Indian Journal of Chemistry Vol. 4SA, June 2006, pp. 1390- 1394

Notes

Derivatisation and transition metal chemistry of a new monophosphinite ligand: 2-( di phen y Iphosph i nox y )naphthy I

Benudhar Punji & Maravanji S Balakrishna*

Departmcnt of Chcmistry. Indian Institute of Technology Bombay.

Powai , Mumbai 400076. India Email: kri shna @chem.iitb.ac . i n

Received ]0 Novell/ber 2005; revised 4 April 2006

Reaction of monophosphinite li gand, 2-(d ipheny lphosphi ­noxy)naphthyl, C IOH70PPh2 (1) with elemental sulphur or se lenium gives the corresponding sulphide C IOH70P(S)Ph2 (2) or selenide C IOH70P(Se)ph2 (3) derivatives. Reac tion of 1 with ICpRu(PPh3h ClI gives monosubstituted complex , [CpRu(C IOH70PPh2)(PPh.1)C11 (4) as wel l as the disubstituted complex . ICpRu(C IOH70PPh2h CII (5) depending upon the reaction conditions. Treatmen t of 1 wi th IRh(COh Clh affords a Irw/s-complcx, IRh(CO)(C IOH70PPh2h ClI (6) . Reaction of 1 wi th I Pd(COD)Cl2J results in the formation of an unexpec ted chloro­bridged dipalladium complex: I Pd(PPh20)( PPh20H)(~I-CI)h (7), whereas similar reaction with [pt(COD)CI2J gives cis­IPt(CIOH70PPh2)2CI21 (8) in good y ield.

IPC Code: Inl. CI. 8 C07F ISIOO

T he syntheses and trans iti on metal chemistry of phosphinite ligands have generated cons iderable in­terest in recent years , because of their potential use­fulness in catalysi s and industrial applications ' . Again, relatively eas ie r synthetic methods, low cost and hi gh activities towards catalytic transformation have made these ligand systems more interesting. Although, bis(phosphir,ite) ligands are extensively used in transition metal chemistry" and various or­ganic transformations3

, s imilar reports on monophos­phinite ligands are sparse. Recently, Mathey el 01.4

have reported some cyclic phosphinites, wh ich act us better catalysts for functionalized o lefin hydrogena­tio n reactions. Similarly, Bedford el at. 5 have synthe­sized several monophosphinite ligands which show excellent activity towards Suzuki coupling reaction. In these cases, ligands form ortho metal lated complex with metal center, wh ich influences the catal ytic ac­tivity. Even tho ugh many monophosphinites are used for organ ic' transformations, their transition metal chemistry is not well studied, which prompted us to explore the metal chemistry of simple monophosphi­nites.

We have explored the tranSttlon metal chemistry and catalytic activi ty of bisphosphini te6 and amino­phosphine ligands7

, which form complexes with a l­most all the transitio n metals and show good activity towards C-C coupling reactions. In view of thi s and in continuation of our research efforts in designing new, inexpensive phosphorus based li gandS for exploring their organometallic chem istry and catalytic studies, herein we describe the derivatization and some transi­tion metal chemistry of the ligand , monophosphinite C ,oH70PPh2 (1).

Experimental A ll experimental manipulati ons were carried out

under an atmosphere of dry nitroge:l or argon using standard Schlenk techniques. Solvents were dried and di stilled prior to use by conventional methods . Mo no­phosphinite ligand 1 was prepared from the reaction of ~-naphtho l with Ph2PCl in the presence of base. The metal precurso rs [M(COD)CI2J (M = Pd , Pt)'i·'o, [CpRu(PPh3)2CI] II and [Rh (CO)2C I h '2 were prepared according to the literature procedures . The 'H and 3'p{ 'H} NMR (8 in ppm) spectra were obtained on a Varian VXR 300 or VRX 400 spectrometer operating at frequencies of 300 or 400 MH z and 121 o r 162 MHz, respectively . The spectra were recorded in CDCI3 solutions with CDCIJ as an internal lock ; TMS and 85 % H3P04 were used as inte rnal and external standards for 'H and 3'p{ 'H} NYlR, respective ly. Positive shifts lie downfield of the standard in all of the cases. Infrared spectra were reco rded on a Nicolet Impact 400 Ff IR instrument in KBr di sk or nujol mull. Microanalyses were carried out on a Carlo Erba (model 1106) e lementa l analyzer. Melting points of a ll compounds were determined on a Veego melting poi nt apparatus and are uncorrected .

