Indian Journal of ChemistryVol. 22A, April 1983, pp. 298-300

Synthesis, Reactions & Characterization of SomeNew Heterocyclic p-Diketone Boroacetates

YASHPAL SINGH, SANJIV SAXENA & A K RAI·Department of Chemistry, University of Rajasthan, Jaipur 302004

Received 27 July 1982; revised and accepted 29 October 1982

Some boron compounds having the general formula (OAc),BOC(R)C:CON(R')N:C CH, (where R =CH" C1Hs, C6HSand p-C1-C6H4; R' = C6Hs), have been synthesised. These on treatment with alcohols, diols, o-aminophenol, 0-aminothiophenol, catechol etc afford boron containing heterocyclic compounds having B -0, B - Nand B - S bondings.These complexes have been characterized by elemental analyses, molecular weight measurements, IR, PMR and II B NMRdata.

Several /J-diketone boroacetates I, (OAC)2B-/J-diketone, and- a number of similar boron derivativesusing monofunctional bidentate ' -4 and bifunctionaltridentate" ligands are reported in literature. In recentpublications Tandon and coworkers:' -5 showed thatthe acetate groups attached to central boron atom arechemically inactive. In contrast to this, the acetategroups attached to boron atom in substitutedheterocyclic /J-diketone boron acetates, synthesisedpresently, are found to be highly reactive and readilyreact with organic compounds like alcohols, diols, 0-aminophenol and o-aminothiophenol to formcomplexes having B-O, B-N and B-S bondings.These complexes could not be synthesised by directroutes.

Materials and MethodsThe Iigands, viz., 4-benzoyl-3-methyl, 4-chloro-

benzoyl-3-methyl, 4-propionyl-3-methyl and 4-acetyl-3-methyl-I-phenyl-2- pyrazolin-S-ones (abbreviated asBMPPO, CMPPO, PMPPO and AMPPO re-spectively) were synthesised by the procedure reportedby Jensen" and were recrystallised from n-heptane.Boric acid (BDH, AR) was used as such. Aceticanhydride (BDH, AR), o-aminothiophenol, lSO-propanol, I, 2-ethanediol, I, 2-ethanethiol and 2, 3-dimethyl-Z, 3-butanediol were distilled before use.Catechol and o-aminophenol (E, Merck) weresublimed under reduced pressure (0.1 mm). All thereactions were carried out under anhydrousconditions.

Reaction of boric acid with LI in I: I molar ratio inacetic anhydride-Boric acid (0.66 g , 10.6 mmol) wasdissolved in acetic anhydride (- 20 ml) by gentlerefluxing. After cooling, the ligand, LI (3.01 g,10.8 mmol) was added to it. The reaction mixture wasrefluxed for 2-3 hr, during which period the colour ofthe solution changed from yellow to red. The solution

298

was left overnight when yellow coloured crystalsseparated out, which were filtered and dried in vacuo.Similar method was followed in the synthesis of otherderivatives with the ligand L2, L3 and L4.

Reaction of bis{acetato) boron (L I) with 2-aminothiophenol in I: I molar ratio-A solution of 0-aminothiophenol (0.41 g, 3.3 mmol) in toluene wasmixed with a solution of the bis(acetato) boron- LI( 1.36 g , 3.34 mmo\) in toluene, the reactionmixture was refluxed and acetic acid liberated,fractionated off azeotropically with toluene. Theprogress of the reaction was checked by estimatingacetic acid in- the azeotrope at different time intervalsby titrating against 0.1 N NaOH. After completion ofthe reaction, excess solvent was distilled off, theresultant product dried in vacuo and recrystallizedfrom toluene.

Similar reactions were carried out with isopropanol,ethane-I, 2-diol, ethane-I, 2-thiol, 2, 3-dimethyl-2, 3-butanediol and o-aminophenol and catechol, theproducts isolated and crystallized from hot toluene.The analytical data of the compounds are given inTable I.

Results and DiscussionThe reactions of the bistacetato)- boronpyro-

zolonate derivatives were carried out with isopro-panol, ethane-I, 2-diol, 2, 3-dimethyl-2, 3-butanediol,catechol, ethane-l , 2-thiol, o-aminophenol and 0-aminothiophenol as shown below.

