Aldimine derivatives of molybdenum carbonyl

Po(vhedronVol.

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13, No. 6/7, pp. 975 982. 1994 Copyright ! , 1994 Elsevier Science Ltd Printed in (Jrcat Britain. All rights reserved 0277 5387/94 $6.00+0.00

Pergamon

A L D I M I N E DERIVATIVES OF M O L Y B D E N U M

CARBONYL

AMAR SRIVASTAVA* Department of Chemistry, G.B. Pant University of Agriculture and Technology, Pantnagar 263 145, India

and A.K. SHRIMAL and S.C. SRIVASTAVA Department of Chemistry, University of Gorakhpur, Gorakhpur 273 009, India

(Received 12 July 1993; accepted 28 October 1993) Abstraet--Aldimines (Ald) such as N,N'-bis(4-methylbenzylidene)-l,2-propanediamine (Ald~), N,N'-bis(4-methoxybenzylidene)-l,2-propanediamine (Ald 2) or N,N'-bis(4-N,Ndimethylaminobenzylidene)-l,2-propanediamine (Ald 3) reacted with Mo(CO)6 to give the respective cis-[(Ald)Mo(CO)4] complexes. N,N'-bis-(4-N,N-dimethylaminobenzylidene)1,3-propanediamine, in spite of comparatively poor reactivity, gave analogous tetracarbonyl, but its 1,4-butanediamine and 1,6-hexanediamine analogues did not give similar derivatives. Ald ~ Ald 3 after reaction with [(Ph3P)Mo(CO)5] gave corresponding aldimine bridged dinuclear [(Ph3P)(CO)4Mo(/~-AId)Mo(CO)4(Ph3P)]. Cis-[(Ald)Mo(CO)4] gave [(Ald) Mo(CO)3X2] when reacted with X2 (X = Br or I), but produced [(AId)MoC14] after reaction with chlorine. NO reacted with tetracarbonyls to yield a mixture of unusual [(NO)(Ald) Mo(CO)2(NO2)] and [(NO)2(AId)Mo(NO2)2], but NOC1 yielded only [(Ald) Mo(CO)2(NO)CI].

Monodentate aldimines are known not to form stable transition metal complexes, probably due to the insufficient basic strength of the imino nitrogen of the ~ N group. Bidentate aldimines with phenolic OH or nitrogen or sulphur of the ring, suitably near to the imino nitrogen, may stabilize the metalnitrogen bond through formation of chelate rings. Aldimines, which are unaided by these donors but contain two azomethine nitrogen atoms, in spite of their facile ligating capability due to easy chances of chelation, have also not been used to an appreciable extent in the CO displacement reactions of group VI metal carbonyls. In the present communication we report the donor behaviour of aldimines (Ald) (I and lI), prepared by the condensation of 1,2- and 1,3-diaminopropanes, 1,4-diaminobutane and 1,6diaminohexane with 4-methyl-, 4-methoxy- or 4N,N-dimethylaminobenzaldehyde in the CO displacement reactions of molybdenum hexacarbonyl. AIdL-Ald 3 yielded corresponding cis-[(Ald)

No(CO)4] fairly easily, but Ald 4 was not as reactive as the former three. Ald 5 and Ald 6, derived from long chain diamines, were reluctant to form similar derivatives. The reactions of Ald I Ald 3 with [(L--L)Mo(CO)4] ( L - - L = o-phen or 2,2'-bipy) and [(Ph3P)Mo(CO)5] have also been studied. Halogen oxidation and nitrosylation of all three cis[(AIdI-Ald3)Mo(CO)4] complexes have also been investigated. R C H = N C H 2CH(CH 3)N~---CHR (Ald 1, R -- 4-CH3C6H4 ) (Ald 2, R = 4-CH3OC6H4) (Ald 3, R = 4-(CH3)2NC6H4)

I R C H = N ( C H 2)nN=--CHR (Alda, n = 3, R = 4-(CH3)2N C6H4) (AldS, n = 4, R = 4-CH3C6H4) (Ald6, n = 6, R = 4-CH3C6H4) II

