title: A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO2.
abstract: We describe the stable and isolable dimetalloxycarbene [(TiX3 )2 (μ2 -CO2 -κ(2) C,O:κO')] 5, where X=N-(tert-butyl)-3,5-dimethylanilide, which is stabilized by fluctuating μ2 -κ(2) C,O:κ(1) O' coordination of the carbene carbon to both titanium centers of the dinuclear complex 5, as shown by variable-temperature NMR studies. Quantum chemical calculations on the unmodified molecule indicated a higher energy of only +10.5 kJ mol(-1) for the μ2 -κ(1) O:κ(1) O' bonding mode of the free dimetalloxycarbene compared to the μ2 -κ(2) C,O:κ(1) O' bonding mode of the masked dimetalloxycarbene. The parent cationic bridging formate complex [(TiX3 )2 (μ2 -OCHO-κO:κO')][B(C6 F5)4], 4[B(C6 F5)4], was simply deprotonated with the strong base K(N(SiMe3 )2 ) to give 5. Complex 5 reacts smoothly with CO2 to generate the bridging oxalate complex [(TiX3 )2 (μ2 -C2 O4 -κO:κO'')], 6, in a C-C bond formation reaction commonly anticipated for oxalate formation by reductive coupling of CO2 on low-valent transition-metal complexes.
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056 Aachen (Germany).
authors.forename: Albert
authors.initials: A
authors.lastname: Paparo
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 (USA).
authors.forename: Jared S
authors.initials: JS
authors.lastname: Silvia
authors.affiliation: Université de Toulouse et CNRS, INSA, UPS, CNRS; UMR 5215 LPCNO, 135 Avenue de Rangueil, 31077 Toulouse (France).
authors.forename: Christos E
authors.initials: CE
authors.lastname: Kefalidis
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056 Aachen (Germany).
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Spaniol
authors.affiliation: Université de Toulouse et CNRS, INSA, UPS, CNRS; UMR 5215 LPCNO, 135 Avenue de Rangueil, 31077 Toulouse (France). laurent.maron@irsamc.ups-tlse.fr.
authors.forename: Laurent
authors.initials: L
authors.lastname: Maron
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056 Aachen (Germany). jun.okuda@ac.rwth-aachen.de.
authors.forename: Jun
authors.initials: J
authors.lastname: Okuda
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 (USA). ccummins@mit.edu.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Cummins
keywords: CO2 fixation; anilides; carbene ligands; structure elucidation; titanium