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Group 3 Dialkyl Complexes with Tetradentate (L, L, N, O; L = N, O, S) Monoanionic Ligands: Synthesis and Reactivity

Marinescu, Smaranda C. and Agapie, Theodor and Day, Michael W. and Bercaw, John E. (2007) Group 3 Dialkyl Complexes with Tetradentate (L, L, N, O; L = N, O, S) Monoanionic Ligands: Synthesis and Reactivity. Organometallics, 26 (5). pp. 1178-1190. ISSN 0276-7333.

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Tripodal, tetradentate phenols, (LCH_2)_2NCH_2-C_6H_2-3,5-(CMe_3)_2-2-OH (L = CH_2OCH_3 (1), CH_2NEt_2 (2), 2-C_5H_4N (3), CH_2SCMe_3 (5), CH_2NMe_2 (6)), were synthesized, and metalations were performed via alkane elimination from yttrium and scandium trialkyl complexes to generate the corresponding dialkyl complexes [(LCH_2CH_2)_2NCH_2-C_6H_2-3,5-(CMe_3)_2-2-O]MR_2 (M = Y, L = OCH_3, R = CH_2SiMe_2Ph (7a); M = Y, L = NEt_2, R = CH_2SiMe_2Ph (7b); M = Sc, L = OCH_3, R = CH_2SiMe_2Ph (8a); M = Sc, L = SCMe_3, R = CH_2SiMe_2Ph (8b); M = Y, L = OCH_3, R = CH_2SiMe_3 (9); M = Sc, L = OCH_3, R = CH_2SiMe_3 (10)). X-ray crystallographic studies show that 7a,b and 8a adopt, in the solid state, mononuclear structures of C_1 symmetry. The ^1H NMR spectra of these dialkyl complexes in benzene-d_6 at high temperatures reveal exchange processes involving the ether groups and the alkyl groups. The dynamic behavior of species 7a, 8a, and 10 in toluene-d8 was investigated by variable-temperature ^1H NMR spectroscopy. The activation parameters of the fluxional processes for 7a, 8a, and 10 were determined by line-shape and Eyring analyses (for 7a, ΔH^⧧ = 7.3 ± 0.3 kcal/mol and ΔS^⧧ = −16 ± 1.4 cal/(mol K); for 8a, ΔH^⧧ = 9.9 ± 0.5 kcal/mol and ΔS^⧧ = −15.3 ± 1.8 cal/ (mol K); for 10, ΔH^⧧ = 10.8 ± 0.6 kcal/mol and ΔS^⧧ = −11.4 ± 1.9 cal/(mol K)). These data establish that the dialkyl complexes 7a, 8a, and 10 undergo a nondissociative exchange process. The scandium dialkyl complex [(C_5H_4N-2-CH_2)_2NCH_2-C_6H_2-3,5-(CMe_3)_2-2-O]Sc(CH_2SiMe_2Ph)_2 (11) was found to undergo clean activation of a C−H bond of a methylene linking a pyridine to the central nitrogen donor. This process follows first-order kinetics (k = [2.8(3)] × 10^(-4) s^(-1) at 0 °C). The yttrium dialkyl complexes 7a and 9 react with 1 equiv of [PhNHMe_2]+[B(C_6F_5)_4]- in chlorobenzene-d_5, to generate a solution that slowly polymerizes ethylene. Compounds 7−10 also polymerize ethylene with low activity upon activation with MAO.

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Agapie, Theodor0000-0002-9692-7614
Additional Information:© 2007 American Chemical Society. Received 21 September 2006. Published online 1 February 2007. Published in print 1 February 2007. This work has been supported by USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431) and the National Science Foundation (Grant No. CHE-0131180). S.C.M. thanks Caltech's Summer Undergraduate Research Fellowship program for funding. We thank Mr. Lawrence Henling for assistance in obtaining the X-ray crystal structures and Ms. Mona Shahgholi for help with HRMS. We thank Prof. John Arnold for an insightful personal communication regarding the structures of some related complexes supported by ligand 3, particularly one related to 12.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-85ER13431
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Issue or Number:5
Record Number:CaltechAUTHORS:20170309-082713121
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Official Citation:Group 3 Dialkyl Complexes with Tetradentate (L, L, N, O; L = N, O, S) Monoanionic Ligands:  Synthesis and Reactivity Smaranda C. Marinescu, Theodor Agapie, Michael W. Day, and John E. Bercaw Organometallics 2007 26 (5), 1178-1190 DOI: 10.1021/om0608612
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74955
Deposited By: Ruth Sustaita
Deposited On:09 Mar 2017 17:07
Last Modified:03 Oct 2019 16:44

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