*Author to whom correspondence should be addressed. 975

976

A. S R I V A S T A V A et al.

RESUI,TS AND I)ISCUSSION Aid' Ald ~ rcactcd

with

nlolybdcnum

hexa-

carbonyl in boiling ben/one under argon lor 3 4 h to give corresponding cis-[(Ald)Mo(CO),l] (yield 76.3 81.9%). In no case were aldimine bridged [(CO)<._,,Mo(It-AId),,Mo(CO). ,,] deriwitives recovered. Repeated attempts to achieve more substitution by prolonged relluxing in tohiene or xylene or by heating the reactants in evacuated sealed pyrex tubes tip to 200 (" were unsuccessful. Similar rellux reaction with Aid 4 gave cis-[(Ald4)Mo(CO)4] in very poor yield (8.2%), but on heating a 1:1 mixture o f the rcactants tip to 200 C in an ewicuated sealed tubc for ca 5 h, it was obtained in appreciably good yield (50.8%). Although Aid" and Aid ~' produccd similar changes, no substituted carbonyl product could be obtained in these reactions. On using identical work tip, brown intractable substances, which did not melt on heating and exhibited insohible behaviour in all organic solvcnts, were isolated. The conclusion which emerges from these reactions is that the live-membered chelate rings in cis-[(Ald' AId~)Mo(CO)4] stabilize them easily. The presence o f a comparatively less stable six-membered chelate ring is responsible for the poor yield of ci,s-[(Alda)Mo(CO)4]. Still longer aliphatic chains contained in Ald s and Aid ~' do not givc stable ci, v[(Aid s or Ald<')Mo(CO)4]. In order to c o m p a r e the effect of aliphatic chain length on the d o n o r behavtour of Aid ( A l d - Aid ~ and Aid ~') and the parent diamines (N N), tile reactions o f Me(C())(, with 1,4-diaminobutane and 1,6-diaminohexanc were also carried out. It is remarkable that tile two diamines displayed enough basic strength to l'ornl stable [(N NaMe(CO)4] under similar conditions. All the cLv-[(Ald)Mo(CO)4] deriwitives are yellow brown, air-stable crystalline solids but show susceptibility towards oxygen in solution, particularly in oxygenated solvenls. The I R spectra o f these complexes are in accordante with cis structures (III). t:our CO stretching

bands due to tile 2a~+h~+h~ modes are invariabls observed in the 1R spectrunl o f each complex. A medium strong band at ~ 2000 cm ~ is assigned to the all mode, w'hicla maiMy involves lrallx-c'drbonyl groups. Bands at 1890 1900, 1870 1880 and 18_5 1 8 3 0 c m ~ may be attributed to the modes h~, ai and h> respectively. The validity of tile vibrational mode assignments have been checked by deducing CO and CO CO force constants. Tile values of/,~ and /<,_, i.e. the stretching force constants for (20 groups Ira#> and ci.v to tile scibstituent nitrogen atoms of Mdimines, respectively citlct the C O CO interaction COtltant,/q, were calculated by C o t t o n Kraihanzel secuklr equations. ~ Tile vahles o f k,, 1<~ and k, (in m d y n / ~ *), respectivcly for different cis[(Aid I AIdl)Mo(('O)a] complcxes arc 13.78, 15.25 and 0.34 for Aid ~" 13.8;5, 15.23 and 0.33 for A i d : : 13.78, 15.25 and 0.34 for Aid ~and 13.81, 15.16 and 0.37 liar AldL These values are vcry close to the wllues deduced for other nitrogcn-contciining cisdiscibstituted group Vl metal carbonyls. :~ Since the force constants have been calculated from the frequencies o f spectra in KBr discs, the vahies can bc considered to bc a lower limit, and wihies 0.10 0.20 units higher might well have been obtained from sohition data. The very small shift of ~ 10 cm ~ in v ( C ~ N ) o f coordinated Mdimines in these derivatives is attributable to the d o n a t i o n o f a lone pair of nitrogen atoms with almost no involvenlent of the C N re-bond. Other aldinline bands appcared with only minor shifts. Mixed ligand derivatives [(L L ) M o ( C O ) : L ] and [(L--L)Mo(('O)_,L:] (L L o-phcn or 2 , 2 ' - b i p y I. = N, P, As and Sb donor) a 7 are easily obtained by heating [(L LaMe(CO)4] and L in retluxing h y d r o c a r b o n s or neat where L is a liquid. On performing sitnilar reactions with aldimines for 10 h there was no indication ¢)1"further CO displacenlent. In spite o f the ease o f chelation, the irlertness of thcsc ligands may be attributed to the decreased basicity of azomcthine nitrogens c o m p a r e d to the nilroo'cn t l t O l l l S o f other n l o n o ;And p o l v d e n t a l e

