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Boletín de la Sociedad Chilena de Química

versión impresa ISSN 0366-1644

Bol. Soc. Chil. Quím. v.45 n.2 Concepción jun. 2000

http://dx.doi.org/10.4067/S0366-16442000000200009 

HEXAMETHYLBENZENERUTHENIUM(II) COMPLEXES
CONTAINING BIS(DIPHENYLPHOSPHINE)AMINE AND THEIR
SULPHUR OR SELENIUM DERIVATIVES AS LIGANDS.

MAURICIO VALDERRAMA,* RAUL CONTRERAS,
VERONICA ARANCIBIA AND PATRICIO MUÑOZ.

Departamento de Química Inorgánica, Facultad de Química. Pontificia,
Universidad Católica de Chile, Casilla 306, Santiago-22, Chile
(Received: December 29,1999 - Accepted: March 9, 2000)

In memoriam of Doctor Guido S. Canessa C.

ABSTRACT

Reaction of dinuclear complex [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] with the ligand NH(PPh2)2 in 1:2 molar ratio affords the mononuclear complex [(h6-C6Me6)RuCl 2{h1-(PPh2)2NH}](1) which in turn reacts with AgPF6 to yield the cationic compound [(h6-C6Me6)RuCl{h 2-(PPh2)2NH}]PF6 (2). Complex 3 reacts with KOBut to give the neutral complex [(h6-C6Me6)RuCl{h 2-(PPh2)2N}](3). The anionic ligand of complex 3 reacts easily with HBF4 regenerating the starting complex and with MeI by N-methylation of the chelate ligand. The non coordinating P atom of complex 1 reacts with sulfur or selenium to form the P-coordinate monosulphide or selenide ligands, [{(h6-C6Me6)RuCl 2{h1PPh2NHP(E)Ph2 }] (5,6). The treatment of complexes 5 and 6 with AgPF6 affords cationic (7,8) or neutral (9,10) complexes depending of the solvent used. The neutral complex 9 can be N-derivatized by reaction with MeI.


KEY WORDS: Ruthenium, bis(diphenylphosphine)anime complexes, bis(diphenylphosphine)
methylamine complexes, hexamethylbenzene complexes, synthesis.

RESUMEN

La reacción del complejo dinuclear [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] con el ligando NH(PPh2)2 en relación molar 1:2 genera el complejo mononuclear [(h6-C6Me6)RuCl 2{h1-(PPh2)2 NH}](1), el que posteriormente reacciona con AgPF6 formando el complejo catiónico [(h6-C6Me6)RuCl{h 2-(PPh2)2NH}]PF6 (2). El complejo 2 reacciona con KOBut con formación del complejo neutro [(h6-C6Me6)RuCl{h 2-(PPh2)2N}](3). El ligando aniónico del complejo 3 reacciona facilmente con HBF4 regenerando el complejo de partida y con MeI a través de la metilación del átomo de nitrógeno del ligando coordinado. El átomo de fósforo no coordinado del complejo 1 reacciona con azufre o selenio con formación del ligando coordinado monosustituído,[{(h6-C6 Me6)RuCl2{h1PPh 2NHP(E)Ph2}] (5,6). El tratamiento de los complejos 5 y 6 con AgPF6 conduce a la formación de compuestos catiónicos (7,8) o neutros (9,10) dependiendo del tipo de disolvente utilizado. El atomo de nitrógeno del complejo neutro 9 puede ser derivatizado por reacción con MeI.

PALABRAS CLAVES: Rutenio, hexametilbenceno, bis(difenilfosfino)amina, bis(difenilfosfino)
metilamina, síntesis.

