Halogenohydrido and halogenocarbonyl-hydrido complexes of rhenium

J.inorg.nucI.Chem.,1969,Vol.31,pp.3211to 3218. PergamonPress. PrintedinGreat Britain

HALOGENOHYDRIDO AND HALOGENOCARBONYLH Y D R I D O COMPLEXES OF R H E N I U M M. F R E N I , D. G I U S T O , P. R O M I T I and E. Z U C C A Centro Nazionale di Chimica del C.N.R., Istituto di Chimica Generale dell'UniversitY, Via Venezian 21, Milano, Italy A b s t r a c t - S o m e new halogenocomplex hydrides of rhenium are described: ReH4LsX (11), where L = P(CeHsh,P(CeH4CH3)3, and X = Br, I, SnCi3. The interaction of these compounds with triphenylphosphine in boiling ethanol, under nitrogen, gives violet crystalline products with formula: ReH~COL3X (V), where L = P(CsHs)s and X = Br, 1. Their i.r. and N M R spectra are given. INTRODUCTION

IN PREVIOUS papers we have observed the different behaviour of the hydrido

complexes of rhenium stabilized by triphenylphosphine [1], from hydrido complexes of other transition metals: in particular we did not succeed in replacing the hydridic hydrogens step by step with halogens by reaction with halogenohydrides. The halogenohydrido complexes of rhenium with triphenylphosphine, unknown previously, have been prepared now, by the method we used with the hydrido complex ReH3L2 [2], where L = 1,2bisdiphenylphosphinoethane. On treating ReHsL3 (I), with the calculated amount of halogen, the compounds ReH4L3X (II), where L = P(CsHs)3,P(CsH4CH3)3 and X = Br, I, SnCI3, were isolated. These compounds are yellow-greenish, diamagnetic, non-electrolytes. EXPERIMENTAL

Apparatus. N M R spectra were recorded on a Varian HA-100, instrument at 100 Mc/s, by using carbon disulphide and deuterobenzene saturated solution, with TMS as internal reference. The measurements were made at 30"C. The data and conditions of measurements are given in Table 5. I.R. spectra were recorded on a Perkin-Elmer, model 457 spectrometer(Table 4). Molecular weights were taken on a Mechrolab, model 301-A osmometer, in benzene or chloroform solution. Dipole moments were determined by the approximate method of Jensen from dielectric constant measurements on 10-1-10-~M benzene solutions with Dipoimeter DM-01 and cell DLF-2 (Wissenschaftlich Technische Werkstatten of Weilheim/Oberbayern). Magnetic susceptibilities were measured on a Gouy balance at room temperature. Rhenium analysis. Rhenium was determined as tetraphenylarsonium perrhenate, after treatment in a Carius tube with nitric acid. (Ib) Pentahydridotris(triparatolylphosphine) rhenium A mixture of 1.5 g of ReO(OC~Hs)(Pptahl2, 1"5 g of paratolylphosphine and 0.15 g of NaB H4 was refluxed in 50 ml of ethanol. Orange crystals formed, which were recrystallized from benzene and ethanol. (Yield, 78%). The compound is soluble in benzene (16,4%) and acetone (1.1%); insoluble in ethanol, methanol, hexane. 1. L. Malatesta, M. Freni a n d V . Valenti, Gazz. chim. itai. 94, 1278 (1964). 2. M. Freni, R. Demich¢fis and D. Giusto, J. inorg, nucl. Chem. 29, 1433 (1967). 3211

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M. F R E N I et ai.

(IIa) Tetrahydridoiodotris(triphenylphosphine) rhenium 2 g of the compound ReHs(PPhs)a (la), were dissolved in 15 ml of benzene, treated drop by drop with 20.5 ml of an 0.1 N solution of iodine in benzene and heated to 60-70°C. 100 ml of ethanol were added to the solution. On standing yellow-greenish crystals separated, which were recrystallized from benzene and ethanol. (Yield, 85%). The compound is soluble in benzene; insoluble in ethanol, methanol, acetone and hexane. Reactions (a) With hydrogen chloride. 0.3 g of the compound (IIa) were dissolved in 20 ml of benzene, treated with an excess of a solution of hydrogen chloride in benzene and refluxed for I hr. Red crystals separated, which, recrystallized from benzene and hexane, (yield, 97%), corresponded to Re(PPhs)2 ClsI (III). The compound is soluble in benzene, dichloromethane, chloroform; insoluble in ethanol, methanol and hexane. (b) With iodine 0.5 g of the compound (IIa) were dissolved in 30 ml of xylene, and treated in air with an excess of iodine in xylene. The violetcrystais, which separated at room temperature on addition of 30 ml of hexane, were recrystallized from benzene and hexane, (yield, 85%); they corresponded to ReO2(PPha)~I [3] (VI). (c) With carbon monoxide 0.5 g of the compound (IIa) were dissolved in 30 ml of benzene and refluxed, under carbon monoxide, for 3 hr. The pale blue crystals, which separated at room temperature on addition of 30 ml of ethanol, were recrystallized from benzene and ethanol, (yield, 84%), corresponded to trans-Re (COh(PPha)2I [41 (IV).

