Complexes of Rhodium(III) with Two Chelating C⁁N Ligands and One Diimine Ligand

Abstract

The synthesis of two series of cyclometalated Rh"' compounds is described, namely of 5 dinuclear chlorobridged species [{Rh(CAN),}(p-C1),] A and of 15 mononuclear complexes [Rh(C/"),(Nr")]+ B; CAN stands for five different cyclometalating ligands, i.e. deprotonated phenylpyridine, deprotonated 2-(thienyl)pyridine, and three deprotonated 1-aryl-lH-pyrazoles, and NAN for six diimine ligands such as 2,2-bipyridine, 2,T-bi-1H-imidazole, and 2,2'-bipyrimidine. For (2,2'-bipyridine)bis[2-(thien-2-yl)pyridinato-~,C3']rhodium(III) chloride, an X-ray structure determination was carried out. In the other cases, 'H-NMR spectra established the configuration of the complexes. All mononuclear and dinuclear complexes show a C,C &-configuration. The UV/VIS-absorption bands at longest wavelength are most likely due to metal-to-ligand charge-transfer (MLCT) transitions, depending on the nature of the cyclometalating ligand CAN and on the diimine ligand NAN. The receptor orbital is in some cases on the cyclometalating ligand, in others on the diimine. All monomer complexes exhibit at least one reversible reduction wave in the cyclovoltammogram in dimethylformamide solutions, attributable to a ligand-cen- Introduction. -Complexes of transition metals comprising purely aromatic chelating ligands CAN recently found widespread interest as subjects of photochemical investigations [ 1-41. The strong ligand-field influence of the C-donor, combined with the possibility of n -back donation into the metallocycle, yields generally high-lying d-d excited states. Charge-transfer states, particularly interesting in photochemistry, become therewith often the lowest excited states.With the aim of tuning excited-state properties, in a way similar to the now well known case of tris(diimine)ruthenium(II) complexes [5], we prepared a series of 4d6 complexes with Rh"' as the central metal, having the general formula [Rh(CAN),(NAN)]'. Watts and coworkers [6] described some complexes of related structures. Two structural characterizations of Rh"' complexes, one with a single metallocycle [7], the other a dinuclear species with two metallocycles on each center [8], were recently reported. In the present paper, we describe the synthesis and give a complete characterization, including the configuration of the bis(cyclometa1ated) Rh"' complexes B, which contain the chelating hgands derived from 1-5 and the diimine ligands 6-11, and of some dimeric precursors A.

Metalloligands: Rhodium(III) Cyclometallated Compounds Containing Multitopological Binucleating Ligands

“…The aim is to get heteropolymetallic complexes in which the electronic communication between the metals is propagated through bridging atoms. Molecules containing different metals with diverse electronic properties are key structures that could display peculiar electronic [6][7][8][9] and magnetic properties [10] and are therefore potentially useful for developing molecular-based devices. [11] We report in this paper: (i) the synthesis of the mononuclear [Rh(2-phenylpyridine) 2 (H 2 R 2 C 2 N 2 S 2 κ-S,S-Rh)] + Cl -species (H 2 R 2 C 2 N 2 S 2 = diisoamyldithiooxamide, 1; diisopropyldithiooxamide, 2; di-{S}-phenylethyldithiooxamide, 3; meso-phenylethyldithiooxamidate, 4) and of their dehydrohalogenated counterparts [Rh(2-phenylpyridine) 2 -(HR 2 C 2 N 2 S 2 κ-S,S-Rh)] (HR 2 C 2 N 2 S 2 = diisoamyldithiooxamidate, 5; diisopropyldithiooxamidate, 6; di-{S}-phenylethyldithiooxamidate, 7; meso-phenylethyldithiooxamidate, 8); (ii) the reaction of [Rh(2-phenylpyridine) 2 {H(isoamyl) 2 -C 2 N 2 S 2 κ-S,S-Rh}] with some chlorido-bridged dimers [ML n Cl] 2 (M = di or trivalent metal ion, L n = set of neutral and anionic ligands such that the charge of the ML n fragment is 1+); (iii) the reaction of [ML n {H(isoamyl) 2 C 2 N 2 S 2 κ-S,S-M}] [ML n = (1,5-cod)rhodium(I), 9 (cod = cyclooctadiene); (η 3 -allyl)palladium(II), 10; (tri-n-propylphosphane)palladium(II), 11; (diphenyl-2-pyridylphosphane)-(chlorido)platinum(II), 12] with the chlorido-bridged [Rh(2-phenylpyridine) 2 Cl] 2 ; (iv) the assessment of the struc-ture of the heterobimetallic compounds [Rh(2-phenylpyridine) 2 …”

Cyclometalated rhodium(III) complex with phen-dione ligand

“…Cyclometalated Rh(III) complexes with triazole ligands showed one irreversible oxidation wave around 1.4 V, which has been assigned to a metal-centered oxidation process [24]. Complexes of Rh(III) with two chelating Ĉ N ligands and one diimine ligand exhibited at least one reversible reduction wave, attributable to ligand-centered reduction [22].…”

“…For the cyclometalated [Rh(Ĉ N) 2 (N N)] + complexes, an absorption band observed around 370 nm is invariable with respect to the polypyridyl co-ligands (N N) and this band is assigned to Rh ! phpy À [14,[20][21][22][23][24]. Therefore, the absorption at 374 nm is most probably due to a Rh !…”

Stereoselective Synthesis of Hexacoordinated Mononuclear Cyclometalated Rhodium(III) Complexes − Transfer of Chirality from the Metal Center to the Ligand

“…The first point concerns the regioselectivity in the synthesis of the dinuclear complex from which the mononuclear species are obtained through cleavage reactions. It was shown earlier [9,10] that the cyclometalation is completely regioselective, yielding the C,C-cis isomer.…”