Trans-dichloro-2,3-naphthalenediamine bis[(2-methoxyethyl)­(diphenyl)phosphine]­ruthenium(II) Complex

Abstract

Trans-dichloro-2,3-naphthalenediamine bis[(2-methoxyethyl)(diphenyl)phos-phine]ruthenium(II) complex Cl₂Ru(η¹-Ph₂PCH₂CH₂OCH₃)₂(C₁₀H₁₀N₂) has been obtained by reaction of equimolar amounts of Cl₂Ru(P^⌒O)₂ complex 2 with one equivalent of 2,3-naphthalenediamine as co-ligand in very good yield. The structure of this new complex 3 was confirmed by elemental analysis, IR, ³¹P-NMR ¹H-NMR, ¹³C-NMR, UV-visible spectroscopy and FAB-MS.

1. Introduction

Bifunctional ether-phosphines (O,P) have significantly affected the isolation of coordinatively unsaturated species [1,2,3,4,5,6,7]. These ligands are provided with oxygen atoms incorporated in open-chain ether moieties which form a weak metal-oxygen contact while the phosphorus atom is strongly coordinated to the metal [3,4,5,6,7,8,9]. In these “hemilabile“ ligands, the ether moiety is regarded as an intramolecular solvent molecule stabilizing the vacant coordination site by chelation. Phosphorus–oxygen hemilabile ligands like 2-(diphenylphosphino)ethyl methyl ether (P~O), reacts with various metals of catalytic relevance due to their ability to act as both a chelate ligand, stabilizing the metal complex, and a monodentate ligand providing a free coordination site for an incoming substrate (through the labilization of the weakly bonded oxygen atom) [1,2,3,4,5,6,7,8,9,10].

2. Result and Discussion

The Ph₂PCH₂CH₂OCH₃ ligand and complex 2 were synthesized according to literature [2]. Treating complex 2 with an equivalent amount of 2,3-naphthalenediamine as co-ligand in dichloromethane at room temperature resulted in the formation of complex 3 without any side products as shown in Scheme 1.

The stepwise formation of the desired complex 3 is monitored by ³¹P{¹H}-NMR spectroscopy, in an NMR tube experiment, where addition of 2,3-naphthalenediamine to a CD₂Cl₂ solution containing Cl₂Ru(P^⌒O)₂ complex as starting material leads to the disappearance of the red color of the Cl₂Ru(P^⌒O)₂ complex and the singlet of this complex at δ_p = 64.2 ppm and the appearance of the singlet at δ_p = 41.3 ppm due to the formation of complex 3 with a trans-Cl₂Ru(P~O)(N^⌒N) formula as shown in Figure 1.

Liquid ³¹P{¹H}-NMR spectra using CD₂Cl₂ show that complex 3 formed as trans-Cl₂Ru(P~O)(N^⌒N), since only a singlet at δ_p = 41.3 ppm is detected without any other singlets. If cis-Cl₂Ru(P~O)(N^⌒N isomer was formed, an AB ³¹P{¹H}-NMR pattern with a J_PP coupling constant of ~40 to 100 Hz would be detected due to the formation of inequivalent phosphorus atoms.

3. Experimental

2,3-Naphthalenediamine (0.04 g, 0.25 mmol) was dissolved in 10 mL of dichloromethane and the solution was added dropwise to a stirred solution of Cl₂Ru(P^⌒O)₂ (0.17 g, 0.25 mmol) in 15 mL of dichloromethane. After the reaction mixture was stirred for approximately 20 min at room temperature, the solution was concentrated to a volume of ~1 mL under reduced pressure. Addition of 30 mL of diethyl ether caused the precipitation of a solid which was filtered (P4), washed well with 25 mL of n-hexane and dried under vacuum.

Melting point: 280 °C

Yield: 89% (0.18 g) of a violet powder.

MS (FAB): m/z = 818.2 (M⁺).

IR (KBr, cm^-1): 3340 (v_NH), 3180 (v_PhH) and 2970 (v_CH). 1540 (v_C=C).

UV-visible absorption: λ_max = 270 nm and 503 nm.

³¹P{¹H} NMR (CDCl₃): δ (ppm) 41.3.

¹H NMR (CDCl₃): δ (ppm) 2.4 (m, 4H, PCH₂), 2.9 (s, 6H, OCH₃), 3.0 (m, 4H, OCH₂), 4.4 (b, 4H, NH₂), 6.6–7.7 (4m, 26H, Ph).

¹³C{¹H} NMR (CDCl₃): δ (ppm) 24.7 (m, 2C, PCH₂), 57.6 (s, 2C, OCH₃), 68.6 (s, 2C, OCH₂), 126.8–132.4 (9s, 34C, Phs).

Elemental analysis: Calcd for C₄₀H₄₄Cl₂N₂O₂P₂Ru. C, 58.68; H, 5.42; Cl, 8.66; N, 3.42%. Found: C, 58.23; H, 5.77; Cl, 8.28; N, 3.32%.