Diazo complexes of osmium: preparation of binuclear derivatives with bis(aryldiazene) and bis(aryldiazenido) bridging ligands

Inorganica Chimica Acta 357 (2004) 1119–1133 www.elsevier.com/locate/ica

Diazo complexes of osmium: preparation of binuclear derivatives with bis(aryldiazene) and bis(aryldiazenido) bridging ligands Gabriele Albertin *, Stefano Antoniutti, Mara Boato Dipartimento di Chimica, Universit
a Ca’ Foscari di Venezia, Dorsoduro 2137, 30123 Venezia, Italy Received 22 July 2003; received in revised form 24 September 2003; accepted 4 October 2003

Abstract Depending on experimental conditions and the nature of the phosphite, the reaction of OsH2 P4 [P ¼ P(OEt)3 and PPh(OEt)2 ] with bis(aryldiazonium) salts [N2 Ar–ArN2 ](BF4 )2 [Ar–Ar ¼ 4,40 -C6 H4 –C6 H4 , 4,40 -(2-CH3 )C6 H3 –C6 H3 (2-CH3 ), 4,40 -C6 H4 –CH2 – C6 H4 and 1,5-C10 H6 ] afford the cis and the trans binuclear [{OsHP4 }2 (l-HN@NAr–ArN@NH)](BPh4 )2 1, 2 aryldiazene derivatives. These complexes 1, 2 further react with the mono(diazonium) (4-CH3 C6 H4 N2 )BF4 salt to give the bis(aryldiazene) [{Os(4CH3 C6 H4 N@NH)P4 }2 (l-HN@NAr–ArN@NH)](BPh4 )4 3, 4 derivatives. Binuclear bis(aryldiazenido) [{OsP4 }2 (l-N2 Ar– ArN2 )](BPh4 )2 (6) [P ¼ P(OEt)3 ; Ar–Ar ¼ 4,40 -C6 H4 –C6 H4 , 4,40 -C6 H4 –CH2 –C6 H4 ] complexes were prepared by deprotonating with NEt3 the nitrile-diazene [{Os(4-CH3 C6 H4 CN)P4 }2 (l-HN@NAr–ArN@NH)](BPh4 )4 (5) derivatives. The aryldiazenido compounds 6 react with HCl to give the new aryldiazene [{OsClP4 }2 (l-HN@NAr–ArN@NH)](BPh4 )2 (7) derivatives. The characterisation of the complexes by IR and 1 H, 31 P, 15 N NMR data is also discussed. The reaction of the hydride OsH2 (PPh2 OEt)4 with mono(diazonium) salts was also studied and led exclusively to the mono(aryldiazene) [OsH(ArN@ NH)(PPh2 OEt)4 ]BPh4 (8) (Ar ¼ C6 H5 , 4CH3 C6 H4 ) derivatives. Spectroscopic data (1 H, 31 P, 15 N NMR) on 15 N-labelled derivatives suggest the presence of two isomers with the N-bonded and the p-bonded ArN@NH ligand, respectively. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Osmium; Aryldiazene; Aryldiazenido; Binuclear complexes

1. Introduction The chemistry of transition metal complexes containing diazene, ArN@NH, diazenido, ArN2 , or other partially reduced dinitrogen ligands continues to attract considerable attention, not only for the relationship with the intermediates of the nitrogen fixation process, but also for the different coordination modes and chemical reactivity that this class of complexes may exhibit [1–3]. A number of studies have been reported in the recent years involving mainly mononuclear complexes obtained from the reaction of common mono(aryldiazonium) salts ArNþ 2 with an appropriate precursor [1,2]. Less is known [3d,3e,4,5] on the behaviour of bis(aryl*

Corresponding author. Tel.: +39-041-234-8555; fax: +39-041-2348917. E-mail address: [email protected] (G. Albertin). 0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2003.10.002

diazonium) salts [N2 Ar–ArN2 ]2þ of the type of Chart 1, and no data are reported for the osmium, although these bis(aryldiazonium) molecule can potentially give rise to di- or polynuclear compounds, in which the bridging unit may induce new properties on the same NN group or on the corresponding complexes. We are active in this research area since 1984 [3,5,6] and have reported the synthesis and reactivity of both mono- and binuclear diazo complexes of several metals, such as Mn(I), Re(I), Fe(II), Ru(II), Co(I) and Ir(III). Also mononuclear aryldiazene and aryldiazenido osmium complexes [7] of the type [Os(ArN@NH)2 P4 ]2þ , [OsH(ArN@NH)P4 ]þ and [Os(ArN2 )P4 ]þ [P ¼ P(OEt)3 and PPh(OEt)2 ] were prepared from the reaction of dihydride OsH2 P4 with the common mono(aryldiazonium) cations. We have now extended these studies to the use of bis(aryldiazonium) cations of the type of Chart 1, with the aim to test whether binuclear

1120

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

H3C +N

N2+

2

+N

N2+

2

N2+ +N

2

CH2

CH3

N2+

cases with downfield shifts considered positive. The SwaN-MR software package [10] was used to treat NMR data. The conductivities of 10
3 M solutions of the complexes in CH3 NO2 at 25 °C were measured with a Radiometer CDM 83. 2.2. Synthesis of complexes

N2+ Chart 1.

complexes can be obtained and, in case, to compare the results with those of mononuclear derivatives. The results of these studies, which also include the reactivity of the dihydride OsH2 (PPh2 OEt)4 with aryldiazonium cations, are reported here.

2. Experimental 2.1. General considerations and physical measurements All synthetic work was carried out in an appropriate atmosphere (Ar, N2 ) using standard Schlenk techniques or a vacuum atmosphere drybox. Once isolated, the complexes were found to be relatively stable in air, but were stored in an inert atmosphere at )25 °C. All solvents were dried over appropriate drying agents, degassed on a vacuum line, and distilled into vacuum-tight storage flasks. (NH4 )2 OsCl6 was a Johnson Matthey product, used as received. Phosphines, PPh(OEt)2 and the PPh2 OEt, were prepared by the method of Rabinowitz and Pellon [8], while P(OEt)3 was an Aldrich product purified by distillation under nitrogen. Diazonium salts were prepared in the usual way [9]. The related bis(diazonium) salts [N2 Ar–ArN2 ](BF4 )2 [Ar–Ar ¼ 4,40 -C6 H4 –C6 H4 , 4,40 -(2-CH3 )C6 H3 –C6 H3 -(2CH3 ), 4,40 -C6 H4 –CH2 –C6 H4 , 1,5-C10 H6 ] were prepared by treating the amine precursors H2 NAr–ArNH2 with NaNO2 , as described in the literature for common mono(diazonium) salts. The labelled diazonium tetrafluoroborates (C6 H5 NB15 N)BF4 and [4,40 -15 NBNC6 H4 –C6 H4 NB15 N](BF4 )2 were prepared from Na15 NO2 (99% enriched, CIL) and the appropriate amine. Alternatively, the (C6 H5 15 NBN)BF4 salt was prepared from NaNO2 and C6 H5 15 NH2 . Other reagents were purchased from commercial sources in the highest available purity and used as received. Infrared spectra were recorded on a Nicolet Magna 750 FTIR spectrophotometer. NMR spectra (1 H, 31 P, 15 N) were obtained on a Bruker AC200 spectrometer at temperatures between )90 and +30 °C, unless otherwise noted. 1 H spectra are referred to internal tetramethylsilane; 31 P{1 H} chemical shifts are reported with respect to 85% H3 PO4 , while 15 N with respect to CH3 15 NO2 , in both

