Rh-FHF and Rh-F complexes containing small N-alkyl substituted six-membered ring N-heterocyclic carbenes

N. Bramananthan, M. Carmona, J.P. Lowe, M.F. Mahon, R.C. Poulten, M.K. Whittlesey

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Abstract

Heating the six-membered ring N-heterocyclic carbenes 6-Me and 6-Et with Rh(PPh)H afforded the rhodium monocarbene hydride complexes Rh(6-NHC)(PPh)H 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 EtN·3HF gave only the trans-P,P isomer of the bifluoride complex Rh(6-Me)(PPh)(FHF) (6b), whereas 5a/b reacted to form Rh(6-Et)(PPh)(FHF) as a mixture of cis- and trans-phosphine isomers (7a/b). Variable temperature H and F NMR spectroscopy showed that 6b and the previously reported 6-Pr carbene analogue cis-Rh(6- Pr)(PPh)(FHF) (2a; Organometallics 2012, 41, 8584) were fluxional in solution. F Magnetization transfer experiments revealed F exchange in both compounds and afforded similar ΛH values (2a, 51 ± 5 kJ mol ; 6b, 60 ± 6 kJ mol) but somewhat different values of ΛS (2a, -70 ± 17 J mol K; 6b, -27 ± 18 J mol K ). The fluoride complexes cis-Rh(6-Me)(PPh) F (8a), cis-/trans-Rh(6-Et)(PPh)F (9a/b), and the previously reported 6-Pr analogue 3a could be formed upon C-F activation of CFCF=CF by 4a/b, 5a/b, and Rh(6- Pr)(PPh)H (1a/b), respectively. Complex 3a reacted slowly with H to partially reform 1a/b but rapidly with CO to give Rh(6-Pr)(PPh)(CO)F (10) and Rh(PPh )(CO)F, and also quickly with MeSiCF to form cis-Rh(6-Pr)(PPh) (CF) (11a). Complexes 4b, 5b, 6b, 7b, and 11a were structurally characterized.
LanguageEnglish
Pages1986-1995
Number of pages10
JournalOrganometallics
Volume33
Issue number8
DOIs
StatusPublished - 28 Apr 2014

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carbenes
Carbon Monoxide
Isomers
phosphine
isomers
rings
analogs
Hydrogen
Rhodium
Organometallics
rhodium
Fluorides
phosphines
Hydrides
Nuclear magnetic resonance spectroscopy
hydrides
fluorides
Magnetization
Ion exchange
Chemical activation

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Rh-FHF and Rh-F complexes containing small N-alkyl substituted six-membered ring N-heterocyclic carbenes. / Bramananthan, N.; Carmona, M.; Lowe, J.P.; Mahon, M.F.; Poulten, R.C.; Whittlesey, M.K.

In: Organometallics, Vol. 33, No. 8, 28.04.2014, p. 1986-1995.

Research output: Contribution to journalArticle

Bramananthan, N. ; Carmona, M. ; Lowe, J.P. ; Mahon, M.F. ; Poulten, R.C. ; Whittlesey, M.K./ Rh-FHF and Rh-F complexes containing small N-alkyl substituted six-membered ring N-heterocyclic carbenes. In: Organometallics. 2014 ; Vol. 33, No. 8. pp. 1986-1995
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abstract = "Heating the six-membered ring N-heterocyclic carbenes 6-Me and 6-Et with Rh(PPh)H afforded the rhodium monocarbene hydride complexes Rh(6-NHC)(PPh)H 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 EtN·3HF gave only the trans-P,P isomer of the bifluoride complex Rh(6-Me)(PPh)(FHF) (6b), whereas 5a/b reacted to form Rh(6-Et)(PPh)(FHF) as a mixture of cis- and trans-phosphine isomers (7a/b). Variable temperature H and F NMR spectroscopy showed that 6b and the previously reported 6-Pr carbene analogue cis-Rh(6- Pr)(PPh)(FHF) (2a; Organometallics 2012, 41, 8584) were fluxional in solution. F Magnetization transfer experiments revealed F exchange in both compounds and afforded similar ΛH values (2a, 51 ± 5 kJ mol ; 6b, 60 ± 6 kJ mol) but somewhat different values of ΛS (2a, -70 ± 17 J mol K; 6b, -27 ± 18 J mol K ). The fluoride complexes cis-Rh(6-Me)(PPh) F (8a), cis-/trans-Rh(6-Et)(PPh)F (9a/b), and the previously reported 6-Pr analogue 3a could be formed upon C-F activation of CFCF=CF by 4a/b, 5a/b, and Rh(6- Pr)(PPh)H (1a/b), respectively. Complex 3a reacted slowly with H to partially reform 1a/b but rapidly with CO to give Rh(6-Pr)(PPh)(CO)F (10) and Rh(PPh )(CO)F, and also quickly with MeSiCF to form cis-Rh(6-Pr)(PPh) (CF) (11a). Complexes 4b, 5b, 6b, 7b, and 11a were structurally characterized.",
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T1 - Rh-FHF and Rh-F complexes containing small N-alkyl substituted six-membered ring N-heterocyclic carbenes

AU - Bramananthan,N.