ligands. On using longer rellux times (illore than I0 I1) alld xylcne as solvent [(L L a M e ( C O b ] they CHR

O

c

dccomposcd to give intractable non-carbonyl products in which the ratio of Mo ' L L w a s 4 ' l . Thesc substances were completely insohible in most

II

Me

organic solvents and rcnlaiiled unidentilied.

X

TIle decreased d o n o r behaviour ol"aldimines was o

X = --

t'urther demonstrated by the rcactions o1"cis-I(Ald j AId*)Mo(CO)4] with L L, which gave cis[(L LaMe(CO)4] (L L o-phcn or ],2'-bipy) by. displacing aldinmles easily tinder mild conditions.

CHR

CI|2CH(Ct|3 )-,

(lid

--

(CH2) 3 --

O11 perfornling thc reactions between cis-l(AId' AId~)Mo(COh] and PhJL dcriwitivcs o f an already known type [(AId)Mo(CO)~(PX0] (Aid P,CIt

977

Aldimine derivatives of molybdenum carbonyl NR'; R=2-pyridyl, R ' = M e , Et, cyclo-C6Hl,, Ph, PhCH2 and fl-naphthyl; 4-RC6H4C(zNR) ---C(zNR)-4-C6H4R, R = H, Me, OMe), ~'9 prepared by an identical method, could not be obtained. Instead, Ph3P displaced aldimines to give cis-[(Ph3P)2Mo(CO)4]. Another interesting type of reaction was between Ald~-Ald 3 and [(Ph3P)Mo(CO)d in refluxing benzene (5 h), where the aldimines displaced one CO molecule each from two molecules of [(Ph3P)Mo(CO)d to give corresponding aldimine bridged [(Ph3P)(CO)4Mo(/tAId)Mo(CO)4(Ph3P)] (IV), yield 78.4~80.7%.

more susceptible to air and moisture than the iodo analogues. The IR spectra of these derivatives, in addition to the aldimine bands, exhibited three strong v(CO) bands in the ranges 200(~2015, 1950 1960 and 1925-1930 cm t. The nature and number of bands were almost identical to the known heptacoordinated halocarbonyls~3 ~6 of group VI metals. The presence of normal aldimine bands indicated that these ligands were intact. CHR

× OC _ - C O c H R Ph3P ~

I t I

OC _-CO t

Mo "4------N - - C H 2 C H ( C H 3 ) - - N - - - - ~ Mo 4--- PPh3 I I

I i

x/

Mo I \N J

[ c u - - ca,

I I

II V 3 RHC O(2--- CO

OC--- CO

II

CHR

(iv) X = --

The IR spectra of [(Ph3P)(CO)4Mo(#-Ald) Mo(CO)4(Ph3P)] exhibited two very strong CO bands, one in the range 1945 1950 cm ~ and the other in the range 1890-1895 cm ', in addition to a weak band at ~ 2000 cm '. The presence of Ph3P and aldimine bands indicated that they were intact in the complexes. The v(C--N) stretching bands of coordinated aldimines in these derivatives also exhibited only minor shifts ( ~ 10 cm '). The spectral patterns of these complexes closely resemble those of other known derivatives '° ,2 of similar type.