2PriOH + (oAc)2 BOPPMAc ---+ (OPri~BOPPMAC + 2AcOH

... (1)

/OH T I ~G + (OAc)2 BOPPMAc ~ OGOBOPPMAc + 2AcOH

"OH reflux ...(2)G • -CH2 CHi' 1CH3lz ~-~(.CH3)2CH3-~HCHz~(CH3)2' 7H2- C(C~12-yH2and C6H4

SINGH" al.: NEW HETEtocycuc P-DIKETONE BOROACETATES

i ~

SINo

Table f-Physical and Analy ical Data for Substituted Boron fJ-Diketonates

Product Physical State Found (calc) %(% Yield) (m.p. 0C)

(85)6 OC6H40BOPPMB

(80)7 OC(CH3hC(CH3)20BOPPMA

(82)8 OC(CH3)CH2(CH3hCOBOPPMC

(89)9 OCH2CH20BOPPMA

I I (86)10 SCH2.CH2SBOPPMB

j (87)II SC6H4NHdoPPMB

(86)12 6C6H4NHnOPPMB Y llow solid

(85) I13 k6H4NHdoPPMC Rrd solid

t I (85)14 OC6H4NHBOPPMC Yellow solid

j (82) I (262)15 SC6H4NHAoPPMP Yfllow sticky solid

I I (86) I16 OC6H4NHBOPPMP Y[llOWsohd

(85) (139)17 SC6H4NH~OPPMA 0 ange yellow sohd

(84) (86)18 6C6H4NHBOPPMA Y llow solid

(83) IBMPPO - =4-Benzoyl-3-methyl-I-phenyl-2-pyrazolin-5-ol?e anion.CMPPO - =4-Chlorobenzoyl-3-methyl-l-phenyl-2-pyrazolin-5-one anionPMPPO - =4-ProPiOnyl-3-methyl-I-phenyl-2-pyrazOlin-5rne anion.AMPPO - =4-Acetyl-3-methyl-l-phenyl-2-pyrazolin-5-on~ anion.For SI Nos 11-18, only 2-aminophenol and 2-aminothioPlhenol were used (Found: C, 55.72; H, 5.06 Calc: C, 55.81; H, 4.94~JFor SI Nos 5-18, amount of acetic acid (in gm) liberated has been given.

11 B

2.67(2.66)2.48

(2.45)3.02

(3.01)3.24

(3.14)2.68

(2.66)2.83

(2.72)2.09

(2.15)2.53

(2.46)3.52

(3.60)3.52

(3.60)2.58

(2.62)2.75

(2.73)2.28

(2.41)2.51

(2.50)2.92

(3.03)3.21

(3.11)3.00

(3.09)3.24

(3.09)

(OAchBOPPMB Lirht yellow crystalline solid(92) (176)

2 (OAchBOPPMC LIht yellow crystalline solid(90) (196)

3 (OAC)2BOPPMP C (am coloured crystalline solid(88) (66)

4 (OAchBOPPMA Pi k crystalline solid(86) (134)

5 (OPri)2BOPPMB Yellow viscous liquid

YrllOWsolid(266)

Red sticky solid

Drk brown sticky solid

D rk brown sticky solid

R d orange solid(90)

o ange solid(185)

(202)

(236)

(119)

Acetoxy

28.55(29.06)25.86

(26.72)32.29

(32.96)33.20

(34.30)0.46

(0.47)0.35

(0.36)0.25

(0.27)0.22

(0.24)0.32

(0.32)0.43

(0.44)0.38

(0.40)0.41

(0.45)0.38

(0.40)0.25

(0.29)0.41

(0.42)0.20

(0.21)0.31

(0.32)0.32

(0.35)

MolwtFound(calc)

415(406)

360(344)421

(406)

424(411)410

(395)

362(349)325

(333)

- CH2, (CH3)2C - C(CH3)2' CH3HCCH2-C(CH3)z] which could not be synthesised by thereaction of 6GOBOPri with AcMPPOH in refluxingbenzene, have also been synthesised by this indirectmethod. The acetoxy groups present in the parentcompound are unidentate in nature 7 and theirreactivity is due to the weakening of B - 0 (acetate)bonds by electron withdrawing tendency of thecarbonyl group and thus are cleaved under theinfluence of ligands having labile protons.