AU - Carmona,M.

AU - Lowe,J.P.

AU - Mahon,M.F.

AU - Poulten,R.C.

AU - Whittlesey,M.K.

PY - 2014/4/28

Y1 - 2014/4/28

N2 - Heating the six-membered ring N-heterocyclic carbenes 6-Me and 6-Et with Rh(PPh)H afforded the rhodium monocarbene hydride complexes Rh(6-NHC)(PPh)H 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 EtN·3HF gave only the trans-P,P isomer of the bifluoride complex Rh(6-Me)(PPh)(FHF) (6b), whereas 5a/b reacted to form Rh(6-Et)(PPh)(FHF) as a mixture of cis- and trans-phosphine isomers (7a/b). Variable temperature H and F NMR spectroscopy showed that 6b and the previously reported 6-Pr carbene analogue cis-Rh(6- Pr)(PPh)(FHF) (2a; Organometallics 2012, 41, 8584) were fluxional in solution. F Magnetization transfer experiments revealed F exchange in both compounds and afforded similar ΛH values (2a, 51 ± 5 kJ mol ; 6b, 60 ± 6 kJ mol) but somewhat different values of ΛS (2a, -70 ± 17 J mol K; 6b, -27 ± 18 J mol K ). The fluoride complexes cis-Rh(6-Me)(PPh) F (8a), cis-/trans-Rh(6-Et)(PPh)F (9a/b), and the previously reported 6-Pr analogue 3a could be formed upon C-F activation of CFCF=CF by 4a/b, 5a/b, and Rh(6- Pr)(PPh)H (1a/b), respectively. Complex 3a reacted slowly with H to partially reform 1a/b but rapidly with CO to give Rh(6-Pr)(PPh)(CO)F (10) and Rh(PPh )(CO)F, and also quickly with MeSiCF to form cis-Rh(6-Pr)(PPh) (CF) (11a). Complexes 4b, 5b, 6b, 7b, and 11a were structurally characterized.

AB - Heating the six-membered ring N-heterocyclic carbenes 6-Me and 6-Et with Rh(PPh)H afforded the rhodium monocarbene hydride complexes Rh(6-NHC)(PPh)H 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 EtN·3HF gave only the trans-P,P isomer of the bifluoride complex Rh(6-Me)(PPh)(FHF) (6b), whereas 5a/b reacted to form Rh(6-Et)(PPh)(FHF) as a mixture of cis- and trans-phosphine isomers (7a/b). Variable temperature H and F NMR spectroscopy showed that 6b and the previously reported 6-Pr carbene analogue cis-Rh(6- Pr)(PPh)(FHF) (2a; Organometallics 2012, 41, 8584) were fluxional in solution. F Magnetization transfer experiments revealed F exchange in both compounds and afforded similar ΛH values (2a, 51 ± 5 kJ mol ; 6b, 60 ± 6 kJ mol) but somewhat different values of ΛS (2a, -70 ± 17 J mol K; 6b, -27 ± 18 J mol K ). The fluoride complexes cis-Rh(6-Me)(PPh) F (8a), cis-/trans-Rh(6-Et)(PPh)F (9a/b), and the previously reported 6-Pr analogue 3a could be formed upon C-F activation of CFCF=CF by 4a/b, 5a/b, and Rh(6- Pr)(PPh)H (1a/b), respectively. Complex 3a reacted slowly with H to partially reform 1a/b but rapidly with CO to give Rh(6-Pr)(PPh)(CO)F (10) and Rh(PPh )(CO)F, and also quickly with MeSiCF to form cis-Rh(6-Pr)(PPh) (CF) (11a). Complexes 4b, 5b, 6b, 7b, and 11a were structurally characterized.

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U2 - 10.1021/om500122e

DO - 10.1021/om500122e

M3 - Article

VL - 33

SP - 1986

EP - 1995

JO - Organometallics

T2 - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 8

ER -