INTRODUCTION

The transition metal chemistry of bis(diphenylphosphine)amines, NR(PPh2)2 (R = H, Me, Ph), has attracted considerable interest in recent years,1 in part due to their relation with the widely used diphosphine CH2(PPh2)2 (dppm). The greater acidity of the NH proton of the coordinated NH(PPh2)2 (dppa) ligand than that of CH2 protons of the dppm, may facilitate functionalization reactions that normaly require drastic conditions for dppm. Thus, it has been recently described the N-derivatization of the chelate or bridging coordinated dppa ligand in iron(II) complexes or MoPd2 clusters affording the corresponding methyl-dppa derivatives.2

These ligands are easily oxydized to form dichalcogenide derivatives [NR(EPPh2)2; E = O, S, Se]. When R = H, the diphosphine can be readily deprotonated with alkali metals or metal alkoxides (e.g. KOBut) to give the corresponding metal salts.3 The anion formed [N(EPPh2)2]-, is a versatile ligand, able to form inorganic (carbon-free) chelate rings with a variety of transition metals.4

In contrast, there are few examples of metal complexes containing monochalcogenides derivatives of the type Ph2PNRP(E)Ph2. These heterodifunctional ligands, containing both a soft and hard donor atom, can show different coordination modes in their neutral or anionic form when R = H.4b Thus, they can act as unidentate P-bonded, P,E-chelating or bridging ligand with formation of bimetallic complexes.5

In this paper we describe the synthesis and characterization of new arene-ruthenium(II) complexes containing bis(diphenylphosphine) amine and their sulphur or selenium derivatives as ligands. In these compounds the ligands act in their monodentate, neutral bidentate or anionic bidentate form. The reactions of N-functionalization of anionic bidentate ligands were also studied.

EXPERIMENTAL

All reactions were carried out under purified nitrogen by using Schlenk-tube techniques. The starting complexes [{(h6-C6Me6)Ru(µ-Cl)Cl} 2]6 and the ligands NH(Ph2P)2 (dppa) and Ph2PNHP(E)PPh2 (dppaE, E = S, Se) were prepared by published procedures.3 Elemental analyses (C, H, N, S) were carried out with a Fisons EA 1108 microanalyzer. Conductivities were measured in ca. 5 x 10-4 mol/L acetone solutions, using a WTW LF-521 conductimeter. The FTIR spectra were recorded on a Bruker Vector-22 spectrophotometer using KBr pellets. The NMR spectra were recorded on a Bruker AC-200P spectrometer. Chemical shifts are reported in ppm relative to SiMe4 (1H) and 85% H3PO4 (positive shifts downfield) in D2O (31P) as internal and external standards, respectively.

Synthesis of ligands

NMe(PPh2)2. This compound was prepared by a modification of the reported method.7 To a solution of NH(SiMe3)2 (10 mL; 46.0 mmol) in toluene (15 mL) at -20°C was added BuLi (33.8 mL; 57.46 mmol) and MeI ( 2.9 mL; 46.35 mmol). The mixture was stirred until the temperature raised to 25°C. To the obtained solution, cooled to 0°C, was added dropwise a solution of ClPPh2(17.4 mL; 92.07 mmol) in toluene (10 mL). The mixture was stirred for 15 min and then evaporated to dryness at high vacuum. The solid was dissolved in boiling ethanol, filtered and the solution cooled in a ice-bath. The white solid formed was filtered, washed with acetone and diethyl ether and dried in vacuo. Yield 13.8 g (75%). m.p. 116-117° (116-118°)7. NMR(CD2Cl2, 23 °C): 1H, d 2.43 (t, 3 H, Me, 3J(PH)= 3.04 Hz), 7.42 (m, 20 H, Ph). 31P{1H}, d 71.69 (s). IR(KBr) : n(CH,Me) 2926, n(P2N) 744 and 697 cm-1.

