Iridium complexes of CCC-pincer bis-N-heterocyclic carbenes, including a newly synthesized trifluoromethyl-substituted complex, were examined as catalysts for the acceptorless dehydrogenation of cyclooctane and n-undecane. Up to 103 turnovers were observed for the dehydrogenation of cyclooctane, and up to 97 turnovers were observed for the dehydrogenation of n-undecane. The catalysts showed high initial turnover frequencies, followed by a gradual loss of activity over 24 h. Experiments indicate that this loss of activity is due to catalyst decomposition rather than product inhibition. Stoichiometric reactivity was investigated for the precatalysts, focusing on the synthesis of dihydride and trihydride complexes as well as the dissociation and addition of neutral ligands.

Boron monofluoride (BF) is a diatomic molecule with 10 valence electrons, isoelectronic to carbon monoxide (CO). Unlike CO, which is a stable molecule at room temperature and readily serves as both a bridging and terminal ligand to transition metals, BF is unstable below 1800°C in the gas phase, and its coordination chemistry is substantially limited. Here, we report the isolation of the iron complex Fe(BF)(CO)2(CNArTripp2)2 [ArTripp2, 2,6-(2,4,6-(i-Pr)3C6H2]2C6H3; i-Pr, iso-propyl], featuring a terminal BF ligand. Single-crystal x-ray diffraction as well as nuclear magnetic resonance, infrared, and Mössbauer spectroscopic studies on Fe(BF)(CO)2(CNArTripp2)2 and the isoelectronic dinitrogen (N2) and CO complexes Fe(N2)(CO)2(CNArTripp2)2 and Fe(CO)3(CNArTripp2)2 demonstrate that the terminal BF ligand possesses particularly strong σ-donor and π-acceptor properties. Density functional theory and electron-density topology calculations support this conclusion.

Mixed isocyanide/carbonyl complexes with rhenium in the oxidation states “+1”, “0” and “−1” were prepared assisted by a sterically encumbered.

Metrics & More Article Recommendations * sı Supporting Information ABSTRACT: [Re(CO)Br(CNAr DArF2 ) 4 ] and [Tc(CO)Cl-(CNAr DArF2 ) 4 ] (Ar DArF = 2,6-(3,5-(CF 3 ) 2 C 6 H 3 ) 2 -4-F-C 6 H 2 ) were prepared by reactions of [Re(CO) 5 Br] or (NBu 4 )[Tc 2 (CO) 6 (μ-Cl) 3 ] with the sterically encumbered isocyanide CNAr DArF2 . These two compounds proved to be excellent starting materials for the synthesis of unprecedented low-valent rhenium and technetium complexes. The reduction of [Re(CO)Br(CNAr DArF2 ) 4 ] with Na/ Hg produces an equimolar mixture of [Re(CO)(CNAr DArF2 ) 4 ] and Na[Re(CO)(CNAr DArF2 ) 4 ] containing the transition metal in the formal oxidation states "0" and "−1", respectively. The reduction of [Tc(CO)Cl(CNAr DArF2 ) 4 ] with Na/Hg produces Na[Tc(CO)-(CNAr DArF2 ) 4 ], which was characterized by 19 F and 99 Tc NMR spectroscopy. The reactivity of Na[Re(CO)(CNAr DArF2 ) 4 ] resembles that of [Re(CO) 5 ] − , proved by reactions with a number of electrophiles such as MeI, HCl, or F 6 C 5 C(O)Cl.