The OsH2 P4 [P ¼ P(OEt)3 ,PPh(OEt)2 and PPh2 OEt] compounds were prepared following the method previously reported [7,11]. To avoid the formation of byproducts, the reactions with aryldiazonium cations were carried out starting from very low temperature ()196 °C). 2.2.1. cis-[{OsH[P(OEt)3 ]4 }(l-HN@NAr–ArN@NH)] (BPh4 )2 (1) [Ar–Ar ¼ 4,40 -C6 H4 –C6 H4 (a), 4,40 -(2CH3 )C6 H3 –C6 H3 -(2-CH3 ) (b), 4,40 -C6 H4 –CH2 –C6 H4 (c), 1,5-C10 H6 (d)] In a three-necked 25-ml round-bottomed flask were placed solid samples of OsH2 [P(OEt)3 ]4 (86 mg, 0.1 mmol) and of the appropriate bis(aryldiazonium) salt [N2 Ar–ArN2 ](BF4 )2 (0.05 mmol) and the flask was cooled to )196 °C. Acetone (7 ml), or dichloromethane (7 ml) in the case of 1c and 1d, was added and the reaction mixture, brought to room temperature, stirred for 4 h. The solvent was removed under reduced pressure to give an oil which was triturated with ethanol containing an excess of NaBPh4 (68 mg, 0.2 mmol). A red solid slowly separated out from the resulting solution which was filtered and crystallised from CH2 Cl2 and ethanol; yield P 90% (Found: C, 50.50; H, 6.81; N, 2.08C108 H172 B2 N4 O24 Os2 P8 (1a) requires: C, 50.66; H, 6.77; N, 2.19. KM ¼ 125 S cm2 mol
1 . Found: C, 51.15; H, 6.98; N, 2.09%. C110 H176 B2 N4 O24 Os2 P8 (1b) requires: C, 51.04; H, 6.85; N, 2.16. KM ¼ 119 S cm2 mol
1 . Found: C, 50.65; H, 6.90; N, 2.11%. KM ¼ 117 S cm2 mol
1 . C109 H174 B2 N4 O24 Os2 P8 (1c) requires: C, 50.85; H, 6.81; N, 2.18. Found: C, 50.08; H, 6.85; N, 2.13%. C106 H170 B2 N4 O24 Os2 P8 (1d) requires: C, 50.24; H, 6.76; N, 2.21. KM ¼ 120 S cm2 mol
1 ). 2.2.2. cis-[{OsH[P(OEt)3 ]4 }(l-4,40 -H15 N@NC6 H4 – 15 C6 H4 N@ NH)](BPh4 )2 (1a1 ) This complex was prepared exactly like the related unlabelled 1a using [4,40 -15 NBNC6 H4 –C6 H4 NB15 N] (BF4 )2 diazonium salt; yield P85%. 2.2.3. cis-[{OsH[PPh(OEt)2 ]4 }(l-HN@NAr–ArN@NH)] (BPh4 )2 (2) [Ar–Ar¼ 4,40 -C6 H4 –C6 H4 (a), 4,40 -(2CH3 )C6 H3 –C6 H3 (2-CH3 ) (b), 1,5-C10 H6 (d)] In a 25-ml three-necked round-bottomed flask were placed solid samples of OsH2 [PPh(OEt)2 ]4 (98 mg, 0.1 mmol) and of the appropriate bis(aryldiazonium) salt [N2 Ar–ArN2 ](BF4 )2 (0.05 mmol) and the flask was cooled to )196 °C. Dichloromethane (7 ml) was added

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

and the reaction mixture, brought to room temperature, stirred for about 4 h. The solvent was removed under reduced pressure to give an oil which was treated with ethanol containing an excess of NaBPh4 (68 mg, 0.2 mmol). A red solid slowly separated out from the resulting solution which was filtered and crystallised from CH2 Cl2 and ethanol; yield P80% (Found: C, 59.89; H, 6.22; N, 1.85%. C140 H172 B2 N4 O16 Os2 P8 (2a) requires: C, 59.70; H, 6.15; N, 1.99. KM ¼ 122 S cm2 mol
1 . Found: C, 59.78; H, 6.29; N, 1.86%. C142 H176 B2 N4 O16 Os2 P8 (2b) requires: C, 59.95; H, 6.24; N, 1.97. KM ¼ 124 S cm2 mol
1 . Found: C, 59.58; H, 6.19; N, 2.05%. C138 H170 B2 N4 O16 Os2 P8 (2d) requires: C, 59.39; H, 6.14; N, 2.01%. KM ¼ 117 S cm2 mol
1 ). 2.2.4. trans-[{OsH[PPh(OEt)2 ]4 }(l-HN@NAr–ArN@ NH)](BPh4 )2 (2-trans) [Ar–Ar ¼ 4,40 -C6 H4 –C6 H4 (a), 4,40 -C6 H4 –CH2 –C6 H4 (c), 1,5-C10 H6 (d)] These complexes were prepared exactly like the related cis-complexes 2 using acetone as solvent instead of dichloromethane; yield P 85% (Found: C, 59.92; H, 6.20; N, 1.90%. C140 H172 B2 N4 O16 Os2 P8 (2a-trans) requires: C, 59.70; H, 6.15; N, 1.99. KM ¼ 125 S cm2 mol
1 . Found: C, 59.66; H, 6.15; N, 1.91C141 H174 B2 N4 O16 Os2 P8 (2ctrans) requires: C, 59.83; H, 6.20; N, 1.98. KM ¼ 120 S cm2 mol
1 . Found: C, 59.23; H, 6.24; N, 1.95%. C138 H170 B2 N4 O16 Os2 P8 (2d-trans) requires: C, 59.39; H, 6.14; N, 2.01. KM ¼ 116 S cm2 mol
1 ). 2.2.5. trans-[{OsH[PPh(OEt)2 ]4 }(l-4,40 -H15 N@NC6 H4 – C6 H4 N@15 NH)](BPh4 )2 (2a1 -trans) This complex was prepared exactly like the related unlabelled 2a-trans using [4,40 -15 NBNC6 H4 –C6 H4 NB 15 N](BF4 )2 diazonium salt; yield P 80%. 2.2.6. [{Os(4-CH3 C6 H4 N@NH)P4 }2 (l-HN@NAr–ArN @NH)](BPh4 )4 (3, 4) [P ¼ P(OEt)3 and Ar–Ar ¼ 1,5C10 H6 (3d); P ¼ PPh(OEt)2 and Ar–Ar ¼ 4,40 -C6 H4 – C6 H4 (4a)] In a 25-ml three-necked round-bottomed flask were placed solid samples of the appropriate binuclear complex [{OsHP4 }2 (l-NH@NAr–ArN@NH)](BPh4 )2 (0.1 mmol) and of a large excess of the aryldiazonium salt [4CH3 C6 H4 N2 ]BF4 (0.206 g, 1 mmol) and the flask was cooled to )196 °C. Acetone (15 ml) was added and the reaction mixture, brought to room temperature, stirred for 20 h. The solvent was removed under reduced pressure to give an oil which was treated with ethanol (3 ml) containing an excess of NaBPh4 (51 mg, 0.15 mmol). A red-brown solid slowly separated out from the resulting solution which was filtered and crystallised from CH2 Cl2 and ethanol; yield P60% (Found: C, 59.02; H, 6.70; N, 3.36%. C168 H224 B4 N8 O24 Os2 P8 (3d) requires: C, 59.16; H, 6.62; N, 3.28. KM ¼ 238 S cm2 mol
1 .

