Transition Met. Chem., 18, 73-76 (1993) Bidentate P, S and Se, Pd n and Rh ~ complexes 73

Preparation and properties of palladium(II) and rhodium(I) complexes containing bidentate phosphine sulphide and selenide ligands Ra61 Contreras, Maurieio Valderrama* and Sandra Ya~ez Departamento de Qulmica Inorgdnica, Facuhad de Qulmica, Pontificia Universidad Cat61ica de Chile, Casilla 306, Santiago, Chile

Summary

The synthesis and properties of cationic complexes of general formula [ML2{CH2(Ph2PE)2}]BF4, where M = Pd H and Rh n, L2 = q3-MeC3H4, {P(O)(OR)z}EH (R = Me, Et), COD, (CO)z, (CO)PPh 3 and E = S, Se are described. The methylene proton of the coordinated phosphine sul- phide or selenide ligands react with strong bases as BuLi in n-hexane or Nai l in THF, to give neutral complexes of the type [ML2{CH(Ph2PE)/}], where M = Pd ll, Rh~; L 2 = q3-MeCaH4, COD and E = S, Se. The complexes have been characterized by elemental analyses, molar conducti- vities, i.r., 1H n.m.r, and 31p{lH} n.m.r, spectroscopy.

Introduction

The synthesis and reactivity of transition metal complexes containing neutral tertiary phosphine sulphide and selenide ligands have been extensively studied~-sk Recently, the preparation of cationic diolefin-rhodium(I) and iridium(I) complexes, and their use as catalyst precursors in homo- geneous hydrogenation of olefins has been reported (6). Related cationic rhodium(I), iridium(I), platinum(II), gold(III) or neutral copper(I) complexes can be obtained using the bidentate ligand PhzP(E)(CH2P(E)PhE)(E = S, Se) (~-1~ These ligand types have been the subject of an increasing interest because their methylene protons react with bases to yield an anionic derivative. When deprotonation was carried out on the coordinated ligand, the resulting complexes contain a methyne carbon-metal bond, with the anionic form acting as a C,S-bonded chelate (8).

Continuing our studies on bis(dialkylphosphonate)- palladium(II) and (diolefin)rhodium(I) complexes (~-14), we now report the synthesis and reactivity of new cationic or neutral complexes containing tertiary phosphine sulphide and selenide ligands of the types: [MLz{CH2(Ph2PE)2}]- BF4, M = palladium(lI), rhodium(I); L 2 = r/3-MeC3H4, {P(O)(OR)2}EH (R = Me, Et), COD (1,5-cyclooctadiene), (CO) 2, (CO)PPh3; E = S, Se and [ML2{CH(Ph2PE)2}] M = palladium(II), rhodium(I); L 2 = ~73-MeC3H4, COD; E = S, Se.

Experimental

Elemental analyses were made with a Heraeus Mikro Standard microanalyser. I.r. were recorded on a Perkin- Elmer 567 spectrophotometer (over the 4000-200 cm- range) using KBr pellets or CH2C12 solutions between KBr plates. Conductivities were measured in ca. 5 • 10-4M MeECO solutions using a WTW LF-521 conductimeter. 1H n.m.r, and 31p{IH} n:m.r spectra were recorded on Varian XL-100 and Bruker AC200P spectrophotometers.

* Author to whom all correspondence should be directed.

The chemical shifts are reported relative to SiMe4 and 85% H3PO 4 (positive shifts downfield) respectively.

All reactions were carried out by Schlenk techniques under purified N2. Reagent grade solvents were dried, distilled, and stored under a N2 atmosphere. The start- ing complexes [PdCI(t/3-MeC3H4)]2 (l-s), [PdCI{(P(O)- (OR)z)2H}]2 (16) (R = Me, Et), [RhCI(COD)]2 (17), [Rh- (OMe)(COD)]2 (~s), [RhCI(CO)2]2 (~9~ and the ligands CHz(Ph2PS)2, CHz(Ph2PSe)2(20,21) were prepared by pub- lished procedures.

