Mixed N‑Heterocyclic Carbene–Bis(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions

In order to facilitate oxidative addition chemistry of fac-coordinated rhodium­(I) and iridium­(I) compounds, carbene–bis­(oxazolinyl)­phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB­(OxMe2)2(Im tBuH) (H­[1]; OxMe2 = 4,4-dimethyl-2-oxazol...

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Published in:Organometallics 2014-12, Vol.33 (23), p.6840-6860
Main Authors: Xu, Songchen, Manna, Kuntal, Ellern, Arkady, Sadow, Aaron D
Format: Article
Language:English
Subjects:
MATERIALS SCIENCE
Organometallic and Organometalloidal Compounds
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Summary:In order to facilitate oxidative addition chemistry of fac-coordinated rhodium­(I) and iridium­(I) compounds, carbene–bis­(oxazolinyl)­phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB­(OxMe2)2(Im tBuH) (H­[1]; OxMe2 = 4,4-dimethyl-2-oxazoline; Im tBuH = 1-tert-butylimidazole) and PhB­(OxMe2)2(ImMesH) (H­[2]; ImMesH = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K­[1] and K­[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB­(OxMe2)2Im tBu}­Rh­(η4-C8H12) (3), {PhB­(OxMe2)2ImMes}­Rh­(η4-C8H12) (4), {PhB­(OxMe2)2ImMes}­Rh­(CO)2 (5), {PhB­(OxMe2)2ImMes}­Ir­(η4-C8H12) (6), and {PhB­(OxMe2)2ImMes}­Ir­(CO)2 (7) are synthesized along with ToMM­(η4-C8H12) (M = Rh (8); M = Ir (9); ToM = tris­(4,4-dimethyl-2-oxazolinyl)­phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in ToM with a carbene donor, and the influence of the donor ligand (CO vs C8H12). The reactions of K­[2] and [M­(μ-Cl)­(η2-C8H14)2]2 (M = Rh, Ir) provide {κ4-PhB­(OxMe2)­2ImMes′ CH2}­Rh­(μ-H)­(μ-Cl)­Rh­(η2-C8H14)2 (10) and {PhB­(OxMe2)2ImMes}­IrH­(η3-C8H13) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C–H bond oxidative addition providing the compounds {κ4-PhB­(OxMe2)2ImMes′ CH2}­RhH­(CO) (12) and {PhB­(OxMe2)2ImMes}­IrH­(Ph)­CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis-[Ir]­(H)­(Ph) complex. Alternatively, the rhodium carbonyl 5 or iridium isocyanide {PhB­(OxMe2)2ImMes}­Ir­(CO)­CN t Bu (15) reacts with PhSiH3 in the dark to form the silyl compound {PhB­(OxMe2)2ImMes}­RhH­(SiH2Ph)­CO (14) or {PhB­(OxMe2)2ImMes}­IrH­(SiH2Ph)­CN t Bu (17). These examples demonstrate the enhanced thermal reactivity of {PhB­(OxMe2)2ImMes}-supported iridium and rhodium carbonyl compounds in comparison to tris­(oxazolinyl)­borate, tris­(pyrazolyl)­borate, and c
ISSN:0276-7333
1520-6041
DOI:10.1021/om500891h