(Ilb) Tetrahydridoiodotris(triparatolylphosphine) rhenium 0.5 g of the compound (Ib) were suspended in 20 ml of hexane and treated drop by drop with an 0. I N etbanolic solution of iodine. O n standing yellow crystals were formed. (Yield, 75%). The compound is soluble in benzene, chloroform, acetone; insoluble in ethanol, methanol and hexane. (IIc) Tetrahydridobromotris(triphenylphosphine) rhenium 0-5 g of the compound (Ia) were dissolved in 4 ml of benzene, and treated drop by drop with 55.9 ml of an 8.95 10-3N ethanolic solution of bromine. O n standing green crystals separated. (Yield, 67%). The compound is soluble in benzene, dichloromethane; insoluble in ethanol, methanol and hexane. Table 1

NO

Compound*

Colour

M.p. (0(2)

la Ib IIa lib Ilc lid lie III IV Va Vb Vi

ReHs(PPh3)a ReHs(Pphh ReH.(PPha)aI ReH4(Ppta)aI ReH4(PPha)aBr ReH4(PPha)aSnCla ReH4(PphhSnCI3 Re(PPha)2Cl3I Re(CO)a(PPhs)2I ReH~CO(PPha)aI ReH~CO(PPha)aBr ReOz(PPha)2I

yellow orange green yellow green cream cream red pale blue violet brown violet

161 154 128 109 163 203 195 220 208 174 163 198

*PPhs = triphenylphosphine;

Mol. wt. Calc. Found 977 1103 1103 1229 1056 1200 1327 955 922 1129 1082 869

945 1070 1098 1180 ---936 900 994 -872

/~(D) 3.4 -2.54 2.31 3.27 ---3-0 --4.5

PPh -- triparatolylphosphine.

3. M. Freni, D. Giusto and P. Romiti, Gazz. chim. ital. In press. 4. F. W. Abel and G. Wilkinson, J. chem. Soc. 1501 (1959). M. Frani, V. Valenti and D. Giusto, J. inorg, nucl. Chem. 27, 2635 (1965).

Halogenohydrido and halogenoearbonylhydrido complexes of rhenium

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(Ild) Tetrahydridotrichlorostannatetris(triphenylphosphine) rhenium A mixture of 1.5 g of (Ia) and 0.85 of SnCl~ were dissolved in 30 ml of hot acetone. On cooling, cream crystals separated(Yield, 80%). The compound is insoluble in common organic solvents. (IIe) Tetrahydridotrichlorostannatetris(triparatolylphosphine) rhenium A mixture of 1 g of (Ib) and 0.65 g of SnCI2 were dissolved in 30 ml of hot ethanol. On cooling, cream crystals separated. (Yield, 70%). The compound is soluble in benzene, dichloromethane, chloroform; insoluble in ethanol, methanol, acetone and hexane. (Va) Dihydridoiodocarbonyltris(triphenylphosphine)rhenium A mixture of 1 g of (IIa) and 0.4 g of triphenylphosphine were refluxed in 20 ml of ethanol, under nitrogen, for 3 hr. Violet crystals were formed, which were recrystallized from benzene and ethanol, under nitrogen. (Yield, 70%). The compound is so'.uble in benzene, dichloromethane and carbon disulphide; insoluble in ethanol, methanol, acetone and hexane.

