Mixed N-Heterocyclic Carbene鈥揃is(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions

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• 作者：Songchen Xu ; Kuntal Manna ; Arkady Ellern ; Aaron D. Sadow
• 刊名：Organometallics
• 出版年：2014
• 出版时间：December 8, 2014
• 年：2014
• 卷：33
• 期：23
• 页码：6840-6860
• 全文大小：1003K
• ISSN：1520-6041

文摘

In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene鈥揵is(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(Ox^Me2)₂(Im^tBuH) (H[1]; Ox^Me2 = 4,4-dimethyl-2-oxazoline; Im^tBuH = 1-tert-butylimidazole) and PhB(Ox^Me2)₂(Im^MesH) (H[2]; Im^MesH = 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(Ox^Me2)₂Im^tBu}Rh(畏⁴-C₈H₁₂) (3), {PhB(Ox^Me2)₂Im^Mes}Rh(畏⁴-C₈H₁₂) (4), {PhB(Ox^Me2)₂Im^Mes}Rh(CO)₂ (5), {PhB(Ox^Me2)₂Im^Mes}Ir(畏⁴-C₈H₁₂) (6), and {PhB(Ox^Me2)₂Im^Mes}Ir(CO)₂ (7) are synthesized along with To^MM(畏⁴-C₈H₁₂) (M = Rh (8); M = Ir (9); To^M = 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 To^M with a carbene donor, and the influence of the donor ligand (CO vs C₈H₁₂). The reactions of K[2] and [M(渭-Cl)(畏²-C₈H₁₄)₂]₂ (M = Rh, Ir) provide {魏⁴-PhB(Ox^Me2)₂Im^{Mes鈥?/sup>CH₂}Rh(渭-H)(渭-Cl)Rh(畏2-C₈H₁₄)₂ (10) and {PhB(OxMe2)₂ImMes}IrH(畏3-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鈥揌 bond oxidative addition providing the compounds {魏4-PhB(OxMe2)₂ImMes鈥?/sup>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)CNtBu (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)CNtBu (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 cyclopentadienyl-supported compounds.}