1121

Found: C, 65.45; H, 6.24; N, 2.97%. C202 H226 B4 N8 O16 Os2 P8 (4a) requires: C, 65.69; H, 6.17; N, 3.03. KM ¼ 245 S cm2 mol
1 ). 2.2.7. [OsH(4-CH3 C6 H4 CN){P(OEt)3 }4 ]BPh4 An equimolar amount of CF3 SO3 CH3 (0.3 mmol, 34 ll) was added to a solution of OsH2 [P(OEt)3 ]4 (0.3 mmol, 0.25 g) in 10 ml of toluene cooled to )196 °C. The reaction mixture was brought to room temperature, stirred for 1 h and then an excess of 4CH3 C6 H4 CN (0.9 mmol, 107 ll) added. After 2 h of stirring, the solvent was removed under reduced pressure to give an oil which was triturated with ethanol (3 ml) containing an excess of NaBPh4 (0.8 mmol, 0.28 g). A white solid slowly separated out from the resulting solution, which was filtered and crystallised from CH2 Cl2 and ethanol; yield P 85% (Found: C, 52.18; H, 6.93; N, 1.01%. C56 H88 BNO12 OsP4 requires: C, 52.05; H, 6.86; N, 1.08. KM ¼ 54:7 S cm2 mol
1 . IR (KBr) cm
1 : 2262 w mCN , 1958 m mOsH . 1 H NMR [(CD3 )2 CO, 25 °C] d: 7.80–6.70 (m, 24H, Ph), 4.40– 4.00 (m, 24H, CH2 ), 2.43 (s, 3H, CH3 p-tolyl), 1.32, 1.28, 1.25 (t, 36H, CH3 ), )8.82 to )9.61 (m, 1H, H
). 31 P{H }NMR [(CD3 )2 CO, 25 °C] d: AB2 C spin system, dA 106.5, dB 104.4, dC 97.4, JAB ¼ 31:4, JAC ¼ 30:0, JBC ¼ 44:5 Hz. 2.2.8. [{Os(4-CH3 C6 H4 CN)[P(OEt)3 ]4 }(l-HN@NAr –ArN@NH)](BPh4 )4 (5) [Ar–Ar ¼ 4,40 -C6 H4 –C6 H4 (a), 4,40 -C6 H4 –CH2 –C6 H4 (c)] Solid samples of [OsH(4-CH3 C6 H4 CN){P(OEt)3 }4 ] BPh4 (0.130 g, 0.1 mmol) and of the appropriate bis(aryldiazonium) salt [N2 Ar–ArN2 ](BF4 )2 (0.05 mmol) were placed in a 25-ml three-necked roundbottomed flask and, after cooling to )196 °C, acetone (15 ml) was added. The reaction mixture was brought to room temperature, stirred for about 20 h and then the solvent removed under reduced pressure. The oil obtained was treated with ethanol containing an excess of NaBPh4 (68 mg, 0.2 mmol). By stirring of the resulting solution, a red-orange solid separated out, which was filtered and crystallised from CH2 Cl2 and ethanol: yield P 70% (Found: C, 60.00; H, 6.71; N, 2.35. C172 H224 B4 N6 O24 Os2 P8 (5a) requires: C, 60.21; H, 6.58; N, 2.45. KM ¼ 239 S cm2 mol
1 . Found: C, 60.12; H, 6.68; N, 2.29%. C173 H226 B4 N6 O24 Os2 P8 (5c) requires: C, 60.31; H, 6.61; N, 2.44. KM ¼ 253 S cm2 mol
1 ). 2.2.9. [{Os(4-CH3 C6 H4 CN)[P(OEt)3 ]4 }2 (l-4,40 -H15 N@NC6 H4 –C6 H4 N@15 NH)](BPh4 )4 (5a1 ) This complex was prepared exactly like the unlabelled 5a using [4,40 -15 NBNC6 H4 –C6 H4 NB15 N](BF4 )2 diazonium salt; yield P65%.

1122

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

2.2.10. [{Os[P(OEt)3 ]4 }2 (l-N2 Ar–ArN2 )](BPh4 )2 (6) [Ar–Ar ¼ 4,40 -C6 H4 –C6 H4 (a), 4,40 -C6 H4 –CH2 –C6 H4 (c)] An excess of triethylamine (0.28 ml, 2 mmol) was added to a solution of the appropriate binuclear [{Os (4-CH3 C6 H4 CN)[P(OEt)3 ]4 }2 (l-HN@NAr–ArN@NH)] (BPh4 )4 complex (0.1 mmol) in 10 ml of CH2 Cl2 and the reaction mixture stirred for 2 h. A white solid ([NHEt3 ]BPh4 ) slowly separated out which was filtered and rejected. The solution was evaporated to dryness leaving a brown oil which was treated with ethanol (5 ml). By slow cooling of the resulting solution, red-brown crystals were obtained which were filtered and dried under vacuum; yield P60% (Found: C, 50.85; H, 6.70; N, 2.23%. C108 H168 B2 N4 O24 Os2 P8 (6a) requires: C, 50.74; H, 6.62; N, 2.19. KM ¼ 126 S cm2 mol
1 . Found: C, 50.70; H, 6.75; N, 2.29%. C109 H170 B2 N4 O24 Os2 P8 (6c) requires: C, 50.93; H, 6.67; N, 2.18. KM ¼ 118 S cm2 mol
1 ).

pressure. The oil obtained was treated with ethanol (2 ml) containing an excess of NaBPh4 (68 mg, 0.2 mmol). An orange solid slowly separated out from the resulting solution, which was filtered and crystallised from CH2 Cl2 and ethanol; yield P70% (Found: C, 67.05; H, 5.77; N, 1.90%. C86 H87 BN2 O4 OsP4 (8e) requires: C, 67.18; H, 5.70; N, 1.82. KM ¼ 50:9 S cm2 mol
1 . Found: C, 67.56; H, 6.70; N, 1.77%. C87 H89 BN2 O4 OsP4 (8f) requires: C, 67.35; H, 5.78; N, 1.81. KM ¼ 54:3 S cm2 mol
1 ). 2.2.15. [OsH(C6 H5 N@15 NH)(PPh2 OEt)4 ]BPh4 (8e1 ) and [OsH(C6 H5 15 N@NH)(PPh2 OEt)4 ]BPh4 (8e2 ) These complexes were prepared exactly like the related unlabelled 8e using the [C6 H5 NB15 N]BF4 and [C6 H5 15 NBN]BF4 diazonium salts, respectively; yield P60%.

3. Results and discussion 2.2.11. [{Os[P(OEt)3 ]4 }2 (l-4,40 -15 NBNC6 H4 –C6 H4 N B15 N)](BPh4 )2 (6a1 ) This complex was prepared exactly like the related unlabelled 6a using 5a1 as precursor; yield P 55%. 2.2.12. [{OsCl[P(OEt)3 ]4 }2 (l-4,40 -HN@NC6 H4 –C6 H4 N@NH)](BPh4 )2 (7a) To a solution of the aryldiazenido [{Os[P(OEt)3 ]4 }2 (l-4,40 -N2 C6 H4 –C6 H4 N2 )](BPh4 )2 (6a) complex (128 mg, 0.05 mmol) in 10 ml of CH2 Cl2 cooled to )196 °C was added a solution of HCl 0.1 M in diethyl ether (1.1 ml, 0.11 mmol). The reaction mixture was brought to room temperature, stirred for about 4 h and then the solvent removed under reduced pressure. The oil obtained was treated with ethanol (3 ml) giving a redbrown solution which was stirred at 0 °C until a solid separated out, which was filtered and dried under vacuum; yield P 70% (Found: C, 49.18; H, 6.45; N, 2.06; Cl, 2.88%. C108 H170 B2 Cl2 N4 O24 Os2 P8 (7a) requires: C, 49.34; H, 6.52; N, 2.13; Cl, 2.70. KM ¼ 124 S cm2 mol
1 ). 2.2.13. [{OsCl[P(OEt)3 ]4 }2 (l-4,40 -H15 N@NC6 H4 –C6 H4 N@15 NH)](BPh4 )2 (7a1 ) This complex was prepared exactly like the related unlabelled 7a by reacting 6a1 with HCl; yield P65%. 2.2.14. [OsH(ArN@NH)(PPh2 OEt)4 ]BPh4 (8) [Ar ¼ C6 H5 (e), 4-CH3 C6 H4 (f)] In a 25-ml three-necked round-bottomed flask were placed solid samples of OsH2 (PPh2 OEt)4 (111 mg, 0.1 mmol) and an excess of the appropriate aryldiazonium salt [ArN2 ]BF4 (0.3 mmol). The flask was cooled to )196 °C and CH2 Cl2 (20 ml) was added. The reaction mixture was brought to room temperature, stirred for 4 h and then the solvent was removed under reduced