Haloyen oxidation ofcis-[(Ald)Mo(CO)4] Cis-[(Ald)Mo(CO)4] ( A l d = A l d L - A I d 3) complexes produced corresponding heptacoordinated [(Ald)Mo(CO)312] derivatives (yield 67.2-74.6%) when reacted with one equivalent of iodine in benzene at ambient temperature under argon. Reaction with chlorine invariably displaced all the carbonyl ligands to give [(AId)MoCI4] (yield 83.3-87.1%). Bromine exhibited intermediate behaviour but the vigour of the reaction could not be controlled in all cases. [(AId)Mo(CO)3Br2] derivatives (yield 51.7 57.6%) were isolated only when strictly one equivalent of bromine was used. On using even a slight excess of bromine a mixture of [(Ald)Mo(CO)3Br2] and [(Ald)MoBr4] always resulted. Excess of bromine produced [(Ald)MoBr4] as the ultimate product in all cases. All the [(Ald)Mo(CO)3X2] (X = Br and I) derivatives were yellow-brown diamagnetic solids which dissolved in most organic solvents except light petroleum (all fractions). The bromo derivatives were

CI, - -

Br

(v) [(Ald)MoX4] (X = Br or C1) (V) were yellowbrown paramagnetic solids (#en"= 2.83-2.90 B.M.). They dissolved only in polar solvents such as acetone, methanol and T H F to give non-conducting solutions. They were unstable even when stored under argon for a few days and ultimately a mixture of aldimine and MoX4 was recovered in all cases. In this way the complexes exhibited marked differences from [MoC14L2] (L = MeCN, n-PrCN or PhCN) or [MoC14(L--L)] ( L - - L = 2,2'-bipy or tetramethylethylenediamine) prepared by other routes.17

Nitrosylation ofcis-[(Ald)Mo(CO)4] Nitrosylation reactions were studied using benzene solutions of nitric oxide or nitrosyl chloride. Nitric oxide reacted instantaneously with cis-[(Ald) N o ( C O ) 4 ] (Aid = Ald~-Ald 3) at room temperature under argon to give a mixture of [(NO)2(Ald) Mo(NO2)2] and [(NO)(AId)Mo(CO)2(NO2)]. The former precipitated immediately out of the reaction mixture as brown solids and were filtered, whereas the latter substances (yellow brown) were recovered by evaporating the supernatant liquid in vacuo. These reactions were quite different from the nitrosylation of other [(L--L)Mo(CO)4] ( L - - L = o-phen or 2,2'-bipy) complexes, in which only metal-metal bonded [(L--L)Mo(CO)2(NO)]2 were isolated. ~xThe derivatives of both types were diamagnetic solids. The non-carbonyls dissolved only in polar solvents but the carbonyls were soluble

978

A. SRIVASTAVA et al.

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in almost all common organic solvents except aliphatic hydrocarbons, in which they exhibited nonconducting behaviour. The IR spectra of [(NO)2(Ald)Mo(NO2)2] exhibited two v(NO) bands, one in the range 1770-1775 cm -~ and the other in the range 1650-1655 cm 1. The appearance of a new very strong band at 13801385 cm -I, in addition to the aldimine bands, clearly indicated the presence of a nitro group in these complexes. The IR spectra of [(NO)(AId)Mo(CO)2(NO2)] exhibited two CO and one NO stretching bands. The CO bands fall in the ranges 2010-2020 and 1930-1940 cm -~ and NO in the range 1770-1780 cm-1. Like [(NO)2(AId)Mo(NO2)2] they also exhibited one strong band at 1375-1385 cm-1, attributable to a coordinated nitro group. The appearance of two CO bands in the spectra is in agreement with the configuration in which the two CO molecules are cis to each other. Although the manner in which the derivatives containing both nitrosyl and nitro groups are formed is not obvious, aerial oxidation during isolation may result in the formation of such complexes.' 1.12It is presumed that originally nitrosyl products are formed but, in spite of great care, they ultimately change into nitro products. When NOC1 was used as a nitrosylating agent in place of NO, different results were obtained. Dropwise addition of a solution of NOC1 to cis-[(Ald) Mo(COM (Aid = Aldl-Ald 3) in benzene at room temperature under argon displaced two CO molecules to give the corresponding [(Aid) Mo(CO)2(NO)CI] derivatives (yield 71.0-72.6%). Soon after the addition of NOCI the reaction mixture became turbid. Filtration yielded a brown solid in all cases, but in insufficient quantity to allow for characterization. [(Ald)Mo(CO)2(NO)C1] derivatives were isolated by evaporating the supernatant liquid in vacuo. All the derivatives were diamagnetic solids and gave non-conducting solutions in acetone ( A m = 0.8-2.0 t2 ~ cm 2 mol-l). Two very strong CO absorptions in the ranges 20102015 and 1930-1935 cm -I and a single medium strong NO absorption in the range 1645-1665 c m - 1 in the IR spectra support the proposed formulae.