[Pd(tl3-MeC3H4) {CH2(Ph2PE)2) ]BF 4 complexes [E = S (1), Se (2)J

A solution of the binuclear complex [PdCl(t/3-MeC3H4)]2 (100 mg; 0.25 retool) in Me2CO (15 cm 3) was treated with T1BF 4 (148 nag; 0.50 mmol) and the stoichiometric amount of the corresponding ligand CH2(PhzPE)2 (0.50retool). The CH2(Ph2PS)2 derivative was added in CHC13 solution. After stirring at room temperature, the mixture was filtered through cellulose to remove the T1C1 formed, and the filtrate was concentrated in vacuo to a small vol. The complexes, precipitated as yellow solids by addition of Et20, were washed with Et20 (2 • 10 cma), dried in vacuo, and recrystallized from Me2CO: n-hexane.

[ Pd {( P( O ) ( O Me)2)2H ] (C HE( Ph2PS )E} ]BF4( 3 )

To a solution of [PdCI{(P(O)(OMe)2)EH}] 2 (300rag; 0,416 retool) in Me2CO (10 cm 3) was added T1BF4 (242 rag; 0.832mmol) and a CHEC12 solution of CH2(Ph2PS)z (376mg; 0.832mmol). After stirring for l h the mixture was filtered through cellulose and concentration of the filtrate left a white-cream solid which was isolated by addition of EtzO. The product was washed with EtaO (3 x 10 cm3), and dried in vacuo.

Complexes (4) and (5) were prepared similarly using [PdCI{(P(O)(OEt)2)2H}] 2, the appropriate ligand, and AgC10 4 (in the absence of light) or T1BF 4 respectively.

[Rh(COD) {CH2(Ph2PE)2} ]BF 4 complexes. [E = S (6), Se (7)J

To a solution of [RhCI(COD)] 2 (78mg; 0.16retool) in Me2CO (10 cm 3) was added T1BF 4 (94 mg; 0.32 mmol) and the corresponding ligand CH2(Ph2PE)2 (0.32 mmol). The CHz(Ph2PS)2 derivative was added in CH2C12 solution. After stirring for 1 h the solution was filtered, concentrated to a small vol. and precipitated by addition of n-hexane. The yellow-orange solids obtained were washed with n- hexane and dried in vacuo.

[Rh(CO)2 {CHE(PhzPS)2)]BF4 (8)

The complex was prepared by two routes:

0340-4285 �9 1993 Chapman & Hall

74 Contreras et al. Transition Met. Chem., 18, 73-76 (1993)

i) To a solution of [-RhCI(CO)2]2 (100 mg; 0.257 mmol) in M%CO (20cm 3) was added T1BF 4 (150mg; 0.510mmol) and CH2(Ph2PS)2 (233 mg; 0.510 mmol). After stirring for 2 h, the solution was filtered and concentrated under reduced pressure. Addition of Et20 caused the formation of a red solid, which was washed with Et20 (3 x 5 cm3), and dried in vacuo. ii) CO (1 atm) was bubbled for 30 min through a CH2C12 solution of complex (6) (300 mg; 0.40 mmol). The dicar- bonyl complex formed was precipitated by addition of n- hexane yielding a red solid, which was filtered, washed with n-hexane (3 x 5 cm3), and dried in vacuo (81~o).

[Rh(CO) (PPh3) {CHz(PhzPS) z} ]BF4 (9)

To a solution of complex (8) (100rag; 0.143mmol) in Me2CO (15 cm 3) was added the stoichiometric amount of PPh 3 (38 mg; 0A42 mmol)in CH2C12 solution. The mixture was stirred for 15 min and the monocarbonyl complex was isolated by partial evaporation and addition of n-hexane. The orange-brownish solid was washed with n-hexane, and dried in vacuo.

[pd(tl3-MeC3H4) {CH(Ph2PS)2}] (I O)

To a solution of CHz(PhePS)z (154 mg; 0.34 mmol) in THF (20 cm 3) at low temperature ( - 72 ~ C) Was added dropwise a hexane solution of BuLl (0.2 ml; 0.34 mmol). After stir- ring for 5 min the mixture was treated with [PdCl(t/3- MeC3H4)]2 (67mg; 0.170mmol) and the stirring con- tinued for 30 rain. The solution was evaporated to dryness, the solid residue extracted with CHzCI2, and the com- plex precipitated by addition of n-hexane. The orange solid obtained was washed with n-hexane, and dried in vacuo.

complex isolated as an orange solid by addition of n- hexane.

