DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2819–2825 2819 Ruthenate(VI)-catalysed dehydrogenation of primary amines to nitriles, and crystal structures of cis-[Ru(bipy)2(NH2CH2Ph)2]- [PF6]2?0.5MeOH and cis-[Ru(bipy)2(NCPh)2][PF6]2?CH2Cl2† William P. GriYth,* Bharti Reddy, Abdel G. F. Shoair, Maria Suriaatmaja, Andrew J. P. White and David J. Williams * Inorganic Chemistry and Chemical Crystallographic Laboratories, Department of Chemistry, Imperial College of Science, Technology and Medicine, London, UK SW7 2AY Catalytic dehydrogenation of benzylic and other primary amines RCH2NH2 to the corresponding nitriles RCN by the system trans-[Ru(OH)2O3]22/S2O8 22 has been investigated. The complex cis-[Ru(bipy)2(NH2CH2Ph)2]21 and the new cis-[Ru(bipy)2(NH2CH2R)2]21 (R = o-, m- or p-ClC6H4, o-MeC6H4, o- or p-MeOC6H4); cis- [Ru(phen)2(NH2CH2R)2]21 (R = Ph or p-MeOC6H4) and cis-[Os(bipy)2(NH2CH2Ph)2]21 have been made, and dehydrogenation of the co-ordinated amine in the ruthenium complexes to the corresponding nitriles in cis-[Ru(L]L)2(NCR)2]21 (L]L = bipy or phen) by peroxodisulfate demonstrated.The crystal structures of cis-[Ru(bipy)2(NH2CH2Ph)2][PF6]?0.5MeOH and cis-[Ru(bipy)2(NCPh)2][PF6]2?CH2Cl2, the latter a product of co-ordinated amine dehydrogenation by peroxodisulfate to give cis-[Ru(bipy)2(NH2CH2Ph)2]21, were determined. Raman, infrared and 1H NMR data for the complexes have been measured; the latter suggest that the cis configurations of the amine complexes are retained in solution.As part of our continuing studies on the application of oxoruthenates and other ruthenium complexes as catalysts for the oxidation of alcohols,2–4 alkyl halides and nitro compounds, 3 sulfides,5 alkenes and alkanes 6 we have extended and developed our earlier brief observations 7 that benzylamine is dehydrogenated to benzonitrile by the catalytic trans-[Ru(OH)2- O3]22/S2O8 22 reagent. We find that the latter is eVective for the catalytic dehydrogenation (or oxidative dehydrogenation) of primary aromatic and some primary aliphatic amines RCH2NH2 to nitriles RCN, and in some cases it will further catalyse the hydration of nitriles to amides RCONH2.The use of other oxoruthenate systems to eVect these conversions has been studied, and a study made of the stoichiometric dehydrogenation of amine complexes cis-[Ru(L]L)2(NH2- CH2R)2]21 (L]L = bipy or phen) to [Ru(L]L)2(NCR)2]21 by peroxodisulfate. A number of new amine and nitrile complexes have been isolated. Relatively few reagents are known for the catalytic conversion of amines into nitriles; there are a number of stoichiometric procedures, e.g.the use of hypochlorite 8 or silver(II) compounds.9 The best catalytic system hitherto reported is a nickel(II) sulfate–peroxodisulfate reagent in 0.4 M aqueous base; this gives good yields and selectivities but is slow, taking a day for most reactions.10 The copper(I) chloride–pyridine–dioxygen system is also slow and requires higher temperatures (60 8C).11 The complex trans-[RuVIO2- (tmp)] (tmp = dianion of 5,10,15,20-tetramesitylporphyrin) in benzene aerobically catalyses dehydrogenation of benzylamine and of n-butylamine quantitatively to the corresponding nitriles at 50 8C over a 24 h period;12 RuCl3?nH2O in toluene dehydrogenates these substrates to a mixture of the nitriles and amides at 100 8C under 2 atm (atm = 101 325 Pa) of dioxygen,13 and [Ru(PPh3)2(NH2CH2Ph)2Cl2] has been shown to catalyse the aerobic conversion of benzylamine into benzonitrile at 80 8C.14 Apart then from the slow nickel system, none of these catalytic reagents operates eYciently at room temperatures.† Studies on transition-metal nitrido and oxo complexes. Part 18.1 Results and discussion (a) Dehydrogenation of amines to nitriles by trans- [Ru(OH)2O3]22/S2O8 22 This reagent comprised of 1 × 1024 M Ru (initially as RuCl3? nH2O or RuO2?nH2O), 0.1 M sodium peroxodisulfate and molar aqueous potassium hydroxide, is an eYcient catalyst for the conversion of a wide range of primary benzylic amines into the corresponding nitriles at room temperatures, and we have optimised the reaction conditions giving good yields and selectivities over relatively short periods of time (1–2 h; Table 1).With primary aliphatic amines however the system is more capricious: n-hexylamine and n-octylamine gave reasonable yields of the nitriles but took much longer (24 h) to react than did the aromatic amines; n-butylamine gave butyric acid, perhaps due to hydrolysis at the high pH of the reagent.None of these reactions occurs to any appreciable extent in the absence of ruthenium. As with most other oxidations involving ruthenate as a catalyst 2,7 these are self-indicating: the orange trans- [Ru(OH)2O3]22 turns dark green on addition of the amine, the orange ruthenate colour returning when the reactions are complete.The GC-MS studies show that in most cases only the nitriles are present after the reaction with traces of aldehyde and amide side-products; only in the case of benzylamine were significant quantities of the imine PhCH2N]] CHPh and benzaldehyde also formed (ca. 28 and 5% respectively as determined by GC-MS). The purity of all the nitrile products was checked by their melting or boiling points as appropriate, and their 1H NMR and GC-MS spectra measured.Two large-scale oxidations were carried out: thus 6.8 g (0.05 mol) of p-methoxybenzylamine gave 3.2 g (0.03 mol) of p-methoxybenzonitrile when treated with 0.1 g of RuCl3?3H2O (3.8 × 1024 mol) in 500 cm3 of 1 M aqueous KOH containing 10.4 g (0.04 mol) of K2S2O8 for 24 h. Under the same conditions 5.4 g (0.05 mol) of benzylamine gave 2.6 g (0.025 mol) of benzonitrile. When the reaction is conducted stoichiometrically the ruthenium-containing product is RuO2, so that 2 mol of ruthenate should dehydrogenate 1 mol of amine (i.e.an overall four-electron reaction). Stoichiometrically, solid barium ruthenate (0.34 g, 1.0 mmol) dehydrogenated 0.07 g (0.582820 J. Chem. Soc., Dalton Trans., 1998, Pages 2819–2825 Table 1 Catalytic oxidation * of amines to nitriles by trans-[Ru(OH)2O3]22/S2O8 22 Substrate Benzylamine o-Chlorobenzylamine m-Chlorobenzylamine p-Chlorobenzylamine o-Methylbenzylamine m-Methylbenzylamine p-Methylbenzylamine o-Methoxybenzylamine p-Methoxybenzylamine o-Bromobenzylamine hydrochloride m-Bromobenzylamine hydrochloride n-Butylamine n-Hexylamine n-Octylamine Product Benzonitrile o-Chlorobenzonitrile m-Chlorobenzonitrile p-Chlorobenzonitrile o-Methylbenzonitrile m-Methylbenzonitrile p-Methylbenzonitrile o-Methoxybenzonitrile p-Methoxybenzonitrile o-Bromobenzonitrile m-Bromobenzonitrile Butyric acid Hexanenitrile Octanenitrile Stirring time/h 1.5 1.0 1.0 1.0 1.0 1.0 1.5 0.5 0.75 1.5 1.5 24 24 24 Yield (%) 61 70 60 60 81 98 70 68 90 83 75 9 15 50 * Oxidations were carried out with 2 mmol substrate, 0.1 mmol RuCl3?3H2O and an excess of K2S2O8 (2.8 g) in 1 M KOH solution (25 cm3).mmol) of p-methoxybenzylamine to give 0.065 g (0.049 mmol) of p-methoxybenzonitrile, corresponding to a 3.8 electron change, in reasonable agreement with the expected four electron change. The use of a phase-transfer catalyst, (NBun 4)OH (following the eVective use of (NBun 4)HSO4 for the stoichiometric oxidations of amines to nitriles by hypochlorite 8), was attempted but did not improve yields or turnovers; and likewise sonication or heating the solution to 50 8C gave little improvement. Other ruthenium-containing systems were also used but were inferior to the trans-[Ru(OH)2O3]22/S2O8 22 reagent.Surprisingly, the use of perruthenate (in the catalytic [RuO4]2/BrO3 2 system), known to be eVective for oxidation of alcohols, halides and nitro compounds,2 was completely ineVectual, as was [RuO4]2/S2O8 22; however, this latter system is known not to function as a catalyst for alcohol oxidations.2 No amine dehydrogenation was observed with the [RuO4]2/BrO3 2 system, suggesting that peroxodisulfate is necessary for the reaction. However, [NPrn 4][RuO4], with N-methylmorpholine N-oxide as cooxidant,4 which has been shown recently to be an eVective and clean reagent for conversion of secondary amines R1CH2- NHR2 into the corresponding imine R1CH]] NR2,15 does convert benzylic amines into nitriles over 3 h periods at room temperatures, but substantial quantities of aldehyde and other side-products are also formed. Over a 24 h period, the amines are dehydrogenated and then hydrated in relatively small yields to the corresponding amides RCONH2 (ca. 10% for benzylamine and p-methoxybenzylamine) as we noted earlier;16 this does not occur in the absence