EXPERIMENTAL

All the experiments were performed under argon or in vacuo. [(L--L)Mo(CO)4] ( L - - L = o-phen or 2,2'-bipy) and [(Ph3P)Mo(CO)s] were prepared by the methods given in the literature. 19'2° The aldimines were prepared by condensing the appropriate aldehydes with the corresponding diaminoalkanes

in methanol. They were characterized by microanalyses, IR and mass spectral measurements. Nitric oxide was purified by passing through a concentrated solution (50%) of NaOH. Halogens were estimated gravimetrically by precipitating them as silver salts. Conductivity measurements were performed on a Toshniwal conductivity bridge (Type CL 01/02 A). IR spectra were measured on a Perkin-Elmer Spectrophotometer model 577 in KBr discs. Details of representative compounds only are given below. Other compounds and their characterizational data are given in Table 1.

Preparation of cis - tetracarbonyl- N , N ' - b/s(4 methylbenzylidene) 1,2 propanediam&emolybdenum(O) Hexacarbonylmolybdenum(0) (0.52 g, 2 mmol) and N,N'-bis(4-methylbenzylidene)-l,2-propanediamine (0.55 g, 2 mmol) were refluxed in benzene (15 cm 3) under dry argon for 3 h. The colour of the reaction mixture turned yellow after ,,~ ½h and finally became orange. A yellow-orange air-stable solid was obtained by cooling the reaction mixture and evaporating the solvent in vacuo. Unreacted reactants were removed by washing the residue several times with light petroleum (40-60 ° C). The product was recrystallized in benzene (yield: 0.76 g, 78.1%). Found: C, 56.9; H, 4.5; N, 5.8. Calc. for C23H22N2OaMo : C, 56.7 ; H, 4.5 ; N, 5.7%. IR v(CO)" 2000m (a11), 1900m (bl), 1870s (al2), 1825s (b2) cm -I.

Preparation of/~-N,N" - bis(4-methylbenzylidene) 1,2 propanediamineoctacarbonylb&( triphenylphosphine )dimolybdenum( O) Pentacarbonyl(triphenylphosphine)molybdenum(0) (0.99 g, 2 mmol) and N,N'-bis(4-methylbenzylidene)-l,2-propanediamine (0.55 g, 2 mmol) were refluxed in benzene (15 cm 3) for 5 h under argon. After cooling the reaction mixture to room temperature, the solvent was removed in vacuo. The unreacted pentacarbonyl(triphenylphosphine)molybdenum(0) and the aldimine were removed by washing the residue with light petroleum (4060°C) several times, and the yellow solid was crystallized in benzene (yield: 0.96 g, 78.8%). Found: C, 62.2; H, 4.2; N, 2.2. Calc. for C63 H52N2OsPzMo2: C, 62.0; H, 4.2; N, 2.2%. IR v(CO): 2000w, 1950s, 1895vs cm -1. Mol. wt (by cryoscopic method): 1208 (calc. 1218).