Results and discussion

The binuclear palladium(II)complexes [PdCIL/]2, where L 2 = q3-MeC3H~, {P(O)(OR)2}2 H (R = Me, Et), and rho- dium(I) complexes [RhCIL2]z, where L 2 = COD, (CO)2, react with the stoichiometric amount of the bidentate ligand Ph2P(E)CH2P(E)Ph 2, (E = S, Se) in dichloromethane or acetone solution, by cleavage of the chlorine bridges to yield a mixture of neutral and cationic complexes with the ligand acting as a monodentate or bidentate form respect- ively, in accord with the following equation:

[MC1L2]2 + 2CH2(PhzPE)2 ~ [MC1L2{CHz(PhEPE)z}]

+ [ML2{CH2(Ph2PE)2}]C1

Consequently, in order to obtain the cationic complexes it is necessary to treat the starting binuclear complexes with thallium tetrafluoroborate or silver perchlorate, form- ing solvated intermediate species, which react immediately with the bidentate ligand, according to reactions:

1/2[MC1Lz]2 + T1BF 4

MezCO [ML2(Me2CO)x]BF4 + T1C1

[ML2(Me2CO)x]BF4 + CH2(Ph2PE)2 ,

Ph /Ph \

L. /E-----P\ ~ M CH2

L / ~ E - - p / ~h/ \ph

BF4

[Rh(COD) {CH(Ph2PS)2)] (11)

The complex was prepared by two routes:

i) To a solution of complex (6) (200 mg; 0.267 mmol) in THF (20cm 3) at 0 ~ C, was added a slight excess of Nai l (7 mg of 80% dispersion in mineral oil). After stirring for 30 min the mixture was evaporated to dryness and the residue extracted with Et2 O (15 cm3). Addition of n-hexane caused the formation of a yellow solid, which was washed with cold n-hexane, and dried in vacuo. ii) To a solution of CH2(Ph/PS)2 (307 mg; 0.68 mmol) in THF (20 cm a) at low temperature ( - 7 2 ~ C) was added dropwise a solution of BuLl in n-hexane (0.4 ml; 0.68 mmol). After stirring for 5 min the mixture was treated with [RhC1- (COD)]2 (168 mg; 0.340 mmol) and the stirring continued for 1 h. The solution was evaporated to dryness and the residue extracted with Et20. The filtered solution was concentrated to a small vol. and a yellow solid was isolated by addition of cold n-hexane. The complex was washed with n-hexane, and dried in vacuo.

[pd(~13-MeCaH4) {CH(Ph2PSe)2}] (12)

To a solution of complex (2) (120 mg; 0.159 mmol) in THF (20 cm 3) was added a slight excess of Nai l (5 mg of 80% dispersion in mineral oil) and the mixture was stirred for 30 min. The solution was evaporated to dryness and the solid state residue extracted with n-hexane. The solution obtained was filtered, evaporated to a small vol. and the

The complexes were isolated as stable microcrystalline solids and behave as 1 : 1 electrolytes in acetone solutions. Analytical results, molar conductivities and yields are collected in Table 1. The rhodium compounds (6) and (7) were previously described as perchlorate complexes tT). In all cases, the solid state i.r. spectra show the presence of the uncoordinated anion (BFg, ca. 1100 and 520 cm- 1; ClOg, ca. 1100 and 620 cm- ~) together with the absorption bands of the P~---S or P ~ S e bonds (Table 2). These stret- ching frequencies have decreased with respect to the free ligands (v(P=S) = 600 cm- 1; v(P~---Se) = 535 cm- 1), due to decrease of bond strength caused by coordination.