of peroxodisulfate. The stoichiometric hydration of amines to nitriles in the presence of [RuII(NH3)5(H2O)]21 has been noted.17 It is clear that the platinum(II) phosphinito complexes recently reported are much better nitrile hydration catalysts.18 (b) Oxidations of co-ordinated primary amines to co-ordinated nitriles by peroxodisulfate We find that when aromatic amines are added to the trans-[Ru- (OH)2O3]22/S2O8 22 reagent or to a pure solution of trans-[Ru- (OH)2O3]22 in aqueous base a green species is formed, probably an amine complex such as [Ru(OH)2O3(NH2CH2R)]22.No such colour is formed with the corresponding nitrile. Attempts to isolate this green species have failed, and no 1H NMR spectrum could be measured owing to the paramagnetism of trans- [Ru(OH)2O3]22 and/or the complex. Direct reaction of amines with solid trans-Ba[Ru(OH)2O3] or solid trans-K2[Ru(OH)2O3] or of trans-[Ru(OH)2O3]22 in solution in the absence or presence of stabilising coligands such as pyridine or 2,29-bipyridyl did not give identifiable products.The intermediacy of such an amine complex seems likely, however: Bailey and James12 found, during their work on trans-[RuVIO2(tmp)] with benzylamine, that trans-[RuII(tmp)(NH2CH2Ph)2] is formed when the amine is present in excess. As a model for our postulated amine complex we treated cis-[Ru(bipy)2(NH2CH2Ph)2]21 with an excess of aqueous peroxodisulfate to establish whether it was dehydrogenated to a co-ordinated benzonitrile complex. No such conversions with peroxodisulfate have been reported, though Meyer and coworkers 19 have shown that cis-[Ru(bipy)2(NH2CH2Ph)2]21 is converted electrochemically into cis-[Ru(bipy)2(NH2CH2Ph)- (NCPh)]21 and cis-[Ru(bipy)2(NCPh)2]21, and Taube and co-workers 20 aerobically dehydrogenated [Ru(NH3)5(NH2- CH2Ph)]21 to [Ru(NH3)5(NCPh)]21.We find that cis-[Ru(bipy)2- (NH2CH2Ph)2]21 is indeed converted into cis-[Ru(bipy)2- (NCPh)2]21 by an excess of aqueous peroxodisulfate; i.e. coordinated benzylamine is oxidised to co-ordinated benzonitrile.The constitutions of these two complexes as their hexafluorophosphate salts 1 and 2 have been unambiguously established by X-ray crystallography (see below). We have made a number of new amine complexes of ruthenium cis-[Ru(L]L)2- (NH2CH2R)2]21 (L]L = bipy or phen) and find that they too are converted into salts of the corresponding new nitrile complexes [Ru(bipy)2(NCR)2]21 by an excess of aqueous peroxodisulfate at room temperatures (Table 2). Although peroxodisulfate is an eVective stoichiometric oxidant for such conversions, it is surprising that bromate, which we have previously shown3 to function as an eVective cooxidant with trans-[Ru(OH)2O3]22, does not oxidise these amine complexes.Neither peroxodisulfate nor bromate will oxidise the co-ordinated amine ligands in [Os(bipy)2(NH2CH2Ph)2]21, [Ru(CO)2Cl2(NH2CH2Ph)2] or [Ru(NH2CH2Ph)6]Cl2. (c) X-Ray crystallography (i) Crystal structure of cis-[Ru(bipy)2(NH2CH2Ph)2][PF6]2? 0.5MeOH 1.Orange-red crystals of the complex were prepared by reaction of cis-[Ru(bipy)2Cl2] and benzylamine under reflux with subsequent addition of NH4PF6, and recrystallised from methanol. The X-ray structural analysis of complex 1 (Fig. 1) confirms it to have the expected cis-configuration for the benzylamine ligands. The co-ordination geometry at ruthenium is slightly distorted octahedral, with angles in the ranges 78.7(2) to 98.9(3)8 and 169.3(2) to 175.6(2)8, the marked contractions in the cis angles being due to the bite of the 2,29-bipyridyl ligands.The six Ru]N bond lengths (Table 3) clearly emphasise their diVering chemical natures, those to the two benzylamine ligands being noticeably longer at 2.166(6) [N(2)] and 2.174(7) Å [N(1)] than those to the chelating 2,29-bipyridyl ligands [ranging between 2.041(6) and 2.075(6) Å]. These diVerences reflect the sp3 and sp2 nature of the respective co-ordinated nitrogen centres. The two N]C (benzyl) distances (average 1.43J. Chem.Soc., Dalton Trans., 1998, Pages 2819–2825 2821 Table 2 Analytical and spectroscopic data for cis-[Ru(L]L)2(NH2CH2R)2]21 andcis-[Ru(L]L)2(NCR)2]21 complexes Analytical data a (%) Vibrational data b/cm21 1H NMRc (d) Complex [Ru(bipy)2(NH2CH2Ph)2][PF6]2 [Ru(bipy)2(NCPh)2][PF6]2 [Ru(bipy)2(NH2CH2C6H4Cl-o)2][PF6]2?H2O [Ru(bipy)2(NCC6H4Cl-o)2][PF6]2 [Ru(bipy)2(NH2CH2C6H4Cl-m)2][PF6]2?H2O [Ru(bipy)2NCC6H4Cl-m)2][PF6]2?H2O [Ru(bipy)2(NH2CH2C6H4Me-o)2][PF6]2 [Ru(bipy)2(NCC6H4Me-o)2][PF6]2 [Ru(bipy)2(NH2CH2C6H4OMe-o)2][PF6]2?H2O [Ru(bipy)2(NCC6H4OMe-o)2][PF6]2?2H2O [Ru(bipy)2(NH2CH2C6H4OMe-p)2][PF6]2 [Ru(bipy)2(NCC6H4OMe-p)2][PF6]2 [Ru(phen)2(NH2CH2Ph)2][PF6]2?H2O [Ru(phen)2(NCPh)2][PF6]2 [Ru(phen)2(NH2CH2C6H4OMe-p)2][PF6]2?H2O [Ru(phen)2(NCC6H4OMe-p)2][PF6]2?H2O C 44.3 (44.5) 44.3 (44.9) 41.3 (40.7) 41.5 (41.8) 40.7 (40.7) 41.3 (41.0) 45.3 (45.7) 46.3 (46.1) 43.5 (43.4) 43.5 (43.0) 44.5 (44.2) 44.5 (44.6) 46.8 (46.4) 47.5 (47.6) 45.3 (46.0) 46.3 (46.4) H 3.8 (3.7) 3.1 (2.9) 3.3 (3.4) 3.4 (2.5) 3.4 (3.3) 2.3 (2.6) 3.7 (4.0) 3.5 (3.2) 4.2 (4.1) 3.5 (3.4) 4.2 (3.9) 3.5 (3.1) 3.4 (3.7) 2.8 (2.9) 3.6 (3.9) 3.2 (3.1) N 8.8 (9.2) 8.8 (9.2) 8.6 (8.4) 8.6 (8.6) 8.5 (8.2) 8.5 (8.4) 8.8 (8.9) 8.9 (9.0) 8.3 (8.4) 8.7 (8.4) 8.8 (8.6) 8.7 (8.7) 8.5 (8.5) 8.6 (8.8) 8.0 (8.0) 8.0 (8.1) nasym(NH2) 3316m 3320m 3314m 3311m 3260m 3320m 3330m 3287m 3280m nsym(NH2) 3188w 3244w 3134m 3266m 3160w 3217m 3233m 3244m 3212m n(CN) – 2240w 2245s, 2240w – 2240w 2245s – 2230w 2241s – 2235w – 2240w – 2241w – 2242w – 2236w 2244s d(NH2) 1600m 1617m 1615m 1603m 1620m 1618m 1622m 1623m CH2 3.2 (m), 3.8 (m) 3.4 (m), 3.7 (m) 3.2 (m), 3.8 (m) 3.3 (m), 3.6 (m) 3.4 (m), 3.7 (m) 3.5 (m), 3.8 (m) 3.2 (m), 3.8 (m) 3.3 (m), 3.7 (m) NH2 4.6 (t), 4.8 (t) 4.4 (t), 4.8 (t) 4.4 (t), 4.7 (t) 4.6 (t), 4.8 (t) 4.4 (t), 4.7 (t) 4.3 (t), 4.8 (t) 4.4 (t), 4.9 (t) 4.4 (t), 4.8 (t) a Calculated values in parentheses.b Raman data italicised.c In (CD3)2CO vs. SiMe4; resonances due to bipy/phen and phenyl omitted. Å) are unexceptional, reflecting their single-bond character; the angles at the benzylamine nitrogen atoms are sightly enlarged at 121.7(7) [N(1)] and 124.6(6)8 [N(2)]. Fig. 1 The molecular structure of the cation in complex 1, showing the overlap between one of the benzylamine ligands and one of the 2,29- bipyridyl units. An interesting feature of the conformation of the cation is the adoption of a gauche geometry about the N]CH2 bond in one benzylamine ligand [N(2)], whereas in the other [N(1)] the geometry is anti.The former conformation is stabilised by an intramolecular p–p stacking interaction between the benzyl ring and adjacent bipyridyl ligand (mean interplanar separation ca. 3.2 Å). The opposite face of the benzyl ring is involved in an intermolecular aromatic–aromatic edge-to-edge interaction with the phenyl ring of the other benzylamine ligand (centroid– centroid separation 4.78 Å).The combined eVect of these two interactions is to produce loosely linked chains of molecules that extend in the crystallographic a direction (Fig. 2). Centrosymmetrically related pairs of chains are cross-linked by additional T type aromatic–aromatic edge-to-edge interactions between the face of the N(1) benzylamine and the edge of the N(5) pyridine ring and vice versa (centroid–centroid separation 4.93 Å). (ii) Crystal structure of cis-[Ru(bipy)2(NCPh)2][PF6]2?CH2Cl2 2.An aqueous solution of cis-[Ru(bipy)2(NH2CH2Ph)2]21 was treated with an excess of aqueous peroxodisulfate and the yellow product, cis-[Ru(bipy)2(NCPh)2][PF6]2, was isolated by addition of NH4PF6. It was recrystallised from dichloromethane as yellow crystals. Fig. 2 Part of one of the aromatic–aromatic edge-to-face linked chains of cations present in the crystals of complex 1.2822 J. Chem. Soc., Dalton Trans., 1998, Pages 2819–2825 Table 3 Selected bond lengths (Å) and angles (8) for complex 1 Ru]N(1) Ru]N(4) N(1)]C(7) N(6)]Ru]N(4) N(6)]Ru]N(3) N(6)]Ru]N(2) N(3)]Ru]N(2) N(5)]Ru]N(1) C(7)]N(1)]Ru 2.174(7) 2.058(6) 1.401(13) 92.2(2) 94.9(2) 89.3(2) 94.6(2) 98.9(3) 121.7(7) Ru]N(2) Ru]N(5) N(2)]C(14) N(6)]Ru]N(5) N(4)]Ru]N(3) N(4)]Ru]N(2) N(6)]Ru]N(1) N(3)]Ru]N(1) C(14)]N(2)]Ru 2.166(6) 2.063(6) 1.454(11) 78.7(2) 78.8(2) 173.4(2) 175.6(2) 87.9(3) 124.6(6) Ru]N(3) Ru]N(6) N(4)]Ru]N(5) N(5)]Ru]N(3) N(5)]Ru]N(2) N(4)]Ru]N(1) N(2)]Ru]N(1) 2.075(6) 2.041(6) 92.7(2) 169.3(2) 93.9(2) 91.6(3) 87.2(3) Table 4 Selected bond lengths (Å) and angles (8) for complex 2 Ru]N(1) N(1)]C(1) N(1)]Ru]N(19) N(2)]Ru]N(29) N(1)]Ru]N(39) C(1)]N(1)]Ru 2.032(4) 1.140(6) 91.9(2) 90.2(2) 96.3(2) 177.6(4) Ru]N(2) C(1)]C(7) N(1)]Ru]N(2) N(1)]Ru]N(3) N(2)]Ru]N(39) N(1)]C(1)]C(7) 