185697-93-2Relevant academic research and scientific papers
Preparation of (1,4,7-triazacyclononane)Rh(hydrocarbyl)3 compounds and their derivatives. Strong donor labilization of RhC1 bonds toward alkylation and preparation of unusually stable alkyl hydride complexes of rhodium
Zhou, Renjie,Wang, Chunming,Hu, Yonghan,Flood, Thomas C.
, p. 434 - 441 (2008/10/08)
(tacn)Rh(R)3 compounds (tacn=1,4,7-triazacyclononane; R=Me, Et, Ph, vinyl) have been prepared in 65-86% yields by treatment of (tacn)RhCl3·H2O with more than a 7-fold molar quantity of RLi in THF, followed by protonation by methanol. The product before protonation is (Li3tacn)RhR3 (Li3tacn = 1,4,7-trilithio-1,4,7-triazacyclononane) which can be isolated. The alkylation is complete in a few minutes to a couple of hours, depending on R, which compares with 3-4 days for CnRhCl3 with MeLi (Cn = 1,4,7-trimethyl-1,4,7-triazacy-clononane) and suggests that the presumably first-formed (Li3tacn)RhCl3 is highly activated toward Cl- dissociation by the strong donor effect of the three LiNR2 groups in the rhodium coordination sphere. Protonation of (Li3tacn)RhR3 by methanol gives the neutral products (tacn)RhR3. X-ray structure determinations of (tacn)RhEt3 and (tacn)RhPh3 have been carried out. Protonolysis of (tacn)RhR3 (R = Me, Et, Ph) by 2 HSO3CF3 (HOTf) affords (tacn)-RhR(OTf)2. Dissolution of the latter in D2O gives [(tacn)RhR(D2O)2](OTf)2, which on standing for up to 2 days undergoes H/D exchange of the two NH groups trans to the aqua ligands. Treatment of (tacn)RhR(OTf)2 with 1 equiv of PMe3 followed by NaBH4 or KBH4 yields a mixture of [(tacn)Rh(H)R(PMe3)](OTf) and [(tacn)Rh(H)2(PMe3))](OTf) which is separated by benzene extraction. Counterion exchange has been carried out where R = Me and Et with Na{B[C6H3-3,5-(CF3)2]4} (NaBArF4) yielding [(tacn)Rh(H)R(PMe3)](BArF4). Heating of [CnRh-(H)Et(PMe3)IX (X = OTf or BArF4), [(tacn)Rh(H)Et(PMe3)]X, and [(tacn)Rh(H)Me(PMe3)]X in C6D6 leads to formation of [(Cn/tacn)Rh(D)(C6D5)(L)]XL)]X in high yield in all cases. The half-lives of these cleanly first-order reactions at 80 °C are 1 min, 1.2 h, and 7.3 h, respectively, illustrating alkyl hydride thermal stabilities unprecedented in rhodium chemistry.