The 1H n.m.r, data are given in Table 2. All complexes exhibit characteristic resonances of the ligands, L2, and the corresponding bidentate sulphur or selenium donor ligands. The methylene protons appear as a triplet in the

4.6-5.3 ppm range, downfield compared with the free ligands [E = S, 6 4, 10; E = Se, 6 4.38 ppm; CDCI 3, 2j(PH) = 13 Hz]. When the spectra of complexes (1) and (2) were recorded in CDCla solution, two triplet signals for the methylene protons were observed, possibly due to the presence of isomers in this solution.

The 31p{ 1H} n.m.r, spectra of the palladium complexes show the expected singlet signal indicated equivalent P(E) groups. Furthermore, complexes (3)-(5) show the charac- teristic signal corresponding to the phosphonate groups. For the rhodium(I) compounds, complex (6) exhibits a doublet at 6 34.73 ppm with a phosphorous-rhodium coup- ling of 4.24 Hz, and for complexes (7) and (8) their spectra show only a singlet resonance (Table 2).

Transition Met. Chem., 18, 73-76 (1993) Bidentate P, S and Se, Pd n and Rh ~ complexes

Table 1. Analytical results, molar conductivities and yields for the palladium(II) and rhodium(I) complexes.

75

Complex Found (Calcd.)~o A~a Yield C H (cm 2 tool- 1 f~- 1) (%)

(1) [Pd(t/3-MeC 3H4) {CH 2(Ph2PS)=} ]BF 4 (2) [Pd(r/3-MeC3H4) {CH2(Ph/PSe)z} ]BF4 (3) [Pd{ (P(O)(OMe)2)zH} {CH2(PhzPS)2} ]BF 4 (4) ['Pd{ (P(O)(OEt)2)aH} {CH2(Ph2PS)2} ]C10 4 (5) [Pd{(P(O)(OEt)2)zH } {CHz(PhzPSe)2}]BF 4 (6) [Rh(COD) {CH2(Ph2PS)2} ]BF 4 (7) [Rh(COD) {CH2(PhzPSe)2} ]BF 4 (8) [Rh(CO)2 {CHE(PhEPS)2} ]BF 4 (9) [Rh(CO)(PPh3) {CH2(Ph/PS)2} ]BF 4

( I0) [Pd(r/a-MeC3H4) {CH(PhzPS)/} ] (11 ) [Rh(COD) {CH(Ph2PS)2 } ] (12) ['Pd(r/3-MeC3H4) {CH(Ph2PSe)2} ]

50.6(49.7) 4.4(4.1) 138 88 44.2(44.5) 3.7(3.7) 136 81 40.1(40.3) 4.5(4.1) 126 84 42.1(42.5) 4.7(4.6) 123 88 39.9(39.1) 4.4(4.6) 128 94 53.3(52.8) 4.3(4.5) 130 87 46.8(47.0) 4.1(4.0) 143 92 46.1(46.5) 3.8(3.2) 127 90 56.6(56.0) 4.1(4.0) 150 69 58.9(58.0) 4.6(4.7) - 95 60.5(59.6) 4.3(4.2) - 77 49.9(50.1) 4.2(4.0) - 28

Table 2. Spectroscopy data of the isolated palladium(II) and rhodium(I) complexes.

Complex 1H n.m.r. [6(ppm), J(Hz)] a 3 tp{ 1H} n.m.r. I.r. (cm- 1)b L2 CH2(Ph2PE) 2 [6(ppm), J(Hz)]a v(P=E)

(1) c 1.91 (s, Me) 5.03 (t, CH> 2j(PH)= 13.22) 36.62 (s) 582 3.18 (s, CH2, H anti) 7.63, 8.03 (m, Ph) 4.22 (s, CH2, H syn)

(2) ~ 1.92 (s, Me) 530 3.14 (s, CH2, H anti) 4.32 (s, CH2, H syn)

(3) a 3.63 (vt, Me, 3j(PH) = 12.67) 580 11.50 (s, br, OH)

(4) d 1.26 (t, Me, 3j(HH) = 7) 582 4.00 (m, CH2)

10.87 (s, br, OH) 1.27 (t, Me, 3j(HH) = 7) 4.01 (m, CH2) 1.93, 2.33 (m, CH2) 4.38 (m, CH=CH) 1.86, 2.33 (m, CH2) 4.40 (m, CH~CH)