Synthesis of C IOH70P(S)Ph2 (2)

A mixture of monophosphinite 1 ( I g, 3.04 mmol) and e lemental sulph ur (0.097 g, 3.04 mmol) in toluer.e

(20 mL) was heated at 90°C for abou t 10 min . It was cooled to room temperature and solvent was removed under vacuum to get a pasty liquid, which was dis­solved in C H2Ch, layered with petro leum ether to get

the pure crystalline product of 2 at ODe. Yield : 76%

(0.83 g) . M. pt. : 100-102°C. Anal. : Calcd. fo r

NOTES 1391

C22 HI70PS: C, 73 .32; H, 4.75 ; S, 8.89%. Found: C, 73.19 ; H, 4.61; S, 8.76%. IH NMR (300 MHz, CDCI3): b 8.04 (s , I H, Ar), 7.95 (d, I H, Ar), 7.33-7.79 (m, 5H, Ar, IOH , OPPh2). 3Ip{IH} NMR (121.4 MHz, CDCi3) : b 80.7 (s).

Synthesis of C IOH70P(Se)phz (3)

A mixture of monophosphinite 1 (1 g , 3.04 mmol) and elemental selenium (0.24 g, 3.04 mmol) in tolu­ene (20 mL) was heated to reflux for 10 h and was cooled to room temperature. It was then filtered and solvent was removed under vacuum to get a pasty liquid, which was dissolved in CH2Ci2, layered with

petroleum ether to get crystalline product of 3 at O°c. Yield: 91% (1.12 g). M. pt.: 118-120 0c. Anal. : Calcd. for C22 HI70PSe: C, 64.87; H, 4.21 %. Found: C, 64.63; H, 4.13%. I H NMR (300 MHz, CDCI3): b 8.07 (s, I H, Ar) , 8.05 (d, I H, Ar), 7.39-8.03 (m, 5H, Ar, 10H, OPPh2). 3Ip{IH} NMR (12l.4 MHz, CDCI3): 0 84.6(s), IJP=Se = 825 Hz.

Synthesis of [CpRuCI(C IOH70PPh2)(PPh3)] (4)

A solution of phosphinite 1 (0.014 g, 0.041 mmol) in 8 mL of CH2Ci2 was added dropwise to the solution of CpRuCI(PPh3h (0.03 g, 0.041 mmol), also in CH2Ch (5 mL). at room temperature and stilTed for 6 h. The solvent was evaporated under reduced pressure and the residue obtained was dissolved in diethyl ether, which gave orange-red microcrystals of 4 at room temperature. Yield : 81 % (0.026 g). M. pt. : 152-154°C (dec). Anal. : Caicd. for C45 H37CIOP2Ru : C, 68.22; H, 4.7 I %. Found: C, 67.92; H, 4.53%. I I NMR (400 MH z, CDCi3): b 7.67 (d, I H, Ar) , 7.52 C', IH , Ar) , 6 .78-7.57 (m, 5H, Ar, IOH, OPPh2. IS H, PPh3), 4.28 (s, 5H, Cp). :l lp{ IH} NMR (161.9 MH z, CDCI3) : b 43 .3 (d, PPh3) , 148.8 (d, OPPh2), eJp.p= 58 Hz).

Synthesis of [CpRuCI(C IOH70PPh2h] (5)

A mixture of CpRuCI(PPh3h (0.044 g, 0.06 mmol ) and phosphinite 1 (0.04 g, 0.12 mmol) in 10 mL of toluene was healed to reflux for 10 h. Then the reac­tion mixture was evaporated to dryness and the resi­due obtained was washed with petroleum ether and dried. The crude product was dissolved in CH2Ci2.

layered with petroleum ether and cooled to O°C to get yellow crystalline product of 5. Yield: 84% (0.043 g). M. pt. : 98-100°C (dec) . Anal. : Calcd. for C4~H39CI02P2Ru: C, 68 .57 ; H, 4 .58%. Found: C, 68 .37; H, 4.53 %. IH NMR (400 MHz, CDCh): b 7. 64 (d, 2H, Ar), 7.47 (s, 2H , Ar), 6 .92-7.45 (m , 10H, Ar,

20H, OPPh~) , 4.22 (s , 5H, Cp). 31p{ IH } NMR (161.9 MHz, CDCh): 0 15 1.4 (s).

