Indian Journal of ChemistryVol. 28A, January 1989, pp. 47-50

Synthesis & Reactions of [OS3(CO)10(MeCN)(PEt3)]

SHARIFF E KABIR* & MOHAMMAD B H HOWLADER

Department of Chemistry, Jahangirnagar University, Savar, Dhaka (Bangladesh]Received 15 December 1987; revised and accepted 11 April 1988

The c1uster[Osl(CO),o(MeCN)(PEt))] (II), obtained by the reaction of [Os)(CO)IIPEt))] with Me)NO/MeCN, reactswith trifluoroacetic acid to give the singly protonated cation [Os)H(CO)\O(MeCNXPEt)W (III), isolated in good yield asthe hexafluorophosphate salt and [Os)H( CF)C02)( CO)IO(PEt))) (IV). Cluster-Tv undergoes decarbonylation on reflux-ing in heptane to give [OS3H(CF)C02)(CO)9(PEt))]. Cluster-Il also reacts with triethylphosphine at room temperatureto give 1,2-[Os)(CO),o(PEt))2j. The cationic c1uster[Os)H(CO)\O(MeCN)(PEt)))PF6 reacts with NEt,CN to give twomain isomers of [Os.1H(NCMeCN)(CO)IO(PEt))). The compounds have been characterised by IR, NMR and elementalanalyses.

The complexes [OS3(CO)II(MeCN)] and [OS3(CO)1O(MeCNU are useful intermediates in the prepara-tion of a wide variety of derivatives of the inert par-ent carbonyl cluster [Os3(CO)d (ref. 1-6), by the fa-cile replacement of MeCN ligands. We have de-scribed? the protonation of [Os3(CO)u(MeCN)] and[OS3(CO)IO(MeCNh] with HBF4.Et20 to give[OS3H(CO)II(MeCN)]BF4 and [OS3H(CO)1O-(MeCN)2]BF4. "The compounds [OS3H(CO)II-(MeCN)]PF6 and [OS3H(CO)IO(MeCN)]BF4 have al-ready been reported by others". Recently we report-ed? the synthesis and reactions of the related cation-ic clusters [OS3H(CO)lo(MeCN)-(PMe2Ph)j+ withEt4NCN to give" [OS3H(NCMeCN)(COk(PMe2PH)]9. Herein we report the synthesis andreaction of cluster [Os3(CO)IO-(MeCN)(PEtJ)].

Materials and MethodsAll reactions were routinely carried out under

oxygen-free nitrogen atmosphere but as the pro-ducts were air stable isolation procedures were car-ried out in air. Infrared spectra were recorded on aPE 983 spectrophotometer and PMR spectra on aVarian XL 200 spectrometer. Solvents were freshlydistilled prior to use.

The cluster [OS3(COltl(PEt3)] (cluster-I) was pre-pared by reacting [OS3(CO)II(MeCN)] with PEt3 atambient temperature and characterised by compar-ing the spectroscopic data with those reported 10.Synthesis ol[ OS3(CO)lo(MeCN)(PEt3)](c!uster-/f)

Trimethylamine oxide (Me3NO.2H20,0.070g; 1.5mol per mol OS3)was added to a solution of cluste-r-I (0.416g) in dichloromethane (75 ml) and acetoni-trile (5 ml) and the solution was stirred at room tem-perature for 30 min. The initial yellow colour turnedto orange. The solution was filtered through silica toremove excess trimethylamine oxide. The solvent

was removed in vacuo and the residue was recrys-tallised from hexane-dichloromethane at - 15° togive cluster-II (0.372 g, 88%) as orange crystals(Found: C,21.95; H, 2.3; N, 1.55; P, 3.2.CisH1SOlONOS3P requires C, 21.4; H, 1.8; N, 1.4; P,3.05%). IR(CH2Clz): ~CO) 2078m, 2024vs,2008vs, 1989vs, 1960s cm': PMR(CDC13): <51.10(td, CH2CH3), 2.05(dq, CH2-CH3) and2.68(s,CH3CN); 31P{IH}NMR (CDC13): <5-160.5.Synthesis ol[ OS3H( CO)1O(MeCN)(PEt3)] PF6(c!uster-III)

Trifluoroacetic acid (0.128 m1, 10 mol per molOS3)was added to a solution of cluster-Il (0.335g) indichloromethane (50 ml) and the solution was al-lowed to stand at room temperature for 30 min. Thecolour changed from orange to yellow. The solventwas removed in vacuo, the residue dissolved inmethanol and to this was added a methanolic solu-tion of NH4PF6 (0.108 g) followed by a few drops ofwater when a yellow precipitate appeared. This wasextracted with dichloromethane and recrystallisedfrom a CH2Cl2-diethyl ether to give cluster-ill(0.287 g, 75%) as pale yellow crystals (Found: C,19.15; H, 1.85; N, 1.2; P, 5.25. ClsHl9F601ONOS3PZrequires C, 18.7; H, 1.65; N, 1.2; P, 5.25%);IR(CH2CI2): v (CO) 2117m, 2083s, 2063s, 2027vs,2009ms cm-l; PMR (CD2CI2): <51.18 (td, CH2CH3

J =7.55 Hz), 2.37 (qd,CH2CH3), 2.65(s,CH3CN),-17.47(d,OsH,J= 10.5 Hz); 31P{IH}NMR(CDCI3):<5-162.3.

