1204007-60-2Relevant academic research and scientific papers
Investigation of Ketone C = O Bond Activation Processes by Heterobimetallic Zr/Co and Ti/Co Tris(phosphinoamide) Complexes
Zhang, Hongtu,Wu, Bing,Marquard, Seth L.,Litle, Elishua D.,Dickie, Diane A.,Bezpalko, Mark W.,Foxman, Bruce M.,Thomas, Christine M.
, p. 3498 - 3507 (2017)
The reactivity of the reduced Zr/Co and Ti/Co complexes (THF)Zr(MesNPiPr2)3CoN2 (1, Mes = 2,4,6-trimethylphenyl) and (THF)Ti(XylNPiPr2)3CoN2 (7, Xyl = 3,5-dimethylphenyl) toward diaryl ketones is explored in an effort to gain mechanistic insight into C = O bond cleavage processes. Complex 1 reacts with 4,4′-dimethoxybenzophenone to generate ((p-OMeC6H4)2CO)Zr(MesNPiPr2)3CoN2 (2), which exists as a mixture of valence tautomers in solution that interconvert via electron transfer from Co-I to the Zr-bound ketone in 2S to form a Zr-bound ketyl radical in 2T. The geometry of 2 in the solid state is most consistent with the singlet ketone adduct tautomer 2S. Upon removal of the Co-bound N2 under vacuum, complex 2 cleanly coverts to the μ-oxo carbene product (·2-MesNPiPr2)Zr(MesNPiPr2)2(μ-O)Co - C(C6H4p-OMe)2 (5) at room temperature in solution. A diamagnetic intermediate, tentatively assigned as ketone-bridged species (·2-MesNPiPr2)Zr(MesNPiPr2)2Co(μ2,·1·2-OC(p-OMeC6H4)2) (6), is observed spectroscopically during the transformation of 1 to 5. Similar reactions between the Ti/Co analogue 7 and diaryl ketones reveal no evidence for electron-transfer to form triplet ketyl radical species. Complex 7 reacts with 4,4′-dimethoxybenzophenone to afford diamagnetic ((p-OMeC6H4)2CO)Ti(XylNPiPr2)3CoN2 (8). In contrast, addition of benzophenone to 7 under N2 generates a mixture of (·2-XylNPiPr2)Ti(XylNPiPr2)2Co(·2-OCPh2) (9) and (Ph2CO)Ti(XylNPiPr2)3CoN2 (10) in solution, and C3-symmetric 10 is found to be favored in the solid state. Complex 9 can be generated exclusively and isolated in the absence of N2. Ti/Co complexes 8-10 are thermally stable and do not undergo C = O bond cleavage even at elevated temperature, in stark contrast to their Zr/Co congeners.
Metal-metal multiple bonds in early/late heterobimetallics support unusual trigonal monopyramidal geometries at both Zr and Co
Greenwood, Bennett P.,Rowe, Gerard T.,Chen, Chun-Hsing,Foxman, Bruce M.,Thomas, Christine M.
, p. 44 - 45 (2010)
(Chemical Equation Presented) Reduction of Zr/Co heterobimetallic complexes ICo(MesNPiPr2)3ZrCl (1) and ICo( iPrNPiPr2)3ZrCl (2) with excess Na/Hg under N2, followed by subsequent benzene extraction to remove coordinated Na halide salts, leads to neutral two-electron reduced, dinitrogen-bound complexes (THF)Zr(MesNPiPr2) 3Co-N2 (4) and Zr(iPrNPiPr 2)3Co-N2 (5). Upon halide loss, a THF solvent molecule coordinates to the axial site of the Zr center in 4, while this axial site remains unoccupied in 5. X-ray crystallography reveals short Co-Zr distances in 4 and 5, indicative of metal-metal multiple bonding, and an unprecedented trigonal monopyramidal geometry about the Zr center in 5. Reduction of 4 under an Ar atmosphere (in the absence of N2) results in another unusual structure type: an unoccupied axial Co coordination site and a trigonal monopyramidal Co center in (THF)Zr(MesNPiPr 2)3Co (6). X-ray crystallography reveals that, in the absence of coordinated N2, the Co-Zr bond can attain full triple bond character with a Co-Zr distance of 2.14 A, the shortest M-M distance in an early/late heterobimetallic complex reported to date. To further assess the electronic structure and bonding in 4, 5, and 6, calculations were performed on these molecules using DFT and the results of these theoretical investigations will be discussed.
Synthesis, structure, and reactivity of an anionic Zr-oxo relevant to CO2 reduction by a Zr/Co heterobimetallic complex
Krogman, Jeremy P.,Bezpalko, Mark W.,Foxman, Bruce M.,Thomas, Christine M.
, p. 3022 - 3031 (2013/04/23)
Oxidative addition of CO2 to the reduced Zr/Co complex (THF)Zr(MesNPiPr2)3Co (1) followed by one-electron reduction leads to formation of an unusual terminal Zr-oxo anion [2][Na(THF)3] in low yield. To facilitate further study of this compound, an alternative high-yielding synthetic route has been devised. First, 1 is treated with CO to form (THF)Zr(MesNPiPr2) 3Co(CO) (3); then, addition of H2O to 3 leads to the Zr-hydroxide complex (HO)Zr(MesNPiPr2)3Co(CO) (4). Deprotonation of 4 with Li(N(SiMe3)2) leads to the anionic Zr-oxo species [2][Li(THF)3] or [2][Li(12-c-4)] in the absence or presence of 12-crown-4, respectively. The coordination sphere of the Li+ countercation is shown to lead to interesting structural differences between these two species. The anionic oxo fragment in complex [2][Li(12-c-4)] reacts with electrophiles such as MeOTf and Me3SiOTf to generate (MeO)Zr(MesNPiPr2)3Co(CO) (5) and (Me3SiO)Zr(MesNPiPr2)3Co(CO) (6), respectively, and addition of acetic anhydride generates (AcO)Zr(MesNP iPr2)3Co(CO) (7). Complex [2][Li(12-c-4)] is also shown to bind CO2 to form a monoanionic Zr-carbonate, [(12-crown-4)Li][(κ2-CO3)Zr(MesNPiPr 2)3Co(CO)] ([8][Li(12-c-4)]). A more stable version of this compound [8][K(18-c-6)] is formed when a K+ counteranion and 18-crown-6 are used. Binding of CO2 to [2][Li(12-c-4)] is shown to be reversible using isotopic labeling studies. In an effort to address methods by which these CO2-derived products could be turned over in a catalytic cycle, it is shown that the Zr-OMe bond in 5 can be cleaved using H+ and the CO ligand can be released from Co under photolytic conditions in the presence of I2.
