XPS Investigations of (1,4,7-trimethyl-1,4,7-triazacyclononane)RhMe₃and [1,1,1-tris((dimethylphosphino)methyl)ethane]RhMe₃and Their Rh−C Cleavage Derivatives. Comparison of Hard- and Soft-Ligated Rhodium Organometallics

Abstract

The new molecules P3RhMe3-n (OTf) n are reported (n = 0−2; P3 = MeC(CH2PMe2)3; OTf = OS(O)2CF3). The known fac-(Me3P)3RhMe3 was converted to mer-(Me3P)3RhMe3-n Cl n (n = 1, 2) by cleavage with HCl in ether. X-ray photoelectron spectra (XPS) of these were recorded, and all except the P3RhMe3-n Cl n series afforded clean spectra. XPS were also obtained for the known CnRhMe3-n X n (n = 0−2; X = Cl, Br, OTf; Cn = 1,4,7-trimethyl-1,4,7-triazacyclononane), CnRhX3 (X = Cl, Br), CnRhMe(OH)(OTf), and [CnRhMe2(CO)]OTf. An X-ray crystal structure of P3RhMe3 is reported, and the geometry at the metal is compared among P3RhMe3, (Me3P)3RhMe3, and CnRhMe3. Core binding energies (BEs) for the series L3RhMe3-n X n (L3 = Cn, P3) change linearly with n for a given L3 and X. For CnRhMe3-n X n , replacement of methyl by chloride or bromide gives similar ΔBE values (∼0.7 eV), while triflate-for-methyl substitution gives a much larger ΔBE (1.2 eV). Triflate-for-methyl substitution in P3RhMe3-n (OTf) n , however, causes a ΔBE of only 0.8 eV. Thus, the Rh(3d5/2) core binding energies in these complexes change less in triflate-for-methyl substitutions when the P3 ancillary ligand is present than in the presence of Cn; apparently P3 compensates for changes in electron density at the rhodium center more effectively than does Cn, presumably as a result of the greater polarizability of phosphorus (softer) compared to nitrogen (harder). The XPS trends for these series effectively mean that P3 makes RhIII a softer metal and Cn makes RhIII a harder metal.

Flower-like mesoporous silica: a bifunctionalized catalyst for rhodium-catalyzed asymmetric transfer hydrogenation of aromatic ketones in aqueous medium

“…4, the XPS spectra of the catalyst 3 gave a Rh 3d 5/2 binding energy of around 309.43 eV, indicating that the rhodium center was in the trivalent state. 19 More importantly, it was found that catalyst 3 had almost the same Rh 3d 5/2 electron binding energy as the parent Cp*RhTsDPEN (309.43 eV versus 309.38 eV), suggesting that the rhodium center within the FFMS silicate network retained its original chiral coordination microenvironment.…”

Synthesis, characterization, and crystal structures of the osmium triflate complexes Cp∗Os(P–P)(OTf) and [Cp∗Os(P–P)(OH2)][OTf]

“…A particularly clean method is the addition of triflic acid to a transition metal alkyl complex, with loss of alkane. For the platinum metals, this route has been used to prepare triflate complexes of Ru [2][3][4], Os [5,6], Rh [7], Ir [8], and Pt [9][10][11]. Formation of triflate complexes by addition of triflic acid to metal hydrides (with loss of H 2 ) is also possible; all the examples of this approach of which we are aware involve the element Ru [12][13][14].…”

Oxidatively Induced Reductive Eliminations. A Mechanistic Study of the Oxidation Chemistry of CnRhMe3 (Cn = 1,4,7-Trimethyl-1,4,7-triazacyclononane)

“…Although intramolecular elimination is again the result, it will be seen that this system differs from Cp*Rh(PPh 3 )Me 2 in interesting ways. Recent publications by Flood and co-workers have focused on the organometallic chemistry of the CnRh moiety. The Cn ligand is bonded to the metal through three “hard”, poorly polarizable N atoms, devoid of π-backbonding capabilities.…”

“…This is in contrast with more conventional ligands like Cp, CO, PR 3 , etc., which are relatively “soft”, polarizable, and capable of accepting electron density from the metal by backbonding. It is hoped that the relatively hard Rh center that results from the coordination of the Cn ligand will significantly alter the chemistry of coordinated hydrocarbon ligands when compared to the behavior of related Rh complexes that are ligated by softer ligands 5a. Although it is not clear whether the effects arise from the altered hardness of the metal, several reports indicate important reactivity differences betweenCnRh and related CpRh and TpRh complexes.…”

“…Although it is not clear whether the effects arise from the altered hardness of the metal, several reports indicate important reactivity differences betweenCnRh and related CpRh and TpRh complexes. For example, Rh(III) complexes CnRh(PR 3 )(H)Me + (R = Me, OMe) are isolable and thermally stable at ambient temperature and only slowly eliminate methane at 50 °C,5d whereas analogous Rh(III) complexes Cp*Rh(PMe 3 )(H)Me,7a Tp‘Rh(CO)(H)Me,7b and Tp‘Rh(CNtBu)(H)Me 7c readily eliminate methane at considerably lower temperatures.…”