CH₂)₃PPh₂)₃Cl], and [Ag₃₈Te₁₃(Te t Bu)₁₂(Ph₂P(CH₂)₂PPh₂)₃] Bidentate phosphine ligands have been found effective to stabilise polynuclear cores containing silver and chalcogenide ligands. They can act as intra and intermolecular bridges between the silver centres. The clusters {[Ag₅(TePh)₆(Ph₂P(CH₂)₂PPh₃)](Ph₂P(CH₂)₂PPh₂)}_∞ ( 1 ), [Ag₁₈Te(TePh)₁₅(Ph₂P(CH₂)₃PPh₂)₃Cl] ( 2 ), and [Ag₃₈Te₁₃(TetBu)₁₂(Ph₂P(CH₂)₂PPh₂)₃] ( 3 ) have been prepared and their molecular structure determined. Compound 2 and 3 are molecular structures with separated cluster cores while 1 forms a polymeric chain bridged by phosphine ligands. ( 1 : space group P2₁/c (No. 14), Z = 4, a = 3518,1(7) pm, b = 2260,6(5) pm, c = 3522,1(7) pm, β = 119,19(3)°; 2 : space group R3 (No. 148), Z = 6, a = b = 3059,4(4) pm, c = 5278,8(9) pm; 3: space group Pccn (No. 56), Z = 4, a = 3613,0(9) pm, b = 3608,6(7) pm, c = 2153,5(8) pm)     

Ligating properties oftert-phosphine/arsine sulphides or selenides,Part IX. Preparation and spectroscopic studies of copper(I)/copper(II) complexes with bis(—phosphine chalcogenides)

Summary The analytical, molar conductance and spectroscopic studies of new complexes of copper(I) and copper(II) with bis(—phosphine chalcogenides), Ph₂P(E)(CH₂)_n-P(E)Ph₂(L-L) are reported. The complexes are of the types: (a) [CuX(L-L)](X, n, E: Cl, 2–4, Br, 2, S; Cl, Br, 1, Se); (b) [Cu₂X₂(L-L)] (X, n, E: Cl, Br, 2, 3, Se) and (c) [CuCl₂(L-L)] (n, E: 2, 3, S). Possible structures have been derived.     

Rhenium(I) and Technetium(I) Tricarbonyl Complexes with Phosphoraneimines

[NEt₄]₂[Re(CO)₃Br₃] and [NEt₄]₂[Tc(CO)₃Cl₃] react with trimethylsilyltriphenylphosphoraneimine, Me₃SiNPPh₃, under exchange of the bromo ligands and the formation of cationic [M(CO)₃(HNPPh₃)₃]⁺ complexes (M = Re, Tc). The required protons are abstracted from the solvent CH₂Cl₂. The steric bulk of the organic ligands causes a marked distortion of the established coordination polyhedra from an idealized octahedron with bond angles between neighbouring donor atoms between 81.81(8)° and 96.66(8)°. The reaction of [NEt₄]₂[Re(CO)₃Br₃] with Me₃SiNP(Ph₂)CH₂PPh₂ in CH₂Cl₂ yields the neutral complex [Re(CO)₃Br{HNP(Ph₂)CH₂PPh₂)], which contains a neutral, chelate‐bonded (diphenylphosphinomethyl)diphenylphosphoraneimine ligand. A similar reaction with the bifunctional phosphoraneimine Me₃SiNP(Ph₂)CH₂(Ph₂)PNSiMe₃ gives only small amounts of a binuclear rhenium(I) complex of the composition [{Re(CO)₃Br₂}₂(HNP(Ph₂)CH₂(Ph₂)PNH)]^2‐, whereas the major amount of the bis‐phosphoraneimine undergoes an intramolecular rearrangement to yield [H₂NP(Ph₂)NP(Ph₂)CH₃]Br. An X‐ray structure analysis shows a widespread delocalization of electron density over the central part of the cation.     

