An unusual feature of free base tetraarylporphyrins (H2TArP) is the small amount of monocation (H3TArP[Formula: see text] observed during titrations with acids. This anomalous behavior has been known for over forty years and has been explained in terms of the saddle deformation of the porphyrin that occurs upon protonation. In this paper, 1H NMR spectroscopy is used to investigate the protonation of H2OETPP, an H2TArP that is pre-deformed into a highly nonplanar saddle structure by steric crowding of its peripheral substituents. The goal of our studies is to determine if the saddle structure of H2OETPP stabilizes the monocation H3OETPP[Formula: see text], and, if it does, to conduct detailed NMR studies of H3OETPP[Formula: see text]. NMR spectra clearly show the formation of H3OETPP[Formula: see text] when one equivalent of acid is added to H2OETPP in organic solvents, and for picric acid in toluene-d8 the monocation is the dominant species (~70%). Crystals of H3OETPP[Formula: see text] (picrate) suitable for X-ray crystallography could not be obtained, but the structure of H4OETPP[Formula: see text] (picrate)2 was determined. Variable temperature NMR studies of H3OETPP[Formula: see text] (picrate) reveal the presence of two dynamic processes. The first is picrate anion exchange in CD2Cl2, where the activation energy ([Formula: see text]G[Formula: see text] is calculated to be 53 kJ.mol[Formula: see text]. A second process, ND tautomerism ([Formula: see text]G[Formula: see text] 42 kJ.mol[Formula: see text] is also detected for D3OETPP[Formula: see text] at very low temperatures in toluene-d8. The much lower activation energy for ND tautomerism in D3OETPP[Formula: see text] vs. D2OETPP ([Formula: see text]G[Formula: see text] 63 kJ.mol[Formula: see text] may be due to destabilization of the ground state of the monocation due to the presence of cis interactions between the inner deuterium atoms.

A new water-soluble porphyrin, 5,10,15,20-tetrakis(4-piperidyl)porphyrin (T(4-Pip)P), has been synthesized. T(4-Pip)P is related to the extensively studied water-soluble porphyrin 5,10,15,20-tetrakis(4-pyridyl)porphyrin (T(4-Py)P) but has substituents with different electronic and hydrogen-bonding properties and is soluble over a much larger pH range due to the higher pKa of its conjugate acid T(4-H-Pip)P4+. Investigations of the ionic self-assembly reactions of T(4-H-Pip)P4+ with anionic water-soluble porphyrins reveal that it forms nanoscale materials.

Sterically bulky substituents at the β-carbons of the pyrrole rings of porphyrins are sufficient to cause large out-of-plane porphyrin distortions even in the absence of substituent groups at the meso carbons. It is well established that substituents at the meso-positions only or at both the β-pyrrole and the meso-positions are sufficiently bulky to result in large non-planar distortions of the macrocycle. However, no systematic studies of the effects of bulky β-pyrrole substituents alone have been reported. Herein, molecular simulations and X-ray crystallography of nickel(II) 2,3,7,8,12,13,17,18-octa(isopropyl)porphyrin reveal that large out-of-plane distortions (>1.5 Å) are induced by the steric repulsion of the β-isopropyl groups but fail to lead to a single strongly energetically favored conformer. The molecular simulations indicate that multiple conformers differing in the orientation of the isopropyl groups and the macrocycle conformation coexist in solution and this is confirmed by resonance Raman spectroscopy. Large downshifts in the structure-sensitive lines result from the non-planar distortion, and line broadenings result from structural heterogeneity. The heterogeneity originates from tradeoffs between energy contributions from steric repulsion and macrocycle distortion. Simulations for 5-nitro-2,3,7,8,12,13,17,18-octa(isopropyl)porphyrin suggest two possible orientations of the nitro group with respect to the macrocycle mean plane — one nearly vertical (as in the crystal structure) and another that is nearly parallel. INDO/S semiempirical calculations indicate an orbital of the NO2 group resides between the porphyrin frontier orbitals with significant mixing of the nitro and porphyrin orbitals.KEYWORDS: porphyrin, non-planar, resonance Raman, X-ray crystallography, crystal structure, isopropyl, nitro, conformer, molecular mechanics, molecular simulations, density functional theory, steric crowding, conformational heterogeneity.

Titanocene-functionalized polymeric dendrimer 8 was prepared via polymerization of styrene with the first-generation dendrimer 7 bearing titanocene and styrene groups as a cross-linking monomer (Ti loading = 0.11 mmol/g; cross­linking = 0.64%). The polymeric titanocene 8 catalyzed the reaction of PhMe2SiCl and CH2=CHMgBr to give 1,4-silylated 2-butene (PhMe2SiCH2CH=CHCH2SiMe2Ph) with TON = 158. The polymeric titanocene 9, in which the titanocene group was more directly anchored onto the PS matrix, showed much lower activity (TON = 39) in a similar catalytic reaction.

Two polymer-supported versions of the Corey, Bakshi, and Shibata (CBS) catalyst were prepared and examined. Polymeric beads, with the auxiliary bound in pendant and crosslinked fashion, were prepared utilizing an improved procedure based upon earlier work. Optimization of a procedure for ketone reduction gives results that match those in solution. Attempted reuse gave mixed results. For comparison purposes, CBS functionalized monoliths were formed and tested but performed poorly.

A series of variously-functionalized first-, second-, and third-generation dendrimers have been prepared and linked via a biphenyl core to a bis-styryl moiety suitable for use as a crosslinker in polymerization. Attachment of titanocene moieties to the first-generation system and copolymerization with styrene affords polymeric disks that exhibit catalytic properties superior to comparable solution-phase systems in a multicomponent coupling of chlorosilanes with Grignards to give bis-allylic silanes.

A simple method for recycling the titanium species used in the Petasis methylenation reaction is described. Treatment of the titanocene oxide byproduct with chlorotrimethylsilane and pyridine allows regeneration, recovery, and successful reuse of titanocene dichloride in amounts corresponding to nearly 90% of the dimethyltitanocene reagent initially employed.

Dichlorotitanocene bound within porous polystyrene disks catalyzes the coupling of vinylmagnesium chloride and chlorosilanes to form 1,4-bis(silyl)-2-butenes. A simple batch-flow reactor permits catalyst reuse by repeated addition of fresh reagents and decantation of products.