Four planar-chiral, enantiomerically pure ferrocene dibromides (3 R1R2 ; [(CHR 1 R 2 )BrH 3 C 5 ] 2 Fe) equipped with two CHR 1 R 2 groups in α position to bromine were synthesized. From the four C 2 symmetrical species, two are already known [CHR 1 R 2 = CHMe 2 (3 MeMe ), CHEt 2 (3 EtEt )] and two are new compoundsThe dibromides 3 R1R2 were in situ converted into dilithio ferrocene derivatives and reacted with Cl 2 BNiPr 2 resulting in mixtures of bora[1]-ferrocenophanes (4 R1R2 ) and 1,1′-bis(boryl)ferrocenes (5 R1R2 ). The aim of this investigation was to test the hypothesis that the alkyl group that is oriented approximately perpendicular to the Cp ring, i.e., R 2 , affects the outcome of the salt-metathesis reaction. The obtained product ratios 4 R1R2 :5 R1R2 were determined by 1 H NMR spectroscopy and revealed that systems with the same R 2 group gave similar 4 R1R2 :5 R1R2 ratios (1.0:0.51 and 1.0:0.49 for R 2 = Me; 1.0:0.30 and 1.0:0.27 for R 2 = Et), confirming the hypothesis. Shown by DFT calculations (B3PW91/6-311+G(d,p)), reaction paths resulting in either product 4 R1R2 or product 5 R1R2 are both concerted steps.
The photophysics of low-chlorin tin(IV) tetraphenylporphyrin dihydroxide, a core building block for axially substituted supramolecular tin porphyrin constructs, has been studied in a variety of hydrogen-bonding, nonpolar, and aprotic polar solvents using steady-state, nanosecond, and femtosecond time-resolved emission, and femtosecond time-resolved absorption methods. In hydrogen-bonding solvents the metalloporphyrin exists as solvated monomers, and its Soret-excited S2 state in these solvents exhibits the expected linear energy gap law relationship with first-order population decay times in the 0.8 to 1.7 ps range. Evidence is presented that this metalloporphyrin aggregates in other solvents at the concentrations typically used for these ultrafast measurements and yields species-averaged time-resolved data. Cw laser excitation in the Q-band under deaerated conditions produces weak S2-S0 fluorescence (photon upconversion) as a result of triplet-triplet annihilation.
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