Palladium complexes with bis(diphenylphosphinomethyl)amino ligands and their application as catalysts for the Heck reaction

Aminomethylphosphine (P–C–N) type ligands, (Ph₂PCH₂)₂NR R = –(CH₂)₃Si(OEt₃)₃ or –CH₂CH₂OH, and their Pd(II) complexes have been synthesized. All the compounds were characterized by ¹H-, ³¹P-NMR, and elemental analysis. The complexes are proposed to have a square planar geometry. They were investigated as catalysts for the Heck reaction of aryl halides (I, Br, Cl) with methyl acrylate. Both complexes showed high activity to give methyl cinnamate in good yields, with the best turnover numbers found for [PdCl₂(Ph₂PCH₂)₂N(CH₂)₃Si(OEt)₃].     

Synthesis and spectroscopic studies of phenyllead halide and thiocyanate adducts with hexamethylphosphoramide

Hexamethylphosphoramide (HMPA) adducts of the type Ph₃PbX·HMPA (X=Cl, Br, I, and NCS), Ph₂PbX₂·2HMPA (X=Cl, Br, and I), and Ph₂PbX₂·HMPA (X=Br and I), have been prepared and characterized by infrared, Raman, mass, and ³¹P nmr spectroscopy. Molecular weight and infrared solution data show that Ph₃PbX·HMPA adducts dissociate in benzene, the degree of dissociation being NCS«Cl<Br<I. The thiocyanate adducts Ph₃PbNCS·HMPA and Ph₂Pb(NCS)₂·2HMPA have v(CN) and v(CS) frequencies in the solid state, and v(CN) frequencies and absorptivities in benzene solution consistent with N-bonded thiocyanate in the solid state and in benzene solution. Vibrational frequencies are reported in the range 260 to 80 cm⁻¹ and assignments are made for v(Pb-X), v(Pb-O0, and v(Pb-NCS) modes. The 1:1 adducts Ph₃PbX·HMPA are monomeric and trigonal bipyramidal, whereas the 1:2 adducts Ph₂PbX₂·2HMPA are monomeric and cis-octahedral and the Ph₂PbX₂·HMPA appear to be halogen bridged polymers with lead six-coordinate. Coordination of HMPA causes a small upfield change in ³¹P chemnical shift values, and ²J(Pb-P) values vary with X in the order: NCS>I-Br>Cl for Ph₃PbX·HMPA adducts. Corresponding tin and lead adducts are compared with respect to mode of adduct formation.     

Tellurium(II) and tellurium(IV) complexes of phosphine chalcogenide ligands,synthesis and X-ray structures

Reaction of TeX₄ (X = Cl or Br) with 2 mol. equiv. of OPR₃ (R = Me, Et or Ph) gives the distorted octahedral cis-[TeX₄(OPR₃)₂], while the bidentates Ph₂P(E)(CH₂)_nP(E)Ph₂ (E = O, n = 1 or 2; E = S, n = 1) give the six-coordinate [TeX₄{Ph₂P(E)(CH₂)_nP(E)Ph₂}]. These species have been characterised spectroscopically (via ¹H and ³¹P{¹H} NMR and IR) and by crystallographic analyses on cis-[TeBr₄(OPPh₃)₂], [TeCl₄{Ph₂P(O)CH₂P(O)Ph₂}] and [TeBr₄{Ph₂P(S)CH₂P(S)Ph₂}]. The TeX₄ (X = Cl or Br) are reduced by Ph₂P(S)(CH₂)₂P(S)Ph₂ and Ph₂P(Se)CH₂P(Se)Ph₂, giving the planar, four-coordinate Te(II) species [Te{Ph₂P(S)(CH₂)₂P(S)Ph₂}₂]²⁺ (isolated as [(TeCl₅)₂{μ-Ph₂P(S)(CH₂)₂P(S)Ph₂}]^2? and [TeBr₆]^2? salts) and [TeBr₂{Ph₂P(Se)CH₂P(Se)Ph₂}], all of which have also been identified crystallographically. On the basis of the structural data the Te-based lone pair associated with the Te(IV) species is assumed to occupy the 5s orbital, whereas in the Te(II) complexes the planar coordination is consistent with the two stereochemically active lone pairs occupying the axial sites.     

