J.J. Teesdale et al. / Catalysis Today 225 (2014) 149–157
151
(d, J = 5.6 Hz, 1H), 8.19 (s, 1H), 7.60 (dd, J = 5.6, 1.5 Hz, 1H), 2.52 (d,
J = 5.1 Hz, 6H), 2.29 (dq, J = 19.0, 7.5 Hz, 4H), 1.46 (s, 3H), 1.30 (s, 3H),
0.96 (dt, J = 19.4, 7.5 Hz, 6H). 13C NMR (101 MHz, CDCl3) ı 197.04,
157.08, 156.55, 156.19, 154.23, 148.72, 138.15, 136.77, 134.94,
134.39, 132.90, 129.80, 129.28, 127.92, 123.95, 32.27, 30.05, 29.71,
23.04, 17.38, 14.89, 14.77, 14.48, 13.30, 13.07. HR-ESI-MS: [M+H]+
m/z: calcd for C47H51B2ClF4N6O3Re, 1067.3391; found 1067.3443.
ꢀmax (KBr)/cm−1 2021.50, 1920.95, 1906.39 (s, C O).
occupancy ratio of 72/28. The disordered solvent molecule was
treated as a rigid body with idealized geometry and with a refined
site occupancy ratio of 52/48.
2.7. Computations
Geometry optimizations and frequency calculations were per-
formed using the Gaussian09 (G09) program package [32], with the
Becke three-parameter hybrid exchange and the Lee–Yang–Parr
correlation functionals (B3LYP). The 6-31G* basis set was used for
H, B, C, N, O, and F, along with the Stuttgart/Dresden (SDD) energy-
consistent pseudopotentials for Re. Crystallographic coordinates
were used as starting points for geometry optimizations. All geome-
try optimizations were performed in C1 symmetry with subsequent
vibrational frequency analysis to confirm that each stationary point
was a minimum on the potential energy surface. Molecular orbital
were visualized using Visual Molecular Dynamics (VMD) software.
2.5. Electrochemistry
Electrochemistry was performed using either
a CHI-620D
potentiostat/galvanostat or CHI-720D bipotentiostat. Cyclic
a
voltammetry (CV) was performed using a standard three-electrode
configuration. The working electrode was a polished glassy car-
bon electrode (GCE, 3.0 mm diameter CH Instruments) and a piece
of platinum wire was used as the counter electrode. All poten-
tials were measured against a silver wire pseudo reference with
a ferrocene internal standard and were adjusted to the satu-
rate calomel electrode (SCE) via the relation Fc/Fc+ = 460 mV + SCE.
Unless otherwise stated, the electrolyte was 0.1 M TBAPF6, the sam-
ple concentration was 1.0 mM, and all CV experiments were carried
out using a scan rate of 100 mV/s.
Controlled potential electrolysis (CPE) experiments were
performed in a single-compartment cell using the same three-
electrode setup employed for CV measurements. These consisted
of a polished glassy carbon working electrode, a platinum mesh
counter electrode, and a Ag/AgCl reference electrode (1.0 M KCl, CH
Instruments) or a silver wire pseudo reference. Prior to electrolysis
the solution was sparged with MeCN saturated CO2 gas for approxi-
mately 30 min, following which, the cell was sealed and electrolysis
initiated. The headspace of the electrolysis cell was sampled peri-
odically by manually removing 1.0 mL aliquots using a gas-tight
syringe. These aliquots were analyzed by manual injection into a
gas-sampling loop of a Shimadzu GC-2014 gas chromatograph (GC).
This GC was equipped with two 10 port injection valves in line with
HaySepT 80/100 columns. Quantification of CO was accomplished
using a flame ionization detector (FID) with methanizer after pas-
sage through a HaySepD 80/100 column using helium (99.999%)
as the carrier gas. Quantification of H2 was accomplished using a
thermal conductivity detector (TCD) after passage through a packed
MolSieve 5A 60/80 column, using argon as the carrier gas (99.999%).
2.8. UV–vis absorption
UV/vis absorption spectra were acquired on an Agilent 8453
Diode Array UV-vis spectrometer using screw cap quartz cuvettes
(6q) of 1 cm pathlength from Starna. All absorption spectra were
recorded at room temperature and all samples were prepared in
DMF.
2.9. Steady-state fluorescence measurements
Spectra were recorded on an automated Photon Technology
International (PTI) QuantaMaster 40 fluorometer equipped with
a 75-W Xenon arc lamp, a LPS-220B lamp power supply and a
Hamamatsu R2658 photomultiplier tube. Samples for fluorescence
analysis were prepared in an analogous method to that described
above for the preparation of samples for UV–vis spectroscopy. Sam-
ples were excited at ꢁex = 500 nm and emission was monitored from
510 to 800 nm with a step size of 1 nm and integration time of
0.5 s. Reported spectra are the average of at least three individual
acquisitions.
Emission quantum yields were calculated using Ru(phen)3Cl2
in water (˚ref = 0.072) [33] as the reference actinometer using the
expression below [34]:
ꢀ
ꢁꢀ ꢁꢀ
ꢁ
2
Aref
Aem
Iem
Áem
Áref
˚
em
= ˚
(1)
ref
2.6. X-ray structure determination
Iref
The ˚em and ˚ref represent the emission quantum yield of the
sample and the reference, respectively, Aref and Aem are the mea-
sured absorbance of the reference and sample at the excitation
wavelength, respectively, Iref and Iem are the integrated emission
intensities of the reference and sample, respectively, and Áref and
Áem are the refractive indices of the solvents of the reference and
sample, respectively (Áref = 1.33 and Áem = 1.43). The optical density
of the samples and references were kept around 0.1 at ꢁex = 500 nm.
[Re(BB2)(CO)3Cl] consistently deposited as red, multiple, crys-
tal masses and the results herein represent the best of several trials.
A crystal was sectioned and mounted on plastic mesh with vis-
cous oil flash-cooled to 200 K. Data were collected on a Bruker-AXS
Apex 2 Duo CCD diffractometer with Gobel mirror focussed Cu-
˚
K␣ radiation (ꢁ = 1.54178 A). Unit cell parameters were obtained
from 60 data frames, 0.3◦ ω, from three different sections of the
Ewald sphere. No symmetry higher than triclinic was observed and
solution in the centrosymmetric space group option yielded chem-
ically reasonable and computationally stable results of refinement.
The data-sets were treated with numerical absorption correc-
with full-matrix, least-squares procedures on F2. All non-hydrogen
atoms were refined with anisotropic displacement parameters. All
hydrogen atoms were treated as idealized contributions. Atomic
scattering factors are contained in the SHELXTL 6.12 program
library [31].
2.10. Time-resolved fluorescence measurements
Time-correlated single photon counting (TCSPC) experiments
were performed on an IBH (Jobin Yvon Horiba) model 5000F instru-
ment equipped with single-grating monochromators on both the
excitation and emission sides of the instrument. The excitation
light source was a NanoLED with a short 1.3 ns pulse width at
458 nm. Emission signals were collected on a picosecond photon
detection module (TBX-04) at an angle perpendicular to excita-
tion for samples and blanks. Data were collected at 550 nm and
averaged (30,000 counts) to obtain the decay profile. Decay anal-
ysis and curve fitting routines to determine sample lifetimes were
Two molecules of [Re(BB2)(CO)3Cl] and one disordered
molecule of methylene chloride solvent were located in the
asymmetric unit and rigid bond displacement restraints were
applied. One ethyl group was found disordered with a refined site