Synthesis, Characterization, and Reactivity of Group 4 Metalloporphyrin Diolate Complexes

A number of group 4 metalloporphyrin diolate complexes were synthesized via various approaches. For example, treatment of imido complex (TTP)HfNAriPr with diols resulted in formation of the corresponding diolato complexes (TTP)Hf[OCR1R2CR1R2O] (R1 = R2 = Me, 1; R1 = Me, R2 = Ph, 2; R1 = R2 = Ph, 3). Treatment of (TTP)TiNiPr with diols generated (TTP)Ti[OCR1R2CR1R2O] (R1 = R2 = Me, 5; R1 = Me, R2 = Ph, 6; R1 = H, R2 = Ph, 7; R1 = H, R2= p-tolyl, 8). Alternatively hafnium and titanium pinacolates 1 and 5 were prepared through metathetical reactions of (TTP)MCl2 (M = Hf, Ti) with disodium pinacolate. The substitution chemistry of hafnium complexes correlated well with the basicity of the diolato ligands. Complexes 1−6 underwent oxidative cleavage reaction, producing carbonyl compounds and oxometalloporphyrin species. For less substituted diolates 7 and 8, an array of products including the enediolate complexes (TTP)Ti[OC(Ar)C(Ar)O] (Ar = Ph, 9; Ar = p-tolyl, 10) was observed. The possible cleavage reaction pathways are discussed

Titanium(II) Porphyrin Complexes: Versatile One- and Two-Electron Reducing Agents. Reduction of Organic Chlorides, Epoxides, and Sulfoxides

Treatment of the well-defined complexes (TTP)Ti(η2-EtC⋮CEt) or trans-(TTP)Ti(THF)2 with vicinal dichloroalkanes or dichloroalkenes results in the production of alkenes or alkynes and 2 equiv of (TTP)TiCl. This net two-electron redox reaction arises from two formal one-electron reduction processes mediated by chlorine atom transfer. Oxygen atom transfer occurs when the Ti(II) porphyrins are treated with several different sulfoxides or epoxides, resulting in two-electron redox products, (TTP)TiO, the sulfide or alkene, and EtC⋮CEt or THF. The electronic properties of the substituents on the sulfoxides or epoxides correlate with the yield and rate of the deoxygenation reactions

Syntheses and Characterizations of Alkyl- and Amidotin Porphyrin Complexes: Molecular Structure of trans-Bis(phenylacetylido)(meso-tetra-p-tolylporphyrinato)tin(IV)

Treatment of (TTP)SnCl2 (TTP = meso-tetra-p-tolylporphyrinato dianion) with an excess of lithium amides (LiNHPh, LiNPh2, o-C6H4(NHLi)2) affords the metathesis products (TTP)Sn(NHPh)2 (1), (TTP)Sn(NPh2)2 (2), and (TTP)Sn(o-C6H4(NH)2) (3). Ligand exchanges of 1 with p-toluidine and 2,3,5,6-tetrafluoroaniline afford the complexes (TTP)Sn(p-NHC6H4Me)2 (4) and (TTP)Sn(NHC6F4H)2 (5), respectively. Treatment of (TTP)SnCl2 with the bulky lithium (2,4,6-tri-tert-butylphenyl)amide or with PhNLiNLiPh does not form the corresponding amido or azobenzene complexes but produces the reduced product (TTP)Sn. In addition, the reaction of (TTP)Sn(NHPh)2 with PhHN−NHPh results in the production of (TTP)Sn, azobenzene, and aniline. The diethyl complex (TTP)SnEt2 (6) can be prepared via the reaction of (TTP)SnCl2 with 1 equiv of ZnEt2. The dineopentyl complex (TTP)Sn(CH2CMe3)2 (7) can be detected in the reaction of (TTP)SnCl2 with neopentyllithium. The methyl derivatives cis-(TTP)SnMe2 (8) and (TTP)SnMeBr (9) can be obtained by the treatment of (TTP)Li2(THF)2 with 1 equiv of Me2SnBr2 at low temperature in toluene and CH2Cl2, respectively. Treatment of (TTP)SnCl2 with an excess of alkynyllithium salts (LiC⋮CPh, LiC⋮CSiMe3) affords the metathesis products (TTP)Sn(C⋮CPh)2 (10) and (TTP)Sn(C⋮CSiMe3)2(11). Complexes 10 and 11 are inert at ambient temperature and are not photosensitive. Complex 10 reacts stepwise with excess MeOH cleanly to convert to (TTP)Sn(C⋮CPh)(OMe) (12) and then to (TTP)Sn(OMe)2 (13) with increasing reaction time. The lability of the axial ligands in these tin porphyrin complexes correlates inversely with the basicity of the axial group. The crystal structure of 10 (monoclinic, P21/c, a = 10.9424(2) Å, b = 14.5565(5) Å, c = 16.4968(6) Å, α = 90°, β = 100.7930(10)o, γ = 90°, R1 = 3.53%, and wR2 = 8.90%) was determined from X-ray diffraction data

