Adsorption and structure of hydrocarbons in MCM-41: a computational study.

The adsorption of linear, branched, and cyclic hydrocarbons in MCM-41 is studied using Configurational Bias Monte Carlo simulations. A new computational model for MCM-41 is proposed which, although simple, is able to predict adsorption isotherms which are in agreement with the scarce experimental data. The structure of the adsorbed phase is analyzed and found to be similar to that of studies using small, hard spheres trapped in pores. The adsorption of mixtures is investigated, and the adsorption hierarchy is discussed. The structure of the adsorbed mixture is revealed and shows that all components of the mixture exhibit structure, even if they are only adsorbed in small quantities. Finally, the model is modified to include surface roughness and the effect on the adsorption isotherms and structure of the adsorbed phase is discussed.

Copper(III) and vanadium(IV)-oxo corrolazines.

As part of our efforts to develop the transition metal chemistry of corrolazines, which are ring-contracted porphyrinoid species most closely related to corroles, the vanadium and copper complexes (TBP)(8)Cz(H)V(IV)O (1) and (TBP)(8)CzCu(III) (2) of the ligand octakis(para-tert-butylphenyl)corrolazine [(TBP)(8)Cz] have been synthesized. The coordination behavior, preferred oxidation states, and general redox properties of metallocorrolazines are of particular interest. The corrolazine ligand in 1 was shown to contain a labile proton by acid/base titration and IR spectroscopy, serving as a -2 ligand rather than as the usual -3 donor. The oxidation state of the vanadium center in 1 was shown to be +4, in agreement with the overall neutral charge for this complex. The EPR spectrum of 1 reveals a rich signal consistent with a V(IV)(O) (d(1), S = 1/2) porphyrinoid species (g(xx) = 1.989, g(yy) = 1.972, g(zz) = 1.962). The electrochemical analysis of 1 shows behavior closer to that of a porphyrazine than a corrolazine, with a positively shifted, irreversible reduction at -0.65 V (vs Ag/AgCl). Resonance Raman and IR data for 1 confirm the presence of a triply bonded terminal oxo ligand with nu(V(16)O) = 975 cm(-1) and nu(V(18)O) = 939 cm(-1). The copper complex 2 exhibits a diamagnetic (1)H NMR spectrum, indicative of a bona fide square planar copper(III) (d(8), low-spin) complex. Previously reported copper corroles have been characterized as copper(III) complexes which exhibit a paramagnetic NMR spectrum at higher temperatures, indicative of a thermally accessible triplet excited state ([(corrole(*+))Cu(II)]). The NMR spectrum for 2 shows no paramagnetic behavior in the range 300-400 K, indicating that compound 2 does not have a thermally accessible triplet excited state. These data show that the corrolazine system is better able to stabilize the high oxidation state copper center than the corresponding corroles. Electrochemical studies of 2 reveal two reversible processes at +0.93 and -0.05 V, and bulk reduction of 2 with NaBH(4) generates the copper(II) species [(TBP)(8)CzCu(II)](-) (2a), which exhibits an EPR signal typical of a copper(II) porphyrinoid species.

Catalytic sulfoxidation and epoxidation with a Mn(III) triazacorrole: evidence for a "third oxidant" in high-valent porphyrinoid oxidations.

The reaction between (TBP)8(Cz)Mn(III) (1) and the oxygen atom donors iodosylbenzene (PhIO) or p-cyanodimethylaniline-N-oxide (CDMANO) leads to the manganese(V)-oxo complex (TBP)8(Cz)Mn(V)O (2), which has been isolated and characterized previously. Under catalytic conditions with 1 as added catalyst and PhIO as oxidant, both sulfoxidation of PhSMe and epoxidation of cis-stilbene is observed, whereas with CDMANO no sulfoxidation takes place, suggesting that 2 is not the active oxidant. Examination of the independent reactivity of isolated 2 toward PhSMe and cis-stilbene supports this conclusion. A mechanism which relies on a novel type of oxidant involving Lewis acid activation of PhIO by the Mn(V)-oxo complex 2 accounts for these observations and is confirmed by 18O-labeling experiments.

Octalkoxy-substituted phosphorus(V) triazatetrabenzcorroles via ring contraction of phthalocyanine precursors.

As part of efforts toward developing the synthesis of novel corrole analogues, the new triazatetrabenzcorrole (TBC) phosphorus(V) compounds (BuO)8(TBC)P(OCH3)2 (3), [(BuO)8(TBC)P(OH)]+OH- (4) ((BuO)8TBC=3,6,10,13,17,20,24,27-octabutoxytriazatetrabenzcorrolate), and [(BuO)8Cl8(TBC)P(OH)]+OH- (7) ((BuO)8Cl8TBC=3,6,10,13,17,20,24,27-octabutoxy-4,5,11,12,18,19,25,26-octachlorotriazatetrabenzcorrolate) were prepared. These TBCs were synthesized via a ring-contraction reaction mediated by PBr3 in pyridine in which a meso-nitrogen atom is extruded from an appropriate phthalocyanine precursor. Two of the compounds prepared, 3 and 4, are contracted analogues of the parent phthalocyanine (BuO8)PcH2 (1) 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine, which has been shown for the first time to be susceptible to ring-contraction despite the potential steric crowding imposed by the butoxy substituents. Likewise, the octachloro-substituted (BuO8)Cl8PcH2 (6), 1,4,8,11,15,18,22,25-octabutoxy-2,3,9,10,16,17,23,24-octachlorophthalocyanine, has also been shown to smoothly afford 7 via the same ring-contraction method. In addition, a rare example of a bona fide phosphorus(V) phthalocyanine, [(BuO)8(Pc)P(OCH3)2]+OH- (2), has been prepared for spectroscopic comparisons with the TBC compounds. These molecules are all extremely soluble in common organic solvents because of the octabutoxy substituents and have been characterized in detail by 1H NMR, 31P NMR, UV-vis, MALDI-MS, elemental analysis, and electrochemical studies. A clear trend in the phosphorus chemical shifts for 5 versus 6 coordination has been delineated: 31P NMR for 2, -179.8; 3, -186.1; 4, -105.1; and 7, -105.1. These data are compared to the 31P chemical shifts for related porphyrinoid(P(V)) molecules. The MALDI-MS data reveal the tendency of the TBC macrocycles to ionize as the radical cations (M(+*)) and has been useful in determining the axial ligands at phosphorus. A consequence of ring-contraction is reflected in the dramatic red-shifts (approximately 200 nm) observed for the Soret bands of the TBC compounds relative to the parent phthalocyanines. The magnitude of the red-shift is much greater than that reported for other TBCs. In addition, insertion of phosphorus causes a large red-shift in the Q-band of 2 found at 889 nm compared to 760 nm for 1. Cyclic voltammetry of the compounds in this study reveals multiple oxidation and reduction waves for each compound, and some interesting trends in redox potentials have been observed. The CV data for the octachloro-substituted compounds 6 and 7 show that the Cl substituents have an expected strong electron-withdrawing effect on the macrocycles. In general, the TBC compounds are significantly easier to oxidize and harder to reduce than the Pc counterparts, supporting the notion that corrole-type macrocycles favor higher oxidation states.