Indian Journal of ChemistryVol. 34A, January 1995, pp. 27-30

Symbiotic reactions between five- and six-membered hypervalent spirobicyclicphosphoranes and transition metal carbonylatest

B N Anand", Rajwant Bains, Kussam Aggarwal & Km UshaDepartment of Chemistry, Panjab University, Chandigarh 160014, India

Received 30 May 1994; revised and accepted 23 August 1994

The nucleophilic substitution reactions of five- and six-membered hypervalent phosphorus containingspirobicyclic phosphoranes with metal carbonylates of high nucleophilic character result in the isolation ofthe corresponding metallated phosphoranes. The presence of five- and six-membered rings in their structuresinhibits the ionising of these compounds into their phosphonium cations in solutions. These have beencharacterised by elemental analysis, molar conductance and spectroscopic (mass and 1H NMR) and TGstudies.

The reported synthesis of both cyclic and- acyclicmetallated phosphoranes! -4 has brought about notonly the symbiotic merger of transition metal andhypervalent chemistry" of phosphorus, but has alsoextended the scope of hypervalent bonding theory.However, synthesis of cyclic species has been limitedto five- membered metallophosphoranes in which thehypervalent phosphorus besides being directlybonded to transition metal is bonded only to oxygen.Though four-membered metallophosphoranes areknown", where the metallated pentacoordinatephosphorus is bonded to heteroatoms other thanoxygen, such moieties are not known in case of five-and six- membered bicyclic metallophosphoranes.We report here the synthesis and characerization ofthese species.

Materials and MethodsAll reactions were carried out in an atmosphere of

nitrogen gas, purified by passage over hot BASFcatalyst R-3-11 and supported by P4010 (aquasorb).Solvents and reagents were degassed by repeatedevacuation and flushing with pure nitrogen beforeuse. Glassware was flame-dried in vacuo before use.Tetrahydrofuran (THF) was distilled fromNa/benzophenone under nitrogen. N,N'-Dime-thylformamide was purified by reported methods 7.

Phosnhorus, sulphur and manganese wereestimated gravimetrically by reported methods".

rAccepted for presentation at Journal of Organometallicconference held at Technische Universitat, Munchen, Germany(November 4-5, 1993).

Microanalyses for C, Hand N were performed by themicroanalytical service of the Panjab University,Chandigarh. Thermal analysis was carried on aMOM Budapest Derivatograph (type Paulik, Paulikand Erdey). Conductances of millimolar solutionswere measured on a Century CC 601 conductivitybridge. Mass. spectral measurements were carried outon a VG Micromass MM 70/70F spectrometer both at70 and 20 eV. 1H NMR spectra were recorded at 90MHz on a Varian-390 spectrometer. The peakpositions in 1H NMR spectra were measured withreference to Me4Si and are uncorrected for theparamagnetic shift of the solvents.

Freshly sublimed dimanganese decacarbonyl andIicobalt octacarbonyl (Strem Chemicals, U.S.A.)were used. The starting materials 1-4 were preparedaccording to published methods".

(i) Preparation of pentacarbonyl-(l-,I'JJ'-tetra-hydro-2,2' -spirobi-[2H-I,3,n 5-ben::.odia::.a-phosphon-2-yl) manganese (5)

The compound [Mn2(CO)IO] (1.47g, 3.8 mmol) intetrahydrofuran (THF) (75 crn') was treated withsodium metal 0.27g (7.6 mmol + 50% excess) inmercury (lOOg).The resulting Na[Mn(CO)s] solutionwas filtered an added dropwise to a SOlution of 1(2.12g, 7.6 mmol) in THF at -78°C with continuousstirring. The dropwise addition was done through apressure equalising (teflon stop-cocked) droppingfunnel. The three-necked reaction flask was fittedwith a nitrogen inlet stop cock and a rubber septum.The stirring was continued for 2h at this temperature.The reaction mixture was thea.allowed to warmslowly to ambient temperature with -continuous

28 INDIAN J CHEM. SEe. A, JANUARY 19<)5

stirring overnight. It was then filtered through afiltration unit in a stream of dry nitrogen. The solventwas removed from filtrate in vacuo and the residuedried. The residue was further purified bycrystallising from THF and petroleum ether(60-80°C) to finally obtain a very light browncrystalline material; yield 1.86g (60%), m.pt. 160°C(decomposed); molar conductance in N,N'-dimethylformamide = 19.85 ohm -lcm2mol-1 [FoundC,45.5I;H,3.01; N,12.67; P,7.50; Mn, 12.70. Calc. forCI7HI~MnN40SP: C,46.58; H,2.74; N,12.78; P,7.08;Mn,12.53]. Its mass spectrum exhibited a molecularion peak im]z 437,5% relative intensity) and peakscorresponding to the following species:[C6H4(NHhhP-Mn(CO); (353,45%);[C6H4(NHhhP-Mn+ (297,38%); and C6H4(NH)zC6HSNHP-Mn + (283,100%).(ii) Pentacarbonyl-(2,2' ,3,3' -tetrahydro-2,2'-spirobi[1 ,3,2 A5-benzothiazaphospholj-2-yT)manganese (6)