Ph2PNMeP(S)Ph2 (dppmaS). A mixture of NMe(PPh2)2 (1.0 g; 2.5 mmol) and sulphur (84 mg; 2.62 mmol) in diethyl ether (20 mL) was stirred for 30 min. The solution obtained was evaporated to dryness and the solid residue extracted with chloroform. The solution was concentrated and a withe solid was precipitated by adding n-hexane. Yield 875 mg (81%). m.p. 142-143°. Anal. Found: C, 69.40; H, 5.28; N, 3.21; S, 7.41%. C25H23NP2S. Calc.: C, 69.59; H, 5.37; N, 3.25; S, 7.43%. NMR(CDCl3, 23 °C): 1H, d 2.64 (dd, 3 H, Me, 3J(PH)= 1.2 and 11.95 Hz), 7.68 (m, 20 H, Ph). 31P{1H}, d 53.33 (d, P) and 74.73 (d, PS). IR(KBr) : n(PS) 648, n(CH,Me) 2927, n(P2N) 745 and 696 cm-1.

Synthesis of complexes

[(h6-C6Me6)RuCl 2(h1-P-NH(PPh2) 2)](1). To a solution of dinuclear complex [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] (1.74 g; 2.6 mmol) in dichloromethane (20 mL) the ligand dppa (2.0 g; 5.20 mmol) was added. After stirring the mixture for 1 h at - 20°C, the solution was concentrated, chromatographed on neutral aluminum oxide (Brockmann I) and eluted with dichloromethane. The solution obtained was evaporated to a small volume and the complex precipitated by adding diethyl ether. Yield 3.06 g (82%). Anal. Found: C, 60.17; H, 5.48; N, 1.99%. C36H39Cl2NP2 Ru. Calc.: C, 60.08; H, 5.46; N, 1.95%. NMR(CDCl3, 23 °C): 1H, d 1.75 [d, 18 H, Me, 4J(PH) = 0.44 Hz], 4.8 [dd, 1 H, HN, 2J(PH) = 7.50 and 9.71 Hz] and 7.55 [m, 20 H, Ph]. 31P{1H}, d 24.70 [d, PB, 2J(PAPB)= 17.4 Hz] and 71.05 [d, PA]. IR(KBr) : n(NH) 3286, n(P2N) 1097 and 860 cm-1.

[(h6-C6Me6 )RuCl{h2-P,P'-NH(PPh2) 2}]PF6 (2). The complex can be prepared by the two following methods:

a) A solution of complex 1 (100 mg; 0.14 mmol) in acetone ( 15 mL) was treated with AgPF6 (35 mg; 0.14 mmol). After stirring the mixture for 0.5 h at room temperature, in the absence of light, the precipitated silver chloride was removed by filtration through Kieselguhr. The solution was evaporated to dryness, dissolved with acetone and the complex precipitated by adding diethyl ether. Yield 95 mg (83%)

b) To a solution of complex [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] (100 mg; 0.15 mmol) in CH2Cl2 (10 mL) was added a solution of AgPF6 (76 mg; 0.30 mmol) in Me2CO (10 mL). After stirring the mixture for 1 h at room temperature, in the absence of light, the precipitated silver chloride was removed by filtration through Kieselguhr. To the filtrate solution, NH(PPh2)2 (126 mg; 0.326 mmol) was added and the mixture stirred for 2 h. The resulting solution was evaporated to a small volume and the complex precipitated by adding n-hexane or pentane. The solid was filtered off, washed with n-hexane, diethyl ether and dried under vacuum. Yield: 220 mg (89%).

Anal. Found: C, 52.21; H, 4.76; N, 1.72. C36H39ClF6NP3 Ru: C, 52.15; H, 4.74; N, 1.69%. NMR(CD2Cl2, 23 °C): 1H, d 2.07 (d, 18 H, Me6C6, 4J(PH)= 0.98 Hz), 7.67 (m, 20H, Ph) and 10.1 (t, 1 H, HN, 2J(PH) = 5.5 Hz). 31P{1H}, d 54.65 (s) and -145.0 [sept, PF6-, 1J(PF) = 708 Hz]. IR(KBr) : n(NH) 3331 , n(P2N) 1105, n(PF6), 840 and 557 cm-1. L= 120 cm2 mol-1 ohm-1.