Reactions (a) With oxygen 0.5 g of the compound (Va) were suspended in 20 ml of benzene and treated with oxygen. Violet crystals were formed, which corresponded to ReO2(PPhz)2I (VI). (Yield, 65.4%). After filtering, 20 ml of ethanol were added to the solution. Pale blue crystals separated which corresponded to trans-Re(CO)s(PPhs)~I. (Yield, 32, 5%). The filtered solution was evaporated to dryness: the residue was identified as triphenylphosphine. (b) With iodine 0-190g of the compound (Va) were suspended in 5 ml of ethanol, and treated with 3"8 ml of an 0.24 N ethanolic solution of iodine (molar ratio 3 : 8). On stirring for 24 hr at room temperature, pale blue crystals were formed, which corresponded to trans-Re(CO)s(PPhs)~I. (Yield 32.7%). The filtered solution was neutralized with 11.0 ml of an 0.01 N ethanolic solution of KOH. From the solution white crystals separated, which were identified as KReO4. (Yield, 61%). The filtered solution was evaporated to dryness: the residue was identified as triphenylphosphine oxide. (c) With hydrogen chloride. 0. I g of the compound (Va) were dissolved in 20 ml of benzene, to which was added 5.0 ml of an ethanolic solution of hydrogen chloride 0.5 N. The mixture was refluxed for 30 min, and evaporated to dryness. On addition of 5.0 ml of benzene, orange crystals separated which corresponded to ReO(PPhs)2CI2I (VII). (Yield, 64.5%). The filtered solution was treated with 5.0 mi of hexane :brown crystals separated, which were identified as Re(CO)~(PPhs)~I (IV). (Yield, 32%). The filtered solution was evaporated to dryness: the residue was identified as triphenylphosphine. (d) With carbon monoxide. 0-1 g of the compound (Va) were dissolved in 20 ml of benzene and refluxed, under carbon monoxide, for 1 hr. Pale blue crystals separated, (yield, 82%), which corresponded to trans-Re(CO)s(PPhs)2I (IV). (Vb) Dihydridobromocarbonyltris( triphenylphosphine ) rhenium A mixture of 0.1 g of the compound (IIc) and 0.1 of tripbenylphosphine were refluxed in 4.0 ml of ethanol, under nitrogen, for I hr. Brown crystals formed, which were recrystallized from benzene and ethanol, under nitrogen (yield, 76%). The compound is soluble in benzene, dichloromethane, carbon disulphide; insoluble in ethanol, methanol, acetone and hexane.

RESULTS AND DISCUSSION

The reaction: ReHs(PPh3)s + ½X~ = ReH4(PPhz)sX + ½H2 takes place quantitatively, as known by the measurement of the hydrogen evolved (Table 3, N°D. The compound (II) reacts in benzene solution either with iodine or with hydrogen chloride to give hydrogen (gas chromatographic analysis). Thus its chemical behaviour is that ofa hydridic compound (Table 3). Like other hydridie complexes of rhenium stabilized with triphenylphosphine, on treating the compound (II) with dilute hydrochloric acid, a derivative of Re(IV) is isolated.

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M. FRENI et al.

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Halogenohydrido and halogenocarbonylhydrido complexesof rhenium

3215

Table 3 N*

Compound

I

ReHs(PPhs)s

II

ReH4(PPhs)sl

V

ReH~CO(PPh3)sI

Reagent Benzene + Benzene + Benzene + Benzene + Benzene + Benzene + Benzene +

I~(l eq.) I~ HCI 12 HCI Iz HC1

Mole of gas/g atom Re 0.48-0-44-0-58 2-33-2.19-2.00 3-90-4.06-4.12 0.86-0.91-0-93 2-23-2.19-2.16 0.24-0.26-0.29 3.98-4-03-4.02

