Reactivity, Structures, and NMR Spectroscopy of Half-Sandwich Pentamethylcyclopentadienyl Rhodium Amido Complexes Relevant to Transfer Hydrogenation

Abstract

The reactivity, structures, and NMR spectroscopy of a series of compounds relevant to asymmetric transfer hydrogenation, of general formula Cp*RhCl(S,S-4-RC6H4SO2NCHPhCHPhNH2) (Cp* = η5-C5Me5, S,S-2a R = Me, S,S-2b R = tBu, S,S-2c R = F), have been studied. 1H/15N HMQC NMR spectra of 2a−2c were recorded with 15N in natural abundance making use of the coupling to the C5Me5 protons; the coupling constants J RhN were ca. 15 and 20 Hz for the amino and amido nitrogens, respectively. 1H/103Rh NMR spectra of 2a and 2c were recorded similarly. The chloride ligand in S,S-2a has been shown to be very labile; reaction with CO afforded the cationic complex [Cp*Rh(CO){C(O)N(Ts)CHPhCHPhNH2}][Cl] (3a) as a mixture of diastereomers, S,S,R Rh and S,S,S Rh, with opposite chirality at Rh; reaction with tBuNC gave [Cp*Rh(CNtBu)(S,S-TsCHPhCHPhNH2)][PF6] (4a), and reactions with LiBr and KI gave Cp*RhBr(S,S-TsNCHPhCHPhNH2) (6a) and Cp*RhI(S,S-TsNCHPhCHPhNH2) (7a), respectively. Complexes S,S-2c, S,S-6a, and S,S-7a have been characterized by X-ray crystallography; the amino N−Rh bond is significantly shorter than the amido N−Rh bond in all cases (difference Δr 0.058(2), 0.085(6), and 0.046(4) Å, respectively), and the complexes all possess intramolecular NH···X (X = Cl, Br, I) hydrogen bonds. The reaction of 2a with formic acid results in complete displacement of the chelating ligand and the formation of dinuclear [{Cp*Rh}2(μ-H)(μ-Cl)(μ-HCO2)][BPh4] (5a), which was also characterized crystallographically. Reaction of 2c with AgOTf resulted in the formation of [Cp*Rh(OH2)(4-FC6H4SO2NCHPhCHPhNH2)][OTf] ([8c·H 2 O][OTf]) or [Cp*Rh(4-FC6H4SO2NCHPhCHPhNH2)]2[OTf]2 ([8c] 2 [OTf] 2 ) depending upon the conditions employed. [8c·H 2 O][OTf] was characterized by X-ray crystallography, and the structure showed that both CHPh centers in the ligand had been racemized, converting the S,S isomer of the starting material into a mixture of both R,R and S,S isomers.

3‐Rhoda‐1,2‐diazacyclopentanes: A Series of Novel Metallacycle Complexes Derived From CN Functionalization of Ethylene

“…For instance, in Schrock's tungsten(V)-bridged species, W 2 Me 6 (NPh) 2 (m-h 2 -h 2 -NHNH)(m-h 1 -h 1 -NH 2 NH 2 ) higher field shifts of d( 15 N) = À323 ppm (NHNH 2À ) and À325 ppm (NH 2 NH 2 ) were observed. [24] These values also compare well with those reported previously for other Rh-containing ring systems, namely the 2-azarhodacyclobutane, [8] + for which d( 15 N) = À379 ppm and the five-membered rhodacycle, [Rh]-TsDPEN [25] (TsDPEN = toluenesulfonyl-1,2-diphenylethylenediamine) for which d( 15 N) = À478 ppm (amido donor) and À530 ppm (amine donor). Moreover, the inherent lack of symmetry present within [3-6] + was observed using 1 H-15 N HMBC NMR spectroscopy.…”

Tuning PtII‐Based Donor–Acceptor Systems through Ligand Design: Effects on Frontier Orbitals, Redox Potentials, UV/Vis/NIR Absorptions, Electrochromism, and Photocatalysis

“…Such rearrangements have been proposed for rhodium complexes employing the same ligands by Perutz and co-workers. [20,21] Also, ap ossible dimerizationc annot be ruled out, as discussed recently by Chang and co-workers. [29] Upon oxidation of compound 3 to 3 + ,t he electron density on the already electron-poor bis(amidosulfonyl) ligand is further reduced, resulting in aw eaker platinum-nitrogen bond.…”

“…[20][21][22] Interestingly,t hey also observed the dimerization of the aforementioned rhodium compounds, in which the oxygen atoms of the sulfonyl group bridge two rhodiumc enters. [20] Kavallieratosa nd co-workerso bserved the formation of coordination polymers using lead(II)s alts, emphasizing the versatile and dynamic coordinationc hemistry these ligandsmay engage in. [17] Results and Discussion Synthesis and structural characterization Complexes 1-5 were prepared by following ap reviously established route (Scheme1).…”

Preparation of 2‐Azarhodacyclobutanes by Rhodium(I)–Olefin Oxidation

“…Through the neighboring N À Ts moiety, C2 is deshielded and appeared at 57.9 ppm (Table 2). [15] The approximately 100 ppm lower field chemical shift of the coupling of the nitrogen to the Rh center can be ascribed to the increased ring strain in the four-membered ring of the present structure versus the five-membered ring of RhÀTsDPEN. [5,7] The Rh-coupling observed in both the 1 H and 13 C NMR spectra clearly demonstrated the RhÀCH 2 connectivity.…”