[(h6-C6Me6 )RuCl{h2-P,P'-N(PPh2) 2}] (3). A mixture of complex 2 (250 mg; 0.30 mmol) and potassium terbutoxide (34 mg; 0.30 mmol) in dry dichloromethane (20 mL) was stirred at room temperature for 3 h. The solution was evaporated to dryness and the solid residue extracted with dry acetone. The solution was concentrated to a small volume and the complex precipitated adding n-pentane. Yield 155 mg (75%). The complex is very unstable to moisture and the microanalytical results do not agree with calculated values. NMR {(CD3)2CO, 23 °C}: 1H, d 1.88 (d, 18 H, Me6C6, 4J(PH)= 0.72 Hz) and 7.61 (m, 20 H, Ph). 31P{1H}, d 20.18 (s).

[(h6-C6Me6 )RuCl(h2-P,P-NMe(PPh2) 2)]PF6(4). To a solution of complex [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] (200 mg; 0.30 mmol) in acetone (30 mL) was added AgPF6 (160 mg; 0.63 mmol) and the ligand NMe(Ph2P)2 (mdppa) (240 mg; 0.60 mmol). After stirring the mixture for 1 h at room temperature, in the absence of light, the solid AgCl was removed by filtration through Kieselguhr. The resulting solution was concentrated to dryness and dissolved in the minimal amount of dichloromethane. The solution was chromatographed on neutral aluminum oxide (Brockmann I) and eluted with a mixture of dichloromethane/acetone (10/1.5 mL). The complex was precipitated by adding diethyl ether. Yield 400 mg (79%). Anal. Found: C, 52.61; H, 4.90; N, 1.64%. C37H41ClF6NP3 Ru: C, 52.70; H, 4.90; N, 1.66%. NMR {(CDCl3, 23 °C}: 1H, d 1.95 (s, 18 H, Me6C6), 2.90 (t, 3 H, 3JPH = 9.7 Hz, Me) and 7.36 (m, 20 H, Ph). 31P{1H}, d 76.42 (s) and -145.0 [sept, PF6-, 1J(PF) = 713 Hz]. IR(KBr) : n(CH3) 2968 and 1437 , n(P2N) 1104, n(PF6), 835 and 557 cm-1. L= 118 cm2 mol-1 ohm-1.

[(h6-C6Me6 )RuCl2(h1-P-Ph2 PNHP(E)Ph2)] [E = S(5), Se(6)]. A suspension of complex 1 (500 mg, 0.69 mmol) in diethyl ether (20 mL) was treated with the stoichiometric amount of sulphur (22 mg; 0.69 mmol) or grey selenium (55 mg; 0.69 mmol) and the mixture was stirred for 3 or 6 h, for the reaction of S or Se, respectively. The reaction mixture was evaporated to dryness and the solid residue dissolved in dichloromethane. For complex 5, the solution was chromatographed on neutral aluminum oxide and eluted with a mixture of acetone/dichloromethane (1:10 mL). The solution was concentrated to a small volume and the complexes precipitated by adding n-pentane. 5: Yield 522 mg (98%). Anal. Found: C, 57.77; H, 5.32; N, 1.89; S, 4.35%. C36H39Cl2NP2 RuS. Calc.: C, 57.52; H, 5.23; N, 1.86; S, 4.27%. NMR(CDCl3, 23 °C): 1H, d 1.73 [s, 18H, Me], 6.24 [t, 1 H, HN, 2J(PH) = 3.8 Hz] and 7.62 [m, 20 H, Ph]. 31P{1H}, d 50.54 [d, PC, 2J(PAPC)= 46.41 Hz] and 67.99 [d, PA]. IR(KBr) : n(NH) 3133, n(P2N) 1101, 852, n(PS) 623, 611 cm-1. 6: Yield 483 mg (87%). Anal. Found: C, 54.35; H, 4.96; N, 1.75%. C36H37Cl2NP2 RuSe. Calc.: C, 54.14; H, 4.42; N, 1.75%. NMR(CDCl3, 23 °C): 1H, d 1.72 [d, 18 H, Me, 4J(PH) = 0.72 Hz], 6.26 [t, 1H, HN, 2J(PH) = 2.78 Hz] and 7.63 [m, 20H, Ph]. 31P{1H}, d45.11 [d, PC, 2J(PAPC)= 47.77 Hz, 1J(PSe) = 774.3 Hz] and 69.34 [d, PA]. IR(KBr) : n(NH) 3070, n(P2N) 1099, 853, n(PSe) 546 cm-1.

