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Cationic Tris N-Heterocyclic Carbene Rhodium Carbonyl Complexes: Molecular Structures and Solution NMR Studies


Reference:

Burling, S., Douglas, S., Mahon, M. F., Nama, D., Pregosin, P. S. and Whittlesey, M. K., 2006. Cationic Tris N-Heterocyclic Carbene Rhodium Carbonyl Complexes: Molecular Structures and Solution NMR Studies. Organometallics, 25 (10), pp. 2642-2648.

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Abstract

The cationic N-heterocyclic carbene (NHC) Rh complexes [Rh(NHC)3(CO)]+ (NHC = ICy (1), IiPr2Me2 (2)) were isolated from the reactions of RhH(PPh3)3(CO) with the free NHCs. The hexafluorophosphate salts of both compds., 1[PF6] and 2[PF6], were characterized by x-ray diffraction. The obsd. temp. dependences of the 1H NMR spectra for 1[PF6] and 2[PF6] are a consequence of restricted rotation assocd. with the three Rh-CNHC bonds. Line shape analyses from the NMR studies on 1[PF6], 1[BAr4F], and 2[PF6] (BAr4F = B(3,5-C6H3(CF3)2)4) afford activation barriers for the two trans-positioned Rh-CNHC bonds of 35, 38, and 40 kJ mol-1, resp. Pulsed-gradient spin-echo (PGSE) NMR measurements show that there is only a relatively small amt. of ion pairing for these salts in CH2Cl2 soln. 1H-19F HOESY data help to place the anions relative to the cations. Preliminary mechanistic studies on the formation of 1 and 2 suggest a role for neutral dinuclear precursors, as revealed by the reaction of (PPh3)2Rh(micro -CO)2Rh(IiPr2Me2)2 with ICy, which affords the structurally characterized mixed NHC complex [Rh(IiPr2Me2)2(ICy)(CO)][PF6] (3[PF6]).

Details

Item Type Articles
CreatorsBurling, S., Douglas, S., Mahon, M. F., Nama, D., Pregosin, P. S. and Whittlesey, M. K.
Uncontrolled Keywordspotential barrier, rh heterocyclic carbene imidazolylidene complex prepn crystal mol structure, ract (reactant or reagent) (reaction of imidazolylidene derivs. with rh hydride to give cationic tris n-heterocyclic carbene rhodium carbonyl complexes), imidazolylidene reaction rh hydride, internal rotation (hindered, restricted rotation activation barrier rh heterocyclic carbene imidazolylidene complex, molecular structure (of imidazolylidene n-heterocyclic carbene rhodium carbonyl complexes), molecular rotation (internal, carbenes role, prp (properties), hindered, rct (reactant), prep (preparation), spin echo (reaction of imidazolylidene derivs. with rh hydride to give cationic tris n-heterocyclic carbene rhodium carbonyl complexes), overhauser spectroscopy (heteronuclear, crystal structure, heterocyclic compounds role, ion pairs, reaction of imidazolylidene derivs. with rh hydride to give cationic tris n-heterocyclic carbene rhodium carbonyl complexes), spn (synthetic preparation)
DepartmentsFaculty of Science > Chemistry
RefereedYes
StatusPublished
ID Code4731

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