2.045(4) 1.415(6) 89.2(2) 87.7(2) 96.9(2) 178.0(6) Ru]N(3) N(1)]Ru]N(29) N(2)]Ru]N(3) N(3)]Ru]N(39) 2.064(4) 175.1(2) 78.9(2) 174.2(2) The X-ray structural analysis of complex 2 (Fig. 3) confirms that the expected stoichiometric oxidation from co-ordinated benzylamine to benzonitrile has occurred. The two benzylamine ligands present in 1 have retained their cis relationship in the oxidised product 2, the N(1)]Ru]N(19) angle being 91.9(2)8. The complex possesses crystallographic C2 symmetry about an axis passing through the ruthenium centre and bisecting the two benzonitrile ligands. The co-ordination geometry at ruthenium is slightly distorted octahedral, with angles in the ranges 78.9(2) to 96.9(2) and 174.2(2) to 175.1(2)8, the marked contractions observed in the cis angles being as expected due to the bite of the 2,29-bipyridyl ligands.The independent Ru]N bond lengths (Table 4) clearly reflect their diVering chemical natures, with those to the benzonitrile ligands [2.032(4) Å] being noticeably shorter than those to the 2,29-bipyridyl ligands (see above). The corresponding bonds to the benzylamine ligands in 1 are longer [at 2.166(6) and 2.174(7) Å], consistent with the change from an sp3 hybridisation in 1 to sp in 2.The bond distances to the sp2 hybridised 2,29-bipyridyl ligands are essentially the same in both structures [2.041(6) to 2.075(6) Å in 1 and 2.045(4) and 2.064(4) Å in 2] being, as expected, intermediate with respect to those to the sp3 and sp hybridised benzylamine and benzonitrile ligands in 1 and 2. The oxidation of the benzonitrile ligand in 1 is clearly demonstrated in 2 by the unambiguous triple-bond Fig. 3 The molecular structure of the C2-symmetric cation in complex 2. character for N(1)]C(1) [1.140(6) Å] and the linear geometries at C(1) and N(1) [178.0(6) and 177.6(4)8 respectively]. The orientation of the terminal phenyl rings of the benzonitrile ligands is such that they lie virtually coplanar with their associated trans 2,2-bipyridyl ligands. There is, surprisingly, a marked absence of any intramolecular p–p interactions.The only intermolecular interactions of any note are weak cation–anion C]H? ? ? F interactions between C(11) and C(14) of one of the PF6 anions (the H ? ? ? F distances are 2.49 and 2.36 Å with C]H]F angles of 173 and 1658 respectively). (d) Vibrational and 1H NMR spectra of amine and nitrile complexes There are very slight diVerences in the elemental analyses between cis-[Ru(bipy)2(NH2CH2R)2]21 and cis-[Ru(bipy)2- (NCR)2]21 salts, but vibrational and 1H NMR spectra clearly demonstrate the presence of either NH2CH2R or NCR ligands.In Table 2 we list infrared, Raman and 1H NMR data on the ruthenium amine and nitrile complexes isolated in this work. The NH2 stretches n(NH2) and deformations d(NH2) are present in the spectra of the amine complexes but absent in those of the nitrile species. Bands near 2240 cm21 of moderate intensity appear in the infrared spectra of the nitrile complexes and as strong bands in the Raman, clearly arising from the CN stretch n(CN).A cis geometry is indicated for the [Ru(bipy)2(NCR)2]21 and [Ru(phen)2(NCR)2]21 species by the fact that the infrared and Raman bands have significantly diVerent frequencies: in the former it is the asymmetric CN stretch nasym(CN) which is the strongest band while the symmetric stretch nsym(CN) is stronger in the Raman. The 1H NMR spectra demonstrate that a cis configuration for the amine complexes is retained in solution. Thus, for cis- [Ru(bipy)2(NH2CH2Ph)2] the peaks due to bipyridyl are very complex suggesting a cis rather than a trans structure; furthermore, the amine protons appear as two multiplets (at d 4.8 and 4.6 vs.SiMe4); on shaking a solution of the complex with 2H2O these peaks disappear due to exchange with deuterium. The methylene protons also appear as two multiplets (at d 3.2 and 3.4); for trans-[Ru(bipy)2(NH2CH2R)2]21 only one set of resonances for amine and methylene groups would be expected, but for the cis isomer there will be two sets since this isomer is diastereotopic.Conclusion We have shown that the trans-[Ru(OH)2O3]22/S2O8 22 reagent isJ. Chem. Soc., Dalton Trans., 1998, Pages 2819–2825 2823 eVective for the dehydrogenation of primary amines (particularly benzylic amines) to the corresponding nitriles under ambient conditions; over longer periods of time nitrile hydration to amides occurs. The reaction may proceed via initial formation of a co-ordinated amine complex; as models for reaction of co-ordinated amine species with peroxodisulfate we made a number of new complexes cis-[Ru(L]L)2(NH2CH2R)2]21 (L]L = bipy or phen) and have shown that these are oxidised by an excess of peroxodisulfate to the corresponding nitrile complexes cis-[Ru(L]L)2(NCR)2]21.The crystal structures of two such species, cis-[Ru(bipy)2(NH2CH2Ph)2][PF6]2?0.5MeOH and cis-[Ru(bipy)2(NCPh)2][PF6]2?CH2Cl2, have been determined. Experimental Chemicals were from Aldrich and used without further purifi- cation.The compounds RuCl3?nH2O and Na2[OsCl6]?nH2O were obtained from Johnson Matthey Ltd. Preparation of the trans-[RuO3(OH)2]22/S2O8 22 reagent The literature procedure 3 was used but with slightly diVerent concentrations: RuCl3?nH2O (0.024 g, 0.1 mmol) was predissolved in water (5 cm3) and an excess of K2S2O8 (2.8 g, 0.01 mol) in aqueous molar KOH (25 cm3) was added to give an orange solution. Catalytic dehydrogenation of amines to nitriles The reactions were performed at room temperature by dropwise addition of the amines (RCH2NH2; 2 mmol) over a period of 5 min to a vigorously stirred solution (100 cm3) of the trans- [Ru(OH)2O3]22/S2O8 22 reagent.The initial reaction mixture is dark green; when the reaction is complete the original orange colour of ruthenate reappears. The mixture was then extracted with diethyl ether (3 × 25 cm3), the ether extracts dried over anhydrous MgSO4 and the ether removed.Products were characterised by 1H NMR, IR spectra and melting points where appropriate. Hydration of nitriles to amides Reactions were carried out as above, but for 24 h periods; benzene was used rather than diethyl ether for extracting the products. Preparation and reactions of ruthenium amine and nitrile complexes The complex [Ru(bipy)2(NH2CH2Ph)2][PF6]2 was made by a method based on that of Meyer and co-workers 19 but the hexa- fluorophosphate salt was isolated in place of the perchlorate salt. The complex cis-[RuCl2(bipy)2], made by the literature method21 (0.2 g, 0.4 mmol), was suspended in 50% aqueous methanol (30 cm3).Benzylamine (2 g, 18.7 mmol) was added and the solution refluxed under nitrogen for 2 h. Methanol was evaporated oV, the solution cooled and extracted with diethyl ether (3 × 20 cm3) to remove the excess of benzylamine. The remaining aqueous solution was filtered and the complex precipitated by slow addition of a saturated solution of NH4PF6, and the red precipitate filtered oV, washed with water, diethyl ether and then dried in vacuo.Yield of red crystals 0.33 g, 0.36 mmol (90%). The methanol adduct 1 was made by recrystallisation of this material from MeOH. Other [Ru(bipy)2(NH2CH2R)2][PF6]2 salts. The complex cis- [RuCl2(bipy)2]?2H2O (0.2 g, 0.38 mmol) was suspended in 50% aqueous methanol (30 cm3). The amine (2 g) was added and the solution refluxed under nitrogen for 2 h. The methanol was evaporated oV, the solution cooled and extracted with diethyl ether (3 × 20 cm3) to remove the excess of amine.The remaining aqueous solution was filtered and the complex precipitated by slow addition of a saturated solution of NH4PF6. The precipitate was filtered oV, washed with water, diethyl ether and then dried in vacuo. The complexes cis-[Ru(phen)2(NH2CH2Ph)2][PF6]2?H2O and cis-[Ru(phen)2(NH2CH2C6H4OMe-p)2][PF6]2?H2O were similarly prepared, cis-[RuCl2(phen)2]?2H2O (made by the literature method21) (0.2 g, 0.35 mmol) replacing cis-[RuCl2(bipy)2]? 