Protonation of (N-N)PtPh(2) (1; N-N = diimine ArN=CMe-CMe=NAr with Ar = 2,6-Me(2)C(6)H(3) (a), 2,4,6-Me(3)C(6)H(2) (b), 4-Br-2,6-Me(2)C(6)H(2) (c), 3,5-Me(2)C(6)H(3) (d), and 4-CF(3)C(6)H(4) (e)) in the presence of MeCN at ambient temperature generates (N-N)Pt(Ph)(NCMe)(+) (2). At -78 degrees C, protonation of 1a yielded (N-N)PtPh(2)(H)(NCMe)(+) (3a), which produced benzene and 2a at ca. -40 degrees C. Protonation of 1a-e in CD(2)Cl(2)/Et(2)O-d(10) furnished (N-N)Pt(C(6)H(5))(eta(2)-C(6)H(6))(+) (4a-e). The pi-benzene complexes 4a-c, sterically protected at Pt, eliminate benzene at ca. 0 degree C. The sterically less protected 4d-e lose benzene already at -30 degrees C. SST and 2D EXSY NMR demonstrate that phenyl and pi-benzene ligand protons undergo exchange with concomitant symmetrization of the diimine ligand, most likely via oxidative insertion of Pt into a C-H bond of coordinated benzene. The kinetics of the exchange processes for 4a-c were probed by quantitative EXSY spectroscopy, resulting in DeltaH() of 70-72 kJ mol(-1) and DeltaS of 37-48 J K(-1) mol(-1). A large, strongly temperature-dependent H/D kinetic isotope effect (9.7 at -34 degrees C; 6.9 at -19 degrees C) was measured for the dynamic behavior of 4a versus 4a-d(10), consistent with the proposed pi-benzene C-H bond cleavage. The fact that the pi-benzene complex 4a is thermally more robust in the absence of MeCN than is the Pt(IV) hydridodiphenyl complex 3a in the presence of MeCN agrees with the notion that arene elimination from Pt(IV) hydridoaryl complexes occurs via Pt(II) pi-arene intermediates that eliminate the hydrocarbon associatively, in this case, promoted by MeCN. Compounds 1a, 1b, 1d, 2a, and 2b have been crystallographically characterized.

The boron trifluoride-catalyzed Rothemund condensation of triisopropylsilyl (TIPS) propynal 1 with 3,4-diethylpyrrole in dichloromethane, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) generates a mixture of products, including [15]triphyrin(1.1.3) H3, corrole H(3)4, porphyrin H(2)2, [24]pentaphyrin(1.1.1.1.1) H(4)5, [28]hexaphyrin(1.1.1.1.1.1) H(4)6, and two linear tripyrromethenes H(2)7 and H(2)8. We report the spectroscopic characteristics of these unusual chromophores, together with the crystal structures of triphyrin H3 (and its zinc complex ZnCl3), porphyrin H(2)2 (and its metal complexes Zn2, Ni2 and Pt2), hexaphyrin H(4)6, and tripyrromethene nickel(II) complex Ni7. When the condensation is catalyzed with trifluoroacetic acid, rather than boron trifluoride, the triphyrin H3 become the main product (26% yield). This novel macrocycle is linked with a TIPS-substituted exocyclic double bond. This C=C bond makes an eta(2)-interaction with the zinc center in ZnCl3 with C-Zn distances of 2.863 and 3.025 A. The porphyrin H(2)2 is severely ruffled, and its absorption spectrum is red-shifted and broadened compared with the analogous compound without ethyl substituents. The hexaphyrin H(4)6 adopts a figure-of-eight conformation with virtual C(2) symmetry in the solid state and C(2) symmetry in solution on the NMR time scale. Oxidation with DDQ appears to convert this nonaromatic [28]hexaphyrin into an aromatic [26]hexaphyrin with a strongly red-shifted absorption spectrum, but the oxidized macrocyle is too unstable to isolate.

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PPV-based polyrotaxanes have been prepared by coupling vinyl boronic acids to aryl iodides in the presence of cyclodextrins, and the crystal structure of a [2]rotaxane of this type has been determined.