This compound was prepared by a method similar tothat used for 5. The product was a pale yellowsolid;yield35%; m.pt 92-9SOC; molar conductance in NN'-dime-thylformamide = 16.57 ohm -lcm2mol-1 [FoundC,42.84; H,1.95; N,5.78; P,6.0; S,12.91; Mn,10.21.Calc. for C17HlOMnN20SS2:C,43.22; H,2.11; N,5.93;P,6.57; S,13.56; Mn,11.63]. Its mass spectrumexhibited a molecular ion peak (m/z471, 3% relativeintensity at 70 e'Vf and peaks corresponding to lh~following species: [C6H4(NHS)hP-Mn(CO)!(443,50/0); [C6H4(NHS)hP-Mn(CO)i (415,5%);[C6H4(NHS)hP-Mn(CO)+ (359,5%); (H4Nh-SPMn+(297,25%); and C6H4SP-Mn+ (193,100%).

(iii) Pentacarbonyl-{ 2,2'(3H,3' H)-spirobi-[l ,3,2-A 5-benzoxazaphosphol-2-yT) manganese (7)

This was prepared by a method similar to that usedfor (5). The pale brown solid was obtained in 53%yield and it decomposed without melting at 140°C;molar conductance in N,N' -dimethylformamide =37.18 ohm -lcm2mol-1 [Found: C,46.02; H,2,40;N,5.95; P,6.50; Mn,11.58. Calc. for C17HlOMn-N207P: C,46.37; H,2.27; N,6.36; P,7.04; Mn,12,48].Its mass spectrum exhibited a molecular ion peak tm]z439,3% relative intensity) and peaks correspondingto (C6H4NHOhPMn(CO)t (411.6%); (C6H4NHOh-PMn(CO){ (355,25%); (C6H4NHOhPMnCO+(327,14%); and (C6H4h02NHPMn + (284,100%).(iv)Pentacarbonylbis-(l.2,3 A-tetrahydro-v.s ,2-benzodiazaphosphorin-Z-yl) manganese (8)

It was prepared by a method similar to that used for(5). The pale yellow crytalline solid was obtained in1C% yield and decomposed at 70°C without melting;molar conductance in N,N' -dimethylformamide=-

18.83 ohm -lcm2mol-1 [Found: C,47.02; H,2.80;N,IO.79; P,6.1O,Calc. forC'9H12MnN407P: C,46.15;H,2,42; N,11.33 and P,6.27). Its mass spectrumexhibited a molecular ion peak (m]z 493, 1% rela-tive intensity) and peaks corresponding to(C6H4NH.CONHhP-Mn(CO)t (465,1%); (C6H4NHCONHhP-Mn(CO)j (437,3%); (C6H4NH CONH)z-P-Mn(CO)+ (381,5%); (C6H4hCO(NHhP-Mn+(310,100%) and (C6H4hP-Mn+ (237,11%).

Results and DiscussionCompounds 1-4 undergo nucleophilic

substitution reactions with Na +Mn(CO)5 in I: I moleratio in THF at -78°C to form five- andsix-membered metallated spirobicyclicphosphoranes 5-8. The reactions show the cleavablenature of P - CI bond 11 in 1-4.

The reactions could be visualised as shown inScheme 1.Such type of substitution reactions are very welldocumented in literature 1,6 and are more general andstraightforward in comparison to the synthetic routereported by Ebsworth and coworkers- for thesynthesis of this class of compounds. However, thesenucleophilic substitution reactions are highly specificin terms of nucleophilicity of metal carbonylates. Thecorresponding reactions of 1-4 with Na +CO(CO)4were not successful, since the products isolated weresticky materials with variable compositions. Thefailure of these reactions is attributed to the lownucleophilicity of cobalt tetracarbonylate!". Thesecompounds behave as true phosphoranes as isevidenced from the molar conductance values' oftheir millimolar solutions in N,N' -dimethyl for-mamide, thus ruling out the possibility of theirexistence as phosphonium salts in solution. This maybe because of the fact that pentacovalent structure isstabilized by the incorporation of five- andsix-membered ringI4",IS as well as because of the wellknown Thorpe-Ingold effect!", These compounds

(©(}-CIII 2

! E=NII ~1 E=S1 E=O

M (CO) Na I Hg + -n2 10 Ihl ~ Na Mn(CO)S

Mn(CO~

{©C:~k::©

+ _ thl ~ ~ ~ E ~NH+ NQMn(CO)s -78·C ~ E=S

~ Mn(CO)S~ L E~O

©CN<, 1 ..••....... N)§J() N~P'N ()