Hydride species OsH2 P4 quickly react with bis(aryldiazonium) salts [N2 Ar–ArN2 ](BF4 ) to give the binuclear complexes [(OsHP4 )2 (l-NH@NAr–ArN@NH)] (BPh4 )2 (1), (2), containing the bis(diazene) bridging unit, as shown in Scheme 1. Studies on the reaction course indicate that, both in acetone and in CH2 Cl2 as solvents, the reaction proceeds, but the nature of the products depends both from the phosphine and the solvent used. While with P(OEt)3 exclusively the complexes I (Chart 2), containing the hydride and the diazene in a mutually cis position, were obtained both in acetone and CH2 Cl2 as solvent, with PPh(OEt)2 the cis complexes I were obtained only in CH2 Cl2 . In acetone, instead, complexes with geometry II (Chart 2) (2-trans), containing the hydride and the diazene in a mutually trans position, were obtained. Since the diazene complexes 1, 2 do not isomerise in solution even after some days, the formation of different isomers changing the nature of the solvent may suggest that a different mechanism of insertion of –ArN2 þ into the OsH bond can take place. This different mechanism may also explain the formation of the two stereoisomers A and B (Chart 3) in the case of complexes 2-trans, obtained in acetone, which will be discussed below. It is worth to note that the hydride OsH2 (PPh2 OEt)4 , containing the bulky phosphine PPh2 OEt, does not give

2OsH2P4 + [N2Ar-ArN2]2+ [{OsHP4}2(µ-NH=NAr-ArN=NH)]2+ eq.1 1, 2 Scheme 1. P ¼ P(OEt)3 (1), PPh(OEt)2 (2); Ar–Ar ¼ 4,40 -C6 H4 –C6 H4 (a), 4,40 -(2-CH3 )C6 H3 –C6 H3 -(2-CH3 ) (b), 4,40 -C6 H4 –CH2 –C6 H4 (c), 1,5-C10 H6 (d).

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

P P

P Os

P

H

H

N H

H N

N

Ar

Ar

N

2+

P Os

P

P P

I

1, 2

H

P

P N

Os P

Ar

Ar

H Os

N N

N P

2+

P

P

H

H

P P

II

2-trans Chart 2.

H Os

H

N

Os N

N

Ar

N Ar

A (cis)

B (trans)

2-trans Chart 3.

binuclear complexes in the reaction with bis(aryldiazonium) salt, but only an intractable mixture of products which was not separated. The complexes 1, 2, which were isolated as BPh4 salts, are stable both as solids and in solution of polar organic solvents, where they behave as 2:1 electrolytes [12]. Analytical and spectroscopic data (Table 1) support the proposed formulation, and the geometries I and II (Chart 2) in solution were also established. The IR spectra of the cis complexes 1, 2 show a weak band at 2030–1965 cm
1 attributed to the stretching of the OsH bond. The 1 H NMR spectra confirm the presence of the hydride ligand, showing a complicated multiplet between 7 and 9 ppm due to the coupling with the phosphorus nuclei. In the spectra also appears a slightly broad signal in the high-frequency region, at 13–15 ppm, attributed to the NH diazene proton. Support for this assignment comes from the spectra of the labelled 1a1 complex, which show a doublet of multiplets centered at the same value (14.73 ppm) of the broad signal of the unlabelled 1a compound, with 1 J15 NH of 66 Hz, in agreement [1a,13,14] with the presence of a diazene ligand. In the temperature range between 20 and )80 °C, the 31 P NMR spectra appear as a multiplet which can be simulated using an A2 BC or AB2 C model, with the parameters reported in Table 1.

1123

On the basis of these data, a geometry of type I with the hydride and the aryldiazene ligand in a mutually cis position can be proposed for these binuclear complexes. Surprisingly, the 1 H NMR spectra of the trans complexes 2-trans show two NH signals between 14 and 15 ppm, each of which are split into a doublet in the labelled 2a1 -trans complex, with a 1 J15 NH value for both signals of 62 Hz. Furthermore, in the low-frequency region of the proton spectra are also present two quintets near )13 ppm, which are attributed to two hydride ligands, each coupled with four magnetically equivalent phosphorus nuclei. Finally, in the temperature range between +20 and )80 °C, the 31 P{1 H} NMR spectra of the trans complexes show two singlets with close values of chemical shift, each of which is split into one doublet in the labelled 2a1 -trans complex, due to the coupling with the 15 N nuclei of the diazene. It can be also noted that the ratio between the two diazene signals is similar to those between the two hydride and the two 31 P signals, and that close chemical shift values were observed for each couple of signals. These results may be interpreted on the basis of the existence of two isomers, each of which must contain the diazene and the hydride ligands in a mutually trans position, with four equivalent phosphite ligands. Two stereoisomers of the types A and B (Chart 3), with the H and the aryl substituent mutually in trans and in cis positions with respect to the N@N moiety, should give two different NH signals, as observed in our complexes. Since the complexes are binuclear, the existence of both isomers A and B bonded to the osmium centre should give four isomers, i.e. cis–cis, trans–trans, cis– trans and trans–cis, with the last two equivalent, as shown in Chart 4. The presence of these isomers for the 2-trans complexes is in agreement with both the 1 H and 31 P NMR spectra and finds a precedent [3d] in the rhenium diazodiazene [Re(CO)5
n Pn (HN@NAr–ArNBN)]2þ (n ¼ 1; 2; P ¼ phosphite) complexes, which were obtained using, also in this case, acetone as solvent. This precedent and the spectroscopic data support the hypothesis of the stereoisomers A and B affording the mixture of Chart 4. The binuclear complexes 1 and 2 still contain a hydride ligand which can potentially further react with aryldiazonium cations to afford bis(aryldiazene) derivatives. We therefore studied the reaction of mono(diazene) 1, 2 with p-tolyldiazonium salt and observed that the reaction slowly takes place to give the bis(aryldiazene) complexes [{Os(4-CH3 C6 H4 N@NH)P4 }2 (lHN@NAr–ArN@NH)](BPh4 )4 3, 4, which were isolated and characterised (Scheme 2). However, in the case of the PPh(OEt)2 ligand, although both the cis and trans complexes 2 react with the aryldiazonium cation, only with the cis were stable and isolable bis(aryldiazene) derivatives obtained.

1124

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

H P P H

P Os

P

H

H

N

N N

P

P

Ar

Ar

Os

N

2+

P

P

N

P

H

Ar

N P

Os

H

Os P

N

trans-trans

2+

H

H

P N

N

Ar

Ar

N

P P

N N

Os H

H

H

N P

N

P

P

P

Ar

P

P

cis-cis

P

Os P

H

2+

P

H

H

P

N P

P

Ar

N

Os P

H P

P Os

P

Ar

2+

P

P H

cis-trans

trans-cis

2-trans Chart 4.

[{OsHP4}2(µ-NH=NAr-ArN=NH)]2+

exc. ArN2+

P P

[{Os(ArN=NH)P4}2(µ-NH=NAr-ArN=NH)]4+ 3, 4 Scheme 2. P ¼ P(OEt)3 (3), PPh(OEt)2 (4); Ar ¼ 4-CH3 C6 H4 ; Ar– Ar ¼ 4,40 -C6 H4 – C6 H4 (a), 1,5-C10 H6 (d).

Os P

P

H

CH3

4+

H

P N N N N Ar Ar N Os N N N P H H3C H

P P

III

3, 4

The complexes are yellow-orange solids stable in the air and in solution of polar organic solvents, where they behave as 4:1 electrolytes [12]. Analytical and spectroscopic data support the proposed formulation. The 1 H NMR spectra confirm the presence of two diazene ligands, showing two slightly broad signals between 15 and 13 ppm. Furthermore, the 31 P{1 H }NMR spectra show a complicated multiplet which, in the case of 4a, can be simulated using an A2 BC model with the parameters reported in Table 1. On the basis of these data a geometry of type III (Chart 5) can be reasonably proposed for the bis(aryldiazene) derivatives 3 and 4. A comparison between the reactivity of both mono2þ ArNþ aryldiazonium ca2 and the bis-[N2 Ar–ArN2 ] tions toward the osmium dihydride OsH2 P4 shows that in both cases the facile insertion of one ArNþ 2 group takes place giving mononuclear hydride-diazene complexes [OsH(ArN@NH)P4 ]þ in one case [7], and binu-

Chart 5.

clear species with di-diazene as bridging unit of type 1 and 2 in the other. Difference was observed, instead, in the geometry of the complexes which result, with the P(OEt)3 ligand, always cis in both mono- [7] and binuclear complexes 1, while with the PPh(OEt)2 both the cis and trans geometries were obtained in the binuclear derivatives 2. Furthermore, the formation of two stereoisomers of the type A and B with a cis or trans arrangement of the substituents on the N@N group was also observed in binuclear complexes 2-trans. Finally, the second insertion of an ArNþ 2 group into the OsH bond of hydride-diazene species was observed in both mono- [7] and binuclear complexes affording, in every case, bis(aryldiazene) derivatives.