The solvent was removed from the mother liquorin vacuo and the residue chromatographed over sili-ca TLC plates. Elution with pentane-diethyl ether(10:1 ,v/v) gave two bands of which the main one wasfound to consist otTOs3H(CF3C02XCO)1O-(PEt3)](c1uster-IV), which rcrystallised as yellowcrystals from n-hexane (Found: C, 20.35; H, 1.95; P,

47

INDIAN J CHEM, JANUARY 1989

2.95. CIsHI6F30120S3P requires C, 19.95; H, 1.5; P,2.85%) IR(CH2Cl2): «CO) 2118w, 2084s, 2065s,2030vs, 2013m, 2005w cm': P~.1R(CDCl3): 01.15(td, CH2CH3), 2.20(qd,CH2CH3) and-15.25(d,OsH).Reaction of cluster- III with NEt4 CN

Tetraethylammonium cyanide (0.022g, 1mol permol OS3) was added to a solution of cluster-III(0.163g) in dichloromethane (25 rnl) and the reac-tion mixture was stirred at room temperature for 1.5hr- by which time the yellow solution had becomeorange. The solvent was removed in vacuo and theresidue extracted with diethyl ether. TLC separationof the residue [Si02, eluent, pentane-diethyl ether(10:1, v/v)] gave several bands, one of which gave[OS3H(NCMeCN)(CO)9 (PEt3)] (0.043 g, 30%) as ayellow solid (Found: C, 22.25; H, 2.65; N, 3.5; P,3.35. CIsHI9N2090S3P requires C, 21.45; H, 1.9; H,1.9; N, 3.05; P, 3.05%); IR(cydohexane): «CO)2092s, 2051 vs, 2020(sh), 2018vs, 2002s, 1994s,1982m, 1973m, 1960w cm:'. The other bands gavesmall amounts of compounds, which could not becharacterised.Thermolysis of[ OS3H(CF3C02)( CO)IO(PEt3)]

A solution of [OS3H(CF3C02)(CO)IO(PEt3)](0.05g) in heptane (30 ml) was heated to reflux for19 hr. Removal of solvent and TLC of the residue[Si02); eluent, pentane-diethyl ether (10:1, v/v)]gave [Os3H(CFJC02)(COMPEt3)](cluster-VII) as

(I)

M. CN\ >",'

C/IN\

(CO)40s - 1/\OS(CO)ltPE1l)

~-I .Os -H

(CO)l

(V)

48

yellow crystals (0.025g, 51%) from hexane-dichloromethane (Found: C, 19.35; H, 1.75; P, 3.1.CI7H16F30110S3P requires C, 18.85; H, 1.5; P,2.85%); IR(cyclohexane): «CO)2097 m, 2056s,2019vs, 2000s, 1981w, 1977w, 1952w cm" PMR(CD2Clz): 0 1.12(td,CH2CH3, J = 7.65 Hz), 2.21 (qd,CH2CH3) and -10.25 (d,OsH, J = 11.85Hz).Reaction of[ OS3(CO)IO(MeCN)(PEt3)] with triethyl-phosphine

A solution of PEt3 (0.037g, 3 mol/mol OS3) and[OS3(CO)IO(MeCN)(PEt3)] (0.105g) in dichlorome-thane (25 ml) was allowed to stand at room temper-ature under nitrogen for 72 hr. Removal of the sol-vent in vacuo followed by chromatographic separa-tion of the residue [TLC, Si02); eluent, pentane -dichloromethane (10:2, v/v)] gave 1,2-[OS3(CO)IO(PEt3)2] (0.09g,80%) and 1,2,3-[Os3(COMPEt3)3](0.005g, 4%) characterised by comparing the spec-troscopic data with those reported 10.

Results and DiscussionThe use of trimethylamine N-oxide to substitute

CO in both mononuclear and polynuclear metalcarbonyls is well establishedl-3,11-15. The mechan-ism of this reaction is considered to involve the nu-cleophilic attack of amine oxide at CO to giveM-C02NMe3 which eliminates CO2 and affordsM-NMe3

1,16. Trimethylamine is very weakly boundand could be easily replaced under particularly mild

+

(IV)

-co I c:

(OSlH(CO)9(CFlC01)(PEll) I

(VII)