Iron Porphyrin Catalyzed N−H Insertion Reactions with Ethyl Diazoacetate

A series of metalloporphyrin complexes were surveyed as catalysts for carbene insertion from ethyl diazoacetate into the N−H bonds of amines. Iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, was found to be an efficient catalyst for N−H insertion reactions with a variety of aliphatic and aromatic amines, with yields ranging from 68 to 97%. Primary amines were able to undergo a second insertion when another equiv of EDA was added by slow addition. N-Heterocyclic compounds were poor substrates, giving low yields or no N−H insertion products. Competition reactions and linear free energy relationships provided mechanistic insights for the insertion reaction. The relative rates for N−H insertion into para-substituted aniline derivatives correlated with Hammett σ+ parameters. Electron-donating groups enhanced the reaction, as indicated by the negative value of ρ (ρ = −0.66 ± 0.05, R2 = 0.93). These results are consistent with a rate-determining nucleophilic attack of the amine on an iron carbene complex. In addition, the decomposition of EDA catalyzed by FeII(TPP) or FeIII(TPP)Cl was examined with various amounts of added pyridine. The Fe(II) catalyst is strongly inhibited by the presence of pyridine. In contrast, catalysis by the Fe(III) porphyrin is accelerated by amines. These experiments suggested that an iron(III) porphyrin carbene complex is the active catalyst

Alkoxido, Amido, and Imido Derivatives of Titanium(IV) Tetratolylporphyrin

Treatment of (TTP)TiCl2 (1) [TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion] with excess NaOR (R = Ph, Me, t-Bu) affords the bis(alkoxide) derivatives (TTP)Ti(OR)2 [R = Ph (2), Me (3), t-Bu (4)] in moderate yield. The corresponding amido derivative (TTP)Ti(NPh2)2(5) is prepared in an analogous fashion employing LiNPh2. The disubstituted complexes 2, 3, and 5 react cleanly with (TTP)TiCl2 to afford the ligand exchange products (TTP)Ti(OR)Cl [R = Ph (6), Me (7)] and (TTP)Ti(NPh2)Cl (8), respectively. The monosubstituted complexes 6−8are also obtained by treatment of 1 with 1 equiv of the appropriate NaOR or LiNPh2 reagent. Treatment of 5 with excess phenol produces the bis(phenoxide) derivative 2 and 2 equiv of HNPh2. The imido derivatives (TTP)TiNR [R = t-Bu (9), Ph (10), C6H4-p-Me (11)] are prepared by the treatment of 1 with excess LiNHR. The t-Bu derivative (9) is also obtained by reaction of 1 with excess H2N-t-Bu at elevated temperatures. The phenyl imido complex (10) may be produced by the reaction of 0.5 equiv of PhNNPh with (TTP)Ti(η2-EtC⋮CEt) in refluxing toluene. Finally, (TTP)TiNTMS (12) is obtained by oxidation of (TTP)Ti(η2-EtC⋮CEt) with N3TMS

Facile Syntheses of Titanium(II), Tin(II), and Vanadium(II) Porphyrin Complexes through Homogeneous Reduction. Reactivity of trans-(TTP)TiL2 (L = THF, t-BuNC)

Facile syntheses of the meso-tetra-p-tolylporphyrin (TTP) complexes trans-(TTP)Ti(THF)2(1), (TTP)Sn (2), and trans-(TTP)V(THF)2 (3) are achieved through homogeneous reduction of high-valent precursors using NaBEt3H. The composition of the new compound trans-(TTP)Ti(THF)2 was determined by spectroscopic and chemical characterization. Ligand displacement reactions of trans-(TTP)Ti(THF)2 with t-BuNC produced a new Ti(II) complex,trans-(TTP)Ti(t-BuNC)2. The ligand-binding preference of (TTP)TiIILn (n = 1, 2) is picoline ∼pyridine \u3e t-BuNC \u3e PhC⋮CPh \u3e EtC⋮CEt \u3e THF

Conversions of Cyclic Amines to Nylon Precursor Lactams Using Bulk Gold and Fumed Silica Catalysts

Bulk gold powder (∼50 μm) and alumina-supported gold catalyzed the oxidative dehydrogenation of 5-, 6-, and 7-membered cyclic amines to amidines. These amidines were hydrolyzed upon treatment with Aerosil 200 (fumed silica gel) and water, producing lactams in 42–73% yields and amines in 36–63% yields. The gold and Aerosil 200 catalysts could also be combined in a one-pot reaction to catalyze the conversion of cyclic amines to lactams in yields up to 51%

Catalytic Reactions of Carbene Precursors on Bulk Gold Metal

Bulk gold metal powder, consisting of particles (5−50 μm) much larger than nanoparticles, catalyzes the coupling of carbenes generated from diazoalkanes (R2C═N2) and 3,3-diphenylcyclopropene (DPCP) to form olefins. It also catalyzes cyclopropanation reactions of these carbene precursors with styrenes. The catalytic activity of the gold powder depends on the nature of the gold particles, as determined by TEM and SEM studies. The reactions can be understood in terms of mechanisms that involve the generation of carbene R2C: intermediates adsorbed on the gold surface