Table 1 IR and NMR spectroscopic data for osmium complexes Compound (1a)

(1a1 )

(1c)

(1d)

(2a)

cis-[{OsH[P(OEt)3 ]4 }2 (l-4,40 -H15 N@NC6 H4 – C6 H4 N@15 NH)](BPh4 )2

cis-[{OsH[P(OEt)3 ]4 }2 l-4,40 -HN@N-4,40 -(2CH3 )C6 H3 –C6 H3 (2-CH3 )N@NH](BPh4 )2

cis-[{OsH[P(OEt)3 ]4 }2 (l-4,40 -HN@NC6 H4 –CH2 – C6 H4 N@NH)](BPh4 )2

cis-[{OsH[P(OEt)3 ]4 }2 (l-1,5-HN@ NC10 H6 N@NH)](BPh4 )2

cis-[{OsH[PPh(OEt)2 ]4 }2 (l-4,40 -HN@NC6 H4 – C6 H4 N@NH)](BPh4 )2

Assignment

1

H NMRb; c d (ppm)/J (Hz)

Assignment

Spin system

31 P{1 H} NMRb;d d (ppm)/J (Hz)

1973 w

mOsH

14.75 m, br 4.32–3.98 m 1.34 t 1.31 t 1.23 t )7.95 to )8.70 m

NH CH2 CH3

A2 BCe

dA ¼ 106:8 dB ¼ 103:3 dC ¼ 101:4 JAB ¼ 45:3 JAC ¼ 31:5 JBC ¼
29:4

14.73 dm 1 J15 NH ¼ 66 4.30–4.00 m 1.33 t 1.30 t 1.22 t )7.95 to )8.70 m

NH CH2 CH3

A2 BCYe

dA ¼ 106:8 dB ¼ 103:3 dC ¼ 101:4 JAB ¼ 46:4 JAC ¼ 31:5 JAY ¼ 3:5 JBC ¼
29:4 JBY ¼ 49:4 JCY ¼ 2:5

A2 BCe

dA ¼ 107:8 dB ¼ 103:0 dC ¼ 100:4 JAB ¼ 45:0 JAC ¼ 31:5 JBC ¼
29:4

A2 BC

dA ¼ 104:4 dB ¼ 102:5 dC ¼ 101:8 JAB ¼ 32:7 JAC ¼ 44:7 JBC ¼ 29:5

A2 BCe

dA ¼ 107:0 dB ¼ 102:7 dC ¼ 100:9 JAB ¼ 46:1 JAC ¼ 31:2 JBC ¼
29:4

AB2 C

dA ¼ 125:8 dB ¼ 123:7 dC ¼ 120:1 JAB ¼ 18:9 JAC ¼ 23:6 JBC ¼ 31:1

1971 w

1978 w

1980 w

1965 w

2013 w

mOsH

mOsH

mOsH

mOsH

mOsH

H


H


14.66 m 4.33–3.98 m 2.64 s 1.34 t 1.30 t 1.21 t )7.93 to )8.73 m

NH CH2 CH3 CH3 phos

14.54 m 4.20–3.95 m 1.28 t 1.26 t 1.18 t )8.16 to )8.75 m

NH CH2 CH3

15.08 m, br 4.15 m 1.32 t 1.31 t 1.18 t )8.03 to )8.63 m

NH CH2 CH3

13.60 m, br 4.20–3.45 m 1.33 t 1.20 t 1.15 t 1.11 t )7.63 to )8.36 m

NH CH2 CH3

H


H


H


G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

(1b)

cis-[{OsH[P(OEt)3 ]4 }2 (l-4,40 -HN@NC6 H4 – C6 H4 N@NH)](BPh4 )2

IRa (cm
1 )

H
1125

Compound (2a-trans)

(2b)

(2c-trans)

(2d)

trans-[{OsH[PPh(OEt)2 ]4 }2 (l-4,40 H15 N@NC6 H4 –C6 H4 -N@ 15 NH)](BPh4 )2 f

cis-[{OsH[PPh(OEt)2 ]4 }2 (l-4,40 -HN@N(2CH3 )C6 H3 –C6 H3 -(2CH3 )N@NH)](BPh4 )2

trans-[{OsH[PPh(OEt)2 ]4 }2 (l-4,40 HN@NC6 H4 –CH2 –C6 H4 N@NH)](BPh4 )2

cis-[{OsH[PPh(OEt)2 ]4 }2 (l-1,5-HN@ NC10 H6 N@NH)](BPh4 )2

Assignment

1

H NMRb; c d (ppm)/J (Hz)

Assignment

Spin system

P{1 H} NMRb ;d d (ppm)/J (Hz)

2038 w

mOsH

14.83 br 14.75 br 3.82 m 3.68 m 1.20 t 1.08 t )13.29 qnt JPH ¼ 20 )13.47 qnt JPH ¼ 20

NH

A4 A4

122.5 s 122.3 s

14.83 d 1 J15 NH ¼ 62 14.75 d 1 J15 NH ¼ 62 3.82 m 3.67 m 1.20 t 1.08 t )13.28 qnt JPH ¼ 20 )13.48 qnt JPH ¼ 20

NH

A4 Y

122.5 d JAY ¼ 2 122.2 d JAY ¼ 2

2040 w

1973 w

2038 w

2030 w

mOsH

mOsH

mOsH

mOsH

CH2 CH3 H


A4 Y CH2 CH3 H


13.53 m 4.10–3.40 m 2.67 s 1.35 t 1.19 t 1.12 t 1.08 t )7.59 to )8.33 m

NH CH2 CH3 CH3 phos

14.65 m 4.03 s 3.80 m 3.67 m 1.17 t )13.57 qnt

NH CH2 CH2 phos

14.01 s, br 4.10–3.50 m 1.33 t 1.11 t 1.08 t )7.55 to )8.28 m

31

AB2 C

dA ¼ 128:0 dB ¼ 126:1 dC ¼ 122:1 JAB ¼ 19:6 JAC ¼ 21:3 JBC ¼ 30:5

A4

122.6 s

AB2 C

dA ¼ 125:0 dB ¼ 123:3 dC ¼ 119:7 JAB ¼ 19:2 JAC ¼ 23:1 JBC ¼ 31:0

H


CH3 H
NH CH2 CH3

H


G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

(2a1 -trans)

trans-[{OsH[PPh(OEt)2 ]4 }2 (l-4,40 HN@NC6 H4 –C6 H4 N@NH)](BPh4 )2

IRa (cm
1 )

1126

Table 1 (continued)

(2d-trans)

(3d)

2029 w

mOsH

cis-[{Os(4-CH3 C6 H4 N@NH) [P(OEt)3 ]4 }2 (l-1,5HN@NC10 H6 N@NH)](BPh4 )4

cis-[{Os(4-CH3 C6 H4 N@NH) [PPh(OEt)2 ]4 }2 (l4,40 -HN@NC6 H4 –C6 H4 N@NH)](BPh4 )4

15.25 s, br 15.11 s, br 4.00–3.30 m 1.21 t 1.20 t )13.02 qnt JPH ¼ 20 )13.42 qnt JPH ¼ 20

NH

H


15.02 m, br 14.67 s, br 4.40–4.00 m 2.44 s 1.43 t 1.35 t 1.15 t

NH

13.71 s, br 13.59 s, br 4.21 m 3.84 m 3.70 m 2.42 s 1.54 t 1.13 t 1.09 t

NH

14.56 s, br 4.30 m 2.45 s 1.43 t 1.38 t 1.29 t

NH CH2 CH3 CH3 phos

(5a1 )

cis-[{Os(4-CH3 C6 H4 CN)[P(OEt)3 ]4 }2 (l-4,40 H15 N@NC6 H4 -C6 H4 N@15 NH)](BPh4 )4