5.31 (t, CHz, 2J(pH) = 13.38) 7.65, 8.04 (m, Ph)

22.38 (s, 1J(PSe) = 309, 26)

4.75 (t, CH2, 2j(PH) = 12.78) 36.37 (s, P(S)) 7.55, 7.90 (m, Ph) 79.71 (s, P(O)) 4.77 (t, CH2, 2j(PH) = 12.65) 36.90 (s, P(S)) 7.58, 7.97 (m, Ph) 76.33 (s, P(O))

(5) a 4.97 (t, CH2, 2j(PH) = 12.82) 7.56, 7.94 (m, Ph)

(6) a 4.73 (t, CH/, =J(PH) = 12.82) 7.49, 7.83 (rn, Ph)

(7) a 4.94 (t, CH2, 2J(PH)= 13.15) 7.54, 7.83 (m, Ph)

(8) a - 4.85 (t, CH 2, 2J(PH) = 13.05) 7.51, 7.86 (m, Ph)

(9) a 7.42, 7.90 (m, Ph) 4.99 (t, CHz, 2j(PH) = 13) 7.44, 8.0 (m, Ph)

(10) d 1.72 (s, Me) 3.99 (t, CH, 2J(PH) = 13) 2.54 (s, CHz, H anti) 7.31, 7.87 (m, Ph) 3.40 (s, CH2, H syn)

(11 )d 1.64, 2.08 (m, CH/) 4.34 (m) 4.00 (m, CH~-CH) 7.32, 7.88 (m, Ph)

23.27 (s, P(Se)) 78.18 (s, e(o)) 34.73 (d,/J(PRh) = 4.24)

20.41 (s, 1J(PSe) = 309.87)

36.43 (s)

29.00 (m, PPh3) 37.53 (m, P(S) cis PPh3) 39.21 (m, P(S) trans PPh3) 34.51 (s)

36.51 (d, 2j(PRh) = 4.38)

531

582

530

562

563

565

555

"Chemical shifts relative to SiMe,~ and HaPO4 (85%) respectively, vt = virtual; bKBr; c(CD3)2; dCDC13

Complex ( 1 ) reacts in chloroform solution with the sec- ondary alkylphosphites HP(O)(OR)z (R = Me, Et) in 1:2 molar ratio, by protonation of the methyl-allyl group and the formation of the corresponding phosphito-phos- phonate complexes (3) and (4) , according to the reaction:

[Pd(I/3-MeC3H4){CHz(PhzPS)z}]BF4

+ 2HP(O)(OR)2

OR OR Ph Ph \ / \ /

,0 ----'~- P ~ / S = P \ I-~ Pd CH 2 '0 .... P / ~ S = P / / \ / \

OR OR Ph Ph

BF 4 + 2-MeC3H 4

These complexes contain a hydrogen-bonded proton which can easily be removed to yield a neutral complex which can act as a chelating O,O-donor ligand (12,22). Attempts to obtain neutral compounds by neutralization of the acidic proton of complexes ( 3 ) - ( 5 ) with the stoi- chiometric amount of KOH in MeOH solution were unsuc- cessful, and the reaction in all cases gives a mixture of uncharacterized complexes. On the other hand, complex ( 4 ) reacts with the binuclear complex [Rh(OMe)(COD)] z in MeOH solution by cleavage of the methoxo bridges with formation of MeOH, the neutral complex [Pd{P(O)- (OEt)/}/{CHz(Ph2PS)2}] and the fragment - Rh(COD)-. However, the formation of the expected heterobimetallic complex does not occur and, possibly due to the lability of the sulphur-palladium(II) bond the migration of the

76 Contreras et al.

bidentate sulphur ligand from the palladium(II) to the rhodium(I) metal centre was observed, yielding the mono- nuclear cationic complex [Rh(COD){CH2(Ph2PS)2}]- C104 (6) and the polymer palladium(II) complex [Pd{P(O)- (OEt)2}2], (16).