Synthesis of [Rh(CO){C IOH70PPh2hCI] (6) A solution of phosphinite 1 (0.068 g, 0 .206 mmol)

in 5 mL of CH2Ch was added dropwise tG a solution of [Rh(COhClh (0.02 g, 0.051 mmol) in CH2Ci2 (5 mL) at room temperature and stirred for 3 h. The or­ange-red color reaction mixture was c;.oncentrated to 3 mL, layered with diethyl ether and cooled to -25 °C to get orange crystalline product of 6. Yield: 81 % (0.068 g). M. pt.: 168-170°C. Anal. : Calcd. for C45 H34Ci03P2Rh: C, 65.67 ; H, 4.16%. Found: C. 65.48; H, 4 .05 %. FT IR (KBr disk) cm·l, Veo: 1972 vs. IH NMR (400 MHz, CDCi3): b 7.72 (d, 2H, Ar), 7.65 (s, 2H, Ar) , 7.22-7.47 (m, 10H, Ar, 20H , OPPh2).

31p{ IH} NMR (161.9 MHz, CDCI3): b 120.8 (d, IJRh.P = 142 Hz).

Synthesis of [Pd(PPh20)(PPh20H)(/l-CI)h (7) A solution of monophosplrinite 1 (0.069 g, 0.21

mmol) in 8 mL of CH2Ch was added dropwise to a solution of [Pd(COD)CI2] (0.03 g, 0.105 mmol) in CH2Ch (5 mL) at room temperature and stirred for 3 h. The light yellow solution was concentrated to 3 mL and layered with petroleum ether, which gave yellow color crystals of 7 with slow evaporation of solvent at room temperature. Yield: 79% (0.045 g). M. pt.: 186-188°C (dec). Anal.: Calcd . for C4sH42C120 4P4Pd2: C, 52.87 ; H, 3.88%. Found: C, 52.59; H, 3.78%. IH NMR (300 MHz, CDCi3): 0 7.20-7.59 (m, phenyl). 3I p{ IHJ NMR (121.4 MHz, CDCI3): b 78.7 (s) .

Synthesis of fPtCll (C IOH70PPh2h] (8) A solution of monophosphinite 1 (0.044 g, 0. 13

mmol ) in 8 mL of CH2CI 2 was added dropwise to the solution of [Pt(COD)Ch] (0.025 g. 0.067 mmol) , also in CH2Ci2 (5 mL ) at room temperature and stirred for 3 h. The colorless ::;olution was concentrated to 3 mL and layered with petroleum ether, which gave whi te crystalline product of 8 at room temperature with slow evaporation of solvent. Yield: 85% (0.053 g). M. pt. : 176-178°C (dec). Anal.: Calcd. for C44H34CIz02P2Pt : C, 57.28 ; H, 3.71 %. Found: C, 56.97 ; H, 3.62%. IH NMR (400 MHz, CDCi3): b 7.70 (d, 2H, Ar) , 7.57 (s, 2H, Ar) , 6 .62-7.41 (m, 10H, Ar, 20H, OPPh2). :l lp{ IH} NMR (1 6 1.9 MHz, CDCI3): 0 85.9 (s), IJpl.p = 4221 Hz.

Results and discussion Monophosphinite ligand 1 was prepared conven­

iently starting from ~-naphthol and chlorodiphenyl -

1392 INDIAN J CHEM, SEC A, JUN E 2006

phosphine in a 1: 1 molar ratio in the presence of one equivalent of triethylamine and catalytic amount of N,N-dimethylaminopyridine (DMAP) as shown in Scheme I . Compound 1 is a white crystalline so lid and is moderately air stable, whose 31p{ 'H} NMR spectrum shows a single resonance at lO9.1 ppm. The stoichiometric reaction of 1 with elemental su lphur and selenium powder in toluene gives the sulphide C loH70P(S)Ph2 (2) and selenide C loH70P(Se)ph2 (3) derivatives, respectively . The su lphide derivative was formed within 10 minutes at 90°C; whereas formation of the selenide was slow and took 10 h for comp letion of the reaction . Compounds 2 and 3 are found to be air stable, but sensitive to light. The 31p{ 'H} NMR spectra of compounds 2 and 3 show singlets at 80.7 and 84.6 ppm, respectively with the latter showing selenium-77 satellites with a Ijpse coupling of 825 Hz.