[(h6-C6Me6)RuCl( h2-P,E-Ph2PNHP(E)Ph2 )]PF6 [E=S(7),Se(8)]. A mixture of complex 5 or 6 (0.13 mmol) and AgPF6 (0.13 mmol) in acetone (15 mL) was stirred for 2 h. The AgCl formed was filtered off and the solution evaporated to dryness. The solid residue was dissolved in dichloromethane, chromatographed on neutral aluminum oxide and eluted with a mixture acetone/dichloromethane (1:10 mL). The solution obtained was concentrated and the complexes precipitated adding n-pentane. 7: Yield 84 mg (73%). Anal. Found: C, 50.41; H, 4.60; N, 1.65; S, 3.77%. C36H39ClF6NP3 RuS. Calc.: C, 50.21; H, 4.56; N, 1.63; S, 3.72%. NMR {(CD3)2CO, 23 °C}: 1H, d 2.00 [d, 18 H, Me, 4J(PH) = 0.72 Hz] and 7.69 [m, 20 H, Ph]. 31P{1H}, d 69.06 [d, PC, 2J(PAPC)= 36.34 Hz], 99.30 [d, PA] and -145.0 [sept, PF6-, 1J(PF) = 708 Hz]. IR(KBr) : n(NH) 3330, n(P2N) 1104, n(PS) 512,n(PF6) 840 and 557 cm-1. L= 119 cm2 mol-1 ohm-1. 8: Yield 79 mg (70%). Anal. Found: C, 48.05; H, 4.39; N, 1.57%. C36H39ClF6NP3 RuSe. Calc.: C, 47.61; H, 4.33; N, 1.54%. NMR{(CD3)2CO, 23 °C}: 1H, d 1.99 [d, 18 H, Me, 4J(PH) = 0.54 Hz] and 7.75 [m, 20 H, Ph]. 31P{1H}, d 52.15 [d, PC, 2J(PAPC)= 36.55 Hz, 1J(PSe) = 595.1 Hz], 101.65 [d, PA] and -145.0 [sept, PF6-, 1J(PF) = 708 Hz]. IR(KBr) : n(NH) 3267, n(P2N) 1102, n(PSe) 557, n(PF6) 840 and 560 cm-1. L= 121 cm2 mol-1 ohm-1.

[(h6-C6Me6)RuCl( h2-P,E-Ph2PNP(E)Ph2 )] [E=S(9),Se(10)]. The complexes can be prepared by the two following methods:

a) A mixture of complex 7 or 8 (0.11 mmol) and potassium terbutoxide (15 mg; 0.13 mmol) in dry dichloromethane (20 mL) was stirred at room temperature for 24 h. The reaction mixture was concentrated, chromatographed on neutral aluminum oxide and eluted with dichloromethane. The solution obtained was concentrated under vacuum and the complex precipitated by addition of dry n-pentane to the cold solution. Yield: 9, 54 mg (65%); 10, 50 mg (60%).

b) A mixture of complex 5 or 6 (0.38 mmol) and AgBF4 (75 mg; 0.39 mmol) in dry dichloromethane was stirred at room temperature for 2 h. The AgCl formed was filtered off through Kieselguhr and the concentrated solution chromatographed on neutral aluminum oxide and eluted with dichloromethane. The solution was vacuum concentrated and the complexes were precipitated adding dry n-hexane or diethyl ether. Yield: 9, 249 mg (87%); 10, 224 mg (78%).