KABIR et al.:SYNTHESIS OF [Os,(CO)J(lMeCN)(PEt3)]

conditions by an appropriate ligand which is usuallypresent in situ". For example, reaction of[Os}(CO)d with Me3NO in the presence of MeCNis a good route for the preparation of [OS3(CO)1t(MeCN))1,3. and [OS3(CO)10(MeCN)2P,2,l7. As ex-pected we have found that treatment of [OS3(CO)11(PEt3))(cluster-I) with trimethylamine oxide in thepresence of acetonitrile at room temperature givescluster-Il in very good yield (88%). The reaction wasmonitored by infrared spectroscopy following thedisappearance of «CO) bands due to[OS3(CO)ll(PEt3)). After usual work-up cluster-Ilwas obtained as air-stable., orange crystalline solidand characterised on the basis of infrared, PMR and3IP(IH}NMR spectra and elemental analyses. Its IRspectrum in 1-C = 0 region was very similar to thoseof corresponding clusters [OS3(CO )lo(MeCNhP,[OS3(CO)IO(PEt3h)IO and [OS3(CO)1O(MeCN)(PMe2Ph))9. Its PMR spectrum exhibitedthe expected quartet of doublets at b 2.05 and dou-blets of a triplet at b 1.10 for the CH2CH3 group,and a singlet at 2.68 attributable to the coordinatedMeCN ligand. The PMR chemical shift of theCH3CN ligand in cluster-Il lies closer to the valuesobserved for the coordinated CH3CN ligands of theclusters [OS3(CO)II(MeCN))\ [OS3(CO)IO(MeCN)j2and [OS3H(CO)IO(MeCN)) BF48.The 31p(IH} NMRspectrum of cluster-Il displayed a single resonanceat b -160.5 relative to ~OMe)3' This characteristicupfield shift is due to coordination of PEt3 to themetal framework.

Cluter-Il reacts with PEt3 at room temperature togive 1,2- [OS3(CO)IO(PEt3)2) in very good yield(80%). The cluster 1,2- [OS3(CO)IO(PEt3h)was pre-viously prepared 10in low yield by the reaction of[OS3(CO)12)with PEt3 in refluxing toluene.".

The affinity of [OS3(CO)12Jand its tertiary phos-phine substituted derivatives for protic acids is wellestablished 19-21.Thus as expected the reaction of[OS3(CO)IO(MeCN) (PEt3)) with fivefold excess ofCF3C02H gives the cation [OS3H(CO)1O(MeCN)(PEt3W (cluster-Ill) isolated as the hexafluorophosphate salt. The cationic cluster-Ill has beencharacterised on the basis of spectroscopic (IR andNMR) data and elemental analyses. Its IR spectrumin the v CO region was identical to that of[OS3H(CO)1O(PPh3)2)+. Its PMR spectrum exhibiteda doublet for the hydride at b - 17.47 with couplingto the phosphorus nuclei, indicating it to be a singleisomer. The methyl protons of CH3CH2 group ap-peared as double triplets at b 1.18 indicating thatthe methyl protons are coupled to both CH2 pro-tons and the 31p nuclei and similarly the CH2 pro-tons appear as double quarter (overlapped) at b2.37 while the CH3CN protons appear as a "in .l-t at

b 2.65 as expected for a coordinated CH3CN group.The 31p{IH}NMR spectrum of cluster-Ill displayeda singlet at b-162.3 [relative to ~OMeM

The formation of the cluster [OS3H(CF3C02)(CO)1O(PEt3))from the above reaction could be ra-tionalized as due to further reaction of [OS3H(CO)IO(MeCN)(PEt3)J+ with CF3COOH in which the ace-tonitrile ligand has been displaced by CF3COz: TheIR spectrum of this compound closely resembles?that of [OS3H(CF3C02)(CO)1O(PMe2Ph)) and on thisbasis we propose structure (IV) involving one bridg-ing and one terminal ligand for this compound. Thecluster-Tv undergoes ready decarbonylation in ref-luxing heptane to give [OS3H(CF3C02)(COM the IRspectrum of which exhibited bands around 2000cm ", similar to that exhibited'? by [OS3H(COMSR)(PR3)) which contains bridging SR and hydride li-gands. The PMR data are also consistent with theproposed structure.

Treatment of [OS3H(CO)IO(MeCN)(PEt3)J+ withNEt4CN produces the new cluster [OS3H(CNMe-CN)(COMPEt3)). The IR spectrum of this clusterclosely resembled those of [OS3H(NCHCN)(CO)9(PMe2Ph)) and [Os3H(NCMeCN)(COMPMe2Ph)).The latter two compounds exist as two isomers insolution. Two sets of hydride signals at b15.20(d,J= 8.5 Hz) and b -15.30 (d,J= 8.5 Hz) areobserved in the PMR spectrum of[OS3H(NCMeCN)(COMPEt3)). We believe that thisis due to the presence of two isomers in solutionwhich probably are clusters-V and VI but the over-lapping of PMR signals prevented proper assign-ments.

AcknowledgementWe would like to thank Dr A J Deeming, Depart-

ment of Chemistry, University College, London forproviding the IR and NMR spectra.

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INDIAN J CHEM, JANUARY 1989

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