The bubbling of CO through CH2C12 or MezCO solu- tions of the complex (6) leads to the displacement of the coordinated COD and formation of complex (8), whose i.r. spectrum shows two strong bands at 2080 and 2018 cm- ~ (KBr) characteristic of cis-(dicarbonyl) deriva- tive [v(CO) = 2060, 1980 cm-1 (CH2C12); v(CO) = 2065, 1985 cm-~ (Me2CO)]. A similar reaction was carried out with the selenium complex (7) showing the corresponding two bands in CHzCI2 solutions but the isolated solid complex was not analytically pure.

Complex (8) reacts with the stoichiometric amount of Ph3P with formation of the monocarbonyl derivative [Rh- (CO)(PPha){CH2(Ph2PS)2}]BF 4 (9), whose i.r. spectrum shows a single strong v(CO) band at 1955 cm -1 (KBr) Iv(CO) = 1990 cm- 1, CH2C12]. The 31p{ a H} n.m.r, spectrum exhibits three multiplets at g 29.00, 37.53 and 39.21 ppm, assigned the Ph3P, the P(S) group bonded eis to the Ph3P and the P(S) group bonded trans to Ph3P, respectively.

The phosphine sulphide or selenide ligands were depro- tonated with BuLi in n-hexane or Na i l in THF at low temperature ( - 7 2 ~ C). The anionic species formed react with the binuclear complexes [MC1L2] 2 [M = rhodium(I), L 2 = COD; M = palladium(II), L z = t/3-MeC3H~] at low temperature, yielding the corresponding neutral complexes, according to reactions:

CH2(Ph2PE)2 + BuLi(NaH) --* Li[CH(Ph2PE) 2]

Li/-CH(Ph2PE)2] + 1/2[MC1L2] --,/-ML 2 {CH(Ph2PE)2}]

+ LiC1

Alternatively, the neutral complexes can be prepared in minor yields, by reaction of the coordinated bidentate ligands in the cationic complexes with an excess of Na i l in THF solutions:

[ML2] {CH2(Ph2PE)2 } ]BF,~ + Nail(excess)

[ML2{CH(Ph2PE)2}] + NaBF4

Complexes (10) and (11) were isolated as stable orange or yellow solids. Their i.r. spectra show only one v (P=E) absorption band for coordinated phosphine sulphide ligand. The 1H n.m.r, spectrum of complex (10) shows a triplet signal for the methylene proton at ~5 3.90 ppm [2j(PH) = 13 Hz] and the 31p{~H} n.m.r spectrum shows a single signal for the P(S) group at 634.51ppm. For complex (11) the methylene proton appears in the 1H n.m.r spectrum as a multiplet at 6 4.34 ppm and the 31p{ 1H} n.m.r, spectrum shows a doublet at ~ 36.51 ppm [2j(PRh)= 4.38 Hz]. These results confirm that the anionic phosphine sulphide deriva- tive CH{Ph2PS}2 is acting as a bidentate S,S'-donor ligand.

Complexes ( I0) and (11) react in acetone solution with HBF 4 regenerating the starting complexes (1) and (6):

[MLz{CH(Ph2PS) 2] + HBF4

[ML2 {CH2(PhEPS) } ]BF4

Transition Met. Chem., 18, 73-76 (1993)

M = P d ; L 2 --- t/3-MeC3H4

M = Rh; L 2 --- COD

Finally, complex (12) was isolated as moderately air- stable orange solid. Its i.r. spectrum shows the characteristic absorption of the coordinated P---Se group at 518 cm- 1. By contrast with the analogue phosphine sulphide complex (I0) , complex (12) rapidly decomposes in deuterated solvents (CDC13, CD2C12) , and the 1Hn.m.r. spectrum always shows the signals corresponding to the free ligand. Nevertheless, the 31p{1H} n.m.r spectrum shows a broad singlet signal at 6 19.58 ppm assigned to the P(Se) group, suggesting a similar above mentioned behaviour of the sulphur donor ligand.

Acknowledgements

The authors thank FONDECYT (Grant No. 798/91) for financial support.

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(Received 6 February 1992) TMC 2733