Aldimine derivatives of molybdenum carbonyl Preparation o f tricarbonyldiiodo-N,N'-bis( 4 - methylbenzylidene)- 1,2-propanediaminemolybdenum(II)

A solution of iodine (0.50 g, 2 mmol) in benzene (20 cm 3) was added dropwise to a solution of cistetracarbonyl-N,N'-bis(4-methylbenzylidene)- 1,2propanediaminemolybdenum(0) (0.97 g, 2 mmol) in benzene (20 cm 3) under argon at room temperature. The reaction mixture was magnetically stirred. When it became turbid it was set aside for ~ ½ h. On filtration a brown residue was obtained in very small quantity, which was insufficient for characterization. Evaporation of the solvent from the supernatant liquid yielded a brown mass. It was washed well with light petroleum (40-60°C) to remove unreacted iodine. To free it from the unreacted parent carbonyl, it was redissolved in a minim u m quantity of benzene and was reprecipitated by adding light petroleum (40-60°C). The precipitated substance was filtered and dried in vacuo (yield: 1.04 g, 73.0%). Found: C, 37.2; H, 3.1 ; N, 3.9; I, 35.4. Calc. for C22H22N20312Mo: C, 37.0, H, 3.0; N, 3.9; I, 35.6% . IR v(CO): 2000s, 1955s, 1925s c m - 1.

N, 11.0%. IR v(CO): 2020s, 1940s cm

981 ; v(NO) :

1775m cm i; v(NO2): 1380s cm i.

Preparation o f dicarbonylchloronitrosyl - N , N ' bis( 4 - methylbenzylidene) - 1,2-propanediaminemolybdenum(O)

Similarly, a magnetically stirred benzene solution of cis-tetracarbonyl-N,N'-bis( 4-methylbenzylidene)1,2-propanediaminemolybdenum(0) (0.97 g, 2 mmol in 20 cm 3) reacted with NOCl-saturated benzene (15 cm 3) at room temperature to give a turbid reaction mixture. Filtration yielded a very small quantity of a brown product which was insufficient for characterization. Evaporation of the supernatant liquid in vacuo yielded a yellow solid which was washed thoroughly with light petroleum (40-60°C) and was dried in vaeuo (yield: 0.72 g, 72.6%). F o u n d : C, 51.0, H, 4.4 ; N, 8.5 ; C1, 7.0. Calc. for C21Hz2N303C1Mo : C, 50.8; H, 4.4; N, 8.4; C1, 7.1% . I R v(CO): 2015s, 1935s c m - l ; v(NO) : 1650s cm -1. Acknowledyement--We greatly appreciate the award of

Preparation o f dinitrodinitrosyl-N,N' bis(4 methylbenzylidene) 1,2-propanediaminemolybdenum(O) and diearbonylnitronitrosyl - N , N ' - bis (4-methylbenzylidene) 1,2-propanediaminemolybdenum(O)

NO-saturated benzene was added dropwise to a benzene solution of cis-tetracarbonyl-N,N'-bis(4methylbenzylidene) - 1,2 - propanediaminemolybdenum(0) (0.97 g, 2 mmol in 20 cm 3) with constant stirring under dry argon at room temperature. A yellow solid immediately precipitated out of the reaction mixture. It was filtered, washed thoroughly with benzene to remove unreacted materials and was dried in vacuo. It was characterized as dinitrodinitrosyl - N , N ' - bis(4 - methylbenzylidene)1,2-propanediaminemolybdenum(0) (yield : 0.40 g). Found: C, 43.4; H, 4.1; N, 16.0. Calc. for CI9H22N606Mo: C, 43.3; H, 4.1; N, 15.9%. IR v(NO): 1770m, 1650m cm J; v(NO2): 1385s c m - 1. Another product was also obtained in the form of a yellow precipitate by adding excess light petroleum (40-60°C) to the supernatant liquid. It was filtered, washed several times with light petroleum (40-60°C) and dried in vacuo. It was found to be dicarbonylnitronitrosyl - N,N" - bis(4 - methylbenzylidene)- 1,2-propanediaminemolybdenum(0) (yield : 0.43 g). Found: C, 49.7; H, 4.4; N, 11.0. Calc. for C21H22N4OsMo: C, 49.8; H, 4.3;

a Senior Research Fellowship (to A.S.) by the Council of Scientific and Industrial Research, New Delhi, India.

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