Dissertation/Thesis Abstract

Isolation of Four-Coordinate Iridium(I) Monohydrides and the X-ray Crystal Structure of a Cobalt Tris-Isocyanide Alkane sigma-Complex
by Millard, Matthew David, Ph.D., University of California, San Diego, 2013, 227; 3594595
Abstract (Summary)

Detailed herein are the synthesis, characterization, and reactivity of three isolable four-coordinate iridium(I) monohydride complexes. Iridium(I) monohydrides containing the simple formula HIrL3 have been postulated as reactive intermediates for over four decades escaping definitive evidence. The judicious use of the C–H activation resistant methyleneadamantyl phosphine P(CH21Ad)(i-Pr) 2 (abbreviated LmAd) and phosphinite P(O1Ad)(i-Pr) 2 (abbreviated LoAd) ligands allowed for the successful isolation and characterization of several four-coordinate iridium(I) monohydride complexes.

These electron-rich monohydride complexes rapidly deprotonate protic reagents, such as H2N(2,6-(i-Pr)2C 6H3) and C6F5OH, and activate N–H, O–H, and H–H bonds. The sequential addition of 12-crown-4 with 1.0 equ. of a strong lewis base, i.e. Li(CH3)3CLi to cyclometallated complexes H2Ir(κ2- P,C-LoAd)(LoAd) and H2Ir(κ 2-P,C-LmAd)(LmAd) produces four-coordinate anionic complexes [Li(12-c-4)][HIr(κ 2-P,C-LmAd)(LmAd)] and Li[12-c-4)2][H3Ir(κ2-P,C-L oAd)(LoAd)], respectively.

Herein we also report the X-ray characterization of coordinated alkanes, n-hexane and n-heptane, forming two cobalt metal complexes. A continued effort to isolate and characterize alkane σ-complexes stems from the desire to control alkane C–H bond transformations, a significant synthetic challenge with high economic benefit.

Support for a distinct &eegr;2-H,C σ-type interaction with n-hexane or n-heptane was provided by DFT and AIM analysis computations as well as rbp parameter calculations. The diamagnetic complex, Co(SiMe3)(CNAr Mes2)3 forms from the addition of (CH3) 3SiCl to the zwitterionic complex (κ2-PPN)(Co(CNAr Mes2)3 (PPN = (C6H5)3P=N=P(C 6H5)3). Crystallization of Co(SiMe3)(CNAr Mes2)3 with 5% v/v of C6H6 in n-hexane or n-heptane at -35 °C under an argon atmosphere produces single crystals of the respective alkane σ-complexes. When n-nonane (C9H20) is employed as the crystallization solvent, the unsaturated Co(SiMe3 )(CNArMes2)3 forms single crystals of Ar 1/7Co((SiCH3)3)(CNArMes2) 3 which were manipulated in single crystal to single crystal (SC-SC) dinitrogen intercalation experiments, resulting in full occupancy and binding of dinitrogen to the cobalt metal center. Persistent in the solid-state are weak Van der Waals interactions from the CNArMes2 ligands to the bound alkanes, n-hexane and n-heptane, possibly mimicking a clathrate-type entrapment mechanism. Distinct from clathrate networks is the strategic placement of a highly Lewis acidic cobalt center of proper electronic structure to engage in bonding.

Indexing (document details)
Advisor: Figueroa, Joshua S.
Commitee: OConnor, Joseph M., Spitzer, Nicholas C., Tezcan, F. Akif, Trogler, William C.
School: University of California, San Diego
Department: Chemistry
School Location: United States -- California
Source: DAI-B 75/01(E), Dissertation Abstracts International
Subjects: Inorganic chemistry
Keywords: Activation alkanes, Alkane complex, Intramolecular alkane, Iridium, Monohydride, Sigma complex
Publication Number: 3594595
ISBN: 9781303392160