Rh鈥揊HF and Rh鈥揊 Complexes Containing Small N-Alkyl Substituted Six-Membered Ring N-Heterocyclic Carbenes

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• 作者：Nicola Bramananthan ; Mar铆a Carmona ; John P. Lowe ; Mary F. Mahon ; Rebecca C. Poulten ; Michael K. Whittlesey
• 刊名：Organometallics
• 出版年：2014
• 出版时间：April 28, 2014
• 年：2014
• 卷：33
• 期：8
• 页码：1986-1995
• 全文大小：475K
• 年卷期：v.33,no.8(April 28, 2014)
• ISSN：1520-6041

文摘

Heating the six-membered ring N-heterocyclic carbenes 6-Me and 6-Et with Rh(PPh₃)₄H afforded the rhodium monocarbene hydride complexes Rh(6-NHC)(PPh₃)₂H as a mixture of cis- and trans-P,P isomers (4a/b, NHC = 6-Me; ratio = 1:20; 5a/b, NHC = 6-Et; ratio = 1:9). Reaction of 4a/b with Et₃N路3HF gave only the trans-P,P isomer of the bifluoride complex Rh(6-Me)(PPh₃)₂(FHF) (6b), whereas 5a/b reacted to form Rh(6-Et)(PPh₃)₂(FHF) as a mixture of cis- and trans-phosphine isomers (7a/b). Variable temperature ¹H and ¹⁹F NMR spectroscopy showed that 6b and the previously reported 6-ⁱPr carbene analogue cis-Rh(6-ⁱPr)(PPh₃)₂(FHF) (2a; Organometallics 2012, 41, 8584) were fluxional in solution. ¹⁹F Magnetization transfer experiments revealed F exchange in both compounds and afforded similar 螖H values (2a, 51 卤 5 kJ mol^鈥?; 6b, 60 卤 6 kJ mol^鈥?) but somewhat different values of 螖S (2a, 鈭?0 卤 17 J mol^鈥? K^鈥?; 6b, 鈭?7 卤 18 J mol^鈥? K^鈥?). The fluoride complexes cis-Rh(6-Me)(PPh₃)₂F (8a), cis-/trans-Rh(6-Et)(PPh₃)₂F (9a/b), and the previously reported 6-ⁱPr analogue 3a could be formed upon C鈥揊 activation of CF₃CF鈺怌F₂ by 4a/b, 5a/b, and Rh(6-ⁱPr)(PPh₃)₂H (1a/b), respectively. Complex 3a reacted slowly with H₂ to partially reform 1a/b but rapidly with CO to give Rh(6-ⁱPr)(PPh₃)(CO)F (10) and Rh(PPh₃)₂(CO)F, and also quickly with Me₃SiCF₃ to form cis-Rh(6-ⁱPr)(PPh₃)₂(CF₃) (11a). Complexes 4b, 5b, 6b, 7b, and 11a were structurally characterized.