9: Anal. Found: C, 60.53; H, 5.39; N, 1.94; S, 4.54%. C36H38ClNP2RuS. Calc.: C, 60.45; H, 5.36; N, 1.96; S, 4.48%. NMR {CD2Cl2, 23 °C}: 1H, d 1.81 [s, 18 H, Me] and 7.84 [m, 20 H, Ph]. 31P{1H}, d 62.72 [d, PC, 2J(PAPC)= 43.8 Hz] and 87.31 [d, PA]. IR(KBr) : n(P2N) 1105 and 808, n (PS) 574 cm-1. 10: Anal. Found: C, 56.80; H, 5.10; N, 1.82%. C36H38ClNP2RuSe. Calc.: C, 56.73; H, 5.03; N, 1.84%. NMR {CD2Cl2, 23 °C}: 1H, d 1.83 [s, 18 H, Me] and 7.54 [m, 20 H, Ph]. 31P{1H}, d 41.33 [d, PC, 2J(PAPC)= 45.2 Hz, 1J(PSe) = 468.7 Hz] and 87.31 [d, PA]. IR(KBr) : n(P2N) 1101 and 796, n(PSe) 545 cm-1.

[(h6-C6Me6)RuCl( h2-P,S-Ph2PNMeP(S)Ph2 )]PF6 (11). The complex can be prepared by the two methods described below.

a) A mixture of complex 5 (100 mg; 0.14 mmol), AgPF6 (25 mg; 0.15 mmol) and methyl iodide (1 mL; 16 mmol) in acetone (15 mL) was stirred for 36 h at room temperature. The solution was filtered through Kieselguhr and concentrated to a small volume. The addition of n-pentane to the cooled solution caused the precipitation of the complex. Yield 82 mg (67%).

b) A mixture of complex [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] (300 mg; 0.45 mmol), mdppaS (390 mg, 0.90 mmol) and AgPF6 (230 mg; 0.91 mmol) in acetone (10 mL) was stirred for 3h at room temperature. The AgCl formed was filtered off through Kieselguhr, concentrated and chromatographed on neutral aluminum oxide and eluted with dichloromethane-acetone (20:5 mL). The solution was evaporated to dryness, dissolved in acetone and the complex precipitated by addition of diethyl ether. Yield 700 mg (89%).

Anal. Found: C, 50.85; H, 4.77; N, 1.62; S, 3.70%. C37H41ClF6NP3 RuS. Calc.: C, 50.77; H, 4.72; N, 1.60; S, 3.66%. NMR (CDCl3, 23 °C): 1H, d 1.85 (s, 18 H, M), 2.62 [dd, 3 H, 3J(PH) = 1.54 Hz, 3J(PH) = 12 Hz] and 7.57 [m, 20H, Ph]. 31P{1H}, d 75.63 [d, PC, 2J(PAPC)= 50.4 Hz], 108.43 [d, PA] and -145.0 [sept, PF6-, 1J(PF) = 713 Hz]. IR(KBr) : n (P2N) 1104, n (PS) 517, n (PF6) 835 and 557 cm-1. L= 115 cm2 mol-1 ohm-1.

RESULTS AND DISCUSSION

The synthetic routes to the complexes are summarized in Schemes 1 and 2. The dinuclear ruthenium(II) complex [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] reacts with the ligand bis(diphenylphosphino)amine [NH(PPh2)2, dppa], in dichloromethane solution at low temperature (- 20 °C), by cleavage of the chlorine bridges to yield the neutral complex [(h6-C6Me6)RuCl 2{h1-P-NH(PPh2)2 }](1). Its 1H NMR spectrum confirm the monocoordination of the dppa ligand, showing a doublet of doublets resonance for the imine proton at d 4.8 ppm. Moreover, the 31P{1H} NMR spectrum shows two resonances corresponding of two different phosphorus atoms; the free phosphorus atom (PB) resonates as a doublet at higher field than the phosphorus bonded to the metal centre (PA). The PA atom shows considerable deshielding upon coordination (free ligand d 42.17 ppm), while the resonances of the free phosphorus PB is shifted to high field. All 31P{1H} NMR data of the isolated complexes are given in Table 1.