2H2O.Dehydrogenation of cis-[Ru(bipy)2(NH2CH2Ph)2]21 to cis- [Ru(bipy)2(NCPh)2][PF6]2. The complex cis-[RuCl2(bipy)2] (0.2 g, 0.4 mmol) was suspended in 50% aqueous methanol (30 cm3). Benzylamine (2 g, 18.7 mmol) was added and the solution refluxed under nitrogen for 2 h. Methanol was evaporated oV, the solution cooled and extracted with diethyl ether (3 × 20 cm3) to remove the excess of benzylamine.The remaining aqueous solution of [Ru(bipy)2(NH2CH2Ph)2]21 was degassed and aqueous K2S2O8 (3%, 10 cm3) was added with stirring under nitrogen at room temperature for 1.5 h; the mixture changed gradually from red to orange and finally to yellow. The yellow solution was filtered and a yellow precipitate was formed by adding a saturated solution (10 cm3, 10%) of NH4PF6. The precipitate of cis-[Ru(bipy)2(NCPh)2][PF6]2 was collected, washed with water, diethyl ether and dried in vacuo.Yield 0.33 g, 0.36 mmol (90%). The dichloromethane adduct 2 was made by recrystallisation of this material from CH2Cl2. General procedure for dehydrogenation of cis-[Ru(bipy)2- (NH2CH2R)2]21 to cis-[Ru(bipy)2(NCR)2]21 by peroxodisulfate. The complex cis-[RuCl2(bipy)2]?2H2O (0.2 g, 0.4 mmol) was suspended in 50% aqueous methanol (30 cm3), the amine (2 g) added and the solution refluxed under nitrogen for 2 h. Methanol was evaporated oV, the solution cooled and extracted with diethyl ether (3 × 20 cm3) to remove the excess of amine.The remaining aqueous solution was filtered and degassed by nitrogen, then aqueous K2S2O8 (3%, 10 cm3) solution added with stirring under nitrogen at room temperature for 2 h; the mixture changed gradually from red to orange and finally to yellow. The yellow solution was filtered and a yellow precipitate formed by adding a saturated solution (10 cm3, 10%) of NH4PF6. The precipitate was collected, washed with water and dried in vacuo.The complexes cis-[Ru(phen)2(NCPh)2][PF6]2 and cis-[Ru- (phen)2(NCC6H4OMe-p)2][PF6]2?H2O were similarly prepared, using cis-[RuCl2(phen)2]?2H2O (0.2 g, 0.35 mmol) in place of cis-[RuCl2(bipy)2]?2H2O. Ruthenium carbonyl complexes. A ruthenium carbonylcontaining solution using ethanol as the solvent was prepared by following the procedure of Chatt et al.22 The compound RuCl3?nH2O (4.2 g) was added to ethanol (75 cm3), heated at reflux and carbon monoxide passed into the solution.A blood red colour was formed after 5 h. This solution was used for the following reactions. [RuCl2(CO)2(NH2CH2Ph)2]. The procedure of Wilkinson and co-workers 23 was used with some modifications. Benzylamine (0.4 g, 3.7 mmol) was added slowly to the red solution (9 cm3). After 5 min a change to green occurred and a pale green precipitate was formed. This was filtered oV, washed with ethanol, diethyl ether and dried in vacuo. Yield 0.3 g, 0.6 mmol (67%) (Found: C, 43.5; H, 4.7; N, 6.3.Calc. for C16H18Cl2- N2O2Ru: C, 43.4; H, 4.1; N, 6.3%). [Ru(NH2CH2Ph)6]Cl2. Benzylamine (2 g, 18.7 mmol) was added slowly to the red solution (9 cm3); there was an immediate change to green and the reaction mixture was heated at reflux for 15 min, after which time a red crystalline precipitate was formed. The precipitate was filtered oV, washed with ethanol and diethyl ether (4 × 25 cm3) to remove the excess of2824 J. Chem.Soc., Dalton Trans., 1998, Pages 2819–2825 benzylamine and dried in vacuo. Yield 0.6 g, 0.73 mmol (73.7%) (Found: C, 61.5; H, 6.5; N, 10.1. Calc. for C42H54Cl2N6Ru: C, 61.9; H, 6.7; N, 10.3%). Neither of the above two complexes could be oxidised to the corresponding nitrile complexes with an excess of peroxodisulfate. Osmium complexes cis-[OsCl2(bipy)2]. This was prepared by a variation of the literature method.24 The salt Na2[OsCl6]?nH2O (1 g, 2.2 mmol) and 2,29-bipyridyl (0.72 g, 4.6 mmol) were added to ethylene glycol (50 cm3) and the mixture was heated at reflux for 45 min under nitrogen.Since the crude reaction mixture contained both cis-[OsCl2(bipy)2] and cis-[Os(bipy)2Cl2]1, an equal volume of saturated sodium dithionite was added to the cooled reaction mixture in order to reduce the excess of OsIII to OsII. The purple-black precipitate formed was isolated by filtration, washed with water to remove [Os(bipy)3]21 and other ionic products, and washed with a large volume of diethyl ether.Yield 0.5 g, 0.87 mmol (87%) (Found: C, 41.6; H, 2.3; N, 9.7. Calc. for C20H16Cl2N4Os: C, 41.9; H, 2.8; N, 9.8%). [Os(bipy)2(NH2CH2Ph)2][PF6]2. The complex cis-[OsCl2- (bipy)2] (0.1 g, 0.17 mmol) was suspended in 50% aqueous ethanol (30 cm3), benzylamine (2 g, 18.7 mmol) was added and the solution refluxed under nitrogen for 4 h. It changed from purple to dark yellow, then ethanol was evaporated oV, the solution cooled and extracted with diethyl ether (3 × 20 cm3) to remove the excess of benzylamine.The remaining aqueous solution was filtered and the complex precipitated by slow addition of a saturated solution of NH4PF6. The brown