Ionic Transformations in Extremely Nonpolar Fluorous Media: Easily Recoverable Phase‐Transfer Catalysts for Halide‐Substitution Reactions

Solutions of the fluorous alkyl halides R_f8(CH₂)_mX (R_fn=(CF₂)_n?1CF₃; m=2, 3; X=Cl, Br, I) in perfluoromethylcyclohexane or perfluoromethyldecalin are inert towards solid or aqueous NaCl, NaBr, KI, KCN, and NaOAc. However, halide substitution occurs in the presence of fluorous phosphonium salts (R_f8(CH₂)₂)(R_f6(CH₂)₂)₃P⁺X^? (X=I ( 1 ), Br ( 3 )) and (R_f8(CH₂)₂)₄P⁺I^? (10 mol %), which are soluble in the fluorous solvents under the reaction conditions (76–100 °C). Stoichiometric reactions of a) 1 with R_f8(CH₂)₂Br and b) 3 with R_f8(CH₂)₂I were conducted under homogenous conditions in perfluoromethyldecalin at 100 °C and yielded the same R_f8(CH₂)₂I/R_f8(CH₂)₂Br equilibrium ratio (≈60:40). This shows that ionic displacements can take place in extremely nonpolar fluorous phases and suggests a classical phase‐transfer mechanism for the catalyzed reactions. Interestingly, the nonfluorous salt (CH₃(CH₂)₁₁)(CH₃(CH₂)₇)₃P⁺I^? ( 4 ) also catalyzes halide substitutions, but under triphasic conditions with 4 suspended between the lower fluorous and upper aqueous layers. NMR experiments established very low solubilities in both phases, which suggests interfacial catalysis. Catalyst 1 is easily recycled, optimally by simple precipitation onto teflon tape.     

Ligating properties of thionitrosoamines: III. Carbonyl complexes of rhodium(I) and rhodium(III) containing N-thionitrosodimethylamine

Me₂NNS reacts with [Rh(CO)₂Cl]₂ to produce the complex cis-Rh(SNNMe₂)(CO)₂Cl (1). The latter undergoes reversible CO substitution by Me₂NNS to give the complex trans-Rh(SNNMe₂)₂(CO)Cl (2a). Complexes 1 and 2a, in solution lose CO and Me₂NSS, respectively, to give the complex trans-(μ-Cl)₂[Rh(SNNMe₂)(CO)]₂ (3). Complex 1 can also be prepared by bubbling CO through a CH₂Cl₂ solution of Rh(SNNMe₂)(diene)Cl (diene = 1,5-cyclooctadiene (4a), norbornadiene (4b)) obtained by a bridge-splitting reaction of Me₂NNS with [Rh(diene)Cl]₂. 1 and 2a react with EPh₃ (E = P, As, Sb) to give the complexes trans-Rh(EPh₃)₂(CO)Cl. The complexes trans-Rh(E′Ph₃)₂(CO)X (X = Cl, E′ = As, Sb; X = Br, NCS, E′ = As) undergo reversible E′Ph₃ displacement upon treatment with Me₂NNS to give the complexes trans-Rh(SNNMe₂)₂(CO)X (X = Cl (2a), Br (2b), NCS (2c)). Oxidative additions of Br₂, I₂, or HgCl₂ to 2a produce stable adducts, while the reaction of 2a with CH₃I gives an inseparable mixture of the adduct Rh(SNNMe₂)₂(CO)(CH₃)ClI and the acetyl derivative Rh(SNNMe₂)₂(CH₃CO)ClI. A mixture of the acetyl derivative (μ-Cl)₂[Rh(SNNMe₂)(CH₃CO)I]₂ and the adduct (μ-Cl)₂[Rh(SNNMe₂)(CO)(CH₃)I]₂ is obtained by treating 1 with CH₃I. The IR spectra of all the compounds are consistent with S-coordination of Me₂NNS. Because of the restricted rotation around the NN bond, the ¹H NMR spectra of the new compounds exhibit two quadruplets in the range 3.5–4.3δ when ⁴J(HH) = 0.7–0.5 Hz. When ⁴J(HH) < 0.5 Hz, the perturbing effect of the quadrupolar relaxation of the ¹⁴N nucleus obscures the spin-spin coupling and two broad signals are observed in the range 3.6–4δ.     