2266 w

mCN

14.58 dm 1 J15 NH ¼ 66 4.30 m 2.46 s 1.43 t 1.38 t 1.28 t

NH

14.10 brg 4.20–3.95 m 2.45 s 1.37 t 1.33 t 1.14 t

dA ¼ 109:8 dB ¼ 107:3 dC ¼ 107:0 JAB ¼ 33:7 JAC ¼ 36:0 JBC ¼ 33:1

A2 BC

dA ¼ 85:0 dB ¼ 83:1 dC ¼ 72:4 JAB ¼ 41:8 JAC ¼ 45:8 JBC ¼ 44:1

CH3 CH3 phos

mCN

mCN

A2 BC

CH2

2264 m

2264 w

95–70 m

CH2 CH3 CH3 phos

cis-[{Os(4-CH3 C6 H4 CN)[P(OEt)3 ]4 }2 (l-4,40 HN@NC6 H4 –C6 H4 N@NH)](BPh4 )4

cis-[{Os(4-CH3 C6 H4 CN)[P(OEt)3 ]4 }2 (l-4,40 HN@NC6 H4 -CH2 –C6 H4 N@NH)](BPh4 )4

122.4 s 121.5 s

CH2 CH3

(5a)

(5c)

A4 A4

83–71 m

CH2 CH3 CH3 phos

NH CH2 CH3 CH3 phos

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

(4a)

trans-[{OsH[PPh(OEt)2 ]4 }2 (l-1,5HN@NC10 H6 N@NH)](BPh4 )2

82–70 m

1127

Compound

IRa (cm
1 )

Assignment

1 H NMRb;c d (ppm)/J (Hz)

Assignment

Spin system

31 P{1 H} NMRb;d d (ppm)/J (Hz)

[{Os[P(OEt)3 ]4 }2 (l-4,40 -NBNC6 H4 – C6 H4 NBN)](BPh4 )2

1642 m

mN2

4.43–4.01 mg;h 1.38 t 1.37 t 1.35 t 1.21 t

CH2 CH3

ABC2 g;h

dA ¼ 105:2 dB ¼ 101:4 dC ¼ 92:6 JAB ¼ 47:7 JAC ¼ 40:6 JBC ¼ 37:2

(6a1 )

[{Os[P(OEt)3 ]4 }2 (l-4,40 -15 NBNC6 H4 – C6 H4 NB15 N)](BPh4 )2

1617 m

m15NBN

4.43–4.00 mg;h 4.06 m 1.38 t 1.37 t 1.35 t 1.21 t

CH2 CH3

ABC2 Yg; h

dA ¼ 105:2 dB ¼ 101:4 dC ¼ 92:6 JAB ¼ 47:8 JAC ¼ 40:6 JAY ¼ 39:0 JBC ¼ 37:2 JBY ¼ 27:0 JCY ¼ 10:2

(6c)

[{Os[P(OEt)3 ]4 }2 (l-4,40 -NBNC6 H4 –CH2 – C6 H4 NBN)](BPh4 )2

1643 m

mN2

4.05 mg ;h 1.32 t 1.29 t

CH2 CH3

ABC2 g;h

dA ¼ 104:6 dB ¼ 100:8 dC ¼ 94:1 JAB ¼ 48:0 JAC ¼ 40:5 JBC ¼ 36:4

(7a)

[{OsCl[P(OEt)3 ]4 }2 (l-4,40 -HN@NC6 H4 C6 H4 N@NH)](BPh4 )2

14.55 m, brg 4.13 m 1.34 t 1.30 t 1.21 t

NH CH2 CH3

AB2 Cg

dA ¼ 85:1 dB ¼ 83:4 dC ¼ 72:1 JAB ¼ 45:9 JAC ¼ 42:7 JBC ¼ 41:0

(7a1 )

[{OsCl[P(OEt)3 ]4 }2 (l-4,40 -H15 N@NC6 H4 – C6 H4 N@15 NH)](BPh4 )2

14.55 dmg 1 J15 NH ¼ 65 4.13 m 1.33 t 1.30 t 1.20 t

NH

AB2 CYg

dA ¼ 85:1 dB ¼ 83:4 dC ¼ 72:0 JAB ¼ 45:9 JAC ¼ 42:7 JAY ¼ 46:0 JBC ¼ 41:0 JBY ¼ 4:0 JCY ¼ 2:3

A4 e A4

109.6 s 96.7 s

(8e)

[OsH(C6 H5 N@NH)(PPh2 OEt)4 ]BPh4

2048 w

mOsH

14.29 s 13.52 s 3.36 m 3.05 m 0.46 t 0.26 t )3.10 qnt JPH ¼ 20

CH2 CH3

NH CH2 CH3 H


G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

(6a)

1128

Table 1 (continued)

)11.89 qnt JPH ¼ 20 (8e1 )

(8f)

a

[OsH(C6 H15 5 N@NH)(PPh2 OEt)4 ]BPh4

[OsH(4-CH3 C6 H4 N@NH)(PPh2 OEt)4 ]BPh4

In KBr pellets. In (CD2 )2 CO at 25 °C, unless otherwise noted. c Phenyl proton resonances are omitted. d Positive shift downfield from 85% H3 PO4 . e At )70 °C. f 15 N{1 H}NMR, d: )24.1 qnt, )25.5 qnt, 2 J15 NP ¼ 2:0 Hz. g In CD2 CI2 . h At )30 °C. i 15 N{1 H}NMR, d: )19.5 br, )22.3 qnt, 2 J15 NP ¼ 1:7 Hz. j At )90 °.

2048 w

2050 w

2048 w

mOsH

mOsH

mOsH

14.30 d 1 J15 NH ¼ 62 13.51 d 1 J15 NH ¼ 62 3.35 m 3.06 m 0.46 t 0.25 t )3.10 qnt JPH ¼ 20 )11.90 qnt JPH ¼ 20 14.29 s 13.52 s 3.36 m 3.04 m 0.46 t 0.27 t )3.10 qnt JPH ¼ 20 )11.90 qnt JPH ¼ 20 14.18 s 13.32 s 3.37 m 3.07 m 2.66 s 2.37 s 0.46 t 0.29 t )3.11 qnt )12.10 qnt

NH

A4 A4 Y

106.0 s, br 94.9 d, br JPY ¼ 1:7

A4 A4

109.3 s 96.6 s

A4 j A4

108.4 s, br 96.9 s, br

CH2 CH3 H


NH CH2 CH3 H


NH CH2 CH3 CH3 phos H


G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

(8e2 )

[OsH(C6 H5 N@15 NH) (PPh2 OEt)4 ]BPhi4

b

1129

1130

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

The synthesis of binuclear complexes 1, 2 with bis(diazene) bridging ligand prompted us to extend the studies to the preparation of binuclear complexes [Os]– N2 Ar–ArN2 –[Os] with the bis(aryldiazenido) bridging unit. The strategy we have employed (Scheme 3) involves the synthesis of binuclear bis(aryldiazene) complexes [{Os(RCN)P4 }2 (l-HN@NAr–ArN@NH)] (BPh4 )4 5, containing a labile ligand such as the nitrile RCN bonded to each central metal. By deprotonation of the diazene ligands followed by the dissociation of the nitrile group, the expected binuclear bis(aryldiazenido) 6 derivatives can be obtained. The hydride-nitrile precursor [OsH(RCN)P4 ]BPh4 was prepared by reacting the dihydride OsH2 P4 first with methyltriflate [15] and then with an excess of nitrile. Reaction of the [OsH(RCN)P4 ]þ cation with bis(aryldiazonium) salt proceeds to give binuclear complexes [{Os(RCN)P4 )2 (l-HN@NAr–ArN@NH)]4þ 5, which were isolated as BPh4 salts and characterised. Treatment of these nitrile-bis(aryldiazene) complexes 5 with an excess of triethylamine in CH2 Cl2 gives a white solid of [NHEt3 ]BPh4 and a red-orange solution, from which the binuclear bis(aryldiazenido) complexes 6 was isolated. The formation of free nitrile and the separation of the ammonium salt in about quantitative yield also support for the reaction the stoichiometry reported in eq. 3. On the basis of these data it can be hypothesised [5a] that the deprotonation of the two diazene moieties in binuclear complexes 5, giving the diazenido N2 Ar–ArN2 group, is followed by the dissociation of the nitrile ligand affording 6 as final product. Both the nitrile-diazene precursors 5 and the bis(aryldiazenido) complexes 6 were isolated in the solid state and characterised in the usual way by analytical and spectroscopic data (Table 1). The infrared spectra of nitrile compounds 5 show a medium-intensity band at 2264 cm
1 due to the mCN of the RCN ligand. The 1 H

