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

Abstract

Rh-containing metallacycles, [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NR)2-]Cl; TPA = N,N,N,N-tris(2-pyridylmethyl)amine have been accessed through treatment of the Rh(I) ethylene complex, [(TPA)Rh(η(2)-CH2CH2)]Cl ([1]Cl) with substituted diazenes. We show this methodology to be tolerant of electron-deficient azo compounds including azo diesters (RCO2N=NCO2R; R = Et [3]Cl, R = iPr [4]Cl, R = tBu [5]Cl, and R = Bn [6]Cl) and a cyclic azo diamide: 4-phenyl-1,2,4-triazole-3,5-dione (PTAD), [7]Cl. The latter complex features two ortho-fused ring systems and constitutes the first 3-rhoda-1,2-diazabicyclo[3.3.0]octane. Preliminary evidence suggests that these complexes result from N-N coordination followed by insertion of ethylene into a [Rh]-N bond. In terms of reactivity, [3]Cl and [4]Cl successfully undergo ring-opening using p-toluenesulfonic acid, affording the Rh chlorides, [(TPA)Rh(III)(Cl)(κ(1)-(C)-CH2CH2(NCO2R)(NHCO2R)]OTs; [13]OTs and [14]OTs. Deprotection of [5]Cl using trifluoroacetic acid was also found to give an ethyl substituted, end-on coordinated diazene [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NH)2-](+) [16]Cl, a hitherto unreported motif. Treatment of [16]Cl with acetyl chloride resulted in the bisacetylated adduct [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NAc)2-](+), [17]Cl. Treatment of [1]Cl with AcN=NAc did not give the Rh-N insertion product, but instead the N,O-chelated complex [(TPA)Rh(I)(κ(2)-(O,N)-CH3(CO)(NH)(N=C(CH3)(OCH=CH2))]Cl [23]Cl, presumably through insertion of ethylene into a [Rh]-O bond.

Ruthenium(II) complexes of some simple classic amine ligands

“…The working electrode was a Pt wire for voltammetry (1 mm diameter, 8.4 mm length) and a Pt disc for rotating disc polarography (3 mm diameter). Proton NMR spectra were obtained at room temperature from samples in CDCl 3 or DMSO-d 6 complexes were collected on a Bruker AXS SMART APEX CCD diffractometer at 100(2) K using monochromated Mo-Kα radiation with the omega-scan technique.…”

“…There has also been increasing focus on second-row transition metal complexes of ruthenium, rhodium and rhenium. [5][6][7] Ru(II) and Ru(III) tripodal amine complexes, especially those of imidazole-based ligands, have been studied for their anti-tumor properties [8] and, in cases where the ligand has π-acceptor groups, such compounds have drawn attention because of their luminescence and redox properties. Oddly, however, some classical coordination compounds of ruthenium with simple multidentate amines appear to be underrepresented in the literature; with tris(2-aminoethyl)amine (Tren), only one Ru(II)-Tren complex [9] and two Ru(III)-Tren [10] complexes having been reported previously (the former during our execution of this work).…”

“…Octahedral d 6 hexachloro-complexes, such as RhCl6 3-and IrCl6 3-, show two bands in the UV region attributed to pπ(Cl)→d and pσ(Cl)→d ligand-to-metal charge transfer (LMCT), with the higher energy band being the pσ(Cl)→dπ LMCT band [36]. TheCl-coordinated [Ru(Tren)(PPh 3 )Cl]Cl (2), Cl)→dπ LMCT, as well as a band around 260 nm typical of a PPh 3 π→π* transition.…”

Formation of azarhodacyclobutanes with varying N-substitution

“…Recently, we discovered the successful deprotection of bis(Ntert-butoxycarbonyl) (Boc)-protected 3-rhoda-1,2-diazacyclopentanes using trifluoroacetic acid (TFA) [17]. Stemming from this success, we were interested whether an N-Bocprotected 2-azarhodacyclobutane would similarly undergo deprotection on exposure to acid.…”