The reaction with hydrochloric acid gives a 98% yield of Re(PPhs)~CIaX, compound (III), and triphenylphosphine has also been found in the reaction residue. Consequently we consider that the reaction has the stoichiometry ReH4(PPh3)aX + 3HCI = ½H2+ Re(PPh3)2CI3X + PPha although considerably less than the theoretical amount of hydrogen was evolved (see Table 3). The compound (III) with X = I is crystalline, brown and paramagnetic with X , = 5560.10 -e cmS/mole. The compound ReH4(PPh3)3I (IIa), treated in air with an excess of iodine in benzene, evolves almost one mole of gas per g atom of Re by the likely reaction: ReH4(PPh3)3I + Is + 02 = ReO2(PPh~)2I (VI) + PPh~I2 + 2H2. The complex (VI) has been isolated and characterized, and the gas, analysed by gas chromatography, is hydrogen, but the yield is lower than the equation requires (See Table 3 and Experimental). The derivative of rhenium(V) ReO~(PPh3)2I (VI), obtained by this reaction, is described here for the first time and a note concerning it, is in press [3]. The compounds (II) react with carbon monoxide, like the compounds (I) [5], giving the well-known trans-Re(CO)a(PPha)2I (IV)[4], in 84% yield. The compound (IV), obtained by this way, is deeply coloured but becomes white after many recrystallizations. The compounds (II), on heating with triphenylphosphine in ethanol, under nitrogen, give violet crystalline products with formula ReH~(CO)(PPhs)aX, where X = Br, I. These compounds are diamagnetic, non-electrolytes, unstable in air. We propose the following reaction for the decomposition of the derivative with X = I in the presence of oxygen. 3ReH2CO(PPh3)3I + 202 = Re(CO)s(PPha)2I + 2ReO2(PPha)eI + 3PPha+ 3H~. All the solid products of this reaction were isolated in quantitative yields and characterized (See experimental). The chemical behaviour of the compound (V), with X = I, shows very clearly its hydridic nature; treating the compound 5. M. Freni, D. Giusto and V. Valenti, J. inorg, nucl. Chem. 27, 755 (1965).

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M. FRENI et al.

(V) with iodine or hydrogen chloride in benzene, gives hydrogen as shown by gas chromatographic analysis. We could suppose that the gas contains some carbon monoxide, too, because of the carbonylic nature of the compounds. However it is completely absent; and no carbon monoxide is formed in these reactions. When the compound (V) is treated with an excess of iodine in benzene solution, it reacts with 5.33 equivalents of iodine per g atom of rhenium, according to the following reaction: 3 ReH2CO(PPha)31 + 812 + 5/20~ ÷ 10HzO = Re(CO)a(PPh3)zl + 2HReO4 + 7PPhaO + 18HI + 3H2. The solid products of the reaction have been isolated in almost quantitative yield and characterized. (See Table 3 and Experimental) The reaction with hydrogen chloride takes place probably according to the equation: 3ReH~CO(PPha)3I + 4 H C I + O~ = Re(CO)3(PPh3)~I + 2ReO(PPhs)2IC12 + 5H2 + 3PPha.

(VII)

Only three of the products of this reaction have been isolated in almost quantitative yield, because considerably less than the theoretical amount of hydrogen was evolved (See Experimental and Table 3). As seen, all these reactions need the presence of oxygen. The compound (V), in the presence of carbon monoxide gives Re(CO)a(PPha)2X. I.R. Spectra. The i.r. spectrum of the compound (II) in nujol mull shows the usual weak and broad bands in the stretching and bending region of the metalhydrogen bond. There are several bands around 2000 cm -1 and very weak ones around 800 cm -1 (See Table 4). As with the rhenium hydrides previously reported[l], we were unable to prepare deuterated compounds, so that the assignment of the absorption bands to Re H stretching vibrations is not quite conclusive. Deuterides have been prepared by other workers for many rhenium hydrides [6]. Therefore, any suggestion on the structure of these compounds, based upon these i.r. data, is tentative. The i.r. spectrum of the compound (V) with X = I in nujol mull, shows a very strong band at 1822 cm -~ which can be assigned to the CO stretching mode, two weak and broad ones at 1917-1945 cm -1 and a very weak band at 1870 cm -1, we can assign to metal-hydrogen stretching modes. The spectrum, recorded in benzene solution, in the absence of air, shows the same pattern. On the basis of this spectrum we can make some suggestions about the structure of the compound: as the CO stretching band is at such low energy we can assign it to bridging CO or, however, to a CO group bonded with a bond order very close to two, as shown by other authors[7], and by us[5]. The measurements 6. J. Chart and R. S. Coffey, Chem. Comm. 545 (1966); S. C. Abrahams, A. P. Ginsberg and K. Knox, lnorg. Chem. 3, 558 (1964). 7. W.J. Kirkham, A. G. Osborne, R. S. Nyholm and M. H. Stiddard, J. chem. Soc. 550 (1965).