OsH2P4 + CF3SO3CH3 RCN

– CH4

OsH(κ1-OSO2CF3)P4

[OsH(RCN)P4]+

4+ P P

CR

RC

N

P

N N

Os

Ar

Ar

N

N P

P P Os N

H

H

P P

IV

5 Chart 6.

NMR spectra confirm the presence of the diazene groups showing a slightly broad signal near 14 ppm, which is split into a doublet with 1 J15 NH of 66 Hz in the labelled compounds 5a1 . In the temperature range between +20 and )80 °C the 31 P spectra appear as a complicated multiplet which, in the case of 5a, can be simulated using an A2 BC model with the parameters reported in Table 1. On these bases, a geometry of type IV (Chart 6) can reasonably be proposed for the binuclear derivatives 5. The bis(aryldiazenido) [{OsP4 }(l-N2 Ar–ArN2 )] (BPh4 )2 (6) complexes are yellow-orange solid stable in the air and in solution of polar organic solvents, where they behave as 2:1 electrolytes [12]. The IR spectra show a medium-intensity band at 1643–1642 cm
1 attributed to mN2 of the aryldiazenido ligand. In the labelled 6a1 compound this band falls at 1617 cm
1 , in agreement with the proposed attribution. Furthermore, a comparison of our mN2 values with the literature data [1,5,6,16] suggests a singly bent arrangement of the aryldiazenido ligand, which can be considered present as þ N2 Ar– ArNþ 2 , with a formal oxidation number of zero [Os(0)] for the two metal centres in the complexes. The 31 P{1 H}NMR spectra of the bis(aryldiazenido) compounds 6 change with the temperature and the broad signal observed at room temperature resolves into an ABC2 multiplet already at )30 °C, which can be simulated with the parameters reported in Table 1. Such spectra seem to exclude, in first approximation, a regular TBP geometry of the type of Chart 7, for which a symmetric A2 B2 spectrum should be expected.

2[OsH(RCN)P4]+ + [N2Ar-ArN2]2+ P [{Os(RCN)P4}2(µ-NH=NAr-ArN=NH)]4+

eq. 2

5 [{Os(RCN)P4}2(µ-NH=NAr-ArN=NH)]4+ + 2NEt3

2+

P Os

N

N

P P P P N

Scheme 3. P ¼ P(OEt)3 ; R ¼ 4-CH3 C6 H4 ; Ar–Ar ¼ 4,40 -C6 H4 – C6 H4 (a), 4,40 -C6 H4 – CH2 –C6 H4 (c).

Os P

2NHEt3+ + 2RCN + [{OsP4}2(µ-N2Ar-ArN2)]2+ eq. 3 6

N

P

6 Chart 7.

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

However, a restricted rotation at low temperature of the ArNN group placed in the equatorial plane of a regular TBP (Chart 7) may cause either the two apical or the two equatorial phosphorus nuclei to be mutually magnetically inequivalent, resulting in an ABC2 -type 31 P spectra. An alternative explanation for the presence of an ABC2 spectra, which does not agree with none regular TBP geometry, may involve a distorted TBP toward SP geometry. An ABC2 -type 31 P spectrum could be expected in this case, as previously proposed for related mono-nuclear complexes [7]. The bis(aryldiazenido) complexes [{OsP4 }2 (l-N2 Ar– ArN2 )](BPh4 )2 (6a) react with HCl in CH2 Cl2 to give the bis(aryldiazene) complexes [{OsClP4 }(l-HN@NAr– ArN@NH)](BPh4 )2 (7), which can be isolated in the solid state and characterised (Scheme 4). The reaction proceeds with the protonation of the aryldiazenido group to give the aryldiazene and the concurrent addition of the Cl
ligand to the metal centre to give the final binuclear octahedral derivative 7. Furthermore, in order to determine the nitrogen site of the protonation, we treated the labelled [{OsP4 }(l15 NBNAr–ArNB15 N)]2þ cation (6a1 ) with HCl and observed that the protonation takes place at the N1 nitrogen atom, affording [{OsClP4 }(l-H15 N@NAr– ArN@15 NH)]2þ (7a1 ) as the final compound. The new bis(aryldiazene) complex 7a is an orange solid stable in the air and in solution of polar organic solvents, where it behaves as a 2:1 electrolyte [12]. The 1 H NMR spectra confirm the presence of the diazene ligand showing a slightly broad signal at 14.55 ppm due to the NH protons, which is split into a doublet with 1 J15 NH of 65 Hz in the labelled 7a1 complex. In the temperature range between +20 and )80 °C the 31 P{1 H}NMR spectra appear as an AB2 C multiplet suggesting the mutually cis position of the diazene and the halogenide ligand. On this basis, a geometry of type V (Chart 8) can reasonably be proposed for the binuclear complex 7. As reported before, the hydride OsH2 (PPh2 OEt)4 containing the PPh2 OEt phosphine ligand does not give binuclear complexes with bridging bis(diazene) ligand like 1 and 2. Since the behaviour of this hydride complex toward the common monoaryldiazonium cations ArNþ 2 had not been reported [7], we thought to begin this study with the aim to compare the data with those obtained with the related OsH2 P4 [P ¼ P(OEt)3 and PPh(OEt)2 ] complexes [7] and to understand why binuclear com-

[{OsP4}2(µ-N2Ar-ArN2)]2+

1131

Cl

Cl

P Os

N

P

2+

P

P N

Ar

Ar

N

P

P Os P

N P

H

H V

7 Chart 8.

plexes were not obtained. The results show that the hydride OsH2 (PPh2 OEt)4 reacts with an excess of aryldiazonium cation to give, after work-up, a red-orange solid characterised as the hydride-aryldiazene [OsH(ArN ¼ NH)(PPh2 OEt)4 ]BPh4 (8) derivatives (Scheme 5). Studies on the reaction course showed that the formation of the aryldiazene 8 is very slow as compared with the formation of the related [OsH(ArN@NH)P4 ]þ cations containing P(OEt)3 and PPh(OEt)2 ligand [7], and therefore an excess of ligand must be used for the synthesis of 8. This slow rate for the insertion reaction of ArNþ 2 unit into the Os–H bond of OsH2 (PPh2 OEt)4 may explain why the syntheses of binuclear bis(aryldiazene) complexes like 1, 2 failed in this case, yielding only mixtures of intractable products. Furthermore, the further insertion of ArNþ 2 into the Os–H bond of [OsH(ArN@NH)P4 ]þ (8) cation to give bis(aryldiazene) [Os(ArN@NH)2 P4 ]2þ species was not observed, even in the presence of a large excess of ArNþ 2 , being the monodiazene 8 the only isolated product. Good analytical data were obtained for complexes 8, which are stable as solids and in solution of polar organic solvents where they behave as 1:1 electrolytes [12]. The spectroscopic data (Table 1) confirm the proposed formulation and seem also to suggest the presence of two isomers. In fact, the 1 H NMR spectra show two NH signals at 14.29–14.18 and 13.52–13.31 ppm, respectively, each of which is split into a doublet with 1 J15 NH of 62 Hz in the labelled 8e1 complex. In the spectra are also present two quintets at 11.90 to 12.10 and at 3.11 to 3.10 ppm, respectively, attributed to two hydride ligands, each coupled with four equivalent phosphorus nuclei. In the temperature range between +20 and )80 °C the 31 P{1 H}NMR spectra show two singlets suggesting the existence of two isomers, each containing four equivalent phosphite ligands. These data may be interpreted, as for the above-discussed trans bis(diazene) 2-trans, on the basis of the existence of two stereoisomers of the

HCl

6a [{OsClP4}2(µ-NH=NAr-ArN=NH)]2+ 7a 0

Scheme 4. P ¼ P(OEt)3 ; Ar–Ar ¼ 4,4 -C6 H4 –C6 H4 (a).