Synthesis of organopalladium(IV) complexes by halogen exchange,and the structure of the azidopalladium(II) complex formed on reductive elimination of ethane from Pd(N)3Me2(CH2Ph)(bpy)

A new route to organopalladium(IV) complexes is described, involving replacement of bromine in the 2,2′-bipyridyl complex PdBrMe₂(CH₂Ph)(by), by other halogen or pseudohalogen groups. ¹H NMR studies of the decomposition of PDXMe₂(CH₂Ph)(bpy) in warm (CD₃)₂CO indicate that a selectivity in reductive elimination of alkanes occurs. to give ethane (X = Br, N₃, NCS), or a mixture of ethane and ethylbenzene in ca. 9/1 ratio (X = F. Cl, I). The reductive elimination product azido(2,2′-bipyridyl)benzylpalladium(II) has been characterized by X-ray crystallography.     

Bromination of silatranyl-, germatranyl-, silyl-, and germyl-phenylacetylenes

Reactions of element-substituted alkynes R₃MCCPh (R₃M = Me₃Si, Et₃Si, Ph₃Si, Et₃Ge, n-Bu₃Sn, N(CH₂CH₂O)₃Si, N(CH₂CH₂O)₃Ge, N(CH₂-CHMeO)₃Ge, and N(CH₂CH₂O)₂(CH₂CHPhO)Ge) with bromine, tetra-n-butylammonium tribromide (TBAT), and N-bromosuccinimide (NBS)/DMSO were investigated. The Z,E-ratio of isomeric dibromoalkenes formed in bromination reaction with Br₂ and TBAT are discussed. The crystal structures of N(CH₂CH₂O)₃SiCCPh and N(CH₂CHMeO)₃GeX (X = C CPh, C(Br)C(Br)Ph, C(Br₂)C(O)Ph), and Ph₃SiC(Br)C(Br)Ph are reported. © 2003 Wiley Periodicals, Inc. 15:43–56, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10211     

Bond dissociation energies and radical heats of formation in CH3Cl,CH2Cl2, CH3Br,CH2Br2, CH2FCl,and CHFCl2

An analysis of thermochemical and kinetic data on the bromination of the halomethanes CH_4–nX_n (X = F, Cl, Br; n = 1–3), the two chlorofluoromethanes, CH₂FCl and CHFCl₂, and CH₄, shows that the recently reported heats of formation of the radicals CH₂Cl, CHCl₂, CHBr₂, and CFCl₂, and the C? H bond dissociation energies in the matching halomethanes are not compatible with the activation energies for the corresponding reverse reactions. From the observed trends in CH₄ and the other halomethanes, the following revised ΔH°_f,298 (R) values have been derived: ΔH°_f(CH₂Cl) = 29.1 ± 1.0, ΔH°_f(CHCl₂) = 23.5 ± 1.2, ΔH_f(CH₂Br) = 40.4 ± 1.0, ΔH°_f(CHBr₂) = 45.0 ± 2.2, and ΔH°_f(CFCl₂) = ?21.3 ± 2.4 kcal mol^?1. The previously unavailable radical heat of formation, ΔH°_f(CHFCl) = ?14.5 ± 2.4 kcal mol^?1 has also been deduced. These values are used with the heats of formation of the parent compounds from the literature to evaluate C? H and C? X bond dissociation energies in CH₃Cl, CH₂Cl₂, CH₃Br, CH₂Br₂, CH₂FCl, and CHFCl₂.