C•.•.I I ..•.•C

II tl H uo 0],

Scheme ·1

ANAND et al: SYMBIOTIC REACTIONS BETWEEN PHOSPHORANES & METAL CARBONYLATES 29

III 0:g 10~•• 20~•••30~•••40e~ 50•••li! 60•••IL 70

ao

Fig. l-rG-DTG-DTA of6

are sufficiently volatile and give a good mass spectra.All these compounds exhibit signals of very lowintensities (1-5% of the base peak) corresponding tomolecular ion peaks. The fragmentation patternfurther show signals corresponding to loss of CO.However, the loss of CO, unlike in pure metalcarbonyls 17 is not stepwise. The non-sequential lossof CO was also observed while studying the thermalbehaviour of these compounds. For example, in thederivatogram of 6 (Fig. 1) obtained by projectingDTG curve on TG, it is possible to identify theinflexion points on TG, which correspond to variousintermediates. It starts decomposing around 40°C,and between 40 and 100°C, a mass loss equivalent totwo molecules of CO is observed in the first step ofdecomposition. It then loses the remaining threemolecules of CO in a single step. This second step ofdecomposition is completed at 170°C.The loss of COis also evidenced by DT A curve corresponding tothese steps which indicate an exothermicdecomposition process. The compound thendecomposes through some unidentifiedintermediates to yield ultimately a stable residue ofcomposition Mn2P207 between 610 and 700°C,through the formation of slightly less stable MnHP04(ref. 18). This type of decomposition pattern isobserved for compounds 5, 7 and 8.

The vP-CI band in 1-4 observed in the infraredregion in the range 500-530 em -I is of diagnosticvalue in monitoring these reactions'<'+. The fact thatCI is completely substituted in 1-4 by Mn(CO)5-

Table 1-1H NMR and infrared (vCO) data

Compound H (8, ppm)5 6.70-8.0*

[12 H, 8 aromatic and4 N-H, m]

6 7.03-8.0*[lOH, 8 aromatic and2 NH, m]

7 6.50-7.56*[10 H, 8 aromatic and2 NH,m]

8 7.30-7.50**[12 H, 8 aromatic, 4 NH,m]

*IH in THF referenced to Me4Si .**IH in d6-DMSO referenced to SiMe4m = multiplet***Solution spectra in THFw=weak; vs = very strong & med = medium

JR***2f}70 w2041 vs2010 m, sh

2070w2045vs2010 med

2070w2045 vs2010 med

2070w2030 vs2000 vs

is exhibited not only by the disappearance of the signaldue to vP-CI but also by the appearance of additionalbands in theregion2100-2000cm-1 (Table l)duetovCO of Mn(CO)5 group. The solution spectra (inTHF) of Mn2(CO)IO show three principal carbonylstretching absorption bands at 2060 em - I (b2mode),2020cm (el mode) and 1983 em (b2 mode). Thepattern and positions of CO stretcing bands in thesecompounds (Table I) are basically no different fromthose of the parent carbonyl. It is thus presumed thatthere is no change of electron density on the transitionmetal as a consequence of its bonding to thepcntacoordinatc phosphorus.

IH NMR data are presented in Table 1.Compounds 5-8 exhibit a broad and complexmultiplet in the aromatic region. This multiplet showsa small upfield shift when compared with the positionof multiplets for 1-49• The N-H protons in thesecompounds seem to overlap with aromatic protonsand D20 exchange studies to locate the position ofN-H protons were not successful as all thesecompounds are hydrolytically unstable.

The frequencies of the CO stretches in the JR, as wellas the ability to obtain a mass spectrum, eliminate thepossibility of formation ionic species, viz.,[C6H4(NHhhP+ -[Mn(CO)5) + , [C6H4SNHhP+-[Mn(CO)sJ , [C6H40NHhP+ -[Mn(CO)sr,[C6H4NH(CONH)hP+ -[Mn(CO)sJ -. The nature oftransition metal-pentacoordinate phosphorus bondcan be viewed in two ways. Riess and coworkers+described it in terms of phosphoranides (R4P-) in

30 INDIAN J CHEM. SEe. A, JANUARY 1995

their bidentate polycyclic systems - since it involvedan abstraction of proton from the coordinatednitrogen, thus allowing the ligand to donate a pair ofelectrons to the metal. However, by referring to 5-8as substituted phosphoranes, the opposite is impliedhere which is consistent with the mode of synthesis.Unfortunately, even after persistent efforts, it has notbeen possible to grow good quality crystals of any ofthese species. The final and definitive assignment oftheir structure would be possible only after X-raydiffraction studies are carried.

AcknowledgementWe thank CSIR, New Delhi for financial assistance

for the project (1989)/84-EMR-II. We thank also Dr.S.P. Berthur and Dr. A.D. McNaught of RoyalSociety of Chemistry, Cambridge (U.K.) forsuggesting IUP AC names of the compounds.

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