OsH2P4

exc. ArN2+

[OsH(ArN=NH)P4]+ 8

Scheme 5. P ¼ PPh2 OEt; Ar ¼ C6 H5 (e), 4-CH3 C6 H4 (f).

1132

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133

type A and B (Chart 9), with the substituents to the N@N group in a mutually cis and trans positions, respectively. This hypothesis, however, cannot be applied to this case, because the 31 P{1 H}NMR spectrum of the labelled [OsH(C6 H5 N@15 NH)P4 ]BPh4 (8e1 ) compound shows that only one signal of the two present is coupled with the 15 N of the diazene ligand, giving a doublet with 2 J15 N31 P of 1.7 Hz. The 15 N{1 H}NMR spectra confirm these data showing a slightly broad singlet at 19.5 ppm and a quintet at 22.3 ppm, due to the coupling with four equivalent phosphorus nuclei, with 2 J15 N31 P of 1.7 Hz. One explanation of these data may involve the existence always of two isomers, one containing a N1-bonded and the other containing a N2-bonded diazene ligand, as shown in geometries C and D (Chart 10). In order to verify this hypothesis, we prepared the labelled [OsH(C6 H5 15 N@NH)P4 ]BPh4 (8e2 ) complex and recorded both the 31 P and 15 N spectra. In every case, no coupling between the 15 N of the diazene ligand and the 31 P nuclei was observed for the two isomers in this complex, whose NMR spectra show two sharp singlets in both 31 P and 15 N, so excluding the existence of an isomer of type D. A further hypothesis to explain the whole of spectroscopic data may involve the presence of two isomers, one of which containing a usual N-bonded diazene ligand such as C and the other containing a p-bonded ArN@NH group of the type E (Chart 11). The p-coordination of a diazene ligand is known but rather rare [1b], and generally involves di-substituted 1,2-diazene bonded to a poor r-acceptor metal fragment + P H

P Os

P

P

N

H N

P

Ar

P Os

P

H N

Chart 9.

+ H

P

P

N1

Os P

+

H

P

H

N2 Ar

P Os

P

C

8 Chart 10.

Ar N2

P D

N

Os N P

P

Ar

E

8 Chart 11.

[17]. Although an X-ray crystal structure was not determined due to the poor quality of the obtained crystals, these precedents support the existence of a geometry E, which agrees with all the spectroscopic data of the complex. The presence of two isomers, probably of types C and E, for the aryldiazene [OsH(ArN@NH)(PPh2 OEt)4 ]þ (8) derivatives is not, however, the only difference observed with the PPh2 OEt ligand as compared with the related P(OEt)3 and PPh(OEt)2 in the reaction of the dihydride OsH2 P4 with ArNþ 2 cations. The absence of binuclear complexes as well as the formation of exclusively monodiazenic species highlight once more the peculiar influence of the ancillary ligand in the chemistry of ‘‘diazo’’ derivatives.

Acknowledgements

References

B

8

P

H

P

N

P Ar

A

P

The financial support of MIUR (Rome), PRIN 2002, is gratefully acknowledged. We thank Daniela Baldan for technical assistance.

+

H

+ H

N1 H

[1] (a) D. Sutton, Chem. Rev. 93 (1993) 995; (b) H. Kisch, P. Holzmeier, Adv. Organomet. Chem. 34 (1992) 67; (c) H. Zollinger, Diazo Chemistry II, VCH, Weinheim, Germany, 1995; (d) B.F.G. Johnson, B.L. Haymore, J.R. Dilworth, in: G. Wilkinson, R.D. Gillard, J.A. McCleverty (Eds.), Comprehensive Coordination Chemistry, Pergamon Press, Oxford, 1987. [2] (a) M.T.A.R.S. da Costa, J.R. Dilworth, M.T. Duarte, J.J.R. Fra
usto da Silva, A.M. Galv~ao, A.J.L. Pombeiro, J. Chem. Soc., Dalton Trans. (1998) 2405; (b) M. Hirsch-Kuchma, T. Nicholson, A. Davison, W.M. Davis, A.G. Jones, Inorg. Chem. 36 (1997) 3237; (c) P. Schollhammer, E. Gu
enin, F.Y. Petillon, J. Talarmin, K.W. Muir, D.S. Yufit, Organometallics 17 (1998) 1922; (d) F. Doctorovich, N. Escola, C. Trapani, D.A. Estrin, M.C. Gonzalez Lebrero, A.G. Turjanski, Organometallics 19 (2000) 3810; (e) L. Fan, F.W.B. Einstein, D. Sutton, Organometallics 19 (2000) 684.

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133 [3] (a) G. Albertin, S. Antoniutti, A. Bacchi, M. Boato, G. Pelizzi, J. Chem. Soc., Dalton Trans. (2002) 3313; (b) G. Albertin, S. Antoniutti, E. Bordignon, F. Chimisso, Inorg. Chem. Commun. 4 (2001) 402; (c) G. Albertin, S. Antoniutti, E. Bordignon, A. Tasin, J. Organomet. Chem. 627 (2001) 99; (d) G. Albertin, S. Antoniutti, A. Bacchi, G.B. Ballico, E. Bordignon, G. Pelizzi, M. Ranieri, P. Ugo, Inorg. Chem. 39 (2000) 3265; (e) G. Albertin, S. Antoniutti, E. Bordignon, F. Menegazzo, J. Chem. Soc., Dalton Trans. (2000) 1981. [4] R.A. Michelin, R.J. Angelici, Inorg. Chem. 19 (1980) 3850. [5] (a) G. Albertin, S. Antoniutti, A. Bacchi, E. Bordignon, G. Pelizzi, P. Ugo, Inorg. Chem. 35 (1996) 6245; (b) G. Albertin, S. Antoniutti, A. Bacchi, E. Bordignon, F. Busatto, G. Pelizzi, Inorg. Chem. 36 (1997) 1296; (c) G. Albertin, S. Antoniutti, A. Bacchi, D. Barbera, E. Bordignon, G. Pelizzi, P. Ugo, Inorg. Chem. 37 (1998) 5602. [6] (a) G. Albertin, S. Antoniutti, E. Bordignon, J. Chem. Soc., Chem. Commun. (1984) 1688; (b) G. Albertin, E. Bordignon, J. Chem. Soc., Dalton Trans. (1986) 2551; (c) G. Albertin, S. Antoniutti, E. Bordignon, J. Am. Chem. Soc. 111 (1989) 2072;

[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

1133

(d) P. Amendola, S. Antoniutti, G. Albertin, E. Bordignon, Inorg. Chem. 29 (1990) 318; (e) G. Albertin, S. Antoniutti, E. Bordignon, S. Pattaro, J. Chem. Soc., Dalton Trans. (1997) 4445; (f) G. Albertin, S. Antoniutti, A. Bacchi, E. Bordignon, F. Miani, G. Pelizzi, Inorg. Chem. 39 (2000) 3283. G. Albertin, S. Antoniutti, E. Bordignon, J. Chem. Soc., Dalton Trans. (1989) 2353. R. Rabinowitz, J. Pellon, J. Org. Chem. 26 (1961) 4623. A.I. Vogel, Practical Organic Chemistry, third ed., Longmans, Green and Co., New York, 1956. G. Balacco, J. Chem. Inf. Comput. Sci. 34 (1994) 1235. G. Albertin, S. Antoniutti, D. Baldan, E. Bordignon, Inorg. Chem. 34 (1995) 6205. W.J. Geary, Coord. Chem. Rev. 7 (1971) 81. K.R. Laing, S.D. Robinson, M.F. Uttley, J. Chem. Soc., Dalton Trans. (1973) 2713. J.A. Carrol, D. Sutton, Z. Xiaoheng, J. Organomet. Chem. 244 (1983) 73. G. Albertin, S. Antoniutti, E. Bordignon, J. Chem. Soc., Dalton Trans. (1995) 719. B.L. Haymore, J.A. Ibers, Inorg. Chem. 14 (1975) 3060. A. Albini, H. Kisch, Top Curr. Chem. 65 (1976) 105.