Scheme 1. i)dppa, ii)dppa/AgPF6, iii) AgPF6, iv)tBuOK, v)HPF6, vi)MeI, vii) dppma/AgPF6

TABLE I. 31P{1H} NMR chemical shifts (d ppm) and coupling constants (Hz) of the isolated complexes.a

a Measured in CDCl3 at room temperature. Chemical shifts relative to H3PO4 (85%) in D2O as external standard. All cationic complexes show a septuplet resonance at ca. d -145 ppm assigned to the PF6 anion. b CD2Cl2. c 1J(PSe)=774.3 Hz. d (CD3)2CO. e 1J(PSe) = 595.1 Hz. f 1J(PSe) = 468.7 Hz.

Complex 1 reacts in acetone solution with AgPF6 with abstraction of one chloride ligand to give a cationic compound with the ligand acting in its bidentate P,P-donor form, [(h6-C6Me6)RuCl{h 2-P,P-NH(PPh2)2}] PF6(2). The 1H NMR spectrum of complex 2 exhibits a triplet signal at d 10.1 ppm assigned to the imine proton and the 31P{1H} NMR spectrum shows a singlet resonance for the equivalent P atoms at d 54.65 ppm.

The reaction of complex 2 with potassium terbutoxide in dry dichloromethane caused the deprotonation of the coordinated dppa ligand with formation of the neutral complex [(h6-C6Me6)RuCl{h 2-P,P-N(PPh2)2}](3 ). As expected, in the 31P{1H} NMR spectrum the resonance of the equivalent phosphorus atoms in the anionic bidentate ligand is shifted to high field, d 20.18 ppm, relative to the starting complex. Complex 3 is easily protonated with HPF6 regenerating the starting cationic compound 2. Moreover, the reaction of complex 3 with methyl iodide caused the N-methylation of the coordinated ligand, affording the complex [(h6-C6Me6)RuCl{h 2-P,P-NMe(PPh2)2}]I. This compound, as the hexafluorophosphate derivative, can be prepared by direct reaction of the dinuclear complex [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] with the preformed dppma ligand in the presence of AgPF6, [(h6-C6Me6)RuCl(h 2-P,P-NMe(PPh2)2}]PF 6 (4). The 1H NMR spectrum of complex 4 shows a triplet resonance at d 2.89 (3JPH = 9.7 Hz) ppm assigned to the methyl group of the ligand, together with the signals of C6Me6 and Ph rings and the 31P{1H} NMR spectrum exhibits a singlet resonance at d 76.42 ppm.

When the dppma ligand was reacted with [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] in chloroform solution at low temperature (-20°C), the very unstable neutral complex [(h6-C6Me6)RuCl2(h 1-P-NMe(PPh2)2}] is formed. This complex rapidly tranforms into the cationic compound [(h6-C6Me6)RuCl(h 2-P,P-NMe(PPh2)2}]Cl. The neutral complex only was detected when the reaction was carried out in CDCl3 at low temperature in a NMR tube. The 31P{1H} NMR spectrum shows two doublet of doublets at d 54.18 and 84.10 ppm (2JPP = 37.2 Hz) assigned to free and coordinated P atoms, respectively. After a few minutes the singlet signal of the cationic compound appears at d 76.42 ppm. The doublet resonances of the neutral complex disappear after 30 min at - 20°C.

When the ligand dppa acts as a unidentate P-donor ligand it is possible that reacts by the un-coordinated P atom. Thus, complex 1 reacts with elemental sulphur or selenium in diethyl ether giving the P-coordinate monosulphide or monoselenide ligands, leading to complexes of the type [{(h6-C6Me6)RuCl2( h1-P-PPh2NHP(E)Ph2 )] [E = S(5), Se(6)]. The 31P{1H} NMR spectra of these complexes show that the oxidation of the free PC(III) atom to form the un-coordinated P(V)E group caused a shifted of their resonances to low field together with an increasing of the P-P coupling. All selenium derivatives exhibit the expected P-Se coupling, which provide valuable assistance for the assignement of the phosphorus resonances.