Halogenohydrido and halogenocarbonylhydrido complexes of rhenium

32 i 7

Table 4 N° Ia Ib IIa lib llc lid IIe Va Vb

Compound

V~-a(Cm -1)

ReH~(PPha)3 1970-1900 ReHs(Ppta)3 1975w- 1945-1900w- 1875 ReH4(PPh3)3I 2050w- 1995vw- 1900-1815w ReH4(Ppt3)3I 1995w-1930-1840 ReH4(PPha)aBr 2015w-1930w-1895 ReH4(PPha)3SnCIa 2097w-1963w-1929-1811w ReH4(Ppto)aSnCI3 2016w-1936--1870w ReH2CO(PPh3)3I 1945w-1917w-1870w ReH2CO(PPha)3Br 1950w-1910w-1880w

6ae-H(Cm-l)

Vc-o(Cm-0

Usa-el(era -1)

850 870 867-805 870-840 850-790 810 850 833 805

-------1822s 1815s

-----328s-304 332s-307 ---

All in nujol mulls, unless otherwise noted.

of molecular weights ought to be very useful. These were carried out, but we obtained very low values even for a monomeric formula, probably because of decomposition of the compound in solution. Only an X-ray diffraction study could resolve the structure, but so far, we have not been able to obtain crystals suitable for this purpose. N M R spectra. Both the stoichiometry and the-hydridic nature of the compounds (II), were confirmed by N M R data. Its spectrum was recorded in deuterobenzene solution. As in other known rhenium hydrides[l, 2,6,8], the N M R spectra show only one signal for the hydridic hydrogens because of their rapid Table 5 Coupling N°

Compound

Ia

ReHs(PPh3)3*

Ib

ReHs(Ppt3)3*

IIa

ReH4(PPha)aIt

IIc

ReH4(PPh3)aBrt

IIe

ReH4(PPt3)3SnCIat

Va

ReH2CO(PPh3)alt

Vb

ReH2CO(PPh3)sBrt

constant(c/s)

Proton resonance r

Relative intensity

Fine structure

Assignment

2.7 14.66 2.2-3.1 8 14.70 2.8 12.86 2.8 11.82 2.9 7.70 13.75 2.85 12.90 2.85 11.85

45 5 36 27 5 45 4 45 4 36 27 4 45 2 45 2

muitiplet quadruplet multiplet singlet quadruplet multiplet quadruplet multiplet quadruplet multiplet sing,let quadruplet multiplet quadruplet multiplet quadruplet

CoH5 Re--H CoH4 CH 3 Re--H C6H5 Re---H C6H5 Re---H C6H4 CHa Re---H Cell5 Re---H CoH5 Re---H

*In deuterobenzen¢ solution. t i n dichloromethane solution. 8. A. P. Ginsberg, Transition Metal Chemistry 1, 111 (1965).

JP-a

19

18.9 24.9 24.5

24 25.5 25

3218

M. F R E N I et al.

intra- or inter-molecular exchange in solution. Therefore, we cannot say anything about the structure of these complexes. It is, however, unlikely that these hydridic hydrogens are equivalent, at least in the solid state. The electric dipole moments of these compounds do not help solve the problem as all the moments are rather low, as in other known hydrido complexes of rhenium[I, 2, 8]. Furthermore, the fact that, the substitution of hydrogen by halogen does not change much the electric dipole moment of the compound, was unexpected, Since when IrHa(PPha)a is converted to IrH2I(PPha)a [9] the electric dipole moment increases from 2.2 to 5.5 D. For the complexes (V) both the hydridic nature and the stoichiometry were confirmed by NMR data, recorded in deuterobenzene or in dichloromethane solution. Very surprisingly the spectra shows a peak at the same position as the peak in the spectrum of the compound(II). So, at first, we thought that the complex (V) was a mixture of compound (II) and a complex which contains the carbonyl group, but the i.r. spectrum of these compounds does not agree with this supposition and we think, therefore, that compound (V) is monomeric and heptacoordinated. We report a scheme of the reactions known so far, for the hydrido complexes (I): Xz

ReHsP~

P ReHaP4

DPE $ ReHa(DPE)2

EtOH + P

> ReH4P3X

> ReH2COP3X

i DPE ~ Re(CO)2(DPE)2

X,

P = PPhs; D P E -- 1,2 bisdiphenylphosphinoethane; X = Br, 1. 9. J. Chatt, R. S. Coffey and B. L. Shaw, J. chem. Soc. 7391 (1965).

> [Re(CO)2(DPE)2]X