Reported herein is the synthesis and characterization of a series of monoand bis-alkynyl Co III (TIM) complexes, where TIM is 2,3,9,10-tetramethyl-1,4,8,11tetraazacyclotetradeca-1,3,8,10-tetraene. The trans-[Co(TIM)(C 2 Ar)Cl] + type complexes (Ar = phenyl (Ph, 1a), naphthalene (Np, 1b), and -C 6 F 5 (1c)) were prepared by the addition of HC 2 Ar to trans-[Co(TIM)Cl 2 ]PF 6 in the presence of Et 3 N. Treatment of the mono-alkynyl complexes with AgOTf in MeCN resulted in the trans-[Co(TIM)(C 2 Ar)-(NCMe)](OTf) 2 complexes (Ar = Ph (2a), Np (2b), and -C 6 F 5 (2c)). Complexes 2a and 2b react with the respective HC 2 Ar ligand in the presence of Et 3 N to afford the symmetrical bis-alkynyl complexes trans-[Co(TIM)(C 2 Ar) 2 ] + (Ar = Ph (3a) and Np (3b)). trans-[Co(TIM)(C 2 C 6 F 5 ) 2 ] + (3c) was obtained directly from the prolonged reaction of trans-[Co(TIM)Cl 2 ]PF 6 with HC 2 C 6 F 5 . Furthermore, the addition of HC 2 Ph to 2c in the presence of a weak base yielded the unsymmetrical bis-alkynyl complex trans-[Co(TIM)(C 2 C 6 F 5 )(C 2 Ph)]OTf (4). Molecular structures of complexes 1a/b, 2a/b, [3a]PF 6 , 3b, and 4 were established through single crystal X-ray diffraction. The absorption spectra for 1−4 display d−d bands between 380 and 470 nm. Complexes 1b−3b exhibited Np-based fluorescence. Electrochemical studies revealed that all complexes display an irreversible reduction characteristic of the Co III center, as well as up to two irreversible reduction(s) localized on the TIM macrocycle.
Reported herein are
the first examples of the formation of Ru–Csp2
bonds in paddlewheel diruthenium species. A series of six
Ru2(ap)4(C6H4-4-X) type compounds (ap = 2-anilinopyridinate;
X = NMe2 (1), N,N-(C6H4-4-OMe)2 (2),
t
Bu (3), H (4), Br (5), CF3 (6)) was synthesized by employing
the lithium–halogen exchange reaction with a variety of para-substituted
aryl halides. These compounds have been characterized via electronic
absorption spectroscopy, cyclic voltammetry, mass spectrometry, and
magnetism studies, and their molecular structures have been established
by single-crystal X-ray diffraction studies. All compounds are in
the Ru2
5+ oxidation state, with a ground-state
electronic configuration of σ2π4δ2(π*δ*)3. Crystal structures
of 1–6 confirm this, indicating a
Ru–Ru bond order of 2.5. Electrochemical data suggest that
the σ-aryls are stronger donors than the σ-alkynyls. A
range of electronically different substituents allows for a closer
inspection of the extent of electronic conjugation across the diruthenium
paddlewheel core and the axial aryl ligand.
Two new nickel(II) complexes of cyclams bearing C‐alkyl groups, Ni(MEC)OTf2 (1, MEC = 5,12‐diethyl‐7,14‐dimethyl‐1,4,8,11‐tetraazacyclotetradecane) and Ni(CTMC)OTf2 (2, CTMC = 5,7,12,14‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane), were prepared, and their similarity to NiII(MPC) (MPC = 5,12‐dimethyl‐7,14‐diphenyl‐1,4,8,11‐tetraazacyclotetradecane) in ring conformation was revealed through single‐crystal X‐ray diffraction studies. Solution electronic absorption spectroscopy indicates the retention of octahedral coordination mode for both 1 and 2 in 20 % aqueous acetonitrile. Cyclic voltammetry studies of 1 and 2 under CO2 in 20 % aqueous acetonitrile revealed significantly increased catalytic currents compared to previously studied NiII(cyclam) and NiII(MPC). Controlled potential electrolysis studies of 2 revealed a 250 % increase in CO turn over frequency from that of Ni(cyclam)OTf2 and a 40 % increase from that of Ni(MPC)OTf2. Such improvements establish the benefit of electronically donating substituents that minimize steric interference around the axial catalytic sites.
Reported herein are the syntheses and characterizations for a series of butadiyndiyl-bridged Co III (MPC) (MPC = 5,4,8, complexes, capped with chloride ([1] 2+ ), phenylacetylide ([2] 2+ ), or 3,5-dichlorophenylacetylide ([3] 2+ ). The MPC ligand was chosen to weaken the ligand field around the equatorial plane, allowing stronger axial coordination. Cyclic voltammetry measurement revealed the first unambiguous examples of stepwise one-electron reductions in bridged Co(cyclam′) complexes (cyclam′ = any ligand bearing the 1,4,8,11-tetraazacyclotetradecane framework). Further voltammetric analysis using NBu 4 BArF (NBu 4 BArF = tetrabutylammonium tetrakis [3,5-bis(trifluoromethyl)phenyl]borate) as electrolyte resulted in well-separated reversible reduction waves with up to 160 mV separation for [2] 2+ . These features hint at the possibility of application of earth-abundant metal complexes to function as molecular wires. These complexes were also characterized with infrared and UV−vis spectroscopy, density functional theory calculations, and single-crystal X-ray diffraction ([1](BPh 4 ) 2 only).
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