Scheme 2. i)E=S,Se, ii)AgPF6/solv., iii)AgPF6/dry solv., iv)MeI/AgPF6, v) MeI/NaPF6


Interestingly, the treatment of these compounds with AgPF6 affords two different type of complexes according of the purity of the used solvents. When the reaction was carried out in acetone or dichloromethane without purification, cationic complexes of the type [{(h6-C6Me6)RuCl(h 2-P,E-PPh2NHP(E)Ph2)]PF 6 [E = S(7), Se(8)] were obtained. If the reaction was carried out in dry solvents, the bidentate coordination of the ligands occurs with simultaneous loss of the imine proton to give the neutral compounds [{(h6-C6Me6)RuCl(h 2-P,E-PPh2NP(E)Ph2)] [E = S(9), Se(10)]. This behaviour is probably due to the increasing acidity of the imine proton produced by coordination of the PE group, and in non dried solvents the anionic coordinated ligands are hydrolyzed in the presence of low quantities of water. As expected, complexes 7 and 8 are deprotonated with KButO in dry solvents to form complexes 9 and 10, respectively, which in turn are easily protonated with HPF6 to regenerate the starting complexes.

The 31P{1H} NMR spectra of complexes 7 and 8 show a deshielding of the PC resonance upon coordination of the PCE group to the metal center. The shifting of this resonance to lower field is probably due to the chelate ring stabilizing effect.8 The spectrum of complex 8 shows that the satellite 1J(PSe) coupling decrease to ca. 170 Hz compared with the starting complex 6. This diminution could be attributed to a decreasing of the P=Se double bond character upon coordination.5d

On the other hand, the 31P{1H} NMR spectra of complexes 9 and 10 show that the loss of the imine proton increases the electronic density on the metallocycle ring producing a shielding of the phosphorus resonances spectra to high field respect to protonated complexes. In a similar fashion to dppa complexes, in these complexes the N-atom of the ligand possesses sufficient electron density for further reaction with an electrophile. Thus, the N-methylation of the coordinated dppaS ligand was carried out by reaction of complex 5 in dry acetone with AgPF6 in the presence of large excess of MeI, affording the corresponding cationic complex [{(h6-C6Me6)RuCl(h 2-P,S-PPh2NMeP(S)Ph2)]PF 6 (11). This compound can be alternatively prepared by reaction of the dinuclear complex [{(h6-C6Me6)Ru(µ-Cl)Cl} 2] with AgPF6 and the preformed ligand dppmaS [PPh2NMeP(S)Ph2]. The 1H NMR spectrum of complex 11 shows a doublet of doublets signal at d 2.62 ppm and the 31P{1H} NMR spectrum shows two doublets signals at d 75.63 and 108.43 ppm, assigned to PC and PA atoms, respectively.

CONCLUSIONS

We have shown that the bis(diphenylphosphino)amine NH(PPh2)2 and its monochalcogenide derivatives PPh2NHP(E)Ph2 (E= S, Se) have the potential to coordinate to the fragment "(C6Me6)Ru" in a variety of bonding modes. In both cases a facile deprotonation of the amine proton of the coordinated chelate ligands generate neutral complexes. In these compounds the N-atom possesses a sufficient electron density to form N-methyl derivatives by reaction with methyl iodide. Further studies are currently in progress on the synthesis and structural determinations of complexes containing similar isoelectronic organometallic fragments.

*Author to whom correspondence should be addressed. jmvalder@puc.cl

ACKNOWLEDGEMENTS

This work was supported by the Fondo de Desarrollo Científico y Tecnológico (Fondecyt), Chile (Grants N 8980007 and 2970079).

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