The reactivity of the above complexes depends onthe nature of substituent group R. If R is an electronwithdrawing group like C6HS or p-ClC6H4, the

©rXH OAc Io + "eOPPMAC- *C6 ••••NHiIoPPMAc+2AcOHNH:! OAc/•.. (3)

where X· S or 0

Thus, by using these bis-acetato boron pyraz?lonatecompounds as starting materials, somr newheterocyclic compounds have been synthesis~d. Thenew heterocyclic compounds could not be syntresisedfrom simple alkoxy- or aryloxy-boranes. Substitutedpyrazolones do not react with isopropyl borate bven onprolonged refluxing. However, the same derivative(OPrl)2BOPPMAc has been synthesised ~y thismethod. Similarly, OGOBOPPMAc [G

1

=CH2

299

1"INDIAN J. CHEM .. VOL. 22A. APRIL 1983

reactivity of the complex towards mono andbifunctional ligands increases.

These derivatives are found to be coloured solids,having sharp melting points, soluble in commonorganic solvents and monomeric in retluxing benzene.

A sharp band at 1720 ern -I in the IR spectrum ofthe complex (OAC)2BOPPMAc assignable to vC = 0 ofthe acetate 1 group, indicates the unidentate nature ofthe acetoxy groups. Another medium intensity band(1510-1520cm -1) has been assigned to vC=O of theliganc 8. This band is present at 1545 em -1 in the freeligand. This shift of 20-30 indicates the coordinationthrough the oxygen of carbonyl group. Further, thetwo medium intensity bands 1280 and 700-720 cm -1have been assigned to vC -0 (acetate)? and B.-010,respectively.

The disappearance of the bands at 1720 and1280 em -1 in the IR spectra of compounds liker----\ , r IOGOBOPPMAc and XGNHBOPPMAc (X =0 or S)shows removal of both the acetoxy groups. The twomedium intensity bands in the IR spectra of the, ,complexes, XGNHBOPPMAc at 3200-3225 and900 ern -1 (X = S) have been assigned to vN - H 11 andvB - S12 respectively.

The PMR spectra of the ligands display signals atb2.3 or 2.1 (s, 3H, CH3), 7.1-7.8 (m, aromatic H) and12.1 (s, IH, OH). In the case of ligand where R= propionyl, in addition to these signals a triplet and aquartet centered at b1.2 and 2.8, respectively due toCH3 and CH2 protons of the propyl group appearwhereas in the ligand where R = CH 3 the singlets dueto two methyl groups overlap at b2.4.

In the case of bis-acetatopyrazolonate complexes,the signal due to - OH protons at (512.r disappearsand a new signal at 2.04 due to the CH 3 protons of theacetate group appears alongwith other signals of theligands with sma\1 downfield shift in their positionswhich may be ascribed to the delocalization of theelectrons during complex formation.

The PMR spectra of the compounds likeXC6H4NHBOPPMAc (X = 0 or S) are similar innature except the replacement of CH3 proton singletsat 2.04 with phenyl proton multiplet at (56.4- 6.9.

The 11B NMR spectrum of a representative, ,compound, (OAc)2BOC(CH3)C:CON(Ph)N: CCH 3

\ I

300

displays a sharp singlet at b 1.52 with reference toBF3.2(C2HshO. 'The appearance of a single signalindicates the presence of boron in one environmentand the chemical shift is in confirmity with tetra-coordinate boron atom 13.

Onjthe basis of molecular weight measurements, IRand ~MR spectral evidences, structure (I) may beassigned to the derivatives of the type

r jXC6H4NHBOPPMAc

R

~ o--c/C( -,/ ------,~I B , C-C-CH3/ / ""- - - - - - - '/ IIx o--c""-N-N

IPh

A similar structure may be proposed for ther-----t

derivatives of the type OGOBOPPMAc where G =-CH2CH2 -, (CH3)2C -C -(CH3h and CH3-CHCH2C(CH3h·

Ackno/edgement .The authors (Y.P.S. and S.S.) are thankful to the

CSIR, New Delhi for financial assistance. Thanks arealso due to Prof. R.C. Mehrotra for useful discussion.

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