The reaction of 1 with [CpRuCI(PPh3h] affords either monosubstituted [CpRuCI(PPh])(C IOH70PPh2)]

(4) or disubstituted [CpRuCI(C loH70PPh2h ] (5) com­plexes depending upon the stoichiometry and the re­action conditions (Scheme 1). The reaction of 1 with lCpRuCI(PPh3h ] in dichloromethane in equ imolar ratio at room temperature affords monosubstituted complex, [C pRuCl(PPh3)(C IOH70PPh2) ] (4) in 8 1 % yield. The 31p NMR spectrum of 4 shows two dou-

E=S, 2;Se,3 , Sa (or)

\ Se

blets centered at 43.3 and 148.8 ppm respectively for PPh] and phosphini te center with a 2jp.p coupling of 58 Hz. The reaction of [CpRuCI (PPh3)2] with two equivalents of 1 in to luene under reflux condition gave the disubstituted product, [CpRuCl(C loH70PPh2hJ (5) in 84% yie ld . The 31p

NMR spectrum of 5 shows a single resonance at 151.4 ppm with a coordination shift of (.0.8) 42.3 ppm. The reaction of [Rh(COhClh with four equivalents of 1 at room temperature results in i.he formation of tralls-[Rh(CO)C I(C loH70PPh2h ] (6) in good yield. The IR spectrum of complex 6 shows uCO at 1972 cm-I

, which suggests that the carbonyl is trails to CI and not to the phosphorus centers. The 3I p NMR spectrum of 6 shows a doublet centered at 120.8 ppm with a I jRh_P coupling of 142 Hz, which supports the trails configuration of the complex.

The reaction of [Pd(COD)CIz] wi th li gand 1 in di­chloromethane at room temperature did not give the expected product, [PdCl2(C IOH70PPh2h] instead , re­sulted in the formation of a chloro-bridged binuclear complex, [Pd(PPh20)(PPh20H)(J..t-C I)h (7). The 31 p{ ' H } NMR spectrum of the complex show a single resonance at 78 .7 ppm. The microanalysis of complex 7 agrees well with the proposed molecular composi­tion. The formation of hydrolysis product 7 was also

Scheme 1

NOTES 1393

Ph2 Ph2

[ ] , , O-P" /C\ /p-O C\ PPh20H H Pd Pd "- .. / "O-p/ "C( '\. , H Pd" , - 2 HCI

P-O CI/ PPh20H Ph2 Ph2 7

Scheme 2 observed in the reaction of [Pd(COD)CI2] wi th ami- binuclear complex has been formed . The utility of nophosphine, Ph2PN(H)Ph7d

. The reaction of ruthenium complexes of 1 in catalytic hydrogenation Ph2POH/PPh2CI with K2PdCI4 in acetone/H20 also reactions is in progress. gives the -:omplex 7 13

; whose molecular structure has been reported previously 14 . The reaction probably proceeds via formation of thermodynamically unsta­ble intermediate, [PdCl ,(Ph2POH)z] from the hydroly­sis of [PdCI2(C IOH70Pf'h2) 2] as shown in Scheme 2.

Al though, ac id/base or moisture assisted P-N or P­Cl bond cleavage is well documented7d

•15

, similar P-O bond cleavages are rarely seen in the li terature6b

.16

.

However, in the above reaction, the cleavage of both naphthoxy groups (P-O bond) from the phosphorus ligand occurs due to the nucleophilic attack by water at coordi nated phosphorus atom. It is also known that the phosphorus coordinated cis complexes of the type [PdCIz(PR3h ] are susceptible to nucleophilic attack at phosphorus center yielding new complexes. The reac­tion of 1 with [Pt(COD)CI2] in dichloromethane in 2: I molar ratio at room temperature gives the cis­[Pt(CIQH70PPh2hClz] (8) in good yield. The 3 1p NMR spectrum of 8 shows a si ngle resonance at 85.9 ppm with 195 Pt satellites. The large lipt. p coupling of 4221 Hz is attributed to cis configuration of the coord inated phosphorous centers6a

. Although, the rhodiu m com­plex 6 shows trans geometry, platinum complex 8, is cis, which may be due to the large size of platinum metal compared to rhodium metal atom.

In conclusion, a versatile and inexpensive mono­phosphinite ligand 1 has been synthesized, which forms complexes with most of the transition metal s. With ruthenium(II), it forms both mono and disubsti­tuted complexes under different experimen lal condi­tions. In the case of palladium(II), a chloro-bridged

Acknowledgements We are gratefu l to the Department of Science and

Technology (DST), New Delhi , for funding through grants SR/S 1IIC-05/2003. BP thanks CSIR, New Delhi, India for JRF and SRF fe llowships. We also thank SAIF, Mumbai, Department of Chemistry In­strumentation Facilities, Mumbai , for spectral and analytical data.

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