precipitate was filtered oV, washed with water, diethyl ether and then dried in vacuo. Yield 0.06 g, 0.06 mmol (35%) (Found: C, 39.8; H, 3.1; N, 8. Calc. for C34H34F12N6OsP2: C, 40.6; H, 3.4; N, 8.4%). This complex was not oxidised by peroxodisulfate under the conditions used for the ruthenium analogue.X-Ray crystallography Crystal data. [C34H34N6Ru][PF6]2?0.5CH3OH 1, M = 933.7, monoclinic, space group P21/c (no. 14), a = 11.987(1), b = 20.692(2), c = 16.544(1) Å, b = 106.73(1)8, U = 3929.7(4) Å3, Z = 4, Dc = 1.578 g cm23, m(Cu-Ka) = 48.4 cm21, F(000) = 1884, T = 293 K, orange-red block, 0.27 × 0.17 × 0.12 mm. [C34H26N6Ru][PF6]2?CH2Cl2 2, M = 994.5, monoclinic, space group C2/c (no. 15), a = 13.644(1), b = 26.405(2), c = 11.371(1) Å, b = 90.21(1)8, U = 4096.7(6) Å3, Z = 4 (the molecule has crystallographic C2 symmetry), Dc = 1.612 g cm23, m(Mo-Ka) = 6.81 cm21, F(000) = 1984, T = 293 K, orange prism, 0.67 × 0.67 × 0.23 mm.Data collection and processing. Data were measured on Siemens P4/PC diVractometers with graphite monochromated Cu-Ka (Mo-Ka) radiation for complex 1 (2) using w scans. 5839 (3596) Independent reflections were measured [2q < 120 (50)8] of which 4278 (2780) had |Fo| > 4s(|Fo|) and were considered to be observed.The data were corrected for Lorentz-polarisation factors, and semiempirical absorption corrections (based on y scans) applied; the maximum and minimum transmission factors were 0.51 and 0.39 for 1 and 0.83 and 0.71 for 2 respectively. Structure analysis and refinement. The structures were solved by direct methods and the non-hydrogen atoms of the cationic complexes refined anisotropically. In 1 both of the hexafluorophosphate anions were disordered; in each case this disorder was resolved into two, discrete, partial occupancy orientations, with the atoms of the major occupancy orientation being refined anisotropically.The half occupancy included solvent methanol molecule in 1 was found to be distributed over three discrete sites, all of which were refined isotropically. The included dichloromethane solvent molecule in 2 was disordered over a crystallographic C2 axis, and this was resolved into two symmetry related half occupancy orientations, both of which were refined anisotropically.The positions of the hydrogen atoms in both structures were idealised, assigned isotropic thermal parameters [U(H) = 1.2Ueq(C/N), U(H) = 1.5Ueq(O)], and allowed to ride on their parent atoms. Refinements were by full matrix least squares based on F2 to give R1 = 0.062 (0.050), wR2 = 0.153 (0.112) for the observed data and 537 (266) parameters for 1 (2) respectively. The maximum and minimum residual electron densities in the final DF map were 0.70 and 20.75 e Å23 for 1 and 0.35 and 20.23 e Å23 for 2 respectively.The mean and maximum shift/error ratios in the final refinement cycle were 0.001 and 20.031 for 1 and 0.000 and 0.000 for 2 respectively. All computations were carried out using the SHELXTL PC program system.25 CCDC reference number 186/1076. Instrumentation Infrared spectra were measured on a Perkin-Elmer series 1720 FTIR instrument, FT Raman spectra on a Perkin-Elmer series 1700 instrument with Nd-YAG laser excitation at 1064 nm and 1H NMR spectra on a JEOL EX-270 spectrometer. Microanalyses were carried out by the Imperial College Microanalytical Service.The GC-MS data were obtained by Mr. John Barton on a Micromass AutoSpec, fitted with a Hewlett-Packard 5890 gas chromatograph and an SGE BPX5 column. Acknowledgements We thank the Egyptian Ministry of Education for a grant to one of us (A. G. F. S.), Johnson Matthey Ltd. for a loan of ruthenium trichloride, Dr.A. J. Bailey for obtaining crystals of cis-[Ru(bipy)2(NCPh)2][PF6]2?CH2Cl2 and John Barton for GC-MS measurements. We also thank the University of London Intercollegiate Research Service (ULIRS) for the Raman spectrometer. References 1 Part 17, A. J. Bailey, M. G. Bhowon, W. P. GriYth, A. G. F. Shoair, A. J. P. White and D. J. Williams, J. Chem. Soc., Dalton Trans., 1997, 3245. 2 A. J. Bailey, L. D. Cother, W. P. GriYth and D. M. Hankin, Transition Met. Chem., 1995, 20, 590; W.P. GriYth, Chem. Soc. Rev., 1992, 21, 179. 3 A. J. Bailey, W. P. GriYth, S. I. Mostafa and P. A. Sherwood, Inorg. 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